Phosphorylation as a means to reduce energy consumption for fibrillation when producing micro- and nanofibrillated cellulose from unbleached Eucalyptus sp. pulps

Lignocellulosic biomass-derived micro- and nanofibrillated cellulose (MNFC) is a promising material for the production of a wide variety of products, but the high energy consumption of mechanical fibrillation limits the material’s industrial potential. This study aimed to investigate the use of monoammonium phosphate ((NH₄)H₂PO₄) and urea (CH₄N₂O) for the pretreatment of unbleached Eucalyptus sp. kraft pulp as a strategy to reduce energy consumption during mechanical fibrillation. Pretreatments were carried out using two reagent molar mass ratios, namely 1:1:1 (1.0 g of fiber/1.2 g of (NH₄)H₂PO₄/4.9 g of CH₄N₂O) and 1:2:2 (1.0 g of fiber/2.5 g of (NH₄)H₂PO₄/10.0 g of CH₄N₂O). Pretreated samples were then oven-heated at 150 °C for 20, 40, or 60 min to promote phosphorylation reactions. MNFC was obtained by mechanical shearing using a Super Masscolloider mill. The resulting samples were analyzed for morphology, turbidity, water stability, Fourier transform infrared spectra, X-ray diffraction patterns, and energy consumption. The derived films were evaluated for mechanical properties. Pretreatments carried out using reagent ratios of 1:1:1 and 1:2:2 and heat-treated for 60 min formed individualized microstructures. These pretreatments reduced energy consumption during fibrillation by 69% and 73%, respectively. Heat treatment time for activation of chemical reactions has a stronger influence on phosphorylation efficiency than reagent ratio. The use of different reagent ratios (1:1:1 and 1:2:2) combined with a heat treatment time of 60 min provided similar results. These conditions were the most effective in facilitating mechanical fibrillation.