RESEARCH Why Not Nonglass Reinforcements? Cotton, synthetic fibers, p a p e r — a l l o f f e r promise in reinforcing plastics, if research will p o i n t the w a y JL H E
MOST
POWERFUL
FACTORS
in
bringing about the present wide acceptance of glass for reinforcing plastics are t b e research effort t h a t has gone into solving related problems and the sales drive of a few aggressive firms." In these terms, Johan Bjorksten called for greater research effort to develop cotton, synthetic fibers, paper, and asbestos as reinforcers. T h e president of the Bjorksten Research Laboratories does not discount the advantages of glass fiber in reinforcement of rigid type plastics for structural applications, but he feels other materials also offer advantages. For example, many a resin manufacturer has considered cotton reinforcement but has discarded it because he obtained less strength and poorer moisture resistance than with glass fiber. But, says Bjorksten, if someone h a d a real incentive to improve the status of cotton (it is now used mainly with phenolic and melamine resins), he would: • Remove oils on the surface of commercial cotton fibers. • Develop a surface treatment to secure firm adhesion between cotton and plastic. • Select (or develop) plastics with elasticity and elongation keyed to those of cotton. • Develop technical service data and provide specialized personnel for helping fabricators use cotton to best advantage. • Synthetic Fibers. Glass fiber has high tensile strength b u t is also stiff and brittle and has relatively poor shear characteristics. There are a number of synthetic fibers, however, which possess relatively high strength, are less stiff and tougher t h a n glass fiber, and can be machined with less tool wear. Bjorksten says reinforcement of plastics with these fibers offers advantages in applications requiring improved resistance to abrasion, erosion, and flexing, as well as high strength. By matching the stress-strain characteristics of the fiber with those of the plastic, it might also be possible to reinforce thermoplastic materials such as the new low pressure poly ethylenes. 1702
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Nylon, Dacron, a n d Orion offer these advantages as reinforcers: • Toughness. • Resilience. • Excellent electrical properties. • Good chemical resistance. • Lighter weight than glass fiber. • Good bonding properties with resins. • Superior surface finish. Their greatest disadvantage is their high initial cost. Lower heat resistance than glass fiber (which shows n o loss in strength a t 475° F. and 5 0 % at 685° F.) could also b e listed as a -disadvantage, but Bjorksten says all three of these fibers are actually very resistant to heat degradation and h a v e melting or softening temperatures of over 450° F. T h e fact that synthetic fibers can be easily bonded into uniform nonwoven structures by mechanical means eliminates the need for binders a n d lubricants, which introduce problems with glass. However, because of the bulk of these structures it is necessary to use some pressure for molding. Gunk, or injection molding with suspended fibers, seems particularly adapted to the nonabrasive, flexible, and easily flowable synthetic fibers. Turning next to rayon, Bjorksten at-
Excellent surface characteristics are obtained with molded products from lay-up of Du Pont's Orion reinforcing batts (resin a d d e d before mold closed)
tributes the limited use it has had for reinforcement of plastics largely to its poor moisture resistance. If this disadvantage could b e removed, possibly by n e w sizing or finishing procedures, the economical combination of light weight and high strength offered by various high tenacity rayons could b e utilized. Teflon fibers have a lower tensile strength than some fibers b u t have exceptional resistance to chemicals, heat, and moisture. Their strength is not affected up to 400° F . and in some a p plications to 500° F. But the present high cost of Teflon may prohibit their use in reinforced plastics, Bjorksten declares. • Paper. The low cost, availability, light weight, a n d excellent dielectric properties of p a p e r reinforcement promote their use where strength requirements are moderate. T h e y have been used mainly with phenolics and melamines for electrical and decorative laminates but also with polyesters to a slight extent. I n general, paper reinforcing m a t e rials provide lower strength than reinforcements made from textile fibers and have poor moisture resistance. As with cotton, it would b e desirable to have a treatment which w o u l d improve a d h e sion to the resin. At present, Bjorksten states, absorbent papers with a minim u m of size must be used t o obtain the best impregnation a n d thus the best electrical properties, but a t a sacrifice of strength properties. If high strength is desired, hard, nonabsorbent, highstrength paper must b e used, but these do not impregnate as well and have poor electrical properties. Other vegetable fibers such as sisal, h e m p , ramie, and jute have not been used to a great extent, even though they are strong natural fibers. T h e y are not easily wetted with resin and are quite readily broken down during processing. In addition, they have greater water absorption or are less available than other fibers. Again, says Bjorksten, proper sizing procedures m i g h t greatly reduce the moisture sensitivity of some of these fibers and improve their compatibility with bonding resins. ^ Inorganics. In addition to glass, other inorganic materials which can b e used for reinforcement of plastics are asbestos and metallic sheets and fibers. T h e relative cost of the metallic reinforcements is very high, however, and their use is limited to applications requiring special mechanical reinforcement, thermal distribution, or electrical shielding properties not obtainable with lower cost reinforcements. Asbestos has been used for many years, mainly with phenolics and melamines. Bjorkstein lists these advantages: resistance to high temperature, nonflammability, low cost, widespread
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9,
1956
C&EN
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RESEARCH
T h e Book You'll Want For R e a d y R e f e r e n c e ! '•; INewly published technical d a t a covering Z o n o l i t e vermiculitei's " p h y s i c a l a.nd chemical properties" the wide range of information you need t o fit this versatile mineral i n t o y o u r manufacturing and processing p a t t e r n .
