Cellulosic fibre mats with improved fibre bonds towards lighter, stronger and stretchable bio-based materials. – FiberBond

To meet environmental challenges, a drastic reduction of the use of petro-sourced polymers in the packaging industry is necessary. Paper material is an attractive bio-based, recyclable, renewable and biodegradable alternative provided that it has the required levels of barrier properties, sealing ability and/or 3D formability. Although intense efforts have been made to develop specific treatments and processes to give paper such properties, many challenges remain. For instance, 3D formability is strongly limited by the lack of ductility of paper. Bonding at fibre crossings is most often the limiting parameter for the paper mechanical performance. Improving the ultimate strength and strain of paper necessarily thus implies improving the mechanical properties of the fibre bonds. They could be significantly improved by increasing the contact area at fibre crossings and by promoting the development of Coulomb interactions and/or covalent bonding at contacts. The objective of the FIBREBOND project is to study, quantify and model the contributions of the fibre properties (morphology, chemical composition, charge density, flexibility modified by refining or chemical surface treatments) and process parameters (wet pressing, free/restrained shrinkage) to the improvement of the contact area, as well as the contribution of modified fibre surfaces (charged or able to form hemiacetal or ester bonds) to the improvement of bond strength and toughness, by using novel experimental approaches that the consortium largely contributes to develop.
The project is organized around four tasks. (A) Production of the model fibre mats. The main objective of Task A is to taylor fibre mats made of fibres with (i) different abilities to collapse, wet flexibilities and wall deformabilities in order to study the contribution of these properties to the development of the relative contact area (RCA) and to the mechanical properties of the resulting fibre mats and (ii) chemically modified surfaces to promote the development of strong interactions between fibres (electrostatic or covalent bonds). (B) Multiscale characterization of the contact area development and fibre/network shrinkage phenomena during pressing and drying of the fibre mat. In this task, we will investigate how the fibre-fibre bonding areas develop during the wet pressing and the drying operations of the fibre mats formulated in Task A, adopting for that a multiscale approach, i.e., the mat scale, the fibre network scale and the fibre scale. The experiments will allow us the effects of the fibre types as well those of the wet pressing and drying conditions on the development of the fibre-fibre bond area and the collapse of the fibres to be explored. (C) Multiscale characterization of the mechanical behaviour of the fibre mats. The objective of the task are (i) to constitute an exhaustive multi-scale experimental database characterizing the hygro-mechanical behaviour of the lab papers, their fibre and their bonds (ii) to understand the effects of the fibre type, refining, functionalization paper making conditions and hygro-thermal environment on the paper responses and (iii) to propose multiscale guidelines to taylor and optimize the specific hygro-mechanical properties of papers, fibres and fibre bonds. (D) Development of a multiscale model for the mechanics of processed fibre mats properties and 3D formability tests. In this task, we will (i) propose a theoretical and numerical multiscale framework to model the hygro-mechanics of the fibre mats, fed from the database of the previous tasks, i.e., with relevant nano, micro and meso-structural descriptors and hygro-micromechanics of fibre and fibre bonds, (ii) implement this model into a macroscale Finite Element code to simulate the forming and the end-use properties of the lab papers, (iii) validate the FE prediction with 3D paper forming experiments.