The Influence of Pressure on the Viscosity of Polymer Melts. Viscosity and Molecular Weight
Polymer melts are compressible liquids of bulk modulus ⋃109Nm−2. Most polymer melt processes operate at pressures of 106 to 107 Nm−2 (10 to 100atm) with a bulk compression of less than 1%. However, in some— notably injection moulding—pressures of the order of 108 N m −2 (1000 atm) may be employed. Bulk compression then is becoming appreciable and the consequent reduction in free volume reduces the mobility of the molecules. This manifests itself as a viscosity increase. Large mouldings may require very high pressures indeed. In such cases allowance should be made for the reduced melt fluidity in the processing specifications.
KeywordsIntrinsic Viscosity Flow Unit Bulk Compression Linear Polyethylene Polymer Rheology
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