Co-solubilization process for preparing modified bitumen and product obtained thereof

Abstract

The present invention relates to a co-solubilization process for preparation of a polymer modified bitumen/asphalt and emulsified polymer modified bitumen/asphalt from bitumen, polymer, emulsifier etc. The present invention further relates to a polymer modified bitumen comprising bitumen and styrene-butadiene-styrene (SBS) linear co-polymer having high softening point. The present invention also relates to the use of the polymer modified bitumen and its emulsion in in micro-surfacing for maintenance of pavements.

Claims

1. A co-solubilization process for preparation of a polymer modified bitumen, the process comprising: (a) heating a softer grade bitumen to a temperature ranging from 150° C. to 200° C.; (b) adding styrene-butadiene-styrene (SBS) linear co-polymer for 10 to 20 minutes to the softer grade bitumen to obtain a mixture; (c) dispersing the mixture obtained in step (b) at a temperature ranging from 150° C. to 200° C. followed by milling to obtain a homogenous matrix; (d) adding a harder grade bitumen to the homogenous matrix obtained in step (c) to obtain a mixture, wherein the mixture comprises styrene-butadiene-styrene (SBS) linear co-polymer in an amount ranging from 3 to 5% by weight of the mixture; and (e) stirring the mixture obtained in step (d) at a temperature ranging from 150° C. to 200° C. followed by milling to obtain the polymer modified bitumen; wherein the polymer modified bitumen has a high softening point ranging from 60° C. to 90° C.; wherein the softer grade bitumen has absolute viscosity ranging from 800 to 1200 poise at a temperature of 60° C. and the harder grade bitumen has absolute viscosity ranging from 2400 to 3600 poise at a temperature of 60° C.

2. The process as claimed in claim 1, wherein the styrene-butadiene-styrene (SBS) linear co-polymer is added in step (b) in an amount ranging from 15 to 20% by weight of the softer grade bitumen.

3. The process as claimed in claim 1, wherein milling of the mixture in steps (c) and (de) is done for 20 to 30 minutes.

4. A process for preparation of a polymer modified bitumen emulsion, the process comprising: (a) heating a softer grade bitumen to a temperature ranging from 150° C. to 200° C.; (b) adding styrene-butadiene-styrene (SBS) linear co-polymer for 10 to 20 minutes to the softer grade bitumen to obtain a mixture; (c) dispersing the mixture obtained in step (b) at a temperature ranging from 150° C. to 200° C. followed by milling to obtain a homogenous matrix; (d) adding a harder grade bitumen to the homogenous matrix obtained in step (c) to obtain a mixture, wherein the mixture comprises styrene-butadiene-styrene (SBS) linear co-polymer in an amount ranging from 3 to 5% by weight of the mixture; (e) stirring the mixture obtained in step (d) at a temperature ranging from 150° C. to 200° C. followed by milling to obtain a polymer modified bitumen; (f) optionally, mixing the polymer modified bitumen obtained in step (e) with an organic solvent to obtain an organic phase; (g) mixing water, an acid, calcium chloride salt solution and an emulsifier to obtain an aqueous phase; and (h) mixing the organic phase obtained in step (f) with the aqueous phase obtained in step (g) by milling to obtain the polymer modified bitumen emulsion; wherein the softer grade bitumen has an absolute viscosity ranging from 800 to 1200 poise at a temperature of 60° C. and the harder grade bitumen has an absolute viscosity ranging from 2400 to 3600 poise at a temperature of 60° C.

5. The process as claimed in claim 4, wherein the styrene-butadiene-styrene (SBS) linear co-polymer is added in step (b) in an amount ranging from 15 to 20% by weight of the softer grade bitumen.

6. The process as claimed in claim 4, wherein milling of the mixture in steps (c) and (e) is done for 20 to 30 minutes.

7. The process as claimed in claim 4, wherein the organic solvent is selected from Straight run Kerosene Oil (SKO) or Mineral Turpentine Oil (MTO).

