碳酸钙填充聚丙烯熔体弹性研究

利用高压毛细管流变仪测量的第一法向应力差（N1）和挤出胀大比（B）研究了纳米CaCO3和微米CaCO3分别填充和同时填充聚丙烯（PP）体系的熔体弹性。对纳米CaCO3或微米CaCO3单独填充PP体系，N1和B随着剪切速率的增加呈非线性上升趋势；随着CaCO3含量的增加，体系的N1和B先减小后增加；在一固定的剪切速率下，纳米CaCO3填充PP的N1高于微米CaCO3填充体系的，但不同粒径的微米CaCO3填充PP体系的N1差别不大。对纳米CaCO3和微米CaCO3同时填充PP体系。当CaCO3总质量分数不高而微米CaCO3与纳米CaCO3的质量比不超过1：1时，体系的N1与纳米CaCO3单独填充PP体系相比有显著下降，但与微米CaCO3单独填充PP体系相比。下降不明显。     

ABS/HGB与PP/HGB挤出流动中弹性性质的研究

应用XNR-400A型熔体流动速率测定仪,比较了ABS/HGB及PP/HGB复合材料的弹性性质。结果表明:ABS/TK 70及PP/TK 70体系熔体的挤出胀大比B均随着剪切应力τw的增大而增大。对ABS/TK 70体系,当τw>120 kPa时,其熔体的挤出胀大比增幅明显增大。ABS/TK 70体系的挤出胀大比随着温度的上升而增大;而PP/TK 70体系的挤出胀大比随着温度的上升而减小。相同剪切应力下ABS/TK 70体系挤出胀大比随着HGB的体积分数增加而增大;而PP/TK 70体系的挤出胀大比随着HGB的体积分数增加而减小。     

挤出条件对PP/硅藻土口模膨胀行为影响

应用熔体流动速率仪测定了3种粒径硅藻土(体积分数为10%)填充聚丙烯(PP)复合材料的口模膨胀比(B),考察口模直径和挤出工艺条件对复合体系口模膨胀行为的影响.结果表明.复合体系的B随着剪切应力和剪切速率的增加而非线性增大,且随着温度的上升而线性下降;当载荷及温度一定时,B随着口模直径增加呈非线性提高,随着口模长径比增加呈非线性减小.     

PP/MRP复合材料熔体挤出胀大行为的研究

采用熔体流动速率仪考察了温度、剪切应力、以及微胶囊红磷(MRP)含量对聚丙烯(PP)/MRP复合体系熔体挤出胀大比的影响。结果表明:PP/MRP复合体系熔体的挤出胀大比随着温度的升高而呈减小的趋势,随剪切应力的增加而显著增大,并且在185℃时,挤出胀大比与剪切应力之间基本符合线性关系;MRP含量增大,则PP/MRP复合体系熔体的挤出胀大比值呈减小的趋势。     

HDPE/OMMT纳米复合材料挤出胀大比的影响因素研究

利用流变分析仪研究了高密度聚乙烯(HDPE)/有机蒙脱土(OMMT)纳米复合材料在挤出过程中的挤出胀大行为及其影响因素,深入讨论了剪切应力、剪切速率、口模温度、口模长径比及OMMT用量对HDPE/OMMT纳米复合材料挤出胀大比B的影响.结果表明,B值随着剪切应力或剪切速率的增加而增大,并且与剪切应力近似呈线性关系;随着口模温度的升高或长径比的增加而减小,当口模长径比较小时,B值受剪切应力或剪切速率的影响尤为显著;同时B值随OMMT用量的增加而逐渐减小.     

FEP/PP共混物熔体挤出胀大行为研究

应用熔体流动速率仪考察了聚丙烯(PP)含量、温度、载荷及口模直径对FEP(聚全氟乙丙烯)/PP共混物熔体的挤出胀大行为的影响.结果表明,在试验条件下,FEP/PP共混物熔体的挤出胀大比(B)基本上随着温度的升高而线性增大,随着载荷的增加而非线性提高,随着PP含量的增加B略为下降;当口模直径小于1.500 mm时,B随着口模直径的增加急速减少,然后,B随着口模直径的增加显著增加.     

