Method for producing rubber-modified bitumen using vulcanized rubber

Abstract

The present invention provides a novel process for producing rubber-modified bitumen using vulcanized rubber.

Claims

1. A process for producing rubber-modified bitumen using vulcanized rubber, the process comprising: devulcanizing the vulcanized rubber by breaking the sulfide bridges thereof by contacting the vulcanized rubber with at least one dialkyl polysulfide of the general formula (1)
R.sup.1S.sub.xR.sup.2(1) where R.sup.1 and R.sup.2 are the same or different and are a linear or branched C.sub.1-C.sub.18-alkyl radical and x represents the numbers from 3 to 12, at temperatures in a range of from 140 C. to 170 C. for a time of from 20 to 60 minutes, where the proportion of the dialkyl polysulfide is from 1.5% to 4% by weight, based on vulcanized rubber, and mixing the devulcanized rubber into the bitumen.

2. The process as claimed in claim 1, wherein the contacting further comprises contacting the vulcanized rubber with the dialkyl polysulfide with an oil.

3. The process as claimed in claim 1, wherein the contacting of the vulcanized rubber to break the sulfide bridges and/or the mixing into the bitumen are effected under mechanical stress.

4. The process as claimed in claim 1, wherein the dialkyl polysulfide is branched dioctyl pentasulfide or branched dioctyl tetrasulfide.

5. The process as claimed in claim 1, wherein x represents the numbers from 3 to 8.

6. The process as claimed in claim 1, wherein R.sup.1 and R.sup.2 are linear or branched C.sub.5- to C.sub.15-alkyl radicals.

7. The process as claimed in claim 1, wherein x represents the numbers from 3 to 8, and R.sup.1 and R.sup.2 are linear or branched C.sub.5- to C.sub.15-alkyl radicals.

8. The process as claimed in claim 1, wherein the dialkyl polysulfides are dialkyl tetrasulfides.

9. The process as claimed in claim 1, wherein the contacting further comprises contacting the vulcanized rubber with the dialkyl polysulfide and up to 30 wt % mineral oil based on the rubber mixture to be devulcanized.

10. The process as claimed in claim 8, wherein the proportion of the dialkyl polysulfide is 1.5% to 3% by weight, based on the vulcanized rubber, the temperatures in the process is 150-160 C., the contacting is for a period of time 35-45 min; and the contacting further comprises contacting the vulcanized rubber with the dialkyl polysulfide and 1 to 6 wt % mineral oil based on the rubber mixture to be devulcanized.

11. The process as claimed in claim 1, wherein the devulcanization time is 30-50 min.

12. The process as claimed in claim 1, wherein the devulcanization time is 35-45 min.

13. The process as claimed in claim 2, wherein the oil is mineral oil.

14. The process as claimed in claim 1, wherein the dialkyl polysulfides are dioctyl tetrasulfides.

Description

EXPERIMENTAL EXAMPLES

(1) The mixing vessels used were aluminum cans having a capacity of max, 900 mL. The rubber mixture was stirred using a modified anchor stirrer having two paddles. A lid was placed onto the can. Gases formed were conducted away via wash bottles. The temperature was measured by means of a probe thermometer which was guided through a further opening into the interior.

(2) In the first step, the granular rubber was introduced into the aluminum vessel which was closed with the lid. The vessel was secured in the oil bath and the stirrer system was started. The dioctyl pentasulfide as dialkyl polysulfide was mixed with a carrier oil and metered in gradually through the small opening in the lid with the aid of a syringe.

(3) After the metered addition, the rubber mixture was stirred at the temperature and for the time specified for the particular experiment number and with a stirrer speed of about 180 rpm.

(4) After the heat treatment, bitumen was added until the rubber content made up 15% of the overall mixture. The rubber/bitumen mixture was stirred at 180 C. for 2 h in order to enable very good distribution of the rubber in the bitumen.

(5) The following were used:

(6) bitumen 50/70, from Shad, Nynas T 22, a naphthenic base oil, branched dioctyl pentasulfide as dialkyl polysulfide (polysulfide), and shredded car and truck tires as used rubber having a particle size of 0.2-0.8 mm.

(7) In a series of experiments, the following experiments were conducted:

(8) TABLE-US-00001 TABLE 1 Conditions of the pretreatment of vulcanized granular used rubber Duration of Bitumen type and, if appropriate, Temperature in the devulcanization No. mixture for rubber devulcanization devulcanization [] [min] Reference bitumen 1 bitumen 50/70 + 10% used rubber (not pretreated) 2 bitumen 50/70 + used rubber (15%), 120 40 pretreated with 1.5% dialkyl polysulfide and 5.5% Nynas T 22 3 bitumen 50/70 + used rubber (15%), 140 40 pretreated with 1.5% dialkyl polysulfide and 5.5% Nynas T 22 4 bitumen 50/70 + used rubber (15%), 160 40 pretreated with 1.5% dialkyl polysulfide and 5.5% Nynas T 22 5 bitumen 50/70 + used rubber (10%), 150 240 pretreated with 7% dialkyl polysulfide and 10.5% Nynas T 22 6 bitumen 50/70 + used rubber (10%), 160 40 pretreated with 3.5% dialkyl polysulfide and 3.5% Nynas T 22
Rheological Measurements:

