SMC, RTM, pultrusion, recycling highlight SPI Composites meeting.
There will be two presentations dealing with low-pressure molding compound (LPMC) technology for SMC. This relatively new process offers compression molding pressures as low as 150 psi and a stable maturation viscosity profile over a period of months, according to a paper coauthored by National Composites Inc. (NCI), South Bend, Ind., and Owens-Corning Fiberglas Corp., Toledo, Ohio. NCI is licensed to make and sell LPMC using technology from Scott Bader Co. Ltd.of England (see PT, April '90, p. 36; Jan. '93, p. 27;
April '93, p. 36). Owens-Corning's participation in this paper suggests a possible future role in marketing LPMC, but company spokesmen indicated that it was premature for them to comment. (Ashland Chemical Co., Columbus,
Ohio, is also working on low-pressure SMC materials.)
The key to LPMC is a special crystalline polyester resin from Scott Bader, used in combination with a standard polyester. This Crystic Impreg resin is a solid below its melting point of about 130 F. LPMC is both compounded and molded abovethat temperature, at which LPMC flows easily. But when cooled, the crystalline polyester solidifies, mechanically thickening the compound without use of chemical thickener. Thus the compound viscosity remains stable for long periods,insensitive to temperature and humidity.
A second paper on LPMC by NCI notes that this thickening technology can be applied to SMC of phenolic and methyl methacrylate resins. NCI also reports thatLPMC tooling requires a shear edge to seal off the mold around the part perimeter. In addition, lower molding pressures translate into wider options in mold materials--e.g., steel, nickel shell, or aluminum--and resultant tooling
IMPROVING SURFACE QUALITY
New low-profile additives for SMC/BMC and other processes will be another theme at the conference. An additive technology will be introduced by
Reichhold Chemicals Inc., Research Triangle Park, N.C., in association with its Japanese parent, Dainippon Ink & Chemicals Inc. The companies decline to provide details on what's described as a new "fine, white powder" shrink-control additive that enables compression molding of onyx-like BMC
parts with good translucency, precise dimensions, and reduced microcracking. A key characteristic of the additive that distinguishes it from other low-profile agents is a refractive index matching that of cured
polyester BMC. Union Carbide Chemicals & Plastics Co., Danbury, Conn., will discuss two recently developed thermoplastic additives designed to minimize problems of hazing and mottled pigmentation in various composite processes. Y-13066 is a pelletized dispersion of carbon black, designed to provide shrinkage control, good deep-black color and superior surface quality in vinyl ester SMC. XLP-4530 is a liquid designed for internal pigmentation of unthickened "wet-mix" formulations, such as pultrusion and preform molding, where it reportedly offersnear-zero shrinkage and minimal hazing.
Akzo Chemicals Inc., Dobbs Ferry, N.Y., will present initial results of a research program studying the interaction of low-profile additives with peroxideinitiator activity. LPAs reduce peroxide activity to varying degrees. Of severalLPAs tested, an SBS block copolymer showed the least cure-retarding effect. Diffracto Ltd., Windsor, Ont., is developing a new noncontact surface-profile height measurement system for plastic parts, based on the company's "D Sight" technology and its TPS-2 hardware platform. The new ZMAP system adds an absolutemeasure of waviness height, whereas the D Sight systems quantifies waviness in arbitrary units. ZMAP is described as a "user-friendly" system
that operates automatically after a test plaque is fixtured, and generates a contour map of surface heights within a 9 x 9 in. measurement area in
about one minute. OTHER SMC/BMC NEWS
A new heat- and corrosion-resistant SMC/BMC resin for under-hood automotive applications will be introduced by Reichhold Chemicals. Reichhold says its new Polylite 31620, a polyester "hybrid" based on dicyclopentadiene (DCPD), exhibitspredictable, consistent thickening characteristics, enhanced glass wet-out, and the ability to accept high filler loadings while retaining a medium viscosity. BMC test formulations contained calcium carbonate and alumina trihydrate to achieve a UL 94V-0 flammability rating. After immersion in motor oil at 320 F for 30 days, a test plaque of the hybrid material revealed equal or better retention of its initial mechanical properties relative to a vinyl ester control. The same was true of plaques exposed to air at 320 F for 30 days.
