One-component Polyurethane Research Articles

Mechanical and physical properties of Cross-Laminated Timber made from Acacia mangium wood as function of adhesive types

In this study, three-layered Cross-Laminated Timber (CLT) manufactured from Acacia mangium wood panels were developed by using two different types of adhesives, namely, phenol resorcinol formaldehyde (PRF) and one-component polyurethane (PUR). The aim of this work is to investigate and compare the physical and mechanical properties of CLT manufactured using PRF and PUR adhesives. Water absorption (WA), thickness swelling (TS), and delamination of both types of samples were investigated as their physical properties. PRF-bonded CLT showed better physical properties than PUR-bonded CLT. In terms of mechanical properties, bending test, shear modulus, and compression parallel to grain were studied. The results revealed that global modulus of elasticity (Em,g) and modulus of rupture (MOR) of panels bonded with PRF adhesive were higher than three-layered panels made from PUR adhesive. Meanwhile, shear modulus (G) of PRF-bonded CLT was 116.50 N/mm2, 20% higher than that of the PUR-bonded CLT which recorded a shear modulus value of 92.48 N/mm2. As for compressive properties, the MOE in compression (Ec,0) and compression strength (fc,0) of the PRF-bonded CLT (5304 N/mm2 and 28.99 N/mm2, respectively) was slightly higher compared to that of the PUR-bonded (4787 N/mm2 and 28.14 N/mm2, respectively). Three main types of bending failure modes were observed in the CLT samples, namely, rolling shear, glue-line failure, and tension. The failure modes of shear were observed by two ways, which is delamination and rolling shear. Lastly, shearing, splitting, and crushing were recorded in compression failure modes.

Bonding quality assessment of cross-layered Maritime pine elements glued with one-component polyurethane adhesive

Abstract This paper presents an experimental study about the bonding quality of Maritime pine (Pinus pinaster Ait.) cross-layered wood elements glued with one-component polyurethane adhesive. The experiments comprised shear and delamination tests according to standard EN 16351 focusing on the influence of the following parameters: bonding pressure, adhesive spread rate, pre-treatment with primer and layer thickness. The results obtained show that increasing bonding pressure increases significantly the wood failure percentage after delamination or shear tests, while the delamination and the shear strength are not significantly affected. Moreover, it was found that the use of primer enhances significantly the bonding quality; nevertheless, EN 16351 requirements are fulfilled even for the lower bonding pressure and adhesive spread rate recommended by the manufacturer of the adhesive used in the experiments. The layer thickness, for the tested range, had no influence on the delamination and shear results and limited one on the wood failure percentage after shear or delamination tests. No relevant influence was found for the adhesive spread rate. In the experiments the combination of gluing Maritime pine with Australian blackwood (Acacia melanoxylon R.Br.) was also investigated and, for this combination, the standard requirements were successfully fulfilled.

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

Bonding of hardwood for structural applications is a complex process. Various factors influence the bond performance and the interface area is considered the most crucial part. The chemical composition of the interface, e.g. wood extractives, is expected to influence the bonding of hardwoods. The subject of this study was to determine the influence of seven model substances that represent common wood extractives on different adhesive systems namely one-component polyurethane, two-component polyurethane, melamine urea formaldehyde and phenol resorcinol formaldehyde. The influence of the model substances on the cross-linking behavior of the adhesives was determined by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and on the rheological properties in terms of gel point and storage modulus. In addition, model substances characteristic for selected wood extractives were applied to the surface of European beech wood [Fagus sylvatica L.] before bonding and consequently tested in tensile shear mode according to EN 302-1. The ATR-FTIR spectra showed an influence of some substances on the crosslinking for all adhesive systems. Further, the curing process was mostly accelerated for phenol resorcinol formaldehyde, while melamine urea formaldehyde and polyurethane showed a less negative change in rheological behavior. The mechanical strength of beech wood bonds at room climate indicated only minor influence of model substances, but samples tested in wet conditions demonstrated a significant effect on some adhesive systems. It was concluded, that polyurethane adhesives degrade by acid substances and melamine urea formaldehyde by starch and gallic acid. Phenol resorcinol formaldehyde system was influenced negatively by starch and acids.

