Abstract
The use of natural sustainable resources such as wood in green industrial processes is currently limited by our poor understanding of the impact of moisture on their thermodynamic and mechanical behaviors. Here, a molecular dynamics approach is used to investigate the physical response of a typical hydrophilic biopolymer in softwood hemicellulose—xylan—when subjected to moisture adsorption. A unique moisture-induced crossover is found in the thermodynamic and mechanical properties of this prototypical biopolymer with many quantities such as the heat of adsorption, heat capacity, thermal expansion and elastic moduli exhibiting a marked evolution change for a moisture content about 30 wt%. By investigating the microscopic structure of the confined water molecules and the polymer–water interfacial area, the molecular mechanism responsible for this crossover is shown to correspond to the formation of a double-layer adsorbed film along the amorphous polymeric chains. In addition to this moisture-induced crossover, many properties of the hydrated biopolymer are found to obey simple material models.
Highlights
Wood and its various hydrophilic cellulosic components are the most abundant polymers on Earth (Arioli et al 1998)
Many important features regarding the role of moisture adsorption in the physical and mechanical responses of hydrophilic polymers remain to be identified to facilitate their implementation in fields such as food engineering (Li et al 1998), biomedical device applications (Lyu and Untereker 2009) and architecture (Vailati et al 2018)
Through the investigation of various mechanical and thermodynamic properties of AGX, we show that all material properties undergo a clear transition in moisture sensitivity at the same transition point of * 30 wt% moisture content
Summary
Wood and its various hydrophilic cellulosic components are the most abundant polymers on Earth (Arioli et al 1998). While these compounds have been used through ages, a better understanding of the physical and chemical properties of such hydrophilic polymers. As an important parameter to be taken into consideration, moisture strongly influences the mechanical and thermodynamic properties of hydrophilic biopolymers. It usually induces drastic changes of material dimension, stability and durability that can present both positive and negative effects. Many important features regarding the role of moisture adsorption in the physical and mechanical responses of hydrophilic polymers remain to be identified to facilitate their implementation in fields such as food engineering (Li et al 1998), biomedical device applications (Lyu and Untereker 2009) and architecture (Vailati et al 2018)
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