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Wood, a natural and abundant source of organic polymers, has been used as a scaffold to develop novel wood-polymer hybrid materials. Through a two-step surface-initiated Atom Transfer Radical Polymerization (ATRP), the porous wood structure can be effectively modified with polymer chains of various nature. In the present study, polystyrene and poly(N-isopropylacrylamide) were used. As shown with various characterization techniques including confocal Raman microscopy, FTIR, and SEM/EDX, the native wood ultrastructure and features are retained and the polymer chains can be introduced deep within the wood, i.e. inside the wood cell walls. The physical properties of the new materials have been studied, and results indicate that the insertion of polymer chains inside the wood cell wall alters the intrinsic properties of wood to yield a hybrid composite material with new functionalities. This approach to the functionalization of wood could lead to the fabrication of a new class of interesting functional materials and promote innovative utilizations of the renewable resource wood.

The hierarchical structure of wood is composed of a cellulose skeleton of high structural order at various length scales. At the nanoscale and microscale the specific structural features of the cells and cell walls result in a lightweight structure with an anisotropic material profile of excellent mechanical performance. By being able to specifically functionalize wood at the level of cell and cell walls one can insert new properties and inevitably upscale them along the intrinsic hierarchical structure, to a level of large-scale engineering materials applications. For this purpose, however, precise control of the spatial distribution of the modifying substances in the complex wood structure is needed. Here we demonstrate a method to insert methacryl groups into wood cell walls using two different chemistry routes. By using these methacryl groups as the anchor points for grafting, various polymers can be inserted into the wood structure. Strikingly, depending on the methacryl precursor, the spatial distribution of the polymer differs strongly. As a proof of concept we grafted polystyrene as a model compound in the second modification step. In the case of methacryloyl chloride the polymer was located mainly at the interface between the cell lumina and the cell wall covering the inner surface of the cells and being traceable up to 2-3 μm in the cell wall, whereas in the case of methacrylic anhydride the polymer was located inside the whole cell wall. Scanning electron microscopy, Fourier transform infrared spectroscopy and especially Raman spectroscopy were used for an in-depth analysis of the modified wood at the cell wall level., (Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Anisotropic and hierarchical structures are bound in nature and highly desired in engineered materials, due to their outstanding functions and performance. Mimicking such natural features with synthetic materials and methods has been a highly active area of research in the last decades. Unlike these methods, we use the native biomaterial wood, with its intrinsic anisotropy and hierarchy as a directional scaffold for the incorporation of magnetic nanoparticles inside the wood material. Nanocrystalline iron oxide particles were synthesized in situ via coprecipitation of ferric and ferrous ions within the interconnected pore network of bulk wood. Imaging with low-vacuum and cryogenic electron microscopy as well as spectral Raman mapping revealed layered nanosize particles firmly attached to the inner surface of the wood cell walls. The mineralogy of iron oxide was identified by XRD powder diffraction and Raman spectroscopy as a mixture of the spinel phases magnetite and maghemite. The intrinsic structural architecture of native wood entails a three-dimensional assembly of the colloidal iron oxide which results in direction-dependent magnetic features of the wood-mineral hybrid material. This superinduced magnetic anisotropy, as quantified by direction-dependent magnetic hysteresis loops and low-field susceptibility tensors, allows for directional lift, drag, alignment, (re)orientation, and actuation, and opens up novel applications of the natural resource wood.

A "grafting-from" polymerization approach within and at the complex and heterogeneous macromolecular assembly of wood cell walls is shown. The approach allows for the implementation of novel functionalities in renewable and functional wood-based materials. The native wood structure is retained and used as a hierarchical multiscale framework for a modular two-step polymerization process. The versatility and potential of the approach is shown by a polymerization of either hydrophobic or hydrophilic and pH-responsive monomers in the wood structure. Characterization of the modified wood reveals the presence of polymer in the cell wall, and the new properties of these wood materials are discussed., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)