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Chlorination of SBS rubbers with different styrene contents using trichloro-isocyanuric acid
Abstract
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).
... Of them, epoxidization of PB subchains has been demonstrated to be effective in improving the polarity of the triblock copolymers. 46,47 For a similar purpose, PS-b-PB-b-PS triblock copolymers have also been modified via chlorination, 48 reactive grafting with maleic anhydride 49,50 or glycidyl methacrylate, 51 and hydrosilylation. 52 Owing to improvement of the polarity, the compatibility of PS-b-PB-b-PS triblock copolymers with polar polymers is significantly improved, and the modified triblock copolymers have been used as good compatibilizing and toughening agents for many polymer blends. ...
In this work, we reported a facile preparation of mesoporous silica materials assisted by a commercial polystyrene-block-polybutadiene-block-polystyrene (PS-b-PB-b-PS) triblock copolymer. For this purpose, the PS-b-PB-b-PS triblock copolymer was first functionalized with (3-mercaptopropyl)triethoxysilane via a thiol-ene radical addition approach, and then the functionalized triblock copolymer with the midblock bearing triethoxysilane moieties was employed to perform intercomponent sol–gel reactions with tetraethoxysilane (TEOS) to obtain the organic–inorganic gels. The organic–inorganic gels with variable compositions were then used as precursors to obtain mesoporous silica via pyrolysis at elevated temperatures. The functionalized triblock copolymer was characterized by means of Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and small-angle X-ray scattering (SAXS). The results of SAXS, transmission electron microscopy, and Brunauer–Emmett–Teller measurements indicate that the mesoporous silica materials were successfully obtained and the porosity of the materials can be modulated with the mass ratios of the functionalized triblock copolymer to the precursor of silica (viz. TEOS).
... Some materials such as thermoplastic rubber (SBSR) are non-polar. In practice it is common to use surface treatment procedures (halogenation, cyclization, treatment with ultraviolet light, etc.) in order to improve their surface properties [2, 21]. Another economically acceptable alternative is the development of adhesives suitable for SBSR bonding. ...
The adhesion properties of polychloroprene can be improved by addition of such materials as piperylene–styrene co-polymer (PSC), VeoVa-10 polymer, VeoVa-11/methyl methacrylate/2ethylhexyl acrylate co-polymer (VeoVa-11/MMA/2EHA) and poly(vinyl acetate) waste (wPVAc). Here, the relationship between adhesion properties and surface tension of polychloroprene was investigated. Contact angle measurements have been used to study the effects of nature and content of polymeric additives on the adhesion and surface properties of polychloroprene. Low-surface-tension VeoVa-10 polymer has the tendency to migrate to the surface of polychloroprene; thus, adhesion is determined mainly by this additive property. Enrichment of polychloroprene film bottom layer by the additive was observed using high-surface-tension PSC and wPVAc. In this case, the adhesion properties of polychloroprene depend on the interactions at the interface. Adhesion properties of polychloroprene were found to depend not only on compatibility between adhesive components, but also on compatibility between the adherend and the adhesive.
As environmental friendly alternative to the halogenation treatment with trichloro isocyanuric acid solutions in organic solvents (TCI/MEK), in this study a water-based surface treatment for rubber materials based in chloramine T aqueous solutions has been proposed. It was found that the effectiveness of chloramine T (CT) (N-chloro-sodium-p-toluenesulphenamide) as chlorinating agent for rubber depends on the pH of the chlorinating solution. The surface modifications and adhesion in one SBS rubber treated with aqueous solutions of CT has been studied. Acidification of CT aqueous solutions produced the formation of dichloramine T (DCT) and hypochlorous acid (HClO), species which reacted with C = C bonds of the butadiene units. A decrease in the pH of the CT aqueous solutions produced more extended surface modifications and improved adhesion properties in the joints produced with chlorinated SBS rubber and waterborne polyurethane adhesive. T-peel strength values obtained were slightly lower than those obtained for the SBS rubber surface treated with the organic solvent chlorinating system (TCI/MEK). The solvent effect leading to local swelling and therefore to deeper modifications in the rubber near surface properties was not present with water based solutions, and then, the modifications were much more superficial. On the other hand, acidification with hydrochloric acid produces deposition of NaCl crystals on the SBS rubber surface. Thus, acidification of the chloramines T solution with sulfuric acid was preferable.
