Polymer-Fibrous Glass Composites: Advances and Potential Properties

28 Polymer-Fibrous Glass Composites: Advances and Potential Properties

Downloaded by NORTH CAROLINA STATE UNIV on May 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0099.ch028

FRED G. KRAUTZ Owens-Corning Fiberglas Corp., Technical Center, Granville, Ohio 43023

The 1960-1970 decade marked the "start of something new" for fibrous glass composites. A remarkable growth in RTP (reinforced thermoplastics) occurred. Chemically tailoring a polymer with the sole intent of combining it with fibrous glass is now a reality. In the thermoset area, SMC (sheet molding compound) and BMC (bulk molding compound), including low profile systems, are getting general industry acceptance. A partial explanation for all the activity with fibrous glass composites is stated in terms of polymer property improvements resulting from the addition of glass. Consideration is also given to the importance of polymer chemistry in obtaining adhesion to glass. Potential strengths are given for a selected system based on a theoretical model.

T t always seems fitting at the start of a new decade to look back on the *** previous one. The topic of fibrous glass composites is no exception. As a clarification, the term fibrous glass composites as used here refers to thermosetting and thermoplastic molding resins reinforced with fibrous glass. Fiber glass reinforced plastics have reached an important milestone. This industry has grown from relative obscurity to a market which has reached the 1 billion pounds of laminate per year level. Also significant is the milestone reached by R T P . This segment of fibrous glass composites is nearing 10% of the entire F R P (fiber glass reinforced plastic) volume. More importantly, essentially all this volume in R T P was generated i n the last decade. The difficult task i n treating this type of subject matter is i n the selection of material. It is impossible to cover everything significant. Omissions are not intentional but unavoidable. The technical highlights are stressed. 452 In Multicomponent Polymer Systems; Platzer, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.


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Polymer-Fibrous Glass Composites

453

T w o specific areas are covered more comprehensively: fibrous glass polyesters and fibrous glass thermoplastics. The advances in reinforced polyesters have been in the materials and process areas. These changes are more profound than those related to mechanical properties. Hence, a treatment of mechanical properties of reinforced polyesters is not attempted. O n the other hand, the reinforced thermoplastics advances are essentially in terms of many new reinforced polymers as well as a greater variety of compounds. For these reasons, it seems appropriate to discuss advances in this area in terms of properties. To give perspective to these technical developments, end-use applications are used to illustrate them. The use of actual parts is hopefully an effective aid in covering such a broad subject. Advances in Terms of Applications One of the most effective ways to gage the advances in a particular field is through the commercial realities based on the new technology. The applications listed below illustrate the technical growth of a diversified industry which has fibrous glass as its common denominator. (1) H i g h appearance exterior polyester parts spanning the width of a car. This is in the form of a combination upper grille and lamp housing as well as lower grille panels. (2) H i g h appearance polyester automotive headlamp housings. (3) H i g h appearance polyester automotive air scoops. (4) Complex structural polyester parts of various appliance applications such as air conditioners and humidifiers. (5) Underground gasoline storage tanks. (6) Polyester bathroom components. (7) Marine applications reflect a remarkable penetration for F R P . (8) Injection molded styrenics span the width of the car in the form of instrument panels and crash pad retainers. Shot weights approach 10 lbs in some cases. (9) Injection molded automotive shift consoles. (10) Injection molded polypropylene automotive tail lamp housings. (11)

Injection molded olefin fender liners for automobiles.

(12)

Injection molded complex appliance fans.

(13) Injection molded polypropylene parts which comprise the complete hot water distribution system for dishwashers. (14)

Injection molded washing machine housings.

(15)

Injection molded calculator housings.

