Cement as an Inorganic Binder for the Production of Formaldehyde-Free Bonded Plywood

For the bonding of veneers into plywood, formaldehyde-containing amino resins are mainly used. The advantages of these adhesives are good properties (e.g. fast curing), high availability, acceptable price and a mature technology. The formaldehyde emission (FE) is the major disadvantage of these adhesives. The limit of FE for wood-based panels has been reduced more and more in recent years. With the decision of the European Union from 1 January 2016, formaldehyde was obligatorily classified as carcinogenic and mutagenic. The result of this decision is a further reduction of FE limits for manufacturing and use of woodbased panels. Without expensive adhesive systems or coatings, plywood and its production will not comply with these limits in the future. Prospectively, the use of formaldehyde-containing adhesives will become uneconomical. For this reason, studies for bonding wood veneers with formaldehyde-free Portland cement were carried out. Ordinary Portland cement (OPC) is widely available, inexpensive and is in use in various industries including the wood-based panel industry (e.g. Cement-bonded particle board = CBPB). A new product called “cementbonded plywood (CBPly)” combines the advantages of organically-bonded plywood (e.g. great strength, low density) and CBPB (e.g. low FE, high fire resistance). In contrast to well-known cement-bonded composites based on wood particles (CBWC) like CBPB, cement-bonded wood-wool boards or wood-fibre-reinforced cement boards, the amount of wood is much higher in CBPly, since the cement is only located between the layers of wood (more specific information). The veneers ensure a high tensile strength of the material. This provides better bending properties compared to other particle-based CBCs. In addition to the increased strength, the handling and machinability is improved due to the lower density and lower cement content. Results from cone calorimeter tests indicate that if cement is also applied to the top veneers, the CBPly can be classified as Euroclass B (EN 13501-1). Due to the advantageous properties of CBPly, markets can be developed that are difficult or inaccessible for organically-bonded plywood and CBPB. Especially the use in applications with high demands on fire resistance and low emissions are regarded

Determination of the swelling velocity of different wood species and tissues depending on the cutting direction on microtome section level

Swelling velocity in dependence on the anatomical cutting direction of yew [Taxus baccata L.] and boxwood [Buxus sempervirens L.] was determined at temperature of 20 °C and at relative humidity of 10% and 100%. The investigations, conducted on a microtome section level, showed a similar behaviour for specimens of both wood species. It was possible to determine that the swelling velocity for yew and boxwood increases in its anatomical cutting directions. The longitudinal direction showed the lowest value, the tangential direction, by distinction, the highest value. Furthermore, a significant influence of early wood and late wood content on the swelling velocity for yew was detected. Keywords: Yew, Boxwood, Microtome, Swelling velocity, Wood tissue, Cutting direction

INFLUENCE OF SURFACE ROUGHNESS OF WOOD FIBRES ON PROPERTIES OF MEDIUM DENSITY FIBREBOARDS PRO LIGNO

Abstract: The properties of medium density fibreboards (MDF) INTRODUCTION The glueability of wood is mainly described by the adhesion behaviour between adhesive and wood surface which is the sum of chemical and physical inter-and intra-molecular powers as well as mechanical interactions The relation between surface roughness and bond quality for bonding of veneer and solid wood is supposed to be at least partially valid for the bonding of wood fibres when producing medium density fibreboards (MDF). Especially for MDF, other properties, such as deep milling quality, are named to be influenced by the surface roughness of the fibres, as well. MDF panels made of beech wood fibres had a better deep milling performance than MDF made of softwood fibres Besides wood species, investigations regarding the influence of the pulping temperature on the resulting fibre surface roughness have been conducted by the use of atomic force microscopy (AFM). With increasing pulping temperature the maximum values of roughness of the sub-micro structure (measuring distance of 6µm) of the fibre surface increased from around 50 to 250nm. The roughness was stated to be the sum of cellulosic fibrillar network, microscopic disruptions (mainly caused by low-temp refining) and reposition of lignin and hemicellulose (mainly caused by high-temp refining). The increasing roughness is discussed to be the result of an increasing plasticization and granular rearrangement of lignin on the fibre surface with increasing temperature In addition to the sub-micro structure the change of the micro structure, including e.g. defects and pits, in longitudinal and perpendicular direction to the fibre axis as well as the distribution of roughness over particle size (e.g. single fibre, fibre bundle, shives) are of great interest for the evaluation of the over all fibre surface roughness. The investigated fibre properties are mainly not comparable, especially regarding the qualitative study. Further investigations with AFM are limited regarding the amount of work needed for sample preparation as well as the duration of measurements with longer measuring distances of e.g. 20 -500µm. In this work a method for a suitable and quick fibre sample preparation is displayed and the possible evaluation of surface roughness on those samples with the use of a confocal laser scanning microscope (CLSM) is presented using the example of Scots pine [Pinus sylvestris L.] and beech [Fagus Sylvatica] wood fibres pulped at different temperatures. Furthermore the influence of the determined surface roughness of the different fibre pulps on the thereof produced MDF are displayed and discussed