VOLUME 63, ISSUE 2/2022

The main objective of this study was to estimate the positive environmental effect of recycling of wood waste for manufacturing of particleboard instead of burning it just to recover the energy, including calculations of accumulated organic carbon “captured carbon” and decrease of emissions of greenhouse gases, describing this in the form of life cycle (LC). The study revealed that the amount of accumulated organic carbon in wood waste in Sweden is 0.7 million tons per year. If the particleboards were made from the wood waste that is today incinerated it could contribute to a decrease in carbon dioxide emission in Sweden with some 0.5 million tons, which is equivalent to almost 1 % of the total Swedish emissions of greenhouse gases. This would contribute to achieve the national goal on reduction of carbon dioxide emissions. In addition, the environmental impact of alternative utilization of wood waste was described in the form of life cycle (LC).

In the field of mobile and immobile interior design, substituting conventional materials with lightweight composites makes sense if material, production, transport or handling costs can be reduced. A preferred material is the sandwich panel, consisting of a paper honeycomb core with thin skin layers on both sides. As part of a research project at the Institute of Natural Materials Technology at the Technische Universität Dresden, the production of an adhesive-free, expandable honeycomb core (“Nested Honeycomb Core”) is being investigated. For this purpose, an associated manufacturing process was developed. The greatest challenge was to develop a technology for nesting individual paper strips into each other, starting from a paper web, in order to produce an expandable honeycomb core. In cooperation with partners from German industry, a technical solution for the manufacturing process was developed at the Technische Universität Dresden and technically implemented as a demonstrator.

The biological durability of wood and wood-based materials, on the one hand, is based on the ingredients of the wood or on artificially introduced active ingredients (preservatives). On the other hand, the moisture behaviour of wood affects its durability and is influenced by ingredients, the anatomical structure of the wood, cell wall modifications or the introduction of hydrophobic substances. The important role of moisture behaviour in durability has been known for a long time, but the corresponding European standard EN 350 (2016) has only explicitly referred to this parameter since 2016. This article presents results from comparative laboratory and field studies on the moisture behaviour of numerous untreated, modified and preservative-treated woods. Standardized and non-standardized test methods are compared and evaluated with regard to their ability to predict moisture behaviour under real conditions. Proposals for implementation in existing standards are developed and put up for discussion.

Originally developed for finishing textile fabrics, there are nowadays numerous studies that report on wood modification with crosslinking chemicals such as 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and its effect on wood properties tested in laboratory and field tests. As a biocide-free wood modification technology, treating wood with crosslinkers like DMDHEU significantly and permanently improves the dimensional stability, surface hardness and resistance to wood-destroying fungi, term-ites and marine organisms. This offers promising perspectives for making wood species with low natural durability usable in exterior applications, so that pine (Pinus sylvestris) modified with DMDHEU has already been approved for window constructions. Recent research activities focused on process optimization (hardwood species, reduction of embrittlement), identified ways for formaldehyde-free treatments and integrated additional effects (fire protection, dyeing, water repellency) into the technology. Modifying the wood cell wall and achieving a uniform distribution of fixated chemicals inside the wood product of choice occur essential for the listed property improvements, which limits the technology to permeable wood species, especially in the field of treating solid wood. For Scots pine and selected hardwood species, the “Technology Readiness Level” (TRL) of the technology based on the textile finishing agent DMDHEU is classified as “high”. However, industrial production has not yet been established. Considering the history of related modification techniques, successful implementation on an industrial scale requires both financial investments and as essential the formation of networks between the chemical indus-try, wood industry, technology providers and material research institutes. Recent research activities between the University of Göttingen, Archroma Management LLC and a variety of wood-processing companies (solid wood, veneer materials) have initiated corresponding networks and are currently focusing on a technological implementation on industrial scale.

The aim of the research work was to develop foamed WPC panels based on bio-polyethylene or polylactide. The density of the WPC foam profiles was to be reduced to the level of particleboard or fibreboard (500-800 kg/m³). At the same time, the bio-based WPC formulations were investigated regarding their suitability for compact extrusion. For this purpose, three different bio-PE and one PLA type were selected and mixed with different contents of different wood fibres. The selected WPC formulations were compounded and then investigated for their extrusion behaviour into compact profiles and their foaming behaviour. The extensive investigations showed that different contents of wood are required for compact and foam extrusion. For a foamed profile, the optimal wood content was lower than 40 wt% to achieve a high degree of foaming and a low density. For a compact profile, on the other hand, the optimal wood content was at least 60 wt% to ensure good extrusion behaviour.

The production process of cement-bonded particleboards (CBPB) ends with drying the boards to a uniform material moisture content between 6 % and 12 %. Afterwards the boards are ready for finishing (sanding, cutting). The hot-air drying system used for this purpose is fed by thermal energy, among others, from the combustion of particle fractions that are not usable for CBPB manufacture. The impact of the drying regime of 80 °C to 110 °C used in this process has not yet been investigated in detail. In the present study, the influence of different drying temperatures between 60 °C and 100 °C on the drying process and the material properties was determined. As expected, the relationship that the drying rate increases with increasing drying temperature applies. However, since convective drying is subject to physical limits, the relationship is not linear. With increasing temperature, the acceleration of the drying rate decreases. For the board properties, only a significant influence of the drying temperature on the internal bond (IB) could be observed. With increasing temperature, the IB decreases linearly. A correlation of the drying temperature with the porosity of the CBPB could not be proven.