Properties of surface acetylated microfibrillated cellulose relative to intra- and inter-fibril bonding

Microfibrillated cellulose (MFC) created via the micro-grinding method was heterogeneously acetylated to different substitution levels using acetic anhydride and heat rather than strong acid catalysis. The acetylated MFC was formed into thin films and characterized by infrared spectroscopy and mechanical testing. Spectral and chemical analysis confirmed controlled acetylation with increased reaction time. Due to microfibrils forming more inter-fibril bonds than whole fibers, it is generally accepted that there are more hydrogen bonds to carry the applied load. However, with increased acetylation, the initial number of possible hydrogen bonds was decreased which led to a lower tensile strength and rupture energy. At 28 % degree of substitution, the tensile index decreased to 50 % of the initial value, whereas the rupture energy was nearly completely eliminated. The acetylated fibrils, thus, created a structure that resembled the energy absorption behavior of whole fiber sheets, but behaved differently when compared in terms of tensile index.