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This study explores the use of propylene oxide-modified ethylenediamine (PPO-EDA) as a novel crosslinker and chain extender in polyurethane (PU) adhesives. PPO-EDA was synthesized and compared with N,N'-dimethylethylenediamine (DMEDA) to assess its impact on mechanical properties and adhesion performance. Key parameters such as NCO conversion, tensile strength, and lap shear strength were thoroughly evaluated. The results demonstrated that incorporating PPO-EDA significantly improved NCO conversion and crosslink density, leading to notable enhancements in tensile strength and elastic modulus compared to DMEDA. Lap shear tests further revealed superior adhesion performance in PPO-EDA-modified PU adhesives, particularly on amine silane-treated steel substrates, where lap shear strength consistently outperformed other samples. This improved performance was attributed to PPO-EDA's dual role as a chain extender and crosslinker, which strengthened the adhesive's structural integrity. This study underscores the effectiveness of PPO-EDA as a modifier for enhancing both mechanical and adhesive properties in PU-based adhesives, offering a promising solution for optimizing high-performance adhesives in automotive and industrial applications. [ABSTRACT FROM AUTHOR]

Recyclability of polyurethane materials is significant to relieve environmental problems caused by damaged polymers. Inspired by plenty of self‐healing properties based on dynamic covalent bonds. A high mechanical strength and thermally reversible polyurethane adhesive are acquired through co‐polymerization of poly‐1,4‐butylene adipate glycol (PBA), soybean oil‐based polyol (MESO), and toluene diisocyanate (TDI) whose linear polymer chains are constructed by Diels–Alder reaction between furfuryl alcohol (FA) and bismaleimide (BMI), named DAPU. Further, the obtained polyurethane adhesives show great recyclability, mechanical performance (Whose tensile strength can reach 91.7 MPa), and appropriate self‐healing ability through the thermally reversible Diels–Alder covalent bonds and hydrogen bonds between urethane groups, which may pave a way for further development of recyclable materials. [ABSTRACT FROM AUTHOR]

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The aim of this research was to investigate the effect of false heartwood of beech wood on the shear strength of glued joints for thermoplastic and reactoplastic adhesives for plywood production. The tensile shear strength of the lap joints was tested for four different types of adhesives according to EN 204 (2016) and EN 205 (2016). The results showed that for lap joints assembled with polyvinyl acetate, urea-formaldehyde, and phenol-formaldehyde adhesives, there was no significant difference in shear strength between beech sapwood and false heartwood. However, for joints bonded with polyurethane adhesive, the shear strength was lower for heartwood compared to the reference sapwood, particularly after exposure to water immersion.

Adhesives are being used ubiquitously, such as automotive, building, electronics, and beyond. Due to the lack of rational design strategies, they have yet to achieve a performance portfolio: mechanically robust, highly adhesive, fire‐retardant, switchable, and sustainable (e.g., biobased, reusable, biodegradable) to ensure their practical applications. Herein, a fire‐retardant phosphorus‐containing pimaric acid bio‐derivative, AD, as functional segments, is rationally engineered to prepare biobased polyurethane (PU) adhesive that realizes such an integrated performance portfolio. Because of dynamic hydrogen‐bonding and π–π stacking of polar AD, the as‐prepared PU adhesive exhibits an ultrahigh adhesion force of 38.8 N cm–1. As‐prepared adhesive can be readily reused benefiting from its good solubility in ethanol and exhibits temperature‐responsive switchable adhesion without degraded adhesion. Also, the adhesive shows intrinsic fire retardance due to its biphasic modes of action. The labile ester bonds in the structure enable the adhesive to completely degrade in the presence of lipase or dilute acid. Further demonstration of its promising applications as an adhesive for nanocomposite heat dissipators shows superior dissipating efficiencies to commercial heat sinks. This work offers a novel design approach for creating next‐generation sustainable high‐performance adhesives with functional integration and circular life cycles, which are anticipated to find extensive real‐world applications. [ABSTRACT FROM AUTHOR]

Wooden structures are becoming increasingly popular in the construction world. However, these structures often rely on synthetic adhesives, raising concerns about the environmental risks associated with their chemical composition. In response to these concerns, this study aims to explore sustainable alternatives, particularly focusing on polyurethane adhesives that incorporate proteins from industrial byproducts. The investigation involved three protein sources: soybean meal, shrimp shells, and skim milk, modified under mild alkaline conditions to obtain protein concentrates. These concentrates were then incorporated into the adhesives at varying protein contents: 5%, 10%, and 15%. Additionally, two isocyanate systems were examined, one being petrochemical-based and the other a partially bio-based blend. Chemical, thermal, optical, and mechanical characterizations were conducted to evaluate the adhesive performance. This study demonstrates that the adhesives’ thermal properties remain unaffected by both the protein content and the isocyanate system. However, these factors influence the adhesive penetration into the wood substrate. Ultimately, the results suggest that higher protein content offers superior retention of mechanical strength in adhesives compared to the petrochemical reference when subjected to humid conditions. Overall, this research demonstrates the potential of proteins from industrial byproducts as sustainable adhesive allies, providing valuable insights into their interactions with different isocyanates.

