Study On The Application Of Nanofibrillated Cellulose In Coatings

The increasingly prominent demand of high-grade cultural printing paper and food safety packaging paper has led to the development of LWC in the paper industry and improves the requirement of coating formulations and coated paper performance.With the addition of various chemical reagents in traditional coatings,the environmental safety problems of coatings can not be guaranteed.As a new green material,nano cellulose has many advantages of high specific surface area,strong hydrophilicity,high aspect ratio and so on which can be regarded as ideal for low-solid paint additives.Its application in coatings has become a new development tendency.In this paper,the raw material is softwood pulp treated by beating and alkali treatment.Nanofibrillated cellulose?NFC?is prepared by refining,TEMPO oxidation and high pressure homogenization.According to the characteristics of NFC,its applications in coating as auxiliary adhesive and pigment dispersant and so on are studied.The main conclusions are as follows:Mechanical pretreatment and TEMPO oxidation could promote the separation of the microfibrils.On this basis,homogenization is carried out to produce NFC having a diameter of about 30 to 50 nm and a length of about 1 to 3 ?m,which existed in a gelatinous state in low concentration.Colloidal solution of NFC showed characteristics of shear thinning and pseudo plastic fluid.With the increase of the concentration,the consistency coefficient of the solution and the pseudo plasticity increased obviously.At the pH near 7,the ionization of the carboxyl group was complete,and the electric resistance of the solution was the strongest.The water holding capacity of the coating was improved,and the coating still belonged to pseudoplastic fluid after adding NFC.The gloss and smoothness of the coated paper were improved with the increase of the NFC ratio,and the water absorption was increased slightly,the whiteness was almost unchanged.When the ratio of SBR and NFC was 96: 4,the indicators of coated paper,including surface strength,bursting resistance and so on achieved the best.The addition of NFC enhanced the negative charges of TiO₂ pigment particles,and the particles were not easy to coagulation as a result of electrostatic repulsion,so as to improve the dispersion stability of the suspension.Without the addition of NFC,the suspension rate of TiO₂ was only 42.788%,pigment particles were prone to subsidence.However,as the addition of NFC is 0.15wt%,the suspension rate was as high as 95.975% and the residual turbidity centrifugation also reach the maximum value.The static supernatant volume and particle size range of TiO₂ suspension increased gradually with the decreased NFC addition.Kaolin pigment should be dispersed under alkaline conditions of pH 9.After adding the modified NFC,the electrostatic repulsion and the steric hindrance competed with each other.The viscosity and percentage of the kaolin suspensions increased with the increase of the modified NFC content,and decreased with the increase of the DS,while Zeta potential showed a trend of increasing first and then tending to be gentle.With the increase of DS of the modified NFC,the electronegativity of the dispersion increases,the water retention value of the low concentration coating enhanced,the plasticity is weakened and the viscosity is reduced.Therefore,NFC not only played effective dispersion effect on pigment but also improved the performance of coated paper,which confers coating good rheology and water retention properties.The coating becomes more environment-friendly and lays a foundation for its application in many fields,such as,micro coating and food packaging coating.