Influence of wood properties and bonding parameters on bond durability of European Beech (Fagus sylvatica L.) glulams

Ohnesorge, Denny; Richter, Klaus; Becker, Günther

doi:10.1051/forest/2010002

Cited by 48 publications

(27 citation statements)

References 8 publications

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“…However, PUR is associated with comparably poor performance on some alternative wood species and some hardwoods, especially when tested for humid or very dry environments. In order to overcome these issues, adhesion deficits were addressed with the combination of different adhesion-promoting agents (primer) as reported in various studies (Ohnesorge et al 2010;Amen-Chen and Gabriel 2015;Kläusler et al 2014a, b). Richter (1999) described the general characteristics of primers by a polar part that enables strong intermolecular interactions, a hydrophobic spacer grid and a part that enhances the wetting with the adhesive.…”

Section: Introductionmentioning

confidence: 99%

Characterization of wood-adhesive bonds in wet conditions by means of nanoindentation and tensile shear strength

Bockel

Harling²,

Grönquist

et al. 2020

Eur. J. Wood Prod.

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The performance of adhesive-hardwood bonds can often be sensitive to humidity and temperature variation. Therefore, it is frequently challenging to achieve standard requirements for structural applications. To gain a better understanding of the wood-adhesive bond, the properties of the individual constituents as well as the local interface of European beech (Fagus sylvatica L.) wood cell walls in contact with structural adhesives were analyzed by means of nanoindentation. These results are compared to classical lap-shear strength. As adhesives two different one-component polyurethane adhesives (1C PUR) and a phenol resorcinol formaldehyde adhesive (PRF) were used. In one case, the beech wood was additionally pre-treated with an adhesion-promoting agent (primer) prior to bonding with 1C PUR. Beech wood joints were analyzed subsequent to several treatments, namely standard climate, after wet storage and in re-dried conditions. In addition, the influence of the primer on the hydroxyl accessibility of beech wood was investigated with dynamic vapor sorption (DVS). The lap-shear strength revealed good performance in dry and re-dried conditions for all adhesives on beech. Both polyurethane adhesives obtained deficits when tested in wet conditions. The use of a primer significantly improved the PUR performance in wet condition. DVS experiment demonstrated a decrease in hydroxyl group accessibility when using a high primer concentration. As novelty, nanoindentation was used for the first time to characterize the local wood-adhesive-interface properties in wet conditions. Nanoindentation showed that all tested 1C PUR perform quite similar in room climate, while PRF achieves considerable higher values for reduced E-modulus and hardness. Wet storage led to a considerable reduction in mechanical properties for all adhesives, while the highest relative change was observed for PRF. After re-drying, the adhesives regained a large part of their original mechanical properties in room climate. No distinct effect of the primer on the local micromechanical properties could be detected with nanoindentation in terms of specific work of indentation.

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Section: Introductionmentioning

confidence: 99%

Characterization of wood-adhesive bonds in wet conditions by means of nanoindentation and tensile shear strength

Bockel

Harling²,

Grönquist

et al. 2020

Eur. J. Wood Prod.

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“…In the 1990s, Vick and Okkonen (1998) developed a hydroxymethylated resorcinol (HMR) coupling agent. This primer significantly improves the WFP of 1C PUR and MUF glued joints at the wet stage (Vick and Okkonen 2000) and also helps to reduce delamination (Lopez-Suevos and Richter 2009;Ohnesorge et al 2010). However, it introduces formaldehyde into the gluing process and requires some laborious process steps (Eisenheld and Gardner 2005).…”

Section: Introductionmentioning

confidence: 99%

Improvement of tensile shear strength and wood failure percentage of 1C PUR bonded wooden joints at wet stage by means of DMF priming

Kläusler

Haß

Amen³

et al. 2014

Eur. J. Wood Prod.

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Tensile shear tests according to EN 302-1 for load-bearing timber structures were performed on European beech wood (Fagus sylvatica L.) and Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] bonded by means of a one-component polyurethane adhesive (1C PUR). Results reveal a substantial loss of tensile shear strength (TSS) and wood failure percentage (WFP) at the wet stage compared to the dry stage. As can be seen from microscopic images, this is accompanied by a loss of adhesion at the boundary layer. Therefore, the aim of this work was to find a priming fluid that improves the load transmission between adhesive and adherend at the wet stage without introducing formaldehyde into the gluing process. A substantial improvement of TSS and WFP was achieved by means of the hygroscopic organic solvent N,N-dimethylformamide (DMF). In addition, contact angle measurements were carried out, revealing that DMF heavily enhances the wettability of the joining surface. Furthermore, it was attempted to integrate the outcomes into the swelling strain model stated by Frihart in 2009. By way of comparison a hydroxymethylated resorcinol coupling agent, a mixture of diphenylmethane-4,4 0-diisocyanate isomers and water were also tested as priming fluids. The data confirm that TSS and WFP of 1C PUR bonded wooden joints do not correlate, whilst WFP is mostly not normally (at wet stage often bimodally) distributed.

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“…On the contrary, this hardwood provokes a strong interest in Europe where it is already utilized for load-bearing structures (Aicher et al 2013). Therefore, several studies have focused on its mechanical performances as solid sawn timber (Frühwald, Schickhofer 2004;Frühwald 2008;Lagaňa, Rohanová 2011;Lagaňa, Babiak 2012;Widmann et al 2012), glued laminated timber (Frühwald et al 2003;Frese, Blass 2005;Ohnesorge et al 2009;Aicher, Ohnesorge 2010) and laminated veneer lumber (Knorz, van de Kuilen 2012). The standard EN 1912:2012 about visual strength graded timbers includes the German beech.…”

mentioning

confidence: 99%

Beech sawn timber for structural use: A case study for mechanical characterization and optimization of the Italian visual strength grading rule

Cibecchini¹,

Cavalli²,

Goli³

et al. 2016

J. For. Sci.

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ABSTRACT:The potential use of beech (Fagus sylvatica Linnaeus) sawn timber for structures has been investigated. Beech stands in transition from coppice to high forest after thinning interventions have been sampled from different Italian sources. A sample of 160 beams of two different cross sections was extracted and tested, according to the normalized procedures for the characterization of wood for structures. The specimens were visually graded considering the strength relevant defects, according to the Italian standard. To determine the mechanical properties of the timber (namely strength and stiffness), four-point bending tests were performed and the main characteristic values were derived. The results of the study reveal that knot ratio was the principal defect that influenced both resistance and yields. The potential strength class D30 was achieved with the resulting characteristic values, although, due to the small number of samples tested, the reached class could not be formally assigned. To improve the effectiveness of the grading rule in the Italian standard, some modifications and a new grade were proposed for the beech sawn timber. Finally the D40 strength class could be theoretically reached, but with reduced yields.

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Influence of wood properties and bonding parameters on bond durability of European Beech (Fagus sylvatica L.) glulams

Cited by 48 publications

References 8 publications

Characterization of wood-adhesive bonds in wet conditions by means of nanoindentation and tensile shear strength

Characterization of wood-adhesive bonds in wet conditions by means of nanoindentation and tensile shear strength

Improvement of tensile shear strength and wood failure percentage of 1C PUR bonded wooden joints at wet stage by means of DMF priming

Beech sawn timber for structural use: A case study for mechanical characterization and optimization of the Italian visual strength grading rule

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