In this study, the mechanical behavior of Single Lap Joints (SLJ) subjected to tensile loading was investigated both experimentally and numerically by considering different SLJ sizes including adherend thickness (T:0.88, 1.76, 3.52 mm), joint width (W:10, 20, 30 mm), and overlap length (L:10, 20 mm). A polyurethane adhesive and carbon fiber composite adherends were used for the experimental activity. The experimental campaign was carried out to assess the effects of the SLJ geometry on the mechanical behavior of SLJ. Further, SLJ tests were used to estimate the fracture toughness in mode I and II by using Finite Element methods (FEM) coupled with optimization analysis. The results showed that all three parameters strongly change the load capacity of the joints. According to the Experiments, for every sample configuration, the higher the adherend thickness the higher the adhesive shear and the lower the substrate normal stresses. Moreover, the width showed negligible effect on adhesive shear and substrate normal stresses. Numerically, the effect of geometric parameters has been analyzed once at relative 25% of ultimate load and once at a fixed load for each sample. At 25% of ultimate load, it was observed that the increase in the joint width has nearly no significant effect on adhesive shear and peel stresses. However, at a fixed common load increasing L, W, and T resulted in a decrease in adhesive shear and peel stresses. A good agreement was found between the experimental and numerical results. [ABSTRACT FROM AUTHOR]

Invasive alien plant species pose a significant challenge to European ecosystems. They displace native vegetation, damage agricultural land, and annually cost the European economy billions of euros. Many of them are removed daily and mainly burned, although some of them produce lignocellulosic material that could be used in place of native wood species. In this study, the bonding properties of selected invasive wood species in Slovenia were tested using standard methods. Wood lamellas were produced according to the SIST EN 205 standard from Ailanthus altissima, Aesculus hippocastanum, Robinia pseudoacacia, Gleditsia triacanthos and Acer negundo and glued with polyvinyl acetate (PVAc) and one-component polyurethane (PU) adhesive. The results showed that selected wood species can be bonded well with both adhesives (bond shear strengths from 7.2 to 15.1 N/mm2), although there were large variations due to the heterogeneity of the wood material. The differences in the shear strength of the bonds were mainly due to the different densities of the wood (479 to 702 kg/m3) species and the high variability in material properties (for example porosity from 0.54 to 0.68 and shear strength in tangential direction from 11.2 to 21.1 N/mm2), which are related to the anatomical characteristics of the individual wood species.

In this study, some physical and mechanical properties of the basalt fiber-reinforced polymer (BFRP) woven fabrics (WF) and plaster mesh (PSM) reinforced glued laminated oak lumber were investigated. The BFRPWF and PSM were used in order to increase the mechanical properties of the laminated elements. One-component polyurethane glue (PUR) was used in the production of lumber. The BFRPWF and PSM were tested in three different locations using non-reinforced laminated oak lumber (LOL), reinforced laminated oak lumber with BFRPWF (LOLBFRPWF), and reinforced laminated oak lumber with PSM (LOL-PSM). Tests were performed on the LOL, LOLBFRPWF, and LOL-PSM to investigate their bending strength (MOR), air-dried density (δ12), and modulus of elasticity (MOE). The three-point MOR and MOE in bending tests were applied to the samples. The results showed that the highest value for MOR was found in the laminated wood samples (135.20 N/mm2) that were prepared using the BFRPWF inter-layer. The lowest value of 112.82 N/mm2 was found in the LOL samples. The highest value of modulus elasticity was found in the samples prepared with the BFRPWF inter-layer (16167 N/mm2). The lowest value of 13786 N/mm2 was found in the LOL samples. It was observed that the samples parallel to the glue line of the laminated material showed higher performance compared to those perpendicular to the glue line. The LOL-BFRPWF samples give better results than LOL-PSM and control samples. Accordingly, the LOL-BFRPWF and LOL-PSM samples have the potential to be used as viable options for both furniture and building materials.

Wood structures generally rely on synthetic adhesives for their strength and versatility. However, environmental concerns linked to the chemical composition of these adhesives have stimulated the search for more environmentally friendly adhesives. Researchers have explored replacing petroleum-based constituents with natural raw materials such as lignins, tannins, and proteins. Of these alternatives, proteins, being biological macromolecules, are recognized for their capacity to enhance adhesion to wood substrates. This study considered the development of protein-based adhesives derived from diverse sources, including soybean meal, microbrewery spent grains, shrimp shells, and skim milk powder. These raw materials were subjected to mild alkaline conditions to yield protein concentrates. The resulting adhesives were formulated at various protein content levels: 5%, 10%, 15%, and 20%. The study's findings showed that the incorporation of proteins into the polyurethane adhesive system not only can preserve but also augment adhesive performance. This enhancement encompasses deeper penetration into wood substrates and an overall improvement in mechanical strength. These results underscore the promise of proteins as a sustainable alternative to petroleum-based polyols in adhesive formulations.

For the sustainability of the polyurethane resin (PUR) industry, petroleum‐based materials must be replaced with renewable resource and economic aspects must be considered. Lignin is a renewable, thermostable biomass consisted with a phenolic polymer. As a thermostable bio‐filler for PUR adhesives, acidic or basic lignin was blended with an amphiprotic inorganic filler, to reduce the resins and product costs due to cheap, unmodified materials. The thermal resistance of the PUR adhesives was evaluated by measuring adhesion before and after heating and with and without a mechanical effect caused by substrate penetration. The results show that after heating at 200°C, the PURs containing 7.5 or 15 wt% of dealkaline lignin or 7.5 wt% of alkaline lignin decomposed more slowly than the lignin‐free PUR. The properties of the PURs were also analyzed using Fourier‐transform infrared spectroscopy and differential scanning calorimetry. Additionally, the PURs containing over 30 wt% of dealkaline lignin show potential as environmentally friendly water‐blown PUR foams. [ABSTRACT FROM AUTHOR]

Glued-laminated timber (Glulam), a structural engineered wood product, is mostly manufactured using structural adhesives including one-component polyurethane (PUR). Nevertheless, the concerns associated with PUR such as unsatisfactory gap-filling properties and lower resistance to delamination create opportunities for newer adhesives with enhanced bonding performance in outdoor environments. In this study, the use of fractionated lignin as a modifier in a polyurethane-based adhesive system was explored. Herein, the effect of lignin content (1, 2, and 3%) on the block shear strength (BSS), wood failure percentage (WFP), and delamination were evaluated. The results indicated that all the lignin-reinforced PUR specimens showed better adhesion performance compared to the controls (without lignin). Markedly, the lignin-PUR adhesive formulation containing 1% lignin addition exhibited superior adhesion properties than those with 2% and 3% lignin content. The statistical analyses also revealed that the lignin content influenced the BSS and WFP of the glulam specimens. Moreover, the lignin-modified PUR specimens showed increased delamination resistance and met the requirements for delamination stipulated in the ASTM D2559 standard, regardless of the lignin content. The lowest percent delamination (0.07%) was obtained from specimens bonded with 1% lignin. The presented data suggest that specimens bonded with 1% of lignin provided better bonding strength compared to other lignin-filled specimens. Thus, this study demonstrated the technical feasibility of fabricating glulam with enhanced adhesion performance using lignin-modified PUR adhesive. [ABSTRACT FROM AUTHOR]

