Preparation Of Starch Composite And Its Application In Paper Barrier Coating

Paper and paperboard have been widely used in various field because they have many merits. Paper-based materials are light and so easy to carry and transport; with good strength and printability, they are recyclable, biodegradable and so on. However, water, oxygen and grease barrier of paper are very poor for the inherent hydrophilicity of fibers and the porous structure of paper. In order to meet the challenges of resources shortage and solve the increasingly serious environmental problems and food safety issues, water-based polymer coating gradually replaced impregnation, Paper-plastic composite, vapor deposition, extrusion coating and waxing now become the main trend to gain barrier properties of paper. Starch as a renewable and biodegradable natural biopolymer, has certain oxygen and grease barrier properties. As a result, starch coating is expected to replace synthetic polymers to achieve better barrier properties. In this work, the application of starch polymer in paper barrier coating was studied, which put a foundation for future research and further application.In order to solve the brittle and sticky problem of oxidized starch acetate coating layer and improve the hydrophobicity of coating layer, organic chromium which meet the food requirements was selected to crosslink with starch, and then applied to white kraft paper. The results showed that after the coating of crosslinked starch, the surface of coated paper become smoother and the air permeability reduced while increasing the coating weight. The oxygen transmission rate could be effectively measured when increasing coating weight to 3.21g/m~2. With the increase of the coating weight, oil resistance, mechanical strength and gloss of the coated paper increased while the brightness decreased. Because of the hydrophilicity of crosslinked starch, Cobb values,dynamic permeability and water vapor barrier of coated paper showed little change compared with the base paper. In addition, with the increase of the dosage of organic chromium, oil resistance of coated paper increased; oxygen and water vapor barrier, water resistance, mechanical properties of coated paper firstly increased and then decreased; brightness and gloss of coated paper decreased.Secondly,to enhance the barrier property of starch polymer, the starch was mixed with chitosan, PVA and gum respectively, which was then applied to the white kraft paper. With the increase of dosage of chitosan, PVA and guar gum, the viscosity of the composites increased to a different degree; optical properties and mechanical properties of coated paper changed little; grease and oxygen barrier of coated paper increased to a different degree. Grease and oxygen barrier of starch/chitosan composite coated paper was best. When the dosage of chitosan was 20%, oil resistance grade was increased by 4 levels, oxygen transmission rate was reduced by 89.7%. Because of the hydrophilicity of chitosan, PVA and guar gum, the Cobb values, water resistance and water vapor barrier of coated paper changed little.Then, in order to further improve the barrier properties, PVA and GO were mixed with starch, then the composite was applied to cigarettes paperboard. With the increase of the dosage of GO, viscosity and stability of the coating increased as well as the oxygen barrier of the coated paper. According to the amount of GO, the oxygen permeability of coated paper was reduced by 81.5% at most under the same coating weight. Due to its hydrophilicity, GO has little effect on the water vapor transmission rate of coated paper. Water vapor and oxygen barrier of coated paper were further improved when organic chromium was added in coating. When the dosage of organic chromium was 4%, water vapor and oxygen permeability were reduced by up to 6.9% and 40.8% under different coating weight. Due to their own inherent color of GO and organic chromium, the addition of GO and organic chromium in coating posed a negative effect on the brightness of coated paper.Finally, in consideration of the poor water vapor barrier of starch/PVA/GO composite, double coating with modified polyurethane was applied to gain oxygen and good water vapor barrier of coated paper. Modified polyurethane single coated cigarettes paperboard could significantly improve the water vapor barrier and water resistance. When modified polyurethane coating weight was 5.06g/m~2, water vapor transmission rate, Cobb value(60s) and Max value were decreased by 81.0%, 97.0% respectively and increased 70.5 times compared with the base paper. Starch/PVA/GO composite and modified polyurethane bilayer coating could gain better good oxygen and water vapor barrier. When starch/PVA/GO composite and modified polyurethane coating weight was 4.05 g/m~2 and 5.06g/m~2, oxygen and water vapor transmission rate of coated paper decreased to 65 cm~3/m~2·24h·0.1MPa and 285.05 g/m~2·24h respectively, which showed that coated paper could gain strong water resistance and maintain a very good printability at the meantime.