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Abstract- Oil-modified alkyd resin was prepared from crude castor oil. The experiment started with investigating the optimum conditions for neutralization of crude castor oil and bleaching of neutralized oil. Then the characteristics (iodine value, viscosity, acid value, refractive index and color) of oils were determined. Refined oil has iodine value of 90, kinemetic viscosity of 4 St, free fatty acid value of 1, refractive index of 1.474 and color number of 8. These results showed that the refined oil was qualified to prepare dehydrated castor oil. Dehydration of refined oil was carried out at 210-220ËšC under 600-640mmHg with the help of 1% (wt%) NaHSO4 catalyst. The dehydrated castor oils were analyzed for iodine value, viscosity and its set to touch time and drying time were also investigated. Dehydrated castor oil has iodine value of 140, kinemetic viscosity of 1.6 St, set to touch time of 4 hr and drying time of 5 days. And then , oil modified alkyd resin (acid value 6.6) was prepared from dehydrated castor oil by alcoholysis method in excess of glycerol and phthalic anhydride in the presence of 0.3% (wt%) NaOH catalyst. The obtained resin was characterized by Fourier Transform Infrared Spectrophotometer (FTIR) and the properties were determined.
Keywords- Alcoholysis method, Alkyd resin, Castor oil, Dehydrated castor oil, Polymerization
Polymerization is one of the most important industrial processes. Resins and emulsion are two main classes of polymer. Alkyd resins are by far the most important class of coating resins. It is estimated that alkyd resins contribute about 70% to the conventional binders used in surface coating today. The popularity of alky resins as vehicle for coatings is largely due to their unique properties such as film hardness, durability gloss and gloss retention, resistance to abrasion, etc. impacted on them through modification with drying oil .
Alkyd resins are used in both clear and pigmented, industrial and trade coating to protect and decorate a wide variety of substances. The industrial coatings or finishes generally are applied during the manufacturing process of the item which they cover. Often they are specifically formulated to meet both conditions desired for their application and the endless use of the article of manufacture. The industrial finishes include primers and top coats for refrigerators, furniture, and electrical equipment. In view of the development of these items and sectors, the positive growth is expected for paint industry .
Further the paint industry envisages a future expansion in view of development in Automobile Industry, utility in Nuclear Power Station, development in Corrosion Resistant Coatings, expansion in housing activity and other industry uses. The demand of alkyd resin being an ingredient in Paint, Varnish and Printing ink industry would be linked with the Paint industry.
There are many significant efforts that have been made to increase alkyd resin production. Many researchers have attempted to search the different sources for alkyd resin preparation. Airegumen I Aigbodion et al  studied enhancing the quality of alkyd resins using methyl esters of rubber seed oil in 2004.
A lot of alkyd resins were imported to Myanmar Paint Industries every year. In order to save foreign currency outflow, it is needed to produce alkyd resin in Myanmar.
The oils that are mostly employed for alkyd resin synthesis are linseed oil, soybean oil, dehydrated castor oil, fish oil and tall oil. Myanmar being rich in aquatic and terrestrial resources, every state and division is pursuing the target of putting 500,000 acres under physic nut (castor oil) in three years. Rural development tasks are included in the national development endeavors that are being carried out by the Nation target.
Castor oil is useful directly in protective coatings as a plasticizer in alkyd systems, and blown castor oil is an important nitrocellulose plasticizer. In commercial manufacture of dehydrated castor oil, the aim is to produce the most valuable material for use as a drying oil. By far the most important coatings use of castor oil is in the form of dehydrated castor. Dehydrated castor oil is now recognized as an individual drying oil with its own characteristic properties and advantages. The drying oils owe their value as raw materials for decorative and protective coatings to their ability to polymerize or "dry" after they have been applied to a surface to form tough, adherent, impervious, and abrasion resistance films. The advantages claimed in surface coating applications include excellent odor and heat bleachability, good drying properties, more uniform polymer structure, and lack of after-yellowing. The dehydrated castor oil is non-yellowing oil and so this can give requirements of coating industries [2,4,5,6,7].
