There is dispute over the relative merits of oxo-degradable and biodegradable polymers in applications where lifetime control is required. While considerable attention has been paid to litter and the ultimate degradability of plastic items, precise control of the time taken to degrade and lose mechanical properties has been considered of less importance than biodegradability as given by the rate of production of carbon dioxide. One of the more challenging applications for controlled lifetime degradable polymers is thin, transparent agricultural crop propagation films which are partly buried and stretched to form a mini-greenhouse and so enable early germination and growth. Degradation must be synchronized with the emerging crop as shown below for the ideal case (a) compared to where degradation has occurred either too slowly (b) or too quickly (c):  Oxo-degradable polyolefins based on photo-initiation and accelerated hydroperoxide decomposition through transition metals fatty acid additives provide the best control of above-ground degradation. Biodegradable polymers such as aliphatic (PHA and PLA) and mixed aliphatic-aromatic (PBAT) polyesters offer superior below-ground degradation but the two systems are often antagonistic and do not form compatible blends. Furthermore the photochemistry of humic acids in the soil may accelerate photo-oxidation of the polyolefins so that the photodegradation may not be simply modelled. This application is one where the best attributes of both oxo-and bio-degradable polymers are required and the challenges in meeting this are considerable.

Challenges in lifetime control of oxo-degradable polyolefins and oxo-biodegradable blends

248th National Meeting (2014)

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