共聚PP及PP/CaCO3高填充体系的流变行为研究

以双螺杆挤出机制备了共聚PP/CaCO₃高填充复合材料,表征了CaCO₃粒子在基体中的分散行为,并对共聚PP及复合体系的流变行为进行了研究。结果表明:纯共聚PP的熔体呈现出明显的假塑性流体行为,提高熔体温度,熔体的弹性有所增强;高填充共聚PP/CaCO₃复合体系及高填充共聚PP/HDPE/CaCO₃复合体系的熔体的剪切行为与纯共聚PP的类似,高填充的CaCO₃粒子仅对共聚熔体的表观粘度产生轻微影响;共聚PP中大量存在的CaCO₃粒子,降低了熔体的假塑性行为;提高剪切速率是调节高填充共聚PP/HDPE/CaCO3_复合体系粘度的有效手段。     

EPDM/PP热塑性弹性体的制备及其流变特性

以聚丙烯(PP)和三元乙丙橡胶(EPDM)等为原料,采用完全动态硫化共混技术制备EPDM/PP热塑性弹性体(TPV),使用毛细管流变仪对TPV熔体的流变特性进行测试。分别研究了剪切速率、挤出温度对黏度、剪切应力和挤出胀大比的影响,以及不同条件下熔体流过毛细管口模时流速对压力降的影响。结果表明,TPV熔体是假塑性流体,其剪切应力随剪切速率增大而增大,随挤出温度的升高而降低;黏度随剪切速率和挤出温度的增大而降低;挤出胀大比则随剪切速率和挤出温度的增大而增大;毛细管口模的压力降也随流速和毛细管口模长度的增大而增大。     

POE/纳米碳酸钙复合材料的流变性能研究

试验研究聚烯烃弹性体（POE）／纳米碳酸钙复合材料的流变性能。结果表明，随着剪切速率的增大，复合材料的剪切粘度和非牛顿指数逐渐减小，挤出胀大比和零口型入口压力降增大，挤出物外观变差；随着纳米碳酸钙用量的增大，复合材料的剪切粘度对剪切速率的敏感性下降，非牛顿指数增大，挤出胀大比总体上呈下降趋势，零口型入口压力降变化较小，在相对低的剪切速率下，挤出物外观得到改善。     

回收料制备人造草丝熔体的流变性能研究

采用聚合物动态流变测试仪研究了含回收料的人造草丝熔体的流变性能,探讨了回收料用量、温度、口模长径比对熔体表观黏度和挤出胀大比的影响。结果表明,人造草丝熔体属于假塑性熔体,其表观黏度随剪切速率和回收料用量的增加而降低。在剪切速率500s-1时,回收料用量越低,熔体的表观黏度降低越明显;剪切速率1800s-1时,熔体的表观黏度变化平缓且较为接近。对于100%回收料草丝熔体,其表观黏度随温度的升高和口模长径比的减小而降低;挤出胀大比则随温度的升高和口模长径比的增大而降低。     

Die design for rigid PVC—the effect of die land length on extrudate swell

PVC profile extrusion compounds have a unique morphology. While other polymers gradually decrease in extrusion die swell with increasing length/thickness (L/D) ratio, PVC profile extrusion compounds have a low die swell, quite independent of the die's L/D ratio in the range of 5 to 20. The fact that the die land length can be changed without changing the extrudate swell is an important consideration, which makes die design and balancing dies simpler and easier for PVC profile extrusion compounds. While other polymers substantially increase extrudate swell with increased shear rate, the swell of the PVC profile compounds is not much affected by shear or extrusion rate. This unique behavior allows wider processing latitude in profile extrusion and faster extrusion rates than with other polymers. Another unique factor in the rheology of PVC profile extrusion compounds is that extrusion die swell increases with increasing melt temperature, while other polymers have decreasing die swell with increasing melt temperature. The unusual rheology of PVC profile extrusion compounds is attributed to its unique melt morphology, where the melt flow units are 1 um bundles and molecules that have low surface to surface interaction and entanglement at low processing temperatures but increased melting and increased entanglement at higher processing temperatures. Other polymers, unlike PVC, have melt flow at the molecular level.     

