BIODEGRADABLE LUBRICANT EMULSION

Technical Field

[0001] The present invention relates to a biodegradable lubricant emulsion based on naturally occurring non-mineral oils and non-toxic emulsifiers, demonstrating improved metal cutting properties and resistance to oxidative degradation.

Background of the invention

[0002] Metal cutting or metal working fluids or coolants are used in the machining activities primarily for three purposes; complete heat removal, to lubricate the chip-tool interface and to remove the chips. Commercially available metalworking fluids have mineral oils as the base oil, along with the different additives for performance enhancement. The use of mineral oils in such metal cutting fluids creates many negative effects on the environment. A major negative effect is particularly linked to their inappropriate use, which results in surface water and ground water contamination, air pollution, soil contamination and consequently, agriculture products and food contamination. Mineral oils are non-biodegradable, highly toxic and non-renewable. Many of the additives used to enhance the performance metal cutting fluids are highly toxic to the ecosystem and they are also non-renewable in nature. Cutting fluids of this nature also cause several allergic reactions to users. The microbial toxins generated by bacteria and fungi present, particularly in the water soluble cutting fluids and the chemical biocides frequently used to kill the microbes also cause potential harm to users.

[0003] Various alternatives were developed by many scientists and tribologists to overcome the limitations of mineral oil based cutting fluids. Synthetic lubricants, vegetable oils, animal tallow and solid lubricants are the alternatives being used.

[0004] Another highly attractive substitute for mineral oils is vegetable oils, because they are renewable, environmentally friendly, relatively highly non-toxic and readily biodegradable. The present development in this field includes the cutting fluid developed from vegetable oils like Soybean oil, Castor oil, Palm oil, Rapeseed oil and Canola oil. These vegetable oils have larger number of unsaturation in their chemical structure that makes it more prone to oxidative degradation. The oxidative degradation of the base oil in cutting fluid hinders its cutting properties. The oxidatively degraded cutting fluids also results in severe metal corrosion.

[0005] Additives used in the mineral oil based cutting fluid and even many biodegradable lubricants are chemically synthesized compounds. Many of these additives are highly toxic, non-renewable in nature.

[0006] Therefore, there is a need for a biodegradable lubricant emulsion for use as metal cutting fluid, which is readily biodegradable, slow in oxidation and relatively non-toxic.

Objects of the present invention

[0007] The primary object of the present invention is provide a biodegradable lubricant emulsion for use as metal cutting fluids, based on naturally occurring non-mineral oils and non-toxic emulsifiers.

[0008] It is also an object of the present invention to provide a biodegradable lubricant emulsion for use as metal cutting fluids that is slower in oxidative degradation.

[0009] Another object of the present invention is to provide a biodegradable lubricant emulsion for use as metal a cutting fluid that is non-toxic to the ecosystem.

[0010] Further object of the present invention is to provide a biodegradable lubricant emulsion for use as metal cutting fluid having enhanced storage stability.

[0011] Yet another object of the present invention is to provide a biodegradable lubricant emulsion for use as metal cutting fluid, having enhanced machining properties.

[0012] It is also an object of the present invention to provide a biodegradable lubricant emulsion for use as metal cutting fluid that is resistant to rancidity and free from undesirable odour. Summary of the present invention

[0013] The present invention provides a biodegradable lubricant emulsion having improved metal cutting properties and resistance to oxidative degradation, comprising, an effective amount of non-mineral oils, an effective amount of non-toxic emulsifiers and a solvent. The non-mineral oils that are advantageously used in the biodegradable lubricant emulsion are coconut oil, lemon grass oil and neem oil along with polyethylene glycol sorbitan monooleate and polyethylene glycol sorbitan trioleate as emulsifiers. The lubricant emulsion of the present invention is completely biodegradable and relatively nontoxic to aquatic system. The lubricant emulsion of the present invention demonstrates enhanced anticorrosion and storage stability properties. The present invention also provides a process for the preparation of the biodegradable lubricant emulsion.

