Mechanical characterisation of wood-adhesive interphase cell walls by nanoindentation

Holzforschung ◽  
2006 ◽  
Vol 60 (4) ◽  
pp. 429-433 ◽  
Author(s):  
Johannes Konnerth ◽  
Wolfgang Gindl
Keyword(s):  
Elastic Modulus ◽  
Cell Walls ◽  
Urea Formaldehyde ◽  
Wood Adhesive ◽  
Interphase Cell ◽  
Adhesive Bonds ◽  
Resorcinol Formaldehyde ◽  
Interphase Region ◽  
Mechanical Characterisation ◽  
Penetration Behaviour

Abstract The elastic modulus, hardness, and creep factor of wood cell walls in the interphase region of four different adhesive bonds were determined by nanoindentation. In comparison with reference cell walls unaffected by adhesive, interphase cell walls from melamine-urea-formaldehyde (MUF) and phenol-resorcinol-formaldehyde (PRF) adhesive bonds showed improved hardness and reduced creep, as well as improved elastic modulus in the case of MUF. In contrast, cell walls from the interphase region in polyvinylacetate (PVAc) and one-component polyurethane (PUR) bonds showed more creep, but lower elastic modulus and hardness than the reference. Considering the different cell-wall penetration behaviour of the adhesive polymers studied here, it is concluded that damage and loss of elastic modulus to surface cells occurring during the machining of wood is recovered in MUF and PRF bond lines, whereas damage of cell walls persists in PVAc and PUR bond lines.

scholarly journals Measurement of moisture-related strain in bonded ash depending on adhesive type and glueline thickness

Holzforschung ◽  
2016 ◽  
Vol 70 (2) ◽  
pp. 145-155 ◽  
Author(s):  
Markus Knorz ◽  
Peter Niemz ◽  
Jan-Willem van de Kuilen
Keyword(s):  
High Strain ◽  
Urea Formaldehyde ◽  
Wood Adhesive ◽  
Image Correlation ◽  
Adhesive Bonds ◽  
Mechanical Loads ◽  
Resorcinol Formaldehyde ◽  
Emulsion Polymer ◽  
Distinct Strain ◽  
Adhesive Type

Abstract Structural wood-adhesive bonds (WAB) have to be durable while subjected to considerable stresses caused by mechanical loads and moisture content changes. To better understand the moisture-related durability of WABs, knowledge is important of how moisture changes generate strain in the bond. In this paper, strain on end-grain surfaces of bonded ash specimens was analyzed by means of digital image correlation. Strains were generated by wood shrinkage, and the evaluation was focused on shear strain (SStr). The bond lines were studied depending on the adhesive type – phenol resorcinol formaldehyde (PRF), melamine urea formaldehyde (MUF), polyurethane (PUR), and emulsion polymer isocyanates (EPI). Moreover, three different glueline (GL) thicknesses of MUF were taken into consideration. Comparing the adhesive types, SStr distributions (SStrD) were strongly influenced by adhesive elasticity. MUF and PRF bonds were quite rigid and were associated with pronounced strain amplitudes in and close to the GL together with strain dissipation reaching deep in the wood. PUR and EPI adhesives were more elastic and therefore allowed for smoother strain transition showing less distinct strain peaks. GL thickness had significant impact on SStrD. A high strain level and direct strain transition between adherends was found for the 0.01 mm GL, whereas a pronounced strain decrease was observed in the 0.1 and 0.2 mm GLs. This indicates different stress levels in the wood-adhesive interface dependent on GL thickness.

Tensile shear strength of UF- and MUF-bonded veneer related to data of adhesives and cell walls measured by nanoindentation

Holzforschung ◽  
2010 ◽  
Vol 64 (3) ◽  
Author(s):  
Frank Stöckel ◽  
Johannes Konnerth ◽  
Wolfgang Kantner ◽  
Johann Moser ◽  
Wolfgang Gindl
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Bond Strength ◽  
Cell Walls ◽  
Urea Formaldehyde ◽  
Lap Joints ◽  
Tensile Shear Strength ◽  
Tensile Shear ◽  
Interphase Cell ◽  
Cure Time

Abstract The tensile shear strength of veneer lap joints was characterised. The joints were produced with an Automated Bonding Evaluation System (ABES) using urea-formaldehyde (UF) as well as melamine-urea-formaldehyde (MUF) adhesive formulated for particleboard production. At a fixed heating temperature of 110°C, a systematic increase in bond strength was observed for both adhesives with increasing cure time. The absolute bond strength was significantly higher for MUF compared to UF. Nanoindentation experiments with the same specimens used for ABES revealed a very hard, stiff and brittle character of the UF resin, whereas the MUF proved significantly less hard and stiff, and less brit-tle. Wood cell walls in contact with adhesive, i.e., where adhesive penetration into the cell wall was assumed, showed significantly altered mechanical properties. Such cell walls were harder, stiffer and more brittle than unaffected reference cell walls. These effects were slightly more pronounced for UF than for MUF. Comparing UF and MUF, the micro-mechanical properties of cured adhesive and interphase cell walls confirm earlier observations that tougher adhesives can lead to higher macroscopic bond strength. In strong contrast to that, no obvious correlation was found between micromechanical properties and the strong cure time dependence of macroscopic bond strength.

