Laboratory-scale Twin-screw Extruder Research Articles

Cellular architecture and its relationship with mechanical properties in expanded extrudates containing apple pomace

Cereal-based puffed foods can deliver significant amounts of fruit and vegetable fiber, however a major hurdle is the accompanying decrease in expansion and poor textural properties. The objective of this work was to develop a comprehensive understanding of the operative rheology, processing conditions, cellular architecture, macrostructure and mechanical properties of high fiber, starch-based expanded matrices produced using extrusion. The combination of phase transition analysis and non-invasive X-ray microtomography provided a unique analytical approach for this purpose. A lab-scale twin screw extruder was used for processing directly expanded products from corn flour and apple pomace blends containing up to 22.5% total dietary fiber. Different levels of pomace (0–28%) and in-barrel processing moisture (17.5–25%) resulted in extrudates with a wide range of microstructures (average cell size 0.05–3.43mm, wall thickness 0.12–0.34mm and void fraction 0.53–0.76). Structural anisotropy biased towards radial expansion was observed in foams without pomace, whereas cellular isotropy, higher cell number density and greater longitudinal expansion were favored in the presence of pomace. A conceptual model for foaming and collapse was developed based on flow temperature of blends (123.7–167.6°C), specific mechanical energy, and anticipated changes in visco-elasticity and extensibility of the high-fiber melt. Cell size was significantly correlated to average crushing force (r=−0.69), crispness work (r=−0.69) and number of spatial ruptures (r=0.74). Microstructure data in combination with standard theory for brittle foams was employed to understand mechanical properties of extrudates under compression.

Polyphenylene Ether/Glycol Modified Polyethylene Terephthalate Blends and their Physical Characteristics

Polyphenylene ether (PPE)/glycol modified polyethylene terephthalate (PETG) blends with various compositions were fabricated via a melt blending method using a laboratory-scale twin-screw extruder. The fracture surface morphology of the PPE/ PETG blends was examined by scanning electron microscopy (SEM) and, based on its data, it was observed that PPE and PETG are immiscible. Thermal stability and mechanical properties of the blends were also examined via thermal gravimetric analysis and a universal testing machine (UTM), respectively. Rheological properties of the PPE/PETG blends were observed with both steady shear and dynamic tests using a rotational rheometer. The effect of poly(styrene-co-maleic anhydride) (SMA) as a compatibilizer on the PPE/PETG blends was additionally investigated. An increase in quantity of PPE in the PPE/PETG blends and the addition of SMA were observed to enhance their thermal and mechanical properties.

Multi-Walled Carbon Nanotube/Biodegradable Poly(butyleneadipate-co-butyleneterephthalate) Nanocomposites and Their Physical Characteristics

Biodegradable poly(butylene adipate-co-terephthlate) (PBAT) nanocomposites with multi-wall carbon nanotube (MWNT) were prepared by using a laboratory-scale twin-screw extruder. The effects of the MWNT-reinforcements on their thermal and mechanical properties were examined by various techniques such as thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and a universal testing machine (UTM). In addition, the morphology of the as-synthesized PBAT/MWNT nanocomposites was investigated by both scanning electron microscope (SEM) and transmission electron microscope (TEM). To compare the physical characteristics of the polymer nanocomposites with those of the pure polymer, samples with various ratios of MWNT in the PBAT matrix were prepared. Rheological properties of the PBAT/MWNT nanocomposites were investigated using a rotational rheometer in a steady shear mode. The steady shear viscosity increased with the MWNT loading, and the shear thinning viscosity data were fitted well with the power law model. Furthermore, UTM, DMA and TGA tests showed that both mechanical and thermal properties were improved by adding MWNT. In particular, the tensile strength and thermal stability of biopolymer/MWNT nanocomposite increased with increasing MWNT contents. These results indicated that filler-polymer interaction is important and the role of the MWNT as a reinforcement in the nanocomposites was evident.

