Surface treatment with UV-ozone to improve adhesion of vulcanized rubber formulated with an excess of processing oil

Abstract

a b s t r a c tAn excess of processing oil was intentionally added in the formulation of vulcanized styrene-butadiene rubber for analyzing the effect on the treatment with UV radiation combined with ozone (UV-ozone) in improving the adhesion to waterborne polyurethane adhesive in footwear. Due to the excess of processing oil in the rubber, poor adhesion was expected. Both the length of the treatment and the distance between the UV radiation source to the rubber surface were studied, and the effects of the treatment on the surface chemistry, wettability and surface energy, and topography of the rubber were analyzed. The treatment of the rubber with UV-ozone removed hydrocarbon moieties and zinc stearate from the surface, and surface oxidation (C-O, C¼ O and COO -groups formation) occurred. As a consequence, improved wettability and increased surface energy (mainly due to the polar component of the surface energy) were obtained. The increase in the length of treatment and for a distance of 3-5 cm from the rubber to the UV radiation source favored the effectiveness of the UV-ozone treatment. Besides, whereas the UV-ozone treatment for 3 min produced the ablation of surface contaminants mainly, longer lengths of treatment (i.e., 6-9 min) caused roughness and cracks on the rubber surface. The UVozone treatment also caused heating of the surface. Finally, the treatment with UV-ozone increased the adhesion of the rubber to waterborne polyurethane adhesive, the highest adhesion was obtained in the joints made with UV-ozone treated rubber for 3 and 6 min at a UV radiation source-rubber surface distance of 5 cm.

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“…It means the formation of carbonyl groups due to photooxidation at the main NR chain. Similar result was signaled by Moyano and Martín-Martínez [24] with UV/ozone treatment for improving the adhesion of vulcanized rubber. On other hand, the NR with hydroxyl terminal groups (as a result of the photochemical degradation of NR) was initiated by hydroxyl radicals, which might undergo similar mechanism proposed by Ravindran et al [25].…”

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“…The exposition distance [21,58,59] or the humidity [56] are inevitably responsible for the degree of ozone-oxidation. In the study of Moyano et al [22], the treatment with UV-ozone increased the rubber's adhesion to polyurethane adhesive. The highest adhesion was obtained for the tests made with UV-ozone treated rubber for 3 min at a UV radiation source-surface distance of 5 cm with a limited concentration of ozone [22].…”

“…In the study of Moyano et al [22], the treatment with UV-ozone increased the rubber's adhesion to polyurethane adhesive. The highest adhesion was obtained for the tests made with UV-ozone treated rubber for 3 min at a UV radiation source-surface distance of 5 cm with a limited concentration of ozone [22]. The reaction of ozone-oxidation allows to have cross-linking reaction causing an increase of the texture.…”

“…A combination of UV radiation and ozone at different concentration has been proven to enhance the rubber surface's bonding performance, thus improving the vulcanized rubber's surface energy ( Figure 6). The use of this physical treatment is considered to be cleaner and faster than others [22,33,57]. However, it has to be made in a very controlled condition in order to avoid the full degradation of the rubber.…”

“…To counteract this phenomenon, several methods aiming to control the swelling behavior of rubber exist. The addition of chemicals to the mixture [13,14], the possible devulcanization [15][16][17][18] or, last but not least, the surface treatment of the CR employing physical or chemical procedures [1,[19][20][21][22][23] are some of the most frequent solutions. The rubber's surface treatment represents an evolving method, preferably used when the dry incorporation method is adopted.…”