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By TA News Bureau:

Although many top tyre manufacturers are still wary of increasing the content of reclaim rubber, this has not deterred some Indian researchers to explore the possibility of its higher use as part of sustainability and cost reduction efforts. One among them is Dr Debapriya De, Professor in Chemistry at the Howrah (West Bengal)-based MCKV Institute of Engineering. His research has spanned from reclaiming rubber from guayule to Hevea. “We have reclaimed guayule natural rubber which was published in Journal of Elastomers and Plastics,” he said in an interview. “We have also reclaimed both natural rubber and styrene butadiene rubber. The detailed work regarding reclaiming of natural rubber vulcanizate was published in Polymer Degradation and Stability,” he said. In this interview to Tyre Asia he details his research

India is one of the leading producers of rubber from Hevea brasiliensis. However, there are researchers who are exploring possibilities of guayule cultivation with one scientist identifying it as an ideal crop for commercial growing and greening of Thar desert which is known as the Great Indian Desert in the north-western part of the country that covers an area of 200,000 sq km. If there is a supply disruption in Hevea rubber, guayule can be developed as an alternative.
Dr Debapriya De, Professor in Chemistry at the Howrah (West Bengal)-based MCKV Institute of Engineering, however says that Indian tyre manufacturers are not using guayule but are depending exclusively on Hevea rubber. “Indian tyre manufacturer are not using guayule till date,” he told Tyre Asia.
But worldwide current consumption of guayule natural rubber is around 10 per cent of the global rubber demand. It is a shrub that is grown in the arid zone from the south-western part of the USA to northern Mexico. Moreover, the rubber constituent contained therein is very much similar to that of the Hevea rubber trees. Therefore, guayule is expected to become a new supplement to natural rubber.
“But the use of guayule natural rubber as an important replacement of Hevea natural rubber is still limited because guayule requires a series of process to produce natural rubber consisting of grinding whole plant, solvent extraction and subsequent removal of impurities, which is more complex than that of the conventional natural rubber production from Hevea rubber tree that requires only collection, coagulation of latex and drying.”
But increasing natural rubber demand and decreasing production necessitate the imperative of tapping of alternative raw materials such as guayule natural rubber for tyre industries.
The Bridgestone Group has started integrated R&D activities from cultivation, natural rubber extraction to subsequent application of guayule in tyre. As a result, in 2015 the first tyre made from guayule-derived natural rubber came to the market by Bridgestone Group.
Natural rubber consumption in India is growing day-by-day: It increased to 1110,660 tonnes in 2017-18 from 1044,075 tonnes in 2016-17 whereas rubber production in 2017-18 was 694,000 tonnes, with a 0.4 per cent increase over the previous fiscal.
Consumption of NR in 2018-19 is projected at 1.2 million tonnes, with an increase of 8 per cent. To meet the growing demand of NR, import of NR had been consistently increasing from 2008-09 to 2017-18 with an exception during 2016-17. Import of NR touched an all-time high of 469,433 tonnes in 2017-18, an increase of 10.1 per cent as compared to 2016-17. The NR is imported from Malaysia, Thailand, Indonesia and Sri Lanka.

Reclaim research

About his recent research work on silica-filled revulcanizates to produce reclaim rubber in the making of green tyre, Dr De said his team has reclaimed both natural rubber and styrene butadiene rubber. His research is funded by the Department of Science and Technology (DST), Science and Engineering Research Board (SERB), of government of India.
He said: “In mechanochemical reclaiming process, a large number of chemical reclaiming agents (various disulfides, monosulfides, thiols etc.) are used for reclaiming of scrap rubber at an elevated temperature under pressure.”
However, almost all disulfides and thiols have very obnoxious smell and are hazardous. Thus, handling of these disulfides and thiols is not desirable and economic for reclaim rubber production.
“In our research, for the first time, we have used bis[3-(triethoxysilyl)propyl]-tetrasulfide (TESPT) as reclaiming agent for vulcanized rubber because the – S – S – bond in TESPT is susceptible to homolytic cleavage during mechanochemical reclaiming of vulcanized rubber,” he said.
“Our subsequent study of extent reclaiming indicates that the fragmented TESPT is attached with reclaim rubber and converted the vulcanized rubber into soft plastic, more tacky, low modulus, processable and vulcanizable essentially thermoplastic product simulating many of the characteristics of virgin rubber.”
The unique devulcanizing agent, TESPT, is not hazardous and safe to handle. Moreover, the as-grown reclaim rubber facilitates the silica dispersion when it is mixed with fresh rubber as blend. This is due to the fact that the ethoxy functional groups of fragmented TESPT attached with reclaim rubber form chemical bond with hydroxyl group present on the silica surface.
“Thus in fresh rubber/reclaim rubber compound, reclaim rubber not only replaces the fresh rubber but also acts as interfacial modifier for silica filler without using any coupling agent. Therefore, costlier carbon black can be replaced by comparatively low-cost silica filler without much compensation of mechanical properties,” Dr De explained.

Environment friendly

Study of the mechanical properties of natural rubber/carbon black vulcanizate with 30 phr carbon black loading shows that the tensile strength of the vulcanizate is 18.8 Mpa whereas natural rubber/reclaim natural rubber/silica vulcanizate in which fresh rubber is mixed with reclaim rubber in 70:30 ratio along with 30 phr silica loading shows 20.1 Mpa tensile strength of the vulcanizate.
Moreover, now-a-days enormous effort has been given in different fields to protect the environment and CO2 emission to control global warming. The tyre industry is also facing the same challenge for improving the energy efficiency in the automobile industry to reduce CO2 emissions.
Says Dr De: “In order to achieve energy savings from tyres, reduction of rolling resistance is very important and which can be achieved by using silica instead of carbon black in tyre compound. Silica/rubber composites show lower rolling resistance without sacrifice of wet skid resistance. It also shows its potential in the manufacturing of ‘green tyres’ with high fuel efficiency, low green house gases emission and high driving safety.”

Role of reclaim

When asked why he thinks tyre makers are still reluctant to use reclaim rubber as a substitute to virgin rubber, he commented that this mindset is changing. “The attitude regarding use of reclaim rubber in tyre industry has been changing slowly. Moreover, the decreasing production of natural rubber, price fluctuations of crude oil that impact the price of natural and synthetic rubber respectively will force tyre makers to be dependent on reclaim rubber.
In the coming years the growing automotive and aerospace industries in China, Thailand and India will meet their rubber demand using reclaim rubber. Incorporation of up to 30 per cent reclaimed rubber in the production of new tyres creates technical efficiencies, enhance production efficiencies and add to raw material cost efficiencies.
Dr De says that these are all significant at a time when the tyre industry has run out of opportunities to drive down the cost of raw materials. “The reclaimed rubber used in automotive tyres, improves mechanical properties, heat, sunlight and ozone resistance property. The so-grown reclaimed rubber may be used in various light-duty applications like tyre inner liners, inner tubes, automobile floor mats, animal mats, insulation tiles etc.”

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