Extruded Moringa Leaf–Oat Flour Snacks: Physical, Nutritional, and Sensory Properties

Expanded snacks based on Moringa (Moringa oleifera) leaf powder (MLP) and oat flour were produced using a lab-scale twin-screw extruder. Four levels of MLP (0, 15, 30, and 45%, dry blend basis) and three levels of in-barrel moisture content (19, 22, and 26%, wet basis) were studied. Expansion of extrudates decreased as MLP level increased. On the other hand, expansion was positively affected by in-barrel moisture for all treatments with MLP. The role of MLP and in-barrel moisture in modifying phase transition, water binding, and gas-holding capacity of the extrusion melt was evaluated and related to product properties.

Effect of material and processing parameters on mechanical properties of Polypropylene/Ethylene–Propylene–Diene–Monomer/clay nanocomposites

Polypropylene/Ethylene–Propylene–Diene–Monomer (PP/EPDM) blends are well known for having a combination of favourable mechanical properties. In this paper, addition of organoclay to PP/EPDM to make PP/EPDM nanocomposites with enhanced mechanical properties is studied. PP/EPDM/organoclay nanocomposites were prepared using a lab scale twin-screw extruder. Maleic anhydride grafted polypropylene (PP-g-MA) was used to enhance the intercalation/exfoliation process and to create good adhesion at the polymer/polymer and polymer/filler interfaces. Taguchi method was employed to deign the experiments and optimize material and processing parameters for optimized mechanical properties. Organoclay (NC) and compatibilizer content were selected as material parameters and the main processing variables were feeding rate and average shear rate (RPM). X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to study the microstructure of the nanocomposites samples. It was observed that NC content and shear rate in extruder improved the tensile strength and modulus. Another important result was the insignificant effect of NC content on impact strength while increasing shear rate first increased and then decreased the impact strength.

A systematic study on notched impact strength of super‐toughened polyamide 6 nanocomposites using response surface methodology

AbstractResponse surface methodology was utilized to optimize the impact strength of polyamide 6 based nanocomposites using three different types of tougheners (ethylene‐methyl acrylate, ethylene‐ethyl acrylate‐maleic anhydride, and hydrogenated butadiene acrylonitrile rubber) at three different levels of clay and rubber. Melt mixing method using a lab scale twin screw extruder was applied to prepare the samples. The wide‐angle X‐ray diffraction, transmission electron microscopy, and atomic force microscopy results indicated intercalated/exfoliated morphology for all of the prepared nanocomposites. The tensile properties as well as the Izod impact strength of the designed samples were evaluated. Impact resistance was correlated to material variables by using a second order polynomial function. The best balanced mechanical properties, between 15 designed experiments, was achieved using ethylene‐ethyl acrylate‐maleic anhydride as toughener, 4 wt % of clay and 17.5 wt % of the toughener, whereas 900% improvement in impact strength and 15% enhancement of Young's modulus was obtained compared with pristine polyamide 6 resin. The formulation meeting the simultaneous optimization of Young's modulus and impact strength was proposed based on mathematical quadratic modeling. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Morphological and rheological characterization of multi-walled carbon nanotube/PLA/PBAT blend nanocomposites

Biodegradable poly (lactic acid) (PLA)/poly (butyleneadipate-co-butyleneterephthalate) (PBAT)/multi-walled carbon nanotube (MWNT) polymer blend nanocomposites were prepared by using a laboratory-scale twin-screw extruder. Fractured surface morphology of the polymer blend/MWNT nanocomposites were examined via SEM. Furthermore, cross sectioned samples obtained using an ultramicrotome was observed via TEM. In addition, effects of both MWNT reinforcement and phase affinity of MWNT on thermal and rheological properties of the PLA/PBAT blends were investigated by TGA and rotational rheometer. Immiscible PLA/PBAT blend with MWNT nanocomposites showed two-step thermal degradation. The onset temperature of thermal degradation started in the PLA much earlier than in the PBAT. Nonetheless, based on TGA data, it was found that the MWNT enhanced thermal property of the PLA/PBAT blend/MWNT nanocomposites. Rheological properties revealed that both shear and complex viscosities showed unique shear thinning behavior due to selectively localized MWNT dispersion state.

