New materials plentiful for composites.

Advanced-composite processors and their suppliers, no longer able to rely on shrinking aerospace and defense contracts, struggle to re-orient themselves to new commercial and industrial markets. Despite--or perhaps because of--this upheaval, there was no lack of new technical developments at the recent SAMPE Symposium and Exhibit in Anaheim, Calif. A host of new resins, prepregs, molding compounds, reinforcements, foam and honeycomb cores, and other materials for advanced composites were introduced. (Next month, Part II will cover new equipment and processing techniques.)

NEW CYANATE ESTERS

A new cyanate ester resin system, EX-1515, from Bryte Technologies, Milpitas, Calif., is said to be unique in that it can achieve an extremely high level of conversion after a 250 F cure. This level of conversion is said to result in optimal mechanical properties, high radiation resistance, low moisture absorption, and low outgassing while retaining high toughness, low (244 F) stress-free temperature, and long out time. It's also said to resist micro-cracking after extreme thermal cycling and high radiation exposure. Low dielectric/loss values are similar to other polycyanates, Bryte says.

Two other new cyanate esters from Bryte Technologies include EX-1505 and EX-1509, both intended for high-temperature applications. They have Tg's of 599 F and 635 F, respectively, and EX-1509 has UL 94V-0 flammability rating. Both reportedly provide easy, low-pressure curing at 350 F and good ablative performance at 700-800 F. (CIRCLE 44)

Cyanate esters are a new class of resins for Ciba-Geigy Matrix Resins, Hawthorne, N.Y., which purchased the AroCy line from Rhone-Polenc Specialty Resins. AroCy resins have Tg's from 482 F to 554 F. (CIRCLE 45)

Ciba-Geigy also recently acquired Rhone-Poulenc's Keramid BMI products, combining them with its own Matrimid BMI line. These resins are rated at 450 F continuous service under dry conditions and 350 F wet. (CIRCLE 46)

Meanwhile, Shell Chemical Co., Houston, has made two recent acquisitions of lines of specialty epoxy resins and curing agents. The products came from Hi-Tek Inc., a subsidiary of Rhone-Poulenc, and from the former Schering Berlin Polymers Inc.

NEW RTM RESINS

A line of resin systems for RTM was introduced by Ciba Polymers, Hawthorne, N.Y. Each system is said to exhibit high mechanical strength with varying degrees of load-carrying capability at higher temperatures. All systems have low viscosity and sufficient pot life for RTM processing.

* GY 282/HY 310 bisphenol F epoxy offers fast cures for parts that can be injected with a short processing window. It can be fully cured at 300 F and offers a hot/wet service temperature of 180 F.

* GY 282/HY 5200 bisphenol F epoxy offers a wide processing window and is suited to injecting large parts. It can also be injected at 350 F for fast cures of small parts. Hot/wet service temperature is 250 F.

* MY 721/HY 5200 multifunctional epoxy, a high-performance system, offers a large processing window and hot/wet service temperature of 250 F.

* MV 723 multifunctional epoxy is a one-component system that can be processed at 230 F and combines superior mechanical performance with hot/wet service at 250 F.

* Matrimid 5293 is a one-component bismaleimide system processable at 260 F. It's said to deliver very high mechanical properties with hot/wet service at 350 F. (CIRCLE 47)

A low-temperature-curing epoxy prepreg designed for producing large, thick structures has been introduced by Ciba Composites, Anaheim, Calif. It's aimed at low-pressure molding processes in typical "industrial" (non-aerospace) molding environments. Features of the new M10E material include curing temperature of 185 F, high flow, low viscosity, progressive tack, and an outlife of 60 days at room temperature. Tg is 261 F maximum. It's available on glass, carbon, aramid, and hybrid reinforcements. (CIRCLE 48)

A new low-viscosity, liquid tetra-functional amine-based epoxy resin, called Epon HPT Resin 1077, was introduced by Shell Chemical. It's said to provide "outstanding" mechanical and thermal resistance for composites and tooling, though few technical details were available. (CIRCLE 49)

New from Cemota of Lyons, France (represented by IFP Enterprises, Inc., N.Y.C.) is Syntorg IP 960 pre-imidized polyimide for composites, available as a powder or solution in diglyme with a high solids content. In addition to high heat resistance, advantages reportedly include low toxicity of the pre-cyclized polyimide (which does not contain any free aromatic amines) and long shelf life of either the polyimide solution or prepreg. Cured resin has a Tg of 599 F and shows a 1% weight loss in air (post-cured) at 815 F. (CIRCLE 50)

