Conceptualisation of an Efficient Particle-Based Simulation of a Twin-Screw Granulator

Discrete Element Method (DEM) simulations have the potential to provide particle-scale understanding of twin-screw granulators. This is difficult to obtain experimentally because of the closed, tightly confined geometry. An essential prerequisite for successful DEM modelling of a twin-screw granulator is making the simulations tractable, i.e., reducing the significant computational cost while retaining the key physics. Four methods are evaluated in this paper to achieve this goal: (i) develop reduced-scale periodic simulations to reduce the number of particles; (ii) further reduce this number by scaling particle sizes appropriately; (iii) adopt an adhesive, elasto-plastic contact model to capture the effect of the liquid binder rather than fluid coupling; (iv) identify the subset of model parameters that are influential for calibration. All DEM simulations considered a GEA ConsiGma™ 1 twin-screw granulator with a 60° rearward configuration for kneading elements. Periodic simulations yielded similar results to a full-scale simulation at significantly reduced computational cost. If the level of cohesion in the contact model is calibrated using laboratory testing, valid results can be obtained without fluid coupling. Friction between granules and the internal surfaces of the granulator is a very influential parameter because the response of this system is dominated by interactions with the geometry

Designing screws for polymer compounding in twin-screw extruders

Tese de doutoramento em Ciência e Engenharia de Polímeros e CompósitosConsidering its modular construction, co-rotating twin screw extruders can be easily adapted to work with polymeric systems with more stringent specifications. However, their geometrical flexibility makes the performance of these machines strongly dependent on the screw configuration. Therefore, the definition of the adequate screw geometry to use in a specific polymer system is an important process requirement which is currently achieved empirically or using a trial-and-error basis. The aim of this work is to develop an automatic optimization methodology able to define the best screw geometry/configuration to use in a specific compounding/reactive extrusion operation, reducing both cost and time. This constitutes an optimization problem where a set of different screw elements are to be sequentially positioned along the screw in order to maximize the extruder performance. For that, a global modeling program considering the most important physical, thermal and rheological phenomena developing along the axis of an intermeshing co-rotating twin screw extruder was initially developed. The accuracy and sensitivity of the software to changes in the input parameters was tested for different operating conditions and screw configurations using a laboratorial Leistritz LSM 30.34 extruder. Then, this modeling software was integrated into an optimization methodology in order to be possible solving the Twin Screw Configuration Problem. Multi-objective versions of local search algorithms (Two Phase Local Search and Pareto Local Search) and Ant Colony Optimization algorithms were implemented and adapted to deal with the combinatorial, discrete and multi-objective nature of the problem. Their performance was studied making use of the hypervolume indicator and Empirical Attainment Function, and compared with the Reduced Pareto Search Genetic Algorithm (RPSGA) previously developed and applied to this problem. In order to improve the quality of the results and/or to decrease the computational cost required by the optimization methodology, different hybrid algorithms were tested. The approaches developed considers the use of local search procedures (TPLS and PLS algorithms) into population based metaheuristics, as MOACO and MOEA algorithms. Finally, the optimization methodology developed was applied to the optimization of a starch cationization reaction. Several starch cationization case studies, involving different screw elements screw lengths and conflicting objectives, were tested in order to validate this technique and to prove the potential of this automatic optimization methodology.Devido à sua construção modular, as extrusoras de duplo-fuso co-rotativas podem ser facilmente adaptadas a sistemas poliméricos que requerem especificações mais rigorosas. No entanto, esta flexibilidade geométrica torna o seu desempenho fortemente dependente da configuração do parafuso. Por isso, a tarefa de definir a melhor configuração do parafuso para usar num determinado sistema polimérico é um requisito importante do processo que é actualmente realizada empiricamente ou utilizando um processo de tentativa erro. O objectivo principal deste trabalho é desenvolver uma metodologia automática de optimização que seja capaz de definir a melhor configuração/geometria do parafuso a usar num determinado sistema de extrusão, reduzindo custos e tempo. Este problema é um problema de optimização, onde os vários elementos do parafuso têm que ser sequencialmente posicionados ao longo do eixo do parafuso de forma a maximizar o desempenho da extrusora. Para isso, foi inicialmente desenvolvido um programa de modelação que considera os mais importantes fenómenos físicos, térmicos e reológicos que ocorrem ao longo da extrusora de duplo fuso co-rotativa. De forma a testar a precisão e a sensibilidade do software às alterações dos parâmetros, diversas condições operativas e configurações de parafuso foram testadas tendo como base uma extrusora laboratorial Leistritz LSM 30.34. Seguidamente, este software de modelação foi integrado numa metodologia de optimização com vista à resolução do problema de configuração da extrusora de duplo-fuso. Para lidar com a natureza combinatorial, discreta e multi-objectiva do problema em estudo, foram adaptadas e implementadas versões multi-objectivas de algoritmos de procura local (Two-Phase Local Search and Pareto Local Search) e Ant Colony Optimization. O desempenho dos diversos algoritmos foi estudado usando o hipervolume e as Empirical Attainment Functions. Os resultados foram comparados com os resultados obtidos com o algoritmo genético Reduced Pareto Search Genetic Algorithm (RPSGA) desenvolvido e aplicado anteriormente a este problema. Com o objectivo de melhorar a qualidade dos resultados e/ou diminuir o esforço computacional exigido pela metodologia de optimização, foram testadas diversas hibridizações. Os algoritmos híbridos desenvolvidos consideram a integração de algoritmos de procura local (TPLS e PLS) noutras metheuristicas, como MOACO e MOEA. Por fim, a metodologia de optimização desenvolvida neste trabalho foi testada na optimização de uma reacção de cationização do amido. Para validar esta técnica e provar o seu potencial, foram realizados vários estudos envolvendo diferentes elementos e comprimentos de parafusos, bem como, a optimização de objectivos em conflito

