Influence of Additives in Adhesion of UV Radiation Surface-Treated SBS Rubber

In this study, the effect of additives (oils, lubricants) included in the formulations of different block styrene–butadiene–styrene (SBS) rubbers on the effectiveness of the ultraviolet (UV) radiation treatment to improve adhesion to polyurethane adhesive was analyzed. The modifications on the UV-treated rubber surfaces for different lengths of treatment have been characterized by contact-angle measurements (ethylene glycol, 25°C), Attenuated Total Reflectance-Infrared (ATR-IR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM). The adhesion properties have been evaluated from T-peel strengths of treated rubber/polyurethane adhesive/leather joints. The UV-radiation treatment on all rubber surfaces produced an increase in wettability, carbon–oxygen polar moieties, and ablation. The oxidation degree produced on the rubber surface treated with UV radiation was less when oils and lubricants were included in the formulation, likely due to competition of the oxidation process with the migration of low-molecular-weight additives to the rubber surface. On the SBS2 rubber surface (rubber containing carbon black and calcium carbonate fillers), the migration of oils and lubricants was also produced during the UV-radiation treatment, but a decrease in adhesion occured likely due to the lower tensile strength and higher extent of oxidation produced by the UV radiation treatment.     

UV-Ozone Surface Treatment of SBS Rubbers Containing Fillers: Influence of the Filler Nature on the Extent of Surface Modification and Adhesion

SBS rubbers containing different loadings of calcium carbonate and/or silica fillers were surface treated with UV-ozone to improve their adhesion to polyurethane adhesive. The surface modifications produced on the treated filled SBS rubbers have been analyzed by contact angle measurements, ATR-IR spectroscopy, XPS and SEM. The adhesion properties have been evaluated by T-peel strength tests on treated filled SBS rubber/polyurethane adhesive/leather joints. The UV-ozone treatment improved the wettability of all rubber surfaces, and chemical (oxidation) and morphological modifications (roughness, ablation, surface melting) were produced. The increase in the time of UV-ozone treatment to 30 min led to surface cleaning (removal of silicon-based moieties) due to ablation and/or melting of rubber layers and also incorporation of more oxidized moieties was produced. Although chemical modifications were produced earlier in an unfilled rubber for short time of treatment with UV-ozone, they were more noticeable in filled rubbers for extended length of treatment, mainly for S6S and S6T rubbers containing silica filler. The oxidation process seemed to be inhibited for S6C and S6T rubbers (containing calcium carbonate filler). On the other hand, the S6S rubber containing silica filler and the lowest filler loading showed the higher extent of modification as a consequence of the UV-ozone treatment. The UV-ozone increased the joint strength in all joints, more noticeably in the rubbers containing silica filler, in agreement with the greater extents of chemical and morphological modifications produced by the treatment in these rubbers. Finally, the nature and content of fillers determined the extent of surface modification and adhesion of SBS rubber treated with UV-ozone.     

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.     

Influence of calcium carbonate added to the SBS rubber formulation on the surface modifications produced by halogenation

To improve the adhesion properties of styrene–butadiene–styrene (SBS) rubber sole to polyurethane adhesive, surface treatments are required, of which halogenation with trichloroisocyanuric acid (TCI) solutions in organic solvents is the most commonly used treatment in the footwear industry. Calcium carbonate filler is commonly added to improve the mechanical properties and to reduce shining of SBS rubber formulations. The influence of the filler on the effectiveness of surface chlorination of SBS rubber had not been considered in the existing literature. Therefore, 10 wt% calcium carbonate filler was added to the SBS rubber formulation and the surface modifications and adhesion properties produced by treatment with TCI solutions were investigated. The resulting surface modifications and adhesion were compared to those obtained in unfilled SBS rubber. It is shown that the treatment with TCI solutions was less effective in the calcium-carbonate-filled SBS rubber and a lower peel strength to polyurethane adhesive was obtained; however, a cohesive failure in the rubber was always obtained.     

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.     

