Anomalous behavior of unplasticized PVC compounds in capillary flow

✍ Scribed by Nobuyuki Nakajima; Edward A. Collins

• Publisher: John Wiley and Sons
• Year: 1978
• Tongue: English
• Weight: 810 KB
• Volume: 22
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/app.1978.070220904

✦ Synopsis

Synopsis

Capillary rheometry was performed over a temperature range of 17Oo-200"C and a shear-rate range of 3-3000 sec-' on an unplasticized poly(viny1 chloride) compound. The data were corrected for the effect of pressure on viscosity, for pressure loss in the barrel and at the capillary entrance, and for the non-Newtonian velocity profile. The pressure coefficient of viscosity was found to be in the same order of magnitude as those previously found with linear polyethylene and butadieneacrylonitrile copolymers. The pressure-shear-rate superposition of the flow curves is valid at least approximately, although the temperature-shear-rate superposition is inapplicable. The shape of flow curves at 180°, 190°, and 200°C are concave downward when they are expressed as log-shearstress-log-shear-rate. Similar plots at 170" and 175"C, however, are very different; shear stress is independent of shear rate a t low shear rates, increases somewhat and becomes independent of shear rate again at high shear rates. There is no detectable temperature dependence of flow behavior at 170" and 175°C. Irregularly shaped extrudates were obtained at higher shear rates. At constant shear rate the irregularity increased with the length of the capillary. The effect of thermal-mechanical history on the particulate and crystalline structure is discussed with possible influence on the reproducibility of the rheological data.