The effect of recycled polymer addition on the thermorheological behavior of modified lubricating greases

This article deals with the influence of temperature on the rheological behavior of lithium lubricating greases modified with three different types of recycled polymers, high‐density polyethylene (HDPE), low‐density polyethylene, and polypropylene (PP), all deriving from waste plastic recycling plants. Grease formulations containing diverse polymers were manufactured and rheologically characterized. Small‐amplitude oscillatory shear and viscous flow measurements over a temperature range of 25–175°C were carried out. The experimental results obtained suggest that a blend of HDPE and PP could be considered a suitable potential viscosity modifier for lithium lubricating greases in a wide range of in‐service temperature. Thus, the lubricating greases studied modified by HDPE or PP show quite promising results at low or high temperature, respectively. In addition, thermomechanical reversibility has been studied by applying different combined stress–temperature protocols. Lubricating greases containing any of the recycled polymers studied show a significant irreversible structural breakdown when the sample is submitted to temperatures and stresses higher than 75°C and 200 Pa, respectively. Regarding lubricating grease viscous flow behavior, a minimum in the shear stress versus shear rate plots appeared at temperatures above 50°C, more pronounced as temperature increased, resulting from material flow instabilities. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

Recycled and virgin LDPE as rheology modifiers of lithium lubricating greases: A comparative study

In this work, a new application for recycled low‐density polyethylene (LDPE), as rheology modifier of standard lithium lubricating grease formulations, was studied. The effectiveness of this additive was compared with that achieved with a virgin LDPE. With this aim, both types of polymers were added to the formulation during the manufacturing process of greases, following the same standard protocol, to reinforce the role of the thickening agent, the lithium 12‐hidroxystearate. The effect that both lithium soap and LDPE concentrations exert on the rheology of lubricating grease formulations and its relationship with grease microstructure were discussed. Lubricating greases were rheologically characterized through small‐amplitude oscillatory shear and viscous flow measurements. In addition to these, scanning electron microscopy observations and mechanical stability tests were also carried out. In all cases, an increase in soap concentration yields higher values of apparent viscosity and linear viscoelasticity functions. On the other hand, the values of the rheological functions obtained for recycled LDPE‐based lubricating greases are, in general, higher than those obtained for virgin LDPE‐based grease formulations. However, the structural skeleton developed in greases containing recycled LDPE demonstrates less resistance to severe working conditions, showing lower mechanical stability than virgin LDPE‐based grease formulations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Influence of soap/polymer concentration ratio on the rheological properties of lithium lubricating greases modified with virgin LDPE

The main goal of this work was to study the feasibility of using a low-density polyethylene (LDPE) as additive to improve the rheological properties of lithium lubricating greases. The combined effect that both soap and LDPE concentrations exerts on the rheology of lithium lubricating greases and its relationship with grease microstructure were studied according to an experimental design based on the response surface methodology (RSM). Different lubricating grease formulations were manufactured by modifying lithium 12-hydroxystereate and LDPE concentrations. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as mechanical stability tests, were performed. In addition to these, environmental scanning electronic microscopy (ESEM) was used to determine grease microstructure. LDPE was found to be a useful additive to modify grease rheology, acting as filler in the entangled soap network. The values of both apparent viscosity and linear viscoelasticity functions increase with soap and LDPE concentration. However, the addition of LDPE distorts soap microstructural network, yielding greases with lower relative elastic characteristics.     

Synthesis and characterization of isocyanate-functionalized PVA-based polymers with applications as new additives in lubricant formulations

This work deals with the incorporation of reactive isocyanate groups into polymer additives, which could be potentially used to modify the rheological properties of lubricating greases by reinforcing the role of traditional thickening agents. Thus, a batch of partially protected poly(vinylalcohol) (PVA) copolymers was successfully synthesized. Some of their  OH groups were blocked as tetrahydropyranyl (THP) ethers (PVA–THP), while the spare hydroxyl groups were further functionalized with  NCO pendant groups by reaction with 1,6-hexamethylene diisocyanate, leading to several isocyanate-functionalized PVA-based polymers (PVA–THP–NCO), which were tested as rheology modifiers of lithium lubricating greases. The highest protection degree of hydroxyl groups achieved as THP-ether was 58.5% and the recovered polymers were isolated with excellent yields (close to 90% in most cases). NCO-functionalized PVA-based polymers (PVA–THP–NCO) exerted a significant rheological modification in lithium 12-hydroxystearate lubricating greases, increasing the values of the linear viscoelastic functions. The influence of the degree of protection and later functionalization of PVA on the rheological properties of PVA–THP–NCO-additivated lubricating greases is discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

