The aim of this project is to propose a biobased, biodegradable and recyclable solution in the paper/board stream to replace certain single-use plastic packaging.
The strategy adopted is to use cellulose fibres from paper pulp to produce three-dimensional functional products, using processes traditionally used in the plastics industry, such as extrusion, injection and thermocompression, thus facilitating the industrial transfer of the technology developed.
To achieve this objective, it was necessary to make high-concentration fibrous suspensions injectable in order to obtain materials with targeted usage properties (including barrier properties), using a multi-scale approach at the interface between the physico-chemistry of suspensions and process engineering. The combination of mechanical and enzymatic pretreatment of the fibres and severe mechanical treatment in a twin-screw extruder produced a concentrated cellulose microfibril (MFC) ‘paste’ (~20% dry matter) with optimized properties comparable to those of conventional MFC suspensions (~3%). This MFC paste was then injected onto the surface of a preformed cellulose object (molded cellulose), to confer oxygen and oil barrier properties.
Despite its good injectability due to its rheological properties and the promising results obtained when applied to the surface, this MFC paste proved to be less suitable for the production of bulk 3D objects. In fact, the amount of water to be removed during drying was still too high, leading to significant shrinkage phenomena during drying. The dry matter content of the MFC paste was therefore increased by up to 50% by raising the temperature during processing in a twin-screw extruder. The rheological properties of the resulting material, similar to those of a powder, were adjusted by the subsequent addition of a small quantity of polymer (less than 10%), which enabled good injectability to be achieved.
After thermopressing, a smooth material was obtained that also had oil-barrier properties. However, shrinkage remained a limiting factor for complex shapes. To overcome this difficulty, a disruptive strategy was adopted. Virgin cellulose fibres (with no mechanical or enzymatic pretreatment) were simultaneously mixed with a polymer with lubricating properties (in quantities of less than 10%) in an extruder. The material obtained after extrusion was injected in a mold and dried to produce cellulosic objects with promising three-dimensional shapes and limited shrinkage.
