Analytical interpretation of mechanical response of green biocomposites based on poly(ε-caprolactone) and granular tapioca starch

The present work focuses on thermal, mechanical, and morphological properties of poly(ε-caprolactone) (PCL) on incorporation of granular tapioca starch (GTS). Biocomposites containing 0–35 wt% (Φ_f = 0–0.36) of the dispersed GTS phase were prepared by melt compounding in a twin screw extruder followed by microinjection molding. From the DSC measurements, sharp decrease in crystallinity was observed for all the compositions studied. The observed marginal decrease in onset degradation temperature suggests that the incorporation of GTS does not compromise thermal stability in PCL/GTS biocomposites. The maximum tensile modulus observed at Φ_f = 0.36 was 225.8 MPa, while a decrease in tensile yield strength with the value 12.44 MPa was observed. After eliminating the effect of crystallinity, these biocomposites showed ~4 times increase in tensile modulus and ~2 times increase in yield strength, whereas the impact properties decreased by 59 %. The enhancement in Young’s modulus was due to the mechanical restraint created by GTS particles which tend to decrease notched Izod impact strength by enhancing the stiffness of PCL. From SEM micrographs, homogeneous dispersion of GTS particles was observed in PCL matrix. Theoretical models were used to analyze tensile modulus and yield strength data for the estimation of various phase-adhesion parameters.