Effect of phenolic resin structure on the bonding properties of nitrile rubber-based adhesives

Three phenolic resins were used to study the effect of resin structure and its percentage content on the bonding properties of nitrile rubber-based adhesives. The phenolic resins studied are derived from phenol, resorcinol and para-t-butyl phenol, and are of novalac type. These resins were characterized by infra-red and thermal studies. Several formulations were prepared by varying the phenolic resin/nitrile rubber ratio and these formulations were tested for viscosity and bonding properties. At a given resin-to-rubber ratio, the viscosity for resorcinol-formaldehyde resin was higher than phenol-formaldehyde resin followed by para-t-butyl phenol-formaldehyde resin. The peel strength of nitrile rubber-based adhesive prepared from resorcinol-formaldehyde resin was higher than adhesives that from para-t-butyl phenol-formaldehyde resin followed by phenol-formaldehyde resin. The lap shear strength of nitrile rubber-based adhesive containing para-t-butyl phenol-formaldehyde resin was higher than of adhesives containing the other two resins. The trend observed in peel strength could be explained on the basis of hydrogen bonding between hydroxyl groups of phenolic resin (adhesive) and hydroxyl groups of the starch-coated canvas cloth (adherend), whereas the trend observed in lap shear strength could be explained on the basis of extent of linearity in the resin structure.     

Investigation of a Critical Irradiance Criterion for Minimizing the Cure Time of a PAW Joint

Photo-activated Adhesive Workholding (PAW) technology is used to hold workpieces for manufacturing processes. This paper proposes a critical irradiance criterion that can be used to determine whether a curing light system is capable of curing a PAW adhesive joint at its maximum rate. It describes a series of experiments that were conducted to investigate the plausibility of this criterion for adhesive joints comprised of a commercially available adhesive mixed with various concentrations of carbon black and at varying thicknesses. Lastly, it provides experimental evidence that indicates that the addition of small concentrations of carbon black to a modified acrylic adhesive does not change its asymptotic, maximum strength. Furthermore, adhesive joints that are exposed to radiation that satisfies the critical irradiance criterion cure at a maximum rate.     

Morphology and Properties of Waterborne Polyurethane/CNT Nanocomposite Adhesives with Various Carboxyl Acid Salt Groups

Three series of waterborne polyurethane (WBPU)/carbon nanotube (CNT) nanocomposites were prepared, and their morphology and properties with various 2,2-dimethylol propionic acid (DMPA) and CNT contents were investigated. The CNTs were homogeneously dispersed up to the optimum content in WBPU/CNT nanocomposite films. The degree of homogeneous CNT dispersion increased with increasing DMPA content in WBPU/CNT nanocomposite films. The optimum CNT content showed maximum tensile strength, Young's modulus and adhesive strength of WBPU/CNT nanocomposite film. The optimum CNT contents for WBPU/CNT nanocomposite samples containing 3.61, 5.16 and 5.86 wt% DMPA were about 0.50, 1.00 and 1.50 wt%, respectively. The WBPU/CNT nanocomposite adhesive showed higher adhesive strength at moderately high temperatures (40/60/80/100°C) compared to conventional WBPU. The highest adhesive strength at moderately high temperatures was found with 5.86 wt% DMPA and 1.5 wt% CNT content.     

Properties of Waterborne Polyurethane/CNT Nanocomposite Adhesives: Effect of Countercations

Two series of waterborne polyurethane (WBPU)/carbon nanotube (CNT) nanocomposites were prepared with various CNT contents (0–1.50 wt%). We used a metal-hydroxide (copper hydroxide, Cu(OH)₂) and amine (triethylamine, TEA) as the countercation in the nanocomposites. The interaction of the countercations with the CNTs in the nanocomposite was characterized by TEM, and the interaction effects on the properties, such as the glass transition temperature (T_g), storage modulus, tensile strength, Young's modulus and adhesive strength, were investigated. The CNTs were homogeneously (optimum) dispersed at concentrations of up to 1.25 and 1.00 wt% for the metal-hydroxide and amine series, respectively. At the optimum CNT content, the tensile strength and adhesive strength were maximized in each series. However, the adhesive strength of the WBPU/CNT nanocomposite with the metal-hydroxide countercation was less affected than with the amine-countercation after immersing the adhesive bonded nylon fabrics in water (for up to 48 h).     

