Kuraray Poval™
for suspension
PVC

Kuraray Poval™
for suspension
PVC
Introduction

Production of PVC resin

Kuraray has much expertise in the use of polyvinyl alcohol(PVA or PVOH) based suspending agents for the needs ofpolyvinyl chloride (PVC) manufacturers. In this application,
polyvinyl alcohol is used as a protective colloid for the polymerisation of vinyl chloride. Vinyl chloride monomer (VCM)
is suspended in water by means of stirring, in combination
with a suspending agent to allow the polymerisation reaction
to proceed. The physical properties of the resulting PVC, including size, shape of the grains and bulk density, are directly
related to the grain forming process during polymerisation.
Kuraray’s primary and secondary suspending agents allow
precise control of the grain formation and its resulting structure and morphology. Furthermore, the surface activity canbe widely tuned by selecting an appropriate combination ofKuraray’s suspending agents. This diversity enables the PVC
manufacturer to produce a very versatile range of PVC resins,varying in morphology and K value according to the intended
end application

PVC can be manufactured in a number of ways from suspension polymerisation to emulsion polymerisation and bulk
polymerisation, but the most popular is suspension polymerisation. PVC resin is manufactured with a mean grain size ofaround 150 µm by adding water and suspending agent, polyvinyl alcohol (PVOH), into the reactor together with liquid
VCM under pressure. This mixture is agitated to create fine
droplets. To achieve PVC resin of this type it is required tocontrol a number of parameters including particle size andmorphology, which will influence bulk density and porosityand help processing of the PVC resin at a later stage.
Polyvinyl alcohol is an important additive as a suspending
agent in this process to influence such properties as mentioned above to control PVC quality and technical performance.
Kuraray Poval™ properties are mainly controlled by the degree of hydrolysis and degree of polymerisation as shown in
Figure 1. For PVC suspension polymerisation the degree ofhydrolysis and degree of polymerisation are important properties for surface activity and protective colloidability in the
PVC polymerisation process.

PVC resin can be used in many applications to replace suchmaterials as wood, glass and some metals. Thanks to the economics, durability and self-extinguishing properties of PVC it
can be used for water pipe, electrical cable and a variety ofbuilding products.
PVC also finds use in wallpaper and window profiles, agriculture and automotive parts, synthetic leather and film for
packaging. Because of its use in many applications it is a material present in our everyday life. The majority of PVC resin
is manufactured by the suspension polymerisation process.
Polyvinyl alcohol is an essential part of this process as themain suspending agent.

2

Protective Colloidability

Low

High

Low

DH88%

80
DH80%

DH70%-78%
L series

60

Surface Activity

Primary suspending agent
40

DH35%-55%
LM series

20

Secondarysuspending agent

High

Degree of hydrolysis (mol %)

100

0
250

550

1000

750

2000

2800

Degree of polymerisation
Figure 1. The role of polyvinyl alcohol for PVC polymerisation and PVC resin properties.

cle around 1 µm in size is precipitated in the monomer droplet
as the PVC resin is not soluble in VCM. In this process it is said
that primary particles agglomerate in the monomer droplet
to form a network structure due to the frequent coalescenceand dispersion of the monomer droplets. Because of this theinternal structure of the PVC resin becomes more porous
leading to benefits in porosity for easier absorbance of plasticiser and additives giving greater processability of the PVC
resin.

The role of polyvinyl alcohol for suspension polymerisation isdifferent depending on the degree of conversion of VCM to
PVC. The required properties of the polyvinyl alcohol for eachstage (<0.1 % compared to 0.1 % to <30 % compared to >30 %)will be explained below.
Figure 2 shows the polymerisation mechanism starting withconversion <0.1 %, which is the stage where the initiator is dispersed throughout the VCM. The initiator and monomer will
be mixed by the monomer droplet coalescence and dispersion
caused by the agitation in the reactor. If this coalescence anddispersion process is poor, the achieved conversion of each
droplet will be non-homogenous. Monomer droplets with highlevels of initiator will have high conversion, which can lead
to issues with fish eyes in thin film applications. To enhance
this coalescence and dispersion behaviour a polyvinyl alcohol
which has a higher surface activity and lower protective colloidability will be required. The most suitable Kuraray Poval™
grades for the above process will be our L and LM grades.

On the contrary if coalescence and dispersion are not efficient during this stage the primary particle will not have a
network structure in the monomer droplet and the PVC resin
will become less porous, which would lead to a resin of poor
processability. To enhance this coalescence and dispersion
behaviour a polyvinyl alcohol which has a higher surface activity and lower protective colloidability will be required. The
most suitable Kuraray Poval™ grades for the above process
will be our L and LM grades.