A paper on computer modeling of shrinkage and warpage of thin SMC parts continues the thrust by several academic groups into computerized SMC process simulation. A paper from the Polymer Processing Research Group in the Dept. of Mechanical Engineering at the Univ. of Wisconsin-Madison reports on successful experimental verification of their simulation model.
UPDATE ON SMC RECYCLING
There continues to be keen interest in technical advances for recycling of thermoset composites--especially automotive SMC. An entire session of six paperswill be devoted to the topic, including presentations on research and commercialefforts in the U.S., Canada, Japan, and Germany.
ERCOM, a consortium of four German SMC manufacturers, will offer details on its two-year experience in recycling SMC. The group began production of SMC recyclate in early 1992, selling back most of its product to SMC makers. In thatperiod, the ERCOM partners commercially processed about 4 million lb of SMC--about 500,000 individual auto parts--containing reground SMC recyclate. Theconsortium is establishing quality guidelines for utilizing the SMC recyclate and projects a sustained, moderate growth in usage of recycled material. A paper from the Institute of Plastics Technology in Erlangen, Germany, reports that when up to 14% by weight of fine-ground SMC is used to replace calcium carbonate filler, no change is seen in static or dynamic properties. At higher levels, the glass fibers can exert a "sieving" effect on the recyclate particles, causing stratification within the SMC.
A new method to recycle uncured SMC via a solvent-separation system will be introduced by Owens-Corning, Eagle-Picher Industries Inc., Joplin, Mo., and Chemical Solvents, Cleveland. The system was developed on behalf of the SMC Automotive Alliance as an alternative to the uncertain economics of pyrolysis recycling. The alliance seeks to recycle all 22 million lb of uncured SMC generated annually by its 10 molder members, which currently goes into landfills.
The new system, which was judged technically viable, involves chemical treatmentof uncured SMC in a solvent bath with mechanical agitation, permitting physical separation of resin, filler, and glass, all of which may potentially be reused. Solvent can be recycled by distillation.
Owens-Corning will discuss "closed-loop" recycling of glass fibers by reclaimingglass from reground composites, remelting it, and producing new
glass fibers. The reclaimed glass may also be used directly--one application would be in mixed-plastic recycle where glass serves as a "mechanical compatibilizer" providing improved properties.
Kyoto Institute of Technology and Fukui University in Japan will jointly presentfindings on the recyclability of stampable glass-mat polypropylene composites. The researchers' concept is to recycle the PP composite sheets without chopping or degrading the continuous-fiber reinforcement. They experimentally recycled a bumper beam by cutting it into several large pieces and then heating and pressing the pieces into sheet blanks that could be used to make new parts. The paper discusses a new heating system using both infrared radiation and forced convection to soften the cut-up pieces of recycled parts. The RP Waste Recycling and Treatment Council of the Japan Reinforced Plastics Society will discuss successful tests involving recycling ground SMC auto parts.Among the alternatives tried were mixing it into polyester resin concrete as a replacement for calcium carbonate or aggregate, adding it to gypsum cement as a reinforcement; and adding it to cement mortar as a substitute for silica aggregate.
ADVANCES IN RTM
Resin transfer molding (RTM) also will receive considerable attention at the conference, particularly in the optimization of methods to eliminate voids and enhance fiber/resin wet-out. One paper will present "a new molding strategy" forstructural RTM that utilizes a twin injection system. Representatives from the Kyoto Institute of Technology say this method was effective in eliminating voidsfrom epoxy/glass composites. Twin injectors also permit two different resin types to be injected into a mold simultaneously or with a controlled time lag. The process could combine different gating configurations (e.g., fan and pinpoint) and could be used to impart different properties to certain areas of apart or to apply in-mold coatings.
Kyoto researchers also report that in tests of conventional single-injector RTM molding, one central pinpoint gate yielded fewer voids in epoxy/glass parts thandid fan gating at one end of the part.
Reichhold Chemicals will discuss the optimum filler particle size for RTM. Aftertesting calcium carbonates from 1 to 21 micron average particle size, Reichhold concluded that 6 microns gave the lowest paste viscosity, most stable
suspension, and best flow through glass mat.
Miles Inc., Pittsburgh, will outline its work on the development of polyurethaneRTM systems used to produce components in high-performance applications. In addition, the latest progress in achieving scientific understanding of RTM processing and preforming variables will be presented in four papers from Ohio State University's Dept. of Chemical Engineering, Columbus; Ecole Polytechnique in Montreal; University of Nottingham, England; and Hitachi
Chemical Co. of Japan.
