Mechanical Modification of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) by Addition of Crosslinked Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Particles.

In the present study, we prepared crosslinked particles of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) to investigate their performance as impact modifiers. The mechanical properties of crystalline PHBH comprising 5.6 mol% 3-hydroxyhexanoate (3HHx) were modified by the addition of amorphous particles of PHBH with 28 mol% 3HHx (PHBH28). The tensile impact strength of the mixture was improved by the addition of PHBH28 particles, particularly when they were crosslinked. The size of the dispersed uncrosslinked PHBH28 particles was sensitive to the processing method. However, the crosslinked PHBH28 particles retained their form under any processing conditions, and a smaller particle size was achieved, leading to shear yielding. The samples containing crosslinked PHBH28 particles exhibited intense stress-whitening after impact testing. The resulting voids were ascribed to cavitation in the particles, which must have been responsible for the improved mechanical properties of the samples. Moreover, the crosslinked particles did not affect the excellent biodegradability of PHBH in seawater.