| Salix psammophila is a common desert shrub in our country which has strong stress resistance, flourishing root system and well germination activity. What’s more, it can also do well in windbreak and sand-fixation, preserving soil and water, improving ecological status and so on. The cellulose content of Salix psammophila is high and if we extract its cellulose and make rational use of biological resources, it will come into huge economic and ecological benefits. As the common organic compound, cellulose is considered an almost inexhaustible source of raw material, due to its excellent chemical properties and biocompatibility, have been widely applied in many fields. Cellulose of the micro-nano size not only has the basic structure and properties of natural cellulose, but also possesses many unique properties such as huge aspect ratio, large specific surface area, high crystallinity, low density, high Young’s modulus and tensile strength etc., all these properties are of great use value.In this paper, we make Salix psammophila as the object of study and discuss the degumming process of fiber in which the technological parameter of the degumming double alkaline pretreatment and bleaching process has been optimized. The technology of fiber first alkaline heating adopt single factor control variable method to obtain the optimal alkaline heating parameter: alkali concentration 20 g/l NaOH, cooking temperature 110 ℃, time 2.5 h, bath ratio 1:15. Add anthraquinone when second alkaline heating, which can remove lignin effectively. Through the orthogonal experiment method, it is concluded that the optimal parameters: 120 ℃, 3.5 h, 0.1% AQ, and 20 g/l NaOH. After the degumming double alkaline treatments, we use hydrogen peroxide to bleach it which acts on the side chain structure of lignin and then remove lignin. Same with orthogonal experiment method to get the optimal parameters: 30% H2O2, 5 g/l NaOH, 60 min, 90 ℃, 0.5% EDTA, 0.5% MgSO4. In the SEM picture, it found that the fiber becomes smooth after double alkaline and bleaching which can explain the removing of colloid. FTIR, XRD and thermal analysis can be concluded that the vast majority of lignin, hemicellulose and other impurities have been removed clean, the crystallinity increased to 83.1%. It proved that the degumming effect is obvious.Then the cellulose of the micro-nano size was extracted by acid hydrolysis. First, microcrystalline cellulose is prepared from degummed Salix psammophila fiber by the nitric acid-ethanol methodology. The short rod-like microcrystalline cellulose has a mean grain diameter of 46±15 μm and a white degree of 83.2. Hydrolysis was performed using 64 wt% sulfuric acid solution at 45 ℃ for 60 min, then wash it by centrifugal and after ultrasonic treatment obtained the average length of about 300 nm cellulose nanowhisker. From the result of XRD, the crystalline texture of cellulose remain unchanged after the acid solution treatment, still emerge typical I crystal type of cellulose, at the same time the amorphous region has been hydrolyzed further in acidolysis, microcrystalline cellulose crystallinity increase to 86.9%, the crystallinity of nanowhisker is 89.1%, the crystallinity becomes more completed. TGA indicates that salix mongolica microcrystalline cellulose has a good thermostability. After treatment of sulfuric acid, the initial of pyrolysis temperature is low and distribution of temperature is large which is due to the decrease of size, increase of specific surface area and enhanced activity. What’s more, sulfo group is generated, which reduce the pyrolytic temperature of cellulose and the thermostability of cellulose nanowhiskers. |
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