As shown in Figure 2 on page 4, the next phase shows the conversion below 30 % which is the stage when the PVC primaryparticles are generated in the VCM droplets. Polymerisation
occurs in each monomer droplet and the PVC primary parti-

3

The final phase for conversion above 30 % which is the stage
when the PVC resin particles will be formed by the agglomeration of primary particles, coalescence and dispersion ofmonomer droplets will not occur due to the increase of conversion. The protective colloidability of the polyvinyl alcohol
can control this agglomeration process. Lower protective colloidability can lead to too much agglomeration and generatelarge particles and the polymerisation will become unstable.
Higher protective colloidability leads to more balanced agglomeration and polymerisation will be stable.

High protective colloidability polyvinyl alcohols which are required for stability in the polymerisation process are called
primary suspending agents. On the other hand higher surface
activity polyvinyl alcohols which are required for greater
porosity generation in the polymerisation process are called
secondary suspending agents.
The required performance of a polyvinyl alcohol as a suspending agent will be different for each polymerisation stage butin the actual process each polyvinyl alcohol is added into thereactor at the same time, at the beginning of the process. It
is important to design the recipe using a combination of suitable polyvinyl alcohols for each part of the polymerisation
process taking into account the attributes of the equipment
being used in terms of agitation, baffles, jacket or condenser
cooling and reactor size and geometry.

For this stage a polyvinyl alcohol with higher protective colloidability will be required. The most suitable Kuraray Poval™
grades for the above process will be products with a degree ofhydrolysis of 80 mol% or higher and our L grades.

Beginning StageVCM Conv. < 30 %VCM Conv. > 30 %Initiator ishomogenized into
VCM droplet.

Network structure
generation

Network structure
generation

Coalescence

Disperse

Coalescence

Disperse

Primary particle (~1 µm)

Figure 2. The polymerisation mechanism

Surface activity

Protective Colloidability

High = small monomer droplets

High = less agglomeration

Low = large monomer droplets

Low = more agglomeration

4

Primary particle agglomeration

Kuraray Poval™ grade list for PVC
suspension polymerisation
Primary Suspending Agents
Viscosity (1)Degree ofNon-volatile(2)Ash(3)[mPa•s]hydrolysis [mol%]content [%]content [%]32-80

29.0 - 35.0

79.0 - 81.0

97.5 ± 2.5≤ 0.4

5.0 - 7.0

35-80

32.0 - 38.0

79.0 - 81.0

97.5 ± 2.5≤ 0.4

5.0 - 7.040-80E

37.0 - 45.0

79.0 - 81.0

97.5 ± 2.5≤ 0.4

5.0 - 7.0

48-80

45.0 - 51.0

78.5 - 80.5

97.5 ± 2.5≤ 0.2

5.0 - 7.0L-8

5.0 - 5.8

69.5 - 72.5

98.5 ± 1.5≤ 1.1

5.0 - 7.0

L-9

5.5 - 6.1

69.5 - 72.5

98.5 ± 1.5≤ 1.1

5.0 - 7.0

L-9-78

6.0 - 6.7

76.5 - 79.0

97.5 ± 2.5≤ 1.2

5.0 - 7.0

L-9P

6.2 - 7.2

71.5 - 73.5

98.5 ± 1.5≤ 0.5

5.0 - 7.0L-10

5.0 - 7.0

71.5 - 73.5

97.5 ± 2.5≤ 1.1

5.0 - 7.0

L-11

5.5 - 7.5

71.5 - 73.5

98.5 ± 1.5≤ 0.4

5.0 - 7.0

L-508W

6.0 - 7.0

71.5 - 73.5

97.5 ± 2.5≤ 0.4

5.0 - 7.0

44-88

40.0 - 48.0

87.0 - 89.0

97.5 ± 2.5≤ 0.4

5.0 - 7.0

49-88

45.0 - 52.0

87.0 - 89.0

97.5 ± 2.5≤ 0.4

5.0 - 7.0

55-95

50.0 - 60.0

95.0 - 96.0

97.5 ± 2.5≤ 0.4

5.0 - 7.0

(2) after 3 hours drying at 105 °C DIN 53189 / ISO 15023-2(3) calculated as Na2O

Kuraray Poval™

(1) of a 4 % aqueous solution at 20 °C DIN 53015 / ISO 15023-2

pH

Secondary Suspending Agents
Viscosity (1)Degree ofNon-volatile(2)Ash(3)[mPa•s]hydrolysis [mol%]content [%]content [%]LM-10HD

