Synthesis of oil based hyperbranched resins and their modification with melamine-formaldehyde resin

Abstract

In this research hyperbranched resins containing fatty acid residues were synthesized. Dipentaerythritol which has six hydroxyl groups was used as the core molecule, and it was transesterified with (i) castor oil, and (ii) a mixture of castor oil and linseed oil at 240 °C. The resulting molecule had hydroxyl containing ricinoleic acid residue coming from castor oil. It was then esterified with dimethylol propionic acid at 140 °C in the presence of para-toluene sulfonic acid used as catalyst. The hyperbranched resin thus produced was then mixed with melamine-formaldehyde resin to improve its properties. The resins were characterized by FTIR spectroscopy, and the thermal properties were determined by DSC. The resins were thermally stable up to 316 °C. The viscosity of the resin that was synthesized by using only castor oil was 3.0 Pa s, while the one synthesized by using 50% linseed oil had a viscosity of 1.0 Pa s. When reacted with dimethylol propionic acid the viscosity of the former resin increased to 7.0 Pa s, and that of the second to 3.7 Pa s. The hyperbranched resins showed excellent adhesion, gloss, flexibility, and formability. The mixed resin (i.e. hyperbranched and melamine-formaldehyde) had higher hardness values but lower gloss, adhesion, and bending resistance. Both types of resins also had good impact and abrasion resistances.