Adhesive Penetration Research Articles

Augmenting bonding properties of OSB and Chinese fir hybrid cross-laminated timber by sandblasting pretreatment

The investigation was conducted into the adhesive performance within hybrid cross-laminated timber (HCLT) composed of sandblasted Chinese fir and oriented strand board (OSB) which was originally covered by cured adhesive during the manufacture leading to very fragile bonding. HCLT specimens with three layers were bonded utilizing three structural adhesives which were polyresorcinol formaldehyde (PRF), polyurethane (PUR), and polyisocyanate (EPI). Surface roughness and wettability testing ascertained that sandblasting could effectively change the original resin layer and microtopography on the surface of OSB laminates, significantly modified the level of roughness on the surface, thereby providing a basis for vertical spreading and permeating of the adhesives. Sandblasting pretreatment consistently augmented the dry bonding shear strength about all the three adhesives, achieving the most substantial increases of 53 %, 39 %, and 37 % for PRF, PUR, and EPI, respectively. The pretreatment further reducing delamination rates to about a half in cyclic delamination tests of all three adhesives. Fluorescence microscopy detection of the bonding interfaces revealed a significant increase in adhesive penetration depth which had been further confirmed by the bonding interface thickness measurement. Surface roughness generally had a negative effect on dry shear bonding strength, especially with EPI adhesive, while surface wettability was positively correlated with bonding strength and adhesive layer thickness. This study introduced an environmental and efficient method to enhance the bonding performance of HCLT.

Novel GSK-3 inhibitor based universal dentin bonding system: A comprehensive analysis of dentinal repair and improved bond strength

The aim of the study was to describe the formulation of a novel universal adhesive system, based on a GSK-3 (glycogen synthetase kinase-3) inhibitor (Tideglusib®), and to evaluate its bond strength and dentinal repair capability. Tideglusib® was added to Ultradent Peak Universal Dentin Bonding Agent to make experimental adhesives (0.5 %, 1 %, 2 % final concentration). They were applied to teeth which were sectioned, stored for 24 h, or 2 years then bond strengths measured. Baseline stiffness of bonded dentin beams was tested using the three-point bending test. Animal experiments were performed to provide specimens for microcomputed tomography imaging after adhesive application. Collagen matrix was evaluated using transmission electron microscopy. The cytotoxicity of the modified adhesives was determined using fibroblastic cells. Molecular modelling evaluated binding of the Tideglusib® molecule to active sites on collagen and the adhesive components. TGFβ-1/and BMP-2 in human dentin matrices were measured and interfaces were scanned using SkyScan 2211. Adhesives’ stability tests were done. ResultsRMSD (root mean square deviation) analysis indicated simulation has equilibrated with changes for globular proteins (p < 0.05). Specimens from 0.5 %, and 1 % Tideglusib® groups displayed adhesive penetration with Micro-CT imaging and a significant increase in dentin density was seen. Specimens from the same groups showed cells with large masses of cytoplasm with focal adhesion points. Bond strength decreased significantly (p < 0.05) with increased storage time. Gradual release (p < 0.05) of both TGFβ-1 and BMP-2 from hTDMs with 0.5 % and 1 % Tideglusib® groups occurred and higher elastic moduli (p < 0.05). Collagen-based amide and proline Raman bands were seen in the Tideglusib® groups. ConclusionIncorporation of Tideglusib® in experimental Universal Adhesive System at 1 % improved adhesive bond strength and promoted dentinal repair. Application of Tideglusib® based adhesive conserve mechanical properties of the tooth structure and promote regenerative capability so can be expected to extend the service life of adhesive restorations in clinical situations.

