Influence of the pre-vulcanization inhibitor on the properties of non-vulcanized rubber compositions for in situ vulcanized reformers applications

Abstract

In the rubber industry, some products are commercialized in a non-vulcanized form and usually present a relatively short shelf life. Therefore, there is a great interest in increasing scorch time of these formulations without affecting other rheometric properties. This study evaluated the use of different accelerators and acceleration systems over time for the rheometric properties of non-vulcanized natural rubber compositions. Twelve compositions were prepared: six using the accelerator 2,2-dithiomercaptobenzothiazole (MBTS) and six using the accelerator N-cyclohexyl-2-benzothiazole sulfenamide (CBS). For each accelerator, three acceleration systems were formulated. The same formulations were also performed including a pre-vulcanization inhibitor (PVI). It was found that the MBTS has greater acceleration stability over 6 months and the CBS provided a longer scorch time in the first months, losing this characteristic over time. The use of PVI has increased scorch times; however, it has also increased the optimum vulcanization time. The need to use the PVI for non-vulcanized materials, which are stored at temperatures up to 45°C, was verified. It is concluded that the rheometric behavior during the shelf life of non-vulcanized compositions depends on the accelerator type, acceleration system, and the use or not of a retarding agent.