Basic Physical
Propertiesof PVOH Resin

Basic Physical
Properties of PVOH
Resin
Table of Contents:
1.

Basic Physical Properties of
PVOH

31-1. Definition of PVOH
1-2. Specific Gravity
1-3. Refractive Index
1-4. Second-order Transition Temperature
1-5. Crystallinity
1-6. Melting Point
1-7. Specific Heat
1-8. Latent Heat of Melting
1-9. Entropy, enthalpy
1-10. Heat of Dissolution
1-11. Heat of Combustion
1-12. Thermal Conductivity and Linear
Expansion Coefficient
1-13. Thermal Decomposition, Thermal
Decomposition Product1-14. Combustion Characteristics (Limiting
Oxygen Concentration)
1-15. Dust Explosion

3-1.
3-2.
3-3.
3-4.
3-5.

2

Microstructure of PVOH

4

2-1.
2-2.
2-3.

Microstructure
Stereoregularity
Heterophilic Bonding (1,2-glycol
Bonding)
Terminal Structure
Branching
Double bond
Chain Distribution of Residual Acetate
Group

2-4.
2-5.
2-6.
2-7.

Behavior of PVOH Aqueous
Solution

Solubility in Water
Solubility in Other Solvents
Viscosity of Aqueous Solution
Stability of Aqueous Solution
Shear Velocity Dependency of Aqueous
Solution
3-6. Specific Gravity and Refractive Index
of Aqueous 0 Solution
3-7. pH of Aqueous Solution
3-8. Surface Active Performance
3-9. Permeability of Aqueous Solution
3-10. Contact Angle for Various Plastics
3-11. Compatibility with Water-soluble
Polymers
3-12. Dispersive/aggregating Action against
Clay Particles
3-13. Influence of Electrolyte
3-14. Gellant, Precipitant
3-15. Cloud Point
3-16. Biodegradability

4.1
4-2.
4-3.
4-4.

Physical Properties of PVOH
Film

Properties for Water
Mechanical Properties
Gas Permeability
Resistance to Oil, Resistance toOrganic Solvent
4-5. Optical Transparency
4-6. Electric Properties

1. Basic Physical Properties of PVOH

Basic Physical Properties of PVOH Resin

1. Basic Physical
Properties of PVOH
Resin
1-1. DEFINITION OF PVOHPOVAL is the popular name for polyvinyl alcohol (PVOH)
described as a organic polymer-based polymeric compound.
Polyvinyl alcohol is a substance that was first created byGerman scientist W. Hermann. It is chemically classified asa polymeric polyhydric alcohol having a secondary hydroxyl
group at every other carbon atom of a carbon chain and isexpressed by the following general structure. There areseveral methods known for the manufacturing of PVOH.
However, from an industrial point of view, the current
mainstream method of production is as follows. Polyvinyl
acetate is manufactured by radical polymerization using vinyl
acetate as a raw material and then hydrolyzing it under analkaline condition. Methanol is mainly used as a solvent in the-(CH2-CH)m-(CH2-CH)nOH

O
C=O
CH3

Figure 1. General structure of PVOH

References
1) Sone et al., Polymer Chemistry, 14, 149 (1970)

polymerization process / hydrolysis process.
The basic properties of PVOH are typically governed by the
degree of polymerization and the degree of hydrolysis. The
degree of polymerization of PVOH is generally indicatedby the viscosity-average degree of polymerization derived
from the viscosity in water. Additionally, when expressing
the degree of hydrolysis using the repeating units m and n in
Figure 1, the degree of hydrolysis can be expressed as follows:
Degree of hydrolysis (mol%) = m / (n + m) × 100. This is thevalue with which the proportion of the vinyl alcohol unit in all
the repeating units is indicated in mol%. For details of theseanalysis methods, refer to JIS K 6726.

3

Basic Physical Properties of PVOH Resin

1. Basic Physical Properties of PVOH

1-2. SPECIFIC GRAVITY
Although the apparent specific gravity of commerciallyavailable “PVOH” is approximately 0.6 to 0.7 g/cc, the values
in Table 1 are described in the Encyclopedia of Chemical
Technology (1970) by Kirk Othmer as the true specificgravities.
According to this table, the specific gravity of PVOH
decreases as the amount of residual acetate group increases,
and the values for partially hydrolyzed products of PVOH bySone, et al. shown in Figure 2 also show the same tendency.
Additionally, Sone reported that the specific gravity offully hydrolyzed PVOH was correlated with crystallinity
regardless of the degree of polymerization, heat treatment

temperature, etc. and the extrapolated specific gravities of
PVOH with crystallinities of 0 and 1 were 1.269 and 1.345,
respectively. On the other hand, there is a published reportthat the extrapolated specific gravity for 100% PVOH
concentration was about 1.27 when it was obtained from theactual measurement of the specific gravity of PVOH aqueous
solution at 30°C and thus the result that agreed well withthe specific gravity of 100% amorphous PVOH describedabove was obtained. In short, the specific gravity of PVOH
can be considered as a value slightly exceeding 1.27 for fullyhydrolyzed material.

Figure 2. Specific Gravity of PVOH (d30)
4Specific Gravity

4

1.30
1.29
1.28
1.27
1.26
1.25
1.24
1.23
1.22
1.21
1.20
1.19
1.18
1.17
0

10
20 30
40 50 60
70 80 90 100
Acetic Acid Content of Polyvinyl Alcohol (mol%)
Source: Sone et al., Polymer Chemistry, 10, 277 (1953)

1-3. REFRACTIVE INDEXIn the Encyclopedia of Chemical Technology (1970) by Kirk Othmer, the values in Table 2 are described. Additionally, values
such as n20= 1.513), n20= 1.50-1.524) are listed.
D
D
Table 2. Refractive Index of PVOH

Table 1. Specific Gravity of PVOH

Residual acetategroup (%)

d20
D

Residual acetategroup (%)

n20
D

0

1.329

0

1.557

5

1.322

5

1.553

10

1.316

10

1.548

20

1.301

20

1.539

30

1.288

30

1.530

40

1.274

40

1.521

50

1.260

50

1.512

60

1.246

60

1.503

70

1.232

70

1.494

Source: Kirk Othmer, Encyclopedia of
Chemical Technology (1970)
References
2) Kawakami et al., Report of POVAL Conference, 33, 113 (1953)
3) R. H. Wiley, Ind. Eng. Cham., 38, 959 (1946)
4) Ullmanns, Encyklopadie der technishen Chemie, 239 (1963)

Source: Kirk Othmer, Encyclopedia of
Chemical Technology (1970)

1. Basic Physical Properties of PVOH

Basic Physical Properties of PVOH Resin

1-4. SECOND-ORDER TRANSITION TEMPERATURE
Although there is much literature on the second-ordertransition temperature of PVOH, major measured values canbe summarized by the measurement method as shown in
Table 3.
These are the results measured for individual samples using
individual methods; however, there are the results of Uematsu

et al. shown in Figure 3 that reveal the difference owing tomeasurement methods for a series of samples. Although thevalue varies depending on the measurement method, it canbe said that the second-order transition temperature of fullyhydrolyzed PVOH is 70 to 85°C regardless of the differencein the degree of polymerization, molecular structure, etc.

Second-ordertransition
temperature (°C)

Measurement
methodSample used

Literature

71±2

Specific volume

Powder after vacuum
drying at 100°C for 8 hr

Yano, Chemical Society of Japan, 73, 708(1952)

65±3

Specific volume

Powder, stretched film

Futaba et al., Bussei-ron Kenkyu (Study on
Physical Properties Theory), 71, 51 (1954)

70±5Specific volume

Powder, stretched film

Futaba et al., Bussei-ron Kenkyu, 71,
51(1954)

70-80

Specific heat

Powder with a degree ofpolymerization of 550,
1550 after vacuum drying
at 65–70°C for 8 hr

Nitta et al., Annual Report of Fiber Science,Vol. 7, 31(1953)

70

Dielectric loss
angle

70

Dynamic
viscoelasticity

87

Staticviscoelasticity

60-70

NMR

Fiber

Nohara et al., Polymer Chemistry, 15, 105(1958)

70-

Moisture
absorption

FiberYano et al., Polymer Chemistry 11, 459(1954)

Hayashi et al., PVOH (by Hirabayashi)
Film

Tokita et al., J. Phys. Soc. Japan, 6, 367,
(1951)
Ofuka et al., Lecture at Chemical Society ofJapan, S30.4

Table 3. Second-order Transition Temperature of PVOH
Uematsu et al., Symposium on Macromoleculees (S28.11)

Second-order Transition
Temperature(°C)

9070Modulus method

50

30

0

Speccific volume
method

20

40

60

80

Acetic Acid Grup (mol%)Figure 3. Second-order Transition
Temperature of PVOH

100

5

Basic Physical Properties of PVOH Resin

6

1. Basic Physical Properties of PVOH

60

40

20

0
5

10

15

20

60

40

20

0

Water Content: 0
5

10

15

20

Water Content (%)

Glycerin Content (%)

Figure 4. Influence of Water Content on Second-order
Transition Temperature of PVOH

Figure 5. Influence of Glycerin Content on Second-order
Transition Temperature of PVOH

(1) Glycerin content
0%
(2)
6.39%
(3)
17.7%

60
Second-order Transition
Temperature(°C)

samples were prepared using a film after heat treatment at
140°C for 10 minutes and changing the water content byhumidity conditioning (films containing plasticizer were also
prepared using a similar method for various additive rates),
and then the values were obtained from the temperature
characteristics of the dynamic torsional rigidity modulus andlogarithmic damping rate that were measured using thesesamples.

Second-order Transition Temperature

Second-order Transition Temperature

Various effects such as the degree of hydrolysis, watercontent, plasticizer content ratio, etc. have been investigatedas the factors influencing the second-order transition
temperature of PVOH. The effect of the degree of hydrolysis
is shown in Figure 3. Additionally, as for the effects of watercontent and plasticizer, the results of actual measurements
using a film of PVOH (Kuraray PovalTM 25-100) with a degreeof polymerization of 1720 and a degree of hydrolysis of 99.85
mol% are shown in Figures 4 to 6. To obtain these values,

40

20

0

5

10

15

20

Water Content (%)
Figure 6. Synergistic Effect of Water Content and GlycerinContent on Second-order Transition Temperature of
PVOH

References
3) R. H. Wiley, Ind. Eng. Cham., 38, 959 (1946)
4) Ullmanns, Encyklopadie der technishen Chemie, 239 (1963)

1. Basic Physical Properties of PVOH

Basic Physical Properties of PVOH Resin

1-5. CRYSTALLINITY

Since PVOH is a crystalline water-soluble polymer, physicalproperties are greatly affected by its crystallinity. As an
example, the swelling volume of the film when it is immersed inwater (at 30°C for 48 hours) is shown in Figure 85). The swellingvolume of the film is correlated to the crystallinity of the film,
and it can be seen that whatever degree of polymerization
sample is used, the swelling volume closely correlates with the
crystallinity.

0.6

DP 309DP 1288

DP 708DP 23170.1
00

DP 4570

Swelling Volume (Times)

8
6
4
2

0.3

0.4

0.5

DP 2317

0.2

10

0.2

DP 708DP 4570

0.3

12

0
0.1

DP 12880.4

It is difficult to obtain the true crystallinity of PVOH. Typicalcrystallinity measurement methods are introduced here. For
details, please refer to the references.

14

DP 3090.5

Crystallinity

PVOH is widely recognized as a crystalline water-soluble
polymer. It is known that the degree of crystallinity varies
depending on the degree of hydrolysis and the degree ofpolymerization. In particular, the influence of the degree ofhydrolysis is large, and the higher the degree of hydrolysis, thehigher the crystallinity tends to be. Additionally, it is known
that the degree of crystallinity changes with external factors,
and it is particularly susceptible to the influence of heat
treatment. As for the crystallinity of a fully hydrolyzed PVOH,
the relationship between the heat treatment temperature(heat treatment time: 10 minutes) and the crystallinity of thefilm is shown in Figure 75). The crystallinity varies depending on
the degree of polymerization and, for PVOH with a low degreeof polymerization in particular, the crystallinity is low in theregion where the heat treatment temperature is low. However,the crystallinity of PVOH with any degree of polymerization
also rises with a rise in the heat treatment temperature; forheat treatment at 200°C, the crystallinity of PVOH with any
degree of polymerization are about the same (0.50–0.55).

0.6

Crystallinity
Figure 8. Crystallinity and Swelling Volume (30°C for 48 hr)

References
5) Ichiro Sakurada, Yasuhiko Nukushina, Yasuo Sone, Polymer Chemistry, 12, 506 (1955)

50

100

150

200

250

Heat Treatment Temperature (°C)
Figure 7. PVOH Film Heat Treatment Temperature (10 min)and Crystallinity

7

8

Basic Physical Properties of PVOH Resin

1. Basic Physical Properties of PVOH

Wide-angle X-ray: This is the most common measurement
method and an absolute value can be measured directly. If
the total scattering intensity curve of X-ray can be separated
into the scattering contribution of the crystalline region andthe scattering contribution of the amorphous region, thecrystallinity can be obtained from the ratios of the respective
areas to the total area. Separation of the crystalline andamorphous scatterings is done by waveform separation by theleast squares method6 - 8). However, in the case of PVOH, since
this waveform separation is difficult, a method of logicallyseparating the crystalline and amorphous scatterings is
performed 9).
Differential scanning calorimetry (DSC): This is a method formeasuring the endothermic amount associated with melting(melting enthalpy: ▲H). ▲H is proportional to the amountof crystallinity and the relative value can be obtained. The
advantages of the DSC are the speed of measurement
and that accurate measurement is possible even with avery small amount of sample. Note that ▲H measured by
the DSC is the relative value of crystallinity. Therefore, inorder to obtain the absolute value, it cannot be determined
unless ▲H is at a crystallinity of 100%, that is, the crystal
melting enthalpy (▲Hm) is known. It is not easy to determine▲Hm and the value varies depending on the measurement
method. The most appropriate method is to calibrate fromthe precisely measured X-ray crystallinity (Xc). Additionally,
for the measurement of ▲H by the DSC measurement,
there is a problem of the influence of the temperature risingprocess. The temperature rising process corresponds to heat
treatment and there is a possibility that ▲H is measured tobe larger than the actual value.

Infrared/Raman measurement: Measurement of crystallinity
by infrared or the Raman measurement is a method for
obtaining crystallinity from the intensity of the crystallization
band. In the case of PVOH, the crystallization band isobserved around 1144 cm-1 in the infrared measurement andit is also observed in the Raman measurement 10). There is aqualitative proportional relationship between the intensity of
the crystallization band and the crystallinity. However, there isa critical point in the appearance of the infrared band and theband does not appear in an ordered structure below a certain
size. For this reason, there is no proportional relationshipbetween the crystallization band intensity and the X-ray
crystallinity in the infrared measurement in a precise sense.
This problem also applies to the Raman measurement.
Density measurement: This is a classical method forcrystallinity measurement. Since the density of the crystalline
part is higher than that of the amorphous part, the sample
with higher crystallinity has a higher density. This relationshipis used to obtain the crystallinity. However, it is necessary toknow the values of the crystalline density and the amorphousdensity in advance. This is a classic but less arbitrary method.
Since this method is based on a crystal-amorphous twophase model, it is a problem that the amorphous density is
assumed to be constant. Actually, the part considered as
the amorphous phase contains the intermediate phase, andtherefore the amorphous density is not constant.

References
6) Yasuhiko Nukushina, Kobunshi Jikken Gaku Koza 2, Edited by The Society of Polymer Science, Japan, Kyoritsu Shuppan (1957)
7) S. L. Aggarwal and G. P. Tilley, J. Polymer Sci., 18, 17 (1955)
8) A. M. Handeleh and D. J. Johnson, Polymer, 13, 27 (1972)
9) Y. Fu, W. R .Busing, Y. Jim, K. A. Affholter, and B. Wunderlich, Macromolecules, 26, 2187 (1993)
10) H. Tadokoro, The Structure of Macromolecule, Chapter5, P.187-351 (1976)

1. Basic Physical Properties of PVOH

Basic Physical Properties of PVOH Resin

1-6. MELTING POINT
The melting point of PVOH is obtained exclusively from theendothermic peak temperature by the differential scanningcalorimetry. As typical differential thermal analysis curvesof fully hydrolyzed PVOH, actual measurement results areshown in Figure 9. To obtain these results, Kuraray PovalTM 2898 in the powder state was re-saponified (fully hydrolyzed)
and then it was extracted with methanol sufficiently to
prepare samples for the measurement. In these curves,

sharp endothermic peaks can be seen around 235°C. As
for the PVOH samples used for the measurement, pyrolysis
may occur before reaching the melting point of PVOH in
the temperature rising process if impurities such as sodium
acetate are mixed, and thus the accurate melting point may
not be measured. Therefore, it is necessary to sufficiently
refine the samples in advance.

Sample A▲H

Sample A: Kuraray PovalTM 28-98 withre-saponifying and methanol extraction by
SoxhletSample B: Sample A with hot-air drying at
115°C for 60 min.
Measurement condition: Atmosphere - Air
Heating rate: 5°C/min

Sample B

20 40 60

80 100

120

140

160

180

200

220

240

260

Temperature (o C)
Figure 9. Differential Thermal Analysis Curves of Re-saponified
Kuraray PovalTM 28-98

Although the melting point of PVOH decreases as theamount of residual acetate group increases, the degree of
decrease depends on the distribution state of the residual
acetate group in the molecule. As shown in Figure 10, in thecase in which the residual acetate group is almost completely
distributed blockwise (a), the melting point of PVOH hardly
decreases. Conversely, in the case in which the residual

acetate group is distributed almost randomly (c), the melting
point of PVOH linearly decreases in proportion to the amountof the residual acetate group. Commonly marketed PVOH issaponified under an alkaline condition in a methanol solventand shows a melting point decrease as shown in (b). Therefore,
it is known that the distribution state of the residual acetategroup is intermediate between block and random.