(9) The viscoelastic properties of the rubber/bitumen mixtures comprising modified rubbers that have been obtained in experiments 1-6 were determined using a temperature sweep of the rheological indices of complex shear modulus G* and phase angle with a dynamic shear rheometer according to DIN EN 14770. Details of the method can be found, for example, in Rahmenbedingungen fr DSR-Messungen an Bitumen [Boundary Conditions for DSR Measurements on Bitumen], Berichte der Bundesanstait fr StraBenwesen [Reports from the German Federal Highway Research institute], StraBenbau [Roadbuilding] issue S 43 et seq. or in the presentation by Mr Wrner Bitumen: Bewertung anhand konventioneller und rheologischer Kennwerte [Bitumen: Assessment on the Basis of Conventional and Rheological Characteristics], XVI. Weimarer StraBenbau- und Baustoffsymposium [XVIth Weimar Roadbuilding and Construction Material Symposium], Mar. 27, 2014, Weimar.

(10) This involved installing the binder sample between two parallel metal plates and subjecting it to varying, in this case oscillating, shear stress.

(11) The diameter of the two parallel plates was 25 mm. A gap of 2 mm was used. The frequency of the sinusoidal stress was 1.59 Hz (angular frequency =10 s.sup.1) and the maximum deformation was 10% of the plate separation. The equilibration time between the test intervals was 15 min.

(12) TABLE-US-00002 TABLE 2 Rheological indices as a function of temperature for bitumen 50/70 or rubber-modified bitumens (RMBs) with used rubber in untreated form or pretreated in accordance with table 1 Reference bitumen 50/70 1 (C) 2 (C) 3 (I) Shear Phase Shear Phase Shear Phase Shear Phase Temp. mod. angle mod. angle mod. angle mod. angle C. Pa Pa Pa Pa 30 362 400 68.9 951 950 47.7 407 845 55.1 355 395 57.2 40 70 385 74.8 290 965 47.9 114 385 54.7 95 500 57.8 50 14 337 79.8 100 113 47.2 36 826 55.1 28 907 59.2 60 3329 84.0 39 783 49.2 13 511 58.7 9902 63.5 70 890 86.8 16 614 54.0 5215 64.3 3591 69.5 80 281 88.6 7069 59.4 2107 69.6 1378 74.9 90 102 89.4 3159 61.7 912 72.6 566 78.8 100 43 90.0 1612 58.5 438 72.2 254 80.5 110 20 90.0 993 50.9 239 68.7 127 80.2 120 10 90.0 744 41.5 154 62.4 72 77.9 130 6 90.0 635 32.8 119 54 46 73.6 140 3 90.0 601 25.4 111 43.7 33 67.7 150 2 90.0 602 19.7 114 34.4 28 60.2 4 (I) 5 (C) 6(I) Shear Phase Shear Phase Shear Phase Temp. modulus angle modulus angle modulus angle C. Pa Pa Pa 30 281 310 58.5 490 000 63.7 482 000 56.6 40 75 024 59.2 104 000 66.7 125 000 57.5 50 22 383 61.5 25 700 70.1 37 900 59.8 60 7400 66.9 7220 74.6 12 900 64.4 70 2547 73.7 2250 79.1 4640 69.9 80 928 79.3 799 82.6 1800 75 90 366 83.1 320 84.7 765 78.8 100 73 86.1 65 87 172 82.4 110 73 86.1 65 87 172 82.4 120 38 86.3 33.1 87.2 89.5 82.6 130 21 86.4 18.2 86.8 50 81.8 140 13 86.6 10.9 86.1 29.9 80.1 150 9 87.2 6.9 86.2 19.1 77.8 (I) = inventive, (C) = comparative

(13) As shown by table 2 and FIG. 1, there is a change in the rubber-modified bitumen of the invention (see examples 3, 4 and 6), especially in the range of 140-150 C. approaching the processing temperature (170-180 C.), with regard to the phase angle toward the behavior known from unmodified bitumen. This corresponds to more homogeneous bitumen and hence better dissolution characteristics.

(14) What is found here, in an impressive manner, is that even 1.5% by weight (experiment 3 and especially experiment 4) or 3.5% by weight (experiment 6) of dialkyl polysulfide is sufficient, provided that the temperature during the devulcanizing is at least 140 C. This becomes clear particularly by comparison with comparative experiment 5, where 7% dialkyl polysulfide was used.

(15) The comparison of experiment 2 (1.5% dialkyl polysulfide with a pretreatment temperature of 120 C.) and experiment 4 (1.5% dialkyl polysulfide with a pretreatment temperature of 160 C.) very dearly shows the importance of the temperature during the devulcanizing. In the case of experiment 4 (inventive), the characteristics of unmodified bitumen are nearly achieved within the higher temperature range; the case of experiment 2 comes very close to the case of RMB with 15% untreated granular rubber (experiment 1).

(16) In addition, it was possible by the process of the invention not just to lower the amount of dialkyl polysulfide if the temperature is at least 140 C.; it was also possible to lower the duration for the devulcanization to below one hour.