Comparison of Adhesive Properties of Polyurethane Adhesive System and Wood-plastic Composites with Different Polymers after Mechanical, Chemical and Physical Surface Treatment.

The cost of most primary materials is increasing, therefore, finding innovative solutions for the re-use of residual waste has become a topic discussed more intensely in recent years. WPCs certainly meet some of these demands. The presented study is focused on an experimental analysis of the effect of surface treatment on the adhesive properties of selected WPCs. Bonding of polymer-based materials is a rather complicated phenomenon and modification of the bonded area in order to improve the adhesive properties is required. Two traditional types of surface treatments and one entirely new approach have been used: mechanical with sandpaper, chemical with 10 wt % NaOH solution and physical modification of the surface by means of a MHSDBD plasma source. For comparison purposes, two high-density polyethylene based products and one polyvinyl-chloride based product with different component ratios were tested. A bonded joint was made using a moisture-curing permanently elastic one-component polyurethane pre-polymer adhesive. Standardized tensile and shear test methods were performed after surface treatment. All tested surface treatments resulted in an improvement of adhesive properties and an increase in bond strength, however, the MHSDBD plasma treatment was proven to be a more suitable surface modification for all selected WPCs.

The effect of cataphoretic and powder coatings on the strength and failure modes of EN AW-5754 aluminium alloy adhesive joints

The aim of this study is to determine the effect of cataphoretic and powder coatings and also the method of application the primer on the adherends surface on the strength and failure modes of EN AW-5754 aluminium alloy adhesive joints. The study is performed on lap joints made of EN AW-5754 aluminium alloy, subjected to three different types of surface treatment; namely a) polyurethane cataphoretic coating, b) powder coating based on black mat RAL 9005 UL polyester resin and c) no coating. The tested adhesive joints were made using a one-component polyurethane adhesive Terostat 8596, which was dedicated for automotive and cured under a constant load of 0.018 MPa at 20 ± 2 °C. In addition, this study investigates the effect of the application of Terostat 8519P adhesion promoter which is a liquid polyurethane-based primer containing solvents and which is corresponding to Terostat 8596 polyurethane adhesive. Terostat 8519P adhesion promoter was applied in two different ways: a) to one substrate and b) to both substrates. The produced adhesive joints were subjected to strength tests using the Zwick/Roell Z150 testing machine. The examination of fracture in the tested adhesive joints was performed in accordance with the EN ISO 10365 standard. The shear strength results have demonstrated that both the method of application of the adhesion promoter (Terostat 8519 P) and the presence of cataphoretic coating had an influence on adhesive joints strength. The use of the adhesion promoter significantly affects the strength of both uncoated EN AW-5754 aluminium alloy adhesive joints and the adhesive joints subjected to powder coating. The use of the adhesion promoter has a less significant effect on the cataphoretic-coated samples.

Effect of thermal postcuring on the micro- and macromechanical properties of polyurethane for wood bonding

The optimization of mechanical properties of adhesive bonds is of interest especially in structural applications. Besides transferring stresses, bondlines can also provide additional functionality, such as measuring deformations in structural timber applications by electrically conductive adhesives. This study investigates the influence of a thermal postcure treatment of polyurethane bonded wood joints. Bonded beech wooden samples were manufactured with three adhesives—a commercial one-component polyurethane for structural laminated timber and two modified ones, filled with electrically conductive particles. Adhesive bonds were subjected to a subsequent postcuring at 80 and 95 °C for 1 and 48 h, respectively. Mechanical properties of the bonds were studied on the macroscopic level by tensile shear tests and the properties of the cured adhesive on the microscopic level by nanoindentation. As a result, the tensile shear strength slightly dropped with addition of filler, while all specimens still fulfilled the requirement of EN 302-1 in dry condition. Nanoindentation revealed minor decreases in mechanical properties of the cured adhesive with postcuring time for two adhesives and a different reaction of carbon black filled polyurethane, as the creep factor decreases with the thermal postcure.