锂基润滑脂热流变特性及其变化机理

采用旋转流变仪探究了变温条件下的锂基润滑脂流动特性和黏弹特性,考察了温度对锂基润滑脂流变特性变化的影响规律,并对热流变过程中壁面滑移效应变化规律进行了讨论。进一步结合锂基润滑脂的微观形貌,探究了锂基润滑脂皂纤维结构与热流变特性变化的关联性。最后基于热流变和皂纤维结构研究结果,分析了锂基润滑脂胶体分散体系结构演化过程,给出了胶体分散体系及壁面滑移效应在热流变条件下的变化机理。     

Impact of polydimethylsiloxanes on physicochemical and tribological properties of naphthenic mineral oil(KN 4010)-based titanium complex grease

Titanium complex greases were prepared by using naphthenic mineral oil and polydimethylsiloxane as the mixed base oil. The effect of polydimethylsiloxane molecular weight and polydimethylsiloxane content in mixed base oil on the physicochemical and tribological properties of titanium complex greases was investigated.As compared to the sole mineral oil-based titanium complex grease, the use of polydimethylsiloxane(H201-350)as a co-base oil increased the dropping point from 310 to 329 °C, decreased the oil separation from 3.7% to 2.3%,reduced the corrosion extent, and obviously improved the tribological properties. When the mixed oil-based titanium complex grease was used as a lubricant, lubricating films of polydimethylsiloxane were probably formed on the surfaces of friction pairs, giving good lubricating property.     

润滑脂流变性影响因素研究现状

润滑脂由于其复杂而独特的流变性能,近年来受到了学界的广泛关注。学者们选用一系列流变参数来定性定量描述润滑脂的流变性能。润滑脂组分、工作条件及制备手段的变化常常会影响和改变润滑脂的流变参数。综述了温度,稠化剂结构、含量及粒度,基础油,添加剂及填料,制备条件,微观结构等因素对润滑脂流变参数的影响情况,总结了润滑脂流变学发展中存在的问题,并对润滑脂流变学未来的发展进行了展望。     

Simple and versatile method for the one‐pot synthesis of segmented poly(urethane urea)s via in situ‐formed AB‐type macromonomers

We present a one‐pot method for the synthesis of poly(urethane urea)s (PUUs) with uniform (monodisperse) hard segments that eliminates tedious approaches to control the exothermic nature of isocyanate–amine reaction, is less sensitive to impurities and involves no isolation of intermediates. Reaction of two moles of hexamethylene diisocyanate with one mole of polycaprolactone of various molecular weights under optimum time and temperature led to NCO‐terminated polyurethane prepolymers. Addition of an equimolar quantity of benzoic acid and excess dimethylsulfoxide at ambient temperature produced quantitative yields of PUUs with high molecular weight. The structure of the PUUs was fully characterized using spectroscopic methods and a reasonable mechanism for the reaction sequences was determined via preparation and characterization of a model compound. Dynamic mechanical thermal analysis data confirmed the phase‐separated structure of the PUUs. Evaluation of stress‐strain curves revealed the wide‐ranging mechanical properties depending on soft‐segment molecular weight. Monitoring the remaining weight and molecular weight of polymers incubated in phosphate‐buffered saline showed hydrolytic degradability with rate depending on soft‐segment molecular weight. Also, a preliminary investigation of the interaction of L929 fibroblast cells with the prepared polymers confirmed no cytotoxicity and acceptable cytocompatibility for the PUUs. Copyright © 2010 Society of Chemical Industry     

