Recycled newspaper fibers as reinforcing fillers in thermoplastics. I: Analysis of tensile and impact properties in polypropylene

Recycled newspaper fibers (ONP) are potentially outstanding nonabrasive reinforcing fibers with high specific properties. A high energy thermokinetic mixer was used to mix these fibers in a polypropylene (PP) matrix, and the blends were then injection molded in order to observe the tensile and impact strengths of the composites. A 40 wt.% of ONP in PP resulted in a tensile strngth of 34.1 MPa and an unnotched Izod impact strength of 112 J/m. Small quantities of maleic anhydride-grafted polypropylene (MAPP, Epolene E-43, Epolene G-3002, PolyBond-3002) and acrylic acid-grafted polypropylene (AAPP, PolyBond-1001) were used to improve the interaction between the hydrophobic PP and the highly polar fibers. The improvement in properties by using MAPP depended on the amount of maleic anhydride in the graft copolymer and the molecular weight of the copolymer. Tensile strengths as high as 57 MPa and an unnotched Izod impact strength of 212 J/m were achieved with the addition of one of the MAPP, while smaller improvements were found with AAPP. Reinforcing efficiencies and scanning electron microscopy have been utilized to aid in the analysis.