Wood structures generally rely on synthetic adhesives for their strength and versatility. However, environmental concerns linked to the chemical composition of these adhesives have stimulated the search for more environmentally friendly adhesives. Researchers have explored replacing petroleum-based constituents with natural raw materials such as lignins, tannins, and proteins. Of these alternatives, proteins, being biological macromolecules, are recognized for their capacity to enhance adhesion to wood substrates. This study considered the development of protein-based adhesives derived from diverse sources, including soybean meal, microbrewery spent grains, shrimp shells, and skim milk powder. These raw materials were subjected to mild alkaline conditions to yield protein concentrates. The resulting adhesives were formulated at various protein content levels: 5%, 10%, 15%, and 20%. The study's findings showed that the incorporation of proteins into the polyurethane adhesive system not only can preserve but also augment adhesive performance. This enhancement encompasses deeper penetration into wood substrates and an overall improvement in mechanical strength. These results underscore the promise of proteins as a sustainable alternative to petroleum-based polyols in adhesive formulations. [ABSTRACT FROM AUTHOR]

The structural use of wood from young trees requires gluing smaller timber pieces to form large elements. In young Eucalyptus timber of structural dimensions, knots do not significantly diminish the mechanical properties, yet their influence on wood adhesion has not been widely studied. Therefore, the aim of the study was to assess the influence of knots on the bond quality of face-glued wood from young E. grandis. Wood from seven-year-old E. grandis trees was tested in shear on the bond-line (polyurethane adhesive) using paired samples of knot-containing and clear wood samples. Knot features did not correlate with shear strength or wood failure percentage. Knot-containing samples had a lower percentage of wood failure (5.8%), but the same shear strength as clear wood samples. Below a wood density of 650 kg m−3, clear and knot-containing wood behaved similarly, but above this value, knots influenced wood adhesion negatively. By simulating glulam beams with high-density wood on the outer lamellas, it was possible to show that shear stress on those bond-lines is lower than the minimum shear strength observed on dense knot samples. Hence, lower adhesion caused by knots on denser wood probably does not represent a significant problem for glued laminated products from young Eucalyptus grandis trees. [ABSTRACT FROM AUTHOR]

The mechanical properties of polyurethane compounds were experimentally investigated by changing the composition of their components. Polyol components (polyoxypropylene glycol: PPG, polyoxytetramethylene glycol: PTMG, and polycarbonatediol: PCD) were mixed with monomeric methylene diphenyl diisocyanate to synthesize polyurethane pre-polymer, mixed with chain extenders (1,4'-butanediol: 1,4'-BD or dimethylthiotoluene diamine: DMTDA), and cured, to prepare four types of polyurethane resins. Tensile tests were conducted using a mechanical testing machine with a strain rate of approximately 0.3 s−1 and a hydraulic high-speed tensile testing machine with a strain rate of approximately 500 s−1. The temperature was controlled to be −40°C, −10°C, or 25°C. When PTMG was used as the polyol, the stress-strain relationship was less sensitive to temperatures and loading rates, and the material properties exhibited a relatively good balance between elongation and strength. Additionally, the use of 1,4'-BD as a chain extender resulted in higher elongation and lower strength than the use of DMTDA. Conversely, the stress-strain relationship was dramatically altered by the test conditions when PPG and PCD were used as the polyol and embrittlement under a combination of low temperature and high strain rate was confirmed. Furthermore, there were certain compositional combinations that exhibit necking at low temperatures. [ABSTRACT FROM AUTHOR]

ABSTRACT The main function of the adhesive is to promote adhesion between materials, as well as provide fluidity and fill in the gaps between joints. Information such as grammage and bonding pressure is fundamental when it comes to the execution of structures in glued laminated wood. In this sense, the objective of this study was to evaluate the shear strength in compression of bonded joints using a one-component polyurethane adhesive with cold curing at three different gram levels, being 150 g.m-2, 200 g.m-2 and 250 g.m-2, with spreading on a single face, applied at two pressure levels, 0.7 MPa, and 1.0 MPa. The apparent density was determined, and with that, four blocks/density groups were obtained, which comprised four repetitions. In addition, the percentage of failure in the specimens after performing the shear test was analyzed. Statistical data analysis was carried out adopting a randomized design in a 2x3 factorial block to analyze the effects of grammage and bonding pressure on wood strength and failure The homogeneity and normality of the data were tested, and later the analysis of variance (ANOVA). The results showed that the joints’ strength was not affected, both for weight and pressure levels. As for the wood failure percentage, the values obtained were low, with averages below 35%.