Chlorination of a thermoplastic styrene-butadiene-styrene rubber (S0) with a solution of 2 wt% trichloroisocyanuric acid (TCI) in ethyl acetate improved its adhesion to polyurethane adhesives. The analysis of the failed surfaces (obtained after T-peel test of S0/PU joints) showed that the locus of failure in the rubber/polyurethane joints progresses from adhesion (in non chlorinated-S0/PU joint) to cohesion in the chlorinated layer (for chlorinated-S0/PU joint) The composition of this chlorinated layer differed from the composition of the non bonded-chlorinated rubber, i.e. the failure of the joint was located in a chlorinated layer with a distinctive chemistry. On the other hand, the analysis of the chlorinated rubber/PU adhesive interface showed that chlorination with TCI produces a crosslinking of the rubber surface as well as strong interactions between the uppermost-chlorinated layer and the PU adhesive.
Traditionally, it has been believed that there is an incompatibility between the chlorinated rubber surface and polychloroprene adhesives resulting in a lack of adhesion. However, in this study it has been shown that a polychloroprene adhesive (PCP30P) produces similar T-peel strength values when using a polyurethane (PU) adhesive in joints produced between a chlorinated thermoplastic SBS rubber and roughened leather. In both cases a cohesive failure mode within the rubber was obtained. This polychloroprene adhesive (PCP30P) contains a thermoreactive phenolic resin in its formulation. The nature of the resin greatly influences the viscoelastic properties of the polychloroprene adhesive. Thus, polychloroprene adhesive with no resin or with resins of a different nature do not produce suitable adhesive joints between the chlorinated rubber and the leather (Terpene phenolic resin (PCP30TP), a glycerol esther colofony resin (PCP30EC) and an aromatic hydrocarbon resin (PCP30AH) were studied). The interactions produced between the chlorinating agent and the adhesive were studied by ATR-IR on solid films of the polychloroprene adhesives and the tackifier resins previously immersed in the chlorinating solution (0.5 and 3 wt% TCI/MEK). All the polychloroprene adhesives were modified by the chlorinating agent, being capable of producing a good interaction with the chlorinated rubber surface at the interface. Therefore, the good performance of the PCP30P adhesive compared with the other polychloroprene adhesives has been ascribed to theological behavior more similar to the PU adhesive assessed by DMTA. The PCP30P adhesive is the most elastic material among all the considered polychloroprene adhesives. This increased elasticity and better viscoelastic properties are imparted by the thermoreactive phenolic resin in its formulation.
Ground rubber tire (GRT) powders were chlorinated by trichloroisocyanuric acid (TCLCA). GRT powders of different chlorination levels were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDAX), attenuated total reflection infrared (ATR-IR) spectroscopy, thermal, dielectric, and stress-strain properties on molded GRT specimens. Surface energy of the powders was estimated. Dynamic mechanical thermal analysis of molded GRT specimen reveals a biphasic structure. Plasticized poly(vinyl chloride) (PVC) compound, when blended with chlorinated GRT, shows improved physical properties in comparison to non-chlorinated GRT.
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.
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.
A styrene–butadiene–styrene (SBS) block co-polymer was functionalized using different amounts of N-carbamyl maleamic acid (NCMA) and benzoyl peroxide as initiator. NCMA, which is a bifunctional monomer, was synthesized in our laboratories. The concentration of NCMA used in the functionalization of SBS ranged from 0.5 to 3% (w/w) based on the co-polymer mass. Benzoyloxy radicals generated from the thermal decomposition of benzoyl peroxide initiated the grafting reaction. The concentration of the initiator was kept constant at 0.076% (w/w). FT-IR spectroscopy was used to determine the amount of NCMA effectively grafted onto the SBS. The maximum amount of monomer grafted was about 0.3% (w/w) when the SBS was modified with 1% (w/w) NCMA. The effect of grafting on the surface properties and the adhesion to polyurethane adhesive of the modified SBS were evaluated. Contact angle values were obtained using liquid droplets. When the concentration of the NCMA used in the grafting reaction was 1% (w/w), the contact angles with water on original and modified SBS were 95° and 77°, respectively. Adhesion properties were evaluated by standard peel tests employing a commercial polyurethane adhesive. The modified SBS having the largest amount of NCMA displayed a T-peel strength value 5-times higher than the corresponding value measured with the original SBS.
