Influence of functionalization degree on the rheological properties of isocyanate-functionalized chitin- and chitosan-based chemical oleogels for lubricant applications

摘要

This work deals with the influence of functionalization degree on thethermogravimetric and rheological behaviour of NCO-functionalized chitosan- andchitin-based oleogels. Chitosan and chitin were functionalized using different proportionsof 1,6-hexamethylene diisocyanate (HMDI) and subsequently dispersed in castor oil topromote the chemical reaction between the –NCO group of the modified biopolymer andthe –OH group located in the ricinoleic fatty acid chain of castor oil, thus resulting indifferent oleogels with specific thermogravimetric and rheological characteristics.Biopolymers and oleogels were characterized through Fourier transform infraredspectroscopy (FTIR) and thermogravimetric analysis (TGA). Small-amplitude oscillatoryshear (SAOS) measurements were performed on the oleogels. Oleogels presented suitablethermal resistance, despite the fact that the inclusion of HMDI moieties in the polymerstructure led to a reduction in the onset temperature of thermal degradation. The insertionof low amounts of HMDI in both chitin and chitosan produces a drastic reduction in thevalues of oleogel viscoelastic functions but, above a critical threshold, they increase with the functionalization degree so that isocyanate functionalization results in a chemical toolto modulate oleogel rheological response. Several NCO-functionalized chitosan- andchitin-based oleogel formulations present suitable thermal resistance and rheologicalcharacteristics to be proposed as bio-based alternatives to traditional lubricating greases.