230
(a)

Melting Point (C)210
Sample:a: Saponified with alkalineaqueous solution
b: Saponified with alkaline/
methanol solution
c: Reacetylated PVOH

190

170
(b)
(c)

150
0

4

8

12

16

20

Residual acetate group (mol%)Figure 10. Influence of Residual acetate Group Amount and Its
Distribution State on Melting Point of PVOH

9

Basic Physical Properties of PVOH Resin

1. Basic Physical Properties of PVOH

It is known that the melting point of PVOH also varies withother factors influencing the crystallinity. One of them isstereoregularity. While ordinary PVOH is atactic PVOH, it ispossible to synthesize isotactic PVOH and syndiotactic PVOH
by changing the polymerization mode and the raw material
monomer 11). The melting points of these stereoregular PVOH
are shown in Figure 11 12).

PVOH crystallizes and has melting points in all thestereoregularities. As the stereoregularity increases,
the melting point increases in both isotactic PVOH andsyndiotactic PVOH, with the melting point of atactic PVOH
as a minimum.

PVOH from Pt-BVE

Model Structure of Fully Hydrolyzed
PVOH withDifferent Stereoregularity(The graphical method by Natta)
Isotactic Structure

PVOH from PVOSi
PVOH from PVAc
250

H

H

H

H

H

H

~C CH2 C CH2 C CH2 C CH2 C CH2 C~
OH

OH

OH

OH

OH

mp (°C)OH

Syndiotactic Structure
H

OH

H

OH

H

OH

H

OH

H

OH

OH

OH

H

H

220

210
100

OH

H

H

OH

OH

80

60

40

20

Figure 11. Relationship between Melting
Point and Tacticity

H

Additionally, 1,2-glycol bond is a factor influencing the
crystallinity of PVOH. The 1,2-glycol bond in PVOH is a resultof heterophilic bond during the polymerization of vinyl acetate
as a raw material. That is, the polymerization of vinyl acetate
usually grows with head-to-tail addition, but trace amountsof the head-to-tail – tail-to-head addition is produced, whichbecomes 1,2-glycol bond. The amount of 1,2-glycol bond is

uniquely determined by the polymerization temperature 13),and it increases as the polymerization temperature increases
and decreases as the polymerization temperature decreases.
The melting points of PVOH with various 1, 2-glycol bondamounts are shown in Figure 12. As the amount of 1,2-glycol
bond, which is a heterophilic bond, increases, the crystallinity
decreases and the melting point also decreases.

250
240

230
220

210

200
0.5

1.0

1.5

2.0

0

Isotacticity in triad (%)~C CH2 C CH2 C CH2 C CH2 C CH2 C~
OH

230

H

Atactic Structure
H

240

OH

~C CH2 C CH2 C CH2 C CH2 C CH2 C~

mp (°C)

10

2.5

3.0

1,2-glycol content (mol%)Figure 12. Relationship between Melting Point and1,2-glycol Bond Amount

References
11) Toshiaki Sato, “PVOH no Sekai (The World of PVOH)”, Kobunshi Kankokai, 1 (1992)12) Masao Sumi, Keiji Matsumura, Ryotaro Ohno, Shunichi Nazakura, Shunsuke Murahasi, Polymer Chemistry, 24, 606 (1967)
13) Naoki Fujiwara, Toshiaki Sato, Hitoshi Maruyama, Kazutoshi Terada, Takuji Okaya, Report of 104th POVAL Conference, 114, (1994)

1. Basic Physical Properties of PVOH

Basic Physical Properties of PVOH Resin

1-7. SPECIFIC HEATAs for the specific heat of PVOH, there are only two measured values reported in the literature and there are considerable
differences between them. These values are shown in Table 4.

Measured Value

Literature

0.4 cal/(deg)(g)Encyc. of Polymer Science andTechnology, Vol. 14, 159 (1971)

0.00105 Kcal/(deg)(g) R

R. W. Warfield, Kolloid Z., 185, 63(1962)
Table 4. Specific Heat of PVOH

1-8. LATENT HEAT OF MELTING
The latent heat of melting of PVOH can be obtained by two methods. That is, a method of indirectly calculating from that of
the copolymer using Flory equation or the Baur’s theory, and a method of measuring the melting heat in a two-component
system containing an appropriate diluent and calculating the melting point of PVOH using Flory’s equation. These values areshown in Table 5.

Measured Value (Kcal/mol) andMeasurement Method

Literature

0.56, copolymer (Flory’s equation)

J.P.S.A-1, 4, 623 (1966)

1.67, copolymer (Flory’s equation)

Kikukawa et al., Polymer Chemistry, 25, 19 (1968)

1.57, copolymer (Flory’s equation)

R. K. Tubbs, Monograph No.30,
Society of Chemical Industry, London, 88 (1968)

1.64, dilution method (Glycerin)

J.P.S.[A]3, 4181(1965)

1.67, copoly 2.47, dilution method (Water)
2.00, dilution method (Ethylene glycol)
1.43, dilution method (Dimethylformamide)
1.47, dilution method (Acetamide)mer (Flory’s equation)

Hamada et al., Polymer Chemistry 23, 395 (1966)

Table 5. Latent Heat of Melting of PVOH

11

12

Basic Physical Properties of PVOH Resin

1. Basic Physical Properties of PVOH

1-9. ENTROPY, ENTHALPY
The melting entropies of PVOH are shown in Table 6.
The melting enthalpies of PVOH are shown in Table 7.

Described Value

Literature

0.2655 cal/(deg)(g) at 245°C

Kirk Othmer, Encyc. of Chem. Tech.,
Vol21 (1970)

3.3 cal/(deg)(mole)

Encyc. of Polymer Science andTechnology, Vol14 (1971)

3.27 (e.u.)

R. K. Tubbs, J.P.S.(A)3, 4181(1965)
Table 6. Melting Entropy of PVOH

Described Value

Literature

32.45 cal/g at 245°C

Kirk Othmer, Encyc. of Chem. Tech.,
Vol21 (1970)
Table 7. Melting Enthalpy of PVOH

1-10. HEAT OF DISSOLUTION
The amount of heat diffused or absorbed when PVOH
is dissolved in water, that is, the heat of dissolution withrespect to water, is the energy generated when the hydrogenbond between PVOH molecules and/or water molecules is
destroyed and new hydrogen bonds are formed between
polymers and water molecules. According to a report by
Meerson et al., when PVOH is dissolved in water, it generates
heat at a water temperature of 55°C or lower and absorbs
heat at a water temperature of 55°C or higher, as shown in
Figure 13. They reported that the relationship as shown in thefollowing formula was established between the dissolution
heat ▲Hd (T) and the dissolution temperature T (°C) inthe temperature range from 25°C to 80°C, and the heat ofdissolution ▲Hd (Tg) of PVOH at its second-order transition
temperature Tg (°C) was 6.25 cal/g.
▲Hd(T) = ▲Hd(Tg) – 0.25 (Tg-T) 14)
As for the heat of dissolution of PVOH with different degreeof hydrolysis, there is a report by Oya 15). As shown in Figure
14, the heat of dissolution of PVOH with respect to waterat 30°C decreases linearly as the acetate group content
increases when the degree of polymerization is 1400 or 165

References
14) Meerson, Kolloid-Z, 18, 447 (1956)
15) Oya et al., Polymer Journal, 12, 122 (1956)
16) Sone et al., Polymer Journal, 10, 277 (1953)(in this case, heat generation is observed and the amount ofheat generation increases linearly). Additionally, the heat ofdissolution is almost constant when the amount of acetategroup is around 20 mol%, about -9.8 cal/g for the degree ofpolymerization of 1400 and about -8.1 cal/g for the degreeof polymerization of 165, and the heat of dissolution shows
almost no change when the amount is more than 20 mol%. The
tendency of the heat of dissolution to decrease in accordancewith increase of acetate group well supports the general factthat PVOH with a low degree of hydrolysis dissolves well at
low temperature. In the report, Oya described that there wasa bending point around the acetate group amount of 20 mol%and this showed good agreement with the case of the specificgravity of PVOH according to the research by Sone et al. 3),
and it could be thought that it was a result of the differencein the aggregation state of PVOH molecules. However, as forthe influence of the degree of polymerization, Oya concluded
that although the difference in the heat of dissolution owing
to the degree of polymerization was supposedly recognized,
it was difficult to make a detailed discussion based on theexperimental result of such extent.

1. Basic Physical Properties of PVOH

-300

4

-400
Heat of Dissolution(cal/mol)6-▲Hd(cal/g)

2
0
-2
-4
-6

Basic Physical Properties of PVOH Resin

-500
-600

Degree ofpolymerization: 165

-700
-800
-900

Degree of polymerization: 1400
-1,000

0

20

40

60

80

Dissolution temperature (°C)
S I Meerson,
Kolloid-Z, 18, 447-('56)
Figure 13. Heat of Dissolution of PVOH

0

5

10

15

20

25

30

35

40

Acetate Group Content of Polyvinyl Alcohol (mol%)Oya, Polymer Journal, 12, 122-('55)
Figure 14. Heat of Dissolution of PartiallyHydrolyzed PVOH (Dissolution Temperature: 30°C)

1-11. HEAT OF COMBUSTIONIn the Encyclopedia of Chemical Technology (Vol. 21, (1970)),
the heat of combustion of PVOH is described as 5902 cal/g
17). In B.C.S.J (Vol.40, 2700–), there is a report that the heatof combustion per monomer unit is 263.2 Kcal. This value isconverted to about 5980 cal/g and shows good agreementwith the value of the former.

1-12. THERMAL CONDUCTIVITY, LINEAR EXPANSION COEFFICIENT
There is little data on the physical properties of PVOH suchas thermal conductivity and linear expansion coefficient.
This is probably because PVOH is not relatively used as a socalled molded product.

As for the values of thermal conductivity, 5×10-4 cal/(sec)(cm2) (°C/cm) for extruded products and 5×10-4 cal/(sec)(cm2)(°C/cm) for casted products are reported in Mod. Plastics, 18,
6, 53 (1941).

13

Basic Physical Properties of PVOH Resin

1. Basic Physical Properties of PVOH

1-13. THERMAL DECOMPOSITION, THERMAL DECOMPOSITION PRODUCTPVOH colors gradually and becomes difficult to dissolve inwater when it is heated in air. In particular, coloring occurs
remarkably at a temperature of 130°C or higher, and thermal
decomposition progresses gradually when the temperature
exceeds 200°C. The thermal decomposition mechanismof PVOH was researched by Yamaguchi et al. 18, 19) and
Tsuchiya et al. 20). An example of the thermal decomposition
mechanism is shown in Figure 15.
It is assumed that the coloring of PVOH during heat
treatment is caused by the formation of the enone structure

OH

OH

OH

in the initial reaction of thermal decomposition of PVOH.
In this reaction, the hydroxyl group is oxidized to a ketone
group and then the hydroxyl group adjacent to the formed
ketone group is dehydrated. It is observed in UV absorption
spectrum that absorptions of PVOH around 230 nm, 280 nm
and 330 nm increase by heating in air. These absorptions
correspond to the repeating unit n = 1 to 3 of the carboncarbon double bonding in the enone structure. In Figure 15 itis thought that the coloring occurs by absorbing light in thevisible light region owing to an increase in their chain length .

OH

Oxidation

[

[n

OH

OH

*

OH

OH

O

OH

Scission

Dehydration

[

[n

OH

O

OH

Scission

[

H
+

O

O

[n *
OH

Scission
acetoaldehyde,
crotonaldehyde various
aldehydes and ketons

Intra and/or inter molecule
cyclization-H

and/orand/orgeneration of char
Figure 15. Thermal Decomposition Mechanism of PVOH

In the temperature range of 200°C or higher, a decrease in weight occurs because volatilization of thermally decomposedcomponents starts to occur. Figures 16 and 17 show the rates of decrease in weight when Kuraray PovalTM 28-98 and Kuraray
PovalTM 5-88 are heated (10°C/min) in air or in nitrogen.
Kuraray PovalTM 28-98

Kuraray PovalTM 28-98

Kuraray Poval

Kuraray PovalTM 5-88

TM

5-88

100

100

90

90

80

80

70

70
Weight loss

Weight loss

14

60
50
40

60
50
40

30

30

20

20

10

10

0

0

100

200

300

400

500

600

700

0

0

100

200

300

400

500

600

700

Temperature (°C)

Temperature (°C)

Figure 16. Thermal Decomposition of PVOH
(Rate of Temperature Rise: 10°C/min, in air)Figure 17. Thermal Decomposition of PVOH
(Rate of Temperature Rise: 10°C/min, in
nitrogen)

References
17) Texas. Rept. Miol. Med. 23(2), 432(1965)

Basic Physical Properties of PVOH Resin

1. Basic Physical Properties of PVOH

In the heating test in air, it is considered that PVOH is almost
completely decomposed thermally around 450 to 500°C andthe decomposition products are volatilized. Meanwhile, inthe heating test in nitrogen, the decrease in weight becomes
gradual at around the same temperature and about 5%of nonvolatile components remain at the time when thetemperature reaches 700°C. The residues are considered tocorrespond to so-called Char in the thermal decomposition
mechanism, as shown in Figure 15. There are many reports onwhat is generated by the thermal decomposition and on thedecomposition products. Some examples are shown in Tables
8 and 9.

Table 8. Thermal Decomposition Product of PVOH 20)

Table 9. Thermal Decomposition Product of PVOH

Thermal Decomposition
Product

Weight % (based on
the starting weight)

Example

1

2

3

Water

33.4

Decomposition
temperature e (°C)

220–
240

270–
280

500

Carbon monoxide

0.12Atmosphere

Air

Air

VacuumCarbon dioxide

0.18

Heating time (h)1010Unknown

Hydrocarbons (C1, C2)

0.01

0.05

0.05

13-15

Acetaldehyde

1.17

Residual acetate groupof sample (mol%)

Acetone

0.38

Rate of weight decrease
(%)

36

41

95

Ethanol

0.29

Decomposition product(mol/PVOH basic mol)

Benzene

0.06

Water

0.62

0.635

0.670

Crotonaldehyde

0.76

Acetic acid

3-Penten-2-one

0.19

Acetaldehyde

0.02140.01170.378

2,4-Hexadiene-1-ol

0.55

Crotonaldehyde

0.01460.01180

3,5-Heptadiene-2-one

0.099

2,4-Hexadiene-1-ol

0

0

0

Benzaldehyde

0.022

2,4,6-Octatriene-1-ol

0

0

0

Acetophenone

0.021

Benzaldehyde

0.00250.00350

2,4,6-Octatriene-1-ol

0.11Acetone0003.5.7-Nonatriene-2-one

0.020

3-Penten-2-one

0

0

0

Other

0.082

3,5-Pentadiene-2-one

0

0

0

3,5,7-Nonatriene-2-one

0

0

0

Acetophenone

0.00190.00510.0051Ethanol

0

0

0.053

Carbon monoxide

0

0

0.070

Carbon dioxide

0

0

0.014

Benzene000

Phenols

Trace

Trace

0

* Sample: Degree of polymerization = 3300, degree of hydrolysis= 99 mol% or higher* Decomposition condition: Heating under vacuum at 240°C for
4 hr

References18) Yamaguchi et al., Polymer Chemistry, 18, 406 (1961)
19) Yamaguchi et al., Polymer Chemistry, 18, 653 (1961)
20) Tsuchiya et al., J.P.S., A-1, 7, 3151 (1969)
21) C.A., 68, 60189-g (1968)
22) Doklady Phys, Chem., 154, 125 (1964)

0.094

15

Basic Physical Properties of PVOH Resin

1. Basic Physical Properties of PVOH

1-14. COMBUSTION CHARACTERISTICS (LIMITING OXYGEN INDEX)
The flammability of PVOH is generally said to be nearly
that of paper. As one method to quantitatively compare
the flammability of plastics, there is a report in which thelimiting oxygen index was determined 23). Considering air asa mixture of oxygen and nitrogen, the oxygen volume ratio
in normal air is about 0.21. Limiting oxygen index (n) is thelowest oxygen concentration required for a specimen to keepburning stably even after removing the ignition source. Thisvalue was measured by burning long and narrow plastics
such as a candle in an atmosphere in which the volume ratioof oxygen and nitrogen is changed. The value (n) of PVOH
specimen with a degree of saponification of 98 mol% anda degree of polymerization of 550 was reported as 0.225 ±0.004. This indicates that an atmosphere with a slightly higher
oxygen concentration than ordinary air is necessary for the
specimen to maintain a stable burn. Based on the value in thispaper, PVOH is less flammable compared to polyethylene (n:0.174 –), polystyrene (n: 0.181 –), etc., but is considered tobe comparable to polyvinyl chloride (n: 0.45), polyvinylidene
chloride (n: 0.60), Teflon (n: 0.95), etc.

1-15. DUST EXPLOSION
The ignition and explosion properties of PVOH powder are
greatly affected by the natures of PVOH such as the average
particle diameter and its distribution, the content of organic
volatiles, moisture content, etc., fine particle size concentration,
humidity conditions and the like. For this reason, it is basically
impossible to obtain a measurement value common to all
PVOH.
Although representative measured values are shown below,
please understand that they are not common to all PVOH, asmentioned above.
Fine powder of Kuraray PovalTM 22-88 (passing a sieve with
an opening of 63 μm, methanol content of 0.01%, methyl
acetate of 0.04%) was used as a measurement sample. A
minimum ignition energy measuring device (Type MIKE3) by
A. Kühner manufactured in accordance with the international
standard “IEC 61241-2-3 (1994-09), Section 3: Method for
determining minimum ignition energy of dust / air mixtures”
was used. This device can change the discharge energy by 7
steps of 1 mJ, 3 mJ, 10 mJ, 30 mJ, 100 mJ, 300 mJ and 1 Jwith the capacity discharge method. Additionally, a method
in which sample powder was blown up by compressed air anddispersed in a 1.2 L explosive cylinder was adopted.

