蛋白质的PEG修饰

蛋白质的化学修饰作为改善蛋白质的物理化学和生物学特性的有效手段,已经得到了越来越多的研究和开发。本文简述了蛋白质PEG修饰的研究概况,涉及PEG化学修饰反应的类型和影响因素,PEG修饰蛋白的性质、应用及局限性。     

介绍一种新型纳米润滑剂

新型纳米润滑剂能溶解于任何矿物、台成油基,甚至植物油基,使润滑机理有了质的改变,由此出现一种全新的薄膜润滑理论.本文介绍新型MWP机械润滑剂的润滑机理、优点、节能效果、经济效益和适用范围.     

滚动轴承的润滑

1．润滑方式 滚动轴承主要采用润滑油作润滑剂。各类矿物油、植物油及合成油都可以作为油润滑剂的基础油，并根据用途不同加入抗氧化剂、极压剂、润滑剂及其他功能成分。矿物油来源丰富、价格低廉、性能优良，是当今润滑油的主流，但它属于不可再生资源，在地球的存量与日俱减；     

纳米微粒在润滑剂中的分散稳定性

论述了可作为载荷添加剂的纳米微粒在润滑剂中分散稳定的理论、表面修饰方法和工艺。提出在研究提高纳米微粒在润滑剂中的长期分散稳定性的同时,要加强纳米微粒在对分散稳定性要求不太苛刻的润滑剂中的应用研究。     

植物油作为环境友好润滑剂的研究概况

对近年来植物油作为环境友好润滑剂的研究状况作了总结。介绍了通过使用添加剂、化学改性、生物改性等方法来提高植物油润滑性能的研究进展，指出国内开展相关研究工作的紧迫性。     

润滑剂对轮轨摩擦与磨损的影响

利用MMS-2A磨损试验机模拟轮轨系统在润滑油、二硫化钼锂基脂、植物油和石墨钙基脂4种润滑剂润滑下的摩擦与磨损行为,研究润滑剂对轮轨副摩擦、磨损特性的影响.结果表明:与干态相比,4种润滑剂均使摩擦副的摩擦因数减小,表面磨痕深度减小,磨损量降低,其中石墨钙基脂的减摩和抗磨效果最好;试验结束后,轮轨试样接触表面的硬度均有不同程度的增加,其中涂有石墨钙基脂的轮轨试样的表面硬度增加最小.     

多糖的化学修饰方法研究进展

作为具有抗氧化、抗肿瘤、抑菌消炎等生物活性的一类大分子物质,近年来多糖类物质引起研究者的广泛兴趣,但部分天然多糖存在溶解性差、活性较弱等问题,为增强其生物活性,可采用化学方法对多糖进行结构修饰。目前化学修饰方法主要集中在硫酸化、乙酰化、羧甲基化、磷酸化、硒化修饰等方面,文章针对化学修饰方法的具体操作及产物活性变化等进行综述,为糖类产品开发利用提供参考和借鉴。     

提高切削性能的植物油基冷却液

加工工艺中采用植物油基冷却液,生产效率可提高20％~30％,刀具的使用寿命可提高50％以上。植物油基冷却液是以植物油为基础的产品,这类冷却液能在切削加工中大幅提高润滑性能。作为一项经过实践验证的技术,自20世纪60年代以来,植物油一直被认为具有超级润滑性能。在这一时期内,提高与水混合的植物油基冷却液的稳定性是一项富有挑战性的工艺技术,也就是说,当时能作为机加工润滑剂使用的只局限于含有各种添加剂的矿物油基冷却液。实际上在直接采用油类的应用领域,大部分都使用植物油。     

钻井液用植物油润滑剂的制备及摩擦学性能研究

为了使钻井液用植物油润滑剂在高压和高温氧化后仍具有良好的抗磨减摩性能,将层状固体润滑剂石墨、蛇纹石加入植物油中,合成了几种含固体润滑剂的钻井液用植物油润滑剂;利用UMT-2球盘式摩擦试验机考察了各润滑剂的摩擦性能;在摇臂钻床上模拟钻探的摩擦工况,考察了合成的润滑剂的抗磨性能,利用扫描电子显微镜观察了钻头的磨损形貌。结果表明,在植物油中添加石墨、蛇纹石可以降低植物油的摩擦因数和摩擦副的磨损,同时可使植物油在高温氧化后仍能保持良好的减摩抗磨性能。     

聚乙二醇黄原酸修饰水溶性铜纳米微粒的制备及其摩擦学性能研究

采用聚乙二醇黄原酸为修饰剂,通过原位表面修饰技术制备得到粒径分布均匀,在水溶液中具有良好分散性及稳定性的铜纳米微粒。将所得聚乙二醇黄原酸修饰铜纳米微粒作为水基添加剂考察其抗腐蚀性能及摩擦学性能。结果表明:聚乙二醇黄原酸修饰铜微粒的加入有效提高了水基润滑剂的承载能力和极压性能,当铜微粒的质量分数为2%时,水基润滑剂的最大无卡咬负荷和烧结负荷分别增加到了274 N和7 840 N;同时聚乙二醇黄原酸修饰铜纳米微粒还可有效提高水基润滑剂的抗腐蚀性能。对磨斑表面进行的EDS及XPS表征显示,磨斑表面形成了含有铜及Fe S的边界润滑膜,该润滑膜能有效减少或避免摩擦表面直接的钢/钢接触,降低摩擦接触压,明显提升水基润滑剂的摩擦学性能。     

