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The processing and structural effects occurring in a poly(vinyl chloride) (PVC) compound processed in a plastograph, at the time at which the maximum value of the torque (point X on the torque curve) was reached, were studied. The unplasticized PVC compound was processed at various temperatures (150-2008C) with a kneader operating at rotors speeds of 5-40 min 21. The changes in the temperature of the compound due to kneading and its influence on the progress of PVC gelation were analyzed. The gelation progress was studied with differential scanning calorimetry, rheological measurements, and scanning electron microscopy. The maximum value of the torque occurred within the temperature range (170-1808C) of the PVC compound, and it was independent of the adjusted temperature of the mixing chamber. The processing of the PVC compound in the kneader, with high mechanical charges and a comparatively low adjusted temperature (150-1708C), spontaneously generated an effect of self-heating, resulting in an increasing temperature of the compound. Despite the surprisingly high degree of gelation (80-98%) of the PVC compound processed under these conditions (as determined by differential scanning calorimetry), the scanning electron microscopy observations indicated significant nonhomogeneity of the fracture surface. Consequently, the kneaded PVC compound at point X of the torque curve could be treated as a two-phase system composed of a liquid, amorphous phase and elements of a grain structure. The transformation of both phases (particularly the quantitative and qualitative changes), which was significantly dependent on the PVC temperature and the shear rate applied by the rotors, determined the state of the melted compound at this point of the torque curve.

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This article discusses the first part of the Brabender typical torque process curves. Rigid poly(vinyl chloride) (PVC; Polanwil S-61) was processed at various temperatures between 160 and 200°C with blade speeds in the range of 5-40 min Ϫ1 . The morphological changes of the processed compound was characterized by scanning electron microscopy and optical microscopy, and the degree of gelation was estimated on the basis of DSC thermograms. The values of torque minimum strongly depends on temperature. Shear rate affects mainly the time of reaching the minimum torque. The grains are disintegrated into the nonuniform particles and aggregates of the dimensions between 20 and 4 m. The significant variation of the gelation degree was found for the sample produced in the same conditions and unloaded from Brabender chamber at minimum of torque. It was found that the value of the minimum of torque described momentary equilibrium state between sliding of breaking grains and increasing degree of PVC gelation