The role of wood extractives in structural hardwood bonding and their influence on different adhesive systems

Bockel, Stefan; Mayer, Ingo; Konnerth, Johannes; Harling, Steffen; Niemz, Peter; Swaboda, Christiane; Beyer, Mario; Bieri, Nicole R.; Weiland, G.; Pichelin, Frédéric

doi:10.1016/j.ijadhadh.2019.03.001

Cited by 36 publications

(18 citation statements)

References 12 publications

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“…), and ash (Fraxinus sp. ), for gluing is known to vary due to their diverse extractive contents (Lüdke et al 2015, Konnerth et al 2016, Bockel et al 2019, Bockel et al 2020. In general, hardwoods have a higher density than softwoods and, consequently, higher mechanical strength and swelling/shrinkage.…”

Section: Influence Of the Wood Substratementioning

confidence: 99%

Selected previous findings on the factors influencing the gluing quality of solid wood products in timber construction and possible developments: A review

Hänsel¹,

Sandak

et al. 2021

Wood Material Science & Engineering

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Various factors affect the bonding quality of elements used for timber construction. This review includes literature studies and personal experiences related to relevant technological variables defining glue bond performance in glue-laminated timber elements during their service life. The gluing of hardwood species receives special focus as it is considered by the industry to be the most challenging process for implementation. In particular, the effects of wood species, type of adhesive, glued-wood surface quality, physical and/or chemical modification of the wood, technological solutions for gluing, and varying climatic conditions during the use phase (relative humidity, temperature, air circulation, etc.) are considered. In addition, overlapping of individual influencing factors often leads to problems with bonding, thus requiring strongly integrating measurement methods (e.g. NIR spectroscopy). The causes of variations in the results when glued wood is tested using different standardized methods are discussed. A list of open research questions is provided, and problem solutions are recommended based on systematized cuttingedge knowledge. The aim of the work is to systematize the state of knowledge of wood gluing to create a basis for controlled and stable manufacturing processes. The progress of the work will be reported in further publications.

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Section: Influence Of the Wood Substratementioning

confidence: 99%

Selected previous findings on the factors influencing the gluing quality of solid wood products in timber construction and possible developments: A review

Hänsel¹,

Sandak

et al. 2021

Wood Material Science & Engineering

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“…acetic acid, gallic acid, linoleic acid etc.) accelerated phenol resorcinol formaldehyde (PRF) adhesive curing as well (Bockel et al 2019).…”

Section: Introductionmentioning

confidence: 99%

“…The differences in the starting pH value of the studied adhesives might also be responsible for the different outputs (He and Yan 2005). Furthermore, remarkably, in most of the studies, a large amount of wood powder and/or extracts (> 10%) was mixed into the PF adhesive (Bockel et al 2019;He and Riedl 2004;He and Yan 2005). While such approaches allow for minimizing the high variabilities due to the complex nature of wood, in parallel, they might complicate the evaluation because of the overlapping chemical and physical interactions.…”

Section: Introductionmentioning

confidence: 99%

A new analytical approach to investigate the influence of wood extracts on the curing properties of phenol-resorcinol–formaldehyde (PRF) adhesives

et al. 2022

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In this study, the interactions between a phenol–formaldehyde resorcinol (PRF) adhesive and water-extractable wood constituents were investigated using combined in-situ FTIR spectroscopy and rheology analysis for a simultaneous examination of the progress of chemical reactions and coherent changes in rheological properties during adhesive curing. Complementary evolved gas analysis and pyrolysis gas chromatography/mass spectroscopy (Py-GC/MS) were performed to detect differences in the final crosslinking and chemical composition of the cured adhesive, respectively. The rheological and chemical analysis results correlated with the tensile shear strength of wood-PRF assemblies. The results showed that adhesive curing was significantly affected by the presence of acidic wood extractives. In particular, the acidic extractives of chestnut wood led to a delay in the resin curing and less final crosslinking of the cured adhesive. This was most likely caused by a reduction in the catalytic effect of the base-catalyzed curing of the adhesive rather than by direct chemical reactions between the extracts and adhesive. These findings can be useful for adapting the resin formulation to the chemistry of acidic wood species.

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“…Only few studies have been dealing with 2C PUR in structural surface bonding, but with the restriction of testing only mechanical performance in dry conditions [8]. Own studies have been investigating the influence of extractives on the curing properties and performance of 2C PUR [9,10].…”

Section: Introductionmentioning

confidence: 99%

Modifying elastic modulus of two-component polyurethane adhesive for structural hardwood bonding

Bockel

Harling²,

Konnerth

et al. 2020

J Wood Sci

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Subject to this study is the modification of an experimental two-component polyurethane (2C PUR) as an alternative adhesive for structural hardwood bonding. The 2C PUR has been adapted by calcium carbonate as filler to increase its modulus of elasticity with the aim of increasing the modulus analogue to the ones typically observed for classic amino- and phenol based adhesives. The 2C PUR system was compared with a commercial one-component polyurethane (1C PUR) and a phenol resorcinol formaldehyde (PRF) adhesive. The wetting properties of the adhesives were tested in terms of surface tension, polar and dispersive part and contact angle on European beech wood (Fagus sylvatica L.). In addition, adhesive polymer films of 2C PUR were tested for tensile strength and modulus of elasticity (E-Modulus) following ISO 527-1. The adhesives bond performance on beech wood was determined by lap-joints according to EN 302-1 in various climate conditions. The results show that 2C PUR has proper wettability properties on beech wood. Adding 60% wt filler to the polyol component increased the E-Modulus from 2.3 GPa (0%) to 4.4 GPa. The tensile strength of the modified 2C PUR polymer films was comparable with the industrial 1C PUR. Tensile shear strength and wood failure percentage of 2C PUR lap-joints were increased by adding filler and met requirements in dry and re-dried conditions according to EN 302-1. However, the addition of filler didn’t result in an improvement in wet conditions. The present study shows sufficient performance for bonding hardwood with 2C PUR in dry conditions, while the system still needs to be improvement regarding its performance in humid conditions.

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The role of wood extractives in structural hardwood bonding and their influence on different adhesive systems

Cited by 36 publications

References 12 publications

Selected previous findings on the factors influencing the gluing quality of solid wood products in timber construction and possible developments: A review

Selected previous findings on the factors influencing the gluing quality of solid wood products in timber construction and possible developments: A review

A new analytical approach to investigate the influence of wood extracts on the curing properties of phenol-resorcinol–formaldehyde (PRF) adhesives

Modifying elastic modulus of two-component polyurethane adhesive for structural hardwood bonding

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