Morphometric Analysis of One-Component Polyurethane Foams Applicable in the Building Sector via X-ray Computed Microtomography.

A detailed morphometric analysis of one-component polyurethane (PU) expanding foams, with densities of 26 and 28 kg/m3 (‘SUMMER’ and ‘WINTER’ product versions), was conducted to evaluate the topology of the foam cells and to discover processing-to-structure relationships. The microstructural analysis of the heterogeneously distributed pores revealed tight relationships between the foam morphology and the cell topology, depending on the growth rate and local environmental conditions, governed by the properties of the blowing gas used. The most significant morphometric output included the following: open/closed porosity and (heterogeneous) pore distribution, relative density and (homogeneous) strut distribution, and total solid matrix surface and closed pore surface area—at the macroscopic level of the foam. While, at the microscopic level of the cells, the results embraced the following: the size of every detected strut and pore, identified two-dimensional (2D) shapes of the cell faces, and proposed three-dimensional (3D) topologies modelling the PU foam cells. The foam microstructure could be then related with macroscopic features, significant in building applications. Our protocol outlines the common procedures that are currently used for the sample preparation, X-ray scanning, 3D image reconstruction and dataset analysis in the frame of the X-ray computed microtomography (µ-CT) testing of the one-component PU foams, followed by a statistical (multiple Gaussian) analysis and conceptual considerations of the results in comparison with thematic literature.

Adhesive properties of laminated veneer lumber poles for use in temporary soil nailing: bonding performance of curved structures in a high-alkaline environment

Circular hollow sections of beech-laminated veneer lumber (LVL) for the use as temporary geotechnical soil nailing systems are currently being developed. Due to their permanent subsoil cement embedment, investigations of the bond line quality of the timber sections are essential. This paper presents the bonding properties of flat and curved beech LVL after cyclic conditioning in a water–cement grout solution aimed at inducing short- and long-term alkaline attack of the timber. In total, 409 and 69 samples were tested in tensile shear tests after short-term and long-term conditioning, respectively. Three different adhesive systems, a one-component polyurethane adhesive, a melamine–urea–formaldehyde adhesive and a melamine–urea–formaldehyde adhesive modified by means of (polyvinyl)-acetate adhesive were investigated and compared. Short-term conditioning by submersion in boiling cement suspension was found to be a reliable method for testing the bonding performance rather than long-term conditioning. In the case of tensile shear tests of samples subjected to long-term treatment, wood material strength was the decisive criterion. Generally, tensile shear test samples of all investigated adhesives achieved reliable bonding for a pressing force up to 1.0 MPa. No relationship was recognised between the determined bonding failure and the wood properties tensile shear strength, wood failure percentage, fracture pattern and bulk density of veneers adjacent to the bond line. For the determination of the bond line integrity of curved veneer poles, it was necessary to test bonding quality in a combined test using curved and flat samples and to compare tensile shear strength with data determined on reference samples in the same veneer population without bond line.

Improvement of ash (Fraxinus excelsior L.) bonding quality with one-component polyurethane adhesive and hydrophilic primer for load-bearing application

