Effects of surface modification by oxygen plasma on peel adhesion of pressure‐sensitive adhesive tapes

Surfaces of poly(isobutylene) (PIB) and poly(butylacrylate) (PBA) pressure‐sensitive adhesive tapes were treated by oxygen plasma, and effects of surface modification on their adhesive behavior were investigated from the viewpoint of peel adhesion. The peel adhesion between PIB and PBA pressure‐sensitive adhesive tapes and stainless steel has been improved by the oxygen plasma treatment. The surface‐modification layer was formed on PIB and PBA pressure‐sensitive adhesive surfaces by the oxygen plasma treatment. The oxygen plasma treatment led to the formation of functional groups such as various carbonyl groups. The treated layer was restricted to the topmost layer (50–300 nm) from the surface. The GPC curves of the oxygen plasma‐treated PBA adhesive were less changed. Although a degradation product of 1–3% was formed in the process of the oxygen plasma treatment of the PIB adhesive. There are differences in the oxygen plasma treatment between the PIB and PBA adhesives. A close relationship was recognized between the amount of carbonyl groups and peel adhesion. Therefore, the carbonyl groups formed on the PIB and PBA adhesive surfaces may be a main factor to improve the peel adhesion between the PIB and PBA adhesive and stainless steel. The peel adhesion could be controlled by changing the carbonyl concentration on the PIB and PBA adhesive surfaces. We speculate that the carbonyl groups on the PIB and PBA adhesive surface might provide an interaction with a stainless steel surface. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1392–1401, 2000     

Pressure-sensitive adhesion in the blends of poly(N-vinyl pyrrolidone) and poly(ethylene glycol) of disparate chain lengths

Adhesive behavior in blends of high molecular weight poly(N-vinyl pyrrolidone (PVP) with a short-chain, liquid poly(ethylene glycol) (PEG) has been studied using a 180° peel test as a function of PVP-PEG composition and water vapor sorption. Hydrophilic pressure-sensitive adhesives are keenly needed in various fields of contemporary industry and medicine, and the PVP-PEG blends, pressure-sensitive adhesion has been established to appear within a narrow composition range, in the vicinity of 36 wt% PEG, and it is affected by the blend hydration. Both plasticizers, PEG and water, behave as tackifiers (enhancers of adhesion) in the blends with glassy PVP. However, PEP alone is shown to account for the occurrence of adhesion, and the tackifying effect of PEG is appreciably stronger than that of sorbed water. Blend hydration enhances adhesion for the systems that exhibit an apparently adhesive type of debonding from a standard substrate (at PEG content less than 36 wt%), but the same amounts of sorbed water are also capable of depressign adhesion in the PEG-overloaded blends, where a cohesive mechanism of adhesive joint failure is typical. The PVP-PEG blend with 36% PEG couples both the adhesive and cohesive mechanisms of bond rupture (i.e., the fibrillation of adhesive polymer under debonding force and predominantly adhesive locus of failure). Blend hydration effect on adhesion has been found to be reversible. The micromechanics of adhesive joint failure for PVP-PEG hydrogels involves the fibrillation of adhesive polymer, followed by fibrils stretching and fracturing as their elongation attains 1000-1500%. Peel force to rupture the adhesive bond of PVP-PEG blends increases with increasing size of the tensile deformation zone, increasing cohesive strength of the material, and increasing tensile compliance of the material, obeying the well-known Kaelble equation, derived originally for conventional rubbery pressure-sensitive adhesives. The major deformation mode upon peeling the PVP-PEG adhesive from a standard substrate is extension, and direct correlations have been established between the composition behaviour of peel strength and that of the total work of viscoelastic strain to break the PVP-PEG films under uniaxial drawing. As a result of strong interfacial interaction with the PET backing film, the PVP-PEG adhesive has a heterogeneous two-layer structure, where different layers demonstrate dissimilar adhesive characteristics.     

