frequency heaters in conjunction with ovens are most promising for thick sections, since the foam interior is heated by radio \caves \chile the exterior is being heated by circulating hot air. Aftertreatment. As Jvould be expected with a thermoplastic material, a cooling step is required to prevent distortion of the foam Lvhile hot. Passage over refrigerated rolls or festooning in circulating room temperature air will lower the foam temperature rapidly. Embossing may be done later as a separate operation.
B
A
Infrared Fuse Fuse time. min. 3.5 Density, lb./cu. ft. 12 Tensile, p.s.i. 50.2 220 Elongatibn, % Compression, p.s.i. 0.54 Compression set, yc 2 5 . 9 AFTER ACING22 Tensile, p.s.i. 45.7 Elongation, yc 210 Compression, p.s.i. 0.45
2
7
2
UNAGED Oven Infrared 9 3.5 12 13.3 70.0 50.1 170 220 0.52 0.71 26.1 21 . 8 HOURSAT 212' F. 44.6 59.6 180 160 0.52 0.56
100
45
...
35 5 15
37 28 5 15
...
Vanyl is a thermoplastic foam of very fine, open-cell uniform pore structure having a n exceptionally soft, silky feel with excellent hand and drape. T h e skin surfaces are "breathable." Ultimate consumer products such as upholstery fabrics, imitation leather goods, and decorative applications are readily fabricated from this foam by existing well known techniques. T h e special features of Vanyl suggest uses as padding for brassieres or insulation in a variety of Lvearing apparel ranging from comfortable long-lasting shoe insoles to weather-shielding headxcare. Potential uses as a cushioning material include public seating in buildings, airplanes, buses, and subway or railway cars where flame resistance may be required. Good outdoor aging characteristics suggest its use in equipment for patios, stadium cushions? svimming pools, and camping equipment.
l'he formulas shown below were used to prepare finished foam to illustrate physical properties and the effect of aging. 'Ihe plastisols \cere foamed in the Oakes continuous mixer. Slabs * ' 4 inch thick Mere spread on release paper. Fusing \cas accomplished in a circulating hot air oven at 335" F. or heticeen infrared panels for the time indicated. ASTM Test hfethod D 1565, Flexible Foams Made from Polymers of \.inyl Chloride, \vas used for measuring physical properties before and after aging.
7
...
Conclusions
Experimental Work
Sample .Vo.
B
A 100
Geon 121 Marvinol VR-53 Santicizer 160 Benzoflex 9-88 DOP Monoplex S-73 Fomade B
Oven 6 15.7 60.6 150 1.04 32.5
T h e authors express their appreciation to the R . T. Vanderbilt Company, Inc., for permission to present this paper.
51.6 150 0.95
Presented in part before Division of Rubber Chemistry, 145th Meeting, ACS, New York, N. Y., September 1963, and 20th Annual Technical Conference, Society of Plastics Engineers, Atlantic City, N. J., January 1964.
Acknowledgment
RECEIVED for review March 9, 1964 ACCEPTED July 16, 1964
FORMULATION AND CURE CYCLE STUDY FOR AN ANHYDRIDE-CURED EPOXY-NOVOLAC SYSTEM A NT H0
N
Y C
.
MA CK
,
Research and Advanced Development Division, Avco Gorp., Lowell, Mass.
A formulation and cure cycle study for an anhydride-cured epoxy-novolac system (with a tertiary amine accelerator) i s presented. Statistical analysis of tensile strength results indicates no significant difference in room temperature strength between the formulations studied, but an increase in strength at 350" F. for formulations of increased accelerator content. No clear preference i s indicated between formulations containing a 1 to 1 or a 1 to 0.85 ratio of epoxide to anhydride equivalents. In general, long cures are preferred to short ones, and an intermediate cure temperature ( 1 15" C.) i s preferred to a low (80" C.) or a high cure temperature ( 1 50" C.). The importance of establishing a sound network system during cure (before exposure to high temperature postcure) on increasing tensile strength and decreasing weight loss during postcure i s shown.
T H E , c o m p l e x curing mechanism of anhydride-cured epoxy resin systems dictates a n empirical approach for the determination of optimum curing conditions. For instance, Robitschek and Nelson (8)found that a ratio of anhydride to epoxide equivalents \\sell under stoichiometric resulted in maximum heat distortion temperatures for H E T (Hooker Chemical Co.) anhydride systems. Likelcise: Delmonte (5) found that
minimum weight loss a t 400' and 500' F. for a Nadic methyl anhydride (NMA, a liquid alicyclic anhydride)-epoxy novolac (D.E.N. 438, the glycidyl ether of phenolic novolac) system occurs for a n anhydride-epoxide ratio of equivalents of about 0.8 to 1.0. A possible explanation for the need for excess epoxide groups is given by Fisch, Hoffman, and Koskikallio ( 6 ) in terms of VOL. 3
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SEPTEMBER 1964
213
Table 1.
