R-134a compatible lubricants based on C4-C6 esters of pentaerythritol and polyalkyleneglycol

The results of work intended to produce inexpensive, synthetic lubricants compatible with R-134a using waste carboxylic acids C₄-C₆ as the base are presented in this paper. The suitability of the products synthesised was first evaluated considering their physical and chemical properties, and their thermostability determined by the standard Philipp test (sealed glass tube method). Two ester bases were then selected for further testing — a pentaerythritol esterified with C₄-C₆ monocarboxylic acids and a polyalkyleneglycol similarly esterified with monocarboxylic acids C₄-C₆. The base oils chosen were tested for their corrosive action on metals in the presence of water in different concentrations. The pentaerythritol ester proved to have the most advantageous properties at that stage. The results of the laboratory tests have been corroborated by trials conducted on real refrigerating compressor systems. Only the lubricant that was obtained using pentaerythritol esterified with monocarboxylic acids C₄-C₆ as the base withstood the severe test.     

Synthesis and testing of ester lubricants for use as R‐134a refrigerants

The aim of the present work was to produce inexpensive synthetic lubricants, compatible with R‐134a, using waste carboxylic acids as the starting point. After initial synthesisation of some candidate materials, the suitability of the synthesised products was first evaluated by their chemical and physical properties including thermostability. Two ester bases were selected for further testing — a pentaerythritol esterified with monocarboxylic acids, and a polyalkyleneglycol similarly esterified with monocarboxylic acids C₄—C₆. The oil bases selected were tested for their corrosion effect on metals. The pentaerythritol ester offered the most advantageous properties in these tests. The results of the laboratory tests have been corroborated by trials conducted on real refrigerating compressor systems. In addition, the synthesis of base oils by methyl ester transesterification in the presence of basic catalysts has been examined.     

Influence of thermo‐oxidative degradation on the biodegradability of lubricant base oils

The paper addresses the problem of how the thermo‐oxidative changes in the chemical structure influence the biodegradability of lubricating base oils. The tests were conducted using synthetic polyolesters, polyalphaolefins (PAO 4) and blended polyolesters with 30 wt % of PAO 4. Oil biodegradability was evaluated in accordance with the International Standards Organization (ISO) 14593 test. The thermo‐oxidative degradation consisted of a 24‐hour exposure of the oil samples to the temperature of 150°C in a universal test apparatus at an air flow rate of 15 L/hour. The results have revealed that the thermo‐oxidative degradation of the chemical structure produces changes in the physico‐chemical properties of the base oils and improves biodegradability. The polyolester oils tested were found to be readily biodegradable both before and after thermo‐oxidative tests. PAO 4 oil and its blends with polyolester oils could not be classified as readily biodegradable. The thermo‐oxidative changes in their chemical structures can exert a positive effect on their biodegradability. Copyright © 2008 John Wiley & Sons, Ltd.     

Experience with evaluating biodegradability of lubricating base oils

Biodegradability analysis of lubricants by standardised tests provides valuable information for both legislation purposes and assessment of how chemical structure influences biodegradability. The choice of an appropriate test for evaluating the ultimate biodegradability of oils raises serious problems as the majority of lubricating base oils display a poor water solubility. The paper summarises the experience gained and the results achieved from the evaluation of primary and ultimate biodegradability of lubricating base oils differing in chemical structure, such as rapeseed oil, synthetic polyolester oils, poly(α-olefin) oils (PAO 4 and PAO 6) and the conventional mineral oil. Primary biodegradability was evaluated using the CEC L-33-A-93 test. To evaluate the ultimate biodegradability of oils in an aerobic aquatic environment, use was made of the testing methods OECD 301 B and OECD 310 for ready biodegradability. Oils that fail to fulfil the “ready biodegradability” criterion, e.g. pentaerythrite tetra(sec-capronate) oil (polyolester with steric hindrance around the ester bonds), PAO 4, PAO 6, and mineral oil, were evaluated for inherent biodegradability using the OECD 302 D (draft) test and the OECD 302 B method where the test vessels were prepared via a modified procedure. The oils belonging to this group differred in inherent biodegradability. Thus, PE tetra(sec-capronate) oil reached an extent of biodegradation amounting to 65%, that of PAO 4 and mineral oil being equal to 48% and 38%, respectively. Experiments have shown that ISO 14593 offers a convenient method for evaluating the ready biodegradability of base oils according to OECD 310 and makes it possible to evaluate (with the same apparatus and reagents) the inherent biodegradability of oils when the conditions and criteria recommended by the OECD 302D (draft) CONCAWE test are satisfied.     

