| With the increasing concern for food safety and environmental protection,paper-based food packaging materials are becoming more and more popular among consumers.However,traditional paper is derived from natural plant fibers,and its own water and oil resistance is poor,so it needs to be enhanced in practical applications to block water and oil.In recent years,petroleum-based plastics have been used as water and oil barrier materials for some paper-based food packaging.However,the difficulty of degradation of plastics can bring a heavy burden to the environment,and the random disposal of plastics can cause serious pollution to the ocean.Currently,bio-based polymers are receiving continuous attention from researchers because of their non-toxicity,biodegradability,and biocompatibility.The use of bio-based polymers to prepare water-and oil-resistant paper with excellent barrier properties has become a hot research topic in the field of food packaging.In this project,bio-based polymers are used to prepare non-toxic and environmentally friendly water-and oil-resistant coatings,and then bio-based water-and oil-resistant packaging paper materials are prepared using a double-layer coating technique.The research in this paper is summarized as follows:The compound oil repellent was prepared by cross-linking chitosan（CS）solution and sodium alginate（SA）solution with ferulic acid（FA）,and coated on the base paper to prepare oil-resistant paper;then the compound water repellent was prepared by using carnauba wax（CW）and hydrophobic silica nanoparticles（HSNPs）as raw materials and coated on the surface of oil-resistant paper to prepare water-and oil-resistant paper.The effect of different ratios and coating amounts on the water and oil repellency of paper and paper properties was investigated.Through the cross-linking effect of FA,CS and SA formed a stable CS/SA oil-resistant film on the paper surface,thus imparting excellent oil resistance to the paper;CW and HSNPs constructed a rough structure on the paper surface,reducing the surface energy of the paper,thus imparting excellent water resistance to the paper.The experimental results showed that that when the compounding ratio of CS and SA was 8:2 and the coating amount of CS/SA was4 g/m2,the oil-resistant paper could achieve the highest oil repellent grade（12/12）;when the compounding ratio of CW and HSNPs was 4:3 and the coating amount of CW/HSNPs was 3g/m2,the Cobb value of the paper was 5.93 g/m2 and the water contact angle was 158.40°,which significantly improved the water-resistant performance of the base paper.In addition,because the surface of the base paper was endowed with CS/SA oil-resistant layer and CW/HSNPs water-resistant layer,the tensile strength of the water-and oil-resistant paper was improved by 29.4%,the air permeability was reduced by 55.5%,and the water vapor transmission rate was reduced by 54.5%compared with the base paper,finally the fluorine-free food packaging paper with excellent water-and oil-resistant effect was prepared.Based on the above findings,novel water-and oil-resistant coatings for paper were prepared using SA,hydroxypropyl methylcellulose（HPMC）,polyvinyl butyral（PVB）and HSNPs in order to make the preparation process easier and the preparation cost more economical.To make the paper oil-resistant,the base paper was first pre-treated using calcium chloride（Ca Cl2）solution,and then SA and HPMC were uniformly mixed and coated on the surface of the base paper.Due to the hydrogen bonding between SA and HPMC molecules and the cross-linking between SA/HPMC and Ca2+ions in the base paper,a stable SA/HPMC oil-resistant coating was formed on the surface of the base paper,and the oil-resistant performance of the base paper was significantly enhanced.By coating PVB/HSNPs on the surface of SA/HPMC oil-resistant paper,the water repellency of the paper was significantly enhanced by using the excellent film-forming property of PVB and the hydrophobicity of HSNPs.The experimental results showed that when the mass fraction of SA was 1.5%,the mass fraction of HPMC was 2.5%,and the coating amount of SA/HPMC was 4 g/m2,the coated paper exhibited excellent oil repellency（oil repellency grade:12/12）;when the mass fraction of PVB was 8.0%,the mass fraction of HSNPs was 1.0%,and the coating amount of PVB/HSNPs was 4 g/m2,the coated paper exhibited excellent water resistance（Cobb value:4.23 g/m2）.In addition,because the surface of the base paper was endowed with SA/HPMC oil-resistant layer and PVB/HSNPs water-resistant layer,the tensile strength of the water-and oil-resistant paper was improved by 85.7%,the air permeability was reduced by 75.7%,and the water vapor transmission rate was reduced by 93.6%compared with the base paper,finally the fluorine-free degradable food packaging paper with excellent water-and oil-resistant effect was prepared.Based on the experimental contents of the previous two chapters,HSNPs were used in the preparation of the water-resistant coating.Although HSNPs have excellent water-resistant effects,there may be migration into food in daily life.In addition,the prepared SA/HPMC oil-resistant coating has high viscosity,which is not conducive to paper coating.To solve these two problems,the water-and oil-resistant coatings were prepared using SA,cellulose nanofiber（CNF）,ethyl cellulose（EC）,and PVB.The base paper was pre-treated with Ca Cl2 solution,and the cross-linking effect of Ca2+ions strengthened the connection between SA/CNF coating and paper,thus enhancing the oil repellency and mechanical properties of the base paper.The excellent hydrophobicity and film-forming properties of EC and PVB,as well as the hydrogen bonding force in EC/PVB coating,served to enhance the water repellency and mechanical properties of the paper.The experimental results showed that when the mass fraction of SA was1.5%,the mass fraction of CNF was 2.0%,and the coating amount of SA/CNF was 4 g/m2,the coated paper exhibited excellent oil repellency（oil repellency grade:12/12）;when the mass fraction of EC was 4.0%,the mass fraction of PVB was 6.0%,and the coating amount of EC/PVB was 4 g/m2,the coated paper exhibited excellent water-resistant performance（Cobb value:1.13 g/m2）.In addition,In addition,because the base paper was given SA/CNF oil-resistant layer and EC/PVB water-resistant layer,compared with the base paper,the tensile strength of the water-and oil-resistant paper increased by 239.5%,the permeability decreased by 94.6%,and the water vapor transmission rate decreased by 94.9%,finally the fluorine-free,degradable and recyclable food packaging paper with excellent water-and oil-resistant effect was prepared. |
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