Method of devulcanizing vulcanized rubber

Abstract

A method of devulcanizing vulcanized rubber is described. The method includes steps of: (a) providing at least one vulcanized rubber composition; (b) grinding the vulcanized rubber into chips or pellets; (c) mixing the ground rubber obtained from step (b) in such a way as to homogenize the form and temperature of same; (d) carrying out a non-degrading mechanical treatment on the mixed rubber at the end of step (c) to obtain a polymeric composite. Also described is a thermoplastic material and an elastomeric mixture which comprise, in the formulation of same, at least one polymeric composite obtained by this method of devulcanization.

Claims

1. A method of devulcanizing a vulcanized rubber comprising: a) providing at least one vulcanized rubber; b) grinding the vulcanized rubber into chips or aggregates; c) kneading at a low rate of shear ranging from about 100 s.sup.1 to about 500 s.sup.1 the ground rubber obtained from step b) in such a manner as to homogenize it in size of aggregates and temperature; d) kneading the product of step (c) to a high rate of shear ranging between 10.sup.3 s.sup.1 and 10.sup.6 s.sup.1 thereby obtaining a polymeric composite.

2. The devulcanizing method according to claim 1, wherein the vulcanized rubber belongs to a first group constituted by the rubbers which become degraded starting from temperatures of the order of 250 C.

3. The devulcanizing method according to claim 1, wherein the vulcanized rubber belongs to a second group constituted by the rubbers which do not become degraded when they are subjected to temperatures in the range of 250 C. to 350 C.

4. The devulcanizing method according to claim 3, wherein after step b) of grinding and prior to step c) of kneading, the vulcanized rubber is subjected in a first tooling to a temperature ranging: between 25 C. and 200 C., when the vulcanized rubber is a rubber of the first group, between 25 C. and 350 C., when the vulcanized rubber is a rubber of the second group.

5. The devulcanizing method according to claim 3, wherein step c) of kneading is achieved in a second tooling of which: the temperature of the tooling ranges between 100 C. 250 C., when the vulcanized rubber is a rubber of the first group, the temperature of the tooling ranges between 100 C. and 350 C., when the vulcanized rubber is a rubber of the second group.

6. The devulcanizing method according to claim 3, wherein the step d) is achieved in a tooling taken to a temperature ranging: between 50 C. and 175 C., when the vulcanized rubber is a rubber of the first group, between 50 C. and 350 C., when the vulcanized rubber is a rubber of the second group.

7. The devulcanizing method according to claim 6, wherein the step d) comprises the following steps: d1) a first non-degrading mechanical treatment on the kneaded rubber after step c) by subjecting it in a third tooling to a shear rate ranging between 10.sup.4 s.sup.1 and 10.sup.6 s.sup.1 and of which the temperature of the third tooling ranges: between 50 C. and 250 C., when the vulcanized rubber is a rubber of the first group, between 50 C. and 350 C., when the vulcanized rubber is a rubber of the second group; d2) a second non-degrading mechanical treatment on the rubber obtained after step d1) by subjecting it in a fourth tooling to a shear rate ranging between 10.sup.3 s.sup.1 and 10.sup.5 s.sup.1 and of which the temperature of the fourth tooling ranges: between 50 C. and 200 C., when the vulcanized rubber is a rubber of the first group, between 50 C. and 300 C., when the vulcanized rubber is a rubber of the second group.

8. The devulcanizing method according to claim 1, wherein after step d) the polymeric composite is conveyed and cooled in a fifth tooling taken to a temperature ranging between 10 C. and 60 C.

9. The devulcanizing method according to claim 1, wherein it further comprises at least one of the following steps: a cooling step; a surface treatment step chosen from the group constituted by the talcing, the soap deposit, a silicone emulsion, an adhesion promoter or a polyethylene film with a low melting point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood using the detailed description exhibited here-below with reference to the accompanying drawing representing, by way of non limiting example, an embodiment of an installation implementing the method according to the invention and the sheath of a co-rotary twin-screw extruder used during this method.

(2) FIG. 1 represents in a schematic manner an installation implementing the method according to the invention.

(3) FIG. 2 is a cross-sectional view of the sheath of a co-rotary twin-screw extruder which may be used for the devulcanizing method according to the invention.

DETAILED DESCRIPTION

(4) The installation 10 comprises a first storage unit 1 in which a vulcanized rubber to be devulcanized is stored according to the method of the invention.

(5) The vulcanized rubber to be devulcanized is channeled to a grinder 2. Once ground, it is channeled to a second storage unit 3, then by means of a vacuum pump 4 to a filler 5.

