半口模在高熔体流动速率聚丙烯测试中的探讨

通过熔体流动速率测试条件的优化,对高熔体质量流动速率(MFR)的聚丙烯(PP)样品进行了标准口模(2.095 mm)和半口模(1.050 mm)测试,得出了之间的换算关系,完成了半口模对超高熔体流动速率样品的测试,进一步拓展了仪器的测试范围.     

聚乳酸熔体流动速率测试方法研究

分别采用标准法、半模口法和外推法测试了聚乳酸(PLA)的熔体流动速率(MFR),研究了3种方法用于测试PLA MFR的可行性。结果表明：采用标准法测试PLA的MFR时，切样操作困难，多次加样所得测试结果的相对误差较大；采用半模口法测试PLA的MFR时，切样操作方便，但测试结果的相对误差偏大；采用外推法测试PLA的MFR时，克服了PLA极易热降解的特性，熔体流速适中，切样操作方便，表现出很好的可重复性，此时，PLA的MFR为5.0 g/10 min。     

硬脂酸钙与硬脂酸锌对双峰HDPE MFR测试值的影响

生产双峰高密度聚乙烯(HDPE)时,熔体流动速率(MFR)随测试次数的增加而增大,为此研究了硬脂酸钙(CaSt)与硬脂酸锌(ZnSt)对双峰HDPE MFR测试值的影响规律。结果表明：CaSt极性强于ZnSt,CaSt与ZnSt同时作用于HDPE时,会在口模内表面形成促进流动的微观润滑膜并且会逐渐积累,肉眼无法观察到这种微观润滑膜,常规操作也不能清理掉微观润滑膜;使用未加润滑剂的纯HDPE“冲洗”一次口模,可清理掉微观润滑膜,消除CaSt和ZnSt的影响。     

口模直径对PP/硅藻土复合材料流动性的影响

熔体体积流动速率(MVR)是表征聚合物流动特性的重要参数之一。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％)填充聚丙烯复合材料的MVR,考察口模直径和挤出工艺条件对复合体系流动特性的影响。复合材料的MVR随着口模直径的增加呈二次函数形式提高,随着填料粒径的增加而下降;当载荷及口模直径一定时,复合体系的MVR与温度呈线性函数关系;当载荷及温度固定时,复合体系的MVR与口模直径呈二次函数关系。     

聚丙烯环管工艺生产高MFR产品

采用聚丙烯(PP)环管工艺,通过提高加氢量来控制产品的熔体流动速率(MFR),提高给电子体用量来保证产品的等规指数,用氢调法生产出高MFR注塑料(PPH-MM45-S)。总结了MFR与氢气加入量、催化剂活性、产品物理性能的关系,及生产高MFR产品时压缩机和造粒机工艺参数调整操作。通过和同类产品进行比较以及下游生产商的使用效果,都表明该产品具有透明度高、光泽度好、韧性优异、加工流动性好等优点。     

硅藻土含量和粒径对聚丙烯/硅藻土复合材料口模膨胀行为的影响

应用熔体流动速率仪测定了3种粒径硅藻土填充聚丙烯复合材料的口模膨胀比,考察了硅藻土含量和粒径对复合材料口模膨胀行为的影响。结果表明:当载荷和温度一定时,复合材料的口模膨胀比随着硅藻土体积分数的增加而非线性减小,随着硅藻土粒径的增加而非线性提高,两者之间成二次函数关系。     

《测定聚乙烯树脂MFR用标准样品PE-T》稳定性的研究

标准样品的稳定性对确定其使用的有效期是至关重要的。本文介绍了《测定聚乙烯树脂MFR用标准样品PE T》稳定性研究的内容、试验安排以及稳定性研究试验的MFR数据与标准值一致性的判断方法。根据稳定性研究试验的结果说明 ,在PE T标样制备后放置不同的时间间隔 ,采用单个实验室和多个实验室测定其MFR值 ,利用PE T标样定值试验重复性r和再现性R的数据 ,判断该标样是否稳定是可行的 ,比用标准值的不确定度来评价标样稳定性更加严格、更加可靠。PE T标样的稳定性研究很有意义 ,应继续下去。在标样判为不稳定时 ,观察MFR值的变化与其他项目的变化有何关系 ,同时积累对检验获得的数据分析方法以及判断准则的数据和经验。     

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.     

