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| 不同加工条件聚酰胺1012纤维的 结构与力学性能研究
摘 要
由于普通聚酰胺存在低温脆化和尺寸稳定性差等缺点，因此近年来长碳链聚酰胺纤维的研究得到了广泛关注。其中包括我国成功开发出的长碳链聚酰胺1012（PA1012），通过对PA1012片材、薄膜、复合材料等多方面的研究，结果表明PA1012具有较低的吸水率，尺寸稳定性好、耐油、耐碱且无毒、耐摩擦性能良好等特性。目前有关PA1012纤维方面的研究较少。为了拓宽PA1012纤维的应用领域，本课题对不同加工条件制备的PA1012纤维分别从变温条件、微观结构演化、耐疲劳性能、界面性能研究四个方面来研究PA1012纤维的结构与力学性能。
不同温度下PA1012纤维的拉伸力学性能研究结果表明：1）常温拉伸过程中，随着牵伸比的增加，PA1012纤维初始模量、屈服强度、屈服伸长率而增加，断裂伸长率减小。加弹后的PA1012纤维没有明显的屈服点，纤维初始模量下降50%以上，纤维的断裂伸长率明显增大；相同规格的PA6纤维的断裂比强度是PA1012纤维两倍，但PA1012纤维的断裂伸长率远大于PA6。2）随着温度的升高，PA1012纤维的屈服强度逐渐降低，屈服应变向右移动，纤维的断裂伸长率逐渐增大，大拉伸的大应变后期出现断脱的现象，不同牵伸比的PA1012纤维变化情况一致；PA1012全牵伸纤维拉伸形变的屈服点逐渐弱化，逐渐与加弹纤维的拉伸形变曲线变化相似。3）随着温度降低，PA1012纤维模量增大，屈服强度增大，全牵伸纤维的断裂伸长小幅减小，加弹后纤维的断裂伸长率未有明显变化。在-70℃时PA1012纤维的断裂伸长率为PA6的两倍，PA1012纤维耐低温性能良好。
拉伸外场下PA1012纤维结构演化过程研究结果表明：1）随着拉伸的进行，（100）晶面与（110/010）晶面对应的双峰逐渐合并为一个单峰，此外，从WAXS衍射图中观察到Brill转变现象，两个衍射环伴随着应变增加逐渐转变为一个衍射环。这表明在拉伸过程中从α晶型与少量γ晶型混合晶型逐渐转变成了γ晶，大应变情况下发生了Brill转变，同时在SAXS衍射光斑图中观察到明显的纤维晶衍射条纹。2)在PA1012纤维拉伸后的红外光谱测试表明，3300cm-1处谱带为氢键键合的N-H伸缩振动，该谱带强度反映了聚酰胺整体氢键作用大小。随着应变增加，3300cm-1处谱带强度先增大后减小，谱峰位置逐渐向高波数移动，这都表明拉伸过程中氢键作用先增强后逐渐减弱。
纤维的耐疲劳性能研究结果表明：1）随着牵伸比的增加，PA1012纤维的蠕变量先减小后增大，在牵伸比为1.9时纤维的蠕变量达到最小值；加弹纤维纤维蠕变量大于全牵伸纤维蠕变量。PA6纤维蠕变量大于PA1012纤维蠕变量。2）纤维的松弛量随牵伸比增大而降低，加弹后纤维的总松弛量上升；由于PA1012纤维的分子链较PA6更长，因此其松弛量较小。3）循环拉伸过程中，随着牵伸比的增加，拉伸功恢复系数呈现先减小后增大，再减小的变化规律。当牵伸比为1.9时，拉伸功恢复系数达到最大值0.862。所有测试的纤维样品中，纤维的多次循环弹性恢复率稳定在90%以上，加弹不影响纤维弹性恢复率。因此PA1012纤维在耐疲劳方面的应用潜在价值很高。
PA1012纤维界面性能研究结果表明：1）正压力相同条件下，随着牵伸比的增大，纤维摩擦系数也逐渐减小；2）加弹后纤维的初始模量减小导致纤维的刚度降低，致使纤维摩擦系数增大，其次加弹之后纤维物理外观发生较大变化，导致加弹后PA1012纤维的摩擦系数增大。3）正压力相同、纤维细度相同时，PA1012纤维比PA6纤维摩擦系数大。4）整体来看，软态环氧树脂与PA1012纤维的界面剪切强度大约是硬树脂的2倍，剪切强度也会受到树脂球的大小影响。
关键词：PA1012纤维；高低温拉伸；微观结构演变；耐疲劳性能；界面性能
ABSTRACT
Due to the low temperature embrittlement and poor dimensional stability of common polyamides,the research of long carbon chain polyamide fibers has been widely concerned in recent years. Including the long carbon chain polyamide 1012 (PA1012) which was successfully developed in China.Through the study of PA1012 sheet, film, composite and so on,the results show that PA1012 has low water absorption,good dimensional stability, oil resistance, alkali resistance, non-toxic and good friction resistance. At present, there are few researches on PA1012 fibers.In order to broaden the application field of PA1012 fibers,the structure and mechanical properties of PA1012 fibers prepared under different processing conditions were studied from four aspects: variable temperature conditions, microstructure evolution, fatigue resistance and interface properties.