In the measurement, a test with a predetermined amountof sample and discharge energy was carried out 10 times tocheck wthether the sample ignites or not. When it ignited atleast once, it was determined that there was ignition underthat condition. Next, this operation was repeated by variously
changing the sample amount and discharge energy to obtain
ignition by the predetermined discharge energy for eachsample amount. The ignition delay time was changed asnecessary to obtain ignition. The results are shown in Table 10.
Figure 18 shows the relationship between the dust
concentration and the discharge energy based on the dataof Table 10. The minimum ignition energy (Emin) is in the range
from the non-ignited maximum discharge energy (E2) to theignited minimum discharge energy (E1) (E2 < Emin <E1). Thatis, the minimum ignition energy (Emin) of this sample is in therange from 30 mJ to 100 mJ(30 mJ < Emin <100 mJ) and its
statistical minimum ignition energy (Es) is 42 mJ. Note thatthe statistical minimum ignition energy was calculated basedon the calculation formula described in European Standard
EN 13 821: 2002.
Therefore, since PVOH has a risk of dust explosion with static
electricity as an ignition source, it is necessary to securely
ground the equipment, piping, etc. and to take measures
such as using conductive materials.

1000

Ignition Zone
Discharge Energy (mJ)

16

100
Figure 18. Relationshipbetween PVOH Dust
Concentration and Discharge
Energy10
Non-Ignition Zone

1
References
23) C. P. Fenimore, Modern plastics, 43, 141 (1966)

0

500

1000

1500

2000

Dust Concentration (g/m )
3

2500

3000

1. Basic Physical Properties of PVOH

Basic Physical Properties of PVOH Resin

Table 10. Minimum Ignition Energy of PVOH Floating Dust

Sampleamount (g)Dustconcentration(g/m3)

Dischargeenergy (mJ)

Ignition delay
time (min)Ignition 1

0.075

62.5

1000

60

×

0.15

125

300

90

×

300

60

O5)

1000

60

×

300

120

O(6)

100

120

×

100

90

×

100

60

×

100

120

×

100

150

O(3)

30

150

×

30

180

×

100

120

×

100

150

O(6)

30

150

×

30

180

×

100

120

×

100

150

O(6)

30

150

×

30

180

×

100

120

×

100

150

O(3)

30

150

×

30

180

×

100

120

×

100

150

O(3)

30

150

×

30

180

×

0.3

0.6

1.2

1.8

2.4

2.4

250

500

1000

1500

2000

2500

1) The test was conducted 10 times under the same condition, and the condition without ignition is marked
with x. The condition with ignition is marked with ○ and the number of times required for ignition is shown inparentheses.

17

18

Basic Physical Properties of PVOH Resin

2. Primary structure of PVOH

2. Primary structure of
PVOH
2-1. PRIMARY STRUCTURE
A PVOH polymer chain is schematically shown in
Figure 19. PVOH is a copolymer of vinyl alcoholand vinyl acetate, and it contains most of the items
that are problematic in the primary structure ofa polymer, such as stereoregularity, short chain
branching, heterophilic bond (1,2-glycol bond),
double bond, end group, as well as sequence
distribution of vinyl alcohol and vinyl acetate.

CH-CH2-(CH=CH)n-C-CH2

|

||
O

OH

CH-CH2-CH2-CH-C-CH2

|

|

OH

|

OH OH

Heterophilic Bond
(1,2-glycol Bond)

Double Bond
CH-CH2-CH2

|

|

OH

CH2

OH

|

CH2-CH2-(CH-CH2)m - C-OH

End group|

OH

CH-CH-CH2

|

|

|

OH

CH2

|

OH OH
OH

|

CH2-CH-CH2-CH-CH2-CH|(CH2-OH)-(CH2-CH)

|

|

OH

OH

OH

Stereoregularity|

OAg

Seaquence Distribution

Figure 19. Primary structure of PVOH

2-2. STEREOREGULARITY
The stereoregularity of PVOH, can be measured by several
methods such as infrared absorption spectrometry 24,25)
and the NMR measurement 25) have been proposed. As amethod that can determine the stereoregularity with thehighest accuracy, there is the 1H-NMR 26-28) or 13C-NMR 29-31)
measurement with the DMSO-d6 solution of PVOH. The
chart of the hydroxyl group part of 1H-NMR is shown in
Figure 20.

As for the effects of stereoregularity on PVOH physicalproperties, the melting point has already described in theprevious chapter. In addition to this, there is the aqueous
solution stability. Figure 21 shows the solution stabilitiy ofconcentrated aqueous solutions with different tacticity.

With respect to 1H-NMR, it is split into isotactic, atactic
and syndiotactic from the low magnetic field side, and thetriad tacticity is determined based on the integral ratio. On
the other hand, with respect to 13C-NMR, the higher-orderstereoregularity up to heptad can be evaluated based on the
splitting of methine carbon of PVOH.

References
24) K. Fujii and J. Ukida, Makrmol. Chem., 65, 74 (1963)
25) Shunsuke Murahasi, Shunichi Nazakura, Masao Sumi, Heimei Yuki, Koishi Hatada, Polymer Chemistry, 23, 605 (1966)
26) J. R. DeMember, H. C. Haas et al, J. Polym. Sci., Polym. Lett. Ed., 10, 385 (1972)27) T. Moritani, I. Kuruma, K. Shibatani, Y. Fujiwara, Macromolecules, 5, 577 (1972)
28) T. K. wu and D. W. Ovenall, Macromolecules, 6 (No.4), 240 (1973)
29) Y. Inoue, R. Cyujo, and A. Nishioka, Polymer J., 4 (No.3), 244 (1973)30) T. K. Wu and M. L. Sheer, Macromolecules, 10 (No. 3), 529 (1977)
31) D. W. Ovenall, Macromolecules, 17, 1458 (1984)

Basic Physical Properties of PVOH Resin

2. Primary structure of PVOH

Racemo diad: 53.0 mol%
Racemo diad: 50.0 mol%
(a)

(b)

(c)

Aqueous Solution Concentration: 12 wt%
Racemic Form: 53.0 mol%
Racemic Form: 50.5 mol%
700
600

Concentration of
aqueous solution: 12%

ŋ (mPa s)

500

5

4

5

4

5

4

400
300
200

S (ppm)100(d6-DMSO, 500Mz)(a) it-PVOH (mm/mr/rr=79.1/18.9/2.0(b) at-PVOH (mm/,mr/rr=22.0/48.8/29.2)(c) st-PVOH (mm/mr/rr= 14.1/48.9/37.0)

0
0

200

400

600

800

Standing Time (hr)Figure 20. 1H-NMR Spectrum of Stereoregular PVOH

Figure 21. Temporal Change of Viscosityof PVOH Aqueous Solution with Different
Stereoregularity

Generally PVOH is basically atactic, it contains a slightly
more racemo diad (syndiotactic structure). Normally, when
the concentrated aqueous solution of general PVOH is left at
low temperature, this solution thickens with time and turns
into a gel (Figure 21: Racemo diad: 53.0 mol%). In contrast,
the solution of PVOH, in which the meso diad increased by
2–3 mol% only, is not changed into gel even if the solution isleft for a long time 32) (Figure 21: Racemo diad: 50.5 mol%).
This is thought to be a result of the decrease in the racemo

diad that can form intermolecular hydrogen bonds and theincrease in the meso diad form that cannot form the bonds.
As described above, the tacticity of PVOH influences greatly
on the physical properties.On the other hand, it is essential
to change the polymerization method and the raw material
monomer in order to change the tacticity. For this reason,
PVOH having a special tacticity is not industrially produced
at the present time.

2-3. HETEROPHILIC BOND (1,2-GLYCOL BOND)
A considerable amount of 1,2-glycol bond exists in the heterophilic bondof PVOH 33). The quantitative determination method of 1,2-glycol bond by
1
H-NMR 34) and 13C-NMR35) has been studied 35).
As for the amount of 1,2-glycol bond and the melting point of PVOH, they
were already described in “Melting Point” of the previous chapter. Here,the correlation between the amount of 1,2-glycol bond and the viscosity
stability of the concentrated aqueous solution is shown in Figure 22 36).

References
32) Kiyokazu Imai et al, Content of 31st Symposium on Macromolecules, p. 1309 (1982)
33) P. J. Flory and F. S. Leutner, J. Polymer Sci., 3, 880 (1948)34) S. Amiya and M. Uetsuki, Analytical Science, 1, 91 (1983)
35) S. Amiya and M. Uetsuki, Macromolecules, 15, 166 (1982)
36) Shigetoshi Amiya, Report of 92nd PVOH Meeting, (1988)
37) K. Imai and M. Matsumoto, J. Polymer Sci., 55, 335 (1961)38) Imoto, Polymer Chemistry 16, 125 (1959)

1.6 mol%
0 mol% (Pn=170)
200

150□ (mPa s)

Figure 22 shows the temporal changes in the viscosity of 12% aqueous
solutions of samples with a nearly identical degree of polymerization,
containing 1,2-glycol bond of about 1.6 mol% and containing no 1,2-glycol
bonding. Although the viscosity of the solution containing no 1,2-glycol
bonding started to thicken quickly after 200 hours had elapsed , the solution
turned into a gel. The viscosity of the ordinary PVOH solution (the amoutof 1,2-glycol bond: 1.6 mol%) hardly changes under the same condition.
This is interpreted to mean that the intermolecular interaction of PVOH is
inhibited by 1,2-glycol bond. Additionally, it is known that 1,2-glycol bond
becomes a factor disturbing the structure, such as decreasing the iodine
coloring ability to PVOH 37), and existing in the amorphous part, not in the
crystalline region 38).

Concentration of aqueous solution: 12%
Standing temperature: 20o C
1, 2- glycol

100

50

0

0

100

200

300

400

500

Standing Time (hr)Figure 22. Temporal Change of Viscosityof PVOH Aqueous Solution with Different
1,2-glycol bond Content

19

20

Basic Physical Properties of PVOH Resin

2. Primary structure of PVOH

2-4. END STRUCTURE
PVOH is obtained mainly from vinyl acetate as a raw material
through a radical polymerization process and a saponification
process. However, in the radical polymerization process
in particular, the growing end radical of vinyl acetate has
extremely high reactivity and the chain transfer reaction
occurs easily. Therefore, PVOH is characterized by theend structure being changed depending on the type andconcentration of the solvent, monomer concentration andinitiator to be used, the conversion of polymerization, thepolymerization temperature and the additives. The end
structure of general PVOH is mostly of the methylol groupformed by the chain transfer to the solvent (methanol) andthe methylol group and methyl group terminated by thechain transfer 39). Additionally, there is a sodium carboxylate
or y-lactone structure where molecules that are chaintransferred to a methyl proton of the acetate group ofvinyl acetate or polyvinyl acetate produced in the reaction
system are produced by hydrolysis of the acetate groupin the saponification process. Although a small amountof the end derived from the initiator can be observed, theamount is extremely small compared with those of other end
structures. It is considered that this is a result of the fact
that, in the radical polymerization system of vinyl acetate,
the rate of chain transfer is larger than that of termination.

2-5. BRANCHING
In the state of polyvinyl acetate before saponification, long
chain branching exists in the side chain owing to the chaintransfer to the methyl proton of an acetate group as describedabove. However, it is considered that such long chain branchingdoes not exist in the PVOH state because it is eliminated by thesaponification reaction. As the branching observed in PVOH,

there is short-chain branching generated by back-biting
reaction. The formation mechanism of short-chain branching by
back-biting reaction is shown in Figure 23. The end methylolgroup of the butyl short-chain branching can be quantified
by the 13C-NMR measurement. However, these short-chain
branches are not detected in general PVOH.

Polymer

OAc

OAc

Polymer

H
AcO

H

Polymer

[

OAc

AcO

OAc

[

*

Polymern

OAc OAc
AcO
AcO

[

[

*

n

OAc OAc
HOHO

Figure 23. Formation Mechanism of Short-chain Branching by
Back-biting reaction

References
39) Shigetoshi Amiya, Report of 86th PVOH Meeting, 37 (1985)

2. Primary structure of PVOH

Basic Physical Properties of PVOH Resin

2-6. DOUBLE BOND
Coloring occurs when PVOH is heated. This is considered tobe caused by conjugated double bonds of a certain length
existing in the main chain. For the formation mechanism of
double bonds etc., refer to the “Thermal Decomposition
Product” in the previous chapter. Although the carbonylgroup produced by oxidation of the hydroxyl group of PVOH
is thought to be the base point for double bond formationin heat treatment, there is a method using chain transfer
polymerization as a method for introducing the carbonylgroup other than oxidation of the hydroxyl group. In the

CH3C-(CH2CH)-HO

OAc

coexistence of aliphatic aldehydes such as acetaldehyde, it ispossible to introduce the carbonyl group to the polymer end
by radical polymerization of vinyl acetate.
An example of the introduction is shown in Figure 24. The
polyene structure is produced by saponifying the obtained
polymer and heat-treating it. The obtained PVOH exhibits
UV absorption peaks at aroud 230 nm, 280 nm, 330 nm which
depend on the length of the conjugated polyene (n = 1, 2 and
3) 40 -41).
Saponification
Heat Treatment

CH3C-(CH=CH)n-(CH2CH)-H
O(n=2~3)OH

Figure 24. Double bond structure contained in PVOH

2-7. CHAIN DISTRIBUTION OF RESIDUAL ACETATE GROUPS
Partially hydrolyzed PVOH shows significant differences ofphysical properties such as surface activity depending on
the amount of residual acetate groups and the sequence
distribution of residual acetate groups. Measurementsof Iodine absorbance 42) and melting point 41) are known
as the indirect methods for estimating the distribution ofresidual acetate groups. For the melting point and thechain distribution, refer to “Melting Point” in the previous
chapter. Meanwhile, as for direct measurement methods,
there is a report using a block character ŋ by the 13C-NMR
measurement 44) and a composition analysis using a liquid
chromatogram by Dawkins et al. 45)

References40) Yamaguchi, Amagasa, Kinumaki, Takahashi, Kobunshi Kagaku, 16,
571 (1959)
41) K. Maruyama, Y. Kuramoto, M. Yagi, and Y. Tanizaki, Polymer, 29, 24(1988)

42) Hayashi, Nakano, Motoyama, Kobunshi Kagaku, 20, 303 (1963)
43) R. K. Tubbs, J. Polymer Sci., A-1, 4, 304 (1966)
44) T. Moritani and Y. Fujiwara, Makromol. Chem., 10, 532 (1977)45) J. V. Dawkins et al., Polymer, 40, 7331 (1999)

21

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

3. Behavior of PVOH
Aqueous Solution
3-1. SOLUBILITY IN WATER
PVOH is used mainly in aqueous solution. Its solubility
in water depends on its degree of hydrolysis, degree ofpolymerization and degree of heat treatment received
during the manufacturing process. The effect of thedegree of hydrolysis is especially significant. PVOH has
many hydroxyl groups with extremely high affinity forwater. These hydroxyl groups act to induce strong interand intramoleculare hydrogen bonding, which significantly
inhibit the solubility in water. On the other hand, the residual
acetate groups in partially hydrolyzed PVOH are essentiallyhydrophobic. As the number of acetate groups increases,
steric hindrance increases, and disturbs the arrangementof the intermolecular chains and inhibits the formation ofhydrogen bonds between the molecular chains. The presenceof an adequate number of these acetate groups improves
the solubility in water. As the amount of the residual acetategroups increases, the amount of heat generation increases

100

75
Solubility (%)

22

Dissolution condition(Concentration 4%)
80o Cx30min

50

60o Cx30min
40o Cx30min
20o Cx30min

25

0

80

85

90

95

Degree of hydrolysis (mol%)Figure 25. Influence of degree ofhydrolysis on solubility of PVOH

100

when PVOH dissolves in water, and the solubility at a constanttemperature improves. However, the critical temperature atwhich phase separation occurs decreases, and the solubility
at high-temperatures tends to decrease gradually. Figure 25
shows the relation between the degree of hydrolysis and thesolubility of PVOH with a degree of polymerization of 1700.
The sample was dissolved at a concentration of 4 % underconstant stirring conditions. As is clear from this figure, thepresence of only 2-3 mol% of residual acetate groups causesa significant difference in the solubility at 40-60°C. The
PVOH with a degree of saponification of 97 mol% is almost
completely dissolved. However, the fully hydrolyzed grade
is only slightly soluble and heating to ≥80°C is necessary
for complete dissolution. At around 20°C PVOH at 88
mol% hydrolysis dissolves well, but the solubility sharply
decreases as the degree of hydrolysis increases further.

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

Figure 26 and Figure 27 show the results of dissolving a
number of PVOH grades with varying temperature for 30
minutes with a solution concentrations of 4% and 10% undera constant stirring condition. The solubility of a so-called
fully hydrolyzed grade of PVOH with a degree of hydrolysis
of about 98 mol% decreases considerably as the degree ofpolymerization increases. However, the solubility of a socalled partially hydrolyzed grade of PVOH with a degree ofhydrolysis of 88 mol% shows very little dependence on the
degree of polymerization. Although PVOH with a degreeof hydrolysis of 80 mol% dissolves better than PVOH witha degree of hydrolysis of 88 mol% in the low-temperature
range, it shows unusual behavior that the solubility decreases
extremely at a temperature of 30–35°C or higher andeventually coagulates.
As described above, as the amount of residual acetate groups
increase, the mutual hydrogen bonding between the hydroxyl
groups in and between the PVOH molecules becomes lessand the bonding between the molecular chains is weakened,thus improving the solubility of PVOH. When the degreeof hydrolysis becomes 80 mol% or less and the amount ofresidual acetate group exceeds 20 mol%, the solubility at low
temperature still tends to increase. The critical temperature
at which phase separation occurs decreases and the solubility
at high temperature decreases. The degree of hydrolysis of
the general grades sold as partially hydrolyzed products ismostly centered at 88 mol%. It can be thought that this value
is set as the degree of hydrolysis that is relatively soluble
at both low and high temperatures, and is stable without
coagulation at the boiling point of water. When PVOH is used
as a warp sizing agent it is dried in the process and is required
to be able to be easily removed even after heat treatment.
It is often desired to also improve water resistance andmoisture resistance as an adhesive. Therefore, the change inthe solubility of PVOH owing to the heat treatment received
in the process is an important issue.

