Multicomponent Polymer Systems - ACS Publications

29 Halogenated Epoxy Matrix Plastics in Filament-Wound Composites Downloaded by CHINESE UNIV OF HONG KONG on March 17, 2016 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0099.ch029

JAMES R. GRIFFITH, ARTHUR G. SANDS, and JACK E. COWLING Naval Research Laboratory, Washington, D. C. 20390

Epoxy resins which contain chlorine, bromine, and fluorine in substantial quantities have been evaluated as matrix materials for glass fiber-reinforced composites. N O L rings containing these systems have beenfilamentwound to determine whether or not low water absorption of the matrix would extend fatigue life under water of a composite. Water absorptions of the bulk plastics and winding variables have been measured for each composite system. Fatigue life has been evaluated in a slow, continuous cycle. Standard epoxy resins based upon bisphenol-A yielded composites with fatigue lives in the 5,000-6,000 cycle range. In general, the composites produced from halogenated materials were superior. One system had nearly triple the fatigue life of the standards.

Qtructural materials for use in the deep ocean as well as in space require ^ high strength-to-weight ratios. The hull of a deep-submersible vehicle, for example, must be able to withstand water under high pressure while not being excessively heavy. For this reason fiber-reinforced plastics offer potential advantages as structural materials for such a purpose, and filament wound composites in which the fibers are placed in orderly patterns are particularly promising. Since such composites contain enormous areas of adhesive bonding, and water is generally quite deleterious to the bond strength of an organic adhesive, there is concern regarding the long term reliability under mechanical stress i n water. It appears likely that a matrix plastic with minimal response to the effects of water should be more effective i n this regard than a more sensitive matrix, but to our knowledge there have been no previous accounts i n the literature of efforts to test this idea. Halogenated epoxies are frequently reported in trade publications to ab471 Platzer; Multicomponent Polymer Systems Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Downloaded by CHINESE UNIV OF HONG KONG on March 17, 2016 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0099.ch029

472

MULTICOMPONENT POLYMER SYSTEMS

sorb less water than the common epoxies, although data on the subject in the chemical literature of epoxy materials are scattered and fragmentary. Consequently, a study was made to evaluate as filament-winding matrices epoxy components containing chlorine, bromine, and fluorine. The chlorinated and brominated materials were obtained from commercial sources, and the fluorinated resins were synthesized locally as part of a continuing study of fluorinated epoxy systems. A l l of the filament windings, sample preparations, and evaluations were done at the Naval Research Laboratory. Experimental Materials. Code designations, chemical compositions, and the commercial sources of the resins, curing agents, and additives containing bromine and chlorine are listed in Table I. T h e fluorine-containing resins are described below. F o r convenience i n the tables, the hydrocarbon resins without halogen are designated by S; those with chlorine are CI; with bromine, Br; and with fluorine, F . The curing agents are designated X regardless of halogen content, and the inert additive, which contains chlorine, is A . The fluorinated resins, F i and F , are the diglycidyl ethers of 4,4'dihydroxyoctafluorobiphenyl and of l,3-bis(hexafluoro-2-hydroxypropyl) 2

Table I. Code

S3

Cli Brx Br F, F Xx 2

2

x, x 4

x A

Diglycidyl ether of bisphenol A Combined Si & S E R L 2256 types E R L A 0400 Epoxidized cyclopentenyl ether Chlorinated hydroDGEHQ quinone derivative ERX-67 N,Af,-diglycidyltribromoaniline D E R 542 Brominated Si type (see below) — (see below) — Curing Agent MetaphenyleneCL diamine NMA Nadic methyl anhydride Z Z L 0820 Aromatic amines MOCA Chlorinated methylenedianiline Tetrafluorometaphenylenediamine Arochlor 1254 Chlorinated biphenyl 3

2

x

Chemical Composition

Epon 828

Si

s

Trade Name

Identification of Materials

6

2

Source

Reference

Shell Union Carbide Union Carbide Velsicol

2

Shell Dow NRL NRL Shell

7

Allied Union Carbide Dupont Narmco, Whittaker Monsanto

Platzer; Multicomponent Polymer Systems Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

4 3


29.

