Recent interests in green nanocomposites and public demands for more environmental friendly materials have sparked the development of nanocomposites derived from renewable sources. One of the most studied materials in the field of green nanocomposites is cellulose. Cellulose is the most abundant organic material in the world. It can be produced by plant or bacteria from the Acetobacter species. However, cellulose is extremely hydrophilic in nature due to the presence of hydroxyl groups. This will result in poor interfacial adhesion between cellulose and hydrophobic biodegradable polymer matrices. Therefore, novel methods are required to improve the compatibility between the cellulose and the matrix.
In this work, we reactively compatibilise bacterial cellulose (BC) and microcrystalline cellulose (MCC) in a single step to produce all-cellulose nanocomposites through organic acid esterification reaction. Due to the differences in the crystal structure and the hydroxyl groups availability of the two cellulose, significant bulk modification of MCC will occur and MCC will be modified into a polymer whilst BC will essentially be only modified on the surface of the nanofibrils. As a result, all-cellulose nanocomposites reinforced by highly crystalline BC nanofibrils can be produced. By preserving the crystalline structure of BC, the Young's modulus of BC (~114 GPa) will not be affected much, leading to the production of green nanocomposites with improved properties. It was found that both the tensile strength and modulus of the nanocomposites improved by as much as 20% at 5 wt% BC loading in MCC esterified with hexanoic acid. We have also developed a method to determine the accessibility of hydroxyl groups on cellulosic materials in this work.