Macro- and micromechanical characterization of wood-adhesive bonds exposed to alternating climate conditions

Holzforschung ◽  
2010 ◽  
Vol 64 (6) ◽  
Author(s):  
Jürgen Follrich ◽  
Frank Stöckel ◽  
Johannes Konnerth
Keyword(s):  
Bond Strength ◽  
Mechanical Performance ◽  
Urea Formaldehyde ◽  
Tensile Tests ◽  
Tangential Direction ◽  
Wood Adhesive ◽  
Bond Line ◽  
Adhesive Bonds ◽  
Climate Conditions ◽  
Micromechanical Characterization

Abstract Three-part specimens were produced from Norway spruce wood (Picea abies Karst.) and bonded with the following adhesives: melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF), and a two-component emulsion polymer isocyanate (EPI). The effect of alternating climate conditions on bond strength was studied by tensile tests. The specimens were exposed to a three-step ageing cycle lasting for 7 days [50°C/95% relative humidity (RH), -20°C/65– 70% RH and 75°C/15% RH] which was repeated 24 times. In general, a decrease in internal bond strength of all exposed specimens was observed but it was highest in the case of MUF-bonded joints. Furthermore, a significant decrease of the tensile strength of the wood adherend perpendicular to the grain in the tangential direction was determined after the cyclic climatic changes. The mechanical performance of the different adhesives in the bond line was tested by means of nanoindentation. Reduced values of elastic modulus, hardness, and total indentation were observed after climatic treatment, particularly for the rigid MUF adhesive, whereas the flexible adhesive EPI did not show such changes.

Microstructure and Quantitative Micromechanical Analysis of Wood Cell–Emulsion Polymer Isocyanate and Urea–Formaldehyde Interphases

2017 ◽  
Vol 23 (3) ◽  
pp. 687-695 ◽  
Author(s):  
Lizhe Qin ◽  
Lanying Lin ◽  
Feng Fu ◽  
Mizi Fan
Keyword(s):  
Cell Wall ◽  
Cell Walls ◽  
Laser Scanning ◽  
Urea Formaldehyde ◽  
Wood Adhesive ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Micromechanical Analysis ◽  
Emulsion Polymer ◽  
Uf Resin

AbstractEmulsion polymer isocyanate (EPI) and urea-formaldehyde (UF) were selected as typical resin systems to investigate the microstructure of wood–adhesive interphases by fluorescence microscopy (FM) and confocal laser scanning microscopy (CLSM). Further, a quantitative micromechanical analysis of the interphases was conducted using nanoindentation. The FM results showed that the UF resin could penetrate the wood to a greater extent than the EPI resin, and that the average penetration depth for these two resin systems was higher in the case of latewood. CLSM allowed visualization of the resin distribution with contrasting colors, showing that the EPI resin could not penetrate the cell wall, whereas UF resin could enter the cell walls. The micromechanical properties of the cell walls were almost unaffected by EPI penetration but were significantly affected by UF penetration, especially in the first cell wall from the glueline. This further confirmed that only cell walls with resin penetration can improve the mechanical properties of the interphase regions.

Adhesive penetration of wood cell walls investigated by scanning thermal microscopy (SThM)

Holzforschung ◽  
2008 ◽  
Vol 62 (1) ◽  
pp. 91-98 ◽  
Author(s):  
Johannes Konnerth ◽  
David Harper ◽  
Seung-Hwan Lee ◽  
Timothy G. Rials ◽  
Wolfgang Gindl
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Surface Temperature ◽  
Cell Walls ◽  
Adhesive Contact ◽  
Wood Adhesive ◽  
Bond Line ◽  
Scanning Thermal Microscopy ◽  
Thermal Probe ◽  
Thermal Microscopy

Abstract Cross sections of wood adhesive bonds were studied by scanning thermal microscopy (SThM) with the aim of scrutinizing the distribution of adhesive in the bond line region. The distribution of thermal conductivity, as well as temperature in the bond line area, was measured on the surface by means of a nanofabricated thermal probe offering high spatial and thermal resolution. Both the thermal conductivity and the surface temperature measurements were found suitable to differentiate between materials in the bond region, i.e., adhesive, cell walls and embedding epoxy. Of the two SThM modes available, the surface temperature mode provided images with superior optical contrast. The results clearly demonstrate that the polyurethane adhesive did not cause changes of thermal properties in wood cell walls with adhesive contact. By contrast, cell walls adjacent to a phenol-resorcinol-formaldehyde adhesive showed distinctly changed thermal properties, which is attributed to the presence of adhesive in the wood cell wall.

scholarly journals Quasi-static and fatigue performance of bonded acetylated rubberwood (Hevea brasiliensis, Müll. Arg.)