The increasing quantity of hardwood growing in the Swiss forest represents an opportunity for the future of the wood industry. Glued laminated timbers made of hardwood offer higher strength and stiffness properties than the softwood equivalents, and they are often used in combination with softwood for local reinforcement. Additionally, their visual aspect can be an attractive selling argument. Until now, phenol resorcinol adhesive (PRF, Aerodux 185) has preferably been used for the bonding of ash wood. Despite its high bonding performance, this adhesive has several disadvantages, including a dark brown glue line and a strong emission of formaldehyde both during the gluing process and when in use. One-component polyurethane (1C-PUR) adhesives, widely used in load-bearing structures made of softwood, represent an interesting alternative for hardwood gluing. These formaldehyde-free adhesives require no mixing and present an invisible glue line without any emissions after full curing. Preliminary results have shown that the combination of a slow-reacting 1C-PUR adhesive with a water-based primer system obtained similar results as Aerodux 185 in laboratory conditions with respect to shear strength and delamination resistance. This paper focuses on the optimization of the gluing process of two different 1C-PUR adhesives and their combination with a special primer on ash wood to develop an economically attractive industrial application process. The influence of several factors, such as primer-water concentration, primer activation time and primer quantity, were investigated using a delamination test according to EN 302-2. It was shown that it is possible with 1C-PUR to reach the normative standard requirements according to EN 15425. The best results were obtained with a primer-water concentration of 10% and a primer-water applied quantity of 20 g/m2. The influence of the primer activation time was shown to have only a small effect. 1C-PUR with a long closed assembly time was shown to perform even better. Additionally, the reduction of the lamellar thickness led to a reduction of delamination. By considering these parameters, it was possible to develop an industrial process for producing high-performance glued laminated timber out of ash wood and glued with a certified and commercially available 1C-PUR adhesive.

Performance optimization of one-component polyurethane healing agent for self-healing concrete

In this work, glass capsules containing one-component polyurethane healing agents are embedded in concrete to realize its self-healing properties. First, one-component polyurethane is diluted with acetone, and the viscosity, area of dispersion, surface tension, and bond strength of the resulting mixture are investigated. By encapsulating the diluted polyurethane inside quartz glass tubes, two different package types of capsules are prepared (capsules I and II), and their compatibility with concrete and survival rate are analyzed. In particular, the microscopic interface between the polyurethane and concrete phases is studied via scanning electron microscopy, while energy-dispersive X-ray spectroscopy is used to determine their elemental compositions. The mechanical properties of the produced self-healing concrete are examined by performing three-point bending tests, and the self-healing efficiency of the polyurethane healing agent is determined. When the acetone/polyurethane mass ratio is equal to 1:5, the viscosity and surface tension of the resulting mixture are low, while its healing effect is the strongest one. The strength recovery rate observed after 48 h of manual crack healing is 75%, and after two different types of glass capsules were placed into concrete, its flexural strength increased by 6–30%. However, the embedded glass capsules break after the crack formation in the self-healing concrete block. Finally, the strongest healing effect is observed for the self-healing concrete containing two type II capsules, which corresponds to the healing efficiency of 67%.

Influence of processing parameters and wood properties on the edge gluing of green Eucalyptus grandis with a one-component PUR adhesive

The predominant plantation hardwood species in South Africa Eucalyptus grandis is, despite relatively good strength and stiffness properties, seldom used for lumber production due to low dimensional stability, splitting, and cracking of the wood. As critical defects often develop or aggravate during the drying process, the edge gluing of Eucalyptus grandis lumber in its wet state, before kiln-drying, was considered a potential inhibiting factor for this behaviour. The objective of this study was to determine how certain material and processing variables influence the bond quality of unseasoned, edge-glued, Eucalyptus grandis, using a moisture-curing one-component polyurethane adhesive. The study considered the effect of four parameters, namely wood density, moisture content, adhesive spread rate and pressure, on the shear strength of bondlines. Micro computed tomography scanning was used to observe adhesive penetration behaviour. Overall, the bonding quality was satisfactory proving the feasibility of edge gluing of this wood in the wet state. Multiple ANOVA showed that generally better results were obtained for samples with a higher moisture content of roughly 60% compared to specimens with lower moisture content around fibre saturation point. Results indicated that the lower spread rate tested (150 g m−2) should be preferred to the higher one (250 g m−2), since it will likely give more stable shear strength results and it would be preferable from an economic point of view. Increasing pressure did not increase the shear strength significantly.

