Aus der Praxis für die Praxis 1 Introduction and background The base oil industry has seen many changes over the last few years and looking back over 10 to 15 years, the changes in the base oil scene within Europe have been significant. And, if anything, the rate of change has sped up with additional types of base oils becoming available, not at least of which has been the introduction of new and higher specification oils. Recently, a new trading platform has evolved, specifically for the plastics and polymer industry [1, 2]. In fact, today there is a growing concern about the future availability of petroleum-based products. In addition, millions of tons of lubricants are dumped into the environment through leakage, exhaust gas and careless disposal. Some of the wastes are resistant to biodegradation and are threats to the environment. Thus, there are two major issues confronting the lubricant industries today: the search for raw materials that are renewable and products that are biodegradable [3]. During time, it became obvious that for the manufacture of fast biodegradable lubricating greases, vegetable and/ or synthetic ester oils, must be used instead of mineral oils. These products show clear advantages regarding lubricity, corrosion protection, viscosity/ temperature behaviour and as mentioned before, biodegradability. However, natural weak points of these derivatives are thermal and hydrolityc stability. As an additional aspect or consideration at this paragraph, it can be said, in principle, that synthetic esters in this respect and under the aspect of constant quality, are definitely superior to vegetable oils. Besides that, one must underline that esters are naturally polar molecules which give them the affinity for each other in the liquid state. This means they are less prone to evaporation than hydrocarbons, aromatics and ethers. At a given temperature and viscosity, synthetic esters are much less volatile than mineral oils, polyalphaolefins (PAO) and other less polar base oils. 48 Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 * Prof.Dr.-Ing Liviu E. Mirci, University Politehnica Timisoara, Faculty of Chemical Engineering, Timisoara, Romania, E-Mail: livius_eduardus@yahoo.com Synthetic Complex Tetra-Esters Base Oils L. E. Mirci* Vorliegende Arbeit stellt die Ergebnisse betreffend die Synthese und Charakterisierung als bioabbaubare Schmiermittel von einigen komplexen Estern dar. Ausgegangen wird dabei von der Malonsäure, verschiedenen Glycolen, wie Triäthylen, Diäthylen, Monoäthylen, 1,3-Propylen, 1,4-Butylen, 1,5-Pentamethylen und Hexamethylenglykol, wobei die Ölsäure als Endglied oder als ein „Capping Element“ verwendet wird. Auf Grund einer regelmäßigen Alternation oder des Prinzips der sukzessiven Verteilung der polaren und nichtpolaren chemischen Funktionen, gleichmäßig verteilt auf die Länge eines genügend langen Moleküls, entstehen wertvolle synthetische bioabbaubare Schmiermittel. Diese Produkte weisen bedeutende tribologische Eigenschaften auf, wie z. B. einen hohen Viskositätskoeffizienten, hohen Flammpunkt und sehr gute Schmiereigenschaften. Schlüsselwörter synthetische Schmieröle; Malonsäure; Glycole, Ölsäure The paper presents results concerning the synthesis and characterisation as base oils lubricants with biodegradability potential of some complex esters realized on the basis of malonic acid, different glycols, such as triethylene, diethylene, (mono) ethylene, 1,3 propylene, 1,4 butylene, 1,5 pentamethylene and 1,6 hexamethylene glycol, respectively, along with oleic acid used/ considered as an end/ final segment or a capping element. On the basis of a theoretical concept of regular alternation or successive distribution principle of the polar and non-polar chemical functions equally issued/ shared out on the length of a sufficient/ satisfactory long/ large molecule, valuable synthetic ester lubricants/ base oils with biodegradability potential, were performed. These products showed remarkable good tribological properties, such as high viscosity indices, high flash points and very good lubricity features. Keywords synthetic ester base oils; malonic acid; glycols; oleic acid. Kurzfassung Abstract T+S_1_17 13.12.16 07: 53 Seite 48 Aus der Praxis