振动力场下聚合物熔体流变行为的响应与分析 Ⅰ.毛细管压力降和熔体表观粘度

在自行设计的恒速型毛细管动态流变装置上 ,对聚合物熔体进行动态挤出实验。借助已建立的振动力场下聚合物熔体流变行为的表征公式 ,分别计算振动力场下聚合物熔体在毛细管壁处的剪切应力、剪切速率和表观粘度。与稳态挤出时相比 ,引入振动力场后 ,发现毛细管压力降、表观粘度均显著降低 ,且随着振动频率和振幅的改变呈非线性变化趋势 ,作者对此进行了深入分析。     

振动力场下聚合物熔体流变行为的响应与分析——I．毛细管压力降和熔体表观粘度

在自行设计的恒速型毛细管动态流变装置上，对聚合物熔体进行动态挤出实验。借助已建立的振动力场下聚合物熔体流变行为的表征公式，分别计算振动力场下聚合物熔体在毛细管壁处的剪切应力、剪切速率和表观粘度。与稳态挤出时相比，引入振动力场后，发现毛细管压力降、表观粘度均显著降低，且随着振动频率和振幅的改变呈非线性变化趋势，作者对此进行了深入分析。     

聚合物振动挤出过程中熔体应力与应变关系的研究

在恒速型毛细管动态流变实验装置上对LDPE熔体进行动态挤出实验，在线测量了毛细管瞬时入口压力、柱塞杆振动位移、振动位移与毛细管入口压力波形的相位差；然后对上述动态流变数据进行时域分析和频域分析，分别得到振动力场下LDPE熔体的入口压力脉动量与体积流量脉动量之间的关系曲线、LDPE熔体在毛细管壁处剪切应力与剪切速率之间的关系曲线、以及入口压力脉动量与体积流量脉动量的比值随毛细管挤出流率Q的变化曲线。     

PVC通信电缆绝缘料流变行为的研究

本文采用毛细管流变仪对聚氯乙烯电缆料的加工流变性能进行了研究，分析并讨论了影响ＰＶＣ流变性能的各种因素。结果表明：在试验温度下，增塑ＰＶＣ的剪切应力均随剪切速率的增加而增大，但当剪切速率增加到一定程度后，剪切速率对剪切应力的影响变小；改性剂ＰＭ－１的加入可以大大降低在相同剪切速率下的剪切应力。改性剂ＰＭ－１使电缆料的剪切敏感性减小，牛顿性增强。虽然ＰＭ－１不能改变临界剪切应力值，但却使当临界剪切应力相应的熔体粘度减小，即临界剪切速率增大，这在实际生产过程中是十分有用的，即可以提高挤出速度而不致于产生熔体破裂。分子量减小，熔体表观粘度明显减小。熔体表观粘度随温度的升高而逐渐减小。     

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。     

聚合物动态挤出流变行为研究

本文论述聚合物材料毛细管动态流变行为的测量原理,介绍了自行研制成功的用于合物熔体挤出的毛细管动态流变仪。在该仪器上对ＬＤＰＥ进行了实验研究,发现熔体的粘度与振动源的频率、振幅呈非线性关系。在振动必场作用下ＬＤＰＥ熔体的粘度减小,随振动频率的变化有一最小值。这对矣合物动态塑化挤出工艺过程控制具有十分重要意义。     

内胎胶料的挤出胀大行为

用Monsanto毛细管流变仪,在100～130 ℃及流动速率1.02～254.00 mm/min的条件下,考察了内胎胶料的挤出胀大行为.结果表明,在一定温度下,挤出胀大比(B)随着壁面表观剪切速率的增加而增大,两者之间呈非线性函数关系,而B与壁面剪切应力则大致上呈线性函数关系;当表观剪切速率一定时,B随着温度的升高而非线性下降.在一定的挤出条件下,B随着流道直径比的增加而有所增大,两者之间近似呈线性函数关系.     

