Antimicrobial And Antioxidant Nanocellulose-based Composite Films: Preparation And Characterization

At present,Green,Low carbon and Health have become a common pursuit of all mankind.This concept has been integrated into our daily life,especially after the implementation of the Plastic Restriction Order in China.Green products represented by bio-based degradable materials are gradually replacing traditional petroleum-based white disposable plastic packaging and entering millions of households.As far as the fresh-keeping storage requirements of fruits,vegetables and food are concerned,bio-based degradable film materials are at the very beginning of industrial development.It has become an important research topic in this field to develop active packaging materials with the function of prolonging the shelf life of fruits and vegetables,guided by functions such as antioxidant and anti-microorganism.This work aims at the goals as described above.Using bio-based nanocellulose as the based material,we fabricated active packaging composite materials,focusing on improving the quality and safety of food packaging.Nanocellulose has the advantages of good biodegradability,excellent mechanical properties,great abundance,good sustainability,etc.It is one of the preferred alternative materials for manufacturing packaging films or coatings.However,the application of nanocellulose alone for packaging purpose is limited due to its lack of antibacterial property,weak anti-oxidation activity and insufficient water barrier capacity.Therefore,a series of nanocellulose-based active composite packaging materials were designed and developed in this paper.By addition of functional auxiliary factors,the antibacterial function of nanocellulose-based materials was obtained.Their anti-oxidation activity,anti-UV performance and waterproof properties were improved.The main research contents and conclusions of this paper are as follows:In the first part of the work,CNF/Zein/C/T composite films were fabricated by tape-casting with nano cellulose(CNF)as substrate,zein,Clove essential oil(CEO)derived from Eugenia caryophyllus leaves,tea polyphenols(TP)as functional additives,and glycerol as plasticizer.The results showed that the addition of Zein decreased the water solubility of CNF films,improved the contact angle of CNF films,and therefore enhanced the hydrophobicity of CNF films.Clove oil and tea polyphenols improved the antibacterial and antioxidant properties of the composite film.The composite also had a good barrier property against the ultraviolet lights.The CNF/Z-10/C/T composite film consisted of 10% Zein had the most efficient antibacterial effect.The measured diameters of antibacterial zones in Escherichia coli and Staphylococcus aureus culture media were 6.54 mm and 4.68 mm,respectively.CNF/Z-10/C/T composite film was coated on the surface of banana.As a result,it could delay the decay of banana and extend the shelf life by 2-3 days.The second part aims to further improve the antibacterial efficiency of nanocellulose-based composite films.Carbon dots(CDs)was synthesized by hydrothermal method using sodium isoascorbate as carbon source.Then a new nano antibacterial composite film material dopped with CDs(CNF/CDs)was prepared by blending casting the mixture of CNF and CDs.The results showed that the average particle size of CDs was 4.6 ± 1.8 nm.The antibacterial and anti oxidation properties of the composite films were positively related to the content of CDs.The addition of CDs improved the UV barrier properties,ductility and water vapor barrier properties of the composite films.However,a high content of CDs finally decreased the hydrophobicity of the composite films as well as the tensile strength of the films.The antibacterial diameters of the composite film containing 7% CDs against E.coli and S.aureus reached 16.88 mm and 14.34 mm respectively.The inhibition activities were significantly higher than that of CNF/Z-10/C/T film.CNF/CDs composite films could delay the decay of strawberry in a subsequent application verification.The third part focused on the improvement of the hydrophobicity of nanocellulose-based films.LCNF/Zn O/Q composite film were prepared by blending lignin preserved nanocellulose(LCNF)as based material,nano zinc oxide synthesized from zinc acetate precursor as antibacterial agent and quercetin as antioxidant.LCNF had good water resistance,while quercetin and Zn O further improved the hydrophobicity of the film.The transmittance of LCNF/Zn O/Q composite membrane in the UV region was near zero.Quercetin and Zn O improved the mechanical properties and oxidation resistance of LCNF.The composite film with addition of 1% Zn O and quercetin had a antibacterial zone diameters of 6.49 mm and 7.62 mm against E.coli and S.aureus.The composite films improved the water retention ability and shelf life of the virgin fruit.