Target Concentration: 4%
Dissolution time: 30 min

Kuraray PovalTM 5-88

Kuraray PovalTM 5-88

Kuraray PovalTM 22-88

Kuraray PovalTM 22-88

Kuraray PovalTM 28-98

Kuraray PovalTM 28-98
100

Kuraray PovalTM 60-98
Kuraray PovalTM 5-98
Kuraray PovalTM 44-88

80

Solubility (%)

100

Solubility (%)

75

60

40

50
20
25
0
0

20
40
60
80
100
Dissolution Temperature (°C)
Figure 26. Solubility of Major PVOH
(Influence of Dissolution Temperature)

20
40
60
80
Dissolution Temperature (°C)
Figure 27. Solubility of Major
PVOH (Influence of Dissolution
Temperature)23

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

Figure 28 shows the results of investigating how heat treatment
influences a slight difference in the degree of hydrolysis using
PVOH with a degree of polymerization of 1750.
Partially hydrolyzed PVOH with a degree of hydrolysis of 88 mol%shows little influence on the solubility at a water temperatureof 40 °C or higher unless it undergoes extreme heat treatment
such as that at 180°C for 1 hour. Meanwhile, PVOH of the fullyhydrolyzed type shows a decrease in the solubility owing toincrease of crystallization when it is subjected to heat treatment
at 100°C or more, particularly at 130°C or more. However, thistendency is considerably different below and over the residual
acetate groups amount of around 2–4 mol% PVOH.
When considering which PVOH grade to use, solution
concentration and viscosity are very important. In general, thepractically usable concentration range is 35–40% when the
degree of polymerization is around 500 and is 15–20% for a highpolymerization degree grade with a degree of polymerization ofaround 2400.

Heat treatment condition:
Treatment at 180o Cx60min
Treatment at 100o Cx60min
Drying at normal temperature, no treatment
Treatment at 100o Cx10min
Treatment at 180o Cx10min

100

75

Solubility (%)

24

50

50

25

0

20

40

60

80

100

100

Degree of hydrolysis (mol%)Sample:Film with Degree of Polymerization of 1750
(Thickness: About 20 μm)
Dissolution Condition:
40°C × 30 min
Target Concentration: 4%
Figure 28. Influence of heat treatment onsolubility of PVOH.

3-2. SOLUBILITY IN OTHER SOLVENTS
Although water is the most commonly used solvent for PVOH,
can also be dissolved in a mixture of water and a lower alcohol
if the concentration is low. The lower the degree of hydrolysis
and the lower the degree of polymerization, the more soluble
it is in a system with a higher alcohol concentration, and themore soluble it is at 50°C over 30°C. Figure 29 and Figure
30 show the solubility of major PVOH in a water-methanol
mixture.
As for other organic solvents, PVOH dissolves to a certain
degree in glycols such as glycerin, ethylene glycol anddiethylene glycol, amides such as formamide, ethanol
formamide and ethanol acetamide, amines such as ethanol
amine, diethylene triamine and triethylene tetramine, as

well as dimethyl sulfoxide, phenol, etc. However, when it isdissolved in glycols such as glycerin, heating is necessary,and when the high temperature solution is cooled to room
temperature, the whole liquid turns into a gel. Table 11 shows
the dissolution temperature of Kuraray PovalTM 25-100 with adegree of polymerization of 1700 and a degree of hydrolysisof 99.5 mol% is dissolved in various glycols at a concentrationof 1%. The cloud point is the temperature at which thesolution becomes turbid. Although heating is also necessary
when dissolving PVOH in dimethyl sulfoxide, the solution
is stable even when cooled to room temperature. PVOH issoluble in diethylene triamine and triethylenetetramine evenat room temperature.

3. Behavior of PVOH Aqueous Solution

Kuraray PovalTM 5-98 at 50°C

Kuraray PovalTM 5-88 at 50°C

Kuraray Poval

22-98 at 50°C

Kuraray PovalTM 22-88 at 50°C

Kuraray Poval

60-98 at 50°C

Kuraray PovalTM 44-88 at 50°C

Kuraray Poval

5-98 at 30°C

Kuraray PovalTM 5-88 at 30°C

Kuraray PovalTM 28-98 at 30°C
Kuraray PovalTM 60-98 at 30°C

Kuraray PovalTM 22-88 at 30°C
Kuraray PovalTM 44-88 at 30°C

TM
TM
TM

100

75

75

Solubility (%)

100

Solubility (%)

Basic Physical Properties of PVOH Resin

50

25

50

25

Methanol 100
Water
0

80

60

40

20

0

20

40

60

80

100

Methanol 100
Water
0

80

60

40

20

0

20

40

60

80

100

Mixed composition (weight ration)

Mixed composition (weight ration)

Figure 29. Solubility of fullyhydrolyzed grade in water-methanol
mixtureFigure 30. Solubility of partiallyhydrolyzed grades in water-methanol
mixture* 96 weight parts of the mixture and 4 weight parts of PVOH were put in a predetermined solution and the solution was stirred at 2,000 rpm for 30
minutes. Then, the concentration of the solution part was measured, and the percentage with respect to the target concentration was taken as thesolubility.

Plasticizer

Melting Point(°C)

Boiling Point (°C)

Dissolution
Temperature of
PVOH (°C)

Cloud Point of
PVOH (°C)

Ethylene glycol

-12

197

140

110

Triethylene glycol

Liquid

214

160

130

Tetraethylene glycol

19.5

235

<200

150

Pentamethylene
glycolLiquid

239

190

175

Hexamethylene
glycol

42

250

240

190

Propylene glycol

Liquid

187

190

150

Glycerin

19

290

160

120

2,3-Butanediol

34.4

184

240

175

1,3-Butanediol

Liquid

204

185

170

Diethylene glycol

-10.5

245

210

160

Triethylene glycol

Liquid

278

210

185

Table 11. Dissolution Behavior of Kuraray PovalTM 25-100 in Various Glycols (Concentration: 1%)

25

Basic Physical Properties of PVOH Resin

26

3. Behavior of PVOH Aqueous Solution

3-3. VISCOSITY OF AQUEOUS SOLUTION
The viscosity of aqueous solutions of PVOH depends onthe grade, concentration and temperature. Figures 31 to 37
show the concentration-temperature-viscosity relationship(using a B-type viscometer) of some of our KURARAYPOVAL™ grades. The viscosity of PVOH increases as thedegree of polymerization increases. At the same degreeof polymerization, the viscosity of the fully hydrolyzed
grade is higher than that of the partially hydrolyzed grade.
Additionally, the viscosity decreases as the temperature of theaqueous solution increases and this tendency is reduced forthe partially hydrolyzed grade. In particular, the temperaturedependence of PVOH with a degree of hydrolysis of 80 mol%is very small. Although the concentration range usuallyhandled industrially seems to be in the range of 0.5–20%, thefollowing can be understood when examining the aqueous
viscosity in this area in detail. When plotting the relationshipbetween the viscosity and concentration of fully hydrolyzed
PVOH in detail, there is a bending point around concentrationof 2–4%, as shown in Figure 38. It is understood that theconcentration at this point agrees well with the bending
point concentration observed in the relationship between theapparent activation energy of the flow of the PVOH aqueous
solution and the concentration shown in Figure 39. There isanother inflection point near a concentration of 10–12% in
the relationship between the activation energy of flow and theconcentration, and it is known that this concentration agrees
well with the inflection point concentration of the melting
point of PVOH gel 46). Based on these facts, it is thought that
the PVOH aqueous solution has different structures before
and after the inflection point.

100000
80000
60000
40000

100000
80000
60000
40000
10o C

20000
10000
8000
6000
4000

40o C
50o C

10000
8000
6000
4000

2000

70o C

2000

1000
800
600
400

90o C

200
100
80
60
40

1000
800
600
400
200
100
80
60
40

20

20

10
8
6
4

10
8
6
4

2

2

1

0

2

4

6

8

10 12

14 16 1820 22

24 26 28

30

10o C
20o C
30o C
40o C
50o C
70o C
90o C

20000

20o C
30o C

Viscosity (mPa s)

Viscosity (mPa s)

In a dilute aqueous solution of 2–4% or less, which is the firstinflection point, the PVOH molecule becomes like a threadball containing a large amount of water, and the molecules
hardly interact with each other, being in a state of so-calledmolecular dispersion. However, with this concentration
as a boundary, the thread ball-like molecules interact witheach other, the degree of the interaction increases as theconcentration increases, and a mesh structure is formed byentanglement of the PVOH molecules. The second inflection
point is considered to be equivalent to the concentration
at which the mesh structure owing to this entanglement iscomplete. There is a perspective that it is better to handle
PVOH aqueous solution in the concentration range to be
used industrially in general by regarding it as a melt of agel. However, PVOH aqueous solutions are actually used invarious conditions.

1

0

2

4

6

8

10

12

14

16

18

20

Concentration (wt%)

Concentration (wt%)

Figure 31.Relation between aqueous solution viscosity ofKuraray PovalTM 5-98 and concentration

Figure 32. Relation between aqueous solution viscosity ofKuraray PovalTM 28-98 and concentration

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

10o Co
20 Co
30 C o
40 C
50o C 70o C

100000
80000
60000
40000

100000
80000
60000
40000
20000

10000
8000
6000
4000

10000
8000
6000
4000

2000

2000

Viscosity (mPa s)

Viscosity (mPa s)

90o C
20000

1000
800
600
400
200
100
80
60
40

100
80
60
40

10
8
6
4

10
8
6
4

2

2

2

4

6

8

10

12

14

16

18

1

20

0

2

6

8

10 12

14 16 1820 22

24 26 28

30

Concentration (wt%)

Figure 33. Relation between aqueous solution viscosity of Kuraray
PovalTM 60-98 and concentration

Figure 34. Relation between aqueous solution viscosity ofKuraray PovalTM 5-88 and concentration

10o C
20o C
30o C
40o C
50o C

20000

100000
80000
60000
40000

10o C
20oo C
30 C
40o C
50oo C
70 C

20000

70o C

10000
8000
6000
4000

90o C

10000
8000
6000
4000

90o C

2000

Viscosity (mPa s)

2000

1000
800
600
400
200
100
80
60
40

1000
800
600
400
200
100
80
60
40

20

20

10
8
6
4

10
8
6
4

2

2

1

4

Concentration (wt%)

100000
80000
60000
40000

Viscosity (mPa s)

90o C

200

20

0

70o C

1000
800
600
400

20

1

10o C
20o C
30o C
40o C
50o C

0

2

4

6

8

10 12

14 16 1820 22

24 26 28

30

Concentration (wt%)
Figure 35. Relation between aqueous solution viscosity ofKuraray PovalTM 22-88 and concentration

1

0

2

4

6

8

10

12

14

16

18

20

Concentration (wt%)
Figure 36. Relation between aqueous solution viscosity ofKuraray PovalTM 44-88 and concentration27

Basic Physical Properties of PVOH Resin28

3. Behavior of PVOH Aqueous Solution

100000
80000
60000
40000

10o C
20o C
30o C

20000
10000
8000
6000
4000

Viscosity (mPa s)

2000
1000
800
600
400
200
100
80
60
40
20
10
8
6
4
2
1

0

2

4

6

8

10

12

14

16

18

20

Concentration (wt%)
Figure 37. Relation between aqueous solution viscosity ofKuraray PovalTM 40-80 E and concentration

3

-0.4

En (kcal/mole)Log ŋ (10-1Pa•s)

0

-0.8
-1.2

2

1.8Kcal/mole

-1.6
-2.0

1

2

3

4

5

6

1

7

2

3

4

5

6

Concentration (wt%)

Aqueous solution concentration (wt%)

Figure 38. Relationship between concentrationand viscosity of various PVOH solution

Figure 39. Relation between concentration andactivation energy of apparent flow

SampleHuggins
coefficient

Degree 0f
polymerization

0.94

3115

0.70

2482

0.67

1906

0.96

1451

0.705

836

7

3. Behavior of PVOH Aqueous Solution

Basic Physical Properties of PVOH Resin

3-4. STABILITY OF AQUEOUS SOLUTION
When a PVOH aqueous solution with a high degree ofhydrolysis is left for a long time in cold conditions < 50C theviscosity rises and the solution eventually turns into a gel.
Figure 40 shows an example of Kuraray PovalTM 28-98, as an
example of a fully hydrolyzed PVOH aqueous solution, thehigher the concentration and the lower the temperature, themore unstable and the higher the viscosity increase. On theother hand, the partially hydrolyzed PVOH with a degree ofhydrolysis of 88 mol% has a very small temporal change inviscosity, as shown in Figure 41. Therefore, the influence ofthe degree of hydrolysis of PVOH on the viscosity stability of
the PVOH aqueous solution is recognized.
Assuming the aqueous solution viscosity immediately after
dissolving PVOH as ŋ0 and the viscosity after t hours of
the initial stage of storage as ŋt, and then examining therelationship between them, ŋt rises almost linearly withrespect to time t at the initial stage. Expression of ŋt = ŋ0
* (1+Þt) is established approximately. We can then show anapproximate relationship of ŋt = ŋ0 * (1+Þt). Therefore, Þ
indicates the gradient of a straight line with respect to time t(Þ is referred to as a thickening coefficient). The relationshipbetween this thickening coefficient Þ and the amount ofresidual acetate groups of PVOH, is shown in Figure 42, thethickening coefficient Þ decreases sharply as the residual
acetate group increases, and the viscosity stability of theaqueous solution is improved when the amount of residual
acetate group is 3 mol% or higher. As the amount of residual
acetate groups increase, the network structure is hardly
formed. It is thought that, owing to its steric hindrance, close
entanglement of the molecules is hindered and and thus
the increase in viscosity is decreased. Note that it has been
confirmed that this thickening coefficient Þ is proportional
to the 5.5th to 6th power of the concentration, and theviscosity stability of the aqueous solution becomes worse as
the concentration is higher and the degree of polymerizationof PVOH is higher.

Gelation
14%(10oC)
14%(30oC)
8%(5oC)

Kuraray PovalTM 28-98

14%(5oC)

Kuraray PovalTM 22-88
2.0

105

5x103
Viscosity (mPa*S)

Viscosity (mPa*S)

5x104

104
5x103

3x103
2x103
103
5x102

10

3

2x103

0.5

1.0

1.5

2x102
0

50

100

Time (hr)Time (hr)Figure 40 Viscosity Change of Kuraray
PovalTM 28-98 Aquesous Solution

Figure 41 Viscosity Change of Kuraray
PovalTM 28-98 and Kuraray PovalTM 2288 with a Concentration of 8%

29

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

Thickening Rate: ŋt/ŋ0

Thickening Coefficient a(h-1)

As shown in Figure 43 and Figure 44, the stability of the
PVOH aqueous solution is also influenced by the preparation(dissolution) conditions and heat history of the PVOH aqueous
solution. The higher the dissolution temperature, the longer
the dissolution time, and the better stirring, the better thestability of the aqueous solution. Additionally, the stronger
the heat treatment applied to PVOH before dissolution, thestability of its aqueous solution becomes worse. That is, thestability of the PVOH aqueous solution is also closely related
to the crystallinity of PVOH itself and the dispersion state

4x103

2x103

0

1

2

3

4

5

6

of the molecules at the time of dissolution. It is difficult tocompletely release the hydrogen bonding between the PVOH
molecules by dissolution. However, the stability improves as
the dispersion state of the PVOH molecules is improved byenhancing the solubility condition. The stability becomesworse when the entanglement of molecules is insufficiently
cleaved. Note that the thickening observed at the initial stageof storage is thought to be a result of very weak interaction
between the molecules because the viscosity returns to theoriginal one when stirring the aqueous solution.

Sample:4

DP: 1600 DH: 99.8 mol%
NaOAc:0.2%
Concentration: 13%
Dissolution Condition:
at 80o C for 75min
at 80o C for 150 min
at 80o C for 150 min+ Under Boiling 90 min

3
2
1

40

80

120

160 200 240

at 80o C for 75 min under Stirring

Time (hr)Residual Acetate group (mol%)Figure 43. Influence of Dissolution
Condition on Thickening of PVOH
Aqueous Solution (30°C) (hr)Figure 42. Influence of Redisualacetate Group on Thickening
Coefficient a

Thickening Rate: ŋt/ŋ030

Sample:4
DP: 1600 DH: 99.8 mol%
NaOAc:0.2%
Concentration: 13%

3
2

Dissolution Condition:
Raw Material
Heat Treatment at 80o C for 90 min
Heat Treatment at 80o C for 4 hr

1
1
20

40

60

80

100 120

Time (hr)Figure 44. Influence of Heat History
before Dissolution on Thickening of
PVOH Aqueous Solution (30°C)

3-5. SHEAR RATE DEPENDENCY OF AQUEOUS SOLUTION
It is well known that PVOH aqueous solutions exhibit nonNewtonian viscosity and the dependence of the aqueous
solution on share rate has been clarified as follows. As for
the PVOH aqueous solution, when it is a dilute aqueous
solution with a degree of polymerization of 3000 or less anda concentration of 5 g/l (0.5%) or less, it can be regarded as
a complete Newtonian fluid in a low-velocity gradient region
where the share rate is 400–500 (1/sec) or less. However,as the concentration increases, the dependence on share
rate increases, and when the concentration exceeds thecritical concentration coinciding with the inflection point
concentration obtained by the relationship between theviscosity and flow activation energy as described above, theshare rate dependency increases sharply. Figure 45 shows
the relationship between the m value 47), which is discussed
References46) Naito, Polymer Chemistry, 14, 117(1957)47) Naito, Polymer Chemistry, 16, 579 (1959)

as a measure of share rate dependence, and the aqueous
solution concentration. The critical concentration at which
the sharp increase of the m value begins is around 2–3% and,in the case of PVOH with a higher degree of polymerization,
the concentration is located on the lower concentration side.
Figure 46 shows the relationship between the degree ofpolymerization and the m value when the concentration is set
to 20 g/l (2%) and Figure 47 shows the relationship between
the residual acetate group and the m value of PVOH with adegree of polymerization of 1600 when concentration is set
to 15 g/l (1.5%). The share rate dependence of the PVOH
aqueous solution increases as the degree of polymerizationof PVOH increases and the degree of hydrolysis increases.