管壁厚度对微挤出成型的影响分析

基于Bird-Carreau黏度模型,运用有限元方法对三维等温微管挤出成型流动模型进行了数值分析,主要研究了管壁厚度对微管挤出成型过程中挤出胀大、速度分布、剪切速率和口模压降等重要指标的影响。结果表明,当熔体入口体积流率相等时,随着管壁厚度的增大,挤出物挤出胀大率和横截面尺寸变化量增大;口模出口端面上熔体的二次流动增强,但挤出速度和剪切速率减小;熔体在口模内的压力降明显下降;适当增加管壁厚度,有利于提高微管挤出质量。     

LDPE熔体在圆锥型短口模挤出过程的粘弹行为研究

主要研究不同入口圆锥角短口模流道挤出流动过程中聚合物熔体的粘弹特性,以及在口模流动过程压力损失,入口弹性贮能和挤出胀大比之间的关系。对于不同的口模入口角,有不同的剪切速率与剪切应力的规律,流变曲线各自不同。同时,不同的圆锥入口角,表现出不同的Bagley校正因子对应不同的挤出胀大值,反映了聚合物熔体在不同圆锥入口角短口模挤出过程拉伸弹性形变特性的差异。聚合物熔体在不同入口圆锥角短口模挤出流动过程的压力降,依赖口模流道的几何形状(入口角、长径比)、温度、流动速率等,入口损失主要归因于拉伸形变的弹性贮能。     

PP/玻璃微珠复合材料的流变性能

制备了聚丙烯/玻璃微珠复合材料,在温度为175～225℃和载荷为1.2～12.5kg的条件下,应用熔体流动速率仪考察了填料粒径、剪切速率、载荷及温度等对复合材料熔体流变特性的影响。结果表明:熔体的剪切流动服从幂律定律;熔体的表观黏度对温度的依赖性符合Arrhenius方程;表观黏度随剪切速率和剪切应力的增加而下降;挤出胀大比随温度的升高而下降,随剪切应力和剪切速率的增大而增大。在此基础上,预测了第一法向应力差,发现其随剪切速率的增大而增大。     

A parallel coextrusion technique for simultaneous measurements of radial die swell and velocity profiles of a polymer melt in a capillary rheometer

This article proposes a new experimental technique to simultaneously measure radial die swell and velocity profiles of polystyrene melt flowing in the capillary die of a constant shear rate rheometer. The proposed technique was based on parallel coextrusion of colored melt‐layers into uncolored melt‐stream from the barrel into and out of the capillary die. The size (thickness) ratio of the generated melt layers flowing in and out of the die was monitored to produce the extrudate swell ratio for any given radial position across the die diameter. The radial velocity profiles of the melt were measured by introducing relatively light and small particles into the melt layers, and the times taken for the particles to travel for a given distance were measured. The proposed experimental technique was found to be both very simple and useful for the simultaneous and accurate measurement of radial die swell and velocity profiles of highly viscous fluids in an extrusion process. The variations in radial die swell profiles were explained in terms of changes in melt velocity, shear rate, and residence time at radial positions across the die. The radial die swell and velocity profiles for PS melt determined experimentally in this work were accurate to 92.2% and 90.8%, respectively. The overall die swell ratio of the melt ranged from 1.25 to 1.38. The overall die swell ratio was found to increase with increasing piston speed (shear rate). The radial extrudate swell profiles could not be reasoned by the shear rate change, but were closely linked with the development of the velocity profiles of the melt in the die. The die swell ratio was high at the center (～1.9) and low (～0.9) near the die wall. The die swell ratio at the center of the die reduced slightly as the piston speed was increased. Polym. Eng. Sci. 44:1960–1969, 2004. © 2004 Society of Plastics Engineers.     

