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Healing of stress‐whitening in polyethylene and polypropylene at or below room temperature
Author(s) -
Pae K. D.,
Chu H.C.,
Lee J. K.,
Kim J.H.
Publication year - 2000
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.11310
Subject(s) - materials science , stress (linguistics) , composite material , hydrostatic pressure , hydrostatic test , hydrostatic equilibrium , polypropylene , ultimate tensile strength , transient (computer programming) , atmospheric pressure , mechanics , philosophy , linguistics , physics , oceanography , quantum mechanics , computer science , geology , operating system
Stress‐whitening occurs in many crystalline polymers when they are subjected to cold‐drawing at atmospheric pressure and at room temperature. The exact structure and morphology of stress‐whitening are still in contention, although it is widely believed that stress‐whitening is a combination of crazes and voids. The healing of stress‐whitening at room temperture may be divided into two stages: transient, which is a short time‐dependent and post‐transient. The post‐transient healing phenomenon involves a long time‐dependent or time‐independent healing. Stresswhitening in the post‐transient stage reaches a steady or permanent state. Healing of stress‐whitening in the post‐transient stage would occur when acted upon by an external agency, such as stress and temperature, or a combination thereof. A methodology has been developed to heal the permanent stress‐whitening at or below room temperature in HDPE and PP. The study involved the following procudure: tensile samples of HDPE and PP were cold‐drawn in an Inston testing machine at atmospheric pressure and room temperature to develop stress‐whitening; the stress‐whitened samples were subsequently, after days of rest, pulled in hydrostatic pressure environment at room temperature; the stress‐whitened section was partially or completely healed depending on the magnitude of the applied stress (or strain) and the intensity of hydrostatic pressure.