Long-term properties and migration of low molecular mass compounds from modified PLLA materials during accelerated ageing

Abstract

The durability of polylactide during accelerated ageing and the entire degradation process were significantly altered by different low molecular mass additives and stereocomplexation. The samples were aged in air at 60 °C and 90 °C and the degradation process was followed by monitoring mass loss, molar mass, presence and formation of low molecular mass compounds, changes in surface structure and thermal properties. Stereocomplexation increased the long-term durability of polylactide materials. Mass loss and molar mass changes also indicated that addition of TiO2 nanoparticles had a stabilizing effect at higher temperature and during longer exposure times. Interestingly addition of linear lactic acid oligomers resulted in lower mass loss compared to materials containing cyclic lactide oligomers. This is interpreted as a result of stronger interactions between the linear oligomers and PLLA chains, resulting in slower migration rate, which was also shown by ESI-MS analysis. However, the linear oligomer additives accelerated the molar mass decrease, probably due to the catalytic effect of the end groups. The stereocomplex displayed the greatest resistance towards degradation, a consequence of strong secondary interactions.