Effect of steam on bonding strength and dimensional stability of laminated veneer lumbers manufactured using different adhesives

Laminated veneer lumbers (LVLs) manufactured from wood with different adhesives are being increasingly used in the construction of furniture frames and buildings. Yet there is little information available concerning the dimensional stability and shear strength of LVLs after being exposed to steam. In this study, LVLs were manufactured from poplar and beech veneers with phenol/formaldehyde (PF), poly(vinyl acetate) (PVAc), Desmodur-VTKA (D-VTKA) and urea/formaldehyde (UF) adhesives. Dimensional stability of LVLs was measured after being exposed to steam for 2, 6, 12, 24, 48 and 96 h, according to the Turkish Standard (TS) 3639, and also shear strength was measured (according to BS EN 205). The highest initial density of 0.93 g/cm³ was for beech LVL with VTKA adhesive. After exposure to steam for 96 h, the highest weight increase of 65.7% was for poplar LVL with PVAc, the highest radial swelling of 5.7% was for beech LVL with UF, the highest tangential swelling of 7.9% was for beech LVL with PF and the highest longitudinal swelling of 0.5% was for beech LVL with VTKA. The highest shear strength value of 15.8 N/mm² among all samples without exposure to steam was obtained for beech LVL with PVAc adhesive and the lowest shear strength was obtained as 4.48 N/mm² for poplar LVL with UF adhesive.     

Reduction of solvent content in toluene–neoprene adhesives and in acetone–polyurethane adhesives

The desorption of toluene in a polychloroprene (neoprene)-toluene adhesive and in a commercial neoprene adhesive was studied in air at three different temperatures by monitoring the weight loss vs time. Similarly, the desorption of acetone in a polyurethane adhesive and in a commercial adhesive was also considered. The experimental weight variations are correlated with the solution of the second Fick law at non-steady state. As the volume is highly reduced when the solvent is evaporated from the solvent-polymer mixture, the correlations obtained are discussed on the basis of the variation of the diffusivity with the solvent concentration, assuming that the product of the diffusivity and the polymer volume fraction to the power 2 is approximately constant. Apparent activation energies were obtained for the four adhesives used.     

Relationship between Phenolic Adhesive Chemistry,Cure and Joint Performance. Part I. Effects of Base Resin Constitution and Hardener on Fracture Energy and Thermal Effects During Cure

In this study the relationships between the composition of phenol resorcinol-formaldehyde resins and paraformaldehyde concentration in the adhesive were explored, using DSC, IR, GPC, and solubility measurements. Differences of chemical composition between base resins and adhesives were compared to the fracture toughness of adhesive bonds.

The cure temperature and cure time effects upon fracture toughness were also investigated. Fracture toughness tests were performed with bonded hard maple tapered double-cantilever beam cleavage specimens.     

Analysis of shear strength of cylindrical assemblies with anaerobic adhesives using Weibull statistics

A statistical method to study the reliability of cylindrical anaerobic adhesively-bonded assemblies is presented in this work. An anaerobic adhesive was used to manufacture four groups of bonds with different gaps, but with the same surface pre-treatment and curing position. Shear strength values were obtained and used to determine reliability of all adhesive bonds using the Weibull statistical distribution. Although the Weibull analysis has been widely used in the study of composite materials, its application in adhesive bonds is being explored now. A two-parameter Weibull distribution was employed to execute the Weibull analysis, using an estimator that renders a more realistic Weibull modulus value, as other estimators were found to subestimate or overestimate this value. Weibull modulus values were obtained for adhesive bonds with different gaps to study their reliability, and these results have been compared with the shear strength results.     

Adhesive bonding of acetylated wood

Eighteen thermoplastic and thermosetting adhesives, including emulsion polymer-isocyanates, polyurethane, moisture-curing hot-melt, polyvinyl acetates, neoprene and waterborn contacts, casein, epoxy, melamine, ureas, resorcinol, phenol-resorcinols, and phenolics, were tested for their adhesion to yellow-poplar wood acetylated to 0, 8, 14 and 20 weight percent gains. Effectiveness of adhesion was determined by measuring shear strength and wood failure in a dry condition and after saturation with water. Adhesion was reduced to varying degrees in proportion to the compatibility of the adhesive with the amount of non-pollar, hydrophobic acetate groups in the acetylated wood. Seven of the adhesives developed bonds of high integrity at all levels of acetylation when tested in the dry condition. Two room-temperature-setting adhesives, one a resorcinol-formaldehyde and the other a phenol-resorcinol-formaldehyde, together with a hot-setting acid-catalysed phenol-formaldehyde, developed bonds of high strength and resulted in wood failure at all levels of acetylation when tested in the water-saturated condition.     