Experimental studies of glued Aluminum-glass joints

Glued steel-glass or aluminum-glass joints are to be found, among other things, in vehicles (cars, buses, trains, trams) as windscreen assembly pieces for the supporting structure. For the purposes of the experiments, samples were made in which the top beam was made of the AW-2017A aluminum alloy and the bottom beam was made of thermally reinforced soda-lime glass whereas the glued joints were made of one-component polyurethane glue Körapur 175. The tests were performed under four-point bending conditions at monotonic incremental bending moment values on the Instron 5965 durability machine. The experimental study of the durability of glued joints under four-point bending conditions with the monotonic incremental bending moment allows to determine the values of stresses, whose value is related to initiation of damage of the tested joint.

Fatigue resistance of an aluminium one-component polyurethane adhesive joint for the automotive industry: Effect of surface roughness and adhesive thickness

Fatigue is a crucial type of loading for many structural components that contain adhesive bonding systems such as the automotive industry. One of the main advantages of adhesives is their weight-reduction aptitudes. Furthermore, adhesively bonded joints allow a good damping to the fatigue's solicitation with fewer sources of stress concentration. In addition, a suitable surface treatment allows a great joint interface adhesion under cyclic loading. Hence, the mechanical preparation of the bonded surface influences directly the bonded joint performance. Therefore, a careful consideration should be given to the choice of the bonded adhesive thickness. The aim of this paper is to investigate the influence of surface roughness of an aluminium alloy and the adhesive thickness of a one-component polyurethane adhesive, to be used in several parts for buses structure, on the fatigue behaviour of single lap joints. To achieve this purpose, four different surface roughnesses were prepared on aluminium specimens, with an arithmetic average height from Ra ≈ 0.6 µm to Ra ≈ 1.5 µm. Bonded specimens with four adhesive thicknesses from 0.3 mm to 2 mm were manufactured and tested in dynamic tests. The results confirm that there is an optimum combination of surface roughness and adhesive thickness providing the maximum fatigue life. Moreover, good agreement was found between this investigation and a previous work using the same parameters under static loading.

Ability of finger-jointed lumber to maintain load at elevated temperatures

This article presents a test method that was developed to screen adhesive formulations for finger-jointed lumber. The goal was to develop a small-scale test that could be used to predict whether an adhesive would pass a full-scale ASTM E119 wall assembly test. The method involved loading a 38-mm square finger-jointed sample in a four-point bending test inside of an oven with a target sample temperature of 204°C. The deformation (creep) was examined as a function of time. It was found that samples fingerjointed with melamine formaldehyde and phenol resorcinol formaldehyde adhesives had the same creep behavior as solid wood. One-component polyurethane and polyvinyl acetate adhesives could not maintain the load at the target temperature measured middepth of the sample, and several different types of creep behavior were observed before failure. This method showed that the creep performance of the one-component adhesives may be quite different than the performance from short-term load deformation curves collected at high temperatures. The importance of creep performance of adhesives in the fire resistance of engineered wood is discussed.

X-ray Radiography to Visualize the Rebar-Cementitious Matrix Interface and Judge the Delay in Corrosion through Self-Repair by Encapsulated Polyurethane

Corrosion of steel reinforcement is one of the most detrimental attack mechanisms for reinforced concrete structures. The presence of cracks, which are inextricably linked to reinforced concrete, accelerates this attack mechanism. The aim of this study is to heal cracks by an autonomous mechanism, which is triggered upon crack appearance. With an accelerated corrosion test on mortar samples with embedded reinforcement bars, it is shown that the presence of cracks indeed accelerates the onset and propagation of corrosion at the interface between the rebar and the cementitious matrix. Moreover, it is shown that crack healing in both the traditional, manual way and the proposed autonomous way, with an encapsulated one-component polyurethane, delays the onset and propagation of corrosion. The difference in corrosion behavior is proven by visual evaluation of the rebar surface and by X-ray radiographic analysis, which is proposed as a successful technique to evaluate the crack healing efficiency and more specifically the potential to delay corrosion.

