Rheological and Fusion Behaviors of PVC Micro- and Nano-composites Evaluated From Torque Rheometer Data Gulsen Albayrak Ari, Ismail Aydin Department of Chemical Engineering, Faculty of Engineering, Istanbul University, Avcılar, 34320 Istanbul, Turkey The effects of calcium carbonate (CaCO 3 ) particle size on the fusion and rheological behaviors of rigid poly- (vinyl chloride) (PVC) composites prepared in a Haake torque rheometer were investigated by means of tor- que data recorded during processing. Increasing the number of particles in the same blend volume by decreasing the particle size resulted in increasing fric- tional forces. This increase led in turn to increased fusion torque and decreased fusion time and tempera- ture. The power-law-index values of the composites increased with decreasing particle size except for 25- nm CaCO 3 . The viscosities of all composites were found to decrease with shear rate; therefore, high pseudoplasticity was observed. At a particular rotor speed, viscosity of the composites decreased with decreasing particle size except for 25-nm CaCO 3 . The overall results showed that the particle size of CaCO 3 altered the fusion characteristics and rheological behavior of PVC. J. VINYL ADDIT. TECHNOL., 16:223–228, 2010. ª 2010 Society of Plastics Engineers INTRODUCTION Inorganic particulate fillers improve the mechanical and thermal properties of polymers as well as sometimes reduce their cost. In recent years, organic-inorganic com- posites, especially nanocomposites, have attracted great interest from scientists because these materials often ex- hibit outstanding properties. The effects of inorganic fill- ers on properties of the composites depend strongly on fil- ler size and shape, type of particles, the fraction of filler, surface characteristics, and degree of dispersion [1]. Vari- ous nanoscale fillers, including montmorillonite, silica, calcium carbonate, and aluminum oxide, have been reported to enhance the mechanical and thermal properties of polymers [2–5]. Among these fillers, nano-sized CaCO 3 is one of the most commonly used spherical fillers in the nanocomposite formulations [6]. PVC is one of the major commercial thermoplastics because of its high mechanical strength, high corrosion resistance, and relatively low cost. PVC/inorganic nano- composites based on silica [7], calcium carbonate [8], montmorillonite [2], and titania [9] have been previously reported. Among these inorganic particles, CaCO 3 has attracted more attention because it eliminates HCl gas during the thermal degradation of PVC [10]. Although PVC/CaCO 3 micro- and nanocomposites have been stud- ied, few works have investigated the comparison of their processability and rheological properties. A torque rheom- eter can provide those comparisons. The torque rheometers, such as Haake, Brabender, etc., have been used effectively to study various rheological properties of polymers in the plastics and rubber industry [11]. They can give quantitative information on the flow behavior of polymers, structural changes during process- ing, and the influence of various additives on the process- ability of new formulations [12]. The torque rheometer also provides for determining the rheological data easily and quickly, as torque is directly proportional to the appa- rent viscosity of the polymer melt. In addition, fusion characteristics of polymers, such as time, temperature, tor- que, and energy, which are the major factors determining the processing conditions, can be studied by using a tor- que rheometer. The torque produced by the resistance of a material to the shearing action of the process is an indirect indication of shear stress, and the rotor speed is an indirect indica- tion of shear rate. The torque and rotor speed data can be converted into viscosity and shear rate by using correla- tions based on the instrument dimensions [13]. Various methods based on assumptions such as assuming linear relationships between torque and apparent shear stress and between angular velocity and apparent shear rate, consid- ering the mixing chamber of the torque rheometer as two irregular adjacent coaxial cylinders, etc., have been devel- oped for the conversion of data obtained from the torque Correspondence to: Gulsen Albayrak Ari; e-mail: gulsen@istanbul.edu.tr Contract grant sponsor: Research Fund of Istanbul University; contract grant number: T-783/27122005. DOI 10.1002/vnl.20241 Published online in Wiley Online Library (wileyonlinelibrary.com). Ó 2010 Society of Plastics Engineers JOURNAL OF VINYL & ADDITIVE TECHNOLOGY——2010