Relationship between Phenolic Adhesive Chemistry, Cure and Joint Performance. Part I. Effects of Base Resin Constitution and Hardener on Fracture Energy and Thermal Effects During Cure

In this study the relationships between the composition of phenol resorcinol-formaldehyde resins and paraformaldehyde concentration in the adhesive were explored, using DSC, IR, GPC, and solubility measurements. Differences of chemical composition between base resins and adhesives were compared to the fracture toughness of adhesive bonds.

The cure temperature and cure time effects upon fracture toughness were also investigated. Fracture toughness tests were performed with bonded hard maple tapered double-cantilever beam cleavage specimens.     

Modeling and Analysis of the Irradiance of Incipient Curing Light Reaching the Adhesive–Workpiece Interface Within a LAAG Joint

Light Activated Adhesive Gripper (LAAG) workholding is a technology used to hold workpieces for manufacturing processes. This paper presents a modeling technique for predicting the irradiance of incipient curing light reaching the adhesive–workpiece interface. It also describes an experimental methodology that can be used to derive the model coefficients for any arbitrary selection of curing lamp, gripper pin and adhesive. Lastly it provides experimental evidence that optical transmission loss increases dramatically during photo-polymerization. This increase is most likely due to increased ray scattering due to shrinkage void formation and densification of the adhesive matrix.     

Rheology and machining performance of waterborne biopolymer labelling adhesives

Machining performance is one of the most important features of waterborne biopolymer labelling adhesives. Various deformation processes on the labelling machine have been analysed in relation to the rheology characteristics of adhesive materials. It has been shown that satisfactory machining performance requires adhesive materials to have particular properties under both shear and extensional deformations. Flow behaviours of commercial labelling adhesive products were tested over a very wide range of shear rate. Time dependences of the apparent shear viscosity were examined at selected shear rates. An adhesive with a smooth flow behaviour and only slight time dependence tends to perform better on the labelling machine. Results found in this work can be used as guide for rheology assessment in the development of new waterborne biopolymer adhesives.     

Effects of Temperature and Loading Rate on the Mechanical Properties of a High Temperature Epoxy Adhesive

The variation of the mechanical properties of adhesives with temperature and strain rate is one of the most important factors to consider when designing a bonded joint due to the polymeric nature of adhesives. It is well known that adhesive strength generally shows temperature dependence. Moreover, in many structural applications, the applied loads can be dynamic and the design of the joint requires the knowledge of the high loading rate mechanical behaviour of the adhesive. In this study, the combined effect of the temperature and test speed on the tensile properties of a high temperature epoxy adhesive was investigated. Tensile tests were performed at three different test speeds and various temperatures (room temperature (RT) and high temperatures (100, 125 and 150°C)). The glass transition temperature (T _g) of the epoxy adhesive investigated is approximately 155°C. The ultimate tensile stress decreased linearly with temperature (T) while increased logarithmically with the loading rate, which is in the accord with the Airing's molecular activation model.     

Upgrading of MUF adhesives for particleboard production using oligomers of hyperbranched poly(amine-ester)

Oligomeric precursors of poly(amine-ester) were synthesized by a two-step condensation reaction of succinic anhydride with diethanolamine under mild conditions. The oligomers formed were characterized at each synthesis step using matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry. This showed that after step (1), the condensation adduct of both reactants (206?Da) was the main product mixed to high proportion of unreacted diethanolamine (106?Da). After step (2), the adduct at 206?Da decreased substantially, while other compounds at 275, 292, and 375?Da started to increase along with the appearance of a new compound at 392?Da. This indicates that the reaction proceeds slowly under these conditions to give higher branched oligomers (HP). In addition, some cyclic compounds were also identified by the 188, 275, and 375?Da peaks. MALDI-TOF of the melamine–urea–formaldehyde (MUF) resin before and after reaction with the hyperbranched oligomers mix showed clear indication of the coreaction of simple melamine–formaldehyde oligomers with several of the hyperbranched oligomers previously identified. Addition of small proportions of a mixture of the formed HP oligomers to a MUF adhesive improved the internal bond (IB) strength, both dry and wet, of wood particleboards bonded with it. The results obtained indicate that the addition of these HP oligomers can improve the dry IB strength by 17–24% according to conditions of preparation and the wet IB strength by as much as 47% when compared to the control sample.     