NEWS IN PULTRUSION
Reichhold Chemicals Inc. will report on an improved pigmentable, low-profile resin system for pultrusion, which provides superior pigmentability, surface characteristics and physical properties. Reichhold executives note that traditional low-shrink/low-profile additives suffer from poor pigmentability andcompatibility.
Using a hybridized dicyclopentadine (DCPD) polyester resin, Reichhold is developing modified polystyrene and styrene-butadiene copolymer additives with functional end groups. Early test results indicate these additives greatly improve pigmenting and resin compatibility while retaining shrinkage and profilecontrol. Reichhold says further development study is needed on processing parameters, filler types and particle size, glass fibers, pigment composition, and mixing conditions.
A joint presentation by the Pittsburgh-based firms of PPG Industries Inc. and Indspec Chemical Corp. will discuss innovations in phenolic pultrusion using Indspec's resorcinol-modified phenolic resin and PPG's phenolic-compatible rovings, as well as stitched fabrics made from the PPG rovings by Advanced Textiles Inc., Pittsburgh. The two firms examined alternative mat reinforcementsin phenolic pultrusion, characterizing the processing,
mechanical, and water- and heat-aging properties, while also exploring the effects of various fillers--including phenolic regrind. The study
concludes that biaxial stitched fabrics offer better processing and mechanical properties than continuous-strandmat.
Finite-element analysis (FEA), process modeling, and thermal-analysis methods will be examined for their potential real-world commercial benefits to the pultrusion processor by Joseph Sumerak of Pultrusion Dynamics Inc., a new pultrusion R&D firm in Oakwood Village, Ohio. He describes practical applicationof FEA for complex pultrusion geometries in order to optimize die mass, die material properties, and location of heat sources and sinks.
Sumerak says pultrusion processing conditions traditionally have been determinedon the factory floor through undocumented trial-and-error methods. However, he says some processors recognize the benefits of a more scientific characterization of processing behavior that Sumerak developed while at Pultrusion Technology Inc., Twinsburg, Ohio. Known as the "process exotherm" method, his technique helps determine the position of reaction within the pultrusion die (see PT, Feb. '84, p. 13; March '85, p. 83).
While it poses some limitations, this technique does represent the state of the art for on-line thermal process characterization. In his paper, Sumerak investigates more advanced off-line modeling of the pultrusion process as an alternative to on-line experimental methods for process optimization. He reviewstwo primary approaches to describe the exothermic reaction behavior of resins inpultrusion: empirical and mechanistic computer process models.
A new resin flow model that incorporates shear-thinning behavior was developed to improve understanding of thermoplastic pultrusion. It will be presented jointly by researchers from the Univ. of Delaware's Center for Composite Materials at Newark and Rensselaer Polytechnic Institute, Troy, N.Y. By predicting resin backflow at the die entrance, the computer model is able to predict die pressures and required pulling forces. Experiments with PEEK/carbon fiber and PP/glass agreed reasonably well with the model's predictions, which
the authors say can be useful for thermosets, too.
Venus-Gusmer, Kent, Wash., will both give a paper and display in the exhibition a new system for spraying or pouring polyester foam (PT, Nov. '93, p. 62).
Unlike several chemical systems that have been tried over the years, this one issaid to eliminate problems of toxicity, sensitivity to ambient conditions, and excessive exotherm generation. Venus-Gusmer's Mechanically Blended Foam system uses a proprietary, nonreactive cell stabilizer as a resin additive and a special pumping system that continuously mixes carbon dioxide gas into the resinas it flows to the spray gun or other dispensing head. Short glass fibers can bechopped into the foam with no rollout. One other paper is aimed at boat builders. Cook Composites and Polymers, Kansas City, Mo., will advocate use of Xycon polyester/urethane hybrid resins
as barrier coats between the gel coat and glass laminate. (Xycon resins were acquired by Cook from Amoco Chemicals.) The barrier coat is
intended to prevent fiber print-through, but the unusual toughness of Xycon hybrids reportedly also increases the impact strength of the gel coat. The hybrid's high molecular weight gives it the hydrolytic stability to prevent blistering, Cook says, and its low shrinkage means it can be used to flood tight corners without pulling the gel coat as it cures.