castor bean oil contains ricinoleic acid , a hydroxy monounsaturated fatty acid as main constituent of its fatty acid profile . ricinoleic acid , cis-12-hydroxy-9-octadecenoic acid , has an unusual polarity due to position of hydroxyl group . castor oil is the only commercially available vegetable oil containing hydroxy functionality of a fatty acid present abundantly ( 7090% ) . its various derivatives like ricinoleyl alcohol , methyl ricinoleate , azelaic acid , and ricinenic acid are used as plasticizer and emulsifier . ricinoleic acid derivatives are used in pigment , printing ink , and textile finishing . however , its main use is as chemical intermediate to produce various oleochemicals . estolides and estolide esters from castor oil , or any source of hydroxy fatty acids , have been explored and show promise as cosmetics , coatings , and biodegradable lubricants . estolides are formed when the carboxylic acid functionality of one fatty acid links to the site of unsaturation of another fatty acid to form oligomeric esters . complex estolides have been synthesized by   where oleic acid and various saturated fatty acids , butyric through stearic , were treated with 0.4 equivalents of perchloric acid at either 45 or 55c to produce a new class of saturated estolides with superior low - temperature properties . the current work involves the synthesis of a new series of estolide ester from ricinoleic acid and various fatty acids . the effect of fatty acid carbon chain length on physical characterization of these estolide esters was determined . castor beans from experimental plot ukm were used to extract castor oil . concentrated sulphuric acid ( 98% ) and potassium hydroxide ( koh ) were purchased from j. t. baker inc . caprylic acid ( 98% ) , capric acid ( 98% ) , lauric acid ( 98% ) , myristic acid ( 99% ) , palmitic acid ( 98% ) , stearic acid ( 96% ) , 2-hexyldecanoic acid ( 96% ) , and 2-butyloctanoic acid ( 96% ) were purchased from sigma aldrich . ethanol ( 95% ) and hydrated sodium sulphate ( 99% ) were purchased from systerm . estolide ester was synthesized in a one - step reaction in a 250  ml three - neck round bottom flask with a magnetic stirrer . the heating mantel was used to maintain the temperature of reaction constant at 60c  3c . ricinoleic acid ( 50  g , 0.1678  mol ) and branched fatty acid ( 0.0839  mol ) were combined and heated to 60c temperature . once the temperature reached 60c , acid catalyst ( 5% ) was added into reaction and the flask was placed under vacuum and stirred for 24  h. after 24 hours , ethanol ( 34  ml , 0.7391  mol ) was added into the flask and reaction was continued for additional 2 hours in vacuum . as the reaction completed , it was neutralized with koh ( 10  ml , 2  mol ) in 90% ethanol . the round bottom flask was disconnected from the heating mantel and the solution was left to cool down to room temperature . the organic layer was transferred to a separation funnel and was washed with distilled water to remove any excess ethanol used to neutralize . the organic layer was then distilled using the simple distillation method at 80140c to remove any lactone , byproducts , excess ethanol and water . ( a ) fourier transform infrared spectroscopyfourier transform infrared spectroscopy ( ftir ) has been carried out according to . ftir of the products was recorded by prkin elmer spectrum gx spectrophotometer in the range 4004000  cm . a very thin film of products covered the nacl cells ( 25  mm i.d  4  mm thickness ) and was used for analysis . ftir of the products was recorded by prkin elmer spectrum gx spectrophotometer in the range 4004000  cm . a very thin film of products covered the nacl cells ( 25  mm i.d  4  mm thickness ) and was used for analysis . ( b ) viscosityviscosity test , astm d445 - 04 , was done in a brookfield viscometer using a number 3 spindle . the speed was set to 100  rpm a minute and was done in room temperature . viscosity test , astm d445 - 04 , was done in a brookfield viscometer using a number 3 spindle . the speed was set to 100  rpm a minute and was done in room temperature . ( c ) pour pointthe pour point test , astm d97 - 05a , was done by using a u - tube . the pour point test , astm d97 - 05a , was done by using a u - tube . ( d ) flash pointthe flash point test , astm d92 - 05a , was conducted by adding 5  ml sample into a small ceramic bowl . the sample in the small container was partially emerged into a glass bowl of silicon oil and was heated on the heating mantel . the heating process will produce gas clouds which were trapped in the ceramic bowl . starting from 100c if there is no spark , the process will be repeated until there is spark . the flash point test , astm