Recycled polyurethane elastomers: a universal adhesive

The practical application of the glycolysis mixture of polyurethane wastes is reported. It was found that in the presence of 4,4′-diphenylmethane diisocyanate (MDI) both the separated upper phase of the glycolysis mixture and the complete two-phase reaction mixture could be used as components of the urethane adhesive mixtures for bonding woods, metals, plastics, glass, ceramics, paper and leather. The adhesive properties were determined by tensile-cutting, cutting- and bending strengths, as well as peel resistance measurements. The method to use the complete glycolysis mixture is also reported. The reaction mechanism of bonding is also discussed.     

改性间苯二酣-甲醒树脂在全钢载重子午线轮胎带束层胶中的应用

研究改性间苯二酚-甲醛树脂B-20-WS或A250等量替代间苯二酚在全钢载重子午线轮胎带束层胶中的应用。结果表明:以B-20-WS或A250树脂等量替代间苯二酚后,胶料的门尼焦烧时间延长,硫化速度加快;硫化胶的定伸应力减小,拉伸强度和粘合力增大;成品轮胎的耐久性能提高,可减少环境污染。     

On the relationship between the adhesive properties and the structural features of fibrin sealants

The relationship between the adhesive properties and network architecture of fibrin sealants was studied at various fibrinogen, thrombin and calcium ion concentrations. Network features were characterized using Scanning Electron Microscopy at cryogenic temperature (cryo-SEM). This technique allows examination of the hydrated gel without drying. It was shown that by gradually increasing the calcium ion concentration, at constant thrombin and fibrinogen concentrations, the network appearance changed dramatically, from an almost isotropic structure at low concentration to highly oriented fibers at higher concentration of 7 mM CaCl₂. In addition, it was found that further increase in the calcium ion concentration induced fiber aggregation and formation of large clusters, co-existing with fine fibers. Changes in thrombin concentration at constant calcium and fibrinogen concentrations induced only slight changes in the gel appearance. Adhesive properties of fibrin sealants were measured using the shear-lap test and were correlated with structural features of the network. Holding fibrinogen and thrombin concentrations constant and varying the CaCl₂ concentration, maximal shear strength was found with 7 mM CaCl₂, corresponding to an oriented network. Holding fibrinogen and calcium chloride concentrations constant, a slight increase in shear strength was observed with increase in thrombin concentration, demonstrating again the correlation between the network structure and its adhesive properties.     

Molecular simulations of deformation and failure in bonds formed by glassy polymer adhesives

The mechanical behavior of glassy polymer bonds is examined with molecular dynamics simulations. We show that the interfacial strength of the bond in mode I (tensile) and mode II (shear) fracture is strongly influenced by the coupling between the adhesive and adherends as well as by the roughness of the substrate surface. Failure occurs at the substrate (interfacial failure) when the interaction is weak, and in the bulk (cohesive failure) when the interaction is strong. The transition from interfacial to cohesive failure under mode I loading is nearly unaffected by roughness, while roughness leads to a dramatic increase in interfacial strength under mode II loading. Stress mixity is another crucial parameter that determines whether the polymer fails through shear deformation or through cavitation and crazing. By varying the geometry of the adhesive bond, we illustrate different limiting behaviors of a rupturing film.     

Durable adhesives for large laminated timber

Large laminated timber (LT) made of hardwood is widely used as the main constitutional element of goods such as furniture, pianos and doors. A high durability of LT is essential to these products. This study focused on finding as to what adhesives were acceptable as highly durable adhesives for LT. Twelve different adhesives such as resorcinol-formaldehyde resin, aqueous emulsion-type isocyanate resin, poly(vinyl acetate) emulsion, epoxy resin, etc. were used. The durability of LT, i.e., the percentage of delamination length of LT under tests such as humidity and temperature cycling tests, and outdoor tests, was discussed in relation to the adhesive shear strength of a lap joint (LJ). The results showed that the percentage of delamination length under both low ?20°C for 16 h and high-temperature 50°C for 8 h cycling tests (temperature-resistance) on LT indicated a strong trend with the adhesive shear strength of the LJ exposed to dry air at 100°C for 24 h. In addition, the percentage of delamination length under outdoor exposure test for three months (outdoor-resistance) of the LT showed a trend with the adhesive shear strength of the LJ exposed to dry air at 100°C for 24 h, as well as with the adhesive shear strength of the LJ immersed in water at 60°C for 3 h. These trends pointed out that the thermal stability of the adhesive from ?20°C for 16 h up to 50°C for 8 h was an important parameter in order to improve adhesive durability for the LT.