In this study, it was shown that the degree of effectiveness produced by halogenation with trichloroisocyanuric acid (TCI) was influenced by previous methyl ethyl ketone (MEK) wiping of a synthetic vulcanized styrene-butadiene rubber (R2) surface. The MEK wiping of the R2 rubber surface prior to chlorination with TCI removed the paraffin wax layer from the surface, which favoured the chlorination and oxidation reactions of the rubber. Chlorination with TCI decreased the contact angle values (increased the wettability) mainly due to the creation of C–Cl and C=O moieties, as well as roughness. The amount of these chemical moieties increased when the MEK wiping was applied prior to chlorination, so higher degrees of chlorination and oxidation were obtained on the R2 rubber surface. T-peel strength values increased more markedly if the MEK wiping was carried out before chlorination with TCI, in agreement with the higher degree of modifications produced in the R2 rubber surface. In fact, a cohesive failure in the R2 rubber was obtained in the adhesive joint produced with MEK wiped + TCI chlorinated R2 rubber.
The effectiveness of the chlorination treatment of synthetic vulcanized styrene-butadiene rubbers is determined by several experimental variables. In this study, trichloroisocyanuric acid (TCI) solutions in butanone have been used as chlorinating agents for a difficult-to-bond vulcanized styrene-butadiene rubber (R2). The influence of the TCI concentration (0.5 and 2 wt% TCI/MEK) was studied and a comparison between the immersion and brushing procedures to apply the chlorinating agent has been carried out. Characterization of the chlorinated surfaces was carried out using contact angle measurements (water, 25°C), ATR-IR spectroscopy, and scanning electron microscopy (SEM). T-peel tests on similarly treated R2 rubber/polyurethane adhesive joints were carried out to quantify adhesion. The chlorination by immersion of R2 rubber with TCI/MEK solutions was less effective than using a brush. The effects of the chlorination were similar using both procedures (creation of roughness, improved wettability, C Cl moieties formation and deposition of TCI particles), but the extent of the modifications was more marked when using a brush. The higher concentration of chlorinating agent allows a higher degree of chlorination. Peel strength values were lower for brush-chlorinated R2 rubber because the migration of wax (which created a weak layer on the rubber surface) from the bulk to the R2 rubber surface was favoured. However, the presence of waxes on the R2 rubber surface still allowed a reasonable level of adhesion due to the predominance of polar moieties.
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.
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.
Chlorination of a thermoplastic styrene-butadiene-styrene rubber (S0) with different amounts of trichloroisocyanuric acid (TCI) solutions in ethyl acetate improved its adhesion to polyurethane adhesives. A strong interaction of the PU (polyurethane) adhesive and the chlorinated S0 rubber chains is produced at the interface. The increase in the concentration of TCI from 0.5 wt% up to 2-7 wt% resulted in the deposition of crystallites of unreacted TCI on the rubber surface. The remaining TCI on the rubber surface migrates through the PU adhesive producing some chlorination of the PU chains. The failure of the joint is located in this interface composed of both chlorinated S0 rubber and partially-chlorinated PU adhesive.
