Screw Mixer Research Articles

Study of the Disintegration of Poly (butylene adipate-co-terephthalate) and Starch Co-Extruded Materials

The disintegration behavior of biodegraded plastics materials including poly (butylene adipate-co-terephthalate) (Ecoflex), Ecoflex/starch blend, poly (butylene adipate-co-terephthalate) (Enpol) and Enpol/starch blend in controlled composting was described. The blends were compounded using a twin screw extruder with co-rotating mixing screw. The aerobic disintegration tests were carried out in the reactors under constant temperature at 58 + 2 °C for 90 days. During testing moisture, mixing and aeration of the samples were periodically determined and controlled according to ISO 20200:2004. The results showed that the percentage of disintegration of Ecoflex, Ecoflex/starch blend (50:50 %wt.), Enpol and Enpol/starch blend (50:50 %wt.) were 25.91%, 80.57%, 56.29% and 91.08%, respectively. It was also found that starch content facilitate the disintegration of the polymers. The morphologies and thermal properties of the residues were studied using SEM and TGA. It was found that the surface morphologies and the thermal properties results are in accordance with the biodisintegration degree.

Monitoring ibuprofen–nicotinamide cocrystal formation during solvent free continuous cocrystallization (SFCC) using near infrared spectroscopy as a PAT tool

The purpose of this work was to explore NIR spectroscopy as a PAT tool to monitor the formation of ibuprofen and nicotinamide cocrystals during extrusion based solvent free continuous cocrystallization (SFCC). Drug and co-former were gravimetrically fed into a heated co-rotating twin screw extruder to form cocrystals. Real-time process monitoring was performed using a high temperature NIR probe in the extruder die to assess cocrystal content and subsequently compared to off-line powder X-ray diffraction measurements. The effect of processing variables, such as temperature and mixing intensity, on the extent of cocrystal formation was investigated. NIR spectroscopy was sensitive to cocrystal formation with the appearance of new peaks and peak shifts, particularly in the 4800–5200cm−1 wave-number region. PXRD confirmed an increased conversion of the mixture into cocrystal with increase in barrel temperature and screw mixing intensity. A decrease in screw rotation speed also provided improved cocrystal yield due to the material experiencing longer residence times within the process. A partial least squares analysis in this region of NIR spectrum correlated well with PXRD data, providing a best fit with cocrystal conversion when a limited range of process conditions were considered, for example a single set temperature. The study suggests that NIR spectroscopy could be used to monitor cocrystal purity on an industrial scale using this continuous, solvent-free process.

Liquid Fuels from Biomass Cracking

Abstract During the catalytic cracking of agricultural lignocellulosic bio-waste it is possible to obtain a liquid condensate with the yield of the bio-oil is up to 19 wt. % in experiments with vegetable oil in input material. Bio-oils originating only from agricultural biomass give the yield of max. 2 wt. % with the respect to the input. In the batch process, better results in the yield of bio-oil were found. Cracking of agricultural waste, running in continuous pilot scale reactor with screw mixers at temperatures from 390 to 450 °C, results in the significant yield of bio-gasses. The portion of gaseous products varies from 25 wt. % (corn combs with vegetable oil, reed) to 62 wt. % (dry leaves), depending on cracking conditions, type of biomass, presence of zeolite catalyst or vegetable oil. These gases are flammable and can be used as motor fuel and/or energetic purposes.

The Power Consumption Performance of an Orbiting Screw Solid-Solid Mixer

In this work we have investigated mixing in a modified orbiting screw mixer (MOSM) designed for solid-solid mixing. Mixing was carried out using urea powder and natural zeolite powder (UZ) of three varying particle sizes (50- 60, 60-80 and 80 mesh). Power consumption was calculated from the measured torque of orbit and screw, obtained from computerized records. It was found that the mixing process in the modified orbiting screw mixer with air injection required a lower power consumption for each particle-size group when compared to mixing without air injection. With UZ mixing in MOSM with air injection, the lowest E was obtained for the 60-80 mesh particle-size group (4,297 Joule/kg -1 ), whereas when mixing without air injection, the value was 10,296 J/kg. The best mixing operation in this experiment was achieved at NFr = 1.18x10 -3 and in the range of values NRe ≈ 8.77x10 7 to 2.63x10 8 . Moreover, in this study, we have developed an equation to estimate the power consumption required for mixing and determined its correlation with dimensionless numbers.