The results of tensile mechanical properties of PA1012 fiber at different temperatures show that: 1) with the increase of draw ratio, the initial modulus,yield strength and yield elongation of PA1012 fiber increase, while the elongation at break decreases. The results show that the PA1012 fiber has no obvious yield point,the initial modulus of the fiber decreases by more than 50%,and the elongation at break of the fiber increases obviously;the specific strength at break of PA6 fiber with the same specification is twice that of PA1012 fiber, but the elongation at break of PA1012 fiber is much higher than that of PA6 fiber. 2) With the increase of temperature, the yield strength of PA1012 fiber decreases gradually,the yield strain moves to the right, and the elongation at break of PA1012 fiber increases gradually. At the later stage of large strain,the phenomenon of "lotus root broken and filamentous" appears,and the change of PA1012 fiber with different drafting ratio is the same; the yield point of PA1012 fiber with full drafting gradually weakens, and gradually coincides with the tensile deformation curve of elastic fiber The line changes are similar. 3) With the decrease of temperature,the modulus and yield strength of PA1012 fiber increase, and the elongation at break of the fully drawn fiber decreases slightly. The elongation at break of the fiber has no obvious change after texturing.At - 70 oc, the elongation at break of PA1012 fiber is twice that of PA6, and PA1012 fiber has good low temperature resistance.
resistance.
The results of the microstructure evolution of PA1012 fiber under external tensile field show that: 1) with the extension,the double peaks corresponding to (100) crystal plane and (110 / 010) crystal plane gradually merge into a single peak. In addition, Brill transition is observed in WAXS diffraction pattern,and the two diffraction rings gradually transform into one with the increase of strain. The results show that the mixed form of α and a small amount of γcrystal gradually transforms into γ crystal during the stretching process, and Brill transformation occurs in the case of large strain. At the same time, obvious diffraction fringes of fibercrystal are observed in SAXS diffraction spot pattern. 2) The infrared spectrum of PA1012 fiber after stretching showed that the band at 3300 cm-1 was N-H stretching vibration of hydrogen bonding,and the strength of the band reflected the overall hydrogen bonding effect of polyamide. With the increase of strain,the band strength at 3300cm-1 increases first and then decreases, and the peak position gradually moves to higher wave number, which indicates that the hydrogen bonding effect increases first and then decreases gradually.
The results of the fatigue resistance of the fiber show that: 1) with the increase of drafting ratio,the creep of PA1012 fiber first decreases and then increases, and reaches the minimum when the drafting ratio is 1.9; the creep of elastic fiber is greater than that of full drafting fiber.The creep of PA6 fiber is larger than that of PA1012 fiber.2) The results show that the relaxation of PA1012 fiber decreases with the increase of drawing ratio, and the total relaxation of PA1012 fiber increases with the increase of drawing ratio. 3) In the process of cyclic drawing, with the increase of drawing ratio,the coefficient of recovery of drawing work decreases first, then increases, and then decreases. When the draft ratio is 1.9, the maximum recovery coefficient of tensile work is 0.862.In all the tested fiber samples,the elastic recovery rate of the fiber is more than 90% after repeated cycles, and the elastic recovery rate of the fiber is not affected by adding elastic. Therefore, PA1012 fiber has high potential application value in fatigue resistance.
The results of the interface properties of PA1012 fiber show that: 1) under the samepositive pressure, the friction coefficient of PA1012 fiber decreases with the increase of draft ratio; 2) the decrease of initial modulus leads to the decrease of stiffness and the increase of friction coefficient; secondly,the physical appearance of PA1012 fiber changes greatly, which leads to the increase of friction coefficient . 3) The friction coefficient of PA1012 fiber is higher than thatof PA6 fiber under the same positive pressure and fiber fineness. 4) On the whole, the interfacial shear strength of soft epoxy resin and PA1012 fiber is about twice that of hard resin, and the shear strength is also affected by the size of resin ball.
KEY WORDS:PA1012 fibers; Stretch at high or low temperature;On the evolution of microstructure; fatigue resistance; interface performance；
TYPE OF THESIS:Application Fundamentals
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