Investigation of Gas Release from Recycled Plastic Shopping Bags during Melting at Low Temperatures

Abstract

Recycling plastic is an excellent way to reduce the environmental impact of its production and use. In a circular economy, recycling of recycled plastic is necessary. Most plastic bags are made of thermoplastic, like high-density polyethylene (HDPE) with a melting point of 130°C, and low-density polyethylene (LDPE). In contrast, recycled plastic bags are made up of many different unknown substances. In this study, the melting of used plastic bags containing 80% unknown recycled material was investigated. FTIR analysis showed that the bags consisted mainly of HDPE. The bags were melted at 160°C, 200°C, and 250°C for 30 min. GC-FID and HP-SPME GCMS analyses showed that the bags released flammable gases (methane, ethylene, and alkane/alkene hydrocarbons) but little acetylene. Aromatic and aliphatic hydrocarbons eluded from the bags at 10% of the gas volume at 250°C. Long-chain alkanes, mostly hexadecane, were the dominant compound, amounting to 28% at 160°C and increasing to 43% at 250°C. On the other hand, alkenes decreased with a rising temperature (23% at 160°C to 3% at 250°C), as they were transformed into alkanes. Methylated compounds, for example, methylated alkanes at 10%, were present at all temperatures. Methane and methylated compounds are released from plastic and contamination of the bags with organic matter. The bags released small amounts of toxic phthalates. The results show that melting recycled plastic bags for remoulding is promising if safety precautions that ensure sufficient ventilation are utilised.