Study of synthesised ecofriendly and biodegradable esters: fire resistance and lubricating properties

Biodegradable esters have been synthesised using Polyols such as 2‐methyl‐2‐n‐propyl 1,3‐propane diol, 2,2‐di methyl 1,3‐propane diol, 1,1,1‐[tris] hydroxyl methyl propane, 1,1,1‐[tris] hydroxyl methyl ethane and carboxylic acids (C6‐C12) both pure and their mixtures with indigenous ion exchange resin (Indion‐130) catalyst. The products were characterised for their physico‐chemical properties and were evaluated for their lubrication performance. These were then compared with VG‐22 grade fire resistant hydraulic fluids (FRHFs).The products were found to have good potential for use as a base stock for formulations as FRHF of VG‐22 grade. Copyright © 2010 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.     

Eco‐friendly base fluids for lubricant oil formulations

There is an increasing move towards the use of environmentally safe lubricants. However, the development of a common biodegradable base stock that could replace conventional ones is a big challenge. Synthetic lubricants, whether synthetic hydrocarbons, organic esters, or others, all have problems associated with their use. However, in general terms synthetic lubricants protect better, last longer, and outperform their conventional mineral‐based counterparts in certain applications. Future lubricant specifications in view of the demand for improved performance to meet stringent environmental regulations are the main drivers for new technological developments. As part of a study to produce polyol ester lubricant base stocks from C₅ polyols and C₆‐C₁₄ carboxylic acids in the presence of eco‐friendly catalysts, a series of products has been synthesised. A biodegradable lubricant formulation for automotive transmission fluids has been developed based on a synthesised product as a base fluid. This paper reports on the physico‐chemical characteristics and performance evaluation results of this formulation, which is a promising base stock for automotive transmission fluids.     

Complex esters as antiwear agents

Diol centered complex esters using diethylene glycol, 1,3-butane diol, neopentyl glycol, polyethylene glycol (molecular weight 200–1000), 1-phenoxy 2,3 propane diol as centered diols and sebacic acid as dibasic acid with outer monohydric alcohols as 2-ethyl hexanol, 1-benzyloxy propanol-2 and methyl digol were prepared and assessed as antiwear agents in aviation turbine fuels, diesel fuels and light mineral oil. These types of complex esters, in general, were found to be effective antiwear agents.     

Tribochemical Wear of Rail Steels Lubricated with Synthetic Ester-Based Model Lubricants

Headchecks are a common type of damage in heavily loaded curved freight tracks. This paper deals with synthetic ester formulations' ability to prevent damage caused by headchecks through mild tribochemical wear. An experimental study pertaining to wear and friction of two rail steels lubricated by two synthetic ester base fluids, TMP-oleate and TMP-C₈-C₁₀, has been carried out. Six different free fatty acids were used in this study to act as performance additives. Three of the fatty acids were mono-acids with different, straight, carbon chain lengths (stearic acid C₁₈, decanoic acid C₁₀ and octanoic acid C₈), one was a mono-unsaturated straight-chain fatty acid (oleic acid C_18:1) while two were dibasic acids with intermediate carbon chain length (C₉ and C₁₀). Each fatty acid was blended with either ester, one at a time. The tests were carried out by using a high frequency reciprocating friction and wear test machine. In these tests, the gage face/wheel flange contact was simulated, and all tests were conducted in the boundary lubrication regime. An initial contact pressure of 316 MPa and a maximum sliding speed of 0.11 m/s were employed during the tests. The tests showed a wide range of wear rates, as well as different surface features depending on the interactions between synthetic esters, fatty acids and steel. The use of stearic and azaleic acid in lubricating rail steels results in very smooth surfaces with significant differences in their wear rates.     

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.     

Application of waste carboxylic acids to the manufacture of biodegradable polyolester base oils

The results described in this paper represent a contribution towards finding feedstocks, such as monocarboxylic acids, for the production of polyolester base oils. The research has shown that it is possible to obtain a mixture of monocarboxylic (butyric, valeric, and caproic) acids from the waste stream produced by the catalytic oxidation of cyclohexane to cyclohexanone in the industrial production of caprolactam. The mixture of C₄—C₆ carboxylic acids separated from this waste by distillation was used to esterify neopentyl alcohols such as trimethylolpropane (TMP) and pentaerythritol (PE). Thus, polyolester synthesis was strongly dependent on the choice of suitable catalyst and the neturalisation of unreacted acids. Polyolester oils obtained from TMP or PE with monocarboxylic C₄—C₆ acids have better physicochemical properties than conventional mineral oils, namely ISO 10 or ISO 22, including higher viscosity indices, higher flash points, lower pour points, and lower volatilities. In addition, the polyolesters tested are readily biodegradable under the conditions of the CEC‐L‐33‐T‐82 test and the Zahn‐Wellens test.     

