高分子薄膜双向拉伸成型过程的计算机仿真

采用速率形式的弹塑性大变形静力显式有限元方法和单向拉伸的KMM模型对高聚物薄膜的双向拉伸过程进行了数值模拟,对比分析了薄膜在双向拉伸过程中考虑速率敏感和不考虑速率敏感时的应变分布变化.     

基于双向拉伸的温度对高聚物薄膜热成型性能的影响研究

以高聚物薄膜材料为研究对象,搭建了双向拉伸试验装置,开展了不同温度下高聚物薄膜材料的双向拉伸实验。结果表明,不同温度下双向拉伸载荷与位移曲线存在一致的变化关系。由于剪张比的变化,双向拉伸作用下高聚物薄膜材料的屈服载荷明显大于单向拉伸,同时,双向拉伸下屈服载荷与当量弹性模量随着温度的增加逐渐减小,且存在负相关关系。     

双向拉伸聚氟乙烯薄膜的拉伸工艺研究

探讨了聚氟乙烯(PVF)流延膜在制备过程中常见的缺陷及产生原因,并给出了具体的加工工艺参数。结合PVF 薄膜的双向拉伸机理,通过力学及热性能测试表明:膜片的纵向拉伸温度为120～135℃,拉伸比为2.5～3.0时,薄膜不会出现细颈现象,且所需拉伸应力较小;当横向拉伸温度控制在130～150℃,拉伸比为2.5～3.5时,薄膜厚度介于23～28μm之间,且力学性能基本保持各向同性;双向拉伸的薄膜经过170～180℃热定型之后,横、纵向收缩率均小于2%,具有良好的尺寸稳定性。     

用平行偏光法研究涤纶薄膜取向度

本文报导了用平行偏光法测定高聚物取向度的原理和实验方法,提出了在正交偏光显微镜下测定拉伸涤纶薄膜取向度的可能性,讨论了取向度、结构形态与薄膜强度的关系,阐明了薄膜收缩率与双折射的联系。     

捆绑式双向拉伸聚烯烃薄膜技术研究

利用捆绑式薄膜双向拉伸设备在不同加工参数下对线型低密度聚乙烯(LLDPE)、高密度聚乙烯(HDPE)和聚丙烯(PP)膜进行拉伸实验,对薄膜的冷热拉稳定性、弓曲现象和力学性能进行了研究。结果表明,捆绑拉伸过程中,连续捆绑的薄膜边缘应力集中不明显,拉伸过程对温度的敏感性较弱;拉伸过程中随着薄膜纵向输送速度的增大,薄膜的弓曲挠度先增大后减小,弓曲挠度最大值出现的位置与拉伸过程中拉伸比无关,选用足够大的纵向输送速度可以显著降低弓曲挠度;薄膜经捆绑式拉伸后其纵横向拉伸强度有较大提升,断裂伸长率有所下降,并且随薄膜输送速率的增大,薄膜的横向拉伸强度先增大后减小,在一定加热功率下存在最佳的薄膜输送速率。     

双向拉伸工艺对聚氟乙烯薄膜性能的影响

在聚氟乙烯（PVF）凝胶法成膜的基础上，通过X-射线衍射及万能材料试验仪等手段，研究了在PVF薄膜双向拉伸过程中拉伸比及温度等因素与双向拉伸聚氟乙烯薄膜（BOPVF）性能的关系，讨论了结晶因素对薄膜性能的影响。实验表明，在横向拉伸比固定情况下，随着拉伸比增加，拉伸强度、拉伸模量明显增加，而断裂伸长率则逐渐降低，反之亦然。透光性能也随着拉伸比增加也有所改善。纵向拉伸温度选择：预热辊温度约140～145℃；拉伸辊温度约130～135℃。横向拉伸温度选择：横向拉伸温度比纵向温度约高20～30℃，具体温度取决于薄膜厚度和拉伸速度。在横向拉伸比固定的前提下，PVF薄膜随纵向拉伸比增加，结晶度增加，薄膜拉伸强度也随之提高，而断裂伸长率逐渐降低。     

生物可降解聚乳酸/Ecoflex共混薄膜拉伸性能研究

对3种不同的聚乳酸/Ecoflex共混薄膜横向、纵向拉伸强度和断裂伸长率进行了对比分析,并研究了薄膜拉伸性能的影响因素。实验结果表明:聚乳酸(PLA)与Ecoflex的相容性越好,薄膜拉伸性能越好;薄膜纵向拉伸强度和断裂伸长率大于横向拉伸强度和断裂伸长率;加载速率对薄膜拉伸强度和断裂伸长率没有显著影响。     

