Preparation,Superhydrophobic Modification And Application Of High Carboxyl Nanocellulose

Cellulose,as the most abundant natural polymer on earth,is biodegradable and reproducible.It is of great significance to fully exploit its application potential to alleviate resource shortage and achieve sustainable development.Nanocellulose(NC)is the product of cellulose,which has high strength,high specific surface area and excellent mechanical strength.It has broad application prospects in the fields of papermaking,food packaging,pharmaceutical dressing,oil-water separation materials and so on.However,the glucose monomer of nanocellulose contains hydroxyl groups,which makes the materials mainly prepared by nanocellulose hydrophilic and easy to absorb water in humid environment.This paper aims to improve the water resistance of nano cellulose.Using Laubhǒlxer bleached kraft pulp(LBKP)as raw material,the pulp samples were pretreated with Na OH/urea and DMAC/Li Cl,and then the nanocellulose with high carboxyl content was prepared by chemical mechanical method.Superhydrophobic modification of nanocellulose was carried out by two systems of octadecylamine/polydopamine and octadecylamine/octadecyl trimethoxy silane two systems.After modification,superhydrophobic films or aerogels were prepared for oil water separation and oil adsorption.The modified nanocellulose was characterized by X-ray diffraction analyzer(XRD),Fourier Transform infrared spectroscopy(FT-IR),thermogravimetric analysis(TGA),scanning electron microscopy(SEM),water contact angle analyzer(WCA),X-ray photoelectron spectroscopy(XPS),and so on.The specific research contents are as follows:In the first part:Using LBKP as raw material.The pulp samples were pretreated with alkali solution(Na OH:urea:water=9:11:80)and Organic solvent system(DMAc:Li Cl=9:1),respectively.After dredging and beating,nanocellulose with high carboxyl content was prepared by TEMPO oxidation-ultrasonic system.It was found that the crystallinity of the fiber was the lowest after DMAC/Li Cl activation pretreatment;When the addition amount of Na Cl O is 20mmol/g,the carboxyl group of nanocellulose is up to 1.89mmol/g,which could provide more specific reaction groups for subsequent hydrophobic modificationIn the second part:Using the nanocellulose with the highest carboxyl content after DMAc/Li Cl activation pretreatment is selected as the raw material.Firstly,the low surface energy material octadecylamine is used as the hydrophobic modifier to prepare the nanocellulose with the maximum contact angle of 138.8°.Further,the viscous material polydopamine is used to adsorb the free octadecylamine molecules,which can increase the surface roughness of the nanocellulose,and the maximum contact angle is 168.2°,reaching superhydrophobic.Because the modified nanocellulose has hydrophobicity and lipophilicity,it can be made into oil-water separation film with the maximum separation efficiency of98.43%.In the third part:The nanocellulose,which was obtained by direct oxidation without pretreatment is used as raw material.Firstly,octadecylamine reacts with carboxyl group,and then octadecyl trimethoxy silane reacts with hydroxyl group.After two steps of modification,the super hydrophobic nanofibers with the maximum contact angle of 158°were obtained,and then made into low density(0.035g/cm~3)aerogel material.The adsorption capacity of dichloromethane and chloroform can reach 272g/g and 290g/g,which is significantly higher than that of similar hydrophobic aerogels.