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 degreesC with blade speeds in the range of 5-40 min(-1). 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 non-uniform particles and aggregates of the dimensions between 20 and 4 mum. 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. (C) 2004 Wiley Periodicals, Inc.