热塑性高分子薄膜蠕变模型的研究

在研究热塑性高聚物变压力拉伸蠕变过程的基础上,应用Boltzmann原理对Maxwell Voigt粘弹性模型进行了改进,建立新的蠕变模型及数据处理软件。实验证明此模型可以较好地应用于PVC薄膜拉伸蠕变试验研究中     

纳米抗菌LDPE包装膜的研究

将处理后的纳米TiO_2加入低密度聚乙烯(LDPE)中,通过双螺杆挤出机造粒得到抗菌母料,然后将抗菌母料与LDPE混合并挤出吹制抗菌LDPE薄膜,研究了薄膜的抗菌及力学性能。结果表明:采用该工艺制得的LDPE薄膜无毒、抗菌性能良好;随抗菌母料的增加(即纳米TiO_2的增加),LDPE薄膜的纵向拉伸强度和横向拉伸强度均有增加,抗菌母料质量分数由1%增加到5%时,抗菌薄膜的纵向拉伸强度由9.2 MPa提高至14.6 MPa;拉伸断裂应变略有下降。     

油酸酰胺改性载银磷酸锆/聚乙烯抗菌薄膜的研究

以油酸酰胺为改性剂,载银磷酸锆为抗菌剂,线型低密度聚乙烯为载体树脂,制备了抗菌母粒和抗菌聚乙烯薄膜。用吸水性测定法、红外光谱法分析载银磷酸锆的改性效果,用扫描电镜观察载银磷酸锆在聚乙烯基材中的分散情况,检测了薄膜的力学性能、透光率、透气量、抗菌率。结果表明:经油酸酰胺改性的载银磷酸锆疏水性好,在基体中分散均匀;当抗菌母粒含量为5%时,聚乙烯薄膜的纵向拉伸强度和横向直角撕裂强度略有下降,断裂伸长率、横向拉伸强度、纵向直角撕裂强度均有不同程度的提高,透光率下降3.4%,透气量提高30.18%,抗菌率达99%以上。     

Improving the dielectric performance of poly(vinylidene fluoride)/polyaniline nanorod composites by stretch‐induced crystal transition

The introduction of conductive polyaniline (PANI) can significantly improve the dielectric constant of polymer‐based materials. However, there is a drawback of high dielectric loss. Herein, a simple and efficient stretching process was applied to improve the dielectric performance of poly(vinylidene fluoride)/PANI (PVDF/PANI) nanorod films through the stretch‐induced crystal transition from non‐polar α‐crystal to polar β‐crystal in PVDF and the oriented distribution of PANI nanorods. XRD, DSC and Fourier transform IR analyses indicate that the stretched PVDF and stretched PVDF/PANI films possess a high content of β‐crystal at the stretching temperature of 135 °C under a stretching ratio of 200%–400%. Furthermore, the stretched PVDF/PANI film with 10 wt% PANI displays a high dielectric constant of 338 at 100 Hz, which is increased by 20% compared to non‐stretched PVDF/PANI film (281). More importantly, the corresponding dielectric loss is reduced from 0.31 for the non‐stretched film to 0.17 for the stretched film. © 2018 Society of Chemical Industry     

Microporous membranes of polyoxymethylene from a melt‐extrusion process: (II) Effects of thermal annealing and stretching on porosity

A two‐part study utilizing polyoxymethylene (POM) was undertaken to investigate a three‐stage process (melt‐extrusion/annealing/uniaxial‐stretching) utilized to produce microporous films. In this report, the thermal annealing (second stage) and subsequent uniaxial‐stretching (third stage) results of selected POM films from two commercial resins, labeled D & F, are discussed. Specifically, the annealing and uniaxial stretching effects on film morphology, orientation, and other pertinent film properties are addressed. Additionally, sequential analysis was performed regarding the influence each stage had on the resulting microporosity. It was found that the melt‐extruded precursor morphology and orientation, as a consequence of the first stage extrusion parameters and resin characteristics, are crucial to controlling the membrane permeability. The annealing parameters were also deemed critical, where a temperature of 145°C applied for 20 min under no tension was the optimum annealing condition for producing a highly microporous film upon stretching. For the conditions studied, the stretching parameters that were found to be optimum for producing the desired characteristics in the final film were a cold temperature of 50°C and hot stretch temperature of 100°C. The optimum extension levels were concluded to be 90% for both the cold and hot stretch steps, and thus a total overall extension level of 180%. However, these results were only with respect to resin F films. Because the resin D melt‐extruded precursors possessed twisted lamellar morphologies and relatively low crystal orientation, their samples could not be produced into microporous films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1762–1780, 2002; DOI 10.1002/app.10587     