Terahertz spectroscopy and effective medium theory for thickness measurement of adhesive bonds

This study deals with the characterization of multilayer adhesive structures via terahertz waves, particularly focusing on inversion analysis of the adhesive layer thickness. Terahertz-time-of-flight (THz-TOF), sensitive to the dielectric properties of materials, serves as an excellent device for non-destructive evaluation. Further, the transfer matrix method is introduced to simulate THz propagation through layered materials with various optical properties. An improved model iteration approach and particle swarm optimization algorithm are employed to effectively determine the adhesive layer thickness. This methodology utilizes effective medium theory (EMT), specifically for adhesive penetration into the cushion, thereby enhancing the thickness measurement accuracy. Among the various EMT models, the Lorentz-Lorenz (L-L) model is commonly regarded as the most effective one. An objective function based on combining the Pearson correlation coefficient and the root mean square error is proposed to refine the iterative inversion process. The results of this approach have been benchmarked with traditional THz-TOF calculations and computed tomography imaging, revealing that the proposed methodology is consistent with CT findings and outperforms conventional THz-TOF calculations.

Gluing parameters optimization and failure mechanism of cross-laminated timber prepared with Chinese fir

Cross-laminated timber (CLT) has become a popular engineered wood product, mainly prepared from imported wood in China. More extensive research is needed to improve the local production of cross-laminated timber with fast-growing coniferous wood species. Chinese fir (Cunninghamia lanceolata) and one component polyurethane (1C-PUR) adhesive were selected to prepare CLT under different process parameters. International standard methods, scanning electron microscopy (SEM), optical microscopy (LM), confocal laser scanning microscopy (CLSM), and nanoindentation (NI) were applied. The bonding performance and failure mechanism of Chinese fir CLT were investigated and clarified. The results showed that the optimal gluing parameters for preparing CLT from Chinese fir wood were 160 g/m2 of glue, 0.9 MPa of pressure, and 180 minutes of pressing time. Failure of CLT made from Chinese fir lumber was mainly due to the shear failure of the vertical layer board. Cracks often appeared in the earlywood cells near the boundary between earlywood and latewood. The impact of adhesive penetration on the mechanical properties of the wood cell wall showed that adhesive penetration increased the elastic modulus of the cell wall at earlywood and latewood cells.

Experimental evaluation of atmospheric plasma treatment effects on different textures of CFRP composite for aircraft applications

This article examines the impact of Atmospheric Plasma Treatment (APL) on the chemical composition and fracture properties of various textured surfaces (tool and bag side) of carbon fiber/epoxy (CFRP) composites utilized in aircraft applications. For this purpose, parameters of atmospheric plasma (APL) surface treatment were evaluated in comparison to chemical cleaning and peel-ply applications, taking into account its effects on surface properties and adhesive bond strength. A comprehensive variety of surface characterization techniques were utilized to analyze surface modifications, including water and diiodomethane contact angle measurements for assessing surface hydrophilicity, Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection (FTIR-ATR) and X-ray Photoelectron Spectroscopy (XPS) for analyzing chemical composition and functional groups, and Profilometry, Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM) for evaluating surface topography and morphology. Experimental results indicated that the reduction in the contact angle following plasma treatment correlated with the elevated oxygen concentration and the presence of polar functional groups (e.g. -OH, -NH2, -NH3, C=O, O-C=O) on the composite surface. Plasma treatment, especially at low nozzle speeds, increased surface roughness on the bag side surfaces. This prevented adhesive penetration and led to gas entrapment, resulting in adhesive failure mode and reduced single lap shear strength for the bag side. In contrast, on the tool side surfaces, the plasma treatment led to a remarkable 19.7% enhancement in shear strength, highlighting its effectiveness.

Industrial byproducts as adhesive allies: Unraveling the role of proteins and isocyanates in polyurethane wood bonding

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.

Mechanical and Fire Properties of Flame-Retardant Laminated Bamboo Lumber Glued with Phenol Formaldehyde and Melamine Urea Formaldehyde Adhesives.