Experimental studies on radial extrudate swell and velocity profiles of flowing PS melt in an electro‐magnetized die of an extrusion rheometer

This article investigates the radial extrudate swell and velocity profiles of polystyrene melt in a capillary die of a constant shear‐rate extrusion rheometer, using a parallel coextrusion technique. An electro‐magnetized capillary die was used to monitor the changes in the radial extrudate swell profiles of the melt, which is relatively novel in polymer processing. The magnetic flux density applied to the capillary die was varied in a parallel direction to the melt flow, and all tests were performed under the critical condition at which sharkskin and melt fracture did not occur in the normal die. The experimental results suggest that the overall extrudate swell for all shear rates increased with increasing magnetic flux density to a maximum value and then decreased at higher densities. The maximum swelling peak of the melt appeared to shift to higher magnetic flux density, and the value of the maximum swell decreased with increasing wall shear rate and die temperature. The effect of magnetic torque on the extrudate swell ratio of PS melt was more pronounced when extruding the melt at low shear rates and low die temperatures. For radial extrudate swell and velocity profiles, the radial swell ratio for a given shear rate decreased with increasing r/R position. There were two regions where the changes in the extrudate swell ratio across the die diameter were obvious with changing magnetic torque and shear rate, one around the duct center and the other around r/R of 0.65–0.85. The changes in the extrudate swell profiles across the die diameter were associated with, and can be explained using, the melt velocity profiles generated during the flow. In summary, the changes in the overall extrudate swell ratio of PS melt in a capillary die were influenced more by the swelling of the melt around the center of the die. Polym. Eng. Sci. 44:2298–2307, 2004. © 2004 Society of Plastics Engineers.     

Basic study of extrusion of polyethylene and polystyrene foams

A fundamental study of bubble morphology development and apparent rheological properties in foam extrusion is reported. The influence of melt temperature, die length/diameter ratio, and blowing agent level on the morphology are considered. Measurements of the influence of blowing agent on viscosity, extrudate swell, and end-pressure losses are described. The viscosity is reduced, but extrudate swell is increased. End-pressure losses were found to become very large relative to the die wall shear stress at low extrusion rates. These results were interpreted in terms of bubble development. The filling of molds by foaming melts was observed and is described.     

Effects of Extrusion Rate,Temperature, and Die Diameter on Melt Flow Properties During Capillary Flow of Low-Density-Polyethylene

The melt flow properties of a low-density polyethylene were measured at test temperatures varying from 140 to 170°C and in a wide range of extrusion rates by means of a capillary rheometer, to identify the influence of extrusion conditions (such as temperature, shear rate, and die diameter) on the melt flow behavior in the present paper. The results showed that the entry pressure drop increased nonlinearly with an increase of the piston speeds, and it decreased with an addition of the die diameter. The melt shear flow obeyed roughly the power law and the melt shear viscosity decreased approximately linearly with an increase of the true shear rates in a bi-logarithmic coordinate system. The dependence of the melt shear viscosity on temperature accorded approximately the Arrhenius expression. Under these experimental conditions, the entrance pressure drop increases as an exponential function with an addition of the channel contraction ratio.     

EPDM橡胶的流变特性实验研究

为了研究橡胶熔体流变性能对其加工成型的影响，利用毛细管流变仪对三元乙丙橡胶（EPDM）的流变特性进行了实验研究。实验结果表明：EPDM橡胶在毛细管挤出时，剪切速率对剪切应力、剪切粘度和挤出胀大的影响最大；挤出温度对三者有一定的影响；在长径比相同时，毛细管半径对剪切应力和剪切粘度几乎没有影响，但对挤出胀大影响较大。     

聚丙烯熔体强度对加工性能的影响

通过对均聚、共聚和高熔体强度PP的离模膨胀，不同温度下的熔体强度，结晶温度和拉伸粘度进行了测量，比较和表征，揭示了熔体强度对PP加工性能的影响因素，以对PP的加工和应用提供必要的参考。