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Understanding the degree of estolide enzymatic polymerization and the effects on its lubricant properties

Authors:Roberto Fernandez-Lafuente
Groups of research:Optimization of biocatalysts and bioprocesses
Greco-Duarte, J. a, Collaço, A.C.A. a, Costa, A.M.M. b, Silva, L.O. b, Da Silva, J.A.C. c3 ,
Torres, A.G. b, Fernandez-Lafuente, R.*,d, Freire, D.M.G. *,a
a  Department of Biochemistry, Institute of Chemistry, Federal University of Rio de
 Janeiro, Cidade Universitária, Centro de Tecnologia, Bl. A, Sl. 549, Ilha do Fundão,
 21949-909, Rio de Janeiro, Brazil.
b  Laboratory of Food Science and Nutritional Biochemistry, Institute of Chemistry,
 Federal University of Rio de Janeiro, Cidade Universitária, Centro de Tecnologia, Bl.
 A, Sl. 528 A, Ilha do Fundão, 21949-909, Rio de Janeiro, Brazil.
c Cenpes, Centro de Pesquisas e Desenvolvimento Leopoldo Américo Miguez de Mello,
 Petrobras, 21941-970, Rio de Janeiro, Brazil.
d Departamento de Biocatalisis, ICP-CSIC, C/ Marie Curie 2, Campus UAM-CSIC,  Cantoblanco, 28049 Madrid, Spain.
Abstract: The aim of this study was to understand estolide enzyme
polymerization from free ricinoleic acid (FRA) and its lubricant
properties, by controlling the reaction time, during the course of a
reaction involving a two-step enzymatic hydroesterification from castor
oil. Adding water increased the reaction rate, reducing the total acidity
to 30% in 24 h. FRA is the major component of castor oil (up to 90%). A
GC analysis of the FRA, expressed as g/100 g of sample, was used to
determine the FRA profile during estolide polymerization. These data
suggested a relationship between the total acidity of the samples and the
FRA concentration. The estolide profile and number (EN) were determined
by GPC and NMR analyses. A 14-hour reaction time was needed for total
consumption of FRA, with an EN of 5.5 and a degree of polymerization of
the major estolide of 6/7. The analysis showed that estolides of several
sizes [dimers, trimers, tetramers, and pentamers (+)] were produced
during the reaction; between 8 and 14 h the EN grew exponentially until
reaching a plateau after about 16 h of reaction. From 14 to 24 h,
although the estolide-size profile did not change significantly, EN
continued to increase with increasing reaction time, until a
polymerization degree of 7/8 at 24 h. The increase in EN corresponds to
the increase in the viscosity index and oxidative stability, reaching 164
and 43 min, respectively, after 20 h of reaction; as well as to the
decrease in pour point and total acidity index, which reached -48 °C and
36.8 mg KOH/g of sample after 20 h of reaction. This is the first
description of a kinetic method to control the degree of estolide
polymerization, by controlling the reaction time and its relationship
between the EN and the lubricant properties of these molecules, aiming
toward the production of different biolubricants for several applications
and desired uses.
Keywords:castor oil, ricinoleic acid, biolubricants, estolides, lipases.
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