| With rapid paper industrialization,higher requirements are put forward for the performance of special paper,such as waterproof,wear-resistant,folding resistance,etc.,which reflects the high requirements for paper-making additives.Surface sizing technology,a method to improve the comprehensive performance of paper,is to flow surface sizing agent into the surface of paper fibers to increase the intermolecular force and chemical bonding force between fibers,resulting in enhanced surface water resistance and mechanical properties.Polyvinyl alcohol(PVA)and polyethyleneimine(PEI)are widely used in special paper surface sizing because of their excellent surface sizing properties.PVA,a water-soluble polymer with many hydroxyl groups in the molecular chain,has excellent hydrophilicity,cohesiveness,emulsification and film-forming properties.However,surface sizing using PVA alone is not ideal,such as limited water resistance and physical properties.PEI has excellent sizing performance due to the large number of amine groups in the molecular chain,which has high cationicity,reactivity,adhesion and adsorption.However,PEI sizing agents are expensive and do not contain groups that chemically crosslink with paper fibers.Here,this work proposes two modified PVA and modified PEI special paper surface sizing agents containing silanol groups by modifying PVA and PEI with alkoxysilanes.In addition,the modified PEI and PVA are compounded to obtain a composite surface sizing agent.The strengthening mechanism of modified PVA,modified PEI and modified PEI/PVA composite surface sizing agent has been deeply studied,as well as the effect on paper physical properties,water resistance and ink adhesion.Its main conclusions are as follows:(1)In order to improve the poor water solubility and water resistance of PVA sizing agent,graft modification of PVA was carried out by silane coupling agent KH560,and the prepared modified PVA was applied to the surface sizing of paper.Its structure was characterized,which proved that the target product KPVA was synthesized successfully in this experiment.The modified PVA with different degrees of alcoholysis and polymerization were compared.Among them,KPVA1799 because of the various properties of good,so choose its application in paper surface sizing.The results showed that the particle size of KPVA1799 was 344 nm,the PDI index was 0.587,the TSI index was the smallest,and the sizing liquid viscosity was moderate.When KPVA1799 is applied to the surface of the paper,the dry tensile index is 86.70 N·m·g-1,the wet tensile index is 25.85 N·m·g-1,the flexion resistance is 232 times,the contact Angle was 63°,and the Cobb30 value was 81.21 g·m-2.Compared with PVA1799 sizing paper,these properties are improved by 17.64%,43.77%,112.84%and 23.53%,respectively,and Cobb30 value is decreased by 22.28%.(2)In order to reduce the cost of PEI alone,cross-linking groups that can react with paper fibers were introduced,and silane coupling agent KH560 was used to modify PEI.By controlling the mass ratios of PEI to KH560 as 10:1,10:1.5,10:2,10:2.5 and 10:3,five kinds of KPEI water dispersions with different mass ratios were prepared and their structures were characterized.The results show that the best KPEI-2 has a particle size of 127 nm,a PDI index of 0.287,a TSI index of the smallest,and a moderate viscosity.When applied to the surface of the paper,the dry tensile index is 79.31 N·m·g-1,the wet tensile index is 23.47 N·m·g-1,the fold resistance is 273 times,the contact Angle was 59°,and the Cobb30 value was 121 g·m-2.Compared with PEI sizing paper,these properties are improved by 56.12%,22.24%,193.55%and 59.46%respectively,and Cobb30 value is decreased by 8.33%.(3)In order to further improve the surface sizing performance of KPEI sizing agent,PVA1799 was used as the carrier of surface sizing.After controlling the content of PVA1799 and the content of KPEI-2 unchanged each time,a series of KPEI/PVA composite sizing systems were formed through physical blending and applied to the surface sizing of paper.Through the study of paper properties,the optimal surface sizing scheme of KPEI/PVA composite sizing system is determined as follows:the content of KPEI-2 is 3%,the content of PVA1799 is 4%.After applying the best sizing agent 3%KPEI/4%PVA on the surface of paper,the dry tensile strength is 115.83 N·m·g-1,the wet tensile index is 41.61 N·m·g-1,the flexion resistance is 1257,the contact Angle was 89°,and the Cobb30 value was 93 g·m-2.Compared with KPEI-2 sizing paper,these properties are improved by 46.07%,77.82%,360.44%and 50.85%respectively,and the Cobb30 value decreases by 23.14%.(4)In this chapter,the adhesive tape stripping test,alcohol wiping test and oil-based marker writing test were used to test the paper writing and ink adhesion after sizing with different sizing systems.In the use of KPVA,KPEI and KPEI/PVA sizing agent sizing,on the one hand to improve the surface roughness of the paper,ink particles through mechanical anchoring effect adsorption on the surface of the paper,on the other hand,sizing agent contains polar groups silicon hydroxyl,so that the polar ink particles through the intermolecular force adsorption on the surface of the paper.In the use of KPEI and KPEI/PVA sizing agent,positively charged PEI and negatively charged ink particles through electrostatic adsorption,so that ink particles adsorption on the surface of the paper,and then enhance the paper ink adhesion.Finally through the ink adhesion test found that the use of KPVA,KPEI and KPEI/PVA sizing agent sizing paper ink adhesion compared with the base paper has been improved. |
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