With the continuous increase of human consumption of oil and natural gas resources and the decline of the reserves of non-renewable resources, the utilization of renewable resources has become the trend of social development.Cellulose was a natural polymer with abundant reserves, cheap and renewable.Nanocellulose was extracted from biomass raw materials, which was one of the effective ways for its high-value utilization.[1].China is a country that produces a lot of peanuts, and the annual output can reach tens of millions of tons. Peanut shells were the residues of peeling peanuts. That were excepting for being rarely used as feed or fertilizer, most of them were discarded or burned, causing more and more waste and pollution of the atmosphere.Peanut shells are composed of cellulose, lignin, hemicellulose and soluble carbohydrates[2], which are similar to wood materials, which are also a good biomass material.After comparison, the proportion of hemicellulose in peanut shells was smaller. If you can make good use of the cellulose in it, you can not only turn waste into treasure, but also improve the utilization rate of peanut shells. Thereby increasing the value of peanuts, reducing waste and pollution to the environment, and also reducing the social demand for wood resources, thereby reducing damage to the environment.We want to extract cellulose from biomass material, generally subjecting the material to different methods such as chemical, biological, etc., and then mechanically processing it. For example, the material is modified and pretreated by alkali treatment[3-4], enzyme treatment[5], TEMPO oxidation treatment[6], etc., first to remove lignin, hemicellulose and other impurities around the cellulose, and then to perform mechanical processing to make the cellulose under mechanical action. It can be better separated because of the pretreatment[7], which can reduce the time of mechanical action, reduce energy consumption, and finally get the final purified cellulose we need.
As the most widely used selective oxidation system, TEMPO/NaClO/NaBr can be oxidized by NaClO and catalyzed by TEMPO or NaBr. At the same time, it can also achieve selective oxidation with polysaccharide polymers. The specific oxidation mechanism is shown in the following figure 1:
The morphology of cellulose before and after the oxidation reaction of cellulose macromolecules is completely the same, and the crystalline structure of cellulose is still in the original state. However, the cellulose structure and morphology on the surface of the amorphous and crystalline regions in cellulose changed significantly.After the oxidation reaction of cellulose, a large number of carboxyl anions will accumulate on the surface of cellulose. Under the action of these ions, the surface of cellulose produced electrostatic repulsion effect, which enhanced the solvent property of cellulose in water and can meet the application requirements in more fields.
Because a large number of hydroxyl groups exist on the surface of cellulose, cellulose has hydrophilic characteristics, which also greatly limits the application range of cellulose. However, it is precisely because of the large number of hydroxyl groups on the surface of cellulose that various functional groups can be introduced for modification through esterification, alkylation[8], amidation and other reactions to produce cellulose materials with different properties. Therefore, in order to prepare cellulose aerogels and combine them with fabrics to improve the hydrophobic properties of fabrics, the cellulose aerogels can be modified to have superhydrophobic properties. It has been found that in order to improve the hydrophobicity of nanocellulose, various treatment methods can be used, including physical adsorption modification[9], esterification/acetylation modification[10], graft copolymerization modification[11], and silane coupling agent modification[12].
Because of its soft texture and affordable price, cotton fabrics are very common on the market and widely used in people's daily life. However, due to the good hydrophilicity of cotton fabrics, it is easy to be polluted, so it is difficult to popularize and apply in many fields. According to the research, the surface of lotus leaf and gecko is hydrophobic[8-12]. Therefore, in the application of cotton fabrics, people treat the surface of cotton textiles to increase the surface roughness, and at the same time combine low surface energy substances to give cotton fabrics super-hydrophobic properties. Cellulose aerogel is a new type of composite material. Compared with traditional silicon aerogel and polymer aerogel, its biocompatibility and degradability are significantly improved, and it has green and renewable characteristics[13-15]. No pollution to the environment and no stimulation and harm to the human body, in line with the requirements of sustainable social development. At present, there are relatively few studies on the rough structure of cellulose aerogels on the surface of fabrics. Combined with the advantages of cellulose aerogels, it is worthwhile to apply cellulose aerogels to fabrics.
In this paper, peanut shell nanocellulose was prepared by chemical-mechanical method using peanut shell as a raw material. Using the prepared peanut shell nanocellulose as raw material and methyltrimethoxysilane (MTMS) as silane hydrophobic modifier, the MTMS-modified nanocellulose was prepared by sol-gel method, and then freeze-dried. Polymethylsiloxane-modified superhydrophobic nanocellulose aerogels were prepared, and then the aerogels were pulverized and treated with low surface energy substances on cotton fabrics by spraying to obtain nanocellulose superhydrophobic cotton fabrics.