PET卷绕丝预取向对后加工拉伸性能和纤维结构、性能的影响

应用ＷＡＸＤ、ＤＳＣ、声速法、密度法、双折射等，讨论了在提高卷绕丝纺速与喷丝头拉伸比后，纤维的预取向增大，对其在后加工中的拉伸性能及其结构、性能的影响。结果表明，预取向高的卷绕丝，在后加工一道拉伸过程中，除了非晶取向外，还产生了“应变结晶”（取向诱导结晶）。由此造成晶态、取向非晶态结构差异大，而导致强度、伸长不匀率上升，产生毛丝、缠辊，但可得到高强度纤维。调整拉伸浴槽温度、拉伸速度，可改变卷绕丝的拉伸性能。     

New insights into thermodynamic description of strain-induced crystallization of peroxide cross-linked natural rubber filled with clay by tube model

Clay changes the strain-induced crystallization behavior of natural rubber and induces a dual crystallization mechanism due to the orientation of clay layers during deformation. The structure evolution was probed by in-situ synchrotron wide-angle X-ray diffraction, while the thermodynamics of the onset of crystallization was analyzed by the tube model. The entropy change required for the onset of the strain-induced crystallization of the clay filled rubber is composed of the entropy reduction due to the rubber-filler interactions and also the stretching. The summation of the two kinds of the entropy reduction is nearly equal to that of the neat rubber. The thermodynamic analysis reveals that the orientation of clay layers along the direction of stretching reduces the chain conformational entropy and changes the crystallization mechanism. These results give some new insights into the strain-induced crystallization process and the reinforcement mechanism for the clay filled rubber.     

Some aspects of nonisothermal crystallization of polymers. I. Relationship between crystallization temperature,crystallinity, and cooling conditions

The changes in temperature and crystallinity of polymer during nonisothermal crystallization were theoretically analyzed assuming a cooling condition under which heat transfer occurs at a rate proportional to the difference in temperature between polymer and the environment. When a plateau appears in the temperature change during crystallization, crystallization temperature can be predicted by a simple method. This method gives nearly the same value as that obtained by successive calculations of temperature and crystallinity throughout the whole process. In addition, a graphic method is presented to predict crystallization temperature. By using the plateau temperature observed in melt-spinning experiments, the crystallization rate under molecular orientation is evaluated. Furthermore, a method applicable to estimating the ultimate crystallinity is proposed. A rough estimation of the increase in the rate of crystallization under molecular orientation was carried out for very high-speed spinning of poly(ethylene terephthalate).     

Comparison of structure development in quiescent crystallization,die extrusion and melt spinning of isotactic polypropylene and its compounds containing fillers and nucleating agents

The influences of fillers and nucleating agents on crystalline structure and stress induced crystallization of isotactic polypropylene were studied under a range of cooling and processing conditions, including die extrusion and melt spinning. Continuous cooling transformation curves were determined for polypropylene and various polypropylene filler compounds. The influence of spinline stress on crystallization was studied. The experiments reveal that under quiescent conditions, the kinetics and crystalline forms produced by the crystallization of polypropylene are dominated by nucleating fillers and impurities. The crystalline orientation‐spinline stress relationship, on the other hand, was found to be the same for polypropylene and its compounds. At high uniaxial stresses, kinetics and orientation development are dominated by homogeneous orientation crystallization.     

Crystallization of running filament in melt spinning of polypropylene

The crystallization kinetics of the running filament in melt spinning have been studied for three cases: isothermal crystallization of an isotropic melt, non-isothermal crystallization of an isotropic melt, and non-isothermal crystallization of a non-isotropic melt. Both the temperature and the orientation dependences of nucleation rate and growth rate are estimated for polypropylene. Calculated curves for non-isothermal crystallization of a non-isotropic melt with partial high orientation closely approximate the experimental data. In particular, the experimental data are best explained by crystallization with two-dimensional growth. The crystallization processes in melt spinning may be governed by localized molecular orientation of the supercooled melt in the initial stage.     

