Silica mixing gets boost from new accelerator & process aid

Mannheim, Germany-Rubber chemicals specialist Rhein Chemie Rheinau GmbH has launched two new products to help makers of silica-filled rubber parts.

Rhenocure ZBOP/S is a highly active dithiophosphate accelerator for use in curing tyres with high silica content, while Aflux GE 1872 is a processing agent that "guarantees improved processing" of rubber compounds highly loaded with silica, says the Mannheim-headquartered company.

Use of dithiophosphate accelerators or sulphur donors in vulcanising diene rubbers has been common practice for many years, said Rhein Chemie. They offer advantages such as lower reversion with natural rubber, better heat stability of vulcanisates, or high solubility in rubbers of varying polarity.

Rhenocure ZBOP/S can replace the secondary accelerator diphenyl guanidine (DPG) in highly loaded silica compounds based on styrene butadiene rubber (SBR) "without any problems," RheinChemie said. Additional benefits are improved vulcanisation, reversion behaviour, heat-ageing resistance and mechanical-dynamic properties of the vulcanisate.

In NR compounds, these benefits are especially marked, with a considerable drop in dynamic heat built up, in particular, the firm added.

Meanwhile, Rhein Chemie, a Lanxess Deutschland GmbH subsidiary, described Aflux GE 1872 as "a revolutionary combination of agents that make it possible to considerably simplify the processing of highly loaded silica rubber compounds." It allows these compounds to be mixed with less energy input, avoiding problems arising from high temperatures during the energy intensive mixing normally required, the firm claims.

As well as faster extrusion, particularly at high loading, the additive gives no swelling and good surface quality of the extrudate.

Rhein Chemie said the efficiency of the agent stems from an optimised combination of surface-active substances, with customised compatibilisation between the low polarity polymer and the highly polar white filler.

Aflux GE 1872 in highly loaded silica compounds gives a marked decrease in mixing viscosity common with traditional processing agents, and the compounds retain their high elastic modulus coefficient and hardness, Rhein Chemie adds.