Moisture related elastic and viscoelastic behaviour of wood adhesives by means of in-situ nanoindentation

Rindler, Axel; Pöll, Carina; Hansmann, Christian; Müller, Ulrich; Konnerth, Johannes

doi:10.1016/j.ijadhadh.2018.06.004

Cited by 16 publications

(21 citation statements)

References 16 publications

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“…Higher stiffness means a low hindered strain can result in high stress. PVAc, UF and ULEF are mechanically sensitive to moisture changes, decrease their elastic modulus and increase their creep behaviour, whereas PUR and EPI do not respond to moisture to the same extent (Rindler et al 2018;Stöckel et al 2013). In fact, the moisture-sensitive adhesives show very similar values after being exposed to the C4 climate for 7 days.…”

Section: Bi-layer Deformationmentioning

confidence: 95%

“…Thus, it is expected that a longer exposure to a specific RH is revealing stronger differences between the adhesive systems. Although the capability of absorbing water vapour (Wimmer et al 2013) and the mechanical response to changing RH and temperature have been experimentally demonstrated for cured adhesive polymers (Jakes et al 2015; Konnerth and Gindl 2008;Rindler et al 2018;Stöckel et al 2013), the effect of moisture sensitivity of adhesive on the warping behaviour of multi-layered panels remains unclear.…”

Section: Principle Of Wood Panel Warpingmentioning

confidence: 99%

“…(1) relation between E and G is typically applicable (Konnerth et al 2006). For simplification, moisture-related in situ E r data were used directly from previous experiments (Stöckel et al 2013;Rindler et al 2018). For PUR, no directly comparable C IT values were available, that is why only E r values were used with a value of 4 GPa in accordance with values collected by Stöckel et al (2013).…”

Section: Micromechanical Properties Of the Adhesivesmentioning

confidence: 99%

“…4 and 5. On the y-axis, the mean moisture-related reduced elastic modulus (E r ) obtained from pure bond lines at 15%, 43% and 66% relative humidity RH of the same adhesives by means of nanoindentation (Rindler et al 2018) is displayed. Higher E r values of a certain adhesive correspond to lower RH as indicated by the arrow All tested panels show both, negative and positive bending curve values indicating that concave as well as convex deformation was achieved depending on the moisture conditions for all adhesive systems in the transverse direction.…”

Section: Bi-layer Deformationmentioning

confidence: 99%

“…4 and 5. On the y-axis, the mean moisture-related indentation creep C IT obtained from pure bond lines at 15%, 43% and 66% relative humidity RH of the same adhesives by means of nanoindentation (Rindler et al 2018) is displayed. Higher C IT values of a certain adhesive correspond to higher RH as indicated by the arrow or the HDF during the pressing.…”

Section: Bi-layer Deformationmentioning

confidence: 99%

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Adhesive-related warping of thin wooden bi-layers

et al. 2019

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Warping of layered wood-based panels is still a challenging problem in the development of thin engineered wood products. Wood as an anisotropic and hydrophilic material tends to change its volume and mechanical properties with changing moisture content. Besides the wood components, also the mechanical properties of certain adhesives are sensitive to moisture changes. A moisture load onto the adhered wood is resulting in different stress and strain states between the adherends. It is expected that adhesives with different moisture-related properties participate differently to this interaction. To observe an adhesive-related warping, thin spruce/HDF (Picea abies and high-density fibreboard) bi-layers with identical material geometries were manufactured under laboratory conditions, using different wood adhesive systems, which are currently used in furniture and flooring industry [polyurethane (PUR), emulsion polymer isocyanate (EPI), polyvinyl acetate (PVAc), urea formaldehyde (UF) and ultra-low emitting formaldehyde amino adhesive (ULEF)]. The bi-layers were exposed to certain relative humidity conditions, and the resulting deformation was measured with a high-precision laser distance detector. Moisturedependent warping of the bi-layers was obtained in relation to the used adhesive systems. As a result of the study, it can be shown that initial warping after panel manufacturing strongly depends on the adhesive curing characteristics and, especially, on the amount of water that is released into the wood adherend. For the post-setting panel warping, a differentiation into two adhesive groups became visible: rigid and flexible adhesives. Rigid adhesives (UF and ULEF) showed a higher degree of warping compared to the group of flexible adhesives (PUR, EPI and PVAc).

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Section: Bi-layer Deformationmentioning

confidence: 95%

Section: Principle Of Wood Panel Warpingmentioning

confidence: 99%

Section: Micromechanical Properties Of the Adhesivesmentioning

confidence: 99%

Section: Bi-layer Deformationmentioning

confidence: 99%

Section: Bi-layer Deformationmentioning

confidence: 99%

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Adhesive-related warping of thin wooden bi-layers

et al. 2019

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Joining and Reassembling of Wood

et al. 2023

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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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Moisture related elastic and viscoelastic behaviour of wood adhesives by means of in-situ nanoindentation

Cited by 16 publications

References 16 publications

Adhesive-related warping of thin wooden bi-layers

Adhesive-related warping of thin wooden bi-layers

Joining and Reassembling of Wood

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

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