PLASTICS

JANUARY 1980

DESIGN & PROCESSING

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Performance Properties

Of Graphite Reinforced Composites

With Advanced Resin Matrices

By Demetrius A. Kourtides. Ames Research Center, NASA Moffett Field, Cal.

Graphite-reinforced compositeshave potential applications in ad-vanced aircraft due to their weight sav-ings and performance characteristics(figure 1 and table 1). Performancecharacteristics of composites depend

on the properties of the materials com-prising the composite and the processby which they are combined. This isparticularly true of graphite-reinforcedcomposites where the mechanicalstrengths are dependent on the type,

.OC._O_TC2.C_V_:,.CA.STAB.,,ZERS

1t "4 \/ CABINFLOOB

__ "_ BEAMS AND

HORIZONTAL / _ //

WING,BO(2W FAIRING __'O,'EBS_...._..._ _"L_ C%O,,,E

Fig. 1, Composite material application. NOSEGEARDOORS

Table 1 -- Metal vs. C,

M,Weig

Wing 1;Fixed trailing edgeAileronSpoilerWing-to-fuselage fairing

TailElevatorRudderHorizontal stabilizer fairing

FuselageCabin floor beams and supportsand cargo floor beams

TOTAL 2:

amount, and orientation of the fibewell as the type of the resin mused. The contribution of the resintrix to the ultimate performance ocomposite has been studied, withticular emphasis on the thermal, fmability, and some mechanical I:erties.

This article looks at the effect oferent resin matrices on thermal

mechanical properties of gralcomposites, and relates the theand flammability properties toanaerobic char yield of the resinsprocessing parameters of grafcomposites utilizing graphite f_and epoxy or other advanced resirmatrices are presented. Therrrresin matrices studied were: arcured polyfunctional glycidyl antype epoxy (baseline), phennovolac resin based on condens_of dihydroxymethyl-xylene and pt-cured with hexamine, two typepolydismaleimide resins, pherresin, and benzyl resin. The theplastic matrices studied wereethersulfone and polyphenylen,forte.

t

2

Table 1 -- Metal vs. Composite Weight-Saving Summary

Metal Composite DifferencesWeight (kg) Weight (kg) Weight (kg) Percent

Wing 1214 992 - 222 - 18.3Fixed trailing edge 477 381 - 95 - 20.0Aileron 98 73 - 24 - 25.0

Spoiler 251 226 - 24 - 10.0Wing-to-fuselage fairing 389 311 - 78 - 20.0

Tail 464 349 - 115 - 24.8Elevator 184 138 - 101 - 25.0Rudder 241 181 - 133 - 25.0Horizontal stabilizer fairing 40 31 - 20 - 22.5

Fuselage 708 531 - 177 - 25.0Cabin floor beams and supportsand cargo floor beams 708 531 - 177 -25.0

TOTAL 2386 1872 - 514 - 21.6

amount, and orientation of the fiber, as

well as the type of the resin matrixused. The contribution of the resin ma-

trix to the ultimate performance of thecomposite has been studied, with par-ticular emphasis on the thermal, flam-

mability, and some mechanical prop-erties.

This article looks at the effect of dif-

ferent resin matrices on thermal and

mechanical properties of graphitecomposites, and relates the thermaland flammability properties to the

anaerobic char yield of the resins. Theprocessing parameters of graphitecomposites utilizing graphite fabric

and epoxy or other advanced resins asmatrices are presented. Thermosetresin matrices studied were: amine-

cured polyfunctional glycidyl amine-type epoxy (baseline), phenolic-novolac resin based on condensation

of dihydroxymethyl-xylene and phenol

cured with hexamine, two types ofpolydismaleimide resins, phenolicresin, and benzyl resin. The thermo-

plastic matrices studied were poly-ethersulfone and polyphenylenesul-lone.

Properties evaluated in the study in-cluded anaerobic char yield, limitingoxygen index, smoke evolution, mois-

ture absorption, and mechanical prop-erties at elevated temperatures in-cluding tensile, compressive, and

short-beam shear strengths. Generally,it was determined that graphite com-posites with the highest char yield ex-hibited optimum fire-resistant proper-ties.