Three thermoplastic block styrene–butadiene–styrene (TR) rubbers were treated with sulfuric acid to improve their adhesion to polyurethane adhesives. T-peel test, scanning electron microscopy (SEM), contact-angle measurements (water, ethane diol), infra red spectroscopy (ATR-IR) and stress–strain experiments were used to analyze the nature of surface modifications produced in the rubber. The length of the treatment and the neutralization procedure (with and without ammonium hydroxide) were considered in this study. The treatment produced the sulfonation of the butadiene units of the rubber and the creation of highly conjugated CC bonds, which produced a change in the color of the TR rubbers. The treatment also produced a decrease in the tensile strength and the elongation at break of the TR rubbers. This suggests that the treatment with sulfuric acid was not restricted to the rubber surface but also produced a bulk modification. The lower the styrene content in the TR rubber, the more significant modifications were produced on the surface. The styrene content (33–55wt%) in three thermoplastic styrene–butadiene (TR) rubbers affected the extent, but not the nature of the surface modifications produced by treatment with sulfuric acid. The H2SO4 treatment increased the T-peel strength of S1 and S2 rubber/polyurethane adhesive joints and produced a mixed failure mode (adhesion+cohesive failure in the rubber). Sulfonation of the TR rubbers is fast and needs only a 30s immersion in sulfuric acid to produce high adhesion. Furthermore, the neutralization of the acidic surface with ammonium hydroxide is critical to assure an adequate durability of the adhesive joints.
The surface modifications of a synthetic vulcanized styrene-butadiene rubber (R1) using a chemical treatment [halogenation with trichloroisocyanuric acid (TCI)] and a treatment with oxygen plasma were compared. Treatment of R1 rubber with 2 wt% TCI produced greater surface modification than the oxygen plasma and the modification was extended over a thicker region of the rubber when it was treated using TCI. The degree of oxidation obtained with only 1 min of oxygen plasma treatment was greater than that obtained by chlorination with different amounts of TCI. This agreed with the improved interaction among polar groups evaluated from the higher acid–base contribution to the surface energy of the oxygen plasma-treated R1 rubber surface. However, higher T-peel strength values and more noticeable cohesive failure in the rubber were obtained for joints produced with chlorinated R1 rubber than for those produced with oxygen plasma-treated R1 rubber, due to the creation of a less rough and weaker oxygen plasma-treated surface.
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
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.
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.
The interface produced between a chlorinated thermoplastic styrene-butadiene-styrene rubber and a polychloroprene (PCP) adhesive has been studied and compared to the interface produced using a polyurethane (PU) adhesive. Chlorination of the rubber was produced by spin coating solutions of trichloroisocyanuric acid in methyl ethyl ketone. The adhesive solution was spin coated on to the chlorinated rubber and the interface between the chlorinated rubber and the adhesive was analyzed by infrared spectroscopy.
Chlorination of the rubber produces cross-linking of the outermost chlorinated and oxidized rubber surface, which becomes insoluble in toluene. The chlorinated rubber chains are able to migrate through the chlorinated rubber/adhesive interface and produce a cross-linked interface. Similar interfaces are obtained with PU or PCP adhesive. However it is the addition of a thermoreactive phenolic tackifier resin to the PCP adhesive, which imparts appropriate rheological properties to the PCP adhesive, responsible for the increased adhesion properties. Copyright
Chlorinated ground rubber tire (Cl-GRT) particles were used as filler in a plasticized polyvinylchloride (PVC) to develop a melt-processable rubber composition. Physical properties of the Cl-GRT-filled PVC compound showed improvement compared to the nonchlorinated counterpart. Interaction between Cl-GRT and PVC was examined on the basis of results of stress relaxation, dynamic mechanical thermal analysis, and solvent swelling studies. The Cl-GRT could be loaded upto 40 parts per hundred parts of PVC, and the composition still retains the elastomeric characteristics. The Cl-GRT-filled composite was found to be reprocessable like the unfilled PVC compound. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 622–631, 2002; DOI 10.1002/app.10352
Two different surface treatments have been applied to a synthetic vulcanized styrene-butadiene rubber (R1): corona discharge and UV treatment. Corona discharge treatment has been carried out on R1 rubber by varying the electrode-sample distance (2–4 mm), the duration (1 to 11 sec) and several parameters in the treatment of R1 rubber with UV treatment (lamp-sample distance between 1 and 5 cm, the duration between 30 sec and 5 min). The effects on both treatments on the surface of R1 were analyzed using contact angle measurements, ATR-IR spectroscopy, Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). A noticeable decrease in contact angles was observed on the R1 rubber by applying both treatments, although the modifications produced on the rubber surface were different. Corona discharge mainly affected the morphology of the R1 rubber surface whereas UV treatment mainly modified its chemistry. The migration of zinc stearate was only produced by UV treatment but not with corona discharge. Therefore, the UV treatment of R1 rubber was more aggressive, facilitating the migration of moieties from the bulk to the surface and producing oxygen moieties.