重载车辆润滑脂流变及润滑特性对比分析

考察了四种重载车辆润滑脂的流变学性能和摩擦学性能,分析了基础油的种类和粘度、稠化剂的种类和含量以及增粘剂等参数在不同温度下对润滑脂流变学性能的影响;使用流变仪的"三板球"测试组件对四种润滑脂摩擦学性能进行测试,考察不同压力和速度下润滑脂摩擦系数的变化情况。结果表明:在流变学测试中,LX-4和LX-2润滑脂表现出了较好的高温性能,说明这两种润滑脂在高温密封性能和高温粘附性上表现优异,其中LX-4在高低温范围都显示出优良的润滑性能。在摩擦学测试中,LX-2润滑脂表现出较低的摩擦系数,特别是在50 N高压区,LX-2表现出更容易进入薄膜润滑区,润滑膜形成更加容易,摩擦系数下降较快。     

Investigation of thermal degradation of polyethylene–polypropylene-based grease

Thermal degradation of polyethylene–polypropylene-based lubricating grease was studied in a differential scanning calorimeter under static air atmosphere, while weight loss with increase in temperature under inert atmosphere of nitrogen gas was recorded thermogravimetrically. The polymer-based grease exhibited higher thermal stability when compared to that of a soap-derived multipurpose lubrcating grease based on lithium 12-hydroxystearate.     

基于变温下圆管内润滑脂流动特性的表征

为研究温度对润滑脂圆管流动特性的影响规律,采用旋转流变仪分析了润滑脂的流变特性,并基于流变特性研究结果和理论分析建立了润滑脂圆管流的速度场和应力场变化模型。结果表明：润滑脂具有高的屈服剪应力,表现出良好的黏温特性和剪切稀化特性,温度升高润滑脂的屈服应力和表观黏度均下降,表现为更好的流动性;利用MATLAB编程绘图对速度场和应力场分析,给出了润滑脂圆管流动特性规律的影响因素及变化关系;揭示了温度对润滑脂圆管流动特性的影响规律,提高输送介质温度利于润滑脂的输送。     

Formulation and processing of virgin and recycled polyolefin/oil blends for the development of lubricating greases

This work has been focused on the development of polyolefins/oil blends potentially suitable as lubricating greases by studying the effect that some thermo-mechanical processing variables exert on their rheological properties and microstructure. Polyolefin/oil blends have been prepared by dispersing recycled and virgin polyolefins such as high-density polyethylenes (HDPEs) and polypropylenes (PPs) in mineral lubricating oil. Linear viscoelasticity functions have been significantly influenced by processing conditions. The nature of polymers used, specially the content of HDPE, has been found to modify the microstructure of blends yielding lower mechanical stability but, on the other hand, higher values of linear viscoelastic functions.     

Effect of structure modification on rheological properties of biodegradable poly(ester‐urethane)

Biodegradable lactic acid based poly(ester‐urethanes) (PEU) were polymerized and their structure and rheological properties were characterized. The polymerization process comprised two steps: lactic acid monomer was oligomerized to low molecular weight prepolymer, and this was then linked to high molecular weight PEU with chain extender, 1,6‐hexamethylene diisocyanate. The properties of PEU were modified by varying the amount of chain extender from 1.05:1 to 1.35:1 (NCO/OH ratio). The modification was mostly seen in the molecular weight distribution of the polymers, which was broadened from 2.2 to 3.5 as the amount of chain extender was increased. The telechelicity of the prepolymer was found to play an essential role in successful linking of the prepolymer units. In addition, the rheological properties of poly(ester‐urethane) were determined with capillary and dynamic rheometers. All PEU samples were pseudoplastic and broadening of their molecular weight distribution was accompanied by increased viscosity and complex viscosity at low shear rates and increased shear thinning. The temperature dependency of the measurement was pronounced. Rheological measurements also showed that PEU starts to degrade at 100°C and further rise in temperature increases the rate of degradation significantly.     

The dual-solvent extraction of wool grease with hexane and aqueous isopropanol

Hexane solutions of three wool greases of different purities—(a) B.P. grade, (b) a typical commercial grade, and (c) a very crude grease-were extracted by countercurrent flow of aqueous isopropanol (60% v/v IPA) in a 12-stage mixer-settler pilot plant. Fractionation performance was in close agreement with that predicted by an ex-traction model developed previously. Concentrations of detergent in the product greases were 0.00%, 0.00% and 0.43%, respectively. However, even with the crude grease the concentration of detergent oligomers with more than 7 ethoxylate units was zero; free acids content was slightly reduced; and the free cholesterol content was unaffected. The color of the wool grease was improved by solvent extraction, but the bleachability was only marginally improved. The complete removal of detergent oligomers indicates that the extrac-tion technique will improve the water-emulsifying capacity of cer-tain wool greases and overcome the synergism responsible for hyp ersensitivity.     