Utilization of Corn Hominy as a New Source Material for Thermoplastic Starch Production

Corn hominy or ampok (in local language) is a by-product from corn milling industry. It is about 35% in weight of dry milled kernel. Corn hominy contains a small amount of fibre (7.26%), protein (10.2%), fat (8.12%), and a large amount of starch (63.21%) which could be used as an alternative source for making starch based thermoplastics (STP), hence reducing the use of starch. The aim of this research is to investigate the effects of weight ratio of tapioca to corn hominy as well as the glycerol content in formula compositions on mechanical properties, i.e. tensile strength and elongation at break and thermal properties (Tg and Tm) of corn hominy based thermoplastic. The ratio of tapioca to corn hominy composition varied from 0:100; 25:75; 50:50; 75:25 and the glycerol content varied from 25% to 35 wt%. The blends were melt processed using counter rotating twin screw mixer with the barrel temperature of 120, 130 and 120°C at 60rpm for 5min. It has been observed that using corn hominy as a sole material for making thermoplastic was not feasible. The tensile strength, elongation at break, and glass transition point (Tg) were greatly affected by increasing the tapioca content. Thermoplastics starch produced by extruder was then pressed by a hydraullic press, and this showed good characteristics which signaled by homogenous surface of SEM images. The surface morphology of thermoplastic starch was unchange by increasing the glycerol content and corn hominy ratio. However, higher corn hominy ratio gave smoother surface morphology at the cross section of thermoplastic starch.

Numerical Simulation on the Mixing Behavior of Pin Unit Under Vibrant Enhancement

With the computational fluid dynamics (CFD) software POLYFLOW, simplified models and numerical simulation are conducted on the single screw pin unit and the single screw unit. Comparative analysis is carried out on the mixing properties of these two mixing units under vibration-less and vibrant operating conditions. It is found that in comparison to the single screw mixing unit, the pin unit has longer residence time, smaller segregation scale, larger mixing index and higher instantaneous efficiency of stretching; it also possesses better diffluence and rearrangement, flow state, fluidity and plasticization performance for the polymer melt particles under vibration field. This provides references for the design and research of new type mixing device.

Mixing Urea and Zeolite for Slow Release Fertilizer using Orbiting Screw Mixer

Slow release fertilizer (SRF) of urea is prepared by using zeolite as the matrix. Mixing of urea and zeolite is carried out in orbiting screw mixer. The effects of rotation speed and orbital speed of the mixer and particle size on power consumption, homogeneity, mixing time and specific energy consumption are evaluated. The experimental results show that higher orbital speed gives higher power consumption. Power consumption is dominated by mixer rotation motion. Smaller particle size needs higher power for mixing process. Nitrogen mass fraction ranges from 0.45 to 0.49 when mixture reaches homogeneity. The mixing time required is about 5 – 12 minutes for particle size of >60 and >80 mesh and 7 – 14 minutes for particle size of >50 mesh. At constant orbit speed, the higher the screw rotation speed, the shorter time needed to reach mixture homogeneity. Specific energy consumption of mixing process increases with decreasing particle size. For the three particle size groups of >80 mesh, >60 mesh and >50 mesh, the lowest specific energy consumption is given by combination of orbital speed of 5 rpm and rotation speed of 50 rpm; while for particle size of >60 mesh and >80 mesh, it can obtained by combination of orbital speed of 5 rpm and rotation speed of 67,5 rpm and orbital speed 5 rpm and rotation speed 30 rpm, respectively. The lowest specific energy consumptions is gained by combination of orbital and rotation speeds of 5 and 50 rpm with particle size of >50 mesh.

