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Construction of cellulose/ZnO composite microspheres in NaOH/zinc nitrate aqueous solution via one-step method

Wang, Sen, Yang, Yiwen, Lu, Ang, Zhang, Lina
Cellulose 2019 v.26 no.1 pp. 557-568
Fourier transform infrared spectroscopy, X-ray diffraction, ambient temperature, antibacterial properties, aqueous solutions, cellulose, cotton, derivatization, light scattering, microparticles, nanoparticles, nitrates, nuclear magnetic resonance spectroscopy, pulp, rheology, scanning electron microscopes, sodium hydroxide, solvents, viscometry, zinc, zinc oxide
In the present paper, NaOH/zinc nitrate aqueous solution was successfully developed as a novel solvent to dissolve cellulose from cotton linter pulp via cooling. The ¹³C NMR result proved that the dissolution was a physical process without derivatization. Dynamic light scattering, viscometry and rheology measurements were used to investigate the solution properties of cellulose in different concentration regimes. The rheological test results proved that cellulose dissolved in NaOH/zinc nitrate solution was relatively stable at room temperature, which benefits commercial scale production of cellulose materials. Interestingly, single cellulose chains tended to aggregate in the solution, which facilitated their self-assembly into regenerated cellulose microspheres (CM). During the regeneration, the precursor zinc salts in the solution precipitated as ZnO nanoparticles, which were further embedded in the porous structure of CM. Thus, composite microspheres (CMZ) consisted of cellulose and ZnO with an average size of about 12 nm were facilely fabricated via one-step method, and mean diameter of the CMZ microspheres was 60 μm. The results of FT-IR, scanning electron microscope, X-ray diffraction, and thermo gravimetric analysis demonstrated that ZnO having hexagonal wurtzite structure were evenly embedded in the cellulose microspheres, leading to the formation of cellulose/ZnO composite. Antimicrobial tests indicated that cellulose/ZnO microspheres displayed good antibacterial properties. This work provided new pathway to utilize a water-based and eco-friendly solvent of cellulose to construct environmentally friendly and sustainable organic/inorganic hybrid materials.