GRIFFITH ET AL.

473

Filament-Wound Composites

benzene respectively. They were made from the corresponding dihydroxy compounds by the method of Kelly, Landua, and Marshall ( 5 ) . The systems of resin and curing agent for which there were manufacturers recommended compositions and cure cycles were prepared and cured according to these recommendations. In compositions for which there were no guides, the ratios of resin and curing agent were determined by the type of curing agent. The systems containing amines were blended for exact equivalence of one amino hydrogen atom for each epoxy ring of the resin—i.e., chemically equivalent amounts. Since the stoichiometry of anhydride-cured systems is so complex that trial-anderror determination of resin-curing agent ratios to obtain optimum rustic properties is common practice, the ratio of epoxy to anhydride functional groups which has been found to be best for bisphenol-A resins was used for the new compositions. In all anhydride-cured systems, a catalytic amount of dimethylbenzylamine was added to accelerate the reactions. Final cure temperatures for all systems were near 160 °C, and final cure times ranged from 6 to 24 hours. Halogenated aromatic amines are considerably slower i n reacting than unhalogenated analogs i n general, and these required the longer cure times. Water Absorption of the B u l k Resins. As filament windings were i n progress, samples of the matrix resins were removed and cast i n 1-inch diameter cylindrical aluminum cups to form discs 1/8-inch thick. These were cured i n the same oven with the filament-wound structures. The discs were then placed into distilled water contained i n small beakers located i n a room air conditioned to maintain 25°C. Periodically, the

MONTHS

Figure 1.

I M M E R S I O N IN

DISTILLED

WATER

@

25°C

Water absorption of bulk matrix plastics containing chlorine



474


MONTHS

Figure 2.

0

IN

DISTILLED

WATER

@

25° C

Water absorption of bulk matrix plastics containing bromine

1

2 MONTHS

Figure 3.

IMMERSION

IMMERSION

3 IN

4 DISTILLED

5 WATER

6 @

7

8

25°C

Water absorption of bulk matrix plastics containing fluorine

discs were removed from the beakers, dried quickly with absorbent paper, and weighed to determine water absorptions. The results of these tests are shown i n Figures 1, 2, and 3. Fatigue of Glass-Fiber Reinforced Plastics (GRP). N O L rings of 6-inch outer diameter and 0.25-inch width were fabricated from 12 single



29.


GRIFFITH ET AL.

Figure 4.

Control console and ring fatigue assembly

Figure 5.

Close-up of ring fatigue assembly


475


476

MULTICOMPONENT

POLYMER SYSTEMS

ends of 204 filaments each of Ferro Corp. S-1014-S24 glass fiber with non-aging finish according to A S T M D2291-67. The thickness of each ring was controlled at 0.125 db .003 inch by machining the circumference; thus, a fresh surface was exposed to water during fatigue. The fatigue performance of rings produced from the various resin systems was evaluated i n the equipment shown i n Figures 4 and 5. The console was programmed to control continuously a hydraulic ram which compressed the rings i n the slow cycle illustrated i n Figure 6. The rings were held i n position by a slotted assembly and restrained from rotation (Figure 5 ) . The force required to compress a ring 2.53 inches along the fatigue diameter was monitored daily (approximately every 1000 cycles). This force produces a strain of 2.2% in the outer fibers of the rings at the 200

160

FAILURE 140

20%

IMIN

LOSS

_ . . . .

v

-o-

D R Y ( A V G . O F 15 R I N G S )

- x -

IN D I S T I L L E D W A T E R (AVG.0F

18 R I N G S )

100

i iiI

80

'

100

'

i

i i I i I

IOOO

10,000

CYCLES

Figure 6.

Typical fatigue behavior of identical rings, wet and dry

points of maximum bending, corresponding to a stress of approximately 280,000 psig for Type S glass. Failure was arbitrarily defined as the number of cycles at which a ring lost 2 0 % of its original force for the 2.53inch compression. A plot of force, or load, as ordinate vs. number of cycles as abscissa on semi-log paper commonly showed a steep decline in the load-bearing ability of the composite as failure was approached— e.g., as shown in Figure 6. This figure also compares the typical behavior of dry rings with the relatively rapid decay of identical rings immersed in water. The glass content was determined by resin burn-off of ring segments in crucibles i n a muffle furnace. The void content was determined by a method of optical microscopy previously reported (6). Horizontal shear was measured by the Short Beam method ( I ) . Table II compares fatigue performances of the chlorinated, brominated, and fluorinated systems.