Brief description of the drawings

[0014] FIG. 1 is a graphical depiction of comparative performance analysis of biodegradable lubricant emulsion of the present invention and other lubricants, during drilling of aluminium.

[0015] FIG. 2 depicts stable nature of the biodegradable lubricant emulsion as compared with other known lubricants.

[0016] FIG.3 is a graphical depiction of inhibition of growth of test organism Staphylococcus Aureus, in known cutting fluids (lubricants) and the biodegradable lubricant emulsion of the present invention.

[0017] FIG.4 is a graphical depiction of inhibition of growth of test organism Escherichia Coli, in known cutting fluids (lubricants) and the biodegradable lubricant emulsion of the present invention.

[0018] FIG.5 is a graphical depiction of inhibition of growth of test organism Salmonella typhimurium, in known cutting fluids (lubricants) and the biodegradable lubricant emulsion of the present invention.

Detailed description of the invention

[0019] The biodegradable lubricant emulsion of the present invention, for use as a metal cutting fluid, comprises a synergistic combination of naturally occurring non-mineral oils and non-toxic emulsifiers. The biodegradable lubricant emulsion of the present invention, while rendering improved machining performance also exhibits properties such as enhanced storage stability, reduced particle size, an enhanced resistance to corrosion, slower oxidation and reduced aquatic toxicity.

[0020] The biodegradable lubricant emulsion prepared in accordance with the present invention comprises plant-based non-mineral oils, having over 90% saturated fatty acids, forming a base component of the emulsion.

[0021] In an aspect of the present invention non-mineral oils for the biodegradable lubricant emulsion are selected from plant-based mineral oils such as coconut oil (Cocos nuciferd), cashew nut oil (Anacardium Occidentale), thyme oil, clove oil, citronella oil, aloe vera, lemon grass oil (Cymbopogon), neem oil {Azadirachta indica) and tangerine oil.

[0022] In another aspect of the present invention the preferred non-mineral oils for the biodegradable lubricant emulsion are coconut oil, lemon grass oil and neem oil.

[0023] In yet another aspect of the present invention, the essential amount of coconut oil as used in the biodegradable lubricant emulsion is in the range of about 1.5-5 percent by weight, preferably about 2.5% percent by weight.

[0024] In further aspect of the present invention the essential amount of lemongrass oil as used in the biodegradable lubricant emulsion, is in the range of about 0.1 -0.7 percent by weight, preferably about 0.3 percent by weight

[0025] In another aspect of the present invention the essential amount of neem oil as used in the biodegradable lubricant emulsion is in the range of about 0.1-0.5 percent by weight, preferably 0.1 percent by weight.

[0026] Oxidation of a chemical compound occurs primarily due to the presence of unsaturation in carbon chain. Mineral oils contain many aromatic compounds along with unsaturated long carbon chains. The presence of unsaturation in the carbon chain makes compounds more susceptible for oxidation at higher temperature. Whereas, vegetable oils are composed of unsaturated fatty acids at higher percentage and these vegetable oils are more prone to oxidation at higher temperatures. However, the biodegradable lubricant emulsion of the present invention with coconut oil as one of the ingredients contains more than 90% of saturated fatty acids and is not much prone to oxidation at higher temperature like other vegetable oils.

[0027] In further aspect of the present invention, the effective combination of plant-based mineral oils, having over 90 % saturated fatty acids, impart resistance to oxidative degradation of the lubricant emulsion.

[0028] The higher resistance to oxidative degradation results in the improvement of good cutting fluid properties during cutting and avoids corrosion of metals.

[0029] It is understood here that the above-mentioned ratios of the non-mineral oils are the preferred ratios and it is well within the scope of the present invention to try and vary the respective ratios of the non-mineral oils or other plant-based mineral oils, depending on its intended use of the lubricant emulsion.

[0030] In yet another aspect of the present invention, the biodegradable lubricant emulsion includes emulsifiers that are non-toxic. The non-toxic emulsifiers include a combination of at least two of alkyl phenol ethoxylate, glycerol monostearate, ethylene glycol monostearate, ethylene glycol distearate, polyoxyethylene glycol sorbitan monolaurate, polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan trioleate, sorbitan mono oleate and sorbitan mono laurate.

