Continuous polymerization of ω‐lauryl lactam in an intermeshing corotating twin‐screw extruder

This article describes the synthesis of poly(ω‐lauryl lactam) by a reactive extrusion process. Anionic ring‐opening polymerization was performed in an intermeshing corotating twin‐screw extruder. We investigated the evolution of conversion of ω‐lauryl lactam as a function of reaction time, screw speeds, different feed rates, and different screw configurations along the screw axis in a twin‐screw extruder. For comparison with continuous polymerization in a twin‐screw extruder, we studied polymerization in an internal mixer, which was considered a batch reactor. We found the final conversion of ω‐lauryl lactam made in a twin‐screw extruder was higher than in an internal mixer. Higher molecular weights are found at lower screw speeds and feed rates. Melt viscosities and mechanical properties of the polymers were measured. Residence time, molecular weights, and shear mixing have the main effect on the mechanical properties of products. The twin‐screw extruder performance was interpreted in terms of commercial software. It was found that twin‐screw extruder reaction rate was higher than those in the batch reactor and increased locally with screw speed and feed rate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1605–1620, 2005     

Determination of twin‐screw extruder operational conditions for the preparation of thermoplastic vulcanizates on the basis of batch‐mixer results

In this study, we attempted to prepare a thermoplastic vulcanizate in a twin‐screw extruder by determining the screw configuration on the basis of batch‐mixer results. In this regard, two sets of information were used: (1) the time length, power consumption, and filling factor of different stages of the reactive blending process in the internal mixer and (2) the mean residence time and power consumption of the twin‐screw extruder. Morphological features of the samples taken from the melt‐mixing and dynamic vulcanization zones of the extruder with the selected screw configuration were found to be comparable with corresponding samples taken from an internal mixer reported in our previous study. The rheological and mechanical properties could provide valuable information to support the reliability of this study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A comparison study of lignocellulosic–thermoplastic composites prepared from different compounding techniques

A comparison study was carried out to determine the effect of different types of compounding technique, i.e., internal mixer, twin screw extruder, and high speed mixer in the preparation of kenaf‐polypropylene composite. The effect of percentage kenaf loading and particle size of kenaf (core) on the flexural properties of the composite was investigated. From the results, the incorporation of kenaf, regardless of particle size had resulted in the reduction of flexural strength of the composite. However, flexural modulus of the composites increased as the percentage of kenaf loading was increased due to the increasing of the stiffness contributed by kenaf fiber. Composites produced from internal mixer had displayed higher flexural properties as compared to those prepared from high speed mixer and twin screw extruder. It was believed that this phenomenon was attributed to the effectiveness of internal mixer with a better compounding mechanism which improved the wetting and distribution on kenaf within the polypropylene matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Styrene grafting onto a polyolefin in an internal mixer and a twin‐screw extruder: Experiment and kinetic model

There has been relatively little effort to quantitatively understand graft copolymerizaution in either batch mixers or twin‐screw extruders. Most efforts have concentrated on grafting maleic anhydride, which does not homopolymerize. In this paper we consider grafting with styrene, which may homopolymerize as well as graft. The influence of residence time on degree of grafting in an internal mixer and a twin‐screw extruder were studied by measuring reaction yields with respect to reaction time in a mixer and along the screw axis in a twin‐screw extruder. The degree of grafting increased with initial monomer and peroxide concentration. Grafting reactions with three different peroxides were also investigated. The degree of styrene grafting in an internal mixer is slightly higher than that in a twin‐screw extruder. The rate of reaction along the screw axis in terms of residence time seems higher than for the batch mixer. The melt viscosity dropped dramatically with addition of peroxide. A kinetic scheme is proposed and the experimental results are critically compared with it.     

