啮合异向双螺杆挤出机中捏合块元件对PE-HD/PS不相容体系混合效果的研究

在常规啮合异向双螺杆上引入不同错列角和不同捏合盘厚度的捏合块元件,将其用于高密度聚乙烯/聚苯乙烯（PE-HD/PS）不相容体系的混合,观察混合体系的相态并分析分散相的粒径。结果表明,增加捏合块元件后啮合异向双螺杆挤出机的分散混合能力得到了提高;捏合块的错列角和捏合盘的厚度对PE-HD/PS不相容体系分散相PS的重均粒径和粒径分布指数有较大影响。     

聚丙烯/无机纳米粒子在双螺杆挤出机内的分散混合效果数值模拟

采用三维有限元数值模拟方法,研究了聚丙烯(PP)/无机纳米粒子在双螺杆挤出机的三种螺杆组合元件流道内的分散混合效果。通过对比分析三种螺杆组合下无机纳米粒子的剪切应力和剪切速率、停留时间分布及粒径分布等结果,发现含错列角45°捏合块的螺杆组合对其流场中大部分粒子的剪切作用最强,含错列角60°捏合块的螺杆组合次之,含错列角90°捏合块的螺杆组合最弱。与另两种螺杆组合相比,含错列角45°捏合块的螺杆组合流场中,无机纳米粒子团聚体的数量最少,剥离出的碎片数量最多,即在含错列角45°捏合块的螺杆组合条件下无机纳米粒子在PP熔体中的分散效果最好。     

新型捏合盘元件不同螺杆构型混合性能的数值模拟

采用POLYFLOW模拟软件分析了啮合同向双螺杆挤出机中新型捏合盘元件下物料的流动模式。考察了新型捏合盘元件的斜棱旋向、捏合块组合的错列角对物料在流道中的剪切速率、出入口压差以及回流量的影响。数值模拟分析结果表明:4种新型捏合块构型的输送特性和混合性能均有所不同。在正向输送能力方面,右旋正向捏合块更佳,在分布、分散混合性能方面,左旋反向捏合块更佳,并且捏合块的正反向比单片捏合块的螺旋方向在输送能力、混合性能上影响更大。     

啮合同向双螺杆捏合块元件混合效果的数值模拟分析与实验研究

对啮合同向双螺杆捏合块元件的动态流场进行了流场模拟与统计学分析，并对分析结果进行了实验验证。通过宽、窄捏合块两种螺杆元件的动态流场模拟，应用统计学分析方法计算了两种流场的停留时间分布、最大剪切速率分布以及固定百分比粒子经受的剪切速率分布随时间的变化。得出了宽捏合块元件的分散混合能力高于窄捏合块的结论，这一结论与实验结果较为一致。     

同向双螺杆支撑元件的流场模拟

对比分析了啮合同向双螺杆挤出机新型滑动支撑元件和滚动支撑元件的结构特点,通过Polyflow流场模拟,得出了2种支撑元件的压力分布与剪切速率分布,基于流体动力学原理及流变学原理分析了支撑元件的压力场与剪切速率场,重点讨论了物料的熔体流动速率对2种支撑元件压力消耗的影响。结果表明:支撑元件属于耗压元件,与双头螺纹元件相比,3种元件的流道出口-入口压差绝对值大小关系为双头螺纹元件滑动支撑元件滚动支撑元件;与捏合块元件相比,3种元件流道的加权平均剪切速率大小关系为捏合块元件滚动支撑元件滑动支撑元件,支撑元件对物料的分散混合不会造成明显的影响;支撑元件更适用于加工高熔体流动速率物料的螺杆组合。     

异向双螺杆S型元件混炼效果的数值研究

使用Polyfl ow软件,数值模拟了高密度聚乙烯(PE-HD)/炭黑熔体在异向双螺杆挤出机流道内的流动,数值计算了不同S型元件流道内熔体的三维等温流场,采用粒子示踪分析法(PTA)分析了不同S型元件流道内粒子的拉伸效果、分离尺度和停留时间,考察了啮合方式和两螺杆装配方式对S型元件混炼效果的影响。研究结果表明,啮合方式主要影响螺杆的输送能力、剪切能力和分布混合能力,非啮合元件的输送能力约为部分啮合元件的1.14倍,停留时间约为部分啮合元件的2.5倍,但是其剪切能力仅为部分啮合元件0.86倍;而螺杆的装配方式则影响其输送能力、拉伸能力和分布混合能力,并列式装配元件的输送能力约为错列式装配元件的1.11倍,停留时间约为错列式装配元件的1.2倍,但是其拉伸能力不如错列式装配的元件。三种元件中,部分啮合元件的分散混合性能最佳。     

数值模拟研究螺纹元件的混合性能

使用FEM方法数值模拟了同向双螺杆螺纹混合元件和普通螺纹元件流道中硬聚氯乙烯的流动过程,计算了2种螺纹元件流道内熔体的非等温流场,使用粒子示踪法统计分析了2种螺纹元件流道内熔体的混合性能.研究结果表明,螺纹混合元件具有较均匀的剪切速率分布、较平缓的温度分布和较强的分散与分布混合能力,但是其输送能力较小.     

