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Open Access Article
1 - Crystallinity of polymers determined by differential scanning calorimetry (II)
Mina AlizadehaghdamDifferential scanning calorimetry (DSC) is widely used to determine the crystallinity of semicrystalline polymers. In the two-phase model, the measured heat of fusion is compared to the melting enthalpy of a completely crystalline polymer to get the crystallinity degree MoreDifferential scanning calorimetry (DSC) is widely used to determine the crystallinity of semicrystalline polymers. In the two-phase model, the measured heat of fusion is compared to the melting enthalpy of a completely crystalline polymer to get the crystallinity degree. Fusion heat of a polymeric sample is identified by area under the melting endotherm and a baseline. A correct baseline is heat capacity of the semicrystalline sample. It varies with both temperature and crystallinity and is difficult to evaluate. Enthalpy of a process is a state-function quantity and is independent of the process path. In polymer melting, temperature increase and fusion process occur simultaneously. This makes evaluation of the fusion heat challenging. Herein, alternative paths are supposed in which temperature increase and fusion process occur separately and sequentially. This leads to a convenient enthalpy evaluation. Two alternative paths can be defined: first, polymer melts at a constant temperature which is followed by temperature increase of the melt; second, polymer temperature increases without any change in crystallinity degree which is followed by polymer melting at a constant temperature. Lastly, an enthalpy deficiency due to the amorphous-crystalline interface and an excess enthalpy due to the defects present in crystalline regions are investigated how to affect the crystallinity. Manuscript profile -
Open Access Article
2 - Studying structural properties of polyethylene waxes with infrared spectroscopy
Mina AlizadehaghdamPolyethylene 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. Inf MorePolyethylene 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. Manuscript profile
List of Articles Mina Alizadehaghdam
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