title: Effect of accelerated aging on the cross-link density of medical grade silicones.
abstract: Four specimens of Nagor silicone of different hardness (soft, medium and hard) were swollen, until they reached equilibrium (i.e. constant mass) in five liquids at 25°C, before and after accelerated aging. For the specimens swollen before accelerated aging, the greatest swelling was obtained in methyl cyclohexane, while for the specimens swollen after accelerated aging, the greatest swelling was obtained in cyclohexane. The cross-link density, υ, was also calculated from the swelling measurements for all the specimens, before and after accelerated aging, using the Flory-Rehner equation. The softer silicones, which swelled the most, had lower υ values than harder silicones. The amount of swelling (measured in terms of ϕ) and υ varied significantly (p<0.05) in some cases, between the different silicone hardness and between different liquids. Furthermore, the cross-link density, υ, significantly (p<0.05) increased after accelerated aging in most liquids.Note: ϕ is defined as the volume fraction of polymer in its equilibrium swollen state. A probability value of statistical significance of 0.05 or 5% was selected, hence if a p value of less than 0.05 was obtained, the null hypothesis was rejected (i.e. significant if p<0.05).
authors.affiliation: School of Engineering, Department of Mechanical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: Aziza
authors.initials: A
authors.lastname: Mahomed
authors.affiliation: School of Engineering, Department of Mechanical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: Negin Bagheri
authors.initials: NB
authors.lastname: Pormehr
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry; D003510:Cyclohexanes / Q000737:chemistry*; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D012828:Silicones / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D003510:Cyclohexanes; D012828:Silicones; C521475:methylcyclohexane
keywords: Cross-link density; Flory–Rehner equation; Hildebrand’s solubility parameter theory; silicones; swelling of polymers in liquids