The potential of using exfoliated graphite nanoplatelets, xGnP
TM, as a reinforcement that can produce multifunctional polymer composites was explored. xGnP–polypropylene (PP) composites fabricated ...by melt mixing using a twin-screw extruder followed by injection molding were investigated for their thermal, viscoelastic and barrier properties as a function of xGnP concentration and aspect ratio. These properties of the xGnP–PP composites were compared to the properties of composites made with PAN-based carbon fibers, VGCF, carbon black and nanoclay. Results indicate that when oriented properly, the xGnP will not only stiffen the composite but also reduce the coefficient of thermal expansion in two directions rather than in one as in the case of aligned fiber composites. Furthermore, the large aspect ratio of xGnP, even at low loadings, increases the oxygen barrier of PP at least as effectively as the commonly used nanoclays and finally, addition of xGnP significantly enhances the thermal conductivity of the polymer matrix.
Cooling and lubrication are very critical to ensure workpiece quality in grinding due to the high friction and intense heat generation involved in the process. Liquid lubricants have traditionally ...been used in flood form or minimum quantity lubrication (MQL), raising however, major environmental and economic concerns. The focus of this study is to evaluate the performance of graphite nanoplatelets as a lubricant in surface grinding. The role of graphite's characteristics such as form, size and concentration; and the effect of the carrying medium and the graphite's application method are determined based on an experimental study. The results indicate that graphite nanoplatelets significantly reduce the grinding forces, specific energy, and improve surface finish during surface grinding of hardened D-2 tool steel. A comparison with results obtained in conventional MQL grinding is also provided. The proper selection of graphite, carrying medium and application method can lead to a low cost, nontoxic and simple alternative to solid lubrication or MQL grinding.
Nanocomposites made of polypropylene reinforced with exfoliated graphite nanoplatelets (xGnP™), are fabricated by melt mixing, polymer solution and coating. Coating is a new compounding method ...proposed in this research, where xGnP and PP powder are premixed in isopropyl alcohol using sonication to disperse the xGnP by coating individual PP powder particles. It is found that the coating method is more effective than the polymer solution method widely used, in terms of lowering the percolation threshold of thermoplastic nanocomposites, and enhancing the probability that the large platelet morphology of xGnP can be preserved in the final composite. The research reported here provides an understanding on how the compounding method used during the fabrication of nanocomposites is important to achieving the optimal flexural properties, electrical conductivity and percolation threshold. This method should have wide applicability to all thermoplastic matrix nanocomposite systems.
We present a new model and extensive computations that explain the dramatic remodelling undergone by a fibrous collagen extracellular matrix (ECM), when subjected to contractile mechanical forces ...from embedded cells or cell clusters. This remodelling creates complex patterns, comprising multiple narrow localised bands of severe densification and fiber alignment, extending far into the ECM, often joining distant cells or cell clusters (such as tumours). Most previous models cannot capture this behaviour, as they assume stable mechanical fiber response with stress an increasing function of fiber stretch, and a restriction to small displacements. Our fully nonlinear network model distinguishes between two types of single-fiber nonlinearity: fibers that undergo stable (supercritical) buckling (as in previous work) versus fibers that suffer unstable (subcritical) buckling collapse. The model allows unrestricted, arbitrarily large displacements (geometric nonlinearity). Our assumptions on single-fiber instability are supported by recent simulations and experiments on buckling of individual beams with a hierarchical microstructure, such as collagen fibers. We use simple scenarios to illustrate, for the first time, two distinct compressive-instability mechanisms at work in our model: unstable buckling collapse of single fibers, and snap-through of multiple-fiber groups. The latter is possible even when single fibers are stable. Through simulations of large fiber networks, we show how these instabilities lead to spatially extended patterns of densification, fiber alignment and ECM remodelling induced by cell contraction. Our model is simple, but describes a very complex, multi-stable energy landscape, using sophisticated numerical optimisation methods that overcome the difficulties caused by instabilities in large systems. Our work opens up new ways of understanding the unique biomechanics of fibrous-network ECM, by fully accounting for nonlinearity and associated loss of stability in fiber networks. Our results provide new insights on tumour invasion and metastasis.
The focus of this study is to determine the effect of the processing method on the mechanical, thermo-mechanical and electrical properties of graphite nanoplatelets (GNP) reinforced polyamide 12 ...(PA12) composites. The two processing methods studied are injection molding (IM) and selective laser sintering (SLS). The composites made by SLS exhibited higher tensile modulus, comparable or better flexural properties and lower impact strength than those made by IM. This enhancement is supported by the higher degree of crystallinity and more effective interfacial interactions observed in the SLS composites compared to those made by IM. At higher GNP content the property enhancement is compromised due to the presence of GNP agglomerates. Furthermore, it was found that the SLS composites filled with 5wt% of GNP exhibited four orders of magnitude higher electrical conductivity compared to their counterpart made by IM which exhibited electrical properties similar to the neat PA12. The understanding of the processing-structure-property relationship investigated here can lead to composites engineered for targeted applications.
The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber ...spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization behavior, thermo-mechanical behavior, and mechanical behavior were determined as a function of CNC content using scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, dynamic mechanical analysis, and tensile testing. Film crystallinity increases with increasing CNC content indicating CNC act as nucleating agents, promoting crystallization. Furthermore, the addition of CNC increased the film storage modulus and slightly broadened the glass transition region.