PRESSURE-SENSITIVE ADHESION IN THE BLENDS OF POLY(N-VINYL PYRROLIDONE) AND POLY(ETHYLENE GLYCOL) OF DISPARATE CHAIN LENGTHS

Adhesive behavior in blends of high molecular weight poly(N-vinyl pyrrolidone (PVP) with a short-chain, liquid poly(ethylene glycol) (PEG) has been studied using a 180° peel test as a function of PVP-PEG composition and water vapor sorption. Hydrophilic pressure-sensitive adhesives are keenly needed in various fields of contemporary industry and medicine, and the PVP-PEG blends, pressure-sensitive adhesion has been established to appear within a narrow composition range, in the vicinity of 36 wt% PEG, and it is affected by the blend hydration. Both plasticizers, PEG and water, behave as tackifiers (enhancers of adhesion) in the blends with glassy PVP. However, PEP alone is shown to account for the occurrence of adhesion, and the tackifying effect of PEG is appreciably stronger than that of sorbed water. Blend hydration enhances adhesion for the systems that exhibit an apparently adhesive type of debonding from a standard substrate (at PEG content less than 36 wt%), but the same amounts of sorbed water are also capable of depressign adhesion in the PEG-overloaded blends, where a cohesive mechanism of adhesive joint failure is typical. The PVP-PEG blend with 36% PEG couples both the adhesive and cohesive mechanisms of bond rupture (i.e., the fibrillation of adhesive polymer under debonding force and predominantly adhesive locus of failure). Blend hydration effect on adhesion has been found to be reversible. The micromechanics of adhesive joint failure for PVP-PEG hydrogels involves the fibrillation of adhesive polymer, followed by fibrils stretching and fracturing as their elongation attains 1000-1500%. Peel force to rupture the adhesive bond of PVP-PEG blends increases with increasing size of the tensile deformation zone, increasing cohesive strength of the material, and increasing tensile compliance of the material, obeying the well-known Kaelble equation, derived originally for conventional rubbery pressure-sensitive adhesives. The major deformation mode upon peeling the PVP-PEG adhesive from a standard substrate is extension, and direct correlations have been established between the composition behaviour of peel strength and that of the total work of viscoelastic strain to break the PVP-PEG films under uniaxial drawing. As a result of strong interfacial interaction with the PET backing film, the PVP-PEG adhesive has a heterogeneous two-layer structure, where different layers demonstrate dissimilar adhesive characteristics.     

Surface modification of aromatic polyamide film by plasma graft copolymerization of glycidylmethacrylate for epoxy adhesion

The graft copolymerization of glycidyl methacrylate, GMA, onto poly(p-phenylene terephthalamide), PPTA, film surfaces was investigated to improve adhesion between the PPTA film and epoxy adhesives. The graft copolymerization of GMA was carried out in two steps; a peroxide formation by a combination of argon plasma irradiation and air exposure, and the polymerization reactions of GMA. XPS analyses showed the graft copolymerization of GMA on the PPTA film surface, and only 31–40% of the PPTA film surface was covered with the GMA graft polymers. The graft copolymerization of GMA improved the adhesion between the PPTA film and the epoxy adhesive. The adhesion strength was improved 2.7 times by the graft copolymerization. The failure from the adhesive joint occurred in the epoxy adhesive layer rather than at the interface between the PPTA film and the epoxy adhesive layer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1179–1185, 1998     

Relaxation Properties of Pressure-sensitive Adhesives upon Withdrawal of Bonding Pressure

Relaxation properties of pressure-sensitive adhesives (PSA) have been studied with the squeeze-recoil tester used in the regime of parallel-plate dilatometer under conditions imitating the removal of compressive force in the course of adhesive bond formation. The relaxation properties of PSAs are compared with their adhesive behavior measured using the 180-Deg Peel Test. Two classes of PSAs are considered: 1) conventional rubbery adhesives based on the mixtures of styrene-isoprene-styrene (SIS) block copolymer with a tackifier resin and a plasticizer, and butyl rubber plasticized with low-molecular-weight polyisobutylene, and 2) hydrophilic PSAs composed of the blends of high-molecular-weight poly(N-vinyl pyrrolidone) (PVP) with oligomeric polyethylene glycol (PEG). By comparing the adhesive and relaxation behaviors of different PSAs, the relaxation criteria for pressure-sensitive adhesion have been stated. Relaxation behavior of the examined PSAs demonstrates two values of retardation time: the shorter retardation time of 10–70?sec and the longer time of 300–660?sec. These times can be associated, respectively, with small- and large-scale mechanisms of strain recovery. By comparing the relaxation and adhesive properties of PVP-PEG blend (which involves the formation of a hydrogen-bonded network through both terminal hydroxyl groups in PEG short chains) with the properties of covalently crosslinked copolymers of vinyl pyrrolidone (VP) with PEG-diacrylate and comb-like VP copolymers with PEG-monomethacrylate, the contributions of covalent crosslinking and H-bonding network have been characterized.     

