Characterisation and properties of homo- and heterogenously phosphorylated nanocellulose. (10th July 2015) - Kokol, Vanja
Highlights: Dibasic phosphate and monobasic phosphite groups are formed at C6 and C3 hydroxyls. 60-Fold higher surface charge density on NFC is created under homogenous conditions. The phosphorylations do not affect the crystallinity of NC. The weight loss is noticeably prevented during the pyrolysis process. High hydrolytic stability to water at all pH mediums is proved. Abstract: Nano-sized cellulose ester derivatives having phosphoryl side groups were synthesised by phosphorylation of nanofibrilated cellulose (NFC) and nanocrystaline cellulose (NCC), using different heterogeneous (in water) and homogeneous (in molten urea) processes with phosphoric acid as phosphoryl donor. The phosphorylation mechanism, efficacy, stability, as well as its influence on the NC crystallinity and thermal properties, were evaluated using ATR-FTIR and 13 C NMR spectroscopies, potentiometric titration, capillary electrophoresis, X-ray diffraction, colorimetry, thermogravimmetry and SEM. Phosphorylation under both processes created dibasic phosphate and monobasic tautomeric phosphite groups at C6 and C3 positioned hydroxyls of cellulose, yielded 60-fold (∼1173 mmol/kg) and 2-fold (∼1038 mmol/kg) higher surface charge density for p-NFC and p-NCC, respectively, under homogenous conditions. None of the phosphorylations affected neither the NC crystallinity degree nor the structure, and noticeably preventing the derivatives from weight loss during the pyrolysis process. The p-NC showed high hydrolytic stability to water at all pH mediums. Reusing of the treatment bath was examined after the heterogeneous process.