Waxes derived from self-metathesis modified plant oil blends – A case for exploiting oligomerization to mitigate low molecular mass and unsaturation

Abstract

The self-metathesis of vegetable oil blends was explored as a means for making functional and environmentally adapted waxes. Several mixtures of soybean oil (SBO) and palm oil (PO), the most readily available triacylglycerol (TAG) oils, were investigated as model unsaturated/ saturated systems to determine the advantages and limits of using such blends. The objective was to control the balance between unsaturation which tend to keep the material fluid at low temperature and saturation coupled with the self-metathesis induced oligomerization which promote crystallization and gelling for optimal wax applications. Five compositions of SBO and PO were metathesized and characterized for thermal transition behavior, solid fat content, microstructure, viscosity and hardness; parameters relevant to the functionality of waxes. The characteristic physical properties versus concentration presented peak-shaped curves with maxima at 15 %w/w SBO. This trend is explained by the modification to the molecular ensemble introduced by the self-metathesis, depleting the low melting species (liquid fraction) and enriching the high temperature melting species (solid fraction). The induced oligomerization combined with the pre-existing saturation which promote solidification are demonstrated to counterbalance the fluidization effect of unsaturation to a tipping point after which the unsaturation is overwhelming. The study shows that although limited in extent, appropriate blending can be an economical and effective tool to shift the crystallization toward room temperature of otherwise liquid TAG derivatives and improve their wax properties.