应力引发官能化EPDM/HDPE及其对PA66/EPDM/HDPE 共混物相形态和力学性能的影响

通过提高双螺杆挤出机螺杆转速的方法,研究了熔融挤出过程中高剪切应力对马来酸酐(MAH)官能化三元乙丙橡胶(EPDM)与高密度聚乙烯(HDPE)共混物的接枝率、熔体流动速率及凝胶含量的影响.随着双螺杆挤出机螺杆转速的增加,强烈的机械剪切应力引发EPDM/HDPE共混物大分子链的断链反应形成大分子自由基,从而引发接枝反应制...     

紫外光辐照高温熔融态聚乙烯的结构与性能

采用螺杆均化段料筒可装设透明石英玻璃的双螺杆挤出机作为反应挤出装置,通过改变喂料量、二苯甲酮(BP)含量和三羟甲基丙烷三丙烯酸酯(TMPTA)含量三个参数,得到不同交联程度的新型聚乙烯材料。紫外光辐照聚乙烯反应挤出后,产物发生了交联,交联产物为假塑性流体,随着剪切速率的增加,表观黏度减小。交联结构的存在使产物的熔体强度有了很大的提升,达7.76 cN,极大的改善了LDPE在高温下的加工性能。     

用反应挤出法制备尼龙6塑料

利用双螺杆挤出机进行了尼龙６阴离子开环聚合反应的研究，通过改变引发剂及活化剂的浓度、螺杆转速、机筒的温度分布以及螺杆元件构型的排布等，研究这些工艺参数对尼龙６反应挤出产物性能的影响。结果表明，反应挤出的尼龙６综合机械性能比水解缩聚法生产，且具有较高的性能价格比。     

加工条件对聚丙烯/尼龙6原位成纤复合材料的影响

分别用不同的加工温度、挤出螺杆转速、牵引速率在单螺杆挤出机中挤出PP／N6（聚丙烯／尼龙6）共混物，得到不同加工条件下的PP／N6原位成纤复合材料．对不同加工条件下得到的共混物的分散相形态、力学性能进行研究．发现螺杆转速越高、牵引速率越快、加工温度越低，分散的N6纤维尺寸越小，复合材料的力学性能越好．     

反应挤出法合成S/B多嵌段共聚物的研究

在阴离子引发体系下 ,以双螺杆挤出机为反应器 ,采用丁二烯、苯乙烯混和单体加料方式 ,本体法一步合成了S B多嵌段共聚物 .考察了螺杆转速、进料速率以及不同丁苯配比对反应挤出合成PS及S B嵌段共聚物聚合转化率的影响 .用1 H NMR、IR、DMA、TEM等方法对S B嵌段共聚物进行了表征 ,结果表明共聚物由多个微小的丁二烯嵌段和少量无规段组成 .当丁二烯含量少至 15 %左右时 ,其嵌段可回缩成球状 ,粒径大约在 30～ 5 0nm .该材料的韧性随着共聚物中丁二烯含量的增加而逐渐提高 ,特别是断裂延伸率的提高尤为显著     

自由基聚合反应挤出过程的化学流变分析

进行了甲基丙烯酸正丁酯在异向旋转双螺杆挤出机内的自由基聚合反应过程数值模拟,描述了单体转化率、重均分子量、流体粘度等物理量的变化特点,分析了其影响因素,获得了材料体系的化学流变规律.模拟结果与实验结果基本吻合.     

小角光散射在线系统研究多相聚合物双螺杆挤出过程中的相尺寸--非相容PE/PA1010体系

利用可视化双螺杆挤出机———光散射在线采集与分析系统对不相容聚合物体系聚乙烯 尼龙 10 10(PE PA10 10 )双螺杆挤出过程进行了在线分析 .相尺寸由Debye理论中的相关距离ac,平均弦长L ,以及分散相平均直径D描述 ,给出了几种参数表征适用的范围 .由在线光散射计算出的平均弦长Lscatt、分散相平均粒径Dscatt与电镜照片计算出的平均弦长LSEM 、分散相平均粒径DSEM 作了比较 ,两者比较符合 .结果表明 ,分散相颗粒尺寸沿螺杆挤出方向逐渐变小 ;随着低组分含量 (PA10 10≤ 5 0 % )的增加 ,分散相颗粒尺寸变大 ,在组成比为 70 30和 6 0 4 0时出现双连续相     

反应挤出合成带不饱和官能团端基的聚己内酯

用带双键官能团的2-烯丙氧基乙醇与四丙醇钛酸酯进行酯交换,可合成用于ε-己内酯配位开环聚合的钛化合物引发剂;利用此引发剂,引发ε-己内酯聚合得到了分子链一端为双键的功能化聚己内酯.研究了物料配比和反应温度对聚合转化率和速率的影响,进而在双螺杆挤出机中实施快速本体聚合,合成了带活性双键的功能化聚己内酯.引发剂和聚合物的化学结构由 1H-NMR予以表征,GPC测定的结果表明聚合物的分子量与物料摩尔比相关.     