[0031] It is also an aspect of the present invention the preferred combination of emulsifiers for the biodegradable lubricant emulsion is polyethylene glycol sorbitan monooleate and polyethylene glycol sorbitan trioleate.

[0032] In another aspect of the present invention, the amount of polyethylene glycol sorbitan trioleate in the biodegradable lubricant emulsion is in the range of about 1-3 percent by weight, preferably 1.5 percent by weight.

[0033] In yet another aspect of the present invention, the amount of polyethylene glycol sorbitan monooleate is in the range of about 0.5-1 percent by weight, preferably 0.5 percent by weight.

[0034] It is understood here that the above-mentioned ratios of the emulsifiers are the preferred ratios and it is well within the scope of the present invention to try and vary the respective ratios of these emulsifiers or other non-toxic emulsifiers, depending on its intended use of the lubricant emulsion.

[0035] In further aspect of the present invention, the biodegradable lubricant emulsion of the present invention also includes a solvent, which is advantageously a polar solvent, to make an emulsion of the lubricant. The polar solvent as used in an exemplary manner is water, which is used in the range of about 95.1 percent by weight.

[0036] In yet another aspect of the present invention Hydrophilic Lipophilic Balance (HLB) for the biodegradable lubricant emulsion is measured. HLB value is determined by measuring the ability of particular molecule to form a stable emulsion with series of emulsifiers with different range of HLB value. A combination of test molecule, water and equal amount of emulsifier with different HLB values are combined. The HLB value, which gives a stable emulsion with the test molecule is considered as its HLB value and used to create a stable emulsion. The required HLB value for coconut oil to create a stable emulsion is 12. Various HLB values for different essential oils are as shown in Table 1.

Table 1

[0037] Once the HLB value of the coconut oil is determined, emulsions of coconut oil are prepared by using the different combination of emulsifiers to evaluate the corresponding long term stability. Combination of polyethylene sorbitan mono oleate and poly ethylene Glycol showed a very stable emulsion after addition of water. Finally, combination of polyethylene sorbitan mono oleate and poly ethylene glycol is chosen, in desired ratios, because of its stability as an emulsifier and emulsion with water.

[0038] In yet another aspect of the present invention a process for the preparation of biodegradable lubricant emulsion having improved resistance to oxidative degradation is described. The process comprises the steps of preparing a mixture of emulsifiers for about 20 minutes in a magnetic stirrer, which is followed by adding non-mineral oils under stirring for about 20 minutes in a magnetic stirrer and preparing an emulsion in the presence of a solvent to obtain an emulsion.

[0039] In the process of the present invention non-mineral oil is selected from the group consisting of coconut oil (Cocos nucifera), cashew nut oil, thyme oil, clove oil, citronella oil, aloe vera, lemon grass oil (Cymbopogori), neem oil (Azadirachta indica) and tangerine oil or a mixture thereof, preferably a mixture of coconut oil, lemon grass oil and neem oil.

[0040] In the process of the present invention the natural emulsifiers is selected from the group consisting of alkyl phenol ethoxylate, glycerol monostearate, ethylene glycol monostearate, ethylene glycol distearate, polyoxyethylene glycol sorbitan monolaurate, polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan trioleate, sorbitan mono oleate, sorbitan mono laurate or a mixture thereof, preferably a mixture of polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan trioleate.

[0041] The solvent as used in the process of the present invention is a polar solvent, preferably water, in the range of about 95 percent by weight.

[0042] The following are non-limiting examples are provided to illustrate the invention.

