Aramid-reinforced composite materials of equal fiber volume and varied polymer thermoset matrices were pultruded and flexurally tested to failure. The objective was to improve the flexural properties of aramid-reinforced pultrusions. Pultrusions of both sized and unsized aramid fiber with four different resin systems were compared to determine the effects of sizing compounds and postcuring on flexural strength, fiber wettability, and fiber-to-resin interface bonding. Improvements in flexural strength resulting from pretreatments with the sizing solutions used were marginal. The most significant improvements in flexural properties resulted from postcuring. Flexural strengths ranged from a low of 39,647 psi (273MPa) to a high of 80,390 psi (554 MPa), an overall increase of 103 percent. The fact that postcuring improved the flexural properties of the pultrusions of the four resin systems indicates that a full cure did not occur in any of the resin systems during the pultrusion process. The increased flexural strengths of the polyester and vinyl ester pultrusions were the most surprising. The four resin systems examined were Interplastic Corporation VE 8300 vinyl ester, Ashland Chemical Company Aropol 7430 Polyester, and Shell Chemical Company Epon 9302 and Epon 9310 epoxides

Johnson, Gary S.

Macconochie, Ian O.

Wilson, Maywood L.

English

NASA Technical Reports Server

NASA 'Technical Memorandum 88997 
Comparison of Flexural Properties 
of Aramid-Reinforced Pultrusions 
Having Varied Matrices, 
Pretreatments, and Postcures 
Maywood L. Wilson, Gary S. Johnson, 
and Ian 0. MacConochie 
https://ntrs.nasa.gov/search.jsp?R=19870005844 2020-03-20T12:25:47+00:00Z
NASA Technical Memorandum 88997 
Comparison of Flexural Properties 
of Aramid-Reinforced Pultrusions 
Having Varied Matrices, 
Pretreatments, and Postcures 
Maywood L. Wilson, Gary S. Johnson, 
and Ian 0. MacConochie 
LangZey Research Center 
Hampton, Virginia 
National Aeronautics 
and Space Administration 
Scientific and Technical 
Information Branch 
1987 
Abstract 
Aramid-reinforced composite materials of equal 
fiber volume and varied polymer thermoset matri- 
ces were pultruded and flexurally tested to failure. 
The objective was to improve the flexural proper- 
ties of aramid-reinforced pultrusions. Pultrusions of 
both sized and unsized aramid fiber with four dif- 
ferent resin systems were compared to  determine the 
effects of sizing compounds and postcuring on flex- 
ural strength, fiber wettability, and fiber-to-resin in- 
terface bonding. Improvements in flexural strength 
resulting from pretreatments with the sizing solu- 
tions used in this study were marginal. The most sig- 
nificant improvements in flexural properties resulted 
from postcuring. Flexural strengths ranged from a 
low of 39647 psi (273 MPa) to a high of 80390 psi 
(554 MPa), an overall increase of 103 percent. The 
fact that postcuring improved the flexural proper- 
ties of the pultrusions of the four resin systems indi- 
cates that a full cure did not occur in any of the sys- 
tems during the pultrusion process. The increased 
flexural strengths of the polyester and vinyl ester 
pultrusions were the most surprising. Of the four 
resin systems examined (Co-Rezynl VE 8300 vinyl 
ester, Aropo12 7430 polyester, and Epon3 9302 and 
Epon 9310 epoxies) for aramid-reinforced pultrusion, 
the highest flexural strength was obtained with Epon 
9310 epoxy. 
Introduction 
The mechanical properties of aramid-reinforced 
polyester pultrusions have been compared with those 
of fiberglass-reinforced polyester and vinyl ester 
pultrusions (ref. 1).  The aramid- and fiberglass- 
reinforced pultrusions contained fiber volumes of 
41 percent and 38 percent, respectively. The 
aramid fiber pultrusion exhibited very poor flexu- 
ral strength (54000 psi (372 MPa)) when compared 
with the strength of fiberglass-reinforced materials 
(132 000 psi (910 MPa)). The low flexural strength of 
the aramid pultrusion agrees with the low compres- 
sive and flexural values reported by others (refs. 2 
and 3). This characteristic is believed to be partially 
related to the need for some type of pretreatment 
or sizing compound application to the aramid fibers 
prior to pultrusion. With this information as back- 
ground, four resin systems were selected as matrices 
for aramid-polymer (thermoset) pultrusion experi- 
ments. Pultrusions were made with sized and unsized 
