Preparation Of Nanocellulose-Plant Polyphenol Composite Films And Their Performance

The development of green,renewable and biodegradable materials is necessary for a sustainable society in the future.Cellulose is the most abundant natural plant biomass on the earth.Due to its low density,high strength,renewability,biocompatibility and biodegradability,cellulose is an ideal choice to replace traditional petroleum-based materials.Nanocellulose based functional composite films show great potential application in various fields.Lignin is the second abundant plant biomass after cellulose,which contains phenolic hydroxyl,methoxy and carboxyl groups in the molecular,and demonstrates various properties such as antioxidant,UV blocking,water resistance,and mechanical reinforcement.Tannin is also a natural plant polyphenol which could be easily extracted from plants.In this article,all-plant-based composite films were fabricated by using cellulose nanofibers（CNF）as matrix and natural polyphenol-lignin and tannin as the fillers.The properties of the films were investigated to discuss their potential application as the packaging and medical materials.First,CNF was oxidized by periodate to obtain dialdehyde nanocellulose（DACNF）.Subsequently,lignin nanoparticles（LNPs）with diameters of 50～150 nm were prepared from alkali lignin and mixed with DACNF to fabricate DACNF-LNP nanocomposite films via a condensation reaction.The addition of LNPs rendered the films with high ultraviolet-shielding and antioxidant properties.The water contact angle increased for the composite films compared with that of pure CNF film,while the water vapor transmission rate（WVTR）decreased.The mechanical properties of the nanocomposite films were significantly improved by the addition of LNPs.The dry tensile stress of DACNF-LNPs5 with 5%LNPs significantly increased from47 to 164 MPa.It was also higher than that of CNF-LNPs5（105 MPa）,in which CNF were not periodate oxidized.After immersion in water for 1 h,the wet tensile strength of DACNF-LNPs5was 31 MPa,3 times higher than that of CNF-LNPs（7 MPa）.These results indicate that the water-resistant properties of the composite films were significantly enhanced.Ag nanoparticles were obtained by reduction of Ag NO₃ with LNPs.It was found that the higher the concentration of Ag NO₃,the smaller size and more amounts of Ag NPs.Then the DACNF-LNP-Ag composite films were prepared by mixing LNP-Ag with DACNF.LNP-Ag imparted the composite films with high UV shielding and antioxidant properties.After the addition of 2%LNP-Ag,the tensile strength of the composite film increased from 44.5 MPa to62.6 MPa,while decreased when the amount of LNP-Ag was 5%.After 1 h immersion in water,the wet tensile strength of the composite film decreased to 18.5～27.5 MPa,but much higher than that of pure CNF film.LNP-Ag improved the surface hydrophobicity of the composite film,while reduced the water absorption of the composite films.The WVTR was comparable before and after the addition of LNP-Ag,exhibiting a medium water vapor permeability.The survival rate of L929 cells was still more than 90%after been co-cultured with leachate of the composite films for 24 h.The composite films demonstrated high amount of protein adsorption and antibacterial activities against E.coli and S.aureus.These advantages of the composite films show an application potential as the wound dressing.CNF and tannin were mixed as the matrix,then 3-acrylamidophenylboronic acid（AAPBA）and the initiator were added to copolymerize and CNF-tannin-poly（AAPBA）composite films with crosslinked structure were obtained by the borate ester bonds between poly（AAPBA）and CNF/tannin.The addition of tannin imparted the composite film with an excellent UV shielding and antioxidant properties.The synergistic effects of tannins and AAPBA improved the surface hydrophobicity of the composite film.The water contact angle of the composite film with 10%tannin and 8%AAPBA was as high as 110.14°,and without decrease within 120 s.When the AAPBA addition was 8%,the tensile strength and Young’s modulus of the composite films increased due to the borate ester bonds,while the toughness decreased at the 12%addition of AAPBA.