叶片挤出机对PBS/木质素共混体系加工性及性能影响

采用以体积拉伸形变为主导的叶片挤出机制备聚丁二酸丁二醇酯(PBS)/木质素可降解复合材料,考察了叶片挤出机加工温度(130~145℃)、加工转速(10~40 r/min)对复合材料停留时间、表观质量、力学性能以及微观形貌的影响.结果表明,复合材料停留时间随着加工温度的提升而逐渐减小,加工转速具有类似变化趋势;复合材料表观质量随加工温度影响不显著,但随加工转速影响剧烈;复合材料力学性能随加工温度变化不明显,而随加工转速影响程度不一;复合材料断面微观形貌在不同的加工温度下有细微变化,而在不同的加工转速下变化明显.以上结果与叶片挤出机的结构和固体输送有关,物料在拉伸流场作用下发生正位移输送和塑性能量耗散,提高了传质效率,在适当加工条件下引起组分间相互作用机制加强.综合考虑产品性能与经济成本,确定叶片挤出机制备PBS/木质素复合材料各段加工温度为115、125、135、125℃,加工转速为20 r/min.     

通过自动加速效应的调控反应挤出制备聚甲基丙烯酸甲酯

利用旋转流变仪、哈克转矩流变仪以及双螺杆挤出机,研究了剪切速率对自加速效应的影响,且通过反应挤出聚合制备了聚甲基丙烯酸甲酯(PMMA)。采用多检测凝胶渗透色谱(GPC)、动态力学分析(DMA)等方法,对聚合物结构和性能进行了表征。结果表明,在反应挤出聚合过程中,改变剪切速率可有效地调控自加速效应。通过新单体补加技术充分利用自加速效应,不仅可以提高聚合速率,而且可以获得高分子量、窄分子量分布的PMMA。制备的PMMA性能优于市售PMMA。     

On-line monitoring of the residence time distribution along a kneading block of a twin-screw extruder

An on-line Residence Time Distribution (RTD) measuring set-up that enables the characterisation of twin screw extruders at short axial increments is presented. It uses the light emission of a fluorescent tracer (perylene) to generate concentration versus time curves, which are then used to determine the usual RTD parameters, delay time, mean residence time and variance. The system is initially mounted on a rectangular die coupled to a single screw extruder, on-line and off-line measurements being directly contrasted. Then, the optical probe is positioned at several points along the axis of a modular co-rotating twin screw extruder, on-line and off-line data being again compared. Having gained confidence in the measuring technique, an experimental unit utilizing a transparent barrel is used to characterize the evolution of RTD along a kneading block of a twin screw extruder.     

Polystyrene prepared by reactive extrusion: kinetics and effect of processing parameters

The conversion and residence time were investigated during the bulk polymerization of styrene in a twin screw extruder. It was found that polymerization mainly occurred in the zone between 400 and 1000 mm along the screw axis in the extruder, corresponding to the residence time of the reactants ranging from 1 to 4 min in the extruder. Furthermore, the processing conditions (feed rate, screw rotation rate) and average molecular weight of the polymer have a great effect on the residence time. Based on dimensionless analysis, a model of the residence time has been built‐up, which has been confirmed by the results of realistic measurements. A kinetic model of the polymerization has also been established under the assumption that the screw extruder can be regarded as an ideal plug flow reactor. Copyright © 2004 John Wiley & Sons, Ltd.     

CHEMICAL MODIFICATION OF STYRENE/ETHYLENE-BUTHYLENE/STYRENE COPOLYMERS

The chemical modification of two thermoplastic elastomer styrene/ethylene-buthylene/styrene copolymers (SEBS) with diethylmaleate (DEM) as functionalizing agent was carried out in a corotating twin screw extruder and in an internal mixer. The residence time distribution of the extruder was studied due to its great influence on the grafting chemical reaction, the degree of functionalization, and the viscoelastic properties of the obtained modified polymers. The influence of copolymer melt viscosities, and DEM and initiator concentration ratio on the grafting degrees was studied as well. In this case, an internal mixer was used.

Optimal processing conditions were established to obtain grafted polymers characterized by good processability and an absence of crosslinking. The grafting degree achieved in the internal mixer was the same for both copolymers with different viscosities and it increased as the DEM and initiator concentrations and concentration ratios were increased.     

Modeling of particle‐dispersed melting mechanism and its application in corotating twin‐screw extrusion

Particle‐dispersed melting is a complex but important melting mechanism in the corotating twin‐screw extruder. In this study, the complex multi‐particle‐dispersed system was simplified into a single‐particle melting model. The finite‐difference method was introduced to solve this problem. The simulation results show that the melting of a particle may involve two steps: the heating stage and melting stage. The heating time and melting time depend on solid concentration, initial melt and solid temperature, and shear rate. Calculations indicate that high solid concentration and solid temperature, low melt temperature and shear rate will result in a more uniform temperature distribution after polymer melting. The model offers valuable information for designing the melting zone in a corotating twin‐screw extruder, especially at high screw speed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2461–2468, 2001     

Screw extrusion of thermoplastics: I. General model of the screw extrusion

New approach to a simulation of single and twin screw extruders for thermoplastics processing was suggested. The approach takes into account real boundary geometric conditions and conditions on velocity (a screw is rotated, cylinder is fixed), and also that there exist phase transformations of the processed material and its heat exchange with surfaces of the screw and cylinder limiting the working channel of the extruder.     

