Abstract
The main objective of this work was the incorporation of reactive isocyanate groups into chitin and chitosan in order to effectively use the products as reactive thickening agents in castor oil. The resulting gel-like dispersions could be potentially used as biodegradable lubricating greases. Three different NCO–functionalized polymers were obtained: two of them by promoting the reaction of chitosan with 1,6-hexamethylene diisocyanate (HMDI), and the other by using chitin instead of chitosan. These polymers were characterized through 1H-NMR, FTIR and thermogravimetric analysis (TGA). Thermal and rheological behaviours of the oleogels prepared by dispersing these polymers in castor oil were studied by means of TGA and small-amplitude oscillatory shear (SAOS) measurements. The evolution and values of the linear viscoelasticity functions with frequency for –NCO–functionalized chitosan- and chitin-based oleogels are quite similar to those found for standard lubricating greases. In relation to long-term stability of these oleogels, no phase separation was observed and the values of viscoelastic functions increase significantly during the first seven days of ageing, and then remain almost constant. TGA analysis showed that the degradation temperature of the resulting oleogels is higher than that found for traditional lubricating greases.
Highlights
Nowadays, there is a general tendency to promote the replacement of non-renewable raw materials by renewable resources in order to avoid or minimize the impact that process technologies and industrial products cause in the environment
Vegetable oils are being increasingly used as lubricant base oils instead of mineral and synthetic oils, the substitution of traditional thickener agents, such as lithium, aluminum, sodium or calcium soaps in lubricating greases by others derived from renewable resources, like some biopolymers, is a complicated task due to the technical efficiency of these metallic soaps to impart the desired functional properties to the final product
Three different types of polymers functionalized with isocyanate groups, chitosan in two of the cases and chitin in the other one, were prepared
Summary
There is a general tendency to promote the replacement of non-renewable raw materials by renewable resources in order to avoid or minimize the impact that process technologies and industrial products cause in the environment. The lubricant industry is especially interested in reducing the environmental impact of its products [1,2]. Vegetable oils are being increasingly used as lubricant base oils instead of mineral and synthetic oils, the substitution of traditional thickener agents, such as lithium, aluminum, sodium or calcium soaps in lubricating greases by others derived from renewable resources, like some biopolymers, is a complicated task due to the technical efficiency of these metallic soaps to impart the desired functional properties to the final product. Chitosan is typically obtained by deacetylation under alkaline conditions of chitin, which is the second most abundant biopolymer in Nature, after cellulose. Chitin and chitosan are linear polysaccharides composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and
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