Abstract
Purpose: Alkyd resins constitute a very high proportion of conventional binders used in surface coatings. In order to enhance the quality of these alkyd resins methyl esters of rubber seed oil (MERSO) were used in the preparation of the resins. Methods: MERSO were obtained by in-situ alcoholysis of rubber seed. Alkyd resins having oil lengths of 45, 50 and 55% were prepared with MERSO, phthalic anhydride and glycerol using alcoholysis method. Lead (II) oxide and xylene were used as catalyst and refluxing solvent, respectively. The physico-chemical characteristics of the MERSO and the resins obtained were compared with the corresponding value of rubber seed oil (RSO) and its alkyd resins. Chemical resistance of the alkyd resins was also determined. Results: The acid value of the finished alkyd resins depends on the rate and extent of esterification. Iodine value of the alkyd shows that the level of unsaturation depends on the oil length of the resins. The free fatty acid (FFA) value (1.99%) of the MERSO was much lower than that of the RSO (9.54%). This supports the choice of methyl ester as a preferred alternative to the use of the raw RSO in alkyd resin preparation. All the alkyd samples were fairly resistant to brine, acid and water but poorly resistant to alkali. However, the MERSO alkyds were observed to have a better resistance than the RSO alkyd resins. The scratch/gouge pencil hardness shows that the hardness of the alkyd films decreases with the oil length. Keywords: Alkyd resins, rubber seed oil, methyl ester. > Tropical Journal of Pharmaceutical Research Vol. 3 (1) 2004: pp. 311-317
Highlights
Alkyd resins are products of polycondensation reaction between polybasic acid and polyhydric alcohol modified with fatty acid or drying oil
This study reports on the in-situ alcoholysis of rubber seed oil (RSO), preparation and characterisation of alkyd resins the RSO and the methyl esters of rubber seed oil (MERSO) aimed at enhancing alkyl resins
The acid value of the MERSO is observed to be much lower than that of the crude RSO. This shows that insitu alcoholysis of RSO in the production of the methyl esters causes less hydrolysis compared to extraction with n-hexane
Summary
Alkyd resins are products of polycondensation reaction between polybasic acid and polyhydric alcohol modified with fatty acid or drying oil. Oil modified alkyd resins constitute a major group of resins used as binders in surface coatings. The oils that are mostly employed for alkyd resin synthesis are linseed, soybean, castor and tall oils[3,4,5]. These oils are largely imported to Nigeria for the formulation of coatings for metal cans used in packing of beverages, drugs, food, etc. Drying oils are available locally, which have remained untapped. These include rubber seed oil, soybean oil, walnut oil and tobacco oil[6]. Research has shown it to be a rich source of oil that is comparable in quality to dry oils commonly used in surface coatings[10,11,12]
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