SURFACE MODIFICATIONS ON EVA TREATED WITH SULPHURIC ACID

In this study, treatment with sulphuric acid was used to increase the adhesion of an ethylene-vinyl acetate copolymer containing 20 wt% vinyl acetate (EVA20). The treatment with sulphuric acid improved the wettability of EVA20 due to thecreation of different oxygen and sulphonic acid moieties on the surface. The treatment also created cracks and heterogeneities on the EVA20 surface, and enhanced T-peel strength values of EVA20/polychloroprene adhesive+5 wt% isocyanate joints were obtained. The loci of failure of the joints were mixed, i.e. , adhesional and cohesive in the adhesive. Peel strength values of both as-received and sulphuric acid-treated EVA20/polychloroprene adhesive joints increased after ageing at 50°C and 95 wt% relative humidity for 72 because the complete cure of the adhesive was thereby was produced. The durability of the EVA20 treated with sulphuric acid was monitored between 15 min and 5 years. High peel strength values were obtained for times up to 61 days; the joints produced with the treated EVA20 five years after treatment showed lower peel strength value due to the creation of a weak boundary layer produced by reaction of the residual sulphuric acid on the surface with EVA20. On the other hand, different experimental variables in the treatment of EVA20 with sulphuric acid were considered. The optimum treatment conditions for EVA20 were obtained by immersion in highly concentrated sulphuric acid (96 wt%) for one minute followed by neutralisation with ammonium hydroxide.     

Improved adhesion of EVAs with different vinyl acetate contents treated with sulphuric acid

Four ethylene vinyl acetate copolymers (EVAs) containing 9, 12, 18 and 20 wt% vinyl acetate (VA) were treated with concentrated sulphuric acid to improve their adhesion to polychloroprene (PCP) adhesive. The tensile strength and Young's modulus of EVAs decreased as the VA content increased, due to the reduction in crystallinity of the polyethylene blocks in the copolymer. The modifications produced in the EVAs by treatment with sulphuric acid were followed using contact angle measurements (water, 25 °C), ATR-IR spectroscopy and scanning electron microscopy (SEM). Adhesive-bond strength was obtained by T-peel tests on treated EVA/polychloroprene adhesive joints. The vinyl acetate content in the EVA affected the extent, but not the nature, of the surface modification produced by treatment with sulphuric acid. The treatment produced both sulfonation and oxidation on the EVA surfaces. The higher the vinyl acetate content in the EVA, the more significant the modifications produced. Increased T-peel strengths of EVA/polychloroprene adhesive + 5 wt% polyisocyanate joints were obtained and a mixed failure (adhesion failure + cohesive failure in the adhesive) was produced. It was found that, to be effective, the treatment of EVAs must be carried out with 96 wt% sulphuric acid.     

Improvement of adhesion and paint ability of EVA copolymers with different vinyl acetate contents by treatment with UV-ozone

The surface modifications produced by UV-ozone treatment of two ethylene-vinyl acetate (EVA) copolymers containing 12 and 20 wt% vinyl acetate (EVA12 and EVA20 respectively) were studied. The treatment with UV-ozone improved the wettability of both EVAs due to the creation of new carbon–oxygen moieties. The extent of these modifications increased with increasing length of the treatment and the modifications produced in EVA20 were produced for shorter lengths of treatment. The UV-ozone treatment also created roughness and heterogeneities on the EVA surfaces. Whereas roughness formation prevailed on the UV-ozone treated EVA12, important ablation was dominant on the treated EVA20. T-peel strength values in joints made with polychloroprene adhesive increased when the EVAs were treated with UV-ozone. Short length of UV-ozone treatment (1 min) produced higher T-peel strength in joints made with EVA20 whereas higher T-peel strength values in joints made with EVA12 were obtained after treatment for 5–7.5 min in which a cohesive failure into a weak boundary layer on the treated EVA surface was found. Furthermore, the adhesion of UV-ozone treated EVA20 to acrylic paint increased. Finally, the ageing resistance of the treated EVA/polychloroprene adhesive joints was good and the surface modifications on the UV-ozone treated EVAs lasted for 24 h after treatment at least.     