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

m: Slope of the linear
part of ŋsp / c and r in theregion of velocity gradientof 300-1200 (1/sec)

m x 106

50
40

Sample DP [ŋ] Critical
Conc. (g/l)
2400 0.109 24.8
2130 0.101 26.01470 0.080 31.2

30
20
10
10

20

30

8
Sample:m x 10660

6Before fractionation

4

Sample (1) purified* once
Sample (2) purified* twice
Fractionnal reprecipitation
Sith water / acetone*21000 1500 2000 2500 3000

40

Concentration (g/l)

Degree of Polymerization

Figure 45. Relationship between
m Value and Dissolution
Concentration (30°C)

Figure 46. Relationship between
Degree of Polymerization and m of
Various Samples (Concentration:
20 g/l, 30°C)

8m x 106

Sample:6

Before fractionation

4

Sample (1) purified* once
Sample (2) purified* twice
Fractionnal reprecipitation
Sith water / acetone*21000 1500 2000 2500 3000
Degree of Polymerization
Figure 47. Relationship between
Residual Acetate Group Amountand m (Concentration: 15 g/l,
30°C)

3-6. SPECIFIC GRAVITY AND REFRACTIVE INDEX OF AQUEOUS SOLUTION
The actual measured specific gravity (Figure 48) and the refractive index (Figure 49) for the aqueous solution of Kuraray
PovalTM 28-98 are shown here. The measurement of the refractive index of an aqueous solution has been put to practicaluse as a quick and qsimple method for investigating the concentration of a PVOH aqueous solution. For example in textile
applications like fiber sizing.

50o C

1.040

70o C
1.021

90o C

1.000

Specific Gravity (g/cc)

Specific Gravity (g/cc)

30o C

1.050

30.60
26.20
21.83
16.84

1.000

10.94
5.74

0.980
5

10

15

0.950
30

20

Figure 48-1. Specific Gravity of Kuraray Poval
98 Aqueous Solution

40

50

60

70

80

90

100

Temperature (°C)

Aqueous Solution Concentration (wt%)
TM(The number indicate the POVAL concentration (%).)

28-

Figure 48-2. Specific Gravity of Kuraray PovalTM 28-98
Aqueous Soltution31

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

1.360
1.355
Refractive Index

1.350
1.345
1.340
1.335
1.330
0

5

10

15

By Abbe refractometer
Aqueous Solution Concentration(wt%)
Figure 49. Refractive Index ofKuraray PovalTM 28-98 Aqueous
Solution (20°C)

3-7. PH OF AQUEOUS SOLUTION
The pH of an aqueous solution of fully hydrolysed PVOH isslightly acidic and close to 7, but it decreases as the degreeof hydrolysis decreases. The pH decreases to close to 5 inthe case of the partially hydrolyzed product with a degreeof hydrolysis of 88 mol%. When the aqueous solution of thepartially hydrolyzed product is heated continuously at hightemperature for a long time, the degree of hydrolysis increases
and the pH tends to decrease. This change is not problematic
under dissolution conditions which are usually carried out at
the site of use. Figures 50 and 51 show examples of actual
measurements of changes in the degree of hydrolysis and pH
owing to prolonged heating.

Sample DP DH
1750 89.2
2400 88.8
550 88.3

90.0

7Sample DP DH
1750 98.8
1759 97.8
1750 89.0

6
89.0

PH

Degree of Hydrolysis(mol%)

32

5

88.0

4
0

40

80

120

Aqueous Solution Concentration: 5.0%
Healing Temperature: 90-95o C

Heating time (hr)Figure 50. Change in Degree ofHydrolysis in PVOH Aqueous Solution
owing to Prolonged Heating

0

10

20

30

40

Heating time (hr)Figure 51. pH Change of PVOH Aqueous
Solution owing to Prolonged Heating50

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

3-8. SURFACE ACTIVE PERFORMANCE OF AQUEOUS SOLUTIONPVOH is often used as a stabilizer for oil-in-water emulsions
and suspensions. PVOH also has a function as a nonionic,
surfactant and as a protective colloid. It is well known thatthe aqueous solution of a partially hydrolyzed PVOH having ahydrophobic acetate group and a hydrophilic hydroxyl groupexhibits lower surface tension than the aqueous solution of afully hydrolyzed PVOH. Figures 52 and 53 show the measured
surface tensions of a few grades of PVOH. The ability to lower
the surface tension of PVOH increases as the amount ofresidual acetate group increases, but almost no dependenceof the degree of polymerization is observed. However,
PVOH 5-88, which is a partially hydrolyzed product with alow degree of polymerization, shows a unique behavior andexhibits extremely low surface tension. Various investigations
have been conducted on the surface activity of PVOH in
association with the molecular structure of PVOH.
In terms of the molecular structure, partially hydrolyzed
PVOH is well explained when considering it as a block polymer
type polymeric surfactant composed of a hydrophobic
acetate group and a hydrophilic hydroxyl group. It is generally
observed that, as the residual acetate group increases andthe distribution of the hydrophobic group and the hydrophilicgroup in the molecule becomes non uniform (blockwise), thesurface activity increases and the protective colloid ability to
the hydrophobic substances also increases.

Kuraray PovalTM 28-98
Kuraray PovalTM 22-88
Kuraray PovalTM 40-80 E
Kuraray PovalTM 5-88
Kuraray PovalTM 22-88
Kuraray PovalTM 44-88

65

Surface Tension (mN/m)

Surface Tension (mN/m)

70

60
55
50
45

0

0.1

0.2

0.3

0.4

70
65
60
55
50
45
0

0.1

0.2

0.3

0.4

0.5

Measured Values using the duNouy Surface Tensiometer

0.5

Concentration (%)

Measured Values using the duNouy Surface Tensiometer

Figure 53. Surface Tension of PVOH Aqueous
Solution (20°C) Influence of Degree ofPolymerization

Concentration (%)
Figure 52. Surface Tension of PVOH
Aqueous Solution (20°C)Influence ofDegree of Hydrolysis

3-9. PERMEABILITY OF AQUEOUS SOLUTIONPVOH is used in large quantities as a surface sizing agent
for both fiber and paper. In these cases, the permeabilityof aqueous solution to the fiber bundle is closely related
to the warp conjugation force, the paper strength, etc. If
the permeability of PVOH is too good and the yield to thesurface layer of fibers and paper is small, fluff binding on
the fiber bundle surface becomes poor and the surface
strength of the paper does not increase. Conversely, if
the permeability is bad, the enhancement of the physicalproperties inside the fiber or paper cannot be achieved.
Regarding the size effect of a warp sizing agent for fiber aswell as the performance required as a surface sizing agent
for paper, it is not yet sufficiently understood how they are
related to the permeability of PVOH. However, it is clear thatthe permeability is one important factor.

References
48) Shiozawa, Japan TAPPI Journal, 20, 668(1966)

By using filter paper (Toyo Roshi No. 1) as a model of aporous material composed of fiber bundle, the height(h) of permeation of water by a method similar to paper
chromatography was obtained with time. A linear relationshipis established between the square value of the permeation
height h (mm) and the time t (s), and this slope a is 0.129
cm2/sec. The a value of 0.5–4% PVOH aqueous solution wasshown in Figures 54 and 55.
Permeation of a liquid into yarn and paper, which areconsidered to be porous materials, is caused by capillary
force and it is known that the apparent permeation speed ofa liquid is given by the following equation48).

dh

m

1

dt

k

h

33

Basic Physical Properties of PVOH Resin

34

3. Behavior of PVOH Aqueous Solution

Kuraray PovalTM 5-88
Kuraray PovalTM 22-88
Kuraray PovalTM 44-88

0.06

0.06

0.05

0.05

0.04

0.04

a (cm2/sec)a (cm2/sec)

Kuraray PovalTM 5-98
Kuraray PovalTM 28-98
Kuraray PovalTM 60-98

0.03
0.02

0.02

0.01

0.01

0

1.0

2.0

3.0

4.0

0

3.0

4.0

Figure 54. a value of Fully
Hydrolyzed PVOH Aqueous
Solution (20°C)

Figure 55. a value of Partiallyhydrolyzed PVOH Aqueous
Solution (20°C)

of water was 0.01 (ps), the surface tension y was 72.8 (dyne/cm) and the contact angle cos0 was 0.952. Using these values,
the contact angle 0 of aqueous solution was calculated
based on the a value of the PVOH aqueous solution obtained
previously. Figures 56 and 57 show the results.
Kuraray PovalTM 5-88
Kuraray PovalTM 22-88
Kuraray PovalTM 44-88
Contact Angle 0 (deg)Contact Angle 0 (deg)

2.0Concentration (%)

Kuraray PovalTM 28-98
Kuraray PovalTM 5-98
Kuraray PovalTM 60-98
50
40
30
20
1

1.0

Concentration (%)

Where, h is the permeated distance of the liquid, y is thesurface tension of the liquid, 0 is the contact angle of theliquid, ŋ is the viscosity of the liquid, and m/k is the constantdetermined by the porous structure. The m/k of the filter
paper used in this test was 0.9325 × 10-5 (cm), the viscosity ŋ

10
0

0.03

2

3

4

5

50
40
30
20
10
0

1

2

3

4

Concentration (%)

Concentration (%)

Figure 56. Contact Angle 0 of Fully hydrolyzed PVOH
Aqueous Solution to Filter Paper (20°C)

Figure 57. Contact Angle 0 of Partially hydrolyzed PVOH
Aqueous Solution to Filter Paper (20°C)

From these results, the following can be seen. The apparent
permeation speed of the PVOH aqueous solution decreases
sharply as the concentration increases, but the degree
becomes gentle when the concentration becomes 2–3% ormore. Additionally, the higher the degree of polymerization,
the slower the permeation speed, but there is almost no
influence of the degree of hydrolysis within the range ofthis test. On the other hand, the contact angle of the PVOH
aqueous solution with respect to the filter paper is almost
constant when the concentration is 2–3% or more. As aresult, it is clear that the permeation speed of the PVOH
aqueous solution is governed by the viscosity, surface
tension and contact angle of the aqueous solution. However,the concentration dependency of the surface tension also
becomes extremely small at a concentration of 2–3% where
the contact angle becomes a constant value; this means

5

that the viscosity has a large influence in this concentration
region. Meanwhile, the wetting energy indicated by the
product of the surface tension and the contact angle iscalculated for the PVOH aqueous solution and the results
are shown in Figure 58. The wetting energy decreases as
the concentration increases. In the concentration region
where the contact angle becomes nearly constant, this value
also becomes nearly constant. As shown in Figure 59, thedependence of the degree of polymerization and the degreeof hydrolysis can be observed for the equilibrium wettingenergy in this concentration region. The equilibrium wettingenergy increases linearly with the increase of the degree ofpolymerization and that with a higher degree of hydrolysis
has a larger value. To summarize the above results, the PVOH
aqueous solution with a higher degree of polymerization
PVOH and a higher degree of hydrolysis PVOH has higher

3. Behavior of PVOH Aqueous Solution

wetting energy and the wettability to filter paper increases.
Meanwhile, the apparent permeation speed is not so much
related to the degree of hydrolysis within the range discussed
so far, and the higher the degree of polymerization, the lower
the penetration speed. The permeabilities of the aqueous
solutions of the same concentration of Kuraray PovalTM
28-98 and Kuraray PovalTM 22-88, Kuraray PovalTM 5-98
and Kuraray PovalTM 5-88 to filter paper can be regarded

as almost the same degree. This is because, although thepartially hydrolyzed product has a considerably low wettingenergy as compared with the fully hydrolyzed product, it has
a low viscosity at the same degree of polymerization andsame concentration. Therefore, it can be understood that it
acts sufficiently for permeability and is a result of simply theoffset of the difference between the wetting power and theviscosity effect.

Fully hydrolyzed PVOH (99.8 mol%)Partially hydrolyzed PVOH (88.0 mol%)

60

50

40

30
2.0

3.0

4.0

Equilibrium Wetting Energy (mN/m)

Wetting Energy (mN/m)Kuraray PovalTM 60-98
Kuraray PovalTM 28-98
Kuraray PovalTM 5-98

1.0

Basic Physical Properties of PVOH Resin

50

40

30

500

1500

2500

Aqueous Solution Concentration (%)

Degree of polymerization

Figure 58. Wetting Energy of Fullyhydrolyzed PVOH Aqueous Solution

Figure 59. Equilibrium Wetting Energy of
PVOH Aqueous Solution

3-10. CONTACT ANGLE FOR VARIOUS PLASTICS
When PVOH is used as an adhesive, or as a warp sizing agent or
paper surface sizing agent, the compatibility and adhesion of
PVOH to yarn and paper are important factors. The first stepof adhesion is wetting of the adherend surface by adhesive.
Table 12 shows the contact angles for various plastic films
actually measured as an indication to understand how muchcompatibility and adhesion the PVOH aqueous solutions havefor various plastics, and the wetting energy values calculated
based on them.
The contact angles of the PVOH aqueous solutions were
measured at a concentration of 3% as the contact angle withrespect to the plastic film reaches an almost equilibrium around
3% concentration as shown in the example in Figure 60.
According to the data, for a plastic with a large contact
angle, or a highly hydrophobic plastic that hardly gets wet
with water, there is a tendency that the difference in thecontact angles between the fully hydrolyzed PVOH and thepartially hydrolyzed PVOH aqueous solution increases as thehydrophobicity increases. That is, it is found that the aqueous

solution of the partially hydrolyzed PVOH is more easily
wetted with respect to the hydrophobic polymer. In this test,
the surface tensions of the 3% aqueous solution were 62.4
mN/m for Kuraray PovalTM 28-98 and 49.9 mN/m for Kuraray
PovalTM 22-88. Figure 61 shows a plot of the correlation
between the wetting energy calculated based on them andthe contact angle of water, which is a rough indication of thehydrophobicity of the adherend.
As the hydrophobicity of the polymer increases, the wetting
power decreases linearly in the case of both the fullyhydrolyzed PVOH and the partially hydrolyzed PVOH. The
fully hydrolyzed PVOH has larger inclination and exhibits
higher wetting power than the partially hydrolyzed PVOH for
polymers having large hydrophilicity. However, for stronglyhydrophobic polymers, the partially hydrolyzed product withmore hydrophobic acetategroups in the molecule has greater
wetting power. That is, from the viewpoint of adhesion it canbe said that it is better to use the partially hydrolyzed PVOH
for polymers having high hydrophobicity.

35Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

Kuraray PovalTM 28-98
Kuraray PovalTM 22-88
Equilibrium Wetting Energy of PVOH
Aqueous Solution (mN/m)Kuraray PovalTM 28-98
Kuraray PovalTM 22-88
Polystyrene Film
Cellulose Acetate Film 6-nylon Film

100
90
Contact angle (deg)

36

80
70
60
50

60
50
40
30
20
10
0
10
20
50 60 70 80 90 100 110

0

1

2

3

4

Contact Angle of Water for
Plastic Film (deg)5Concentration (%)

Figure 61. Correlation
between Equilibrium Wetting
Energy of PVOH Aqueous
Solutions for Various Plastic
Films and Contact Angleof Water for Plastic Film
(PVOH Concentration: 3%,
Temperature: 20°C)

Figure 60. Contact Angleof PVOH Aqueous Solution
for Various Plastic Films(Influence of Concentration)

Equilibrium Wetting
Energy (mN/m)Contact angle

Water

Kuraray
PovalTM
28-98
solution

Kuraray
PovalTM
22-88
solution

Kuraray
PovalTM 2898 solution

Kuraray
PovalTM
22-88
solution

Teflon

109.2

104

95

-15.1

-4.4

Polypropylene

102

95

89.5

-5.5

0.5

Delrin

99.9

91

82

-1.1

7

Polyethylene

96.8

93.2

84.8

-2.4

4.5

Polyester

96.1

86.5

76

3.8

12.1

ABS

94.7

91

81.2

-1.1

7.7

Polyvinyl chloride

84.6

78.8

69.9

12.1

17.2

Polyester

83.7

86.5

76

3.8

12.1

Phenolic resin

77.3

71

62.6

20.4

23

PMMA

74.2

68.6

62

22.8

23.5

Polyvinyl acetate

65.5

55.3

47

35.4

34

Melamine resin

65.3

60.8

58.2

30.5

26.2

Acetylcellulose

63.6

53.1

49

37.5

32.3

6-Nylon

54.6

44.3

42.4

44.5

37.4

Film type

Table 12. Contact angle and Equilibrium Wetting Energy of PVOH Aqueous Solution for Various Polymer Films (PVOH
Concentration: 3%, Temperature: 20°C)

3. Behavior of PVOH Aqueous Solution

Basic Physical Properties of PVOH Resin

3-11. COMPATIBILITY WITH WATER-SOLUBLE POLYMERSPVOH is often used in combination with other watersoluble polymers as a mixed aqueous solution. For
application as a warp sizing agent for fibers, it is usedin combination with corn starch, CMC (carboxy methyl
cellulose), partially hydrolyzed products of polyacrylicacid ester, It is also used in combination with oxidized
starch in the surface sizing of paper. When PVOH is usedin combination with other water-soluble polymers like
this, it is necessary to carefully consider the issue of theseparation speed in the process from the occurrence ofphase separation of the mixed solution to an equilibrium
and the problem of the compatibility after reaching theequilibrium. In particular, the compatibility is a very large
factor and an important problem not only for the stabilityof the mixed solution and workability together with theseparation speed, but also for the physical propertiesof the film. As for the compatibility in the equilibrium
state, the separation critical concentrations have been
determined based on various mixing ratios of various
combinations of polymers. As an example, the separation
critical concentration curves obtained by combining three
types of PVOH with different degrees of polymerizationand dextrin are shown in Figure 62.

