Thermal degradation of polylactide/aluminium diethylphosphinate

•Pyrolysis of aluminium diethylphosphinate generated dimeric four coordinate compounds.•Thermal stability of PLA in the presence of aluminium diethylphosphinate was decreased.•The decrease was mainly due to the interactions of diethylphosphinic acid.

Direct pyrolysis mass spectrometry analyses of polylactide, PLA, reveal two dominating decomposition pathways; chain homolysis and trans-esterification reactions under the experimental conditions yielding mainly low mass fragments and cyclic oligomers. The main pyrolysis products of aluminium diethylphosphinate, AlPi, are determined to be the dimeric four coordinate compounds possessing AlOP linkages. Thermal stability of polylactide in the presence of AlPi is decreased due to the attack of phosphinates groups on carbonyl groups. Eventually, extensive fragmentation of PLA takes place and generation of four coordinate dimeric compounds involving AlOP linkages is suppressed. On the other hand, strong evidence for generation of polyphosphinates is detected. Collision induced dissociation experiments are used to confirm the proposed structures.