Effects of surface treatment and adhesives on bond performance and mechanical properties of cross-laminated timber (CLT) made from small diameter Eucalyptus timber

The feasibility of manufacturing cross-laminated timber (CLT) using fast-grown small diameter Eucalyptus timber was explored in preliminary studies. However, eucalyptus bonded with commercial one-component polyurethane adhesive usually provides poor resistance to delamination and shear force. The effects of priming surface of eucalyptus CLT lamella intended for a bondline and different adhesives on block shear strength (BSS), wood failure percentage (WFP), and rate of delamination (RD) of Eucalyptus CLT made from small diameter lumber were studied via block shear and cyclic delamination tests at both dry and wet states. Four different types adhesives: epoxy resin (EP), emulsion polymer isocyanate (EPI), phenol resorcinol formaldehyde (PRF), and polyurethane (PUR) adhesives were used to manufacture three-layer Eucalyptus CLT panels following adhesive manufacturers’ instructions. Hydroxymethylated resorcinol (HMR) and hygroscopic organic solvent N,N-dimethylformamide (DMF) primers were adopted to priming surfaces of Eucalyptus CLT lamella intended for a bondline. The results indicated that eucalyptus CLT made of small diameter lumber with the four adhesives were comparable to commercial softwood CLT. The maximum wood failure percentage (WFP) and block shear strength (BSS) values of specimens bonded with PUR adhesive at dry state were 85.2% and 3.51 MPa whereas those values of specimens bonded with EPI adhesives at wet state were 58.2% and 1.62 MPa respectively. The minimum rate of delamination (RD) value was 7.6%, which was obtained from specimens bonded with PUR adhesive. The enhancing effects of HMR and DMF priming treatment on bond performance and mechanical properties of Eucalyptus CLT bonded with the above four adhesives did not show a clear trend because their effects depended on the coupling effects of the adhesive and primer. Generally, HMR priming treatment was effective to enhance bond performance and mechanical properties of eucalyptus CLT. After HMR priming, the WFP values of eucalyptus CLT at wet state bonded with PRF and PUR adhesives increased by 27.8%, 12.4% meanwhile the BSS values increased by 31.5%, 4.9%. The RD values of specimens bonded with PRF and PUR adhesives at wet state were close to 0.0% after HMR priming.

About the influence of a water-based priming system on the interactions between wood and one-component polyurethane adhesive studied by atomic force microscopy and confocal Raman spectroscopy imaging

In recent years one-component polyurethane (1C-PUR) adhesives have been increasingly applied in loadbearing timber constructions. However, a low wood fracture percentage at wet stage and a comparatively low performance in delamination tests need to be overcome to fulfill certain technical standards and to achieve an even higher acceptance in the global market of wood adhesives. Via the use of suitable primers, in this case a water-soluble primer (WSP) system, it is possible to significantly improve these parameters. Nevertheless, the exact mode of action of the primer remains so far unclear. In this study, primer treated wood surfaces were characterized in detail by atomic force microscopy (AFM) and the influence of the primer on the penetration of the 1C-PUR adhesive into wood cell walls was further analyzed by confocal Raman spectroscopy imaging. AFM investigations of primer treated surfaces reveal a significant increase in adhesion compared to non-primer treated surfaces and indicate a penetration of the primer into the cell wall. However, Raman spectroscopy shows that the primer application does not lead to a substantial and deep penetration of the 1C-PUR adhesive into wood cell walls. Slight changes in the spectral properties of the primer treated samples at the interface between the bond line and the adjacent cell wall, point towards changed interactions between wood and polyurethane.