Effect of model fillers on the adhesive strength of pressure-sensitive tapes

—The effect of various model fillers, namely glass beads, 'Spheriglass', and PTFE powder, on the adhesive strength of natural rubber (NR) and poly(n-butyl acrylate) (PBA) tapes has been investigated. Glass fillers treated with alkyl chlorosilane were also used. The adhesive strength was measured over a range of rates and temperatures, and corrections for the thickness of the adhesive and volume fraction of the polymer were introduced into the rate term. It was observed that the adhesive strength of PBA tapes filled with 20% PTFE is comparable to that of the control sample without filler. The strength measured over a range of strain rates increased for both untreated and treated Spheriglass-filled adhesives. Filled NR adhesives showed an enhanced strength only at very high strain rates. With 40% PTFE, this increase was quite apparent. The mechanism of improvement of the strength of adhesion due to the incorporation of a filler is explained. The addition of a filler introduces an additional mechanism of energy dissipation during deformation of the adhesive and a higher energy will be expended due to debonding of the filler and hysteresis.     

Effect of Temperature on Probe Tack Adhesion: Extension of the Dahlquist Criterion of Tack

At a molecular level adhesive joint strength of pressure-sensitive adhesives (PSAs) is governed by the ratio between two generally conflicting factors: high energy of cohesive molecular interactions and large free volume. Increase in temperature leads to domination of the free volume contribution over the cohesive strength, affecting mechanisms of the debonding process, examined with a probe tack test. Linear viscoelastic properties and probe tack adhesion of five types of PSAs have been studied: polyisobutylene (PIB); acrylic, styrene-isoprene-styrene (SIS) triblock copolymer; hydrogen-bonded complex of high molecular weight poly(N-vinyl pyrrolidone), PVP; with oligomeric poly(ethylene glycol), PEG; and plasticized polybase—polyacid polyelectrolyte complex (PEC). The transition from solid-like mechanism of debonding to ductile type of adhesive bond failure with fibrillation of adhesive layer has been established to occur for all examined PSAs under temperature increase within the range from ?20 to 80°C. The Dahlquist criterion of tack, which defines the value of the storage modulus, G′, below 0.1 MPa, featured for all the PSAs demonstrating maximum work of debonding, has been found to have a universal character and holds at corresponding temperatures for all the PSAs examined, including both typical and innovative adhesives. In addition to this adhesion predictor we have also established that for all the PSAs the transition from a solid–like debonding mechanism to a ductile type of debonding is observed in the range of G′ = 0.09–0.34 MPa. The value of the dissipation factor, tan δ, is also included in the analysis of correlation between linear viscoelasticity and probe tack behavior.     

Adhesion Properties of Acrylic Copolymers Modified with Si-Containing Copolymer

We made clear the cause of the increase in peel strength of pressure sensitive (PS) adhesives as a function of contact time, and investigated how to modify PS adhesives to maintain a low and constant peel strength for a long time. It was found that polar groups in the adhesive orient to the interface between the adhesive and the (stainless steel) metal substrate (SUS 304) so as to minimize interfacial free energy during adhesion, and the orientation increased affinity between the adhesive and the metal material and increased the peel strength as a result. The use of modifier which contained both P(MMA-co-SiMA) and PDMS showed an excellent modification effect, although modification with only PDMS or P(MMA-co-SiMA) was not sufficient. It was suggested that PDMS which migrated to the surface was extended uniformly over the surface by PDMS segments of P(MMA-co-SiMA) and that the enriched layer of PDMS on the adhesive surface worked as a barrier to prevent the orientation of polar groups in bulk. Therefore, low and constant peel strength could be achieved.     

Adhesion Properties of Acrylic Copolymers Modified with Si-Containing Copolymer

We made clear the cause of the increase in peel strength of pressure sensitive (PS) adhesives as a function of contact time, and investigated how to modify PS adhesives to maintain a low and constant peel strength for a long time. It was found that polar groups in the adhesive orient to the interface between the adhesive and the (stainless steel) metal substrate (SUS 304) so as to minimize interfacial free energy during adhesion, and the orientation increased affinity between the adhesive and the metal material and increased the peel strength as a result. The use of modifier which contained both P(MMA-co-SiMA) and PDMS showed an excellent modification effect, although modification with only PDMS or P(MMA-co-SiMA) was not sufficient. It was suggested that PDMS which migrated to the surface was extended uniformly over the surface by PDMS segments of P(MMA-co-SiMA) and that the enriched layer of PDMS on the adhesive surface worked as a barrier to prevent the orientation of polar groups in bulk. Therefore, low and constant peel strength could be achieved.     

