Hydrolytic degradation of biodegradable poly(butylene adipate-co-terephthalate) (PBAT) - Towards an understanding of microplastics fragmentation

The long-term behaviour of PBAT subjected to hydrolytic ageing is investigated in this paper. Samples were aged in water at several temperatures ranging from 80 to 100 degrees C for different durations. Changes in physico-chemical properties were investigated through NMR, GPC, DSC and X-Ray analyses and embrittlement was assessed by tensile tests. It is demonstrated that hydrolysis of PBAT occurs first on the ester group located between the terephthalate and adipate groups leading to a decrease in molar mass. For longer ageing durations, the ester situated within the adipate group undergoes hydrolysis. An increase in crystallinity ratio and a decrease in amorphous layer thickness was observed as consequences of the chain scission process. Finally, a clear change in mechanical behaviour is noted; for the early stages of ageing, the polymer exhibits a ductile behaviour while for longer ageing durations, the polymer is brittle due to a lack of chain entanglement. This transition takes place once the molar mass of PBAT falls below 11 kg/mol, i.e. when a critical molar mass M'(c) is reached.