Example 1

[0043] The biodegradable lubricant emulsion of the preis prepared by mixing 1.36% (1.36g) glycerol mono stearate self-emulsifiable and 0.64% (0.64g) polyethylene glycol sorbitan mono oleate for 20 minutes in a magnetic stirrer. The above mixture is added to 2.5% (2.5g) of coconut oil and stirred for another 20 minutes in a magnetic stirrer. The mixture is added to 95.5% (95.5g) of water and stirred mechanically to obtain an emulsion. However the emulsion is found to be unstable after 24 hours.
Example 2

[0044] The lubricant emulsion is prepared by mixing 1.50% (1.50g) of polysorbate 85 and 0.5% (0.5g) of polysorbate 80 for 20 minutes in a magnetic stirrer. The above mixture is added to 2.5% (2.5g) of coconut oil and stirred for another 20 minutes in a magnetic stirrer. The mixture is added to 95.1%) (95.lg) of water and stirred mechanically to obtain an emulsion. Emulsion produced from this method is found to be stable for 24 hours.

Example 3

[0045] The lubricant emulsion is prepared by mixing 1.50% (1.50g) of polysorbate 85 and 0.5%) (0.5g) of polysorbate 80 for 20 minutes in a magnetic stirrer. The above mixture is added to 2.5% (2.5g) of coconut oil and stirred for another 20 minutes in a magnetic stirrer. The above mixture mixed with 0.1%) (0.lg) of lemon grass oil and 0.1% (0.lg) of neem oil and stirred for another 20 minutes. The mixture is added to 95.3% (95.3g) of water and stirred mechanically to obtain an emulsion. Emulsion produced from above method is stable for 24 hours. However, produced emulsion is found to be not inhibiting the growth of microorganisms like Escherichia coli, Staphylococcus aureus, Pseudomonas oleovorans and Salmonella typhimurium.

Example 4

[0046] The lubricant emulsion is prepared by mixing 1.50% (1.50g) of polysorbate 85 and 0.5%) (0.5g) of polysorbate 80 for 20 minutes in a magnetic stirrer. The above mixture is added to 2.5% (2.5g) of coconut oil and stirred for another 20 minutes in a magnetic stirrer. The above mixture mixed with 0.1 %> (0.lg) of lemon grass oil and 0.3%> (0.3g) of neem oil and stirred for another 20 minutes. The mixture is added to 95.1% (95.lg) of water and stirred mechanically to obtain an emulsion. Emulsion produced from above method is stable for 24 hours. However, produced emulsion is found to be not inhibiting the growth of microorganisms like Escherichia coli, Staphylococcus aureus, Pseudomonas oleovorans and Salmonella typhimurium.

Example 5

[0047] The lubricant emulsion is prepared by mixing 1.50% (1.50g) of polysorbate 85 and 0.5% (0.5g) of polysorbate 80 for 20 minutes in a magnetic stirrer. The above mixture is added to 2.5% (2.5g) of coconut oil and stirred for another 20 minutes in a magnetic stirrer. The above mixture mixed with 0.3% (0.3g) of lemon grass oil and 0.1% (O.lg) of neem oil and stirred for another 20 minutes. The mixture is added to 95.1% (95. lg) of water and stirred mechanically to obtain an emulsion. Emulsion produced from above method is stable for 24 hours. The emulsion thus prepared is found to nhibit the growth of microorganisms like Escherichia coli, Staphylococcus aureus, Pseudomonas oleovorans and Salmonella typhimurium.

[0048] In another aspect of the present invention different ratios of base oil coconut oil and emulsifiers are tested to obtain a stable emulsion, as shown in Table 2.

Table 2

[0049] In another aspect of the present invention the particle size of the biodegradable lubricant emulsion is determined to be as about 190.06 nm. The lower particle size of ingredients facilitate in the formation of a stable emulsion. The particle size of various other known lubricants is provided in the following Table 3. In comparison, it can be observed that the particle size of the biodegradable lubricant emulsion thus obtained in the present invention is much lesser vis-a-vis other lubricants.