Preparation and characterization of vinyltriethoxysilane grafted ethylene propylene diene terpolymer/linear low density polyethylene (EPDM‐g‐VTES/LLDPE) blends

Graft polymerization of vinyltriethoxysilane (VTES) onto ethylene‐propylene‐diene terpolymer (EPDM) was carried out in toluene using dicumylperoxide (DCP) as initiator. Effects of various parameters (EPDM content, VTES content, reaction time, reaction temperature and initiator concentration) on the grafting efficiency of VTES onto EPDM were investigated. At the optimum grafting efficiency conditions, EPDM‐g‐VTES was developed by melt mixing in a twin screw extruder and then linear (l), statically vulcanized (s) and dynamically vulcanized (d) blends of EPDM‐g‐VTES with linear low‐density polyethylene (LLDPE) with varying percentage compositions were prepared by melt mixing in the twin screw extruder. The grafting of VTES onto EPDM and its crosslinking was confirmed by FT‐IR. The characterization of mechanical properties such as tensile strength, elongation at break, Young's modulus and hardness, differential scanning calorimetry (DSC) analysis and morphology were studied and compared for the EPDM‐g‐VTES/LLDPE blends. The study reveals that the dynamically vulcanized blend improves the mechanical and thermal properties due to the presence of efficient interaction between component polymers when compared with other blends. Copyright © 2005 John Wiley & Sons, Ltd.     

Study on In-Situ Compatibilization of the PP/PA6 Blends in Twin Screw Extruders

The in-situ compatibilization of PP/PA6 blend was studied in a twin screw extruder. The maleic anhydride (MA) content, peroxide concentration, shear rate and feeding order were among the variables investigated. Degree of grafting of samples collected prior to feeding of PA6 into the extruder was measured using titration combined with FTIR technique. From the SEM results it was found that the increasing of initial MA concentration led to larger PA particle size which could be related to secondary reactions between excess MA and PA. The melt linear viscoelastic measurements performed on the blend samples and the obtained relaxation time spectra showed shorter form relaxation time and interfacial relaxation time for one-step compatibilized sample compared to the sample prepared by the two-step method with the same degree of grafting. This was attributed to the stronger interfacial interaction of the one-step compatibilized blend samples which could be resulted from greater efficiency of grafting and/or compatibilization. These results were supported by SEM results which showed smaller particle size for the one-step compatibilized samples. It was demonstrated that melt linear viscoelastic measurement could provide a great insight into understanding the compatibilization process in twin screw extruder.     

Modelling non-homogeneous flow and residence time distribution in a single-screw extruder by means of Markov chains

Non-homogeneous velocity distribution of the flow in the channel of a single-screw extruder is taken into account by a new model developed on the basis of the Markov chains. This model allows calculating the Residence Time Distribution (RTD) as well as the influence of the operating conditions on the process at any velocity distribution in the channel. It has been used to represent experimental results on mass flow rate and RTD previously obtained by extrusion of an acrylic polymer, Eudragit E100, at different temperatures and screw rotation speeds. The diffusion coefficient is the only adjusting parameter of the model. It was shown that it does not depend on the screw rotation speed and a correlation between this diffusion coefficient and the barrel temperature was found. The model provides global understanding of the transport kinetics of the flowing material through the extruder according to its behaviour and better describes the progress of the polymer flow all along the barrel from the hopper to the die.     

Vibrational spectroscopic studies of laboratory scale polymer melt processing: Application to a thermoplastic polyurethane nanocomposite

A laboratory scale twin screw extruder has been interfaced with a near infrared (NIR) spectrometer via a fibre optic link so that NIR spectra can be collected continuously during the small scale experimental melt state processing of polymeric materials. This system can be used to investigate melt state processes such as reactive extrusion, in real time, in order to explore the kinetics and mechanism of the reaction. A further advantage of the system is that it has the capability to measure apparent viscosity simultaneously which gives important additional information about molecular weight changes and polymer degradation during processing. The system was used to study the melt processing of a nanocomposite consisting of a thermoplastic polyurethane and an organically modified layered silicate.     

Effect of Organoclay Mixture on the Rheological Properties of ABS-Clay Nanocomposites

Summary: In this work, poly(acrylonitrile-butadiene-styrene) (ABS) and different organically modified montmorillonite clay nanocomposites were prepared by melt intercalation in a co-rotating twin screw extruder. The influence of the screw torque during processing and of the mixture of the modified organoclays in the intercalation/exfoliation of the clay in the polymeric matrix was evaluated through low angle X-ray diffraction range and capillary and parallel plate-plate rheometry.