混炼设备结构对PP/GF复合材料中GF残存长度及其力学性能的影响

基于熔融共混法,分别采用双转子连续混炼挤出机和同向啮合双螺杆挤出机制备了20 %玻璃纤维增强聚丙烯（GFRPP）复合材料,并对制备出的GFRPP复合材料中玻璃纤维残存长度及其力学性能进行了相应表征,在此基础上探讨了具有不同混炼特性的混炼设备结构对GFRPP复合材料中玻璃纤维残存长度及其力学性能的影响。结果表明,GFRPP复合材料的力学性能随玻璃纤维残存长度的增加而明显提高;双转子连续混炼挤出机相对于同向啮合双螺杆挤出机更有利于保留长玻璃纤维,同时适当减弱双转子连续混炼挤出机的转子的分散混合能力,降低转子转速,有利于提高玻璃纤维的残存长度,制备出更高性能的GFRPP复合材料。     

Effect of supercritical carbon dioxide on morphology development during polymer blending

Supercritical carbon dioxide (scCO₂) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The compounding took place in a twin screw extruder and a high‐pressure batch mixer. Viscosity reduction of PMMA and polystyrene were measured using a slit die rheometer attached to the twin screw extruder. Carbon dioxide was added at 0.5, 1.0, 2.0 and 3.0 wt% based on polymer melt flow rates. A viscosity reduction of up to 80% was seen with PMMA and up to 70% with polystyrene. A sharp decrease in the size of the minor (dispersed) phase was observed near the injection point of CO₂ in the twin screw extruder for blends with a viscosity ratio, ηPMMA/ηpolystyrene, of 7.3, at a shear rate of 100 s^?1. However, further compounding led to coalescence of the dispersed phase. Adding scCO₂ did not change the path of morphology development; however, the final domain size was smaller. In both batch and continuous blending, de‐mixing occurred upon CO₂ venting. The reduction in size of the PMMA phase was lost after CO₂ venting. The resulting morphology was similar to that without the addition of CO₂. Adding small amounts of fillers (e.g. carbon black, calcium carbonate, or nano‐clay particles) tended to prevent the de‐mixing of the polymer blend system when the CO₂ was released. For blends with a viscosity ratio of 1.3, at a shear rate of 100 s^?1, the addition of scCO₂ only slightly reduced the domain size of the minor phase.     

Maleic anhydride modification of polyolefin in an internal mixer and a twin‐screw extruder: Experiment and kinetic model

There has been little effort. to quantitatively understand graft copolymerization in batch and continuous mixers. Little information exists on the evolution of grafting reactions with respect to residence time in an internal mixer or along the screw axis in a twin‐screw extruder. In this study, maleic anhydride was grafted onto polypropylene in both an internal mixer and a twin screw extruder. The influence of residence time on degree of grafting in an internal mixer and a twin screw extruder was studied through measuring reaction yields with respect to reaction time in the internal mixer as well as along the screw axis in the extruder. The dependence of the degree of grafting with monomer and peroxide concentration was determined. A free radical kinetic model of the process was developed and compared to experiment. Kinetic parameters were determined.     

Development of a novel microcompounder for polymer blends and nanocomposite

In this article, we introduce a new type of small scale compounder. The compounder developed is for mixing of polymeric samples of 0.5–10 g. It consists of a heated cylindrical metal having two cylindrical cavities connected through a narrow channel and two cylindrical pistons, which squeeze molten polymers from one cavity to the other cavity through the narrow channel. During mixing procedure, the molten polymers flow from one cavity to the other cavity, repeatedly, and this operation generates the extensional flow in the converging and the diverging geometry. Because the compounder has mixing chamber of very simple geometry, the cleaning is very easy and the material lost is very small. We evaluated the mixing efficiency of the compounder by comparing with the commercialized small‐scale mixers including a cup and rotor batch mixer, an internal batch mixer, and a recirculating conical twin‐screw extruder. It was found that the compounder developed has many advantages over the existing small‐scale mixers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Experimental study of maleation of polypropylene in various twin‐screw extruder systems

