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PLASTICS
JANUARY 1980
DESIGN & PROCESSING
https://ntrs.nasa.gov/search.jsp?R=19980215575 2018-06-04T13:31:23+00:00Z
NASA/TM--- _o--
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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).
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