Corona discharge treatment of EVAs with different vinyl acetate contents

Four ethylene vinyl acetate (EVA) co-polymers with different vinyl acetate (VA) contents (9–20 wt%) were treated with corona discharge to improve their adhesion to polychloroprene (PCP) adhesive. The thermal properties of the EVAs decreased as their VA content increased, caused by a decrease in crystallinity. The elastic and viscous moduli of the EVAs decreased and the temperature and modulus at the cross-over between these moduli decreased with increasing VA content. Contact-angle measurements (water), infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to analyse the surface modifications produced in the corona-discharge-treated EVAs. The corona discharge treatment produced improved wettability and created roughness and oxygen moieties on the EVA surfaces. The higher the VA content and the higher the corona energy, the more significant modifications were produced on the EVA surface. The VA content also affected the T-peel strength values of treated EVA/polychloroprene + isocyanate adhesive joints, as the values increased with increasing VA content. Mixed failure modes (interfacial + cohesive failure in the EVA) were obtained in the adhesive joints produced with corona discharge treated EVAs containing more than 9 wt% VA. The accelerated ageing of the joints did not affect the T-peel strength values, but the locus of failure in most cases became fully cohesive in the EVA, likely due to the higher extent of curing of the adhesive.     

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.     

A new water-based chemical treatment based on sodium dichloroisocyanurate (DCI) for rubber soles in the footwear industry

A new water-based chemical treatment based on sodium dichloroisocyanurate (DCI) solutions for rubber soles of different natures is reported in this study. Different concentrations (1-5 wt%) of DCI and two rubber formulations (vulcanized styrene-butadiene rubber, R2; thermoplastic rubber, TR) were considered. The effects produced by treatment of the rubber soles with DCI were compared with the standard halogenation method using trichloroisocyanuric acid (TCI) solutions in an organic solvent (ethyl acetate). The effects of chlorination on the rubber surfaces were studied using contact angle measurements, ATR-IR spectroscopy, and scanning electron microscopy. The adhesion strength was obtained from T-peel strength tests on canvas/PUD adhesive/treated rubber joints. The adhesive used throughout this study was a water-based polyurethane dispersion (PUD). The surface treatment with aqueous DCI solutions modified the surface chemistry of both the TR and R2 rubbers, creating C—Cl moieties on the surface and removing the zinc stearate from the R2 rubber surface. The use of a low DCI concentration in water was less effective in modifying the TR rubber, but was sufficient to obtain good T-peel strength values for the R2 rubber joints. On the other hand, heterogeneities and cracks were created on the rubber surface (mainly on the R2 rubber surface), which may contribute to an increase in the mechanical interlocking with the adhesive. A noticeable increase in the T-peel strength and a cohesive failure in the rubber for the joints produced with TR rubber were obtained when the rubber was treated with aqueous DCI solutions. For the canvas/PUD adhesive/chlorinated R2 rubber joint, the failure was located in a thin surface layer on the canvas. Finally, the surface treatment with TCI in ethyl acetate produced a more significant surface modification on both the TR and the R2 rubber, creating deeper roughness on the R2 rubber surface. Consequently, higher peel strength values were obtained using TCI solutions in ethyl acetate. Furthermore, the T-peel strength values were high in all joints produced with TR rubber treated with either TCI solution in ethyl acetate or aqueous DCI solution.     

Selective surface modification of ethylene-vinyl acetate and ethylene polymer blend by UV–ozone treatment

Ethylene-vinyl acetate (EVA) copolymers intended for sport sole manufacturing may contain noticeable amounts of polyethylene (LDPE) for improving abrasion resistance and decrease cost; however, this blend (EVA–PE) had low polarity and showed poor adhesion. In this study an effective environmentally friendly and fast surface treatment based on UV–ozone has been used to increase the wettability, polarity and roughness of EVA–PE material. Both the length of the UV–ozone treatment and the distance between the material surface and the UV-radiation source were tested. The UV–ozone treated EVA–PE material was characterized by ATR-IR spectroscopy using Ge prism, water contact angle measurements, X-Ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Adhesion properties were obtained from T peel tests of as-received and UV–ozone treated EVA–PE/polyurethane adhesive/leather joints.The more extended length of treatment and the shorter UV source–substrate distance increased the wettability of the EVA–PE material. Oxidation of the EVA–PE surface was produced by UV–ozone treatment creating new carbonyl groups mainly, and the amounts of hydroxyl and carboxylic groups were increased. The UV–ozone treatment produced ablation and etching of the EVA–PE material surface, mainly in the vinyl acetate, creating a particular roughness consisting on ruffles with deep crevices; this topography was also produced by heating produced during UV–ozone treatment. For low length of UV treatment or high UV source–material distance, the modifications of the EVA–PE material were mainly produced in the ethylene causing the selective removal of vinyl acetate, whereas more aggressive conditions produced strong oxidation in the EVA–PE material. Finally, adhesive strength was noticeably increased in the UV–ozone treated EVA–PE/polyurethane adhesive joints, and a cohesive failure in the leather was obtained.     

