Heterogeneous Stress Distribution and Hierarchical Structure in the Highly Oriented Nylon 6 Strings Annealed at Various Temperatures to Evaluate the True Crystallite Modulus
Heterogeneous Stress Distribution and Hierarchical Structure in the Highly Oriented Nylon 6 Strings Annealed at Various Temperatures to Evaluate the True Crystallite Modulus
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在不同温度下退火的高取向尼龙 6 线中的不均匀应力分布和层次结构，以评估真实的微晶模量
DOI：
10.1021/acs.macromol.1c00142
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发表时间：
2021
期刊：
影响因子：
5.5
通讯作者：
Tashiro Kohji
中科院分区：
文献类型：
--
作者：
Kummara Sreenivas;Tashiro Kohji
用X射线衍射法测定了一系列在不同温度下拉伸退火的尼龙6熔体拉伸丝沿链轴的表观微晶模量Ecap。表观杨氏模量是在应力分布均匀或结晶应力与本体应力相等的假设下得到的。在30-180 °C温度范围内退火后，Ecapp从未退火样品的160 GPa急剧下降到60 GPa（I区），然后在180-220 °C温度范围内退火后，Ecapp急剧上升到230 GPa（II区）。体样品的弹性模量约为3.5GPa，在I区变化不大，在II区退火后弹性模量增加到5GPa。为了从结构的角度解释所观察到的EcappandEbulk的变化，基于广角和小角X射线散射、偏振红外（IR）光谱和热分析，收集了本文所用的所有样品的各种实验数据，从中获得晶胞参数、各向异性微晶尺寸、结晶度、已经确定了结晶和非晶区域中的链取向度、堆叠薄片的长周期和平均厚度等。由此衍生的结构特征可以描述如下：原始熔融拉伸样品由高度取向的结晶相和机械应变且相对高度取向的无定形相组成，所述无定形相包含少量的拉紧的连接链。在区域I中的热处理引起这些连接链的增加，而在结晶区和非晶区中的链取向保持不变。在区域II中的退火诱导了具有更规则地堆积和更高度延伸的链的较大微晶的显著结构演化。引入了机械串并联模型，并适当地选择参数（pandq），以给出令人满意的良好再现性。退火对这些参数的影响被认为是对应的结构演变所揭示的X-射线和IR数据分析。对于在熔点以下立即退火的样品，最终获得的最大Ectrue或沿链轴的真实杨氏模量沿着为约290 GPa，其接近但略低于理论上预测的晶格中完全伸展的尼龙6链的值312 GPa。
The apparent crystallite modulusEcappalong the chain axis has been measured by the X-ray diffraction method for a series of melt-drawn nylon 6 strings annealed at various temperatures under tension, where “apparent” means Young’s modulus obtained under the assumption of the homogeneous stress distribution or the assumption of the equality between the crystalline stress and the stress of the bulk sample. TheEcappdecreased drastically from 160 GPa of the original unannealed sample to 60 GPa for the sample annealed in a temperature region of 30–180 °C (region I) and then increased steeply up to 230 GPa by the annealing in 180–220 °C (region II). TheEbulkor Young’s modulus of the bulk sample was about 3.5 GPa and did not change very much in region I, and it increased to 5 GPa by annealing in region II. In order to interpret the observed change inEcappandEbulkfrom the structural point of view, various experimental data have been collected for all of the samples used here on the basis of the wide-angle and small-angle X-ray scattering, the polarized infrared (IR) spectra, and the thermal analysis, from which the unit cell parameters, the anisotropic crystallite size, the degree of crystallinity, the degree of chain orientation in the crystalline and amorphous regions, the long period and averaged thickness of the stacked lamellae, and so forth have been determined. The thus-derived structural features may be described as follows: the original melt-drawn sample consisted of the highly oriented crystalline phase and the mechanically strained and relatively highly oriented amorphous phase containing a small amount of the taut tie chains. The heat treatment in region I caused an increase of these tie chains with the chain orientation kept unchanged in both of the crystalline and amorphous regions. The annealing in region II induced the remarkable structural evolution of the larger crystallites with the more regularly packed and more highly extended chains. The mechanical series–parallel model was introduced, and the parameters (pandq) were chosen suitably to give a satisfactorily good reproduction of the observedEcapp. The annealing effect on these parameters was found to correspond well to the structural evolution revealed by the X-ray and IR data analysis. The finally obtained maximalEctrueor the true Young’s modulus along the chain axis was about 290 GPa for the sample annealed immediately below the melting point, which is closer to but slightly lower than the value 312 GPa predicted theoretically for the fully extended nylon 6 chains in the crystal lattice.