für die Praxis One must also emphasize that synthetic lubricants are not an attempt to recreate mineral oil. It should be an impossible task to identify and synthesize all the mineral oil hydrocabon structures and mix them together to make a synthetic mineral oil. To come close would cost a fortune and its only use would be as a museum piece. There are many other structures in addition to hydrocarbons, such as esters, polyethers, silicones and halogenated fluids, which did not even occur in mineral oil but have unique and useful lubricating properties. Within each of these classes a variety of structures can be created with properties ranging from poor to excellent. Only those structures with particularly useful tribological properties are chosen for synthesis [4]. It should be remembered, however, that individual synthetic lubricants cannot be all things to all machines. One type of base stock may be perfect for one application but not good for another. A certain structural change may enhance one property at the expense of another. Additive differences in the same base stock can make or break a product. It is the lubricant formulator’s job to select the correct base stock and additive system so that the synthetic formulation shows measurable application benefits over mineral oils. The promise of synthetics has generated considerable research efforts to this end in recent years. This has resulted in in a broad spectrum of products which, in most cases, depend on unique additive systems to fully realize that promise [4]. Assured long-term availability of synthetic products enables the development of advanced designs whose successful operation depends on the properties of a synthetic. Ester-based lubricants, for example, are used in essentially all commercial and military jet engines due to the high temperatures encountered and mineral oils are out of this picture. The cost of a lubricant fill, even with synthetics, is small compared with the development and production costs of most equipment, and, as the engineering properties of synthetics become better appreciated, the trend to exclusive use of synthetics in certain applications will increase [4]. The review of the literature of the last several years offers some references that fall in this frame of interest. Thus, biodegradable lubricants and their production via chemical catalysts, represents the subject of an interesting paper. The main research emphasis has been placed on ways to produce biolubricants with suitable viscosity and liquid-state temperature range, and this aim was based on castor oil [3]. An US patent describes the production of synthetic biodegradable lubricants and functional fluids. More particularly, this invention relates to biodegradable synthetic oils which exhibit improved lubricity and anti-wear properties and also satisfy environmental standards for aquatic toxicity. The present invention is based on the discovery that esters of certain polyols with C 12 -C 28 carboxylic acids are highly effective as lubricity additives when combined with a base oil ester of an alcohol and a C 5 - C 10 carboxylic acid, which can be linear or branched, aromatic or aliphatic. This ester combination provides an oil which is a suitable biodegradable lubricant or functional fluid and exhibits lubricity and anti-wear properties [5]. A study of pentaerythritol tetraoleate ester as industrial gear oil was reported and the product was found to have good potential for use as a base stock for formulation as extreme pressure (EP) type of industrial gear oil VG-68 [6]. Ester based lubricants derived from renewable resources represent the theme of a study and this reports that the oxidation stability of saturated based ester formulation is better compared to the unsaturated ester based formulation. Especially regarding the rapeseed oil based formulation. The sensitivity to oxidative attack is caused mainly by multiple unsaturated (double) bonds present in the fatty acid part of the molecule and also by the “beta-CH group” of the glycerol. Ester based oils formulations exhibit less friction than mineral based oil, while unsaturated based synthetic ester formulation exhibits the best antiwear protection, especially in the boundary