4.5 - 5.7

38.0 - 42.0

98.5 ± 1.5

≤ 0.6

NA

LM-20

3.0 - 4.0

38.0 - 42.0

98.5 ± 1.5

≤ 1.0

NA

LM-30

9.3 - 10.3(4)45.0 - 51.0

98.5 ± 1.5

≤ 0.6

NA

Kuraray Poval™

(1) of a 4 % methanol / water (1/1) solution at 20 °C DIN 53015 / ISO 15023-2(4) of a 10 % methanol / water (1/1) solution at 20 °C(3) calculated as Na2O

5(2) after 3 hours drying at 105 °C DIN 53189 / ISO 15023-2

pHCharacteristics of Kuraray Poval™ for
PVC suspension polymerisation
Kuraray Poval™ grades with a degreeof hydrolysis of 80 mol%
These grades have a high degree of hydrolysis and a high degree of polymerisation among our primary suspending agents.
With these grades suspension polymerisation can be carriedout in a stable manner, especially for the combination witha secondary suspending agent. It is possible to stabilise the
PVC resin particle size.

32-80

48-80

35-80

40-80E

Viscosity (mPa•s)

1000

Kuraray Poval™ L grades
These grades have a low degree of hydrolysis and low degreeof polymerisation among our primary suspending agents.
Compared to our grades with a degree of hydrolysis at 80
mol% they can reduce the polyvinyl alcohol use in the recipe.
They can also control the PVC particle size easily by adjusting
the amount used. They can provide good porosity PVC resin
maintaining good bulk density. Plasticiser absorbance speed,
fish eye level and residual VCM level will be improved leading
to a good balance of properties for the PVC resin produced.
These grades also provide a narrow PVC resin particle size
distribution and improved morphology giving more sphericalparticles leading to better processability.

100

10

1
0

2

4

6

8

Concentration (wt%)
Figure 3. Viscosity of aqueous PVOH solutions
at 20 °C vs. concentration.

L-8

L-10

L-9

L-9-781000

Viscosity (mPa•s)

Kuraray Poval™ grades with a degreeof hydrolysis of 88 mol% to 95 mol%
These grades have a high degree of hydrolysis and a high degree of polymerisation among our primary suspending agents.
Combining these grades with grades of hydrolysis at 80 mol%
it is possible to obtain high bulk density PVC resin. Kuraray
Poval™ 55-95 can also be used in recipes to increase the bulk
density of the PVC resin.

100

10

1

Kuraray Poval™ LM grades

0

Kuraray Poval™ LM grades are secondary suspending agent
products with a degree of hydrolysis below 50 mol%. They
provide high porosity and excellent plasticiser absorption for
PVC resins whilst maintaining good bulk density. The products are supplied as solid dry powders but can be dispersed inwater without the need for organic solvents.

Figure 4. Viscosity of aqueous PVOH solutions
at 20 °C vs. concentration.

5

10

15

Concentration (wt%)

6

L-11

L-9P

49-88

L-508W

55-95

1000

Viscosity (mPa•s)

Viscosity (mPa•s)

1000

100

10

1

100

10

1
5

0

10

0

15

2

4

6

8

Concentration (wt%)

Concentration (wt%)

Figure 5. Viscosity of aqueous PVOH solutions
at 20 °C vs. concentration.

Figure 6. Viscosity of aqueous PVOH solutions
at 20 °C vs. concentration.

LM-20

LM-10HD

LM-30

Viscosity (mPa•s)

100

10

1
0

5

10

15

Concentration (wt%)
Figure 7. Viscosity of PVOH solutions inwater / methanol (1:1) at 20 °C vs. concentration.

Kuraray Poval™ solution preparation
Method 1

Method 2

Kuraray Poval™ L grades are partially hydrolyzed polyvinyl
alcohols varying in their degree of hydrolysis from 69.5 - 73.5
mol%. As such they are cold water soluble and solutions canbe made either in cold water or in hot water.
Kuraray Poval™ is slowly added to a stirred tank of cold waterto avoid lump formation. The product can be passed througha coarse mesh (10 mesh) to catch any extraneous items that
may fall into the solution mixer. After adding all the L-grade,the mixture is heated up to 70 - 80 °C with agitation. There
should be sufficient agitation in the mixer for efficient dissolution but not too intense to cause foam build up at the surface.
Mix for 2 hours or until the solution is homogenous. The solution is then cooled to below the cloud point to obtain a clear
solution. The solution concentration can then be checked andadjusted if necessary. Before pumping to the charge vessel orreactor the solution is passed through a 200 micron filter asa final “cleaning process”. L-grades exhibit a cloud point andthe prepared solutions have to be stored below the product's
cloud point to avoid separation during storage.

