Abstract
This paper aims at providing a methodological framework for investigating wood polymers using atomistic modeling, namely, molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. Atomistic simulations are used to mimic water adsorption and desorption in amorphous polymers, make observations on swelling, mechanical softening, and on hysteresis. This hygromechanical behavior, as observed in particular from the breaking and reforming of hydrogen bonds, is related to the behavior of more complex polymeric composites. Wood is a hierarchical material, where the origin of wood-moisture relationships lies at the nanoporous material scale. As water molecules are adsorbed into the hydrophilic matrix in the cell walls, the induced fluid–solid interaction forces result in swelling of these cell walls. The interaction of the composite polymeric material, that is the layer S2 of the wood cell wall, with water is known to rearrange its internal material structure, which makes it moisture sensitive, influencing its physical properties. In-depth studies of the coupled effects of water sorption on hygric and mechanical properties of different polymeric components can be performed with atomistic modeling. The paper covers the main components of knowledge and good practice for such simulations.
Highlights
Introduction and ContextWood is a hierarchical material, where the configurations at different scales play different roles in adsorption/desorption and in the resulting swelling/shrinkage and mechanical softening
From cellular and sub-cellular investigations, it has become clear that a full understanding of the wood polymer–water interactions requires investigating at the scales of the cell wall composite material, which are the focus of this paper and is described
We focus mainly on the force fields used for modelling cellulose, since most work has been done with respect to this wood component
Summary
Wood is a hierarchical material, where the configurations at different scales (i.e., lumber, growth ring, cellular and cell wall material) play different roles in adsorption/desorption and in the resulting swelling/shrinkage and mechanical softening. Wood polymers have different distribution and configuration in the cell wall primary (P), secondary (S1, S2 and S3) layers, and in the middle lamella (Figure 1). Wood structural hierarchical levels can be considered as lumber, growth ring, cell, and layered cell wall material. From cellular and sub-cellular investigations, it has become clear that a full understanding of the wood polymer–water interactions requires investigating at the scales of the cell wall composite material, which are the focus of this paper and is described next. Of the of wood cell walls primary layer, S: secondary secondary layer, ML: middle lamella (based on Reference [7]), MF: microfibril, A:. 3×3 hydrophilic depending on the of theof crystal, with crystal dimensions roughlyroughly
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