Studying structural properties of polyethylene waxes with infrared spectroscopy
Subject Areas :
1 -
Keywords: polyethylene wax, branching degree, oxidation, unsaturation, crystallinity,
Abstract :
Polyethylene waxes are ethylene oligomers with unique properties, high crystallinity, linearity and low solubility in the solvents which provides a variety of applications in different industries such as electrotechnique, rubber, textile, fertilizer production, etc. Infrared spectroscopy (FTIR) is a simple and common analysis to examine the chemical and physical properties of polyethylene such as structure identification, chemical composition and crystallinity evaluation. Physical properties of a polyethylene wax largely depends on its branching degree. Absorption at the wavelength 1378 cm-1 associated with methyl groups symmetric deformation is used for determining the number of branches. Rocking vibration of methyl and methylene groups in the wavelength ranges of 800-1200 cm-1 and 720-770 cm-1 respectively are applied for identification of the branch type. Absorption of vinyl, trans vinylene and vinylidene unsaturation and carbonyl groups introduced into the structure by wax oxidation, were investigated. Absorption intensity was related to the number of absorbing species by molar absorption parameter or absorption coefficient based on the Beer-Lambert law. Some experimental relations were also introduced based on nuclear magnetic resonance spectroscopy. Deconvolution of the double absorption in the range 720-730 cm-1, associated with rocking vibration of methylene groups, to the crystalline and amorphous bands led to the crystallinity estimation.
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