Effect of TiO<sub>2</sub> Nanoparticle on Thermal and Tensile Behavior of Polypropylene/ Polylactic Acid Composite

The role of both nano-sized of plasma treated Nano Titanium Dioxide particles and strain rate on the tensile properties of plasma treated Nano Titanium Dioxide particles/PP/PLA nano-composites filaments (PTNTOPPCF) was studied. Filaments tensile samples of PTNTOPPCF were prepared by a twin screw mixer- twin screw extruder with a particle content of 0.3~1%. The influence of surface treatment of the particles, with and without low-temperature oxygen plasma treatment, on the physico-mechanical properties was studied. The tensile tests were carried out, differential scanning calorimetry (DSC) and SEM were used in this investigation. Tensile tests were done at different strain rates. The addition of plasma treated Nano Titanium Dioxide particles to PP/PLA caused a change in Young's modulus and yield stress of its composites. The experimental results also showed that the strain-rate sensitivity of PTNTOPPCF changed as plasma with and without oxygen treated Nano Titanium Dioxide particles was added to it with different o.w.f.. We found that the models lead to estimates of activation volumes in the range 4−40nm3 for truly nanocrystalline material. Activation volumes were found to changing un-monotonically with oxygen plasma treatment. The findings were found to be in accord with available experimental evidence in both a quantitative and qualitative manner. Deficiencies in the available experimental evidence were noted, specifically in the context of explaining some of the difficulties in comparing theoretical predictions to experimental observation.

Ultrasonic diagnosis of the single screw behavior during extrusion—A case study

AbstractUltrasonic diagnostic method of screw behavior during extrusion has been designed, developed, and carried out on a 63.5‐mm single screw extruder, equipped with either a basic conveying screw or a mixing screw. It was found that the screw behavior depends on the screw speed and the die pressure. Whereas initially at low speed, the screw centered by the hydrodynamic forces rotates smoothly in the axial position, at higher screw speeds and high die pressures the screw starts vibrating. Thus, (1) the screw tip vibrated with the amplitude of 10–210 μm as the screw speed varied from 5 to 100 revolutions per minute; (2) the screw vibrations in the vertical and horizontal directions were asymmetrical; (3) the vibration pattern repeated itself at every two revolutions; (4) the vibrations originated in the poorly aligned engagement in the gearbox sleeve when the screw was pushed deeply into it by backpressure; (5) once pushed in the screw oscillated at any screw speed or die pressure. POLYM. ENG. SCI., 2009. Published by the Society of Plastics Engineers

The effect of nano-sized calcium carbonate on thermodynamic parameters of HDPE

One of the main limitations in application of polymers, particularly thermoplastic polymers such as high density polyethylene (HDPE) and polypropylene (PP), is their poor thermal properties. To promote mechanical and thermal properties of HDPE, ceramic phases are added to it. In the current research, to enhance thermal properties of HDPE, nano-sized calcium carbonate was used. For this purpose, HDPE/10%CaCO 3 nanocomposite was fabricated using a twin screw mixer–single screw extruder. The properties of HDPE and its nanocomposite were investigated through differential scanning calorimetery (DSC) and thermo mechanical analyzer (TMA) tests. The results of DSC tests showed that the addition of nano-sized calcium carbonate to HDPE caused to increase the heat capacity, sensible heat and crystallinity index. The TMA results illustrated an increase in dimensional stability of HDPE as nano-sized of calcium carbonate added to it.

