engleski

ESR study of anisotropic natural rubber crosslinked by gamma irradiation

Natural rubber (NR) samples, prepared in the form of films having the thickness of about 1 mm, were obtained by removing the liquid phase from NR latex. Latex was previously irradiated in a γ-source with total doses of 100 kGy and 200 kGy. NR films were then uniaxially stretched with different degree of deformation (λ) and irradiated with the secondary dose of 100 kGy or 200 kGy. The aim of this study was to investigate how the crosllinking of natural rubber in the state of deformation affects the matrix structure and dynamics of chain segments. Moreover, the structural and dynamic changes induced by accelerated thermal aging of investigated samples were determined. The basic characterization of the samples, associated with the macroscopic properties of material, was carried out by swelling, sol phase extraction and differential scanning calorimetry (DSC). Electron spin resonance (ESR) − spin probe method was applied to study the dynamics of polyisoprene chain segments. It was shown that the deformation of the samples during the crosslinking process leads to changes in the local matrix structure, free volume and segmental dynamics. These changes introduce restrictions in the spin probe dynamics. Accelerated thermal aging results in a rapid increase of gel phase, which affects the dynamics of chain segments and it is reflected in a higher amount of broad component in the ESR spectra and longer correlation times.

natural rubber; gamma-irradiation; anisotropy; ESR - spin probe

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