尼龙-6 18的晶型转变研究

以偶偶尼龙-6 18为例, 通过示差扫描量热分析(DSC), 广角X射线衍射(WAXD)与傅里叶变换红外光谱(FTIR)等方法研究了其Brill转变的过程, 探索了脂肪族聚酰胺的晶型转变的本质. X射线衍射结果表明， 随着温度的升高, 尼龙-6 18由三斜晶系转变为假六方晶型, 同时其DSC曲线上出现一个较宽的吸热峰. 红外光谱结果表明, 在其晶型转变过程中, 晶体内氢键强度逐渐减弱, 与酰胺键相连的C—C和C—N键发生扭曲. 酰胺基团之间的亚甲基链段的振动逐渐增强, 部分亚甲基单元由反式构象变成旁式构象, 最后整齐排列的亚甲基链段逐渐变得无序化.

Investigation on the Crystalline Transition of Nylon-6 18

The Brill transition of even\|even nylon-6 18 was investigated by using differential scanning calorimetry(DSC),  temperature-dependent wide angle X-ray diffraction(WAXD) and Fourier transform infrared(FTIR). The X-ray diffraction results indicate that the melt-crystallized sample of nylon-6 18 transforms from the triclinic unit cell to the pseudo-hexagonal phase in the  temperature range of 120—180  ℃. In this range,  the thermograph of nylon-6 18 presents a broad endothermal peak. From the FTIR spectra,  it can be found that,  during the transition process of nylon\|6 18,  the intensity of the intrasheet hydrogen bonds  becomes weak. At the same time,  the CH2-amide bonds twist and the all\|trans conformation of methylene sequences is disordered by inserting the gauche conformation. The CH2 segments are in a mobile state because of the enhanced stretching and twisting vibrations of  C—CO and C—N bonds.