Crystallization, mechanical properties and processability of calcium carbonate-filled syndiotactic polypropylene

Abstract

Calcium carbonate (CaCO3)-filled s-PP was prepared in a self-wiping, co-rotating twin-screw extruder. The effects of CaCO3 content (0 to 40% by weight), particle size (1.9, 2.8 and 10.5 um), and surface modification (neat, stearic acid-treated, and paraffin-treated) on crystallizationb ehavior, mechanical properties and processability of the compounds were investigated. Both non-isothermal and sothermal crystallization studies indicated that CaCO3 acted as a good nucleating agent for s-PP. Nucleation efficiency of CaCO3 was found to depend strongly on its crystal structure, surface treatment, and size. Tensile strength was found to decrease, while the Young's modulus increased, with increasing CaCO3 content. Both types of surface treatments on CaCO3 reduced the tensile strength and the young's modulus, but helped improve impact resistance. Melt viscosity of CaCO3-filled s-PP was found to increase with increasing CaCO3 content and decreasing particle size. Both types of surface treatment resulted in a reduction in melt viscosity, probably due to reduced inter-particular interactions and extent of agglomeration of the filler. Morphology observations ot the fracture surfaces of CaCO3-filled s-PP samples revealed an improvement in CaCO3 dispersion as a result of surface treatment.