Vibrational spectroscopic studies of laboratory scale polymer melt processing: Application to a thermoplastic polyurethane nanocomposite

A laboratory scale twin screw extruder has been interfaced with a near infrared (NIR) spectrometer via a fibre optic link so that NIR spectra can be collected continuously during the small scale experimental melt state processing of polymeric materials. This system can be used to investigate melt state processes such as reactive extrusion, in real time, in order to explore the kinetics and mechanism of the reaction. A further advantage of the system is that it has the capability to measure apparent viscosity simultaneously which gives important additional information about molecular weight changes and polymer degradation during processing. The system was used to study the melt processing of a nanocomposite consisting of a thermoplastic polyurethane and an organically modified layered silicate.

Composition and Consumer Acceptability of a Novel Extrusion‐Cooked Salmon Snack

The objectives of this study were to develop a value-added jerky-style snack from salmon flesh and to minimize loss of healthful lipids during processing. Three formulations were extruded in a laboratory-scale twin-screw extruder. The base formulation included Atlantic salmon (82%, w/w), sucrose (4%), pregelatinized starch (3%), modified tapioca starch (3%), salt (2%), and teriyaki flavoring (2%). Three oil binding agents (tapioca starch, high-amylose cornstarch, oat fiber) were each studied at the 4% level. Barrel temperature, from feed to die, was 65, 155, 155, and 80 degrees C. Screw speed was 250 rpm. Feed rate was 220 g/min. Extrudates were convection-dried at 93 degrees C for 40 min. A texture analyzer was used to evaluate textural properties. Sixty-three consumers evaluated the hedonic attributes of the snacks. Extrusion cooking did not adversely affect content of omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in Atlantic salmon. The oat fiber formulation had the highest lipid (17.49%) content. The other formulations had higher moisture content. A serving (28 g) of the oat formulation provides 0.6 g EPA + DHA. Snacks containing oat fiber had the highest CIE L* and b* values. Snacks containing oat fiber required greater force to bend, cut, and puncture. The oat fiber formulation had the lowest overall acceptability. This portable snack could appeal to consumers who are interested in the health benefits of fish and omega-3 fatty acids and provide salmon processors with a value-added solution for processing by-products.

Processing, rheology and structure of melt compounded PBTclay nanocomposites having different chemical composition.

AbstractIn this study the melt flow behavior of poly(butylene terephthalate)-clay nanocomposites produced by melt compounding was investigated. Four commercial organo-modified montmorillonites, differing mainly by the organic treatment used in the modification, were employed as nanometric fillers and blended with the poly(butylene terephthalate) (PBT) at two weight percentages each (6 and 9wt%). The process was carried out using a laboratory-scale twin-screw extruder at two different extrusion rates, in order to evaluate the effect of the shear rate during the process on microstructure and flow properties. In this regard, the nanocomposite samples were submitted to morphological analyses and rheological measurements in the dynamic regime. The effect of temperature on the flow behavior of the hybrids with respect to the neat PBT matrix was also investigated. The obtained data were related to the hybrid compositions and then to the chemical affinity between polymer and clay type. All the reported results have shown a gradual transition from a pseudo-Newtonian trend towards a pseudo-solid-like flow behavior with the increase of the clay loading and the dispersion/exfoliation level of the clay particles, due to the corresponding increase of the polymer-silicate interactions that slow the relaxation times of the PBT chains. Moreover, it was also evident that for the fillers having the higher affinity towards the PBT the nano-scale dispersion benefit from higher residence times, and therefore slower extrusion rates; on the contrary, for the fillers having poor interaction with the polymer, higher shear stress, and therefore higher extrusion rates, are needed to disrupt the clay tactoids in smaller particles. In the last part of the work, in order to verify if a relationship between flow properties and degree of exfoliation does actually exist, the rheological data were also processed using a simple semi-quantitative empirical method proposed in literature. The method failed for our systems, thus underlining the insufficiency of the rheological response alone in quantifying the exfoliation degree of an organoclay in the matrix.

