Comparison of a New Estolide Oxidative Stability Package

Abstract

AbstractThe rotating pressurized vessel oxidation test (RPVOT) was used in the analysis and determination of a new oxidative stability package (OSP) for a series of estolide based materials. Three antioxidants (BHT, two different alkylated diphenyl amines) were used in either 0.5 or 1.0 wt/wt%, in different ratios, and in conjunction with one another (hindered phenol/alkylated diphenyl amines or hindered phenol/mixed alkylated diphenyl amines). The estolide‐based samples analyzed for their resistance to oxidation were two pure (distilled) estolides (oleic estolide 2‐EH esters and coco‐oleic estolide 2‐EH esters), an estolide mixture that was analyzed straight from the reaction (coco‐oleic estolide 2‐EH esters with coco 2‐EH esters) and finally the ester fraction from the estolide mixture (coco 2‐EH esters). The coco estolide mixture and coco 2‐EH esters had the best overall RPVOT times with 1.0% of the alkylated diphenyl amine, coco estolide mixture, 326 min, and coco 2‐EH esters, 310 min. Coco estolides were expected to have an advantage over the simple oleic estolides due to the increase in saturation in the estolide. Unexpectedly, the two distilled estolides (oleic and coco) had very similar RPVOT max times with all the antioxidants, and were much higher than the other oxidative packages tested to date. In general, the alkylated diphenyl amine outperformed mixed alkylated diphenyl amines in the majority of the individual samples tested specially the coco 2‐EH esters and distilled coco‐oleic estolide 2‐EH esters material at 1% OSP. Overall, a series of new antioxidants were tested and compared to other commercial products. A variety of physical properties of the four estolide based material were collected and compared to commercially acceptable material. Coco‐oleic estolide 2‐EH esters were formulated to have excellent pour points (−36 °C), were both oxidatively and hydrolytically stable (RPVOT, 310 min), with expected good biodegradability which should help commercialization.