A range of continuous mixing machines were used as continuous reactors for grafting maleic anhydride onto polypropylene. The machines used were (1) a nonintermeshing modular counterrotating twin‐screw extruder, (2) an intermeshing modular corotating twin‐screw extruder, (3) intermeshing modular counterrotating twin‐screw extruder, and (4) a Kobelco Nex‐T continuous mixer. The grafting reaction of maleic anhydride onto polypropylene and degradation of polypropylene during the grafting reaction were investigated as means for comparing these different machines for reactive extrusion. The influence of processing variables such as screw speed and processing temperature on polymer characteristics also was investigated. Generally, in a comparison of the different machines, the intermeshing counterrotating twin‐screw extruder had the lowest levels of grafted maleic anhydride, whereas the Kobelco Nex‐T continuous mixer under the conditions used had the highest levels of grafted maleic anhydride. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1755–1764, 2003     

Continuous polymerization of ε‐caprolactone initiated by titanium phenoxide in a twin‐screw extruder

The continuous polymerization of ε‐caprolactone initiated by titanium phenoxide was carried out in both an internal mixer and a twin‐screw extruder. The polymerization was performed under different processing conditions, including various temperatures and screw speeds. To perform a kinetic study, samples were collected along the time axis (internal mixer) and along the screw axis (extruder). Size exclusion chromatography and proton nuclear magnetic resonance were used to study the evolution of the conversion degree with mixing time and with the extruder. The rheological behavior was also characterized. Temperature had a strong effect on conversion in the internal mixer, whereas in the twin‐screw extruder, both temperature and screw speed played major roles. The specificity of the titanium phenoxide to lead to high‐molar‐mass poly(ε‐caprolactone) under these processing conditions was also confirmed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

螺杆组合对玻纤增强聚酰胺66纤维长度及力学性能的影响

研究了在同向双螺杆挤出机不同混合段螺杆组合下制备玻璃纤维(GF)增强聚酰胺66(PA66)复合材料时的纤维破坏情况,并通过沿螺杆轴向取样分析纤维长度沿挤出方向的变化规律,研究了不同螺杆组合对制品力学性能的影响,设计出适合于PA66/马来酸酐接枝乙烯辛烯共聚物(POE-g-MAH)/GF体系的螺杆组合。结果表明,合理设计纤维加入后的螺杆组合可以有效提高剩余纤维长度及制品的力学性能,同捏合块相比,使用反向齿形盘能够在提供较强混合能力的同时保证较低的剪切强度,从而有利于保持纤维长度,并有助于纤维的分散及物料的混合;将混合元件分开布置,并用输送元件将其分隔开,有助于提高输送能力,保持纤维长度。     

EVA‐Montmorillonite Nanocomposites: Effect of Processing Conditions

Summary: The aim of this study is to examine the effect of the compounding apparatus and of processing conditions on the properties of an organoclay‐poly[ethylene‐co‐(vinyl acetate)] (EVA) nanocomposite. The filled materials were prepared using either a discontinuous batch mixer, a single screw extruder, a counter rotating intermeshing twin‐screw compounder or a corotating intermeshing twin‐screw extruder. The characterization of the obtained nanocomposites was performed by XRD, thermogravimetry, mechanical and rheological measurements. The study has shown the possibility of producing nanocomposites based on EVA and a commercial organoclay (Cloisite 15A) by several mixing equipments. In fact all the prepared composite materials exhibit a larger interlayer clay spacing in comparison with the pristine organoclay. Moreover their elastic modulus is significantly increased from 50 to 100% depending on the processing conditions.

X‐ray diffraction of the master (Sample A) and the clay used for its preparation (Cloisite 15A).     