HARDENERS FOR FAST CURES

A new aromatic diamine from Ciba Polymers reportedly permits rapid, low-temperature (300 F) curing of multifunctional epoxies for aerospace castings, laminates and adhesives. This MDA-free curative is based on diamino diphenyl sulfone (DDS). It is a high-melting solid in micronized form, which can be combined with epoxy resin in a slurry that affords long tack-free time or room-temperature latency. Compared with a system cured with Ciba-Geigy Hardener HT-9664 (also based on DDS), the new diamine cured at 300 F instead of 350 F and gave good green strength after curing at only 250 F, plus improved strength and modulus (dry or water-conditioned, cool or hot) and decreased water absorption. (CIRCLE 51)

New epoxy Research Curing Agent, RSC-2215 from Shell Chemical is a low-viscosity, liquid aliphatic amine that gives fast cures at room temperature. Resins cured with RSC-2215 are said to have low viscosity, low color, and good mechanical properties, toughness, and chemical resistance. (CIRCLE 52)

Other news in hardeners includes a new polymeric anhydride that can be used to formulate very impact-resistant epoxies, developed by Ricon Resins, Inc., Grand Junction, Colo. Ricon 130MA13, a liquid polybutadiene maleic anhydride adduct, is said to toughen unmodified systems with no change in the formulation. (CIRCLE 53)

NEW SILICONE PREPREGS

A new SM8000 family of prepregs containing the S-826-A silicone resin system is offered by BP Chemicals (Hitco) Inc. Santa Ana, Calif. This stem was specifically formulated to resist direct flame impingement. Low thermal conductivity and ceramic characteristics of these products are said to provide excellent fire-barrier materials for aerospace and industrial applications.

The SM8000 series can be conventionally fabricated like other organic resin systems (3-hr cure at 275-375 F). Then, after post-curing at over 750 F, the matrix resin converts to an inorganic ceramic, which can withstand 1100-2200 F. The material has even withstood short-term testing at 4500 F, according to the company. (CIRCLE 54)

HIGH PERFORMANCE SMC 

Sheet molding compound (SMC) systems based on high-performance thermosets can be alternatives to prepregs, offering less labor-intensive, lower-cost component manufacturing and wider design freedom, to Quantum Composites Inc., Midland, Mich., a subsidiary of Premix Inc. New SMC materials that have been added to Quantum's product line include a polyimidester SMC, based on a resin supplied by DSM. Earlier this year, a method was developed to thicken the resin, which is reportedly moldable under conditions similar to those of typical SMC. The polyimidester SMC is said to have a higher onset-of-decomposition temperature than polyester or vinyl ester SMCs.

A phenolic triazine SMC, using a phenolic-based cyanate ester, is expected to be available from QCI shortly. It's said to have an impressive onset-of-decomposition temperature of 887 F, as well as a high char level of 62%. Another new system is phenolic SMC, one of the few materials to meet the FAA smoke and heat-release specs with the OSU test (see PT, April '93, P. 13). QCI has also made SMC of epoxy and PMR-15 polyimide. (CIRCLE 55)

MORE ECONOMICAL TP COMPOSITES

Several recent developments at ICI Fiberite, Tempe, Ariz., are said to open up new opportunities for thermoplastic advanced composites where materials costs have been a limiting factor. Improvements include ICI's ability to manufacture its APC-2 PEEK prepreg with longer continuous lengths between splices and defects. Continuous lengths of up to 250 ft are now made of 12-in.-wide sheet and up to 1000 ft for narrower tapes.

In addition, ICI is using a new grade of PEEK that's made on a larger scale and is therefore less expensive. APC-2A prepreg using this polymer is identical in properties to APC-2 but costs approx. 10% less. As shown in the graph on p. 28, further cost reductions are possible using different matrix polymers--such as polyethersulfone (PES), polyetherimide (PEI), and PPS--or "commercial"-grade carbon fibers like Hercules' AS4C in place of aerospace grades like AS4. (CIRCLE 56)

WATER-BASED RELEASE AGENTS

New semi-permnanent water-based release systems, Mono-Coat 341W and slightly denser 342W, have been formulated by Chem-Trend Inc., Howell, Mich., for molding aerospace prepregs and other thermosets. The releases may be used on metallic and plastic tooling, and may be heat- or room-temperature cured. They're said to give low transfer of release agent and good high-temperature stability. And they're ready to use as shipped. (CIRCLE 57)

Two new Frekote water-based semi-permanent release agents, Aqualine C-200 and C-210, have been developed by Dexter Corp.'s Automotive Materials Div., Seabrook, N.H. They contain no CFCs or chlorinated, aromatic, or petroleum-based solvents and are capable of releasing all thermoset composites, the company says. C-200 can be applied to molds at up to 400 F. C-210 Touch-Up is designed for applications where a hot-mold (above 140 F) back-up is required or where spray application is used. (CIRCLE 58)