Corona discharge and ultraviolet (UV) radiation treatments have been used as environmental friendly alternatives to the common surface treatment of halogenation for a styrene–butadiene–styrene (S6) rubber. The corona energy and the length of treatment under UV radiation of the S6 rubber have been studied and the surface modifications produced have been assessed by contact angle measurements, ATR-IR spectroscopy, XPS and SEM. Adhesion properties were obtained from T-peel tests of surface treated S6 rubber/polyurethane adhesive/leather joints.Corona discharge and UV radiation treatments modified the S6 rubber surface by creating C–O, C=O and COO− moieties that improved wettability. The extent of the surface modifications of S6 rubber was different by treatment with UV radiation or corona discharge. The higher the corona discharge energy or the higher the length of the UV radiation treatment, the more marked modifications were achieved on the S6 rubber surface. On the other hand, corona discharge and UV radiation treatment produced different morphologies on the S6 rubber surface. The poor adhesion obtained with the corona discharge treatment has been ascribed to a lack of surface roughness and/or the creation of weak boundary layer on the S6 rubber. On the contrary, UV radiation treatment produced cracks on the S6 rubber surface that favored the mechanical adhesion. The modifications produced by both treatments were compared to those produced by the solvent-based halogenation treatment.
The aim of this paper is to contribute to the understanding of the nature of the changes produced in SBR samples by modifying their surface characteristics and using different techniques: peel strength tests, scanning electron microscopy (SEM), contact-angle measurements, and infrared spectroscopy (FTIR). The combination of all of these experimental procedures would give a more detailed idea about the SBR surface modifications. On the other hand, a comparison with previously published papers relating to the same subject will also be considered.
Thermoplastic rubber is truly a useful and versatile class of polymer. It has the solubility and thermoplasticity of polystyrene, while at ambient temperatures it has the toughness and resilience of vulcanized natural rubber or polybutadiene. This characteristic results from its unique molecular structure. Visualize the simplest thermoplastic rubber molecule: a rubbery midblock with two plastic endblocks. This situation is pictured schematically in Fig. 1 where the diamonds represent monomer units in the plastic endblocks and the circles represent monomer units in the rubbery midblock. Such a molecule is called a block copolymer.
Five polycaprolactone polyurethane adhesives of similar chemical nature but different viscosities were used to bond ultrasonically cleaned, unchlorinated and chlorinated, styrene-butadiene rubber adherends. The peel strengths of the joints were influenced by the adhesive viscosity. Contact angle measurements using several liquids (water, ethane diol, glycerol, 1-bromonaphthalnene and tricresyl phosphate) and the adhesives did not display the same trend as that noted in the peel strength experiments. Therefore, the changes in peel strength could not be ascribed to thermodynamic factors only, since there was also a reaction between the chlorine in the surface modified adherends and the polyurethane. On the other hand, it has been shown that an increase in polar and a decrease in non-polar groups of the polyurethane adhesives is produced for those adhesives having a viscosity less than 2 Pa s.