The aerospace industry has an issue of disposing of waste, unused carbon fiber unidirectional prepreg tapes. This paper explores producing chips using sheet-molding compounding equipment (SMC) for ...conversion into products via compression molding, which are stronger than traditional glass-reinforced SMC parts due to the carbon fiber and high strength epoxy resin. Without a means to convert the continuous tape prepreg into chips, it will not be possible to convert the prepreg into a useful product and provide a way to reduce flow to the landfill and produce less expensive, lighter, and stronger parts for the transportation industry. The cure state of the epoxy resin in the prepreg tapes, which is affected by the amount of time the material has spent stored at elevated or room temperatures, significantly changes the ability of the material to be chopped into short fiber chips. In addition, equipment-related factors affect the material’s ability to be chopped by the SMC equipment. This paper accounts for each of these factors and uses statistical methods to design experiments to investigate the impact each of these material-related and equipment-related factors on the success of the cutting portion of the process. The level of cure, as defined by endothermic peak, glass-transition temperature (T
g
), or heat of reaction/degree of cure, has the greatest impact on the cutting process. For material with a moderate level of cure, the sharpness of the blades in the cutting roller also has a major impact on the success of the process. The cutting pressure, roller speed, and tape tension also have an impact on the success of the process, but impact of these factors lessens for feedstock prepreg with a sufficiently high level of cure. An optimal setup was determined, and general rules of thumb for selecting material and equipment settings were established.
The major issue of raw materials’ depletion, and more specifically, of phosphorous (an important fertilizer) has currently become an emergent aspect due to expected depletion problems needing ...immediate handling. This was the reason for the implementation of the PhoReSe project that aimed to remove and recover phosphorus from the secondary (biologically treated) effluent of a municipal wastewater (biological) treatment plant (WWTP “AINEIA”, located near Thessaloniki, N. Greece), treating the wastewaters of the nearby touristic area. Regarding the phosphorous supplementary removal and recovery treatment options, two methods were examined, initially at the laboratory scale (batch experiments), i.e., (1) the adsorption of phosphorous, and (2) the chemical precipitation of phosphorus. Both methods were further applied at the pilot scale by initially performing the adsorption of phosphorous onto the AquAsZero commercial sorbent, which is a mixed manganese iron oxy-hydroxide, followed by the chemical precipitation of phosphorous implemented after the desorption process of the previously saturated adsorbent. The final precipitate of this procedure was examined as an alternative/supplementary fertilizer, this way returning phosphorus into the natural cycle. These experiments, as applied successfully in at the pilot scale, set the basis for larger-scale relevant applications for similar WWTP facilities.
Fine rejected fraction run of mine (ROM) material, which is rich in magnesite and cannot be further exploited, was mixed with mining wastes by-products of magnesite mine “Grecian Magnesites SA” ...(Gerakini, Chalkidiki, N. Greece), to produce refractories. The exploitation of the ROM in combination with mining wastes was investigated with the application of different thermal treatments, aiming to find the optimum thermal treatment process for upgrading the refractory properties of these samples. The examined firing process parameters, were the two final temperatures of 1300 °C and 1600 °C at different dwell times. Firing shrinkage, water absorption, apparent porosity, bulk density, and mechanical strength were determined, as the main parameters of importance. Furthermore, optical microscopy micrographs were appropriately received, while the mineralogical characterization was determined by X-Ray Diffraction (XRD) measurements. Concerning the optimum firing process regarding final temperature and dwell time for improving refractoriness of mining samples mixed with ROM, the results indicate that the best results were obtained firing at 1300 °C for 120 min. In that thermal treatment process, were observed the minimum values for firing shrinkage, water absorption, and apparent porosity and maximum values for bulk density and mechanical strength, which is the desired scope regarding these properties for improving refractoriness of the samples. The XRD patterns reveal that firing at 1300 °C with increasing dwell time olivine (forsterite) percentage increased, while pyroxenes (enstatite ferroan) decreased. Preheating of the samples at 850 °C did not significantly affect the physical properties of the samples, since firing shrinkage had a small decreasing trend, while bulk density and mechanical strength also decreased, degrading the properties of the samples. Thermal treatment at 1600 °C, showed a negative effect due to the significant reduction of mechanical strength combined with the major increase in firing shrinkage. Also, quantification of mineral phases at 1600 °C is rather misleading, due to the presence of high glassy/amorphous phases.
•Mining waste/by-products combined to produce added-value forsterite refractories.•Forsterite formation is maximized at the thermal treatment at 1300 °C for 120 min.•Optimization of the properties reported when firing at 1300 °C for 120 min.•Preheating of the mining by-products at 850 °C not recommended.•Initial FeO, MgO and SiO2 content affects the final products.
•Mathematical modeling framework for the optimal design of closed-loop supply chain networks.•Flexible configuration of the network constituted of generalized/multifunctional nodes.•Generalized ...nodes’ location and mission is determined by the optimization procedure.•Evaluation of the proposed MILP model in a real case study.•Comparison with mainstream counterpart models revealed superiority in terms of cost.
This paper introduces a general mathematical programming framework that employs an innovative generalized supply chain network (SCN) composition coupled with forward and reverse logistics activities. Generalized echelon will have the ability to produce/distribute all forward materials/products and recover/redistribute simultaneously all the returned which are categorized with respect to their quality zone. The work addresses a multi-product, multi-echelon and multi-period Mixed-Integer Linear Programming (MILP) problem in a closed-loop supply chain network design solved to global optimality using standard branch-and-bound techniques. Further, the model aims to find the optimal structure of the network in order to satisfy market demand with the minimum overall capital and operational cost. Applicability and robustness of the proposed model are illustrated by using a medium real case study from a European consumer goods company whereas its benefits are valued through a comparison with a counterpart model that utilizes the mainstream fixed echelon network structure.
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