Melt temperature variations in the barrels of an injection moulder and a twin screw extruder

This article investigated temperature variations of a polypropylene melt in the barrels of an injection moulding and a twin screw extruder under an isothermal state. The melt temperature profiles in the barrel of an injection moulding machine were observed to be different from those a twin screw extruder, this being associated with differences in the flows occurring in the barrels of each processing equipment. The major parameters influencing the melt temperature profiles were shear heating and heating conduction effects, residence time, flow length and the flow patterns of the flowing PP melt in the barrel. Received: 4 January 2000 / Reviewed and accepted: 15 February 2000     

四螺杆挤出机中聚合物流动特性的计算机模拟

利用计算流体力学法(CFD),对聚合物熔体在四螺杆挤出机螺纹元件中的流动规律进行了数值模拟.利用计算所得的速度场和压力场,计算了四螺杆挤出特性,并和双螺杆、一字型排列和三角形排列的三螺杆挤出机进行了对比分析.结果表明,四螺杆的四个啮合区具有较大的压力和速度梯度,在中心区有明显的环流现象,延长了物料的停留时间分布,且中心区物料没有滞留现象.由于中心区的存在导致了四螺杆挤出机的建压能力较弱;但四螺杆挤出机在产量、分布性混合和分散性混合等方面好于双螺杆和三螺杆挤出机.     

挤出机螺杆转速对马来酸酐官能化POE性能及增韧PA66效果的影响

采用在熔融挤出过程中添加引发剂与提高双螺杆挤出机螺杆转速的复合引发方法,研究了引发剂的含量、螺杆转速对马来酸酐官能化POE的接枝率、熔体流动速率和凝胶含量的影响。结果表明,提高双螺杆挤出机的螺杆转速可以较好地抑制POE在官能化过程中的交联副反应,控制制得具有较高接枝率(Gd=0.6%~0.92%)、较好熔体流动性(MI=0.4~4.0g/10min)和较低凝胶含量(≤0.3%)的官能化产物。复合引发所得官能化产物POE-g-MAH对PA66的增韧效果明显优于单纯采用引发剂引发所得产物。25%复合引发官能化POE产物可使PA66的缺口冲击强度由6.5kJ/m2提高至110kJ/m2。     

Compatibilized Polypropylene/Ethylene–Propylene–Diene-Monomer/Polyamide6 ternary blends: Effect of twin screw extruder processing parameters

Polypropylene (PP)/Polyamide6 (PA6)/Ethylene–Propylene–Diene-Monomer (EPDM) (70/15/15) ternary polymer blends compatibilized with Maleic-anhydride grafted EPDM (EPDM-g-MA) were prepared by melt blending using a twin screw extruder (TSE). Effect of TSE processing parameters including barrel temperature, screw speed and blending sequence on the mechanical properties of ternary polymer blends was investigated by application of Taguchi experimental design methodology. Three different levels of barrel temperature (220 °C, 230 °C, 240 °C), screw speed (90 rpm, 120 rpm, 150 rpm) and blending sequence (nominated as: S1, S2 and S3) were selected. The response variables were tensile properties and impact strength of the prepared samples which are directly affected by the blend microstructure. Investigation of the statistical–mathematical analysis results performed by the software depicted that the optimum processing conditions for the ternary blends investigated here, to achieve balanced tensile and impact properties, are 220 °C, 150 rpm and S2 blending sequence.     

Evolution of lignocellulosic fibre lengths along the screw profile during twin screw compounding with polycaprolactone

Composites made of polycaprolactone reinforced by 20% hemp fibres were prepared by melt blending in a twin screw extruder (TSE). The influence of the extrusion parameters (feed rate and screw speed) on the fibre length evolution along the screw profile was investigated. The fibre length rapidly decreased after the introduction of the fibres and during the flow through the kneading blocks. Fibre fragmentation was increased at high screw speeds and low feed rates. The flow conditions along the TSE were calculated using Ludovic© software, focusing on the specific mechanical energy (SME) provided to the fibres. The fibre length evolution can be correctly estimated for various flow conditions using an exponential function of the SME.     

