Manufacture Of Carboxylated Cellulose Nanocrystals By Persulfate And Its Derivatives

Nanocellulose and its derivatives are high value-added products of cellulose, and have become the hot research spot in the field of new materials based on cellulose, In order to improve dispersability and compatibility of nanocellulose in different solvents or matrices, various chemical modifications have been carried out. Furthermore, much research attention has been focused on surface functionality of nanocellulose to expand the potential applications of cellulose and nanocellulose.In this study, carboxylated cellulose nanocrystals (CCN) were prepared with ammonium persulfate(APS) by oxidative degradation of microcrystalline cellulose (MCC) under ultrasonic-assisted condition. Response surface methodology (RSM) was used to investigate the effect of three selected factors (reaction time, APS concentration and reaction temperature) on the yield of CCN, and the optimization experiment and mathematical model were carried out. The results showed that the model fitted well, as the determination coefficient between the predicted value of the model and the actual value reached99.31%, and the maximum CCN yield of46.93%was obtained under the optimal condition of204min,2.03mol/L and62.30℃, respectively. With the optimal condition from the developed model modified, the actual experiments were performed and the yield of CCN was46.41%, which was consistent with the predictive value of the model. The experiments results also showed that this model used to study the optimal preparation conditions of CCN by oxidative degradation with APS was reasonably practicable.The amino modified carboxylated cellulose nanocrystals (A-CCN(W) and A-CCN(D)) were prepared by an amidation reaction between CCN and diethylenetriamine in aqueous and DMF media, respectively, via EDC/NHS activation of the surface COOH groups. Chemical structure of MCC, CCN, A-CCN(W) and A-CCN(D) were characterized and analyzed by Fourier transform infrared spectrometry (FTIR), Nuclear magnetic resonance (NMR) and Elemental analysis (EA), the results of which confirmed the successful carboxylation of MCC and amination of CCN. The morphology and size distribution of CCN and A-CCN were investigated using transmission electron microscopy (TEM). It can be observed that rod-like CCN, A-CCN(W) and A-CCN(D) had diameters in the range of nanometer, but relatively longer length for A-CCN(W) and A-CCN(D). The X-ray diffraction (XRD) pattern showed that the MCC, CCN, A-CCN(W) and A-CCN(D) had the cellulose I crystal form and the crystallinity of MCC, CCN, A-CCN(W) and A-CCN(D) were81.66%、78.35%、79.52%and77.96%, respectively. Compared with MCC, the crystallinity of CCN, A-CCN(W) and A-CCN(D) decreased slightly after a series of chemical treatment.To obtain novel nanocomposites with excellent properties, the nanocellulose and its derivatives were incorporated in polymer matrices as reinforcement, which could overcome certain deficiencies of the polymer itself. In this study, nanocellulose/epoxy composite films were prepared by the reinforcement of CCN and A-CCN(W) and A-CCN(D) into an epoxy matrix. Mechanical properties of neat epoxy films, CCN/epoxy films, A-CCN(W)/epoxy films and A-CCN(D)/epoxy films were determined by a universal testing machine. The results showed that epoxy composite films reinforced by nanocellulose exhibited improved mechanical properties as compared to the neat epoxy film. When the CCN, A-CCN(W) and A-CCN(D) content were all only0.1%, CCN/epoxy composite films, A-CCN(W)/epoxy composite films and A-CCN(D)/epoxy composite films could get a maximum of tensile strength, which was59.76、61.14and66.16MPa, respectively, increasing29.41%、32.39%and43.27%, respectively, compared to the neat epoxy film. Consequently, aminated CCN could improve the mechanical properties of epoxy resin significantly.