Thermal Stabilitv of PolvesterJ
J
Styrene Resin Systems J
J
E. S. EBERS, W. F. BRUCBSCH, P. M. ELLIOTT, R. S. HOLDSWORTH,
AND H. W. Naugatuck Chemical Division, United States Rubber Company, Naugatuck, Conn.
A
ROBINSON
A commercial melamine laminate, Formica FF-55, was also obtained for testing. SILICONE. A Fiberglas laminate of silicone, G. E. Silicone 11523 (The General Electric Company, Schenectady, N. Y.), was the only resin of this type studied.
comparison is made of the influence of heat on a number of physical properties of polyester-styrene laminatesand laminates of some commercial condensation-type resins. A number of chemical modifications of the polyester-styrene resins are examined and the correlation of structure with thermal behavior is discussed.
TEST METHODS AND EVALUATION PROCEDURE
FLEXURAL STRENGTH.Flexural strength was determined with an Olsen-Tour-Marshall stiffness tester (Tinius-Olsen Testing Machine Company, Willow Grove, Pa.) One end of the sample wa8 clamped in the apparatus and the 1o:td was applied at the opposite end. The strength was calculated from the breaking load and the dimensions of the sample, using the cantilever beam equation. Reported values are the averages of three determinations. The flexural strength was measured at room temperature initially and after 1, 3, and 5 hours' exposure a t 260" C. in a circulating air oven. The rate at which the strength decreased with aging time was accepted as a measure of the over-all heat resistance. The curve frequently showed an anomalous behavior during the initial aging period, but usually decreased with an almost constant slope after the first hour. In order to rule out the initial short range effects, only the latter portion of the curve was considered in the evaluation of the heat resistance. HARDNESS.Laminate hardness was determined with a WilsonRoclrwell hardness tester according to A.S.T.M. Method D 78547T ( I ) , with the exceptions that the thickness of the sampleR
L
AMIKATES which are bonded with polyester-styrene type resins are finding many new applications as both structural and decorative materials. The very low pressures (0 to 15 pounds per square inch) required for curing these laminates, together with the resulting high strength, enable the fabricator t o produce pieces of large size and great complexity in relatively simple, lightweight equipment. Some of the proposed uses require that the structure possess heat resistance. This study was undertaken to determine the thermal stability of standard polyester-styrene laminates relative t o laminates of resins that are known to have good stability, and also to investigate the factors that control heat resistance in polyester-styrene resins. PREPARATION O F LAMINATES
The alkyds for these resins were prePOLYESTER-STYRENE. pared by condensing a suitable dibasic acid with a glycol in allglass equipment. The reactor was a 2-liter three-necked flask equipped with a gas inlet tube, a stirrer, and a Stark and Dean trap fitted with a reflux condenser. The flask was heated by a spherical heating mantle, A stream of carbon dioxide was passed through the reaction mixture during condensation to exclude air and to aid in the removal of water, Esterification was carried out a t a temperature of 140' to 200 C. to an acid number of 20 to 60. The resin was completed by the incorporation of about 150 p.p.m. of hydro uinone as an inhibitor to prevent premature gelation, and then bglended with the cross-linking monomer (usually styrene). Laminates were prepared by saturating 5 plies of Fiberglas ECC-162 (Owens Corning Fiberglas Corporation, Kewark, Ohio) with resin containing 1.5% benzoyl peroxide catalyst. Plies were built up with the warp of the cloth parallel. The assembly was cured between cellophane sheets a t a pressure of about 0.2 pound per square inch for 1 hour at 80 O C., followed by 2 hours in an air oven a t 110" C. Test strips 0.5 inch wide were cut parallel to the warp with a high speed bandsaw. Resin content of the laminates varies from 40 to Soy0 as determined by a weight-area calculation. A phenol-formaldehyde laminating solution was PHENOLIC. prepared by refluxing 2 moles of phenol with 3 moles of formaldehyde and 0.15 mole of 50% aqueous sodium hydroxide for 1 hour. This solution was used to impregnate 5 sheets of Fiberglas ECC162, which were then dried for 1 hour at 110" C. and plied with warp parallel. The laminate was cured a t 160' C. for 20 minutes at a pressure of 500 pounds per square inch. A panel of a commercial Fiberglas phenolic laminate, Formica FF-10 (The Formica Insulation Company, Cincinnati, Ohio), was obtained for comparative purposes. MELAMINE. A commercial laminating resin, Melmac 402 (American Cyanamid Company, New York 20, N. Y.), was dissolved in a water-alcohol mixture and the solution was used to impregnate Fiberglas ECC-162. The impregnated Fiberglas was dried for 1 hour at 110' C., plied, and cured for .20 minutes at 160" C. under a pressure of 500 pounds per square inch. A melamine-formaldehyde resin was prepared by the interaction of melamine (2 moles) with formaldehyde (6 moles) in the presence of ammonium hydroxide. Water was removed to yield a solution of 50y0 solids. The solution was used to impregnate Fiberglas ECC-162, which was plied and cured as above.