三螺杆挤出机挤出特性的数值模拟

利用计算流体力学的方法对聚合物熔体在三螺杆挤出机中的流动规律进行了数值模拟,分析了物料在三螺杆中心区的流动和混合情况。通过速度和压力分布,计算了三螺杆挤出机的螺杆挤出特性参数,并和双螺杆挤出机进行对比分析。结果表明,由于中心区环流的存在,延长了物料在三螺杆挤出机的停留时间分布。三螺杆挤出机在分布性混合、分散性混合、能耗等方面均好于双螺杆挤出机,而产能比又为双螺杆挤出机的1.3倍。三螺杆挤出机具有较好的工程应用前景。     

A novel method for velocity profile measurements in flowing polymer melts

This article introduced a novel technique for the determination of velocity profiles in flowing polymer melts in the barrel of an injection moulding machine, this technique being called Cooled-Stainless Tube (CST). An experimental arrangement of such technique involved making use of a novel temperature sensor coupled with an experimental test rig. The CST technique was found to be novel, simple, and reliable for velocity profile measurements of flowing polymer melts. The preliminary results showed that the velocity profiles in the barrel changed continuously with changing screw position. Received: 3 May 1999 / Reviewed and accepted: 8 May 1999     

Blending of modified polyphenylene ether with a liquid crystalline copolyester

Blending of poly (2,6-dimethylphenylene ether) (PPE), polystyrene (PS) and a thermotropic liquid crystalline polymer (LCP) was performed using a continuous co-rotating twin-screw extruder. The influence of LCP content on the blending process was studied by changing the barrel heater temperature and the screw speed. The torque of the screw shafts generated during the blending process was influenced by LCP content; its influence was not simple. The generated torque was found to depend not only on the melt viscosity of LCP but also on its distortion temperature. Further, the effects of matrix viscosity on the morphology and mechanical properties of the PPE/PS/LCP blends were studied. Well-developed fine LCP fibrils were formed during the melt-drawing process when the matrix viscosity was high. The formation of well-developed fine fibrils was found to improve the mechanical properties of the PPE/PS/LCP blend. Two mechanisms are proposed for the formation of well-developed fine LCP fibrils.     

轮胎胶应力诱导脱硫及对聚丙烯的增韧作用

在轮胎胶粉的熔融挤出过程中添加线型高分子材料作为溶胀剂和承载流体,并通过提高双螺杆挤出机转速的高剪切应力诱导方法,研究了螺杆转速和挤出反应温度对轮胎胶脱硫共混物凝胶含量、熔体流动速率、溶胶特性黏数及红外光谱(FT-IR)的影响。结果表明,双螺杆挤出机的高剪切应力可诱发轮胎胶颗粒中交联网络的断链反应和氧化降解作用,引起脱硫共混物凝胶含量的明显下降、熔体流动速率的明显增加、溶胶特性黏数的明显减小及溶胶分子链中碳碳双键和醚键基团明显增加。在最佳脱硫反应条件下,所得脱硫共混物可使聚丙烯(PP)(J430)材料的缺口冲击强度由10.5kJ/m2提高至47.7kJ/m2。     

双重引发POE官能化及其增韧PA66的研究

采用双螺杆加工过程中的机械力引发同时添加引发剂的双重引发方法,研究了引发剂的用量、螺杆转速和接枝反应温度对马来酸酐接枝POE产物的接枝率、熔融指数的影响.对单纯采用引发剂引发方法和引发剂与机械力双重引发方法所得接枝产物增韧PA66的效果也进行了比较.     