Variation in adhesion properties and film morphologies of waterborne pressure-sensitive adhesives containing an acid-rich diblock copolymer additive

One challenge for waterborne pressure-sensitive adhesives (PSA)s is the typical tradeoff between cohesion and adhesion. Others have shown that waterborne PSA films with thin, hard boundaries formed from short poly(acid) segments surrounding soft particles can have simultaneous improvements in adhesion and cohesion. To study this approach in commercial-type acrylic waterborne PSAs, a diblock copolymer (BCP) composed of poly(acrylic acid)-block-(n-butyl acrylate) (PAA-b-PBA) is added at 1–5 wt% to PSAs composed of 100% PBA (PSA (0% acid)) or 99% BA/1% AA (PSA (1% acid)). Films of these blends prepared using industrially relevant conditions reveal complex nanodomains in atomic force microscopy (AFM) images. PSA performance tests showed that 1–2 wt% BCP additive nearly tripled adhesion to stainless steel for PSA (0% acid) while improving cohesion. Nonetheless, AFM images of PSA (0% acid) with 1–2 wt% BCP display ill-defined morphologies, with clear percolated structures apparent primarily in films with 5% BCP. This indicates that film morphologies which enhance adhesion may not correlate with AFM features. Moreover, the balance of adhesion and cohesion of PSA (1% acid) without BCP exceeds that of any of the BCP blends, demonstrating the challenge of using designed microstructures to improve upon conventional PSAs containing copolymerized acids.     

Preparation and properties of polyisobutene/organic montmorillonite hot melt pressure-sensitive adhesive (HMPSA)

To enhance the interfacial adhesion between Na-montmorillonite (Na-MMT) and polyisobutene (PIB) matrix, it is necessary to modify Na-MMT in organic way. Organic montmorillonite (OMMT) was successfully modified by Na-MMT with cetyltrimethyl ammonium bromide (CTAB) intercalation reagent. The X-ray diffraction (XRD) result showed that the d-spacing of Na-MMT was increased from 1.424 to 2.480 nm after organic modification. PIB/OMMT hot melt pressure-sensitive adhesive (HMPSA) samples were prepared by melt-intercalation process. The amount of OMMT was optimized according to the system stability and adhesion performance. The effects of OMMT content on rheological, adhesion and thermal properties of PIB HMPSA were investigated. Adhesion performance and system stability of PIB HMPSA were greatly improved by adding moderate amounts of OMMT. In addition, the sample containing 1 wt% OMMT exhibited optimal adhesion property and excellent stability, meanwhile, its 180° peel strength was 1.19 times greater than pristine sample.     

Stress Relaxation During Bond Formation and Adhesion of Pressure-Sensitive Adhesives

Relaxation properties and adhesion of pressure-sensitive adhesives (PSAs) have been studied with the Probe Tack method under the conditions corresponding to the adhesive bond formation. Typical representatives of various PSA classes are examined: adhesives based on the styrene-isoprene-styrene (SIS) block copolymer, polyisobutylene of two molecular weights, acrylic and silicone PSAs. By comparison of the adhesive and relaxation behaviors of different PSAs it has been established that the PSA relaxation contributes appreciably to the strength of the adhesive bond and underlies the impact of contact time on adhesion. Direct correlation has been established between the compressive stress relaxation in the course of bond formation and the mechanism of debonding. All the examined PSAs can be classified into two groups: 1) the fluid-like PSAs that are capable of relaxing fully under compression (PIB, silicone adhesives) and 2) the PSAs, which reveal a residual unrelaxed stress. Physically crosslinked SIS and chemically crosslinked acrylic adhesives exemplify the PSAs of the second group. The occurrence of two peaks on the debonding stress–strain curves is typical of the PSAs of the second group. High adhesive strength requires the contribution of the longer relaxation times that vary for different PSAs in the range from 150 to 800 s. Minimum values of the longer relaxation times are featured for fluid adhesives, whereas the maximum values are found for crosslinked, network, and entangled adhesives. The adhesive strength achieves its maximum when the slow relaxation processes become dominating. Relative contributions of viscous and elastic deformations to relaxation properties of PSAs are assessed in terms of the Deborah number.     