Kuraray Poval™ 80 mol% hydrolysis grades are partially hydrolysed polyvinyl alcohols varying in their degree of hydrolysis
from 76.5 - 81.0 mol%. For these grades it is recommended
to utilize hot water to prepare solutions.
Kuraray Poval™ is slowly added to a stirred tank of cold waterto avoid lump formation. The product can be passed througha coarse mesh (10 mesh) to catch any extraneous items that
may fall into the solution mixer. After adding all the Kuraray
Poval™, the mixture is heated up to 80 - 90 °C with agitation.
There should be sufficient agitation in the mixer for efficientdissolution but not too intense to cause foam build up at thesurface. Mix for 2 hours or until the solution is homogenous.
The solution is then cooled to below the cloud point to obtain a clear solution. The solution concentration can then be
checked and adjusted if necessary. Before pumping to thecharge vessel or reactor the solution is passed through a 200
micron filter as a final “cleaning process”.

7Method 3

Method 4

Kuraray Poval™ 88 mol% and 95 mol% hydrolysis grades are
partially hydrolyzed polyvinyl alcohols varying in their degreeof hydrolysis from 87.0 - 96.0 mol%. As such they are only
completely soluble in hot water and solutions can only bemade utilizing hot water.

Kuraray Poval™ LM grades are solid products and are classed
as low hydrolysis polyvinyl alcohols varying in their degree ofhydrolysis from 40.0 - 50.0 mol%. As such they are not fullywater soluble but can be easily dispersed into water.
The Kuraray Poval™ LM grade is slowly added to a stirred tankof cold water to avoid lump formation. The product can bepassed through a coarse mesh (10 mesh) to catch any extraneous items that may fall into the dispersion mixer. There
should be sufficient agitation in the mixer for efficient dissolution but not too intense to cause foam build up at the surface. Mix for 1-2 hours or until the dispersion is homogenous.
The solution concentration can then be checked and adjusted
if necessary. For storage of LM-grade aqueous dispersion,
solid content should be less than 5 % and the temperature
below 40 °C.

The Kuraray Poval™ is slowly added to a stirred tank of cold
water to avoid lump formation. The product can be passed
through a coarse mesh (10 mesh) to catch any extraneous
items that may fall into the solution mixer. After adding all the
Kuraray Poval™, the mixture is heated up to 90 - 95 °C withagitation. There should be sufficient agitation in the mixer for
efficient dissolution but not too intense to cause foam build
up at the surface. Mix for 2 hours or until the solution is homogenous. The solution is then cooled to room temperature.
The solution concentration can then be checked and adjusted
if necessary. Before pumping to the charge vessel or reactor
the solution is passed through a 200 micron filter as a final“cleaning process”.

Method 5
Kuraray Poval™ LM-30 is slowly added to a stirred tank of a
mixture of cold water and methanol or ethanol (50:50 mix)
passing through a coarse mesh (10 mesh) to catch any extraneous items that may fall into the solution mixer. There should
be sufficient agitation in the mixer for efficient dissolution
but not too intense to cause foam build up at the surface. Mix
for 4 hours or until the solution is homogenous. The solution
concentration can then be checked and adjusted if necessary. Solutions of Kuraray Poval™ LM-30 should be charged
through the VCM charge line or a dedicated line due to their
low solubility in water.

Kuraray Poval™

Method

L-8

1

L-9

Recommended

Recommended

Kuraray Poval™

Method4-6%40-80E

2

4-5%

1

4-6%

48-80

2

4-5%

L-9P

1

4-6%

44-88

3

4-5%

L-9-78

2

4-6%

49-88

3

4-5%

L-10

1

4-6%

55-95

3

4-5%

L-11

1

4-6%

LM-10HD4

2-4%

L-508W

1

4-6%

LM-20

4

3-7%

32-80

2

4-5%

LM-30

5

3-7%

35-80

2

4-5%

concentration

8

concentration

Cloud point
The cloud point is the temperature at which a solution of polyvinyl alcohol starts to phase separate into lower and higher
concentration phases and the solution gets turbid because of
the difference in refractive index of the two phases. Low hydrolysis polyvinyl alcohols are more hydrophobic and exhibit
cloud points at lower temperatures. As the degree of hydrolysis of a polyvinyl alcohol increases the product becomes lesshydrophobic and more hydrophyllic so their cloud points tend
to be at higher temperatures.