2020 ◽  
Author(s):  
Samuel Oluyinka Olaniran ◽  
Gaspard Clerc ◽  
Etienne Cabane ◽  
Andreas J. Brunner ◽  
Markus Rüggeberg
Keyword(s):  
Cyclic Loading ◽  
Urea Formaldehyde ◽  
Fatigue Behaviour ◽  
Quantitative Information ◽  
Resorcinol Formaldehyde ◽  
Bonding Performance ◽  
Wet Condition ◽  
Dry Conditions ◽  
Timber Products ◽  
Latex Production

Abstract Rubberwood is widely planted for latex production. At the cessation of latex yield it becomes a viable timber source in the wood industry. While good bonding performance of rubberwood has been reported, quantitative information to support this statement is missing. In this study, the tensile shear strength (TSS) and wood failure percentage (WFP) of unmodified and acetylated rubberwood in both wet and dry conditions were examined. Three frequently used adhesives were selected: one-component polyurethane (1C PUR), melamine-urea-formaldehyde (MUF), and phenol-resorcinol-formaldehyde (PRF). Furthermore, fatigue behaviour was analysed for PRF-bonded samples by cyclic loading. Results showed that in dry state, the TSS and WFP of acetylated rubberwood is comparable to the unmodified samples for all adhesives. In wet condition, the performance of bonded rubberwood was improved by acetylation. Cyclic loading revealed comparable fatigue behaviour of bonded unmodified and acetylated rubberwood. This investigation provides first quantitative information on the performance of bonded rubberwood, which can be a valuable input for the production of laminated timber products for structural purposes.

Influence of extender on Thermo-mechanical Properties of melamine-urea-formaldehyde [MUF] for wood adhesive applications

2020 ◽  
Vol 24 ◽  
pp. 2274-2282
Author(s):  
M. Nagamadhu ◽  
S. Ravi Kumar ◽  
R. Suraj ◽  
K.B. Manjunath Iyer ◽  
G.C. Mohan Kumar
Keyword(s):  
Mechanical Properties ◽  
Urea Formaldehyde ◽  
Wood Adhesive

scholarly journals EFFECT OF THE HEAT TREATMENT OF Hovenia dulcis Thunb. WOOD ON THE PRODUCTION OF EGP PANELS WITH DIFFERENT ADHESIVES

FLORESTA ◽  
2020 ◽  
Vol 50 (4) ◽  
pp. 1761
Author(s):  
Raquel Marchesan ◽  
Edison Toledo Corrêa dos Santos ◽  
Rosilani Trianoski ◽  
Morgana Cristina França ◽  
Pedro Licio Loiola ◽  
...  
Keyword(s):  
Shear Strength ◽  
Urea Formaldehyde ◽  
External Environment ◽  
Treated Wood ◽  
Polymer Emulsion ◽  
Resorcinol Formaldehyde ◽  
Minimum Standards ◽  
Heat Treated ◽  
Pre Treatment ◽  
Hovenia Dulcis

The objective of this work was to analyze the shear strength of edge-glued panels (EGP) made from the H. dulcis Thunb. wood thermally modified by the VAP HolzSysteme® process. Initially, the Hovenia dulcis samples were heat-annealed by the VAP HolzSysteme® process, and then bonded with Resorcinol-formaldehyde (RF), Melamine-urea-formaldehyde (MUF), Isocyanate Polymer Emulsion (EPI) and Polyvinylacetate (PVAc) and submited to pre-treatments for dry, humid and external environment and without pre-treatment to evaluate the shear strength, 5th percentile and failure in the wood. It was observed a decrease in the shear strength of the thermorrectified H. dulcis wood for all adhesives. All adhesives obtained results superior to the minimum required by the standard EN13354 (2009) for the wood without pre-treatment as for the wood without thermoregulation as well as for the heat treated wood, and may be used for non-structural purposes. However, for the external environment (three cycles) only the MUF adhesive obtained value that meets the minimum standards of the standard, in this way, it is suggested to glue the EGP of H. dulcis without thermortification and with thermorrectification using the MUF adhesive, which has achieved better performance offering greater resistance in dry, wet and external environments.

Experimental and theoretical investigations of lignin-urea-formaldehyde wood adhesive: Density functional theory analysis

2021 ◽  
Vol 104 ◽  
pp. 102737
Author(s):  
Abdelghani Boussetta ◽  
Anass Ait Benhamou ◽  
Francisco J. Barba ◽  
Mohammed EL. Idrissi ◽  
Nabil Grimi ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Urea Formaldehyde ◽  
Wood Adhesive ◽  
Theory Analysis ◽  
Functional Theory ◽  
Theoretical Investigations
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