Preparation Of Nanocellulose With Deep Eutectic Solvent And Its Application

With the increasingly severe problem of fossil resources,the use of renewable resources has become the focus of attention.Nanocellulose(NC)has attracted increasing attention due to its high reactivity,excellent chemical and physical properties(such as high specific surface area,reproducibility and biodegradability).In general,cellulose nanocrystal(CNC)and cellulose nanofibril(CNF)are prepared by chemical and mechanical treatment.However,these methods are difficult to be applied in industry because they involve contamination,corrosion and high price of reagents,as well as the problem that mechanical equipment is easy to be blocked and the cost of equipment is high.In recent years,deep eutectic solvent(DES)has shown good removal capacity of hemicellulose and lignin in the research,and it is easy to be recovered by rotary evaporation and reused in the subsequent process.Therefore,DES treatment can be regarded as a green and sustainable method for lignocellulose refining and NC preparation.In this paper,the newly prepared formic acid/choline chloride(F-DES)and urea/choline chloride(U-DES)were used to pretreat the cellulosic raw materials,and then the simultaneous preparation of CNF and CNC was realized with subsequent ball milling treatment.Functional film materials were prepared by using CNF and Polydopamine(PDA)to explore their photothermal conversion applications.After the exploration of the pretreatment conditions of DES,ball milling was carried out under the optimal 2h treatment time.The influence of different ball milling time on the product was studied.The ratio of CNC and CNF in the product was determined to be related to the ball milling time through TEM,SEM and particle size test,and the NC yield reached92.09%(UNC2)and 93.1%(FNC2).In addition,F-DES and U-DES can be easily recovered by rotary evaporation,and the recovery efficiency after three reuses can reach92.24%and 92.58%.The recovered DES also showed good pretreatment effect on cellulose.With the combination of DES pretreatment and ball milling,CNF was prepared from conifer wood pulp,and then mixed with PDA to prepare composite film.The effect of PDA on the mechanical performance of nanocellulose film was studied.The results show that the content of PDA has a great influence on the structure and mechanical properties of the composite film,with 5%content of PDA the best.5%PDA/U-CNF(U-5%)and5%PDA/F-CNF(F-5%)has tensile strength 11.58%and 7.50%higher than corresponding blank film respectively,while has a similar elastic modulus and elongation at break to it.In addition,a small amount of PDA helps to improve the mechanical properties of the composite film and imparts it good application potential as nanomaterials.Finally,an evaporator system(including composite film,lighting device,temperature device)was established to study the photothermal conversion effect of PDA/CNF composite film.The results show that U-5%and F-5%have up to 81.79%and 78.44%photothermal conversion efficiency,respectively.With the increase of light intensity,the temperature of the composite film increases,with temperature increased to 75℃(U-5%)and 72.4℃(F-5%)under the condition of 0.8w/cm~2.Under the condition of 0.6w/cm~2,U-5%and F-5%shows water evaporation rates of 8.45kg/(m~2·h)and 7.70kg/(m~2·h).