Counter-rotating Twin Screw Extruder Research Articles

Effect of Zeolite Mineral on the Formulation of a Wood-plastic Composite

The present work studies the positive or negative effect of zeolite mineral on the tensile and flexural mechanical behavior of a wood-plastic composite. Eight different blends were developed, the components used were wood flour (WF), polypropylene (PP), zeolite (Z) and maleic anhydride modified polypropylene (MAPP) as coupling agent. The eight blends were made using a counter-rotating twin-screw extruder, while the specimens were produced on a plastic injection molding machine with a 60ton clamping capacity. The standards used to determine the tensile and flexural mechanical properties were ASTM 638 and ASTM 790, respectively. Ten repetitions of each mixture were carried out. In addition, a reference (100% polypropylene) was used to compare the results obtained to determine whether the effect of using the zeolite mineral generated positive or negative results in the compounds obtained. Both studies showed that as the proportion of zeolite increases in the blend, the tensile and flexural properties are affected. However, the mixture (M7) with proportions in its components of, 34.375% WF, 55.875% PP, 6.75 % Z and 3% MAPP, showed an increase in the tensile and flexural mechanical properties, indicating a strong relationship between the components that integrate the wood-plastic composite (WPC), mainly between wood and mineral.

Grafting of poly(stearyl acrylate) on cellulose fibers as 3D-printable HDPE composites

This paper aimed to produce a bio-based filament, suitable for 3D printing (fused deposition modeling), made of surface modified cellulose fiber and high density polyethylene. The cellulose fibers (CF) were first surface modified and transformed into a CF-based macroinitiator through an esterification reaction with the 2-bromoisobutyric acid. We finally studied the ability of this CF-based macroinitiator to initiate a single electron transfer-living radical polymerization (SET-LRP) with an hydrophobic monomer: the stearyl acrylate. The grafting of poly(stearly acrylate) onto the cellulose fibers did strongly increased the adhesion, compatibility of the modified fibers with the hydrophobic host matrix (HDPE). Finally, the resulting hydrophobic fibers were extruded with the high density polyethylene (HDPE) through a counter-rotating twin-screw extruder, yielding a bio-based filament suitable for FDM 3d printing. The successful surface modification, such as the correct incorporation of the modified fibers into the thermoplastic matrix, were characterized through ATR-FTIR, 13C CP-MAS NMR, FE-SEM, and mechanical testing. Throughout those characterization techniques, it was concluded that the fiber surface modification significantly improved the compatibility of the fibers with HDPE. Finally, the 3D printing properties of the composite were tested and compared to those of pure HDPE through the 3d printing of simple objects. It was concluded that the printability of the composite made with poly(stearyl acrylate)-grafted cellulose overcomes the problem (shrinkage, warpage, print fidelity) encountered with the printing of pure HDPE.Graphical abstract

Sustainable composites based on post-consumer polypropylene and mineral filler

In this work, composites based on post-consumer polypropylene and two types of bentonites (in natura and organophilic) with different contents (2, 5 and 8% by weight) were prepared in a counter-rotating twin-screw extruder. The pelletized samples obtained by extrusion were stamped from plates obtained by compression in a bench press and these materials were characterized through measurement of hardness and impact resistance, as well as optical microscopy (OM) and scanning electron microscopy (SEM). The results indicated decreased hardness and impact resistance. The SEM micrographs showed the absence of agglomerates in the composites prepared with organophilic bentonite.

Hydrodynamics and mixing performance in a continuous miniature conical counter-rotating twin-screw extruder

Abstract The mixing performance in a miniature conical counter-rotating twin-screw extruder was investigated by means of experimental technique and computational fluid dynamics (CFD) simulation. An on-line experimental device based on the fluorescence detection was built to study the residence time distribution (RTD). Polypropylene was selected as the flow material and the blend of Polypropylene and anthracene was used as the tracer. This on-line detection device has good reproducibility. The hydrodynamics in the extruder was simulated by the finite element method (FEM) combined with the mesh superposition technique (MST). The particle tracking technique was carried out to evaluate the RTD and mixing efficiency. The effect of screw speed and feed rate on the hydrodynamics and mixing performance was investigated. The velocity magnitude and local shear rate tend to become smaller from inlet to outlet due to the decreasing diameters of screws. The mean length of stretch increases exponentially from inlet to outlet and the mean value of time averaged mixing efficiency remains positive along the axial direction.