Volume Fraction of Dextrin

(9:1)
(8:2)

0.2

(7:3)

Value in (): Mixing Ratio of Dextrin: PVOH
Value in []: Polymer Total Concentration (wt%)

(6:4)
(5:5)

(3:7)

[30]
[10]
0
0

PVOH
Sample

(4:6)

0.1

[14]

[18]

0.1

[22]

(2:8)

[26]

Degree ofPolymerization
550
1100
1750

Degree of
Saponification
88
88
88

(1:9)
0.2

Volume Fraction of PVOH
Figure 62. Separation Critical Concentration Curve of PVOH / Dextrin Mixture

In the case of a combination of PVOH and dextrin, although
the influence of the degree of hydrolysis of PVOH on theseparation critical concentration is hardly observed, thedependence on the degree of polymerization is large. As thedegree of polymerization increases, the separation criticalconcentration decreases. Depending on the type of watersoluble polymer, the shape of the critical concentration
curve is not alwaysuniform. However, as in the case of dextrin,
the separation critical concentration of the mixed PVOH
aqueous solution and another polymer tends to become
higher as the degree of polymerization of PVOH and thedegree of polymerization of the polymer to be fitted arelower or as the mixing ratio is extremely shifted to either side.
For some polymers, general trends in the separation speed,compatibility, influence of the degree of hydrolysis of PVOH,
etc. are summarized as follows.
Hydroxyethyl Cellulose (HEC)
The separation speed is fast. The higher the degree ofhydrolysis of PVOH, the better the compatibility.
Carboxymethyl Cellulose (CMC)
Slight separation is observed at a mixing ratio of around 1:1,
but the compatibility is very good at other mixing ratios.
Almost no difference owing to the degree of hydrolysis of
PVOH and the degree of etherification of CMC is observed.
Methyl Cellulose (MC)The separation speed is relatively fast and the higher the
degree of hydrolysis of PVOH, the better the compatibility.
Partially Hydrolyzed Product of Acrylic Ester
As the degree of hydrolysis of PVOH decreases, thecompatibility improves considerably and no separation isobserved in PVOH with a degree of hydrolysis of 88 mol%.
The compatibility is better as the number of carbon atomsof the acrylic acid ester group decreases and the degree ofhydrolysis of the ester increases. Sodium polyacrylate hardly
separates when it is mixed with the fully hydrolyzed PVOH.
Polyethylene Glycol
It is not compatible with fully hydrolyzed PVOH. As the degreeof hydrolysis of PVOH decreases, it becomes compatible.
Oxidized Starch
In general, the higher the degree of hydrolysis, the betterthe compatibility. In particular, the compatibility with themodified PVOH (K-series) having the anionic group (carboxylgroups) is excellent. Figure 63 shows an example of observing
the phase separation state when a mixed solution of the PVOH
aqueous solution and oxidized starch aqueous solution (Total
concentration: 10%, mixing ratio: PVOH / oxidized starch = 2/ 8 (wt)) is left at 50°C.
The mixed solution was placed in a measuring cylinder andwas left at 50°C to observe the rate of the supernatantphase appearing by phase separation as an indication of thecompatibility. Figure 63 shows the result. When the mixed
solution of a total concentration of 5% and PVOH / oxidized
starch = 2 / 8 (wt) is left at 50°C, both Kuraray PovalTM 2898 of normal fully hydrolyzed grade and the carboxyl groupmodified Kuraray PovalTM K-series show no phase separationand exhibit good compatibility within the range of 100 hours
or less. However, as shown in Figure 63, it is recognized thatthe compatibility of Kuraray PovalTM K-series is better thanthat of Kuraray PovalTM 28-98 at a total concentration of 10%.

37

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

Kuraray PovalTM 28-98
Kuraray PovalTM K-series
60
Supernatant Relative Rate (%)

25
20
15
10
5
0
0

20

40

90

80

100

Time (hr)Figure 63. Compatibility of PVOH-starch
Mixture (Left Stability at 50°C)

Other
PVOH is extremely compatible with casein and sodium
alginate, and no apparent separation is observed. The
separation speed from gelatin is very fast. Based on theexperimental values of the separation critical concentration
described above, an interaction parameter a2349) which isdetermined only by the type of the partner polymer to bemixed with PVOH has been calculated as a measure foruniquely expressing the compatibility between the two typesof polymers.
This parameter a23, which is a thermodynamic constant, is auniversal constant between two polymers unrelated to thedegree of polymerization of polymer, and the smaller thevalue, the better the compatibility between the two. These
values are shown in Table 13. As described above, a23 of thepartially saponified product of CMC and polyacrylic acid
ester, which are easily compatible with PVOH, is clearlysmaller than that of MC and HEC. Meanwhile, even if thesemixed polymer aqueous solutions are in the phase equilibrium
state or below the separation critical concentration as asolution, in the compatible state, when they are actually used

Polymer

a23

CMC

0.059

MC

0.128

HEC

0.177

Dextrin

0.29

Polymethyl Acrylate(Degree of Hydrolysis:
20%)

0.006

Polyethyl Acrylate(Degree of Hydrolysis:
20%)

0.074

in some application, the concentration gradually increases
in the drying process; A dry film must be formed throughthe demixing region after exceeding the separation criticalconcentration. Therefore, even if the appearance varies
depending on the drying speed and the separation speed, thedry film of the mixed polymer generally does not become ahomogeneous phase and has a structure in which one takes
the matrix structure and the other is dispersed as minutegranular particles therein. Figure 64 shows the relationshipbetween the mixing ratios of both polymers investigatedbased on the microscope photograph of a film dry-formed
from the mixed solution of “PVOH” and cellulose derivative
and the size of dispersed particles in the film. The mixing
ratios at which the dispersed particle diameter becomesthe maximum are HEC:PVOH = 3:7, MC: PVOH = 6:4, and
CMC:PVOH = 5:5. These mixing ratios are in good agreementwith the mixing ratios at which the mixed solutions show
the lowest separation critical concentrations, respectively.
Additionally, the maximum value of the dispersed particle
diameter becomes smaller in the case of the combination of
the polymers with smaller interaction parameters a23.

H.E.C / Kuraray PovalTM 5-88
M.C / Kuraray PovalTM 22-88
C.M.C / Kuraray PovalTM 5-88
Average Particle Diameter in
Dispersed Particles (micron)

38

10

5

0
0

Table 13. Interaction Parameter between
PVOH and Various Water-soluble Polymers,a23 (ml-1)
References
49) Poval (Nagano et al., Kobunshi Kankokai, 1970)

2:8

4:6

6:4

8:2

10:0

Mixing Ration of Wate-soluble Polymer PVOH
Figure 64. Size of Dispersed Particles Exist in PVOH /Cellulose Derivative Mixture Film

3. Behavior of PVOH Aqueous Solution

Basic Physical Properties of PVOH Resin

3-12. DISPERSIVE/AGGREGATING ACTION AGAINST CLAY PARTICLESIn PVOH, which is a non-electrolytic linear polymer, uniqueaggregating and dispersive actions from the electrolyte
linear polymer are observed. As an example, the pH of thesuspension system was changed in advance by processing
Japanese Pharmacopoeia kaolin containing quartz andpyroferrite with a particle size of 20 μm or less as the mainminerals with caustic soda; fully hydrolyzed PVOH with adegree of polymerization of about 1400 was added to thissuspension up to 1%, and then the system was left for 2
hours. The relative turbidity in this case is shown in Figure 65.

The maximum aggregation point exhibited by PVOH is not
influenced by the pH of the system as described above, andit does not change even if salts such as aluminum sulfate areused in combination. The maximum aggregation point forthe same type clay particles is closely related to the surface
area of clay particle and irrespective of the clay particle
concentration. Clay with stronger hydrophilicity will achieve
maximum aggregation by adding a smaller amount of PVOH.
The following order is observed for the aggregability ofrepresentative ones.

In the high pH range where the mutual repulsion of clay
particles is increased by the addition of caustic soda, theaggregating action of PVOH is weakened. However, in any
system, the maximum aggregation is observed when the
addition amount of PVOH is around 0.15%. In other words,
PVOH exhibits the maximum aggregating action at a fixedamount ratio with respect to clay particles irrespective of
the pH of the suspension system, and this phenomenon isessentially different from the case of electrolytic polymers
such as sodium polyacrylate. The PVOH molecule is strongly
adsorbed to the clay particle by the hydrogen bonding
formed between the oxygen atom of the silicic acid layer on
the surface of the clay and the hydroxyl group of the side
chain. As a result, the surface of the clay particle is covered
with the adsorbed hydrocarbon main chain of PVOH andrendered hydrophobic. This causes aggregation by the Van
der Waals force in a form that minimizes the free surface
energy in water. The major aggregation action by PVOH is
the hydrophobization of the surface of the clay particle
like this and the hydrophobic group interaction between
some particles is considered to be involved. Furthermore,
as for the state of redispersion observed when the amountof PVOH is increased, it is estimated that the secondary
molecule of PVOH adsorbs to the primary molecular filmof PVOH adsorbed to the clay surface by the Van der Waals
force between the ethylene main chains. The surface of theparticle becomes hydrophilic again owing to the hydroxyl
group facing the aqueous phase, resulting in redispersion.

Titanium oxide < Talc < Kaolin < Pyrophylite

Figure 66 shows an example indicating the influence of thedegree of polymerization of PVOH on the aggregating action.

it has been confirmed that the PVOH molecules adsorb to
the clay surface in a thin and considerably spread state andthe amount decreases as the spread of the PVOH moleculesin the aqueous solution widens. Note that when mixing the
inorganic suspension system and PVOH, an aggregation
phenomenon of inorganic substances may occur, which is cocalled “clay shock”. When mixing them, there is no problem
if the suspension solution of inorganic substance is added
and mixed into the PVOH aqueous solution. When this is
not possible in practice, for example, when using PVOH as apigment binder for paper, the “PVOH shock” can be prevented
by adding PVOH with a low degree of polymerization to theclay suspension solution at first to minimize the aggregationand then adding PVOH with a high degree of polymerization
after passing the aggregation region (concentration).

The aggregating power of PVOH weakens as the degree ofpolymerization decreases, but the concentration of PVOH
that causes the maximum aggregation does not change.
This also suggests that the mechanism of creating abridge between the clay particles and forming a block also
contributes to the aggregation action of PVOH. Meanwhile,
Figure 67 shows the correlation between the additive amountand adsorption amount of PVOH for clay for PVOH withdifferent degrees of hydrolysis.
Figure 67 shows that saturated adsorption is reached whenmore than a certain amount of PVOH is added, except for
PVOH with a significantly lower degree of hydrolysis. However,pH 5.6pH 6.8pH 9.1100

Relative Turbidity (%)

80

60

40

20

0
0

0.2

0.4

0.6

0.8

1.0

PVOH Addition Amount (wt% to Dry Soil)
Figure 65. Aggregating and Dispersive Actions of PVOH
in Kaolin Suspension System (Kaolin Concentration: 1%)

39

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

PVOH Adsorption Amount (wt% to Dry
Soil)

DP1750DP550

80Relative Turbidity (%)

40

60

40

20

0.1

0.2

0.3

67.4
2.0
75.5
99.8
99
95.3
87.9

1.0

0
0

2

4

6

8

10

12

Value: Degree of Hydrolysis of
Sample PVOH

PVOH Addition Amount (%)

PVOH Addition Amount (wt% to
Dry Soil)Figure 66. Influence of Degreeof Polymerization of PVOH on
Aggregation of Kaolin Suspension
SystemFigure 67. Adsorption Amount of
PVOH to Clay* Particle (Influenceof Degree of Hydrolysis)* Shokozan Clay

3-13. INFLUENCE OF ELECTROLYTE
In general aqueous solutions of PVOH are considerably stableagainst strong acids and bases. Even when a large amountof ammonium hydroxide, acetic acid, hydrochloric acid, nitricacid, phosphoric acid or or similar is added, PVOH aqueous
solution is stable.
Table 14 summarizes the minimum concentrations of salts
required to coagulate and precipitate PVOH in solution. A
5% aqueous solution of Kuraray PovalTM 28-98 shows theinfluence and the precipitation/coagulation effects of salts
for PVOH aqueous solution. The coagulation effect of salts

for the PVOH aqueous solution is strong with sulphate ion,carbonate ion and phosphate ion the coagulation power for
negative ions listed for example chlorine ion and nitric acidion is extremely weak. As for positive ions, those with a large
ionization tendency are more effective. Potassium, sodium,ammonium and the like are strong, and sodium sulfate,ammonium sulfate and the like have a particularly greater
coagulation power. Note that the coagulation actions of thesesalts are a result of the dehydration action and are promoted
as the temperature rises.

3. Behavior of PVOH Aqueous Solution

Basic Physical Properties of PVOH Resin

Table 14. Minimum Concentration of Various Salts Required to Coagulate PVOH from 5% Aqueous Solution of Kuraray PovalTM 28-98

Minimum Salt
Concentration
for Coagulation

Coagulation
EffectCoagulation

Minimum Salt
Concentration
for Coagulation

Coagulation
EffectCoagulation

(N)

(g/1)

(1/N)

(N)

(g/1)

(1/N)

(NH4)2SO4

1

66

1

Al(NO3)3

3.6

255

0.28

Na2SO4

0.7

50

1.43

HNO3

-

-

0

K2SO4

0.7

61

1.43

NH4Cl

-

-

0

ZnSO4

1.4

113

0.71

NaCl

3.1

210

0.32

CuSO4

1.4

112

0.71

KCl

2.6

194

0.38

FeSO4

1.4

105

0.71

MgCl2

-

-

0

MgSO4

1

60

1

CaCl2

-

-

0

Al2(SO4)3

1

57

1

HCl

-

-

0

KAL(SO4)2

0.9

58

1.11

Na2PO4

1.4

77

0.71

H2SO4

-

-

0

K2CrO4

1.4

136

0.71

NH4NO3

6.1

490

0.16

Potassium

0.8

38

1.25

NaNO3

3.6

324

0.28

Citrate

KNO3

2.6

264

0.38

H3BO3

0.8

165

1.25

Salt TypeSalt Type* Condition: The minimum salt concentration at which cloudy precipitation of PVOH occurred was determined when 2 drops of a 5% aqueous
solution of Kuraray PovalTM 28-98 was dropped into 10 cc of various salt aqueous solutions and it was shaken immediately. (Measurement
temperature: 30°C)

3-14. GELLANT, PRECIPITANT
Besides coagulation by salts, it has long been known that
aqueous solutions of PVOH thicken and gelate throughchemical bonding with borax, boric acid, etc. An equal amountof an aqueous solution of borax or boric acid was mixed witha 3–10% aqueous solution of a fully hydrolyzed PVOH, thesolution was stirred well and then left for 2 minutes to checkthe gelation. The results are shown in Table 15.
A small amount of Borax forms a gel compared with boricacid. Additionally, this gelation by chemical bonding shows astronger tendency as the temperature becomes lower, and aso-called thermoreversible gel is produced. PVOH aqueous

solution also forms a thermoreversible gel with certain
types of organic compounds. Although an aqueous solution
containing 8.5% of Kuraray PovalTM 28-98 and 1.5% of Congo
red flows at a temperature of 40°C or higher, it turns into
a red gel at room temperature. Direct dyes having the same
molecular structure as Congo red, such as Benzopurpurine 4B
and Japan violet extra, etc., have the same action. Resorcinol,catechol, phloroglucinol, vansan, gallic acid, etc. are known
as those which produce a thermally reversible gel without
color. Figure 68 shows the relation between temperature andelastic modulus of PVOH - Congo red gel. heck the gelation.
The results are shown in Table 15.

41Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

Table 15. Gelation Tendency of Fully Hydrolyzed PVOH Aqueous Solution by Boric Acid and Borax

PVOH Conc.(%)

10

8

5

3

DP

Temp.
(°C)

Boric
Acid

Borax

Boric
Acid

Borax

Boric
Acid

Borax

Boric
Acid

Borax

2010
2010

20
20

2.7
>12

0.1
0.6

3.1
>12

0.2
3.1

4
>12

0.5
7.3

4
>12

1.2
18

1470
1470

20
60

4
>12

0.3
4.6

4.5
>12

0.5
7.6

5
>12

1
15

>5
>12

1.5
>20

980
980

20
60

4.5
>12

0.8
1.3

4.5
>12

0.9
14

5
>12

1.2
18

>5
>12

1.7
>20

300
300

20
60

5
>12

1
1.5

5
>12

1.3
>20

5
>12

1.5
20

>5
>12

2
>20

* Condition: An equal amount of a PVOH aqueous solution and boric acid (or borax) aqueous solution are mixed, and theconcentration of the boric acid (or borax) aqueous solution is shown when the solution turns into a gel.
Kuraray PovalTM 28-98 15.0%
Kuraray PovalTM 28-98 8.5%
Kuraray PovalTM 28-98 4.5%

1.6
Elastic Modulus (dynamic/cm2)

42

1.2

0.8

0.4

0

20

40

60

80

100

Temperature (oC)
Figure 68. Relation between Temperature andElastic Modulus of PVOH – Congo Red Gel(Congo Red Concentration: 1.5%)

Additionally, if an appropriate amount of boric acid is used,
it is effective as a thickener for the PVOH aqueous solution
and there are many practical examples of its use. As otherspecific inorganic gellants, trivalent chromium is generated
when the alkali metal salt of chromic acid or dichromic acidis reduced, vanadate or tetravalent titanium generated byoxidation of titanium trichloride, and their gelation abilities
can often be adjusted by pH. As described in another chapter,the precipitants of PVOH include sodium sulfate, sodium
carbonate and they are effective especially when PVOH isseparated and removed from the aqueous solution. For the
purpose of simply precipitating and removing PVOH froman aqueous solution, copper ion which forms a complex
compound by coordination bonding can be used.
Note that the adsorption behavior of halogen, the thickening
behavior of a special surfactant, etc. are known as the otheradsorption phenomena to PVOH in the dissolved state.
Halogen, especially iodine, adsorbs to PVOH and causes
a unique color reaction and it is used for the quantitative
concentration measurement etc. of the dilute PVOH aqueous

solution. The color reaction of PVOH and iodine changes
depending on the degree of polymerization and degree ofhydrolysis of PVOH, the fully hydrolyzed PVOH exhibits
blue and the partially hydrolyzed PVOH exhibits red. This
discoloration point shifts to the range of a lower degreeof hydrolysis as the degree of polymerization increases.
These colorations are strengthened and stabilized in thepresence of boric acid. For partially hydrolyzed PVOH, thedegree of coloration varies depending on the distributionof the residual acetate group in the molecule even if thedegree of polymerization and the degree of hydrolysis are
the same. Additionally, there is a tendency that the degreeof coloration tends to become larger as the residual acetategroup is distributed nonuniformly in a block and this is used
as a qualitative confirmation method of the block charactor.
Meanwhile, as an example of a surfactant exhibiting a specificthickening effect, it is known that a significant increase inviscosity is observed when sodium dodecyl sulfate, sodium
laurate, sodium dodecylbenzenesulfonate is added to a dilute
PVOH aqueous solution.