同向双螺杆捏合盘错列角对不相容体系共混物相态结构的影响

双螺杆挤出机螺杆构型对不相容体系共混物的相态结构有一定影响。将捏合块置于熔融段,通过改变捏合盘错列角,在熔融段末端位置进行在线取样,对所取试样(HDPE/PS共混物)应用扫描电子显微镜考察其相态结构,由此分析研究双螺杆挤出过程熔融段捏合盘错列角对不相容体系共混物相态结构的影响。结果表明:正向30°和反向60°错列角的捏合块元件具有较强的分散混合能力。     

PE-HD/CBCNT与PE-HD/CNT复合材料的制备和性能对比

以高密度聚乙烯(PE-HD)作为聚合物基体,炭黑改性碳纳米管(CBCNT)和碳纳米管(CNT)作为填料,采用传统熔融共混法分别制备了PE-HD/CBCNT和PE-HD/CNT两种复合材料,并对二者的结构和性能进行对比研究.结果表明,CBCNT结构疏松,更易于在PE-HD中均匀分散,其与PE-HD的相容性优于CNT.当填...     

基于香农熵的超细粉体填料混合均匀度的评价研究

以香农熵理论为基础,提出了一种量化表征超细粉体填料在基体中混合均匀度的方法。以高密度聚乙烯/碳酸钙(PE-HD/CaCO3)复合材料为研究对象,首先用Photoshop和Image-pro-plus对样品扫描电子显微镜照片中的颗粒和团聚体尺寸进行统计,计算出了相对香农熵和团聚系数,分别表征超细铝粉的分布混合和分散混合,然后引入混合系数对混合均匀性进行综合评价。结果表明,添加了分散剂的PE-HD/CaCO3,CaCO3混合系数较高,拉伸强度和弯曲强度较大,验证了此方法对超细粉体填料混合均匀度评价的适用性。     

Mixing mechanism of three‐tip kneading block in twin screw extruders

In recent years, twin screw extruders have been applied to various kinds of polymer processing. It has been important to find their optimum geometrical configurations and operational processing conditions for the best performance of extrusions and products. Many engineers have been evolving numerical and the experimental methods to characterize the mixing performance for twin screw extruders. We have carried out three‐dimensional flow simulations of kneading blocks in intermeshing co‐rotating twin screw extruders by using the finite element method to quantify their ability in distributive and dispersive mixing. We discuss their performance in distributive mixing for three different type of kneading blocks in terms of the residence time distribution and the nearest distance between markers at various periods of time, by using the marker tracking method. Those numerical techniques and applications of mixing indices have enabled us to quantify and evaluate their abilities in distributive mixing of kneading blocks in twin screw extruders.     

同向双螺杆捏合盘厚度对MAH接枝LDPE反应挤出过程的影响

研究了同向双螺杆挤出机中,捏合盘元件的不同厚度对低密度聚乙烯(LDPE)接枝马来酸酐(MAH)反应挤出过程的影响,并将其与常规螺纹元件进行对比。对挤出沿程中的3个位置和挤出机出口处进行取样,用滴定法测定这些样品的接枝率。结果表明,捏合盘元件所对应的样品接枝率高于常规螺纹元件,并且随着捏合盘厚度的增加,其所对应的样品接枝率下降。此外对于接枝反应而言,捏合盘元件的分布混合能力所起到的作用要高于其分散混合能力。     

3‐D non‐isothermal flow field analysis and mixing performance evaluation of kneading blocks in a co‐rotating twin srew extruder

We have developed a three‐dimensional non‐Newtonian and non‐isothermal flow analysis of the twin screw extruder (TSE) using the finite element method. This code can simulate the fully filled parts of several kinds of screw elements, such as full flight screws, kneading blocks, rotors and their combinations. A marker particle tracking analysis has also been developed to evaluate the mixing performance of the screw elements. In this paper, simulations for the kneading blocks in a co‐rotating TSE were carried out. The screw configurations are combinations of 2‐lobe kneading blocks with several stagger angles and disk widths. The effects of screw configurations on pressure and temperature distributions are examined. We also evaluate the dispersive and distributive mixing via stress magnitude and area stretch obtained by marker particle tracking analysis. Additionally, we discuss the desirable stagger, disk width and their combinations that promote the mixing performance.     