Crystallization and orientation behaviors of poly(vinylidene fluoride) in the oriented blend with nylon 11

Oriented films of nylon 11/poly(vinylidene fluoride) (PVDF) blend were prepared by uniaxially stretching the melt-mixed blends. The drawn films of fixed length were heat-treated at 170 °C for 5 min to melt the PVDF component, followed by quenching in ice water or isothermal crystallization at various temperatures. The crystal forms and orientation textures of the obtained samples were studied using wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). It was found that PVDF can crystallize into both and β forms in the nylon 11/PVDF blends, and that the content of the β form increases with increasing crystallization temperature above 120 °C. The orientation behavior of the -form PVDF was observed to be dependent on the crystallization conditions: c-axis orientation to the stretching direction was produced for the sample crystallized below 50 °C; the a-axis of crystals was tilted from the stretching direction when PVDF was crystallized at about 75 °C; the parallel orientation of the a-axis to the stretching direction becomes dominant at higher crystallization temperatures (above 100 °C). In contrast, the β crystalline form maintains the c-axis orientation irrespective of crystallization temperature. It was shown by the confocal laser scanning microscopy that cylindrical domains of PVDF were dispersed in the oriented matrix of nylon 11. The mechanism for the formation of the unique orientation textures is discussed in detail. It was proposed that the a-axis orientation is a result of the trans-crystallization of PVDF in the cylindrical domains confined by the oriented matrix of nylon 11. The crystallization kinetics, WAXD analysis, and morphology studies preferred the trans-crystallization mechanism. The mechanical properties of the as-drawn and heat-treated samples were measured not only in the stretching direction but also in the direction perpendicular to it. It was found that the heat-treated samples show slightly lower tensile strength, but more elongation at the break in the two directions than the as-drawn samples.     

Effects of talc orientation and non-isothermal crystallization rate on crystal orientation of polypropylene in injection-molded polypropylene/ethylene-propylene rubber/talc blends

The effects of talc orientation and non-isothermal crystallization rate on the crystal orientation of polypropylene in the injection-molded PP/EPR/Talc blends were studied by using AFM, DSC, SEM and XRD. Polypropylene was transcrystallized on the talc surface and the polypropylene crystal was oriented perpendicular to the talc surface. Therefore, the crystal orientation was affected by the talc orientation. At the surface of injection-molded specimens, the crystal orientation increased with decreasing the molecular weight of EPRs and increasing the talc content. Because talc particles were nearly oriented parallel to the flow direction in the skin layer of the specimens, the crystal orientation was amplified by the increased crystallization rate. The non-isothermal crystallization behavior of PP/EPR/Talc blends was investigated in terms of the molecular weight of EPRs and the talc content. Non-isothermal crystallization rate increased with decreasing the molecular weight of EPRs due to the plasticizing effect of EPRs and increasing the content of talc which acts as nucleating agent.     

β-羟基丁酸-羟基戊酸共聚物初生纤维力学演变机理初探

β-羟基丁酸-羟基戊酸共聚物(PHBV)初生纤维存放过程中,其力学行为存在明显的演变过程:初生纤维在固体状态表现出由弹性行为为主向塑性行为为主的转变直至最后表现为脆性体特征。为了探究这一特有力学演变的聚集态结构致因,对力学演变的整个过程做了详尽跟踪,并对此过程中纤维内部聚集态结构(包括结晶和取向)的相应变化做了同步测试。结果发现,在初生纤维力学性能发生巨大变化的同时,纤维的结晶度和取向度也有了很大提高,但WXRD图谱显示纤维的晶态结构没有明显改变。由于PHBV在室温下存在二次结晶,还探讨了二次结晶对无定形区的作用及对力学演变的影响。认为在纤维存放过程中,由于二次结晶造成的结晶度(包括晶粒的大小和完善程度)和取向度增大是PHBV纤维变脆的原因。     

Pulsed magnetic field as a new technique to control the crystallization and orientation of poly(trimethylene terephthalate)

Magnetic influence on the crystallization and orientation of poly(trimethylene terephthalate) (PTT) were studied by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), and X-ray diffraction (XRD) during isothermal crystallization at 195 °C under pulsed magnet. The results showed that the crystallization properties of PTT are changed under the influence of pulsed magnetic field. It should be emphasized that the pulsed magnetic field can be applied as a new method to control the crystallization and orientation of polymers.     

Modelling of liquid crystalline compound fibres

A model for slender, liquid crystalline, bicomponent fibres at low Reynolds and Biot numbers based on the slenderness ratio as the perturbation parameter, is presented. The model results in one-dimensional equations for the fibre's radii, axial velocity component and temperature, to which we have added two transport equations for the molecular orientation and crystallization and the effects of these variables on the elongational viscosity. The crystallization kinetics is based on Avrami–Kolmogorov theory and is affected by the molecular orientation, while the latter is based on Doi's slender body theory for liquid crystalline polymers. It is shown that the model depends on a large number of dimensionless parameters, and shows that the axial strain rate and the degree of molecular orientation increase as the activation energy of the dynamic viscosity of the core, the heat transfer losses, the thermal conductivity ratio and the pre-exponential factors ratio are increased, whereas they decrease as the thermal capacity of the core is increased. It is also shown that the degree of molecular orientation increases and reaches a value equal to one, whereas no complete crystallization is achieved. It is also shown that the crystallization first increases sharply and then at a smaller pace. It is also shown that the axial stresses on liquid crystalline bicomponent fibres are much higher than those on amorphous ones.     

