ANISOFILM

The ANISOFILM project aims at developing a new and scalable method of processing by combining crossflow ultrafiltration with frontal photopolymerization to produce innovative cellulosic composite films with controlled anisotropic textures from nanometric to micrometric lengthscale. Although nanocelluloses have a large potential as building blocks in biosourced composites, it remains challenging to achieve optimal performance of the materials due to the necessity of a near-perfect organization, ideally from nanometer to macroscopic scales. When applying current processing methods (extrusion, injection molding, compression molding, film casting, electrospinning and spin coating), one of the main difficulties is to achieve a control of the orientation of cellulosic nanoparticles and to maintain their homogeneous organization over a wide range of lengthscales. Currently, the homogeneity of the spatial distribution and the degree of orientation imparted by these processes are limited because they are implemented at the final nanoparticle content of the designed nanocomposites. This concentration is too high for colloidal interactions to predominate over pressure, shear flow, or capillary forces applied during these processes, preventing an effective control of the orientation. This limitation can be overcome using cross-flow ultrafiltration. Indeed, membrane separation processes have the advantage of starting the process from a low initial volume fraction at which the shear flow and pressure forces are sufficiently high to overcome the internal colloidal interactions between nanoparticles. This allows achieving a regular deposition and alignment of the colloids near the membrane surface. It has been recently demonstrated that this process followed by air drying of the deposit allows generating well-defined layered structures with a uniform orientation over distances from nanometers to several tens of micrometers. (Semeraro et al. Colloids Surf. A 584, 124030 (2020) - doi.org/10.1016/j.colsurfa.2019.124030). Nevertheless, our previous studies have also evidenced that partial relaxation phenomena could occur upon switching off cross-flow and transmembrane pressure. (Rey C. et al. J. Membrane Sci. 578, 69-84 (2019) - doi: 10.1016/j.memsci.2019.02.019). Consequently, we propose a challenging strategy that involves a cross-flow ultrafiltration to reach a well-oriented state followed by the impregnation under frontal filtration of the deposit by a UV-curable polymer and finally in situ photopolymerization to freeze the resulting texture. The nanocomposite thin films will be designed from nanocelluloses (nanofibrils or nanocrystals) combined with conductive nanoparticles like multiwalled carbon nanotubes or nanofillers like natural clays. UV-curable polymers will consist of an aqueous polyester acrylate oligomer and a photo-initiator. Aiming at understanding the organization mechanisms involved during this processing method over a wide spatial range, both during ultrafiltration and photopolymerization, the materials will be characterized by in situ small-angle X-ray and light scattering (SAXS-USAXS and SALS) coupled with ex situ direct observation by electron microscopy (SEM and TEM) and X-ray diffraction (WAXS). Their functional properties (conductive, barrier, mechanical or optical properties) will be evaluated as well in relation with the texture of the nanocomposites. This new processing method will allow industrial activities to emerge for designing new nano-to-micro nanocellulose-biobased composite materials with superior functional properties such as: i) improved dielectric and conductivity properties, ii) enhanced oxygen or water vapor barrier properties, iii) reinforced mechanical properties, or iv) broad-band reflecting, scattering and transparent optical properties.