The effects of joint geometry parameters, such as adherend thickness (1.76, 3.52 mm), joint width (10, 20, 30 mm), and overlap length (10, 20 mm), on the behavior of single-lap joints (SLJs) under tensile loading are investigated in this study. Peak force, joint stiffness, shear stress, and normal stress are the investigated properties. SLJs are manufactured with carbon fiber composite adherends and two different types of adhesives, polyurethane and epoxy, which present a flexible and rigid mechanical response. The results showed that increasing all 3 geometric parameters (L, W, T) leads to a significant increase in the load capacity of polyurethane joints (on average, 88.4, 101.5, and 16.9%, respectively). For epoxy joints, these increases were 47.7, 100, and 46%, respectively. According to these results, W is the parameter with the most influence on the load capacity of the joints. However, it was observed that an increase in joint width has no significant effect on adhesive shear and a substrate's normal stresses. Epoxy SLJs behave approximately elastically until failure, while polyurethane SLJ load-displacement curves include an initial linear elastic part followed by a more ductile behavior before the failure. Joint stiffness is affected by all the parameters for both adhesive types, except for overlap length, which led to a negligible effect on epoxy joints. Moreover, the damage surfaces for both types of joints are analyzed and the internal stresses (shear and peel) are assessed by using the analytical model of Bigwood and Crocombe. [ABSTRACT FROM AUTHOR]

The investigation of the behaviour of adhesive joints under high strain rates is an active area of research, primarily due to the widespread use of adhesives in various industries, including automotive manufacturing. Understanding how adhesives perform when subjected to high strain rates is crucial for designing vehicle structures. Additionally, it is particularly important to comprehend the behaviour of adhesive joints when exposed to elevated temperatures. Therefore, this study aims to analyse the impact of strain rate and temperature on the mixed-mode fracture characteristics of a polyurethane adhesive. To achieve this, mixed-mode bending tests were conducted on test specimens. These specimens were subjected to three different strain rates (0.2 mm/min, 200 mm/min, and 6000 mm/min) and tested at temperatures ranging from −30 °C to 60 °C. The crack size was measured using a compliance-based method during the tests. For temperatures above Tg, the maximum load supported by the specimen increased with an increasing loading rate. GI increased by a factor of 35 for an intermediate strain rate and 38 for a high strain rate from low temperature (−30 °C) to room temperature (23 °C). GII also increased for the same conditions by a factor of 25 and 95 times, respectively. [ABSTRACT FROM AUTHOR]

The subject of this study was the application of a novel CO2-based low-molecular weight poly (propylene carbonate) diol (PPCD) in the field of adhesive. Two-component polyurethane adhesive (PPCD-PU) was prepared with PPCD and polymethylene polyphenyl polyisocyanate (PAPI) as raw materials, propylene carbonate diol (PCD-EDA) as extender. The effects of the molecular weight, carbonate linkage content of PPCD and content of PCD-EDA on the properties of PPCD-PU were also investigated. The results showed that the novel CO2-based low-molecular weight poly (propylene carbonate) diol had higher carbonate linkage content (35%). The PPCD-PU synthesized by the PPCD had good adhesion performance, and the lap shear strength reached to 15 MPa. The addition of PCD-EDA not only improved the bonding properties of the adhesive, but also made PPCD-PU adhesive achieved higher lap shear strength in a shorter curing time. When the amount of PCD-EDA was 20 wt.%, the lap shear strength increased to 17 MPa, and the lap shear strength increased significantly from 3.7 to 10.6 MPa after curing at 80 °C for 30 min. Water absorption rate of PPCD-PU film was about 1.7%, and the lap shear strength was almost unchanged after 24 h of immersion in water. The temperature of 5%-weight loss of PPCD-PU was 284 °C, and the glass transition temperature was 79.3 °C. All the polyurethane adhesives obtained performed good heat and water resistance. [ABSTRACT FROM AUTHOR]

To study the creep and aging behavior under the combined effect of temperature, humidity and static load, polyurethane adhesive was selected to make butt joints. The creep properties of the joint were analyzed experimentally under different static loads in hygrothermal environment. At the same time, an aging test under the combined effect of temperature, humidity and static load was carried out, and the variation law of the residual strength of the joint with the load and loading time was obtained. The complex fracture behavior of polyurethane adhesive joints was studied from macro to microscale. The results show that the hygrothermal environment had a significant effect on the creep properties of polyurethane adhesive joints. The creep strain rate of the joint was significantly higher, and the failure fracture time was shorter in the high temperature and humidity environment. When the temperature, humidity and static load were coupled, the joint failure strength decreased with time. With increasing load, the decline rate of the failure strength increased significantly. The interface failure of the joints and the hydrolysis reaction of the polyurethane adhesive were the main reasons for reducing the failure strength. [ABSTRACT FROM AUTHOR]

Tissue adhesives constitute a great possibility to improve conventional wound closure. In contrast to sutures, they enable nearly immediate hemostasis and can prevent fluid or air leaks. In the present study, a poly(ester)urethane-based adhesive was investigated which already proved to be suitable for different indications, such as reinforcing vascular anastomosis and sealing liver tissue. Using in vitro and in vivo setups, the degradation of the adhesives was monitored over a period of up to 2 years, to evaluate long-term biocompatibility and determine degradation kinetics. For the first time, the complete degradation of the adhesive was documented. In subcutaneous locations, tissue residues were found after 12 months and in intramuscular locations, tissue degradation was complete after about 6 months. A detailed histological evaluation of the local tissue reaction revealed good biocompatibility throughout the different degradation stages. After full degradation, complete remodeling to physiological tissue was observed at the implant locations. In addition, this study critically discusses common issues related to the assessment of biomaterial degradation kinetics in the context of medical device certification. This work highlighted the importance and encouraged the implementation of biologically relevant in vitro degradation models to replace animal studies or at least reduce the number of animals in preclinical testing prior to clinical studies. Moreover, the suitability of frequently used implantation studies based on ISO 10993-6 at standard locations was critically discussed, especially in light of the associated lack of reliable predictions for degradation kinetics at the clinically relevant site of implantation. [ABSTRACT FROM AUTHOR]

The effects of the adhesive thickness and overlap of a polyurethane adhesive have been studied by using different substrate configurations. Single lap joint (SLJ) specimens have been tested with homologous substrates, carbon fibre-reinforced plastics and painted metal substrates. Furthermore, a configuration with dissimilar substrates has been included in the experimental campaign. Both types of these adhesive and substrates are used in the automotive industry. The bonding procedure has been carried out without a surface treatment in order to quantify the shear strength and stiffness when surface treatments are not used on the substrates, reproducing typical mass production conditions. Three different ageing cycles have been used to evaluate the effects on SLJ specimens. A finite element model that uses cohesive modelling has been built and optimised to assess the differences between the different adopted SLJ configurations. [ABSTRACT FROM AUTHOR]