单螺杆橡胶挤出机三维非等温流动数值模拟

为研究胶料在挤出过程中的流动模式,本文建立了具有复杂几何构型的主、副螺纹单螺杆螺槽内胶料三维非等温流动的有限元模型,采用Bird-Carreau模型和Arrhenius shear stress方程分别表征胶料黏度随剪切速率和温度的变化,并通过热力学估算确定了合理的机筒壁热学边界条件.在此基础上求解了20 r/min转速下的速度场、温度场和压力场,并将温度数值计算结果与实测结果进行了对比,两者吻合较好,这表明了模型的有效性.此外,通过模拟发现主、副螺纹构型的热喂料螺杆确实可以避免挤出过程中的"死区"并提供更强剪切作用;螺杆挤出段的副螺纹阻碍了胶料的流动,使得该处压力更大;由于受剪切时间更长、更强烈,胶料在挤出段温度最高.最后考察了不同转速下的压力和温度,结果发现挤出过程的最大压力与最高温度均随转速增大而升高,与此同时由于胶料自身的剪切变稀特性和温度依赖性,压力与温度上升的趋势会随着转速的升高而减缓.     

轮胎胶应力诱导脱硫及热塑性弹性体的制备

采用提高双螺杆挤出机螺杆转速的高剪切应力诱导方法,研究了螺杆转速、挤出反应温度及螺杆长径比对脱硫轮胎胶共混物凝胶含量、熔体流动速率和溶胶红外吸收光谱的影响。研究了脱硫工艺条件对脱硫轮胎胶/HDPE/EPDM热塑性弹性体力学性能的影响。实验结果表明,挤出机的高剪切应力作用,可诱发轮胎胶粒中交联网络的断链和氧化降解作用,引起脱硫共混物凝胶含量的下降、熔体流动速率的增加和脱硫共混物溶胶分子链中醚键、酯键、过氧酸和磺酸酯基团的明显增加。挤出机螺杆转速越快、挤出反应温度越高或螺杆长径比越大,其所得热塑性弹性体中未脱硫凝胶颗粒尺寸就越小。     

振动场作用下聚合物的新型动态塑化熔融模型

将振动场引入聚合物塑化挤出的全过程,建立了振动挤出机的聚合物动态解析熔融模型．振动场的引入使挤出机的熔融塑化能力得到了很大的提高,熔融段的长度随着振动频率和振幅的增大而减少．在该模型中,随着熔融过程的进行,熔体的厚度缓慢增加,而固体床缓慢减少,直到聚合物熔体填满整个螺槽横截面;在稳定情况下,熔融段的长度不变,聚合物颗粒进入料筒的速度与挤出机的熔融速度以及产量相等．但是,当熔融段的长度达到某一稳定值后,再增大振幅或频率,熔融段的长度不再发生明显的变化．用该模型能很好地预测振动挤出机的成型参数,得到优化条件．将计算值与实验值比较验证了各振动参数（振幅和频率）对振动挤出机塑化熔融能力的影响．     

Finite element analysis of a thermoplastic elastomer melt flow in the metering region of a single screw extruder

The flow of a thermoplastic elastomer melt in the metering region of a single screw extruder was studied by the use of a mathematical model. In this model the continuous penalty finite element scheme was combined with generalized Newtonian rheological model to solve the governing equations of continuity and momentum in three-dimensional Cartesian coordinate system. A non-isothermal flow regime was assumed and the energy equation was solved by a streamline upwind Petrov–Galerkin method. The nonlinear nature of the derived set of working equations was also treated using the well-known Picard’s iterative technique. The applicability of this model has been verified by the comparison between the results of the computer simulation of the flow of a NBR/PP thermoplastic elastomer in the metering zone of a single screw extruder with experimentally measured data at different process conditions. These comparisons show that there are very good agreements between the model predictions and experimental data.     

In-process rheometry as a PAT tool for hot melt extrusion

Real time measurement of melt rheology has been investigated as a Process Analytical Technology (PAT) to monitor hot melt extrusion of an Active Pharmaceutical Ingredient (API) in a polymer matrix. A developmental API was melt mixed with a commercial copolymer using a heated twin screw extruder at different API loadings and set temperatures. The extruder was equipped with an instrumented rheological slit die which incorporated three pressure transducers flush mounted to the die surface. Pressure drop measurements within the die at a range of extrusion throughputs were used to calculate rheological parameters, such as shear viscosity and exit pressure, related to shear and elastic melt flow properties, respectively. Results showed that the melt exhibited shear thinning behavior whereby viscosity decreased with increasing flow rate. Increase in drug loading and set extrusion temperature resulted in a reduction in melt viscosity. Shear viscosity and exit pressure measurements were found to be sensitive to API loading. These findings suggest that this technique could be used as a simple tool to measure material attributes in-line, to build better overall process understanding for hot melt extrusion.     