29.

GRIFFITH ET AL.

477



Discussion The most outstanding results of this study were obtained with the 2v*,2V-diglycidyltribromoaniline, B r i , both i n water absorption and i n fatigue of the rings produced by curing it with metaphenylenediamine, X i . After four months immersion i n distilled water, discs of the plastic absorbed only 0.25% water by weight, which was the lowest of the materials evaluated. Since this system was derived from glycidylamine, whereas all others contained glycidyl ethers, there is some uncertainty whether the low water absorption is attributable to this, to the presence of bromine in the molecule, or to both factors. The resin also had good filamentwinding characteristics since it was a moderate viscosity liquid of relatively slow thickening rate at 55 °C, the impregnation temperature used. Because of the long fatigue lives obtained from rings with the B r i / X i system under water, a more extensive evaluation was made. Ten sets of rings were prepared with glass contents ranging from 63 to 7 5 % . The fatigue results are shown in Figure 7, i n which each point represents the average of six rings. A very rough linear relationship between glass content and fatigue life may be seen with the points falling into two groups. Above 69% glass, the over-all average life was about 6,500 cycles, and below 69% glass the over-all average was about 14,000 cycles. Some individual rings of the latter sets survived more than 17,000 cycles. These results suggest that there may be a critical glass content for this system around 69% at which performance characteristics change abruptly. Such behavior could possibly result from several causes, two of which would be lack of total fiber encapsulation by resin above 6 9 % glass or strain magnification i n the resin during stress at higher glass contents. The data of Table II, part B do not eliminate the possibility that glass content is a more significant factor than resin composition insofar as fatigue life is concerned since all the other compositions had higher glass percentage than the B r i / X i system. However, an extensive fatigue evaluation of unhalogenated matrix resins has been performed, and rarely did an individual ring exceed 10,000 cycles regardless of glass content, void content, or horizontal shear. It can be seen i n Figure 1 and Table II that the Arochlor additive, A , which could not react chemically into the resin, was also beneficial i n suppressing water absorption and extending fatigue life when incorporated into unhalogenated systems to the extent of 10% by weight. Thus, the water absorption during four months of immersion of the S / X plastic was reduced from 2.6 to 1.8% by 10% of A . The average fatigue life of rings produced was extended from 5,300 cycles to 7,900 cycles while all other factors remained essentially constant. 2


3

478


Table II. Glass Content, wt %

Matrix Resin Composition

Fatigue Life under Water of GRP

Void Content, vol %

Horizontal Shear Strength, psig

Shear Std. Deviation, psig

A . Chlorine-Containing Resins S,/X « S,/A/X 10/1


2

S /A/X 10/1 2

S /A/X 4/1 2

2

3

3

cn/x

2

Cli/A/X 10/1

2

S1/X4

74.0 74.0

0.2 0.2

14,000 13,800

280 225

72.0

1.6

16,000

176

74.1

2.5

15,700

395

64.0 71.2

2.3 1.5

12,200 12,000

175 95

73.5

1.1

12,400

278

B . Bromine-Containing Resins Br2/S2/X2

74.0 81.8

0.2 5.6

14,000 12,500

280 221

75.3 77.5

2.5 4.0

12,100 14,600

227 235

72.2 63.8

2.0 1.4

13,600 14,300

114 99

1/1 Br /X Br /S /S /A/X 5/5/1/2 2

2

2

2

3

Brx/Xx B /X! r i

3

C . Fluorine-Containing Resins F /X F /X F2/S2/X3 1/1 2

6

2

t

F2/S3/X3 1/2

69.6

5.6

12,100

1,044

F /B /X, 1/19

73.7

4.0

12,600

393

81.1

2.7

10,700

93

2

r i

F /X Fx/S^X, 1/2 2

4

" Unhalogenated standard for comparison.