Ultrasonic cleaning of SBR rubber to improve the performance of subsequent plasma torch treatment

Paraffin wax and other moieties in sulfur vulcanized styrene-butadiene rubber formulations may migrate to the surface, reducing the adhesive strength in joints produced with polyurethane adhesive. In this study, with the aim to remove paraffin wax and other anti-adhesion moieties on the rubber surface to improve adhesion, prior to plasma torch treatment, a methyl ethyl ketone (MEK) cleaning in an ultrasonic bath has been carried out. The surface modifications produced on the rubber surface have been analyzed by contact angle measurements, ATR-IR spectroscopy, XPS and SEM. The adhesion properties have been evaluated by T-peel strength of treated rubber/polyurethane adhesive joints. Ultrasonic cleaning in MEK resulted in partial removal of paraffin wax on the rubber surface and, thus, lower contact angle values, decreased relative intensity of the infrared bands due to hydrocarbon moieties and lower percentage of carbon assessed from XPS spectroscopy were obtained. The ultrasonic cleaning in MEK of the rubber increased the effectiveness of the atmospheric pressure plasma torch treatment, and surface oxidation was produced. However, the oxidation degree decreased with time after plasma torch treatment, likely due to ageing of the surface treated rubber.     

Weak boundary layers on vulcanized styrene–butadiene rubber treated with sulfuric acid

A synthetic vulcanized styrene-butadiene rubber (R2) was used in this study. The presence of paraffin wax and zinc stearate in the rubber composition prevented the adhesion of R2 rubber to solvent-based polyester-urethane adhesive. To increase the adhesion properties of R2 rubber, a surface treatment with sulfuric acid (cyclization) was applied, and the length of the immersion in sulfuric acid and the time between the immersion time and the neutralization were varied. The treated R2 rubber surfaces were characterized using ATR-IR spectroscopy, contact angle measurements (water, ethanediol), and scanning electron microscopy (SEM). The mechanical properties of the treated rubber were obtained from stress-strain experiments. The joint strength was obtained from the T-peel test on treated R2 rubber/polyurethane adhesive joints. Due to the penetration of the sulfuric acid into the R2 rubber bulk, the mechanical properties decreased. The treatment with sulfuric acid produced several chemical modifications on the rubber surface: sulfonation of the butadiene and the creation of C C and C O bonds. Furthermore, the surface treatment of the R2 rubber with sulfuric acid removes paraffin wax from the rubber surface, which had a beneficial effect on adhesion to the polyurethane adhesive. To remove the wax layer, the surface was wiped with petroleum ether solvent after treating the R2 rubber with sulfuric acid. However, in some experiments a progressive migration of wax from the R2 rubber bulk to the surface with time happened. The migration of wax was prevented by increasing the immersion time in H₂SO₄ by more than 5 min.     

Effect of temperature on the extent of migration of low molecular weight moieties to rubber surface

Vulcanized rubbers contain different low molecular weight additives in their formulation, including antiozonants, plasticizers, oils, etc. These moieties - mostly paraffin wax - often migrate to the surface causing a weak boundary layer of non-rubber contaminants which is deleterious for adhesion of rubber to adhesives (such as polyurethane and polychloroprene adhesives). One of the key steps in the manufacturing of rubber/adhesive joints is the reactivation, i.e. sudden heating of the thin adhesive layers on the substrates to be joined under infrared (IR) radiation to 80-90 °C for a few seconds to allow diffusion of the polymeric chains under pressure. This reactivation may cause the migration of low molecular weight additives to the rubber surface causing a lack of adhesion. The main aim of this study was to .identify the influence of the reactivation temperature (40 to 170 °C) on the surface properties of sulphur vulcanized styrene-butadiene rubber and determine the extent of the diffusion of paraffin wax and zinc stearate to the rubber surface. The changes produced on the rubber surface were measured immediately after reactivation treatment by ethylene glycol contact angle measurements, attenuated total reflectance infrared spectroscopy (ATR-IR) and scanning electron microscopy (SEM). Additionally, the weight loss of the rubber after reactivation at different temperatures was recorded.The reactivation of the rubber at different temperatures produced changes in the morphology and thickness of the paraffin wax layer on the surface. By heating at temperature close to that of the paraffin wax melting point, the paraffin wax migration was favoured and at the same time the crystals of paraffin wax on the rubber surface were melted. As a consequence a thicker and smoother film of melting paraffin wax was formed. By increasing the reactivation temperature, a partial removal of paraffin wax was produced and the thickness of the paraffin wax film on the rubber surface was reduced. For reactivation temperatures below 90 °C, the higher the temperature, the lower the weight loss of the rubber, because the increase in the surface area of the melted paraffin wax layer that prevented migration from the rubber bulk. However, for reactivation temperature higher than 90 °C, the weight loss of the rubber increased with the reactivation temperature and this was likely due to sublimation of the paraffin wax on the rubber surface. Besides, even after reactivation at 170 °C, a thin film of paraffin wax always remained on the rubber surface as was evidenced by contact angle measurements. On the other hand, a critical reactivation temperature at 90-100 °C existed at which the migration of zinc stearate to the paraffin wax layer on the rubber surface was favoured.     

