A Brabender torque rheometer equipped with an internal mixer was used to study the influence of compounding method on the properties of (rigid PVC)/(treated and untreated nano‐CaCO3) nanocomposites. Two different methods were studied for the addition of surface treated and untreated nano‐CaCO3 during the melt mixing of rigid PVC. Direct dry mixing of rigid PVC and nano‐CaCO3, and addition of nano‐CaCO3 at the onset of PVC fusion were investigated. Dispersion of treated and untreated nano‐CaCO3 was studied by X‐ray diffraction and scanning electron microscopy. Results showed that using direct dry mixing improved the dispersion of nano‐CaCO3 in the PVC matrix by lowering the fusion time. The mechanical properties of the nanocomposite samples such as impact strength, tensile strength, and elongation at break were improved by using this method. The addition of treated nano‐CaCO3 at the onset of fusion caused a simultaneous decrease in torque. Also, rigid PVC nanocomposites prepared with treated nano‐CaCO3 showed better mechanical properties than those of nanocomposites prepared with the untreated nano‐CaCO3. J. VINYL ADDIT. TECHNOL., 18:153–160, 2012. © 2012 Society of Plastics Engineers

The surface of micro and nanoparticles of calcium carbonate (CaCO3) was modified by 3-mercaptopropyl trimethoxysilane and polymethylhydrogensiloxane. Fourier transform infrared spectra of extracted CaCO3 particles revealed interfacial bonding between coupling agents and CaCO3 particles. Poly(vinyl chloride) (PVC)/surface-modified CaCO3 with different mass ratios of (micro/nano)-CaCO3 particles were melt blended using a Brabender torque rheometer and kept with a constant content of CaCO3. The impact strength, tensile strength, elongation at break, and Young’s modulus of the composites were considerably enhanced at 9/6 mass ratio of (micro/nano)-CaCO3. The mechanical properties were improved relative to the pure PVC due to the interfacial bonding between the filler and the matrix. Scanning electron microscopic images of fractured surfaces of the test specimens showed larger voids with nonsmooth edge around the cavities, as compared with the nano-CaCO3/PVC composite, which is more pronounced by the increase in the micro particles contents.