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Crystallinity variations in the double yield region of polyethylene
Author(s) -
Manzur Angel,
Rivas Juan I.
Publication year - 2007
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.25905
Subject(s) - crystallinity , materials science , recrystallization (geology) , orthorhombic crystal system , yield (engineering) , polyethylene , melting point , composite material , crystallization , elongation , crystal (programming language) , crystallography , crystal structure , thermodynamics , chemistry , ultimate tensile strength , physics , geology , paleontology , computer science , programming language
Numerous specimens of a linear low density polyethylene sample were uniaxially deformed up to different elongations to study the double yield phenomenon. Extruded samples were analyzed to calculate the crystallinity and to estimate the mean crystal size, under stressed state and released state (after removal of the stress), using the wide angle X‐ray scattering technique. The crystallinity degree and the mean crystal dimension associated to the (110) orthorhombic reflection of the specimen without deformation were of 55% and 16 nm. These parameters in the stressed state, as functions of the elongation, presented a multi‐step behavior. A decrement after the first yield point (48%, 13 nm), then another decrement, and an abrupt increment followed by a decrement at higher strain values around the second yield point (28, 40, and 30%; 12, 14.5, and 11 nm). The behavior was more notorious in the stressed state than in the released state. The latter results were interpreted in terms of a partial melting followed by a recrystallization process. These experimental findings show that the second yield is not only associated with the deformation of the crystalline region. This partial melting–recrystallization process is one of the main mechanisms of the double yield phenomenon. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007