Study of biodegradation properties of phthalate esters in aqueous culture conditions

Several kinds of esters are widely used in synthetic lubricants. The evaluation of their influence on the environment is a matter of considerable interest. This paper studies the ultimate aerobic biodegradation of several phthalates, such as dimethyl phthalate (DMP), diethyl phthalate (DEP), di‐n‐butyl phthalate (DBP), di‐n‐octyl phthalate (DOP) and di(2‐ethylhexyl) phthalate (DEHP), and their degrading kinetics by quantitative assessment of the carbon dioxide produced. The production of CO₂ was chosen as the evaluation parameter to determine the biodegradability of phthalates in aqueous solution. A kinetic model was established to describe the biodegradation process of phthalates. The results indicated that biodegradation of phthalates followed the first‐order kinetic equation; the rate constant (k_b) of biodegradation decreased as the carbon number of the alkyl chain increased, and linear phthalates had better biodegradability than branch phthalate. When the initial concentration was over 200 mg/L, a lag phase was evident during the degradation of phthalates, which was prolonged with increased carbon number in the alkyl chain. Easily biodegradable organics, such as glucose, had a favorable effect on the aerobic biodegradation of phthalates. Copyright © 2006 John Wiley & Sons, Ltd.     

Interaction of anti-wear additives with friction surfaces

The effect of esters of phosphonic acids on frictional wear under diverse loads and sliding speeds has been investigated. The efficiency of such phosphonates as anti-wear additives depends on their structure and varies with the frictional modes. Principal groups of phosphonates have been grouped as esters which are ineffective under both high and low loads (esters with no chlorine atoms); esters which are effective under both high and low loads (CCl₃-group containing esters), and esters which are effective under either high or low loads. The interaction of phosphonates with metal (steel) has been studied. Dissimilarity in the efficiency of esters as lubricating oil additives is explained by their different adsorption and chemical actions.     

The effect of gasses on the viscosity of dimethyl ether

Dimethyl ether (DME) has been recognised as a clean substitute for diesel oil as it does not form soot during combustion. DME has a vapour pressure of 6 bar at 25 °C; so pressurisation is necessary to keep DME liquid at ambient temperature. Inert gases are good candidates as pressurising media, but their effect on DME viscosity is unknown.Argon (Ar), nitrogen (N₂), carbon dioxide (CO₂), hydrogen (H₂) and propane (C₃H₈) have been investigated at pressure levels of 12–15 bar. A Cannon-Manning semi-micro capillary glass viscometer, size 25, enclosed in a cylindrical pressure container, of glass, submerged completely in a constant temperature bath, has been used. A distinct reduction of efflux times was found only for the gas, CO₂. The reduction in efflux time was about 9%.The kinematic viscosity of pure DME was determined to be: 0.188±0.001 cSt, 25 °C. A previously reported viscosity of pure DME has been corrected for the surface tension effect. Viscosity determination was initially based on a direct comparison of efflux times of DME with that of distilled water. The calculation gave a revised viscosity of 0.186±0.002 cSt, 25 °C, consistent with the above experimental result.     

Impact of polymer structure and confinement on the kinetics of Zdol 4000 bonding to amorphous‐hydrogenated carbon

