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Adhesion of Styrene-Butadiene Rubbers with Different Silica Content
Abstract
The influence of silica content of four styrene-butadiene rubbers on their adhesion to polyurethane adhesives was studied. Untreated rubber shows no adhesion due to a weak boundary layer of zinc stearate. Roughening removed zinc stearate from the rubber surface, increased the surface energy and produced surface roughness, so improved adhesion was obtained. The adhesion increased as the silica content in rubber increased, due to an improvement in intrinsic adhesion, and mechanical and physical properties of the rubbers. Chemical surface treatments (halogenation with trichloroisocyanuric acid, treatment with fumaric acid) provided higher adhesion than roughening. In general, chlorination was somewhat more effective than the treatment with fumaric acid, especially in roughened rubbers. Improved adhesion of chemically surface-treated rubbers was due to enhanced mechanical, thermodynamic and chemical adhesion, and to the improved physical, mechanical and viscoelastic properties of rubbers.
... Numerous studies have been done on SBR blends and adhesives for making them useful to be used in variety of applications. Torró-Palau et al. [101] have studied the improvements to styrene butadiene rubbers after the addition of silica particles. The adhesion between polyurethane and SBR was increased. ...
Adhesives are materials that can bond to various substrates to form a connection that can be either temporary or permanent. These materials exhibit remarkable versatility, making them suitable for a wide array of industrial applications, including those in automotive, construction, packaging, aerospace, textiles, leather, glass, and wood. This review provides an in-depth examination of rubber-based adhesives. The types of rubbers used in adhesives, their properties, applications, and the ingredients that can be added to enhance their properties are discussed. Rubber-based adhesives are widely employed across various industries due to their superior versatility and performance characteristics in a variety of applications, with each requiring certain specific characteristic. These adhesives can be tailored by incorporating a variety of solvents, fillers, plasticizers, resins, curing agents, and antioxidants to meet the demands of each application. This review also examines studies focused on improving the properties of rubber-based adhesives by adding different ingredients. This leads to endless possibilities for developing new rubber-based adhesives that can meet the ever-evolving demands of modern industries.
Non-vulcanized styrene-butadiene rubber thin films were exposed to Radio-Frequency low-pressure air plasma. Two different configurations corresponding to direct and downstream RF plasmas were compared. Optical emission spectroscopy provided information about plasma composition and temperature. The plasma treated SBR surfaces were characterized by contact angles and XPS spectroscopy. Two different phenomenological mechanisms are proposed to describe the observed differences according to the plasma configuration used and account for the impact of the activated gas phase on the structure of plasma-treated non-vulcanized SBR surface..
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.
We have prepared composites of polyvinyl acetate (PVAc) reinforced with solution exfoliated graphene. We observe a 50% increase in stiffness and a 100% increase in tensile strength on addition of 0.1vol% graphene compared to the pristine polymer. As PVAc is commonly used commercially as a glue, we have tested such composites as adhesives. The adhesive strength and toughness of the composites were up to 4 and 7 times higher, respectively, than the pristine polymer.
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.
The influence of unmodified clay, Cloisite Na+ on adhesion between prevulcanized EPDM rubber and unvulcanized EPDM rubber containing nanoclay was investigated using 180° peel test. The rubber showed improvement in peel strength with increasing clay concentration up to 4 phr, beyond which it decreased. A maximum of 51% improvement in peel strength was obtained for 4 phr Cloisite Na+. This was attributed to enhanced tensile strength, monomer friction coefficient, marginal improvement of polarity and micro-roughness of the clay filled rubber. At higher clay loading (8 phr), the peel strength reduced due to formation of boundary layer of Zn-stearate, accelerators and clay on the outermost surface, diffusion of the fewer rubber chains, agglomeration of the clay particles and increased modulus of the rubber.
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.
