| Nano cellulose is an excellent polymer-reinforced material with its unique performance, the incorporation of nano cellulose into waterborne coatings is expected to improve the film properties of waterborne coatings, thus expanding the application of nano cellulose in the field of coatings. In the previous study, cellulose nanocrystals have been widely applied to enhance waterborne coatings, but the application of cellulose nanofibers is less, for the problem that the poor dispersion stability and compatibility of CNF in organic polymer matrixis has not been completely solved. In view of this problem, cellulose nanofibers was modified by a amphiphilic coupling agent and the chemical cross linking between CNF and coating matrix was successfully formed in this study. Consequently, the good dispersion, long-term stability and good interface compatibility of CNF in waterborne coatings was achieved, and improve the comprehensive properties of the coating film.In this paper, preparation of cellulose nanofibers was through the chemical treatment combined with high-intensity ultrasonic treatment. The effect of different concentrations of silane coupling agent KH550 on the surface modification and dispersion stability was studied, and the composite coating was prepared by incorporating the KH550-modified CNF into waterborne acrylic coating and the solution casting method and brushing method were used to achieve the composite coating films. The dispersion state, surface chemical structure, rheological and phase transition properties of modified CNF was studied by means of Transmission electron microscopy, X-ray photoelectron spectrum, differential scanning calorimeter, and the composite coating film properties of transparency, gloss, micro structure, fracture form, thermal and mechanical properties, hardness and wear resistance were comprehensively surveyed. The main results are as follows:(1) Cellulose nanofiber concentration has a great influence on the dispersion stability. Low concentration will lead to sedimentation and highly viscous hydrogel was formed in high concentration.Adding silane coupling agent KH550 can improve the dispersion stability of CNF water suspension, but it cannot achieve good dispersion effect when the adding dose is less or excessive.The results show that the optimum adding amount of KH550 was 0.16%.(2) KH550-modified CNF were well dispersed and have a good interface compatibility in the coatings matrix. Adding modified CNF aqueous suspension will affect the monolithic properties of the composite coatings.With increasing content of CNF, the viscosity, storage modulus, loss modulus, glass transition temperature, the hardness and abrasive resistance of composite coating were significantly improved. The highest modulus can be increased by 5 times, and the hardness increased by 2 times, the abrasive resistance is reduced by 35%.(3) The composite coating film has good optical transparency, because CNF uniformly dispersed in the paint film and no agglomeration was formed, so the transmittance of visible light has not been affectd. The visible light transmittance can be maintained at 86%-90%, and the gloss almost do not change.In conclusion, adding KH550-modified CNF will not affect the transparency and gloss, but can significantly improve the overall performance of the waterborne acrylic coatings. |
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