All-PP Composites Could Challenge GMT In Markets

All-polypropylene composites, a recent development, are being considered for a broad range of thermoforming applications in diverse markets such as automotive, luggage, and sporting goods, among others. The materials could become formidable competitors to glass-mat-reinforced thermoplastics (gmt).London-based BP was first to reach market with its Curv composite, and in April, at the JEC composites exhibition in Paris, industrial yarns supplier Lankhorst, in Sneek, Netherlands, unveiled its Pure product. Both Curv and Pure consist of pp reinforced with pp tape. Although they are suitable for several processes, they are expected to see most use in thermoforming.Rick Johnson, general manager of BP’s Curv business, based in Gronau, Germany, says a 5000-tonne/yr production line was brought onstream last year. “The plan is to seed the market from here,” he says, with capacity to be added when required.Curv sheet is made using hot-compaction, in which the surfaces of highly drawn fibers in the fabric are melted and then recrystallized, forming a matrix that holds the fibers in place. Curv has strength and stiffness levels similar to gmt-pp, but higher impact strength, abrasion resistance, and elongation at break. BP acquired exclusive global patent rights for hot-compaction technology developed by the University of Leeds (England) and commercialized by BTG plc, in London.Though it was marketed as a standalone thermoformable sheet, Johnson says much of the interest in Curv is its application in sandwich structures, with foamed plastics (pp and others) or paperboard as inner materials and Curv on the exterior to provide stiffness or other properties. It is also being considered as a coating on aluminum and other metals to realize abrasion resistance, or as a core material to improve puncture resistance.Mercedes-Benz is considering Curv for thermoformed vehicle undershields, and processors are testing it as an insert molding material for local reinforcement in injection-compression and compression molded parts. Though Curv melts at about 175°C, injection is rapid enough that the Curv insert is not negatively affected and still offers sufficient strength and stiffness that glass-fiber levels can be reduced.Curv’s pricing is grade-dependent, but is usually twice the level of gmt, Johnson says. He emphasizes, though, that part weight usually can be reduced by 40 to 50%, so Curv is cost-neutral on a systems basis.Lankhorst is an established industrial yarns supplier. It is entering the thermoplastics market and working with thermoformer Linecross, Rutland, England, to develop automotive parts. Much of the development for Pure was done in conjunction with researchers at Queen Mary College (part of the University of London) and at Eindhoven University of Technology in the Netherlands, says Hans Jacobs, a Lankhorst director.Jacobs says compression molding of Pure is feasible, but thermoforming — especially automotive parts — is the target market. He did not provide pricing details, but says the pp tape costs much less than carbon fiber.Each tape is wound of three layers of pp, with the outer layers melting at a lower temperature than the inner one. “That way, during processing, the outer layers melt enough to facilitate processing, but you retain the strength and e-modulus of the inner layer,” explains Jildert De Rapper, managing director. Jacobs says, “You have the [0.8] density of pp, compared with 1.3 or so for fiber-reinforced pp, at lower weight, plus higher stiffness and better abrasion resistance.” The processing window of the material is between 135°C, at which point the outer layers of the tape start to melt, and 180°C, when the core layer begins to melt.Pure is gray or white in color. Lankhorst is currently offering only test amounts. Should some of the automotive projects come to fruition, Jacobs says the firm will likely license the technology for tape manufacturing to manufacturers that could ensure global production and availability. Plastics as well as venture-capital firms have expressed interest, he says.[email protected]