To study the creep and property degradation behavior of adhesive joints under the coupling action of temperature, humidity and load, polyurethane shear joints were prepared and tested. Different static loads were applied to joints at high temperature (80 °C) and high temperature and humidity (80 °C/95% RH) to test and analyze the creep deformation, and a suitable creep model was established. At the same time, the performance degradation test of the joints under the effect of multifactor coupling was carried out to obtain the variation law of the failure load, and the failure mechanism was discussed based on the failure section. The research shows that the creep strain of the joint at high temperature and humidity was significantly larger than that at high temperature, and the failure fracture time was shorter, in which water molecules played a role of softening and hydrolysis. The viscoelastic multi-integral creep model was used to analyze and predict the creep behavior of the joints. It was found that the creep model could better describe the creep behavior of the joints under uniaxial constant loading. Under the coupling effect of temperature, humidity and load, the failure load decreased with time, and with the increase in static load, the decline range and rate of failure load increased. It was found that the mechanical properties in the high temperature and humidity environment decreased significantly more than those in the high temperature environment. When a static load was applied during creep, cracks easily occurred inside the adhesive layer, and water molecules easily diffused inside the cracks, which increased the decay rate of the mechanical properties. This study provides good theoretical significance and engineering value for the application of polyurethane adhesion structures in rail vehicles. [ABSTRACT FROM AUTHOR]

Background The current standard for open and laparoscopic repair of incisional hernia consist of an abdominal wall augmentation by mesh implantation. However, the ideal fixation method of the prothesis material remains under discussion, due to potential complications of conventional fixation methods such as chronic abdominal pain or intestinal obstruction. As the use of adhesive based mesh fixation is an option of growing interest, the aim of this experimental study was to investigate the strength and biocompatibility of two newly developed polyurethane-based adhesives in comparison to a cyanoacrylatic adhesive, which is currently in clinical use. Methods Two experimental polyurethane/urea-based adhesives (Adhesive-A and Adhesive-B) were compared to a conventional cyanoacrylatic adhesive and an untreated control group. Biomechanical testing was carried out using a pull-out test in uniaxial tensile mode, while biocompatibility assessment was performed in a rat model with 40 Sprague-Dawley rats receiving a subcutaneous implanted PVDF mesh fixed by the corresponding adhesive. Histological and immunohistochemical analysis by a Tissue FAXS system examined the tissue integration of the mesh/adhesive combination and characterized the foreign body reaction. Results Biomechanical testing of the mesh/adhesive combinations showed a minimal strength of 15.08 N without a significant difference between the groups. Cellular penetration into the mesh/adhesive interface was significantly improved after application of polyurethane adhesives and Adhesive-A showed a significantly lower migration of CD68 positive cells to the adhesive sites compared to cyanoacrylate after 7 days. Conclusion The developed polyurethane-based adhesives are a promising alternative with sufficient adhesive strength and superior short-term biocompatibility to cyanoacrylate.

The structure of hard and soft segments of polyurethane has an important effect on its properties. A two-component solvent-free polyurethane adhesive was prepared with self-made polyester polyol, castor oil and isophorone diisocyanate as raw materials. The effects of different mass ratios of two polyester polyols with average molecular weight Mn=400 g/mol and Mn=2000 g/mol on the properties of adhesives were studied. The results show that with the increase of polyester polyols of Mn=2000 g/mol, the water absorption of the adhesive increases, the heat resistance increases, and the peel strength increases first and then decreases. When the mass ratio of Mn=400 g/mol and Mn=2000 g/mol polyester polyols is 4: 1, the comprehensive performance of the adhesive is the best. [ABSTRACT FROM AUTHOR]

Polyurethane mixture, made of waste rubber particle, aggregate, and polyurethane adhesive, has low raveling resistance which affects the durability of the mixture. The objective of this study is to enhance the raveling resistance of polyurethane mixture. The content of polyol in the hydroxyl component was determined by Fourier transform infrared spectroscopy. The suitable curing conditions for polyurethane adhesive to enhance the raveling resistance were selected by the orthogonal experiment and mechanical tests. The relationship of the raveling resistance with crosslink density and elastic modulus was tested and calculated through the wear test. The results showed that when the ratios of the isocyanate component to the hydroxyl component were 1:3.2, 1:6.3, and 1:9.5, respectively, the isocyanate component was excessive. The ranking of the significance of the influence factors, from high to low, was first the curing temperature, then curing time, and finally the blending ratio; within the ranges of blending ratio, curing temperature, and curing time selected in this study, the appropriate blending ratio was 10:2, and the curing time was 6 h. For the polyurethane mixture involved in this study to obtain high raveling resistance, if a crosslinking agent or a new polyurethane adhesive is added, the tensile strength and tensile elastic modulus should be in the range of 3.02 to 3.27 MPa and 5.50 to 6.02 MPa, respectively; when using the FS2 polyurethane adhesive directly, the suitable curing conditions for the mixture are 90 °C and 6 h or 80 °C and 6 h. The results from this study could be beneficial for obtaining a high raveling resistance for the polyurethane mixture. [ABSTRACT FROM AUTHOR]

