NATIONAL BUREAU OF STANDARDS REPORT

8157

MEASUREMENT OF WATER ABSORPTION

OF EXPANDED POLYSTYRENE THERMAL INSULATION

BY

Robert D. Stiehler and Richard W. Young

U. $. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NIS PROJECT NIS REPORT

0705-^-07505 January 6, 196k 8157

MEASUREMENT OF V/ATER ABSORPTION

OF EXPANDED POLYSTYRENE THERMAL INSULATION

by

Robert D. Stiehler and Richard W, Young

Polymer Evaluation and Testing Section

Polymers Division

Sponsored by

Office of the Chief of Engineers

Department of the Air Force

Bureau of Yards and Docks

NATIONAL BUREAU OF S

for us* within the Government, and review. For this reason, t whole or In part, is not autlv Bureau of Standards, Washinj

the Report has been specifical

IMPORTANT NOTICE

s subjected to additional evaluation

* listing of this Report, either in Approved for public release by the , n Stmg ot tms «epon, enner in Director of the National Institute of he Office of the Director, National Standards and Technology (NIST) iy the Government fl « ency

for which ^

v ' copies for its own use. on October 9, 2015.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

MEASUREMENT OF WATER ABSORPTION

OF EXPANDED POLYSTYRENE THERMAL INSULATION

Summary

The porosity of some samples of expanded polystyrene used for

thermal insulation makes the measurement of water absorption

extremely difficult „ As a consequence , there is no reliable

method that can be used for specification purposes. Where water

absorption is a critical factor in the use of this material,, it

is recommended that the porosity be determined and only material

that is non-porous be used. The water absorption of non-porous

material can be determined from the change in buoyancy during

immersion in water.

The requirement in CE-20^, Change 2, dated February 15j* 1961 for

moisture absorption of expanded polystyrene is 0.25 per cent by

volume maximum. None of the materials tested met this requirement.

This limit must be increased to, at least, 1.5 per cent in order

to have at least one product comply. A limit of 3 per cent maximum

is more realistic.

Methods are given for determining the porosity of expanded polystyrene

and for determining the water absorption of non-porous material.

Background

Manufacturers reported to the Office of Chief of Engineers, Department of Army that large variations were obtained in interlaboratory

tests on water absorption of expanded polystyrene. As a consequence,

a project was established at the National Bureau of Standards under

the Tri-Service Program to investigate existing and new methods for

determining water absorption of this material and to develop a

reliable method for use in Government procurement.

The following existing methods for determining water absorption were

considered

- 2 -

(1) Federal Specification HH-I-524, Section 4,3.10

(2) Military Specification MIL-P-16591D, Section 4.4.4

(3) Guide Specification for Military Construction CE-204,

Change 2, Section q; (3)(c)

(4) ASTM Designation; C 272-53

(5) ASTM Designation; D 2127-62T

All of these methods determine the weight of a specimen before

and after immersion in water. They differ in the preconditioning of the specimen, period of immersion, method of removal

of surface water after immersion, and expression of results.

Materials

Expanded polystyrene used in this project was furnished gratis

by the following manufacturers;

Armstrong Cork Company

Dow Chemical Company

Dyfoam Corporation

Dyreiite Corporation

Gilman Brothers Company

The samples were 12 inches long, either 10 or 12 inches wide,

and 1,2,3 and 4 inches thick. Most of the work was done on

specimens 1 or 2 inches in thickness, either as originally

supplied or cut from the pieces 3 and 4 inches in thickness.

The samples supplied by Dow Chemical Company were extruded polystyrene. The other samples were prepared from polystyrene beads.

In this report; the material from the various manufacturers are

coded A,B,C,D >( and E, the codes being assigned at random.

-3

The materials had the following characteristics:

Material Density

^

Water Solubles-^'

lb/ft 3 % by weight

A 1.80 - 1.92 0.4

B 0.97 - 1.46 0.7

C 0.79 - 0.88 0

D 0.86 - 0.94 '0.

E 1.16 - 1.30 0.1

1/ Calculated from weight and dimensions of samples.

2/ Calculated from loss in weight after 7 days immersion in

water at 23° C and 2 days drying in oven at 70° C.

