Carboxymethyl and dialdehyde microfibrillated cellulose from hemp hurds: Role of fibrillation energy in chemical reactivity and functional properties

In response to the growing demand for bio-based packaging materials, this work investigates the interplay between fibrillation intensity and the chemical reactivity of microfibrillated cellulose (MFC) derived from hemp hurds, an underutilized agro-residue from industrial hemp processing. MFCs were produced by controlled mechanical fibrillation at specific energy inputs ranging from 0 to 5000 kWh t -1 to systematically tailor fibril morphology, hydroxyl accessibility, and subsequent chemical modification behavior. Carboxymethylation and periodate oxidation were employed as model reactions to probe the relationship between fibrillation intensity and chemical substitution. For carboxymethylation, the degree of substitution (DS) increased with fibrillation energy up to 3000 kWh t -1 , reaching approximately 0.9 in aqueous systems and up to 2.5 in butanol-mediated reactions. Further increases in fibrillation energy resulted in a reduced DS despite increased fibrillation. This behavior is attributed to the formation of strongly bound water and enhanced hydrogen bonding at higher fibrillation levels, which generates persistent hydration shells around microfibrils and kinetically limit reagent diffusion and substitution efficiency. This hydration-controlled reactivity constraint is identified for the first time in cellulose carboxymethylation derived from agro-residue feedstocks. At the 3000 kWh t -1 , periodate oxidation produced dialdehyde cellulose with a surface charge of ∼27 µeq g -1 , while carboxymethylation enabled tunable ionic functionality and covalent cross-linking potential. Overall, these results demonstrate that maximum chemical functionality does not require maximum mechanical energy input, establishing a sustainable pathway for producing highly functionalized MFC materials for packaging films and coating applications. • Functional, high-aspect-ratio microfibrillated cellulose (MFC) produced from hemp hurds agro-residue. • Synergistic mechanical fibrillation and chemical modification of MFC for enhanced barrier and mechanical properties. • Aqueous chemical substitution of hemp hurd MFC for sustainable materials development. • Degree of substitution influenced by fibrillation and water hydration shells around fibrils. • Balanced fibrillation and modification reduce energy use and enhance MFC functionality.