Effectiveness of CO2-mediated pyrolysis for the treatment of biodegradable plastics: A case study of polybutylene adipate terephthalate/polylactic acid mulch film

Despite the widespread use of biodegradable mulch films, they are often unsuitable for disposal in open environments and cannot be recycled in the same manner as conventional plastics; hence, an effective disposal method needs to be suggested. Herein, pyrolysis of biodegradable mulch film made of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) was considered. The pyrolysis of the PBAT/PLA mulch film in CO2 yielded more non-condensable gases than the pyrolysis in N2 due to an enhanced thermal cracking of volatiles at 800 °C. At higher than 600 °C in CO2, reverse water-gas shift reaction considerably increased CO selectivity. Using CO2 in the pyrolysis suppressed the generation of wax and char, attributed to CO2 enhancing not only thermal cleavage of pyrolytic volatiles released from the PBAT/PLA mulch film but also O–H and C–H bonds existing on the substance. The CO2 pyrolysis agent forwarded the cleavage of the polymeric bond of PBAT to produce more monomeric compounds (e.g., adipates and phthalates), while it suppressed radical reactions to produce less polycyclic compounds and phenyls. Rising temperature raised the gaseous pyrolyzate yield and lowered the char and wax yields. The use of CO2 agents in pyrolysis has a significant feature of upcycling biodegradable plastic wastes.