Premium
Pressure‐Induced densification in injection molding
Author(s) -
Greener J.
Publication year - 1986
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760260804
Subject(s) - materials science , polystyrene , slab , molding (decorative) , composite material , amorphous solid , annealing (glass) , polymer , volume (thermodynamics) , thermodynamics , crystallography , structural engineering , engineering , chemistry , physics
Abstract The effect of pressure on the densification of amorphous polymers in the Injection‐molding process is examined. Density distributions in molded polystyrene slabs were measured for several well‐defined molding histories. In all cases the density of the molded part was spatially inhomogeneous, and its distribution in the slab was closely related to the pressure and temperature histories that prevailed in the molding cavity during the process cycle. The density profile in the gapwise direction followed a characteristic “parabolic” pattern with a minimum at the midplane of the slab. A simple phenomenological model, based on the pressure‐induced densification effect, was constructed to explain the observed density profiles, and close agreement with experimental data was found. Annealing of the molded article at a high temperature (< T g ) caused the density to decrease overall and become more uniform across the part. This is generally consistent with volume‐recovery data for the densified material, which were generated independently in a controlled pressure‐densification experiment.