TREATMENT OF VULCANIZED STYRENE-BUTADIENE RUBBER (SBR) WITH MIXTURES OF TRICHLOROISOCYANURIC ACID AND FUMARIC ACID

In this study, mixtures of trichloroisocyanuric acid (TCI) and fumaric acid (FA) solutions were applied to a difficult-to-bond, vulcanized styrene-butadiene rubber (R2) to analyze the combined effect of both surface treatments. The treated R2 rubber surfaces were characterized using advancing contact angle measurements, ATR-IR and XPS spectroscopy, and SEM. T-peel tests of treated R2 rubber/ polyurethane adhesive/leather joints have been obtained in order to quantify the adhesion properties. The wettability of R2 rubber was improved by treatment with 3 wt% TCI/EA (ethyl acetate) or 0.5 wt% FA/EtOH, and lower contact angles were obtained by treatment with both 3 wt% TCI/EA and 0.5 wt% FA/EtOH. The improved wettability was ascribed to the creation of carbon-chlorine moieties, the removal of zinc stearate and paraffin wax, and the creation of surface roughness on the R2 rubber surface. Treatment of R2 rubber with 3 wt% TCI/EA before or after treatment with 0.5 wt% FA/EtOH, or with a solution containing 3 wt% TCI/EA + 0.5 wt% FA/EtOH mixture produced a noticeable increase in peel strength. Always, the effects of the treatment of R2 rubber with 3 wt% TCI solution were dominant over those produced by treatment with 0.5 wt% FA solution in ethanol (FA/EtOH). On the other hand, the treatment of R2 rubber with 3 wt% TCI/EA + 0.5 wt% FA/EtOH mixture was more effective than the treatment with 0.5 wt% TCI/EA+ 2 wt% FA/EtOH because the lower amount of chlorinating agent in this mixture.     

Improved peel strength in vulcanized sbr rubber roughened before chlorination with trichloroisocyanuric acid

The effectiveness of chlorination as surface treatment to improve the adhesion of synthetic vulcanized styrene-butadiene rubber (SBR) depends on several experimental variables. Solutions of trichloroisocyanuric acid (TCI) in methyl ethyl ketone (MEK) have been used as effective chlorination agents for several rubbers. In this study, the influence of roughening prior to chlorination treatment of a SBR rubber (R2) and the durability of the modifications produced as the time after chlorination increased have been considered. Two concentrations of the chlorination agent (0.5 and 2 wt% TCI/MEK) have been used and the chlorination treatment was applied on the R2 rubber surface using a brush. Characterization of the treated surfaces was carried out using contact angle measurements, ATR-IR spectroscopy and Scanning Electron Microscopy (SEM). T-peel tests of treated R2 rubber/polyurethane adhesive joints have been carried out to determine the adhesion properties. Roughening was an effective treatment to remove paraffin waxes (antiadherent moieties) from the R2 rubber surface. When the chlorination is produced on the roughened R2 rubber, more noticeable chemical and morphological modifications were produced, and higher adhesion was obtained. On the other hand, TCI particles appeared on the roughened and unroughened chlorinated R2 rubber surface, and the size of these TCI particles were decreased by increasing the time after treatment. Furthermore, similar peel strength values were obtained for time after halogenation higher than 2 hours; for shorter time, a decrease in peel strength was found by increasing the time, due to the migration of paraffin wax to the rubber surface.     