Resin Chemistry --Thermoset Matrices

The chemistry of the resin matricesstudied is outlined in figure 2. The

baseline epoxy resin is amine-curedpolyfunctional glycidyl amine-typeepoxy resin.

The phenolic resin is essentially theproduct of the condensation of dihy-droxymethyl-xylene and a phenol (1).These phenolic novolac-type resins are

usually cured with hexamine to yieldthermally stable, cross-linked polymers

possessing good long-term perfor-mance to 230°C.

Two types of bismaleimide resinswere studied. Bismaleimide A is a sol-

vent resin system. Prepregs from thisresin are prepared from a resin solu-tion containing N-methylpyrrolidinone

RESIN/CURING AGENT/TYPICAL CHEMICAL STRUCTURE

EPOXY (CONTROL1

H2C-CH-CH2 )-N_/ O ?-CH2_' O _N-ICH2-CH CH21

AMINE

PHENOLIC

OH OH OH

n

BISMAL EIMIDE A

0

IF_N_"O';.o c-_J-o - c,2 ,Foo_>-N._

O O O

i-"._o-. . ,T_.->7o C-N<,5/-c.__o,'__-c' o

0 0

BISMALEtMIDE B

0 0 0 0

N-R-N ; N R N

O O O O

PHENOLIC NOVOLAK

OH OH OH OH OH

I

OH

BENZYL

UNKNOWN

POLYETHERSULFONE

o<o I-.POLYPHENYLSULFONE

CH 3

-SO2-_O _- 0 /_ i o>c@o@CH 3

Fig. 2, Resin matrices for graphitecomposites

as the solvent. Bismaleimide B is a hot-melt maleimide-type resin which formsa low-viscosity fluid after being molten.This resin is processed by hot-meltcoating techniques into graphite pre-preg with excellent tack and drape.

The bismaleimide A resin is pro-duced by reacting m-maleimidoben-zoic acid chloride with an aromatic dia-

minocompound in the molar proportionof difunctional amine acid halide 1.4:2.The resin consists of a mixture of abismaleimide and an aminoterminatedmonoimide. This mixture, close to theeutectic mixture, is cured by melting at120-140°C, which causes polymeri-zation by addition of the free-aminogroups to maleimide double bondsfollowed by a vinyl polymerization ofthe terminating maleimide doublebonds. The advantage of this materialis that the bismaleimide obtained in the

first reaction provides a cured resinwith a higher elongation to break ascompared with other state-of-the-artbismaleimide-type resins reported pre-viously. (2, 3).

Bismaleimide B is a eutectic ternarymixture of bismaleimides. Cure is ac-complished by both chain extensionand polyaddition. This resin mixture iscapable of "B" staging by prepolymeri-zation to provide a suitable high meltviscosity on the prepreg.

The fourth resin was a conventionalphenolic-novolak resin. Its chemistryhas been described previously (1). Thisphenolic resin is compounded for non-flammability and low smoke emission.

The fifth resin was a benzyl-typeresin. The exact chemistry of this com-mercial resin system is not known.

Resin Chemistry --Thermoplastic Matrices

The thermoplastic resin matricesstudied included polyethersulfone and

polyphenylsulfone. The chemishthese thermoplastics has beenscribed previously in detail (4, 5)sulfone resins consist of the diaryphone and benzoxy groups andpropylidenyt linked together in vaconfigurations (figure 2). TIlinkages are present in both polyrThey permit rotation about the linwhich imparts inherent toughne,'the resins. Similar to other th_plastics that have predominaromatic nuclei in their backbone.of these resins should be hydrolytstable, though no actual testingconducted on these resins in this ,'to confirm this speculation.

Processing of CompositesAll composites were fabric

utilizing 8-harness satin-w_graphite* designated as stylefabric weighing 360.9 g/m 2. Prel:were prepared utilizing this gracloth as a standard reinforcemeorder to assess the effect ofmatrix on the flammability andchanical properties of the compo

Prepreg PreparationThe prepregs were prepare,

follows:Epoxy�graphite -- The preprec

prepared by passing the graphitethrough a solution of the epoxyThe coated fabric then was p_through a vertical drying tower, _,provided a programmed drying pdure for the prepreg. Drying wacomplished at 120 °C for 10 min.

