Engineering Green Lubricants I: Optimizing Thermal and Flow Properties of Linear Diesters Derived from Vegetable Oils

The crystallization, melting, and flow behaviors of a series of linear aliphatic diesters (chemical formula (C₁₇H₃₃COO)₂[CH₂]_<i>n</i>) derived from vegetable oil feedstock were investigated as a function of the methylene spacer units between the two ester moieties (given by the diol chain length, <i>n</i>). The crystallization and melting behaviors were determined by differential scanning calorimetry and flow behavior and viscosity by rotational rheometry. The results show that quantifiable structure–property relationships exist between the methylene spacer units of the molecules and their physical properties, which can be used to custom-design green materials with controlled phase composition and physical properties such as melting and viscosity suitable for use in applications such as lubricants, phase change energy storage, or waxes

Engineering Green Lubricants IV: Influence of Structure on the Thermal Behavior of Linear and Branched Aliphatic Fatty Acid-Derived Diesters

Fatty acid-derived aliphatic diesters and their branched derivatives are lubricating compounds that demonstrate predictable viscosity temperature profiles and remain fluid at extremely low temperatures. In this work, the influence of molecular structure on the high temperature thermal behavior of several series of aliphatic fatty acid-based diesters was investigated using thermogravimetric analyses (TGA). Evaporation behavior was determined as a function of molecular weight, saturation, symmetry and double bond position, and decomposition behavior as a function of molecular weight, branching, saturation and symmetry. The results revealed that the diol-derived diesters underwent predictable molecular weight-mediated evaporation, and that further refinement of the predicted evaporation temperatures could be obtained by accounting for saturation in the fatty acid moieties. Double bond position and symmetry did not measurably influence the evaporation temperatures of the diesters. Evaporation was successfully suppressed with increasing molecular weight, with the fatty acid chain length and the nature of the branched group being most important in the linear and branched diesters, respectively. Overall, these results are fundamentally significant because they provide the background necessary to make informed changes to molecular structure so as to effect the desired high temperature behavior in renewably sourced specifically engineered materials for lubricant applications

Engineering Green Lubricants II: Thermal Transition and Flow Properties of Vegetable Oil-Derived Diesters

Six homologous series of linear aliphatic diesters were prepared from commonly available fatty acids (chain lengths 10–22 carbons) and diols (chain lengths, <i>n</i>, 2–10 carbons). The thermal transition and flow properties are presented as functions of their molecular structures, namely chain length, symmetry, end group interactions, and saturation. Predictive relationships between the total chain length of the diesters and their characteristic thermal transition temperatures were obtained. The thermal transition temperatures were affected by intramolecular steric repulsion of the ester groups at small diol chain lengths (<i>n</i> ≤ 4) and by the odd–even effect associated with large diol chains (<i>n</i> > 4), allowing for further refinement of the crystallization and melting prediction models. All of the diesters presented Newtonian flow behavior above their melting points, making them particularly suitable for use in lubricant formulations and other flow-dependent applications. The influence of mass on the viscosity was significantly greater than any other structural feature of the linear aliphatic molecules. Viscosity scaled predictably with total chain length, from ∼6 mPa·s for the smallest diester to ∼41 mPa·s for the largest diester at 40 °C. This range is significantly larger than that accessible to native vegetable oils (33–66 mPa·s at 40 °C), affording a vastly improved application range for biobased materials