-172 24033
O
$15033
9033
t
A
C
A
L D
6mt
I
I
I
2 HOURS AGlkG
1 3
1
I
4
AT 260'C.
Figure 1. Heat Stability of Standard Resin Laminates A. B.
C
d. 114
Ethylene glycol (1.0)-fumaric acid (l.O)-styrene (0.4) G. E. Silicone 11523 Melamine-formaldehyde (Melmac 402) Phenol-formaldehyde (lab. prep.)
styrene. [Compositions of this type are represented by “ e t h y l e n e glycol ( 1 . 0 ) fumaric acid (1.0)-styrene (0.4)” t h r o u g h o u t t h i s article.] Thermal data for the laminate of this resin, the standard melamine and phenolic resins, together with the silicone laminate are given in Table I and Figure 1.
OF STANDARD RESINS TABLE I. COMPARISON
Resin Melamine-formaldehyde (Formica FF-55) Melamine-formaldehyde (Melmac 402) Melamine-formaldehyde (lab. prep.) Phenol-formaldehyde (Formica FF-10) Phenol-formaldehyde (lab. prep.) Silicone (G. E. 11529) Ethylene glycol (1.0)fumaric acld (1.0)styrene (0.4)
Wt. Loss
Resin in Laminate,
Flexural Strength, Lb./Sq. Inch-Rockwell M Hardness Aged at 260’ C. Unaged 1 hour 3 hours 5 hours
%
if$gc:,t % of
Resin
Distortion Temp.a T K O Tier
..
41,900-107
24,500-100
20,800- $39
19,300- 99
16
140
166
35
10,400-109
8,400- 99
9,500-100
8,400-101
2
128
..
30
7,500-114
7,500-105
7,000-102
6,800-103
6
..
..
17,500-108
15,300-103
15,200-104
15,000-103
4
123
44
..
17,000-105 17,000- 86
10,600-103 17,000-
7,700- 96 15,800- 87
7,600- 98 15,300- 88
..0
i26
49
22,600-106
22,500-102
20,100-102
16,500- 91
9
.,
.
I
The ultimate rate of loss
156
of flexural strength and tKe hardness degradation ratre of the polyester are inferior to all the standard condensation-type r e s i n s The high temperature dist o r t i o n is also g r e a t e r . Weight losses are of the same order of magnitude] with the polyester generally inferior. Some of the factors which could be responsible for these deficiencies were investigated and are discussed in t h e f o l l o w i n g sections.
i59
Special test method discussed in text. Tso. Temperature in C. a t which bar, loaded to 25% of room temperature flexural strength, deflects 50 mil6 &tcenter of 4-inch span. Tleo. As above except temperature for 100-mil deflection. (1
R
115
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
January 1950
TABLE11. EFFECTOF GLYCOLVARIATION IN RESIN SYSTEM GLYCOL ( I.O)-FUMARIC ACID STYRENE (0.4) Wt.
Loss,
Redn ._ . .