II . MATERIALS AND METHODS
Neutralization of Crude Castor Oil
Oil (100g) was heated to 55ËšC. Then, the calculated amount of strong (45ËšBe, 2N NaOH) lye was added to neutralize the free fatty acids exactly, with constant stirring. Completion of neutralization reaction was determined by testing the mixture with phenolphthalein indicator. When the indicator color of the sample mixture turned to pink, neutralization was completed. Then, NaCl solution was heated to 90ËšC and 20ml of hot NaCl solution was added to the mixture to ensure adequate salting or graining out of soapstock. After that the mixture was poured into separating funnel. Three hours later, the mixture was separated into two distinct layers. Then the lower layer or soap layer was drain out. The upper layer or oil layer was washed with hot water. Washing was carried out until color of phenolphthalein indicator did not change to pink. After complete washing, the oil was dried at 100ËšC in oven to evaporate the moisture. Drying and cooling was carried out until the weight of dried oil remained unchanged.
The neutralized oils were weighed to calculate oil loss and then their free fatty acid content (FFA) were determined . The characteristics of crude oil and neutralized oil were determined by American Society of Testing and Materials (ASTM) standard methods.
Bleaching of Neutralized Oil
The neutralized oils were heated to 100ËšC and different amounts of activated charcoal were added. After the mixture was stirred for 45 minutes, the mixture was cooled to room temperature and activated charcoal was removed by filtering with filter paper.
The neutralized oils were also bleached with different amounts of bentonite and a mixture of activated charcoal and bentonite (1:1 ratio). Then the process was carried out above procedure.
The colors of bleached oil samples were determined by a spectrophotometric method . In this method, optical densities were measured at the wavelength of 460nm, 550nm, 620nm and 670nm. Then the photometric colors were calculated by the following equation.
Photometric color = 1.29D460 + 69.7D550 + 41.2D650 -
Dehydration of Castor Oil
Bleached oil (50g) and 2% (wt%) of NaHSO4 catalyst were placed into round bottom flask and the apparatus was set up. The system was heated to 210-220ËšC for dehydration time were taken for 15, 30, 45, 60, 75 minutes.
Dehydration was also carried out under 600-640 mmHg (vacuum) as described in the above process. In this process, the effect of NaHSO4 catalyst amount on the properties of dehydrated castor oil was also investigated.
Then, the iodine values of dehydrated castor oil were determined by ASTM D1541-86 and viscosities were determined by ASTM D 1545-63 method. The drying time and set to touch time were also determined by ASTM D 1953-70 .
Preparation of Alkyd Resin
Oil modified alkyd resin was prepared with dehydrated castor oil, glycerol and phthalic anhydride using NaOH catalyst. The preparation was done in a 4-neck round bottom flask fitted with a motorized stirrer, a nitrogen inlet, a thermometer pocked and a hold for sampling. In the preparation of alkyd resin, two stages were involved. The first stage was alcoholysis stage and the second stage was esterification stage.
Stage 1 (alcoholysis): In this stage, monoglyceride was first prepared by reacting the oil with glycerol. Alcoholysis of oil was carried out with different percentages of (0.03%, 0.05%, 0.1%) (by weight) PbO catalyst and (0.1%, 0.2%, 0.3%)(by weight) NaOH catalysts.
In alcoholysis reaction, the oil was heated with agitation speed of (700 rpm) and N2 sparging rate of about (0.06ft3/sec) to 230-240ËšC. Glycerol and selected catalyst was added and alcoholysis reaction was carried out at 230-240ËšC. The reaction was continued until a sample of the reaction mixture became soluble in two to four volumes of anhydrous methanol. After alcoholysis reaction was completed, the reaction mixture was cooled to 140ËšC.
Stage 2 (esterification): In this stage, phthalic anhydride was added to the monoglyceride mixture. The temperature was maintained at the range of 230-240ËšC and maintained at this temperature. The sparging rate of N2 was increased to (0.1ft3/sec). The reaction was monitored by periodic determination of the acid value of the mixture until acid value dropped to nearly 5.
The acid value of alkyd resin was determined by ASTM D 1639-90 and the chemical resistances also determined. The prepared resin was standardized by FTIR [12, 13].
III. RESULTS AND DISCUSSIONS
Characterization of Crude Castor Oil
The characteristics of crude castor oil are shown in Table 1.
Table 1. The Characteristics of Crude Castor Oil
Crude castor oil
Free fatty acid value
Iodine value, wiji's
Neutralization of Crude Castor Oil
Table 2 show the FFA content of neutralized oil.
Table 2. The FFA Content of Neutralized Oil
Initial weight of crude castor oil = 100g
FFA (%) of crude oil = 19%
Neutralization temperature = 55ËšC
20% NaCL solution = 40ml
of Neutralized oil
Weight of Neutralized oil (g)
Characterization of Refined Castor Oil
The characteristics of refined castor oil are described in
Table 3 by comparing with ASTM standard castor oil.
