Evaluation of O/W microemulsions to penetrate the capillary structure of woody biomass: interplay between composition and formulation in green processing

Abstract

The ability of microemulsions to overcome the complex capillary structure of wood is revealed in relation to its composition and formulation. The oil phase (limonene in this study) of O/W microemulsions is found to be critical for effective flooding. The type of amphiphile molecule used, including sodium lignosulfonate and alkyl polyglucosides as well as reference sodium dodecylsulfate and silicone-based surfactants, together with the viscosity of the resulting microemulsions were the main factors determining the dynamics and extent of fluid penetration. The associated observations were ascribed to the balance of the affinities of the surfactants for the substrate and its conductive elements. Owing to the inherent morphological and chemical features, large differences were observed as far as impregnation susceptibility of different wood types is concerned. By using appropriate surfactant mixtures it was possible for the microemulsions to penetrate the most recalcitrant woody biomass studied, with efficiencies up to 83% higher than that of water, at atmospheric pressure and room temperature. Application of microemulsions is a new alternative for green and efficient pre-treatment of woody biomass in biorefineries, to deliver (bio) chemical functions to the constrained spaces of the cell wall and to increase its accessibility.

Capillary and Non‐Capillary Absorption of Wood Evaluated by FT–Raman Spectroscopy and Capillary Rise Method

“…In spite of the liquid absorption of wood has been broadly studied, [ 5–27,35–37 ] the observed truth is the less in the use of polar and non‐polar solvents as probes to describe the absorption process related polar Lewis acid–base, AB, and non‐polar Lifshitz–van der Waals, LW, interactions and yet unknown the absorption difference between the capillary and non‐capillary of wood.…”

“…[ 1–4 ] These assumptions are probably due to wood consisting of both the hydrophilic and hydrophobic functional groups corresponding to different AB properties. [ 27 ]…”

“…In terms of reported cases, [ 5–27 ] the wood absorption process followed two mechanisms. The one is the liquid penetration referring to the liquid flowing into the air‐filled voids of the wood chip under a pressure gradient, and the another is the concentration gradient dominated diffusion process when the ions or other soluble matter diffused into the wood.…”

“…Since wood is a natural porous material with native capillary and non‐capillary structure, this can lead the wettability difference in these two sections. [ 27 ] To study and quantitatively compare the absorption in the capillary and non‐capillary sections are thus of interest and necessary. However, such results seem to be less reported because all reported cases focused on the bulk wood absorption.…”

“…However, such results seem to be less reported because all reported cases focused on the bulk wood absorption. [ 5–27 ]…”