Triethyl citrate-based oligomeric plasticizers for poly(lactic acid)

Poly(lactic acid) (PLA) is a bio-based, biocompatible, biodegradable polymer that can be produced from renewable resources including starch from corn and potatoes, sugar from beets and sugar cane. Poly(lactic acid) and its copolymers have attracted significant attention in environmental, biomedical, and pharmaceutical applications and as alternatives to petroleum-based polymers. Due to the relatively high glass transition temperature (55°C) and low crystallization rate which respectively result in a brittle behaviour and low production efficiency, the use of a plasticizer is critical to meet technological requirements. Low molecular weight plasticizers show migration issues over time while blending PLA with lower Tg polymers may result in phase separation. Our approach to tackle those issues was to synthetize a novel type of plasticizer containing an oligomeric PLA chain to which a triethyl citrate functionality is grafted as end-chain group. This system guarantees maximum compatibility with the polymeric matrix while still providing an improvement in the material properties. Triethyl citrate (TEC) is a bio-based and biocompatible compound so the “green” properties of PLA are retained. Synthesis and characterization of the plasticizer are described in this research project. The thermal properties of the plasticizers have been investigated using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Upon addition of the plasticizer PLA shows a decrease in the glass transition temperature and an increase in the crystallinity which results in a higher storage modulus.