Influence of the Configuration of the Plasma Chamber on the Surface Modification of Synthetic Vulcanized Rubber Treated with Low-pressure Oxygen RF Plasma

• Published in: Plasma processes and polymers 2011-11, Vol.8 (11), p.1080-1092
• Main Authors: Torregrosa-Coque, Rafael, Martín-Martínez, José Miguel
• Format: Article
• Language: English
• Subjects: adhesion; Adhesive strength; Applied sciences; ATR FT-IR; Chambers; Coating, metallization, dyeing; Contact angle; Exact sciences and technology; Machinery and processing; Migration; Oxygen plasma; Paraffin wax; plasma treatment; Plastics; Polymer industry, paints, wood; Polyurethane resins; radio frequency glow discharges (RFGD); Rubber; surfaces; Technology of polymers
• ISSN: 1612-8850; 1612-8869; 1612-8869
• DOI: 10.1002/ppap.201100013

Three different configurations of RF low‐pressure oxygen plasmas were used to modify the surface of vulcanized styrene–butadiene rubber. Direct, etching and downstream oxygen plasma treatments of the rubber were carried out for length of treatment between 1 and 10 min. The oxygen plasma treated rubber surfaces were characterized by ethylene glycol contact angle measurements, ATR‐IR and XPS spectroscopy and scanning electron microscopy (SEM). Adhesion of the oxygen plasma treated rubber to polyurethane adhesive was carried out by means of T‐peel test and the loci of failure of the joints were characterized by means of ATR‐IR spectroscopy. Three different oxygen plasma configurations obtained by changing the position of the rubber sample in the plasma chamber and by changing the shelves (power, ground, floating) were used to modify the extent of surface modification and the temperature reached on rubber surface. The direct oxygen plasma was the most aggressive treatment and the secondary downstream plasma the less one. The increase in the length of the oxygen plasma treatment allowed the most efficient removal of antiozonant paraffin wax from the as‐received rubber. Furthermore, the oxygen plasma treatments created CO moieties on the rubber surface. On the other hand, only 1 min treatment time was sufficient to decrease noticeably the contact angle value on the rubber surface, irrespective of the oxygen plasma chamber configuration and the length of treatment. Oxygen plasma treatment caused surface oxidation and ablation on the rubber surface, as well as an increase of the temperature that also determined the extent of paraffin wax migration, the migration was favoured for temperature higher than 45 °C. Finally, the migration of paraffin wax was produced for at least 24 h after oxygen plasma treatment and poor adhesion to polyurethane adhesive was obtained, due to the creation of a weak boundary layer of paraffin wax at the rubber–polyurethane interface. The migration of paraffin wax caused during plasma treatment was the dominant factor in decreasing the adhesion of rubber to polyurethane adhesive. The configuration of the plasma chamber determines the extent of chemical and topography modification reached during oxygen RF plasma treatment of vulcanized rubber. An innovative strategy is proposed for modifying vulcanized rubber surfaces by minimizing the migration of low‐molecular weight additives to the surface controlling the temperature of the rubber sur