The bonding of molecularly‐thin (10 Å) Zdol 4000 films to amorphous, hydrogenated carbon (CH_x) was investigated as a function of the Zdol structure, i.e., the ratio of the perfluoromethylene oxide (C₁) to perfluoroethylene oxide (C₂) monomer units in the backbone. The influence of the C₁/C₂ ratio on the intrinsic mobility of the Zdol polymer was also investigated by computing the energetic barriers to internal rotation about the C–O and C–C bonds in model compounds by both ab initio and molecular mechanics methods. The calculations indicate that increasing the C₁/C₂ ratio increases the relative flexibility of the Zdol polymer. The kinetic results demonstrate that the rate at which submonolayer Zdol films bond to CH_x is non‐classical (time‐dependent) regardless of the Zdol chain stiffness. The Zdol bonding rate can best be described by a kinetic equation of the form, dB/dt=k(t)A, where the rate coefficient, k(t) can be expressed as a power function in time: k(t)= k_B t ^-h. The values of the initial bonding rate constant, k _B, and the functional form of the time dependence, t ^-h, are both strongly dependent on the Zdol backbone flexibility. The magnitude of the initial bonding rate constants generally increase with increasing Zdol chain mobility. A discontinuous change in both the magnitude of k _B and the functional form of the time dependence is, however, observed at 64°C when the C₁/C₂ ratio is increased from 0.97 to 1.08. The bonding rate coefficient scales as t ^-0.5 for the relatively rigid Zdol backbone structures with C₁/C₂ < 1, while a t ^-1.0 time‐dependent bonding rate is observed for the more flexible Zdol backbones with C₁/C₂ < 1. The initial rate constant, k _B, also changes abruptly near C₁/C₂ ≈ 1, with k _B of the flexible Zdol chains (samples with C₁/C₂) being approximately an order of magnitude greater than the more rigid chains (C₁/C₂ < 1). These results indicate that the physical state of the confined Zdol film can be either liquidlike or solidlike depending upon the molecular stiffness of the backbone employed. The t ^-0.5 time‐dependent bonding rate is shown to be consistent with a one‐dimensional, diffusion‐limited reaction from a solidlike Zdol structure, whereas the t ^-1.0 bonding rate results when bonding occurs from a liquidlike Zdol film structure. The temperature dependence of the Zdol 4000 bonding rate coefficient for the Zdol backbone characterized by C₁/C₂ = 0.97 (solidlike at T = 64°C) was found to undergo a transition from a t ^-0.5 time dependence for T < 150°C, to a t ^-1.0 time dependence at T > 180. This transition occurs over relatively narrow temperature range (150 < T < 180°C) and is attributed to a 2D melting of the confined Zdol film.     

Investigation of anti-wear additives for low viscous synthetic esters: Hydroxyalkyl phosphonates

Various synthetic esters are widely applied as lubricating fluid to reduce friction and wear at tribological contact. Among them low viscous synthetic esters are expected to improve fuel efficiency by minimizing the fluid friction. These low viscous esters are composed of short-chain fatty acids. Therefore, low viscous synthetic esters are inherently polar molecules. Since efficiency of anti-wear additives decreases with increase of polarity of the base oil, new additive technology is requested.In this work, hydroxyalkyl phosphates [P(O)(OCHRCH₂OH)₃], and hydroxyalkyl phosphonates [P(OH)_n(OCHRCH₂OH)_3−n, where n=1,2] are proposed as novel anti-wear additives for polar synthetic esters. The anti-wear additives are evaluated under the boundary conditions. The additives prevent wear in polar esters, in which conventional anti-wear additives do not work at all. Interestingly, effects of substituent in additive molecule on anti-wear properties are found. Alkyl and aryl derivatives reduce wear remarkably, whereas allyl derivatives exhibit poor results. It is speculated that the anti-wear inefiiciency of allylic compounds is due to auto-oxidation of the additives.A facile preparative method for hydroxyalkyl derivatives characterizes the present additive system. They are prepared in situ by simply mixing phosphonic acid and substituted epoxides. Flexiblity of lubricant design can be made possible by the present additive system.     

Synthesis and characterisation of antioxidant‐modified esters of dipentaerythritol as lubricating base oil

In this paper, five antioxidant‐modified esters were synthesised through two steps of simple esterification. Antioxidant‐modified multi‐hydroxyl compound was synthesised at the first step, and antioxidant‐modified esters were synthesised at the second step. This kind of esters is useful in many fields, such as lubricating oil and cutting compound, because of two important functions (antioxidant and lubricant) in the same compound. The active antioxidant group attached to these esters was 3‐(3,5‐di‐tert‐butyl‐4‐hydroxy‐phenyl)‐propionic acid. The esters were characterised with Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis. The analytical results of FTIR demonstrates the changes of alcoholic hydroxyl and carboxyl and suggests that this synthesis was feasible. The TG analysis and rotating pressure vessel method show that this kind of esters has excellent oxidative stability. The physical properties of lubricating base oil, such as viscosity, viscosity index, pour point and flash point, suggested that this kind of esters can be used as lubricating base oil. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

Synthesis of some additives from upgraded petroleum residues of lubricant oil refineries

