852 resultados para PLASTICS


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Rotational molding suffers from a relatively long cycle time, which hampers more widespread growth of the process. During each cycle, both the polymer and mold must be heated from room temperature to above polymer melting temperature and subsequently cooled to room temperature. The cooling time in this process is relatively long due to the poor thermal conductivity of plastics. Although rapid external cooling is possible, internal cooling rates are the major limitation. This causes the process to be uneconomical for large production runs of small parts. Various researchers have strived to minimize cycle times by applying various internal cooling procedures. This article presents a review of these methods, including computer simulations and practical investigations published to date. The effects of cooling rate on the morphology, shrinkage, warpage, and impact properties of rotationally molded polyolefins are also highlighted. In general, rapid and symmetrical cooling across the mold results in smaller spherulite size, increased mechanical properties and less potential warpage or distortion in moldings. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers.

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Fibre-reinforced mouldings are of growing interest to the rotational moulding industry due to their outstanding price performance ratio. However, a particular problem that arises when using reinforcements in this process is that the process is low shear and good mixing of resin and reinforcement is not optimum under those conditions. There is also a problem of the larger/heavier reinforcing agents segregating out of the powder to lay up on the inner part surface. In this paper we report on studies to incorporate, short glass fibres into rotationally moulded parts. Four different approaches were investigated; direct addition of fibre in between two powder shots, addition of a layer of pre-compounded polyethylene-glass fibre pellets between two powder shots, addition of a layer of pre-compounded polyethylene-glass fibre powder between two powder shots and a single layer of glass-reinforced, pre-compounded powder. Results indicate that pre-compounding is necessary to gain performance enhancement and the single layer part made from glass-reinforced, pre-compounded powder exhibited the highest tensile and flexural modulus.

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This paper details the results from a large European Union rotomoulding research project on the adaptation and development of industrial microwave oven technology to the rotational moulding process. Following computer modelling, an industrial scale microwave oven was specifically designed, manufactured and attached to the drop-arm of a convention rotational moulding machine where extensive moulding trials were carried out. The design and development of the microwave oven and test mould, together with the savings in terms of energy efficiency and mould heating rate that were achieved are discussed.

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The particle size, shape and distribution of a range of rotational moulding polyethylenes (PEs) ground to powder was investigated using a novel visual data acquisition and analysis system (TP Picture®), developed by Total Petrochemicals. Differences in the individual particle shape factors of the powder samples were observed and correlations with the grinding conditions were determined. When heated, the bubble dissolution behaviour of the same powders was investigated and the shape factor correlated with densification rate, bubble size and bubble distribution.

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The melting and densification behaviour of a range of Polyethylenes (PEs) produced from 2 different catalysts, Ziegler-Natta and Metallocene types, were investigated using a novel visual data acquisition and analysis system (TP Picture®), developed by Total Petrochemicals Research Feluy [1]. Differences in the dissolution behaviour of the bubbles were observed and correlations with the material density, densification rate, bubble size / distribution and MFI were determined.

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Rotomolded containers for solvents and hydrocarbons require the use of high-permeability resins such as polyamide (PA). The published studies with this material are very scarce. In this work, a commercial grade of PA11 was rotational-molded using different processing temperatures and characterized with a range of techniques. The study aims at investigating the influence of the processing conditions on the microstructure and properties of molded parts. The results showed that the spherulitic morphology and the mechanical properties are affected by the processing temperature, the optimum processing range being between 220°C and 240°C. Overheating causes a decrease of the impact strength and a severe increase in the formation of pinholes at the outer surface due to polymer degradation and formation of volatile products. The thermo-oxidation reactions occurring at the inner surface of the samples result in the formation of products that absorb in the UV and visible light regions and cause the microhardness and the melt viscosity of the material to increase. The extent and severity of the degradation at the inner surface may be easily assessed by fluorescence microscopy. © 2008 Wiley Periodicals, Inc.

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This paper presents the results from investigations into the differences in moulding with a novel anodised machined aluminium mould material and a conventional machined aluminium mould material. Significant differences in terms of cycletime were observed between the moulding carried out with the anodised moulding and the conventional aluminium mould surface material with no change in the shrinkage, part appearance or mechanical properties noted between either.