A Composite Model for Melting, Pressure and Fill Factor Profiles in a Metered Fed Closely Intermeshing Counter-rotating Twin Screw Extruder

Abstract A composite model of solids conveying, melting and melt flow in a closely intermeshing counter-rotating twin-screw extruder of modular design has been developed. This is based on combining melt conveying models with new melting and solids conveying models. Computations are made for axial fill factor, pressure, temperature and melting profiles. The results are compared with experiment.

Effect of high shear rate on the mechanical properties of polyethylene, poly(ethylene terephthalate), polystyrene and polypropylene waste blend

The effect of high shear rate on the mechanical properties of polyethylene (PE), poly(ethylene terephthalate) (PET), polystyrene (PS) and polypropylene (PP) waste blend was investigated. The process was carried out at a temperature of 120°C using a counter-rotating twin-screw extruder. A constant screw speed of 250 rpm and a constant weight ratio of the PE/ PET/PS/PP components of 1:1:1:1 were used. The preliminary research showed that the high shear rate had no effect on the impact strength. However, the significant improvement in the flexural properties was observed as compared to those obtained at a lower screw speed of 80--120 rpm.

Effect of Conversion on Chain Addition Copolymerizations Performed in a Backmixed Drag Flow Extruder Reactor

Abstract The use of a drag flow device such as a twin screw extruder for polymerization and/or copolymerization processes has been studied extensively over the years. Due to the high viscosities (100 to 100 000 poise) that are produced, poor backmixing is experienced in these drag flow devices. As a result, these studies have shown the extruder reactor to exhibit a ‘‘plug flow’’ behavior. A drag flow device has been developed that achieves good backmixing with high viscosity materials. This device incorporates two counter-rotating, nonintermeshing, screws; one screw conveying material forward, while the other conveying material backward. Theory suggests that in a plug flow reactor the copolymer composition varies (drifts) as a function of time (position) in the reactor in most cases. Conversely in a micromixed continuous stirred tank reactor (CSTR) the copolymer produced does not drift as a function with position in the reactor. It has also been shown that this drift in copolymer composition becomes more pronounced at higher conversion. Experiments were performed in a counter-rotating nonintermeshing twin screw extruder using the ‘‘backmixed’’ configuration and a ‘‘conventional’’ configuration. Two copolymer systems were investigated; butyl acrylate/styrene and butyl acrylate/butyl methacrylate. The copolymerizations were conducted at three residence times for each system and configuration to provide materials of a wide variety of conversions (13 to 97 %). Monomer samples were taken at two ports in the extruder and at the die. Samples were analyzed for composition by two methods; FTIR and refractive index (RI). It was shown that the copolymer composition of samples produced in the backmixed extruder reactor does not change significantly as a function of position in the reactor. This is an indication that the copolymer composition does not drift in the reactor. Theoretically this is the behavior that exists with a chain addition copolymerization that occurs in a CSTR. Two methods (RI, FTIR) were used in the copolymer formulation (BA/Sty) and one method (FTIR) was used in the other copolymer formulation (BA/BMA). It was further shown that the difference in copolymer compositions in the two extruder reactors is more pronounced at higher conversions than at lower conversions.

The Role of Calender Gap in Barrel and Screw Wear in Counterrotating Twin Screw Extruders

It has been known in the industrial sector that in closely intermeshing counterrotating twin screw extruders, large separating forces develop in the calender gap, which push the screws towards the barrel wall. The result is significant wear in the region defined by 30°- and 60°-degree angles from the vertical. In the present investigation, pressures were measured around the barrel in extrusion of two rigid PVC resins in a laboratory extruder of 55 mm diameter and the forces on the screw core were determined. Numerical flow simulations were also carried out using the power-law viscosity parameters of the resins. From the experimental results, it was determined that the resultant forces are in the 30 degree angle direction, and from the computer simulations, the angle is between 18° and 25°. It is argued that the resultant force angle will be somewhat larger in large diameter extruders, due to the additional contribution of gravity.

The effect of nano, micro and dual scale filler reinforcement on the morphology, mechanical and barrier properties of polypropylene composites

In the current work the reinforcement effect of nano and micro scale fillers separately and in combination (dual scale filler reinforcement) in polypropylene thermoplastic was investigated. The composites was prepared using counter rotating twin screw extruder at a screw speed of 100 rpm and the set temperature profile varying from 150 to 210 °C. The morphological investigations performed by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) revealed the uniform distribution and dispersion of fillers within the matrix. The tensile strength and modulus obtained was notable at 2 wt% of nanosilica amongst the nanocomposites, whereas in the dual scale filler reinforced composite 4 wt% of nanosilica content displayed the enhanced tensile and barrier properties. The hybrid composite incorporated with 4 wt% of nanosilica and 15 wt% of glass fiber offered higher restrictions to the solvent flow and is evinced with least permeability and diffusivity parameters.