8. The process as claimed in claim 4, wherein the aqueous phase comprises: 30 to 35 wt % of water, 1 to 2 wt % of acid, 0.15 to 0.5 wt % of calcium chloride salt solution, and 0.25 to 1.5 wt % of emulsifier; wherein the wt % of each of the components is calculated based on the total weight of the polymer modified bitumen emulsion.

9. The process as claimed in claim 8, wherein the acid in the aqueous phase is a mineral acid.

10. The process as claimed in claim 8, wherein the emulsifier in the aqueous phase is an amine selected from the group consisting of secondary, tertiary amine, and long chain fatty amines.

11. The process as claimed in claim 4, wherein the polymer modified bitumen emulsion is used for micro-surfacing flexible pavements, construction and maintenance of roads and pavements, resurfacing and construction of parking lots.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 Comparison of the general conventional manufacturing processes (A) of Polymer Modified Bitumen Emulsion (PMBE) with the present invention (B) producing PMBE with having high softening point

DETAILED DESCRIPTION OF THE INVENTION

(2) The present invention provides a cost effective co-solubilization process whereby a softer grade bitumen, which contain aromatics and lighter component that assist in dissolving higher dosage of SBS polymer, and harder grade bitumen are co-added in the blending process to for obtaining PMB and PMBE with desired polymer content and characteristics. Thus, the present invention provides a micro-surfacing product, PMBE with softening point more than 60° C. and to achieve this it is necessary to have high polymer content while maintaining the cost of product lower.

(3) The present invention relates to a co-solubilization process for preparation of a polymer modified bitumen and polymer modified bitumen emulsion which are useful in micro-surfacing of flexible pavements (Bituminous pavements/roads). The present invention further relates to a polymer modified bitumen comprising bitumen and styrene-butadiene-styrene (SBS) linear co-polymer. The present invention also relates to a Styrene-Butadiene-Styrene (SBS) based Polymer Modified Bitumen Emulsion (PMBE) which has higher Polymer concentration and is prepared without any stabilizer/cross linker additive.

(4) The present invention thus relates to a two steps process for the preparation of modified bitumen emulsion for micro-surfacing flexible pavements, wherein the process comprises:

(5) (I) preparing a polymer modified bitumen, wherein the polymer modified bitumen comprises bitumen and styrene-butadiene-styrene (SBS) linear co-polymer; and

(6) (II) preparing a polymer modified bitumen emulsion by mixing an aqueous phase with an organic phase containing the polymer modified bitumen.

(7) According to the main feature, the present invention provides a co-solubilization process for preparation of a polymer modified bitumen, the process comprising: (a) heating a softer grade bitumen to a temperature ranging between 150-200° C.; (b) adding styrene-butadiene-styrene (SBS) linear co-polymer for 10-20 minutes to the softer grade bitumen to obtain a mixture; (c) dispersing the mixture obtained in step (b) at a temperature ranging from 150-200° C. followed by milling to obtain a homogenous matrix; (d) adding a harder grade bitumen to the homogenous matrix obtained in step (c) to obtain a mixture, wherein the mixture comprises styrene-butadiene-styrene (SBS) linear co-polymer in an amount ranging between 3-5% by weight of the mixture; and (e) stirring the mixture obtained in step (d) at temperature ranging from 150-200° C. followed by milling to obtain the polymer modified bitumen;

(8) wherein the polymer modified bitumen has a high softening point ranging from 60° C.-90° C.;

(9) wherein the softer grade bitumen has absolute viscosity ranging from 800-1200 poise at a temperature of 60° C. and the harder grade bitumen has absolute viscosity ranging from 2400-3600 poise at a temperature of 60° C.

(10) In an embodiment, the steps (a), (c) and (e) in the co-solubilization process of preparation of the polymer modified bitumen are preferably performed at a temperature range of 160-170° C.

