Preparation And Properties Of Cellulose Based Active Packaging Materials

Plastics have brought great convenience to our life in many aspects,especially as food packaging materials.However,plastics come from petroleum and cannot be biodegraded.The overuse of plastic products poses a serious threat to nature and human beings.Therefore,development of packaging materials from renewable natural resources has received increasing attention.Cellulose is the most abundant renewable biomaterials on earth and can be used as eco-friendly packaging materials due to its biodegradability,renewability and safety.Renewable and biodegradable active packaging materials can be obtained by adding functional substances into cellulose matrix,and will have prospective application in active packaging.In this work,lignincellulosic fibers were used as raw material,tannin and alkali lignin with rich phenolic hydroxyl groups were introduced into cellulose matrix to prepare cellulose paper-based and film based packaging materials with ultraviolet blocking,anti-oxidation and antibacterial properties.The structure and morphology of the composites were characterized,and the antioxidant,UV shielding,barrier and mechanical properties of the materials were measured and evaluated their potential application as packaging materials.The kraft pulp fibers were firstly periodate oxidized to obtain the dialdehyde cellulosic fibers,and then reacted with varied dosages of tannin to incorporate them into the fibers by covalent bondings between aldehyde groups on kraft fibers and active hydrogen on tannin molecules.Handsheets were prepared using the tannin incorporated kraft fibers through paper making process and the properties were characterized.The percentage of tannin in the paper increased with the increase of the tannin dosage and can be easily adjusted.FT-IR results confirmed the successful incorporation of tannin into the cellulosic fibers.It was found that the paper after incorporation of tannin turned to be surface hydrophobic with contact angles higher than 90o,which may probably due to the covalent bonds between tannin and cellulose.The handsheets show high antioxidative and UV-shielding properties,which both increased with the increase of the tannin percentage in the paper.Water vapor transmission rate(WVTR)decreased after the incorporation of tannin,and this could facilitate its application in food packaging.The breaking length of tannin incorporated paper decreased insignificantly,less than 10% with the tannin percentage as high as 45%.The cotton linter dissolving pulp was dissolved in an ionic liquid(Amim Cl)to form a film in a specific mold,and then immersed in deionized water for exchange to produce regenerated cellulose film(CF).CF was then oxidized by sodium peroxidate to get dialdehyde cellulose film(DACF)with aldehyde groups on the film surface.DACF was immersed in tannin solution to prepare cellulose tannin film(TCF).Tannin was covalently bonded on the film surface by condensation reaction between tannin and aldehyde groups on DACF surface.The properties of films were measured and it was found that TCF-3 with approximately 20% weight percentage of tannin could continuously scavenge DPPH free radicals within 7 hours.Meanwhile,with the increase of tannin loading on the film surface,the antioxidant activity of TCFs increased gradually.TCF also shows high UV blocking properties.The introduction of tannin also improved the hydrophobicity and water vapor barrier properties of the cellulose film,The WVTR of TCF composite membrane also decreased with the increase of tannin loading.The tensile strength of TCFs decreased after the introduction of tannin.When the tannin loading was 19.2%,the tensile strength was 80 MPa,and the elongation at break was 11.3%.The high anti-oxidation,UV shielding properties and acceptable mechanical properties make the composite films a good application prospect in the field of food packaging.Cotton linter dissolving pulp was firstly blended with alkali lignin(AL),and then dissolved in Amim Cl.Cellulose-lignin films(LC)were obtained by the following water phase exchange.The effects of alkali lignin content on the UV barrier,thermal stability,antioxidant activity,mechanical properties and hydrophobicity of the LCs were investigated.The hydrophobicity,antioxidant and water vapor barrier properties were improved compared with pure CF.The thermal stability of LC films was also improved,and the mass residual ratio of LC-3 at 600 ? is 14% higher than that of CF.Excellent thermal stability,hydrophobicity,barrier property and antioxidant activity make LC a promising food packaging material.