lubrication regime [7]. An elaborated study deals with the biodegradability testing of synthetic lubricants-effects of additives and usage. The results reported clearly show that the mineral oil is far less biodegradable than the ester oils and that their biodegradability is not affected by usage. Biodegradability of the ester oils is mainly depending on the characteristics of the base fluids and not affected by the additives. Antioxidants are influencing stability respectively biodegradability indirectly, since they prevent oxopolymerization effects. In this context, the antioxidants ensure ready biodegradability and have a positive effect on the environmental fate of synthetic ester lubricants [8]. The behaviour of esters in blend and its possible application was studied and it was found that a mixture of 32: 68 weight ratio of pentaerythritol-tetra-oleate (PETO) and dioctyladipate (DOA) was assigned as a suitable one to be used in two diesel engines [9]. A review of non-edible oil as a source of bio-lubricant for industrial application was published recently, and it pointed out that these materials present consistent advantages such as high lubricity, viscosity-temperature relationship, low lubricant consumption, energy efficiency combined with public health, safety and environmental contamination, more than offset the disadvantages of initial costs in most of these applications. It has been suggested that modified and stabilized oils of wasteland and forest origin and other non-edible oils and their che- Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 49 T+S_1_17 13.12.16 07: 53 Seite 49 Aus der Praxis für die Praxis mically modified derivatives, can be produced at relatively cheaper cost than similar oils marketed in the developed world and can be introduced in India with immense environmental and performance benefits [10]. Much attention is also recorded in the last years literature in order to understand the mechanism of action of phosphate esters, thiophosphate esters and metal thiophosphate which have been used as lubricant additives for over 50 years. The mechanisms of these materials interacting with a range of iron and steel based bearing material are examined [11]. By analyzing the most representative directions of research recorded, one can observe that there is a constant effort in order to realize biodegradable lubricants, strongly requested by the market. These offered examples also indicate that this goal is accomplished either via chemical alteration of a triglyceride molecule of a vegetable oil, or via the realization of various esters, with more or less biodegradability capability. One can also firmly remark that, almost exclusively, the long, unsaturated chain (oleic, being the most representative) is responsible for the valuable, unique characteristics of vegetable oils, when considered as biolubricants. Any chemical modification of their structure will obviously diminish drastically (even up to extinction) the intrinsic features of the considered/ discussed vegetable oil. Under this situation we have considered a new route of research. That is: We realized an absolutely new class of special complex (tetra) esters which contain the valuable part of a triglyceride, that is the long, unsaturated aliphatic chain, mainly of oleic type, as such, that is unaltered or without any chemical modification. By using an original principle, unreported in the literature, which means the regular alternation or the successive distribution of the chemical polar functions (in fact, ester bridges) with the non-polar ones (aliphatic segments, saturated and/ or unsaturated hydrocarbon chains), equally distributed on the length of a sufficient/ satisfactory long/ large molecule, valuable complex esters have been synthesized. In an essential general schematic representation the situation could be described/ depicted by the following graphic form: ---------O--------O--------O--------O-------where: --------represents the non polar (aliphatic chain) chemical function O represents the polar chemical function (esteric group) Under this way, by arranging in an uniformly alternating manner the polar chemical function groups with the nonpolar ones, or by assembling these chemical