Stress Relaxation During Bond Formation and Adhesion of Pressure-Sensitive Adhesives

Relaxation properties and adhesion of pressure-sensitive adhesives (PSAs) have been studied with the Probe Tack method under the conditions corresponding to the adhesive bond formation. Typical representatives of various PSA classes are examined: adhesives based on the styrene-isoprene-styrene (SIS) block copolymer, polyisobutylene of two molecular weights, acrylic and silicone PSAs. By comparison of the adhesive and relaxation behaviors of different PSAs it has been established that the PSA relaxation contributes appreciably to the strength of the adhesive bond and underlies the impact of contact time on adhesion. Direct correlation has been established between the compressive stress relaxation in the course of bond formation and the mechanism of debonding. All the examined PSAs can be classified into two groups: 1) the fluid-like PSAs that are capable of relaxing fully under compression (PIB, silicone adhesives) and 2) the PSAs, which reveal a residual unrelaxed stress. Physically crosslinked SIS and chemically crosslinked acrylic adhesives exemplify the PSAs of the second group. The occurrence of two peaks on the debonding stress-strain curves is typical of the PSAs of the second group. High adhesive strength requires the contribution of the longer relaxation times that vary for different PSAs in the range from 150 to 800 s. Minimum values of the longer relaxation times are featured for fluid adhesives, whereas the maximum values are found for crosslinked, network, and entangled adhesives. The adhesive strength achieves its maximum when the slow relaxation processes become dominating. Relative contributions of viscous and elastic deformations to relaxation properties of PSAs are assessed in terms of the Deborah number.     

Adhesive joints in glass structures: effects of various materials in the connection,thickness of the adhesive layer,and ageing

This paper reports on an investigation of glued joints in glass load-bearing structures, with reference to the effect of various substrates (glass, steel, stainless steel, aluminium) and their surface treatment (sandblasting for the glass surface) on the adhesion of selected adhesives. The thickness of the adhesive layer and the effect of artificial ageing – a simulation of 5 years of ageing in outdoor central-European conditions – are also discussed. Tensile and shear tests were carried out on three series of specimens with various adhesives and substrates – two series for tensile and shear tests, and one series for shear tests on specimens exposed to ageing. Our results show that sandblasting the glass surface can improve the adhesion, and thus the strength values, of an adhesive joint in cases where, with a smooth glass surface, cohesive failure is not reached. The thickness of the adhesive layer had a significant effect for a semi-rigid acrylate adhesive, where the joint achieved higher strength values with less thickness of the glue. The effect of ageing varied according to the adhesive. The most visible changes were observed for a two-component acrylate adhesive and for methacrylate UV-adhesives. One of the selected glues was marked as unsuitable for load-bearing connections due to significant worsening of its mechanical properties after ageing.     

Behavior of Pressure-Sensitive Adhesives Filled with Metallized Inorganic Particles

The electrically conductive pressure-sensitive composite adhesives based on acrylic polymer and silver-coated inorganic particles have been investigated in this article. The electrical conductivity of the pressure-sensitive adhesives containing silver coated spherical inorganic particles is lower at the same concentration of the filler in comparison with silver coated inorganic fibers, the strength of adhesive joint to aluminum being higher in the case of the pressure-sensitive adhesive containing silver-coated inorganic fibers. After the thermal treatment the strength of adhesive joint to aluminum of electrically conductive pressure sensitive adhesives increases significantly. The suitable concentration proposition of the silver-coated inorganic filler in the pressure-sensitive adhesive requires a compromise solution of the problem taking into account the ultimate adhesive and electrical properties of the investigated pressure-sensitive adhesives composites.     

Studies on tack of pressure-sensitive adhesive tapes: On the relationship between pressure-sensitive adhesion and surface energy of adherends

The relationship between wetting and pressure-sensitive adhesion was studied using an adhesive composed of poly(butyl acrylate) and various adherends of different surface tension. The amount of adhesive deposit was determined quantitatively by tracer technique although the unbonding process was apparently observed as interface failure. The adhesive force and amount of deposit were both dependent on the critical surface tension of the adherends. Maximum tack value and contamination were observed with adherends whose critical surface tension was close to that but a little higher than that of the adhesive. The adhesive force obtained was lower than cohesive strength of adhesive. From this evidence, a mechanism for pressure-sensitive adhesion was discussed: the bond breaks in the addesive mass around the very minute spots where interaction is at work between adhesive and adherend. Inasmuch as the density of the minute spots per unit area depends on the surface tension, the adhesive force also depends on the surface tension.     

