Microfibrillated Cellulose Moisture Sorption Fundamentals in Fiber Packaging
Microfibrillated cellulose moisture sorption degrades barrier performance at high humidity, requiring chemical cross-linking and verified compliance dossiers.
TEMPO Oxidation
Regioselective Chemistry
Catalytic oxidation systems selectively convert primary alcohol groups on polysaccharide backbones into carboxylic moieties under mild aqueous conditions. In cellulosic pulp processing, TEMPO oxidation employs stable nitroxide radicals alongside sodium hypochlorite to convert C6 primary hydroxyls into sodium carboxylates. Crystalline fibril cores remain intact during surface modification.
Selectivity diminishes if reaction pH drops below ten.
Nanofibril Delamination
Surface charge accumulation creates severe electrostatic repulsion across adjacent cellulose microfibrils. Following TEMPO oxidation, mechanical homogenization at low energy yields uniform dispersions of individual cellulose nanofibrils without damaging crystal morphology. Fibril diameters narrow to three to four nanometres with aspect ratios exceeding one hundred.
Suspension viscosity increases drastically at solids contents as low as one percent, transforming the aqueous slurry into a transparent thixotropic gel.
Barrier Application
Papermaking applications incorporate these carboxylated nanofibrils to form gas-impermeable films and dense coating layers. Applied as a surface treatment on packaging board, TEMPO oxidation products reduce oxygen transmission rates to near zero under bone-dry test conditions. Tensile index and internal bond strength of multi-ply paperboard improve substantially when small dosages are added to furnish blends.
Water sensitivity remains the principal operational barrier, because ionic carboxylate groups absorb atmospheric humidity, deteriorating oxygen barrier integrity when ambient relative humidity surpasses seventy percent. Dewatering rates on forming wires drop significantly, limiting high-speed wet-end addition on commercial paper machines.