Effect of filler dispersion on polypropylene morphology

The evaluation of filler dispersion in compounding machines is an important part of their design. Calcium carbonate–filled polypropylene (PP) was used as a model compound to study filler dispersion. The evolution of dispersion was followed in a twin‐screw extruder where several types of mixing sections were evaluated. Reverse kneading blocks were found to be very efficient for breakup of agglomerates. Depending on extrusion conditions, agglomeration was observed even after the matrix was melted. To study dispersion in a single‐screw extruder, Maddock and reverse Maddock mixing elements were tried. A quantitative evaluation of the dispersion state allowed a better understanding of nucleation in the PP/CaCO₃ matrix. A significant content of the β‐phase of polypropylene was observed when the agglomerate size was relatively small. The level of shear stress was also important for the formation of the β‐phase of PP. The quantification of dispersion was mainly evaluated from micrographs of samples obtained by reflected light microscopy in conjunction with image analysis. The characterization of β‐spherulites was carried out using polarized light microscopy and scanning electron microscopy. Polym. Eng. Sci. 44:880–890, 2004. © 2004 Society of Plastics Engineers.     

Agglomerate size evolution in modular twin‐screw extruder: Modeling and validation with CaCO3/LLDPE compounding experiments

The screw combination of twin‐screw extruder affects the filler size in inorganic filler‐reinforced polymeric compounds. This article tried to conveniently and precisely model the agglomerate size evolution in modular co‐rotating twin‐screw extruder. The break‐up process of agglomerate was analyzed to obtain the relationship between average deagglomerating energy (M) and agglomerate size, the result presented a mathematic relationship between M and agglomerate size. Numerical simulation study was conducted to consider the effect of kneading blocks (KB) or flight elements (FE) number on dispersion capacity of screw combination. The average deagglomerating energy, calculated based on POLYFLOW simulation, was introduced as major parameter to evaluate the dispersion capacity, which presented a proportional relationship to the KB or FE number. The model was developed by combining the agglomerate break‐up process and simulation results. In validation, CaCO₃/linear low‐density polyethylene (LLDPE) compounds were prepared by modular co‐rotating twin‐screw extruder with different screw combinations. The optical image analysis showed that CaCO₃ agglomerate size decreased with the KB or FE number rising, while it achieved minimum when the KB number was 4. The model was in accordance with the experimental results, and proved to be valid for KB and FE combinations in preparing CaCO₃/LLDPE compounds. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45535.     

Effect of processing conditions on the formation of polypropylene/organoclay nanocomposites in a twin screw extruder

Polypropylene (PP)/organoclay (Cloisite^©20A) nanocomposites are prepared via direct melt intercalation in a co‐rotating twin screw extruder. Maleic anhydride (MA)‐grafted PP (PP‐g‐MA) is used as a compatibilizer to improve the dispersion of the clay. The formulation used to prepare the nanocomposites is fixed and is equal to 80/15/5 (PP/PP‐g‐MA/Cloisite^©20A), expressed in mass fraction. The objective of the present study is to investigate the effects of processing conditions as well as screw profile upon the formation of PP nanocomposites. The parameters studied are the feed rate and the screw speed, which are varied independently, from 4.5 to 29.0 kg/h and from 100 to 300 rpm, respectively. The state of dispersion is quantified by wide angle X‐ray diffraction (WAXD), transmission electron microscopy, and rheological measurements. WAXD results show that the nanocomposites obtained in different conditions have an intercalated structure, with an increase in interlayer spacing. However, this interlayer spacing is globally unaffected by processing parameters. On the opposite, the proportion of exfoliation, estimated by rheological measurements, is depending on operating conditions (screw speed and feed rate). It increases when the feed rate decreases and the screw speed increases. Investigations on the state of dispersion along the screw profile are also presented. They show that no evolution of intercalated structure is observed along the screws and that screw geometry is only efficient in particular extrusion conditions to delaminate clay platelets. Numerical simulations of the twin screw extrusion process, using the software Ludovic^©, put in evidence that the total strain is a key factor for characterizing the level of exfoliation in the nanocomposites. POLYM. ENG. SCI. 46:314–323, 2006. © 2006 Society of Plastics Engineers     

