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.     

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     

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.     

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     

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.     

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.     

Experimental characterization and modeling of twin‐screw extruder elements for pharmaceutical hot melt extrusion

In this study we characterized various screw elements of a co‐rotating twin‐screw extruder used for pharmaceutical hot melt extrusion (HME) and measured the pressure characteristic, i.e., the correlation between the axial pressure gradient and the material throughput in a completely filled screw section at different screw speeds. A typical HME matrix material, Soluplus, was used for the experiments and its required rheological properties were determined. A three‐parameter model based on a dimensionless formulation of the measured quantities was used. These parameters could not be determined uniquely by fitting to experimental data. Therefore we developed an approach to approximate one empirical parameter based on the mechanistic consideration of a pressure‐driven channel flow. The model was extended to account for the variable melt temperature. The results confirmed the expected tendencies and established an essential input parameter set for one‐dimensional simulations of co‐rotating twin‐screw extruders. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4440–4450, 2013     

Monitoring the evolution of the properties of PA‐6/EPM‐g‐MA blends in a twin‐screw extruder

The evolution of the properties of PA‐6/EPM‐g‐MA blends are investigated along a twin‐screw extruder in terms of chemical conversion, morphology development, and rheology evolution. Despite the interfacial structure of the various blends with different composition being distinct, an important decrease of the MA content at the first kneading zone from 0.5 to approximately 0.1 wt.% MA and only a slight decrease further downstream is generally observed. In all cases in‐situ compatibilization reactions occur in the melting zone within a few seconds. The relative differences in morphology can be directly explained by differences in blend composition. Although the morphology development along the extruder of the various blends as monitored by electron microscopy seems to follow a pattern similar to that of chemical conversion, their viscoelastic response shows a more gradual evolution.     

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.     

Mixing analysis of reactive polymer flow in a single‐screw extruder channel

In this study, the finite element method was used to investigate the influence of screw speed, entering peroxide distribution, pressure‐to‐drag flow ratio, and channel geometry on the mixing characteristics of steady non‐isothermal reactive flows. The reaction considered was the peroxide‐initiated degradation of a polypropylene resin in the metering zone of a single‐screw extruder. The predicted average degree‐of‐freedom profiles from the simulations largely conformed to expectations. The average flow efficiencies for all runs were found to vary little along the channel length, remaining at values close to that for two‐dimensional flow. No significant effect of either screw speed or peroxide distribution was found on the flow efficiencies. However, both the pressure‐to‐drag flow ratio and the channel aspect ratio were found to have significant influences.     

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     

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.     

Theoretical analysis of the devolatilizing performance of an intermeshing co‐rotating twin‐screw extruder with a type of square‐channel flighted element

The local film interfaces in the long vent section of an intermeshing, co‐rotating twin‐screw extruder (ICoTSE) with square‐channel flights (SFs) and the exposure time to the vapor phase were analyzed. A theoretical overall film‐interface geometry factor (OFIGF_cal) was calculated from a new devolatilization (DV) model proposed previously by the authors, and the predictions were compared to the experimental results (OFIGF_exp) for polystyrene/ethylbenzene (PS/EB). The OFIGF represents a measure of the devolatilization performance of the long vent section. The ratio of the experimental to the predicted apparent film interface areas was 5.5, which demonstrates the enhancing effect of the roughness and bubble‐forming behavior of the film interfaces on DV. The predicted concentrations of EB in the PS melt at the exit of the long vent section agreed well with experimental results.     

Melting model for intermeshing counter‐rotating twin‐screw extruders

Previous experimental studies of melting of pellets in an intermeshing counter‐rotating twin‐screw extruder have shown that melting is initiated both between the screws and at the barrel. Models are developed for melting in both those regions. The melting between the screws is initiated by frictional work on the pellets by the calendering stresses between the screws. The melting action at the barrel is induced by a barrel temperature higher than the melting point and propagated by viscous dissipation heating of the melt film produced.     

Effect of composition and processing conditions on the chemical and morphological evolution of PA‐6/EPM/ EPM‐g‐MA blends in a corotating twin‐screw extruder

This study investigated the effect of blend composition and processing conditions on the chemical conversion and morphological evolution of PA‐6/EPM/EPM‐g‐MA blends along a twin‐screw extruder. The maleic anhydride (MA) content of the modified rubber was found to decrease strongly, to a level of almost zero, and in the melting zone the particle size was dramatically reduced, from millimeters to submicrometers. Blend composition had a secondary effect on both chemical conversion and morphological development. The processing conditions, particularly the temperature profile and the screw speed, affected both the chemical conversion and the morphological evolution. Using low temperatures and low screw rotation it was possible to follow in detail the evolution of morphological development of a reactive blend in a twin‐screw extruder. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1535–1546, 2001