DD211575B1 - METHOD FOR THE DEVULACANIZATION OF OLD RUBBER - Google Patents

Description

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Field of application of the invention

The invention relates to a method for Devulkanisation of waste rubber, as obtained generally in the rubber industry and when applying the rubber products.

Characteristic of the known technical solutions

Known is the thermal-oxidative regeneration of waste rubber at temperatures between 150-200 ° C and the influence of atmospheric oxygen. This method has long been used technically.

The disadvantage of this method is the fact that in addition to devulcanization also a considerable depolymerization of

Rubber molecules takes place. The energy expenditure of the overall procedure is very high.

Recent methods for devulcanization of waste rubber are based on the application of microwave energy for the breaking of the S-S bonds (Elastomerics, Jan. 1981), pp. 13-16).

Temperatures between 260-350 ⁰ C are reached. The method is therefore better suited for the replastication

saturated elastomers.

Another method of devulcanization is known, according to which coarsely ground rubber crumbs are rolled with fatty acid and alkali and are converted into an aqueous emulsion. A dry finely divided rubber powder is formed by

Coagulating with acid and removing the water (Rubber Chemistry Technology, Vol. 53, pp. 1215-1225).

Technically, this process can be very complex.

Other methods of devulcanization result in reductive sulfur bridge cleavage. These reactions proceed at lower temperatures while sparing the polymer chain of the rubber.

In DD-PS 148 500 such a method is described. The reducing agents used in this process are Fe ⁺⁺ ions and phenylhydrazine or diphenylguamidine. The reducing agents used are themselves highly toxic, especially phenylhydrazine, as a byproduct can be benzene.

Object of the invention

The aim of the invention is the development of a process for devulcanization of waste rubber using readily available non-toxic agents.

Explanation of the essence of the invention

The object of the invention is to develop a method for devulcanization of waste rubber by sulfur bridge cleavage

 According to the invention, this object is achieved by a process in which a replasticization is carried out by the action of thiazolyl sulfenamide accelerators from the rubber industry, in particular N-cyclohexyl-mercaptobenzothiazolyl sulfenamide and N-diethylbenzothiazyl sulfenamide or equivalent substances in a neutral medium. The equivalent substance may be an equimolar mixture of mercaptobenzothiazole and amine, especially diphenylguanidine or di-o-tolylbiquamide.

embodiment

The invention will be explained in more detail below by exemplary embodiments.

example 1

According to the invention, the replication is effected by the action of thiazolyl sulfenamide accelerators from the rubber industry, in particular N-cyclohexyl-mercaptobenzothiazolyl sulfenamide and N-diethylbenzothiazyl sulfenamide or equivalent substances, such as. B. an equimolar mixture of mercapto-benzothiazole and amine, in particular Diphenylguamidin and di-o-Tolylbiquamid in a neutral medium

 The course of the reaction is as follows:

Gu-S-S-Gu +

Likewise:

Gu-S-S-Gu +

- ^ Gu-S-S-

.CH ₁

^Gu ~ ^s ~ ^N

C ₂ H ₅

The reaction products formed are mixed-in disulfide and a sulfenamide. The advantage of this reaction is that no oxidation-sensitive mercaptan compounds occur.

At the practical laboratory approach, the effects of the solution according to the invention are to be presented.

500 g of waste rubber with a particle size of up to 1.2 mm are mixed with 30 g of N-cyclohexyl-mercaptobenzothiazolyl sulfenamide in 3 l of ethanol for 3 h. cooked under reflux. Then the product is filtered off and washed with ethanol and dried

The following swelling values in benzene vapor at 55 ⁰ C over 5h. are achieved:

Sulfenamide / 500g scrap rubber 9

Weigh g

Benzenaufnahme g

30 g sulfenamide 60 g sulfenamide

lOOgSulfenamid

1,98 2,12 2,15

0.17 0.18 0.23

Example 2

If the process according to the invention is carried out under an inert gas atmosphere, a thermal-oxidative degradation of C-C double bonds of the elastomeric space lattice can be completely avoided. Here is a devulcanization exclusively

via sulfide exchange reactions.

500 g of waste rubber with a particle size of up to 1.2 mm are added with 30 g of N-cyclohexyl-mercaptobenzothiazyl-sulfenamide in 31% ethanol. The ethyl alcohol is previously pure for 2 h with argon or nitrogen to remove dissolved oxygen

do the washing up.

The mixture is then refluxed for 3 hours while maintaining the inert gas atmosphere, the product is filtered off, with ethanol

washed and dried.

Based on specific application test mixtures, the following values are achieved:

Application test mixtures I Il III

Waste rubber / sulfenamide (air atmosphere) waste rubber / sulfenamide (inert gas atmosphere) known regenerate (oxide) plasticizer SE zinc oxide sulfenax sulfur stearic acid

300 g 37 g

6g

2.4 g

4.5 g

9g

337 g

6g

2.4 g

4.5g 9g

Physical-mechanical values (15min heating time, 150 ° C)

Waste rubber / sulfenamide I Il

known regenerate (oxide) III

Strength (kp / cm ² ) Elongation at break (%) Elasticity (%) Attrition (mm ³ )

58 35 138 192 40 46 203 153

The higher residual elasticity and abrasion resistance of the replicated by disulfide exchange waste rubber when re-use in application test mixtures can be seen that the elastomeric chains are largely spared and a non-oxidative process is present.

It is therefore possible compared to the known thermal-oxidative regenerate higher Versatzätze with fresh mixtures, as the attached diagram shows.

Claims (2)

1. A method for devulcanization of waste rubber, characterized in that by the action of Thiazolylsulfenamidbeschleunigem from the rubber industry, a replastering due
Disulfide exchange is carried out in a neutral medium. 2. The method according to item 1, characterized in that an equimolar mixture of
Mercaptobenzothiazole and an amine, in particular Diphenylguamidin or Di-o
Tholylbiguamide, is used.