Treatment of vulcanized styrene-butadiene rubber (SBR) with mixtures of Trichloroisocyanuric Acid and Fumaric Acid

In this study, mixtures of trichloroisocyanuric acid (TCI) and fumaric acid (FA) solutions were applied to a difficult-to-bond, vulcanized styrene-butadiene rubber (R2) to analyze the combined effect of both surface treatments. The treated R2 rubber surfaces were characterized using advancing contact angle measurements, ATR-IR and XPS spectroscopy, and SEM. T-peel tests of treated R2 rubber/ polyurethane adhesive/leather joints have been obtained in order to quantify the adhesion properties. The wettability of R2 rubber was improved by treatment with 3 wt% TCI/EA (ethyl acetate) or 0.5 wt% FA/EtOH, and lower contact angles were obtained by treatment with both 3 wt% TCI/EA and 0.5 wt% FA/EtOH. The improved wettability was ascribed to the creation of carbon-chlorine moieties, the removal of zinc stearate and paraffin wax, and the creation of surface roughness on the R2 rubber surface. Treatment of R2 rubber with 3 wt% TCI/EA before or after treatment with 0.5 wt% FA/EtOH, or with a solution containing 3 wt% TCI/EA + 0.5 wt% FA/EtOH mixture produced a noticeable increase in peel strength. Always, the effects of the treatment of R2 rubber with 3 wt% TCI solution were dominant over those produced by treatment with 0.5 wt% FA solution in ethanol (FA/EtOH). On the other hand, the treatment of R2 rubber with 3 wt% TCI/EA + 0.5 wt% FA/EtOH mixture was more effective than the treatment with 0.5 wt% TCI/EA+ 2 wt% FA/EtOH because the lower amount of chlorinating agent in this mixture.     

Effects of overhalogenation of a synthetic vulcanized styrene–butadiene rubber sole on its adhesion behavior

The effects of halogenating the same synthetic vulcanized styrene–butadiene rubber (R2) (used as a sole material in the shoe industry) twice (double halogenation) using solutions of trichloroisocyanuric acid (TCI) in MEK were studied. The R2 rubber was treated with 0.5 and 2 wt% TCI/MEK solutions and after 1 h re-treated with additional 0.5 (0.5 + 0.5 wt% TCI/MEK) and 2 wt% TCI/MEK (2 + 2 wt% TCI/MEK) solutions. The results obtained were compared with those obtained by treating the R2 rubber once with 1 and 4 wt% TCI/MEK solutions. The surface modifications produced by the double halogenation of the R2 rubber were analyzed using advancing and receding contact angles (variations in wettability), XPS and ATR-IR spectroscopy (characterization of chemical modifications) and SEM (morphological modifications). T-peel tests on doubly halogenated R2 rubber/polyurethane adhesive joints were carried out to quantify the adhesion properties of the treated R2 rubber. The degree of chlorination was higher with increasing amount of chlorinating agent. Furthermore, the most efficient removal of hydrocarbon substances from the R2 rubber surface was obtained by double halogenation and by increasing the TCI concentration. Similar trends in surface chemistry of the R2 rubber were obtained using 0.5–2 wt% TCI/MEK, with or without double halogenation. On the other hand, by comparing the effects of treatments with 0.5 + 0.5 wt% TCI/MEK and 1 wt% TCI/MEK or with 2 + 2 wt% TCI/MEK and 4 wt% TCI/MEK, less effective removal of zinc stearate and less degree of chlorination were obtained by double halogenation although similar outermost surface modifications were produced. The second application of the TCI/MEK solution on the already halogenated R2 rubber dissolved the unreacted TCI and/or the isocyanuric acid crystals on its surface. The mechanical properties of the treated R2 rubber decreased because it became stiffer. Higher and relatively similar peel strength values were obtained in all adhesive joints prepared using treated R2 rubber. A cohesive failure in the rubber close to the chlorinated layer was always obtained.     

Influence of the vinyl acetate content and the tackifier nature on the rheological,thermal, and adhesion properties of EVA adhesives