Enhancing product differentiation through direct extrusion addition

Significant growth is predicted for the bi-axially oriented polyethylene terephthalate films market, in part due to increased number of applications. Besides reduced manufacturing costs and improved material properties Direct Extrusion Addition technology offers faster new product development. Critical to success in retrofitting the technology onto existing film lines is achieving the differing dispersion requirements of flame retardant, opaque and handleable films within the constraints of the film line operating window and conventional equipment. The optimum conditions for process parameters, the role of material properties and screw design required in delivering the desired level of dispersion were identified experimentally. Fundamental understanding of average shear rate/stress coupled with characterisation of mixing via film surface analysis and/or cross-sectional analysis of pellets (shown to adequately describe the filler dispersion in films) yielded promising relationships between the total strain and the degree of dispersion achieved. The results highlighted the importance of screw speed and the minimal impact of the screw configuration. A compromise between mechanically induced chain scission led viscosity reduction and high shear required for mixing was identified. Through the development/understanding of the fundamental principles and processing requirements for good dispersion, the basis for a design guide has been developed for the technology

PP/clay nanocomposites: compounding and thin-wall injection moulding

This research investigates formulation, compounding and thin-wall injection moulding of Polypropylene/clay nanocomposites (PPCNs) prepared using conventional melt-state processes. An independent study on single screw extrusion dynamics using Design of Experiments (DoE) was performed first. Then the optimum formulation of PPCNs and compounding conditions were determined using this strategy. The outcomes from the DoE study were then applied to produce PPCN compounds for the subsequent study of thin-wall injection moulding, for which a novel four-cavity injection moulding system was designed using CAD software and a new moulding tool was constructed based upon this design. Subsequently, the effects of moulding conditions, nanoclay concentration and wall thickness on the injection moulded PPCN parts were investigated. Moreover, simulation of the injection moulding process was carried out to compare the predicted performance with that obtained in practice by measurement of real-time data using an in-cavity pressure sensor. For the selected materials, the optimum formulation is 4 wt% organoclay (DK4), 4 wt% compatibiliser (Polybond 3200, PPgMA) and 1.5 wt% co-intercalant (erucamide), as the maximum interlayer spacing of clay can be achieved in the selected experimental range. Furthermore, DoE investigations determined that a screw speed of 159 rpm and a feed rate of 5.4 kg/h are the optimum compounding conditions for the twin screw extruder used to obtain the highest tensile modulus and yield strength from the PPCN compounds. The optimised formulation of PPCNs and compounding conditions were adopted to manufacture PPCN materials for the study of thin-wall injection moulding. In the selected processing window, tensile modulus and yield strength increase significantly with decreasing injection speed, due to shear-induced orientation effects, exemplified by a significantly increased frozen layer thickness observed by optical microscopy (OM) and Moldflow® simulation. Furthermore, the TEM images indicate a strong orientation of clay particles in the flow direction, so the PPCN test pieces cut parallel to the flow direction have 36.4% higher tensile modulus and 13.6 % higher yield strength than those cut perpendicular to the flow direction, demonstrating the effects of shear induced orientation on the tensile properties of thin-wall injection moulded PPCN parts. In comparison to injection speed, mould temperature has very limited effects in the selected range investigated (25-55 °C), in this study. The changes in moulding conditions show no distinctive effects on PP crystallinity and intercalation behaviour of clay. Impact toughness of thin wall injection moulded PPCN parts is not significantly affected by either the changes in moulding conditions or clay concentration (1-5 %). The SEM images show no clear difference between the fracture surfaces of PPCN samples with different clay concentrations. TEM and XRD results suggest that higher intercalation but lower exfoliation is achieved in PPCN parts with higher clay content. The composites in the thin sections (at the end of flow) have 34 % higher tensile modulus and 11 % higher yield strength than in the thicker sections, although the thin sections show reduced d001 values. This is attributed to the significantly enhanced shear-induced particle/molecular orientation and more highly oriented frozen layer, according to TEM, OM and process simulation results. In terms of the reduced d001 values in the thin sections, it is proposed that the extreme shear conditions in the thin sections stretch the PP chains in the clay galleries to a much higher level, compaction of clay stacks occurs as less interspacing is needed to accommodate the stretched chains, but rapid cooling allows no time for the chains to relax and expand the galleries back. Overall, data obtained from both actual moulding and simulation indicate that injection speed is of utmost importance to the thin-wall injection moulding process, development of microstructure, and thus the resulting properties of the moulded PPCN parts, in the selected experimental ranges of this research

