Enhancing melt-processing and 3D printing suitability of polyhydroxybutyrate through compounding with a bioplasticizer derived from the valorization of levulinic acid and glycerol

Abstract

In the near future, polyhydroxybutyrate (PHB) may become a valuable widespread alternative to the conventional fossil-based commodity plastics, if drawbacks related to its melt-processability and mechanical properties are overcome. In this work, PHB disadvantages are mitigated by compounding with glycerol trilevulinate (GT) bioplasticizer. The additive synthesis has been studied and optimized, starting from bio-based reagents that are wastes from other productions. GT has shown a remarkable plasticizing effect, making it to compete with commercial green plasticizers, for which several health concerns have recently arisen. The hindrance of GT allowed to increase the free space among the polymeric chains, producing a reduction of the glass transition temperature of PHB of approx. 10 °C with only 5 wt% of additive. The same content of GT also decreases the typical high stiffness of PHB of approx. 30 % and reduces its melt viscosity of 28 %, which are similar or even better plasticization effects that can be obtained with commercial plasticizers. Moreover, GT has made PHB suitable for extrusion to obtain filaments and fabrication of complex architectures by injection-molding and 3D printing, importantly reducing the processing temperature from 200 to 180 °C, thus limiting the associated thermal degradation phenomena. This work opens a new approach based on polymer-compounding to simply mitigate the limiting properties of polyhydroxyalkanoates towards a new class of sustainable commodity plastics.