Mechanical Properties, Microstructure and Surface Quality of Polypropylene Green Composites as a Function of Sunflower Husk Waste Filler Particle Size and Content

Agricultural waste is a still untapped source of materials that can, in case of proper utilization, significantly improve the sustainability of polymers and their composites. In this work, polymer composites based on isotactic polypropylene were produced incorporating ground sunflower husk in the amount of 10 wt% and 20 wt%. The work’s main objective is to evaluate how preliminary fractioning of this agricultural waste filler affects the thermomechanical properties, microstructure and surface topology of polypropylene-based injection molded composites. The composites were analyzed for mechanical properties (tensile, impact strength and hardness), thermomechanical properties (Vicat softening point VST, heat deflection temperature HDT, and dynamic thermomechanical analysis DMTA) with reference to morphological changes evaluated using scanning electron microscopy (SEM). The quality of the produced composites was assessed on the basis of the analysis of the surface topology of the injected composites. It has been shown that the larger particle size of used filler has a direct impact on increasing composite stiffness in the room and elevated temperature. Moreover, a relationship was demonstrated between the size of the filler and the deterioration of the tensile strength in the case of composites with a higher content of filler. The results show that the addition of sunflower husk as a particle-shaped waste filler is an effective method to increase sustainability of polypropylene-based green composites with beneficial thermomechanical properties and to reduce the residue of sunflower husk from industrial oil production.