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

454

MULTICOMPONENT POLYMER SYSTEMS

Advances in Fibrous Glass Thermosets


The materials and process development relating to sheet molding compounds ( S M C ) and bulk molding compounds ( B M C ) represent the most significant breakthroughs i n this broad field. The development of S M C and B M C in conjunction with the development of low profile polyester resin systems are contributing to a great amount of interest in glassreinforced polyesters. The addition of S M C and B M C to reinforced polyesters has changed the basic mechanical property picture very little. The same is true for low profile polyesters. The mechanical performance is at the same general level that is attained with the older wet systems, such as preform and mat, and premix molding. Sheet and Bulk Molding Compounds. The activity with S M C and and B M C is based on resin technology which was known more than 20 years ago ( 3 ) . The key concept involves increasing the viscosity of the unsaturated polyester resin. The polyester resin with an initial viscosity of several thousand centipoise is advanced chemically to a viscosity of several million centipoise. This thickening reaction is accomplished by using Group 2a metal oxides and hydroxides, such as calcium hydroxide. Although all the variables affecting this mechanism are not fully understood, it is generally accepted that the metal ion acts as a bridge between residual acid groups on the polyester chain. A t first, it may not seem significant to be able to increase the viscosity of a polyester resin without crosslinking it. The following points w i l l illustrate the advantages that such a system brings to molding reinforced polyesters: (1) The viscosity of the resin can be maintained at a much higher level in the heated mold. This allows the material to hold molding pressure, which results i n much improved surface finish. (2) There is little separation of fiber and resin during flow i n the mold. This is also attributable to maintaining viscosity. (3) Material efficiencies are high since the molding compound is charged within the confines of the mold. This results i n no flash waste. (4) The "mess factor" or dispensing a liquid resin onto a preform or mat is eliminated. (5) The handleability of the molding compound makes it more suitable for an automated molding process. The compounds are tack-free as ready to mold. The development of low profile polyester resin adds an additional dimension to S M C and B M C . The post-molding finishing steps with F R P have been a strong deterrent in high appearance requirement applications. The low profile resins utilize thermoplastic additives to obtain


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KRAUTZ

Table I.

Typical Mechanical Properties of Polyester BMC and SMC

Flexural strength, psig Flexural modulus, psig Tensile strength, psig Notched Izod, ft lbs/inch


455


BMC 20% Glass

SMC 30% Glass

19,000 1.5 X 10 7000 6

33,000 1.4 X 10 17,000 13

6

6

the very high quality as molded surfaces, and post-molding operations are essentially eliminated. For example, one of the commercial systems developed employs an acrylic additive in the polyester resin (7). This additive reduces polymerization shrinkage to the point where the fibrous glass pattern is essentially eliminated from the surface. The process by which S M C is made is usually based on fibrous glass in roving form. The polyester resin containing the catalyst system, mineral fillers, and the Group 2a metal oxide or hydroxide is dispensed onto polyethylene film. The roving is then cut onto the liquid resin. Since the thickening reaction has not started, it is easy to impregnate the cut glass. Compaction rolls then remove air while aiding in the wetting. After a relatively short aging time, the thickened S M C is ready for molding. B M C is processed by premix techniques, using the standard sigmablade mixer. The only change is the use of Group 2a metal oxides and hydroxides. Table I lists some properties of S M C and B M C . These are a function of resin composition, reinforcement, and molding conditions and may be regarded as typical. This w i l l serve as a frame of reference as to the property levels obtained with S M C and B M C . The differences which exist between S M C and B M C in tensile, flexural, and impact strengths are attributable to more than just the difference in glass loading. Fiber attrition arising from the compounding techniques for B M C as well as the shorter input fiber length account for the lower strengths. Advances in Fibrous Glass

Thermoplastics

The growth of these materials is reflected in the number of polymers which are being glass reinforced. These include polypropylene, polystyrene, styrene acrylonitrile, nylon, polyethylene, acrylonitrile-butadienestyrene, modified polyphenylene oxide, polycarbonate, acetal, polysulfone, polyurethane, poly (vinyl chloride), and polyester. In addition, the reinforced thermoplastics available now include long-fiber compounds, shortfiber compounds, super concentrates for economy, a combination of long and short fibers, and blends of polymer and fibrous glass.



