The general chemical formula of the main chain of styrene-butadiene elastomer (SBS) used in our investigations 

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... to evaporate the organic solvent. This is the main reason why substitutes for the organic solvent adhesives are intensively searched. The alternative is a polyurethane adhesive in the form of an aqueous emulsion. Aqueous polyurethane dispersions seem to be quite promising replacement for solvent adhesives [19]. One of the major drawbacks, however, is the decline of bond strength observed in some cases after hydrothermal aging, which causes risk of such connections separation during their utilization. Although this problem has already been paid some attention [21], yet it still remains open and requires further studies, particularly in specific cases of polyurethane dispersions use. Generally, our knowledge on the molecular mechanism of bonding with use of polyurethane solvent adhesives is much greater than in the case of the use of aqueous polyurethane emulsions [1, 21]. The study was conducted on commonly used, vulcanized industrial rubber based on styrene-butadiene elastomer (SBS). The general formula of the main chemicals chain of SBS presents Figure 1. The rubber was supplied by the manufacturer of rubber compounds "Kwarciak" (Poland) Ltd. The detailed composition of the rubber is contained in Table 1. 13 Pa. Glow discharge power was 50 W. Treatment time ranged from 15 s to 15 min. In order to determine the surface adhesion of the rubber to dispersive polyurethane adhesive, 180°-peel tests for adhesive-bonded joints were carried out. Such joins were made of the rubber samples before and after plasma modification and standard strips of leather (tanned with dichromate, uncolored). The polyurethane dispersive adhesive “Bonidur US-100” from the Chemical Establishment “Bochem” LLC was spread on each surface to be glued and it was dried for 15 minutes. The dry adhesive layer on the rubber was reactivated at temperature of 353 K and the surfaces were immediately contacted under pressure of 0.4 MPa for 10 s. Then the adhesive joints were conditioned at room conditions for 48 h. The above procedure for the preparation of samples for the peel test is consistent with the European Standard EN 1392:2006. The peel tests were performed using Instron 5566 measuring instrument (tear speed – 1.67 × 10 –3 m/s). To study surface topography and composition of SBS rubbers a scanning electron microscope FEI's Quanta 200 F model with X-Max EDS-Detector (EDX) from Oxford Instruments was used. All measurements in the SEM were carried out under water vapor atmosphere of 100 Pa. Composition of rubbers for about 100 nm penetration depth of electrons beam was studied, using 3.5 keV of electrons energy. However topography micrographs were obtained using 20 keV of electrons energy. In order to compare the wet chemical treatment and the plasma treatment, samples with chemically chlorinated surface were prepared. The process was carried out by immersing the samples for 30 s in a chlorination solution (2 % trichlorocyanuric acid (TCl) in butanol). Then, the samples were left for 1 h and after this time they were immersed in an aqueous solution of ethanol (25 %) for 30 s to stop the chlorination process. Finally, the samples were dried at room temperature in air for several hours. achieved for 10 min of the modification, followed by its rapid decline. As one can see, in the case of not roughened samples without acetone washing, the Ar plasma treatment almost five times improves the peel strength of the joint, in comparison to unmodified samples and three times in comparison to samples modified with the wet chemical treatment. About twofold increase is noticeable already for 5 min time of the plasma treatment. Maximum strength is achieved for 10 min of the modification, followed by its rapid decline. An analysis of the joint peel strength for unroughened, washed with acetone, SBS rubber samples modified by Ar plasma also shows the significant improvement in comparison to untreated and wet chlorinated samples. Additionally, slight increase of the peel strength is noticeable for all samples when compared with analogical not roughened samples without washing. Acetone cleans the surface from impurities, which increases the surface energy and leads to increased thermodynamic adhesion. Maximum strength is achieved for 2 min – 10 min of the plasma modification, and for longer treatment it rapid decline. The achieved maximum value is almost four times greater than those obtained for unmodified samples and almost tripled in comparison with samples treated by the wet chlorination. Roughening, similarly to washing in acetone, improves values of the peeling forces for samples unmodified and modified in Ar plasma, as well as wet chlorinated ones. An increase of surface roughness, leading to development of contact with the adhesive, significantly affects the growth of mechanical adhesion. For surfaces not treated with plasma, the peel strength increase is almost doubled in comparison to not roughened samples. The Ar plasma treatment, similarly as for not roughened samples influences on an increase of the peel strength, and the maximum values are very similar for these both cases. They are also achieved in a similar duration of treatment (2 min – 10 min). Longer time of the modification causes quite sharp decline in the strength of joints. In general, the Ar plasma treatment, in power 50 W, gives a few times higher values of the peel strength in comparison to unmodified samples. Regardless of the preparation method of the SBS rubber samples before the plasma treatment (roughened, not roughened, washed in acetone, without washing), similar maximum values of the joint peel strength were achieved. This is a very important result from the point of view of the probable future introduction of this plasma method to industry. It will enable simplification of the current technological process. Mechanical roughening, washing in organic solvents and wet chlorination will be replacing only with the single plasma treatment process. However, further, more detailed studies are necessary. As far as the Ar plasma treatment mechanism is concerned, it should be noted that the plasma generates radical centers, which create hydroxyl and carbonyl groups after contacted with air. According to our previous investigations [21], in that case the peel strength is proportional to the concentration of these groups, which in turn depends on the time and the power of the glow discharge. Longer plasma treatment causes a decrease in the concentration of the groups, which is manifested as a peel strength maximum. The maximum values of the peel strength observed in the current investigations for the SBS rubber samples can indicate that in this case also the chemical adhesion takes place. Generally, in the case of samples modified by carbon dioxide (CO 2 ) plasma, an increase in the peel strength for unroughened and unwashed rubbers was observed (Figure 4) in comparison to unmodified samples and samples subjected to the wet chemical treatment, for all times of the treatment in practice. The exception is time of 15 s. With an increase in the treatment time, the peel strength increases, reaching its maximum for 10 min – 15 min with a value about one-and-a-half times higher than those for untreated samples. The washing of the unroughened SBS samples with acetone, which were then modified by CO 2 plasma (Figure 4), improves the joint strength in comparison to untreated samples and ...