Influence of degradation on the film‐forming properties of polyolester oils

The film thicknesses of two polyolester degraded oils were measured over a wide range of temperatures to investigate the influence of degradation on film‐forming properties. The results have been interpreted in the light of the idea that degradation of an ester lubricant can produce two different types of product which have opposing influences on film‐forming properties. One is the formation of smaller, polar molecules, such as acids, which may result in a decrease in effective pressure—viscosity coefficient. The other is the formation of larger, bulky molecules such as sludge, which result in increased pressure—viscosity coefficient. The effective pressure—viscosity coefficient decrease with degradation of the oil thus is made up of an earlier stage involving a series of reactions, followed in a later stage by an increase.     

Structure effect of refrigeration polyolester oils for use in HFC-134a compressors

A study of polyolester oils (POE) for compressors using an ozone-friendly refrigerant is presented here. The effect of the chemical structure of POE was studied in relation to three lubricant properties: miscibility with HFC-134a (CF₃-CH₂F), lubricity (steel-on-steel and aluminium-on-steel contacts), and viscosity. The paper shows the strong structure effect of POE on miscibility and lubricity. Based on the data obtained, some model lubricants were blended, and the performance of these lubricants was assessed on refrigeration test rigs.     

New synthetic esters with a complex structure considered as tribological fluids

The paper presents results concerning synthesis and characterisation as lubricant fluids of some esters of different monocarboxylic acids with variable chain length, along with aliphatic‐aromatic complex alcohols and/or with superior alcohols (exclusive of aliphatic). The monocarboxylic acids taken into account were n‐butyric, n‐octanoic and oleic, respectively, while the alcohols considered were isodecyl and isotridecyl as purely aliphatic, and 2‐phenoxy‐ethanol, 2‐[(o‐sec‐butyl)phenoxy]ethanol and 2‐[(p‐nonyl)phenoxy]ethanol, as part of the complex aliphatic‐aromatic alcohols group. Under these circumstances, it became possible to study the influence of the structure on the main physico‐chemical properties of these synthetic oils as well as on their tribological representative features. The results recorded certified the validity of the proposed research programme. Copyright © 2009 John Wiley & Sons, Ltd.     

Temperature‐dependent effects in base oils: Carbon‐13 NMR spin‐lattice relaxation time and viscometry studies

Carbon‐13 NMR spin‐lattice relaxation time (T₁) data have been used to study the molecular dynamic aspects of base oils with different physical properties. Relaxation time measurements have been carried out on a few model compounds and a number of mineral base oils at various temperatures (273–373 K). Effective correlation time (°_C) and rotational mobility data obtained for the model compounds and base oils have provided evidence of relationships between molecular flexibility and the temperature dependence of viscosity. It is possible to determine the average carbon alkyl chain lengths and the molecular weights of the base oils from the ratio of the T₁ values of C_β and C_int carbons and the optimised value of the microviscosity factor (f_r), respectively. A qualitative correlation between Arrhenius energies (E_a) for microscopic motion and macroscopic bulk properties such as viscosity and viscosity‐temperature characteristics has been observed. Base fluids having better viscosity‐temperature characteristics were also associated with lower values of E_a for micro‐ as well as macroscopic processes.     

Studies of inherent lubricity coatings for low surface roughness galvanised steel for automotive applications

Surface lubricity on TiO₂‐coated galvanised steels can be controlled by solution depositing perfluorooctanoic ( C8 ), lauric ( C12 ) or stearic ( C18 ) acids to avoid lubricating oils/emulsions or substrate pre‐etching to remove surface oxide that add cost and waste. Water contact angles reveal increased surface hydrophobicity on coated samples that correlate with linear friction testing, suggesting water contact angle can be used to screen lubricity compounds. Linear friction testing shows that C12 and C18 lower the coefficient of friction (μ ) by 50–60% compared with uncoated substrates whilst C8 drops μ from 0.31 to 0.22. Surfaces have been characterised by X‐ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy, whilst infrared confirms that as‐deposited coatings contain physisorbed and deprotonated acids chemisorbed through esters and thermal gravimetric analysis confirms increasing loadings from C8 to C12 to C18 . Surface washing removes physisorbed material and lowers μ by increasing surface organisation and alkyl chain packing that enhances frictional energy dissipation through steric quenching. Copyright © 2017 John Wiley & Sons, Ltd.     

New synthetic ester type base oils with biodegradability potential

The present paper presents the results of some research into the production of synthetic ester oils of mixed structure on the basis of citric acid (2‐hydroxy‐1,2,3 propane tricarboxylic acid) with beneficial tribological properties and potential biodegradability. Two series of unsymmetrical triesters have been synthesised by varying the molar relationship between branched aliphatic alcohols from C₄ to C₁₃ along with a special alcohol of a complex aliphaticaromatic structure, namely 2‐(o‐sec‐butyl)phenoxy‐ethanol. Based on this, it has been possible to obtain products with various properties. The introduction of the aromatic function into the structure of these triesters induces interesting features, and the natural source of the citric acid holds potential for having good ecological characteristics, which are intended to be the subject of further research.     

