Synthesis, characterisation and evaluation of heated rubber seed oil and rubber seed oil-modified alkyd resins as binders in surface coatings

Abstract

Rubber seed oil (RSO) heated at 300 ± 5°C for six hours and RSO-modified alkyd resins were evaluated as binders for surface coatings. During heating of rubber seed oil, the bulk viscosity varied exponentially with time. GPC analysis showed that RSO consists of a very high molecular weight fraction that is uncommon in vegetable oil in addition to free fatty acid, mono-di-, tri-glycerides and oligomeric tryglycerides. Values of <img src='http://www.niscair.res.in/jinfo/mbar.gif' border=0>_n<i> </i>and <img src='http://www.niscair.res.in/jinfo/mbar.gif' border=0>_w of 7393 and 13076 respectively were found for RSO. Heated rubber seed oil (HRSO) gave <img src='http://www.niscair.res.in/jinfo/mbar.gif' border=0>_n of 475 and <img src='http://www.niscair.res.in/jinfo/mbar.gif' border=0>_w of 599: while RSO-modified alkyd samples of oil contents of 40% (I), 50% (II) and 60% (III) gave <img src='http://www.niscair.res.in/jinfo/mbar.gif' border=0>_n<i> </i>of 3234, 1379 and 3304 respectively; and <img src='http://www.niscair.res.in/jinfo/mbar.gif' border=0>_w of 6186, 2147 and 8406 respectively. HRSO is narrowest in size distribution compared to RSO and all the alkyd samples as indicated by their polydispersity indices. RSO was found to be semi-drying as the film remained tacky after long period (about 48h) of exposure. Heating enhanced its drying ability. The HRSO films exhibited reasonable pencil hardness and excellent resistance to acid and salt solution but poor resistance to alkali solution compared to the alkyd samples. The drying ability and chemical resistance of HRSO and RSO-modified alkyd were greatly enhanced by modification with cashewnut shell liquid-formaldehyde resin (10% <i>wl w</i>)<i>.</i>