New market for thermoplastics

A notable trend is the scramble to develop fiber-reinforced thermoplastic offsets to established thermoset FRP rebar. Several companies (each declined comment for this article) are reportedly working with a variety of technologies that range from thermoplastic tapes and fiber winding to pultrusion of basalt fiber-reinforced thermoplastics. It is possible that the basalt/thermoplastic product could be produced in exceedingly long lengths and wound onto large spools at or near large civil engineering projects (e.g., sizeable buildings or long stretches of concrete pavement). This would enable crews to lay the rebar out in continuous sections with fewer breaks or splices than are necessary with steel rebar.

Only one developer was willing to talk about its new fiber-reinforced thermoplastics technology. Stephen Bowen, president of Plasticomp LLC (Winona, Minn.) and the inventor of the patented and trademarked Pushtrusion process, revealed that a new patent was issued on Aug. 9 for his newest process innovation, which builds on five previous patents related to the Pushtrusion process. The machinery joins a continuously reinforced tension member to a discontinuously reinforced wrap that complements the tension member.

The two-layer molding process begins with Plasticomp’s Pushtrusion process, where continuous fibers are pulled into a stream of high-pressure and fast-moving molten resin. A rotary cutter, positioned in the flow path, is programmed to cut the fiber/resin mix into shorter lengths. Further downstream, a mixing screw combines the chopped fibers and resin into a consistent molten and extrudable compound. Typically, this compound would be used in a conventional injection or compression molding process. But in this case it is injected into a cross-head die. There, continuous fiber strands are pulled through the die where they are first impregnated with resin (via a conventional pultrusion), and, immediately thereafter, is encased in the molten compound created by the Pushtrusion process, which forms a discontinuous fiber-reinforced resin sheath. The resulting composite can be cut to specified lengths or spooled to permit onsite cutting.

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