3. Behavior of PVOH Aqueous Solution

Basic Physical Properties of PVOH Resin

3-15. CLOUD POINTA PVOH aqueous solution is known as an aqueous solution
exhibiting the lower critical solution temperature (LCST) or
cloud point. The phase diagram of the LCST of an aqueous
solution is schematically shown in Figure 69. The cloud
point of an aqueous solution is the boundary between
the uniformed-phase region and the separated-phaseregion, and is a temperature at which the aqueous solution
becomes cloudy owing to the difference in the refractive
indexes between the dense phase and the dilute phase whenphase separation to the two phases occurs. In the case of
PVOH, owing to various distributions such as the degree ofpolymerization and the degree of hydrolysis, it is difficult
to determine the clear boundary. In general, however, thelower the degree of hydrolysis and the higher the degree ofpolymerization, the lower the temperature of the separatedphase region and the lower the cloud point.

Figure 70 shows an example of the correlation between
the concentration and the cloud point of a PVOH aqueous
solution. In the case of the a PVOH aqueous solution, it
generally exhibits a downward phase diagram with the apex
at around an aqueous solution concentration of 0.5–2%. In
the case of PVOH with a relatively high degree of hydrolysisof 88 mol% or more, since the separated-phase region
becomes 100°C or higher, the phase diagram and cloud point
shown in Figure 69 are not observed. However, in the case of
PVOH with a low degree of hydrolysis 80 mol% or less, thecloud point can be seen. Additionally, as shown in Figure 71,
when comparing at the same degree of hydrolysis, the cloud
point decreases as the degree of polymerization of PVOH
increases.

Kuraray PovalTM 5-82
Kuraray PovalTM 40-80E
Kuraray PovalTM L-8

Separated-phase Region

Temperature

8060

Uniformed-phase Region

Concentration

Cloud Point (oC)

70%mol
67%mol
65%mol40
63%mol80%mol

79%mol
78%mol
77%mol
76%mol
75%mol20

Figure 69. Phase Diagram of PVOH Aqueous Solution(Schematic Diagram)
0100

Kuraray PovalTM L-8
Kuraray PovalTM L-9

500

1000

5000

10000

Degree of polymerization
Figure 71. Influence of Degree of Hydrolysis andDegree of Polymerization on Cloud Point of PVOH
Aqueous Solution (4%)

Cloud Point (oC)

45
40

35
30
25

0.05 0.1

0.51

5.0 10.0 15.0

Clouding Point of PVOH aq. Solution
Concentration (wt%)
Figure 70. Correlation Example between Cloud
Point and Concentration of PVOH Aqueous
Solution4344

Basic Physical Properties of PVOH Resin

3. Behavior of PVOH Aqueous Solution

3-16. BIODEGRADABILITY
It has been confirmed that PVOH is biodegradable using
a biodegradability test method of plastics 50), and it is
now practically used for industrial wastewater treatment
containing PVOH using activated sludge. Many studies on the
microbial degradation of PVOH have been made since theseparation of PVOH degrading bacteria (Pseudomonaspace
0–3 strain) by Suzuki et al. in 1973 51). Sakai et al. 52), Shimao
et al. 53) estimate that the 1,3-diol part in the PVOH chain
is converted into 1,3-diketone by oxidase and then cleaved
by hydrolase, the polymer chain is randomly cut into low
molecules, and finally the PVOH is completely decomposedby being incorporated into the fungus body. Figure 72 shows
the mechanism Tsuji et al. 54) investigated the relationshipbetween the PVOH molecular structure and biodegradability
using PVOH dehydrogenase (PVOHDH) isolated and purified
from the degrading bacteria. Using commercially available
representative PVOH with different degrees of polymerizationand degrees of hydrolysis, the Michaelis constant Km (halfof the substrate concentration at which the enzyme reaction
rate becomes the maximum), which is a typical parameter ofthe enzyme reaction kinetics, and the maximum reaction rate
Vmax, are determined. The results are shown in Table 16.
Where, Vmax / Km is an index showing the enzyme activity
in the low concentration region. In commercially available

PVOH, dependence of the enzymatic activity on the degreeof hydrolysis is observed and the enzyme activity increases
as the degree of hydrolysis decreases. This indicates thecorrelation with the content of the hydrophobic group in
PVOH and it is thought that low degree of hydrolysis PVOH
which has water solubility increases the enzyme activity(biodegradability) owing to the hydrophobic structure andaffinity with the enzyme 55).
The influence of the degree of polymerization of commercial
grades of PVOH biodegradeability is small. However,products with a degree of polymerization of about 20–100
are excellent in biodegradability. Furthermore, as for the
influence of stereoregularity, PVOH with high isotacticity is
excellent in biodegradability.
Activated sludge is usually used in waste water treatment for
PVOH. Table 17 shows the examples of the BOD value and
COD value of various polymer aqueous solutions with generalactivated sludge 56).
As shown in Table 17, since the PVOH aqueous solution ishardly decomposed in a general activated sludge, it is usual
to cultivate PVOH assimilating bacteria to turn them into
active sludge.
OH OH OH OH

PVOH

DP

DH
(mol1%)

Km(mg/l)

Vmax

Vmax/
Km

Kuraray
PovalTM 28-98

1700

98.5

33.2

85.6

2.5

Kuraray
PovalTM 3-98

330

98.5

24.2

73.6

3.0

Kuraray
PovalTM 3-88

330

Kuraray
PovalTM 3-80

88.5

7.2

29.1

*
O2
O2

81.0

4.8

31.4

sec-alcoholoxidase

H2O2
OH

OH OH

O

*

PQQ

4.0

O2

sec-alcoholoxidase

6.5
OH O

Kuraray
PovalTM 5-98

550

Kuraray
PovalTM 5-88

550

88.5

8.1

30.5

3.8

Kuraray
PovalTM 5-82

550

81.0

5.8

28.6

4.8

98.5

21.1

53.0

PVOHdehyfrogenase

PQQH2

*

H2O2

330

*

PVOH

O

OH

*

2.5

*
H2O

ß-diketone hydrolase

OH O
*

+

O

OH

OH
*

Figure 72. Biodegradation Mechanism of PVOH

Table 16. Biodegradation Rate of PVOH

PVOHPolymer

Kuraray Poval
28-98

Kuraray PovalTM
22-88

Cornstarch

CMC

BOD

0.5

1.2

107

2.1

COD(Mn)

124

113

98.5

121

TM

Table 17. BOD Value and COD Value of Various Polymer Aqueous Solutions (150 ppm)
References50) JIS K 6950 (1994)
51) T. Suzuki, Y. Ichihara, M. Yamada, and K. Tonomura, Agric. Biol. Chem., 37, 743 (1973)
52) K. Sakai, M. Morita, N. Hamada, and Y. Watanabe, Agric. Biol. Chem., 45(1), 63 (1981)
53) C. Sakazawa, M. Shimao, Y. Taniguchi, and N. Kato, Appl. Environ. Microbiol., 41(1), 261 (1981)
54) T. Hatanaka, T. Kawahara, N. Asahi, and M. Tsuji, Miosci. Biotech. Biochem., 59(7), 1229 (1995)
55) Masao Tsuji, Yoshito Ikada, “Seibunkaisei Kobunshi No Kiso To Oyo (Basics and Applications of Biodegradable Polymers)”, IPC, 323 (1999)
56) Tominaga, Miyamoto, Ueda, Kagaku Kojo (Chemical Factory), 20, 67 (1976)

Basic Physical Properties of PVOH Resin

4. Physical Properties of PVOH Film

4. Physical Propertiesof PVOH Film
4-1. PROPERTIES FOR WATER

How the solubility of the film with water changes dependingon the degree of heat treatment was also described inanother chapter, “Solubility in Water”. The solubility of thefilm hardly changes even when subjected to a heat treatment
at a drying temperature of about 100°C for 60 minutes,
and the film dissolves completely at 40°C in the case of apartially hydrolyzed PVOH with a degree of hydrolysis of 97
mol% or less. If the heat treatment temperature is raised
to 180°C, the solubility decreases considerably even if thetreatment is only for 10 minutes. If the treatment time isprolonged to 60 minutes, the partially hydrolyzed PVOH does
not completely dissolve at 40°C. However, it is impossible toincrease the water resistance against boiling water only byheat treatment even for the fully hydrolyzed PVOH which
is susceptible to the effect of heat treatment. In practice,
the temperature actually experienced by PVOH during thedrying process in which a PVOH film is formed from the
PVOH aqueous solution is estimated to be 100–130°C and
it is considered that the solubility of PVOH does not changeby the heat treatment received during this process. PVOH
with a higher degree of hydrolysis as (and preferably with ahigh degree of polymerization) may be used to give a film ofhigh water restance under a condition where heat treatment
is performed at the highest temperature for a prolonged
time. However, since thermal decomposition of PVOH occurs
at 200°C or higher, it is desirable to set the heat treatment
temperature around 180°C.

However, the influence of the degree of hydrolysis of PVOH
is relatively large and, as shown in Figure 73, the equilibrium
moisture contents of those with a low degree of hydrolysis
become high at a high humidity of 65% or higher.

40
38

94.9

36

Relative Humidity

34
32
30
28
Equilibrium Moisture Content (%)

When PVOH is used as a molded product, for example, as afilm, or as an aqueous solution for fiber sizing, paper sizing,an adhesive, the properties of the PVOH film that is formed
through the drying process for water, that is, solubility,
swelling property and hygroscopicity are very important.

90.1

26
24
22
20
18
16
80.4
14
Degree of hydrolysis (mol%)
12

The water resistance required for PVOH film in practicaluse may be the water resistance in the sense of solubility
in water as described above, but water absorption rate andswelling ratio are indicated as the water resistance. Figure 73
shows the results for various grades of PVOH with a various
degree of hydrolysis and a degree of polymerization of 1750,
the equilibrium moisture content of a film with a thicknessof about 30 μm air-dried from a 10% aqueous solution andsufficiently dried at 50°C was obtained under each relative
humidity. The results are shown in Figure 73.
In the low humidity range where the relative humidity is 50%
or less, the equilibrium moisture content increases almost
proportionally with the increase in the humidity, but theincrease rate increases in the high humidity range exceeding
60%, and it increases considerably at 90% or more. In general,
the equilibrium moisture content of the PVOH film does notdiffer when the temperature is in the range of 20–40°C. The
influence of the degree of polymerization is hardly observed
except for those with a low degree of polymerization.

10

64.0

8
6
4
2
0
80

50.0
40.0
30.0
20.1
10.1
4.3
82

84

86

88

90

92

94

96

98

100

Degree of hydrolysis (mol%)Figure 73. Equilibrium Moisture Content of PVOH
Film

45

Basic Physical Properties of PVOH Resin

4. Physical Properties of PVOH Film

The equilibrium moisture content of the PVOH film also
varies depending on the drying condition and heat treatment
as with the solubility in water. As an example, the influenceof heat treatment on the equilibrium moisture content isshown in Figure 74. It is considered that the decrease of
the hygroscopic content by heat treatment is a result of theincrease of crystallization of the film. When the PVOH film isimmersed in water, the film absorbs a large amount of waterand swells. Additionally, when the weight swelling degree(the ratio of the water absorption amount to the film weight
before immersion) after immersion in water at 30°C for 48
hours is obtained, the influences of the degree of hydrolysis
of PVOH and the heat treatment condition of the film areextremely noticeable as compared with the equilibrium
moisture content of the film.
The films of Kuraray PovalTM 25-100 (degree of hydrolysis:>99.3mol%) and Kuraray PovalTM 28-98 (degree of hydrolysis:
98.8 mol%) were formed under the same condition and heattreated at a predetermined temperature for 10 minutes toobtain the degrees of swelling. The results are shown in Figure
75. As is clear from this figure, when the heat treatment
temperature is low, the difference owing to the degree ofhydrolysis of 1 mol% is remarkably observed in the weight
degrees of swelling of the PVOH films.
Although the degree of swelling of the PVOH film decreases
significantly as the treatment temperature is raised, it isalmost constant around 180°C and it is extremely difficult toachieve a lower level only with heat treatment even for Kuraray
PovalTM 25-100. Figure 76 shows the moisture permeability
measured at 35°C for the Kuraray PovalTM 25-100 film witha thickness of 20 μm containing 5% diethylene glycol andheat-treated at 130°C for 10 minutes as an example showing
the moisture permeability of the PVOH film. Although the
moisture permeability of the PVOH film tends to rapidly
rise when the relative humidity of both surfaces of thefilm exceeds 60%, it can be considered in general that the
moisture permeability of PVOH is roughly comparable to thatof cellophane.
Kuraray PovalTM 28-98
Kuraray PovalTM 25-100

8
1.4
7

Weight Degree of Swelling

Equilibrium Moisture Content (%)

6

5

4

1.2

1.0

0.8

0.6
3
60

90

120

150

180

210
0.4
80

Heat Treatment Temperature (°C)
Figure 74. Influence of Heat Treatment on
Equilibrium Moisture Content of PVOH Film*

100

120 140

160

180

Figure 75. Influence of Heat
Treatment on Weight Degree of
Swelling of Kuraray PovalTM 25-100
and Kuraray PovalTM 28-98

1000

800
*According to JI S Z-0208 Sample Symbol
Commercial Cellophone (Thickness: 20 μm) Kuraray PovalTM 25-100(Thickness: 20 μm, Containing 5 phr of diethylene glycol)
Commercial biaxially streched 6-nylon (Thickness: 20 μm)

600

400

200

0

20

40

60

80

100

Relative Humidity on High
Humidity Side (%)(Low Humidity Side: 0%RH)
Figure 76. Moisture Permeabilityof Hydrophilic Polymer (35°C)

200

Heat Treatment Temperature (°C)

* The equilibrium moisture content at 20°C and 65%RH for thefilm of Kuraray PovalTM 25-100 which was dried at 50°C andthen heat-treated at each temperature of 90–210°C for 10
minutes

Moisture Permeability* (g/m2/24 hr)

46

Basic Physical Properties of PVOH Resin

4. Physical Properties of PVOH Film

4-2. MECHANICAL PROPERTIES
are improved by heat treatment, embrittlement of the filmis also accelerated as the temperature becomes equal toor higher than 160°C. Note that when a plasticizer such as
glycerin is added, the PVOH film becomes flexible and theelongation and tear strength increase significantly, but thetensile strength and Young’s modulus decrease greatly.

Kuraray PovalTM 60-98
Kuraray PovalTM 28-98
Kuraray PovalTM 5-98
15

Tensile Strength (kg/mm2)

PVOH aqueous solutions have good film forming properties
and the film is tough and resistant to tearing and friction. In
particular, the tensile strength belongs to the higher classwhen compared with plastic films widely available in themarket as well as other water-soluble polymers. Although
the physical properties of the PVOH film differ dependingon the grades of PVOH, it greatly changes not only by the
moisture content and the plasticizer addition but also by
the degree of stretching and heat treatment related to thefilm forming condition. PVOH film used in general industrial
applications is rarely subjected to stretching and heat
treatment. Therefore, it can be considered as a film in a state
dried at a temperature of 100°C at the highest. Figures 77
to 84 show the physical properties measured with films witha thickness of 0.03 mm, which were obtained by preparing
aqueous solutions of around 10% concentration from generalcommercial grades, casting them on a glass plate, and drying
them at 80°C for 2 hours after air-drying. The tensile strengthand elongation of the PVOH film increase as the degree ofpolymerization increases. The partially hydrolyzed producthas a slightly lower tensile strength than the fully hydrolyzed
product, but the elongation increases somewhat underhigh humidity. Under high humidity, the tensile strength
decreases for both the fully hydrolyzed product and partiallyhydrolyzed product, and the elongation tends to increase.
However, unlike in the case of high degree of polymerization
PVOH, a low degree of polymerization PVOH with a degree ofpolymerization of 550 exhibits a decrease in the elongation
regardless of the degree of hydrolysis when the relative
humidity is 60% or higher.

10

5

0

40

60

80

Relative Humidity(%)

The tear strength of the PVOH film tends to increase as
the moisture content of the film is higher, and the partiallyhydrolyzed PVOH with higher equilibrium moisture content
has higher tear strength under the same humidity. The
Young’s modulus of the film decreases sharply as the humidity
increases and the modulus of the partially hydrolyzed PVOH
with higher equilibrium moisture content is lower than thatof the fully hydrolyzed PVOH over the whole humidity range.

On the other hand, the elongation and tear strength are
improved according to the degree of heat treatment up toa temperature of 140–150°C, but they decrease sharply
when further subjected to an excessive heat treatment. Thatis, although the mechanical properties of the PVOH film

Kuraray PovalTM 44-88
Kuraray PovalTM 22-88
Kuraray PovalTM 5-88
15

Tensile Strength (kg/mm2)

Overall, the mechanical properties of the PVOH film are at ahigher level for the fully hydrolyzed PVOH with a high degreeof polymerization and the film with a degree of polymerizationof 550 is at a substantially low level. Additionally, it can besaid that the dependence of the relative humidity, that is,
the moisture content dependency on the physical propertiesof the partially hydrolyzed PVOH, is large. The propertiesof the PVOH film to water such as the hydroscopicity are
improved after heat treatment, as described in anotherchapter, “Properties of PVOH Film in Water”; the mechanicalproperties can also be improved by heat treatment. Amongthe mechanical properties, the tensile strength, Young’s
modulus, etc. tend to increase almost linearly according to
the degree of heat treatment.

