Abstract
Six grades of biopolymers formulated to have oil content of 40% (M1), 50% (M2), and 60% (M3) melon seed oil (MESO) and 40% (C1), 50% (C2), and 60% (C3) cottonseed oil (COSO) respectively, were prepared with phthalic anhydride, and glycerol using alcoholysis-polycondensation process. The extend of polycondensation was monitored by determining the acid value of aliquots of the reaction mixture at various intervals of time. Molecular weight averages and polydispersity index (PDI) of the finished alkyds were determined by Rast method and end-group analysis. Molecular weight averages and PDI vary with differences in oil length of the alkyds, with samples M2 and C2 respectively exhibiting the highest PDI. Molecular weight average obtained from end-group analysis and those determined by Rast method in brackets are 1338.92 (597.00), 982.33 (696.25), 1316.09 (754.03), and 1160.57 (448.13), 765.96 (583.57), 1049.92 (696.25) for samples M1, M2, M3 and C1, C2, C3 respectively. Number molecular weight averages calculated from end-group analysis are larger than those obtained by Rast method for both MESO and COSO alkyds and seem to grossly overestimate their molecular weights. The mode of variation of these properties indicates that the synthesis of MESO and COSO alkyds are complex. Correlation of PDI with the quality of the finished alkyds shows that the higher the PDI value the better the quality of the alkyd. Performance properties such as rate of drying, film hardness and resistance to chemicals were optimum at 50% oil length for both triglyceride oil alkyds.
Highlights
Alkyd resins have been identified as one of the biopolymers synthesised from triglyceride oils [1]
cottonseed oil (COSO) was purchased at Sabongari market, Kano, while melon seeds were purchased at Akpan Andem market, Uyo, processed and the oil soxhlet extracted using the method described in our previous work [11]
50% oil length alkyds (M2 and C2), which has the highest polydispersity index (PDI), exhibited the best characteristics such as excellent adhesion, good hardness, fast drying time and resistance to chemicals followed by 40% oil length alkyds (M1 and C1). 60% oil length alkyds (M3 and C3) with the least PDI had the least performance characteristics. It can be inferred from these results that reactions leading to the formation of melon seed and cottonseed oils alkyd resins are complex
Summary
Alkyd resins have been identified as one of the biopolymers synthesised from triglyceride oils [1]. It is a key ingredient of all surface-coating products like paints, primer, adhesives, printing ink [2] and varnishes. They are tough resinous materials prepared via an esterification reaction among polybasic acids, polyols and monoacids (commonly fatty acids from vegetable oils or fats) [3]. The physical, chemical and mechanical properties of alkyd resins like other polymers are dependent on their relative sizes or molecular weight [5] [7] [8]
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