Renewable Semi-Interpenetrating Polymer Networks Based on Vegetable Oils Used as Plasticized Systems of Poly(3-hydroxyalkanoate)s

Biobased semi-interpenetrating polymer networks (semi-IPNs) in which poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s, PHBHV, are embedded in a tridimensional network were developed to improve the mechanical properties of polyesters. Semi-IPNs are obtained by cross-linking sunflower oil (SO) and trimethylolpropane tris(3-mercaptopropionate) (TriSH) using a photoactivated thiol-ene reaction in the presence of 2,2'-dimethoxy-2-phenyl acetophenone. The SO-TriSH contents in the network varied from 20 to 45% wt. Homogeneous semi-IPNs containing from 20 to 40% of SO-TriSH content exhibited lower glass temperature from 4 to -15 degrees C, higher strain at break values from 7 to 150%, and better thermal stability than those of pristine PHBHV. This reveals an improvement of the deformability of PHBHV due to the plasticization domains by the SO-TriSH domains. The fact that a fraction of the interpenetrating networks follows Fox equation, which is usually verified by well-mixed plasticizer/polymer systems, could be a positive signature of an interpenetrating effect between reticulated SO-TriSH and PHBHV chains. Those properties were achieved without degrading the intrinsic crystalline structure of PHBHV as demonstrated by WAXS measurements.