Chem­i­cal process to re­cy­cle tyres back to tyres

The Witness - Wheels - - MOTORING - AARON TURPEN

RE­SEARCHERS at Durham Univer­sity in the United King­dom have de­vel­oped an ap­proach to break­ing down rub­ber in ma­te­ri­als at room tem­per­a­ture.

The chem­i­cal process uses cat­alytic dis­as­sem­bly, elim­i­nat­ing the en­ergy- in­ten­sive meth­ods of cur­rently- used tyre re­cy­cling pro­cesses.

In a pa­per pub­lished in the jour­nal Green Chem­istry, the Durham re­searchers ex­plain how the process works and how it could be used to re­cy­cle ve­hi­cle tyres, la­tex gloves and other poly­mer- based items that are man­u­fac­tured in the millions of tons ev­ery year.

The long- chain hy­dro­car­bon mol­e­cules and un­sat­u­rated car­bons in these rub­bery ma­te­ri­als are tra­di­tion­ally very dif­fi­cult to re­cy­cle or re­pro­cess eas­ily, es­pe­cially ve­hi­cle tyres.

The tra­di­tional method for re­pro­cess­ing rub­ber is to change dras­ti­cally the tem­per­a­ture of the rub­ber com­pounds to break them down, ei­ther by heat­ing them for milling or freez­ing them to frac­ture them.

These are en­ergy- in­tense and leave a crumb prod­uct which is then mixed with new elas­tomers to pro­duce new ma­te­rial, of­ten with a loss in hard­ness or mal­leabil­ity.

These losses mean that most re­cy­cled rub­bers are not reused for the pur­pose they were orig­i­nally formed, but are in­stead re- cy­cled into other prod­ucts lower down the use chain.

This of­ten means that the cost ben­e­fit for re­cy­cling is di­min­ished.

The Durham re­searchers be­lieve that their chem­i­cal process may be used to al­low the ma­te­ri­als to be re­cy­cled back into their orig­i­nal use, so a re­cy­cled tyre could be made into a new tyre.

Their cross metathe­sis re­ac­tion breaks down rub­bery poly­mers into vis­cous liq­uids that can then be re­formed with­out degra­da­tion.

The process could also be used to cre­ate the crumb now com­monly pro­duced, but at much lower cost.

The process dis­cov­ered uses Grubbs’s cat­a­lysts to break down polybu­ta­di­ene ( PBd) net­works at their dou­ble bonds via cross­metathe­sis ( CM) re­ac­tions to pro­duce read­ily sol­u­ble mol­e­cules. As the chains frag­ment, the ma­te­rial dis­in­te­grates into rub­ber crumb at room tem­per­a­ture. Grubbs’s cat­a­lysts are eas­ily syn­the­sised and are read­ily avail­able com­mer­cially.

The re­searchers also dis­cov­ered that in­creas­ing tem­per­a­ture and re­ac­tion time im­proved the break­down process, also of­fer­ing a faster way to fa­cil­i­tate rub­ber com­pound break­downs when pro­duc­ing crumb.

The re­sult­ing oil is low in molec­u­lar weight and non- poly­mers ( oligomers), both con­ducive to easy re­use of the poly­mers be­ing re­cy­cled. — Giz­mag.

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