Functionality of fruit powders in extruded corn breakfast cereals

Consumer interest in naturally colored foods such as breakfast cereals is growing. Degermed white cornmeal, sucrose, citric acid and dehydrated fruit powder (blueberry, cranberry, Concord grape and raspberry) were mixed in 84.3%:14.3%:0.4%:1.0% proportions, then extruded in a laboratory-scale twin-screw extruder. Feed rate was 255 g/min; water was pumped at a rate of 12.5 g/min; screw speed was 175 rpm. Cooking temperature during extrusion was generally <130 °C. Samples were cut into small spheres and dried to 5% moisture. Cereals were stored at room temperature in opaque bags. The control samples were lighter and less red than the fruit cereals. Soluble phenolics and anthocyanins were higher in the fruit cereals. At three and six weeks of storage, fruit cereals had smaller levels of hexanal, as measured by gas chromatography of headspace of ground cereals. Although anthocyanins from fruit powders survive extrusion and retain some antioxidant activity, the levels used in this study may have been too low. Higher levels of fruit will increase production costs, but the expense may be offset by the more attractive and functional cereals that result.

Rheological behavior of new melt compounded copolyamide nanocomposites

In this paper the rheological behavior of new polyamide-based nanocomposites produced by melt compounding using three different silicate loadings and screw speeds was investigated. The thermoplastic matrices selected were a polyamide 6 and its statistical copolymer having partially aromatic structure, whereas the clay was a commercial organo-modified montmorillonite. Hybrid systems were prepared by means of a laboratory-scale twin screw extruder and were submitted to rheological and structural investigations. The rheological experiments (dynamic frequency sweep, steady rate sweep and stress relaxation tests) were performed to evaluate the effect of both system composition (kind of matrix and clay content) and extrusion rate on the flow behavior of the nanocomposites. Rheology, that is highly sensitive to the nanoscale structure of the materials, put out a pseudo-solid like flow behavior at long times in the hybrids with silicate content higher than 6 wt% and produced with high extrusion rate; this response was related to the formation of an extended structural network across the polymer matrix due to strong polymer–silicate interactions that slow the relaxation times of the macromolecules. Corresponding to this behavior, TEM micrographs have shown a quite uniform dispersion of clay particles on micron-scale and a fair level of silicate exfoliation on nanoscale with a macroscopic preferential orientation of the layers in samples. The rheological measurements also reveal that this flow response is more marked for nanocomposites based on the copolyamide matrix, suggesting that this resin may have a higher silicate affinity respect to polyamide 6 homopolymer.

Microstructure changes of a polypropylene/montmorillonite nanocomposite in a single screw extruder

Polymer nanocomposites based on organically modified layered silicates, e.g., organic-montmorillonite (org-MMT), exhibit attractive properties, such as increased mechanical properties, reduced gas and liquid permeability, improved heat, solvent and UV resistance, greater dimensional stability at elevated temperature, improved optical and electrical properties, and enhanced flame retardant properties [1–4]. Three different methods, in situ polymerization, polymer intercalation from solution, and direct polymer melt intercalation, have been used to synthesize layered silicate-based polymer nanocomposites [5]. The third method would greatly expand the commercial opportunities for nanocomposite technology because of its low cost, high productivity and compatibility with current polymer processing techniques [6]. In recent years, some researchers employed the direct melt intercalation technique to prepare the polymer nanocomposites [6–12]. However, these studies used a laboratoryscale twin screw extruder or internal mixer to yield nanocomposites and then investigated the microstructure and properties of only the as-extruded pellets or samples. Recently, the authors [13] used an industrial-scale extrusion blow molding machine to make packaging bottles from polypropylene (PP) or high-density polyethylene (HDPE)/org-MMT nanocomposites prepared by using a twin screw extruder. The changes of the microstructure of nanocomposites occurring after processing using a single screw extruder were investigated preliminarily. In this work, PP/org-MMT nanocomposites were prepared by direct melt intercalation using an industrial-scale co-rotating twin screw extruder. The as-extruded pellets were then extruded into ribbons by using an industrial-scale single screw extruder. The major focus was on the effects of mixing type of the screw on the microstructure changes of polymer nanocomposites. The microstructure of specimens was investigated by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). The org-MMT (Fenghong Clay Co.) was supplied as particles with an average size of 25 μm. The polymer matrix was isotactic PP homopolymer (F401,

