Potentiometric back titration as a robust and simple method for specific surface area estimation of lignocellulosic fibers

Abstract

The specific surface area (SSA) of cellulosic or lignocellulosic fibers is seldom reported in the recent literature on papermaking, despite its close relation with the degree of refining and other key pulp properties. Amidst outdated assays (Pulmac permeability test) and methods that, while accurate, are of doubtful usefulness for papermaking purposes (N2 adsorption–desorption), we suggest a methodology based on the cationic demand. A commonly used cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC), became adsorbed onto thermomechanical pulp samples. Then, a potentiometric back titration with an anionic polyelectrolyte measured the cationic demand, expressed as microequivalents of PDADMAC per gram of pulp. Multiplying this value by the surface area of a microequivalent of polymer, considering rod-like conformation in the case of minimum ionic strength, yielded the SSA of the lignocellulosic pulp. Our system assumes that the quaternary ammonium groups were anchored through electrostatic and ion–dipole interactions. Measuring the carboxyl content allowed for discriminating between both kinds of forces. Finally, the model could be validated by plotting the estimated SSA values against the Schopper-Riegler degree, attaining high correlation coefficients (R2 ~ 0.98). Owing to the high molecular weight of the polyelectrolyte of choice (107 kDa), and more particularly in the case of fine-free pulps, SSA values estimated from the cationic demand were consistently lower than those from dye (Congo red) sorption. Instead of being a drawback, the limited diffusion of PDADMAC through fibers can enable papermakers to attain a more helpful quantification of the available surfaces in operations with low residence times.

Critical comparison of the properties of cellulose nanofibers produced from softwood and hardwood through enzymatic, chemical and mechanical processes

“…Therefore, the evaluation of both characteristics proportionate comparable information and in an industrial perspective, transmittance would be the most affordable parameter since it would require less-time consuming and low cost equipment, due to fact that centrifugation is not required [8]. As for the surface charge, it becomes higher when all nanofibrils have been released, having the whole surface full of hydroxyl groups with a negative charge [64]. At this point CD reach the highest value.…”

Micro- and Nanofibrillated Cellulose from Annual Plant-Sourced Fibers: Comparison between Enzymatic Hydrolysis and Mechanical Refining

“…In this work, we report the production and characterization of MNCF from jute, sisal and hemp after mechanical and enzymatic pretreatments. In a previous article of ours, nearly completely nanofibrillated cellulose was obtained from said raw materials, following oxidation of hydroxyl groups to carboxylates [32]. Despite the success of that process, we hereby suggest two approaches that, even though not for the same applications, are expected to be more feasible for production at an industrial scale.…”

Dynamic Light Scattering Plus Scanning Electron Microscopy: Usefulness and Limitations of a Simplified Estimation of Nanocellulose Dimensions

“…Charge density ( CD ) was estimated by potentiometric back titration [ 26 ]. Approximately 0.05 g of nanocellulose was suspended in 50 mL of PDADMAC 0.001 N. Then, the excess PDADMAC was titrated with PES-Na 0.001 N until the isoelectric point (0 mV) was reached.…”