| In recent years, under the current situation of the exhausting non-renewable resources such as coal, oil and natural gas, there is a general interest in the sustainable production of chemicals and/or materials from biomass, which may play a major role in producing systems traditionally produced from petroleum. Cellulose is one of the most widely distributed renewable biopolymers. Nanocellulose prepared from renewable and biodegradable lignocellulosic materials is green and environmental-friendly. It holds promise in a wide range of applications due to its nanoscale dimension and some unique properties, such as high modulus, high crystallinity, low density, biodegradable, and modifiable surface properties due to reactive-OH side groups. These properties impart NC an extensive application value in the nano-composites, medicine, packaging, food additives, paint coating and building materials industry. In this work, nanocellulose (NC) were obtained from kraft pulp and mixed office waste pulp by cellulase hydrolysis and characterized. The feasibility of producing ethanol using hydrolysis liquor by fermentation was investigated. Their applications in the pulp and papermaking processes were also discussed.Firstly, Acid cellulase and Fiber Care D (neutral cellulase) were used to prepare NC from fully bleached Kraft pulp and mixed office waste pulp. The influence of enzymes consumption, hydrolysis duration and substrate concentration on the crystallinity, zeta potential, yield of NC and reducing sugar concentration of hydrolysate were investigated. The experimental results showed that stable NC suspensions could be obtained by hydrolysis of both cellulases. With the increase of cellulase addition, the yield of NC decreased while the reducing sugar in the hydrolysate increased, indicating that the amorphous region was degraded. Under the same conditions, the hydrolysis efficiency of acid cellulase was higher than that of Fiber Care D. NC from acid cellulase hydrolysis has lower yield but higher reducing sugar. The morphology of NCs was observed by AFM. The AFM images showed that NC obtained by acid cellulase hydrolysis gave better dispersibility than that by Fiber Care D, with a relatively lower aspect ratio. FT-IR spectra indicated that the chemical structure of NC kept the same as the raw material. TG analysis showed that compared to that of the raw material, thermostability decreased a little. The hydrolysates were analyzed by Ion Chromatography. It was found that its main components were glucose and xylose. The hydrolysate was concentrated to a total sugar content of 57.02g/L, and then fermented for 72 h. the sugar content after fermentation was 4.16 g/L, indicating a 92.7% fermentation efficiency.Then, NCs obtained by both enzymes were applied in the unbleached deinked pulp alone or constitution of microparticle system with cationic polyacrylamide (CPAM) or cationic starch (CS), and their effect on the retention of fines and fillers were investigated, it was found that the retention could be improved by adding NC alone, while the drainage property was deteriorated. The retention of fines and fillers could be further improved by both CPAM/NC and CS/NC systems without deterioration of drainage rate. CPAM/NC provided the maximum retention (88.98%),7.0 higher than the control. CPAM/NC system was applied to flocculate kaolin clay. It was found that the clay could be flocculated, and the optical micrograph images showed that flocculation was more denser.Finally, the influence of NC addition on the pulp physical properties was investigated. NC obtained by acid cellulase hydrolysis performed better in pulp strengthening. The pulp breaking length, tearing index and bursting index were improved by 19.93%* 6.18% and 16.99%, respectively, with an addition of 0.8% NC aloneo The air permeability and bulk of pulp were decreased by adding NC. Both CPAM/NC and CS/NC gave better strength properties than adding NC only. |
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