Effect of ternary monomer graft copolymers on morphology and properties of rice chaff filled polypropylene composites

Ternary monomer graft copolymers (PPTM) were synthesised by solid phase grafting maleic anhydride (MAH), methyl methacrylate (MMA) and butyl acrylate (BA) onto polypropylene (PP) and used as compatibilisers for rice chaff (RC) filled recycled polypropylene (rPP) composites. How the graft copolymers affected the mechanical properties, water absorption, morphology, crystallisation and melting behaviour and thermal stability of rPP/RC composites was investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermal-gravity analysis (TGA), etc. Results showed that the graft copolymers can dramatically improve the interface adhesion of rPP/RC composites. The strong interface adhesion of the composites primarily came from the formation of the ester bonds between the hydroxyl groups of cellulosic fibres and the anhydride carbonyl groups of PPTM, and the hydrogen bonding between the hydroxyl groups of cellulosic fibres and the carbonyl groups of PPTM. The mechanical properties increased with the increasing loadings of the ternary monomer graft copolymers. The preferable loadings of the graft copolymers were approximately at 8–10 phr. The tensile strength and flexural modulus increased with the increasing loadings of RC while the impact strength decreased with the increasing loadings of RC. The loadings of RC were too high for the interface adhesion to compensate the impact strength. The ternary monomer graft copolymers also enhanced the hetero-nucleation of RC to the PP matrix during the crystallisation and increased the thermal stability of the rPP/RC composites.