Analysis of the pour point of coconut oil as a lubricant base stock using differential scanning calorimetry

One of the major disadvantages of vegetable oils as base stock for lubricants is their high pour points. In this paper the crystallisation behaviour of coconut oil and the effect of additive addition and the chemical modification on its pour point were analysed using differential scanning calorimetry (DSC). Coconut oil showed the highest pour point among the vegetable oils considered in the study. This can be attributed to the predominantly saturated nature of its fatty acid constituents. Addition of additives did not show any significant improvement in the pour point of coconut oil. The chemical modification procedures described in this work have been effective in improving the pour point of coconut oil to some extent. The DSC method used in the present work has been found to be helpful in understanding the crystallisation behaviour of vegetable oils with different fatty acid compositions, the effect of additive addition and the chemical modification on pour point of coconut oil. Copyright © 2008 John Wiley & Sons, Ltd.     

Vegetable oil-based lubricants—A review of oxidation

Vegetable oils are being investigated as a potential source of environmentally favourable lubricants, due to a combination of biodegradability, renewability and excellent lubrication performance. Low oxidation and thermal stability, poor low-temperature properties and narrow range of available viscosities, however, limit their potential application as industrial lubricants. This review addresses oxidation as a limitation of vegetable oil-based lubricants. The basic mechanism of vegetable oil autoxidation is presented, along with methods used to monitor and analyse the products of oxidation. The potential impact of such oxidation products on lubrication performance is discussed. A brief discussion of methods used to assess and improve oxidation stability completes the review.     

Study of some non-edible vegetable oils of Indian origin for lubricant application

Due to growing environmental concerns, eco-friendly processes and materials have become one of the key interests of research and in the area of tribology, natural esters are gaining popularity as lubricants. Natural esters are being used in many applications as eco-friendly lubricant base. In Europe, canola/rapeseed oil and sunflower oil are mainly used, whereas in the USA, soybean oil is in use for formulating environmentally friendly lubricants. Native and genetically modified high oleic varieties of these oils are being widely used. In the Indian scenario, since the above-mentioned oils are scarcely available for industrial applications, there is a need to look for other viable alternatives. Some candidate non-edible vegetable oils of Indian origin were selected which were unexplored or less explored in the field of lubricant application, and their suitability in lubricant application focusing mainly on physico-chemical characteristics, thermo-oxidative stability and lubrication characteristics was studied. These oils were found to be promising candidates for application in lubricants in view of their physico-chemical characteristics and better thermo-oxidative and hydrolytic stability. Copyright © 2007 John Wiley & Sons, Ltd.     

Mixtures of vegetable oils and di‐2‐ethylhexyl‐sebacate as lubricants

Lubricants based on vegetable oils are growing in popularity in various applications. Environmentally friendly, vegetable oils and their derivatives constitute alternatives to mineral‐based lubricants. Soybean oil, sunflower oil and rapeseed oil have better viscosity indices than mineral oils and even some synthetic oils, are biodegradable and have low production costs. However, vegetable oils have disadvantages, such as poor thermo‐oxidative stability due to the carbon–carbon double bonds and poor low‐temperature properties, which limit their use as lubricant base stocks. This study describes new base‐stock oils obtained from mixture of vegetable oils and di‐2‐ethylhexyl‐sebacate synthetic oil, which become lubricants when additives are introduced. These mixtures offer a large range of kinematic viscosities, while their pour points are under −33°C and their flash points over 240°C. The copper strip corrosion test result is 1a. The diameters of wear scars measured under four‐ball testing (40dyn) are less than 1mm. A differential scanning calorimetry study and a thermo‐gravimetric study under a nitrogen atmosphere for the mixed oils are reported. In the former study two‐endothermic processes were observed between −15°C and −50°C. In the thermo‐gravimetric analysis curve the weight loss is specific for each vegetable and synthetic oil component. From these studies a higher thermal stability was observed for vegetable oils than for ester oils, and it was concluded that the mixtures of vegetable and synthetic oils of diester type are physically homogeneous mixtures. The low production cost of lubricants based on vegetable oils makes them attractive alternatives for mineral oil based lubricants. Overall the mixtures of vegetable and ester oils can be competitive base oils for environmentally friendly lubricants. Copyright © 2006 John Wiley & Sons, Ltd.     

