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Lampertswalde, Germany

Gavrilovic-Grmusa I.,University of Belgrade | Dunky M.,Kronospan GmbH Lampertswalde | Miljkovic J.,University of Belgrade | Djiporovic-Momcilovic M.,University of Belgrade
Journal of Adhesion Science and Technology | Year: 2010

Penetration of adhesives plays an important role in wood adhesion, since wood is a porous material. Objectives of this work were (i) the evaluation of the influence of the degree of condensation of urea-formaldehyde (UF) resins on their penetration into beech, showing the distribution of the adhesive in the cell layers close to the bondline using microscopic detection, and (ii) the comparison of data for beech with results for fir obtained earlier. The degree of penetration mostly depends on the permeability and porosity of the wood surface as well as on the resin type and the size of the resin molecules. The process parameters, which also can affect penetration, were kept constant throughout all tests performed. The results show a significant correlation between the penetration behavior and the degree of condensation (molecular size, viscosity) of the resins and adhesive mixes based on these resins. The higher the degree of condensation, the lower the possibility for penetration, expressed as "Average penetration depth" (AP). AP into beech is higher than into fir. The portion of filled tracheids and vessels on the whole cross section of the interphase ("Filled interphase region" FIR) increases slightly with the degree of condensation, but this increase is not statistically significant. FIR in fir is higher than in beech. © Koninklijke Brill NV, Leiden, 2010. Source


Gavrilovic-Grmusa I.,University of Belgrade | Dunky M.,Kronospan GmbH Lampertswalde | Miljkovic J.,University of Belgrade | Djiporovic-Momcilovic M.,University of Belgrade
Holzforschung | Year: 2012

This paper is the final part of a series reporting on the penetration (P) and bonding behaviour of urea-formaldehyde (UF) resins of different viscosities based on different degrees of condensation (DCs). The various resins were applied onto radial and tangential wood surfaces, and solid wood assemblies were prepared by hot pressing. P t and P r were observed by evaluation of photomicrographs of the bond lines. The mean and maximum depth of penetration was inversely proportional to the DC. The average depth of P t was found to be slightly higher than P r because of the abundance of pits on the radial walls. However, the maximum P was higher in radial direction, due to the elliptic shape of vessels in poplar as well as due to rays improving the resin flow. The lap shear strength (σm) of the same bonded assemblies was determined. Despite the fact that the wood failure always was very high, the σm increased with the better penetration of the resins with low viscosity. The higher strength values measured has been interpreted as a fortification effect of the interphase by bulk resin penetration, as cell wall penetration cannot be expected due to the large size of such resin molecules. Copyright © by Walter de Gruyter. Source


Standfest G.,Salzburg University of Applied Sciences | Kranzer S.,Salzburg University of Applied Sciences | Petutschnigg A.,Salzburg University of Applied Sciences | Dunky M.,Kronospan GmbH Lampertswalde
Journal of Adhesion Science and Technology | Year: 2010

The microstructure of a medium density fiberboard (MDF) has attracted much interest, because it determines most of the properties during production as well as during use of this type of board. In this paper the sub-micrometer computer tomography (sub-μm-CT) with very high resolution was used in order to investigate an industrially produced MDF. The data obtained were analyzed using mathematical morphology and image analysis in order to obtain information on the distribution of voids and the fiber material. Resulting distributions were found to follow Λ-law which was confirmed using the maximum likelihood estimation. Eventually, good correlations between void distribution and local density as well as between the proportion of cell wall material and local density were found in this investigation. © 2010 Koninklijke Brill NV, Leiden. Source


Gavrilovic-Grmusa I.,University of Belgrade | Dunky M.,Kronospan GmbH Lampertswalde | Djiporovic-Momcilovic M.,University of Belgrade | Popovic M.,University of Belgrade | Popovic J.,University of Belgrade
BioResources | Year: 2016

This work deals with the influence of specific pressure during the press process on the radial and tangential penetration of urea-formaldehyde (UF) adhesive into poplar, as well as on the shear strength of lap joints prepared at these different pressures. An epi-fluorescence microscope was used for measuring the adhesive penetration when investigating microtome slides (20-μm thick) cut from the joint samples. The average penetration depth (dap) and the size of the interphase region (I) increased with the increase of pressure from 0.5 to 1.0 N/mm2. Further increase in the pressure to 1.5 N/mm2 did not produce a significant change in dap or I. On the contrary, the area of filled lumens and rays (A) showed a steady decrease as the specific pressure increased. Such behavior influenced the filled interphase region (If), which also decreased with increased pressure. Tangential samples (radial penetration) obtained higher values of lap shear strength and showed less dependence on the specific pressure than the radial samples (tangential penetration). Higher shear strength based on radial penetration corresponded to the thicker interphase region of these samples. The highest shear strength for both directions of penetration was obtained for the specific pressure of 1.0 N/mm2. Source


Gavrilovic-Grmusa I.,University of Belgrade | Dunky M.,Kronospan GmbH Lampertswalde | Miljkovic J.,University of Belgrade | Djiporovic-Momcilovic M.,University of Belgrade
European Journal of Wood and Wood Products | Year: 2012

The objective of this work was to evaluate the influence of the degree of condensation of urea formaldehyde (UF) resins on the tangential penetration into fir and beech and on the tensile shear bond strength of wood joints. Tangential penetration was determined by epi-fluorescence microscopy on microtome slides, exposing the bond line on a cross-sectional surface. The higher the degree of condensation (viscosity) of the resins, the lower is the possibility for penetration; beech showed higher penetration than fir. Bond strengths decreased with increased degree of condensation (viscosity) of the adhesives. Shear strength based on radial penetration was higher than for tangential penetration. The higher the penetration and the thicker, hence, the interphase, the higher was the achieved shear strength. © Springer-Verlag 2012. Source

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