Fracture and thermal behaviour of biomass ash polypropylene composites

Abstract

In this work, the fracture and thermal behaviour of environmentally friendly composites based on polypropylene (PP), an olefin block copolymer (OBC) and ash from biomass combustion was investigated. PP/OBC/ash composites with different ash contents and 10 wt% OBC were prepared by extrusion followed by compression moulding. Ash particles were treated with a silane coupling agent before blending to promote interfacial adhesion between polymer matrix, OBC and ash. An approach to fracture mechanics was investigated and showed that the fracture parameters increased when OBC was used. Fracture surface analysis by scanning electron microscope revealed that the presence of OBC promotes the material ductile failure and that one of the main failure mechanisms was fibrillised debonding of ash particles encapsulated by OBC from the matrix and its subsequent elongation around them. Free OBC inclusions distributed within the PP matrix would have also induced toughening in the composites investigated. The crystalline state of PP analysed by differential scanning calorimetry is clearly modified by the presence of ash particles, increasing the crystallisation rate and the crystallinity degree of the matrix due to the nucleating effect of the filler. However, the presence of the copolymer counteracted these effects and the PP crystalline state remained practically unchanged in the composites with OBC. Finally, environmentally friendly composites with significantly higher toughness than the matrix or binary PP/ash composites were obtained by introducing an OBC copolymer in the formulation.