Studies on copra oil self-cured ester as a sustainable material for surface coatings

Abstract

In this paper, synthesis, characterization, and optimization of a copra oil self-cured ester have been studied. The oil was first analyzed to examine the physico-chemical properties (iodine value, viscosity, refractive index, acid value, and specific gravity) and subsequently neutralized and dehydrated. The synthesis of self-cured ester was accomplished by reduction of the triglycerides in the oil by alcoholysis and functional group modification with phthalic anhydride and styrene via free radical co-polymerization reaction. Structural elucidation of the resin was enhanced by the Fourier transform infrared (FT-IR) spectroscopic technique. The response surface methodology (RSM) based on a central composite rotatable design (CCRD) involving 30 experiments of four process variables at five levels was employed for the optimization study as an economical way of obtaining an optimal response with fewest number of experiments. The studied process parameters were reaction temperature, reaction time, catalyst concentration, and phthalic anhydride-to-monoglyceride oil (PA:MGO) ratio. A predictive model describing the fractional conversion in terms of process variables was derived from multiple regression analysis. An optimum fractional conversion of 96.55% was predicted at a reaction temperature of 241.94 °C, reaction time of 124.2 min, catalyst concentration of 0.1% and PA:MGO ratio of 0.38:1, for the process. The extent of reaction at 135 min of polycondensation of the monomers was more than 85%. A model validation experiment shows a good agreement between the actual (97.19%) and predicted (96.55%) values. Physico-chemical properties and performance characteristics of the ester indicate its suitability in surface coating applications.