LLiGlycol Ethylene glyool 2-Ethyl-l,3-hexanediol 2,2-Dimethyl-l,3-propanediol
nate,
%
49 45 42
Flexural Strength, Lb./Sq. Inch-Rockwell M Hardness Aged a t 260° C. Initial 1 hour 3 hours 5 hours 22,600-106 22,400-102 20,100-102 16,500-91 12,900- 50 7,400-a 17,100- 99 tfJ,000-103 16,300- 83 12,300-70 18,800- 96 20,300- 92
5 Hours’ $$$gc::
% Of
Resin 9 42 10
Too soft to measure on M-scale.
ranged from 0.1 to 0.15 inch instead of the recommended 0.25 inch, and the tests were run a t room temperature without special conditioning, Rockwell M scale hardness was recorded as the average of measurements on three laminate specimens. Samples were aged as above for heat-resistance data. WEIGHTLoss. The change of weight of a laminate after heat aging 5 hours a t 260” C. was also measured. It was shown that the cloth alone lost only about 1% of ita initial weight when aged. Laminate weight decreases were therefore reported as per cent loss of resin. HIGH TEMPERATURE PROPERTIES. As a measure of the behavior of a laminate a t high temperatures, a modification of the tentative method of test for heat distortion temperature of plastics, A.S.T.M. Method D 648-451’ ( I ) ] was adopted. The apparatus used is described by Sauer, Schwertz, and Worf (4). The test was run using a load which was 25% of the flexural strength of the laminate a t 25 C. The temperature was raised a t the rate of 2 ” per minute, and a plot was made of distortion versus temperature. The data reported are the flexural strength of the laminate and the temperatures at which the distortion due to heating was 50 and 100 mils.
24000
I
??COO
QOOOO
le000
O
I
HEAT RESISTANCE OF STANDARD RESINS
The thermal behavior of the melamine, phenolic] and silicone resin laminates, together with a “standard” polyester-styrene laminate] is given in Table I. The final rates of degradation of the flexural strength of all the melamine resins examined are found to be similar. Hardness and weight loss data also indicate that the laminates are comparable, although the weight loss of the commercial resin is somewhat higher than expected. By the same criteria, the two phenolic resins are judged equivalent. In order to have only a single representative of each resin, the Melmac 402 melamine resin and the laboratory-prepared phenolic resin laminates were selected as standards, inasmuch as the cloth used in laminate preparaeion was the same as that used for the polyester-styrene laminates. As a basis for comparison the following resin was selected as the standard polyester-styrene: One mole of ethylene glycol is condensed with 1.0 mole of fumaric acid. The resulting alkyd is blended with 0.4 mole of
-
16000
v)
a
S
G
14W
h _I
2
z
I2W
I?
10033
\
BDCT,
6000
I 1
1 HOURS AT
Figure 2.
I 3
2
I 4
26OoC.
Effect of Glycol Variations in PolyesterStyrene Laminates E: 2Eth A %-~met~yl-l,3-propanediol lene ycol
C. Z~Ethyl-1.3-bexanediol
INDUSTRIAL AND ENGINEERING CHEMISTRY
116
Vol. 42, No. 1
the weight loss data indicate, however, that the hexanediol resin is considerably inferior Wt. to the ethylene glycol. and Composition of Resin, Mole Loss TetraResin Flexural Strength, Lb./Sq. Inch~ ~ ~ ~i ~ ~ dimethylpropanediol ~ ~ ~ ~~ - f r e s i n si chloroin Rockwell M Hardness It is concluded that methyl Fu; Phthalic phthalic EthylLami. 260” C., Aged a t 260° C. maric anhyanhyene Sty- nate side chains do not affect the % of acid dride dride glycol rene % Initial 1 hour 3 hours 5 hours Resin Tso Tioa heat resistance, but extended 0.87 0.13 , . 1.0 0.87 42 12,90014,70013,30011,30016 104 129 hydrocarbon side chains are 78 83 66 60 .. 1.0 0.75 44 15,30017,20016,20013,40016 ., .. 0.75 0.25 detrimental. 91 92 80 70 0.50 0.50 .. 1.0 0.50 47 16,10019,40019,10016,70021 70 78 The absolute values of the 90 85 82 67 flexural strength are highest 0.87 .. 0.18 1.0 0.87 48 13,00015,00013,60011,80018 111 134 95 95 91 91 for the glycol of lowest molec0.75 .. 0.25 1.0 0.75 51 17,500.,, 15,000.. . .. 110 127 108 99 ular weight, and decrease 0.50 .. 0.50 1 . 