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

저밀도 폴리에틸렌의 결정화도에 대한 저온 열처리 효과: 수소 핵자기공명 연구

  • Lee, Chang-Hoon (Dept. of Polymer Science & Engineering, Chosun University) ;
  • Choi, Jae-Kon (Dept. of Polymer Science & Engineering, Chosun University)
  • 이창훈 (조선대학교 응용화학소재공학과) ;
  • 최재곤 (조선대학교 응용화학소재공학과)
  • Published : 2008.12.31

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.

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