Maleated natural rubber as a coupling agent for paper sludge filled natural rubber composites

Paper sludge filled natural rubber composites were prepared by incorporation of different loadings (10-40 phr) of paper sludge fillers. Two series of composites were studied, i.e. composites with and without maleic anhydride grafted natural rubber (MANR). Grafting of maleic anhydride onto the natural rubber was done prior to compounding using an internal mixer. The curing characteristics, dynamic properties and tensile properties of the composites were studied. Results indicate that the scorch time and cure time decrease with increasing filler loading whereas the maximum torque, viscous torque and tan delta exhibit an increasing trend. Increasing paper sludge content also increases the tensile modulus but the tensile strength and elongation at break decrease slightly. As the filler loading increases, the rubber-filler interactions of the composites decrease. The interfacial interaction of paper sludge filler and natural rubber matrix was enhanced by the addition of MANR, as exhibited by the tensile fracture surfaces of the composites using a Scanning Electron Microscope (SEM) and rubber-filler interaction studies. The presence of MANR has prolonged the curing time and scorch time and enhanced the tensile properties. The viscous torque and tan delta values also decrease with the addition of MANR.