高剪切应力对PS/SEBS/CaCO3材料力学性能影响

采用在材料熔融挤出共混过程中提高双螺杆挤出机螺杆转速的方法,研究了较高螺杆转速条件下双螺杆挤出机的高剪切应力对PS/SEBS/CaCO3共混材料力学性能的影响。结果表明,双螺杆挤出机的高剪切应力可促进SEBS橡胶颗粒和碳酸钙颗粒聚集体的分散、引发聚苯乙烯(PS)、SEBS分子链的断链反应、形成大分子自由基、产生原位增容作用,并引起共混材料力学性能的明显改善。在220℃的挤出温度下,当螺杆转速由120 r/min提高至960 r/min时,其PS/SEBS/CaCO3共混材料的缺口冲击强度将由5.7 kJ/m2提高至11.0 kJ/m2,同时共混材料的拉伸强度和弯曲强度也获得一定的增加。双螺杆挤出机的熔融挤出温度对PS/SEBS/CaCO3共混材料力学性能的影响存在最佳值。     

四段式单螺杆反应挤出机的研制

反应挤出机除了塑化功能处，在设计上应充分考虑反应挤出工艺的要求。虽然不同反应体系的反应类型和工艺要求有很大的差别，但它们对挤出机反应功能的要求，主要包括传递、物料停留时间及其分布。在对乙烯基硅烷－聚乙烯体系熔融接枝反应动力学深入研究的基础上，我们对三段式单螺杆挤出机进行了改进，增设了反应段，首次提出了适于聚乙烯硅 烷接枝反应过程的四段式单螺杆反应 出机的设计原理和方法。所设计的四段式单螺杆反应挤出     

嵌套式螺杆挤出机的固相温度分布

介绍了一种新型嵌套式螺杆挤出机。在考虑离心力和物料可压缩性条件下,通过非等温模型求解了新型螺杆挤出机内外螺杆固相界面温度沿螺杆轴向和槽深方向的分布。计算结果表明,内外螺杆的固相界面温度沿轴向均按近似指数函数的规律增加,一直到固相界面温度达到熔点并出现熔膜为止,内螺杆固体输送段的长度大于外螺杆。机筒温度较高时可缩短固体输送段的长度,但不利于固体输送段压力梯度的建立。热量沿内外螺杆槽深方向传入固体床的深度都只有在15%~20%槽深的范围。     

三维单螺杆熔体输送理论与有关问题研究

提出了简化的准三维模型 ,由于实际螺槽内物料性能变化使模型的数值求解很难 ,因此采用沿流方向逐步计算的有限元法数值求解。解出了螺槽内三维温度场和速度场 ,压力曲线 ,剪切速率等。比较非牛顿流体的实验结果与模型计算结果 ,二者吻合很好。此外由计算结果发现在流道横截面内存在强烈的环流 ,而只有三维模型才反映了这种环流影响 ,进一步证实三维模型研究是必要的。     

The influence of carbon nanotube functionalization route on the efficiency of dispersion in polypropylene by twin-screw extrusion

The joint effect of chemical functionalization and polymer melt blending conditions on carbon nanotube dispersion in polypropylene, as well as its influence on the electrical and mechanical properties of the resulting composites were investigated. Melt blending was performed using a prototype twin screw extruder enabling sampling along the barrel. The carbon nanotube dispersion was assessed by optical and scanning electron microscopy. The functionalization reaction was tailored for compatibility with the polymer, and characterized by X-ray photoelectron spectroscopy. In particular, nanotubes covalently bonded to polypropylene showed distinctive dispersion ability, while the carbon nanotube dispersion remained stable even after re-melting. However, the polypropylene-functionalized nanotubes produced composites with higher electrical resistivity, possibly due to the insulating effect of the polymer bonded to the nanotubes surface.