jrups
Abstract : Thermal Resistance Properties of Polyurethanes and its Composites: A Short Review
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Abstract: The nature of starting materials and the conditions of polyurethane (PU) preparation are regarded as the main general parameters that determine PU thermal resistance. The effect of structure and presence of additives were identified as the major general factors on this regard. Structural factors include phase microstructure, i.e. chemical structure, proportion and segregation of soft and hard segments); polyol type (petrochemical or natural oil-based); isocyanate and chain extender type and thermoplasticity of PU. Respect to the effect of additives, the incorporation of fillers is the most direct strategy to increase PU heat resistance. With respect to fiber additives, in general a positive effect is found on improving thermal resistance, although this generalization could not apply, considering the large number of different PU and environmental conditions of usage. Keywords: Polyurethane, thermal resistance, structure, additives, stability. |
Abstract : Thermal Stability of Polyurethanes from Soybean Oil as Natural Source and its Chemical Modifications
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Abstract: In this contribution, a summary of recent publications about the thermal stability of polyurethanes from soybean oil as natural source for polyols was made. From the review, it can be concluded that polyurethanes from natural oil-derived polyols decomposed at a temperature up to 30°C higher than petrochemically-based polyurethanes. Chemical modification of soybean oil for polyol synthesis is mainly based on epoxidation. However, we highlighted the possibility of functionalizing soybean oil by maleinization, a route that was very scarcely studied. Maleinization allows the introduction of labile reactive hydrogen to react with isocyanates for polyurethane synthesis with a broad range of properties. Keywords: Polyurethanes, modified soybean oil, natural polyol, thermalproperties, maleinization. |
Abstract : Mono- and Bis- Maleimide Resins in Preimpregnated Fibres
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Abstract: Fibres are preimpregnated by solutions of mono- and bis-maleimides with comonomers. Imides alone polymerize to resins with too low energies of fracture. In the presence of Methylene dianiline or Aniline Diphenylmethylenebismaleimide reacts via Michael addition to equimolar addition products. When fibres are preimpregnated with these addition compounds alone or in combination with flame retardants, B-prepregs are obtained, which after curing show high glass temperatures and sufficient energies of fracture. 2.5 moles of Diphenylmethylene bismaleimide and 1mol Methylene dianiline or 1mole Aniline react to resins with glass temperatures of 350 and 380°C and energies of fracture of 75 and 100J/m2. The resins contain no carcinogen or blood harming free amines. A one pot reaction starting from Methylene dianiline and Maleic anhydride is possible and more economic. As polymerized bismaleimides possess their imide bonds in the side chain, they are strictly spoken no polyimides with imide bonds in the main chain. Diphenylmethylenebismaleimide and styrene as copolymer react to an insoluble crosslinked polymer. Fibres are preimpregnated with equimolar mixtures of 2- Bromophenylmaleimide and styrene. After curing laminates with 285°C glass temperature and sufficient energies of fracture are obtained. The heat resistant resins are charring polymers and display higher Limiting Oxygen Indices, when the heats of combustion are increased. Differential Scanning Calorimetry determines the temperatures and the heats of glass transition, which indicate that the glass temperature is raised, when the enthalpy is increased and the entropy reduced, which is achievable by Diphenylbismaleimide and 2-Bromophenylmaleimide with their large side groups appropriate for intermolecular forces and steric hindrance. Keywords: Thermodynamic, heat resistant, burning behaviour, brittleness, toxicity. |
Abstract : Innovations in Polymer Applications - Plastic Packaging
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Abstract: Polymer materials are used in several industrial sectors such as, paints and varnishes, packaging, and the automotive sector. The countless applications of this type of material stem from several factors such as lightness and ease of processing when compared to metals and ceramics. The possibility of chemical modification of polymers is worth mentioning, which can result in a new material with mechanical properties superior to those of the original ones. Another unique characteristic of polymer material is related to the ease with which they can be mixed with other elements (vegetable and synthetic fibers, metals, ceramics) to obtain a composite or hybrid material, thus expanding the spectrum of polymer applications. In this sense, the present work aims to show the uses of polymers in the packaging segment, addressing the main physicochemical and mechanical characteristics that are necessary for manufacturing packaging items as well as innovative technologies to obtain those materials. Keywords: Polymer, film, packing, product, researches. |
