Solid State Shear Pulverization of Multicomponent Polymeric and Waste Materials
INVENTION: Northwestern researchers have developed the solid state shear pulverization of polymeric materials (S3P Process), converting thermodynamically incompatible polymers to particulates suitable for direct melt processing without added compatibilizing agents. The process has been operated at scale with a range of polymer mixtures including HDPE, LDPE, LLDPE, PP, PS, PET, PVC, polycarbonate, acrylonitrile butadiene styrene, polyphenylene oxide, and rubber.
ADVANTAGES: S3P provides an efficient process to recycle and upgrade mixtures of thermodynamically incompatible polymers to a feedstock suitable for direct melt processing without added compatibilizing agents. Resultant polymer blends exhibit improved processability without diminishing physical properties.
SUMMARY: Decreasing landfill space, rising disposal fees and cost of polymer feedstocks have significantly raised the potential value of recycled polymer materials. The present invention enables the conversion of mixed polymer streams into pulverized particulate feedstocks that are directly melt processable for product manufacture. A variety of thermodynamically incompatible polymers have been blended without the aid of compatibilizing agents. The process entails supplying flaked polymeric scrap, virgin polymers and mixtures to specially designed intermeshing extruder screws, provided with temperature control zones. The mechanical energy effects chemical change of the polymers under sufficient cooling to maintain the material in the solid state during processing. The compatibilized homogenous polymeric blends are directly melt processable, with improved processing properties, including a higher melt flow rate than the moldable base polymer, without sacrificing tensile strength, impact strength and elongation properties. The pulverized particulates are more intimately mixed than provided by melt mixing only and can be melt processed without a significant delay in achieving phase inversion. The resulting products exhibit a stable microstructure. Polymeric film waste derived from S3P output, containing high proportions of LDPE, yield molded articles of superior notched izod impact strength and elongation. Compatibilized polymeric particles can be formed with polymeric scrap containing cellulose materials including paper, cardboard and wood. The process has been operated at scale with a range of polymer mixtures and offers broad utility. S3P applications in polymer fabrication, polymer recovery and waste recycling have been demonstrated.
STATUS: The S3P process has been operated on pilot and commercial scale equipment. A series of patents covering the technology have issued and Northwestern University seeks partners to develop the invention.
U.S. Patent Numbers 5,814,673 , 6,180,685 , 6,479,003 , 6,494,390 , 6,797,216 , 6,818,173 , 6,849,215,
Klementina Khait, John Torkelson, Erin Riddick, Naomi Furgiuele
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