Table 3

[0050] In further aspect of the present invention storage stability the biodegradable emulsion of the present invention is determined by measuring the peroxide value of emulsion before and after oven test. Lipid molecules upon storage in room temperature or at higher temperature undergo auto oxidation resulting in the formation of peroxides. According to ASTM D1832, the peroxide values indicate the quantity of oxidizing constituents present in the test solution. Lower the peroxide value, lesser the auto oxidation and hence more storage stability. Therefore, measuring the peroxide concentration indirectly provide information about storage stability of various lubricants. The peroxide values and their corresponding stability factors of known lubricants and the biodegradable lubricant emulsion of the present invention are determined and shown in the Table 4.

Table 4

stability of biodegradable lubricant emulsion as prepared in accordance with the present invention and other known lubricants such as Castrol Cool Cut and Servo Super Cut of the present invention are determined by storing these lubricants for an exemplary period of 15 days to identify the extent of separation of emulsion phases such as water, oil and emulsion. A stable emulsion demonstrates least separation of emulsion into water, oil and emulsion, whereas the least stable lubricants show enhanced separation of emulsion into water and oil. A visual examination of the above-mentioned known lubricants and the biodegradable lubricant emulsion is made as shown in FIG.l. It is observed here that the middle container holding the biodegradable lubricant emulsion of the present invention has not demonstrated any separation of phases and found to be stable. Whereas, the other lubricants have shown separation of phases of various degrees.

[0052] In another aspect of the present invention, in order to determine the machining performance or the effect of biodegradable lubricant emulsion of the present invention, drilling operations are performed by placing a work piece in submerged condition within the lubricant fluid. To compare the effect of lubricant on drilling, a set of dry cutting is performed on the Aluminium grade II plates. The drilling experiments are carried out on a vertical milling machine of Hindustan Machine Tools (HMT). The tests are carried on Aluminium Grade II plates with the thickness of 32mm. The dimension of work piece is 100mmx70mmx32mm. One hundred holes of 30mm depth per plate are drilled, the sequences being randomized to avoid localized hardness variations. In this test a standard High Speed Steel (HSS)-twist drill bits of 12 mm diameter are used. The drilling test results for (i) dry drilling, (ii) known lubricants that are designated in FIG.2 as Commercial Oil I (Castrol Cool Cut), Commercial Oil II (Servo Super Cut) and Commercial Oil III (Shell S Cut), and (iii) biodegradable lubricant emulsion (designated as coconut oil emulsion) of the present invention, are obtained and plotted as shown in FIG.2. It can be observed from FIG.2 that the biodegradable lubricant emulsion of the present invention exhibits the surface roughness factor, which is on par with other known lubricants.

[0053] In yet another aspect of the present invention, anti-corrosive properties of biodegradable lubricant emulsion are examined. Anti-corrosion tests are done by following ASTM-D4627 method. In this method cast iron chips are placed in a petri dish containing filter paper and cutting fluid/lubricant. The dish is covered and allowed to stand overnight, to measure the amount of formation of rust stain on the filter paper. The test ingredients are combined in different concentrations of ingredients of the biodegradable lubricant emulsion of the present invention and other known lubricants. These samples are tested for its anti-corrosion properties and the results are tabulated in Table 5.

Table 5

[0054] It can be seen from the above that biodegradable lubricant emulsions of the present invention in the concentration levels of about 100% found to be least corrosive, in comparison with other known lubricants. It is also observed that whenever concentration of reagent water is increased, the corrosion levels of all lubricants have increased. In any case, in all the concentrations biodegradable
lubricant emulsion of the present invention showed better corrosion properties than commercial cutting fluids. [0055] In yet another aspect of the present invention, in order to assess the aquatic toxicity of the biodegradable lubricant emulsion of the present invention, a test method (OECD 203) standardized by the Organisation for Economic Co-operation and Development (OECD), is adopted. In this method aquatic toxicity of the lubricants is defined in terms of lethal concentration 50 (LC50). The LC50 is the level of concentration of a test sample, where the mortality rate of the test specimens is about 50%, due to toxicity of the lubricant. The test specimens used in this method are Zebra fish, for evaluating the toxicity of biodegradable lubricant emulsion of the present invention and other lubricants. The toxicity of test samples is evaluated by exposing the fish to a known concentration of test samples for duration of 96 hours. The mortality of fish is monitored in intervals of 24 hours. The concentration of test sample is increased in a geometric series of 2.2 and the concentration, which kills the 50 percent of the fish in 96 hours is observed. The results of toxicity test, which are compiled in the following Table 6, indicate the non-toxic nature of the biodegradable lubricant emulsion of the present invention to the aquatic system.