Phenolic�graphite, phennovolak/graphite, and benzyl/gra-- The prepreg preparation was etially the same as the epoxy/gr_

*"Thornel" graphite yarn, Union Carbide

New York.

J

4

polyphenylsulfone.The chemistryofthesethermoplasticshas beende-scribedpreviouslyindetail(4,5).Thesulfoneresinsconsistofthediarylsul-phoneandbenzoxygroupsand iso-propylidenyllinkedtogetherinvariousconfigurations(figure 2). Theselinkagesarepresentinbothpolymers.Theypermitrotationaboutthelinkagewhichimpartsinherenttoughnesstothe resins.Similarto otherthermo-plastics that have predominantlyaromaticnucleiintheirbackbone,bothoftheseresinsshouldbehydrolyticallystable,thoughnoactualtestingwasconductedontheseresinsinthisstudytoconfirmthisspeculation.

Processing of CompositesAll composites were fabricated

utilizing 8-harness satin-weavegraphite* designated as style 133fabric weighing 360.9 g/mL Prepregswere prepared utilizing this graphitecloth as a standard reinforcement inorder to assess the effect of resinmatrix on the flammability and me-chanical properties of the composites.

Prepreg PreparationThe prepregs were prepared as

follows:Epoxy�graphite -- The prepreg was

prepared by passing the graphite cloththrough a solution of the epoxy resin.The coated fabric then was passedthrough a vertical drying tower, whichprovided a programmed drying proce-dure for the prepreg Drying was ac-complished at 120°C for 10 min.

Phenolic�graphite, phenolic.novolak/graphite, and benzyl/graphite-- The prepreg preparation was essen-tially the same as the epoxy/graphite

*"Thornel" graphite yarn, Union Carbide Corp,

New York.

35O NMP, 105°C, DRY RESIN CONTENT 34

I-I NMP, 140°C, DRY RESIN CONTENT 35 %

P, NMP, 160°C, DRY RESIN CONTENT 39 '/=3(

-F NMP, 180°C, DRY RESIN CONTENT 3g %

2'I

w

lo

5

I I ] I5 t0 15 20

TIME, mln

Fig. 3, Drying cycles for bismaloimide Aprepregs.

prepreg. The benzyl/graphite prepregwas staged at 135°C for 10 min. inorder to reduce volatile content to3-4%.

Bismaleimide A/graphite -- A resinsolution consisting of 16 part-by-weight(pbw) of resin, 16 pbw of NMP, and 8pbw toluol, was prepared by heatingthe components in a glass-enamelledvessel to 90 °C under constant stirring.The solution is further diluted, pro-viding a 35%-by-weight solution. Theprepregs are fabricated by use of stan-dard prepregging equipment. Dip-coating techniques are used for wet-ting the fabric, followed by drying in avertical drying tower with a tempera-ture range of 150 ° to 170°C. Theprepregging speed is 0.6 cm/min. Theresin solution is further diluted to pro-vide a 30-32%-by-weight solution. Theprepreg is passed through the dryingtower twice at a speed of 0.6 cm/min.The effect of drying temperature onsolvent content in the prepreg is shown

in figure 3. Only a small amount of sol-vent loss was achieved by increasingthe drying cycle from 160-180°C. The

optimum temperature for minimizingthe amount of residual solvent was170 °C.

Bismaleimide B/graphite -- A resinsolution consisting of 17.4 pbw ofresin, 5.2 pbw of resin, 5.2 pbw di-

ethyleneglycolmonoethylether, and12.2 pbw of dioxane was prepared byheating the components at 100°C for 2

hr. The prepreg is fabricated in thesame manner as bismaleimide A. The

impregnation bath is heated to 40°C toprevent the resin from crystallizing.

Polyethersulfone/graphite -- The

polyethersulfone was dissolved in 12 %methylene chloride solution which wasused for the prime coat, and a 20%solution for prepregging. The prepregwas dried for 15 min. at 150 °C.

Polyphenylsulfone/graphite -- Theresin was dissolved in NMP. A 12%

solution was used for the prime coat,and a 20% solution for prepregging.The prepreg was dried at 288 °C for 1hr.