This study investigated the effects of different adhesives, phenol formaldehyde (PF) and melamine urea formaldehyde (MUF), on the mechanical and fire properties of flame-retardant laminated bamboo lumber (LBL). The results demonstrated that the flame-retardant treatment using phosphorus-nitrogen-boron compounds endowed the LBL with excellent flame retardancy and smoke suppression properties, even though the bending strength and bond shear strength were slightly reduced. The PF-glued LBL exhibited superior mechanical and shear properties to the MUF-glued ones, primarily due to its higher processing temperature and deeper adhesive penetration. In addition, the MUF-glued flame-retardant LBL displayed better heat release reduction and smoke suppression properties than the PF-glued LBL, which resulted from the synergistic flame retardancy between the melamine element in MUF and the applied flame retardant. The analysis of the influence of adhesive type on the mechanical and fire properties of flame-retardant LBL holds significant importance for the future design and production of high-performance LBL material.

Bonding performance and surface characterization of cold-bonded acetylated beech (Fagus sylvatica L.) laminated veneer lumber.

Acetylation of wood with acetic anhydride reduces the wood-moisture interaction, improves the dimensional stability and resistance against biodegradation. However, the adhesive bonding is affected by the modification, which is crucial to manufacture engineered wood products, such as laminated veneer lumber (LVL). In this study we report the bonding of 8-layered acetylated beech (Fagus sylvatica L.) LVL boards to 2-layered LVL beams. The beams were glued together at room temperature adding three common load-bearing construction adhesives: melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF), and one-component polyurethane (PUR). The bonding performance was tested by assessing its dry and wet tensile shear strength(TSS) and wood failure percentage(WF). Also evaluated were the material's density and moisture content(MC). The surface was characterized prior to bonding by its pH, roughness, and contact angle(CA). The adhesive penetration was observed by fluorescence microscopy. Aside from MUF, applying PRF and PUR adhesives achieved good bonding performance on acetylated LVL and references. Acetylated LVL displayed a more hydrophobic behaviour, a higher pH, a somewhat smoother surface, and an increased density.

Comparative Study of Carbon Nanotubes and Lignosulfonate as Polyvinyl Acetate (PVAc) Wood Adhesive-Reinforcing Agents

This study aimed to reinforce a polyvinyl acetate-D3 (PVAc-D3) adhesive to improve its mechanical and thermal properties. The goal was to reach a polyvinyl acetate-D4 (PVAc-D4) adhesive performance that could make PVAc-D3 more attractive and add value to wood products. PVAc-D3 was modified by adding 0.05% and 0.5% (wt.) of multi-walled carbon nanotube particles (MWCNTs) as well as 0.5% and 2.5% (wt.) of lignosulfonate (LIGNO) particles. Adhesive blends were compared to neat PVAc-D3 and PVAc-D4, evaluating their physical–chemical properties. Also, they were analyzed using Fourier transform infrared spectroscopy (FT-IR) and mechanical dynamic analysis (DMA) with a storage module (E′). The blends were used to fabricate laminated wood pieces, pressed at 60 and 120 min (min), to be tested at shear strength under dry, elevated temperature and vacuum-pressure conditions. Delamination and adhesive penetration were determined by microscopy. Incorporating fillers into PVAc resulted in a decrease in viscosity. FT-IR evidenced that the PVAc-D4 adhesive had a bigger cross-linked degree than the other adhesive samples. The DMA showed that LIGNO and MWCNT fillers help increase E′ at the bond line, reaching a higher stiffness level than neat PVAc-D3. In dry conditions, specimens glued with D3-LIGNO 0.5% at 120 min reached shear strengths that were 100%, 28%, and 3% higher than the standard requirement, PVAc-D4, and neat PVAc-D3, respectively. Also, those glued with D3-MWNTC 0.05% reached shear strengths that were 91%, 21%, and 3% higher than the standard requirement, D4, and neat D3, respectively. Only PVAc-D4 reached the standard requirement for elevated temperature and vacuum-pressure conditions. Delamination of ≤5% (standard requirement) was achieved by wood specimens glued with neat PVAc-D3, D3-MWNTC 0.5%, D3-LIGNO 0.5%, and PVAc D4 adhesive samples. In this study, it was found specific ranges of average penetration (AP) to ensure a glue line good quality. To conclude, LIGNO and MWCNT particles improved the PVAc-D3 adhesive’s performance in dry conditions, but they were not very relevant to the D3 adhesive’s behavior. At high temperatures, the LIGNO filler worked very well as a thermic stabilizer compared to the MWCNT filler. The solubility of the reinforcing agent can affect an adhesive’s blend quality and its cohesion properties. An adequate penetration depth procures a good quality bond between an adhesive and substrate with less possibilities of delamination. An extensive pressing time may cause a weak interphase and poor mechanical properties in an adhesive bond in the presence of humidity.