Chemical modification of styrene–butadiene–styrene (SBS) rubber by reactive grafting with maleic anhydride

A procedure to increase the adhesion of block styrene-butadiene-styrene (SBS) rubber consisting of the reactive grafting with maleic anhydride (MA) in the presence of an organic peroxide radical initiator is proposed. The influence of the reactive grafting on the surface properties of SBS has been studied with special emphasis on the improvement of the adhesion to polyurethane adhesive. The grafting of MA onto SBS was carried out in the presence of different concentrations of 2,5-dimethyl-2,5-di(tertbutyl peroxy) hexane (DBPH) as initiator to generate oxygen radicals by thermal decomposition, which induce the grafting reaction. The modification process was performed in the molten state using a Brabender mixer to premix the reactants and a hot press to initiate the functionalizing reaction. ATR-IR and XPS spectroscopies were employed to verify the grafting of MA on SBS. The changes in wettability on the modified SBS rubber were determined by contact angle measurements. Adhesion properties were evaluated from T-peel tests of SBS rubber/polyurethane adhesive joints. Reasonable extents of MA grafting on SBS were obtained (evidenced by the presence of a weak carbonyl vibration at 1700 cm^-1 in the ATR-IR spectra and by the carbon- oxygen band at a binding energy of 287.0 eV in the XPS spectra). The higher the DBPH amount, the higher the MA amount grafted onto the SBS surface. The maximum grafting level was obtained using 2 wt% MA. Grafted species seemed to be mainly concentrated on the surface of the SBS-molded sheets. The wettability of the modified rubber increased with respect to the original polymer, new carbon-oxygen moieties were created and the C/O ratio increased. A noticeable enhancement in peel strength values was observed, which was ascribed to the creation of interfacial interactions between the polyurethane and the SBS rubber surfaces.     

Chlorination of SBS rubbers with different styrene contents using trichloro-isocyanuric acid

In order to improve their adhesion to polyurethane adhesives, three unvulcanized block styrene-butadiene-styrene (SBS) rubbers with styrene contents between 33% and 55% were surface-treated with solutions of 2 wt% trichloro-isocyanuric acid (TCI) in ethyl acetate. The joint strength was estimated using T-peel tests and the failed surfaces were analyzed to assess the locus of failure. The failed surfaces were analyzed using ATR-IR spectroscopy, contact angle measurements, XPS, and SEM. An unexpected trend in the joint strength was obtained because the locus of failure depended on both the styrene content and the mechanical properties of each SBS rubber. A mixed mode of failure was obtained in joints produced with S 1 rubber (33 wt% styrene content), whereas failure in the chlorinated layer was observed with S3 rubber (55 wt% styrene content); cohesive failure in the adhesive was found for the joints produced with S2 rubber (44 wt% styrene content).     

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.     