(11) In another feature, the present invention also provides a process for preparation of a polymer modified bitumen emulsion, the process comprising: (a) heating a softer grade bitumen to a temperature ranging between 150-200° C.; (b) adding styrene-butadiene-styrene (SBS) linear co-polymer for 10-20 minutes to the softer grade bitumen to obtain a mixture; (c) dispersing the mixture obtained in step (b) at a temperature ranging from 150-200° C. followed by milling to obtain a homogenous matrix; (d) adding a harder grade bitumen to the homogenous matrix obtained in step (c) to obtain a mixture, wherein the mixture comprises styrene-butadiene-styrene (SBS) linear co-polymer in an amount ranging between 3-5% by weight of the mixture; (e) stirring the mixture obtained in step (d) at a temperature ranging from 150-200° C. followed by milling to obtain a polymer modified bitumen; (f) optionally, mixing the polymer modified bitumen obtained in step (e) with an organic solvent to obtain an organic phase; (g) mixing water, an acid, calcium chloride salt solution and an emulsifier to obtain an aqueous phase; and (h) mixing the organic phase obtained in step (f) with the aqueous phase obtained in step (g) by milling to obtain the polymer modified bitumen emulsion;

(12) wherein the softer grade bitumen has absolute viscosity ranging from 800-1200 poise at a temperature of 60° C. and the harder grade bitumen has absolute viscosity ranging from 2400-3600 poise at a temperature of 60° C.

(13) In a preferred embodiment, the SBS linear co-polymer is added to the softer grade bitumen in step (b) of above processes for 15 minutes.

(14) In an embodiment, the steps (a), (c) and (e) in the process of preparation of the polymer modified bitumen emulsion are preferably performed at a temperature range of 160-170° C.

(15) In an embodiment, the styrene-butadiene-styrene (SBS) linear co-polymer is added in step (b) of the co-solubilization process in an amount ranging from 15-20% by weight of softer grade bitumen. The mixing of 15-20% of SBS polymer in softer grade bitumen (VG10) at 150-200° C. and then adding required amount of harder grade bitumen (VG30) enables to attain a final PMB and PMBE concentration with 3-5 wt % of SBS modified bitumen having softening point of PMBE residue greater than 60° C.

(16) In a preferred feature, milling of the mixture obtained in steps (c) and (d) of the co-solubilization process is done for 20-30 mins to reduce polymer particle size.

(17) In another preferred feature, the mixture obtained in the steps (c) and (d) of co-solubilization process is stirred with an agitator for 2-3 hrs.

(18) In yet another embodiment, the aqueous phase for the preparation of the emulsion comprises 0.5-2 wt % of acid, 0.2-0.5 wt % of calcium chloride, 0.25-1.5 wt % of emulsifier and water. Further, the aqueous phase comprises an acid, wherein the acid in the aqueous phase is a mineral acid preferably sulfuric acid, hydrochloric acid and nitric acid, more preferably the acid is hydrochloric acid. Again, the emulsifier in the aqueous phase is secondary and/or tertiary amine, preferably long chain fatty amines (for examples Polyram L920, Redicote 500, Rodhaval CS6 and others).

(19) In another embodiment, the organic solvent used in the preparation of the emulsion is Straight run Kerosene Oil (SKO) or Mineral Turpentine Oil (MTO) etc.

(20) In a preferred embodiment, the organic phase is maintained at a temperature ranging between 140-150° C. and the aqueous phase is maintained at a temperature ranging between 40-50° C.

(21) In another feature, the present invention provides a polymer modified bitumen prepared by the co-solubilization process comprising bitumen and styrene-butadiene-styrene (SBS) linear co-polymer, wherein the SBS polymer is present in an amount ranging from 3-5% by weight of the polymer modified bitumen.

(22) In yet another feature, the present invention provides polymer modified bitumen emulsion obtained by the above process comprising: (a) 60 to 65 wt % of polymer modified bitumen; (b) 0 to 5 wt % of organic solvent; and (c) 35 to 40 wt % of aqueous phase;

(23) wherein the wt % of each of the components is calculated based on the total weight of the emulsion.

