Surface esterification of cellulose nanofibers by simple organocatalytic methodology

Abstract

Bacterial cellulose nanofibers were esterified with two short carboxylic acids by means of a simpleand novel organic acid-catalyzed route. The methodology proposed relayed on the use of a non-toxicbiobased -hydroxycarboxylic acid as catalyst, and proceeded under moderate reaction conditions insolventless medium. By varying the esterification interval, acetylated and propionized bacterial cellu-lose nanofibers with degree of substitution (DS) in the 0.02?0.45 range could be obtained. Esterifiedbacterial cellulose samples were characterized by means of Solid-State CP/MAS13C Nuclear MagneticResonance spectroscopy (CP/MAS13C NMR), Fourier Transform Infrared spectroscopy (FTIR), X-rayDiffraction (XRD), Thermogravimetric Analysis (TGA) and chosen hydrophobicity test assays. TGA resultsshowed that the esterified nanofibers had increased thermal stability, whereas XRD data evidenced thatthe organocatalytic esterification protocol did not alter their crystallinity. The analysis of the ensuingmodified nanofibers by NMR, FTIR, XRD and TGA demonstrated that esterification occurred essentiallyat the surface of bacterial cellulose microfibrils, something highly desirable for changing their surfacehydrophilicity while not affecting their ultrastructure.