Modification of glass surfaces adhesion properties by atmospheric pressure plasma torch

This work is focused in the surface modification of glass samples by an atmospheric pressure plasma torch (APPT), with the aim of properly characterizing every chemical surface modification which could contribute to the assessment of reliable adhesive bonding with polyurethane, silicone, epoxy and cyanoacrylate adhesives.Characterization of glass surfaces both pristine and plasma treated is achieved by surface energy determination through contact angle measurements, Fourier transform infrared spectroscopy in attenuated total multiple reflection mode (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and surface roughness determination. Moreover, the hydrophobic recovery processes suffered by the samples throughout a period of 30 days of storage after APPT treatment is evaluated. Finally, adherence tests are carried out following the ASTM D4541 standard. Results show an increased surface energy with treatment, which partially recovered its initial value with aging. For the adhesive bonding, only the polyurethane shows an improvement on resistance among all the tested adhesive fluids. It is possible to conclude a cleaning, etching and activation effects on the glass surfaces after plasma treatment, with a change in the locus of failure from adhesive to cohesive in some cases, and a reduction in data standard deviation.     

Improving the adhesion strength of polymers: effect of surface treatments

Abstract

To improve their adhesion strength, polymeric surfaces are usually modified through different treatments. This study investigates the effect of mechanical, chemical, and energetic treatments on the bonding strength of ethylene propylene diene methylene (EPDM), polyvinyl chloride (PVC), and acrylonitrile butadiene styrene (ABS) materials. Three adhesives based on different chemical compositions, namely silicone, polyurethane, and modified-silane (MS) polymer, were considered. Results show that the effect of the applied treatments on the adhesion strength of EPDM surfaces is insignificant. Only a slight improvement is obtained in the case of polyurethane-based adhesive, while the failure modes remained adhesive. As for PVC, most treatments were effective in the case of the silicone-based adhesive, especially grit blasting, primer, and UV/ozone treatments. Only UV/ozone treatment improved the adhesion strength and altered the failure mechanisms of this material when polyurethane and MS-based adhesives are used. The adhesion of ABS increased and the failure modes changed from adhesive to cohesive for most treatments. Particularly, a significant improvement is obtained when primer coating and UV/ozone radiation are applied. This comparative study paves the way for the design of polymeric joints with highly enhanced adhesion performance.     

Improvement of polyurethane adhesion to glass using novolac primer

The adhesion of polyurethane (PU) coatings based on toluene diisocyanate, poly(propylene glycol) (PPG) 2000, polyethylene adipate (PEA) 2000 and castor oil (CO) was studied. The coatings were applied to glass slides with and without novolac primer (due to the high functionality of castor oil, the resultant PU coatings have limited shelf life). Our studies showed that satisfactory adhesion strengths were achievable for immediate bonding. Furthermore, our study also found that the adhesion of polyurethane to glass surfaces was increased by using a thin layer of novolac primer.     

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

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

A comparative study on the use of photoreagents for the enhancement of adhesion on heavy-duty leather (Salz leather)

This paper aims to expand on work presented by us in previous publications regarding the enhancement of adhesion on leather substrates with photoreagent type primers. Two new reagents were synthesized: 3,5-dihydroxyphenyl-4-azidobenzoate (7) and 4,4′-ethylene-1,1′-diphenyl azide (8) and used as an intimate mixture with commercial polyurethane adhesive (Solibond PU39), to enhance the adhesion of Salz leather surfaces. The molecular design of the primer molecule was intended to provide 2- and 3-point fixation between the substrate and adhesive.

The strength of adhesive joints do not seem to be highly dependent on the molecular structure of the primers investigated in respect to the type of OH groups present (aliphatic or aromatic), both confer high adhesive strengths under dry and wet testing conditions. Cyanuric chloride (CNCl)₃ a commercially used primer when tested under the same conditions for comparison purposes, gave good results but with a high standard deviation.

Overall, the azide primers generate good, reliable joint strengths under extreme testing conditions and we believe they present negligible technological problems to industrial scale implementation.     