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This paper presents the results from investigations into the differences in the rotational moulding and mechanical properties between pigmented polyethylene powder and micropellets. Both high shear and low shear pigment blending methods were examined, as were a range of pigment addition levels. This was followed by a series of mechanical and analytical tests on the rotomoulded articles to determine properties. Whilst micropellets tended to produce a different surface porosity than powder, few bubbles were evident within the wall thickness for both high shear and low shear blending. For high shear blending, with pigment addition levels up to 0.05%, similar impact properties were noticed for both powder and micropellets. Low shear blending resulted in more inconsistent impact values. There were also more visual inconsistencies in articles produced from powder.

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A plasma gas bubble-in-liquid method for high production of selectable reactive species using a nanosecond pulse generator has been developed. The gas of choice is fed through a hollow needle in a point-to-plate bubble discharge, enabling improved selection of reactive species. The increased interface reactions, between the gas-plasma and water through bubbles, give higher productivity. H2O2 was the predominant species produced using Ar plasma, while predominantly  and NO2 were generated using air plasma, in good agreement with the observed emission spectra. This method has nearly 100% selectivity for H2O2, with seven times higher production, and 92% selectivity for , with nearly twice the production, compared with a plasma above the water.

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In vielen Anwendungen der Intralogistik lassen sich Führungssysteme mit Stützrollen finden, die hohen Belastungen ausgesetzt sind. Hierbei werden oftmals Profilträger aus Stahlwerkstoffen als führende Bauteile eingesetzt. Deren Bewegung erfordert aufgrund der hohen Eigenmassen einen erheblichen Energiebedarf. Im vorliegenden Artikel wird die Entwicklung von derartigen Komponenten aus faserverstärkten Kunststoffen beschrieben. Der Fokus liegt auf der Eintragung hoher Kontaktkräfte in das Bauteil. Es werden die notwendigen Anforderungen dargestellt sowie die Entwicklung eines speziellen Rollenprüfstandes erläutert. Zudem beinhaltet der Artikel die systematische Entwicklung neuer Funktionselemente und die Herleitung einer Methodik zur Untersuchung der Belastbarkeit des faserverstärkten Kunststoffes beim Einwirken einer Rolle als Teilergebnisse des Forschungsvorhabens.

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Research in the fields of ceramic pigments is oriented towards the enlargement of the chromatic set of colors together with a replacement for more expensive and less stable organic pigments. Novel non-toxic inorganic pigments have been required to answer environmental laws to remove elements like lead, chromium, cobalt entering in the composition of usual pigments widely used in paints and plastics. Yellow is particularly an important color in the pigment industry and consumption of yellow exceeds that of any other colored pigments. Apart from this, high infrared reflective pigments are now in great demand for usage in coatings, cement pavements, automotives and camouflage applications. They not only impart color to an object, but also reflect the invisible heat from the object to minimize heat build–up, when exposed to solar radiation. With this in view, the present work aims at developing new functional yellow pigments for these applications. A series of IR reflecting yellow pigments have been synthesized and analyzed for their crystalline structure, morphological, composition and optical characteristics, coloring and energy saving applications

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Succinate is a naturally occurring metabolite in organism’s cell and is industrially important chemical with various applications in food and pharmaceutical industry. It is also widely used to produce bio-degradable plastics, surfactants, detergents etc. In last decades, emphasis has been given to bio-based chemical production using industrial biotechnology route rather than fossil-based production considering sustainability and environment friendly economy. In this thesis I am presenting a computational model for silico metabolic engineering of Saccharomyces cerevisiae for large scale production of succinate. For metabolic modelling, I have used OptKnock and OptGene optimization algorithms to identify the reactions to delete from the genome-scale metabolic model of S. cerevisiae to overproduce succinate by coupling with organism’s growth. Both OptKnock and OptGene proposed numerous straightforward and non-intuitive deletion strategies when number of constraints including growth constraint to the model were applied. The most interesting strategy identified by both algorithms was deletion combination of pyruvate decarboxylase and Ubiquinol:ferricytochrome c reductase(respiratory enzyme) reactions thereby also suggesting anaerobic fermentation of the organism in glucose medium. Such strategy was never reported earlier for growth-coupled succinate production in S.cerevisiae.