The resin content and the residual

solvent (volatile content) from theabove prepregs was determined by ex-

tracting them with dimethylacetamide(DMAC). The resin and volatile contentwas determined by the equation:

W_ W_-W2 x 100O W,

(Wl = weight of prepreg and W2 =weight of fibers).

The resin content

(_._)_ W_-W2 x 100Wl

- volatile content (-_-).

The resin, solvent, and fiber content for

the above prepregs is indicated in table2.

i

Table 2 -- Resin/Solvent Content

For Prepregs

Composite Content -- %, WeightResins Resin Fiber Volatile

Epoxy 39.9 59.2 0.9Phenolic 39 50.9 10.1Bismaleimide A 38 45.5 16.5Bismaleimide B 42.4 49.4 8.2Phenolic-Novolak 51 40.7 8.3Benzyl 39.4 48 12.6Polyethersulfone -35 -- --Polyphenylsulfone - 35 -- --

Composite FabricationThe prepregs containing the resins

described above were laminated usingthe pressures, curing, and postcuringconditions outlined in table 3. All

laminates fabricated consisted of 10

plies of graphite cloth.

Characterization Studies

Flammability, thermochemical, andmechanical tests were conducted to

characterize the properties of both theneat resins and the laminates consist-

ing of resin with the 133 graphite cloth.Measurements were conducted to

evaluate the following properties of thematerials: thermal stability, ease of ig-

nition and propensity to burn, smokeemission, moisture absorption, andmechanical properties at ambient and

elevated temperatures.The thermal stability was measured

by thermogravimetric analysis. Thechar yields of the various composites

and neat resins were investigated bythermogravimetry (table 4). Thermalanalyses of the composites were con-ducted on a thermogravimetric

analyzer ('IGA)** using nitrogen at-mosphere. The TGA data for a heatingrate of 10°C/min. in nitrogen are

.... Thermographic analyzer" (TGA)950, E.I. Du-Pont de Nemours & Co., Wilmington, Del.

Table 3 -- Processing and Curing

Resin Matrix

Epoxy

Phenolic

Bismaleimide A

Bismaleimide B

Phenolic-Novolak

Benzyl

30 min @ 23°C,15 min @ 116°C,45 min @ 116-124°C160-200 min @ 177-1

Cool,

1 hr @ 82°C,1 hr @ 121°C,4 hr @ 232°C,4hr @ 246°C,

In autoclave

30 min @ 121°C,4 hr @ 177°C,

In autoclave

15 min @ 9°C,80 min @ 150°C,315 min @23°C,

In autoclave

1 hr @ 93°C,1 hr @ 93°C,4 hr @ 149°C,

Cool

20 min @ 59°C,20 min @ 79°C,40 min @ 104°C,4 hr @ 129°C,

Polyethersulfone 15 rain @ 149°C,30 min @371°C,

Polyphenylsulfone 60 min @ 288°C,30 min @ 343°C,

shown in table 4. The TGA behavior otthe bismaleimide A and B resins are

quite different, as indicated by the char

yield and the temperature at which themaximum weight loss occurs in thethermogram. Bismaleimide B, which isa highly cross-linked resin, seems to be

more stable because of the higher de-composition temperatures. The higher

Table 3 -- Processing and Curing Conditions for Graphite Composites

Resin Matrix Cure Postcure

Epoxy 30 min @ 23°C, Vacuum15 min @ 116°C, Vacuum45 min @ 116-124 °C, 690 kn/m 2 None160-200 min @ 177-182°C, 690 kn/m _

Cool, Vacuum

Phenolic

Bismaleimide A

Bismaleimide B

Phenolic-Novolak

Benzyl

1 hr @ 82°C, t380 kn/m _ 6 hr @ 175°C1 hr @ 121 °C, 1380 kn/m 2 4 hr from 175-200°C4 hr @ 232°C, 1380 kn/m 2 13 hr from 200-250°C4 hr @ 246°C, 1380 kn/m 2 Slow cool down to

In autoclave ambient in air oven

30 min @ 121 °C, Vacuu.rn only 2 hr @ 154°C4 hr @ 177°C, 690 kn/m 2 2 hr @ 182°C

15 hr @ 210°CSlow cool down to

In autoclave ambient in air oven

15 min @ 9°C, Vacuum 15 hr @250°C80 min @ 150°C, Vacuum tn air oven315 min @23°C, 400 kn/m 2