Application of extrusion-cooking technology in hatchery waste management.

The purpose of the present study was to examine the extrusion-cooking process of cereal blends with addition of hatchery waste (HW). The effect of HW addition on the physical properties and chemical composition of the extrudates was examined. The share of the HW in blends with corn meal was variable in the range of 5–30%. The study was conducted using a counter-rotating twin-screw extruder (L:D ratio 12:1, screw speed 75 rpm, die diameters 3 mm × 6 mm, profile of barrel temperature 120/140/180/180/130°C, and material moisture 28%). Increase in the content of the HW from 5 to 30% reduced the expansion ratio, pellet durability index, water absorption index, and water solubility index of the extrudates. The microstructure of the extrudates with HW addition is non-homogeneous; the areas with densely packed and adherent granules, interwoven with fibrous structures, can be observed. Increase in the share of HW leads to a lowering of the levels of crude fiber and total dietary fiber in the extrudates. Moreover, a significant increase in the content of protein, crude fat, and mineral elements such as calcium, sodium, magnesium, and iron was observed.

The Effect of Construction and Demolition Waste Plastic Fractions on Wood-Polymer Composite Properties.

Construction and demolition waste (CDW), including valuable materials such as plastics, have a remarkable influence on the waste sector. In order for plastic materials to be re-utilized, they must be identified and separated according to their polymer composition. In this study, the identification of these materials was performed using near-infrared spectroscopy (NIR), which identified material based on their physical-chemical properties. Advantages of the NIR method are a low environmental impact and rapid measurement (within a few seconds) in the spectral range of 1600-2400 nm without special sample preparation. Limitations include its inability to analyze dark materials. The identified polymers were utilized as a component for wood-polymer composite (WPC) that consists of a polymer matrix, low cost fillers, and additives. The components were first compounded with an agglomeration apparatus, followed by production by extrusion. In the agglomeration process, the aim was to compound all materials to produce uniformly distributed and granulated materials as pellets. During the agglomeration process, the polymer (matrix) was melted and fillers and other additives were then mixed into the melted polymer, being ready for the extrusion process. In the extrusion method, heat and shear forces were applied to a material within the barrel of a conical counter-rotating twin-screw type extruder, which reduces the risk of burning the materials and lower shear mixing. The heated and sheared mixture was then conveyed through a die to give the product the desired shape. The above-described protocol proved the potential for re-utilization of CDW materials. Functional properties must be verified according to the standardized tests, such as flexural, tensile, and impact strength tests for the material.

CFD modelling and performance analysis of a twin screw hydrogen extruder

An intermeshing counter-rotating twin-screw extruder is reported to be more reliable and stable among various methods of extrusion techniques in pellet production systems for the plasma reactors. In the present study, CFD modelling has been successfully carried out using POLYFLOW module of ANSYS, which employs the Mesh Superposition Technique. The shear rate dependent shear stress of solid hydrogen modelled using Herschel-Bulkley equation has been used in the present analysis. A three-dimensional computation neglecting inertia and gravity effects has been carried out to simulate the flow through the extruder which involves leakage flows through the calendar, tetrahedron, flight and side gaps. The flow characteristics of the die was simulated independently and superimposed with the extruder pumping characteristics to arrive at the operating point. The CFD results have been compared with those obtained from an analytical model adopted from the literature on polymer extrusion research. It has been found that the deviation between them becomes narrow when the mechanical clearances of the extruder are made smaller. A systematic parametric analysis was carried out to arrive at an optimum design to produce a 3 mm diameter filament at about 400 mm3/s with a minimum viscous dissipation rate. The analysis revealed that an increase of pitch length or decrease of mechanical clearance gaps in association with either decrease of the number of ‘C’ chambers or the speed will result in smaller viscous dissipation rate.

The effect of dynamic vulcanization on the morphological and mechanical properties of the toughened poly (lactic acid)/epoxidized natural rubber

Poly (lactic acid)/epoxidized natural rubber (PLA/ENR) was prepared by using counter-rotating twin-screw extruder. For dynamic vulcanization process, ENR was compounded with 3 phr of N, N’-m-phenylenebismaleimide (HVA-2) as a crosslinking agent. The aim of this study is to determine the effect of unvulcanized and dynamically vulcanized of ENR on the properties of PLA/ENR blend. The blending of PLA with ENR was prepared with the various composition of ENR (0 wt% to 30 wt%). The morphology and mechanical properties of the blends were investigated by using scanning electron microscope (SEM), tensile test, and impact test. The unvulcanized blend produced a co-continuous morphology of PLA and ENR and the dynamically vulcanized blend shows the dispersed ENR rubber particles in PLA continuous matrix. For both systems, the tensile strength value was dropped with the increasing amount of ENR content. The impact strength of both systems shows the maximum value at 20 wt% of ENR content. However, dynamically vulcanized PLA/ENR blend shows a better tensile strength and impact strength value as compared with unvulcanized blend.