The plasticizing effect of alginate on the thermoplastic starch/glycerin blends

Corn starch and corn starch–alginate (5–15%) blends plasticized with 35% glycerin were prepared, water was intentionally excluded from the formulations. Torque rheometry measurements were carried out during the processing of the blends in a batch counterrotating twin screw mixer. A progressive decrease in the plasticization energy of the blends was observed as the alginate content was increased, with a 5-fold decrease for the blend with the higher alginate content (15%). The steady state torque of the plasticized melted blends also showed a decrease as alginate content was increased; with a drastic drop occurring for the formulation with higher alginate content. After mixing, test specimens for mechanical, thermal and microstructural testing were made by compression molding. A decrease in the elastic properties and an increase in elongation at break and impact resistance was observed when alginate content was increased in the blends. The transition of the materials towards a more viscous behavior, as alginate content was increased, was confirmed by differential scan calorimetric analysis. For the corn starch–alginate blends glass transitions were detected in the temperature range −60 to −90 °C. Scanning electron microscopy was used to examine the morphology of cryofractured surfaces of the molded test specimens. A reduction of the granular crystalline structures typical of corn starch was observed as alginate content was increased in the blends. The experimental evidence presented in this work indicates that, when water is excluded from thermoplastic corn starch preparation, alginate acts synergistically with glycerin increasing the degree and efficiency of the plasticization process.

Alginate production by Pseudomonas mendocina in a stirred draft fermenter

In this study alginate production by Pseudomonas mendocina in a laboratory-scale fermenter was investigated. In the experiments the effect of temperature (25–31°C) and agitation (500–620 rev min−1) at a constant air flow of 10 v/v/h were evaluated in relation to the rate of glucose bioconversion to alginate using response surface methodology (RSM). The fermenter configuration was also adapted to a system with a screw mixer and draft tube, due to the change in rheological characteristics of the fermentation broth. The adjusted model indicates a temperature of 29.1°C and agitation of 553 rev min−1 for optimum alginate synthesis. In this fermentation system a Yp/s of 44.8% was achieved. The alginate synthesized by P. mendocina showed a partially acetylated pattern as previously reported for alginates obtained from other Pseudomonas spp and Azotobacter vinelandii.

Examination of the mixing ability of single and twin screw mixers using 2D finite element method simulation with particle tracking

The mixing in model 2D single screw and co-rotating twin screw dough mixers is evaluated using the commercial CFD package Polyflow with a Carreau flow model for dough to generate velocity profiles and particle trajectories. The mixed Galerkin FEM simulations use a rotating reference frame technique with the single paddle mixer and a mesh superposition technique in the twin paddle mixer. Differences in the velocity profiles are noted. Distributive mixing is evaluated visually as well as using the segregation scale and cluster distribution index; stretching is evaluated using the length of stretch and mixing efficiency; and dispersive mixing is evaluated using the mixing index in combination with the shear stress. Since material points stay on their streamlines in the 2D single screw mixer, the 2D twin screw mixer is found to be generally more effective and efficient, although there are still areas of poor mixing.

Properties and preparation of compatibilized nylon 6 nanocomposites/ABS blends using functionalized metallocene polyolefin elastomer. I. Impact properties

AbstractThe impact behaviors of nanoclay‐filled nylon 6 (nano‐nylon 6) blended with poly(acrylonitrile–butadiene–styrene) terpolymers (ABS) prepared through a twin screw mixing process were investigated here using metallocene polyethylene grafted maleic anhydride (POE‐g‐MA) as a compatibilizer to enhance the interface interaction. No clear effect of compatibilizer on the dispersion of clay and crystalline structure of nano‐nylon 6 has been observed. In view of morphology and rheological behaviors, the effect of compatibilizer on the mechanical properties could be elucidated. It is found that impact strength increases with the addition of compatibilizer at various ABS compositions. Similar effects are also observed with decreasing test temperature at the nano‐nylon 6/ABS blend composition of 80/20. As for thermal properties, the heat distortion temperature shows a marginal decrease in the nano‐nylon 6/ABS blends. Rheological behavior indicates that increased viscosity is found for the investigated compatibilized systems. Through morphology observations, the etched ABS particle sizes tend to decrease with the addition of compatibilizer for the blends, but are larger with higher contents of ABS concentrations. Those observations account for impact behaviors of the investigated blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1364–1371, 2006