0 0.50 51 21,50021,50016,90012,60029 90 101 as the hydrocarbon content 93 82 63 37 of the glycol increases. A de0 Special test method discussed in text. Tso. Temperature in C. a t whioh bar, loaded to 25% of room temperature flexural strength, deflects 50 mils a t crease in the molecular weight oenter of 4-inch span. of the glycol yields a higher conAs above except temperature for 100-ml. deflection. !7‘100. centration of polar (ester) groups. This study has led to the general conclusion that an THERMAL STABILITY V S . CHEMICAL STRUCTURE OF POLYincrease in the concentration of polar groups in the resin proESTER-STYRENE RESIN SYSTEMS duces a laminate of improved flexural strength. Further evidence appears below. GLYCOL VARIBTI~IWUsing the ethylene glycol (l.O)-fumaric DIBASIC ACID VARIATION^. E$ect of Cross-Linking Density. acid (1.Otstyrene (0.4) system &s a standard, the effect of glycol Because the polyester chains are linked to one another through variation on the heat resistance was studied. Resins of thr the unsaturated linkages in the chain, the density of possible formulation glycol (1.0)-fumaric acid (1.O)atyrene (0.4) were cross linking can be altered by changing the spacing of the unprepared in which the glycols were Zethyl-1,3-hexanediol and saturated links. This “cross-linking density” was changed by 2,2-dimethyl-1,3-propanediol. The heat-resistance data of the replacing varying amounts of the fumaric (unsaturated) acid by laminates from these resins are given in Table I1 and Figure 2. phthalic and tetrachlorophthalic (saturated) acids. HeatThe heat resistance of the resins is determined from the rates at resistance data for the laminates of these resins are given in which flexural strength and hardness decrease, arid from 5-hour Table I11and Figures 3 and 4. weight loss. The flexural strength curves are all found to have The heat-aging resistance of the three resins containing phthalic about the same slope, although the strength of the hexanediol esters is about equal, as determined from flexural strength and laminate exhibits a tendency to decrease rapidly in the latter part weight loss data. The tetrachlorophthalic ester resins, however, of the 5-hour aging period. Rate of degradation of hardness and
TABLE111. EFFECTO F PHTHaLATE AND TETRACHLOROPHTHLATE RESIDUES IN POLYESTERS WITH FUMARIC A C I D AND ETHYLENE GLYCOL
MlXED
.
T$z,”.a
eooa,
t
t
locoo
6000
t
1 I
HOURS AT 2 2sO°C.
3
10000
0
I
HOURS
Figure 3.
Effect of Variation of Cross-Linlting Density i n Laminates
A . Ethylene glycol (1.0)-fumaric acid (0.5)-phthalic anhydride (0.5)-styrene (0.5) S. Ethylene glycol (l.O)-fumaric acid (O.l?l)-phthalic anhydride (0 .ZS)-styrene (0.7 5) d;: Ethylene glycol (1.0)-fumaric acid (O.t7)-phthalic anhydride (0.13)-styrene (0.87)
Figure 4.
2 AT
3
4
260’C.
Effect of Variation of Cross-Linking Density in Laminates
A . Ethylene glycol (1.0)-fumaric acid (0.5)-tetrachlorophthalic anhydride (0.5)-styrene (0.5) B . Ethylene glycol (1.0)-fumaric acid (0.75)-tetrachIorophthalic anhydride (0.25)-styrene (0.73) C. Ethylene glycol (l.O)-fumaric acid (0.87)-tetrachlorophthalic anhydride (0.13)-styrene (0.87)
117
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1950
I I
1
e
I HOURS
Figure 5.
1 3
I 4
I
\
P
AT e 6 O o C .
Effect of Unsaturated Acid Variations in Polyester-Styrene Laminates
I I
C. Maleic acid
Figure 6.
show progressively poorer heat resistance as the saturated acid content is increased, Other studies have shown tetrachlorophthalic acid to decarboxylate during esterification (3) much more readily than phthalic acid. It is concluded, therefore, that within the range tested, variations in cross-linking density do not greatly affect the heatcaging resistance unless the diluent is of lower stability than the original structure. The unaged high temperature properties of the above resin laminates, as measured by the heat distortion test, deteriorate as the fraction of phthalic acid increases. Improved strength a t high temperature thus appears to result from high cross-linking density. Furthermore, the room temperature values of the flexural strength increase as the concentration of the phthalic acid is increased. The resin containing 0.13 mole of phthalic acid has 36.8% of -COGgroups; the resin with 0.25 mole of phthalic has 37.9% of -COO-; and with 0.50 mole of phthalic the resin This increased strength is in agreement has 40.3% of -COO-. with the earlier suggestion that a high concentration of the polar -COOgroups yields a laminate of high flexural strength. The use of tetrachlorophthalic acid decreased the fraction of -COO-, but added the CI groups, which are also strongly polar. Efect of Monomer Alternation. The cure of the polyesterstyrene resin occurs mainly by the addition polymerization of the monomer with the alkyd unsaturation. This structure may be represented as follows:
I
A I
.
