Rigid poly(vinyl chloride) gelation in a Brabender measuring mixer. III. Transformation in the torque maximum

Abstract

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.

The Rheological and Mechanical Properties of PVC-Lignin Blends

“…At point X, the degree of PVC gelation induced by entanglement between macromolecular chains reaches the maximum. The kneaded PVC compound at point X of the torque run may be treated as a two-phase system of solid grain structure and liquid amorphous phase (Tomaszewska et al, 2007).…”

Preparation and Characterization of Novel PVC/Silica–Lignin Composites

“…The torque of the rotors was recorded as a function of time. The processing of all materials was performed up to the time when the equilibrium state of torque was achieved, i.e., to the point E on the torque-time curve (see the description of the characteristic points on the torque curve according to [52,53]). Both the values of torque at the maximum (M X ) and the time required to reach the point X (t X ) were analyzed.…”

“…The shape of all plastograms is characteristic for the processing of rigid PVC compounds and is closely linked to the occurrence of the gelation effect, which takes place depending on the applied shear rate, temperature and PVC composition ( Figure 1). This PVC gelation effect may be noted on the plastogram as a maximum of torque, followed by a relatively high constant value in the equilibrium state [52,53].…”

Principles of Thermal Degradation

“…6,14 Figure 4.15 shows time required to emission of 1% HCl. 171 At this point of compounding, the primary grains are mostly disintegrated into particles with average dimensions between 4 and 20 μm. 163 Figure 4.16 shows plasticizer loss at relatively low temperatures during 2 hours of exposure of PVC containing dioctyl phthalate and benzyl butyl phthalate (PVC:plasticizer=2:1).…”