The nature and formulation of two synthetic sulfur-vulcanized styrene-butadiene rubbers affected the extent, but not the nature, of the surface modification produced by halogenation with different amounts (1-7 wt%) of trichloroisocyanuric acid (TCI) solutions in ethyl acetate. R1 rubber had a low oil and plasticizer content, whereas R2 rubber contained a smaller amount of styrene than R1, and a relatively significant amount of oil and plasticizer. Chlorination of the rubbers decreased their tensile strength (more markedly in R2) without noticeable changes in elongation at break, and heterogeneities and cracks were created on the rubber surface (mainly in R2). The surface modifications were not influenced by the manner in which the post-chlorination agent was removed (air or vacuum). Chlorination with TCI created C-Cl, C-O, and COO- moieties on the rubber surface which were responsible for its enhanced acid-base contribution to the surface energy. The extent of chlorination was more extensive in R1 (the rubber with a smaller butadiene content). The surface modification was less effective for R2, due to its noticeable amount of oil and plasticizer. On the other hand, when the chlorination was carried out with 7 wt% TCI, removal of the excess of the post-chlorination agent in vacuum prevented the formation of weak boundary layers (due to isocyanuric acid + mechanically damaged surface) in the treated surfaces. The nature and formulation of the rubber determined the thickness of the weak boundary layer (thinner in R1). On the other hand, a relatively deep penetration (at least 10 nm) of the chlorination agent into the rubber bulk was produced.
Surface modifications produced by treatments (mainly halogenation) of synthetic vulcanized styrene-butadiene rubber (SBR) leading to increased adhesion properties with polyurethane adhesives have been studied. T-peel tests, scanning electron microscopy (SEM), advancing contact angle measurements, infra-red (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC) were used to analyze the nature of surface modifications produced in the rubber. Although some surface heterogeneities were created, physical treatments (ultrasonic cleaning, solvent wiping, abrasion) did not noticeably increase the adhesion strength because certain abhesive substances (e.g. zinc stearate, paraffin wax) cannot be removed from the rubber surface by such treatments. Chemical treatment (chlorination) was carried out using ethyl acetate solutions of trichloroisocyanuric acid (TCI) (1,3,5-trichloro-1,3,5-triazine-2,4,6-trione). Chlorination of SBR with trichloroisocyanuric acid produced a significant improvement in T-peel strength, due to the contribution of mechanical (surface roughness, microcracks), thermodynamical (increase of polar contribution to the surface energy) and chemical (removal of abhesive substances, creation of polar groups) rubber surface modifications. The strong adhesion between the chlorinated SBR surface and the polyurethane adhesive was due to the presence of oxidized species of >C=O, -C-OH and -COR type. Chlorination of SBR is a fast reaction which needs only a small concentration of chlorination agent (< 1 wt% TCI/ethyl acetate) to produce high adhesion levels. An increased amount of TCI facilitated the chlorination reaction progressing from the exterior to the internal rubber bulk; however, although a thicker layer of chlorinated rubber created no further increase in adhesion strength was obtained.
Halogenation of styrene-butadiene rubbers has been carried out using solutions containing different amounts (0.1-5 wt%) of trichloroisocyanuric acid in butan-2-one. The treated rubber surface showed increased peel strength in joints made with polyurethane adhesive. The effects of chlorination on the rubber surface were studied using scanning electron microscopy, contact angle measurements, and infrared spectroscopy. It was shown that cracks appear in the rubber surface after halogenation, a factor which favours adhesion; the larger the amount of trichloroisocyanuric acid used, the larger the number of cracks. On the other hand, chlorination of the carbon double bond (butadiene) and the formation of carboxylic acid groups seem to be the most important chemical changes in the chlorinated rubber surfaces. Chlorination increases the surface energy of the rubber, although this increase is a function of the rubber composition. In fact, for a simple rubber formulation, the polar component of the surface energy increases for the highest concentrations of chlorine on the rubber surface; but for rubber with a more complicated formulation, the same value of surface energy after chlorination was obtained, independently of the amount of trichloroisocyanuric acid added. A good correlation was found between the contact angle measurements, the infrared spectra, and the peel strength values.
Epoxy adhesives were used to produce strong and durable bonds between steel and four types of vulcanized elastomer. Chlorination of the elastomer surface prior to bonding and the use of an epoxy primer on the grit blasted steel surface gave the best results in laboratory trials as well as after tropical marine immersion for three years. A layer of natural rubber approximately 6 mm thick was found to be sufficient, if correctly bonded, to prevent completely the corrosion of mild steel during three years' immersion in tropical seawater. This system also performed well under dynamic flow conditions which were equivalent to a vessel travelling at a speed of 20 knots for 450,000 km.