(24) Upon addition of SBS copolymers into bitumen, the intermolecular interactions between bitumen and the PB blocks are stronger than those with the PS blocks indicating that the PB blocks interact with positively charged groups in bitumen through their π-electrons, whereas PS blocks interact with electron-rich groups in bitumen through their aromatic protons. Mixed with bitumen, PS blocks in SBS copolymers absorb some saturated branches and a few rings in light components of bitumen, which leads to the swelling of PS blocks and the hardening of bitumen. When the polymer content is low, SBS is dispersed as a discrete phase in the bitumen. As the SBS concentration increases, phase inversion starts in the modified bitumen. Within the SBS-rich phase, there are two sub-phases: swollen PB matrix and essentially pure PS domains.

(25) Bitumen with high aromatic content helps in producing a compatible and stable SBS modified bitumen and addition of aromatic oils improve the compatibility between SBS and some bitumen with low aromatics content. Too high aromatic content in modified bitumen, however, leads to the swelling and anti-plasticization of some PS blocks, which is not good for the resulting properties of the modified bitumen. Thus, softer and harder grade bitumen are together chosen for preparation of PMB with high polymer (SBS) content without any catalyst or additive and without gel formation. Further, the softening point of PMB and PMBE being much higher than the conventional one, the present invention favours the usability of the emulsion in terms of road application preventing weeping of roads resulting in damage of pavements that might lead to leaks and other adverse phenomenon in roads.

(26) In yet another feature of the present invention, the emulsion serves as an extremely fast breaking polymer modified asphalt emulsion called a micro-surfacing emulsion and finds its application for micro-surfacing flexible pavements, construction and maintenance of roads and pavements. The emulsion also favours resurfacing of existing parking lots and construction of new parking spaces.

(27) The following examples are given for the purpose of further illustrating the invention. All percentages and parts are based on weight unless otherwise indicated.

(28) Chemical Used for the Process of Preparation of PMB and PMBE: 1. VG10 Grade Bitumen: Softer Grade Bitumen having Absolute Viscosity at 60° C. [ASTM D2171 and IS 1206 (Part 2)] in the range of 800-1200 Poise. 2. VG30 Grade Bitumen: Harder Grade Bitumen having Absolute Viscosity at 60° C. [ASTM D2171 and IS 1206 (Part 2)] in the range of 2400-3600 Poise. 3. SBS (Linear) (501W) Polymer used from M/s LG Chemicals Ltd Korea. 4. Various emulsifiers were used as supply from different sources. 5. Chemicals like Hydrochloric acid (HCl) and Calcium Chloride (CaCl.sub.2) were supplied locally. 6. M/s ENH Ltd Denmark bitumen modification and bitumen emulsion laboratory scale R&D plants were used for study.

(29) Experimental Work: Manufacturing Process of PMB is as Follows: 1. Manufacturing of Precursor PMB for PMBE: 2 kg of Softer grade bitumen/vacuum residue (say VG10 in this case) was heated in pilot plant to attain a temperature of about 150-170° C. Then, about 0.3-0.4 kg (15-20%) Styrene-Butadiene-Styrene (SBS) Linear co-polymer (M/s LG Ltd make) was added over 15 minutes in reaction vessel. The mixture was stirred at about 160-170° C. for about 2 hrs to ensure dissolution of polymer in bitumen matrix. This matrix was then passed through mill for about 20-30 minutes to reduce polymer particle size and make the matrix homogenous. To this mixture, 4-8 kg of harder grade bitumen/vacuum residue (VG30 in our case) was added to make the effective concentration of SBS polymer in bitumen matrix to 3-5%. Then this mixture was stirred for about 3 hrs at 160-170° C. and passed through mill for about 20-30 minutes to obtain the precursor PMB. This PMB was be used as PMB binder in hot mix asphalt composition preparation and on pavement laying. However, this precursor was further used for manufacturing of better quality PMBE. 2. Manufacturing of PMBE: Bitumen emulsion was obtained by combining about 60-65% of organic phase (comprising bitumen matrix mixed with solvent (e.g. SKO)) and 35-40% aqueous phase (made of a HCl, amine based emulsifier (any one of Rodhaval CS6/Polyram L920/Redicote 500), calcium chloride, and water) at suitable temperature and is obtained by passing through colloidal mill in bitumen emulsion plant. Organic phase as discussed above was placed in one tank and was maintained at 140-150° C. Aqueous phase as discussed above was taken in another tank and was maintained at room temperature to 50° C. Both these phases were mixed by passing through a colloidal mill at appropriate proportion (predetermined) to obtain PMBE having desired properties (especially higher softening point). Using this process, a better product for micro-surfacing and paving was formulated. The polymer modified bitumen emulsion was also prepared without using the solvent based on the above described method.