Effect of molecular orientation on the crystallization and melting behavior in poly(ethylene terephthalate)

Amorphous poly(ethylene terephthalate) fibers in which the skin was removed were studied to expressly study the effect of amorphous molecular orientation on crystallization behavior. Thermal analysis was carried out on fibers with a wide range of molecular orientation using differential scanning calorimetry (DSC) under constrained and unconstrained conditions. The thermal behavior was correlated with structural characteristics such as amorphous orientation determined using wide-angle X-ray diffraction. We show for the first time a quantitative inverse linear relationship between the degree of amorphous orientation and the cold crystallization temperatures and heat of crystallization. Crystallization begins at a critical amorphous orientation of 0.18, and extrapolation shows that even at modest amorphous orientation of 0.27, the cold crystallization can start spontaneously at T_g and with no change in free energy.     

The onset of orientational crystallization in poly(ethylene terephthalate) during low temperature drawing

It is well known that crystallization can be induced in amorphous poly(ethylene terephthalate) (PET) by orientation below the isotropic crystallization temperature. The magnitude of the strain necessary for crystallization varies inversely with molecular weight because of relaxation. However, lower molecular weight PET might be expected to, crystallize at a lower extent of molecular orientation, since the crystallization rate also varies inversely with molecular weight. Chain conformations were measured during low temperature drawing of PET of various molecular weights. The molecular configuration associated with strain induced crystallization was found to be independent of chain length. The onset of orientational crystallization was associated with a particular conformation, and this critical trans/gauche ratio was equivalent for PETs of various molecular weights. The drawing behavior is thus in accord with theory concerning the transition of flexible chain polymes from isotropy to an ordered state. This result is congruent with previous studies suggesting the presence of extended chain crystallinity in amorphous PET after low temperature drawing.     

涤纶短纤维在纺程中的取向与性能研究

应用ＷＡＸＤ法、声速法、双折射法等研究了涤纶在纺丝与后加工过程中取向的形成变化及和性能的关系,以及工艺条件对纤维结构和性能的影响。结果表明,纤维非晶区取向和结晶度与纤维的刚性和柔韧性密切相关,但决定纤维力学性能的主要的结构因素是纤维的非晶区有序化程度的高低。一次拉伸主要是非晶区链段沿张力方向进行有序排列的过程,伴随生成大量晶核,导致应变结晶;热定型时结晶产生于高度取向的非晶区域,是应变结晶（取向诱导结晶）和热结晶共同作用的结果;高温机械卷曲是在机械挤压条件下的热力学控制的非晶区解取向过程     

聚酯饮料瓶结晶与取向研究

应用广角 X射线衍射及密度法研究了聚酯饮料瓶结晶与取向及其原料和半成品的结构。结果表明 ,聚酯饮料瓶坯已有晶核生成 ,在聚酯瓶成型过程中 ,由于纵向拉伸与横向吹胀阶段拉伸张力的各向异性 ,聚酯产生了方向不同的结晶与取向作用 ,导致 PET瓶料的结晶与取向的差异。广角 X射线衍射法可以测定聚酯饮料瓶结晶与取向结构 ,可为固相缩聚 PET的聚合及吹瓶工艺提供参考。     

PET纤维结晶动力学测试方法的研究

本文描述了用解偏振光强度测定聚合物结晶动力学的仪器。该法不仅可用于无取向聚合物薄膜的测定,亦可用于取向纤维、甚至是在线结晶动力学的研究。本文还研究了光强度与纤维结晶、取向之间的关系。     

聚合物流动诱导结晶取向模型及数值模拟

流动使结晶性聚合物的结晶行为发生很大变化,不仅加速了整个结晶发展过程,还使结晶形态发生变化,形成不同的取向结构。将晶体假设为刚性哑铃,介绍描述晶体取向的数学模型,并结合模型根据闭合近似法模拟稳态简单剪切流场下聚合物的取向行为。     

Computer modeling of isothermal crystallization in short fiber reinforced composites