Thermal degradation behaviour of isotactic polypropylene blended with lignin

The influence of lignin on the thermal degradation of isotactic polypropylene, investigated by thermogravimetric analysis, is reported in this article. Polypropylene blends containing 5 and 15 wt% of lignin were prepared by mixing the components in a screw mixer. An increase in the thermal degradation temperature of the blends was observed as a function of lignin content, in both oxidative and non-oxidative conditions. The increase is noticeably marked for the experiments carried out in air atmosphere, where the interactions between the polypropylene and the lignin lead to the formation of a protective surface able to reduce the oxygen diffusion towards the polymer bulk. Morphological analyses were carried out with optical and electronic microscopy, to evaluate the degree of dispersion of the lignin in the polypropylene matrix. X-ray techniques were employed to study the influence of lignin on the structure of the blended polypropylene.

HDPE/PA-6 blends: Influence of screw shear intensity and HDPE melt viscosity on phase morphology development

Blending is an economically viable, versatile method of manufacturing new materials with a wide range of properties. The parameters most frequently targeted for the improvement by blending are: the mechanical properties, impact strength, processability, heat deflection temperature, and the cost-to-performance ratio. When designing a blend, first the polymers and their approximate concentrations must be selected, then the most appropriate blend morphology for the envisaged application. For example, the need to improve impact properties implies that the minor phase ought to be dispersed as spherical droplets with micron or submicron diameter. On the other hand, if the material is to be used in vapor on solvent barrier applications, the minor phase should be dispersed in the form of relatively large, thin lamellas. The desired morphology is obtained by selecting the appropriate compatibilization and compounding/processing methods [1]. The studies on the morphology development of polymer blends in the single screw extruders [2] and twin screw extruders [3–5] demonstrated that significant changes in morphology occur in the melting zone and only comparatively minor changes take place in the following metering zone. The objective of the present work was to examine, using a single screw extruder combining with a convergent die, the effect of screw design of the metering zone on the morphology of HDPE/PA-6 blends with different HDPE melt viscosity. Three commercial grades of HDPE were used as the matrix phase: HHM TR-144 (HDPE1), 60550AG (HDPE2), and HD5218EA (HDPE3). The HDPE1, HDPE2, and HDPE3, with a melt index of 0.18, 7.2, and 15 g/10 min, were manufactured by Phillips Petroleum Singapore Chemicals, Petrochina Dushanzi Petrochemical Co., and Petrochina Lanzhou Petrochemical Co., respectively. The PA-6 1030B manufactured by UBE Industries Ltd. was used as the dispersed phase. This PA-6 is a blow molding grade resin with a high melt viscosity. For the compatibilizer, Polybond 3009 manufactured by Uniroyal Chemical, a maleic anhydride grafted polyolefin copolymer, was used. The weight content of HDPE, PA-6, and compatibilizer is 85, 12, and 3% in the blend, respectively. The melt shear viscosity measurements of individual resins were made using a slit die rheometer directly connected to an extruder with a screw diameter of 25 mm. The melt shear viscosity curves for three HDPEs and PA-6 at 240 ◦C are presented in Fig. 1. The corresponding melt viscosity ratio (VR) of the dispersed phase to the matrix phase is shown in Fig. 2. As can been seen, the VR for HDPE1/PA-6, HDPE2/PA6, and HDPE3/PA-6 blends is about 0.46–0.94, 3.1– 3.5, and 5.9–6.9 in the shear rate range of 20–400 s−1, respectively. The single screw extruder used has a screw diameter of 45 mm and a length-diameter ratio of 25:1. In order to investigate the influence of the screw elements in the metering zone on the morphology development of blends, the screw is constructed in a modular form. The core shaft of its metering zone can accommodate different screw elements to change the mixing type and intensity. Two different screw geometries, conventional metering and mixing screws, were employed. The mixing screw is outfitted with a fluted mixing element with a length of two times of screw diameter. Mixing screws in turn included two kinds, one with low shear intensity, and another with high shear intensity. If being approximatively estimated by the Couette shear rate, the shear rate in the channel of the metering screw, at a 40 rpm screw speed, is about 31 s−1; in the barrier clearance of low and high shear intensity fluted mixing element, it is about 157 and 314 s−1 at the same speed, respectively. The slit die mounted on the extruder exit to yield ribbons was a convergent one, having a 1.5 mm × 20 mm slit dimension. The PA-6 and compatibilizer were dried at 100 ◦C for 12 hr and 85 ◦C for 4 hr in a oven, respectively. The HDPE and the dried components of PA-6 and compatibilizer were dry mixed thoroughly and then fed into the extruder. The extruder was operated at 185 ◦C in the feeding zone and at 240 ◦C toward the extrusion

