Plasticizer migration in bloodmeal-based thermoplastics

Abstract

Tri-ethylene glycol (TEG) is an effective plasticizer for many protein-based thermoplastics because of its low volatility, however, partial miscibility with the protein matrix may still lead to some phase separation. Spatial variation of TEG concentration in bloodmeal-based thermoplastics as a result of processing was investigated using synchrotron-based FT-IR micro-spectroscopy. Although TEG forms strong hydrogen bonding with proteins, for the protein to fold into β-sheets bound plasticizer must be released. TEG can then migrate, pooling into localized areas, rich in plasticizer. Further heating causes further migration towards the edge of plasticized bloodmeal particles where the TEG may evaporate. Thermo-gravimetric analysis confirmed that loss of TEG by evaporation may occur at 120°C, given enough time for diffusion. Efficient mixing combined with a short residence time at elevated temperature mean significant plasticizer loss is unlikely during processing. However, it does limit long-term use at elevated temperatures.