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The effect of stretching conditions on properties of amorphous polyethylene terephthalate film
Author(s) -
Sharma S. K.,
Misra A.
Publication year - 1987
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1987.070340615
Subject(s) - materials science , crystallinity , amorphous solid , ultimate tensile strength , composite material , polyethylene terephthalate , crystallization , birefringence , elongation , annealing (glass) , tenacity (mineralogy) , modulus , stress relaxation , relaxation (psychology) , crystallography , chemical engineering , optics , creep , chemistry , engineering , psychology , social psychology , physics
The effect of stretching condition on stress‐induced crystallization of amorphous polyethylene terephthalate (PET) film has been studied. Cast PET film was stretched at 85°C with stretching rates ranging from 100% per minute to 600% per minute for various stretching ratios. The stretched film samples were annealed at 140°C both under tension as well as under relaxed conditions. Tensile properties were determined using Instron Tensile Tester and results were compared. Tenacity, yield stress, and initial modulus were found to increase while elongation at break decreased with the increase in stretching rate. The degree of crystallinity was measured by x‐ray diffraction as well as density methods. Birefringence and crystalline orientation factor values were determined experimentally and using these, amorphous orientation factor values were calculated. Birefringence, crystalline orientation and amorphous orientation values were found to increase with the increase in stretching rate. These studies showed that at low stretching rates a significant amount of relaxation takes place, resulting in lower orientation and strength. On the other hand, at higher stretching rates relaxation is minimized thus providing high orientation and strength. Upon annealing the crystallinity values increased as expected, however the trend of orientation and mechanical properties with respect to stretching rate was similar to those of unannealed films.