Exploratory Tests

In discussions with representatives of Tri-Service, it was

decided to use the following procedure for exploring the

behavior of various expanded polystyrene materials in the

absorption of water:

A specimen approximately 12 inches long, 10 inches wide and +•’ o thickness of the material is prepared so that all exposed faces

are cut surfaces. The specimen is conditioned at 70° C for

16 hours, cooled to room temperature in a desiccator, and then

weighed to within 0.1 per cent. The dimensions of the specimen

are measured to within 0.1 per cent, making at least 5 measurements in each direction. The specimen is immersed in water for

10 seconds, dipped in 95 per cent ethanol, and dried on the

surface in a current of air. The specimen is reimmersed in water

and the process repeated after 1,2,3 and 7 days immersion. After

the last weighing, the specimen is placed in an oven at 70° C

for 16 hours, cooled to room temperature In a desiccator, and

weighed to within 0.1 per cent. The weight increase of the

specimen is calculated in per cent by volume for each period

of immersion, from which the weight increase after 10 seconds

immersion is subtracted..

Preliminary tests to determine the rate of evaporation of the

ethanol from the surface indicated a gradual decrease in weight

rather than a rapid decrease followed by a slow decrease as

anticipated. Thus, it was not possible to select drying

conditions in air which would remove only the liquid on the

surfaces. The same general behavior was observed when the

ethanol dip was omitted, but the initial rate of decrease in

weight was less. Since the procedure for removing the surface

liquid had to be arbitrary, it was decided to use the procedure

adopted in ASTM Designations D 2127 -62T which allows the

specimen to drain for 10 seconds on a screen held at an angle

of 30° from the vertical. At least, this procedure was the

simplest of those in use. With this modification in the above

method, measurements were made on four of the materials using

specimens 1, 2 and 3 inches in thickness.

The results are given in Table 1. The large amount of water

retained by some specimens after 10 seconds immersion indicated

that more than water on the surface of the specimen might be

involved. The test was repeated using water containing 0,1

per cent of a non-ionic wetting agent (Triton X-100). The

results given in Table 2, when compared with those in Table 1,

confirmed the previous indication that the water retained by

the specimen after 10 seconds immersion is not all on the surface.

Appreciable amounts of water were retained in open pores. This

comparison also indicated that the discrepancies in results

reported by various manufacturers may have been due in large

part to differences in the surface tension of the water used in

the tests. It was concluded from the results in Tables 1 and 2

that existing methods or minor modifications of them would not

be suitable for determining water absorption of expanded poly-*

styrene, and that the uptake of water must be considered as the

sum of (1) water in open pores, and (2) water adsorbed on the

cell walls of the polystyrene.

Water Adsorption

The results in Tables 1 and 2 indicate that water containing a

wetting agent fills the open pores rapidly ; whereas, water is
' >; :
=5

adsorbed on the walls of the closed cells relatively slowly.

Although there is no time sharply dividing the two processes, it

appears that most pores are filled within seconds after the

specimen is immersed. The adsorption of water on the cell walls

can then be followed by noting the change in buoyancy of the

specimen with time.

The following procedure was developed for determining the

adsorption of water on the polystyrene surfaces;

Cut with a fine-tooth band saw having no set, rectangular

specimen having a volume of approximately 1200 cc and approximately 2.5 or 5 centimeters in thickness. Remove any skin from

uncut surfaces. Dry the specimen at 70° C in a circulating

air oven for at least 16 hours, and weigh the dried specimen.

Measure to the nearest 0.01 centimeter the length, width and

thickness of the specimen at five points for each dimension

(near 4 corners and center of each face). Calculate the volume

in cubic centimeters from the median values for each dimension.

Prepare a suitable vessel with about 15 liters of distilled

water containing 0.1 per cent of a non-ionic detergent. Place

the specimen in an open cage constructed as shown in Figure 1 of

a corrosion-resistant metal weighing about 1300 grams. Weigh

the specimen plus cage totally immersed in the water at 23 ± 1° C

30 seconds after immersion. Allow the specimen and cage to

remain immersed for 7 days at 23 ± 1° C e At intervals, reweigh

the specimen plus cage while immersed. Calculate the water

absorption of the specimen to the nearest 0.1 per cent by the

following equation;

(Wo _ Wq\ i on d

Water adsorption, per cent by volume = 1 i lz_

Where: W, - Weight of specimen in grams plus cage immersed in

water at 23° C for not more than 30 seconds

W0 = Weight of specimen in grams plus cage immersed in

water at 23® C for specified period

V = Volume of specimen in cubic centimeters

After the test, redry the specimen at 70° C for at least

16 hours and weigh the dried specimen. Subtract this weight from

the original weight to determine water solubles. (Note: If the

loss in water solubles could appreciably affect the values for

water adsorption, the test should be repeated on the same specimen.)