Characterization of Polyphenolics in Cranberry Juice and Co-Products

Historically, cranberry juice has been consumed to prevent urinary tract infections. These and other health benefits, including reduced risks of cancer and cardiovascular disease, are believed to be due to the presence of polyphenolics, specifically flavonoids. Cranberry pomace is the by-product of cranberry processing which consists of seeds and skins. This research focuses primarily on the effects of processing on the flavonoid composition of cranberries and cranberry pomace. First, the concentration of flavonoids during juice processing was evaluated. It was determined that anthocyanins were degraded readily compared to other flavonoids, and a significant amount of flavonoids were retained in the pomace. Additionally, hydrolysis of flavonol glycosides to aglycones occurred due to heat treatment. Next, dried cranberry pomace from industry was characterized based on its proximate and polyphenolic content. The pomace consisted primarily of insoluble dietary fiber and had high concentration of anthocyanins (111.5 mg/100 g DW), flavonols (358.4 mg/100 g DW), and procyanidins of DP 1-6 (167.3 mg/100 g DW). Next, extrusion processing was used to alter the flavonoid composition of cranberry pomace. Extrusion processing increased the amounts of DP1 and DP2 procyanidins and decreased the amounts of procyanidins with DP\u3e4. Total flavonols and antioxidant capacity also increased after extrusion. Alkaline hydrolysis was also used to extract procyanidins from cranberry pomace and alter their composition. When compared to conventional extraction, alkaline hydrolysis increased procyanidin oligomer extraction with the greatest increase being DP1 (14.9x) and A-type DP2 (8.4x) procyanidins. Treatment of the residue remaining after conventional extraction using alkaline hydrolysis resulted in further procyanidin extraction, indicating that procyanidins are not fully extracted by conventional methods. This was confirmed by staining samples of cranberry pomace and residues remaining after conventional extraction and alkaline hydrolysis with dimethylaminocinnamaldehyde to visualize procyanidins. Alkaline hydrolysis was also used on other fruit processing by-products, and it was revealed that these by-products also contained bound procyanidins. This research indicates that cranberry pomace is a rich source of polyphenolics, which could be extracted for nutraceutical purposes. Additionally, the composition of procyanidins in the pomace could be altered by extrusion or alkaline hydrolysis to increase their bioavailability and health-promoting properties

Modulating the glycaemic response of ready to eat extruded snack products utilising dietary fibre and fibre rich waste stream materials.