Mechanisms of two types of flattening treatments on the bonding characteristics of bamboo and the effect of laminate design on flexural properties

Bamboo has potential for building structures, but the mechanism of flattened bamboo boards (FBs) is unclear, which is not conducive to FBs to manufacture large-size structure materials. This paper compares the bonding of FBs and bamboo strips, and studies the bending of FBs laminated in different ways. Results show that FBs produces cracks favorable for adhesive penetration. The assembly method affects the bonding performance of notched FBs. The residual stresses influence the form of bending damage of laminated FB. FBs exhibited fine bonding strength (2.9–3.4 MPa) and excellent flexural strength (up to 141.2 MPa) after lamination.

Transforming interface properties of wood laminate composites functionalized by adhesive penetration

Quantitative analysis of interface mechanical properties of wood laminate composites has been an urgent task of the interface mechanics, however, which is hindered by the lack of knowledge of the correlation between physiochemical structure and micromechanics of the whole wood bonding interphase. This work aimed to evaluate the influence of adhesive distribution with different variables (i.e., adhesive types, grain directions, and cells from the glue line) on the transforming interface properties. The results showed that the physiochemical structure and micromechanics performance were significantly affected by adhesive types, grain directions, or wood cells with the interphase microstructure of earlywood laminates being more sensitive to adhesive penetration than that of latewood laminates. The Phenol-formaldehyde (PF)-laminated interphase possessed a more complicated resin behavior and distribution, and microstructure compared to the one component polyurethane (1C-PUR)-laminated interphase. The distribution of resins near the glue line could recover and enhance the loss of the Er caused by the pressing and machining process. Compared with the control cells (C1, C2), the improved range of Er and H are 9.2%–41.2% and 6.7%–22.2% for the PF-laminated interphase, respectively, and 1.7%–27.6% and 2.1%–8.5% for the 1C-PUR-laminated interphase, respectively. This improvement was mainly attributed to chemical fixing and physical filling into nanopores and physical supporting within cell walls, which could avoid the stress concentration to a different extent and protect the cell walls from the compressive deformation. The initial cracks probably resulting from the machining and/or shear slipping during the pressing process, could incur the global failure of wood laminates interphase.

Investigation of the microstructure, chemical structure, and bonding interfacial properties of thermal-treated bamboo

Thermal-treated (TMT) bamboo and TMT bamboo-based panel have a great potential application in the outdoor constructions. In this paper, the effects of the changes in terms of microstructure, chemical structure, and surface wettability of bamboo after TM on the adhesive penetration and shear strain distribution of glued TMT bamboo were investigated with scanning electron microscopy (SEM), Fourier transform infrared (FTIR), fluorescent microscopy, and digital image correlation (DIC). Results indicated that the partial pits on cell walls became smaller due to the shrinkage of bamboo cells and partial pits were covered by the coagulation of lignin after thermal treatment (TM). Both the changes in surface morphology, microstructure and the degradation of hemicelluloses decreased the permeability of phenol-formaldehyde adhesive on bamboo surface. The average penetration and effective penetration depth of phenol-formaldehyde adhesive on the TMT bamboo which was treated at 190 °C for 3 h decreased by about 24% and 37%, respectively, as compared to the control. The failure mode of glued TMT bamboo was mainly manifested as interlayer slipping and the strain accumulated in the bonding interphase of glued TMT bamboo during lap-shear test, which indicated that TM negatively affected the bonding performance of bamboo and phenol formaldehyde (PF) adhesive. As expected, the bonding strength of glued TMT bamboo at 190 °C for 3 h decreased by 63% in comparison with the control.