Two styrene–bTwo styrene–butadiene–styrene block rubbers, one with 10wt% calcium carbonate filler (S6C), and one without (S6) were surface treated with UV radiation. The resulting surface modifications and adhesion properties with polyurethane adhesive were studied. The surface modifications produced on these rubber surfaces were analyzed by contact angle measurements, ATR-IR spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. The adhesion properties were evaluated using T-peel tests of treated SBS rubber/polyurethane adhesive/leather joints. Treatment with UV radiation produced improved wettability as well as chemical (surface oxidation) and morphological modifications (roughness, ablation) of the rubber surface. These modifications were more pronounced with increasing treatment time. Although the improvement in wettability was similar in the UV-treated SBS, without and with calcium carbonate filler, the presence of calcium carbonate inhibited the modifications produced at short treatment times, while surface oxidation of filled SBS rubbers was favored at longer treatment times. Financial support from CICYT (project MAT2002- 02463) is gratefully acknowledged.
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.
The effectiveness of predicting rubber performance based on measured silica physical properties in silica- and carbon black-filled compounds is presented for three rubber formulations: an off-the-road tire tread, a wire coat stock and a V-belt. Correlation and regression analyses were performed using SAS software for sixteen physical properties of thirteen precipitated silicas, and sixteen rubber compound performance characteristics of the three compounds. Silica physical properties studied include various measurements of surface area and structure, particle size, pH and impurities. Rubber performance characteristics studied include cure properties and physical properties such as stress/strain, tear strength, cut growth resistance, abrasion resistance and heat build-up. The present study confirms that silica surface area is the single best predictor of the effect that varying silica physical properties have on the physical performance of cured, carbon black-filled rubber compounds containing precipitated silica. Silica structure, as measured by DBP absorption and nitrogen or mercury pore volume, is a secondary predictor of certain rubber physical properties. The confidence limits of the predictions is dependent upon the concentration of precipitated silica used in the carbon black-filled rubber compound.
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.
Measurements have been made of the forces required to peel a thin layer of a model viscoelastic adhesive off a rigid substrate. Over a wide range of temperature and rate of peel the results were found to yield a single master relation in terms of peel rate when reduced to a reference temperature by means of the Williams, Landel & Ferry rate-temperature equivalence for viscous materials. The relations obtained were complex, however, with two main features: a cohesive-adhesive failure transition at low rates and a sharp decrease in peel strength at high rates. The first effect is shown to be due to a change in the deformation process in the adhesive, from a liquid-like to a rubber-like response. An approximate relation between peel strength and the tensile stress-strain behaviour of the adhesive is developed in terms of a single empirically-determined parameter, the interfacial bond strength. Values of this parameter are deduced for several substrates. Measurements of peeling under hydrostatic pressure showed that cavitation of the adhesive did not occur in these experiments. The second effect is shown to be due to the transition from a rubber-like to a glass-like response of the adhesive. It is also shown to depend on the way in which separation is effected. Some general principles governing the mode of failure and the development of maximum peel strength are outlined.
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.
The addition of dicarboxylic acids to polyurethane adhesives, to improve their adhesion to vulcanized synthetic rubbers, may cause the degradation over time of the adhesives. To avoid the degradation of polyurethane adhesives, this study proposes a surface treatment on vulcanized synthetic rubbers with carboxylic acid solutions instead of adding them to the adhesives. In all the styrene-butadiene rubbers studied, a great improvement in adhesion to polyurethane adhesives has been obtained. The nature of the solvent used to disperse the fumaric acid over the surface, as well as the nature of the rubber, determined the effectiveness of the surface treatment. The use of fumaric acid solutions provided optimum results when the surface of the rubber was slightly roughened. The increase in the adhesion properties of styrene-butadiene rubbers, treated with fumaric acid, has been attributed to an increase in the degree of the surface roughness and to an enhancement in the surface energy (due to the elimination of abhesive substances on the surface of the rubber and to the formation of C-O groups by surface oxidation). The effectiveness of the surface treatment on rubbers with fumaric acid in the adhesion of styrene-butadiene rubbers has been compared with those produced by other common treatments, such as halogenation and roughening. In general, T-peel strengths obtained in the rubbers treated with fumaric acid were similar to those obtained through halogenation and were always higher than those obtained through roughening. Therefore, surface treatment of styrene-butadiene rubbers with fumaric acid can be considered as an alternative method to chemical treatments currently used, especially in the footwear industry.