18 research outputs found
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 10â22 carbons)
and diols (chain lengths, <i>n</i>, 2â10 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 oddâeven 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
âŒ6 mPa·s for the smallest diester to âŒ41 mPa·s
for the largest diester at 40 °C. This range is significantly
larger than that accessible to native vegetable oils (33â66
mPa·s at 40 °C), affording a vastly improved application
range for biobased materials
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 (C<sub>17</sub>H<sub>33</sub>COO)<sub>2</sub>[CH<sub>2</sub>]<sub><i>n</i></sub>) 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 structureâproperty 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