(6) The filler 5 allows regulating the volume of ground vulcanized rubber which enters in the co-rotary twin-screw extruder 6 which has been designed so that the steps of kneading and shearing of the devulcanizing method according to the invention be achieved thereto.

(7) At the output of the co-rotary twin-screw extruder 6, it is obtained a polymeric composite which is channeled towards a unit for cooling and applying a surface treatment 7, regulated at a temperature ranging between around 15 and 35 C. and in which the polymeric composite is conveyed.

(8) The surface treatment comprises a deposit of talc or an aqueous solution of soap, etc.

(9) Then, the polymeric composite covered with talc or soap is channeled towards a drying unit 8 which comprises air knives. The temperature of the air is in the range of 30 to 40 C. The polymeric composite describes a complex travel in this drying unit 8 and the drying time thereof is in the range of 45 to 50 minutes.

(10) After the drying, the polymeric composite is stored in a conditioning unit 9.

(11) On FIG. 2 is represented the sheath 13 of an extruder 6 which comprises a heater band 11 surrounding the sheath 13, and in which are housed the two screws 14 and a plurality of ducts 12. The ducts 12 are intended for a water circulation in order to cool the extruder 6.

(12) Experimental Part:

(13) The devulcanizing method according to the invention has been implemented with the following vulcanized rubbers:

(14) 1) polyisoprene (IR);

(15) 2) natural rubber (NR);

(16) 3) ethylene-propylene-diene monomer rubber (EPDM) with a hardness of 80 ShA;

(17) 4) ethylene-propylene-diene monomer rubber (EPDM) with a hardness of 40 ShA;

(18) 5) isobutene isoprene rubber (IIR).

(19) The tooling used was a co-rotary twin-screw extruder of which the speed of the screws is indicated in the last line of the table 2 here-below according to the considered rubber 1) to 5).

(20) Moreover in this table 2 are detailed, according to the considered rubber 1) to 5), the temperatures of the co-rotary twin-screw extruder according to the progress of the method according to the invention, namely: before step c); during step c); during step d1); during step d2).

(21) TABLE-US-00002 TABLE 2 Temperatures of the steps of the method according to the invention and screw speed according to the rubber to be devulcanized. Temperature ( C.) of the twin-screw extruder EPDM EPDM hardness hardness IR NR 80 ShA 40 ShA MR Before 90 160 280 270 100 step c) Step c) 160 185 320 300 260 Step d1) 180 190 310 260 260 Step d2) 115 145 260 240 230 Screw 225 200 250 300 275 speed (rev/min)

(22) The example here-below illustrates the use of around 20% in weight of a polymeric composite obtained from a method according to the invention in a rubber formulation.

(23) This rubber formulation corresponded to a standard formulation of the range of vulcanized rubbers commercialized by the PLYMOUTH FRANCAISE company.

(24) The starting raw elastomer (or rubber) was polyisoprene.

(25) The polymeric composite was obtained by applying the method according to the invention to a sample of the formulation A such as described in table 3 here-below after vulcanization.

(26) In order to do this, a sample of the formulation A has been subjected to the devulcanizing method according to the invention which has been achieved in a co-rotary twin-screw extruder of which the technical features were the following:

(27) The ratio of the length of the screws on the diameter of the screws was equal to 60. The rotational speed of the screws was of 185 rev.Math.min.sup.1.

(28) The extruder comprised the following portions: a first portion for which the length of the screws was equal to 4 times the diameter of the screws; a second portion for which the length of the screws was equal to 28 times the diameter of the screws; a third portion for which the length of the screws was equal to 12 times the diameter of the screws; a fourth portion for which the length of the screws was equal to 8 times the diameter of the screws; a fifth portion for which the length of the screws was equal to 8 times the diameter of the screws;

(29) The sample of the formulation was first of all introduced into the first portion of the extruder which was at a temperature of 85 C.

(30) Then, the sample was kneaded in the second portion of the extruder (step c)), of which the input temperature of this second portion of the extruder was of 200 C. and the output temperature of this second portion of the extruder was of 150 C.

(31) The sample was then subjected to a first shearing carried out with a rate of shear in the range of 10.sup.4 s.sup.1 to 10.sup.6 s.sup.1 in the third portion of the extruder which was at a temperature of 165 C. (step d1), followed by a second shearing carried out with a rate of shear in the range of 10.sup.3 s.sup.1 to 10.sup.5 s.sup.1 in the fourth portion of the extruder which was at a temperature of 125 C. (step d2).

(32) The sample was finally cooled in the fifth portion of the extruder which was at a temperature of 30 C. in such a manner as to obtain a polymeric composite.

(33) The formulation B, which contained 35 pc (percent of rubber) of this polymeric composite thus obtained, exhibited a weight composition identical to formulation A.