In autoclave

1 hr @ 93°C, Vacuum1 hr @ 93°C, 690 kn/m 24 hr @ 149°C, 690 kn/m 2

Cool 690 kn/m 2

20 min @ 59°C, 172 kn/m 220 min @ 79°C, 172 kn/m 240 min @ 104°C, 172 kn/m 24 hr @ 129°C, 345 kn/m 2

Polyethersulfone 15 min @ 149°C,30 min @371 °C, 1380 kn/m 2

Polyphenylsulfone 60 min @ 288 °C,30 min @ 343 °C, 1380 kn/m 2

None

4 hr @ 121 "C

None

None

shown in table 4. The TGA behavior of

the bismaleimide A and B resins are

quite different, as indicated by the charyield and the temperature at which themaximum weight loss occurs in thethermogram. Bismaleimide B, which isa highly cross-linked resin, seems to be

more stable because of the higher de-composition temperatures. The higher

char yield of the bismaleimide A resinis an indication that this resin has

higher aromaticity.The calculated char-yield values in-

dicated are based on the fact that the

graphite fiber has 100% char yield inan anaerobic environment (actual charyield approximately 98-99% at900°C). Also, the resin removal is

, 7

Table 4 -- Char Yield of Graphite Composites and Resins

Resin Composite Resin Neat PDT* * °CComposite Content Char Yield Char Yield Resin Char dT/dt = Max dWldtResins %, Wt. %, Wt. %, Wt. Yield,%, Wt.,* 10°C/min. At°C

Epoxy 33.2 79 37 38 360 425Phenolic 24.6 83 31 46 430 525Bismale-

imide A 25.6 82.5 32 50 420 382Bismale-

imide B 43.3 71.5 34 46 425 470Phenolic-

Novolak 25.7 86 46 46 380 550Benzyl 26 84.5 40 53 330 545Polyether-

sulfone 36 77.5 38 40 545 595Polyphenyl-

sulfone 36 81 47 47 556 595

*Char yield at 900°C, N2.**Polymer decomposition temperature* * *Calculated values

100% when the samples are subjectedto the nitric acid immersion procedureto determine fiber and resin content in

the laminate. The actual char yield ofthe neat resin samples is higher inmost of the resins (table 4).

The ease of ignition was measuredby the oxygen index. The oxygen index

el = 02/(02 + N2) of the compositewas determined per ASTM D-2863.Table 5 is the oxygen index of the

graphite composites at ambient tem-perature. The polyethersulfone/graphite composite exhibited the

Table 5 -- Lirnltlng Oxygen IndexFor Graphite Composites

Composites LOI, %

Epoxy 41Phenolic 46Bismaleimide A 47Phenolic-Novolak 50Bismaleimide B

Polyethersulfone 54Polyphenylsulfone 52

Note: Data unavailable for bismaleimide B andbenzyl.

highest oxygen of all the compositestested. This is in agreement with

previous studies (6) which have shownthat polyethersulfone has a high ox-

ygen index when tested as a neatresin.

The smoke evolution from the graph-

ite composites was determined usingthe NBS-Aminco smoke-density cham-

ber. The specific optical density (Ds)values were obtained from individual

test data and then averaged. The testresults obtained are presented in

figures 4 and 5. It can be seen that asignificant smoke reduction wasachieved in the thermoset-graphite

composites with the phenolic and bis-maleimide resins when compared with

the epoxy/graphite composites. Thephenolic exhibited high smoke evolu-tion. In the case of the thermoplastic-

graphite composites (figure 5), bothpolyethersulfone and polyphenylsul-fone exhibited extremely low smoke

evolution.The moisture absorption of three of

the composites was determined bywater immersion. Previous studies (7)have shown moisture has a detrimen-

tal effect on the physical propertie

composites. In this study, moisequilibrium studies were conducte(

the epoxy and the neat bismaleir"resins and composites. Before esure, the samples were dried i

200 OKEDENSITY EXPOSI/ _ 2.5W/cm2, FLAMING

II

1" / / ......... e|S_AL_t|MIOE A

I" _ PHENOLICEBU --- PH,,o,c

0 2 4 6 8 1(TIME, rain

Fig. 4, Smoke evolution history ofmoset/graphite composites.

