VOLUME 55, ISSUE 5/2014

The rate of timber production by Germany’s forestry sector cannot be increased to any significant degree, yet the supply available on the market is subject to a growing demand with wood required for traditional material uses (sawn wood, fibre/paper, derived timber products) and for use in the provision of energy. In future, the demand for wood from various sectors of an evolving “bio-economy” will also increase. For these reasons, there has been much discussion of possible means to produce additional wood in short rotation coppice plantations outside the boundaries of existing forests in order to meet the growing market demand. While the area given over to tree plantations globally has increased considerably over the last thirty years, and in Germany there have been numerous research initiatives focusing on short rotation coppice plantations for the production of “woodfuel”, to date the timber industry nationally has demonstrated no interest in the production of timber assortments from such plantations for a material use. The wider application of the current experiences gleaned from the establishment and use of short rotation coppice in Germany could, however, create opportunities for the production of wood assortments for the wood-based industries. One of the most important areas to be addressed in this respect is the issue of innovative business models involving long term contracts between the potential market partners. Future innovations in the sector cannot be only of a technical nature but will also have to be economic, for example in the form of novel business models, if the security of the supply of wood is to be guaranteed. Short rotation coppice plantations cultivated on agricultural land are not a long term substitute for the production of wood in the forests but represent an economically and ecologically worthwhile means of supplementing the wood supply to the market.

Decisive for the occurrence of ring shake from a technical point of view, are tensions in Sweet chestnut wood (Castanea sativa Mill.) caused by fluctuations in growth. As part of a comparative study on cell wall level, several hypotheses have been analysed with different methods.

The investigations included the key aspects (i) of the qualification and testing of suitable, commercially available cellulose derivatives (such as hydroxyethyl cellulose (HEC), methylcellulose (MC)) as an adhesive for wood-based materials, (ii) the testing of crosslinking possibilities of cellulose derivatives by addition of reactive additives (e. g. glyoxal), (iii) the assessment of the suitability of CD for the use in the wood-based materials industry by processing selected cellulose derivatives (CD) with laboratory and industry-like methods, and (iv) the development of wood-based materials with CD as an alternative adhesive, based on renewable resources, taking into account normative specifications. The ABES adhesive tests show that the cellulose derivative variant HEC-Gly has enormous adhesive potential. The tensile forces are in the range of industrially used UF resins. It is assumed that when the process is properly controlled particle-based wood materials can be bonded with cellulose derivatives and meet the requirements for physical properties of panels for indoor use.

In this paper, results of relevant pollutants (Cl, As, Cd, Cr, Cu, Pb) of waste wood assortments are presented. The samples were as-signed to the categories without wood preservatives A I (natural), A II (painted, coated) and A III (treated with halogenated organic compounds) according to the guidelines and examples of the Waste Wood Ordinance (AltholzV, 2002). The pollutant contents of 58 samples were determined by X-ray fluorescence and mass spectrometric analysis methods (XRF and ICP-MS). The surfaces of the samples and homogenised samples were analysed by XRF and compared with the results of digested sub-samples (ICP-MS). The results demonstrate that in the above mentioned categories for the recycling of waste wood 36 % of the samples show higher pollutant levels than allowed. Therefore the division of waste wood according to the Waste Wood Ordinance and optical criteria is inadequately to exclude a diffuse input of pollutants in wood materials. A similar statement is obtained when comparing the levels of pollutants with the more restrictive maximum allowable values for wood chips for non-industrial use (DIN 14961-4, 2011).

Wood bondings are an important basis for constructive timber building. To improve the use, the following points are important: Understanding of the transfer of forces in the glue joint, optimizing adhesives for the respective application (e. g. wood species, temperature and humidity load, creep) and inclusion of the properties of the material (wood, glue) at differing environmental conditions. Here the results of the work in the wood physics group at ETH Zurich obtained during the last 10 years, leading to multiple dissertations, are presented. Despite the multitude of experiments, a complex calculation of the properties and behaviour of the glued element during long time exposure to load under real life conditions (e. g. prediction of delamination) was improved but is still not fully understood.

Products made from natural fibre-reinforced plastics serve the worldwide rapidly growing market of so-called Wood Polymer Composites (WPC), the highest growth rates of which are currently reported for North America and China. The primary source for the natural fibres required for such composites is wood flour – a very versatile raw material which in recent times has faced an increasingly fierce competition from many sides. A competition which inevitably will result in rising prices and thus give a strong motivation for the search for alternatives. Such an alternative could possibly be found in various fibre-containing residues generated in large quantities by paper mills mainly or entirely based on recovered paper. There is currently no real or at least no economical use for such residues but rather burdensome and ultimately costly strategies to get rid of them. The most commonly applied options are disposal by an accredited disposal company or thermal utilization by which at least some of the residues’ inherent energy is regained. Both options are costly and therefore regarded a competitive distortion in particularly by small enterprises. Against this background a recently finished, publicly funded research project focused on whether, and if so to which extent said paper manufacturing residues could replace wood flour in natural fibre-reinforced plastic material as a more economic and abundantly available substitute. For this purpose coarse rejects, residues from pressurized screens as well as deinking sludges were collected in a number of paper mills and analysed as to their characteristics relevant for the intended use. Prior to the manufacture of first PPC samples the residues were dried and pelletised together with synthetic polymers and finally injection moulded to standard test specimens. The cooperation between the Institute of Wood and Paper Technology of Technische Universität Dresden and the Institute of Lightweight Structures and Polymer Technology of Technische Universität Chemnitz permitted to perform all necessary steps from the procurement of appropriate residues all the way down to the production of prototypes. The results of the project gave strong evidence that the paper manufacturing residues investigated can well be considered a very close substitute to wood flour as a component of fibre reinforced plastics. As they address the demand for an as holistic as possible utilisation of renewable resources in a very convincing way and as they as well exhibit a number of additional features these new materials should be named Paper Polymer Composites (PPC) in order to differentiate them from the standard WPC.