HZMMA对离子聚合物/聚氨酯(脲)弹性体合金增强机制的研究

采用热失重分析(TG)和原位红外研究了含有不饱和双键和羟基的单甲基丙烯酸锌(HZMMA)的化学反应行为;采用X射线衍射(XRD)、扫描电子显微镜(SEM)研究了HZMMA由于其官能团的反应而发生的结构与形态变化。结果表明,针状的HZMMA晶体在引发剂的作用下能自聚形成大小不等的粒子,证实了HZMMA作为反应型增强剂用于制备离子聚合物/聚氨酯(脲)弹性体合金的可能性。以HZMMA作为增强剂,采用预聚体法,以PTMG-1000/甲基二异氰酸酯(TDI)为原料制备预聚物,与自制的混合扩链剂制备出了含有不同量的离子聚合物聚氨酯(脲)弹性体合金,研究了HZMMA的用量对离子聚合物/聚醚型聚氨酯(脲)合金力学性能的影响。当HZMMA的质量分数为0.2%、过氧化二异丙苯(DCP)质量分数为0.2%时,离子聚合物/聚醚型聚氨酯(脲)合金表现出最优的力学性能。     

Application of nitriding to electroless nickel–boron coatings: Chemical and structural effects; mechanical characterization; corrosion resistance

Electroless nickel–boron coatings, synthesized on mild steel, were submitted to nitridation treatments in varying conditions of pressure, temperature and atmosphere composition. One treatment was carried out under a reduced pressure of a nitrogen-based gas, the other under ambient pressure in a ammonia-based atmosphere.The modifications of the samples’ chemistry after those treatments were investigated by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy), GD-OES (Glow Discharge-Optical Emission Spectroscopy) and ToF-SIMS (Time of flight-Secondary Ions Mass Spectroscopy) analysis. Their structures and morphology were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy. The mechanical properties of the samples were investigated by micro- and nanohardness measurements successively on the free surface of the sample and on polished cross-sections; their roughness and resistance to scratch test were measured. Electrochemical corrosion tests were also carried out.The effects of both treatments were then compared: after the treatment carried out under lowered pressure, the coatings are dense, present signs of solution hardening and are characterized by a high hardness (close to 1600 hv₁₀₀). A combination layer is observable on the samples treated under an ammonia-based atmosphere. This outer layer possesses poorer mechanical properties but the inner layer of the coating presents properties similar to those of vacuum nitrided coatings. The corrosion resistance of the coatings is as good as that of heat treated coatings.     

Tribological performance of pullulan additives in water-based lubricant

Water can be used as an ecological lubricant base if the water-based additives are properly developed to modify its tribological properties. Additionally, those additives should be friend both to human and nature. Pullulan is a naturally occurring polysaccharide, which is biodegradable and non-toxic and widely used in food and nonfood applications. We focus here on understanding the lubrication properties of pullulan, in aqueous solution in absence and presence of sodium salts. Lubrication is studied using a ball-on-disk tribometer with steel–steel surfaces and the friction coefficient and wear are measured in the boundary lubrication regimes. The adsorption of pullulan molecules onto steel surface is determined by measuring wettability of friction couples. It was found that the addition of pullulan improves the lubricating properties of water. The lubricating performance of Pullulan solution could be further improved if sodium chloride or sodium fluoride is added. The tribological results obtained were correlated with the adsorption capacity of pullulan molecules onto steel surface.     

Production of High-Melting Symmetrical Monounsaturated Triacylglycerol-Rich Fats from Mango Kernel Fat by Acetone Fractionation

1,3‐Distearoyl‐2‐oleoyl‐glycerol, 1‐palmitoyl‐2‐oleoyl‐3‐stearoyl‐glycerol and 1‐stearoyl‐2‐oleoyl‐3‐arachidoyl‐glycerol are typical high‐melting symmetrical monounsaturated triacylglycerols (Hm‐SMT) found in cocoa butter improver (CBI). These triacylglycerols help to increase the hardness of chocolate products in tropical climates. In the present study, natural CBI products were produced from mango (Mangifera indica, Linn) kernel fat (MKF) by selective three‐stage fractionation using acetone. The second stearin (fraction I) from the first precipitate of MKF by fractionation for 180 min at 15 °C contained 86.9% of Hm‐SMT, and the third stearin (fraction II) obtained from fraction I by further fractionation for 180 min at 18 °C was enriched with 94.4% Hm‐SMT. High percentages of such triacylglycerols in these products contributed to higher slip melting points (36.5–37.7 °C) than commercial cocoa butter and cocoa butter equivalent (26.7 and 27.9 °C). Also, their differential scanning calorimetry properties and solid fat content values were superior to those in traditional confectionery fats, indicating that the tailored stearins could be used as ideal CBI. In particular, the hard fat blends consisting of 55–70% cocoa butter (CB) and 30–45% fraction II were considered as the preferred heat‐resistant chocolate ingredients. In addition, the mixture of the oleins (fraction III) was rich in diunsaturated and triunsaturated triacylglycerols and showed similar thermal properties to super palm oil, thus making it more suitable as special fat ingredients and modified fat sources.