Tensile, thermal and morphological characterization of cocoa bean shells (CBS)/polycaprolactone based composites

In this work, cocoa bean shells (CBS), which were ground, then sieved to less than 150 μm and dried in a vacuum oven, have been introduced in a polycaprolactone (PCL) matrix in three different amounts, 10, 20 and 30% wt. The obtained composites were tested under tensile loading, which indicated an enhanced rigidity with a slight decrease of strength with respect to the neat polymer and a reduced elongation, particularly evident for composites with 30 wt% CBS, where final collapse took place for strains only slightly exceeding the yielding point. Differential scanning calorimetry (DSC) indicated a rather negligible variation of melting temperature with respect to pure PCL, whilst thermogravimetric analysis (TGA) for CBS showed evident peaks for degradation of hemicellulose, pectin, then most clearly for cellulose at 313 °C and a final residue of 33.3% at 900 °C. Scanning electron microscopy images taken on the 30% wt. composite offered evidence of brittle fracture with appearance of irregular structures, related to the pull-out and fibrillation of cocoa shells.