共查询到20条相似文献,搜索用时 171 毫秒
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汇总了膜裂、乳液纺丝、糊料挤出等三种聚四氟乙烯(PTFE)纤维成型方法。研发了强剪切挤出口模等六项技术控制裂膜纤维的细度、均匀性、力学性能、热收缩率,形成工业化裂膜长丝和短纤加工技术;提出PTFE/PVA(聚乙烯醇)共混、利用硼酸与PVA的络合特性制备凝胶纺丝液并纺制PTFE短纤的思路,研究了烧结和牵伸对纤维的影响,形成凝胶法PTFE短纤加工技术;根据PTFE树脂剪切作用下原纤化特征,设计了导入口、导入段锥度和毛细孔长径比控制初生纤维强度的糊料挤出口模,筛选了润滑剂,形成糊料挤出PTFE长丝加工技术。 相似文献
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基于多重缠结网络结构模型和高分子链上缠结点在流动中可进行动态解缠和再缠结的多重蠕动机理,用统计力学和动力学相结合的方法,分别计算出了缠结链组的末端距分布函数;处于缠结状态下高分子链构象统计分布函数;受力下聚合物熔体粘弹性形变自由能和解除外力下高分子挤出体可回复性粘弹性形变自由能,提出了高分子挤出体可回复形变的粘弹性分子理论。推导出的高分子熔体的回忆函数、简单剪切流下的本构方程和物料函数,并采用一种新的方法测定出物料的四种参数: η0、 GN0、 n′和 a。对于高分子挤出体,可回复性粘弹性形变由快速弹性形变和慢速粘弹性形变两者组成,当把两种形变量的复合结构参数-分子链的反式构象分数引入两种形变自由能表达式后,就从理论上得到了可回复形变量同挤出胀大比间的定量表达式,从而建立起一个具有分子链结构参数的新的挤出胀大比方程,可回复形变量同挤出条件(温度、挤出速率和量以及口模长径比不同的挤出机)和树脂结构特征(分子量及分布)的关系式以及在特殊情形下的简化表达式,并用几种高分子熔融体系的挤出胀大比和可回复性形变量的实验数据对理论进行验证,理论方程同实验数据较好的符合。 相似文献
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丙烯-乙烯共聚物/乙烯-1-辛烯共聚物层状复合材料的力学性能研究 总被引:3,自引:0,他引:3
利用自主设计的一套可进行微层共挤出的口模,分别制备了2层、16层、32层和64层丙烯-乙烯共聚物(PPE)/乙烯-1-辛烯共聚物(POE)交替层状复合材料。研究了制得的层状复合材料的应力-应变行为,利用等效盒子模型(equivalent box model)描述了层状复合材料与相应的常规PPE/POE共混材料力学行为的区别.通过对共挤出材料和共混材料的拉伸数据进行分析后发现,具有层状结构特别是多层结构的共挤出材料具有比共混材料更为优异的屈服和断裂伸长性能. 相似文献
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An unusual crystalline aggregate, which is toroidal in shape, has been formed at the entrance region to capillary dies during the high-pressure extrusion of poly(ethylene terephthalate) melts in an Instron capillary rheometer. The toroidal remnant was discovered in capillary dies removed from the rheometer after the occurrence of oscillating flow. Detailed observations of the rheological factors involved in the formation of the crystalline toroid were made. Examination of recovered entrance plugs disclosed that the crystalline toroid was a hard, stagnant zone which throttled the bulk flow of polymer melt into the capillary during the extrusion experiments. Hot-stage optical microscopy, differential scanning calorimetry, and wide-angle x-ray techniques were used to initiate a structural study of the crystalline toroid. The toroid contained clusters of fibrous crystals which persisted to high temperatures. The fibrous clusters were randomly oriented in a matrix polymer which melted normally. Based upon the rheological and structural evidence, a mechanism of crystalline toroid formation is proposed. 相似文献
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The numerical simulation of viscoelastic flow problems is nowadays an effective way of investigating the complex flow mechanism related to practical engineering problems, such as plastic injection, blow molding and extrusion. The mathematical model of a three‐dimensional (3D) viscoelastic flow in a typical contraction die for polymer extrusion is established and a stable solving method is investigated. The penalty finite element method (FEM) is performed to simulate the viscoelastic melts flow in the channel with a differential constitutive model. The discrete elastic‐viscous split stress (DEVSS) formulation and the streamline‐upwind Petrov–Galerkin (SUPG) technology are employed to improve the computation stability. Both the implementation of the numerical scheme and its application in the practical process analysis are investigated. The effects of various calculation control parameters and different material parameters upon the numerical results are discussed. The 3D flow patterns in the extrusion die with different contraction angles are further investigated based on the above discussions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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The solidification of polymer melts in practical processing such as extrusion, injection molding and blow molding can significantly influence the inner structure and performance of final products. The investigation of its mechanism has both scientific and industrial interests. In the study, the three‐dimensional mathematical model is developed for the simulation of morphology variation in the solidification of polymer melts with amorphous and semi‐crystalline phases. The amorphous phase is simulated as the finite extensible nonlinear elastic dumbbell with a peterlin closure approximation (FENE‐P) fluid and the semi‐crystalline phase is approximated as rigid rods that grow and oriented in the flow field. The model of amorphous phase and semi‐crystalline phase are coupled through the stress and momentum balance and the feedback of crystallinity to the system relaxation time. The evolution of crystallization kinetics process are described by using a set of Schneider equation that discriminating the relative roles of the thermal and the flow effect on the crystallization behavior. With the standard Galerkin formulation adopted as basic computational framework, the discrete elastic viscous stress splitting algorithm in cooperating with the streamline upwinding approach serves as a relatively robust numerical scheme by using penalty finite element–finite difference simulation with a decoupled solving algorithm. The proposed mathematical model and numerical method have been successfully applied to the investigation of