Polymer formation during thermal-oxidative ageing of aviation turbine oils

Oligomers/polymers formed during the thermal-oxidative ageing of ester-based aviation turbine oils have been investigated, using pentaerythritol tetraheptanoate as a model ester. The principal polymer structures in the primary ageing state were revealed by means of chromatographic and spectroscopic methods. The most probable structures are dicarboxylic acid polyesters with variable amounts of α,ω-dicarboxylic acids having chain lengths of C₂ up to C₇ The C⁷-branches also contained ester-bonded hydroxy as well as oxo substituents. Pentaerythritol triheptanoate discarboxylic acid mono esters were active precursors in polymer formation.     

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.     

Extending the retention of friction‐reducing capability in low‐phosphorus engine oils

In advanced fuel‐efficient engine oils containing molybdenum dialkyldithiocarbamate, Mo(dtc)₂, as a friction‐reducing additive, the friction‐reducing capability is gradually depleted with mileage accumulation and is dependent on the presence of other additives, such as zinc dialkyldithiophosphate, Zn(dtp)₂. Indeed, it has been shown that the loss of the friction‐reducing capability of Mo(dtc)₂ coincides with the depletion of Zn(dtp)₂. The next generation of oils will specify a lower phosphorus content (e.g., 0.08% in ILSAC GF‐4 and even lower in the specification after GF‐4) to reduce the detrimental effects of phosphorus on catalyst systems. This will necessitate the use of less Zn(dtp)₂, which could have an adverse effect on the retention of friction‐reducing capability. The aim of this study was to determine if the retention of friction‐reducing capability could be maintained or even increased at 0.05% phosphorus with newer molybdenum trinuclear, Mo₃S₇(dtc)₄, additives. To facilitate the study, a modified laboratory‐based ageing test was developed which correlated with the loss of friction‐reducing capability in the Sequence VIB engine test. This ageing test was used to evaluate model blends of Mo₃S₇(dtc)₄ with Zn(dtp)₂ at 0.05% phosphorus and added antioxidants. The results indicate that it is possible to extend the retention of friction‐reducing capability. However, whether or not it can be extended beyond the current drain intervals is still an open question.     

Biodegradable lubricants — Analysis of metalworking oils and hydraulic fluids by mass spectroscopy

Biodegradable metalworking oils and hydraulic fluids were screened for their base oil composition using a special mass spectrometric technique — direct exposure probe chemical ionisation mass spectrometry (CI(NH₃)-MS). All but one of the hydraulic fluid samples were rapeseed oil or trimethylolpropane trioleate based, the other sample being a neopentylglycol ester trimethylolpropane ester mixture. Ethylhexyl ester of rapeseed oil fatty acids (or similar) was present in some of the metalworking fluids in addition to rapeseed oil, whilst other samples were pure rapeseed oil. In several cases a trimethylolpropane/neopentylglycol ester base was found. Preliminary results for additive isolation/identification show the usefulness of preparative gel permeation chromatography.     

Study of synthetic complex esters as automotive gear lubricants

A number of di‐ and triol‐centered polyols such as 2, 2‐dimethyl‐1, 3‐propane diol, 2, 2‐diethyl‐1, 3‐propane diol and 1, 1, 1‐tris hydroxy methyl propane complex esters have been synthesized using di‐carboxylic acids like adipic and sebacic acids (C₆–C₁₀) and 2‐ethyl 1‐hexanol with indigenous ion‐exchange resin (Indion‐130) catalyst. The applicability of these esters as automotive gear lubricants has been evaluated. The products were found to be compatible with extreme pressure additives. In addition, the products are readily biodegradable. Copyright © 2008 John Wiley & Sons, Ltd.     

Coordinating scheduling with batch deliveries in a two-machine flow shop

In the demanding world of supply chain management, traditional scheduling models which only address the optimization of production sequence at certain stage are often not globally optimized. Rather, the extension, including the distribution stage following the production, can bring a more holistic view to the decision makers. This research focuses mainly on a class of two-machine flow shop problem in which jobs need to be delivered to customers by vehicles after their production stages. Two performance measures—the sum of job completion times (∑C _j ) and the makespan (C _max)—are investigated separately. For the objective of ∑C _j , this study shows that it is strongly NP-hard whether the job sizes are assumed to be equal or not. On the other hand, with regard to the C _max objective, this paper concentrates only on the problem of different job sizes and provides a proof of its NP-hardness. A heuristic method that guarantees to contain a worst-case performance ratio of 2 is developed for the C _max problem.     