Table 3.Characteristics of Refined Castor Oil
Refined castor oil
(ASTM D 960-79)
Free fatty acid value
1.476 to 1.4778
0.957 to 0.961
6.3 to 8.9
Iodine value, wiji's
83 to 88
Bleaching of Neutralized Castor Oil
Effect of bleaching on color and yield of neutralized castor oil is shown in Table 4. Oil was bleached with 0-11% of activated carbon, 0-9% of bentonite and 0-7% of 1:1 mixture of activated charcoal and bentonite
Table 4. Effect of Bleaching On Color and Yield of Neutralized Castor Oil
Initial weight of neutralized oil = 100 g
Bleaching temperature = 100ËšC
Bleaching time = 45 minutes
(wt%) of bleaching agent
Photometric color number*
Wt. of Refined oil (g)
Activated charcoal (A)
Activated charcoal and bentonite (1:1 ratio) (C)
*Photometric color = 1.29D460 + 69.7D620 + 41.2D650 âˆ’ 56.4D670 .
Dehydration of Refined Castor Oil
Table 5 present the yield of dehydrated castor oil at different dehydration conditions. The changes of iodine value and viscosity by dehydration of castor oil at different dehydration conditions are shown in Fig. 1 and Fig. 2.
Table 5. Yield of Dehydrated Castor Oil at Different Dehydration Conditions
Initial weight of sample C2 = 50g
Dehydration time (minutes)/Yield (%)
Fig. 1.Change of Iodine Value with Reaction Time
for Dehydration Temperature at 210-220ËšC
Fig. 2. Change of Viscosity with Reaction Time
for Dehydration Temperature at 210-220ËšC
Characterization of Dehydrated Castor Oils
The characteristics of typical dehydrated castor are presented in Table 6 by comparing with ASTM standard dehydrated castor oil.
Table 6.Characteristics of Typical Dehydrated Castor Oils
Vacuum pressure = 600-640 mmHg
Dehydrated castor oil1
Dehydrated castor oil 2
Standard dehydrated castor oil
Set to touch time (hour)
Drying time (hour)
1dehydration with 1% NaHSO4 catalyst for 60 minutes
2dehydration with 2% NaHSO4 catalyst for 45 minutes
Preparation of Alkyd Resin
Reaction condition of alcoholysis reaction condition in alkyd resin preparation is described in Table 7. Fig. 3 shows the acid value control of esterification reaction. Yield of dehydrated castor oil-modified alkyd resin and the calculation for percentage of reaction complection are presented in Table 3.8.
Table 3.7. 1st Stage Alcoholysis Reaction Conditions
Reaction temperature = 230-240ËšC
Agitation speed = 500 rpm
N2 sparging rate = 0.06 ft3/minutes
Catalyst % (wt%)
Reaction time (hr)
Completion of alcoholysis reaction*
*It was determined by testing the solubility of alcoholysis mixture in anhydrous methanol.
Fig. 3. Acid Value Control of Esterification Reaction
Table 8. Yield of Dehydrated Castor Oil-Modified Alkyd Resin
DCO alkyd resin (100% solid)
IAV-initial acid value
FVA-final acid value
P-degree of reaction complection
Characterization of Alkyd Resin
The physico-chemical properties of alkyd resin are presented in Table 9. The chemical resistances of alkyd resin film are shown in Table 10. Table 11 show FTIR absorption band of dehydrated castor oil-modified alkyd resin.
Table 9. Characteristics of Dehydrated Castor Oil-modified Alkyd Resin
DCO alkyd resin
RSO alkyd resin*
DCO alkyd resinw
RSO- rubber seed oil
Source [1, 14]
Table 10. Chemical Resistances of Alkyd Resin Films
Immersion time (hours)
Appearance of film*
3 N NaOH
*It was examined after the films were air dried for 30 minutes.
Table 11. FTIR Absorption Band of Dehydrated Castor Oil-Modified Alkyd Resin
According to Table 1 FFA content of crude castor oil was high and it was not within the ASTM specification limit. The only reason to reduce the FFA content of oil was to neutralize the crude oil.
In neutralization process, it was found that 30 ml of 2 N NaOH per 100g of oil was required to obtain neutralized oil with an acceptable FFA content and to be a minimum of oil loss. The neutralization time of 10 minutes was sufficient to reduce FFA content from 19% to 1%. The two layers can be easily separated when NaCL solution was added to the neutralized mixture because NaCL can help to ensure adequate salting or graining out of the soapstock. Other impurities in oil were removed by washing with hot water.