Lignocelluloses-Based Furan-Acetone Adducts as Wood Adhesives for Plywood Production.

Plywood is made of wood veneers that are bonded with adhesives such as urea-formaldehyde, phenol-formaldehyde and melamine-formaldehyde resins. The plywood made from formaldehyde-based adhesives not only releases formaldehyde but also relies on fossil resources. In this article, we synthesized furan-acetone adducts from lignocellulosic biomass in one pot. The furan-acetone adducts could be directly used as adhesives with the addition of phosphoric acid as a curing catalyst. Particularly, with the addition of 5 wt% diphenylmethane diisocyanate (MDI) as a crosslinking agent, both the wet and dry bonding strength of the plywood prepared from the adhesives could meet the minimum requirement of 0.7 MPa (Chinese National Standard GB/T 9846-2015). The possible adhesion mechanism is that the penetration of furan-acetone adhesives into vessels and cell lumens followed by crosslinking during hot-pressing forms mechanical interlocking at the interface of wood veneers, which provides the main bonding strength of plywood. The findings presented here could provide a new way for the efficient preparation of aldehyde-free green wood adhesives and the value-added utilization of woody biomass.

Evaluation of the bonding effectiveness of a universal adhesive to the plasma‐activated dentin surface

This study aimed to evaluate the effect of non-thermal atmospheric pressure plasma on the bond strength of a universal adhesive used in etch-and-rinse mode. Dentin surfaces were etched with phosphoric acid and samples were divided into groups exposed to either dry bonding, plasma-dried bonding, plasma-dried and rewetted bonding, or wet bonding (n = 10). Dentin surfaces of the plasma-dried specimens were treated with a plasma jet before the adhesive procedure. After application, composite blocks were built, and specimens were subjected to micro-tensile bond strength testing after 24h and after 10,000 thermal cycles. The hybrid layer formation was evaluated by micro-Raman spectral analysis; the resin-dentin interface was analyzed by scanning electron microscopy. One-way ANOVA and Tukey's post hoc multiple comparison tests were used to statistically analyze the data. The bond strength values of the plasma-dried bonding groups were statistically higher than the non-plasma-treated groups both before and after aging. After the thermal cycles, bond strength values decreased significantly only in the wet bonding group. Micro-Raman spectral analysis revealed that plasma-drying increased adhesive penetration, especially hydrophobic monomer infiltration. This may increase the mechanical properties and durability of the resin-dentin interface, provide long-term stability, and improve the polymerization rate of the adhesive layer.

Influence of varying dry air temperatures on postoperative sensitivity, penetration depth, and push-out bond strength of an ethanol/water-based adhesive: An in vivo double-blind clinical trial and in vitro analysis.

Incomplete monomer infiltration into the etched dentin causes postoperative sensitivity (POS) with total-etch adhesives. Increasing the temperature of the air to dry the adhesive has shown to improve its infiltration into the dentin. The aim of this research is to evaluate the effectiveness of dry air temperatures of 15°C ± 5°C and 50°C ± 5°C on the POS, depth of penetration, and bond strength of an ethanol/water-based etch-and-rinse (ER) adhesive under in vivo and in vitro conditions. Forty-four premolars from 11 patients scheduled for orthodontic extraction were allocated into cold air (Group 1) and warm air (Group 2) groups using a split-mouth design. A 2 mm × 2 mm × 2 mm cavity was prepared on the middle third of the buccal surface of the teeth, acid etched, and two coats of an ethanol/water-based adhesive resin mixed with 0.1% rhodamine B was applied for 10 s. A dental air gun customized to deliver warm and cold air was used to dry the adhesive prior to its light polymerization. The cavities were restored with resin composite incrementally. POS was assessed using visual analog scale at 24 and 72 h using cold test. The teeth were atraumatically extracted and analyzed for depth of adhesive penetration using confocal laser scanning microscope (n = 11) and push-out bond strength (n = 11). The data were analyzed using sample t-test and Wilcoxon signed-rank test (P < 0.05). A significantly lower POS and greater adhesive penetration into the dentin was observed in the warm air group compared to cold air (P < 0.05). No significant difference could be elicited between the push-out bond strength of both the groups (P > 0.05). Warm air alleviated POS and improved the penetration of an ethanol/water-based ER adhesive into the dentin.

