Bioresource-based blends of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and stereocomplex polylactide with improved rheological and mechanical properties and enzymatic hydrolysis

Novel bioresource-based blends of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) and stereocomplex polylactide (sc-PLA) were prepared herein via a simple melt blending method at various sc-PLA loadings at the temperature above the melting points of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), and much lower than that of sc-PLA. Wide-angle X-ray diffraction and differential scanning calorimetry results verified that complete stereocomplex crystallites without any evidence of the formation of homocrystallites in the P34HB melt could be achieved. Scanning electron microscopy observation indicated that sc-PLA was nicely dispersed in the P34HB matrix as spherical particles; the dispersed size of the sc-PLA did not display a pronounced increase with an increase in the content of PLLA and PDLA. As solid fillers, sc-PLA could reinforce the P34HB matrix in a relatively wider temperature region. Accordingly, the rheological and mechanical properties of P34HB were greatly improved after blending with sc-PLA, particularly when a percolation network structure of spherical filler (a characteristic solid or gel-like structure) had formed in the blends. Moreover, the most intriguing result was that the enzymatic hydrolysis rates had been clearly enhanced in the P34HB/sc-PLA blends than that in the neat P34HB, which may be of significant use and importance for the wider practical application of biosourced P34HB. The erosion mechanism of the neat P34HB and the P34HB/sc-PLA blends was discussed further.