-6

Table 3 lists the water uptake during the first 30 seconds

calculated from the measured volume of the specimen and the

measured buoyancy at the end of 30 seconds immersion, and the

water uptake from 30 seconds to 7 days. These results indicate

that the reproducibility of the procedure is satisfactory,, The

values for water absorption from 30 seconds to 7 days are

reliable, but those for water absorption during the first

30 seconds are subject to the uncertainty in the measured volume

due to the roughness of the surface . Consequently, the measured

volume is greater than the true volume and the values for

0 to 30 seconds are high by amounts depending on surface

roughness

„

Volume of Specimen

Various methods of estimating the true volume of the specimen

were investigated « The first method tried was an extrapolation

of the absorption curve . The absorption after 30 seconds was

found to be approximated by the equation:

W = m (t-p) n

where: W is the per cent by volume of water absorbed

t is time of immersion

m, n and p are constants for the material

The constants m, n and p for each material were calculated from

the absorption curves, and the water absorption during the first

30 seconds determined from these constants. Meaningful results

were obtained only for materials A and E. The water uptake

during the first 30 seconds for the other materials did not

follow this absorptio]

estimate the true volume o. equation so that it could not be used to

: pec amen,

Another method investigated was to coat the specimen with a

waterproof coating at the end of the test for water absorption

and then determine the volume of water displaced by the waterproofed specimen, making corrections for the volume of coating

applied. Three types of coating were tried: (1) the surface

of the specimen was coated with melted paraffin, (2) the

specimen was dipped in a silicone oil to coat all surfaces,

and (3) three coats of an acrylic paint were applied to the

surfaces, allowing each coat to dry before applying the next.

In all cases, there was evidence that the coating material had

penetrated into the specimens, particularly those of materials

B, C and D.

These tests indicated that the absorption c

: f water during the

first 30 seconds immersion was between the following limits:

Material Minimum Maximum

volume, °/o volume, °/o

A -0.23 2.79

B 0.72 4.30

C 2.82 7.23

D 0.70 3.27

E 0.24 1.85

The project was terminated so that other methods for estimating

the volume of the specimen were not tried. 'However, the results

indicated that the development of a reliable method suitable

for specification purposes was not promising, and that a test

for porosity in conjunction with water absorption between

30 seconds and several days might be useful.

Porosity

Specimens about 15 centimeters by 15 centimeters by 2.5 centimeters were cut with a fine-tooth band saw having no set. The

apparatus for measuring water permeability of textiles (Method

5516, Federal Specification CCC-T-191b) was modified to accommodate these specimens. A force of approximately 25 kilograms

was applied by means of a lever and weights to the rubber ring

on the upper surface of the specimen. The rate of flow of

water through the specimen was measured under a constant pressure

of 10 centimeters of water,. , The results given in Table 4 were

obtained

.

Materials B, C and D are porous, the rate of flow during the

first minute through these materials is nearly as large as in

subsequent periods. Material E is slightly porous. These

results confirm the conclusions reached in the investigations

of water absorption.

Discussion

It is extremely difficult, if not impossible, to determine

reliably the water absorption of expanded polystyrene that is

porous. For applications where the amount of water absorption is

- 8 -

important, the porosity should be determined first and material

rejected that is porous. The water absorption of non-porous

material can then be determined from the change in buoyancy

of specimens immersed in water.

In applications where a separate waterproof barrier is used

or where water absorption is not a factor in its use, the

requirement for water absorption should be waived.

The results in Table 3 show that none of the materials

can meet a requirement for water absorption of 0,25 per cent

maximum. In fact, only material A meets a requirement of

1.5 per cent maximum for water absorption during immersion

between 30 seconds and 7 days. A realistic requirement for a

non-porous expanded polystyrene might be 3 per cent maximum

for water absorption.

