Lubricating and Waxy Esters. VI. Effect of Symmetry about Ester on Crystallization of Linear Monoester Isomers

The crystal structure development of jojoba-like esters incorporating either 1-decenoic acid and/or 1-decenol, namely octadec-9-enyl dec-9-enoate (JLE-281), and its isomer dec-9-enyl oleate (JLE-282) was investigated to reveal the effect of symmetry about the ester group on crystallization of aliphatic fatty monoesters. The phase transformation path was investigated with temperature-time resolved X-ray diffraction during stepped isothermal crystallization, and while cooling from the melt at a fixed rate. Startling differences in phase behavior were uncovered between the isomers. When stepped isothermals were used, selective extinctions occurred at a transition temperature for JLE-281 but not for JLE-282. The extinctions, which are due to dramatic changes in the electronic density of certain families of planes, indicate a phase transition attributed to a brusque rearrangement of the oxygen atoms in the crystal subcell. The phase transition did not occur when the JLEs were cooled continuously. The crucial role played by the position of the alkyl chain and its orientation relative to the easy rotation site of the C–O bond in the phase trajectories of the JLEs was particularly highlighted

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

Lipid shortenings: a review

A critical introduction to lipid shortening systems is provided. The review covers types, formulations, functionality, and processing conditions required for the production of lipid shortening systems. Furthermore, lipid shortenings and their production are placed within the context of recent advances in the areas of crystallization, structural elucidation, and mechanical modeling of fat crystal networks in general. The various unit operations involved in the production of lipid shortenings are examined in light of the evolution of structure (both at the crystalline and microstructural levels) and derived physical functionality

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

Vegetable Oil Derived Solvent, and Catalyst Free Click Chemistry'' Thermoplastic Polytriazoles

Azide-alkyne Huisgen click chemistry provides new synthetic routes for making thermoplastic polytriazole polymers-without solvent or catalyst. This method was used to polymerize three diester dialkyne monomers with a lipid derived 18 carbon diazide to produce a series of polymers (labelled C18C18, C18C9, and C18C4 based on monomer chain lengths) free of residual solvent and catalyst. Three diester dialkyne monomers were synthesized with ester chain lengths of 4, 9, and 18 carbons from renewable sources. Significant differences in thermal and mechanical properties were observed between C18C9 and the two other polymers. C18C9 presented a lower melting temperature, higher elongation at break, and reduced Young's modulus compared to C18C4 and C18C18. This was due to the odd-even effect induced by the number of carbon atoms in the monomers which resulted in orientation of the ester linkages of C18C9 in the same direction, thereby reducing hydrogen bonding. The thermoplastic polytriazoles presented are novel polymers derived from vegetable oil with favourable mechanical and thermal properties suitable for a large range of applications where no residual solvent or catalyst can be tolerated. Their added potential biocompatibility and biodegradability make them ideal for applications in the medical and pharmaceutical industries

Lubricating and Waxy Esters, V: Synthesis, Crystallization, and Melt and Flow Behaviors of Branched Monoesters Incorporating 9‑Decenol and 9‑Decenoic Acid

Branched derivatives of waxy monoesters incorporating 9-decenol and 9-decenoic acid were synthesized using epoxidation and ring-opening esterification. The reactions were conducted at two different temperatures and monitored over time. The crystallization, melting, and viscosity of the compounds were all controlled strongly as a function of incremental branching. Isomerism was shown to be critically important: an OH group at the end of the hydrocarbon chain completely suppressed crystallization, whereas its isomer with a terminal acyl chain did not. The structure of the linear monoesters were shown to provide the templates for crystallization, melting, and flow behavior, whereas the branching effect extended but could not erase the effect of the base molecular architecture. These compounds present a large range of properties that are suitable for a variety of applications ranging from waxes to lubricants

Synthesis and Physical Properties of Triacylglycerol Oligomers: Examining the Physical Functionality Potential of Self-Metathesized Highly Unsaturated Vegetable Oils

Seven model oligomers (from dimer to octamer) of the triacylglycerol (TAG) triolein were synthesized from oleic acid and fully characterized by ¹H NMR, ¹³C NMR, mass spectroscopy, and gel permeation chromatography (GPC). The thermal stability of the oligomers as determined by TGA was excellent, with degradation beginning at 342 °C for the most thermally labile samples. The samples all presented glass transitions at low temperatures, with <i>T</i>_g continuously shifting to higher temperatures with increasing numbers of monomers. The crystallization and melting behavior scaled with molecular size and relative number of double bonds in the trans- configuration. Flow behavior was investigated over a large range of temperatures (−10 to 110 °C), and application of the Herschel–Bulkey model to shear stress versus shear rate data evidenced a flow behavior dependent on molecular size and temperature. The oligomers presented a thinning to Newtonian flow transition temperature proportional to molecular size. The viscosity versus temperature data, fitted with a generalized van Velzen equation, suggested that it is the competition between the trans- character and size of the molecules which determines the rheology of these molecules. Overall, all the investigated properties plateaued at the hexamer, suggesting that no further marginal utility can be obtained with larger oligomers