中空玻璃微珠粒度分布与填充聚丙烯MFR的灰色关联分析

采用熔体流动速率(MFR)测定仪测定了230℃时不同载荷条件下中空玻璃微珠(HGB)填充聚丙烯(PP)复合材料的MFR,运用灰色关联分析法计算了HGB的粒度分布与PP/HGB体系MFR的灰色关联度,以考察HGB粒度分布对PP/HGB体系MFR的影响。结果表明,粒径为0.00～24.72μm的HGB使体系的MFR降低;粒径为27.72～256.00μm的HGB使体系的MFR提高,尤其是粒径为39.50～256.00μm的HGB使MFR提高较为明显。     

添加剂对双峰型HDPE熔体质量流动速率测试的影响

熔体质量流动速率(MFR)是树脂生产过程中重要的控制指标,本文主要分析四川石化产双峰型100 N高密度聚乙烯粒料MFR测试值重复性与准确性差的原因。粒料中含有氟弹性体,硬脂酸锌,硬脂酸钙润滑剂,有效的改善了树脂的流动性。氟弹性体吸附、聚集在口模内表面,测试100 N粒料MFR时,测试值突然开始逐渐增大,给生产装置正常生产带来非常大的困难。测试前清除口模内表面残留的氟弹性体、硬脂酸盐与树脂形成的润滑膜,能够显著提高分析结果的精密度与准确度。     

粘弹性流体在挤出口模中入口区长度的确定

讨论了粘弹性流体在圆孔口模流动中入口区的流动状态。分析结果表明,当流体进入口模后的停留时间为其弛豫时间的７倍时,流体将达到充分发展流动状态。在此基础上,导出一估算挤出口模入口区长度的表达式。考察了两种混炼胶经毛细管挤出时的入口区长度,发现入口区的长径比约为１￣２。     

聚合物熔体在任意长径比圆锥口模的挤出胀大唯象研究

深入讨论了聚合物熔体在不同长径比、不同角度圆锥口模的挤出胀大现象及机理。对口模长径比较小的挤出胀大,由于熔体入口拉伸弹性变形来不及松弛,产生较大的挤出胀大;对长径比较大的口模,熔体在平直流道内停留时间较长,入口弹性形变逐渐松弛,这时主要是流动剪切应变引起的弹性变形,产生较弱的挤出胀大,比长径比小的挤出胀大来得小,并且聚合物熔体的挤出胀大随着长径比的增大而趋向一恒定值。结果还表明:聚合物熔体在圆锥口模的挤出胀大受到挤出口模入口角影响。当L/D较小时,挤出胀大与口模入口角有关;当L/D较大时,口模入口角对挤出胀大影响较小。     

熔体流动性对聚丙烯材料结晶度和力学性能的影响

用X射线法测定了不同熔体流动速率下聚丙烯材料的结晶度。结果表明 ,材料熔体流动性的变化将会影响其结晶行为 ,随熔体流动速率降低 ,结晶度越低 ,拉伸强度下降 ,断裂伸长率增大。熔体流动性对冲击强度的影响较为复杂 ,发现存在一极大值 ,该极值的出现预示可能与分子量和分子量分布的变化有关。     

Melt fracture,melt viscosities,and die swell of polypropylene resin in capillary flow

The melt fracture, shear viscosity, extensional viscosity, and die swell of a polypropylene resin were studied using a capillary rheometer and dies with a 0.05‐cm diameter and length/radius ratios of 10, 40, and 60. A temperature of 190°C and shear rates between 1 and 5000 s^?1 were used. A modified Bagley plot was used with consideration of pressure effects on both the melt viscosity and end effect. The shear viscosity was calculated from the true wall shear stress. When the true wall shear stress increased, the end effect increased and showed critical stresses at around 0.1 and 0.17 MPa. The extensional viscosity was calculated from the end effect and it showed a decreasing trend when the strain rate increased. Both the shear and extensional viscosities correlated well with another polypropylene reported previously. The die swell was higher for shorter dies and increased when shear stress increased. When the shear rates increased, the extrudate changed from smooth to gross melt fracture with regular patterns (spurt) and then turned into an irregular shape. In the regular stage the wavelength of the extrudates increased when the shear rate increased. The frequency of melt fracture was almost independent of the shear rate, but it decreased slightly when the die length increased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1587–1594, 2003     

Practical interpretation of laboratory die swell behavior of PVC extrudates—through correlating circular with non-circular die performance

