Devulcanizing additive, relative method of devulcanization and devulcanized product

A devulcanizing additive for vulcanized elastomers, in particular sulfur-vulcanized rubbers, consisting of:

• an acid-base adduct obtained starting from a dicarboxylic organic acid having a number of carbon atoms ranging from 2 to 18 and from urea or mono-, di- or tri-substituted derivatives of urea having the following formula:
• wherein R1, R2 and R3, the same as or different from each other, are taken from the group consisting of hydrogen, and linear alkyl chains having from 2 to 18 carbon atoms;
• a peroxide, said peroxide optionally mixed and absorbed on an inert inorganic filler, taken from the group consisting of silicas, calcium carbonates, kaolins, aluminum silicates, clays and mixtures thereof;
• and
• optionally, a compatibilizer selected from the group consisting of ethylene-vinyl acetate copolymer, zinc dimethylacrylate, NR-g-PDMMMP (grafted copolymer of natural rubber (NR) and poly(dimethyl(methacryloyloxymethyl)phosphonate (PDMMMP)), liquid butadiene-isoprene copolymer rubber, GMA & MAH (grafted polyolefin polymers), epoxidized natural rubber, trans-polyoctenamer (TOR) and mixtures thereof,
• wherein the acid-base adduct is obtained from organic dicarboxylic acid and urea or mono, di or trisubstituted derivatives of urea, in a molar ratio ranging from 1:1 to 1:2.

A method for the devulcanization of sulfur-vulcanized rubbers, batchwise, comprising the following steps:

• i) mixing the devulcanizing additive consisting of:
• an acid-base adduct obtained from a dicarboxylic organic acid having a number of carbon atoms ranging from 2 to 18 and from urea or mono-, di- or tri-substituted derivative of urea having the following formula:
• wherein R1, R2 and R3, the same as or different from each other, are taken from the group consisting of hydrogen and linear alkyl chains having from 2 to 18 carbon atoms, and
• a peroxide;
• with the vulcanized elastomer to be devulcanized;
• the acid base adduct being obtained from the dicarboxylic organic acid and from urea or the derivatives of mono-, di- or tri-substituted urea, in a molar ratio ranging from 1:1 to 1:2;
• with the possible addition of a compatibilizer;
• ii) optionally heating the mixture thus obtained;
• iii) compressing and mechanically stretching, in an open or closed mixer;
• iv) repeating the compressing and mechanically stretching step iv) for a number of times ranging from 0 to 40.

A method for the devulcanization of sulfur-vulcanized rubbers, in continuous, comprising the steps:

• i) mixing the devulcanizing additive consisting of:
• an acid-base adduct obtained from a dicarboxylic organic acid having a number of carbon atoms ranging from 2 to 18 and from urea or mono-, di- or tri-substituted derivatives of urea having the following formula:
• wherein R1, R2 and R3, the same as or different from each other, are taken from the group consisting of hydrogen and linear alkyl chains having from 2 to 18 carbon atoms, and
• a peroxide;
• with the vulcanized elastomer to be devulcanized;
• the acid base adduct being obtained from the dicarboxylic organic acid and from urea or the derivatives of mono-, di- or tri-substituted urea, in a molar ratio ranging from 1:1 to 1:2;
• with the optional addition of a compatibilizer;
• ii) optionally heating the mixture thus obtained;
• and
• iii) extruding the devulcanized product.