Extraction Of Cellulose Nanocrystals By Oxalic Acid And Preparation Of Self-healing Hydrogel

Cellulose nanocrystals(CNC)are widely involved in the preparation of chemicals and materials due to its excellent and unique properties.It is necessary to find a simple,green and low-cost method to produce modified CNC.In this paper,oxalic acid was used to extract carboxylated CNC,its structure and optical properties were further explored,and its mechanical properties were used to prepare self-healing hydrogel.The main research results are as follows:1.Preparation of CNC by oxalic acid method and its structural characteristics were studied.In the absence of other solvents,filter paper was used as raw material,carboxylated CNC was prepared by one-step hydrolysis and esterification of cellulose with oxalic acid,and the yield of the final product was more than 70%.The optimal process parameters were 8.75 g OA/g FP with oxalic acid dosage and 60 min reaction time.The structural characteristics of carboxylated CNC were characterized by HPLC,FT-IR,NMR spectra,DLS,Zeta,TEM and XRD.2.The effects of different extraction methods of oxalic acid and sulfuric acid on the structure and optical properties of CNC were compared.CNC was mixed with PEG in different proportions,and the chiral nematic structure of CNC was retained in the solid films by evaporation-induced self-assembly.The films were characterized by POM,SEM,TGA.The results showed that the carboxylated CNC films obtained by oxalic acid method presented brilliant snowflake pattern.In addition,cations were added to 1.27%CNC solution,and the carboxylated CNC could easily form a stable liquid crystal phase gel.3.CNC self-healing hydrogels and temperature-sensitive materials were prepared.Inspired by biomineralization,the carboxyl group of carboxylated CNC interacted with Ca2+,and CNC was cross-linked with polyacrylic acid and calcium carbonate to form hydrogels that could be deformed,stretched,self-healing and recoverable.Introducing PCDA-MA vesicles into the gel,a temperature sensitive material that responded to UV light and presented reversible color change under heating could be prepared.