Preparation and properties of dried nanfibrillated cellulose and its nanocomposites

Abstract: The production of fully degradable nanocomposites with biopolymers as matrix and cellulose nanofibrils with high aspect ratios as reinforcement is still a challenging task. Also, due to the large amount of hydroxyl groups on the surface of these nanofibrils, they tend to irreversibly agglomerate during drying. This process, known as hornification, decreases the aspect ratio of the nanofibrils. Consequently, their reinforcing potential in nanocomposites is lowered. Thus, the objective of this PhD project is to produce novel biopolymer composites that are reinforced by functionalised cellulose nanofibrils in powder form. A successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In order to induce an optimal compounding of the fibrils with different biopolymers, good fibril/matrix embedding is required. Therefore, the cellulose nanofibrils have to be modified appropriately to match the hydrophilic or hydrophobic nature of the polymer matrix.The production of fully degradable nanocomposites with biopolymers as matrix and cellulose nanofibrils with high aspect ratios as reinforcement is still a challenging task. Also, due to the large amount of hydroxyl groups on the surface of these nanofibrils, they tend to irreversibly agglomerate during drying. This process, known as hornification, decreases the aspect ratio of the nanofibrils. Consequently, their reinforcing potential in nanocomposites is lowered. Thus, the objective of this PhD project is to produce novel biopolymer composites that are reinforced by functionalised cellulose nanofibrils in powder form. A successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In order to induce an optimal compounding of the fibrils with different biopolymers, good fibril/matrix embedding is required. Therefore, the cellulose nanofibrils have to be modified appropriately to match the hydrophilic or hydrophobic nature of the polymer matrix. In the first study, water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by carboxymethylation and mechanical disintegration. The sequence of the treatments influenced the stability of the final products in water. When carboxymethylation was applied first, enhanced disintegration of RBP into its sub-structural elements was observed. The prepared powder of this route formed a stable gel in water without sedimentation after 20 h. SEM images affirmed a significant reduction of cellulose nanofibrils agglomeration compared to unmodified NFC. The results suggest that NFC in dry form could be used as an alternative to conventional NFC in aqueous suspensions used as starting material for derivatization and compounding with biopolymers.