Development of sunflower husk reinforced polypropylene based sustainable composites: An experimental investigation of mechanical and thermal performance

Climate change, shrinking resources, and rising raw material costs have pushed the industry to create more sustainable, and lightweight materials. Natural fiber composites are materials of interest for replacing conventional materials such as steel. Sunflower husks (SH), among many other natural fibers, are readily accessible as agricultural waste and have advantageous properties. In this study, sunflower husks were mixed with polypropylene (PP) matrix using a twin-screw extruder, and then tests specimens for experimental characterizations were manufactured through injection molding. The tensile tests revealed that the inclusion of SH into PP decreased the load-bearing capacity of the composites by around 20% and increased their impact resistance by over 200%, while reducing the ductility by about eight times. Moreover, magnesium hydroxide (Mg(OH)₂) was incorporated into the composites as a flame retardant, and it has improved the stiffness and impact resistance of the composites. Besides, incorporation of SH and Mg(OH)₂ elevated significantly the glass transition temperature of the composites. The use of Mg(OH)₂ delayed 60% the flame retention of the composites observed from UL-94 HB flammability testing. In summary, they could be suitable for components such as spare wheel wells, seat backs, trunk floor, the acoustic panel behind the door, and airbag housing.