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Thesis Title: Use of twin-screw extruder for innovative cellulose based packaging by injection and thermocompression

The main objective of this thesis is to propose bio-based and recyclable alternatives to plastic packaging, using existing plastics manufacturing processes such as extrusion, injection-molding, thermocompression. The final packaging must be recyclable in the current paper/cardboard recycling stream. 
The first idea was to use microfibrillated cellulose (MFC). MFCs would compose 100% of the packaging's composition. Thanks to the twin-screw extrusion process, it is possible to produce these MFCs at 25 wt% dry matter (usually 2-3 wt%). These 25 wt% MFCs can then be injection moulded. When optimising thermocompression drying, the material contracts, causing cracks in the packaging. However, the barrier properties of MFCs were exploited by using injection-coating. This process consists in coating a thin layer of MFC onto the surface of a preformed cellulose structure to protect it from fats and oxygen. This process constitutes Patent 1. 
The second strategy was to reduce the amount of water initially present in the MFCs in order to limit shrinkage during drying. By working on the parameters of the extrusion process (temperature gradient 50-200°C), it was possible to evaporate part of the water contained in the MFCs, reaching 50 wt% at the outlet. Natural additives were added to improve the flowability. Following thermocompression drying, crack-free prototypes with a very smooth surface and grease barrier properties were obtained. However, drying times and shrinkage during drying remained significant. 
The third strategy was to use cellulose fibres to form the structure of the packaging. Mixing a natural additive with the fibres enabled the fibres to be injected. The additive adheres to the surface of the fibres. The main hypothesis is that this additive creates a lubricating layer. This lubrication allows the fibres to move without degradation under mechanical stress. During drying, the entanglement of the fibres drastically limits shrinkage. Several prototypes have been produced, including tensile and flexural test specimens, caps and coffee capsules. The final packaging contains at least 90% cellulose fibres, making it a paper-like material that is recyclable. The process and product are protected by patent 2. This packaging can then be protected by a layer of MFC applied by injection coating (Patent 1). The thermocompression-dried layer provides grease and gas barrier properties.
The results of this thesis have led to funding for the Injectose project. The aim of Injectose is to bring the cellulose fibre injection moulding process to industrial scale.

Key words: Twin-screw extrusion,Injection,Microfibrillated cellulose,Fibrillation,Thermocompression,Sustainable packaging

Doctoral School: ED I-MEP² - Engineering - Materials, Mechanical, Environment, Energetics, Processes, Production
Research laboratory: Laboratoire de Génie des Procédés pour la Bioraffinerie, les Matériaux Bio-sourcés et l'Impression Fonctionnelle (LGP2 - CNRS/UGA - Grenoble INP-UGA/AGEFPI) in collaboration with The Centre Technique du Papier (CTP)
Thesis supervision: Julien BRAS, Evelyne MAURET and Elisa ZENO

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