Kevlar 4g4 unidirectional roving (22 720 denier). All 
materials tested had identical volume fractions of 
aramid fiber. Three-point flexural tests were con- 
ducted and fiber wettability was evaluated. The 
objective of these experiments was to  improve fiber 
wetting characteristics and fiber-to-matrix interface 
bonding and thereby increase flexural strength. 
This report describes the investigation of the pul- 
trusions of four resin systems with aramid reinforce- 
ment fibers, presents test results, and gives an anal- 
ysis of the results. The authors acknowledge the 
assistance of Jane M. Hogge and James E. Justice 
for mechanical testing and Edward W. Covington I11 
for scanning electron microscope (SEM) work and 
evaluation. 
Approach 
The pultrusion die used throughout the exper- 
iment was 30 in. (76.2 cm) in length, machined 
from 17-4 PH stainless steel. The die cavity sur- 
faces were polished to 4 microinches (1.02 x 10-7m) 
root-mean-square. The die produced pultrusions 
having cross sections 0.243 in. (0.62 cm) thick and 
0.296 in. (0.75 cm) wide. The four resin systems 
used in the experiment were (1) Aropol 7430 isoph- 
thalic polyester, (2) Co-Rezyn VE 8300 vinyl ester, 
(3) Epon 9302 epoxy, and (4) Epon 9310 epoxy. (See 
table I.) Both epoxy systems are new experimen- 
tal epoxy resins of the bisphenol A/ephichlorohydrin 
type. Unsized aramid fiber roving was unwound, 
sized, dried, and rewound fer use in the program. 
Test and Results 
The pultruded materials were flexurally tested 
in the as-pultruded condition and also after various 
postcuring treatments. Test specimens 3 in. (7.6 cm) 
in length were used in accordance with the American 
Society for Testing and Materials (ASTM) Standard 
D790 (three-point flexural test). This test was used 
to evaluate improvements in the strength of the pul- 
trusions obtained by varying processing parameters. 
The failure mode of the specimens was a combination 
of compression, tension, and shear (ref. 4). The test 
results are given in table 11. The mean strength of 
five specimens tested in each condition is reported. 
In the as-pultruded condition, the material with 9310 
epoxy matrix exhibited the highest flexural strength; 
and the material with the polyester 7430 matrix, the 
lowest. Aramid fiber roving sized with a polyester so- 
lution5 was used with the polyester and 9302 epoxy 
Trademark of Interplastic Corporation. 
Trademark of Ashland Chemical Company. 
Trademark of Shell Chemical Company. 
Trademark of E. I. Du Pont de Nemours & Co., Inc.; the 
generic name for Kevlar is aramid fiber and its chemical name 
is poly (P-phenylene terephthalamide). 
Aropol 7430 polyester, 0.5% by weight in acetone. 
pultrusions, whereas aramid fiber roving sized with 
a vinyl ester solution6 was used with the vinyl es- 
ter and 9310 epoxy pultrusions. The changes in 
flexural strength resulting from sizing applications 
for the as-pultruded state were (1) an increase of 
6.4 percent for polyester, (2) a 17.3-percent decrease 
for vinyl ester, (3) a 7.6-percent increase for 9302 
epoxy, and (4) a 4.3-percent increase for 9310 epoxy. 
Table I1 shows that for the aramid-polyester pultru- 
sion, sizing the aramid fibers with a polyester so- 
lution increased flexural strength up to postcuring 
temperatures of 325°F (162°C); however at 400°F 
(204°C) sizing decreased flexural strength. This sug- 
gests that the sizing compound might have begun 
to degrade. This effect may also explain the re- 
duction caused by sizing in flexural strength of the 
aramid-epoxy pultrusions above a postcuring tem- 
perature of 450°F (232°C). The most significant 
changes resulted from postcuring. Flexural strengths 
ranged from a low of 39647 psi (273 MPa) for un- 
sized polyester in the as-pultruded condition to a 
high of 80390 psi (554 MPa) for unsized 9310 epoxy 
postcured at 450°F (232°C) for 2 hr, an overall in- 
crease of 103 percent. The maximum increase in flex- 
ural strength of the unsized pultrusions because of 
postcuring was (1) for the polyester matrix, 87 per- 
cent; (2) for the vinyl ester matrix, 50 percent; (3) for 
the 9302 epoxy matrix, 19 percent; and (4) for the 
9310 epoxy matrix, 17 percent. The two conventional 
pultrusion matrices, polyester and vinyl ester, exhib- 
ited the greatest flexural strength increases resulting 
from postcuring. This was contrary to the expected 
results (the epoxies were expected to benefit most 
