Reproducibility of Colloidal Lignin Particle Preparation: An Interlaboratory Evaluation

Abstract

The reproducibility of the preparation of colloidal lignin particles (CLPs) was evaluated through a coordinated interlaboratory study involving seven independent research groups from around the world. The objective was to assess the robustness of the anti-solvent precipitation method and identify parameters requiring further standardization, while also setting a unified terminology. Laboratories prepared CLPs following a common procedure and characterized key physicochemical properties, including the pH and concentration of both lignin solution and CLP dispersion, as well as the mass yield of the dispersion. The particle hydrodynamic diameter (reported based on number, intensity, and volume) and PDI were compared to the diameter and particle-diameter dispersity (Ð_d) obtained from SEM image analysis. Additionally, four shape descriptors derived from the same analysis were used for the morphological characterization of the CLPs. This study represents the first systematic interlaboratory quantification of CLP preparation reproducibility and provides a direct comparison of characterization approaches, including dynamic light scattering (DLS) and SEM-based analysis. Statistical evaluation of the data included z-score assessment, outlier testing, and estimation of repeatability and reproducibility using mixed-effects modeling. The results demonstrate that the overall preparation route is largely reproducible across laboratories. Increased variability was observed for dispersity-related parameters and morphology metrics, primarily reflecting methodological differences in data evaluation and reporting. These findings identify critical sources of variability and establish practical guidelines for standardizing CLP preparation and characterization across laboratories, supporting reliable comparison and continued development of lignin-based colloidal materials.