Assessment of processing parameters suitable for 3D shaping of Dialcohol Cellulose by wet melt processing

The increase in the world population has led to increasing demand for food production and packaging products that can limit food spoilage and contamination. Packaging represents a third of the overall use of not biodegradable fossil-based plastics, and a large amount of it is for food packaging. The awareness of the environmental impact of such plastics is driving their replacement with renewable alternatives. Being cellulose world’s most abundant biopolymer, it emerges as a valid alternative for food packaging applications. Cellulosic materials are biodegradable and possess high mechanical strength, low thermal expansion coefficient, and neutral sensory and organoleptic properties, such as colour, appearance, aroma, flavour, and taste. They are lightweight and enable the incorporation of various natural antimicrobial and antioxidant agents. They have good barrier properties against oxygen but are strongly influenced by environmental humidity since these materials are sensitive to water. Higher humidity level loosens the strong hydrogen bonding in the cellulose structure, decreasing its oxygen and moisture barrier ability. The high amount of hydroxyl groups creates strong hydrogen bonds between cellulose fibres, which remain to a large extent upon the increase in temperature. These strong mutual fibre interactions lead to cellulose degradation before melting, hindering its production by melt processing techniques. A chemical modification of the cellulose fibres to lower their glass transition can be a strategy to improve their melt processability. The fibre modification consists of an oxidation with sodium periodate followed by a reduction with sodium borohydride to create a dialcohol cellulose (DAC). The hypothesis is to have a crystalline cellulose core surrounded by an amorphous cellulose shell formed by the progress of the reaction from the outer to the inner part of the fibres. This amorphous shell would provide some thermoplastic character to the material, leading to a melt processing window between the glass transition and degradation. After modification, the dialcohol cellulose fibres keep high interaction with water molecules, which can play the role of a green plasticizer. The work investigates the melt processability (compounding and injection moulding) windows of DAC. We assessed how different processing conditions and water amounts affect the fibre properties, such as fibre length, thermomechanical properties, and possible DAC degradation. For this purpose, the study includes analyses of fibre length distribution (using a Kajaani), morphology (using a scanning electron microscope, SEM), thermal (using thermogravimetric analysis, TGA) and dynamic thermomechanical properties (DMTA).