Study On The Characteristics And Surface Modification Of Cellulose Nanofibrils Hydrogel

Cellulose nanofibril(CNF)have attracted much attention for using as a starting material to produce various commercial products due to their biodegradability,renewability,biocompatibility,large specific surface area,high reaction activity and nano-morphology.TOCNF prepared from bleached wood pulps through the sequential process of TEMPO-mediated oxidation and high-pressure homogenization,have been extensively investigated for various applications.However,the study on the characteristics of TOCNF hydrogel is not comprehensive,and the high hydrophilicity of TOCNF limits its application in hydrophobic systems(to produce high-value products).To resolve this problem,chemical surface modification of the separated nanofibrils from the TOCNF hydrogel is considered to be an alternative approach.In this paper,the characteristics of TOCNF were studied,and the hydrophobicity of TOCNF was improved by surface modification,which promoted its further application in non-water systems.The preparation of high-concentration TOCNF hydrogel was conducted,and the potential value of its application in food emulsification was discussed.The main research contents and results are as follows:1.The TEMPO-mediated oxidation cellulose was prepared TOCNF hydrogel by high-pressure homogenization,and the characteristics of TOCNF hydrogel were analyzed by Zeta potential,FBRM and rheological measurements.The experimental results showed that the excellent TOCNF hydr ogel with the carboxyl group content of 2.17mmol/g and Zeta potential of-60.1mV was prepared.The structure of TOCNF hydrogel was destroyed and the viscosity decreased under the acid and alkali environment.Moreover,rheological analysis results showed that the addition of NaCl destroys the structure of the hydrogel.The addition of NaCI damaged the structure of the hydrogel,resulting in obvious salting out,and the flocculation and stratification of TOCNF hydrogel.2.The modification of TEMPO-mediated oxidized cellulose nanofibrils(TOCNF)with cetyltrimethylammonium bromide(CTAB)was investigated to increase the hydrophobicity,improve the fibril separation from the hydrogel,and enhance the redispersibility of the separated nanofibrils.The results showed that when modifying the original TOCNF at a CTAB loading of 2.16 mmol/g cellulose,the charge coupling was close to 100%.Moreover,with increasing the CTAB dosage,the turbidity of the modified CTAB-TOCNF was significantly increased while the viscosity and water retention value were decreased.The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated that the molecular chain of CTAB was su ccessfully grafted onto the backbone of TOCNF following modification.The thermogravimetric analysis results also indicated the modification of TOCNF with CTAB improved its thermal stability.Water contact angle measurements of the original and CTAB modified TOCNF showed that the modified CTAB-TOCNF had better hydrophobicity.Moreover,the results from the evaluation of the redispersibility of the fibrils separated from both the original TOCNF and CTAB-TOCNF suspensions demonstrated that the modification of TOCNF with CTAB improved the redespersibility in N,N-dimethylformamide(DMF).Additionally,the increase of CTAB loading also significantly decreased the particle size of the redispersed fibrils in DMF.3.The surface adsorption modification of TOCNF with surfactant was investigated to preparation the High concentration of TOCNF hydrogel.The results showed that the addition of polyethylene glycol(PEG),polyacrylate sodium(PAAS)and sodium dodecyl benzene sulfonate(SDBS)weakened the hydrogen bond force on the surface of the fiber,resulting in the decrease of the viscosity and the particle size of TOCNF hydrogel with the increase of the surfactant.Zeta potential gradually increased,but the hydrogel still maintained stability.The SEM micrograph shows that the surfactant could change the spatial structure of the hydrogel to a certain extent and make the fiber arrangement in the gel tend to be oriented.Adding 4wt%PAAS modified TOCNF,the 4wt%concentration of TOCNF hydrogel was successfully prepared.The fiber size was uniform and the preparation efficiency was improved.4.The high carboxyl content of TOCNF-OSA was prepared through the surface modification of octenyl succinic anhydride(OSA)onto the TOCNF surface through esterification.The carboxyl content and degree of substitution(DS)of TOCNF-OSA increased with the increase of the amount of OS A,the carboxyl content and DS of TOCNF-OSA was as high as 5.44mmol/g and 0.95,respectively.While the Zeta potential and thermal stability of the modified TOCNF-OSA decreased slightly.In addition,the esterification modified TOCNF of OSA is an effective method to improve the emulsification,and it is used to prepare stable emulsion.With the increase of the addition of OSA,the stability and dispersion of the TOCNF-OSA emulsion were improved.