New Insights into the Multiple Melting Behaviors of the Semicrystalline Ethylene-Hexene Copolymer: Origins of Quintuple Melting Peaks.
作者：Jie Qiu, Donghua Xu, Junchai Zhao, Yanhua Niu, Zhigang Wang*.
關(guān)鍵字：crystallization,polyolefins,thermal properties
論文來源：期刊
具體來源：Journal of Polymer Science: Part B: Polymer Physics 2008, 46, 2100-2115.
發(fā)表時(shí)間：2008年
A semicrystalline ethylene-hexene copolymer (PEH) was subjected to a
simple thermal treatment procedure as follows: the sample was isothermally crystallized
at a certain isothermal crystallization temperature from melt, and then was
quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating
scan of the sample by using differential scanning calorimeter (DSC). Particularly, an
intriguing endothermic peak (termed as Peak 0) was found to locate at about 45 C.
The multiple melting behaviors for this semicrystalline ethylene-hexene copolymer
were investigated in details by using DSC. Wide-angle X-ray diffraction (WAXD) technique
was applied to examine the crystal forms to provide complementary information
for interpreting the multiple melting behaviors. Convincing results indicated that
Peak 0 was due to the melting of crystals formed at room temperature from the much
highly branched ethylene sequences. Direct heating scans from isothermal crystallization
temperature (Tc, 104–118 C) were examined for comparison, which indicated
that the multiple melting behaviors depended on isothermal crystallization temperature
and time. A triple melting behavior could be observed after a relatively short isothermal
crystallization time at a low Tc (104–112 C), which could be attributed to a
combination of melting of two coexistent lamellar stack populations with different lamellar
thicknesses and the melting-recrystallization-remelting (mrr) event. A dual
melting behavior could be observed for isothermal crystallization with both a long
enough time at a low Tc and a short or long time at an intermediate Tc (114 C), which
was ascribed to two different crystal populations. At a high Tc (116–118 C), crystallizable
ethylene sequences were so few that only one single broad melting peak could be
observed.