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The acceptance of these materials largely arises from the property improvements obtained on adding glass. Table II shows some typical property improvements on adding 30% glass to polystyrene, nylon 66, and polypropylene. Both tensile and flexural strengths can be approximately doubled by adding glass. The modulus is improved by a factor of 3. The heat distortion improvements range from a modest 20 ° F for polystyrene to 140°F for polypropylene, to 2 8 0 ° F for nylon 66. Tensile and Flexural Properties of Thermoplastics. It is interesting to show graphically the effect of introducing reinforced thermoplastics on the properties available in injection molding materials. In Figure 1 tensile Table II.

Effect of Glass on Base Polymer Properties at 30% Glass Level Polystyrene

Tensile strength Flexural strength Modulus Heat distortion

1.9 1.5 2.8 +20°F

0

0

Nylon 66 2.1 2.1 3.3 +280°F

Polypropylene 1.8 2.1 3.1 + 140°F

°Strength numbers are ratios of properties of reinforced polymer to unreinforced polymer.

40r


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457

strength is used to illustrate this point. The range of tensile strengths for unreinforced polymers is ca. 2000-12,000 psig. The addition of 4 0 % glass extends this to around 30,000 psig for the highest strength polymer (upper line). The lower line shows the improvement i n the lowest strength polymer. The portion i n the figure above the dashed line then represents properties not attainable without glass reinforcement.


2.0

r

GLASS CONTENT, WT. % Figure 2.

Composite elastic modulus of thermoplastics

A similar situation is illustrated in Figure 2 for elastic modulus. Thermoplastics fall in a rather narrow range of 100,000-500,000 psig. This is extended to approximately 2,000,000 psig by using 4 0 % glass (upper fine). The lower line shows the effect for the lowest modulus polymer. The area above the dashed line is the contribution made b y fibrous glass to available properties i n injection molding. Figure 3 shows the effect on the available flexural strengths i n injection molding. The upper limit of approximately 20,000 psig is more than doubled by using fibrous glass. The area above the dashed line again represents an extension of available properties i n injection molding compounds.



458


Impact Strength of Reinforced Thermoplastics. Impact strength is a difficult topic to treat rigorously mainly because of the shortcomings of the most common test—notched Izod (12). The most serious shortcoming is the extreme complexity of the stress field which does not allow an accurate calculation of maximum local strain rates. The effect on impact strength of specimen width and the method of introducing the notch are two other factors which make it difficult to analyze data. It is important not to use notched Izod data as an absolute indicator of enduse impact performance. Special precaution must be taken in comparing notched Izod impact strength of an unreinforced polymer to its reinforced analog. One of the important considerations in describing impact behavior of reinforced thermoplastics is the markedly different stress-strain rela-

0

10

20

30

GLASS CONTENT, WT. Figure 3.

%

Composite flexural strength of thermoplastics

tionship. Figure 4 illustrates this for a linear polyethylene. The ultimate elongation of approximately 200% is reduced to approximately 3 % . A c tually, almost all reinforced thermoplastics with 20% or more glass w i l l fall in a 1 - 5 % range. Polymers that have a yield point, such as nylon and A B S , do not exhibit a yield point upon adding glass. Common to


28.

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459


all reinforced thermoplastics is low ultimate elongation regardless of polymer type. Another important factor i n relation to impact strength is illustrated in Figure 5. A brittle polymer and a tough polymer, polystyrene and A B S respectively, are used as an example. Their impact strengths differ by a factor of 32, with impact strengths of 0.25 ft lb/inch for polystyrene and 8 ft lbs/inch for A B S . The addition of fibrous glass is the great

GLASS CONTENT, WT. % Figure 4.