Effects of Selected Process Parameters on Expansion and Mechanical Properties of Wheat Flour and Whole Cornmeal Extrudates

Mechanical properties of cereal extrudates are recognized by consumers as quality criteria. These properties are affected by process variables. The effect of process variables, such as water injection rate, barrel temperature, and screw speed on the expansion and selected mechanical properties of wheat flour and whole cornmeal extrudates was determined. A laboratory-scale twin-screw extruder with an L/D ratio of 25.0 was used. The cross-sectional expansion, the specific length, and the elastic moduli and breaking strength in bending and compression were measured. Water injection rate and barrel temperature significantly affected the cross-sectional expansion index (SEI) (P < 0.01), specific length (P < 0.01), elastic modulus in compression (P < 0.05), and breaking strength in bending (P < 0.05). The SEI was increased with a decrease in water injection rate and/or an increase in barrel temperature. The elastic modulus and breaking strength in bending decreased with the decrease in water injection rate. The SME input, which was dependent on the process variables tested, also influenced the expansion and mechanical properties of extrudates. The higher the SME input was, the lower the elastic moduli and breaking strength were. This result confirmed that the texture of extruded product was controlled by changing the SME input.

THERMAL AND MECHANICAL PROPERTIES OF POLY(LACTIC ACID) AND STARCH BLENDS WITH VARIOUS LASTICIZERS

Poly(lactic acid) (PLA) has potential for use in disposable and biodegradable plastics. Blending starch with PLAwould increase biodegradability and reduce costs. However, the brittleness of the starch/PLA blend is a major drawback formany applications. The objective of this study was to characterize thermal and mechanical properties of PLA/starch blendswith addition of six plasticizers at various levels. Three groups of plasticizers were used: (1) acetyl triethyl citrate (AC) andtriethyl citrate (TC); (2) poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) of low molecular weight andcontaining an ether group that might interact with PLA; and (3) glycerol and sorbitol, which are miscible with starch. ThePLA and cornstarch were blended at a 60:40 weight ratio by using a labscale twinscrew extruder with addition of theseplasticizers ranging from 5% to 25%. The thermal transition temperatures (glass transition, crystallization, and melting) ofthe extruded PLA/starch blends decreased as AC, TC, and PEG contents increased. The PPG almost had no effect on thetransition temperatures of the blends. Cold crystallization and melting temperatures of PLA increased slightly with increasingsorbitol content. Glycerol reduced the cold crystallization and melting temperatures but had no effect on the glass transitiontemperature. Starch formed a continuous phase in the presence of 25% sorbitol or 15%, 20%, or 25% glycerol. The TC andPEG enhanced the crystallization of PLA. The annealed samples containing glycerol had the highest crystallinity. Asconcentration of AC, TC, PEG, PPG, and glycerol increased, tensile strength and Youngs Modulus of the extruded andmolded blends decreased, and elongation increased in comparison to the blend without plasticizers.

Influence of processing on PVC structure property relationships

AbstractThe influence of the rheology of extruded PVC on the developed morphology and properties was explored. Extrusion conditions for PVC siding formulations with CPE impact modifiers have been investigated on a lab scale twin screw extruder using a factorial model in the experimental design. The independent variables were the barrel temperatures, the die temperature, the hopper feed rate, and the screw rpms. The dependent variables examined include the torque, melt temperature, output rate, fusion level, morphology, and impact resistance. The correlations of the dependent variables with the independent variables were evaluated with the statistical analysis package SASTM. The correlations among several of the dependent variables were also evaluated.