functions in order to be equally distributed on the length of a long/ large molecule, and by observing that the unsaturated long aliphatic chain obtained/ derived from natural vegetable oils (oleic rest) blocks / closes both ends of this realized molecule, one can expect from these compounds at least valuable lubrifying properties. In a more suggestive representation, this new conceived principle could be visualized within the following graphic form shown in Figure 1, in which the position of a lubricant and its supposed mechanism of action are also imagined/ represented. On the occasion of some recent (2012, 2014) International Congresses, held in Germany (Intern. Colloquiums on Tribology, Stuttgart/ Ostfildern) we have firstly presented/ proposed this elaborated representation, defined/ called consequently as the “myriopod (myriapod) concept” [12,13]. By using the principle mentioned above, we have realized some special complex synthetic ester lubricants of an elaborated tetraester type on the basis of malonic acid, oleic acid, considered as an end/ final segment or a capping element, and different glycols, respectively, with biodegradability potential. These products are defined by the general formula (I): R - COO - A - OOC - B - COO - A - OOC - R (I) where: A = radical of (mono) ethylene, 1,3 propylene, 1,4 butylene, 1,5 pentamethylene, 1,6 hexamethylene, diethylene and triethylene glycol, respectively B = malonic acid radical -CH2 - R = oleic acid radical, CH 3 -(CH 2 ) 7 -CH = CH-(CH 2 ) 7 - For sure we must underline that the use/ choice of oleic acid radical as an end/ final or a capping element was not 50 Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 Figure 1: The regular alternation or successive distribution principle, the “myriopod (myriapod) concept” T+S_1_17 13.12.16 07: 53 Seite 50 Aus der Praxis für die Praxis fortuitous, and this reason was firmly grounded on the well-known opinion that this part of the vegetable oil confers them such valuable lubricant properties. On the basis of this program, and by evaluating these new created lubricant models, it becomes possible to quantify the influence of different chemical functions that are present in each considered molecule on overall properties, and we also could investigate the variation of the representative tribology properties as a function of the general chemical structure, that is of the variation in length/ structure brought in by the chosen glycol. The synthesized products showed some excellent tribological properties, such as high viscosity indices, very good/ high flash points and remarkable lubricity properties. The results of some of our attempts were firstly presented, for instance, in an International Congress in Singapore [14], when the acid “B” was adipic acid, while the specific structure of these malonic derivatives, as well as the synthesis procedure, were protected by a patent [15]. Note: We have also produced the so-called “reversed series” of such complex esters, that is when “B” in formula (I) was a glycol, while “A” was malonic acid and “R” was isotridecanol, which results will be published subsequently. We must underline that the results of our researches were reported accordingly in the case of series of adipic and sebacic acids, respectively [16-19], while for this series some of the first results were presented in an International Congress [22]. 2 Experimental The glycols used, that is (mono) ethylene, 1,3 propylene, 1,4 butylene, 1,5 pentamethylene, 1,6 hexamethylene, diethylene and triethylene glycol, respectively, were pure chemical samples supplied by Merck, as well as malonic acid, while oleic acid was purchased from Aldrich. The synthesis of these special complex esters was performed in a solution esterification process, by using an aromatic solvent, which acted also as an azeotropic agent for the extraction of water (toluene, preferably), within either an autocatalytic system or by using solid a catalyst, via two steps, according to a specific method described elsewhere [20,21]. The adequate purified products were characterized by chemical and physical indices specific to this class, while the rheological characteristic tribological features were determined by using