Preparation And Study Of Chitosan/Sodium Alginate Waterproof And Oil-proof Paper

Waterproof and grease-resistant paper is a paper-based material with barrier properties to water and oil,and is used for a variety of packaging applications in production and life.Traditional methods mostly use petroleum-based compounds or fluorinated compounds to enhance the paper's barrier properties to water or oil,often using large amounts of organic solvents in the paper production process,in addition to the migration of fluorinated organic compounds and degradability of the material.With the increasing awareness of environmental protection and health,safe,reliable and easy-to-use methods and easily degradable environmentally friendly materials have become a hot research topic.In this study,we firstly prepare a waterproof coating and use stearic acid to modify the sample pretreated with chitosan to prepare paper with waterproof function;then we compound sodium alginate and chitosan to improve the oil-blocking property of paper;finally,we combine these two methods to prepare an oil-resistant coating on the surface of paper first,followed by hydrophobic modification,so as to prepare waterproof and oil-resistant paper and verify the effect of using these two methods together.First,the filter paper was pretreated with ZnCl₂/chitosan(CA)solution,and then the treated filter paper was modified with stearic acid(SCA).The optimal reaction conditions were established by orthogonal experimental method as follows:pretreatment temperature of 70°C,heating time of 2 h,modification temperature of 70°C and modification time of 1 h.Contact angle measurements showed that the micro/nano surface structure of the SCA-modified filter paper made the filter paper hydrophobic and water resistant.Further study revealed that the water absorption of the modified filter paper decreased to 7.1%of the original in30 s and 12.8%of the original in 60 s.The soaking tensile strength of the modified filter paper increased significantly in 30 s and 60 s,while the air permeability decreased to 3.6%of the original.Next,different ratios of chitosan/sodium alginate coating solution were prepared to coat the paper,and the effects of water and oil repellency as well as air permeability on the oil repellency level of the coated filter paper were investigated.It was found that with the increase of coating amount,the oil-proof grade reached 12.As the SA component decreased and the CS component increased,the oil repellency became better,but the air permeability also became smaller at this time.The air permeability of the paper is negatively correlated with the oil resistance level,and the air permeability of the paper and the surface energy of the paper coating both affect the paper's barrier to oil.Finally,the paper with the coating amount increases,the oil resistance grade also continues to improve,when the coating amount reaches13.32g/m²,the oil resistance grade reaches the highest grade 12;air permeability then decreases.As sodium alginate is hydrophilic,the unmodified paper has poor water barrier and the contact angle to water is between 70 and 80°.The hydrophobic angle of the paper decreases sharply to 0 contact angle within 10 s.The tensile strength also decreases from the highest 59.21 k N/m to 0 after 60 s of wetting.In addition,the optical properties of the paper also increase slowly with the increase of coating amount.After the paper was modified,the oil-proof grade were raised 1 to2 grades,the air permeability was also reduced,and the paper's barrier to water and paper physical strength also increased with the coating amount.In the modified paper sample with a coating volume of 13.23 g/m²,the stearic acid was lost because it could not bind to zinc ions,so the water barrier and the gloss/roughness and evenness of the paper decreased.