The objective of this work is to evaluate the efficacy of the gel and nanostructured fluids in the removal of polyurethane adhesive stuck to an archeological textile fragment that suffers from many deterioration forms. The study is divided into two sections; (a) in-vitro experiments, which were conducted on modern sheep woolen textile mock-ups after brushing with fresh polyurethane adhesive and accelerated aging. Three techniques were used in the removal of polyurethane from these mock-ups. Colorimeter, Fourier transform infrared spectroscopy, stereo microscope, and weight measurements were used to assess the selected experiments. The obtained results revealed that Nanorestore Cleaning®Polar fluid confined in Nanorestore Gel®Peggy is the most effective and suitable technique among the examined ones. (b) The applied section, which was assigned to using Nanorestore Cleaning®Polar fluid confined in Nanorestore Gel®Peggy in the removal of polyurethane adhesive from the case-study fragment, after identifying its fibers and dyes using a Fourier transform infrared spectroscopy and a high-performance liquid chromatography-diode array detector-mass spectrometry. The obtained results revealed using blank linen and sheep wool dyed with weld dye (beige color) and indigo natural dye (brown color). Beige and brown yarns were used in weaving the fragment background using the tapestry structure, and the beige wefts were used in the additional embroidery stitches. The used gel-confined fluid Nanorestore Cleaning®Polar fluid confined in Nanorestore Gel®Peggy was capable of the safe removal of the adhesive form the fragment, which was then washed and supported by a new linen fabric using thin needles and dyed silk threads. The fragment was finally re-exhibited in a standard museum display.

The article presents the results of research on a lightweight floor system (LFS) with a heat diffuser made of metal lamellae. It differs from traditional layered floors in the absence of a screed layer, which reduces thermal inertia and predisposes it to be used with renewable energy sources. As part of the research, a real model of the floor, consisting of nine ceramic tiles, was made. Polyurethane adhesive was used to connect the individual layers of this composite. The model was subjected to a thermal action. It was constructed with the measuring equipment consisting of strain gauges. These were located at the boundaries of the composite layers and measured the material's deformation. The measurement results were verified by numerical calculations. For this purpose, a computational model was made using FEM (finite element method). Comparable results of deformations were obtained (the differences did not exceed 6.1%), which made it possible to perform numerical calculations of light floor materials stresses. Additionally, the displacement of the tested model was measured and numerically verified. The results of these verifications can be useful not only in the heated/cooled LFS with aluminium lamellae, but also in other building partitions inside and outside the building. [ABSTRACT FROM AUTHOR]

The effects of joint geometry parameters, such as adherend thickness (1.76, 3.52 mm), joint width (10, 20, 30 mm), and overlap length (10, 20 mm), on the behavior of single-lap joints (SLJs) under tensile loading are investigated in this study. Peak force, joint stiffness, shear stress, and normal stress are the investigated properties. SLJs are manufactured with carbon fiber composite adherends and two different types of adhesives, polyurethane and epoxy, which present a flexible and rigid mechanical response. The results showed that increasing all 3 geometric parameters (L, W, T) leads to a significant increase in the load capacity of polyurethane joints (on average, 88.4, 101.5, and 16.9%, respectively). For epoxy joints, these increases were 47.7, 100, and 46%, respectively. According to these results, W is the parameter with the most influence on the load capacity of the joints. However, it was observed that an increase in joint width has no significant effect on adhesive shear and a substrate’s normal stresses. Epoxy SLJs behave approximately elastically until failure, while polyurethane SLJ load-displacement curves include an initial linear elastic part followed by a more ductile behavior before the failure. Joint stiffness is affected by all the parameters for both adhesive types, except for overlap length, which led to a negligible effect on epoxy joints. Moreover, the damage surfaces for both types of joints are analyzed and the internal stresses (shear and peel) are assessed by using the analytical model of Bigwood and Crocombe.

Abstract Composite materials are employed as an alternative of conventional materials due their attractive properties, such as, environmental resistance and high strength-to-weight ratio. However, a limitation to the application of the composites is the low resistance to high temperatures, due their polymeric matrix. Alternatively, geopolymers are inorganic polymers used mainly instead Ordinary Portland Cement (OPC) in civil engineering. They combine good mechanical properties, corrosion resistance and thermal stability, allowing the use as a thermal barrier. This work regards the combined application of composites and geopolymers through adhesive bonding. The main objective is to evaluate the effect of adhesive type and surface treatment on the adhesion between geopolymer and composite pultruded substrates. Pull off tests were carried out in composite-adhesive-geopolymer sandwich specimens. Different surface treatments were examined: unidirectional abrasion and bidirectional abrasion. Specimens were bonded either with an epoxy or a polyurethane adhesive. The influence of the geopolymer manufacturing process on the performance of the structure was also observed.

In honeycomb core and composite face sheet sandwich panels, it is essential to understand the bonding characteristics of adhesive in relevance with its properties to observe synergistic effects of reinforcing nanoparticles such as multi-walled carbon nanotubes (MWCNTs). This study investigates the effects of MWCNT inclusion on polyurethane (PU) adhesive, which directly affects sandwich structures' structural and mechanical performance. MWCNTs are added to PU adhesive up to 0.2%, and their RAMAN spectroscopic analysis, Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analyses (TGA) and differential-scanning calorimetry analyses (DSC) are evaluated. Aluminum honeycomb carbon-fiber-reinforced composite (CFRC) sandwich panels are fabricated using an out-of-autoclave manufacturing process. Carbon-fiber prepreg is used for top/bottom face sheets. Mechanical strength of face/core bonding evaluated as a function of MWCNT addition and core cell sizes. Manufactured sandwich composite structures are investigated for flat-wise tensile strength and three-point bending strength. Results show that MWCNT reinforcement to PU adhesive and lower cell size increases bending and flat-wise tensile resistances. [ABSTRACT FROM AUTHOR]