Continuous flow cracking of waste plastics

Experiments of waste polymers cracking in a continuous flow tube reactor were carried out. The main components of the reactor unit were a screw extruder as a waste plastics feeder and a tube cracking reactor equipped with an internal screw mixer. Cracking process was realized at the temperature range 420–480 °C and raw material feeding rate from 0.3 up to 2.4 kg/h. The principal process products, gaseous and liquid hydrocarbon fractions, are similar to the refinery cracking products. They are unstable due to the high olefins content (especially from polystyrene cracking) and their chemical composition and properties strongly depend on the applied feed composition, i.e. shares of polyethylene, polypropylene and polystyrene. The material balance experiments showed that the main products, liquid or solid materials in ambient temperature, contain typically 20–40% of gasoline fractions (range of boiling point 35–180 °C) and 60–80% of light gas oil fractions (initial boiling point>180 °C). The solid carbon residues are similar to coal cokes and contain even of 50% mineral components. Their calorific values attain 20 MJ/kg and they are solid fuels of quality similar to brown coals.

Morphology, crystallization and melting properties of isotactic polypropylene blended with lignin

AbstractThe influence of lignin (L) on the thermal properties and kinetics of crystallization of isotactic polypropylene (PP) is reported in this article. PP blends containing 5 and 15 wt % of L were prepared by mixing the components in a screw mixer. An increase of the thermal degradation temperature of the blends was observed as a function of L content. The crystallization and thermal behavior of the pure PP and of the PP/L blends were analyzed by differential scanning calorimetry (DSC). Isothermal crystallization kinetics were described by means of the Avrami equation, which suggests a three‐dimensional growth of crystalline units, developed by heterogeneous nucleation. The isothermal growth rate of PP spherulites was studied using a polarizing optical microscope. The enhancement of PP crystallization rate for the PP/L blends was observed and ascribed to the nucleating action of lignin particles. Non‐isothermal crystallization kinetics were applied, according to the results elaborated by Ziabicki and the method modified by Jeziorny. The kinetic crystallizability of the PP is not influenced by the L present in the blend. In the presence of L, PP can simultaneously crystallize in both the α and β crystalline forms, and the ratio between the α and β forms was determined by X‐ray diffraction analysis. Two melting peaks relative to the two crystalline form of PP were observed for the PP/L blends, for all isothermal crystallization temperatures investigated by means of DSC. The equilibrium melting temperature for α‐form of pure PP was obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1435–1442, 2004

Screw Machines with Longitudinal Circulation of Fluid. Communication 3. Intensification of Mixing Processes

Flow of melts and solutions of polymers with Newton's law of flow was investigated in a double screw mixer with screw channels of different depth and width in the presence of a radial gap on one screw ridge. With the radial gap, the pressure gradients along both channels are the same, the pressure along the entire length of the shallow and deep channels differ by a constant value and the higher pressure is always established in the second channel along the path of movement of the upper plate. By intensive exchange between channels, flow which gives zero flow of fluid in each section in the direction across the channels is organized in the deep and shallow channels of the mixer. The overall pressure differential and output of the mixer do not decrease in the presence of a radial gap on one of the ridges of the screw.

Screw Machines with Longitudinal Circulation of Liquid. Note 2. Effect of Radial Gaps on Performance

The effect of radial gaps between mixer screw ridges and body on the pressure-flow characteristics of equipment and the power consumed is investigated. It is shown that the presence of radial gaps worsens the performance characteristics of the screw mixer, manifested by a reduction in output and developed pressure.