Study of Conversion of Cellulose into Micro-and Nano Crystalline Particles during Acidic Hydrolysis

Acid hydrolysis is a common process used for the production of microcrystalline (MCC) and nanocrystalline cellulose (NCC). When the starting cellulose feedstock is treated with dilute mineral acid (1-3 M), a sharp decrease in degree of polymerization (DP) is observed until achieving a minimum constant value called level-off degree of polymerization (LODP), which is associated with DP of elementary nanocrystallites. Despite achieving of LODP, after such chemical treatment the micron-size particles of MCC are formed instead of nanoparticles - a paradox that requires an explanation. It was found that dilute acid causes a selective degradation of non-crystalline domains (NCD), which leads to transverse splitting of relatively long fibers and obtaining of shorter low-molecular fragments of the fibers, namely micron-size particles of MCC. On the other hand, concentrated acids (7-9 M) cause the degradation not only NCD, but also tightly packed lateral surfaces between nanocrystallites of cellulose microfibrils connected via strong intercrystalline contacts, thus facilitate the release free particles of NCC.

Keywords: Cellulose, Acid Hydrolysis, Degree of Polymerization, Degree of Crystallinity, Microcrystalline Particles, Nanocrystalline Particles.