I
1 3
2 HOURS AT
A. Fumaric acid B. Itaconic acid
A
,
1 4
260°C.
Effect of Styrene Variations in PolyesterStyrene Laminates
A. 6.4 Mole of styrene B.
1.3 Moles of styrene C. 2.2 Moles of styrene
The extent to which alternation occurs in place of self-polymerization has been cakulated from reactivity ratios of the monomers (2). Using these data, it is found that the styrene-fumarate system should produce a copolymer having a structure approaching that of ideal alternation, and that the styrene-maleate system should yield large amounts of self-polymerized material. Resins were accordingly prepared in which fumaric acid was replaced by maleic acid and itaconic acid (estimated to be intermediate between maleic and fumaric in reactivity). The results of the study are given in Table IV and Figure 5. The heatraging resistance of these laminate9 is about constant. It is concluded, therefore, that either the copolymer effect is absent, or some other degradation reaction occura to such a large extent that the effect is masked. VARIATIONS IN RATIOOF MONOMER TO ALEYD. Extending the study of the effect of alternation on heat resistance, the ratio of monomer to alkyd unsaturation was investigated. Copolymerization theory predicts that a maximum alternation will occur in the styrene-fumarate system when the molar ratio is 1.3 to 1.0. The quantity of styrene added to a fumaric acid (1.0)-2,2-dimethyl1,3-propanediol (1.0) alkyd was varied. The results of heat aging are shown in Table V and Figure 6. Again, no significant difference is found. Increasing styrene-Le., reducing -COOconcentration-again lowers the flexural strength.
TABLEIV. EFFECT OF ACID VARIATION IN RESIN SYSTEM
A
ETHYLENE GLYCOL (l.O)-Acu, (~.~)-STYBENE (0.4)
II LI -
-R-GR-
where A = monomer and B = unsaturation in the alkyd. In addition to this main structure, the resin has varying amounts of self-polymerized monomer and probably also direct links between alkyd chains.
Resin
2 ~ Flexural - Strengtl, Lb,/Sq. Inch-Rockwell M Hardness Acid Fumaric Maleic Itaconic
Wt. Loss 5 Hourb' Aging
at 260" C.,
48 51
Initial 22.800-106 14,600-
Aged at 260° C. 1 hour 3 hours 22,400-200 20,100-102
5 hours 16,500-91
Resin 9
48
13,500- 74
17,50010,100- 74
13,30014,300-59
28 7
nate,
%
15,10016,800- 60
% 9'
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1118
TABLEV. EFFECTOF STYRENE VARIATIONIN SYSTEM ~ , ~ - D I M E T H Y ~ P ~ , ~ - P R O P A N EFUMARIC DIOL ACID (l.O)-STYRENE Wt
Moles
Resin In per LamiMole nate, Fumarate yo 0.4 42 1.3 52 2.2 37
styrene
Flexural Strength, Lb./Sq. Inch-Rockwell M*Hardness Unaged 18,800- 96 12,500-101 13,700- 75
Aged a t 260° C. 3 Hours 5 Hours 16,300-83 12,300-70 12,600-99 8,100-88 10,600-29 9,000-'
1 Hour 20,300- 92 18,800-101 13,800- 82
LOSS 5 Hou;s' Aging a t 260' C.,
% of
Resin 10
12 23
pared on Fiberglas ECC-182, finish 114. This cloth was reported to have a weave designed to produce higher strength laminates, and a finish that would result in better resin-glass adhesion. Aging data for these laminates are given in Table VI and Figure 7, and lead to the conclusion that, although the initial strength is dependent on glass cIoth type, the aging characteristics are unchanged.
Too soft to measure on M-scale.