Three ethylene vinyl acetate (EVA) copolymers with different vinyl acetate (VA) contents (28-40 wt%) were mixed with rosin ester and polyterpene resin tackifiers in a 1 : 1 (weight/weight) ratio. The rheological and thermal properties of the tackifiers were determined and the use of rheological measurements as a precise way to measure the softening point of the tackifiers is proposed. The glass transition temperature of the tackifiers was obtained from the second heating run, after the thermal history of the tackifiers was removed. The addition of the rosin ester to EVA produced a compatible mixture, whereas for the terpene resin a less compatible mixture was obtained. The increase in the VAamount decreased the crystallinity of EVAand both the storage and the loss moduli also decreased, but the peel strength and the immediate adhesion were increased. The immediate adhesion of EVA/tackifier blends was affected by both the compatibility and the rheological properties of the blends. In fact, a relationship between the mechanical storage modulus (E^t′) - obtained from DMTA experiments - of the adhesives and the immediate adhesion to thin rubber substrates was obtained. The adhesives containing the T tackifier showed higher moduli than those containing the G tackifier, and therefore higher peel strength values were obtained. An increase in the VA content increased the flexibility of the adhesives and thus a decrease in peel strength was obtained.     

Hygrothermal ageing of adhesive joints with nanoreinforced adhesives and different surface treatments of carbon fibre/epoxy substrates

The effect of water absorption on the strength of single lap adhesive joints subjected to accelerated hygrothermal ageing (55 °C, 95% relative humidity, 800 h) was analysed. Two different variables were studied: the surface treatment of the carbon fibre/epoxy laminates (peel ply, grit blasting and atmospheric pressure plasma) and the addition of carbon nanofillers (0.5 wt% nanofibres and 0.25 wt% nanotubes) to the epoxy adhesive. The joint strength and the failure mode of the joints were investigated. Furthermore, the amount of water absorbed by the adhesive was determined.Adhesive joints with peel ply-treated laminates exhibit an increase in their strength, which is attributed to a relaxation of stresses in the adhesive/laminate interface; with grit blasting, this property remains almost constant. Plasma treatment provides the worst ageing behaviour because this treatment results in a surface with a higher surface free energy, which is more susceptible to environmental attack. The nanoreinforcement of the adhesive has a beneficial effect: it decreases the amount of absorbed water.     

Surface Analysis of Debonded Chlorinated Vulcanized Styrene-Butadiene Rubber Joints

A synthetic vulcanized styrene-butadiene rubber (R) was treated with a halogenation agent (TCI = trichloroisocyanuric acid) to produce improved adhesion (i.e. high T-peel strength) in joints prepared with a one-component, solvent-based polyester urethane adhesive. Several amounts (0.5 to 7 wt%) of TCI solutions in ethyl acetate were applied to the rubber surface and, after T-peel tests were carried out, the surfaces of the debonded chlorinated rubber pieces were analyzed with XPS, ATR-infra-red (ATR-IR) spectroscopy, Scanning Electron Microscopy (SEM) coupled with EDX analysis, and contact angle measurements. The T-peel strength of unchlorinated rubber (0 wt% TCl) joints was small due to the migration of low molecular species (mainly microcrystalline wax) to the rubber surface during the cure of the adhesive, creating a weak layer in which the failure was produced. Chlorination with amounts of TCI up to 2 wt% produced a noticeable increase in T-peel strength, but treatment with higher amounts of TCI resulted in a decrease in joint strength. Although chlorination with TCI created chlorinated hydrocarbon groups and C-O moieties on the rubber surface, the surface in contact with the adhesive was additionally degraded and, consequently, the locus of failure of the joints varied in a manner which depended on the amount of TCI applied to the surface. Treatment with amounts of TCI up to 2 wt% did not greatly degrade the rubber surface and the mode of failure of the joint was mainly interfacial. Chlorination at higher TCI concentration produced a weak chlorinated surface layer which was was mechanically weak, facilitating the failure in this layer during the T-peel test. The thickness of the chlorinated layer created on the treated rubber is about 5 Fm, and the thickness seemed to be independent of the amount of TCI applied to the rubber surface.     

Water-based chlorination treatment of SBS rubber soles to improve their adhesion to waterborne polyurethane adhesives in the footwear industry

