Solvent‐free polymer emulsification inside a twin‐screw extruder

Solvent‐free extrusion emulsification (SFEE) is new technique for a twin‐screw extruder to prepare submicron‐sized particles (100–500 nm) without using hazardous solvents. The particle size is reliant upon the thickness of striated lamellae, which can be monitored rheologically based on the viscosity change occurring at the SFEE process. The lamellae coarsening rate is predominantly affected by the interfacial energy of the system when a surfactant is added but shows stronger dependency on viscosity change when interfacial growth between the polymer and water phases is solely determined by the end‐groups conversion into carboxylate species. For this latter case, the dissolution of the sodium hydroxide species and the kinetics of end‐groups conversion prove to be rate‐limiting phenomena to generating thinner striated lamellae. Additionally, the ionic strength of the system is notably important to the viscosity response and particle size produced, particularly when surfactant is not added. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2113–2123, 2018     

Behavior of fully filled regions in a non‐intermeshing twin‐screw extruder

Twin‐screw extruders are operated with sequential filled and partially filled regions in order to perform the required unit processes. Channel fill length, defined as the length of fully filled regions in an extrusion screw, is gaining importance as a design parameter because of its implications on residence time distribution, distributive and dispersive mixing, and also process stability. A detailed study—experimental and theoretical—of the behavior of fill lengths in response to operating conditions (throughput, screw speed) and screw geometry is presented in this paper. Mean residence times were also measured for each geometry and operating condition. The apparatus consisted of a non‐intermeshing counter‐rotating twin‐screw extruder (NITSE) with a transparent (acrylic) barrel, fed with corn syrup (Newtonian at room temperature). Fill length exhibits a nonlinear relationship with specific throughput (Q/N), with the slope increasing monotonously as the throughput Q increases at a given screw speed N. The mean residence time exhibits a strong linear relationship with inverse specific throughput and inverse fill length. A theoretical model was developed to predict the filled length based on pressure‐throughput relationships taken from literature for this system, and the predictions were found to agree very well with experimental observations.     

A theoretical approach to solid filler dispersion in a twin‐screw extruder

Compounding of highly filled minerals in a polymeric matrix has never been an easy task. The objective of this work was to build a theoretical model to predict the evolution of dispersion of an inorganic filler in a polymer matrix along a twin‐screw extruder as a function of the screw geometry and processing conditions. We developed a general kinetic model of agglomeration/breakup of the fillers, based on chemical‐like equations. It allowed us to describe the evolution of a population of agglomerates, taking into account the deformation field. When implemented in a flow model of a twin‐screw extrusion process, the model can be used to pinpoint the main effects of twin‐screw operating conditions on dispersion.     

Morphological evolution of polypropylene/polystyrene blends in a twin‐screw extruder

The effects of the blend composition and rotation speed on the morphological evolution of polypropylene (PP)/polystyrene (PS) blends were investigated in a twin‐screw extruder. When PS was the major component, the rate of melt and the rate of dispersion played final roles in the morphological development of the polymer melts. However, when PP was the major component, the rate of dispersion and the rate of coalescence played key roles. A high tendency to coalesce occurred at a high rotation speed and/or a high content of the dispersed phase. When the PP/PS blend composition was close to 1, a cocontinuous morphology was observed to transmute into a coarse one with increasing rotation speed. Attempts were made to correlate the morphology and mechanical properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Flow patterns and mixing mechanisms in the screw mixing element of a co‐rotating twin‐screw extruder

Non‐Newtonian and non‐isothermal flow simulations based on 3‐D FEM were applied to a special and conventional elements of a twin‐screw extruder. The screw mixing element (SME), a kind of special element, was a distributive mixing promoter consisting of a standard screw profile with slots cut across the flight tip to increase leakage flow. The full flight screw (FF) and the kneading block (KB) were examined as conventional elements in order to contrast the mixing behavior with the SME. The accuracy of numerical results was verified by experimentally measuring pressure and temperature. Additionally, marker particle tracking analysis was carried out to evaluate the distributive and dispersive mixing. Using the above analyses, the following results were obtained: The pumping capability of the SME was smaller than that of the FF and was the same as for the KB. The SME suppressed heat generation and showed the lowest temperature distribution of the three elements. For distributive mixing, the SME showed the best performance judging from the mixing coefficient G, residence time distribution, and area stretch distribution based on a laminar mixing mechanism. A higher rotational speed achieved better distributive mixing performance. For dispersive mixing defined by stress distribution, the SME showed the second best performance next to the KB. It also showed better dispersive mixing performance with increasing rotational speed. The SME had the advantages of low heat generation and good distributive mixing.     