-SiTable 1. Water absorption of expanded polystyrene

after immersion in distilled water

Immersion period

Material Thickness 10 sec. 2 days* ~7 days*

volume , % volume, % volume , %

A 1 0.8 2.6 2.8

2 0.3 1.0 0.9

3 0.4 1.1 1.2

B 1 1.3 6.0 6 ,

8

2 1.2 5.8 6.1

3 1.1 5.7 6,6

C 1 1.5 5.1 4.9

2 0.5 3.0 3.2

3 1.9 3.5 3.5

D 1 1.0 3.5 3.6

2 0,7 3.1 3.2

3 0,8 2.7 2.8

Values for 2 days and 7 days immersion repre sent the difference between the total water Increase and the water inc

after 10 seconds immersion*

A-*,

- 10 -

A

B

D

Thickness 1 f) qpo

Immersion oeriori

"inch

-1- Vw# O C- L, 0 volume.

2 days*

/° volume, J0 7 days*

volume, Jo 1

2

3

1.8

0.9

0.8

1.5

0.5

0.8

2.1

0,6

0,9

1

2

3

6.4

5.1

2.4

. 2.5

13.8

9.4

3,3

24.7

17.3

1

2

3

4.1

1.6

3.6

2,1

2,1

2,0

1.9

2.1

0.9

1

2

3

2.7

1.9

1.7

1.4

1.7

1.8

1.6

2,0

1.9

between the totarwater

7

inorIasr

iInd

i

the

l:’ eP

?

eSe

?

t the dlffe rence

10 seconds Immersion.

* “ and the water increase after
./ p.x

.
- 11 -

Table 3. Water absorption of expanded polystyrene during

immersion in water containing 0.1 per cent wetting agent

Water absorption

Material Specimen 0 to 30 sec.* 30 sec. to 7 days**

volume, °/o volume, %

A 1 2.90 1.19

2 2.90 1.12

3 2.66 1,21

4 2,74 1.20

5 2,73 1.31

average 2.79 "172]“

B 1 4,36 4.46

2 4.27 3.01

3 4.16 3.56

4 4,06 4.39

5 4.67 3.32

average 'T35 “3773“

C 1 8.38 2.04

2 7.10 2.12

3 6.88 2.25

4 7.05 2.31

5 6.73 2.32

average r. 23" 2.21

D 1 2.88 1.93

2 3.11 2.13

3 3.52 2.00

4 3,30 2.30

5 3.54 2.08

average THTT" 2.09

E 1 1,94 2.63

2 1.86 2.61

3 1.94 2.47

4 1.74 2.61

5 1.75 2.49

average ~ra~5“ “2756“

Calculated from measured volume of specimen and measured

buoyancy.

Calculated from change in buoyancy during immersion.

Table 4. Water permeability of expanded polystyrene

Rate of flow per minute

Material Specimen 0-1

ml

1

* — 2

* ml

2

r~3*

ml ml

4'~5'

ml

mean

ml

A 1 0 0 0 0 0 0

2 0 0 0 0 0 0

3 0 0 0 0 0 0

4 0 0 0 0 0 0

5 0 0 0 0 0 0

average 0 0 0 0 0 0

B 1 250 280 290 290 290 280

2 330 320 310 320 320 320

3 300 330 320 330 330 320

4 300 350 340 330 340 330

5 300 340 340 330 340 330

average 295 325

~J$Q 320 325 315

C 1 108 112 121 124 123 118

2 36 50 54 52 54 49

3 80 96 90 96 §4 91

4 66 70 74 7 It

i 4" 72 71

5 76 88 90 90 90 87

average 73 83 8b "B7” 8? 83

D 1 10 14 14 15 14 13

2 39 48 ^9 49 49 47

3 8 11 13 13 14 12

4 43 53 53 60 55 53

5 8 13 13 13 15 12

average 22 28 28 30 29 2^

E 1 0 0 0.2 0.4 0.4 0.2

0 0*2 0.3 0.5 0„5 0.5 0.4

3 0 0 0.2 0.3 0.3 0.2

4 0 0 0.2 0.4 0.4 0.2

3 0 0 0 0.1 0.2 0.1

average 04" 0 » 3-- 0.24- 0 0 3+ 0.2

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*