Rheological and mechanical properties of PVC/CaCO 3 nanocomposites prepared by in situ polymerization

Abstract

Poly(vinyl chloride) (PVC)/calcium carbonate (CaCO 3) nanocomposites were synthesized by in situ polymerization of vinyl chloride (VC) in the presence of CaCO 3 nanoparticles. Their thermal, rheological and mechanical properties were evaluated by dynamic mechanical analysis (DMA), thermogravimetry analysis (TGA), capillary rheometry, tensile and impact fracture tests. The results showed that CaCO 3 nanoparticles were uniformly distributed in the PVC matrix during in situ polymerization of VC with 5.0 wt% or less nanoparticles. The glass transition and thermal decomposition temperatures of PVC phase in PVC/CaCO 3 nanocomposites are shifted toward higher temperatures by the restriction of CaCO 3 nanoparticles on the segmental and long-range chain mobility of the PVC phase. The nanocomposites showed shear thinning and power law behaviors. The ‘ball bearing’ effect of the spherical nanoparticles decreased the apparent viscosity of the PVC/CaCO 3 nanocomposite melts, and the viscosity sensitivity on shear rate of the PVC/CaCO 3 nanocomposite is higher than that of pristine PVC. Moreover, CaCO 3 nanoparticles stiffen and toughen PVC simultaneously, and optimal properties were achieved at 5 wt% of CaCO 3 nanoparticles in Young's modulus, tensile yield strength, elongation at break and Charpy notched impact energy. Detailed examinations of micro-failure micromechanisms of impact and tensile specimens showed that the CaCO 3 nanoparticles acted as stress raisers leading to debonding/voiding and deformation of the matrix material around the nanoparticles. These mechanisms also lead to impact toughening of the nanocomposites.