Effectiveness of a backward mixing screw element for glass fiber dispersion in a twin‐screw extruder

In the kneading of glass–fiber‐reinforced plastics by twin‐screw extrusion, the use of a backward‐mixing screw (BMS) element for melt mixing has been found to be effective in dispersing glass–fiber bundles. In this study, we use computational fluid dynamics (CFD) to investigate the mechanism for the effectiveness of BMS for glass fiber dispersion. CFD of BMS melt mixing revealed that there is high uniformity of transport in the direction of extrusion and efficient transportation occurs from low‐stress to high‐stress regions. These findings demonstrate that BMS melt mixing is highly effective at imparting stress to the overall resin passing through. In addition, there is a correlation between the incidence of nondispersion of glass–fiber bundles measured experimentally and the stress history minimum value. On the basis of the above factors, we propose a method for predicting the operating conditions in which the nondispersion of glass–fiber bundles is controlled. The operating conditions for controlling glass–fiber nondispersion can be determined for various different mixing elements and the possible production rate can be predicted. Predictions for the operating conditions were applied to BMS and a forward kneading disk element (FKD). The effectiveness of BMS for controlling glass fiber nondispersion is characterized for a broad range of operating conditions. POLYM. ENG. SCI., 54:2005–2012, 2014. © 2013 Society of Plastics Engineers     

Evolution of morphology and of chemical conversion along the screw in a corotating twin‐screw extruder

A new sampling device is used to perform near‐real‐time investigations of physical and chemical processes occurring inside a laboratory twin‐screw extruder. Polyamide‐6–ethylene propylene rubber (PA‐6–EPM) blending and styrene–maleic anhydride (SMA) imidation experiments are reported in terms of morphology development and evolution of the chemical conversion along the extruder, respectively. Comparison of the results obtained using this new technique with those of classical screw‐pulling experiments evidenced the potential erroneous conclusions than can be drawn from the latter. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 135–141, 1999     

Continuous polymerization of lactam–lactone block copolymers in a twin‐screw extruder

Continuous copolymerizations of ?‐caprolactone with ?‐caprolactam and ω‐lauryl lactam were carried out in a modular intermeshing corotating twin‐screw extruder. Sodium hydride (initiator) and N‐acetyl caprolactam (coinitiator) were used to synthesize lactam–lactone copolymers in a twin‐screw extruder. We consider the variables of feeding order and feed rate of comonomers on the reactive extrusion of lactam–lactone copolymers. It was observed that simultaneous feeding of both monomers with initiator and coinitiator in the first hopper produced a mixture of homopolymers. When we fed the lactam into the first hopper and caprolactone sequentially into the second hopper, we obtained the lactam–caprolactone block copolymers. However, when we fed caprolactone first into the first hopper and the lactam into the second hopper, the extruded product was a mixture of poly(?‐caprolactone) and lactam monomer. We synthesized high molecular weight copolymers of poly(caprolactam‐b‐caprolactone) and poly(lauryl lactam‐b‐caprolactone) with different block lengths by sequential feeding of monomers. The block length of the block copolymer could be adjusted by controlling the feed rate of each monomer during reactive extrusion. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1429–1437, 2003     

Steady and transient flow of a non‐Newtonian chemically reactive fluid in a twin‐screw extruder

The flow of chemically reactive non‐Newtonian materials, such as bio‐polymers and acrylates, in a fully intermeshing, co‐rotating twin‐screw extruder is numerically investigated. A detailed study of the system transient behavior is carried out. The main transient aspects, including response time, variation of system variables, and instability of operation, are studied for both single‐ and twin‐screw extruders, since single‐screw extruder modeling closely approximates the region away from the intermeshing zone in a twin‐screw extruder. The effect of a time‐dependent variation in the boundary conditions is studied. The coupling due to conduction heat transfer in the screw barrel is found to be very important and is taken into account for single‐screw extruders. In the absence of this conjugate coupling, the response time is much shorter. Several other interesting trends are obtained with respect to the dependence of the transient response on the materials and operating conditions. Steady state results are obtained at large time. The calculated velocity distributions in the screw channel are compared with experimental results in the literature for steady state flow and good agreement has been obtained. The calculated results for transient transport agree with the few experimental observations available on this system. Chemical reaction, leading to chemical conversion of the material, is also considered and the resulting effects on the flow and transport determined. These results will be useful in the design, control and optimization of polymer extrusion processes.     

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     

Transient compositional effects from feeders in a starved flow modular co‐rotating twin‐screw extruder

A process dynamics model of transient output composition variations in a moduar self‐wiping twin‐screw extruder caused by input disturbances from feeders is developed. The changes of output mass flow rate and weight fraction of additives in the output stream were predicted for various time dependent input modes into a second feeder and other ports part way along the length of the machine.     

Online light scattering measurements: A method to assess morphology development of polymer blends in a twin‐screw extruder

Light scattering has proved itself an efficient technique to determine particle diameters in heterogeneous dilute dispersions in the micrometer range. Extrusion of polymer blends is expected to give rise to very small particles, typically in the range from hundreds of nanometers to tens of micrometers. A light scattering device developed in our laboratory has been used to study the morphology of polymer blends obtained in a twin‐screw extruder. The main advantage of this technique is the immediate response obtained without any surface or interface modification that can occur during the sample preparation by using more conventional techniques like electron microscopy. To show the possible applications of this light scattering device, preliminary tests have been carried out. First, we present a comparison between experimental measurements and theoretical results for dilute systems. Second, we have investigated the effect of shear flow on the droplet deformation. Finally, we have studied the variations of the light scattering pattern for a reactive blend.     

