The diversity of products that contain polyethylene (PE), polypropylene (PP) and polystyrene (PS), as well as the varying levels of additives, such as fillers and colorants that are in the materials, makes recycling difficult. But a company that produces waxes, additives and other chemicals from recycled plastics has patented an approach to extract more value from waste PE, PP and PS.
The process, patented by GreenMantra Recycling Technologies Ltd., Brantford, Calif., involves heating waste plastics, together with a solvent, in a reaction vessel, in some cases to temperatures of up to about 800 degrees Fahrenheit. The reaction vessel is then depressurized to remove contaminants suspended in the solvent, and the remaining materials are cooled.
“Supercritical Fluid Extraction has the potential to efficiently remove contaminants from polymers without a risk of thermal oxidation and/or degradation of the polymer material,” GreenMantra’s patent states.
In addition to PE, PP and PS, the process could be used to derive value from waste ethylene vinyl acetate, polyethylene terephthalate and polyvinyl chloride, and both virgin and recycled plastics. “Suitable waste plastic material feeds can include, but are not limited to, mixed polyethylene waste, mixed polypropylene waste, and/or a mixture including mixed polyethylene waste and mixed polypropylene waste,” and products such as plastic bags, milk containers, pails, caps, agricultural film and packaging material, the patent states.
Some of the products that can be made from the depolymerized plastics include surface polishers and protectants, adhesives, lubricants, asphalts, inks, coatings, extruded products, plastic composites, emulsions and binders.
Patent 10,723,858; issued July 28