Abstract
Polymers have large bulk compressibility in the molten state, and their rheological properties are largely affected by pressure applied in polymer processing. The volumetric strain induced by the pressure consists of an instantaneous and a retarded elastic strains, both of which are proportional to the pressure, and recover reversibly on removal of the pressure. In many crystalline polymers, as observed by Maxwell for polyethylene, the retarded elastic strain is large, and it is mostly due to pressure crystallization.
This paper describes results of experimental studies relating pressure effects on rheological properties of melt polymers with polymer processing and bulk properties of the products. Following items are discussed; pressure-induced shear stress, analysis of local deformation pattern, critical shear stress for melt fracture, relation between power-law index and bulk compressibity, effects of hydrostatic pressure on melt flow behavior, pressure efficiency of injection molding, jetting phenomena, shrinkage in injection molding, residual strain, and high pressure injection molding precess.