Enhancing adhesive joints between commercial rubber (SBS) and polyurethane by low-pressure plasma surface modification

The paper presents research on the two-stage process of low-pressure plasma surface modification of a commercial SBS rubber, improving its adhesion to both the polyurethane adhesive in an organic solvent (PU) and the aqueous polyurethane adhesive dispersion (ADPU). The plasma surface modification process was carried out in a flow reactor with parallel plate electrodes, in which plasma was generated by an RF glow discharge (13.56 MHz). In the first stage of the process, the Ar or O₂ plasma was used, and then, as the second stage of the modification process, the treatment was performed in H₂O plasma. The adhesive properties of the plasma-modified SBS rubber surface were determined using the 180^o-peel strength test (PS). These results were correlated with surface properties investigated using contact angle (CA) measurements, FTIR-ATR spectroscopy, XPS spectroscopy and scanning electron microscopy (SEM). The observed improvement in wettability of the plasma modified surface was attributed to the formation of hydroxyl groups, which was confirmed by spectroscopic methods (FTiR-ATR and XPS). The results of the 180^o-peel strength test showed, in turn, a clear relationship between the capacity of adhesive bonding and the amount of oxygen groups (mainly the hydroxyl groups) as well as the surface roughness, determined by SEM microscopy. It was also found that the effects of the plasma surface modification of the SBS rubber were stable for at least 72 h. The results of this work prove that cleaning and etching of the commercial SBS rubber surface in the first stage of its plasma treatment, followed by chemical modification in the second stage, lead to very strong adhesive joints.     

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.     

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.     

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.     

Treatment of thermoplastic rubberwith chlorine bleach as an alternative halogenation treatment in the footwear industry

Avoidance of solvents in bonding operations is a current demand in the footwear industry. Halogenation of rubber soles with solutions of trichloroisocyanuric acid (TCI) in different solvents has been successfully used to improve bonding to the leather uppers. In this study, the use of chlorine bleach as an alternative water surface treatment for a rubber has been tested. A thermoplastic block styrene thermoplastic (TR) was treated with bleach to improve its adhesion to a water-based polyurethane dispersion adhesive (PUD). T-peel testing, scanning electron microscopy (SEM), contact angle measurements (ethanediol, 25°C), and infrared spectroscopy (ATR-IR) were used to analyze the modifications produced on the rubber surface. Adhesion values were obtained from T-peel testing of joints produced with similarly treated TR rubber test pieces. Different experimental variables were considered in this study, namely the immersion time (0.5-2 min) in bleach, the active chlorine content (43.9- 55.6 g/l) in the bleach, the addition of a wetting agent (1-octyl-2-pyrrolidone) to the bleach, and the application of the surface treatment using an ultrasonic bath. The treatment with bleach produced the chlorination of the hydrocarbon chains on the TR rubber surface and slightly changed the surface roughness. Chlorination of the TR rubber with bleach (free active chlorine=55.6 g/l) was fast and needed only 30 sec immersion in the reagent mixture to produce high adhesion. Furthermore, the active chlorine content in the bleach was critical to assure an adequate T-peel strength value. The addition of 1-octyl-2-pyrrolidone to the bleach increased the wettability of the rubber surface, although it was necessary to carry out the surface treatment in the ultrasonic bath to obtain adequate adhesion to the PUD adhesive. Thermoplastic styrene-butadiene rubber Water-based polyurethane adhesive Bleach Halogenation Water-based surface treatment Contact angle ATR-IR spectroscopy SEM T-peel strength     

TREATMENT OF THERMOPLASTIC RUBBERWITH CHLORINE BLEACH AS AN ALTERNATIVE HALOGENATION TREATMENT IN THE FOOTWEAR INDUSTRY

Avoidance of solvents in bonding operations is a current demand in the footwear industry. Halogenation of rubber soles with solutions of trichloroisocyanuric acid (TCI) in different solvents has been successfully used to improve bonding to the leather uppers. In this study, the use of chlorine bleach as an alternative water surface treatment for a rubber has been tested. A thermoplastic block styrene thermoplastic (TR) was treated with bleach to improve its adhesion to a water-based polyurethane dispersion adhesive (PUD). T-peel testing, scanning electron microscopy (SEM), contact angle measurements (ethanediol, 25°C), and infrared spectroscopy (ATR-IR) were used to analyze the modifications produced on the rubber surface. Adhesion values were obtained from T-peel testing of joints produced with similarly treated TR rubber test pieces. Different experimental variables were considered in this study, namely the immersion time (0.5-2 min) in bleach, the active chlorine content (43.9- 55.6 g/l) in the bleach, the addition of a wetting agent (1-octyl-2-pyrrolidone) to the bleach, and the application of the surface treatment using an ultrasonic bath. The treatment with bleach produced the chlorination of the hydrocarbon chains on the TR rubber surface and slightly changed the surface roughness. Chlorination of the TR rubber with bleach (free active chlorine=55.6 g/l) was fast and needed only 30 sec immersion in the reagent mixture to produce high adhesion. Furthermore, the active chlorine content in the bleach was critical to assure an adequate T-peel strength value. The addition of 1-octyl-2-pyrrolidone to the bleach increased the wettability of the rubber surface, although it was necessary to carry out the surface treatment in the ultrasonic bath to obtain adequate adhesion to the PUD adhesive.