啮合同向双螺杆挤出机中新型螺杆元件S型元件与捏合块元件的性能对比研究

应用FEM模拟计算了啮合员向双螺杆挤出机正反向螺纹组合的新型螺杆元件S型元件与捏合块元件的流场，考查了两种元件流场的特性，对比了两种元件流场的挤出特性、分散和分布混合能力。得出在相同有操作条件下，相同外径的S型元件和捏合盘元件相比具有相当的分散混合能力、更加优异的分布混合能力和更加优异的生产能力的结论。     

Relationship between local residence time and distributive mixing in sections of a twin‐screw extruder

Local residence time and distributive mixing were measured in conveying sections and kneading blocks of a twin screw‐extruder. The residence time measurements were completed using carbon black as the tracer and an infrared temperature probe to detect the temperature decrease caused by the changing surface emissivity. The validity of this experimental technique was extensively evaluated. A mixing limited interfacial reaction between polymer tracers was used to directly measure the distributive mixing in the twin‐screw extruder. Possible relationships between mixing and residence time in the sections of the twin‐screw extruder were investigated by combining these two measurements. Distributive mixing in conveying sections was related to the local average residence time and the fill. In contrast, distributive mixing in kneading blocks was related to the local average number of screw revolutions experienced by the polymer. Forward stagger kneading discs achieved the greatest amount of distributive mixing, which was attributed to a combination of local stagnant flow regions and more frequent interfacial reorientation.     

啮合同向双螺杆3种构型的模拟分析和实验研究

通过数值模拟方法对3种含捏合盘元件螺杆构型的剪切速率、停留时间和回流量等指标进行了分析,通过实验对3种螺杆构型的混合性能进行了对比。结果表明,90°捏合盘元件与反向捏合盘元件组合可以达到较好的分布混合效果,45°捏合盘元件与反向捏合盘元件的组合可以达到较好的分散混合能力,捏合段加入反向螺纹元件并不能提高分布混合能力,但可以延长停留时间。     

3‐D numerical analysis on the mixing performance for assemblies with filled zone of right‐handed and left‐handed double‐flighted screws and kneading blocks in twin‐screw extruders

We have calculated and visualized numerically the mixing performances of four kinds of assemblies in twin‐screw extruders that were composed of right‐handed or left‐handed double‐flighted full flight screws and neutral or left‐handed stagger angle kneading blocks, taking into consideration industrial usage. We have found that the mixing performance of a kneading block interposed between full flighted screws is strongly influenced by the flow of full flighted screws, in particular that of a neutral kneading block. Furthermore, we have proposed the simple mixing indices, which could describe both uniform mixing and heterogeneous mixing, and also applied them to our marker tracking results of four kinds of assemblies. We found that more uniform mixing is obtained for the assembly that has a neutral kneading block before the right‐handed full flight screw, and a more enhanced heterogeneous mixing is obtained for the assembly that has a left‐handed kneading block before the left‐handed full flight screw. The reason for the latter mixing ability will relate to the quasi‐channels of the left‐handed kneading block, through which marker clusters flow while elongating.     

增容剂对PE-HD/PC/CB导电复合材料PTC效应的影响

研究了增容剂马来酸酐接枝聚乙烯(PE-g-MAH)、乙烯-醋酸乙烯酯(EVA)、苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)对高密度聚乙烯(PE-HD)/聚碳酸酯(PC)/炭黑(CB)复合材料导电性能的影响。结果表明,加入增容剂有利于增强复合材料的正温度系数(PTC)效应,其中嵌段共聚物SBS对复合材料PTC效应的改善效果相对较好,SBS含量为4%(质量分数,下同)时,复合材料的PTC强度最高,比未添加时提高了14.3%;接枝共聚物PE-g-MAH的加入对复合材料PTC效应的增强效果弱于SBS;无规共聚物EVA的加入对负温度系数(NTC)现象具有明显的抑制作用,使复合材料的NTC强度从0.3下降至0.08。     

Analytical and Experimental Evaluation of Dispersive Mixing Performance of Special Rotor Segments in a Corotating Twin-Screw Extruder

An intermeshing corotating twin-screw extruder is often used for producing polymer composites. In this study, we discussed mixing performance of special rotor segments in molten zone. These rotor segments have several tip clearances for achievement of self-cleaning and effective mixing, and these are named various clearance mixing technology. We studied about dispersive mixing performance of configuration, which consists of various clearance mixing technologys (various clearance mixing technology configuration) using numerical analyses and experiments. For the analytical evaluation of mixing performance, we have adopted a particle tracking method. As evaluation indices of dispersive mixing performance, we focused on following three values (1) maximum value in a history of first principal stress of each particle, (2) time-integrated shear rate of each particle, and (3) time-integrated first principal stress of each particle. And we made the probability distributions of the indices. We adopted weighted probability as approximation of volume probability in each region. The results were compared with those of kneading disk segments configuration (kneading disk configuration). Furthermore, we validated the accuracy of the analytical evaluation by performing experiments under same conditions as those of numerical analyses. For the experimental evaluation of mixing performance, we used twin-screw extruder. Polypropylene was selected as suspending media. And CaCO₃ was selected as filler. To compare just the mixing performance of various clearance mixing technology configuration with that of kneading disk configuration, side feeding and screw configuration which had third mixing segments zone were adopted. From the experimental result, it is found that various clearance mixing technology configuration dispersed better than kneading disk configuration. And from the comparison between the experimental evaluation and the analytical evaluation, it is found that the first principal stress is more appropriate for evaluation index of dispersive mixing. Finally, it can be mentioned that various clearance mixing technology configuration has better mixing performance than kneading disk configuration, and large stress is important for dispersive mixing.