solidification of polymer melts in the extrusion process. The variations of orientation and crystallization morphology during the solidification process are further discussed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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A unique retainer/transparent quartz die assembly was designed and fabricated to fit on a melt extruder. It permitted visualization of polymer flow behavior during melt spinning. Tracer particles were mixed with polymer chips prior to extrusion. A laser beam was directed through a lens system and used to illuminate the tracer particles in the melt only in a thin, vertical cross section of the transparent quartz die. Streak photography was used to determine the cross-sectional velocity distribution of the melt as it passed through the die. 相似文献
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Hong Zheng Wei Yu Chi-xing Zhou 《高分子科学》2005,(5):453-462
A new coupled finite element formulation is proposed to calculate a conformation tensor model in two complex flows: a planar contraction flow and a planar flow around a symmetrically placed cylinder. The components of conformation tensor are first computed together with the velocity and pressure to describe the change of morphology of polymer chain coils in flow fields. Macroscopic quantities of viscoelastic flow are then calculated based on the conformation tensor. Comparisons between the numerical simulations and experiments for stress patterns and velocity profiles are carried out to prove the validity of the method. 相似文献
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Marian Żenkiewicz Józef Richert Piotr Rytlewski Krzysztof Moraczewski Magdalena Stepczyńska Tomasz Karasiewicz 《Polymer Testing》2009,28(4):412-418
The effect of multiple (up to 10 times) extrusion of polylactide on its mechanical properties (determined by a static tension test), Charpy impact strength, melt flow rate, phase transition temperatures, degradation temperature, and permeability of water vapour and oxygen is presented. It was found that, with raising the number of the extrusion cycles, the tensile strength at break slightly diminished and the impact strength clearly decreased, while the melt flow rate and water vapour and oxygen transmission rates steadily increased. Variation of the number of extrusion cycles did not affect the glass transition temperature, whereas it did cause a lowering of the cold crystallisation temperature and slight diminishing of the melting point. The presented results indicate that PLA technological waste is suitable to be reused as an additive to a neat polymer. 相似文献
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This paper explores the rheological characteristic and molecular mechanism of the polymer melts during extrusion when ultrasound is applied to them at the entrance of the die. Applying of ultrasound disturbs the convergent flow of polymer melt in the entry zone and changes the stream patterns, which leads to lesser elastic tensile strains happen. It also activates the molecular chains, so that the elastic tensile strains can be recovered very quickly. That is why the ΔP measured is reduced. These conclusions are made based not only on rheological calculations but also on looking‐inside characterizations of the molecular conformations. Ultrasound irradiation increases the free volume of PS, reduces the molecular entanglements of polymer melt. All these effects of ultrasound contribute to the productivity raising and product quality improvement of extrusion processing. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1226–1233, 2007 相似文献
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Davis H. Crater John A. Cuculo 《Journal of polymer science. Part A, Polymer chemistry》1984,22(2):329-332
A streak photographic technique was used to determine the velocity distribution in a capillary produced by the flow of poly(ethylene terephthalate) (PET). This uniquely designed quartz die assembly, which was fitted onto a melt extruder, permitted visualization of polymer flow behavior during melt spinning. Aluminum tracer particles were mixed with polymer chips prior to extrusion. A laser beam was directed through a lens system that illuminated the tracer particles in the melt only in a thin, vertical cross section of the transparent quartz die. A pressure-drop analysis was also performed on PET, under the same experimental conditions, to determine rheological properties of the polymer. By using these rheological properties theoretical velocity distributions were calculated for PET and then compared with the profiles obtained by the streak photographic technique. 相似文献
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塑料挤出吹塑的机理问题 总被引:2,自引:0,他引:2
挤出吹塑过程由型坯成型,型坯吹胀与制品冷却三个阶段构成。采用不同的方法对该三阶段的机理问题进行了研究。采用神经网络方法预测了受模口温度和挤出流率影响的型坯成型阶段的膨胀,利用建立起来的神经网络模型预示的膨胀与实验结果很吻合,且可在一定范围内,预示不同工艺条件下型坯的直径膨胀和壁厚膨胀。为型坯的直径和壁厚的在线控制提供了理论依据。基于薄膜近似和noe-Hookean本构关系。建立了描述型坯自由吹胀的数学模型,并通过实验方法获得了型坯吹胀的瞬态图象,比较发现,理论预示的型坯轮廊分布与实验观察结果较吻合,该模型还可预示型坯的自由吹胀对材料性能,型坯尺寸和工艺条件等的依赖性,基于ANSYS有限元软件,对吹塑制品的三维冷却进行了模拟,预示了制品厚度方向任一位置的瞬态温度分布,并可预示成型工艺参数,制品壁厚,塑料与模具材料的热性能以及吹塑模具冷却的强度与时间等对吹塑制品冷却的影响,这可为进一步分析吹塑制品的显微结构和性能提供温度数据。 相似文献