by postcuring). The 9310 epoxy pultrusion had the 
highest flexural strength in all conditions. 
Figures 1 through 4 are SEM photomicrographs 
showing the fractured faces of specimens machined 
from materials with the lowest and highest flexural 
strengths in each resin system. The polyester resin 
system (fig. l(a)) appears t o  have wetted the aramid 
fibers least, as indicated by loose and bare fibers, 
whereas the 9310 epoxy system (fig. 4(b)) appears 
to have wetted the fibers best of the four resins. 
The vinyl ester (fig. 2) appears t o  be second best in 
wettability. These findings support the quantitative 
flexural test results listed in table I1 and graphically 
compared in figure 5. 
Concluding Remarks 
Four thermoset resin systems were used as matri- 
ces for aramid fiber pultrusions. Fiber volumes were 
held constant. Pultrusions with both sized and un- 
sized fiber were subjected to varied postcuring tem- 
peratures and flexurally tested to failure. Test results 
are presented to determine the effects of postcuring 
and sizing pretreatments on the flexural strength of 
aramid-reinforced pultrusions. The objective was to 
improve flexural properties by improving fiber wetta- 
bility and fiber-to-resin interface bonding. Improve- 
ments in flexural strength resulting from pretreat- 
ments with the sizing solutions used in this study 
were marginal. More effort needs to be directed to- 
ward this approach. The most significant improve- 
ments in flexural strength resulted from postcuring. 
The overall increase was 103 percent. The fact that 
postcuring improved the flexural properties of the 
pultrusions indicates that a full cure did not occur 
in any of the systems during the pultrusion process. 
The increased flexural strengths of both the polyester 
and the vinyl ester pultrusions were the most surpris- 
ing. Of the four resin systems examined for aramid- 
reinforced pultrusion, the greatest flexural strength 
was obtained with 9310 epoxy. More tests need to be 
conducted to determine the thermo-oxidative stabil- 
ity at postcuring temperatures of sizing compounds 
and resin systems used in pultrusion. In future ex- 
periments designed to study wetting characteristics 
of aramid fibers pultruded in epoxy matrices, very 
low concentrations of epoxy sizing solutions are rec- 
ommended to increase fiber wettability. It is also rec- 
ommended that a tube-type curing oven be installed 
between the cure die and the pullers to perform the 
postcuring operation. 
NASA Langley Research Center 
Hampton, VA 23665-5225 
October 30, 1986 
References 
1. MacConochie, Ian 0.; and Wilson, Maywood L.: Pul- 
trusion Process for Fabrication of Tethers (Preliminary 
Concepts) for Application of Tethers in Space Workshop 
(Technology and Test). Applications of Tethers in Space, 
Volume 2, Alfred C. Cron, compiler, NASA CP-2365, 
Characteristics and Uses of Kevlar@dS Aramid High Mod- 
ulus Organic Fiber. Bull. K-2, E. I. Du Pont De Nemours 
& Co., Inc., Feb. 1978. 
3. Lubin, George, ed.: Handbook of Composites. Van 
Nostrand Reinhold Co., c.1982. 
4. Tsai, S. W., ed.: Composite Materials: Testing and 
Design (Fifth Conference). ASTM Spec. Tech. Publ. 674, 
1978. 
1985, pp. 5-218-5-223. 
2. 
Co-Rezyn VE 8300 vinyl ester, 3% by weight in acetone. 
2 
..-I 
u 
(d 
1 
- 
E 
& 
2 
3 
k 
a 
a, Y
cn 
c 
m 
.,-4 
2 
Y 
a, 
3 
Table 11. Ultimate Flexural Strength for Aramid-Reinforced Pultrusions 
Ultimate flexural stre 
I All test specimens contained fiber volume fraction 0.46; fiber orientation was unidirectional. All tests were conducted at room temperature 
;th, psi, for- 
9302 
Condition 
Sizing 
Unsized 
Sized 
Unsized 
Sized 
Unsized 
Sized 
Unsized 
Sized 
Unsized 
Sized 
Unsized 
Sized 
Postcure 
As pultruded 
As pultruded 
285"F, 2 hr 
285"F, 2 hr 
325"F, 1 hr 
325°F. 1 hr 
400°F, 2 hr 
400°F, 2 hr 
450"F, 2 hr 
450°F, 2 hr 
500°F, 35 min 
500°F. 35 min 
7430 
polyester 
39 647 
42 192 
65 312 
68 009 
68 322 
68 489 
74 361 
70 430 
VE 8300 
vinyl ester 
50 045 
41 376 
67 662 
69 377 
70 935 
69 974 
75 088 
78 844 
epoxy 
57 372 
61 751 
67 121 
59 115 
67 488 
66 780 
62 164 
68 298 
62 344 
68 053 
68 061 
65 278 
9310 
epoxy 
68 554 
71 474 
74 230 
72 749 
75 273 
75 214 
77 335 
79 452 
80 390 
76 550 
80 014 
77 108 
4 
(a) Unsized aramid fiber; as pultruded; 
39 647 psi flexural strength. 
(b) Unsized aramid fiber; 400'F postcure; 
74 361 psi flexural strength. 
