聚合物短口型挤出胀大方程

研究了聚合物熔体经短口型挤出时的胀大行为及机理，并应用变流体微元分析方法，导出了短口型挤出胀大方程，即Ｂ＝〔１＋１．５（Ｌｅ／Ｄｃ）（△Ｐ０／τｗ）（ｎ＋１）ｔａｎ＾２α０〕＾０．５。同时，引进文献发表的混炼胶毛细管挤出实测值对该方程的简化式Ｂ＝〔１＋１．５（△Ｐ０／τｗ）（ｎ＋１）ｔａｎα０〕＾０．５进行了初步验证。结果表明，理论预测值与实测值有较好的一致性。     

混炼胶在圆锥口型挤出膨胀行为的研究

分析了混炼胶在收敛流变中的粘弹特性，应用张量分析方法，在高聚物熔体入口收敛流动中，引入纯拉伸流变概念，导出了描述胶料在圆锥口型挤出膨胀的方程：Ｂ￣２＝３［１＋（ＫＳ＿Ｒ）￣２］￣（－２／３／７）．实验结果表明，当圆锥口型入口角较大时，对混炼胶挤出膨胀的影响，是拉伸流变效应起主导作用。     

聚合物流体入口收敛流动的数值模拟

聚合物流体从大截面流道进入小截面流道时产生的入口收敛流动,是工业中常见的流型之一。基于聚合物流体入口收敛边界流线方程,应用MATLAB对入口收敛流动进行了数值模拟,讨论了Bagley校正因子(e)、非牛顿指数(n)、流道收缩比(λ)等因素对入口收敛流线和入口自然收敛半角(α0)的影响。结果表明:在一定的条件下,入口收敛边界流线的半径r随着e的增加而增大,但随着n的增加而减小,而λ对入口流型的影响不明显;另外α0随着e的增加而减小,但随着n的增加而增大,α0与λ之间呈非线性关系。模拟结果与实验观测较为接近。     

混炼胶入口压力降和入口自然收敛半角的数值模拟

基于非牛顿流体人口收敛压力降和人口自然收敛半角方程,应用Matlab软件对NR/SBR混炼胶挤出过程中入口收敛流动进行数值模拟,并讨论非牛顿指数、流道收缩比、表观剪切速率、流体粘附特性系数和BagIey校正因子等因素对人口压力降和人口自然收敛半角的影响.结果表明,在一定条件下,人口压力降随着非牛顿指数、流道收缩比、表现剪切速率和流体粘附特性系数等增大而增大;人口自然收敛半角随着Bagley校正因子增大而减小等.模拟结果与文献报道有较好的一致性.     

炭黑填充NR／SBR毛细管挤出流动中进口自然收敛角的估算

当聚合物流体（熔体或液体）从容器进入挤出机的小机筒后，流体不会成平行状态，由于流体的粘弹性作用和机筒断面的收缩，会在机筒前端形成圆锥形界面。这是一种进口收敛流动。机简进口的收敛流动是聚合物加工（例如挤出、注射等）时常见的流动形状。界面流线的切线和机筒的中心轴线之间的角度（α）称为流体自然收敛半角（θ）。当α〈θ时，会形成一个“环流区”。而且，流体成环流形式运动，如图1所示。     

加压流态化Ⅱ床层与垂直埋管的传热研究

基于两相理论建立了加压流态化床中垂直埋管与床层之间的传热模型，研究表明ｈ＝（１－δｗ）（２ｋ０ｅｗｄｐ＋αｗＣｐｇρｇＵ０）模型能较好地模拟实验值。并得到如下结论：气速对传热系数影响不明显，而随着压力的提高，传热系数明显增大，大约为每加０．５ＭＰａ传热系数增加２０Ｗ／ｍ２℃，从常压下２００Ｗ／ｍ２℃，增加到２．０ＭＰａ下３２０Ｗ／ｍ２℃，说明了加压流态化传递特性是与常压下有明显的差别     

氯化钙－正丙醇－水溶液稀释热

使用ＬＫＢ－２１０７型流动式微量热计测量了２８８．１５Ｋ，２９８．１５Ｋ和３０８．１５Ｋ下ＣａＣｌ_２－ｎ－Ｃ_３Ｈ_７ＯＨ－Ｈ_２Ｏ溶液的稀释热。混合溶剂中正丙醇摩尔分数Ｘα：０．００，０．１３，０．２５，０．５０，０．７５，０．８７和１．００。测量结果用扩展的Ｄｅｂｙｅ－Ｈｕｃｋｅｌ方程关联，计算了不同溶剂组成下溶液无限稀释热△Ｈ_Ｄ（ｍ＝０．５，Ｘα）。结果表明：Ｘα相同时，－△Ｈ_Ｄ随温度增加而增加；温度相同时，随Ｘα变化，当Ｘα≈０．８７时，－△Ｈ_Ｄ具最大值。     