Solutions of trichloroisocyanuric acid (TCI) in different organic solvents are commonly employed in the footwear industry to improve the adhesion of SBS (styrene-butadiene-styrene) rubber soles to polyurethane adhesive. To avoid the use of organic solvents in the chlorinating solutions, several water-based chlorinating treatments were investigated in this study: (i) inorganic chlorine compounds (HCl-acidified sodium hypochlorite solution; free active chlorine (FAC) = 47.8 g/l); (ii) organic chlorine donors (aqueous solution of 3 wt% TCI/H₂O, and ethanol solutions of 3 wt% HD (1,3-dichloro-5,5-dimethylhydantoine), or NCS (N-chlorosuccinimide); (iii) organic chlorine donor salts (aqueous solutions containing 3 wt% DCI (sodium dichloro isocyanurate), CB (chloramine B, N-chloro-sodium-phenylsulphenamide), or CT (chloramine T, N-chloro-sodium-p-toluenesulphenamide). The surface modifications produced by treatment of SBS rubber with the aqueous chlorinating agents were compared with those obtained by using the current solvent-based chlorinating treatment (3 wt% TCI/MEK). The FAC concentration and the chlorine stability in the solutions were determined by iodine titration, and the SBS rubber surface pH was determined with a flat pH probe. The surface modifications on the SBS rubber were analyzed by ATR-IR spectroscopy, XPS, contact-angle measurements and SEM. The adhesion properties were evaluated by T-peel strength tests on treated SBS rubber/waterborne polyurethane adhesive/roughened leather joints. The failed surfaces obtained after peel tests were analyzed by ATR-IR spectroscopy to precisely assess the locus of failure of the adhesive joints. The nature of the modifications produced on the SBS rubber surface depended on the chlorinating system used, the SBS rubber surface pH value, and the free active chlorine concentration of the chlorinating solution. The most effective chlorinating agents were TCI/H₂O and HD/EtOH, but they were not stable over time due to quick chlorine evolution. Treatment with NaClO/HCl and DCI/H₂O provided acceptable adhesive strength values although there was fast chlorine evolution in the NaClO/HCl solution; the free active chlorine concentration in the DCI/H₂O solution was stable for at least 4 days after preparation. Finally, the treatment with NCS/EtOH, CB/H₂O and CT/H₂O did not chemically modify the SBS rubber surface, so the adhesion to polyurethane adhesive was not improved.     

IMPROVED PEEL STRENGTH IN VULCANIZED SBR RUBBER ROUGHENED BEFORE CHLORINATION WITH TRICHLOROISOCYANURIC ACID

The effectiveness of chlorination as surface treatment to improve the adhesion of synthetic vulcanized styrene-butadiene rubber (SBR) depends on several experimental variables. Solutions of trichloroisocyanuric acid (TCI) in methyl ethyl ketone (MEK) have been used as effective chlorination agents for several rubbers. In this study, the influence of roughening prior to chlorination treatment of a SBR rubber (R2) and the durability of the modifications produced as the time after chlorination increased have been considered. Two concentrations of the chlorination agent (0.5 and 2 wt% TCI/MEK) have been used and the chlorination treatment was applied on the R2 rubber surface using a brush. Characterization of the treated surfaces was carried out using contact angle measurements, ATR-IR spectroscopy and Scanning Electron Microscopy (SEM). T-peel tests of treated R2 rubber/polyurethane adhesive joints have been carried out to determine the adhesion properties. Roughening was an effective treatment to remove paraffin waxes (antiadherent moieties) from the R2 rubber surface. When the chlorination is produced on the roughened R2 rubber, more noticeable chemical and morphological modifications were produced, and higher adhesion was obtained. On the other hand, TCI particles appeared on the roughened and unroughened chlorinated R2 rubber surface, and the size of these TCI particles were decreased by increasing the time after treatment. Furthermore, similar peel strength values were obtained for time after halogenation higher than 2 hours; for shorter time, a decrease in peel strength was found by increasing the time, due to the migration of paraffin wax to the rubber surface.     