The mechanical properties of adhesives are sensitive to both temperature and humidity. A modified Arcan device was proposed to characterize the failures of adhesive joints under mixed mode loading. Aluminum alloy butt joints (BJs), 45°scarf joints (45°SJs) and thick-adherend shear joints (TASJs) were manufactured to investigate the effects of loading conditions. Moreover, these joints were subjected to various durations of high-temperature aging (80°C) and hygrothermal aging (80°C/95% RH): 0 (unaged), 6, 12, 18, 24, and 30 days. The adhesive joints were analyzed by Fourier transform infrared (FTIR) spectroscopy, and the load–displacement curves, failure strengths, failure modes were analyzed. The results showed under high-temperature conditions, humidity can accelerate the rate of decrease in the failure strength of the adhesive joints, which resulted from the fracture of the polymer chains and the influence of internal stresses. As the hygrothermal aging duration increased, the fracture surfaces of the joints changed significantly. The number of cracks and cavities in the fracture surface increased as the aging duration increased. After aging, the failure strength values of the adhesive joints conformed to the quadratic stress failure criterion. Two curved surface equations reflecting the relationship between the quadratic stress criterion and the aging duration were established. [ABSTRACT FROM AUTHOR]

The current standard for open and laparoscopic repair of incisional hernia consist of an abdominal wall augmentation by mesh implantation. However, the ideal fixation method of the prothesis material remains under discussion, due to potential complications of conventional fixation methods such as chronic abdominal pain or intestinal obstruction. As the use of adhesive based mesh fixation is an option of growing interest, the aim of this experimental study was to investigate the strength and biocompatibility of two newly developed polyurethane-based adhesives in comparison to a cyanoacrylatic adhesive, which is currently in clinical use. Two experimental polyurethane/urea-based adhesives (Adhesive-A and Adhesive-B) were compared to a conventional cyanoacrylatic adhesive and an untreated control group. Biomechanical testing was carried out using a pull-out test in uniaxial tensile mode, while biocompatibility assessment was performed in a rat model with 40 Sprague-Dawley rats receiving a subcutaneous implanted PVDF mesh fixed by the corresponding adhesive. Histological and immunohistochemical analysis by a Tissue FAXS system examined the tissue integration of the mesh/adhesive combination and characterized the foreign body reaction. Biomechanical testing of the mesh/adhesive combinations showed a minimal strength of 15.08 N without a significant difference between the groups. Cellular penetration into the mesh/adhesive interface was significantly improved after application of polyurethane adhesives and Adhesive-A showed a significantly lower migration of CD68 positive cells to the adhesive sites compared to cyanoacrylate after 7 days. The developed polyurethane-based adhesives are a promising alternative with sufficient adhesive strength and superior short-term biocompatibility to cyanoacrylate. [ABSTRACT FROM AUTHOR]

Tissue adhesives constitute a great possibility to improve conventional wound closure. In contrast to sutures, they enable nearly immediate hemostasis and can prevent fluid or air leaks. In the present study, a poly(ester)urethane-based adhesive was investigated which already proved to be suitable for different indications, such as reinforcing vascular anastomosis and sealing liver tissue. Using in vitro and in vivo setups, the degradation of the adhesives was monitored over a period of up to 2 years, to evaluate long-term biocompatibility and determine degradation kinetics. For the first time, the complete degradation of the adhesive was documented. In subcutaneous locations, tissue residues were found after 12 months and in intramuscular locations, tissue degradation was complete after about 6 months. A detailed histological evaluation of the local tissue reaction revealed good biocompatibility throughout the different degradation stages. After full degradation, complete remodeling to physiological tissue was observed at the implant locations. In addition, this study critically discusses common issues related to the assessment of biomaterial degradation kinetics in the context of medical device certification. This work highlighted the importance and encouraged the implementation of biologically relevant in vitro degradation models to replace animal studies or at least reduce the number of animals in preclinical testing prior to clinical studies. Moreover, the suitability of frequently used implantation studies based on ISO 10993-6 at standard locations was critically discussed, especially in light of the associated lack of reliable predictions for degradation kinetics at the clinically relevant site of implantation.

In the last years, the use of adhesive bonding is increasing as an alternative to traditional joining techniques due to their advantages such as ease of application, low weight and the good mechanical properties. To ensure good adherence between the substrates, adequate materials and surface treatment are required. The main objective of this work is to evaluate the adherence of epoxy and polyurethane adhesives between a pultruded composite material and a geopolymer. Two different surface treatments were evaluated: unidirectional abrasion (UA) and bidirectional abrasion (BA). Epoxy and polyurethane adhesives were tested. The epoxy and polyurethane adhesives showed, respectively, ductile and fragile behavior. The adherence of the bonded joints was evaluated using pull-off tests. Pultruded samples treated with UA and bonded with the polyurethane adhesive presented higher strength (13MPa). Geopolymer samples bonded with the epoxy adhesive and treated with UA reached a failure tensile of 8MPa. Considering the different testing conditions evaluated in this work, the best combination of an adhesive type and surface treatment produced an increase in the pull-off strength of 220 and 240% in pultruded composite bonded joints and geopolymer bonded joints, respectively. [ABSTRACT FROM AUTHOR]

Over the years, using adhesive joints in structural applications widespread all industrial domain, achieving an amazing current usage. This is due to the benefits that this technology is capable of providing to complex-shaped structures, both in aerospace and automotive applications. Indeed, new polyurethane adhesives are a recently fastening method. This newest adhesive types bid great advantages especially on damping, impact and fatigue which are critical characteristics in the transportation industry. Besides, the current bus manufactures use this adhesive kind to join doors' structures aluminium assembly. As like, the Tunisian automotive industry ICAR uses a one-component polyurethane for doors' structure assembly. Crack problems due to fatigue are evident in those areas since they are continuously stressed. Thereby, working on more understanding polyurethane fatigue performance we investigate over this work, the response of the assembly aluminium-alloy polyurethane adhesive joints using SLJ with two design's parameters sorted from a static study under five distinct load levels. To achieve this purpose, substrates' surfaces roughness with an arithmetic average of surface heights Ra ≈ 0.6 µm, was used. Bonded specimens with 1 mm adhesive thicknesses were manufactured and examined using cyclic fatigue testing. Furthermore, the obtained results are also compared with others from literature using epoxy adhesives. Worthy results are obtained rising the effectiveness of this adhesive's type in the transport industry.