ABS熔体挤出流变性质的研究

考察了毛细管挤出过程中温度和流动速率对ABS树脂熔体流变行为的影响。结果表明 ,当剪切速率大于 10 3s 1后 ,熔体的剪切流动不服从幂律 ;而剪切粘度对温度的依赖性符合Arrhenius方程 ;入口压力降和入口拉伸应力均随着剪切应力的增加而呈非线性函数形式增大     

动态充模过程熔体表观黏度的实时测量与研究

修正了脉动压力诱导注射成型充模过程浇口流道中熔体壁面表观剪切黏度的数学模型,并介绍了建立在此基础上的通过实时测量并记录螺杆位置变化以及浇口流道两端熔体压力变化来表征脉动压力诱导注射成型充模过程熔体实时表观剪切黏度的方法,通过实验研究发现,脉动压力的引入对熔体的实时表观剪切黏度产生了深刻的影响,且降低了充模过程单振动周期内壁面熔体的平均表观剪切黏度及受到的平均剪切应力。在此过程中,还提出了特定振动参数下熔体剪切应力与剪切速率之间相位角的计算方法。     

聚乙烯熔体的挤出畸变与非线性粘弹性的关系

采用毛细管流变仪等仪器研究了一类聚乙烯熔体的挤出畸变与熔体非线性粘弹性的关系。实验发现线形大分子或带小侧基的大分子熔体，容易发生壁滑和挤出压力振荡；而有较大侧基、或相对分子质量分布宽、或带大量短支链的熔体，挤出畸变现象较轻。挤出畸变与熔体的弹性及熔体一壁面吸附状态紧密相关：容易发生壁滑和挤出压力振荡的熔体，弹性较大(人口压力降大)；在壁面的吸附作用强(壁面临界剪切应力大).稳态剪切粘度大小与挤出畸变和压力振荡的关系不大；而拉伸应力和拉伸粘度大的熔体较易发生壁滑和挤出压力振荡。     

Relationship between shear stress and shear strain of polymer melt under vibrating force field

Abstract

When a sinusoidal vibration was superimposed in parallel on the flow direction of a polymer melt being extruded through a capillary, the shear stress and shear rate of the polymer melt were analysed with a constant velocity type dynamic rheometer of capillary (CVDRC) devised by the authors. By measuring the instantaneous data of capillary entry pressure, capillary volume flux (or absolute velocity of piston rod) and their phase difference in a vibrating force field, it was found that the relationship between the pulsating amplitude value coefficient of entry pressure and that of volumetric flowrate was an approximate power series; the wall shear stress and wall shear rate of low density polyethylene (LDPE) melt extruded dynamically under various amplitudes and frequencies also exhibited a non-linear proportional relationship.     

Rheological equation for polymer melt under the action of vibration

Abstract

The entire extrusion process of a polymer melt within a capillary was analyzed thoroughly when a sinusoidal vibration of small amplitude was superimposed in parallel on the flow direction of the polymer melt. On the basis of rheological measurement, an equation for a polymer melt under parallel vibration, i.e. the apparent viscosity, was obtained. Calculation of the apparent viscosity was established by making use of novel experimental equipment. After collecting and analyzing the instantaneous data of capillary entry pressure, capillary volume flux and their phase difference in a superimposed vibration, the apparent viscosity of low-density polyethylene (LDPE) within a capillary was calculated. Meanwhile, the relationship of shear stress vs. shear rate for a LDPE melt with and without imposed vibration was presented.     

The Formula for Apparent Viscosity of Polymer Melt Extruding Through a Capillary Under a Superimposed Vibration

The apparent viscosity of a polymer melt within a capillary was analyzed based on experimental measuring when a sine vibration of small amplitude was superimposed in a parallel manner on the extruding direction of polymer melt. The theoretical model for apparent viscosity of polymer melt under an superimposed vibration was set up independent of any existing constitutive equations. Meanwhile, the calculating steps for previously apparent viscosity were established by making use of novel rheological measurement equipment that was designed by the author. Through collecting and analyzing the instantaneous data of a polymer melt dynamic extruding through a capillary under definite frequency and amplitude of vibration, the apparent viscosity of a polymer melt within a capillary was then calculated.     

