Preparation Of Nanocellulose By Anhydrous Phosphoric Acid Method And Its Acetylation

In this paper, polyphosphoric acid and phosphoric acid was mixed to prepare anhydrous phosphoric acid system. Then microcrystalline cellulose (MCC) was added to obtain NCC. Finally, the mixtures were separately poured into icy aqueous, the target products were obtained after centrifugation and dialysis to remove impurities. The organic functional groups of the NCC and ANC were analyzed with Fourier Transform Infrared Spectroscopy (FT-IR). To further investigate morphological features, FEI Sirion field-emission scanning electron microscope (FE-SEM) images were gathered for NCC powders. Single microfibrils of NCC were rod-like or thread-like with diameter of 25.85±8. In the XRD pattern, the treatment with anhydrous phosphorus acid turned the crystal structure into Cellulose II structure compared with the original Cellulose I crystals of MCC.To overcome the problem of NCC particles often aggregate and hard redispersion, a single-step method was adopted to prepare acetylated nanocrystalline cellulose (ANC) with anhydrous phosphoric acid as the solvent and acetic anhydride as the acetylation reagent, under different reaction temperatures (from 20 to 40℃). As the same, the pure ANC was obtained after centrifugation and dialysis. To thoroughly investigate the degree of substitution (DS) of the ANCs, FT-IR, solid-state 13C CP-MAS NMR, elemental analysis, and XPS analyses were performed. When temperature increased, the DS of the ANCs increased. FE-SEM was used to investigate the morphology of the ANC (reaction at 20,30, and 40℃) with diameter of 33.94±16,32.98±9, and 24.67±7nm, respectively. The hydrodynamic particle sizes and ζ, potentials of the NCC and ANC in aqueous solutions were measured using Zeta-Plus Microelectrophoresis Apparatus. Cellulose shows negative potential on its surface due to its free hydroxyl groups. After modification, some free hydroxyl groups were acetylated, resulting in a reduction of ζ potential. In this work, the ζ potential was significantly decreased by the acetylation. The contact angles of NCC or ANC film were different. When the DS of ANC increased, the angle increased due to the ANC hydrophilic nature was reduced. The redispersibility of the NCC and ANC samples was observed by preparing dispersions in a series of solvents with decreasing polarity (water>methanol>chloroform>n-butanol). With increased DS of the ANCs, the dispersion of NCC or ANCs in water decreased, and increased in chloroform.In this study, polylactic acid (PLA), a bio-based and biodegradable polymer that shows largely favorable properties, is selected as the matrix. The NCC or ANC was introduced into a polylactic acid (PLA) matrix as a reinforcement, then resultant composites were obtained by solvent casting method. With increase of DS, tensile and tear property of PLA composite films measurements increased considerably. Rheology is a powerful tool for examining the rheological properties of PLA composite films. Rheology is a powerful tool for examining the internal structure of complex material, PLA-0.5-30-ANC and PLA-0.5-40-ANC showed larger moduli compared to PLA-0.5-NCC, especially if ANC-40℃ was added. This result implies that there is a strong particle-particle interaction and favorable particle dispersion in the films. PLA film possesses a higher complex viscosity; additionally, viscosity decreases with increase in angular frequency. The state of cross-section of the PLA composite films were also observed using SEM. FE-SEM was used to investigate the morphology of the NCC and ANC embedded in the PLA matrix. Aggregates appeared on the surface of PLA-0.5-NCC to some extent, but ANC-40℃ dispersed in PLA largely homogeneously. The thermal stability of the composite films was also evaluated by TGA and DSC, where results showed that the use of higher DS of ANC with improved the thermostability of the films.