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Analysis of molecular orientation and internal stresses in extruded plastic sheets
Author(s) -
Chan T. W. D.,
Lee L. J.
Publication year - 1989
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.760290303
Subject(s) - materials science , composite material , birefringence , shrinkage , core (optical fiber) , orientation (vector space) , extrusion , stress (linguistics) , dichroic glass , polypropylene , die (integrated circuit) , optics , geometry , linguistics , philosophy , physics , mathematics , nanotechnology
Abstract The development of molecular orientation and internal stresses in extruded sheet made of polypropylene was analyzed, and their correlations to operating conditions such as draw ratio, cooling rate, die temperature, melt temperature, and die gap opening were studied. Measurements of attenuated‐total‐reflectance infrared dichroic ratio for the surface molecular orientation, birefringence for the orientation stress distribution in the thickness direction, and free shrinkage ratio for the overall frozen‐in stresses were carried out to determine the amount of orientation stresses in the extruded samples. As expected, the overall orientation stress depends strongly on draw ratio, while higher melt temperature reduces the overall orientation. It was found that faster cooling rates and lower die temperatures cause surface orientation stresses to increase as the core orientation stresses remain almost unchanged.