Thesis (M.Eng.)--Chulalongkorn University, 2000

The aim of this research is to study the possibility in recycling plastic wastes of high density polyethylene (HDPE) crates used for soft-drink bottle transportation. The raw materials are HDPE crates produced under the same condition, which has been used for bottle transportation for 8, 3 and 0 years, respectively. The properties of plastic crates including the mechanical and physical properties, the processability and the degradation of polymer were studied systematically. It was found that the melt flow index, %elongation at break, flexural strength at yield and impact resistance were decreased with increasing utilization time. This could be a result from the photo-oxidative degradation occurred, leading to changes in the structure of polymer molecules. The poor properties of post-used HDPE crates can be improved by blending with two types of modifying agents, stabilizer "Recyclossorb 550" (R550) and ethylene vinyl acetate copolymer (EVA). The addition of EVA (5% and 15% by weight) in post-used HDPE crates has stronger property improvement than that of R550 (0.2% and 0.4% by weight) in post-used HDPE crates. The blends of post-used HDPE crates with EVA showed a remarkable increase in %elongation at break and impact resistance. Furthermore, the blends of post-used HDPE crates with modifying agents had been recycled to produce caps for beer keg by injection process. These products were inspected and shown to satisfy the customer requirement standard.