Background

In modern society, plastics are widely used across numerous sectors due to their lightweight nature, durability, and low cost. However, this has led to the generation of substantial plastic waste. Among this waste stream, low-grade plastics – such as mixed plastic waste, food packaging films, printed films, and paper mill reject strands – present a significant challenge. Their complex composition and high contamination levels make them traditionally difficult to process, posing a major environmental problem.

Recycling methods

1. Energy Recovery via Pyrolysis:
Pyrolysis is a vital energy-recovery pathway for low-grade plastics. When dried mixed plastic waste undergoes pyrolysis—a thermal decomposition process in an oxygen-deprived, high-temperature environment—its polymer chains break down. This triggers a series of chemical reactions converting it into liquid fuels like diesel. This process not only significantly reduces plastic landfill volume but also transforms persistent plastics into usable energy, alleviating energy shortages. The resulting pyrolysis oil can be further refined into diesel suitable for industrial boilers and diesel generators, enabling resource circularity.

2. Conversion to Refuse-Derived Fuel (RDF):
Producing RDF offers another efficient utilization route. RDF is a standardized fuel manufactured by processing solid waste (including shredding, drying, and blending). Low-grade plastics, with their inherently high calorific value (typically 25-35 MJ/kg), serve as ideal feedstock. Mixed plastics and food packaging films can be shredded, dried, and blended with other combustible wastes to produce stable, high-energy RDF. This fuel is widely used in waste-to-energy plants and cement kilns (co-processing), partially replacing coal or natural gas. It reduces energy costs while achieving waste reduction and safe disposal.

3. Material Recycling through Pelletization:
Mechanical recycling into pellets remains a fundamental route for material recovery. Despite higher contamination levels in mixed plastics or printed films, processes like sorting, shredding, washing, and extrusion can remove impurities (dirt, paper, oils). The resulting recycled pellets, while potentially having slightly lower performance than virgin resin, are suitable for manufacturing non-critical plastic products like pipes, netting, or strapping. This extends plastic lifecycles, reduces reliance on virgin plastics, and lowers petroleum consumption.

4. Direct Molding into Products:
For lower-contamination or pre-processed low-grade plastics, direct compression molding provides a streamlined solution. This flexible process tolerates complex material compositions, forming plastic under high heat and pressure in molds. It efficiently produces durable items like pallets, containers, or chairs for everyday use. By bypassing intensive purification steps, this method offers lower processing costs and enables rapid upcycling of low-grade plastics.