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Dynamic study of free volume properties in polyethylene/styrene butadiene rubber blends by positron annihilation lifetime method
Author(s) -
Mostafa N.,
Ali E. Hassan,
Mohsen M.
Publication year - 2009
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.30311
Subject(s) - materials science , low density polyethylene , differential scanning calorimetry , natural rubber , polyethylene , glass transition , styrene butadiene , high density polyethylene , temperature coefficient , volume (thermodynamics) , composite material , polymer chemistry , analytical chemistry (journal) , polymer , thermodynamics , copolymer , styrene , chemistry , organic chemistry , physics
Positronium (Ps) formation in low and high‐density polyethylene (LDPE and HDPE) and styrene butadiene rubber (SBR), as well as in their blends (LDPE/SBR: 50/50 and HDPE/SBR: 50/50) has been investigated by positron annihilation lifetime (PAL) measurements as a function of low temperature (100–300 K). The glass transition temperature ( T g ) for the initial polymers and their blends are determined by ortho‐positronium (o‐Ps) lifetime, τ 3 versus temperature as well as by differential scanning calorimetry (DSC) measurements. The temperature dependence of nanoscale free volume size shows similar trend for all the investigated samples indicating an abrupt change at T g , which is found to be higher for SBR sample characterized by its high chain mobility. In addition, The T g values deduced from PAL measurements are compared with the corresponding data deduced from DSC. The variation of o‐Ps formation probability I 3 versus temperature for polyethylene and their blends were interpreted in the frame work of spur reaction model of Ps formation. On the other hand, the lifetime coefficient below and above T g is found to be one order of magnitude larger than the linear expansion coefficient. This constitutes evidence that Ps is only probing free volumes. The results obtained from change in free volume–hole distribution with temperature reflect both thermal expansion and increase in free volume–hole size with the rise in temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009