Nontarget Analysis via LC-QTOF-MS to Assess the Release of Organic Substances from Polyurethane Coating.

A novel approach was investigated for the assessment of leaching from a one-component polyurethane (1C-PU) coating used for hydraulic structures using nontarget analysis via LC-QTOF-MS. Leaching behavior of the 1C-PU coating was studied using experiments in which the coating was exposed to water for defined periods (6 h, 24 h, 3 d, 14 d). Three hardening durations for the 1C-PU coating were tested (0 h, 24 h, 14 d) as well as two water matrices (ultrapure water and river water), including a successive water renewal. Dissolved organic carbon, total nitrogen bound and nontarget measurements via LC-QTOF-MS showed that under all tested conditions organic substances were leached out of the 1C-PU coating. The shorter the hardening duration and the longer the leaching duration, the higher were the number and quantities of the eluted substances, while the influence of the water matrix was minor with respect to substance elution. Based on the MS2 spectra from the LC-QTOF-MS measurements, 30 substances released from the 1C-PU coating were tentatively identified. These substances belong to five chemical groups: derivatives of (i) N-(tosyl)carbamate, (ii) p-toluenesulfonamide (PTSA), (iii) 4,4'-methylenediphenyl diisocyanate (4,4'-MDI), (iv) toluenediisocyanate (TDI), and (v) oligo(ethylene) ([C2H4O]n) as well as p-toluenesulfonic acid. The identity of seven substances was confirmed by authentic reference standards, all of which exhibited an elevated bacterial toxicity to Aliivibrio fischeri. p-Toluenesulfonic acid was present in a German canal (Teltowkanal) with concentrations of up to 11 μg L-1.

Improvement of shear strength, wood failure percentage and wet delamination of cross-laminated timber (CLT) panels made with superheated steam treated (SHST) layers of larch wood

AbstractCross-laminated timber (CLT) panels – consisting of several cross-wise stacked layers of glued boards – have a high dimensional stability. However, the outer surfaces of CTL are exposed to environmental humidity changes and thus to swelling and shrinking. To improve CLT’s dimensional stability further, the layers of kiln dried (KD) CLT were substituted partly (on the surfaces) and entirely with superheated steam treated (SHST) wood. The effects of SHST wood and the performance of the one-component polyurethane resin (PUR) were tested by block shear and delamination tests after water soaking. Under various conditions, the shear strength ranged from 1.3 MPa to 4.7 MPa and the wood failure percentage (WFP) from 76% to 92%. The optimal parameter were ascertained as pressing time (30–45 min), pressure (0.98 MPa) and adhesive amount (175–200 g m−2). The water soaked delamination of CLT manufactured with SHST wood was approximately 50% lower than that of CLT made of KD wood.

Characterization of aluminium one-component polyurethane adhesive joints as a function of bond thickness for the automotive industry: Fracture analysis and behavior

The automotive industry is increasing, nowadays, its use of high performance structural adhesives in order to reduce vehicle weight and increase the crash resistance of automotive structures. One-component polyurethane adhesives are attracting rising interest as an alternative to conventional rigid structural adhesives. This is due to several benefits such as the excellent impact resistance they provide. This paper investigates experimentally the mechanical behavior of one-component polyurethane adhesive joints and specifically the effect of the adhesive layer to be used in several parts for buses structure. Furthermore, it characterizes the fracture behavior of the adhesive layer with various bond’s thicknesses using mode-I and mode-II fracture testing. The fracture toughness under both modes is determined using Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) tests, respectively. Assessment of the various fracture tests indicated that DCB and ENF provide the same shape of evolution of the fracture energy versus adhesive thickness. Moreover, the test results were able to fully mechanically characterize the adhesive and demonstrate that the adhesive has not only high mechanical strength but there is an optimal adhesive thickness, which allows a high toughness for bonded joints. This result proves that it is worthy to use the one-component polyurethane adhesive in the automotive industry.