Thermoplastic styrene-butadiene rubber Water-based polyurethane adhesive Bleach Halogenation Water-based surface treatment Contact angle ATR-IR spectroscopy SEM T-peel strength     

Chlorination of vulcanized styrene-butadiene rubber using solutions of trichloroisocyanuric acid in different solvents

The chlorination of vulcanized styrene-butadiene rubbers (SBRs) with trichloroisocyanuric acid (TCI) has been studied. The solvent used to apply the TCI chlorinating solutions on the rubber plays an important role in the effectiveness of the treatment since the solvent determined the degree of penetration of TCI into the rubber and also different chlorinating species were produced depending on the nature of the solvent. Surface modifications produced on a synthetic sulfur-vulcanized SBR using TCI solutions in ethyl acetate (EA), methyl ethyl ketone (MEK), and EA + MEK mixtures have been compared. Furthermore, the effects of a solvent wipe with EA or MEK prior to the chlorination process were also considered. Surface modifications produced by the treatments were analyzed using ATR-IR spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Adhesion was obtained from the T-peel strength of treated rubber/polyurethane adhesive joints. TCI/MEK solutions produced a higher degree of surface modification than TCI/EA solutions, but TCI/EA solutions were more effective in removing zinc stearate from the rubber surface. When high TCI percentages (5-7 wt%) in EA solutions were used, a weak boundary layer (WBL) was created on the rubber surface as a consequence of the deposition of an excess of chlorinating agent on the rubber surface and of by-products (cyanuric and/or isocyanuric acid). The formation of the WBL led to a lack of adhesion in the rubber towards the polyurethane adhesive. When MEK was used as a solvent for TCI, this WBL was not produced on the rubber surface, and thus adhesion was considerably higher even when high concentrations of TCI/MEK were used. Similar effects were produced using EA + MEK mixtures as the solvent for TCI. The wiping of the rubber surface with MEK prior to the chlorination treatment led to good adhesion, irrespective of the percentage of TCI and the solvent used in the chlorinating solution.     

Treatment with Ar–O2 low-pressure plasma of vulcanized rubber sole containing noticeable amount of processing oils for improving adhesion to upper in shoe industry

Vulcanized rubber (L3 rubber) containing intentionally noticeable excess of processing oils in its formulation was treated with Argon–Oxygen (Ar–O₂) (2:1, vol/vol) low-pressure (LP) plasma for achieving a satisfactory level of adhesion to waterborne polyurethane adhesive. The effectiveness of the Ar–O₂ LP plasma treatment of L3 rubber depended on both the configuration of the plasma chamber shelves and the treatment time. Surface modifications were assessed by attenuated total reflectance-IR and X-ray photoelectron spectroscopy, contact angle measurements, and scanning electron microscopy. Ar–O₂ LP plasma treatment in direct configuration provided the most effective surface modification of the L3 rubber, and the increase in the treatment time improved the extent of the surface modifications. However, even important surface modifications were produced by Ar–O₂ LP plasma treatment, adhesion of treated L3 rubber was not improved due to the creation of weak boundary layer at the polyurethane–rubber interface after joint formation. Heating at 80 °C for 12 h of the as-received L3 rubber prior to Ar–O₂ LP plasma treatment enhanced the extent of the surface modifications, and improved adhesion was obtained for Ar–O₂ LP plasma treatment times higher than 600 s.     

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.