Laboratory die swell measurements are routinely measured on many viscoelastic polymer extrudates to characterize thier ability to maintain a specified shape during extrusion operations. The diameters of downstream extrudates obtainable through selected round dies can then be routinely scanned by optical or laser type devices to compare the degree of swell relative to the die diameter itself. Such measurements, while yielding good relative die swell performance between compounds, frequently do not predict the actual die swell levels observed later when the same compound is extruded through production dies of different cross-sectional shapes and land lengths. This study discusses an alternate method of correlating die swell between dies of different shapes by using a technique derived from fluid mechanics. This concept, used to characterize fluid velocity through non-circular channels with that observed through circular pipes and ducts, involves the inclusion of a shape factors known as the “Hydraulic Radius” in fluid flow comparisons. When this technique was applied to die swell measurements for extrudates of both a flexible PVC wire jacket compound and a rigid PVC pipe compound, good agreement in actual die swell measurements through both round dies and dies with non-circular cross sections was obtained. This approach can lend credibility to laboratory die swell measurements and greatly expand their use in predicting production extrusion performance.     

Finite element analysis of thermoplastic melts flow through the metering and die regions of single screw extruders

This research work is devoted to the development of a mathematical model for the simulation of the flow of polymer melts through the metering and die regions of single screw extruders. The sets of the governing equations (flow and energy) are solved using the finite element method. The power‐law model is used to describe the non‐Newtonian rheological behavior of the fluid. The standard Galerkin technique is used in conjunction with the continuous penalty scheme to solve the flow equations. Due to the low thermal diffusivity of the polymer melts, a streamline upwinding Petrov–Galerkin method is used to obtain convergent and stable results for the energy equation. This method is based on the extension of a previously developed scheme. The overall solution strategy is based on the Picard iterative scheme. Simulation results are obtained for the flow of a polypropylene melt through the metering and die zones of a laboratory scale extruder. To validate the proposed model, the results of the computer simulations are compared with experimentally measured mass flow rate and pressure profile. These comparisons show that there is very good agreement between the model predictions and actual data. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 676–689, 1999     

聚合物熔体在圆锥短口模的挤出胀大方程

深入讨论了聚合物熔体在不同长径比、不同角度圆锥短口模的挤出胀大现象及机理，利用生产用挤出机进行不同角度的圆锥短口模实验。结果表明，圆锥短口模挤出过程中，熔体在收敛流道受到拉伸流变，导致强烈的入口弹性效应，表现为熔体在短口模挤出时显著的挤出胀大。理论和实验研究结果进一步表明不同圆锥口模入口角对实验材料表现出有不同的挤出胀大值。     

过氧化物对抗冲共聚聚丙烯结构与性能影响的研究

通过凝胶渗透色谱(GPC)、二甲苯溶出、多次挤出等方法研究过氧化物对抗冲共聚聚丙烯结构与性能的影响,获得结构与性能均可控的高熔指抗冲共聚聚丙烯产品。结果表明:随着过氧化物量的增加,材料摩尔质量变低,分布变窄,且橡胶相较非橡胶相分子链断裂更为严重;经过多次挤出发现,材料的加工稳定性好,过氧化物残留低。     

Experimental and theoretical investigation of extrudate swell of polymer melts from small (length)/(cross-section) ratio slit and capillary dies

An experimental and theoretical study is presented of extrudate swell from short capillary and slit dies. The polymer melts studied were polystyrene and polypropylene. The swell from slit dies is greater than the swell from capillaries. Decreasing die entry angle for capillary dies decreases swell. The argument is made that elongational How existing in the die entry region and for short dies determines extrudate swell. Dimensional analysis arguments are used to relate extrudate swell to a Weissenberg number based on elongational flow at the die entrance and the detailed die geometry. Correlations are developed. The theoretical study is based on unconstrained elastic recovery following elongational How through the die entrance region.     

Effect of wall slip on the uniformity of flow from sheeting extrusion dies

A theoretical study for analyzing the uniformity of flow from sheeting extrusion dies is presented. In this study it is assume that a slip condition exists at the wall of the die, the magnitude of slip velocity is proportional to the shear stress at the wall, the flow is isothermal and steady state, and a power law model is valid for viscosity. Two extrusion dies, T-dies and coat-hanger dies, are examined. The flow uniformity at the exit of the die is calculated and compared with that for a nonslip analysis. The discrepancies between the slip and nonslip models imply that the wall slip condition induces a significant nonuniform flow distribution. Traditional design criticism based on the nonslip model are invalid for flow with the wall slip condition, and it is necessary to increase the length of the die land to even the flow distribution at the exit of the die.