Effects of polyacrylic acid primers on adhesion and durability of FPL-etched aluminum/polyurethane systems

It has been determined that when a polyacrylic acid [p(AA)] macromolecule primer is used in polyurethane (PU)/p(AA)/FPL-etched aluminum joint systems, it interacts preferentially both with the hydrated Al₂O₃ or aluminum hydroxide adherend surface through the formation of hydrogen bonds and with the isocyanate groups in the PU adhesive to yield polymer-to-polymer chemical bonding. This chemical crosslinking between the hydrated adherend and the polymeric adhesive acts significantly to promote interfacial adhesive bonds. It appears that a near monolayer of p(AA) is enough to occupy all the available functional groups at the PU and aluminum surface sites. This arrangement plays a key role in improving the adhesion durability of the joint system upon exposure to a hot NaOH solution. It was also determined that the presence of excessive carboxylic acid groups resulting from the use of a thick p(AA) layer caused gel-formation-induced adhesion failures; namely, the locus of failure of the joint after exposure was clearly identified to be cohesive failure in the primer.     

Characterization of polyurethane adhesives containing nanosilicas of different particle size

Three nanosilicas with different particle sizes were added to a polyurethane adhesive (PU). The filled adhesives were characterized by thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and contact angle measurements. Adhesive strength was evaluated from single lap shear test of solvent wiped stainless steel/polyurethane adhesive joints.Addition of nanosilica filler altered the degree of phase separation between the hard and soft segments in the polyurethane, in different extent depending on the nanosilica particle size. Furthermore, upon curing higher degree of crosslinking was obtained in the nanosilica filled polyurethane. The nanosilicas agglomerated into the polyurethane matrix. On the other hand, the addition of nanosilica increased the surface energy of the polyurethane to a greater extent by increasing the nanosilica particle size and moderate increase in the single lap shear strength of stainless steel/polyurethane adhesive joints was obtained.     

提高PU胶粘剂粘接EPDM材料强度的研究

为了提高聚氨酯胶粘剂粘接三元乙丙非极性橡胶材料的粘接强度，在三元乙丙橡胶配方中添加石油树脂和聚丁烯作增粘剂。测试了新配方产品的力学性能和与聚氨酯胶粘剂的粘接强度。结果表明，聚丁烯和石油树脂都可以提高PU胶对EPDM的粘接性能，但是聚丁烯对EPDM的力学性能有一定的影响。当在每百份EPDM中添加15份石油树脂，可使之保持良好的力学性能，其与PU胶粘剂的粘接性能亦获得了改善。     

UV treatment of synthetic styrene-butadiene-styrene rubber

The effectiveness of the treatment with ultraviolet light (UV) on several polymeric surfaces has previously been established. In this study, a low pressure mercury vapour lamp was used as a source of UV radiation for the surface treatment of a difficult-to-bond block styrenebutadiene-styrene rubber (S6), the treatment time ranging from 10 s to 30 min. The UV-treated S6 rubber surfaces were characterized by contact angle measurements (ethylene glycol, 25°C), ATR-IR spectroscopy, XPS, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). T-peel tests on UV-treated S6 rubber/polyurethane (PU) adhesive/ leather joints (before and after ageing) were carried out to quantify adhesion strengths. The UV treatment of S6 rubber produced improved wettability, the formation of C—O, C=O and COO^- moieties, and ablation (removal of a thin rubber layer from the surface). The extent of these modifications increased with increasing treatment time. The extended UV treatment produced greater surface modifications, as well as the incorporation of nitrogen moieties at the surface. Furthermore, noticeable ablation of S6 rubber surface occurred. Peel strength values increased with increased treatment time of UV treatment of S6 rubber. Also, with increasing treatment time, the adhesive joints showed different loci of failure: adhesional failure for the as-received and 2 min-UV treated S6 rubber/polyurethane adhesive/leather joints changed to mixed failure (cohesive in the treated S6 rubber + adhesional failure) for the 30 min-UV treated S6 rubber/polyurethane adhesive/leather joint.     

Improved adhesion of low-density polyethylene/EVA foams using different surface treatments

The adhesion between a polyurethane (PU) adhesive and four foams containing different low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) blends was improved by using different surface treatments. UV-ozone, corona discharge, and low-pressure oxygen plasma treatments for different times were used to increase the surface energy of the foams. The low-pressure oxygen plasma was the most successful surface treatment to promote the adhesion of the foams. A reduced length of treatment was needed to improve the adhesion of the foams containing higher EVA content. The surface treatments produced a noticeable decrease in contact angle values due mainly to the creation of different carbon–oxygen moieties and to the formation of cracks/heterogeneities on the foams surfaces. After oxygen plasma, removal of non-polar material from EVA surfaces allowed to expose acetate groups which are likely to be important for increasing the adhesion of the foams.     