Poly(ethylene terephthalate) nucleation as studied by shrinkage of film of low orientation level

Poly(ethylene terephthalate)s of weight average MW 74,000 and 30,000 have been uniaxially stretched, cooled under restraint, reheated, and shrunk unrestrained. Five stretch temperatures between 80 and 120°C and elongations up to 280 percent have been employed. Density and wide-angle X-ray diffraction results indicate conventional crystallization to have occurred only for the highly oriented samples, e.g., stretching above 200 percent at 90°C. The majority of stretching conditions studied produced only nucleated polymer. A sensitive, qualitative measure of nucleation is the degree of stretch imposed. Sufficiently high stretch temperature and low stretch rate lead to negligible nuclei formation. Nucleation in stretched, unshrunk films correlates with relatively high shrinkage, low orientation, low density and the absence of crystallinity until after the film has been shrunk. Crystallization on the other hand correlates with relatively high density, relatively low shrinkage and high orientation.     

正交试验法在PAN原丝纺丝工艺中的应用

利用正交设计方法确定了PAN湿法纺丝过程中影响原丝性能最主要的因素。结果表明 :以计量泵转速、凝固浴温度、负拉伸以及蒸汽拉伸倍数作为考察对象 ,影响原丝性能的最显著因素是蒸汽拉伸倍数 ,其次是负拉伸。以负拉伸、第二拉伸、第三拉伸以及蒸汽拉伸的倍数作为考察对象 ,影响原丝性能最显著的是蒸汽拉伸倍数 ,负拉伸几乎没有影响。利用正交实验结果 ,适当调节蒸汽拉伸倍数 ,制得强度为 6.5～ 7.0cN/dtex ,线密度为 1.1～ 1.3dtex的原丝     

Microporous membranes of isotactic poly(4‐methyl‐1‐pentene) from a melt‐extrusion process. II. Effects of thermal annealing and stretching on porosity

A two‐part study utilizing isotactic poly(4‐methyl‐1‐pentene) (PMP) was undertaken to investigate a three‐stage process (melt‐extrusion/annealing/uniaxial stretching) (MEAUS) utilized to produce microporous films. In this report, the thermal‐annealing (second stage) and subsequent uniaxial‐stretching (third stage) results of selected PMP films from three resins, labeled A, B, and C, are discussed. From sequential analysis of the effect each stage had on the resulting microporosity, it was discovered that the melt‐extruded precursor morphology and orientation, as a consequence of the first‐stage extrusion parameters and resin characteristics, were crucial to controlling the membrane permeability. The annealing parameters were also critical, where a temperature of 205°C applied for 20 min under no tension was the optimum annealing condition for producing highly microporous PMP films upon stretching. For the conditions studied, the stretching parameters that were found to be the optimum for producing the desired characteristics in the final film were cold‐ and hot‐stretch temperatures of 70 and 180°C, respectively. The cold‐ and hot‐stretch extension levels concluded to be the best were a cold‐stretch extension of 80%, followed by hot stretching to 90%, and, thus, a total overall extension level of 170% for the processing window studied. However, these results were only with respect to resin A films, while resin B and C samples could not be produced into microporous films via the MEAUS process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1076–1100, 2002; DOI 10.1002/app.10395     

Resonance and fibre formation in the process of spinning melts of flexible-chain polymers

Conclusions The reason for onset of the polymer jet stretch resonance phenomenon during the spinning process has been found.A mechanism for the uniaxial stretching of a jet of viscoelastic liquid under conditions of fibre stretching resonance has been proposed.Some features in the spinning of a polycaproamide melt have been determined.This article was published to stimulate discussion.Translated from Khimicheskie Volokna, No. 1, pp. 24–26, January–February, 1990.     