European ecolabels for biodegradable hydraulic oils — a challenge to base material producers and formulators

‘Ecolabels’ are a means to guide the user to more environmentally favourable products. With regard to lubricants, the German Blue Angel UZ‐79 and the Swedish standard SS 155434 for biodegradable hydraulic fluids are perhaps the most important. Whereas the Blue Angel is optional, the Swedish standard SS 155434 is a legal requirement: hydraulic fluids not fulfilling the criteria of SS 155434 are not permitted on the Swedish market. Version 4 of SS 155434, which came into effect in July 2000, introduced new and more stringent ecological requirements. In view of the growing importance of the Swedish market for biodegradable hydraulic oils, the authors' company launched a research programme in early 2000 with the aim of offering SS‐155434‐compliant oleochemical base oils by the end of the year. First, the effects and the plausibility of the new assessment criteria for the ready biodegradability of raw materials were studied. A systematic comparison based on chemical oxygen demand (COD) and theoretical oxygen demand (ThOD) evaluations confirmed that unqualified reliance on the COD parameter can lead to false positive evaluations. The studies also showed, however, that results based on COD determined by chemical analysis are valid, provided a suitable oxidation method is used and the completeness of the oxidation is carefully monitored. Moreover, it was shown that the required use of the reference parameter ThOD does not necessarily require complicated elementary analyses of the test substance. Even in the case of oleochemical products with indefinable structural formulas (C‐chain fractions, alkoxylated compounds), structural estimates enabled sufficiently accurate ultimate oxidation values to be calculated. The studies also showed that the restriction to only two degradation test methods is scientifically unfounded. An extension of the approved test methods to include the scientifically accepted CO₂ headspace test and two‐phase closed bottle test would enable existing data to be used without detracting from the environmental standard. On the basis of more recent degradation studies, it has been shown that synthetic esters, especilay various saturated and unsaturated TMP fatty acid esters, satisfy the stringent sriteria of the new SS 155434, Supplementary studies of low‐viscocity XXX‐oils (hydrocrackates) and mixtures of XXX‐oils and synthetic esters indicated that this product class could be optimised to make it satisfy the criteria of the Swedish ecolabel.     

Thermal oxidation behaviour of synthetic oils: Basic studies in the polymerization of polyol ester oils

The oxidation behaviour of synthetic oils has been extensively studied during recent decades, and there is general agreement on both the mechanism and products of the oxidative degradation of oils. However, the other phenomenon of oil ageing, polymerization has been little studied. These polymers are responsible for the increase of viscosity, production of sludge and the formation of deposits. In the investigation reported here, oligomers have been isolated and studied at an early ageing stage. The dependence of viscosity on the degree of polymerization is demonstrated. A polymerization mechanism and a monomer for polyolester oils are proposed and discussed.     

Properties of synthetic oils derived from waste polyolefins

Synthetic oils are mainly used in lubricant compositions meeting strict or special technical requirements. Most synthetic oils presently manufactured belong to three types of oils, i.e. polyalphaolefins (PAO), esters and alkyl benzene derivatives. Elsewhere, the authors have described results obtained in synthesising polyolejin oils starting from olefin mixtures produced by mild thermal degradation of waste polyethylene.^1,2 In the present paper, the dependence of the flow properties of polyolefin oils on the average molecular mass of the starting olefin mixture is discussed, and some preliminary results are given on synthesising alkenyl succinic esters and alkyl benzene derivatives starting from the same raw materials obtained from waste polyethylene.     

Tribological Study Comparing PAG and POE Lubricants Used in Air-Conditioning Compressors under the Presence of CO2

Polyalkylene glycol (PAG) and polyolester (POE) synthetic lubricants are good candidates for air-conditioning systems that work with alternative refrigerants such as carbon dioxide (CO₂). Both synthetic lubricants are widely used in air-conditioning compressors and have been optimized for use with hydrofluorocarbon (HFC) refrigerants. However, it is still not clear which lubricant is more suitable for use in compressors operating with CO₂ as a refrigerant. This study compares the performance of PAG and POE lubricants of the same viscosity (ISO VG 68) used in air-conditioning compressors. The materials used were Al390-T6 disks and hardened steel SAE 52100 pins. The tests were performed using a high pressure tribometer (pin-on-disk configuration) in the presence of CO₂. The results showed that scuffing and wear resistance of Al390-T6 tested with PAG were superior compared to the samples tested with the POE lubricant. Chemical analysis using X-ray photoelectron spectroscopy showed that PAG tends to promote the formation of carbonate layers on the surface, leading to improvement in the tribological performance of the interface.