Microstructure of Bio-Based Building Materials: New Insights into the Hysteresis Phenomenon and Its Consequences

Abstract

Considering the current energy environment, both efficient and environmentally friendly solutions have to be developed for building construction. Bio-based building materials offer new perspectives through their insulating and natural humidity regulation capacities. Nevertheless, these materials are as complex as they are promising, and grey areas still remain regarding their behavior. Their water sorption and desorption curves recorded in experimental work demonstrate a hysteresis phenomenon and, although plausible hypotheses have been formulated in the literature, there is currently no consensus on its causes. Furthermore, it is important to emphasize that no reference considers the hydrophilic nature of the resource. Yet, this is a specificity of raw material coming from the plant world. In this context, this paper explores the microstructure and chemical composition of plant aggregates to propose a new explanation for the hysteresis. It is based on recent work demonstrating the existence of differentiated hydrogen bonds between the water sorption and desorption phase in cellulose. Obviously, hysteresis also has an origin at the molecular scale. Lastly, the hypothesis put forward here is supported by the swelling of bio-based materials that has been observed at high relative humidity, and this study aims to identify a link between the mechanics of bio-based materials and their hygroscopic behavior. A swelling/shrinking is macroscopically observed. Combining the fields of chemistry, physics, and civil engineering allowed us to demonstrate that it comes from a molecular-scale hydromechanical coupling. This is a major breakthrough in the understanding of bio-based composites.

Research of structure and durability of natural polymer modified clays

“…2.7). Sorption hysteresis can provide some insights into the internal structure of the materials with complex porous networks (Latapie et al, 2023). In the current research, the maximum sorption hysteresis rate was taken at relative humidity (RH) equal to 80% due to the complexity of adequately determining the desorption degree at 90%.…”

“…The specified biopolymers modify the surface of the investigated clay, smoothing its surface and partially filling its structural defects (cracks, pores, and grooves), which were observed on the surface of the control clay (Fig.3.18a). Apart from modifying the pores with biopolymers and the ink-bottle effect(Arrigoni et al, 2017;Pinson et al, 2018), additional hydrogen bonds can attract water molecules, thus enhancing the hygroscopicity of the observed clay composites(Rosa Latapie et al, 2023). Application of all the biopolymers (starch, alginate, and chitosan) of different preparation technologies (biopolymer gelation and starch retrogradation processes) increased the moisture adsorption of the clay composites by 13.3% to 34.2%.…”