Wood modification is now widely recognized as offering enhanced properties of wood and overcoming issues such as dimensional instability and biodegradability which affect natural wood. Typical wood modification systems use chemical modification, impregnation modification or thermal modification, and these vary in the properties achieved. As control and understanding of the wood modification systems has progressed, further opportunities have arisen to add extra functionalities to the modified wood. These include UV stabilisation, fire retardancy, or enhanced suitability for paints and coatings. Thus, wood may become a multi-functional material through a series of modifications, treatments or reactions, to create a high-performance material with previously impossible properties. In this paper we review systems that combine the well-established wood modification procedures with secondary techniques or modifications to deliver emerging technologies with multi-functionality. The new applications targeted using this additional functionality are diverse and range from increased electrical conductivity, creation of sensors or responsive materials, improvement of wellbeing in the built environment, and enhanced fire and flame protection. We identified two parallel and connected themes: (1) the functionalisation of modified timber and (2) the modification of timber to provide (multi)-functionality. A wide range of nanotechnology concepts have been harnessed by this new generation of wood modifications and wood treatments. As this field is rapidly expanding, we also include within the review trends from current research in order to gauge the state of the art, and likely direction of travel of the industry.

The present research aimed to assess the moisture properties and viscoelastic behaviour of artificially degraded pine wood, intended to serve as a model material for ongoing studies on new conservation treatments for waterlogged archaeological wood. Sorption isotherms and hydroxyl accessibility were measured using a Dynamic Vapour Sorption (DVS) system, while the investigation of the selected wood rheological properties was performed using Dynamic Mechanical Analysis (DMA). Fungal decomposition of pine by Coniophora puteana decreased the maximum equilibrium moisture content (EMC) from 20.3% to 17.7% in the first and from 19.9% to 17.1% in the second DVS run compared to undegraded pine, while chemical degradation using 50% NaOH solution increased the wood EMC to 24.6% in the first and 24.2% in the second run. The number of free hydroxyls measured for the biologically degraded sample was similar to sound wood, while chemical degradation reduced their number from 11.3 mmol g⁻¹ to 7.9 mmol g⁻¹. The alterations in the wood chemical composition due to different degradation processes translated into changes in viscoelastic behaviour. For biologically degraded wood, a reduction in the loss modulus and storage modulus at the temperature of 25 °C was observed compared to undegraded pine. Surprisingly, for chemically degraded pine, the values were more similar to sound wood due to the considerable densification of the material resulting from shrinkage during drying. The loss factor values for both degraded wood types were higher than for undegraded ones, indicating an increase in damping properties compared to sound pine. Distinct changes were visible in the storage modulus and loss factor graphs for DMA of chemically and biologically degraded pine. The degradation processes used in the study produced wood types with different moisture and viscoelastic properties. However, both seem useful as model materials in the research on the new conservation agents for waterlogged archaeological wood.

Waterlogged wood treatment with methyltrimethoxysilane (MTMS) proved effective in stabilising wood dimensions upon drying (anti-shrink efficiency of 76–93%). Before the method can be proposed as a reliable conservation treatment, further research is required that includes the evaluation of the mechanical properties of treated wood. The aim of the study was to characterise the effect of the treatment on the viscoelastic behaviour of archaeological waterlogged elm and oak wood differing in the degree of degradation. Dynamic mechanical analysis in the temperature range from −150 to +150 °C was used for the study. To better understand the viscoelastic behaviour of the treated wood, pore structure and moisture properties were also investigated using Scanning Electron Microscopy, nitrogen sorption, and Dynamic Vapour Sorption. The results clearly show that methyltrimethoxysilane not only prevents collapse and distortions of the degraded cell walls and decreases wood hygroscopicity (by more than half for highly degraded wood), but also reinforces the mechanical strength by increasing stiffness and resistance to deformation for heavily degraded wood (with an increase in storage modulus). However, the MTMS also has a plasticising effect on treated wood, as observed in the increased value of loss modulus and introduction of a new tan δ peak). On the one hand, methyltrimethoxysilane reduces wood hygroscopicity that reflects in lower wood moisture content, thus limiting the plasticising effect of water on wood polymers, but on the other hand, as a polymer itself, it contributes to the viscous behaviour of the treated wood. Interestingly, the effect of silane differs with both the wood species and the degree of wood degradation.

This paper describes dynamic mechanical analysis (DMA) experiments on archaeological and contemporary elm tested under air-dry conditions, to explore the suitability of this technique for increasing understanding of the viscoelastic behaviour of archaeological wood. A strong reduction of storage modulus of archaeological elm (AE) was seen in comparison with contemporary wood (CE), resulting from the high degree of wood degradation, notably the reduction in hemicelluloses and cellulose content of AE, as demonstrated by Attenuated Total Reflection–Fourier Transform Infra-Red spectroscopy (ATR-FTIR). The γ relaxation peak was observed in all samples. The γ peak in AE shifted to a higher temperature, and the activation energy for γ-peak motions was lower in AE (29 kJ/mol) than in CE (50 kJ/mol) indicating that motion is less restricted within the degraded AE cell wall, or possibly a difference in the monomer undergoing rotation. Detection of changes in storage modulus are well known, but the DMA temperature scan technique proved to be useful for probing the degree of wood degradation, relating to the changes in location and intensity of secondary relaxation peaks. The γ peak in loss factor can be used to confirm that cell wall degradation is at an advanced stage, and to improve understanding of the internal spatial structure of the degraded wood cell wall.

There is great interest in using bio-based materials to reduce the climate impact of materials. Similarly, there is an increased focus on the circular economy and recycling of materials to increase material efficiency and reduce waste. In the case of wood waste, this provides a cluster of benefits but has led to a high demand for the reclaimed material. This review provides updates on several technologies where wood fibre recycling and products from recycled wood fibre are breaking into new markets, including wood fibre insulation products, wood plastic composites, oriented strand boards, and fibreboards. Emerging technologies, such as the ability to recycle medium-density fibreboards, in addition to the more commonly recycled solid wood or particleboard, will allow for a new set of options within the wood cascading chain. Looking ahead, there are likely to be advances in new composite products, as well as other feedstock materials derived from reclaimed wood, such as nanocellulose, pyrolysis oils, or wood polymers reclaimed from the wood feedstock. This review arose from an investigation into the wood recycling sector in the UK. So, the horizon scanning exercise presented here considers the needs and challenges that may arise, if the volume of recycled wood fibre can be increased, in an already highly active market. Such developments would permit an increase in the manufacture of new-generation long-service-life products to enhance carbon storage, and potentially a shift away from bioenergy generation.