Effect of glass on elongation of thermoplastics

equalizer. A t the 2 0 % level, the impact behavior of the vastly different matrix resins is shown to be equivalent. This behavior is also seen i n a l l other brittle and tough thermoplastics. Generally, irrespective of the polymer, the addition of fibrous glass w i l l result i n a notched Izod impact strength ranging from 1.0 to 4.5 ft lbs/inch. A n important corollary to impact behavior of reinforced thermoplastics is shown i n Figure 6. T w o different A B S resins are used for this illustration relating to low temperature impact strength retention. The unreinforced A B S w i l l retain from 20-30% of its room temperature i m pact strength i n going to —20°F. The graphs for both the low and high


460


toughness A B S show the benefits obtained from fibrous glass. The low toughness A B S with 2 0 % glass actually retains 100% of its room temperature impact strength i n going to —20°F. Further, the low temperature impact strength of reinforced thermoplastics is equal to the room temperature impact strength. This is important since all unreinforced thermoplastics lose impact strength i n going to lower temperatures.


8

GLASS CONTENT, WT . % Figure 5.

Fibrous glass and impact strength of thermoplastics

D T U L at 264 psig (Heat Distortion) for Reinforced Thermoplastics. B y definition, thermoplastics have limitations at elevated temperatures. It is i n this particular property that fibrous glass can lead to remarkable improvements. However, a sharp division exists for reinforced thermoplastics. The various reinforced thermoplastics can be put i n two groups relative to D T U L . These consist of amorphous and crystalline or semicrystalline polymers. The amorphous polymers such as styrene-acrylonitrile, polystyrene, polycarbonate, poly (vinyl chloride), and acrylonitrile-butadiene-styrene are generally limited to modest D T U L improvements, usually on the order of 20 ° F with 2 0 % glass. However, crystalline polymers such as the nylons, linear polyethylene, polypropyl-



28.

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461

ene, and polyethylene terephthalate, can be increased remarkably. The case for nylon 66 and linear polyethylene is illustrated in Figure 7. Nylon 66 is raised from a D T U L of approximately 160°F to ca. 500°F, which is near its crystalline melting point. Linear polyethylene is improved from ca. 120° to ca. 260°F, which is also within a few degrees of its crystalline melting point. Although the D T U L temperatures do not translate directly to end-use temperatures, they serve as an indicator of much improved elevated temperature performance for reinfouced thermoplastics. Dimensional Stability of Reinforced Thermoplastics. Thermoplastics have relatively large linear coefficients of thermal expansion. This can

Figure 6.

Impact strength retention at low temperatures

lead to difficulties when plastic parts are used in combination with metal and where temperature extremes are encountered. This is, of course, magnified when large parts, such as a 5-ft wide instrument panel, are exposed to a surface temperature range of approximately 200°F. Figure 8 shows the effect of fibrous glass on linear coefficient of thermal expansion for A B S , one of the more dimensionally stable thermoplastics. The improvement in dimensional stability is on the order of


462


500 IYL0N 66 400


o.

300 CM

LINEAR POLYETHYLENE = 200 o

100

0

10

20

GLASS CONTENT, Figure 7.

x

30

40

WT. %

Composite DTUL at 264 psig

3

ABS o 2 o

in i

- 1

o 0

10

20


30

40

WT. %

Composite thermal expansion


28.

KRAUTZ

463


three-fold with 3 0 % reinforcement. This improvement is characteristic for a l l reinforced thermoplastics, with the effect of glass being more pronounced in some polymers than others.


Physical and Chemical Concepts of Fibrous Glass Composites In a discussion of why fibrous glass is used in combination with various polymers, two important questions must be answered. First, what properties of fibrous glass are responsible for its use in combination with plastics? Secondly, why does it work? Properties of Glass. Some important properties of fibrous glass are listed i n Table III. The 400,000-psig tensile strength and 10,000,000-psig modulus are the two key mechanical properties. When these are cornTable III.

Properties of " E " Glass

Tensile strength, psig Elastic modulus, psig Coefficient of thermal expansion, /°C Softening point, ° F Material class

0 I 0

• .25

• .50


400,000 10,000,000 5 X 10 ~1500°F Elastic - 6

• .75 VOL.