29.

479


GRIFFITH ET AL.

w i t h Halogen-Containing M a t r i x Resins Coeff.of Variation, psig

Initial Load, lbs

No. of Rings

Average Fatigue Life Cycles

High

Low


A . Chlorine-Containing Resins 2.0 1.6

160 160

27 5

5,300 7,900

6,100 8,400

4,100 6,900

1.1

141

7

10,900

11,800

9,600

2.5

155

7

7,900

8,600

6,900

1.4 0.8

130 153

7 7

8,300 5,600

13,200 6,400

5,100 3,700

2.2

161

6

5,100

6,000

4,000

B . Bromine-Containing Resins 2.0 1.8

160 177

27 7

5,300 3,900

6,100 4,300

4,100 3,600

1.9 1.6

153 144

6 7

5,000 6,440

5,600 7,200

3,600 5,400

0.8 0.7

166 150

6 7

7,000 15,700

7,400 17,100

6,000 13,200

2,800

C . Fluorine-Containing Resins 130 134.5 159

3 2 1

1 3,850 6,700

(sheared) 4,900

8.6

135

7

2,500

4,000

900

3.1

155

7

4,900

6,800

3,700

0.9

129 178

8 6

1,000 1,800

(sheared) 2,600

1,400



480


6

8

10

12

14

CYCLES IN DISTILLED WATER

Figure 7.

16

20

(xlO»)

Effect of glass content upon the fatigue life of rings produced with the Br /X matrix 1

1

The glycidyl ether of the chlorinated hydroquinone derivative, C l i , also demonstrated low water absorption (Figure 1). The resin was somewhat difficult to use for filament winding because of a relatively high melt viscosity, but the system C l i / X had a respectable fatigue life of 8,300 cycles, with one ring surviving over 13,000 cycles. The addition of Arochlor to this heavily chlorinated resin detracted from the fatigue life of the rings produced therefrom. 2

The brominated bisphenol-A resin, B r , was also too viscous for convenient filament winding, and in this case the halogen appeared to have small effect upon water absorption or fatigue life. 2

The fluorinated diglycidyl ethers were available only in small quantities which could be produced in glassware. Fluorine was fairly effective in suppressing the water absorption of the cast plastics (Figure 3), but the fatigue lives of rings produced from F i and F were less than those of conventional materials (Table II, part C ) . Rings which contained fluorine were usually more opaque than any of the others, and it appeared that the glass finish was not optimum for these resins. Shearing of rings during cycling occurred more frequently than normal, and this also indicated poor bonding between resin and glass. N e w finishes which contain fluorine may be required to realize the full potential of these resins. 2


29.

GRIFFITH

E T

A L .


481


Conclusions Epoxy resins which contain appreciable amounts of halogen absorb less water on a weight percentage basis than unhalogenated resins. Resins which contain bromine or chlorine, and are suitable for filament winding, often yield composites more resistant to fatigue under water than similar composites produced from common resins. Other than resin composition, glass content in G R P appears to be the most significant factor which i n fluences underwater fatigue life. Halogenated glycidylamines appear particularly promising as matrix resins for G R P subject to stress under water. Literature Cited (1) American Society for Testing and Materials Designation D 2344-65 T, ASTM Standards, Part 26, p. 499, 1967. (2) Dissen, I. J., U. S. Patents 3,235,569 (Feb. 15, 1966) and 3,366,602 (Jan. 30, 1968). (3) Farah, B. S., Gilbert, E. E., Sibilia, J. P., J. Org. Chem. 30, 998 (1965). (4) Griffith, J. R., Quick, J. E., ADVAN. C H E M . SER. 92, 8 (1970). (5) Kelly, P. B., Landua, A. J., Marshall, C. D., J. Appl. Polymer Sci. 6 (22), 425-532 (1962). (6) Kohn, E. J., Sands, A. G., Clark, R. C., Ind. Eng. Chem., Prod. Res. De velop.7,179(1968). (7) Newey, Η. Α., U. S. Patent 3,449,375 (June 10, 1969). RECEIVED January 16, 1970.


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