Alternative to glass shatters reinforced plastics recycling ideas

Looking for a low-cost, light alternative to glass- and natural-fiber-reinforced parts, Hans-Peter Fink of the Fraunhofer Institute for Applied Polymer Research believes he has found the answer in car tires.

His idea is to use cellulosic tire yarns in place of glass to reinforce commodity polymers, thereby achieving a value-added effect. Parts molded or extruded today with glass-fiber-reinforced polypropylene (GFR-PP) provide good strength, but they are heavy and do not recycle well.

Natural fibers, by contrast, recycle well, but their mechanical properties often fail to make the grade. The solution from the Fraunhofer researchers is to drench cellulose (Rayon) fibers in molten PP and use them as the reinforcing agent.

"Cellulosic yarn has the advantages of having very high strength, low weight, and particularly high impact resistance," says Fink, division director, natural polymers. "Add to these features better [mechanical] recycling possibilities, ability to incinerate, reduced abrasive wear on processing equipment, and you''ve got a great material."

Working with industry partners, Fraunhofer (Goim, Germany) has been marketing small-lot quantities of an injection moldable PP with a 25% Rayon mix, PPRayCo, for tests since November. The cellulose-reinforced PP is also a low-cost alternative to PC/ABS blends.

Stiffness, heat-deflection, and flammability behavior of the low-density material can be altered depending on the application''s demands by varying the fiber type and/or changing the additive package. The material targets non-load-bearing interior vehicle parts and housings for the electrical and electronics industry. No alteration to injection presses is required to mold PPRayCo and the good viscosity allows it to flow easily into complex geometries and ribbed molds.

Today the material is produced in a two-stage process at pilot compounding plant Dr. Pohl-Textil-und-Thermoplast (Forst) from homo- or copolymer PP and cellulosic fibers supplied by Cordenka (Obernburg), the same as those used to reinforce vehicle tires.

In the first step, a specially developed extrusion nozzle is used to coat the filaments with a mix of PP melt and a maleic anhydride coupling agent. The strands are water quenched, cut into 3- to 6-mm-long pellets, and dried.

In the second step, the compound is homogenized in a corotating twin-screw extruder before granulation and drying. The resulting compound is free-flowing and dust free. Fibers show a reduced tendency to break compared to glass. Fink says exterior vehicle parts are a possibility, along with applications such as extruded pipes and high-strength containers.

Fink admits the one drawback may be the complexity of the two-step process, giving the polymer a double-melt history. Therefore the three Fraunhofer Institutes working on the project are looking at the possibility of inline compounding and compression molding as an alternative.

Fraunhofer ICT (Pfinztal) is working with processing equipment maker Dieffenbacher (Eppingen) on a long-fiber thermoplastic direct compression molding (LFT-D) method to produce the reinforced materials inline from cellulose fiber rovings cut and added in a mixing extruder prior to injection or extrusion.

Europe''s third-largest automotive equipment supplier, Faurecia (Nanterre, France), is currently sampling selected interior parts from PPRayCo to test its suitability.

Faith in natural fibers remains

Paolo Pisoni, VP of Italian equipment maker Meccaniche Moderne (Busto Arsizio) nevertheless sees substantial opportunities for processors who concentrate on natural-fiber-reinforced thermoplastic vehicle part production. He says the sector is growing 15% annually. His company recently patented a process using a single-screw extruder to more gently mix the fibers without breaking them to produce long-fiber composite sheet with low-cost natural fibers.

In addition to natural fibers, Pisoni says the company is testing synthetics, such as polyester yarn, to determine their performance in making composite sheets for interior vehicle components. These and natural fibers provide recyclability, light weight, and lower cost than glass.

Robert Colvin [email protected]

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