PA6/不锈钢热压复合界面性能研究

采用机械抛光、化学刻蚀以及退火分别对304不锈钢表面进行预处理,并利用自制模具将聚酰胺6（PA6）注塑试样与不锈钢进行热压成型。力学性能测试结果表明,经过机械抛光后的不锈钢与PA6热压的搭接强度为3.31 MPa, 而经过抛光、化学腐蚀和退火处理后,复合制件的搭接强度达到17.48 MPa,失效模式由界面失效变为内聚失效;扫描电子显微镜、原子力显微镜观察结果表明,化学刻蚀后的不锈钢表面具有微纳米孔洞,热压时塑料熔体进入金属表面微纳米孔洞形成锚定效果;傅里叶红外光谱分析结果表明,PA6与退火处理后的金属表面氧化物形成了化学键;锚定结构与化学键合有利于提高复合件的力学性能。     

Surface modification of Kevlar® fiber by a combination of plasma treatment and coupling agent treatment for silicone rubber composite

To improve the adhesion between poly(p-phenylene terephthalamide), PPTA, fiber and silicone rubber, the surface modification of PPTA was investigated. Combining plasma treatment and coupling agent treatment with the silicone adhesive was found to be effective in improving adhesion. The combination process made the pull-out force of the PPTA yarn/silicone rubber composite 2.5 times higher, compared with the plasma treatment or the coupling agent treatment alone. The plasma treatment led to the elimination of carbonized layer from the PPTA yarn surface and the formation of oxygen functionalities including C-O and C=O groups. The elimination of the carbonaceous deposits from the PPTA surface and the interaction between the silicone adhesive and the oxygen functionalities created by the plasma treatment contribute to the improvement of adhesion with silicone rubber.     

Effects of surface modification by remote hydrogen plasma on adhesion in poly(tetrafluoroethylene)/copper composites

Poly(tetrafluoroethylene) (PTFE) sheet was modified with the remote hydrogen plasma, and the effect of the modification on adhesion between the PTFE sheet and copper metal was investigated. The remote hydrogen plasma was able to make PTFE surfaces hydrophilic without etching. In the modification process, defluorination and oxidation occurred on the PTFE surface. Reactivity of defluorination was 25% (estimated from the concentration of CF₂ component) −39% (estimated from the F/C atom ratio). Surface modification of PTFE surface by remote hydrogen plasma contributed to the adhesion between PTFE and copper metal. Peel strength was improved from 7.5 to 92 mN/5 mm by surface modification by a factor of 12. Failure of the PTFE/copper adhesive joint occurred at the interface between the PTFE and copper metal layers, rather than in the inner layer of the PTFE polymer or copper metal layers. Remote hydrogen plasma treatment is a preferable pretreatment of PTFE surface for the fabrication of PTFE and copper metal composites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2191–2200, 1999     

Effect of geometry and hybrid adhesive on strength of finger joints of Pinus elliottii subject to humidity and temperature

The optimized bonding of glued finger joints is required for structural and nonstructural applications. The use of nonspecific adhesives, combined with the joint geometry and exposure of joints to humidity and temperature, are factors that can compromise the durability of glued joints. The main objective of this study is the development of cross-linking poly(vinyl acetate) (PVAc) hybrid adhesive to produce nonstructural finger joints of Pinus elliottii with finger lengths of 6.5 and 4.5 mm. The adhesives were produced by emulsion copolymerization of vinyl acetate with n-butyl acrylate with different amounts of N-methylol acrylamide and blended with resorcinol-formaldehyde resin (RF) and aluminum chloride (AlCl₃). The rheological behavior of adhesives was investigated. We found that the joint configuration and the exposition time employed influenced joint strength. The PVAc/RF adhesive showed a thicker bond line and consequent deeper penetration into the pores of the wood as verified by microscopy analysis. Statistically differences in bond strength of the adhesive joints were found with respect to different conditioning times and finger length. The highest values were exhibited by the joints produced with a finger length of 6.5 mm and glued with the hybrid adhesive (AD-4) than that joints produced with a finger length of 4.5 mm.