Periodic Reporting for period 1 - MFCPF (Multifunctional cellulose photonic films)
Période du rapport: 2018-08-01 au 2020-07-31
The pigment industry uses complex synthetic dyes or inorganic particles to produce colours, such as using titanium dioxide for whiteness. However, such pigments and dyes have brought lots of environmental and health problems. So, there is an urgent demand for more natural and sustainable alternatives for the pigment industry that can avoid the concerns on potential environmental and health impacts. By controlling the interaction of biological building blocks at the nanoscale, natural photonic nanostructures have been optimized via evolution to produce intense coloration. Inspired by such biological nanostructures, the possibility to design the optical appearance of material by guiding the hierarchical self-assembly of its constituent components, ideally using natural materials, is an attractive route for rationally-designed, sustainable manufacturing. Cellulose which is the most abundant biopolymer on the planet, and what’s more, cellulose is biocompatibility and biodegradability. I aim to use cellulose as a starting material to achieve various “photonic” pigments, which can eventually be scalable to replace the current pigments and dyes.
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).
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).
We demonstrated that by tailoring the morphology of cellulose on the meso-scale we were able to completely engineer light transport to produce both highly reflective white materials to transparent materials with high optical haze. In specific, by tuning the size of the cellulose nanoparticles CNPs and CMPs, we were able to achieve materials with unprecedented scattering mean free path is as small as ~1µm and high transmittance (92%) and haze (98%) outperforming results previously reported in the literature. The renewable and biocompatible characters of the system, combined with its excellent optical properties, allow the use of our various types of cellulose-based particles not only for applications in paints, LEDs, and solar cell devices but also in the application where the biocompatibility of the component with minimal impact on the environment and human health is essential such as in food and pharmaceutical coatings. We believe that such remarkable optical materials have huge potential applications in the next generation of sustainable and biocompatible materials.