LANXESS investigates greenest synthetic rubber

Specialty chemicals company LANXESS is investigating how the carbon foorprint can be reduced further during the processing of so-called 'green rubber'.

Processors wishing to develop articles made of green rubber can turn to LANXESS' Keltan Eco

EPDM rubber as an alternative to conventional synthetic rubber made using fossil fuels

LANXESS experts have now examined which plasticiser oils and fillers can be combined with this bio-based rubber to reduce the carbon footprint of the resulting compounds still further. The extensive study, which examined amongst others the use of natural oils and carbon black from tyre waste, will be presented to a wide audience of experts at the German Rubber Conference 2015 in Nuremberg. 

The LANXESS researchers have come to concrete conclusions. For example, they will be presenting on a seal for use in automobiles that is based on sulfur-vulcanised EPDM. The seal consists of 90 per cent sustainable components and exhibits broadly the same technical properties as its conventional equivalents.

"In many cases, EPDM products contain up to four times as much ingredients – such as fillers and oils – next to the rubber," explained Martin van Duin, Rubber Expert at LANXESS High Performance Elastomers Business Unit.

"Our Keltan Eco grades made from ethylene, which is produced using bio-based raw materials, are therefore one key building block in the development of ‘greener’ rubber articles – but only one of many. Since improving the sustainability of our products is one of our most important goals at LANXESS, we have now also taken an intensive look at the possibilities and technical conditions involved in ‘green’ compounds using Keltan Eco."

Theoretically, there is a whole range of possible components made from sustainable raw materials available to the rubber compound developers that could replace, for example, extender oils from fossil sources in EPDM rubber products. The challenge is in the detail. If the natural oils are too polar, the mixture can cause problems during mixing or bleeding from the final product. If they contain too much unsaturation, they can affect the network density, because they compete with the rubber for the sulfur during vulcanisation. Van Duin and his colleague Philip Hough, expert in application development, therefore examined a whole series of oils with varying levels of unsaturation – from linseed oil to olive oil. In a second phase of their study, they also included modified oils such as hydrogenated coconut oil, and squalane, a naturally occurring saturated C30 hydrocarbon. In terms of potential 'green' fillers, candidates included micro-crystalline cellulose (from wood), silica ash (from rice husks) and pyrolysis carbon black (from waste tyres).

"Even this black is better than conventional furnace black obtained through the incomplete combustion of fossil fuels in terms of its sustainability," explained Hough, "because it avoids waste and increases the recycling rate. On top of that, the tyre waste itself contains a certain proportion of natural rubber."

Using standard procedures and equipment, all these components were processed at LANXESS into rubber samples that were then thoroughly examined in terms of their technical properties, including after artificial aging.

"We made a conscious decision to prioritise practicality, so we could transfer experience to industrial rubber application technology as easily as possible and offer valid compounding recommendations," said van Duin. 

Some effects were expected, and have now been comprehensively documented.

"We have shown what can already be achieved using these findings by creating a Keltan Eco seal that is made up of 90 per cent sustainable raw materials and is totally comparable with conventional compounds," Hough said. "Even after aging at 125 °C."

This shows EPDM’s key characteristic – its outstanding heat stability – is also present in 'green' compounds.

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