高速纺PET纤维结构第三态的初步探讨

本文应用计算分峰的原理,用系数不同的不对称高斯函数去分别表征PET纤维的中介态和无取向非晶态的X衍射,并在实验上设法把这两种衍射区分开来,从而建立了能够测算纤维中晶态、中介态和无取向非晶态的相对含量的方法。用这方法研究了高速纺PET拉伸丝在各温度下热处理时的结构,结果表明,纤维的结晶度随热处理温度升高而相应增加,但中介态含量、无取向非晶态含量及许多性质在130—160℃之间出现转折。作者从中介态在热理处时可能发生解取向松驰和发生结晶的综合变化加以解释,DSC的研究结果符合上述观点。     

取向非晶态聚对苯二甲酸乙二酯(PET)膜的结晶

采用小角和广角X-散射法比较了未拉和热拉PET膜在结晶性能方面的差别,热拉试样在分子链段的小尺度范围内基本上是无规取向,而在分子链的大尺度范围内却是高度取向的。研究结果表明:热拉PET膜的结晶诱导期较短,长周期发展得较快,结晶后小角X-线散射表现出明显的各向异性,在热处理过程中先出现显著的热收缩,随后又表现出结晶伸长现象,这些都和未拉试样有明显的差别。     

聚对苯二甲酸乙二酯非晶态膜片单轴热——拉伸中的结晶与松弛

用动态力学损耗温度谱作为测试手段,研究了非晶态PET膜片在78—112℃温度范围内的单轴拉伸。实验结果说明,在较低温度下所得结晶的拉伸试样,完全由于应变诱发结晶,发生在应力-应变曲线的屈服后应力开始上升的阶段。在较高温度下(90℃或更高)拉伸可得非晶态而且光学各向同性的试样,是由于分子链的小尺度取向在拉伸过程中已完全热松弛所致,而分子链的大尺度取向要通过高弹态流动而松弛,其速率较慢,用拉伸后试样两端固定时的应力松弛进行了观察。在较低温度下应力松弛后仍为非晶态,在较高温度下应力松弛到起始应力的1O％下才开始结晶。FTIR研究表明在这种状态下的结晶有一结晶诱导期,其时间尺度与应力松弛阶段相当。     

不同结晶速率的PET薄膜在拉伸过程中的结晶与取向

用多种方法对两个结晶速率不同的PET样品在拉伸过程中的结晶和取向进行了研究。结果表明在同样的拉伸条件下,结晶速率较快的样品的结晶度和取向程度均比另一样品要高得多,这种结构变化上的差别说明把拉伸行为的差别归因于结晶速率的不同是合理的。     

取向态聚对苯二甲酸乙二酯膜热弛豫过程的偏振红外光谱研究

用升温在位偏振红外光谱测量方法，研究了不同取向态的聚对苯二甲酸乙二酯（ＰＥＴ）膜在热弛豫过程中的尺寸变化以及分子链构象和取向的变化．结果说明，ＰＥＴ小尺度取向链段的热弛豫较大尺度取向分子链的热弛豫在较低的温度下发生，取向ＰＥＴ膜的热收缩主要与分子链大尺度取向的弛豫有关，而其后的自发伸长是结晶过程引起的，分子链的取向程度对结晶伸长的幅度有着重要影响．     

试样两端固定或松弛态结晶对取向非晶态聚对苯二甲酸乙二酯膜结晶的影响

<正> 在研究聚合物的结晶过程中,有时(如在同步辐射法、X-衍射法和红外法的测定中)须将试样两端固定,有时(如研究热处理过程中取向聚合物的尺寸和结构变化)须将试样处于松弛状态。因而研究两端固定或松弛状态对取向聚合物结晶速率和结构的影响引起了人们的兴趣。一些研究结果得出,与松弛状态结晶相比,试样两端固定态结晶使取向聚合物的结晶速率变慢,但有时也出现相反的结果。此外,在上述文献中所用的原始试样都已具有较高的结晶度。为了弄清这一问题,我们用密度、双折射和应力测量等方法对取向程度不同的非晶态PET膜进行了深入和系统的研究。结果表明,试样两端固定与否对结晶速率的影响与试样原始的取向程度有关。     

拉伸取向对绦纶纤维结晶过程的影响

拉伸取向是合成纤维生产过程中的重要环节,几乎所有的合成纤维都须要经过拉伸过程。至目前为止,对高聚物本体结晶过程的研究已有了很多的工作,但有关拉伸取向后的纤维结晶过程却研究得很少.聚对苯二甲酸乙二酯的分子链比较刚性,当它从熔融状态骤冷淬火时容易得到完全透明的非晶态聚合物(薄膜或纤维).有许多工作业已证实,     