From Table 3, it can be seen that the neutralization process can reduce the FFA content of crude oil from 19% to 1%. Then, it can give the refined oil color of 8 and refractive index of 1.474. Therefore, neutralization process can offer great effect on FFA content, color and refractive index of oil.
In Table 4, it can be seen that the highest color removal efficiency was obtained by bleaching with 5% of bleaching agents. Bleaching with (1:1) mixture of activated charcoal and bentonite can offer better result. So, it can be chosen as bleaching agents in bleaching of neutralized oil.
According to the Table 5, the yield of dehydrated castor oil decreased with increasing the dehydration time. In Fig. 1 and 2, it was observed that the dehydrated castor oil with a maximum iodine value and a minimum viscosity could be obtained at the proper reaction time. From Fig. 1, the dehydration of oil without vacuum system could not give acceptable iodine value to qualify as drying oil. When dehydration of oil was done by using 2% of catalyst and vacuum pressure of 600-640 mmHg and the optimum reaction time is 45 minutes, this system could give the dehydrated castor oil with iodine value of 139.05.
Table 7 described that the iodine value and viscosity of dehydrated castor oils were in the limit of ASTM standard dehydrated castor oil.
According to the literature , the alcoholysis reaction is usually completed within an hr or two hrs after the batch had reached operating temperature. In Table 8, it was found that the samples of the alcoholysis mixture did not completely soluble in anhydrous methanol although the alcoholysis reactions were carried out for 4 hrs by using different amount of litharge catalysts (0.03%, 0.05%, 0.1%) and NaOH catalysts (0.1%, 0.2%). In alcoholysis of oil with 0.1% (wt%) and 0.2% (wt%) NaOH catalyst, it cannot also give complete alcoholysis mixture after reaction was carried out for 2 hrs.
In esterification reaction, it was observed that the longer the reaction time, the more viscous the mixture is. In Fig. 3.3, the oil-modified alkyd resin with acid number of 6.6 was obtained after the esterification reaction was carried out for 150 minutes. In Table 8, it was observed that 97.72 % of reaction was completed when the final acid number of alkyd resin was 6.6. The alkyd resin that has acid number of less than 15 is suitable for application of paint, according to literature [1, 7, 8].
Table 10 described that there was no effect on alkyd film after immersion in distilled water for 18 hours. The immersion of alkyd film in water for 18 hours was sufficient time to examine the water resistance. When the alkyd film was immersed in strong alkali solution, 3N NaOH, the film got whitening after immersion time for 8 hours, blistering after immersion time for 16 hours and removal after immersion time for 24 hours. So, these results show that the prepared alkyd resin has high chemical resistance.
The FTIR spectrum of prepared alkyd resin exhibits a characteristic of straight chain ester band at 1738.64 cm-1 and aromatic ring ester band at 1730.09 cm-1. The present of O=C-O-C- also exhibit a characteristic ester band at 1125.26 cm-1. The appearance of CH2, -CH- confirms the present of methyl group at 1460.43 cm-1 and 2856.67 cm-1. The adsorption band at 3008.99 cm-1 is characteristic of alkene carbon (=C-H) according to literature [12, 13].
IV . CONCLUSION
The characteristics of refined castor oils were found to be standardized with ASTM standard castor oils and it was suitable to carry out the next step. The refined castor oil was done by using NaHSO4 catalyst to carry out the dehydration process. Dehydration under vacuum pressure system was effective processing method and this pressure influenced the quality of dehydrated castor oil. A typical dehydrated castor oil (iodine value 140, viscosity 1.6 stroke, set to touch time 3.5 hr and drying time 5 day) was prepared with 1% NaHSO4 catalyst under vacuum of 600-640 mmHg at 210-220ËšC. In alcoholysis of oil by using 0.3% (wt%) NaOH catalyst, it gave complete alcoholohysis mixture to preceed the esterification reaction after reaction time for 2 hrs. Dehydrated castor oil has been used in the preparation alkyd resin. Dehydrated castor oil-modified alkyd resin (acid value 6.6) was prepared by alcoholysis method from dehydrated castor oil, glycerol and phthalic anhydride with a help of 0.3% NaOH catalyst. The physico-chemical properties and high chemical resistance of alkyd resin film showed that they were promising in formulating of paint.