Optimization and Numerical Simulation of Outlet of Twin Screw Extruder

In view of the unreasonable design of non-intermeshing counter-rotating twin screw extruder die, the problem of productivity reduction was discussed. Firstly, the mathematical model of extruder productivity was established. The extruder die model was improved. Secondly, the force analysis of twin screw extruder physical model was carried out. Meanwhile, A combination of mechanical analysis and numerical simulation was adopted. The velocity field, pressure field and viscosity field were calculated by Mini-Element interpolation method, linear interpolation method and Picard iterative convergence method respectively. The influence of die model on the quantity of each field before and after improvement was analyzed. The results show that the improved model had increased the rheological parameters of the flow field, the leakage and reverse flow decreased. Through post-processing calculation, the productivity of the third dies extruder was 10% higher than before. The research results provide a theoretical basis for the design and optimization of die model of non intermeshing counter-rotating twin screw extruder.

Morphology and properties of biodegradable poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends with different viscosity ratio

Phase morphology exerts a tremendous influence on the properties of polymer blends. The development of the blend morphology depends not only on the intrinsic structure of the component polymers but also on extrinsic factors such as viscosity ratio, shearing force and temperature in the melt processing. In this study, various poly (butylene adipate-co-terephthalate) (PBAT) materials with different melt viscosity were prepared, and then poly (lactic acid) (PLA)/PBAT blends with different viscosity ratio were prepared in a counter-rotating twin-screw extruder under constant processing conditions. The influence of viscosity ratio on the morphology, mechanical, thermal and rheological properties of PLA/PBAT (70/30 w/w) blends was investigated. The experimental results showed that the morphology and properties of PLA/PBAT blends strongly depended on the viscosity ratio. Finer size PBAT phase were observed for viscosity ratio less than 1 (λ < 1) compared to samples with λ > 1. It was found that the interfacial tensions of PLA and PBAT were significantly different when the viscosity ratio was changed, the lowest interfacial tensions (0.12 mN/m) was obtained when the viscosity was 0.77. Additionally, the maximal tensile strength in PLA/PBAT blends were obtained when the viscosity ratio was 0.44, while the maximal impact properties were obtained when the viscosity ratio was 1.95.

THE INFLUENCES OF POPLAR INNER AND OUTER BARK CONTENT ON MECHANICAL PROPERTIES OF WOOD/POLYPROPYLENE COMPOSITES

This study evaluated the individual and interaction effects of inner bark flour (IBF), outer bark flour (OBF), wood flour (WF), and blending of IBF, OBF, and WF content of poplar tree on the morphology and mechanical properties of wood-plastic composites (WPCs). The IBF, OBF, and WF with 2 wt% maleic anhydride-grafted polypropylene (MAPP) and polypropylene were compounded into the pellets using a counter-rotating twin-screw extruder. Test specimens were prepared by injection molding machine. The results indicated that the WF alone significantly (P<0.05) increased the flexural strength, flexural modulus, and tensile strength. The composites made with IBF/WF exhibited higher tensile modulus compared to those made with WF alone and IBF/OBF alone. Moreover, the results showed that the IBF/OBF alone increased the notched impact strength compared to all of reinforced composites. The neat polypropylene had higher notched impact strength than the other reinforced composites (P<0.05).

The effects of surface treated carbon fibers and CaCO3 nanoparticles inclusions on the mechanical performances of PA6/ABS-based composites

