Preparation Of Nanocrystals By Natural Cellulose And Its Application

The main contents of this paper were the pretreatment of cotton fiber and ramie fiber and the preparation of nanocellulose crystal(NCC) by enzymatic hydrolysis of treated cotton fiber, with the sulfuric acid hydrolysis of cellulose as the comparison. We had a try to explore a new method to get NCC and its application in soybean milk powder, in order to provide some basis for related research.Before enzymatic hydrolysis of cellulose material, the pretreatments of it were divided into two parts, wax removal and combined pretreatment. With N-hexane as a solvent to remove the waxy, the optimum conditions were:cotton fiber as the raw material, the solid-liquid ratio1:35(g:ml), refluxing time2.5h, wax content was0.17%which compared with untreated cellulose decreased71.7%; ramie fiber as the raw material, the solid-liquid ratio1:25(g:ml), refluxing time3h, wax content was0.82%which compared with untreated cellulose decreased59%. Then we explored the different content of wax in cellulose material impact on the rate of enzymatic hydrolysis, the results showed that with the decrease in wax content, the rate of enzymatic hydrolysis would rise.In order to make a better pretreatment result, the combination of pretreatment was used for waxy removed materials, which contains dilute acetic acid-ultrasonic pretreatment and dilute ammonia-ultrasonic pretreatment. After the pretreatment, we studied the content change of main components of raw materials such as cellulose, hemicellulose, and lignin and their impacts on the enzymatic hydrolysis, in which the content of cellulose and the hydrolysis rate as the indicator to select the optimum experimental conditions. The optimal experimental conditions in dilute acetic acid-ultrasonic pretreatment:cotton fiber as the raw material, the concentration of acetic acid was9%, processing time80min, solid-liquid ratio(g:ml)1:40, the amount of cellulose was93.4%, the rate of enzymatic hydrolysis was64%; ramie fiber as the raw material, the concentration of acetic acid was5%, processing time and solid-liquid ratio(g:ml) were100min,1:40, the amount of cellulose was80.2%, the rate of enzymatic hydrolysis was47%。 The optimal experimental conditions in diluted ammonia-ultrasound pretreatment:when cotton fiber as the raw material, the concentration of ammonia was10%, solid-liquid ratio(g:ml)1:40, processing time80min, the amount of cellulose was92.5%, the rate of enzymatic hydrolysis was61%; when ramie fiber as the raw material, the concentration of ammonia was10%, solid-liquid ratio(g:ml)1:40, processing time100min, the amount of cellulose was80.4%, the rate of enzymatic hydrolysis was52%. According to the above results, we know the cotton fiber have a better pretreatment by the dilute acetic acid-ultrasonic pretreatment and the ramie fiber have a better pretreatment by dilute ammonia-ultrasonic pretreatment.In order to improve the efficiency of enzymatic hydrolysis of cellulose, shorten the reaction time, we chose three substances namely Tween80, trehalose, rhamnolipid as the activator for cellulase, in which rhamnolipid has the most significant effect.When enzymatic hydrolysis of pretreated cotton fiber, rhamnolipid as an activator for cellulose,the optimal experimental conditions: the cellulase activity was15FPU/g, the dosage of rhamnolipid was1.5cmc, the substrate concentration was2%, the time of enzymatic hydrolysis was30h, under the above conditions, the yield of NCC would be41.2%. The sulfuric acid hydrolysis was choosed as the comparation to enzymatic hydrolysis, we knowed the yield of NCC would be higher as cellulose materials pretreated by dilute acetic acid-ultrasonic, the optimal experimental conditions:when cotton fiber as the raw material, processing time was160min, the temperature was50℃, the concentration of sulfuric acid was55%,the yield of NCC was70.6%. Compared with the yield of NCC got by the enzymatic hydrolysis, the method of enzymatic hydrolysis at a disadvantage, but advantages of enzymatic hydrolysis were mild reaction conditions,strong specificity,produces a small amount of waste liquid in the latter process, environmentally friendly, so it has great potential for future development.A variety of characterization shows that, the type of crystal of NCC which obtained by enzymatic hydrolysis was still the polymorphs I, the shape was micro-spherical and its size was about15nm. The X-ray diffraction (XRD) patterns showed that the crystallinity of NCC was increased to be84%, which greater than the untreated cotton fiber. Finally, we exploered the application of NCC in soybean milk powder, the results showed that a certain amount of NCC in soybean milk powder would increase the viscosity of solution and the mixed solution had the nature of shear thinning, so it has the potential of practical application in food industry.