TABLEVI. EFFECT OF FIBERGLAS TYPEUSINGRESINSYSTEM ETHYLENE GLYCOL(I.O)-MALEIC ANHYDRIDE (0.5)-PHTHALIC ANHYDRIDE(0.5)STYRENE (0.7)
50.1
Flexural Strength, Lb./Sq. Imh-Rockwell M Hardness Aped at 260' C. Unaged 1 Hour 3 Hours 5 Hours 16,300- 99 19,200- 98 16,700-81 13,600-60
48:6
44,800-
in Laminate, Fiberglas ECC-162 raw ECC-162 heat treateda ECC-182-114 a
%
29,800-113
28,200-106 25,700-97 40.40037,800-
21,900-91 33,700-
Heated 10 hours at 265" C. in air.
GLASS CLOTH. The preceding experiments were conducted using Fiberglas ECC-162 as a reinforcing filler. This material was used as received and contained the sizing which was used to facilitate weaving. Slayter (6) has reported that improved initial properties are obtained when the cloth is subjected to a "heat treating" process before laminating. Sheets of cloth were accordingly heated for 10 hours a t 265' C. in a circulating air oven and Eaminated. As a basis for further comparison, a laminate was pre-
RELATIVE STABILITY OF POLYESTER-STYRENE COMPONENTS
A cured polyester-styrene resin has a threedimensional structure bound together by two Wt. Loss, of chemical linkage, ester bonds principal types Hours' Aging at and polymerized vinyl groups. In an attempt 260" C., to evaluate each of these separately, laminates of % of Resin resins which contained only one of these linkages 26.0 were prepared. Examples of vinyl linkages studied were polystyrene and poly [styrene (l.a)-diethyl 16:4 fumarate (l.O)]. L4resin with only ester linkages was a linear polymer, glycerol (1.0)-succinic acid (1.0) cross-linked through condensation with phthalic anhydride (0.5). For comparison, combined ester and vinyl groups were represented by a selfcured ethylene glycol (1.0)-fumaric acid (1.0) resin and the standard polyester-styrene. Data for these laminates are given in Table VI1 and Figure 8. The heat resistance of the ethylene-linked structures, both the homopolymer and the copolymer, is very poor. The alkyd and alkyd plds monomer are both much better and approximately equal. However, when unsaturation is completely removed and 32003,
44000
-
40000
-
36000
-
32000
Irn
c
I 0
Figure 7. A.
I
1 2 HOURS AT
1
I
3
4
HOURS
Figure 8.
260'C.
Effect of Variation of Fiberglas Filler in Laminates
Fiberglas ECC-182 finish 114 B . Fiberglas ECC-162 heat-treated C. Fiberglas ECC-162 raw
A. B. C. D. E.
AT
?SOoc,
Comparison of Polyester-Styrene
Components in Laminates
Glycerolj(l.0)-succinic acid (l.O)-phthalic anhydride (0.5) Ethylene glycol (1.0)-fumaric acid (1.0)-styrene (0.4) Ethylene glycol (l.O)-fumaric acid (1.0) Polystyrene Diethyl fumarate (1.0)-styrene (1.3)
lanuary 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
anomalous case in view of tlie above experiments in which the styrene decrease from 2.2 to 0.4 mole, yielded improved strength.
COMPARISON OF POLYESTER-STYRENE COMPONENTS
TABLE VII.
119
Wt.
Loss.