Grafting of telechelic poly(lactic‐co‐glycolic acid) onto O2 plasma‐treated polypropylene flakes

An operating window, which is bounded by two temperatures and draw ratios, defines the stable and defect‐free stretching region of a polymer film. Physical properties including the coefficient of thermal expansion (CTE), birefringence, and Young's modulus of a recyclable polyimide (PIR) film were measured under stretching conditions. While values of birefringence and Young's modulus increased with increasing stretching stress in the machine direction, the CTE was found to decrease. A semiempirical model for the prediction of birefringence and Young's modulus under stretching conditions was developed, from which the CTE could be estimated from the Young's modulus data. Theoretically evaluated physical properties were found to be in qualitative agreement with the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

原位气泡拉伸法在高聚物中纳米粒子的分散机理及超声振荡研究

探讨了利用原位气泡拉伸法(ISBS法)分散添加在高聚物中的纳米无机添加物的分散机理。ISBS方法可以用来分散添加在高聚物熔体中的固体颗粒团聚体。结果表明：首先ISBS方法是一种有效的原位双向拉伸分散方法；理论计算表明，当气泡膨胀时，在气泡周围可以产生高达10^6s^-1的拉伸速率场，它比传统的挤出设备所能提供的10^3～10^4s^-1的拉伸速率高两个数量级。     

Limitations of Reptation Theory for Modeling the Stress-Dependent Rheological Behavior of Polyethylene Terephthalate Above the Glass-Transition Temperature

The biaxial stretch blow molding is an established process for manufacturing plastic containers, in which preforms are stretched both in circumferential and axial directions while being blown into a mold. In the development phase of these products, computer-aided analysis tools are extensively used to increase the material and process efficiency. The accuracy of these tools depends on the underlying material models and parameters. The aim of this article is to investigate the suitability of reptation theory for the prediction of the strain-dependent rheological behavior of polyethylene terephthalate (PET) in the stretch blow molding process. Reptation theory has already been successfully applied to a number of polymer melts in the past decades. However, the practical applicability of reptation theory for predicting the strain-dependent rheological behavior of highly viscous polymers slightly above the glass-transition temperature, as is the case with stretch blow molding, has not yet been fully investigated. In the first step, the constitutive material model equation of reptation theory is implemented and the necessary model parameters are determined using various measurement methods. However, the measurements could not be conducted with the same accuracy as in the case of polymer melts, because the measurement methods used showed instabilities in the glass-transition temperature range, which led to high measurement uncertainties. Consequently, the application of the material model does not match quantitatively to biaxial stretch tests. Qualitatively, on the other hand, the material model successfully reproduces the stress–strain behavior of PET films at low strains. In case of temperature dependence, the model results are neither qualitatively nor quantitatively satisfactory. The temperature dependency of the material model has been further investigated in the second step. It was shown that the derivative of the Doi–Edwards memory function with respect to the temperature has an inflection point if the stretching duration is equal to the disengagement time. For very small disengagement times compared to the stretching duration, the results of the model match the experimental observations. For high disengagement times induced by the large viscosities near the glass-transition temperature and for low stretching times induced by high strain rates; however, the Doi–Edwards memory function cannot predict the experimental observations correctly. The investigations show that reptation model qualitatively predicts the strain behavior of biaxial stretched PET films at low strains correctly. However, different measurement approaches for a more accurate and reproducible determination of the material properties and a modification of the model are required in order to adapt the model to highly viscous melts above the glass-transition temperature. The results have shown that the process conditions of the two-stage stretch blow molding, such as high strain rates and low processing temperatures, exceed the validity limits of reptation theory. POLYM. ENG. SCI., 60:765–772, 2020. © 2020 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers.     

Nonrigid microporous PVC sheets: Preparation and properties

The non‐rigid microporous PVC films are prepared by mono‐axially stretching nonporous sheets containing fillers which show an average particle size of 2 to 10 μm. The nonporous PVC film is generated from paste‐like PVC. The influence of recipe components on the mechanical properties, morphological behavior and permeability to water vapor and water was investigated as well as the influence of the stretching ratio. Filled PVC pastes exhibit higher values for viscosity than those of pure polymer mixtures. For processing the compounded paste by means of a doctor blade a low viscosity is required meaning the amount of filler is limited by the resulting paste viscosity. Due to dewetting, the filler initiates the holes of the microporous system during the stretching process. Empirically, a minimum of about 15 vol % filler particles are necessary in order to achieve an interconnected air hole system. Varying the components PVC, plasticiser and filler, PVC membranes could be prepared with high water vapour permeability and high waterproofness simultaneously. To utilize the membranes commercially a continuous preparation process was developed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010