| 英文摘要 |
Polylactic acid (PLA) has become a safe and green alternative for food packing application in recent years. Excluding the exported products and reused “post-industrial” materials, there are still 1,500 tons of PLA used in Taiwan and are mostly one-time use packagings. Since the recycled post-consumer PLA (PCR) from municipal solid waste (MSW) are often mixed together with PE, PET or PS, the process for PCR is the most complex and results in high impurity in PLA recycle stream. Moreover, the collected PLA wastes are typically deteriorated. This project focuses on the development of market orientated rPLA resin with two different grades: general purpose rPLA resin and injection grade rPLA resin. Finally, the injection molded products will be demonstrated. Waste PLA bales from the municiple solid waste (MSW) recyclers have been treated and sorted via the following processes: unpackaging and crushing, cleaning and dehydrating, NIR sorting. The impurity of the final sorted rPLA flakes was about 1.75% and the molecular weight of the rPLA flakes were typically downgraded from 190,000 of neat PLA (2003D) to ~140,000. The molecular weight was further degraded to <110,000 after melt and extrusion process because rPLA posseses higher moisture and more carboxylic functional group than neat PLA does. In this project, we developed a cost effective chain extender by copolymerization of glycidyl methacrylate and styrene monomers. The general purpose rPLA resin consisted of 0.6phr chain extender and 100phr PCR was produced using single screw extruder. Its molecular weight was ~170,000 and the mechanical properties were close to neat PLA. The tensile strength, flexural strength and impact strength was ~50MPa, ~93MPa and 0.45 ft-lb/in, respectively. The overall cost of general purpose rPLA resin was estimated to less than NTD 42/kg. The injection grade rPLA resin consisted of 50phr PCR, 10phr PIR, 0.4phr chain extender and 11phr talc was produced by a two step single screw extruder. The overall cost of the resin was estimated around NTD 65/kg.This resin showed good rheology for injection processing at 180~190℃ (melting index was 8~20 g/10 min). The respective tensile strength, flexural strength and impact strength of the resin was 61MPa, 105MPa and 0.55 ft-lb/in. The heat distortion temperature after annealing at 100℃ for 60s was 109℃.
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