Effect of interfacial modification on the rheological properties and nucleation behaviour of PP-BaSO₄ composites

Polypropylene-barium sulfate (PP-BaSO₄) composites were prepared by pretreating the filler with stearic acid, silane and polypropylene-g-maleic anhydride, respectively. The effects of the PP-BaSO₄ interfacial interaction on the rheological properties and nucleation behaviour of the composites were studied. Surface treatment with reactive coupling agents enhanced the matrix-filler interfacial interaction and caused an increase in the melt viscosity, whereas the use of non-reactive coupling agents reduced the particle-particle interaction and led to a decrease in melt viscosity. The plain BaSO₄ had a weak nucleating effect on PP. When the PP-BaSO ₄ interaction was enhanced, a remarkable increase in nucleation activity of the filler was observed. It is suggested that the enhanced adsorption of PP molecules onto the BaSO₄ surface is of benefit in lowering the thermodynamic potential barrier for the formation of primary nuclei.