Dynamic rheological behavior of polypropylene melts with pulsatile pressure flow in a dynamic capillary rheometer

A self‐made dynamic capillary rheometer (DCR) was designed to investigate the dynamic viscoelastic characteristic of polypropylene (PP) melt during the pulsatile pressure extrusion. A vibration force field was parallel superposed upon steady shear flow in this DCR by means of a vibration driven piston. During the pulsatile pressure extruding process in DCR, the PP melt displayed apparent viscoelasticity. The experiment results proved the pressure pulsatile extrusion could reduce the viscosity of polymer melts effectively. The phase difference between the shear stress and the shear rate decreased with the superposed vibration. But, at large amplitude conditions, the viscosity has an increasing tendency. This maybe illuminated that large amplitude could be harmful for the vibration‐assistant polymer processing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1834–1838, 2006     

LLDPE在振动剪切复合场中挤出成型的流变行为

利用振动剪切挤出装置研究了线性低密度聚乙烯(LLDPE)在振动与旋转剪切复合力场中挤出成型时的流变行为。结果表明:LLDPE熔体在复合力场中的表观黏度受振动频率、振幅、剪切速率等影响很大。在复合力场中存在使黏度降低最大的振动频率和剪切速率的最佳搭配。     

Unusual rheological behaviors of linear PE and PE/kaolin composite

The unusual flow behaviors of linear PE melts are caused by high molecular weight, tight entanglements of molecular chains, and strong adsorption of the melt at the capillary wall. Especially, the extreme change of interface adsorption is followed by an unusual flow, and at the molecular level, the dynamic variety of entanglement and disentanglement between the adsorption chain near the wall and the nonadsorption chain is the cause of the extrusion pressure vibration. Ultrahigh molecular weight polyethylene (UHMWPE)/kaolin composites prepared by polymerization filling could be smoothly extruded through the capillary. Also, with increase of the kaolin content, the apparent viscosity of the composite decreased and the processability was improved. Under slip boundary conditions, the real shear rate and shear stress of the melt near the capillary wall were reduced. The viscosity descent (desorption) and the deformation energy decrease of the melt near the wall were the important preconditions to gain a steady flow in a second glossy zone. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2154–2161, 2001     

Mathematical model of shear rate of polymer melt dynamic extruding through capillary

With superimposing a sine vibration of displacement on the extruding direction of a polymer melt, the characterization formula of the shear rate of a polymer melt within a capillary was set up. By making use of the experimental equipment of a constant velocity type dynamic rheometer of capillary (CVDRC) designed by the authors, the calculating steps of the shear rate of the polymer melt at the wall of the capillary under a vibration force field were established. Through measuring and analyzing the instantaneous data of capillary entry pressure, capillary volume rate, and their phase‐difference under the superimposed vibration, the polymer melt's shear rate at the wall of the capillary can thus be calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1056–1061, 2005     

Improving rheological property of polymer melt via low frequency melt vibration

A pulse pressure was superimposed on the melt flow in extrusion, called vibration extrusion. A die (L/D = 17.5) was attached to this device to study the rheological properties of an amorphous polymer (ABS) and semicrystalline polymer (PP, HDPE), prepared in the vibration field, and the conventional extrusion were studied for comparison. Results show that the melt vibration technique is an effective processing tool for improving the polymer melt flow behavior for both crystalline and amorphous polymers. The enhanced melt rheological property is also explained in terms of shear thinning criteria. Increasing with vibration frequency, extruded at constant vibration pressure amplitude, the viscosity decreases sharply, and so does when increasing vibration pressure amplitude at a constant vibrational frequency. The effect of vibrational field on melt rheological behavior depends greatly on the melt temperature, and the great decrease in viscosity is obtained at low temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5292–5296, 2006