Figure 77. Tensile Strength of Fully
Hydrolyzed PVOH Film (20°C)

10

5

0

40
60
80
Relative Humidity(%)
Figure 78. Tensile Strength of PartiallyHydrolyzed PVOH Film (20°C) P. 31/36

47

Basic Physical Properties of PVOH Resin

4. Physical Properties of PVOH Film

Kuraray PovalTM 60-98
Kuraray PovalTM 28-98
Kuraray PovalTM 5-98

Kuraray PovalTM 44-88
Kuraray PovalTM 22-88
Kuraray PovalTM 5-88
300

200

Elongation (%)

Elongation(%)

300

100

0
20

200

100

0
20

40
60
80
Relative Humidity(%)

Figure 79. Elongation of Fully Hydrolyzed
PVOH Film (20°C)

Kuraray PovalTM 22-88
Kuraray PovalTM 44-88
Kuraray PovalTM 5-88
100

50

50

20

20

Tear Strength (kg/mm2)

100

10
5
2
1
0.5
0.2
0.1

40
60
80
Relative Humidity(%)
Figure 80. Elongation of PartiallyHydrolyzed PVOH Film (20°C)

Kuraray PovalTM 28-98
Kuraray PovalTM 60-98
Kuraray PovalTM 5-98

Tear Strength (kg/mm2)

48

10
5
2
1
0.5
0.2

40

60

80

0.1

40

60

80

Relative Humidity(%)

Relative Humidity(%)

Figure 81. Tear Strength of Fully
Hydrolyzed PVOH Film (20°C)

Figure 82. Tear Strength of PartiallyHydrolyzed PVOH Film (20°C)

Basic Physical Properties of PVOH Resin

4. Physical Properties of PVOH Film

Kuraray PovalTM 44-88
Kuraray PovalTM 5-88
Kuraray PovalTM 22-88

Kuraray PovalTM 5-98
Kuraray PovalTM 60-98
Kuraray PovalTM 28-98

80

Young’s Modulus (kg/mm2)

Young’s Modulus (kg/mm2)

80

60

40

25

0

40

60

60

40

25

0

80

40

60

80

Relative Humidity(%)

Relative Humidity(%)

Figure 83. Young’s Modulus of Fully
Hydrolyzed PVOH Film (20°C)

Figure 84. Young’s Modulus of PartiallyHydrolyzed PVOH Film (20°C)

4-3. GAS PERMEABILITY

Oxygen Permeability Coefficient*(cc*cm/cm2 * sec* cmHg)

It has long been known that it is difficult to pass various gases
such as carbon dioxide, nitrogen, hydrogen, etc. through
PVOH film, and many reports on the matter have been
published. The gas barrier property of PVOH film is certainly
remarkable. Table 18 shows the permeability coefficients ofcarbon dioxide gas and nitrogen gas measured by Ito 57). All
the values for PVOH are in the order of 10–13 (cc*cm/cm2/
sec/cmHg) and they are extremely low even as a packaging
material. However, since the PVOH film is strongly hydrophilic
and is susceptible to humidity, the moisture content of thefilm increases and the permeability coefficient increases
markedly under high humidity. Figure 85 shows how thepermeability coefficient of oxygen changes depending on the
moisture content of the film. When the PVOH film absorbs
moisture, the adsorbed water first breaks the hydrogenbonding between the hydroxyl group of the PVOH molecules
and then bonds with the hydroxyl group. As the moisture
content increases, the water exists as free water between the

PVOH molecules. Therefore, it is considered that this freewater plasticizes PVOH and activates the molecular motion,and the gas permeation increases. The gas permeability of
the PVOH film also increases if there are other factors that
activate the molecular motion of PVOH. In PVOH with a low
degree of hydrolysis, the crystallinity of the film decreases
and the mobility of the side chain owing to the acetategroup increases, thus the gas permeability increases. Notethat the gas permeability has a temperature dependency,
and it generally tends to increase as the temperaturerises, but the permeability coefficient increases sharply
when the measurement temperature is above the secondorder transition temperature of the polymer. It is thoughtthat this is because the molecular motion of the polymer
molecule becomes active when the temperature is above thesecond-order transition temperature and the diffusion andpermeation of the gas increase rapidly.

10-10

10-11
*By vacuum pressure method sample:
Kuraray PovalTM 25-100 (Unplasticized, Dreied at 80o C x 2hr
Kuraray PovalTM 25-100 (Containing of DEG 5%, heat-treted at 130oC x 10min
K cellophane ( Vinylidene Chloride Applied)Commercial biaxially stretched 6-nylon

10-12

10-13

10-14
0

5

10

15

20

25

30

Moisture Content (%)
Figure 85. Influence of Moisture Content
on Oxygen Permeability of Film (35°C)
References
57) Ito, Polymer Chemistry, 18, 158 (1961)

49

50

Basic Physical Properties of PVOH Resin

4. Physical Properties of PVOH Film

Table 18. Gas Permeability of Various Polymer Films

Gas

Temperature(°C)

Humidity(%RH)

Permeability
Coefficient 1)
P x 1011

CO2

23

0
44
94

0.01
0.52
119

N2

14

Cellophane

CO2

15

0
90

0.1
10.5

6-nylon

CO2

30

0
44
95

1
1.7
2.9

CO2

15

0
43
95

61.4
57.8
85.3

N2

15

0
95

4.5
5

CO2

20

0
86

4.2
3.5

Polymer

PVOH

0
90

Polyethylene(d=0.9203)

Vinyl Chloride

<0.01
3.3

1) Unit: cc*cm/cm2*sec*cmHg
Cited reference: Ito, Polymer Chemistry, 18, 158 (1961)

4-4. RESISTANCE TO OIL, RESISTANCE TO ORGANIC SOLVENTPVOH has many hydrophilic hydroxyl groups and has strong
resistance to many organic chemicals such as animal oils/
vegetable oils, mineral oils, aliphatic hydrocarbons, ethers,
esters and ketones. Films with a thickness of 0.03 mm ofKuraray PovalTM 28-98 and Kuraray PovalTM 22-88 preparedby drying at 80°C for 2 hours were immersed in a chemicalsolution at 40°C for 70 hours and the weight swelling
degree and the area expansion degree of the films were
determined according to the method prescribed in JIS
K-6301. The results are shown in Table 19. No swelling wasobserved in the PVOH films within the scope of this test,
and a slight tendency of weight reduction and shrinkage
was observed. However, this is thought to be a result of thefact that there is some moisture in the sample films and it

is dehydrated during immersion in the chemical solution. In
general, the oil resistance and organic solvent resistance of
PVOH increase as the degree of hydrolysis increases, but
the influence of the degree of polymerization has no effect.
Resistance to lower alcohols such as methanol and ethanol
has a relatively large dependency on the degree of hydrolysis
and the partially hydrolyzed product tends to swell.

4. Physical Properties of PVOH Film

Basic Physical Properties of PVOH Resin

Table 19. Oil Resistance / Organic Solvent Resistance of PVOH Film, Weight and Area Change after Immersion at 40°C x 70 hr

Weight Degree of
Swelling (%)
Chemical Solution

Area Degree of
Swelling (%)

Kuraray
PovalTM
28-98

Kuraray
PovalTM
22-88

Kuraray
PovalTM
28-98

Kuraray
PovalTM
22-88

Hydrocarbon

BenzeneIsooctane
High-octane Gasoline

-0.6
-0.5
-0.6

-1.3
-1.1
-1.2

-1.6
-2.6
-2.6

-2.4
-2.3
-2.1

HalogenatedHydrocarbon

Monochlorobenzene
Carbon Tetrachloride

-0.8
-0.5

-1.4
-1.1

-2.4
-2

-1.4
-0.9

Oil

Soybean Oil
Castor Oil

-0.4
-0.2

-0.6
-0.9

-1.2
-0.3

-1
-1.3
According to JIS K-6301

4-5. OPTICAL TRANSMITTANCE
The infrared absorption spectrum of PVOH is measured
using a casted and dried film. Figure 87 and Figure 88 show
the examples of Kuraray PovalTM 25-100 and Kuraray PovalTM
22-88 as representative infrared absorption spectra of the
fully hydrolyzed PVOH and partially hydrolyzed PVOH.

Transmittance (%)

PVOH film allows good transmittance of light. The visible
light transmittance of Kuraray PovalTM 25-100 film with athickness of 0.025 mm containing 10 phr of glycerin is very
high and, for example, the transmittance at 560 nm reaches
91%. The PVOH film also allows ultraviolet rays to passthrough. An example of the measurement of Kuraray PovalTM
25-100 film is shown in Figure 86. Generally, ultraviolet
absorption spectrum of PVOH is used for detection of the
carbonyl group using the aqueous solution as a sample and
PVOH with a low degree of polymerization tends to exhibit
a stronger absorption than PVOH with a high degree ofpolymerization.

90
80
70
60
220

260

300

340

380

Wavelength (μm)*Kuraray PovalTM 25-100 film with a thickness of 0.025 mm
containing 10 PHR of glycerin
Figure 86. Ultraviolet Ray Transmittance of PVOH Film*

51

Basic Physical Properties of PVOH Resin

2.5μ

3

4

4. Physical Properties of PVOH Film

5

6

7

8

9

10

11

12 13 14 15

90

Transmittance (%)

80

50

10

20

0
4000 3500 3000 2500 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900

800

700 650

Wavenumber (cm-1)
Figure 87. Infrared Absorption Spectrum of Kuraray PovalTM 25-100 (Film)

In the infrared absorption spectrum, there is a characteristic
absorption band owing to the existence of a specific atomic
group in the molecule, called characteristic frequency.
The major characteristic frequencies are shown in Table
20. Although the absorption at 1700–1800 cm-1 (1740 cm1) based on the carbonyl group belonging to the acetategroup is hardly observed in the fully hydrolyzed PVOH, it
is quite remarkable in the partially hydrolyzed PVOH. The
intensity of the absorption at 1141 cm-11 in the infraredabsorption spectrum is used for the quantitative analysisof the crystallinity of PVOH, and the absorptions at 916
cm-1 and 849 cm-1 are used for detailed investigation in the

2.5μ

3

4

5

6

quantitative analysis of the stereoregularity. In this manner,
the infrared absorption spectrum analysis is one of theeffective methods for estimating the bonding state of PVOH.
It was described that the PVOH film allows a ray to passthrough well at the beginning of this section and the filmcertainly allows the visible ray and the ultraviolet ray well, but
the infrared transmittance in the longer wavelength region
is considerably lower than that of other transparent plastic
films and it is substantially difficult for infrared rays to go
through the film. Therefore, a heat retention effect can be
expected.

7

8

9

10

11

12 13 14 1590

80
Transmittance (%)

52

50

10

20

0
4000 3500 3000 2500 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900
Wavenumber (cm )-1Figure 88. Infrared Absorption Spectrum of Kuraray PovalTM 22-88 (Film)

800

700 650

4. Physical Properties of PVOH Film

Basic Physical Properties of PVOH Resin

Table 20. Major Characteristic Frequencies on Infrared Absorption Spectrum

Characteristic
Frequency Range

Atom Group

3700-3500

H-O

Stretching Vibration

3500-3300

H-N

Stretching Vibration

3400-3300

H-C ≡ C

Stretching Vibration

3100-3000

H-C = C

Stretching Vibration

3100-3050

H-C (Aromatic Ring)

Stretching Vibration

3000-2800

H-C-

Stretching Vibration

2650-2550

H-S

Stretching Vibration

2300-2200

N≡C

Stretching Vibration

2270-2170

C≡C

Stretching Vibration

2160-2100

N≡N

Stretching Vibration

1800-1700

C=O

Stretching Vibration

1690-1630

C=N

Stretching Vibration

1650-1550

H-N

Bending Vibration

1650-1600

C=C

Stretching Vibration

1600-1500

S=C

Stretching Vibration

1460-1300

H-C

Bending Vibration

1400-1250

C-N

Stretching Vibration

1200-1050

C-OH

Stretching Vibration

1300-1100

F-C

Stretching Vibration

750-650

Cl-C

Stretching Vibration

650-550

Br-C

Stretching Vibration

550-400

I-C

Stretching Vibration

53

54

Basic Physical Properties of PVOH Resin

4. Physical Properties of PVOH Film

4-6. ELECTRIC PROPERTIESThe electrostatic propensity of PVOH film is very small.
PVOH film with a strong hydrophilic property generates very
little static electricity by friction and has antifouling property
because dust, etc., in air do not electrodeposit on it. Table
21 shows the friction-charged electrostatic potential while
comparing that of Kuraray Poval TM 25-100 film containing 10
phr of glycerin with those of various packaging films. Although

there is not much detailed data on the electric properties of
PVOH, an example of how the electric properties change
depending on the moisture content of the film is cited inTable 22. Additionally, Table 23 shows the dielectric constantand dielectric loss of Kuraray PovalTM 25-100 film in absolute
dry condition.

Table 21. Electrostatic Propensity of Plastic Film

Type

Charged Voltage (Volt*)

Kuraray PovalTM 25-100

1Cellophane

1

Vinyl Chloride

40

Polyethylene

50-90

Polystyrene

120-150* The film after humidity conditioning at 30°C, 40% RH was rubbed with arotary static tester at a speed of 800-1000 rpm and then the voltage wasmeasured.
Table 22. Electric Properties of Fully Hydrolyzed PVOH*)

Moisture content
of Film (%)

0.5

1

2

4

8

16

32

Specific
Resistance (20°C),
Ohm-cm

1011

1010

3x109

109

3x108

108

2x107

Dielectric
Constant (20°C,
103 cycle)

3.5

4.5

6.5

13

>13

>13

>13

Surface
Resistance (20°C),
Ohm

1010

1010

1010

3x107

3x107

8x106

2x106

* Ullmanns Enzyklopädie der technischen Chemie (1963)
Table 23. Dielectric Constant & Dielectric Loss of Kuraray PovalTM 25-100 film in absolute dry condition

Frequency

Temperature

Dielectric
ConstantTan ∂ x 104

102

18

1.74

9.4

103

18

1.745

14

104

18

1.75

29

105

18

1.76

42

106

18

1.79

47.7

Precautions for Handling and Storage of PVOH

Basic Physical Properties of PVOH Resin

Precautions for
Handling and Storageof PVOH

Please refer to ourseparate health andsafety guidelines forhandling our Handling:
1. Since this product contains fine
powder and dust may stirred up
when feeding it into a dissolution
tank, wear rubber gloves andprotective glasses etc. to protect
your skin and eyes.
2. Install a dust collector whenhandling a large amount of thisproduct. Additionally, since there
is a risk of dust explosion withstatic electricity or spark as an
ignition source, measures suchas secure grounding and use of
conductive materials are required.

Storage

Safety1. Since this product dissolves inwater, store it so that it will not be
exposed to rain water or the like.

For detailed information on safety,
refer to the Material Safety Data
Sheet.

2. Since this product absorbs
moisture and tends to become ablock, store it away from hot andhumid place.
3. When storing 3,000 kg or moreof this product, it is subject to regulations as flammable material(combustible solids) specified by
the Fire Service Act.

Although the description contents of this document are prepared based on the materials, information and data available atthe time of preparation for accuracy, this does not guarantee the accuracy. The cautions and notes are intended for ordinary
handling and do not necessarily conform to all situations and uses. Therefore, be sure to set and use safe management and use
conditions at the responsibility of the user.

55

Adding value toyour products –worldwide
Kuraray Poval™, Exceval™, Elvanol™ and Mowiflex™ are the trademarks for polyvinyl alcohols
made by Kuraray. Their key characteristics — outstanding film-forming properties and highbinding strength — add real value to your products. Our polymers are water-soluble, highly
reactive, crosslinkable and foamable. They have high pigment binding capacity, protective
colloid characteristics and thickening effects. The physical and chemical properties of Kuraray
Poval™ make it ideal for a wide variety of applications, ranging from adhesives through paper andceramics to packaging films. Many of our polymers are food contact-approved and thus suitablefor food applications. Ecologically Kuraray Poval™ is advantageous due to its biodegradability andthe fact that combustion does not generate residues. It is available in various particle sizes from
granules to fine powders.
Kuraray produces its wide range of Kuraray Poval™ grades in Japan, Singapore, Germany andthe USA. Kuraray’s global production and service network make us your partner of choice forinnovative high-quality PVOH resins.
Kuraray – Here to Innovate.

Headquarters
Kuraray Co., Ltd.
Tokiwabashi Tower
2-6-4, Otemachi
Chiyoda-ku
Tokyo, Japan 100-0004
Phone: +81 3 67 01 1000
infopoval.jp@kuraray.com

Kuraray Poval™
product portfolio
Please contact your local
Kuraray office to discuss theright Kuraray product foryour needs.

Kuraray America, Inc.
2625 Bay Area Blvd.,
Suite 600 Houston, TX77058
United States of America
Phone: +1 800 423 9762

Kuraray Asia Pacific Pte., Ltd.
250 North Bridge Road
#10-01/02 Raffles City Tower
Singapore 179101
Phone: +65 6337 4123

info.kuraray-poval@kuraray.com

infopoval.sg@kuraray.com

Kuraray Europe GmbH
Philipp-Reis-Str. 465795 Hattersheim am Main,
Germany
Phone: +49 69 305 85 351

Kuraray China Co., Ltd.
Unit 2207, 2 Grand Gateway
3 Hongqiao Road, Xuhui District,
Shanghai 200030, China
Phone: +86 21 6119 8111

info.eu-poval@kuraray.com

infopoval.cn@kuraray.com

06/2022