Study On Modified Nanocellulose-Based Composite Films With UV Blocking Properties

With the destruction of the ozone layer and the intensification of ultraviolet radiation on Earth,the demand for UV-resistant materials is increasing among people.Traditional anti-UV materials made from petroleum-based plastics are gradually being replaced by green bio-based materials due to their non-renewability,difficulty in degradation,and poor biocompatibility.In this article,cellulose nanocrystals（CNCs）and cellulose nanofibers（CNFs）were used as raw materials,with benzyl acrylate（BA）,nicotinamide（NA）,and L-phenylalanine（L-Phe）as UV absorbers,glycerol（Gly）,tannin acid（TA）,and 4ARM-PEG-NH₂ as enhancers,and octadecyltrichlorosilane（OTS）as a hydrophobic modification agent to prepare cellulose-based composite films with UV absorption as the main function.Then,the films were characterized,and the materials were explored for applications such as antibacterial and oil-water separation.The effects of the addition of various modifiers on the mechanical properties,crystalline,UV absorption,hydrophobicity,thermal stability,and antibacterial properties of the materials were studied.The morphology,surface element distribution,and chemical structure of the modified cellulose-based films were analyzed by POM,SEM,EDS,FTIR,and XPS.The optimal ratio of various modifiers in cellulose films was determined by optimizing the experimental conditions based on the characterization tests mentioned above.The natural cellulose materials have insufficient UV resistance,which can be enhanced by physically crosslinking BA with cellulose chains using Gly.By measuring the UV absorption performance of the modified CNCs film,the optimal amount of BA added during the reaction was determined.When the ratio of BA to cellulose was 1:1（W/W）,the UV absorption rate was the highest at 95.49%in the range of 200-320 nm.When the ratio of BA to cellulose was 1:1.5（W/W）,the maximum stress increased from 4.45 MPa to 11.4 MPa,and the maximum strain increased from 0.46%to 0.97%.In order to optimize the UV resistance and mechanical properties of the film materials,tougher CNFs with longer particle size were selected as raw materials,and the film was modified by the amidation of natural compound NA and the crosslinking of TA.The effects of different amounts of NA and TA on the mechanical properties,UV absorption,and thermal stability of CNFs films were studied.The obtained modified composite film has the ability to completely shield UV light in the range of 200-320 nm wavelength.The maximum stress increased from 69.8 MPa to 116.3 MPa,the maximum strain increased from 0.53%to 2.36%,and the toughness increased from 17.21 MJ/m³ to 131.58 MJ/m³.CNFs contain a large amount of hydroxyl groups,which make the cellulose-based film hydrophilic and limit its applications.Therefore,further hydrophobic modification is necessary.Herein,OTS was used as a hydrophobic modifier,natural compound L-Phe was used as a UV absorber,and 4ARM-PEG-NH₂ was used as a reinforcing agent to prepare modified films.Compared to natural cellulose films（70.7°）,the contact angle of the modified material reached up to 121.1°,and it also had complete UV resistance in the wavelength range of 200-320 nm.The stress increased from 35.08 MPa to 174.09 MPa,the Young’s modulus increased from 24.53 MPa to 71.11MPa,and the toughness increased from 15.36 MJ/m³ to 295.33 MJ/m³.At the same time,the modified film achieved separation of oil-water mixtures with a maximum separation efficiency of 93.87%.Based on the anti-UV function of cellulose,the film material will replace plastic derived from petrochemicals and show great potential value in building protection,optical sensing,and medical devices.