We developed the methods to allow us to prepare two new class of cellulose materials, CNPs (Cellulose nanoparticles), that have diameter between 40 and 520 nm, and CMPs and Cellulose Macro particles with a diameter in micro-meter range (about 20 μm). CNPs with three different sizes were obtained from microcrystalline cellulose and cotton, The three types of CNPs, namely CNPs-L (large width, about 520 nm), CNPs-M (medium width, about 200 nm) and CNPs-S (small width, about 40 nm) were obtained, then highly scattering thin films were prepared by using two different approaches. In the first method, free-standing films were obtained by vacuum filtration followed by freeze-drying. The second method is a vacuum-free way in which CNPs were first turned into partially hydrophobic by modification with trichloromethylsilane vapor then directly drop-casted via ethanol. Extremely short scattering mean free path (~1 μm) was achieved by optimizing the dimension of rod-shaped cellulose nanoparticles as cellulose building blocks and adjusting porosity via filtration and freeze-drying process. Only 9 μm-thick cellulose-based film exhibits a reflectance of ~80% in the entire visible range.
CMPs were produced by TEMPO in a one-step reaction from cotton. TEMPO oxidation selectively converts the hydroxyl groups on C6 of cellulose glucose ring into negatively charged carboxyl groups. As a result, this treatment increases the repulsion force and decreases the hydrogen bonding among the native cellulose nanofibers, resulting in fibers with a width of around 20 µm. For CMPs, when embedded in carboxymethyl cellulose matrices allow achieving exceptionally high haze with high values of transmittance (high transmittance (92%) and ultrahigh optical haze (98%), which are the highest values in literature so far).
