Preparation of Citric Acid-Modified Cellulose Composites and Elucidation of Their Toughening Mechanism

Cellulose is a plant-based and highly abundant biobased resource and widely used as a filler for polymer composite materials because cellulose fillers have a high aspect ratio and high crystal modulus. Introducing high contents of cellulose fillers into polymer composites reduces the use of petroleum-derived synthetic polymers, increases the mechanical strength, and decreases the toughness due to the aggregation of fillers. In this study, we introduced hydrogen bonds between the polymer matrix and cellulose fillers. Citric acid-modified cellulose (CAC) has many carboxyl groups and forms hydrogen bonds with polymers that have hydroxy groups. The interactions between the polymer matrix and the CAC fillers were evaluated by the glass transition temperature, Fourier transform infrared spectroscopy, and a simulation study based on first-principles calculations. Noncovalent interactions between the polymer matrix and CAC fillers improved the toughness of the CAC composites and enabled mechanical recycling at a high CAC content. This study contributes to the reduced use of petroleum-derived synthetic polymers and longer lifetimes of the materials.