d92 - 05a , was conducted by adding 5  ml sample into a small ceramic bowl . the sample in the small container was partially emerged into a glass bowl of silicon oil and was heated on the heating mantel . the heating process will produce gas clouds which were trapped in the ceramic bowl . starting from 100c if there is no spark , the process will be repeated until there is spark . a series of estolide ethyl esters were synthesized from ricinoleic acid and a series of saturated fatty acids with sulphuric acid catalyst at 60c for 24  h. the structures are shown in figure 1 . esterification process was continued with synthesis of estolide ester by adding an alcohol , ethanol to stop the estolide chain by capping it . the temperature of the process should be kept stable and not exceed 70c because the productions of byproducts such as lactone   will increase and decrease the temperature to less than 45c because of the slower rate of estolide formation . ftir spectra of ricinoleic acid and reaction products were compared to show that condensation had occurred . as a result , the ftir spectrum of ricinoleic acid shows c = o stretching band at 1713  cm wavenumber and the presence of a hydroxyl group in the ricinoleic acid structure is shown 3445  cm wavenumber   where else the reaction product , a sharp and long carbonyl c = o ester transmittance peak was observed at 1737  cm . the presence of ch2 bending at 723  cm wavenumber indicates long - chain compound . the , c = c transmittance peak are pot clearly presence because it , showed a weak transmittance peak due to only a small amount of alkene was present . from the observation , no lactones were present because of there is no transmittance peak at 1790  cm . other absorbance indicates c  h alkane bond and bend alkane at transmittance peaks 2926  cm , 2854  cm and 1464  cm , respectively . the yield of these estolides increased from 52.51  0.03% to 96.57  0.05% for the neat and capped estolide esters . this estolide was synthesized with ricinoleic acid and capric acid .   the pour point of saturated estolide ethyl esters pour point is the lowest point or temperature where the sample sustains in liquid form . this property is important because low pour point enables the sample usage in cold countries and in low - temperature machineries . low pour point helps in keeping the estolides in liquid condition which makes transportation and storage easy . it is because the longer estolide esters have bigger  molecular structure and bulky which makes them easier to solidify at a higher temperature compared to small compounds . even though the pour point pattern is increasing , the values of pour point are still negative and are low . it also determines fluid properties involved in lubricant , resistant to the initiation of relative movement of moving part . the highest viscosity is obtained at 86  0.01  cp for ee18 and the lowest at 51  0.08  cp for ee16 . the value of viscosity reduces as the length of fatty acid increases . the flash point , or the temperature at which a lubricant momentarily flashes in the pressure of a test flame , aids in evaluating fire - resistance properties . it also shows that there is a possibility that there are hazardous gasses in the sample . it is important to have a high flash point to ensure it will not harm the user or the environment by releasing gas emission at low - temperature . the flash point temperature should also be high to ensure its usage is commercially accepted . they are high and are not easily to emit any dangerous gaseous or potential fire occurrence during usage of the estolides . these new estolide esters were compared with saturated branched - chain estolide esters . ee12 and the comparison of physical characterisations between these estolide ethyl esters is shown in table 2 . saturated branched - chain estolide ester has lower pour point and viscosity especially if ee16-compared to eehd . this may be caused by the addition of branched fatty acid that causes the structure to become asymmetric thus reduces the pour point tremendously and increases the viscosity value . . branched  molecules can not be arranged very neatly because of its jagged structure . this condition will lower the freezing temperature of the estolide ester because more energy is used to freeze it . longer saturated branched - chain has a bigger  molecule weight which makes it is easier to lose intramolecule force , leading the solution to have a small viscosity value . the value of viscosity reduces as the length and quantity of branched fatty acid increase . estolide ethyl esters from ricinoleic acid and saturated fatty acid have excellent low - temperature properties and high flash points .