(528e) Fabrication and Characterization of Superparamagnetic Hybrid Cellulose Nanocrystals (CNC)/Iron Oxide (Fe3O4) Nanoparticles

Cellulose nanocrystals (CNC) were coated with iron oxide (Fe₃O₄) nanoparticles by a single-one step co-precipitation method. In this project, two types of CNCs were used: (a) longer bacterial cellulose nanocrystals (BCNC) isolated in-house from nata de coco with a length of 505.06 ± 200 nm and a height of 7.66 ± 4.5 nm and (b) shorter wood pulp CNC obtained from southern bleached softwood kraft (SBSK) pulp with a length of 122 ± 70 nm long and a height 6.1 ± 3 nm. In both cases, CNCs were isolated by sulfuric acid hydrolysis. The sulfur content in CNC was measured by conductometric titration with sodium hydroxide solution, and it was found to be 0.41 ± 0.5 wt% in wood pulp CNC and 0.24 ± 0.4 wt% in BCNC.

Each CNC was then coated with Fe₃O₄ by in-situ co-precipitation of FeCl₂ and FeCl₃ in the presence of ammonium hydroxide. The reactions were done with theoretical mass compositions of CNC/Fe₃O₄ and BCNC/Fe₃O₄ of 1:1, 1:2, and 1:4. The resultant magnetic cellulose nanocrystals (MagCNC) were found to have moderate dispersibility in water and can be easily recovered by a magnetic field. Transmission Electron Microscopy (TEM), Thermal Gravimetric Analysis (TGA), and Fourier Transform Infrared (FTIR) spectroscopy experiments confirmed the successful assembly of CNC with magnetite. TEM images showed that increasing the magnetite concentration increased the coated area of CNC and apparently more aggregation between the hybrid MagCNC. The actual amounts of CNC and Fe₃O₄ in MagCNC were calculated by TGA. The actual amounts of CNC in the MagCNC were lower than the theoretical values due to some loss of CNC not attached to magnetite during the purification steps. Increasing the magnetite concentration decreased the loss of CNC indicating a greater number of coated CNC. The FTIR spectroscopy results indicated the interaction of magnetite nanoparticles with the hydroxyl group of CNC surface. Moreover, the colloidal stability of MagCNC in water was tested by Dynamic Light Scattering (DLS), UV-Vis spectroscopy and zeta potential measurements. The UV-vis spectroscopy data suggest that particles with higher ratios of Fe₃O₄/CNC are less colloidally stable than neat CNC at neutral pH. The hydrodynamic radius of neat CNC, neat Fe₃O₄, and MagCNC were determined by DLS. Increasing the magnetite composition in the MagCNC increased the hydrodynamic radius, providing additional evidence for aggregation among the particles. Zeta potential measurements showed that MagCNCs were moderately stable in water from pH 5 to pH 9 (zeta potential values ≈ -30 mV). Furthermore, the magnetic properties of MagCNC were measured by Vibrating-Sample Magnetometer (VSM). The normalized saturation magnetizations of MagCNCs were 31.79 emu/g, 45.36 emu/g and 45.40 emu/g for CNC/Fe₃O₄-1:1, CNC/Fe₃O₄-1:2, CNC/Fe₃O₄-1:4, respectively while for neat Fe₃O₄ nanoparticles it was 77.37 emu/g.

Many papers reported various methods for the modification of CNC and their applications but only a few have been done with metal oxide particles. The prepared magnetic cellulose nanocrystals can be used to stabilize magnetically-controlled emulsions and foams for applications in drug delivery or low energy separations.