Effect of coupling agents on mechanical property of AN/PU energy Composite

Silicon and titanate coupling agents are used to process the surface of ammonium nitrate (AN) particles in order to decrease their surface tension, improve affinity to the adhesive and the adhesive strength of the surface, and improve the mechanical property of an AN/polyurethane (PU) energy composite. SEM and ESCA analyses verify the effect of coupling agents on the mechanical property of the AN/PU energy composite. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1259–1263, 1997     

Comparison of the Properties of Polyurethane Adhesives Containing Fumed Silica or Sepiolite as Filler

Fumed silica is a well-known mineral filler of epoxy and polyurethane adhesives. Although effective, the small particle size and the relative high cost of fumed silicas suggest the need for an alternative filler. In this study, the usefulness of adding a natural hydrated magnesium silicate (sepiolite) as a new filler in solvent-based polyurethane (PU) adhesive formulations has been demonstrated. The rheological and adhesion performance of the sepiolite-filled PU adhesive was compared with that in PU adhesives containing fumed silicas. The addition of a filler to PU adhesives provided an increase in viscosity, imparted thixotropy and pseudoplasticity to the adhesive solution, produced an increase in storage and loss moduli, and improved the rheology of the PU. The mechanical properties of adhesive films were increased by adding filler, mainly with fumed silica. On the other hand, the immediate T-peel strength of roughened or (roughened + chlorinated) styrene-butadiene rubber/PU adhesive joints was greatly improved in filled PU adhesives. The effects produced by adding sepiolite or fumed silica to the adhesives were very similar, although in general more noticeable in fumed silica filled PU due to the formation of hydrogen bonds between the filler and the solvent and/or the polyurethane (in sepiolite-filled adhesives, van der Waals forces seemed to be responsible for the interactions between the filler and the solvent and/or polyurethane).     

Surface modifications of EVA copolymers induced by low pressure RF plasmas from different gases and their relation to adhesion properties

Two ethylene vinyl acetate (EVA) copolymers (12 and 20 wt% of vinyl acetate,VA, content) have been treated with low pressure RF plasmas from non-oxidizing gases (Ar, N₂) and oxidizing gases (air, a mixture of 4N₂: 6O₂ (v/v), O₂ and CO₂). The formation of polar moieties on both EVAs was more noticeable by treatment with plasmas from non-oxidizing gases than from oxidizing ones (the higher the reactivity, the lower the difference with respect to untreated EVA surfaces). The surface etching with the non-oxidizing plasmas, giving rise to a high roughness, depends on the wt% of VA in the composition of the copolymer because of the different resistances of VA (low) and PE (high) to the non-oxidizing plasma particles bombardment. The adhesion properties obtained using a polyurethane adhesive (PU) showed high T-peel strength values and adhesion failure in EVAs treated with plasmas from oxidizing gases, due to roughness produced causing mechanical interlocking of the adhesive. Lower T-peel strength values were obtained with non-oxidizing plasmas: the values for EVA12 being, in general, lower than those obtained for EVA20. The durability of the treated EVAs/PU adhesive joints after ageing in humidity and temperature was quite good.     

Shear strength of calabrian pine (Pinus brutia Ten.) bonded with polyurethane and polyvinyl acetate adhesives