Review paper: properties of low molecular weight phenol formaldehyde – treated bamboo composite

Impregnation of bamboo in phenol formaldehyde (PF) solution is one of the promising solutions to overcome the drawback of the material. The use of low molecular weight PF resin (LMW PF) in the production of bamboo composite materials not only improves the dimensional stability but also increases the mechanical strength of the material. The bonding interface between bamboo elements and adhesives is presumed to be significantly influenced by the degree of adhesive penetration into the porous network of interconnected cells of bamboo surfaces. The permeation of PF resins in bamboo is closely related to their molecular weight. LMW PF resin will overpenetrate and lead to an undesirable starved bondline while high-MW PF resins only remain in the bondline and it is difficult to form mechanical interlocking. This paper discusses the research results on the bonding quality of bamboo strips when impregnated in LMW PF solution with different ratios and different pressing technology parameters; at the same time, physical and mechanical properties of bamboo composite materials treated with PF PTLT such as: water absorption resistance, dimensional stability, bonding strength, modulus of rupture (MOR), modulus of elasticity (MOE) are also significantly improved. This is a scientific basis that can serve as a premise for the research on technology to produce composite materials from bamboo and LMW PF in Vietnam.

Теоретическое и экспериментальное обоснование характера взаимодействия модифицированных связующих с древесиной

There are numerous methods for analyzing surface phenomena when bonding wood materials, mutual arrangement of pores in the wood substrate, and depth of liquid adhesive penetration into wood. Electron microscopic methods such as atomic force and scanning tunneling microscopy are used along with optical methods. They allow evaluating the influence of factors describing the interaction between the liquid adhesive molecules and the porous wood surface. Phenol formaldehyde resin modified with pectol and urea formaldehyde resin modified with lignosulfonates were used for substantiation of the interaction mechanism between modified adhesives and wood. Electron microscopy was used to study the depth of adhesive penetration into veneer. The plywood was produced using modified urea and phenol formaldehyde adhesives. After conditioning, samples with a thickness of 0.025 mm were cut out and examined with a scanning electron microscope. The article shows that the interaction between liquid phenol formaldehyde adhesive modified with pectol and wood results in a sequential increase in the molecular weight of the substances and, consequently, in the penetration degree (depth). The studied wood species (birch, pine and larch) and modified thermosetting urea and phenol formaldehyde adhesives are polar materials (adhesive interacts with wood molecules with the formation of intermolecular bonds, including hydrogen bonds). The molecular weight growth and the freely joined nature of the main chain (liquid modified adhesive macromolecules), which contains a large number of polar functional groups (adhesive and wood), promote intermolecular association. The formation of an adhesive bond between urea formaldehyde adhesive modified with lignosulfonates and wood occurs due to chemical interaction between hydroxyl groups of cellulose macromolecules and methoxyl groups of urea resin with the formation of esters (hydrogen atoms of hydroxyl groups OH are substituted with hydrocarbon radicals R). The formation of a bond between the adhesive and the wood surface is the result of molecular interaction forces at the liquid adhesive – wood interface, when the distance between molecules of the same polarity (adhesive and wood) is less than 0.5 nm. Then, adsorption equilibrium sets in. For citation: Rusakov D.S., Varankina G.S., Chubinsky A.N. Theoretical and Experimental Substantiation of the Nature of Interaction between Modified Binders and Wood. Lesnoy Zhurnal = Russian Forestry Journal, 2022, no. 6, pp. 153–163. (In Russ.). https://doi.org/10.37482/0536-1036-2022-6-153-163

