High-purity monomer recovery from commercial engineering plastics by vacuum pyrolysis depolymerization

Abstract

Plastic waste pollution is one of the most pressing global issues. Addressing this challenge requires energy transformation through chemical recycling of waste plastics. However, recycling rates remain low. A primary reason for this is that chemical recycling has yet to establish a closed-loop system, largely due to the inability to recover monomers with sufficient purity for reproducing the original products. This study demonstrates that vacuum pyrolysis can recover monomers with purities high enough to produce their materials comparable to those made from pure monomers. Conducted at 1 mmHg and 420 °C, the pyrolysis recovered methyl methacrylate (MMA) with 95% purity and 87% yield. The recovered MMA was used to produce poly(methyl methacrylate) (PMMA) via radical polymerization, resulting in the PMMA with molecular weight characteristics almost identical to those of PMMA produced from pure MMA, with only a slight increase in low-molecular-weight oligomers. The vacuum pyrolysis also successfully recovered high-purity monomers from commercial products such as cross-linked polystyrene (PS), acrylonitrile/styrene (AS) resin and acrylonitrile/butadiene/styrene (ABS) resin. This simple and convenient method, which requires no additional purification or temperature control due to heating with a spirit lamp flame, has the potential to establish a chemical and economic closed-loop recycling system, offering a promising solution to reducing plastic waste pollution.