Deposition behavior of lignin on solid surfaces assessed by stagnation point adsorption reflectometry

Abstract

The deposition behavior of lignin on a solid surface was studied using stagnation point adsorption reflectometry (SPAR) comprehensively. In this study, the light absorption coefficient of lignin (τ = 20 476 m⁻¹) at 633 nm wavelength was considered to define a new imaginary refractive index (k) used in the SPAR technique for adsorption analysis. The inclusion of k in the adsorption model yielded an adsorbed amount (Γ) of 1.11 mg m⁻², leading to the quality factor (Q_f) of 31.71 mg m⁻². At a lower concentration, the deposition of lignin on the surface was increased, and it generated a maximum sticking coefficient of β = 0.71 at 25 mg L⁻¹ on the surface. At the concentration range of 35 and 45 mg L⁻¹, lignin formed clusters and its deposition dropped. The use of Quartz crystal microbalance (QCM) and SPAR techniques also confirmed that the proportion of water in the deposited lignin adlayer was greater when a lower concentration (5–25 mg L⁻¹) of lignin solution was used for adsorption. The findings of this study revealed the potential use of the SPAR technique for evaluating the deposition performance of lignin-based materials on varied surfaces, which would facilitate the development of coating and composite applications for lignin.