Revealing the Structural Transformation of Biopolymer-Modified Clay Materials Through Microtomography and Hygroscopic Analysis

Abstract This study focuses on the structural assessment of unfired clay materials (UCM) treated with different biopolymers using microtomography (microCT) and hygroscopic analysis. It addresses a significant research gap, as the analysis of hygroscopic properties in biopolymer-modified clays remains limited in the literature, while microCT investigations of such materials have been scarcely explored. The clay materials were modified using aqueous gelled biopolymer solutions of starch, alginate, and chitosan, each prepared under processing conditions adapted to their chemical characteristics and solubility: starch was dissolved in hot water, alginate in cold water, and chitosan in a slight acid solution. Moisture adsorption of the clay-biopolymer materials (CBM) increased up to 32.2%, as observed in the CBM, modified with a 7.5% alginate-based solution. Sorption hysteresis analysis revealed an increase in the hysteresis rate from 0.30% to 0.76–1.01% in CBMs, indicating that biopolymer modification enhanced the structural complexity of the clay matrix and promoted additional molecular interactions with water molecules within the CBM. MicroCT results demonstrated that within the CBM, biopolymers can function either as surface-coating agents (starch and alginate) or as organic clusters within the clay structure (chitosan). The obtained results highlight that biopolymer incorporation significantly enhances the hygroscopic buffering capacity of clay materials, offering a pathway toward sustainable building composites that can be applied in humidity-regulating finishes, eco-friendly construction blocks, and heritage conservation, where both moisture control and structural cohesion are essential.