Regenerating of vulcanized rubber

Process for regenerating rubber from its vulcanizates by heating Many processes have been proposed for the regeneration of vulcanized natural rubber. For example, the vulcanizates were heated in the presence of indifferent high boiling solvents such as tetrahydronaphthalene. Furthermore, heating with concentrated sodium hydroxide solution or with mineral acid has been proposed. In general, these processes require quite high temperatures (about 18o °), with heating times of several hours. For vulcanized synthetic rubber, these regeneration processes are generally not applicable.

It has now been found that aromatic mercaptans are valuable tools for the regeneration of vulcanized rubber under heating. An advantage of said products is that they allow the regeneration of both natural and synthetic rubber in the same way. Furthermore, the. Presence of these auxiliaries the effect that the regeneration can be carried out at lower temperatures or in a shorter time and thus runs more gently. For example, when this aid is used, a heating time of from i to z hours at a temperature of about 1.5 to 15 ° is sufficient. In general, working at about 13o °. Examples of auxiliaries of the type mentioned are thiophenols, thionaphthols, thiocresol and substitution products thereof. In general, a few percent (about 3%) of said auxiliaries are sufficient to achieve the desired effect. The auxiliaries mentioned are further distinguished by their easy incorporation into the vulcanized rubber.

The method according to the invention is carried out, for example, by grinding the vulcanizate to be regenerated into crumbles, mixing with the auxiliaries mentioned and then subjecting it to the required regeneration temperatures. Incorporation of the excipients, insofar as they are liquid as such, can take place by direct mixing. It is also possible to work in a kneading or rolling apparatus. Of course you can also work with the addition of solvents. Further, plasticizers such as stearic acid, paraffin or rosin may be added.

As stated above, the new process is suitable for both regenerating natural and synthetic rubber vulcanizates. Examples of suitable. synthetic rubbers. are polymers of utadiene hydrocarbons and copolymers of Butadienkohlenwassers, substances with other polymerizable compounds, such as styrene or Vinylme.thylketo.n.

It has already been proposed to use organic sulfides as regenerants for rubber vulcanizates. Comparative experiments have shown that mercaptans are significantly superior in their regenerating effect of the sulfides. For example, with a vulcanizate using β - ß'- dinaphthylthioether a deficit of 615o (ie only a small and technically not usable effect) could be achieved, whereas with a smaller amount of thionaphthol a deficit of about aoo (ie: a very high good effect).

EXAMPLE 100 parts by weight of ground natural rubber vulcanizate are intimately mixed with 3 parts by weight of β-thionaphthol. This mixture is obtained until i. 2 hours on 13o. After repeated rinsing on a refiner, a taut, soft coat is obtained, which can easily be incorporated into a fresh rubber mixture. The β-thionaphthol can be replaced with equal success by m-tliiocresol or m-methoxythiophenol. Example 2 100 parts by weight of ground vulcanizate from a copolymer of 75 parts of butadiene and 25 parts of styrene are intimately mixed with 3 parts by weight of β-thionaphthol. This mixture is heated to 13o 'for 2 hours. After several passes on a refiner to obtain a coherent smooth coat, which can be easily incorporated into a fresh rubber compound. Also in this case, the β-thionaphthol can be replaced with the same effect by m-thiocresol or m-Me @ thoxytliiophenol.

EXAMPLE 3 1 part by weight of ground vulcanizate from a mixed polymer of equal parts of butadiene and vinyl methyl ketone are mixed with 3 parts by weight of m-methoxythiopheniol. This mixture is heated for one hour at 13o °. Obtained by repeated passage on a refiner a coherent smooth and highly adhesive coat, which can be easily incorporated into a fresh rubber mixture.