The mechanical and morphological characteristics of PA6/ABS (60/40)-based hybrid composite containing HNO3-treated short carbon fibers (HSCF) and CaCO3 nanoparticles have been experimentally studied. A counter-rotating twin-screw extruder and an injection molding machine were employed to produce different samples containing 10 wt % of HSCF and 0, 2, 5 and 8 wt % of CaCO3 nanoparticles. The SEM observations indicated high-quality adhesion between HNO3-surface treated carbon fibers and PA6/ABS polymer matrix. In addition, the morphological studies showed that the inclusion of CaCO3 nanoparticles caused a significant effect on the ABS particle dispersion in PA6/ABS matrix. The mechanical properties assessments revealed that the incorporation of 10 wt % HSCF into the PA6/ABS can significantly improve tensile strength (82%), tensile modulus (107%), flexural strength (98%), flexural modulus (104%) and impact resistance (24%). The inclusion of CaCO3 nanoparticles, in the presence of 10 wt % HSCF, led to the noticeable improvements of tensile strength (128% for 2 wt % CaCO3), tensile modulus (199% for 5 wt % CaCO3), flexural strength (146% for 5 wt % CaCO3), flexural modulus (204% for 5 wt % CaCO3) and impact resistance (46% for 2 wt % CaCO3). The surface treatment of carbon fibers, dispersion conditions of nanoparticles and ABS phase in polymeric matrix were found to be the major important factors affecting the mechanical properties.

Enhanced mechanical and thermal properties of hybrid graphene nanoplatelets/multiwall carbon nanotubes reinforced polyethylene terephthalate nanocomposites

The effects of graphene nanoplatelets (GNP) and multiwall carbon nanotube (MWCNT) hybrid nanofillers on the mechanical and thermal properties of reinforced polyethylene terephthalate (PET) have been investigated. The nanocomposites were melt blended using the counter rotating twin screw extruder followed by injection molding. Their morphology, mechanical and thermal properties were characterized. Combination of the two nanofillers in composites formulation supplemented each other which resulted in the overall improvement in adhesion between fillers and matrix. The mechanical properties and thermal stability of the hybrid nanocomposites (PET/GNP1.5/MWCNT1.5) were significantly improved compared to PET/GNP3 and PET/MWCNT3 single filer nanocomposites. However, it was observed that GNP was better in improving the mechanical properties but MWCNT resulted in higher thermal stability of Nanocomposite. The transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) revealed uniform dispersion of the hybrid fillers in PET/GNP1.5/MWCNT1.5 nanocomposites while agglomeration was observed at higher filler content. The MWCNT prevented the phenomenal stacking of the GNPs by forming a bridge between adjacent GNP planes resulting in higher dispersion of fillers. This complimentary geometrical structure is responsible for the significant improvement in the thermal stability and mechanical properties of the hybrid nanocomposites.

Foam extrusion of PP-based wood plastic composites with chemical blowing agents and the Celuka technique

Wood plastic composites have gained relevance in recent years as an alternative to wood boards. However, because the cavities in wood fibres are compressed by high processing pressure during the extrusion of wood plastic composites, the product densities show a range of up to 1.5 g/cm3 depending on wood content and base material. Particularly in large-sized products, this may be disadvantageous for processors and end users. Foaming of the plastic matrix is a promising approach to reduce the density of wood plastic composites products. This article discusses the foam extrusion of PP-based wood plastic composites with chemical blowing agents in combination with the Celuka technique. Integral wood plastic composites foam with a rigid and plain outer layer was produced using a parallel, counter rotating twin screw extruder. The profiles obtained were analysed with respect to foam structure and mechanical properties. It was possible to achieve a density reduction of up to 0.7 g/cm3 in the foamed wood plastic composites profiles. Furthermore, we demonstrate that wood fibre length and type of chemical blowing agent have a strong effect on the resulting foam morphology.

Mechanical and Thermal Properties of Rubber Toughened Poly(Lactic Acid)

The effect of rubber toughening on mechanical and thermal properties of poly (lactic acid) (PLA) was investigated by using three types of rubbers; natural rubber (NR), epoxidized natural rubber (ENR) and core-shell rubber (CSR). The PLA/rubber blends were prepared by melt blending in a counter-rotating twin-screw extruder, where the rubber content for all blends was kept at 5 wt%. It was found that the addition of the rubbers increased the impact strength for all blends as compared to pure PLA. On the other hand, all PLA/rubber blends showed notable decrease of Young’s modulus especially for PLA/NR blend which decreased by 72% than pure PLA. Similarly, significant decrease of tensile strength was also observed for all PLA/rubber blends. PLA/ENR blend showed a morebalance mechanical properties with fairly significant improvement of impact strength and moderate decrease of tensile strength, Young’s modulus and elongation at break. In general, PLA/NR blend showed the highest overall impact strength, while the PLA/CSR showed the highest tensile strength and Young’s modulus among the blends. Thermal analysis revealed that the Tg of PLA decreased with incorporation of the three types of rubbers with NR showing the largest decrease. This study indicates that NR, ENR and CSR are effective in enhancing toughness of PLA