橡胶挤出扩胀工艺及挤出机头的初步研究

橡胶挤出扩胀法，是一种新的橡胶加工方法，适宜于宽幅橡胶薄片材料的生产。该法使用的挤出机，具有机头结构简单、价廉、占地面积小，挤出物质量好等优点。对三组不同结构的扩胀机头进行试验，结果得出：橡胶挤出扩胀方法的适宜扩胀比为２．０～２．５；在挤出扩胀过程中对胶片施加纵向牵引力比横向牵引力好。     

LDPE熔体在挤出口模流动时入口区流型的观测

应用毛细管流变仪测量了在接近实际挤出工艺条件下低密度聚乙烯熔体的流变性质，应用流动可视化技术，观测了试样熔体流经突然收缩的轴对称口模时的入口收敛流型，发现，在口模入口前区的两侧存在明显的环流区，环流区长度随着挤出速率和流道收缩比的增加而增大，而随着温度的升高而减小，采用环流区长度的公式估算了实验条件下试样的环流区长度值，结果表明，预测值与实测值之间有较好的一致性。     

混炼胶长口型挤出胀大比的预测

研究了聚合物熔体于长口型挤出过程中的流变行为，提出了描述挤出胀大比与可回复切应变之间关系的数学模型：Ｂ＝（１＋ＳＲ＾２）＾０．２５。用此方程预测了混炼胶挤出膨胀行为，表明Ｂ的计算值与实测值为接近，二者之间相对误差的绝对值小于４％。     

Planar Entry Converging Flow During Extrusion of Polymer Melts

In this article, a planar entry converging flow during die extrusion of polymeric melts was analyzed and a differential equation of entry converging boundary streamline equation with rheological parameters and channel geometry is established. By applying limit theory, the entry converging boundary streamline equation in the case with different non-Newtonian index (n) was discussed, and the corresponding expressions of entry natural convergent half angle and convergent region length were derived. The entrant flow pattern might be described with the half angle of entry natural convergence (α₀) and the convergent region length (L _e ) of the melts, and α₀ and L _e were mainly a function of the entry elastic storage deformation energy (e) and n. The values of α₀ and L _e were calculated by means of these simplified expressions. It was found that the estimations of α₀ decrease nonlinearly white L _e increases linearly with an addition of e. Finally, a preliminary verification of the natural converging half angle equation was made. The results showed that the estimations of 2α₀ based on the experiments of a low-density-polyethylene (LDPE) and a high-density-polyethylene (HDPE) were close to the data reported in reference.     

聚合物异型材气辅口模挤出成型气辅滑移对异型材挤出胀大的影响

基于流变学和流体动力学理论，经合理假设，建立了描述异型材气辅口模挤出成型过程的三维等温黏弹性理论模型，并通过DEVSS／SUPG、最小元法Mini—Element和罚函数法等稳态有限元技术，建立了与该模型相适应的快速收敛的稳态有限元数值算法，并以此通过有限元数值模拟，系统研究了聚合物异型材气辅口模挤出成型过程的机理。研究结果表明：在异型材的挤出成型过程中，随着滑移系数的增大，离模膨胀也增大。聚合物异型材气辅挤出成型能基本消除挤出成型中的离模膨胀和翘曲变形。同时，解决了由于离模膨胀和翘曲变形引起的挤出口模难于设计的技术难题。     

Effect of convergent–divergent flow on thermal and crystallization properties of PP/MWCNTs nanocomposites

A melt‐mixing process based on convergent–divergent flow has been used to prepare PP/MWCNT composites with a self‐built convergent–divergent die (C‐D die) composed of different numbers of convergent plates. Dynamic extensional deformation was generated in the C‐D die, which improved the mixing effect and mixing efficiency of the composites during extrusion. The C‐D die acted as a mixer for composites when mounted onto a capillary rheometer. The residence time of PP/MWCNTs melt in the extensional flow field is adjusted by changing the numbers of convergent plates and the velocity of the ram. The intensity of extensional flow field is controlled by the structure of the convergent plate and the ram velocity. Influences of convergent–divergent flow on PP/MWCNTs composites were characterized in terms of transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). TEM results showed that MWCNTs disperse more homogeneously with the increase of convergent plates. DSC showed that the crystallinity of PP/MWCNTs composites increased and the crystallization temperature shifted to higher temperature with the increase of the numbers of the convergent plates. TGA showed that the thermal stability of composites improved remarkably. The decomposition temperature increases from 381 to 408.2°C when the numbers of convergent plates increased from 2 to 8. In addition, the increase of ram velocity also has the same influences on the dispersion of MWCNTs in the resin and the properties of PP/MWCNTs nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42330.     

