Investigation of hydrocyclones for the separation of shredded fridge plastics

The recycling of fridges produces a mixed plastic product of limited value. In order to maximise its value, the separation of the individual polymers that include high impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC) and polyethylene (PE) must take place. The effectiveness of a hydrocyclone system for the separation of these plastics, using both water and calcium chloride solutions, has been investigated. In addition a qualitative procedure for the determination of the HIPS content of a mixed ABS/HIPS product, by selective dissolution in R-limonene, has been developed. It was found that the effective density of separation depended on the particle size and aspect ratio. As the particle size and aspect ratio decreased, the separation became more efficient and the offset between separation density and hydrocyclone medium density decreased. This suggests that, for efficient density separation, closely sized, fine plastic fractions are required. Using these criteria, it was found that the removal of high density plastic such as PVC was readily achieved using a hydrocyclone. A partial separation of HIPS from ABS was found to be possible, taking advantage of a small density difference, using a hydrocyclone medium density of 1035 kgm−3.