Effects of polyol ester structure on their viscosity and solidification trends

This research is dedicated to turning non-edible Camelina and Crambe oils into
sustainable source of basestocks for lubricants, preferably hydraulic fluids. From diverse
spectra of possible products, based on these non-food oils, medium chainlength fatty acids
(MCFA) appear as promising candidates for basestock building blocks. Esters of polyhydric
alcohols with tertiary β-carbon, a.k.a. polyols, are frequently used for the basestocks, because
of improved thermal and oxidative stability. During this study, MCFA esters of neopentyl
glycol (NP), trimethylol propane (TMP) and pentaerythritol (PE) were synthesized to
investigate the influence of molecular structure on viscosity and low temperature
solidification of obtained fluids. Kinematic viscosities at 40°C were measured using capillary
viscometers. Pour points were determined using the same thermal cooling regime, as
instructed by ASTM D97. The results are presented in Fig. 1. As expected, synthesized esters demonstrate a distinct tendency to increase in viscosity with
higher molecular weights. In order to design a basestock of necessary viscosity grade,
conventional methods of viscosity prediction can be used both for individual esters and their
blends. The relationship between ester structure and pour points is much more complex (Fig.
1 b). Compared to tri-esters (i.e. TMP+MCFA), NP esters of the same MCFA (i.e. di-esters)
solidify easier despite significantly lower mol. wt. Nearly as counterintuitive is the
observation that tri-ester pour points are lower than those of tetra-esters of similar mol. wt.
This suggests that polyol tri-esters, such as those of TMP, give more beneficial low
temperature fluidity than polyol esters of NP or PE. Further improvement can be achieved by
esterifying not one, but several MCFA during the synthesis. When NP and TMP esters were
synthesized using a 1:1 blend of C9 and C11 MCFA, their pour points appeared in between of
those for respective esters of pure MCFA, but much closer to those of C9 than C11. Synthesis
iterations can provide further improvement in low temperature fluidity of MCFA esters and
provide excellent opportunities to utilize Crambe and Camelina oils in industrial applications.