Glass fiber breakup in corotating twin screw extruder: Simulation and experiment

The damage of glass fibers at various conditions was investigated in a corotating twin screw extruder by varying viscosity, screw speed, and screw configuration. Increasing the screw speed and melt matrix viscosity were found to increase the extent of fiber breakage. Based on the experimental data and Euler buckling theory, a composite modular kinetic model to describe glass fiber breakage was developed. Regions of the major and minor fiber breakage in a corotating twin screw extruder were found. The simulation program based on the experimental data and kinetic constants was developed for fiber breakage along the screw length. Comparisons were made between simulated results and experimental data indicating a reasonable quantitative agreement between them. Predictions of the model are also in general qualitative agreement with many published data on fiber breakage in twin screw extruders. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of screw design on fiber damage in extrusion compounding and composite properties

The mechanism of fiber length degradation during twin screw extrusion compounding and methods to reduce it through process and machine design are extremely important in discontinuous fiber reinforced composites. Fiber damage along the screw and the extruder die are determined for three screw designs with different mixing sections. The pellet quality, wet-out, and fiber dispersion in the extruded strands are compared. The fiber orientation distributions in the screw are determined to identify regions of higher fiber interaction. The fiber damage during subsequent injection molding has also been determined. The tensile, flexural, and impact properties of the tensile bars are compared. It is found that the residence time, fill-up, and the intesity of mixing during extrusion compounding have a predominant effect on fiber length degradation. The screw designs were seen to have a greater effect on the fiber damage in the 40 wt% glass-filled polymer than the 30 wt% glass-filled polymer. However, the mechanical properties of the 30 wt% glass-filled polymer showed an increasing trend compared to the 40 wt% glass filled polymer. A screw design that provides a balance of the fiber length, wet-out, and fiber dispersion was noted to give consistent mechanical properties.     

Compounding of nanocomposites by thermokinetic mixing

Nanocomposites have been prepared by melt mixing poly(propylene) (PP) and different levels of a premixed montmorillonite‐organoclay masterbatch (PP/clay concentrate). Melt mixing was achieved using a Gelimat, a high‐speed thermokinetic mixer. The Gelimat system is designed to handle difficult compounding and dispersion applications and can achieve mixing, heating, and compounding of products within a minute. Therefore, the thermal history of the compounded polymer is short, which limits degradation. The structure and properties of the nanocomposites prepared with a Gelimat were compared to ones prepared with a twin‐screw extruder. The structure and properties of PP/clay nanocomposites were compared by TEM, X‐ray diffraction, mechanical testing, and rheological analysis. Results indicate that a better dispersion of the clay can be achieved by thermokinetic mixing when compared to extrusion, resulting in better mechanical properties. Calculations, based on simplifying assumptions, showed that the shear rates generated in a Gelimat are at least one order higher than those generally generated in an extruder. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1557–1563, 2005     

Effects of processing conditions on the fiber length distribution and mechanical properties of glass fiber reinforced nylon‐6

The effects of processing conditions on fiber length degradation were investigated in order to produce composites with higher performance. Nylon‐6 was compounded with glass fibers in a twin‐screw extruder for various combinations of screw speed and feed rate. Collected samples were injection molded and Izod impact and tensile tests were performed in order to observe the effect of fiber length on the mechanical properties. Also, by using the extruded and injection molded smaples, fiber length distribution curves were obtained for all the experimental runs. Results show that when the shear rate is increased through the alteration of the screw speed and/or the feed rate, the average fiber length decreases. Impact strength, tensile modulus and tensile strength increase, whereas elongation at break decreases with the average fiber length.     

Free radical grafting of glycidyl methacrylate onto polypropylene in a co-rotating twin screw extruder

Free radical grafting of glycidyl methacrylate (GMA) onto molten polypropylene (PP) was studied in a co-rotating twin screw extruder. Grafting yields of GMA obtained under various experimental conditions along the screw length allowed for a good appreciation of the effects of chemical parameters (the presence of styrene and the concentrations of peroxide and monomers) and those of processing parameters (feed rate, screw speed, and specific throughput). Similar to the results obtained in a batch mixer,¹ free radical grafting of GMA carried out in the extruder in the presence or absence of styrene proceeded rapidly, as it was virtually completed half-way down stream of the extruder. Additionally, the presence of styrene as a second monomer increased the GMA grafting yield reatly with reduced PP chain degradation. The ultimate GMA grafting yield increased with increasing concentration of peroxide, 1,3-bis(tert-butylperoxyisopropyl)benzene. This similarity between the batch mixer and the extruder is related to the fact that in both cases it is the concentration of the peroxide and its half lifetime that determine the grafting rate and the ultimate grafting yield. On the othe hand, the GMA grafting yield decreased with increasing screw speed or feed rate. For a particular specific throughput (the ratio of throughput to screw speed), an increase in throughput with a concomitant increase in screw speed brought about a decrease in GMA grafting yield. It was concluded that the GMA grafting yield is affected primarily by the residence time in the zone in which free radicals are not depleted. The effects of screw speed, feed rate, and specific throughput manifest mainly through this local residence time distribution. Specific energy is not a good measure of the performance of the extruder with respect to the free radical rafting of GMA onto PP. © 1995 John Wiley & Sons, Inc.     

