Second plateau observed in solutions of gum rubbers containing gels

摘要

Viscoelastic behavior of solutions of rubbers containing macro-gel and micro-gel were examined. Macro-gel is a giant molecule of the rubber having many long branches. Micro-gel is also a giant molecule but a cross-linked particle. The sample of macro-gel was butadiene-acrylonitrile copolymer (NBR) and the solvent was a plasticizer, dibutylphthalate (DBP). The latter was polyethylacrylate (ACM) in diethylphthalate (DEP). Both rubbers contained about 70% gel, which swelled in the solvent. The rubber concentration was 20%, 10%, and 5%. The frequency range was from 10(-2) to 10(2) rad/s. Measurements were made at room temperature.At 20% and 10% concentration, the storage modulus, G(I), and the loss modulus, G(II), had the following relation; with NBR-DBP, G(I) was slightly lower than G(II) and with A CM-DEP they were about equal. The gels in the former solution had a degree of swelling lower than did those in the latter. The behavior persisted over the entire range of the frequency. The swollen gel particles are touching each other or almost so.At 5% concentration G(I) and G(II) curves showed shapes similar to those of the rubber plateau. However, the concentration is much too low to expect to see the rubber plateau. The plateau appears to be the manifestation of the deformation of the gel particle.While the bulk rubber behavior is distinctly different between macro-gel-containing and micro-gel-containing rubber, the gel type is not distinguished in the behavior of the semi dilute solution.