Premium
Interrelationship of strength and flow characteristics of polystyrene
Author(s) -
Crowder Mark L.,
Ogale Amod A.,
Moore Eugene R.,
Dalke Brian D.
Publication year - 1994
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.760341910
Subject(s) - materials science , polystyrene , flexural strength , composite material , ultimate tensile strength , shear rate , viscosity , molding (decorative) , melt flow index , izod impact strength test , volumetric flow rate , polymer , mechanics , physics , copolymer
This study investigated the interrelationship between strength and flow characteristics of general‐purpose polystyrene (GPPS) used in injection molding applications. The ease of flow was chosen as a measure of processability and was evaluated using the melt flow rate and capillary rheometer techniques. Of the different strength tests that were examined, flexural and notched tensile strength tests were most effective in differentiating between commercial grades of high and low molecular weight GPPS. While characterizing strength of injection molded specimens, the degree of molecular orientation was taken into consideration. For unplasticized resins, increasing the weight average molecular weight by about 100,000 enhanced the flexural strength by 10%, but also increased the viscosity at low shear rates (10 to 100 s −1 ). The increase in molecular weight had virtually no effect on viscosity at the highest shear rates (up to 10,000 s −1 ). Plasticized resins displayed a 6% loss in flexural strength as well as a significant reduction in viscosity (throughout the shear rate range) as compared with the unplasticized resins. As expected, the improvement in strength achieved by increasing molecular weight leads to a simultaneous increase in the viscosity, i.e., a deterioration of processability. In addition, our study indicates that for samples without preferential molecular orientation, narrowing the molecular weight distribution significantly improves the balance of strength and melt flow rate properties.