Functionalization of biopolymers with reactive groups to be used as thickeners in oil media

Abstract

During the last decades, there has been an increasing interest in the use of natural components in a wide variety of manufactured products, due to the general tendency to promote the replacement of non-renewable raw materials by renewable resources. The lubricant industry is especially involved in the minimization of the environmental impact caused by their products due to the serious consequences of their discharge to the environment. With this aim, vegetable oils, promising candidates to biodegradable lubricants and potential substitutes of the currently used mineral oils, are being more strongly considered in the market. However, the manufacture of lubricating greases completely based on renewable raw materials is a much more complicated task due to the difficulty of replacing the traditional thickening agents, such as metallic soaps and poliureas, which exhibit high technical efficiency and confer several specific properties to the final product. In this sense,the target of this work is the production of biodegradable chemical oleogels with lubricating applicability consisting of a vegetable oil, like castor oil, and chemically modified natural polymers that play the role of thickeners. With this aim, some renewable raw materials have been selected, such as cellulose, which is the most abundant polymer in nature; some cellulose derivatives, like methylcellulose, among others; chitin, the second more important biopolymer after cellulose; chitosan, the deacetylated derivative of chitin; and some lignocellulosic materials that differ in their origins and pulping treatments. All of them have been NCO-functionalized, in some cases in different degrees, and subsequently dispersed in castor oil, promoting a chemical reaction between them that is the responsible of their physical stability. Furthermore, the specific functional properties of each of the obtained products were studied through different techniques and they were also compared to commercial benchmarks. Therefore, the thermal stability of modified polymers and the corresponding dispersions in castor oil was explored, oleogels were Theologically and tribologically characterized, the mechanical stability evaluated as well as the possible chemical structure of the modified biopolymers and oleogel microstructures. As a result, a number of formulations completely based on renewable raw materials with suitable functional properties (thermal, rheological and tribological) to be proposed as potential substitutes of the current commercial lubricating greases were developed.