Correlation between processing conditions and fiber breakage during compounding of glass fiber‐reinforced polyamide

The inter‐relationship between processing conditions and fiber breakage has been studied for glass fiber‐reinforcedpolyamide 12, prepared using (i) an internal batch mixer, (ii) a laboratory scale corotating twin screw extruder, and (iii) an industrial scale twin screw extruder. The average fiber lengths and fiber length distributions were measured for various compounding conditions (screw or rotor speed, mixing time, feed rate). Experimental results have shown that fiber breakage depends on both screw speed and mixing time, the later being controlled, in an extruder, by the feed rate. For a given compounding system (batch mixer or twin screw extruder), the energy input (specific mechanical energy, SME) during the compounding process is found to be a reliable parameter, which governs fiber length (average, minimal, and maximal) evolution. Experimental data are correctly described with a model defining change in fiber length as a function of SME. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Computation of starch cationization performances by twin‐screw extrusion

A theoretical model for the cationization of plasticized wheat starch in a modular seIf‐wiping co‐rotating twin screw extruder was developed. Our objective was to build a model which would be able to predict the evolution of the cationization reaction along the screws, in relation with the processing conditions and the geometry of the twin screw extruder. Based on previous studies on reactive extrusion modeling, the present model takes into account the interactions occurring between the flow conditions encountered in the extruder and the kinetics of the reaction. It allows one to predict the influence of operating parameters such as reagent concentrations, feed rate, screw speed, and barrel temperature on the reaction extent. Depending on conditions, degrees of substitution in the range 0.01–0.05 are obtained, with efficiencies between 30 and 90%. A good agreement is found between theoretical results and experimental measurements, allowing future use of the model for optimization and scale‐up purposes. POLYM. ENG. SCI., 47:112–119, 2007. © 2007 Society of Plastics Engineers     

Contribution of the melting stage to the evolution of the morphology and chemical conversion of immiscible polyamide/polyethylene blends in twin‐screw extruders

This study investigates the effects of processing conditions (the screw speed, throughput, barrel temperature, and screw configuration) on the chemical conversion and morphology evolution of polyamide/polyolefin blends along a twin‐screw extruder. Polymer samples were collected rapidly at specific barrel locations with a special sampling device for subsequent chemical and morphological characterization. Increasing the screw speed or using more restrictive screw modules at the beginning of the melting zone promoted a faster reaction and better dispersion along the extruder. Increasing the throughput or decreasing the barrel temperature slowed the evolution of the morphology and chemical conversion along the extruder because of the lower melting rate. As soon as melting started, the chemical reaction took place. However, high chemical conversion rates required extensive melting, that is, significant interface generation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

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     

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     

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.     

State of dispersion: Polypropylene filled with calcium carbonate

The influence of mixing conditions on the state of dispersion of calcium carbonate filled polypropylene composite was studied. The polymer and the filler were compounded in a twin screw extruder under various controlled processing conditions. The variables studied were the screw speed, the feed rate, the filler concentration, the barrel temperature profile and the surface treatment of the filler. The state of dispersion of calcium carbonate filled polypropylene composites was characterized using a scanning electron microscope, and was correlated to the residence time and the shearing conditions that were prevailing within the extruder. Degradation of the polymer matrix was also observed.     