In this study, the change in shear strength on radial and tangential surfaces of Calabrian pine (Pinus brutia Ten.) wood having different roughness values as the result of sawing with a circular ripsaw, planning, and sanding, and bonded with polyurethane (PU) and polyvinyl acetate (PVAc) adhesives at the pressure levels of 3, 6, and 9 kg f/cm² were studied. A total of 360 specimens of each, prepared with the objective of being able to determine the effect of the variables on bond performance, were subjected to the shear test in the universal test machine in accordance with the ASTM D 905–98 standard. The values obtained were analyzed statistically and the results were interpreted. The highest shear strength (11.83 N/mm²) for plane of cut was obtained on the tangential surface after sanding and applying PVAc adhesive with a pressing pressure of 9 kg f/cm². The lowest shear strength (6.01 N/mm²) was obtained in the joinings made on the planed surfaces by using PU adhesive and a pressing pressure of 3 kg f/cm². The highest shear strength (9.10 N/mm²) on the radial surface was obtained after sanding and applying PVAc adhesive and pressing with a pressure of 6 kg f/cm². The lowest shear strength (3.76 N/mm²) was obtained in the specimens whose surfaces were sanded and by using PU adhesive and with a pressing pressure of 3 kg f/cm². In general, in the radial surfaces, just like in the tangential surfaces, the specimens bonded with PVAc produced a higher shear strength compared to those glued with PU. According to these results, it is definitely necessary to sand the surfaces prior to the bonding process to have a higher shear strength. The bonding process should be made on the tangential surfaces with higher pressures. The PVAc adhesive should be preferred instead of the PU adhesive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4856–4867, 2006     

The shear strength of Calabrian pine (Pinus brutia Ten.) bonded with polyurethane and polyvinyl acetate adhesives

In this study, the change in shear strength on radial and tangential surfaces of Calabrian Pine (Pinus brutia Ten.) wood having different roughness values as the result of sawing with a circular ripsaw, planing and sanding, and bonded with polyurethane (PU) and polyvinyl acetate (PVAc) adhesives at the pressure levels of 3, 6, and 9 kgf/cm², was studied. Each of the 360 specimens prepared to determine the effect of the variables on bond performance were subjected to shear test in an universal test machine in accordance with the ASTM D 905–98 standards. The values obtained were analyzed statistically and the results were interpreted. The highest shear strength (11.83 N/mm²) for plane of cut was obtained on the tangential surface after sanding and applying PVAc adhesive with a pressing pressure of 9 kgf/cm². The lowest shear strength (6.01 N/mm²) was obtained in the joinings made on the planed surfaces by using PU adhesive and a pressing pressure of 3 kgf/cm². The highest shear strength (9.10 N/mm²) on the radial surface was obtained after sanding and applying PVAc adhesive and pressing with a pressure of 6 kgf/cm². The lowest shear strength (3.76 N/mm²) was obtained in the specimens whose surfaces were sanded and glued with PU adhesive with a pressing pressure of 3 kgf/cm². In general, in the radial surfaces, just like in the tangential surfaces, the specimens bonded with PVAc exhibited a higher shear strength compared with those glued with PU. According to these results, it is definitely necessary to sand the surfaces prior to the bonding process to have a higher shear strength. The bonding process should be made on the tangential surfaces with higher pressures. The PVAc adhesive should be preferred instead of the PU adhesive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3050–3061, 2006     

Comparative Properties of Hydrophilic and Hydrophobic Fumed Silica Filled Two-Component Polyurethane Adhesives

Two fumed silicas, one hydrophilic and another hydrophobic, were added to a two-component polyurethane (PU) adhesive and their properties compared. The filled polyurethanes were characterized by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and water and diiodomethane contact angle measurements. The adhesive strength was evaluated from single lap-shear tests of solvent wiped stainless steel/polyurethane adhesive joints. The fumed silicas were well-dispersed in the polyurethane matrix as bundles of nanometric spherical silica particles. However, some micron size agglomerates of fumed silica appeared in the filled polyurethane. The addition of fumed silica favoured the degree of phase separation between the hard and the soft segments in the polyurethane. The polyurethanes were not fully cured under the conditions used in this study and the addition of fumed silica inhibited the curing reaction; the extent of the curing reaction was not affected by the hydrophilic or hydrophobic nature of the fumed silica. The filled polyurethanes were further cured during DSC experiments and this was noticed by the appearance of the melting of the hard segments and the displacement of the second glass transition to a higher temperature. On the other hand, the addition of fumed silica increased the wettability and the surface energy of the polyurethane; this increase was mainly due to an increase in the polar component of the surface energy. The increase in surface energy is somewhat more marked in the case of the hydrophilic silica filled polyurethane, indicating that the polarity of the fumed silica affected the surface properties of the polyurethane. Finally, the addition of the hydrophilic fumed silica increased the adhesion of the filled polyurethane adhesive to stainless steel which was in agreement with the higher surface energy of the hydrophilic fumed silica filled polyurethane.     

