Feature: Evonik tracks silica trends in tire sector

For the Tires in the Lab feature in the May/June issue of ERJ, Dr Hans-Detlef Luginsland of Evonik talks to Shahrzad Pourriahi about how analytic technologies are helping to improve the effectiveness to reinforcing filler systems:

Essen, Germany-based Evonik is a performance chemical producer that has recently announced plans to invest E4 billion over the next decade in R&D.

Dr Hans-Detlef Luginsland, vice president product line rubber silica Evonik Industries, explained to ERJ that the company’s current R&D work is focussed on two major trends in the tire industry: the development of a silica/silane system for natural rubber and the development of new silica grades with improved dispersion characteristics

“Active fillers are essential for the performance and durability of rubber,” said Luginsland while explaining the silica-organosilane reinforcing system developed by Evonik.

“They act as coupling agents, because the bifunctional molecules are able to connect to both the silica surface and the rubber,” he noted.

Luginsland is of the view that only with this silica-silane system, is it possible to extend the magic triangle for passenger car tires, with its corners “rolling resistance”, “wet grip” and “abrasion resistance”.

For further optimisation of the tire performance, silica with high reinforcement properties and high surface areas are needed. A technical barrier, however, is that high performance products may also cause some challenges regarding processability.

“Our researchers, however, recently found solutions to improve the processability of this high-performance silane. Our latest development is XP Si 466 GR, which is a solid silane for easy dosage and zero-VOC (volatile organic compound) emissions during the silanisation reaction,” said Luginsland.

Another focal points, he said, is to develop a system for truck and bus tires, where natural rubber is used in the tread.

“Regarding truck tires, we are facing a completely different polymer. The silica-silane system works perfectly with modern S-SBR grades, but still has weaknesses in the abrasion resistance in NR compounds,” he went on to say.

Increased investment

To address the difficulties, Evonik has increased its R&D investment, recently building a research centre for silanes in Rheinfelden, south of Germany, and setting up an additional nuclear magnetic resonance (NMR) device to allow analysis of complex molecules.

In the R&D labs in Rheinfelden, said Luginsland, new functional silanes are designed and synthesised.

The NMR device is particularly helpful with Evonik’s new development XP Si 466 GR silane, for which common analytical techniques such as gas chromatography (GC) or high pressure liquid chromatography (HPLC) are not suitable.

In contrast to the typical silanes, said Luginsland, this product is solid. It has been developed to be a VOC-free, easy-to-handle, solid coupling agent and therefore modern NMR-techniques are used to characterise this product.

After the synthesis, purification and characterisation, and the in-rubber performance of this new silane has been evaluated in the applied technology centre in Wesseling, compounding studies are made in a lab-scale kneater and open mill to find the best recipe for this new silane.

The relevant physical and dynamic properties of the specimen such as Mooney viscosities, rheometer data, green strength etc., are determined in the process, he added.

“After vulcanisation, the physical and dynamic properties of the rubber specimen at different temperatures serve as indicators for the relevant tire properties: rolling resistance, wet grip and abrasion resistance.

“On the micro- and nano-scale, the quality of the dispersion of the silica-silane-polymer-system is measured. A good dispersion of all ingredients is the key for a good performance of the tire,” said the Evonik rubber expert.

Commenting on optimum improvement of tires in terms of energy efficiency, Luginsland said: “Theoretically a very high level of energy-efficiency is possible. But… we are dealing with tires, a complex multi-component part with conflicting performance indicators and driving safety being of paramount importance.

“So optimising the tire tread compound towards the rolling resistance will have an impact on other performances such as grip and abrasion resistance. For further improvements, the complete system of the tire tread compound has to be adopted: polymer, filler and coupling agent.”