1.0 FRACT.

Composite elastic modulus (orientation considerations)


464



pared with typical tensile strengths and modulus numbers of 8000 psig and 500,000 psig, respectively for unreinforced resins, it is easy to develop a case for composite systems. Orientation effects are important in utilizing fibrous composites. The theoretical relationships are shown i n Figure 9. The greatest benefit is obtained with unidirectional fibers. The more common case i n practice is closer to the random orientation i n two dimensions. The theoretical modulus that is obtained i n this fiber configuration is one-third of the fully oriented composite. O f interest is the fact that glass is an elastic material. Thermoplastics are viscoelastic and, therefore, exhibit creep or cold flow. The use of glass is an efficient means of reducing creep. One of the shortcomings of thermoplastic materials is dimensional stability owing to the high coefficient of thermal expansion. Typically, this can be on the order of 50 X 10" cm/cm/ °C. The coefficient for glass is a much lower 5 X 10" cm/cm/ °C, and it is, therefore, effective in reducing dimensional changes. 6

6

A typical unsaturated unreinforced polyester resin has an extremely low notched Izod impact strength. The addition of fibrous glass can change this extremely brittle material into a high impact strength composite. The same phenomenon occurs with some brittle thermoplastics, such as polystyrene and styrene—acrylonitrile. In an oversimplication, it is the combination of high strength, high modulus, creep resistance, dimensional stability, and impact modification of the brittle matrices which leads to the selection of fibrous glass i n composites. Achieving Glass-to-Matrix Adhesion. This subject has been expanded upon i n several papers and is summarized well b y Sterman and Marsden (13). A review of some of the key concepts i n glass-to-polymer adhesion as it relates to thermosets and thermoplastics w i l l serve the purposes of this paper. The approach to obtaining adhesion is to use an intermediate chemical compound between the glass and the matrix. The bridging agents used are organofunctional silanes. These materials bond to the glass surface as well as to the matrix. The organosilane chemicals utilized i n glass composites are trifunctional silanes—i.e., they contain three hydrolyzable groups per silicon atom. Upon hydrolysis, the silanol group adheres strongly to the glass surface. The mechanism b y which this takes place is inherently difficult. The indirect confirmation is much better documented through mechanical property data.


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Polymer-Fibrous Glass Composites Table IV.

465

Ambifunctional Silanes

R—Si(OR')

3

NH (CH ) NH(CH ) — NH (CH ) — CH2=CH— HS(CH ) — C1(CH ) — 2

2

2

2

2

3

2


2

2

3

3

3

CH

3

CH2=C—C—(CH ) — 2

3

CH —CHCH 0(CH ) — 2

2

2

3

Adhesion to the glass surface completes only one-half of the bridge. The other half must adhere to the matrix. This mechanism is even more difficult to study. Again, direct confirmation is much easier to show through property improvements. Table I V shows some of the common functionalities for various commercial silanes. The adhesion of thermoplastic to glass cannot be explained by copolymerization of the coupling agent with the matrix. The polymers have essentially fully reacted. Chemical reactivity on the polymer backbone is now of interest. The picture is also more complex in that the number of polymers to be reinforced is much larger than for the thermosetting materials. Virtually every polymer which is being injection molded is also being used in its reinforced form. Several papers have been published on the effects of silane coupling agents in thermoplastics (4, 9, 10, 11, 14, 15). Silanes are very effective i n improving the strengths of fibrous glass thermoplastics. The functionality of the silane as well as time-temperature conditions in the molding cycles are of great importance. The area of question is on how much of this increase can be realized in an injection molding environment. The work of Sterman and Marsden and Plueddeman was carried out with glasscloth polymer laminates (10,11,14,15). In this way the effect of the silane could be optimized as to time and temperature of the molding cycle. Additionally, the glass was being used in its maximum strength form i n that it was continuous. A n additional factor is the absence of any shear forces. As an example, for a polystyrene laminate, the use of an epoxyfunctional silane increased the flexural strength 90% over the bare