competing reactions. They state that, because of the etherification reaction between epoxide and hydroxyl groups (catalyzed by anhydride), epoxide groups are used u p in greater quantity than anhydride groups. Dearborn et al. (3, 4) maintain, however, that complete cure corresponds to stoichiometric equivalence of anhydride and epoxide oxygen. Similarly, the cure temperature-time history affects final properties of the cured system. T h e rate of cure increases with curing temperature, but as Dearborn et al. ( 3 ) show, better properties (in terms of yield temperature) can be obtained by long cures a t low temperatures than by high temperature cures for the system phthalic anhydride-Epon 834 (the glycidyl ether of bisphenol A, Shell Chemical Co.). This conflicts with Kobitschek and Selson's (8) data on the effect of cure temperature-time on heat distortion temperature of H E T anhydride systems. Optimum temperature-time conditions are a result of the slow polymerization favored by low temperatures and the rapid crosslinking favored by high temperatures. The former case can result in a system requiring long cure times to establish a network, and then perhaps a t best one lvith insufficient crosslinking, Lvhile the latter can result in a nonuniform and inefficient crosslinked system. Finally, the use of an amine to accelerate the epoxy reaction serves a function similar to that of cure temperature, and the amount of amine is subject to optimization (7).
Formulations
100 parts b y weight (p.b.w.) D.E.N. 438"
Bate:
Epoxide/ N I W A , ~ P G E , . FR-2,d D.M.P. Anhydride System p.6.w. p.6.w. p . 6 . w . 3 0 , e p . b . w . Equivalentf A 101 15 10 0.5 1 .0/0.85 15 10 1.3 1 .0/0.85 B 101 C 119 15 10 1.5 1.0/1 . o 15 10 0.5 1. O / l . o D 119 10 0 5 1 0/0 85 E 87 F 101 15 1 0/0 85 0 5 Dow epoxy novolac, Dow Chemical Co. A'adic methyl anhydride, Allied Chemical Co. Phenyl glycidyl ether, Shell Chemical Co. d CelluJ e x FR-2, Celanese Chemical Co. e Tridimethylaminomethylphenol, Rohm & H a a s Co. f Calculated using the following values: D.E.AV. 438 epoxide equivalent weight 175; P.G.E. epoxide equivalent weight 150; N M A anhydride equivalent weight 178. Table II.
Group I Hours 1. 4 15 2. 6 8 3. 6 15
O
Curing Cycles
Group I I Hours 4. 2 15 5. 4 8 6. 4 15
c.
80 150 80
150 80
150
Group II', Hours C.
c. C. 115 150 115 150 115 150
7.
1
150 250 150 250 150 250
8
3 4 3
8. 9.
8
Objective
Obviously, interactions are possible between the variables mentioned above. Cure temperature, by affecting reaction mechanisms, can shift the optimum epoxy-anhydride ratio (7),as can the amount of amine accelerator (3, 70). All these variables associated with the curing of epoxy resins make a n empirical approach necessary for optimizing a particular system. T h e objective of this study is to optimize formulation and cure conditions for a D.E.N. 438-NMA system. T h e optimizing parameter used is the ultimate tensile strength, a t room temperature and a t 350" F., of cast tensile specimens.
-"00.4+
Figure 1 .
Tensile test specimen
Table 111.
Formulationb -
A
n R
R
B
n R
R
C
n f
R
E
n R
R F
n .il
R
1
3 6180 59406400 3 9703 798012000 3 6137 35508640
Ultimate Tensile Strengths at Room Temperature"
2
3
4
3 12233 1140012700 3 10867 1040011300 3 7283 55808440
3 9787 759011900 3 7767 65609020 3 10633 1010011200
3 6593 57207040 3 5780 34807200 3 9607 672011100
...
...
... 3 6730 51708560 3 6745 62907400
~
Cure Cycle 6
5
3 5710 47806640 3 7160 44308550 3 6040 51807620 2 8190 618010200
3 10297 849011400 3 8547 614011400 3 6877 63807860
...
, . .
, . .
.
I
.
7
Samples cracked on postcure; not tested
8
l&EC
PRODUCT RESEARCH A N D DEVELOPMENT
Eliminated from program
3 1337 1030-1 630
3 5323 4150-6530
2 496 300-691
3 1147 1080-1230
Eliminated from program
Samples cracked on postcure; not tested
...
...
1
615 , .
..
...
Strain rate, 0.05 inch linchlminute. Tensile tests follow '4ST.V D 638. Seoeral specimens broke while being handled. groups having only one or trco specimens tested. h n = sample size; .W = auerage tensile strength, p.s,i,; R = range of tensile strength, p.s.i.
214
9
3 312 232-410
T h i s accounts for some
Table IV.
Formulationb 3 X n
x B
R n R
R C
n R
D
R n R
E
F
R n x R
Ultimate Tensile Strengths at 350' F.a
Cure Cycle 1
122 71-176 2 90 70-111 1 176
...
2
2 61 38-85 3 112 97-140 3 197 187-214
3
3 77 47-112 2 135 127-144 2 106 97-114
3 43 36-47 3 153 108-195 3 196 134-250
5 All broke while being heated 3 257 142-408 3 108 90-137 1 60
...
...
4
3 166 93-248
...
, ,
.
n R
2 386 231-541 1 206
...
,
.
