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Effect of Low-temperature Thermal Treatment on Degree of Crystallinity of a Low Density Polyethylene: $^{1}H$ Nuclear Magnetic Resonance Study  

Lee, Chang-Hoon (Dept. of Polymer Science & Engineering, Chosun University)
Choi, Jae-Kon (Dept. of Polymer Science & Engineering, Chosun University)
Publication Information
Elastomers and Composites / v.43, no.4, 2008 , pp. 259-263 More about this Journal
Abstract
An effect of low-temperature long-term thermal degradation on a degree of crystallinity of a low density polyethylene (LDPE) was investigated by using $^1H$ solid state nuclear magnetic resonance (SSNMR). Firstly, the long-term thermal treatment makes a color of LDPE from white to pale yellow which is indicative of thermal oxidation. Secondly, it makes the $^{1}H$ NMR spin-spin and spin-lattice relaxation times ($T_1$) to be long. Lastly, the degree of crystallinity of the semicrystalline aged-LDPE also decreases with thermal treatment. Above all, the $T_1$ increase is envisaged to be due to either a decrease of the amorphous regions governing overall spin-lattice relaxation mechanism in LDPEs or a dynamically restricted motion of specific molecular motions by intermolecular hydrogen bonding or crosslinking. However, since the decrease of crystallinity implies an increase of amorphous regions by the thermal treatment, the former case is contrast to our results. Accordingly, we concluded that the latter effect is responsible for the $T_1$ increase.
Keywords
LDPE; thermal treatment; Degree of crystallinity $^{1}H$-NMR;
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