Effects of glue spreading rate and veneer density on sugi (Cryptomeria japonica) plywood adhesive penetration

An optimum adhesive penetration is needed to provide satisfactory bonding strength at the veneer-veneer interface. The effect of veneer density and glue spreading rate on the phenol formaldehyde adhesive penetration plot profile was determined. An X-ray apparatus was used to visualize the adhesive penetration of the plywood. The heartwood and sapwood veneer of Cryptomeria japonica with low, medium, and high veneer densities were made into plywood. The glue spreading rate was applied from 75 g/m2 to 225 g/m2 for the heartwood plywood and up to 300 g/m2 for the sapwood plywood (plus 75 g/m2 at every level of glue spreading rate). An X-ray apparatus with a low tube voltage successfully visualized the adhesive penetration plot profile. Based on the half-width calculation, the adhesive penetration depth ranged from 0,3 - 0,9 mm. The mean half-width was 0,5 mm. The adhesive concentration increased with increasing glue spreading rate. In contrast, it also showed that using different veneer densities and increasing glue spreading rates does not affect the half-width value as the adhesive penetrates deeper.

Microtensile bond strength of resin composite to dentin using different adhesive systems and directions of electric current

Thisstudy aimed to evaluate the effect of the electric current direction application on the resin composite-dentin bond strength using three adhesive systems. Human molar teeth were distributed according to the adhesive system (two-step self-etch - Clearfil SE Bond, Kuraray [CSE]; one-step self-etch - Single Bond Universal, 3M ESPE [SBU]; and two-step etch-and-rinse - Adper Single Bond 2, 3M ESPE [SB2]), electric current direction (without electric current - control, direct and reverse electric currents - 35µA), and storage time (24h - immediate and 6 months). Resin composite blocks (Filtek Z350XT, 3M ESPE) were bonded to dentin. The teeth/resin composites specimens were stored in distilled water at 37ºC for 24 hours and 6 months for the microtensile bond strength (µTBS) test (n = 10; ~12 sticks for each tooth). Failure patterns were analyzed on a stereomicroscope and classified as cohesive-dentin, cohesive-resin, adhesive or mixed. Adhesive penetration into dentin and hybrid layer formation were evaluated in a scanning electron microscope (n = 6). Data were submitted to a three-way ANOVA followed by Tukey's post hoc test (α = 0.05). There are no differences in µTBS when the adhesive systems were applied under direct and reverse electric currents, but both electric currents increased the µTBS for all adhesive systems. SBU showed the lowest µTBS values for control groups in both storage times and direct electric current in 6 months of storage. The adhesive failure pattern was more frequently observed in all groups. The electric current formed long resin tags for all adhesive systems. Storage for 6 months did not significantly decrease µTBS values. Both directions of electric current (positive and negative charges) at 35µA can increase the µTBS of the adhesive systems tested to dentin.

Comparison of methods to characterize the penetration of hot melt adhesive into paper

Abstract In the use of hot melt adhesives in the production of paper-based packaging, the controlled penetration of the adhesive is important to obtain rapid setting rates, good bond strength, and the efficient use of adhesive. Measuring adhesive penetration depth has been limited to cross-sectional images, but quantifying the depth of penetration is difficult from these images. No quantitative method is well established in the literature. Four different techniques are compared to quantitatively measure adhesive penetration depth. Two methods involve separating the paperboard from the adhesive layer. Two other methods use of silicone oil penetration and mercury porosimetry to measure the decrease of pore volume after the adhesive is applied. These methods are compared with samples generated for various parameters. Experiments were conducted using a typical hot melt glue on uncoated and coated paperboard sample. Cross-sectional images from Scanning Electron Microscopy (SEM) confirm the penetration of some samples. The accuracy and repeatability of these methods were compared. Because of some issues with trying to repeatably remove the paper layer for the weight and thickness methods, and the time and cost of the mercury porosimeter method, the silicone oil method is a nice method to characterize the adhesive penetration depth.