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     

Modeling of peroxide initiated controlled degradation of polypropylene in a twin screw extruder

In this work, experimental and theoretical studies of the free‐radical initiated molecular weight degradation of polypropylene in a modular self‐wiping corotating twin screw extruder have been investigated. Our objective was to build a model that would be able to predict the evolution of the average molecular weight along the screws, in relation to the processing conditions and the geometry of the twin screw extruder. Modeling the process involves resolving interactions occurring between the various flow conditions encountered in the extruder, the kinetics of the reaction and the changes in viscosity with changes in molecular weight. We have studied the influence of operating parameters such as the initial peroxide concentration, the feed rate and the screw speed on the degradation reaction. Good agreement was found between theoretical results and experimental values obtained by size exclusion chromatography measurements.     

Comparison of scale‐up methods for dispersive mixing in twin‐screw extruders

Twin‐screw extrusion processes are commonly refined on laboratory‐scale extruders then scaled‐up to manufacturing systems. When using twin‐screw extrusion to compound filler into a polymer, the dispersion of the filler must be considered during scale‐up. In this work, two scale‐up methods are evaluated for how accurately they scale dispersion as measured by the Residence Stress Distribution, an experimental method that quantifies stress developed in a twin‐screw extruder. The first scale‐up method evaluated is the industry‐standard scaling based on maintaining equivalent volumetric flow rate across extruder sizes. Volumetric scaling is compared to a second, novel scale‐up method, the percent drag flow rule, which maintains the same degree of fill in the strongest dispersive screw elements on all extruder sizes. Both scale‐up rules have been used to scale between three extruder sizes and have been evaluated for how accurately the larger extruders recreate the dispersive mixing of the smallest machine. Results indicate that the percent drag flow scale‐up more accurately maintains dispersive mixing behavior than the volumetric scaling. Furthermore, percent drag flow scale‐up resulted in all three extruder sizes behaving similarly to changes in operating conditions. These results indicate that percent drag flow scale‐up is a valid technique to scale real industrial processes. POLYM. ENG. SCI., 57:345–354, 2017. © 2016 Society of Plastics Engineers     

Twin‐screw extrusion of polypropylene‐clay nanocomposites: Influence of masterbatch processing,screw rotation mode,and sequence

This work seeks to optimize the twin‐screw compounding of polymer‐clay nanocomposites (PCNs). Proportional amounts (3:1) of maleic anhydride functionalized polypropylene compatibilizer (PP‐g‐MA) and organically modified montmorillonite clay at clay loadings of 1, 3, and 5 wt% were melt‐blended with a polypropylene (PP) homopolymer using a Leistritz Micro 27 twin‐screw extruder. Three melt‐blending approaches were pursued: (1) a masterbatch of PP‐g‐MA and organoclay were blended in one pass followed by dilution with the PP resin in a second pass; (2) all three components were processed in a single pass; and (3) uncompatibilized PP and organoclay were processed twice. Both corotation and counterrotation operation were utilized to investigate the effect of screw rotation mode and sequence on organoclay exfoliation and dispersion. X‐ray diffraction was employed to characterize basal spacing; however, since rheology is known to be highly sensitive to mesoscale organoclay structure, it is an ideal tool to examine the relationship between the various processing methods and exfoliation and dispersion. A holistic analysis of rheological data demonstrates the efficacy of the masterbatch approach, particularly when compatibilizer and organoclay are blended in counterrotating mode followed by dilution with matrix polymer in corotating mode. POLYM. ENG. SCI., 47:898–911, 2007. © 2007 Society of Plastics Engineers     

A spectroscopic approach for structural characterization of polypropylene/clay nanocomposite

This study focuses on the degree of dispersion and structural development of organomodified MMT clay (OMMT) during processing of polypropylene clay nanocomposites using both conventional and nonconventional characterization techniques. PP‐g‐MA and Cloisite 15A were melt blended with three different grades of PP separately in a micro‐twin screw compounder at selected screw speed and temperature. The clay was modified with fluorescent dyes and the adsorbed dye content in the clay gallery was estimated by using UV‐spectrophotometric method. The effects of residence time and molecular weight of the PP matrix on the clay dispersion were studied. The extent of dispersion and exfoliation of the clay in polymer matrix determined from the torque versus time data obtained from microcompounder. It was further supported by XRD, SEM, TEM, and DSC analysis. Offline dielectric and fluorescence spectrophotometric studies were also carried out. Changes in dielectric constant and dielectric loss with both frequency and temperature yielded quantitative information about the extent of clay exfoliation and intercalation in the polymer matrix. It was observed that with an increase in MFI (decrease in molecular weight) and mixing time, the extent of clay dispersion and exfoliation were also improved due to easy diffusion of polymer chains inside clay gallery. POLYM. COMPOS., 31:2007–2016, 2010. © 2010 Society of Plastics Engineers     