Aromatic extract residues occur as by‐products in petroleum refineries, through the process of refining lubricant oil. These residues are considered as having low economic value, and their disposal may even cause problems for the refineries. The present work looks at upgrading these residues by using them to synthesise different petroleum additives, e.g., antioxidants, ashless dispersants, pour‐point depressants, and flow improvers for lubricating crankcase oils and for fuels. The antioxidants were synthesised by reacting mono‐aromatics with phosphorus pentasulphide (P₂S₅) in the presence of zinc oxide (ZnO). Ashless dispersant additives were synthesised by reacting alkylated mono‐aromatics (using chlorinated paraffin wax as an alkylating agent) with formaldehyde solution (37%) in the presence of polyisobutylene succinimide. Fuel pour‐point depressants and flow improvers can be synthesised by acylating di‐aromatics via a Friedel‐Crafts reaction. Comparative evaluation of the synthesised products with commercial additives showed them to have good comparative performance properties.     

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.     

Investigation of C3S hydration by environmental scanning electron microscope

Tricalciumsilicate (C₃S, Alite) is the major component of the Portland cement clinker, The hydration of the Alite is decisive for the properties of the resulting material due to the high content in cement. The mechanism of the hydration of C₃S is very complicated and not yet fully understood. There are some models that describe the hydration of C₃S in various ways. The Environmental Scanning Electron Microscopy (ESEM) working in gaseous atmosphere enables high‐resolution dynamic observations of structure of materials, from micrometre to nanometre scale. This provides a new perspective in material research. ESEM significantly allows imaging of specimen in their natural state without the need for special preparation (coating, drying, etc.) that can alter the physical properties. This paper presents the results of our experimental studies of hydration of C₃S using ESEM. The ESEM turned out to be an important extension of the conventional scanning microscopy. The purpose of these investigations is to gain insight of hydration mechanism to determine which hydration products are formed and to analyze if there are any differences in the composition of the hydration products.     

Automated focusing in bright-field microscopy for tuberculosis detection

Pulsed‐laser atom‐probe tomography is used to compare the field‐evaporation mass spectrum and spatial distribution of molecular fragments from various poly(3‐alkylthiophene) films deposited on sharpened aluminium specimen carriers using two different deposition methods. Films deposited via a modified solution‐cast methodology yield small fragments with a uniform structural morphology whereas films deposited via an electrospray ionization methodology yield a wide range of fragments with a very non‐uniform structural morphology. The main field‐evaporated chemical species identified for both deposition types were, in order of typical relative abundance, C₂H₅⁺, CH₃⁺, C₂H₄⁺, followed by C₃H_7,8⁺/SC⁺ and SCH⁺. Thick electrospray depositions allowed investigation of the influence of laser‐pulse energy on the analysis. Evidence is presented supporting the presence of a critical laser‐pulse energy whereby changes in film morphology are signalled by the appearance of a new mass fragment at 190 Da.     

New citric esters with aromatic content and a complex structure considered for use as tribological fluids

This paper presents the results of research carried out to produce synthetic ester oils with a mixed structure, based on citric acid, with beneficial tribological properties and potential biodegradability. Two series of unsymmetrical triesters have been synthesised by varying the molar relationship between aliphatic alcohols from C₁, to C₁₃ along with an alcohol of a complex alkyl‐aryl structure, namely 2‐[(p‐nonyl)phenoxy]ethanol. The variation of the principal properties as a function of the length of the aliphatic chain introduced by the aliphatic alcohol and the aromatic content introduced by the alkyl‐aryl alcohol has been assessed. The wide range of viscosities of these triesters demonstrates their versatility, and the natural citric acid origin holds potential for their having good ecological characteristics.     

Preparation and tribological properties of the N‐containing heterocyclic borate esters and Cu microparticles as lubricant additives in base oil

In this paper, four kinds of N‐containing heterocyclic borate esters and polyvinyl pyrrolidone‐protected Cu microparticles were synthesised and characterised. Their tribological properties as lubricant additives in industrial white oil were evaluated using a four‐ball tribometer, and their lubrication mechanisms were investigated by X‐ray photoelectron spectroscopy. The results showed that the anti‐friction and anti‐wear performance of the base oil can be significantly improved by the addition of N‐containing borate esters and Cu microparticles, and they present synergistic tribological effect. Moreover, X‐ray photoelectron spectroscopy results showed a lubricating tribochemical reaction film containing B₂O₃, FeB, FeO, Fe₂O₃ and so on is formed on the worn surface. In addition, Cu microparticles as rolling bearings, which transform sliding friction to rolling sliding and the formation of the Cu microparticles deposited film, are probably responsible for the improvement of tribological performance. Copyright © 2017 John Wiley & Sons, Ltd.