466



glass control. The wet flexural strength improvement was an even greater 140%. To a producer of fibrous glass reinforcements it is distressing that the results demonstrated with glass fabrics could not be translated to glass subjected to an injection molding environment. T o account for this apparent anamoly, an investigation was undertaken ( 2 ) . The earlier experiments with fabric laminates were essentially duplicated with respect to time and temperature, and compression molding was used. The difference was i n the form of the reinforcement used. For this work, the glass and polymer were combined in a compounding extruder, and this compound was plasticized i n an injection molding machine. The molten compound was compression molded, and the mechanical properties were determined. Table V .

Shear Effects for Silane-Only Systems"

Property Improvements over Bare Glass

Flexural strength Wet flexural strength

Fabric Laminate, Continuous Fibers

High Shear History, Discontinuous Fibers

+90% + 140%

+ 10% + 10%

Polystyrene, 20% by weight glass, 32% for fabric laminate, epoxy silane compression molded at 500°F. c

Table V illustrates the results obtained by the experimental technique which essentially simulates injection molding while satisfying the time-temperature conditions effective i n the fabric laminate work. The large strength increases were reduced to only approximately 10% over the bare glass controls. The conclusion is that the high shear environment of injection molding which yields discontinuous fibers does not allow the same strength increases obtained in earlier experimental work. Table VI.

Reducing Shear Effects on Glass"

Property Improvements over Bare Glass

Flexural strength Wet flexural strength Tensile strength Notched Izod

Epoxy Silane Only

No Silane Film Former

Epoxy Silane Film Former

+10% + 10% + 10% +40%

+ 15% + 10% +30% +90%

+25% +30% +50% + 100%

°Polystyrene, 20% by weight glass, compression molded 15 min at 500°F.



28.

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467

In addition to the work using silanes only, the presence of polymeric material at the glass surface was investigated. Table V I illustrates the beneficial effects obtained by protecting the glass filaments with a polymer, commonly referred to as a film former. The combination of silanes with appropriate film formers was shown to be essential in developing satisfactory strength levels. The improvements still d i d not equal the fabric laminate results. However, the importance of protecting the filaments was illustrated when an injection molding environment is involved. Polymer chemistry is important in obtaining adhesion to the glass surface (Figure 10). The tensile reinforcement factor—the ratio of tensile strengths of the reinforced system to the matrix resin—is used as a measure of adhesion. T w o dissimilar polymers, polypropylene and nylon, are used to illustrate the importance of polymer chemistry. Polypropylene is an inherently difficult polymer to reinforce because of its nonpolar nature and lack of reactivity. Nylon, on the other hand, is highly polar and is one of the easiest thermoplastics to reinforce. The modified poly-


468


propylene refers to a polymer specifically developed to be used with glass ( I ) . It can be considered a second generation reinforced thermoplastic. The remarkable difference i n the ease of reinforcement can be attributed entirely to a chemical modification of the polypropylene.


Potential of Fibrous Glass Composites Thermosets. The potential of thermosets is not solely a function of mechanical performance. These materials have established themselves as suitable for many demanding environments. The potential must be measured i n terms of their ease of fabrication into parts. This is where limitations have existed for reinforced thermosets, specifically polyesters; this, in combination with the limitation related to the necessity of postmolding operations to obtain high appearance surfaces. W i t h the introduction of S M C and B M C which give much improved process techniques, the fabrication shortcomings have been largely overcome. The introduction of low profile resin systems has eliminated the costly post-molding operations for high appearance parts. Table VII. Theoretical Strength Model for Fibrous Glass Thermoplastics

V l l d T a a a/ a f

c

a

c

m

= = = = = = = = =

volume fraction of glass fiber critical fiber length actual fiber length fiber diameter shear strength of matrix resin ratio of actual to critical fiber length composite tensile strength fiber tensile strength matrix tensile stress at failure strain of the composite

The potential of these materials should then be a function of these two technical advances. It is entirely related to how well this technology is converted to general practice. Although additional progress i n materials w i l l be a factor, the existing technology can take reinforced polyesters a long way.