An increase in applications of pultruded composite material has been noted in the last decades. The material is usually employed in sectors that require high mechanical properties as well as chemical and corrosion resistance. The pultruded profiles can be joined by mechanical fasteners (i.e. bolts) or adhesive bonding. Bonded joints present many advantages, such as low weight, design flexibility and corrosion resistance. However, an inherent property of the polymers is the low superficial energy, which tends to be detrimental to the adhesion quality of the structure. In this sense, is important to perform a proper surface treatment and select an adequate adhesive.The present work investigates the influence of the adhesive type and surface treatment on the adhesion of pultruded composites. Three polyurethane adhesives and an epoxy adhesive were evaluated using tensile tests in bulk specimens. Then, the composite bonded joint was tested using single lap joints (SLJs). Two methods of mechanical abrasion were applied as surface treatment: unidirectional abrasion (UA) and bidirectional abrasion (BA). The treated samples presented rougher and more homogeneous surface profiles. Results revealed that the surface treatments improved the adhesion quality of the bonded materials compared to untreated samples. The high surface roughness produced by the BA together with a ductile adhesive resulted in the best improvement of the joint strength.

A new elastic polyurethane (PU) adhesive was reported in this study to improve the stability and durability of the dental adhesion interface. A polyurethane oligomer was synthesized by the solution polymerization method, and a diluent and solvent were added to prepare PU adhesives. The water sorption, water solubility, contact angle, thermal stability, degree of conversion and mechanical properties of the PU adhesives were evaluated. Experimental applications for tooth restoration (microtensile bond strength and microleakage) were also performed, and cytotoxicity test was carried out. The water sorption and solubility of the PU adhesives were significantly lower than those of three commercial adhesives. The microtensile bond strength of the PU adhesives was improved after thermocycling test, and the extent of microleakage was diminished when compared with that of commercial adhesives. Biocompatibility testing demonstrated that the PU adhesive was non-toxic to L929 fibroblasts. This study shows the ability of PU adhesive to improve the stability and durability of the dental adhesion interface and may refocus the attention of scientists from rigid bonding to flexible bonding for dental adhesion, and it sheds light on a new strategy for the stable and durable bonding interface of dentine adhesives.

Carbon fiber reinforced plastics (CFRP) is widely used in the aerospace and automotive industries due to their light weight and high strength. The effective joining method of CFRP is bonding, and the surface state of CFRP is the main reason that affects the shear strength of the bonded joints. In order to improve the surface state of CFRP and shear strength, this paper systematically studied the effects of different power (80 W, 120 W, 180 W) laser treatment on the surface characteristics and bonding performance of CFRP and compared with the mechanical treatment (alcohol ultrasonic cleaned, sandpaper sanding). Four different adhesives were used in the adhesive joints, which were performed lap-shear tests. The SEM, XPS and contact angle measuring instrument were used to analyze the changes of physicochemical properties of CFRP after different surface treatment. The results showed that compared with alcohol cleaned and sandpaper sanding, 120 W laser treatment greatly improved the surface roughness of CFRP and formed micron-sized gaps. The water contact angle was reduced from 85° to 59.5°, and the surface energy increased from 25.6 mJ/m2 to 62.7 mJ/m2. The lap-shear results showed that the shear strength of the epoxy joints was improved after laser treatment, and the failure type was changed from interface failure to substrate failure. The polyurethane joint shear strength was not obviously improved and the combination failure of interface and cohesion was transformed into a pure interface failure after surface treatment. [ABSTRACT FROM AUTHOR]

Lignin is a good candidate for the polymerization and chemical modification to prepare sustainable chemicals and materials, but a relatively low hydroxyl content becomes an obstacle for the preparation of lignin-based polyurethane (PU) adhesives. In order to improve its reactivity, the acetic acid lignin (AAL) was hydroxymethylated before copolymerized with isocyanate during the preparation of PU adhesives. The hydroxymethylation was carried out in an alkaline formaldehyde solution and it was found that 85 °C is the optimal temperature. On that condition, the free formaldehyde content of the corresponding product HL-6 was as low as 0.32%, while the hydroxymethyl was increased by 189.11% compared with original AAL and reached 2.92 mmol/g. In the polymerization of PU adhesives, the hydroxymethylated lignin with a higher aliphatic hydroxyl content formed a more compact three-dimensional urethane cross-linking network with isocyanate. The mechanical properties and thermal stability of the lignin-based PU adhesive were improved by 15–30 wt% in HL-6, and particularly the tensile strength was increased by 21–41 MPa, which indicated that the hydroxymethylation is an efficient way to enrich the hydroxyl in lignin, and the modified lignin is adequate to partially replace petroleum-based polyols for the preparation of PU adhesives with excellent properties. Hydroxymethylated lignin with higher aliphatic hydroxyl content was obtained to prepare lignin-based polyurethane adhesives with excellent properties. Unlabelled Image [ABSTRACT FROM AUTHOR]

The cork composite (RC16) is prepared by using one-component moisture curing polyurethane (U030) as cork adhesive, and the cork composite exhibits excellent mechanical properties and flexibility, and its density is 0.40g/cm3. The effect of adhesive content, moisture content in cork granules, and curing condition on the thermal insulation property, flexibility, and mechanical properties of the RC16 cork was investigated. The results show that:the synthetic adhesive U030 has good compatibility and adhesion with cork granules, which can wrap the cork granules completely and distribute evenly; the mechanical properties of the cork composite exhibit first increasing and then decreasing with increasing moisture content in cork granules, and the maximum value is reached at 7.0%; with the increase of U030 content, each performance of the RC16 cork show rising firstly, and then towards a stabilizing trend, but the thermal conductivity increases correspondingly, so when U030 content is 30%, the comprehensive performance of composite is the best; the optimum curing condition of the RC16 cork is defined:curing temperature is 110℃ and curing time is 1.5h. RC16 exhibits good heat resistance, which can bear 800℃ ablation within 20s.