Hansen solubility parameters drive development of green plasticizers compatible with Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or PHB-co-HHx

Most “green” plasticizers have poor compatibility with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or PHB-co-HHx. Researchers at the University of Georgia New Materials Institute developed novel plasticizers derived from biobased furan-2,5-dicarboxylic acid (FDCA) that were compatible with PHB-co-HHx, utilizing Hansen solubility parameters as a guide. Of seven synthesized derivatives, the team found two to be promising plasticizers—dipropyl furan-2,5-dicarbocxylate (DPF) and di(2-ehtylhexyl) furan-2,5-carboxylate (DEHF)—and compared both to a conventional plasticizer in their study.  

Plasticizers are added by manufacturers to rigid plastics to make them softer and more flexible, and to gain other favorable properties. Globally, most commercially available plasticizers are phthalates developed for polyvinyl chloride, or PVC. Studies have demonstrated phthalates to be endocrine disrupters that negatively impact human and animal health. Predicting plasticizer performance when paired with a polymer can be challenging, leading the team to utilize HSP in guiding its selection of derivatives from FDCA.  

In the study, DPF and DEHF were compared to the toxic phthalate plasticizer diethyl phthalate (DEP). Analyses included thermal, tensile, and dynamic mechanical properties as well as plasticizer migration and phase separation. DPF and DEP were found to have similar plasticizing efficiencies, but DPF had superior mechanical performance. DEHF did not plasticize at loadings greater than 20% w/w and had poorer mechanical properties compared to DEP and DPF. Both DEP and DPF leached out of the PHB-co-HHx matrix, but DEHF did not. Polarized optical microscopy revealed the DEHF phase separates at 15% loading, limiting its plasticization but also preventing it from leaching outside the polymer matrix.  

“Hansen Solubility Parameter Guided Development of Furan-2,5-Dicarboxylate Plasticizers for Poly(3-Hydroxybutyrate-co-Hydroxyhexanoate),” published recently in the Journal of Applied Polymer Science, was coauthored by Kush G. Patel, Ryan K. Maynard, Grant H. Crane, Daniella Cardona, Angela Sun, Graham T. Fenn, Michael L. Brioch II and Jason J. Locklin.