M. Mercedes Pastor-Blas

Adhesion improvement of SBR rubber by treatment with trichloroisocyanuric acid solutions in different esters

Abstract Ethyl, propyl and butyl acetates (EA, PA, BA, respectively) were used as solvents for trichloroisocyanuric acid (TCI) to chlorinate styrene–butadiene rubber (SBR). Characterization of the treated surfaces was carried out using ATR-IR spectroscopy, scanning electron microscopy (SEM), and contact angle measurements. Stress-strain measurements were also carried out to determine the mechanical properties of the treated rubber. Adhesion properties were studied using a polyurethane adhesive and the failed surfaces obtained after performing T-peel tests were analyzed in order to precisely locate the joint failure. The results showed that the solvent is a key factor in the effectiveness of the chlorination of R2 rubber. The solvents with slower evaporation rate led to more pronounced modifications on the R2 rubber surface. But these solvents could favour the migration of wax from the bulk rubber to the surface creating a weak antiadherent layer that prevented adhesion. The increase in TCI percentage in the chlorinating solution produced more marked modifications on the R2 rubber surface, avoiding the migration of wax. The solvent in the chlorinating solution also affects the effectiveness of the zinc stearate elimination from the R1 rubber surface; however, good adhesion was obtained even though this compound was not completely removed, indicating that the presence of zinc stearate in the rubber formulation did not produce a detrimental effect in the adhesion of SBRs.

Surface modification of synthetic vulcanized rubber

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 si...

Surface characterization of synthetic vulcanized rubber treated with oxygen plasma

The surface of a synthetic vulcanized styrene-butadiene rubber (R2) was treated in an oxygen plasma to improve adhesion in joints prepared with a one-component solvent-based polyester-urethane adhesive. The modifications produced on the rubber surface by plasma treatment were assessed using advancing and receding contact angle measurements, x-ray photoelectron spectroscopy, (XPS), infrared-attenuated total reflection spectroscopy and scanning electron microscopy. Adhesion was obtained from T-peel tests of treated R2 rubber/polyurethane adhesive joints. Several experimental variables were considered, such as the radio-frequency power and the length and lifetime of the plasma treatment. The treatment in the oxygen plasma produced a noticeable decrease in contact angle, which can be mainly ascribed to the creation of C-O and C=O moieties on the rubber surface. Advancing and receding contact angles only differed by ∼10°. Depending on the experimental conditions used, some ablation was produced on the surface, which was more noticeable as the length and power of the treatment increased. An adequate performance of adhesive joints was obtained using a power of 50 W and a time for oxygen plasma treatment of <10 min. The changes in the rubber surface remained for 2 h after plasma treatment, as indicated by the variation in peel strength and XPS data. Although improved adhesion was obtained by treating the rubber in an oxygen plasma, the T-peel strength values are not sufficient to assure technical use, probably due to the migration of waxes and zinc stearate to the surface once the treatment was carried out. Finally, sulfur oxidation was produced by the plasma treatment, and for severe conditions solid crystals of a sodium salt of an oxidized sulfur compound (sodium sulphate or an organic sulphate) appeared on the treated rubber surface.

Structural modification of sepiolite (natural magnesium silicate) by thermal treatment: effect on the properties of polyurethane adhesives

Abstract A sepiolite silicate was heat-treated at 550 and 1000°C to modify its structure, and was used as a filler in a solvent-based polyurethane (PU) adhesive. The treated sepiolites were characterized by X-ray diffraction and infra-red spectroscopy, and it was observed that the water was irreversibly removed from the structure and pores of the sepiolite, changing the structure. The increase of temperature produced a collapse of the sepiolite structure. The rheological, mechanical, thermal and adhesion properties of the filled PU adhesives were measured. In general, the addition of treated sepiolite to PU adhesives resulted in a loss of adhesive properties with respect to the blank (PU adhesive with untreated sepiolite). The loss in properties was more noticeable as the treatment temperature increased. Thus the PU adhesives containing treated sepiolite had reduced rheological properties (lower viscosity, lower storage and loss moduli, and they did not provide thixotropy and pseudoplasticity to the solutions) with respect to the PU adhesive filled with untreated sepiolite. On the other hand, the addition of treated sepiolite decreased the mechanical and thermal mechanical properties of PU films. The T-peel strength of roughened and roughened + chlorinated (with 1 wt% trichloroisocyanuric acid in 2-butanone) styrene-butadiene rubber/PU adhesive joints was improved if the PU adhesive contained untreated sepiolite, but it decreased if the sepiolite was heat-treated. Interactions between the untreated sepiolite, the solvent and the polyurethane were responsible for the improved properties of PU adhesives. These interactions disappeared when the sepiolite was heat-treated, because of the destruction of the structure of the sepiolite and the removal of surface silanol groups.

Surface modifications of a vulcanized rubber using corona discharge and ultraviolet radiation treatments

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.

Properties of Polyurethane Elastomers with Different Hard/Soft Segment Ratio

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

Failure analysis of surface-treated unvulcanized SBS rubber/polyurethane adhesive joints

Abstract 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 CCl and CO 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.

Weak Boundary Layers in Styrene-Butadiene Rubber

Abstract 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 chlor...

Environmentally friendly reduction of a platinum catalyst precursor supported on polypyrrole

Supported metals are traditionally prepared by impregnating a support material with the metal precursor solution, followed by reduction in hydrogen at elevated temperatures. In this study, a polymeric support has been considered. Polypyrrole (PPy) has been chemically synthesized using FeCl3 as a doping agent, and it has been impregnated with a H2PtCl6 solution to prepare a catalyst precursor. The restricted thermal stability of polypyrrole does not allow using the traditional reduction in hydrogen at elevated temperature, and chemical reduction under mild conditions using sodium borohydride implies environmental concerns. Therefore, cold RF plasma has been considered an environmentally friendly alternative. Ar plasma leads to a more effective reduction of platinum ions in the chloroplatinic complex anchored onto the polypyrrole chain after impregnation than reduction with sodium borohydride, as has been evidenced by XPS. The increase of RF power enhanced the effectiveness of the Ar plasma treatment. A homogeneous distribution of platinum nanoparticles has been observed by TEM after the reduction treatment with plasma. The Pt/polypyrrol catalyst reduced by Ar plasma at 200 watts effectively catalyzed the aqueous reduction of nitrates with H2 to yield N2, with a very low selectivity to undesired nitrites and ammonium by-products.

Surface Characterization of Vulcanized Rubber Treated with Sulfuric Acid and its Adhesion to Polyurethane Adhesive

Abstract Modifications produced on a vulcanized styrene –butadiene rubber surface by treatment with sulfuric acid were studied and several experimental variables were considered. The treatment of R1 rubber with sulfuric acid produced a noticeable decrease in contact angle which was mainly ascribed to an increase in surface energy due to the formation of sulfonic acid moieties and C˭O bonds, and the removal of zinc stearate. The rubber surface swelled and became brittle as a result of the treatment, and when flexed microcracks were created. A rubber surface layer modification was produced with a consequent decrease in tensile strength and elongation-at-break values. The treatment enhanced the T-peel strength of R1 rubber/polyurethane adhesive joints and the locus of failure was cohesive in the rubber. The optimum immersion time in H2SO4 solution was less than 1 min., and the reaction time in air was not found to be critical; the neutralization with ammonium hydroxide and the high concentration of the sulfuric acid (95 wt%) were essential to produce adequate effectiveness of the treatment.