standardized techniques. Thus, dynamic viscosity was measured by means of a rotation viscometer (Rheotest Type RV, VEB Prüfgerate-Werk Medingen/ Dresden, Germany), at 20 °C, measuring device S1, shear rate within the interval 1.6- 1310 / s. The four ball test was accomplished on a SETA machine (SETA-Shell Four Ball Lubricants Tester, Stanhope Seta, England), according to ASTM 2783-03. Kinematic viscosity was determined with an Ubbelohde viscometer (Schott-Geräte GmbH, Hofheim, Germany) according to ASTM D 445-06, while the viscosity index,VI, was calculated from the data, conformably to ASTM 2770. The pour point was measured according to ASTM D 97- 06, and the flash point according to ASTM D 92-05. Note that in order to facilitate the reading of tables and make easier the identification of products, a coding system was used involving an abbreviation principle by taking into account the glycol used which represents in fact the only variant factor of the chemical structures of these derivatives, and also by mentioning the abridged forms MAL and OL, with the purpose that all chemical factors should have been considered. Consequently, the denominated terms are the following: MAL-(mono)-ethylene-OL, MAL-1,3-propylene-OL, MAL-1,4-butylene-OL, MAL-1,5 pentamethylene-OL, MAL-1,6 hexamethylene-OL, MAL-diethylene-OL and MAL-triethylene- OL, respectively. 3 Results and Discussion The main chemical and physical values of this series are presented in Table 1. From the data recorded in this table one can observe the following: (1) The molecular mass presents values between 720 and 896 mass units, which falls in the usual domain of synthetic oils. (2) The density shows a remarkable smooth variation, being a function of the long aliphatic chain brought in by the glycol. However, the high content in oleic acid radical, long aliphatic chain, sets the fashion of the very close values recorded, and that is in good agreement with theoretical presumptions. In the same time this smooth variation emphasize the high purity level of these complex synthetic esters. (3) The refractive index follows a similar behavior being not able to record/ discern a logical variation. This fact is also explainable, in general, by the high molecular mass of these derivatives and by observing that the variation is due to the content of glycol rest, which has a small Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 51 T+S_1_17 13.12.16 07: 53 Seite 51 Aus der Praxis für die Praxis 52 Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 Table 1: Values of the main physical-chemical characteristics No. Parameter Molecular Molecular Density, Refractive Dynamic Code formula mass g/ cm 3 , 20 °C index, n 20 D viscosity, mPa∙s 1 MAL-(mono) C 43 H 76 O 8 720 0.9112 1.4662 40.1 ETYLENE-OL 2 MAL-1,3 C 45 H 80 O 8 748 0.9242 1.4675 42.0 -propylene-OL 3 MAL-1,4 C 47 H 84 O 8 776 0.9255 1.4683 47.3 -butylene-OL 4 MAL-1,5 C 49 H 88 O 8 804 0.9198 1.4672 45.6 -pentamethylene-OL 5 MAL-1,6 C 51 H 92 O 8 832 0.9160 1.4680 57.3 -hexamethylene-OL 6 MAL-diethylene-OL C 47 H 84 O 10 808 0.9436 1.4668 53.0 7 MAL-triethylene-OL C 51 H 92 O 12 896 0.9495 1.4670 47.7 Table 2: Representative tribologic parameters No. Parameter Kinematic viscosity, Viscosity Flash Pour mm 2 / s index, point, point, Code 40 °C 100 °C VI °C °C 1 MAL-(mono) 17.40 4.73 214 173 -8 -ethylene-OL 2 MAL-1,3propylene-OL 22.26 5.77 222 195 -4 3 MAL-1,4 butylene-OL 25.36 6.39 223 202 -1 4 MAL-1,5 -pentamethylene-OL 25.15 6.08 205 205 -12 5 MAL -1,6 31.34 6.97 193 204 0 -hexamethylene-OL 6 MAL-diethylene-OL 24.13 5.52 177 197 -15 7 MAL-triethylene-OL 24.40 5.81 195 203 -23 Table 3: Four ball test No. Parameter Wear scar diameter, mm, 20 daN, 100 min Base oil Additivated oil Code 1,0 % Zn 1,0 % dithiocarbamate dithiophosphate ashless 1 MAL-(mono)ethylene-OL 0.60 0.60 0.55 2 MAL-1,3 propylene-OL 0.40 0.40 0.40 3 MAL-1,4 butylene-OL 0.40 0.40 0.40 4 MAL-1,5 pentamethylene-OL 0.55 0.50 0.45 5 MAL-1,6 hexamethylene-OL 0.60 0.50 0.45 6 MAL-diethylene-OL 0.60 0.55 0.50 7 MAL-triethylene-OL 0.50 0.45 0.40 T+S_1_17 13.12.16 07: 53 Seite 52 Aus der Praxis für die Praxis weight contribution to the global mass. Refractive index underlines, again, the high level of purity of these products. (4) The