A STUDY OF COMPATIBILISERS FOR RECOVERING THE MECHANICAL-PROPERTIES OF RECYCLED POLYETHYLENES

When polyethylenes are recycled, 'contamination' by small amounts of o ther residual polymers can occur, following incomplete separation in t he waste stream. The tolerance of polyethylenes to the incorporation o f such contaminants has been investigated using extrusion compounded b lends of virgin polymers. In some cases (e.g. adding LDPE to HDPE) mec hanical performance was little affected. However, the Charpy impact st rength of HDPE (of most relevance to the performance of thick-walled a rticles) fell substantially on adding 5-10% PP, or as little as 1-2% H IPS, uPVC or PET. The impact performance of LLDPE was substantially re duced on adding only 2% PP. The scope for counter-acting property loss by adding commercially available 'compatibilisers' to the mixtures wa s also investigated. An EP random copolymer and a very low density pol yethylene (VLDPE) were both found to offer cost-effective solutions fo r PE blends containing PP. The impact performance of LLDPE/PP and LDPE /PP blends was fully recovered at only 2 pph addition, while HDPE/PP b lends required up to 10 pph. The impact performance of HDPE containing HIPS could be completely recovered by adding around 10 pph styrene-et hylene butene-styrene (S-EB-S) random copolymer, but at high cost.