Table 6

*Toxicity level explained in lethal concentration where 50% of fish were dead during experiment.

[0056] It can be observed from the above table that the aquatic toxicity of biodegradable lubricant emulsion is much lesser when compared with aquatic toxicity levels of other known lubricants, since the other known lubricants have demonstrated higher toxicity levels, even at very low concentration of test samples.

[0057] In further aspect of the present invention a study of rancidity of different lubricants is conducted by keeping the lubricants in an open environment for period of about one month. Rancidity of an oil emulsion occurs primarily due to oxidation of raw materials in the emulsion, hydrolytic instability of the oils, and metabolic products resulting from microbial contamination. The effect of rancidity is determined by stability of emulsion through visual appearance and smell of the emulsion. The known lubricants when exposed to environment have developed rancidity and bad odor in a short period of time. Whereas, the biodegradable lubricant emulsion of the present invention demonstrated better anti-rancid property and found to be stable for more than three months. It is also observed that known lubricants after test period have demonstrated separation of emulsion into oil and water. Formation of thick creamy layer on the surface of these known lubricants is also observed.

[0058] In yet another aspect of the present invention the enhanced anti-microbial activities of biodegradable lubricant emulsion of the present invention are determined through microbiology tools such as serial dilution and plating technique method. In this method, pathogenic organisms, which normally grow profusely in the cutting fluids or lubricants, are used as test organisms. In the present invention, in an exemplary manner, organisms such as Staphylococcus aureus, Escherichia coli, Staphylococcus aureus, Pseudomonas oleovorans and Salmonella typhimurium are used as test organisms. The cultures of test organisms are inoculated into the lubricant samples for which the inhibitory characteristics are to be determined and studies are conducted for the duration of 45 days. These samples are viz., (i) distilled water (ii) combination of polyoxyethylene sorbitan mono oleate, polyoxyethylene sorbitan tri oleate and distilled water (iii) combination of coconut oil, polyoxyethylene sorbitan mono oleate, and polyoxyethylene sorbitan tri oleate (Coconut oil emulsion), (iv) combination coconut oil emulsion + 0.1 % Neem oil, (v) combination of coconut oil emulsion + 0.1 % Neem oil +0.3% Lemongrass oil, (vi) combination of coconut oil emulsion + 0.1 % neem oil +0.5% lemongrass oil, (vii) Castrol Cool Edge (Trade name) lubricant and (viii) Servo Super Cut (Trade name) lubricant. Bacteria containing plates are incubated at 37°C for about eighteen hours. After incubation, colonies of test organisms are counted and the inhibitory effects of various lubricants including the biodegradable lubricant emulsion of the present invention are determined and compared. The comparative results are plotted in FIGS. 3-5.

[0059] As we can observe from FIGS. 3-5 the biodegradable lubricant emulsion inoculated with E. coli has displayed better inhibition characteristics as compared with known lubricants for the values obtained on 30th day of the inoculation. However, on 1st day, known lubricants have demonstrated better antimicrobial properties than biodegradable lubricant emulsion. Whereas, on the 45th day of experiment, biodegradable lubricant emulsion of the present invention completely inhibited the growth of E. coli. It is also observed that known lubricants though inhibited E. coli. growth but the rate of inhibition displayed the signs of decreasing when compared to 1st and 30th day. As regards, Staphylococcus aureus, both biodegradable lubricant emulsion and known lubricants exhibited complete inhibition. In the case of Salmonella typhimurium on the lstday, the biodegradable lubricant emulsion showed complete inhibition of organism, while known lubricants permitted the growth of the organism. During 30th and 45th day of the experiment biodegradable lubricant emulsion has demonstrated better inhibition of organism than known lubricants.