Long fiber reinforcement of polypropylene/polystyrene blends

The recycling of inseparable polymer mixtures usually results in blends with poor mechanical properties. A mixture of PP and PS was taken as a model compound for a recyclate. The effect of adding glass fibers to a mixture of PP/PS (70/30) was studied, with special attention to long glass fiber reinforcement. Test specimens were made in three different ways: by dry blending (direct injection molding), mild compounding with a single screw extruder, and compounding with a twin screw extruder. The fiber concentration was varied from 0 to 30 wt%. The fiber lengths were determined to investigate fiber attrition. The fiber lengths in the samples were 1.09 mm for dry blending, 0.72 mm for single screw compounding, and 0.33 mm for twin screw compounding. The mechanical behavior was studied by unnotched and notched Izod impact and tensile tests. The PP/PS blend had a low fracture strain and low unnotched Izod impact strength compared with a PP homopolymer. With an increasing fiber concentration and fiber length, the modulus, tensile strength, and particularly the impact strength increased. With a 30 wt% glass fiber of the long fiber compound (dry blended), the modulus was raised by a factor of 3.5, the fracture stress by a factor of 2.5 and the unnotched Izod impact strength by a factor of 10. The product quality as judged by the scatter of the data was best for the twin screw compound and poorest for the dry blend. Compounding with a single screw extruder gave fairly constant injection molding product properties, combined with excellent mechanical properties.     

Morphology development of EPDM/PP uncross‐linked/dynamically cross‐linked blends

Ethylene‐propylene‐diene‐terpolymer (EPDM) and polypropylene (PP)‐based uncross‐linked and dynamically cross‐linked blends were prepared both in an internal mixer and in a corotating twin‐screw extruder. The effects of composition, plasticization and mixing equipment on the morphology development and the final viscoelastic properties were studied. In the uncross‐linked blends, the plasticization resulted in a coarser morphology. Furthermore, it was shown that the majority of the plasticizer resided in the EPDM phase, enabling its deformation in the flow direction. In addition, the intensive mixing conditions inside the twin‐screw extruder resulted in a finer morphology. In the dynamically cross‐linked blends, the twin‐screw extrusion process resulted in a higher level of gel content with larger EPDM domains. The plasticization showed again a coarsening effect, resulting in interconnected cross‐linked EPDM domains. An interesting interfacial phenomenon was observed especially in the plasticized vulcanized blends where nanometer size occluded PP domains were stripped off and eroded into the EPDM phase. With the exception of the nonplasticized uncross‐linked blends, the viscoelastic properties of all other blending systems were found to be directly affected by the morphology, gel content (in the case of cross‐linked blends), and the presence of the plasticizer. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

A comparative study of fiber breakage in compounding glass fiber-reinforced thermoplastics in a buss kneader,modular Co-rotating and counter-rotating twin screw extruders

The breakage of glass fibers was measured for several different types of continuous mixers including (i) Buss Kneader, (ii) modular intermeshing co-rotating twin screw extruder, and (iii) modular intermeshing counter-rotating twin screw extruder. Comparisons are made using different screw configurations, loadings, feeding ports, and mixing elements. Downstream feeding of glass fibers and milder screw configuration favor less breakage of glass fibers.