Influence of the crosslinking content on the structural properties of polybutadiene rubbers with different isomeric composition

A. L. RODRÍGUEZ GARRAZA; M. A. MANSILLA; C. MACCHI; A. J. MARZOCCA; A. SOMOZA

Wuhan

Conferencia; 17th international conference on positron annihilation; 2015

Polybutadiene rubber (BR) is the second largest volume synthetic rubber produced at global scale, next to styrene-butadiene rubber.  The tire industry is the main consumer of BR. The huge interest in this kind of synthetic polymer is due to its excellent mechanical properties, especially when is used as cured rubber blends. In the present work first results on structural properties of three commercial isomers of BR are presented. To this aim rheometry, PALS and swelling techniques were used. This work is part of a general study aimed to get structural information on  BR compounds. In fact, recently results on the evolution of the free nanohole volume and glass transition temperature (Tg) with the degree of cure of two isomers of BR were reported [1]. In this research, samples of the commercial BR compounds Buna CB25 (96 % cis, 3 % trans and 1 % vinyl), Buna CB55 (38 % cis, 52 % trans and 10 % vinyl) and Eni-Versalis HV (10 % cis, 20 % trans and 70 % vinyl) were studied.  For each kind of BR, different samples were prepared containing diverse amounts of dycumil peroxide (DCP) as crosslinking agent.  The vulcanization temperature chosen to cure the samples was 433 K. In Ref. [1] samples of the CB25 and CB55 compounds were prepared using a different crosslinking agent, sulfur (S), and the same curing temperature, 433 K. The network structure in a cured elastomer is strongly dependent on the compound formulation and the processing conditions; so to go deeper in the analysis about the role of the crosslinking agent in BR compounds we have used DCP instead of S. Additional results were obtained studying the HV polybutadiene rubber. From the rheometrics curves the time taken to achieve the maximum degree of cure (t100) was obtained.  In all cases the samples studied were vulcanized until reach t100.  Furthermore, using differential scanning calorimetry the Tg was also obtained. From our measurements the evolution of the free nanohole volume, the volume fraction and the polymer fraction at the maximum degree of swelling as function of the DCP content was analyzed. The correlation among PALS, swelling results and Tg values is discussed. [1] M.A. Mansilla, A.L. Rodríguez Garraza, L. Silva, W. Salgueiro, C. Macchi, A.J. Marzocca, A. Somoza. Pol. Test. 32, 686 (2013).