CHARACTERIZATION OF EVA-BASED ADHESIVES CONTAINING DIFFERENT AMOUNTS OF ROSIN ESTER OR POLYTERPENE TACKIFIER

Different amounts (50-170 php--parts per hundred parts of EVA, 33-63 wt%) of two tackifiers (hydrogenated rosin ester, polyterpene resin) were added to an ethylene vinyl acetate (EVA) copolymer containing 28 wt% vinyl acetate. The EVA and the tackifier were characterized using infrared (IR) spectroscopy, DSC measurements, and stress-controlled plate-plate rheology. The properties and compatibility of the EVA-tackifier mixtures were studied using DSC, DMTA, and stress-controlled plate-plate rheology. Immediate adhesion was measured as a quantification of tack, and the T-peel strength of roughened styrene-butadiene rubber/EVA-tackifier adhesive joints was also obtained. The increase in the amount of tackifier noticeably changed the crystallinity of polyethylene blocks in the EVA, and the temperature at the cross-over between the curves of the storage and loss moduli as a function of the temperature was displaced to a lower value. Whereas the hydrogenated rosin ester was compatible with the amorphous ethylene vinyl acetate copolymer regions of the EVA (Tg value increased) reducing its crystallinity, the polyterpene resin was compatible with the polyethylene blocks of the EVA (T g value was not modified), increasing its crystallinity. Immediate adhesion of the EVA-tackifier mixtures was improved by adding both hydrogenated rosin ester and polyterpene tackifiers. On the other hand, there was an optimum tackifier content at which the maximum T-peel strength value was obtained.     

Characterization of eva-based adhesives containing different amounts of rosin ester or polyterpene tackifier

Different amounts (50-170 php--parts per hundred parts of EVA, 33-63 wt%) of two tackifiers (hydrogenated rosin ester, polyterpene resin) were added to an ethylene vinyl acetate (EVA) copolymer containing 28 wt% vinyl acetate. The EVA and the tackifier were characterized using infrared (IR) spectroscopy, DSC measurements, and stress-controlled plate-plate rheology. The properties and compatibility of the EVA-tackifier mixtures were studied using DSC, DMTA, and stress-controlled plate-plate rheology. Immediate adhesion was measured as a quantification of tack, and the T-peel strength of roughened styrene-butadiene rubber/EVA-tackifier adhesive joints was also obtained. The increase in the amount of tackifier noticeably changed the crystallinity of polyethylene blocks in the EVA, and the temperature at the cross-over between the curves of the storage and loss moduli as a function of the temperature was displaced to a lower value. Whereas the hydrogenated rosin ester was compatible with the amorphous ethylene vinyl acetate copolymer regions of the EVA (Tg value increased) reducing its crystallinity, the polyterpene resin was compatible with the polyethylene blocks of the EVA (T g value was not modified), increasing its crystallinity. Immediate adhesion of the EVA-tackifier mixtures was improved by adding both hydrogenated rosin ester and polyterpene tackifiers. On the other hand, there was an optimum tackifier content at which the maximum T-peel strength value was obtained.     

Addition of Silica to Polyurethane Adhesives

The influence of the addition of silica (Aerosil-200) (5-25 wt%) to polyurethane adhesives on their adhesion properties with non-chlorinated and surface-chlorinated rubbers has been studied. The chlorinating agent was Trichloroisocyanuric acid (TIC) in 2-butanone solution at a concentration of between 1 and 9 wt%. In general, silica produced an increase in the adhesive viscosity and an improvement of green (immediate) peel strength (especially with chlorinated rubber). The best results were obtained for a silica content of 10-20 wt%. However, the addition of silica did not improve the peel strength after a thermal ageing process. Polyurethane adhesives containing silica undergo an improvement in their resistance to degradation by chlorine on the rubber surface. On the other hand, the chlorination of silica produces the rupture of Si-O bonds and the formation of Si-H and Si-Cl groups. Furthermore, the stirring speed (directly related to the dispersion) of silica into the adhesive is an important parameter which affects the viscosity and peel strength. A stirring speed of 1000 rpm gives the best silica dispersion.     

Addition of Silica to Polyurethane Adhesives

The influence of the addition of silica (Aerosil-200) (5-25 wt%) to polyurethane adhesives on their adhesion properties with non-chlorinated and surface-chlorinated rubbers has been studied. The chlorinating agent was Trichloroisocyanuric acid (TIC) in 2-butanone solution at a concentration of between 1 and 9 wt%. In general, silica produced an increase in the adhesive viscosity and an improvement of green (immediate) peel strength (especially with chlorinated rubber). The best results were obtained for a silica content of 10-20 wt%. However, the addition of silica did not improve the peel strength after a thermal ageing process. Polyurethane adhesives containing silica undergo an improvement in their resistance to degradation by chlorine on the rubber surface. On the other hand, the chlorination of silica produces the rupture of Si-O bonds and the formation of Si-H and Si-Cl groups. Furthermore, the stirring speed (directly related to the dispersion) of silica into the adhesive is an important parameter which affects the viscosity and peel strength. A stirring speed of 1000 rpm gives the best silica dispersion.