NEWS IN REINFORCEMENTS

Owens-Corning Fiberglas Corp., Toledo, and Lockheed Fort Worth Co., Fort Worth, Texas, jointly presented data demonstrating that Owens-Corning's new Hollex S-2 hollow glass fiber (see photo) provides composite mechanical and dielectric properties virtually identical to those of quartz fiber, but at one-sixth the cost. At 60% fiber volume in cyanate ester laminates, Hollex fiber gave 9% lower density than quartz fiber at equal stiffness. Hollex also gave 16.5% lower density than standard S-2 glass, as well as lower dielectric constant. Hollex thereby appears to be a cost-effective substitute for quartz in electrically transparent structures such as radomes. (CIRCLE 59)

Another new option for radomes, "electromagnetic windows," circuit boards, and stealth applications is a low-dielectric D glass fiber from Vetrotex France, now available in the U.S. from Erskine Johns, Los Angeles. Composites made with D glass are said to have the same level of dielectric performance as quartz-fiber composites. The fiber is available as yarn or roving with a new sizing chemistry, VP216, that reportedly provides good compatibility with BMIs, cyanate esters, epoxies, and phenolics. (CIRCLE 60)

New lines of Conform fabrics, which do indeed conform to complex molds in RTM and other processes, were introduced by JPS Glass Fabrics, Slater, S.C. In addition to the aramid and graphite Conform fabrics introduced last year (PT, July '92, p. 31), JPS has new hybrids of quartz and thermoplastic liquid-crystal polymer fibers. (LCP fibers, called Vectran M, come from Hoechst Celanese Corp., Charlotte, N.C.) The hybrid fabric is, in effect, a "dry" prepreg, in which the resin fibers melt, flow, and form a thermoplastic composite matrix at autoclave and vacuum bag moldng temperatures above 525 F. (CIRCLE 61)

JPS is also developing a fabric from hollow quartz fibers. It is expected to offer lighter weight and lower dielectric constant than solid quartz fibers, while maintaining the same strength, JPS says. JPS is also developing fabrics based on Owens-Corning's Hollex hollow S-2 glass. (CIRCLE 62)

A new high-strength PAN carbon fiber, T800/42X12K, will be introduced by Amoco Performance Products, Alpharetta, Ga., during the third quarter of this year. The fiber will have a tensile strength of 800 kpsi and tensile modulus of 42 Mpsi. (CIRCLE 63)

A newly developed "2.5-D" fabric, developed at Katholieke Universiteit in Leuven (Louvain), Belgium, is said to provide cost-effective, impact- and delamination-resistant composites.n e 2.5-D fabric is derived by slicing a 3-D fabric (one with vertical warp or pile yarns) horizontally in two. The result is a sort of "hairy" fabric--two weft "skins" of the original 3-D fabric with cut pile yams protruding in the third dimension. Fracture toughness tests of the 2.5-D fabric showed better results than a plain-weave fabric and performance better than or equal to 3-D fabric.

Heat-dissipation properties of electronic packaging materials can be improved with a combination of aluminum nitride particles and silicon carbide whiskers, according to a paper presented by Lin Li and D. D. L. Chung of the State University of New York at Buffalo. The mixture of particles and whiskers showed higher conductivity than either one alone and also greatly reduced the polymer's thermal-expansion coefficient. The high aspect ratio of the whiskers also increased the toughness of the composite.

RECYCLABLE HONEYCOMB

New thermoplastic honeycomb core products have been developed by Hexcel Corp., Pleasanton, Calif. These include CeCore, a low-cost, recyclable, high-strength honeycomb product. CeCore is currently supplied in PE and PP, though it will be available in other polymers later this year, Hexcel says. (CIRCLE 64)

Hexcel also showed new polyimide honeycomb core products, including HFTG-327, a high-temperature product with mechanical properties said to be similar to aluminum. A new HFTGP-327 carbon-polyimide honeycomb core is said to have thermal conductivity equivalent to aluminum. Both of these core materials have been qualified for use on the Boeing 777 project, the latter in an engine application. (CIRCLE 65)

Hexcel has also developed HRH-427 woven glass honeycomb. It can be used for 700 F service. (CIRCLE 66)

A lightweight, rigid, high-temperature-resistant polyimide foam has been developed by Cemota (distributed by IFP Enterprises). Syntorg IP 1960 Cemofoam is recommended for critical aerospace and marine applications including cores for sandwich composites, heat or cryogenic insulating layers, and fire barriers. Cemofoam has a Tg above 572 F, onset-of-decomposition temperature of 716 F, and compressive strength of 420 psi. It's available in densities from 4 to 31 lb/cu ft. (CIRCLE 67)