Composites produced from waste plastic with agricultural and energy sector by-products

A three-stage route to chemically upcycle post-consumer poly(ethylene terephthalate) (PET) to produce high compressive strength composites is reported. This procedure involves initial glycolysis with diethylene glycol to produce a mixture (GPET) comprising oligomers of 2-7 terephthalate units followed by trans/esterification of GPET with fatty acid chains supplied by brown grease, an agricultural by-product of animal fat of relatively low nutritional or fuel value. This process yields PGB comprising a mixture of mono-terephthalate ester derivatives. The olefin units provided by unsaturated fatty acid chains in brown grease were crosslinked by an inverse vulcanization reaction with elemental sulfur to give composites GBSx (x = wt% S, varied from 80%-90%). The compressive strengths of GBS(80) (27.5 +/- 2.6 MPa) and GBS90 (19.2 +/- 0.8 MPa) exceed the compressive strength required of ordinary Portland cement (17 MPa) for its use in residential building foundations. The current route represents a way to repurpose waste plastic, energy sector by-product sulfur, and agricultural by-product brown grease to give high strength composites with mechanical properties suggesting their possible use to replace less sustainably sourced legacy structural materials.