240

200

160

DS 120

80

40

0

-- f NBSSMOKEDENSITYEX• 25 W/cm2, FLAMII_

......... POLYETHERSU

-- / _ POLYPHENYLS'

i i 1 " _ EPOXY

iI

-ii

.

' / .,'°"'""

i/" L........,........t.......2 4 6 8 10

TIME, rain

Fig. 5, Smoke evolution history of

moplastic/graphite composites.

tal effect on the physical properties ofcomposites. In this study, moistureequilibrium studies were conducted onthe epoxy and the neat bismaleimideresins and composites. Before expo-sure, the samples were dried in a

°r S,oo[- l i .,, SMo,,,,,,,,,i.,xpo,..,.

/ I : _.sw/cm2.FL_.ING

160L // ......... 91SMALEIMIDE A

,,120 / II --TJ" "_ _E_NE)q!LL:_

r / -[I

4o_....../--t- ----_--- I

0 2 4 6 8 10

TIME. rain

Fig. 4, Smoke evolution history of ther-moset/graphite composites.

240-,/

/200 /

160 /

D$120 i

I.o I

I40 / ............. .."

2 4 6 8 10 12

TIME. rain

Fig. 5, Smoke evolution history of ther-moplastic/graphite composites.

NOS SMOKE DENSITY EXPOSURE,

2.5 W/cm 2, FLAMING

......... POLYETHERSULFONE

POLYPHENYLSULFONE

_'_ EPOXY

J14

vacuum oven at 110°C for 4 hr. The

sample was immersed in distilledwater, and the water take-up was mea-sured over a period of 28 days.

Simultaneously, equivalent valueswere measured for neat resin samplesand laminates. The moisture equili-brium data on the bismaleimide resinsas well as the epoxy are shown infigure 6. Bismaleimide B has a waterabsorption of around 5% after 28 daysimmersion in water. Since the compo-site fabricated with this resin contains

50% by volume of resin, the laminateabsorbs approximately 2.5%. The ab-sorption of both the neat resin and thecomposites is almost complete after28 days. Bismaleimide A absorbs ap-proximately 4.3% by weight after 28days. The composite with this resinshows a slow water take-up. Equili-brium conditions are not reached after28 days of water immersion. In allcases, the bismaleimide resin exhibit-ed lower moisture absorption than thebaseline epoxy resin.Mechanical Properties

Flexural, tensile, compressive, and

D FJ_DXY

O INImALEIMIDt A

• lel_U_LemlC*[ A,_lq_ste

6 immALelwoe Ii

• llllilA L| IM ID| I_0 IIkPHI t e

i i I J i l i l i i i i

2 I • I 10 lZ _ 11 1I :m :n 24 111 m

IMMIeMIO_ TNi_

Fig. 6, Moisture equilibrium data on neatresins and composites.

70

EPOXY

30 PHENOLIC

BI_MALEIMIDE B

20 III_I¢IALE|M|OE/I.

lO

o t0o 200 _(i

TEMPERATURE. "C

ig. 7, Effect of temperature on short-beam_ear strength of graphite composites.

short-beam shear-strength tests wereconducted on graphite fabric-rein-forced laminates prepared with fourdifferent matrix resins: epoxy, pheno-lic, bismaleimide A, and bismaleimideB. The effect of temperature on thesemechanical properties is shown infigures 7-13. The samples were heatedfor 30 min. at the temperatures in-dicated prior to testing at these tem-peratures. The highest mechanicalvalues at 23 °C were obtained with theepoxy/graphite composite followed bythe bismaleimide A/graphite compo-site. The short-beam shear, flexural,tensile, and compressive strength ofthe bismaleimide A/graphite is veryclose 'io that of the epoxy/graphite at23°C (figures 7-10). However, a signifi-cant degradation of these propertiesoccurs at 150 °C. This property loss forbismaleimide A is the consequence ofresidual solvent.