A potential biodegradable lubricant from castor biodiesel esters

Worldwide, 12 million tonnes per year of lubricants are disposed of in the environment through leakages, exhausted gas, incorrect disposal, water–oil emulsions and so on. Some are resistant to biodegradation, representing an environmental threat. One solution to modify this situation is the replacement of mineral oils by biodegradable synthetic lubricants. Esters, whose chemical structures are similar to natural triglycerides, are excellent substitutes for mineral oils. Castor oil contains around 90% ricinoleic acid, and as a result, castor oil has a higher viscosity and a lower viscosity index, compared with other vegetable oils. This work was based on the production of biodegradable lubricant base fluids from castor biodiesel esters, using various chemical catalysts to yield products with interesting properties, such as high viscosity index and good oxidation stability, compared with mineral oils. This route to lubricants is safer, more economical and more efficient. Copyright © 2012 John Wiley & Sons, Ltd.     

Metalworking emulsions from industrial vegetable oils

In the present work, an attempt has been made to develop the indigenous formulation for metalworking lubricants by replacing mineral oils partially with non‐edible industrial oils like rapeseed and karanja oil. Metalworking formulations consist of vegetable oil, mineral oil, an emulsifier and commercial additives for better performance. Non‐edible vegetable oils such as karanja and rapeseeds are renewable, biodegradable and cheaper than synthetic fluids. The constituent vegetable oils and mineral oils were evaluated for physico‐chemical characteristics and blended as per the saponification value and viscosity requirements of the reference oils. The so formulated oils are taken as 5% oil‐in‐water emulsion and tested for lubricity, load bearing capacity, particle size distribution, wear test, weld load test and plate‐out test. Performance of all formulated oils was compared with that of the reference oils, and optimized to meet the market requirements. Copyright © 2008 John Wiley & Sons, Ltd.     

Development of ecologically responsive lubricants

As a result of growing environmental concerns, vegetable oils are finding their way into lubricants for both industrial and transportation applications. These oils can offer significant environmental advantages with respect to resource renewability and biodegradability, as well as offering satisfactory performance in various applications. Formulating with vegetable oils does, however, present unique challenges. These are, most notably, the oxidative and hydrolytic instability, and low temperature rheological problems associated with triglycerides. However, through advanced plant breeding techniques, vegetable oils are becoming available which exhibit good thermal and oxidative stability and other improved performance properties. An overview comparing the physical and chemical characteristics of vegetable oils with those of mineral oils, with particular emphasis on their oxidative stability and wear performance, is presented. Development of lubricant formulations for, in particular, farm tractors and hydraulic fluids, using combinations of vegetable oils and additives, will be discussed in comparison with field trial data.     

Determination of synthetic lubricant concentrations in soil during laboratory-based biodegradation studies

The use of synthetic, biodegradable lubricants for two-stroke engines has become widespread due to increased concern over the build-up of hydrocarbons, derived from mineral oil-based lubricants, in the aquatic environment. A method for assessing the biodegradation potential of new lubricants was developed by the Co-ordinating European Council (CEC) for the Development of Performance Tests for Lubricants and Engine Fuels in 1982. However, this method deals only with the aquatic environment. The use of such lubricants in agricultural machinery led to a modification of the CEC method to assess the relative biodegradability of lubricants in soil. After incubation of oil-treated soil in a simple and inexpensive incubation assembly, samples were extracted with solvent and the level of lubricant determined by infrared spectroscopy. The method was found to be both accurate and reproducible, giving excellent recoveries. It compared favourably with a gravimetric method and was so sensitive that it gave appreciable blank values from untreated soils owing to their content of long chain aliphatic natural products. The incubation and extraction methods were used successfully to assess the biodegradability of a range of synthetic lubricants in soil in comparison to a mineral oil-based lubricant and a natural vegetable oil. The synthetic oils were found to degrade more rapidly and extensively than the mineral oil-based lubricant but not as rapidly or extensively as the vegetable oil. Amendment with nitrate considerably enhanced the loss of all the oil tested, indicating the importance of nitrogen availability when assessing the inherent biodegradability of hydrocarbons in soil. As the data generated is from laboratory-based studies the results do not necessarily translate directly to the field situation. However, the method is suitable for screening new materials and for comparative purposes.     

Improvement of thermooxidative stability of non‐edible vegetable oils of Indian origin for biodegradable lubricant application

For environmental reasons, as well as the dwindling source of petroleum, a new class of environmentally acceptable and renewable lubricants based on vegetable oils is available. Even though vegetable oils possess excellent lubricant‐related properties, there are some concerns about using it as lubricant base oil. Still, unmodified and modified varieties of soybean, rapeseed, sunflower and canola oils have been in use in the USA and Europe. In India, with the shortage of edible oil, alternate sources of vegetable oils stocks are being explored. With this aim, a comprehensive study has been conducted earlier in the authors' laboratory. In this study, numerous options of non‐edible vegetable oil sources were explored, and a few potential vegetable oils were studied in the laboratory. It was found that even though the oils performed much better in comparison with other vegetable oils, it still required improvement in thermooxidative stability. Therefore, in the later part of the study, different options were explored to improve thermooxidative stability. With a background on the initial studies of the authors as described above, the present paper deals with the studies on improvement of these non‐edible candidate vegetable oils of Indian origin for lubricant by treating with selected antioxidants for applying them in lubricants. Copyright © 2010 John Wiley & Sons, Ltd.