Current research progress of physical and biological methods for disposing waste plastics

Overuse of plastic products has caused serious hazards to ecological environment, and effective technologies were needed urgently to overcome the drawbacks of existing methods. Mechanisms and representative studies of physical and biological methods to dispose plastics were summarized in this review, and the advantages and disadvantages of both methods were pointed out. Physical treatment of plastics involved the extrusion or deformation of plastics, which were subsequently used in virgin plastics, construction, concrete and some composites. This disposal method was simple and non-polluting, but has limited fields of application. Biodegradation of plastics could be achieved by microorganisms (fungi, bacteria and algae) in the ecosystem, undergoing colonization, biodeterioration, biofragmentation, assimilation and mineralization, eventually converting plastics into CO₂ and H₂O. Conditions for biodegrading plastics were mild and products were non-polluting, but the process was very slow. From the results, single method for treating plastics has certain limitations, and combining different methods has become hot topic of study. Such as the combination of physical and chemical methods could improve the miscibility of polymers or modify plastics to produce copolymers. Plastics could be pretreated by heat or ultrasound to reduce the hydrophobicity and activation energy of the reaction. Moreover, combining biodegradation and photodegradation of plastics was also an effective way to improve the degradation efficiency of plastics.