This paper describes detailed studies on the chlorination of vulcanized elastomer surfaces by an organic chlorine donor and the bonds obtained between such surfaces using a polyamide-cured epoxy adhesive. The bonds produced with a range of commercially important elastomers were found to retain their strength during extended seawater immersion better than those produced using the earlier surface treatments. The practical parameters of this technique have been investigated to establish the requirements for reliable and effective bonding. The chlorinated elastomer surfaces have been examined and explanations are offered for the changes observed.
The paper presents the results of chemical investigations into some of the bonding problems of the footwear industry and pays particular attention to the importance of the substrate surfaces.The importance of the presence of metal soaps on rubber surfaces and their detrimental effect on adhesion is pointed out together with the concomitant beneficial effects of solvent soap dispersing treatments on subsequent adhesion.The special needs of the footwear industry for a single adhesive system capable of adhering strongly to a wide range of substrates led to the requirement of improving the bond of urethane adhesives to rubber surfaces. The role of free isocyanates in promoting this bond is outlined.The practical advantages of halogenating rubber surfaces in conferring excellent adhesion properties on moulded rubber surfaces when used with solvent urethane adhesives are pointed out. The observed phenomena associated with halogenation are discussed qualitatively in relation to proposed theories of adhesion.
In this paper two kinds of weak boundary layers (WBL) in synthetic vulcanized styrene-butadiene rubber are described.
i) WBL produced by the presence of antiadhesion compounds of the rubber formulation (zinc stearate, microcrystalline paraffin wax). These WBL cannot be effectively removed by solvent wiping, whether followed by washing with an ethanol/water mix or not. Although this treatment allowed a significant removal of zinc stearate, the paraffin wax concentration on the surface was not greatly reduced, thus, poor adhesion of rubber was obtained. Chlorination with small amounts of ethyl acetate (EA) solutions of trichloro isocyanuric acid (0.5–5 wt% TCI/EA) and/or an extended halogenation treatment increased the adhesion strength and effectively eliminated the zinc stearate from the rubber surface. If an additional heat treatment (50°C/24h) of the chlorinated rubber was also carried out, the WBL was more effectively eliminated and the resulting adhesion was independent of the amount of chlorination agent applied to the rubber surface. Furthermore, this heat treatment favoured the elimination of WBL in the untreated rubber and also contributed to the removal of WBL produced by an excess of halogenation agent.
ii) WBL created by an excess of chlorination agent applied to the rubber surface. The excess of chlorination agent produced lack of adhesion in the rubber because there was significant damage of the rubber surface and a non-rubber surface layer was formed (mainly due to oxidized, chlorinating agent residues and cyanuric acid), which contributed to the formation of WBL. To avoid the creation of WBL, a postchlorination treatment of rubber with a solution of 25 wt% ethanol in water followed by a vacuum-drying process produced excellent results. The effectiveness of this treatment relied on combining an adequate degree of chlorination with no external surface deterioration of the rubber by the excess of chlorination agent.
The surface of an unvulcanized styrene-butadiene-styrene (SBS) rubber (S0) was chlorinated with 0.5–7wt% trichloroisocyanuric acid (TCI) solutions. The adhesion strength of surface-treated SO rubber/polyurethane adhesive joints was obtained from T-peel tests. The failed surfaces after peeling were characterized by ATR-IR spectroscopy, contact angle measurements, SEM coupled with EDX analysis and XPS. The untreated SO rubber shows no adhesion because of a lack of compatibility with the polyurethane adhesive. Chlorination of SO rubber with O.5wt% TCl produced a noticeable increase in T-peel strength which was due to the formation of CCl and CO species on the rubber surface, the failure of the joint being produced at the chlorinated surface (weak boundary layer). Treatment of S0 rubber with greater concentrations of TCI, up to 2wt%, resulted in a decrease in the joint strength because the locus of failure was directed deeper into the chlorinated layer. On the other hand, the treatment of S0 rubber with 7wt% TCI produced different joint strength values in replicate joints that were tested under similar experimental conditions, mainly owing to differences in the locus of failure in the joints. Failure occurred randomly throughout the adhesive, the interface or the surface chlorinated layer.