[0060] A comparative account of various properties exhibited by the known lubricants and biodegradable lubricant emulsion of the present invention are tabulated in the following Table 7.

[0061] The foregoing properties of the biodegradable lubricant emulsion of the present invention vis-a-vis known lubricants clearly establish the synergistic nature of the biodegradable lubricant emulsion of the present invention.

[0062] It will thus be seen that the embodiments as set forth above, are efficiently attained and since certain changes may be made in carrying out the present invention without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

[0063] It is also understood that the following claims are intended to cover all the generic and specific features of the invention herein described and all statements of the scope of the invention, which as a matter of language might be said to fall therebetween.

Advantages

[0064] The cutting force of the biodegradable lubricant emulsion is more in comparison with other vegetable oils like ground nut oil, palm kernel oil etc.

[0065] Completely biodegradable and relatively non toxic to aquatic system.

[0066] Developed product is a complete green product.

[0067] Developed product is having better anticorrosion and storage stability than commercial cutting fluids.

We Claim:

1. A biodegradable lubricant emulsion having improved metal cutting properties and resistance to oxidative degradation, comprising: an effective amount of non-mineral oils; an effective amount of non-toxic emulsifiers; and a solvent.

2. The lubricant emulsion as claimed in claim 1, wherein the non-mineral oils are selected from the group consisting of coconut oil (Cocos nucifera), cashew nut oil (Anacardium occidentale), thyme oil {Thymus vulgaris), clove oil {Syzgium aromaticum), citronella oil, aloe vera, lemon grass oil (Cymbopogon citrates), neem oil (Azadirachta indica) and tangerine oil or a mixture thereof, preferably a mixture of coconut oil, lemon grass oil and neem oil.

3. The lubricant emulsion as claimed in claim 2, wherein coconut oil is in the range of about 2.5 percent by weight, lemongrass oil is in the range of about 0.3 percent by weight and neem oil is in the range of about 0.1 percent by weight.

4. The lubricant emulsion of claim 1, wherein the non-toxic emulsifiers is selected from the group consisting of alkyl phenol ethoxylate, glycerol monostearate, ethylene glycol monostearate, ethylene glycol distearate, polyoxyethylene glycol sorbitan monolaurate, polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan trioleate, sorbitan mono oleate, sorbitan mono laurate or a mixture thereof, preferably a mixture of polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan trioleate.

5. The lubricant emulsion of claim 4, wherein polyethylene glycol sorbitan trioleate is in the range of about 1.5 percent by weight and polyethylene glycol sorbitan monooleate is in the range of about 0.5 percent by weight.

6. The lubricant emulsion as claimed in claim 1, wherein the solvent is a polar solvent, preferably water, in the range of about 95.1 percent by weight.

7. A process for the preparation of biodegradable lubricant emulsion having improved resistance to oxidative degradation, said method comprising the steps of preparing a mixture of emulsifiers for about 20 minutes in a magnetic stirrer; adding non-mineral oils under stirring for about 20 minutes in a magnetic stirrer; and preparing an emulsion in the presence of a solvent to obtain an emulsion.

8. The process as claimed in claim 7, wherein the non-mineral oil is selected from the group consisting of coconut oil (Cocos nucifera), cashew nut oil, thyme oil, clove oil, citronella oil, aloe vera, lemon grass oil (Cymbopogori), neem oil (Azadirachta indica) and tangerine oil or a mixture thereof, preferably a mixture of coconut oil, lemon grass oil and neem oil.

9. The process as claimed in claim 7, wherein the natural emulsifiers is selected from the group consisting of alkyl phenol ethoxylate, glycerol monostearate, ethylene glycol monostearate, ethylene glycol distearate, polyoxyethylene glycol sorbitan monolaurate, polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan trioleate, sorbitan mono oleate, sorbitan mono laurate or a mixture thereof, preferably a mixture of polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan trioleate.

10. The process as claimed in claim 7, wherein the solvent is a polar solvent, preferably water, in the range of about 95 percent by weight.