Detailed below are the cloud points of some of our differenthydrolysis grades. When the solution is stored above its cloud
point without agitation sedimentation of the higher concentration phase happens. Generally aqueous solutions of primary suspending agents have cloud points as shown in the following graph. So the solution of DH 80 mol% grade should be
stored below 45 °C and DH 72 mol% grades (L-grades) should
be stored below 25-30 °C to avoid sedimentation issues.

Cloud point was measured by UV/Vis spectroscopy at 660 nm with a heating rate of 1 K/min. The cloud point is defined as thetemperature at which the transmission of the solution drops below 85 %.
80

70

L-8

Cloud point (°C)

60

L-9
L-10
L-9-7850

L-508W
L-11
40

L-9P

30

20
0.01

0.1

10

1

Concentration (wt%)
Figure 8. Cloud points of aqueous Kuraray Poval™ solutions vs. concentration.
70

Cloud point (°C)

60
32-80
35-80
40-80E
48-80
50

40
0.01

0.1

10

1

Concentration (wt%)
Figure 9. Cloud points of aqueous Kuraray Poval™ solutions vs. concentration.

9

Foaming
There are two types of foam that can be generated when using
polyvinyl alcohol in suspension polymerisation.
The first is the production of wet foam when polyvinyl alcohol
solutions are made. Polyvinyl alcohols by their nature areused to alter the surface tension of water and reactor contents so it is no surprise that they foam when being made into
solution with possibly fast agitation. It is also possible to get
wet foam during the beginning of the PVC polymerisation as
the polyvinyl alcohol is dispersed in the water VCM mixture.
The other type of foam is dry foam (or still could be classed
as wet foam)! As suspension reactions progress they generateheat which causes VCM to boil. The VCM gas bubbles rise to
the surface of the reactor either to cool in the space above or
via a condenser. As reactions run more quickly due to fasterinitiators more heat needs to be removed from the reactor
and the use of condensers becomes the norm. The boiling
VCM droplets rise to the surface of the reactor and can at-tach themselves to PVC resin particles. At the same time the
PVC resin slurry increases in viscosity so it becomes moredifficult for the VCM droplets to be released from the slurry
which looks like a foam / cream at the top of the reactor contents. To reduce the generation of foam you need good end to
end agitation and a good vortex at the top to try and wet out
the PVC slurry. You can increase the water / monomer ratio
to reduce the slurry viscosity. An injection of water will also
reduce the viscosity and also help cooling. The last option
is to use an antifoam. This can be a proprietary antifoam or
polyvinyl alcohol. The decision on what to use would be basedon performance vs cost as antifoams are more effective but
are considerably more expensive than polyvinyl alcohols. If a
polyvinyl alcohol is to be used it is better to use one of highmolecular weight and of high degree of hydrolysis.

Handling and storage

SafetyKuraray Poval™ is an industrial chemical and as such whenhandling the necessary personal protective equipment (PPE)should be used for handling a fine powder. Care should betaken when discharging from plastic packaging as static
charges can be generated. It is recommended that packaging
and equipment is earthed to prevent static build up.
Kuraray Poval™ should be stored in clean dry conditions andnot exposed to water or high humidity for long periods of time.
Kuraray Poval™ solutions should be stored below their cloud
points in clean vessels with gentle agitation or circulation
pumps. They should be protected from biological attack by
micro organisms.

Kuraray Poval™ is not classified as hazardous to health and is
not classified as dangerous for transport.
For more detailed information please refer to our productsafety data sheets.

For more detailed information please refer to our Kuraray
Poval™ handling brochure which is available upon request.

Descriptions are based on materials, information and data available at this moment, and we do not guarantee it although we are accurate. The notes areintended for ordinary handling and do not necessarily conform to all situations, uses, and usage. Therefore please set and use safe management and use
conditions as these are at the responsibility of the user.

10

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Adding value toyour products – worldwide
KURARAY POVAL™, EXCEVAL™, ELVANOL™, and MOWIFLEX™ are the trademarks for polyvinyl alcohols (PVOH) madeby Kuraray. Their key characteristics — outstanding film-forming properties and high binding 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 and ceramics topackaging films. Many of our polymers are food contact-approved and thus suitable for food applications.
Kuraray produces its wide range of KURARAY POVAL™ grades in Japan, Singapore, Germany and the USA. Kuraray’s global
production and service network make us your partner of choice for innovative high-quality PVOH resins.

PLEASE CONTACT US

kuraray-poval.com

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