A sustainable hybrid strengthening/stiffening approach for injection molded polypropylene matrix thermoplastic composites

Hybrid interaction/co-working mechanisms of waste cellulose (WC) fibers and expanded vermiculite (V) in polypropylene (PP) resulted in stronger, stiffer, and thermally durable composites are presented. Fibrous WC and particulate V inclusions were mixed with the PP matrix via high shear thermokinetic mixer under 4000 rpm. Thermal and mechanical characterization efforts assisted with fractographic investigations are performed on five sample sets such as (i) two-phase WC fibrous PP composites and (ii) three-phase WC–V hybrid composites. Results suggested that as the main reinforcement agent WC is able to increase the axial stiffness of PP (1.7 GPa) up to 4 GPa (30WC) as the weight fraction increases with a reduction in ductility. However, a strength threshold due to WC cluster entanglement, which leaves partially non-wet clusters of WC and limited crystallization volume for PP at high WC weight fractions, is noted. In situ formed V platelets placed between WC fibers are proven to provide PP crystallization loci to further increase the axial stiffness (4.1 GPa) and matrix brittleness. When used with 10WC, they significantly increased the ability of PP matrix r to resist the failure events associated with the presence of randomly aligned WC fibers. Such ability is further highlighted in the 20WC10V case where the inherent problem of WC entanglement increased the contribution of polymer shear failure to the overall tensile response of manufactured composites. A significant increase in tensile strength (55%) for this case was recorded which makes the proposed hybridization effort more advantageous to conventional short fiber reinforcing strategies. Highlights: Stiffer and stronger PP-based hybrid composites with waste cellulose and vermiculite. Tensile failure/toughening mechanisms in hybrid PP composites Sustainable approach for reinforcement selection.