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.     

In‐line monitoring and analysis of polymer melting behavior in an intermeshing counter‐rotating twin‐screw extruder by ultrasound waves

An ultrasound in‐line monitoring system that includes a homemade probe and a fast data acquisition system was used to investigate the melting behavior of linear low density polyethylene (LLDPE) in pellet form and four polyvinyl chloride (PVC) compounds in powder form in an intermeshing counter‐rotating twin‐screw extruder. Ultrasound signal patterns obtained from experiments revealed various melting phenomena in C‐chambers, depending on materials, processing conditions, and screw configurations. The experimental results suggest that PVC particles were suspended in the polymer melt in the melting process of most PVC compounds, while melted film was still observed in the melting process of the PVC/dimethyl phthalate (DMP) system and the PVC/polybutylene adipate (PBA) system. Based on the analysis of wave attenuation, the normalized amplitude ratio K was used to characterize the melting level and uniformity across screw channels at screw speeds of 40 and 50 rpm, respectively. POLYM. ENG. SCI., 45:998–1010, 2005. © 2005 Society of Plastics Engineers     

Investigation on the uniformity of high‐density polyethylene/wood fiber composites in a twin‐screw extruder

Uniform dispersion of wood fiber in high‐density polyethylene can improve the mechanical properties and surface finish of the wood plastic composites. However, it is difficult to achieve uniform dispersion when the wood content is high, due to its low thermal stability, incompatibility with polymer, and affinity for agglomeration. This work was undertaken to improve the uniformity of high‐density polyethylene/wood composites by designing screw configurations, optimizing screw speed, and altering material compositions. The rheological properties and scanning electron microscope micrograph were used to characterize the uniformity. The results showed that the medium dispersive and distributive mixing, medium screw speed, and lubricant were all beneficial in improving uniformity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Devulcanization of waste tires using a twin‐screw extruder: The effects of processing conditions

During recent decades, for both economic and environmental reasons, recycling of waste tires that are based on SBR/NR has been widely considered. In this study the devulcanization process of the tread section of waste tires was carried out by using a twin‐screw extruder. The effects of barrel temperature and screw speed were investigated. Percent of devulcanization, sol fraction, and curing behavior of devulcanized samples were studied. After the addition of curing agents into the devulcanizates, the general behavior of the rheometry test for rubber compounds was observed. Percent of devulcanization and sol fraction depended on the screw speed and barrel temperature, respectively. The devulcanized samples were formulated with virgin rubber (15/85 wt% ratio) and re‐cured successfully. Tensile strength, elongation at break, compression set, hardness, and resilience were evaluated. It was found that the mechanical properties of the compound containing devulcanizates were slightly inferior to those of the virgin compound. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Study of the different flow patterns in the melting section of a co‐rotating twin‐screw extruder

Understanding the phenomena of twin‐screw extrusion (TSE) is the first step in investigating this process. Visualization technology incorporated in a co‐rotating twin‐screw extruder was developed for this purpose. This technology enabled the extrusion phenomena to be directly observed and analyzed. The present work focuses on the melting process. It is revealed and verified that there are different flow patterns in the melting section during extrusion, with different degrees of fill. A melting model for one type of flow pattern is established. The significance of the present work is to establish the variety conception for the flow patterns. According to this conception, corresponding models should be established for each flow pattern identified.     

Methyl methacrylate modification of polyolefin in a batch mixer and a twin‐screw extruder experiment and kinetic model

Free radical grafting with methyl methacrylate onto molten polypropylene was investigated in both an internal mixer and a modular co‐rotating twin‐screw extruder. There has been little open literature on melt free radical grafting copolymerization of methyl methacrylate. There is also little information on the evolution of grafting reaction with respect to reaction time in an internal mixer and along the screw axes with methyl methacrylate. The influence of residence time on the degree of grafting in an internal mixer and a twin‐screw extruder was studied through measuring reaction yields with respect to reaction time in a mixer and evolution of reaction yield along the screw axis. The degree of grafting increased with initial monomer and peroxide concentration. The grafting reactions with three different peroxides were also investigated. The grafting levels were similar to maleic anhydride and suggested that only an individual methyl methacrylate unit be grafted. The melt viscosity was dramatically reduced with addition of peroxide. A kinetic scheme of our reaction system for methyl methacrylate was proposed and compared with the experimental results.     

A composite model for an intermeshing counter‐rotating twin‐screw extruder and its experimental verification

A composite simulation model of solids conveying, melting and melt flow in a closely intermeshing counter‐rotating twin‐screw extruder has been developed. The model is based on combining new melt conveying models with melting and solids conveying models, and the die is included into considerations. A general approach is applied using fully three‐dimensional non‐Newtonian FEM modeling for melt conveying to develop screw pumping characteristics which are implemented into the composite model. Several screw configurations are considered including non‐classical elements. Computations are made for axial fill factor, pressure, temperature, and melting profiles. The results are validated experimentally. POLYM. ENG. SCI., 55:2838–2848, 2015. © 2015 Society of Plastics Engineers     

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.