The aim of this Ph. D. was to utilise commercial dietary fibre (DF) sources as well as DF from food waste streams to create snacks capable of reducing glycaemic response (GR). Obesity is a rising global epidemic due to changes in lifestyle, eating and exercise habits. Consumer demand for convenience has led to greater consumption of highly processed and refined foods so that even though cereal consumption is still high, many of the associated phytochemicals are removed, creating snacks high in energy and low in DF. High energy, low DF, diets have been linked to diabetes, certain types of cancer and heart disease. Health conscious consumers are demanding ‘healthy’ snack foods. In phase one DF rich products (at 5, 10 and 15 % w/w wheat flour replacement levels; total of 23 different samples) were incorporated into extruded snacks to determine the role of DFs in altering their physicochemical and nutritional characteristics. Starch digestion was shown to be lowered with all of high DF snacks (P ≤ 0.05), however, this was not always dose responsive (oat bran and super gum showed no difference with increasing concentrations). Product texture and viscosity parameters were also affected by DF although no general pattern could be observed. In phase two oat bran and psyllium material were incorporated into snack foods at 15 % (w/w) to evaluate potential GR in vitro and also in vivo (intervention study of 12 healthy subjects aged 18-40 yrs, with BMI 22.5-28, a total of 184 finger prick samples). Psyllium extruded snacks achieved attenuated in vitro and in vivo GR, (P ≤ 0.05). Oat bran reduced the in vitro but not in vivo response (P ≤ 0.05). Water absorption was negatively correlated with in vitro digestion (20 min) and in vivo AUC (P ≤ 0.05). In conclusion, the findings from this Ph. D. indicate the mechanism of DF ability to attenuate GR is related to its ability to bind water, and not all DFs behave in a similar fashion. Further research is required to elucidate the role of water in starch digestion and the impact on GR

Concurrent development of a rotationally-symmetric barb joint for modular storage systems through product innovation research

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.Includes bibliographical references (p. 305-307).by Christopher M. Ho.Ph.D

Preparation, characterisation and secondary crystallisation of PHB based copolymers and carbohydrate blends

Poly(hydroxybutyrate) copolymers are sustainable and biodegradable, but they are known to exhibit secondary crystallisation, which severely reduces the ductility of these materials, thus hindering their current commercial use. Therefore, the main focus of this research was to explore a number of strategies to control the secondary crystallisation behaviour of two Poly(hydroxybutyrate) based copolymers. Blends of P(HB-co-HV)(3 wt % HV) with carbohydrate molecules of varying chain lengths were prepared by melt blending, characterised, and monitored over time to assess their capability to reduce secondary crystallisation. Additives were found to hinder the secondary crystallisation process, demonstrated by a reduction in the percentage change of mechanical properties as the concentration and chain length increased. The effect of storage temperature on the secondary crystallisation behaviour of P(HB-co-HHx)(33 % HHx) was also reported. Samples were stored at a range of storage temperatures and the effects on thermal, chemical and mechanical properties discussed. Increasing storage temperature caused the secondary process to occur to a greater extent, with greater increases in the melting temperature recorded in samples stored at 100 $^∘$C (128 $^∘$C - 135 $^∘$C) compared to samples stored at 7 $^∘$C (128 $^∘$C – 128 $^∘$C). Sub-melting point degradation of the material was also noted

Preparation, characterisation and secondary crystallisation of PHB based copolymers and carbohydrate blends

Poly(hydroxybutyrate) copolymers are sustainable and biodegradable, but they are known to exhibit secondary crystallisation, which severely reduces the ductility of these materials, thus hindering their current commercial use. Therefore, the main focus of this research was to explore a number of strategies to control the secondary crystallisation behaviour of two Poly(hydroxybutyrate) based copolymers. Blends of P(HB-co-HV)(3 wt % HV) with carbohydrate molecules of varying chain lengths were prepared by melt blending, characterised, and monitored over time to assess their capability to reduce secondary crystallisation. Additives were found to hinder the secondary crystallisation process, demonstrated by a reduction in the percentage change of mechanical properties as the concentration and chain length increased. The effect of storage temperature on the secondary crystallisation behaviour of P(HB-co-HHx)(33 % HHx) was also reported. Samples were stored at a range of storage temperatures and the effects on thermal, chemical and mechanical properties discussed. Increasing storage temperature caused the secondary process to occur to a greater extent, with greater increases in the melting temperature recorded in samples stored at 100 $^∘$C (128 $^∘$C - 135 $^∘$C) compared to samples stored at 7 $^∘$C (128 $^∘$C – 128 $^∘$C). Sub-melting point degradation of the material was also noted