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Continuous ultrasonic devulcani­sation – comparison of carbon black filled IR and NR

von Dr. Ximei Sun, Avraam I. Isayev

Continuous ultrasonic devulcanisation of carbon black (CB) filled isoprene rubber (IR) was carried out. Similar to unfilled IR, power consumption during the devulcanisation of the filled IR increased with the increase of ultrasonic amplitude indicating a greater extent of devulcanisation.

This was in contrast with the devulcanisation of CB filled natural rubber (NR) where power consumption showed a maximum at an intermediate amplitude suggesting a lesser extent of devulcanisation at higher amplitude.

Such a behaviour evidently resulted from the difference in the amount of stereoregular structures in the IR and NR rubbers. Gel fraction and crosslink density of the virgin vulcanisates, devulcanisates and revulcanisates were characterised. Kinetics of revulcanisation, rheological properties of the devulcanisates and mechanical properties of revulcanisates were compared with those of virgin uncured IR and their vulcanisates.

The effect of processing oil on the IR vulcanisation, devulcanisation and revulcanisation was examined indicating a slightly delay the vulcanisation and lower torque without affecting the degree of reversion. The addition of oil caused more devulcanisation as indicated by an increase in the ultrasonic power consumption and a reduction of the gel fraction and crosslink density of devulcanised rubbers.

The revulcanisation of the IR occurred without the induction period, regardless of the presence of CB and processing oil. The retarder introduced in the recipe was effective in improving the scorch safety and minimising the reversion in revulcanisation.

The experimental data on normalised gel fraction versus crosslink density of filled IR and NR at low CB loadings was found to fall into the master curve, which is probably determined by the main chain structure of both rubbers consisting of cis-1,4 isoprene. At high CB loadings, some differences were observed. The simulation results predicted such a behaviour.