Abstract
This contribution presents the development of a dry-cast method for the one-step preparation of bio-based films from wood polymers that mimic the bilayered structure of tree bark, the natural protective layer of the tree. In a simplified view, natural bark can be considered as the superposition of an external homogeneous and non-porous layer (outer bark) and a porous substructure layer (inner bark). This work is a first step for the future development of bio-based biomimetic wood coatings. The film had a bark-like appearance and its total density, bulk density and porosity were similar to values measured in natural bark. Furthermore, the structural characteristics of the studied film, namely specific surface area (BET) and pore size distribution, as well as the performance of the water adsorption ability were investigated and discussed.
Highlights
In living trees, wood is protected by bark, a non-technical term to describe a complex multilayered tissue, formed by dead and living portions (Crang et al 2018)
Based on the method described by Musa et al (2018) for the dry-cast preparation of macroporous films from cellulose acetate (CA) and acetylated lignin (LA), the objective of this work was to prepare bilayered films (BF) from CA and kraft lignin (KL) that mimic the structure of tree bark, which—in a simplified view—can be regarded as the superposition of outer bark as a solid non-porous film and inner bark as a porous sublayer
The structures of the prepared coatings were analyzed by laser scanning microscopy (LSM) (OLS 4100, Olympus) and scanning electron microscopy (SEM) (JSM 7401F, Jeol)
Summary
Wood is protected by bark, a non-technical term to describe a complex multilayered tissue, formed by dead and living portions (Crang et al 2018). In dry-cast operations, polymer/solvent/non-solvent systems are only subject to liquid-liquid demixing in a defined set of compositions, building a so-called mixing gap and leading to porous structures. For compositions outside of the mixing gap, the solutions remain homogeneous leading to homogeneous and non-porous structures. The contour of this gap is defined by a binodal curve, which describes phase equilibria in the considered polymer/solvent/non-solvent system (Metze et al 2017). The main idea of the presented process relies on formulating a polymer system that allows for the composition of the upper part of the cast film to remain outside of the mixing gap during drying while the lower part of the film is forced to undergo liquid-liquid demixing. The product is an asymmetric bilayered film, with an external skin (outer bark) supported by a porous substrate (inner bark)
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