I
R
6 7 2 Samples cracked on 170 postcure; not 96-244 tested 3 2 242 184 210-306 164-203 3 3 136 120 74-178 92-134
8 9 3 Eliminated from 162 program 126-185 3 1 44 433 394-47 9 3 Eliminated from 377 program 321-423 Samples cracked on postcure; not tested
...
...
...
...
, . .
..
I
.
.
Strain rate is 0.05 inchiinchlminute. Tensile tests follow A S T M D 638. Seueral specimens broke while being heated; this accounts for somegroups having , f r i w r than three specimens tested. h n = snmple sire; R = aueragt tensile strength, p.s.i.; R = range of tensile strength, p.s.i.
Experimental Of The system under study consists Of D . E . S . 438 (Dow Chemical Co.), the triglycidyl ether of phenolic novolac (a phr:nolic novolac may be defined as the linear reaction product of phenol and formaldehyde) ; NRlA ('4llied Chemical Corp.), a liquid alicyclic anhydride (methylbicyclo-2,2,1-heptene-2:3-dicarboxylic anhydride isomers) ; D . M . P . 30 (Rohm and Haas Co.). a tertiary amine accelerator (tridimethylaminomethyl phenol) ; phenyl glycidyl ether (PGE, Shell Chemical Co.), a reactive diluent; and tris(dichloropropy1)phosphate (Celluflex FR-2, Celanese Chemical C o . ) , a flame retardant. T h e latter t\vo components are present for processing reasons, and their concentration, based on epoxy resin, is not varied. All these components are commerciallv available ixoducts and their chemical structures are not always accurately knoLl-n. -4thorough search of the available literature and past experience \.r.ith this system led to the selection of study formulations containing either a 1 to 1 or a 1 to 0.85 ratio of epoxide to anhydride equivalents, and either 0.5 or 1.5 parts by weight (based on 100 parts of D . E . S . 438) of D.M.P. 30. Table I lists the compositions chosen for study. The curing schedules, similarly chosen, consist of three groups of three, each group having the same cure and postcure temperatures, Lvith time of cure and postcure varying. Table I1 lists the curing c)-cles chosen for study. Preparation and Testing of Samples. T h e test plan involves the testing of formulations 4 . B, and C for all nine curing cycles. formulation D for cycles 1: 5, and 8, and formulations E and F for cycle 4. For each formulation-cure cycle studied, six tensile bars were cast into a stainless steel mold preheated to the initial cure temperature. The dimensions of the tensile bars are sho\.r.n in inches in Figure 1. Three bars were tested for ultimate tensile strength a t room temperature (77' F.)? the remainder a t 350' F. (strain rate 0.05 inch/inch,'minute; tensile tests follow ASTM D 638). T h e results of this study \Yere then subjected to statistical analysis.
In addition to the tensile tests, bveight loss during postcure \vas measured. as \ \ a s the gel time for each of the formulations studied. Results and Discussion
Tables I11 and IV present the ultimate tensile strength
(average and range) at room temperature and at 350' F., respectively, for each formulation-cure cycle interaction. These results were statistically analyzed to determine significant differences among them (at the 95% confidence level, see Appendix) and the followhg conclusions are drawn (where the symbol > indicates significantly higher tensile strength and the symbo]s =, indicate no significant difference) : 1.
Strength a t room temperature a. b. c.
Formulation. A = B = C for c)-cles 1 to 6, 8 Cure Cycles. 2: 3$ 6 > 1, 4 > 5 > 8 for formulations A, B, and c, excluding cycles 7 and 9 Formulation-Cure Cycle Interactions Formulation A. 2 > 3 , 6 > 1 , 4 , 5 > 8 7, 9 B, 1 = 2 = 3 = 4 = 5 = 6 = 8 excluded C . 3? 4 > 1, 2, 5, 6 > 8 Cure Cycle 1, 8. B > A, C 1' 2' A, > D , E, F excluded 3. 5, 6. A = B = C , 4. C > .4,B 1.5. A = B = C = D 4. A = B = C = E = F
1
I
2.
Strength at 350' F . a. b. c.
FormuIation. B, C > A for all cure cycles, excluding D, E, and F Cure Cycles. 8 > 6 > 1, 2, 3, 4 for formulations A, B, and C , excluding cycles 5, 7, and 9 Formulation-Cure Cycle Interactions Formulation A .
B. L.
Cure Cycle
1. 2. 3.
4, 8.
5. 6. I.
4. 5.
1, 6. 8 > 2, 3, 4 > 5 )7, 9 excluded 8 > 2, 3 , 4 , 5, 6 >I 8 > 1, 2, 3, 4, 5, 6 J A C > B C > B > A l 4 = B = C B, > A } D , E, F excluded B > C > A ' B>A,C J A = B = C = D E > B, C, F > A B>C,D>A
1
Table V presents gel times and weight loss on postcure for most of the formulation-cure cycle interactions studied. VOL. 3
NO. 3
SEPTEMBER
1964
215
Table V.
Gel Time and Weight Loss on Postcure Liquid to Gel.
Formulation
3
250
250 0.07
250 1.10
45
...
45 0.21
45 0.02