It is well known (11) that residual sol-vent acts as a plasticizer for the com-posites. The prepregs used for moldingcontain approximately 3.5 % of n-methylpyrrolidone which cannot be dried off

1000

?00

z

5

EPOXY

BI_MAL EIMIDE B

PHENOLIC

100

0 100 200 3(XI

TEMPEI_ATURE, °C

Fig. 8, Effect of temperature on flexuralstrength of graphite composites.

quantitatively during cure and post-cure. Previous studies (8,9,10) haveshown that it is very difficult to dry offresidual prepregging solvent fromcured laminates, and in many casesthe solvent forms complex structureswith the polymer. The bismaleimide Asystem was primarily designed as alow-temperature resin matrix posses-sing excellent fire-resistant properties.

The bismaleimide B resin was de-

signed as a high-temperature resin,and it retains its mechanical propertiesup to 250°C without any significantdegradation (figures 7 and 8).

Figure 10 illustrates the rigidity re-tention of bismaleimide B at elevated

temperatures. The modulus is almostconstant over the entire temperature

7OO

200--

100-

I IIOO 2O0

TEMPERATURE, °C

Fig. 9, Effect of temperature on totstrength of graphite composites.

Fig. 11, Effect of temperature onural modulus of graphite composit

80 f BISJVIAL

70 PHENOLIC

6O

lo

h Io 100 2_

TEMPERATURE°C

I

10

70(I

"z-_

0_ ENOLIC

BISMALEIMIDE A

I I I100 200 300

TEMPERATURE,"C

70O

"s

=

2O0

IO0

Fig.Fig. 9, Effect of temperature on tensile pressivestrength of graphite composites, posites.

L

PHENOLIC

BISMALEIMIDE _1 __

TEMPERATURE, °C

10, Effect of temperature on com-strength of graphite com-

Fig. 11, Effect of temperature on flex-ural modulus of graphite composites.

6O

E

84O

38

2O

BISMALEIMIDE A/_

[ 1

tOo ZOO

TEMPERATURE, _C

BISMALEIMIOE B

/,

PHENOLIC

Fig. 12, Effect of temperature on ten.

sile modulus of graphite composites.EPOXY

PHENOLIC

7O

g

_1

_ 4o

10

o 300too 2_

TEMPERATURE,°C

, 11

80

70

60E

_ _o

2O

10

EPOXY

100 200 300

TEMPERATURE, C

Fig. 13, Effect of temperature on com-pressive modulus of graphite com-posites.

range for this composite. Figures 12and 13 illustrate the tensile and com-

pressive modulus for the epoxy,phenolic, and bismaleimide A compo-sites. The phenolic retains its compres-sive modulus up to 300°C (figure 13),however, its tensile modulus (figure 12)was lower than that of the epoxy andbismaleimide A at 23°C.

Conclusions

Improved fire-resistant propertieswere demonstrated with advancedthermoset and thermoplastic matricesin the graphite composites. This isevidenced by the high oxygen indexand low smoke evolution from these

composites. Among the highlights ofthis preliminary study are the following:

• Epoxy composites demonstratethe lowest fire-resistant properties ofall composites tested.

• Bismaleimide A composites ex-

hibit excellent fire-resistant properties,low moisture absorption, and ambienttemperature mechanical properties.This bismaleimide resin is primarilydesigned as a fire-resistant, high char-yield resin.

• Bismaleimide B and phenolic re-tain their mechanical properties atelevated temperatures, however, theyhave lower mechanical properties atambient temperatures than the epoxycomposites. The bismaleimide B is pri-marily designed as a high-temperatureresin.

• Phenolic-novolac, polyether-sulfone, and polyphenylsulfone com-posites exhibit high oxygen index andlow smoke evolution. •

Footnotes1. W. Collins and T. Villani, SPE

RETEC, Tech. Papers, p. 1 (1977).2. R. T. Alverez and F. P. Dormory, 32nd

SPE ANTEC, Tech. Papers, p 687(1974).

3. R. W. Vaughan, M. K. O'Rell, and B.J. Buyny, National SAMPE Symposium(1976).

4. D. G. Chasin and J. Feltzin, NationalSAMPE Symposium, 7, 350 (1975).

5. J. D. Domine, L. A. McKenna, and R. K.Walton, SPE RETEC, Tech. Papers, p.12 (1977).

6. D. A. Kourtides and J. A. Parker, J.Polymer Eng. and Sci., 18 855 (1978).

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