涤纶薄膜拉伸过程中的电镜研究

<正> 聚对苯二甲酸乙二酯(PET)是用于纤维和薄膜的最重要的高分子材料之一。在拉伸过程中拉伸温度、拉伸比、应变速率等不同因素对PET的结晶、取向以及所形成的织态等的影响已有过广泛的研究。但用电镜直接观察PET薄膜在不同拉伸条件下的高分子聚集态结构的变化则报道很少。我们选择丙烯胺作刻蚀剂处理拉伸方式、拉伸温度、应变速率和拉伸比不同的PET试样,用扫描电镜直接观察其形态的变化。     

硬弹性聚丙烯纤维分子链的取向特征

硬弹性聚丙烯是在应变结晶和热结晶两个复合过程中形成的。利用双折射并结合广角X射线衍射（WAXD）等方法，研究了硬弹性聚丙烯在制备过程中晶相及非晶相分子链取向的变化，讨论了分了链的取向与硬弹性的关系。结果发现：降低熔体温度或提高熔体拉伸比可以提高晶相及非晶相分子链的取向，热处理时，晶相分子链的取向程度有所提高，而非晶相分子链的取向程度有所下降。在所研究的热处理温度的范围内，硬弹性聚丙烯的弹性回复率越高，晶相分子链的取向程度越高。     

PET/PTT双组分弹性长丝的结晶取向结构和卷曲性能

为研制军官礼服用PET/PTT双组分弹性长丝,在纺丝加工工艺研究的基础上,通过声速法、WAXD、DSC、Instron5566对典型工艺下的弹性长丝进行了结晶和取向结构及卷曲性能的测试分析.在可纺的前提下,PET/PTT两组分复合纺丝中,PET组分优先结晶,具有高于其单组分纤维的拉伸诱导取向和结晶;而PTT组分只有形变,其结晶度和晶区取向均低于其对应的单组分纤维.在实验条件范围内,两组分粘度差异越大,纤维的卷曲伸长率和收缩率越大、声速取向因子增加、各单组分结晶度增加;两组分质量比为50/50时,纤维有最大的卷曲伸长率和收缩率,且各单组分结晶度随该两组分含量差异的增加而减少,而声速取向变化相反;随牵伸比的增加,纤维的整体取向、各组分结晶度均有所增加,卷曲伸长和收缩率也增加.牵伸温度和定型温度对双组分纤维的结构和卷曲性能影响较小.     

超拉伸聚乙烯的弹性模量和导热性能

为了揭示聚合物分子链伸展、取向的本征特性，发展了两个新的测量方法和实验装置，用于研究拉伸比高达２００的超拉伸聚乙烯凝胶的弹性性能、传热性能和聚合物结构的关系．应用激光脉冲热致超声法给出材料拉伸方向和横向杨氏模量，应用激光脉冲光热辐射法给出拉伸方向，横向和厚度方向的导热系数．随拉伸比λ的增加，轴向杨氏模量急剧的增加，而横向的仅有少许减小．导热系数具有相似的特性．本文发现当λ＝２００时，这种拉伸取向聚乙烯的轴向模量可达钢的８０％，而导热系数甚至可达２倍，直至成为热的良导体，这是由于在高拉伸比时形成了相当数量的伸展分子链构成的针状晶体———晶桥．本文提出晶桥作为短纤维分散相的取向聚合物的结构模型，对于超拉伸聚乙烯的上述特性可以进行统一描述和定量化分析，和实验结果很好符合．     

Effect of draw ratio on the microstructure, thermal, tensile and dynamic rheological properties of insitu microfibrillar composites

Microfibrillar composites (MFCs) were prepared using different draw/stretch ratios [viz. 2, 5, 8 and 10] from polypropylene/polyethylene terephthalate (PP/PET) blends. Scanning electron microscopy [SEM] images revealed that PET microfibrils were highly oriented after melt blending and drawing. After the conversion of drawn (stretched) blends to MFCs the PET microfibrils were found to be randomly distributed in the PP matrix. The tensile strength and modulus of the MFCs were found to be higher for the samples drawn at stretch ratios 5 and 8 on account of the long PET microfibrils they possessed. The non isothermal crystallization behaviour of the neat blend (as extruded), stretched blend and the MFC was compared. The oriented PET fibrils in the stretched blend were found to have a greater nucleating effect for the crystallization of PP than the spherical PET particles in the neat blend and randomly oriented short PET fibrils in the MFC. Dynamic rheology studies indicated the storage modulus and loss modulus of MFCs were enhanced as draw ratio increases up to an optimized level beyond which they decrease. When the draw ratio increased up to the optimized level the MFCs tended to be more viscous, especially at low frequency, whereas further increasing the draw ratio resulted in a decrease in the complex viscosity. The microfibrils of PET in the MFC were found to perturb the relaxation of molten PP matrix.     

