Characterization of bamboo nanocellulose prepared by TEMPO-mediated oxidation

Abstract

The synthesis of TEMPO-oxidized bamboo cellulose nanofibrils (TOBCNs) was attempted using two locally available species in Thailand (Dendrocalamus asper and D. membranaceus). Bamboo powder was first delignified with NaClO2. The obtained bamboo holocelluloses (BHs) were then oxidized via a TEMPO/NaBr/NaClO system in water at pH 10 for 2 h. The effects of NaClO addition level on the weight recovery ratio, carboxylate content, and nanofibrillation yield were studied. At a higher level of NaClO addition, the weight recovery ratio of TEMPO-oxidized bamboo holocelluloses (TOBHs) decreased from 90% to 70%, while the carboxylate content of TOBHs increased up to 0.8 mmol/g to 0.9 mmol/g for both species. Fourier transform infrared spectra indicated that C6-hydroxyl groups of cellulose were converted to negatively-charged carboxylate groups. After a gentle mechanical treatment with water, transparent liquid of TOBCNs were obtained after the removal of unwanted fraction, which gave a nanofibrillation yield of more than 90% at a NaClO addition level of 7.5 mmol/g to 15.0 mmol/g-BHs. Well individualized TOBCNs were successfully prepared and had a length of several microns and an average width of 5 nm to 7 nm under transmission electron microscopy. Thus, ultra-long TOBCNs are applicable for use as nano-reinforced polymer composites in non-food industries.