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VERMICULITE Product o f Z o n o l i t e Company Zonolite verxniciilite is t h e remarkable mineral witti many unique characteri s t i c s of i n t e r e s t t o r e s e a r c h mend e s i g n e r s , a n d p r o d u c t developers N e w book d e s c r i b e s c h e m i c a l a n d p h y s i c a l p r o p e r t i e s . Countless u s e s , including: • Fertilizer conditioner • Carrier of insecticides, herbicides, fungicides, fumigants • Cushioning material • Insulation of liquid air storage vessels
availability, good chemical resistance, and water resistance; it also imparts high flexural modulus. Its disadvantages are brittleness, poor resistance to abrasion, higher specific gravity than organic fibers, and poorer electrical properties than cellulose paper or glass, unless special grades a r e used. T h e strength properties of present commercial plastics reinforced with asbestos fabric are generally considered s o m e w h a t lower than t h o s e of plastics reinforced with glass fabric, according t o Bjorksten. T h e use of asbestos in mat or felt form, however, should result i n very high strength properties and offers promise of meeting t h e demands of extreme temperatures a n d stress encountered in high speed aircraft and guided missiles. Also of interest is t h e reinforcing affect of non glass, nonfiber compounds, such as silica particles t r e a t e d with b u t y l alcohol so t h a t butyl radicals prot r u d e from t h e silica surface. As little as x / 2 % may e n h a n c e the flexural strength of laminates w i t h glass fabric b y a s much as 10%. T h e reason app e a r s to b e t h a t t h e silica increases the modulus of t h e resin, a n d thus brings a b o u t a closer matching o£ the moduli of trie resin and glass, which in turn l e a d s to a more favorable stress distribution under load, a n d thus to overall strength. These examples, Bjorksten told the 12th annual national technical conference of the Society of Plastics Engineers, a r e only indicative of the advantages a n d disadvantages which must be considered in promoting t h e wider use
of nonglass reinforcements. Some have an overshadowing advantage for a specific application, but for them to attain the same general acceptance as glass fiber, other related properties must be worked out t o a corresponding degree.
New Light on Collagen Study of helica! structures of proteins can aid understanding key biological processes PHILADELPHIA.-The building blocks of collagen fibrils, t h e major components of the body's connective tissue, exist in solution a s rodlike molecules 3000 A. in length a n d 14 A. in diameter, says Harvard's Paul M. Doty. I n his recent Edgar F a h s Smith Memorial Lecture, he outlined details of structure a n d properties of collagen, as well as various other helix-coil transitions. His talk w a s jomtly sponsored by the ACS Philadelphia Section and the University of Pennsylvania» Collagen molecules, millions of which m a y b e present in every fifc>ril, are of essentially uniform size. In cross-sectional structure, these molecules closely resemble t h e x-ray structure of t h e fibrils in t h e solid state, as recently described by F . H. C. Crick, A. Rich, a n d others. Collagen molecules can b e reconstituted from solutions to form once again t h e collagen fibrils of characteristic structure. E a c h collagen molecule consists of three helical polypeptide chains t h a t have been hydrogen-bonded to one an-
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Zonolite verrmculite, readily available from our 4 0 plants is a granular crystalline mineral of low d e n s i t y . Possesses high tfciermal a n d a b s o r p t i v e properties, and is available i n a wide r a n g e of particle sizes. Send today for free book and inspection sample.
ZONOLITE
COMPANY
135 So. La Salle St., Chicago 3, 111. Zonolite Company, Dept. CEN 46 1 3 5 S o . La Salle Street, Chicago 3,11L. D Please send me my fzree copy of your readyreference book, "Zonolite Vermiculite CXhemical and Physical Properties." D Please send sample of processed vermiculite. Name Firm Address ! City Zoxi _State.
1704
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APRIL
9.
1956
Prior to his E d g a r F a h s Smith Memorial Lecture, Harvard's Paul M. D o t y (center) chats with Glenn E . Ullyot (left), c h a i r m a n of the ACS Philadelphia Section, cosponsor of the event, a n d R. E. Hughes, c h a i r m a n of t h e lecture committee