L-86-404 
Figure 1. Fracture face SEM photomicrographs of aramid-polyester 7430. 
(a) Sized aramid fiber; as pultruded; 
41 376 psi flexural strength. 
(b) Sized aramid fiber; 400°F postcure; 
78 844 psi flexural strength. 
L-86-405 
Figure 2. Fracture face SEM photomicrographs of aramid-vinyl ester 8300. 
I 5 
I 
ORIGINAL PA&. fS 
OF POOR QUAL+ 
(a) Unsized aramid fiber; as pultruded; 
57 372 psi flexural strength. 
(b) Sized aramid fiber; 400'F postcure; 
68 298 psi flexural strength. 
L-86-406 Figure 3. Fracture face SEM photomicrographs of aramid-epoxy 9302. 
(a) Unsized aramid fiber; as pultruded; 
68 554 psi flexural strength. 
(b) Unsized aramid fiber; 450°F postcure; 
80 390 psi flexural strength. 
L-86-407 
Figure 4. Fracture face SEM photomicrographs of aramid-epoxy 9310. 
6 
100 Polyester 7430 1 Epoxy 9302 = Epoxy 9310 a Vinyl ester 8300 
80 
70 
60 
flexural 
strength 50 
ks i  40 
30 
20 
10 
0 
bns ized  postcured 
325' F, 1 hr 
Sized postcured 
285' F, 2 hr 
Unsized as 
p u t t r u d e d l  / 
Sized as pultruded 
Unsized postcured 285' F, 2 hr 
Condition 
ESl Polyester 7430 
0 Vinyl ester 8300 
U Epoxy 9302 
I Epoxy 9310 
90 c 
Flexural 
strength 
ks i  
70 
60 
50 
40 
30 
20 
10 
n 
Sized posycured 
325' F, 1 hr / \ \ \  Sized postcured 500' F, 35 min 
Unsized postcured - Unsized postcured 
500' F, 35 min 
Sized postcured Sized postcured 
400' F, 2hr 450' F, 2hr 
Unsized postcured 
450' F, 2hr 
Figure 5. Flexural strengths of 46 percent aramid fiber pultrusions. 
7 
Standard Bibliographic Page 
.. Report No. 12. Government Accession No. 13. Recipient's Catalog No. 
NASA TM-88997 
L .  Title and Subtitle 
- 
5. Report Date 
Comparison of Flexural Properties of Aramid-Reinforced 
Pultrusions Having Varied Matrices, Pretreatments, and Postcures 
January 1987 
6. Performing Organization Code 
.5. Supplementary Notes 
This paper was presented at the 41st Annual Conference of the Society of the Plastics Industry, Reinforced 
Plastics/Composites Institute, held in Atlanta, Georgia, January 27-31, 1986, and is published in the 
vroceedings. 
Maywood L. Wilson, Gary S. Johnson, and Ian 0. MacConochie 
~ ~~ ~ 
16. Abstract 
Aramid-reinforced composite materials of equal fiber volume and varied polymer thermoset matrices 
were pultruded and flexurally tested to failure. The objective was to improve the flexural properties of 
aramid-reinforced pultrusions. Pultrusions of both sized and unsized aramid fiber with four different resin 
systems were compared to determine the effects of sizing compounds and postcuring on flexural strength, 
fiber wettability, and fiber-to-resin interface bonding. Improvements in flexural strength resulting from 
pretreatments with the sizing solutions used in this st,udy were marginal. The most significant improvements 
in flexural properties resulted from postcuring. Flexural strengths ranged from a low of 39647 psi (273 MPa) 
to  a high of 80390 psi (554 MPa), an overall increase of 103 percent. The fact that postcuring improved 
the flexural properties of the pultrusions of the four resin systems indicates that a full cure did not occur 
in any of the resin systems during the pultrusion process. The increased flexural strengths of the polyester 
and vinyl ester pultrusions were the most surprising. The four resin systems examined were Interplastic 
Corporation VE 8300 vinyl ester, Ashland Chemical Company Aropol 7430 Polyester, and Shell Chemical 
- 
8. Performing Organization Report No. 
L-16152 
Company Epon 9302 and Epon 9310 epoxies. 
j. Performing Organization Name and Address 
NASA Langley Research Center 
Hampton, VA 23665-5225 
17. Key Words (Suggested by Authors(s)) 
Pultrusion 
Aramid-fiber-reinforced 
Epoxy matrices 
10. Work Unit No. 
11. Contract or Grant No. 
18. Distribution Statement 
Unclassified-Unlimited 
12. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration 
Washington, DC 20546-0001 
Subiect Cateaorv 24 
13. Type of Report and Period Covered 
Technical Memorandum 
14. Sponsoring Agency Code 
19. Security Classif.(of this report) 20. Security Classif.(of this page) 21. No. of Pages 22. Price 
Unclassified 1 Unclassified 1 9  1 A02 
For sale by the National Technical Information Service, Springfield, Virginia 22161 
NASA-Langley, 1987 


Comparison of flexural properties of aramid-reinforced pultrusions having varied matrices, pretreatments and postcures

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