On oxygen plasma-treated polypropylene interfaces with air,water, and epoxy resins. II. Epoxy resins

XPS, SEM, SSIMS, FTIR-ATR, water-in-air, and air-in-water contact angle measurements have been used to unambiguously characterize the locus of failure of PP/epoxy joints. In the case of untreated PP, the fracture has been found adhesive, whereas in oxygen plasmatreated PP, it is cohesive, within bulk PP, but close to the modified PP-bulk PP interface. The smoothness of fracture surfaces allowed us to exclude mechanical interlocking effects. Shear-strength measurements showed that the mechanical strength of the joint was improved by plasma treatment. Preliminary thermal equilibration of the plasma-treated PP sample and changes in the curing cycle of the epoxy resin did not change either the locus of failure or the shear strength of the joint. The reason is probably because the number of polar functions left at the surface after thermal equilibration is sufficient to induce adhesion. The mechanical strength of the PP surface layer may be the determining factor. Fracture energy calculations showed that the observed locus of failure is the same as predicted on the basis of surface energy considerations.     

Properties of Polyurethane Elastomers with Different Hard/Soft Segment Ratio

Three polyurethane elastomers (PU) containing different hard/soft (h/s) segment ratios were prepared. The PUs were characterized using Gel Permeation Chromatography (GPC), DSC, Wide Angle X-ray Diffraction (WAXD). Dynamic Mechanical Thermal Analysis (DMTA), and Stress-controlled rheometry. The surface properties were evaluated from contact angle measurements. The PUs were used as raw materials for solvent-based adhesives, whose adhesion properties were measured from T-peel tests of solvent-wiped polyvinyl chloride (PVC)/polyurethane adhesive joints. The increase in the amount of h/s segment ratio affected the structure and morphology of the PUs, reducing the degree of phase separation and the extent of the secondary interactions between polymer chains. The h/s segment ratio determined the thermal, mechanical, rheological and adhesion properties of the PUs.     

Properties of Polyurethane Elastomers with Different Hard/Soft Segment Ratio

Three polyurethane elastomers (PU) containing different hard/soft (h/s) segment ratios were prepared. The PUs were characterized using Gel Permeation Chromatography (GPC), DSC, Wide Angle X-ray Diffraction (WAXD). Dynamic Mechanical Thermal Analysis (DMTA), and Stress-controlled rheometry. The surface properties were evaluated from contact angle measurements. The PUs were used as raw materials for solvent-based adhesives, whose adhesion properties were measured from T-peel tests of solvent-wiped polyvinyl chloride (PVC)/polyurethane adhesive joints. The increase in the amount of h/s segment ratio affected the structure and morphology of the PUs, reducing the degree of phase separation and the extent of the secondary interactions between polymer chains. The h/s segment ratio determined the thermal, mechanical, rheological and adhesion properties of the PUs.     

Hydrophobic or Hydrophilic Fumed Silica as Filler of Polyurethane Adhesives

Two hydrophilic and two hydrophobic fumed silicas of different characteristics were added to solvent-based polyurethane adhesives (PU). IR spectroscopy, contact angle measurements and rheology (viscosity measurements, determination of viscoelastic properties) were used to monitor the variation of properties of PU adhesives produced by addition of silica. Immediate (green) adhesion was determined by T-peel testing of halogenated synthetic rubber/PU adhesive/halogenated synthetic rubber joints. Silica addition produced a noticeable increase in the PU adhesive viscosity which can be related to the variation of viscoelastic properties. Viscosity of PU adhesives containing hydrophilic silica slightly increased with time after preparation; the increase was less significant in PU adhesives with hydrophilic silica. In the rheological studies, silica imparted shear thinning and negative thixotropy to PU adhesives due to a better dispersion of the silica in the polyurethane during shearing. The addition of silica produces an increase in the storage modulus (G') of PU adhesives, the values obtained being independent of the hydrophilic or hydrophobic nature of the fumed silica. The increase of G' and the changes in tan δ of PU adhesives containing silica corresponded to an improvement in the green adhesion properties of chlorinated rubber/PU adhesive/chlorinated rubber joints. In general, in disagreement with previous results,¹ the presence of silica did affect the properties of solvent-based PU adhesives, but these properties were not dependent on the type of silica (hydrophobic or hydrophilic) used in this study.