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

Utilization of olive-residue oil in the formulation of lubricating calcium greases

Calcium greases were manufactured from olive-residue oil in a closed reactor by substituting olive-residue oil for animal tallow. The results of the performance tests applied to the obtained greases showed that their physicochemical and mechanical characteristics are comparable to those of calcium grease manufactured industrially by using animal tallow. The substitution of part of the animal tallow with olive-residue oil increased the thermal and mechanical stability of the grease. Olive-residue oil could constitute, alone or in combination with animal tallow, a raw material in the formulation of lubricating calcium grease.     

Synthesis and characterization of maleic acid polymer for use as scale deposits inhibitors

The problem of scale formation in oil field production facilities is encountered as a result of mixing of injection water (Lias) rich in sulfate with formation water (Ordovicien) rich in barium. 1 A large number of methods have been developed for the prevention of these deposits. In this work, poly(maleic acid) was studied to ascertain its suitability as an inhibitor of barium sulfate scale deposits. It was synthesized by a free radical solution polymerization. Two different initiators were used namely a potassium persulfate and a redox system composed of potassium persulfate/sodium‐hypophosphite monohydrate. Their concentrations were varied to obtain low‐molecular weight polymers. Physical and chemical properties of the polymers obtained were measured by infrared and UV/VIS spectrometry, solubility test, viscosimetry, refractometry, and liquid chromatography. The effectiveness of poly (maleic acid) formulations as scale inhibitor was studied by turbidimetric tests. The most effective inhibitor formulation was found to be that based on poly(maleic acid) prepared via a redox initiating system. This polymer, used at a concentration of 3 ppm, presented the highest effectiveness namely 96% and 88% at room and oil well temperature, respectively, when compared with two commercial inhibitors. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A unifying approach for melt rheology of linear polystyrene

Several studies of melt rheological properties of polystyrene have been conducted over the past 50 years. Several approaches, including empirical models, have been developed to understand the behavior of materials using simple equations. The existing melt rheology models are best suited for high‐molecular‐weight polymers whose T_g does not vary. In this work, a semiempirical viscosity equation has been derived, including the effect of T_g dependence on molecular weight, to describe the melt rheology of low‐molecular‐weight polymers. The equation is derived based on a combination of well‐known concepts, such as the effects of free volume and molecular dynamics on polymer rheology. This provides a better understanding of the rheological behavior in the low‐molecular‐weight regime with respect to temperature and molecular weight. Because of the industrial trend towards lower molecular weight materials for applications such as high solids coatings, this unifying approach, based on the free volume theory with a simple expression, is of extreme practical significance. This equation can predict the zero shear viscosity behavior for different molecular weights, including low‐molecular‐weight regions, and temperatures. Viscosity calculations using the empirical equation agree with published experimental data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2597–2607, 2007     

复合锂基润滑脂的基础研究

锂基润滑脂是由天然脂肪酸锂皂稠化中等粘度的矿物润滑油或合成润滑油制成。复合锂基润滑脂具备了锂基润滑脂优良的机械安定性、胶体安定性和氧化安定性,还具有滴点高等高温使用性能。利用硼酸或己二酸为复合剂合成了两种复合锂基润滑脂,并利用差动热分析仪对其进行滴点的测定,得到最佳配方。研究表明,硼酸或己二酸对提高复合锂基润滑脂脂滴点可以起到一定的的作用,但用一步法的生产工艺更适合硬脂酸／己二酸复合锂基脂的生产。     

Lubricating greases

Summary A brief review has been given of the principal types of lubricating greases and of the fatty materials used therein. No attempt has been made to include a discussion of all conditions which may affect grease structure. However it has been indicated that various factors, as far as the grease itself is concerned, influence performance because they either affect the size and shape of the dispersed particles of the thickening agent, or affect the solubility relationship between the dispersed particles and the oil.