The effect of twin screw extrusion on structural,electrical, and rheological properties in carbon nanotube poly‐ether‐ether‐ketone nanocomposites

The influence of twin screw extruder dispersion of multiwalled carbon nanotubes (CNTs) on the structural, electrical, and rheological properties in poly(ether ether ketone) is studied. Intermediate rotational speeds (200 rpm) of co‐rotating twin screws yield higher electrical conductivity and dynamic shear modulus than for lower or higher speeds when using 3 wt % multiwall CNTs. These improved properties at intermediate speeds are correlated with the dispersion state of nanotubes in the polymer matrix by using transmission electron microscopy and multispectral Raman mapping. We find that the complex shear modulus near structural percolation depends on the dispersion of the CNTs and the residence time in the extruder plays an important role in the final properties of the nanocomposite. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polymer blends of carboxylated butadiene‐acrylonitrile copolymer (nitrile rubber) and polyamide 6 developed in twin screw extrusion

Polymer blends of carboxylated butadiene‐acrylonitrile copolymer (nitrile rubber) and polyamide 6 (PA6) were developed in twin screw extrusion. The rubber was cured with SP 1045 methylol phenolic resin during melt mixing in twin screw. Effect of degree of carboxylation in the rubber phase on blend properties has been assessed. Phase morphologies have been characterized using transmission electron microscopy. A compatibilizing NBR‐g‐Nylon 6 graft copolymer generated in situ during melt mixing via interfacial reaction between the ? COOH groups in NBR and the ? NH₂ end groups in nylon 6 has been effective in generating a fine and stable dispersion of the rubber within the polyamide matrix. The graft copolymer has been characterized by DMTA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 372–377, 2007     

Synchronous toughening and reinforcing of polypropylene with ultrahigh‐molecular‐weight polyethylene via melt blending: Mechanical properties,morphology, and rheology

Blending systems based on polypropylene (PP) and ultrahigh‐molecular‐weight polyethylene (UHMWPE) were prepared via a melt extrusion by the four‐screw and the twin‐screw extruders, respectively. The mechanical evaluation demonstrated that the synchronous toughening and reinforcing effects could be achieved from the combination of the PP and the UHMWPE, in which the toughness and the tensile properties could be improved with increasing the UHMWPE content, and achieved optimal values at a weight ratio of PP/UHMWPE (85/15). EPDM can be used as a compatibilizer to improve the compatibility and the interfacial adhesion between the PP and the UHMWPE. This resulted in more effective toughening and reinforcing effects. In contrast, for the PP/UHMWPE blends prepared by the normal twin‐screw extruder, the poor dispersion capacity for the UHMWPE resulted in a deterioration of all mechanical parameters. Morphological observation revealed that the UHMWPE domain was well distributed as tiny particles in the PP matrix, which was confirmed by the differential scanning calorimetry analysis. The toughening effect was attributed to the energy dissipation caused by these rigid tiny particles that detached from the matrix to initiate the local matrix shear yield and formed the void. Rheological investigation demonstrated that there was an interesting composition dependence of viscosity, for which the melt viscosities of the PP/UHMWPE blends decreased when 5 wt % UHMWPE was added, and then began to increase as the UHMWPE content continued to increase. However, this dependence on composition became weaker because of the compatibilization of the EPDM. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3498–3509, 2006     

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