dynamic viscosity follows a logical rule which means that it presents progressive increasing values as the length of the glycol used (that is implicitly the aliphatic content) increases. Generally, the values recorded are reasonable small. The values of the physical and rheological characteristics that are important with respect to the tribological properties, are included in Table 2. First of all, one can easily remark the excellent level recorded for the viscosity index, VI, with values ranging from 177 up to 223. This behavior means a very good dependence/ relationship of the viscosity versus temperature, which signifies, mainly, that temperature has a little influence on the viscosity, and this fact is a basis criterion as regards the choice of a lubricant which has to prove its application versatility. The values recorded for the flash point are also very good, the maximum value registered being 205 °C. As for the pour point, the values level is reasonable good, ranging from 0 °C to -23 °C. The complex structure of these derivatives has a substantial contribution for this behavior. To check the lubricity properties of these complex synthetic esters, some four-ball tests were performed, and the results of these measurements are recorded in Table 3. As one can see from this table, when these compounds are evaluated as (simply) base oils, that is without any anti-wear additive, they perform very well, by observing also that the values recorded fall in a homogeneous interval. When additivated, some of the terms show improved values, to a certain extent. One can also remark that they show a good compatibility with the additive system used. 4 Conclusions On the basis of the regular alternation or successive distribution principle of the polar and non-polar chemical functions, equally distributed on the length of a sufficient/ satisfactory long/ large molecule, principle that could be integrated in a so-called myriopod (myriapod) concept, some complex synthetic esters, considered as synthetic base oils with biodegradability potential, built on the basis of malonic acid, oleic acid which is considered/ used as an end/ final segment or a capping element, and by using different glycols such as (mono) ethylene, 1,3 propylene, 1,4 butylene, 1,5 pentamethylene, 1,6 hexamethylene, diethylene and triethylene glycol, respectively, were synthesized and evaluated as tribological fluids. These absolutely new compounds show excellent values for the viscosity index, VI, with values which are ranged from 177 up to 223 units.They also possess very good/ high values for the flash point, the best value being 205 °C, while the pour point presents also good values. On the other hand, this elaborated structure of these complex (tetra) esters permitted to reach a very good level of lubricating characteristics, as proved by the four-ball test. By taking into consideration the overall features described above of these special conceptualized absolutely new complex synthetic esters, considered as base oils with biodegradability potential, one can consider that the theoretical premises that have been considered, or the fundamental principles that grounded the whole program, were fully certified/ validated by the remarkable good level of general properties of these compounds. Acknowledgements Special thanks must be addressed to our former students Prof. Dr.-Eng Waltraut Brandl, Prorector at Gelsenkirchen University, Germany, and to Dr.-Eng Livius Cotarca, Scientific Director, Head of R&D Zambon Group, Italy, respectively, for their valuable support in order to acquire the raw materials used in this work, as well as to Dipl.-Eng Victor Boiangiu Head of Analytic Department at ICERP Institute,Ploiesti, Romania, for performing the specific tribological tests. References [1] Masson R., Europe: Last of the Group I Clubs ? , Lubes’n Greases Europe-Middle East-Africa, 2015, June,p.6. [2] Masson R., (Ex) Change for the Better? Lubes’n Greases Europe-Middle East-Africa, 2015, August p.6. [3] Cavalcanti da Silva J.A. Biodegradable Lubricants and their Production via Chemical Catalysis, Tribology-Lubricants and Lubrication, 2011, October, pp 185-200. [4] Jackson A., Synthetic Versus Mineral Fluids in Lubrication, International.Tribology Conference, 1987, Melbourne, Australia, December 2-4, p.2. [5] Hartley R.J., Duncan C.B. and Tiffany G.M, Synthetic Biodegradable Lubricants and Functional Fluids, 2000, US Patent 6054420, April 25, 2000. [6] Nagendramma Ponnekanti, Study of Pentaerythritol Tetraoleate Ester as Industrial Gear Oil, Lubrication Science, 2011, Vol. 23, pp 355-362, DOI: 101002/ ls. 161. [7] Krzan B. And Vizintin J., Ester Based Lubricants Deriwed from Renewable Resources, Tribology in Industry, 2004, Vol. 6, No 1&2, pp 58-62. Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 53 T+S_1_17 13.12.16 07: 53 Seite 53 Aus der Praxis für die Praxis [8] Eisentrager A., Schmidt M., Murrenhoff H., Dott W. and Hahn S., Biodegradability Testing of Synthetic Ester Lubricants-Effects of Additives and Usage, Chemosphere, 2002, Vol. 48, pp 89-96. [9] Langeroodi H.S. and Semnani A., Behavior of Esters in Blend and its Possible Application, African Journal of Pure and Applied Chemistry, 2009, Vol. 3 (11) November, pp. 241-246. [10] Chauhan P.S. and Dr. Chhibber V.K., Non-Edible Oil as a Source of Bio-Lubricant for Industrial Application; a Review, International Journal of Engineering Science and Innovative Technology (IJESIT), 2013, Vol. 2, Issue 1, January, p 299. [11] Johnson D.W. and Hils J.E., Phosphate Esters, Thiophosphate Esters and Metal Thiophosphates as Lubricant Additives, Lubricants, 2013, Vol. 1, pp. 132-148, DOI: 103390/ Lubricants 1040132. [12] Mirci L.E., New Sebacic Complex Ester Lubricants/ Base Oils with Biodegradability Potential, 18 th Intern. Coll. Tribology-Industrial and Automotive Lubrication, (ISI) 2012, Technische Akademie Esslingen, TAE, Germania, Stuttgart/ Ostfildern, January 10-12, 2012, Session A-8. “Environmentally Acceptable Lubricants”, 8 pp CDROM, Program p 14, Book of Synopses, p 75 [13] Mirci L.E. and Patrut A., Synthetic Complex Sebacic Tetraesters Base Oils Lubricants, The 19 th International Colloquium Tribology, 2014, (ISI), Technische Akademie Esslingen, TAE, Stuttgart/ Ostfildern, 21-23 January 2014, Session: “Synthetic Base Oils”(1), 12 pp CDROM, Abstracts p 101, Paper scheduled Room B 4, 21 January, 18,00-18,30 [14] Mirci L.E., Synthetic complex esters as tribological fluids with biodegradability potential, 2 nd International Conference on Advanced Tribology (iCAT), 3-5 December, 2008, Singapore, National University of Singapore, Extended Abstracts, 490-492 [15] Mirci L. E., Synthetic Malonic Biodegradable Lubricants and Method of Obtaining Thereof,RO Patent Appl., 2014, A/ 00733, October, 2, 2014 [16] Mirci L.E. and Patrut A., Synthetic Adipic Complex Tetraesters as Eco-Friendly Lubricants, Lubrication Science/ Synthetic Lubrication, (John Wiley), (ISI), 2013, Vol 25, Isue.5,August, p 330-350, DOI Number 10.1002/ ls.1226 [17] Mirci L.E., Patrut A. And Resiga D., New Sebacic Complex Ester Base Oils Lubricants with Biodegradability Potential, Tribologie und Schmierungstechnik, Expertverlag, 2014, ISI, 61. Jahrgang, Heft 2, 2014, pp.. 33-46 [18] Mirci L.E. and Patrut A., Synthetic Adipic Complex Tetra-Esters Base Oils, Tribologie und Schmierungstechnik, Expertverlag, 2014, ISI, 61. Jahrgang, Heft 3, 2014, pag 21-27 [19] Mirci L.E. and Patrut A., Synthetic Complex Sebacic Tetraesters Base Oils Lubricants, Tribologie und Schmierungstechnik, Expertverlag, 2014, ISI, 61. Jahrgang, Heft 4, 2014, pag 12-20 [20] Mirci L.E., Synthetic Biodegradable Ester Lubricant and Method of Obtaining Thereof, RO Patent, 2010, 125100, 20.10.2010. [21] Mirci L.E., Synthetic Sebacic Lubricants and Method of Obtaining Thereof, RO Patent, 129562, 2015, 29.05. 2015 [22] Mirci L.E. and Tamas A., Synthetic Complex Malonic Esters as Eco-Friendly Base Oils, The 20 th International Colloquium Tribology, 2016, (ISI), Technische Akademie Esslingen, TAE, Stuttgart/ Ostfildern,12-14 January 2016, Poster Session (Synthetic Base Oils), 10 pp CDROM, Abstracts p.207 54 Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 Hier könnte auch IHRE Firmen-Information zu finden sein! Wenn auch Sie die Leser von T + S über Ihre aktuellen Broschüren und Kataloge informieren möchten, empfehlen wir Ihnen, diese Werbemöglichkeit zu nutzen. 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