jrups
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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. |
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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. |
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Abstract: Copolymerization reactions of ethylene with three α-olefins, 1-hexene, 1-octene and 1-decene, were carried out with a new post-metallocene catalyst based on Ti complex with a bidentate saligenin-type ligand I and two co catalysts, MAO and a combination of AlEt2Cl and MgBu2. Ability of the I - AlEt2Cl - MgBu2 system to copolymerize α-olefins with ethylene is far superior to that of the I - MAO system. Reactivity of α-olefins in copolymerization reactions with ethylene decreases in the sequence: 1-hexene>1-octene>1-decene. Both catalyst systems, I - MAO and I - AlEt2Cl - MgBu2, contain several populations of active centers that greatly differs both in the average molecular weights and in composition of the copolymer molecules they produce. Active centers in both catalytic systems show significant tendency to alternate monomer units in copolymer chains. Keywords: Post-metallocene catalysts, molecular weight distribution, compositional distribution, differential scanning calorimetry, nuclear magnetic resonanc.Download Full Article |
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Abstract: The effects of injection temperature, shear and part thickness on the linear shrinkage of injection-molded poly (lactic acid) (PLA) were intensively analyzed using the Autodesk Moldflow software. The obtained results showed that both melt temperature and shear rate had obvious effects on the linear shrinkage of PLA, i.e., the linear shrinkage of PLA increases significantly with the increase of melt temperature and shear rate. In addition, the shrinkage of high-crystallinity PLA was remarkably larger than that of low-crystallinity PLA, and thin-walled parts was larger than thick-walled ones in shrinkage.. Keywords: 3D simulation, poly (lactic acid), temperature, shear rate, thickness, shrinkage.Download Full Article |
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Abstract: The study presents a set of copolymers synthesis based on N-isopropylacrylamide, 2-dimethylaminoethyl methacrylate and itaconic acid comonomers found in different gravimetric ratio, acquired through polymerization in water in the presence of ammonium persulfate as radical initiator. The purpose was to prepare polymeric structure with dual sensitivity to temperature and pH respectively, and able as well to ensure intramolecular strategies for coupling applications of inorganic or bioactive compounds. The polymers composition was confirmed by FTIR and 1H-NMR spectra. The thermal stability of the polymeric compounds was evaluated, and SEM investigations of the polymer morphology are also presented. The polymers dispersions were characterized from the viewpoint of their hydrodynamic radius, zeta potential and conductivity. Keywords: N-isopropylacrylamide, 2-dimethylaminoethyl methacrylate, itaconic acid, radical polymerization, dispersion.Download Full Article |