Computer modeling and simulation for the isothermal crystallization of short fiber reinforced composites with athermal nucleation is presented. The “pixel coloring” technique which is capable of capturing the morphology evolution and calculating the crystallization kinetics is implemented. A parametric study is used to explore the influences of fibers on the crystallization in the reinforced system. The results indicate that the fibers depress the crystallization rate when compared to that of neat polymers or accelerate the crystallization rate by providing nucleation sites. The constraining effect is mainly dependent on fiber content while the enhancing effect is mainly determined by fiber surface and fiber nucleation density. Fiber orientation has almost no effect on the crystallization kinetics but changes the ultimate morphology. Fiber length and fiber diameter have different influences on crystallization kinetics and mean size of spherulites. Results show that fiber diameter affects the crystallization much more than that of fiber length.     

Oriented crystallization of xanthine derivatives sublimated on self-assembled monolayers

The oriented crystallization of caffeine and theobromine on self-assembled monolayers (SAMs) is reported. The SAMs were prepared by reacting 1-decanethiol, 11-mercapto-1-undecanol, or 11-mercaptoundecanoic acid on flat Au surfaces to form methyl, hydroxyl, or carboxylic acid functionalities on the substrates. Crystallization was conducted by sublimating the xanthine alkaloids on the SAMs. X-ray diffraction and morphology observation/simulation were combined to identify the preferred orientation of caffeine and theobromine crystals. Also, the identified crystal orientation was examined through molecular models to understand the nature of the interfacial interactions that direct the nucleation process. CH/π interaction as well as strong hydrogen bonding appeared to act as the specific interactions to control the molecular orientation of caffeine and theobromine in stereochemically determined manners that persisted during the crystallization process. More importantly, the stability of the orientational regulation showed a clear correlation to the cohesiveness of the xanthine molecular layer parallel to the nucleating substrate. We believe this indicates that the structural coherence of the precursors or nuclei of the crystallization is essential to effectively utilize the interfacial interactions in a cooperative manner to firmly control the crystal orientation.     

Orientation and crystallization in poly(ethylene terephthalate) during drawing at high temperatures and strain rates

We review some recent research developments on structure development during drawing of poly(ethylene terephthalate) film, and we report a study of constant-load drawing of amorphous PET film at temperatures of 120°C and 132°C, including the effects of redrawing high-temperature drawn film at lower temperature. To permit constant-load drawing at high temperature without inducing crystallization in the undrawn specimen, a drawing instrument was built that permits very rapid heating of the sample, and its operation is described. The initial stage of drawing at high temperatures is characterized by polymer flow where, owing to high rates of molecular relaxation, neither molecular orientation nor crystallization occurs. Strain-rate increases sharply in the course of the deformation, reducing the time available for relaxation, and the chains start to orient at a draw ratio that depends on temperature. Orientation rapidly reaches a saturation level, which is lower at the higher draw temperature. Crystallization onset seems to lag only slightly behind orientation onset because the critical orientation for inducing crystallization is very low at these temperatures. It appears that there is time for crystallization to proceed to pseudo-equilibrium values corresponding to a particular orientation level, which differs from previous results obtained from constant-force drawing at lower temperatures, and possible reasons for this are discussed. In two-stage drawing, where film drawn at 132°C was redrawn along the same axis at 100°C, high draw ratios were obtained despite the high strain rates, and the levels of noncrystalline orientation and crystallinity were similar to the levels expected from single stage drawing at 100°C.     

Shear induced crystallization of poly(m-xylylene adipamide) with and without nucleating additives

The shear induced crystallization of the poly(m-xylylene adipamide) (MXD6) which is a semi-aromatic polyamide, was studied for a virgin (PA1) and a nucleated (PA2) grades using a shearing hot stage coupled with a microscope. Half crystallization times were measured according to the crystallization conditions (crystallization temperature, shear rate and shearing time). The effect of shear on the crystallization kinetics was shown by a strong decrease of the crystallization times for both materials. PA2 sensitivity to shear was much lower than that of PA1. This was attributed to the presence of nucleating agents which increased the primary nucleation density in the unsheared quiescent melt, leading to a higher necessary shear rate to overcome the quiescent nucleation. Kinetic models were proposed to predict the crystallization process as a function of the crystallization conditions. They were based on both Avrami and Hoffman-Lauritzen theories and modified to take into account the effect of shear. In the model the nucleation rate of the crystalline entities was related to the shear rate by a power function. Besides, crystalline morphology and orientation were studied by wide and small angle X-ray scattering to confirm the orientation effect of the shear in the crystalline part of the material.