异型材挤出成型过程三维等温黏弹性的数值模拟

针对异型材挤出成型流动过程的特点，基于PTT黏弹性本构模型，经合理假设，建立了描述其成型过程的三维等温黏弹性理论模型，并通过DEVSS／SUPG、最小元法Mini—Element和罚函数法等稳态有限元技术，建立了与该模型相适应的快速收敛的稳态有限元数值算法，并以此通过有限元数值模拟，系统研究了松弛时间和进口流量对异型材挤出成型过程的影响，得出了离模膨胀随松弛时间、进口流量增大而增大的规律。并通过理论分析，揭示了第一法向应力差决定离模膨胀的机理。数值模拟结果与传统的挤出实验研究结论相吻合。     

临界状态下温度对挤出自增强PP片材结构性能的影响

采用楔形收敛流道挤出口模，临界挤出状态下获得了聚丙烯自增强片材。研究结果表明：PP自增强片材在此状态下挤出成型其纵、横向拉伸强度均有明显上升，其结晶形态为串晶互锁结构，而结晶的晶型与常规成型的PP片材相比则没有变化。     

层叠流道中天然高分子挤压流动过程的数值模拟

为探究层叠流道中天然高分子材料挤压流动过程与混合特性，建立层叠流道的三维物理模型和有限元网格模型，利用POLYFLOW软件计算了食品熔体在不同的入口流量，挤压过程中的压力、速度、剪切速率分布。结果表明，压力沿着挤出方向呈梯度递减，随着入口流量增大中间位置压力差增大；剪切速率在流道中变化明显，剪切速率从流道中间位置向四周递减，从壁面到流道内部递减；速度在流道内沿着挤出方向先增大后减小，靠近壁面速度小；层叠扭转流道的结构和尺寸设计，有助于提高天然高分子物料的混合效果，并且第1、4层流道混合效果优于第2、3层流道，提高入口流量也有利于提高物料的混合效果。     

近熔点状态下聚乙烯在收敛流道模具连续挤出自增强

采用楔形收敛流道挤出口模，通过控制挤出成型工艺获得了聚乙烯自增强片材，研究了制品结构性能之间的关系，结果表明：聚乙烯自增强片材连续挤出成型存在成型温度窗口，在此成型温度窗口内，聚乙烯自增强连续挤出片材在平行于拉伸方向可以形成大量排列有序，取向程度很高的微纤结构，这些微纤结构成为片材的增强相，赋予片材以极高的纵向强度。     

The effect of the feed section groove taper angle on the performance of a single‐screw extruder

A new mechanism is described that allows adjustment of the groove geometry in grooved feed extruders. This mechanism enables efficient, continuous and independent change of the groove geometry during the extrusion process. The patented solution of the activated grooved feed section enables one to change the number of grooves, taper angle and, connected with it, groove depth. The paper contains the graphical presentation of the selected results of experimental studies of autothermal extrusion of a medium density polyethylene in an extruder with the grooved feed section in which the groove taper angle, and thus groove depth, was changed during the extrusion process. The influence of changing the groove taper angle in the range from 0 to 5.236 × 10^?2 rad and screw speeds ranging from 177 to 279 rev/min on extruder output was studied. The energy efficiency of the extruder was studied as well.     

Measuring of coalescence in polymer melt blends flowing through converging channels

Droplets of polymer blends flowing through convergent channels undergo collisions and coalescence because of the appropriate wineglass‐shaped flow paths with essential flow constriction at the entrance zone. Therefore, an attempt has been undertaken to use capillary flow for studying coalescence phenomena in polymer blends. When the initial drop diameters in a barrel (before extrusion), d_b, and in the extrudate, d_e, are measured, coalescence efficiency can be easily calculated as E_c = d/d, provided that no breakup of elongated domains occurs. Compared with methods employing simple shear flow, it has several advantages. For example, the convergent flow pattern combining both shear and extensional flows is directly related to industrial processing operations like extrusion, injection molding, blowing, etc. The method imposes minor limitations on processing parameters and materials used. Applicability of the technique proposed was verified by systematic studies of coalescence in PMMA/PS binary melts blends during capillary extrusion and by comparing these results to theoretical predictions and experimental data from literature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

拉伸作用对采用超临界CO2发泡时气泡成核的影响

分析采用超临界CO2流体挤出发泡成型时拉伸作用对聚合物分子自由体积的影响,以及由此引起的对气泡成核的影响。利用具有不同入口收敛角的锥型挤出口模进行了验证,结果显示,拉伸作用可增加气泡的成核数目,减小气泡的平均直径。