Threshold temperature luminescent indicators from biodegradable poly(lactic acid)/poly(butylene succinate) blends

In this work, a new thermal stimuli sensitive multiphase polymer system consisting of a bio-related mixture of poly(lactic acid) (PLA, 85 wt%) and poly(1,4-butylene succinate) (PBS, 15 wt%) was prepared by the controlled incorporation of moderate amounts (<0.2 wt%) of 4,40-bis(2- benzoxazolyl)stilbene (BBS, a food-grade dye). Films obtained from the blend with less than 0.2 wt% of dye showed after melt mixing luminescence typical of monomeric BBS chromophores (blue emission). Composite films containing 0.07 wt% of BBS (the highest concentration allowing dye monomeric dispersion) appeared extremely sensitive to thermal solicitations when annealed at temperatures higher than PLA's Tg (>60 to 70 C) leading to a clear change of the emission properties due to the occurrence of dye aggregation. Thermal analysis by DSC showed an evident connection between blend morphology features and luminescence response. The results are here discussed with reference to the transition temperatures of the two polymer phases and their effect on aggregation/disaggregation of dispersed BBS.