单轴取向聚对苯二甲酸乙二酯非等温结晶动力学研究

采用等速升温DSC方法对单轴取向聚对苯二甲酸乙二酯 (PET)的结晶过程进行了研究 ,发现单轴取向PET的冷结晶峰表现为多重结晶峰 .等温DSC方法的研究结果进一步证实结晶重峰的存在 .为此 ,本文提出了一种依据非等温DSC曲线解析高聚物结晶动力学参数的新方法 .对单轴取向PET的研究结果表明 ,与其他方法相比较 ,由新方法计算出的理论曲线与实验数据能更好地吻合 .单轴取向PET的总的结晶过程由三个子结晶过程组成 .根据不同拉伸比 ,各个子过程的Avrami指数和质量分数的变化 ,对结晶机理进行了解释 .与各向同性PET样品相比 ,单轴取向PET在低温部分的结晶速率明显增快     

Visualization of structural rearrangements during annealing of solvent-crazed poly(ethylene terephthalate)

A direct microscopic procedure is used for studying structural rearrangements during the annealing of PET samples after solvent crazing. Even at room temperature, solvent-crazed PET samples experience shrinkage which is provided by processes taking place in crazes. This shrinkage is observed at temperatures up to the glass transition temperature of PET and proceeds via drawing together of crack walls. Once the glass transition temperature is attained during annealing, the spontaneous self-elongation of the polymer sample occurs. The mechanism of this phenomenon is proposed. The low-temperature shrinkage of the polymer sample is related to the entropy contraction of highly dispersed material in crazes that has a lower glass transition temperature than that of the bulk polymer. This shrinkage cannot be complete, owing to crystallization of the oriented polymer in the volume of the crazes. As a result of crystallization, the oriented and crystallized polymer in the crazes coexists with the regions of the unoriented initial PET. As the annealing temperature approaches the glass transition temperature of the bulk PET, its strain-induced crystallization takes place. As a result, the regions of the unoriented polymer between crazes are elongated along the direction of tensile drawing and the sample experiences contraction in the normal direction.     

高取向聚对苯二甲酸乙二酯纤维的热收缩应力

为得到具有更高拉伸强度和模量的半晶聚合物纤维,需要使分子链充分结晶和取向,然而这种高度取向样品受热时,随着温度的升高,取向的非晶态分子链熵力增大,解取向可以自发进行.在外加张力较小时,纤维产生热收缩;在定长状态下,表现为外加张力增大,此过程被视为取向材料中＂冻结＂内应力的释放,通常将这种内应力称为热收缩应力。     

Solid-state coextrusion of poly(ethylene terephthalate). I. Drawing of amorphous PET

Films of uniaxially oriented poly(ethylene terephthalate) (PET), M _v = 81,000, have been drawn by solid-state coextrusion in the range 40–100°C surrounded by polyethylene. This is well below the PET melting temperature and in some cases below its glass transition temperature. Properties of the extrudates, such as degree of crystallinity, mechanical and thermal properties, were investigated as a function of coextrusion temperature and draw ratio (EDR ≤ 4.4). The results show that the percent crystallinity depends strongly on draw ratio, whereas its sensitivity to extrusion temperature is limited only to the highest draw ratio (4.4). On the other hand, Young's modulus was sensitive to both extrusion temperature and draw ratio, exhibiting a maximum at EDR = 4.4 and T_ext = 65°C. Above this temperature, moduli decrease apparently because of increased chain mobility, resulting in dissipation of chain orientation. Furthermore, changes in yield and tensile strength followed the changes in mechanical properties, suggesting that they are dominated by the same factors. The cold-crystallization temperature T_CC also revealed information about the morphological changes occurring during the extrusion drawing. For samples of EDR = 4.4, T_CC increased with extrusion temperature, suggesting again dissipation of orientation by thermal motions. On the other hand, T_CC decreases with EDR, and a ΔT_CC as high as 73°C was found. Conventional drawing of amorphous PET has been widely reported. To our knowledge this is the first time oriented PET has been prepared using the advantages of solid-state coextrusion.     

Biaxial stretching of pet films: A molecular description

Biaxially oriented poly(ethylene terephthalate) films were prepared under well defined stretching conditions in order to mimic the three stages of the industrial inverse drawing process. Molecular orientation has been characterized through X-ray diffraction and infrared dichroism. The main orientation mechanisms in the constant-speed drawing of an amorphous film as well as in the constant-force transverse drawing of monodrawn samples are described. It is shown that relaxation phenomena dominate the orientation of an amorphous sample. Reorientation along the second drawing direction involves rotation of crystalline blocks along the draw direction and further crystalline growth. The high-temperature heating stage leads to an almost four-fold increase in the size of the crystallites. The orientation of the amorphous phase is controlled by the mechanisms occurring during crystallization (relaxation followed by extension).     

Crystallization in oriented poly(ethylene terephthalate) fibers. II. Consequences in subsequent deformation

When a melt-spun poly(ethylene terephthalate) (PET) fiber is heat treated at a temperature above its glass transition temperature, the relative rates at which the crystallization and major orientational relaxation processes occur have been shown to have a pronounced effect on the structure of the fiber and its deformability. The present study describes the consequences of this aspect, with examples from drawing of melt-spun PET fibers subsequent to their crystallization by thermal annealing. Additional features of the highly ordered PET fibers which can be produced through a combination of oriented crystallization and drawing at high temperatures are also given.