28.

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469


Thermoplastics. This segment of fibrous glass composites came out of its infancy in the 1960 s. The potential of these materials is tremendous because no new molding process technology is required. Advances w i l l be i n the area of materials performance.


If it were possible to develop a theoretical strength model for reinforced thermoplastics, it would be much easier to measure their poten-

GLASS Figure I I .

CONTENT,

VOL.

FRACT.

Effects of polymer chemistry—potential strengths of styrene

tial. It would then be possible to predict optimum strength levels. It appears that such a theoretical strength model exists for reinforced thermoplastics, based on the plastic stress transfer model for fiber reinforced metals (5, 6) (Table V I I ) . It is supported by experimental data for metals as well as for fibrous glass reinforced thermoplastics ( 8 ) . Using this strength model it is interesting to predict strengths of a composite, assuming satisfactory adhesion of matrix to glass. This was done with polystyrene, which is regarded as difficult to bond to the glass surface. Figure 11 shows the property improvements which could be obtained i n glass-reinforced polystyrene if improved adhesion could be achieved. It is suggested that a chemical polymer modification must be



470


made to attain the required adhesion. Since the feasibility of this has been demonstrated for polypropylene, the predicted strength levels could well be within reach. Glass-reinforced polystyrene points out that some reinforced thermoplastics have not reached their performance potential. The continuing activity i n developing improved reinforcements coupled with development work in the area of designing polymers to be chemically compatible with glass w i l l determine the true potential of these composites. Since less than 2 % of the thermoplastics injection molded in the United States contain fibrous glass at this time, the growth curve of these materials is highly unpredictable. It is estimated that these materials are growing at a current annual rate exceeding 25%. There is little doubt that a tremendous potential exists for these composites. Literature Cited (1) Cessna, L. C., Thomson, J. B., Hanna, R. D., SPE J. 25, 35 (1969). (2) Englehardt, J. T., Krautz, F. G., Philipps, T. E., Preston, J. A., Wood, R. P., SPI Reinforced Plastics Div. Ann. Tech. Conf., 22nd, 1967. (3) Frilette, Vincent J., U. S. Patent 2,568,331. (4) Hall, N. T., SPI Reinforced Plastics Div. Ann. Tech. Conf., 21st, 1966. (5) Kelly, A., Davies, G. J., Metallurgical Rev. 10 (37) 1. (6) Kelly, A., Tyson, W. R., J. Mech. Phys. Solids 13, 329 (1965). (7) Kroekel, C. H., Bartkus, E. J.,SPIAnn. Tech. Conf., Reinforced Plastics/ Composites Div., 23rd, 1968. (8) Lees, J. K., Polymer Eng. Sci. 8 (3), 195 (1968). (9) Murphy, T. P., "Abstracts of Papers," 150th Meeting, ACS, Sept. 1965, T12. (10) Plueddeman, E. P., SPI Reinforced Plastics Div. Ann. Tech. Conf., 20th, 1965. (11) Plueddeman, E. P., SPI Reinforced Plastics Div. Ann. Tech. Conf., 21st, 1966. (12) Stephenson, C. E., British Plastics 30 (3) 99 (1957). (13) Sterman, S., Marsden, J. G., Union Carbide Publ. F41920, 10M-368. (14) Sterman, S., Marsden, J. G., SPE Ann. Tech. Conf., 21st, 1965. (15) Sterman, S., Marsden, J. G., SPI Reinforced Plastics Div. Ann. Tech. Conf., 21st, 1966. RECEIVED February 25, 1970.


Polymer-Fibrous Glass Composites: Advances and Potential Properties

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