(34) The conditions of mixing, shaping and vulcanization used for formulation A and for formulation B were strictly identical.

(35) However, in order to obtain exactly the same mechanical performances with formulations A and B, the vulcanization system (accelerators+sulfur) and the capacity factor had to be adjusted.

(36) Table 3 here-below summarizes: The compositions of respectively: 2.sup.nd column: formulation A; 3.sup.rd column: formulation B which comprises 35.25 g of polymeric composite; 4th column: formulation B but expressed by distributing the constituents of the 35.25 g of polymeric composite in the different constituents of the rubber of formulation A. The ratio expressed in % of sulfur/elastomer for formulations A and B. The ratio expressed in % of accelerator/elastomer for formulations A and B. The ratio expressed in % of fillers/elastomer for formulations A and B.

(37) TABLE-US-00003 TABLE 3 Compositions of the formulations A and B Formulation B Formulation B with distribution with of the constituents Formulation A polymeric of the polymeric (g) composite (g) composite (g) elastomer 100.00 76.92 97.21 Polymeric 35.25 composite Fillers and 50.00 38.46 52.67 additives sulfur 1.25 0.96 1.26 accelerators 1.50 1.15 1.26 Total 152.75 152.75 152.75 Sulfur/ 1.25% 1.30% elastomer ratio Accelerators/ 1.50% 1.67% elastomer ratio Fillers/ 5.00% 5.42% elastomer ratio

(38) An ageing composed of the 3 following cycles: machine wash at 90 C.; followed by drying in an oven for 6 hours at 120 C. has been achieved on formulations A and B.

(39) The following measurements were carried out on formulations A and B: The measurement of the module at 100%; The measurement of the elongation at break; The measurement of the percentage of loss of module after an ageing such as detailed above. The measurement of the percentage of the tear resistance.

(40) Table 4 here-below exhibits the compared mechanical features of the two formulations A and B:

(41) TABLE-US-00004 TABLE 4 characterization of formulations A and B Features Formulation A Formulation B Module at 100% 1.1 MPa 1.1 MPa Elongation 650% maximum 650% minimum break % loss of the module 30% maximum 10% to 30% maximum after ageing % tear resistance 400% minimum 400% minimum

(42) It has been noted from table 4 that the physical features of module at 100%, of elongation at break and the percentage of tear resistance are similar for formulations A and B. And regarding the percentage of loss of module after ageing, that of the formulation B (namely according to the invention) is even a bit better than that of formulation A.

(43) Also, the UV resistances of the two formulations A and B have been evaluated to be compared: they are also similar.

(44) Thus, these results show that the substitution of a virgin rubber mixture by a polymeric composite obtained according to the method of the invention in a rubber formulation intended to be vulcanized, and thus to the amount of 20% in weight, changes nothing to the physical properties of the final vulcanized rubber.

(45) In other words, this example emphasizes the fact that the polymeric composite obtained according to the method of the invention which constitutes a method for recycling a vulcanized rubber may be used by replacing a mixture of virgin rubber in a new mixture to be vulcanized, and thus without altering the mechanical and physical properties of the final achieved product.

(46) In addition, it has been emphasized that the damping power and the compression resistance of a formulation of vulcanized rubber were not modified by introducing 30 to 40 per of polymeric composite obtained according to the method of the invention in said formulation.

(47) The polymeric composite according to the invention also has, owing to its molecular structure, a strong aptitude to incorporating fillers such as rubber crumb. Thus, it is possible to increase the rate of incorporation of the polymeric composite and the crumb in a rubber formulation. The incorporation of this rubber crumb allows to significantly lower the cost of the raw material.

(48) Table 5 here-below exhibits two formulations of which the mechanical and elastic properties (module, elongation at break, ageing, UV resistance, hardness . . . ) are similar.

(49) The formulation C has been achieved with mixtures of virgin rubbers.

(50) Formula D incorporates 70 per of the polymeric composite obtained according to the method of the invention and 42 per of rubber crumb.

(51) TABLE-US-00005 TABLE 5 composition of formulations C and D. Formulation D Formulation D with with distribution polymeric of the constituents composite of the polymeric Component Formulation C and crumb composite Natural 42.00 26.90 35.65 rubber SBR 14.00 8.97 11.88 Polymeric 25.12 composite Crumb 15.07 15.07 Sulfur 1.40 0.90 1.19 Accelerator 0.85 0.54 0.71 Filler and 41.75 22.50 35.50 additives Total 100.00 100.00 100.00 Sulfur/ 2.50% 2.45% elastomer ratio Accelerators/ 1.52% 1.50% elastomer ratio Fillers/ 74.6% 106.4% elastomer ratio