Research On The Preparation Of Cellulose Hydrogels And Their Application In Stabilizing Pickering Emulsions

Cellulose is the most abundant organic raw material and has wide applications in various areas such as composite materials, textiles, drug delivery systems and personal care products. The inexpensive, biodegradable and renewable resource has received a great deal of attention for its physical properties and chemical reactivity. Choosing natural cellulose as raw material, we prepared the cellulose hydrogel which has favorable water uptake capability via low-temperatured dissolution technique. Cellulose microgel nanoparticles (CMNs) were prepared with cellulose hydrogel to stablize pickering emulsions. In addition, magnetic cellulose hydrogels were obtained from cellulose hydrogel through chemical co-precipitation method. The main content of the research and results are listed as follows:(1) Fabrication of cellulose self-assemblies and high-strength ordered cellulose filmsBased on the dissolution of natural cellulose by low-temperature dissolution technique, cellulose hydrogel was obtained through crosslinking reaction using methylene bisacrylamide (BIS) as cross-linking agent. Cellulose microgel used as self-assembly precursor was acquired by ultrasonicating of the cellulose hydrogels. With varying crosslinking degree (CLD) and concentration of cellulose, a variety of morphologies of cellulose self-assemblies, including sheets with perfect morphology, high-aspect-ratio fibers, and disorganized segments and network, are formed through evaporation. Furthermore, cellulose films are fabricated by diecasting and evaporating the cellulose hydrogels, resulting in a 3D-ordered structure of closely stacking of cellulose sheets. The morphologies and structure of cellulose were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) measurements and Fourier transform infrared spectroscopy (FTIR). The strength properties of materials was examined by universal testing machine. The tensile strength (σ) have significantly been enhanced from～60 MPa to～135 MPa as r increases from 0.375 to 0.473, and the value of strain to failure (ε) is also enhanced significantly, from 10% to 25%. The mechanical test indicates both tensile strength and flexibility of the cellulose films are greatly improved.(2) New pickering emulsion stablized by CMNBased on the formation of cellulose solution, cellulose hydrogel was obtained through crosslinking reaction with BIS. Cellulose microgel nanoparticles (CMNs) was acquired from hydrogel by ultrasonicating. CMNs dispersed in water are presented in this investigation to stabilize paraffin oil-water interfaces and produce pickering emulsions with excellent stability. The AFM result shows that CMN possesses nature film-forming ability no matter in air or at solid interface. The Pickering emulsions were characterized by confocal laser scanning microscope (CLSM), SEM and freeze fracture transmission electron microscopy (FF-TEM) and the emulsification indexes are calculated while varying the CLD in CMNs and the oil/water ratios. It was found that the CLD has an important influence on the stability of CMN suspension. As modified degrees of CMN increases, the ability of floculation resistance is enhanced, meanwhile, the ability of stabilizing oil in water pickering emulsion is improved.(3) Preparation and characterization of magnetic cellulose composite hydrogelBased on the cellulose hydrogel, magnetic cellulose composite hydrogel was obtained by in-situ synthesis of Fe3O4 nanoparticles in the hydrogel. The morphologies, structure were characterized by SEM, TEM, XRD measurements, and FTIR. The magnetic property of the products was examined by superconducting quantum interference device (SQUID). The results showed that as-prepared magnetic products had better magnetic response ability, and the high magnetic saturation (Ms) was 88.43 emu/g when the concentration of Fe2+ was 0.250 mol/L, r was 0.473. Magnetic CMN suspension was acquired from magnetic cellulose hydrogel by ultrasonicating, which was found able to prepare magnetic pickering emulsion and can be applied in magnetic separation.