Chemical-free production of lignocellulosic micro- and nanofibers from high-yield pulps: Synergies, performance, and feasibility

Abstract

Far from being devoid of improvement, mechanical fibrillation benefits from high-yield pulping and refining to produce lignocellulosic micro- and nanofibers (LCMNFs). Spruce thermomechanical pulp was pretreated in a PFI mill to 10,000–30,000 revolutions and then passed, from 3 to 12 times and at 300–900 bar, through a high-pressure homogenizer. Mainly depending on those variables, the yield of nanofibrillation (in weight) ranged from 3% to 23%. The successive passes in the homogenizer significantly increased the specific surface area of the LCMNFs, hereby determined by Congo Red (from 115 to 164 m2/g) and poly(diallyldimethylammonium chloride) (from 54 to 89 m2/g) adsorption and contributed to higher cationic demands and water retention values, reaching values up to 229 μeq/g and 2.53 g/g, respectively. The performance of LCMNFs as a strengthening additive in papermaking was assessed, addressing the feasibility of the process. For instance, LCMNFs that had undergone 20,000 PFI revolutions and 6 passes through the homogenizer produced a 73% relative increase in breaking length of a virgin pulp, with an energy input of 19.2 kWh/kg (implying ~1.3 $/kg). Considering the synergic effects between mechanical treatments, a high fines content and the presence of lignin and hemicellulose, this can be a step towards waste minimization and reduction of hazardous chemicals, including sulfur and chlorine compounds.