Resin Polystyrene Styrene (1.3)-diethyl fumarate (1.0) Ethylene glycolfumarate Ethylene glycol (1.0)fumario acid (1.0)styrene (0.4) Glycerol (1.0)-suocinic acid (1.0)-phthalic anhydride (0.6)
P
Resin in Laminate,
yo
Flexural Strength, Lb./Sq. Inch-Rookwell M Hardness Aged a t 260" C. Initial 1 hour 3 hours 5 hours 12,600- 92 0 0 0
260'
e.,
% of
MOLECULAR WEIGHT DISTRIBUTION STUDIES
Resin 87
Under the microscope, laminates aged in air exhibit severe surface cracking, with fissures 32 4,6000 0 0 27 which extend into the body of the laminates. In an effort to explore this effect, samples were 43 13,600- 90 13,200- 88 10,000- 85 7,800-22 30 aged in a sealed tube (Table VI11 and Figure 9). 49 22,600-106 22,400-102 20,100-102 16,500-91 9 Aging under these conditions eliminated cracking and actually increased flexural strength. 12 53 30,800- 44 27,50026,30026,300This experiment indicates either that the norma8 heat degradation is due to distillation of low molecular weight materials, which were held in OF AGINGCONDITIONS ON RESIN SYSTEMETHYLENE TABLE VIII. EFFECT the resin by the pressure in the sealed tube, or GLYCOL(2.0)-MALEIC ANHYDRIDE(l.O)-PHTHALIC ANHYDRIDE (1.0)that air oxidation is causing breakdown. STYRENE (1.8) The alkyd components of low molecular weight wt. Lost, were removed by extraction with methyl alco5 Hours Aging a t hol. This treatment greatly reduced the degree Flexural Strength, Lb./Sq. Inch 260' C., Aged a t 260° C. of cracking in the aged laminates but did not % pf Aging Conditions Unaged 1 hour 3 hours 5 hours Resin improve the heat resistance of the laminates as Aged in air 16,300 17,700 14,800 12,600 29 measured by the rate of flexural strength degradaAged in sealed tube 16,300 .... 19,900 0 Alkyd extracted, aged in air 12,000 16,400 l2;300 12,600 .. tion (Table VI11 and Figure 9). The effect of Aged in nitrogen 16,300 15,600 16,200 18,100 .. low molecular weight material is therefore thought to be of secondary importance. 2
only the polyester linkages are retained, the heat resistance is very good and is comparable with that of the standard condensation resins. It is therefore assumed that the thermal degradation is due almost entirely to failure of the vinyl portion of the resin, and that the polyester linkage is relatively stable. The high flexural strength of the straight polyester, which contained a large percentage of -COOgroups (55.20/,), is additional evidence of the polar influence on strength. Low strength values for the unsaturated alkyd with 62% -COOrepresent an
THERMAL STABILITY OF A POLYESTER-STYRENE RESIN SYSTEM UNDER NONOXIDATIVE CONDITIONS
TO determine the effect of oxygen, samples were aged in a stream of preheated nitrogen. This treatment actually improved the strength, although cracking was present as before (Table VI11 and Figure 9). The principal effect in heat aging is therefore oxidative. CONCLUSIONS
22000
-
The heat resistance of polyester-styrene glass cloth laminates, as measured by the rate of loss of flexural strength and hardness during aging at 260' C., is significantly poorer than that of similar melamine-formaldehyde, phenol-formaldehyde, or silicone lamial structure of the polyester nates. Changes in through variation of ycol, type and proportion of saturated and unsaturated acids, ratio of alkyd unsaturation to monomer unsaturation, etc., had relatively little effect on the thermal stability of the system except that certain structures, which were in themselves less stable, hurt the heat resistance of the system. The thermal degradation i s mainly the result of an oxidative process. The absolute flexural strength of polyesterstyrene laminates is influenced by chemical structure with increased polarity in the resin producing increased flexural strength in the laminate.
t
le000
,
m
ri
i L 16000 E
W
;i
14000
W X
d LITERATURE C-ITED 12000
10030
Am. SOC.Testing Materials, Standards, 1948. (2) Lewis, F. M., Walling, C., Cummings, W., Briggs, E. R., and Mayo, F. R., J. Am. Chem. Soo., 70,1619-23 (1948). (3) Nordlander, B. W., and Cass, W. E., Ibid., 69,2679-82 (1947). (4) Sauer, J. A., Gchwertz, F. A., and Worf, D. L., Modern Plastics, 22, 163-6, 192-4 (Maroh 1946). (6) Slayter, C.,Ohio Stat? Univ., Eng. E s p t . Sta. News, 16, No. 4; (1)
10
1 I WURS
Figure 9.
1
I
1
2
3
4
AT 260aC.
Effect of Aging Conditions on PolyeeterStyrene Laminates A . Sealed t u b e aged B. Nitrogen aged C. A i r a g e d D. Extracted alkyd, aged in air
3-8 (1944). R E C B I V June ~ D 13, 1949.
This investigation was supported by the Offioe of Naval Researoh and the Bureau of Ships, U. S. Navy.