(30) Further, an analysis was performed for investigating the maximum amount SBS polymer that can be dissolved in softer and harder grade bitumen without any additive or catalyst to produce stable PMB and product thereof. The blending properties of bitumen with different percentages of SBS Polymer have been shown in Table 1.

(31) TABLE-US-00001 TABLE 1 Blending properties of Bitumen with SBS Polymer % % Type of Bitumen Bitumen SBS Intermediate PMB Remark Softer Grade 95 5 Stable Can be used (VG10) 90 10 Stable but difficult directly for 85 15 to handle and further 80 20 workability is poor blending 75 25 Required high Not useful. temperature, handling, mixing is difficult and further Gel formation occurs. Harder Grade 98 2 Stable Can be used (VG30) 97 3 Stable directly for 96.5 3.5 Stable further blending 96 4 Gel formation Not useful. 95 5 Gel formation

(32) From the above table it can be understood that the requirement of Softening Point in Micro-surfacing can be met by either increasing dosage of SBS polymer in softer grade bitumen or by adding harder grade bitumen into the system while maintaining lower percentage of polymer. Addition of more polymer increases cost of product drastically. Therefore, the later method of co-solubilizing harder grade bitumen (VG 30) with softer grade bitumen (VG10) and polymer matrix yielded a cost effective PMB product. Based on the above table, it is observed that: SBS Polymer blended with softer grade bitumen (VG10) worked well up to concentration of 5% SBS and was stable and workable. This PMB was emulsified to obtain polymer modified bitumen emulsion (PMBE). However, PMBE developed out if this process did not meet softening point requirement of minimum 57° C. for micro-surfacing of pavements. With increasing dosage of SBS up to 10%, intermediate PMB obtained, although isolable, was difficult to handle and work with and high temperature (>180° C.) was required for further processing. PMBE formed out of this intermediate PMB was not cost effective. Using harder grade of bitumen (VG30), PMB and PMBE containing up to 3% SBS was formed. Although stable, PMBE did not meet softening point requirement. While increasing dosage of SBS above 4% lead to gel formation (without any catalyst or additive). Therefore, PMBE with higher polymer content could not be made using only harder grade bitumen. Gel formation was due to higher concentration of asphaltenes in harder grade bitumen (VG30) as compared with softer grade bitumen (VG10).

(33) The PMBE commonly used for micro-surfacing as prepared by the conventional process is characterised based on Indian specification MORTH 5.sup.th Edition Table 500-32 as shown in Tables 2.

(34) TABLE-US-00002 TABLE 2 Requirement of Modified Bitumen Emulsion for Micro-surfacing (MORTH 5.sup.th Edition Table 500-32) Specification Test method Test Name Residue on 600 micron IS Sieve (% by 0.05 IS: 8887 mass), Maximum Viscosity by Saybolt Furol Viscometer, at 20-100 IS: 8887 25° C., in second Coagulation of emulsion at low NIL IS: 8887 temperature Storage stability after 24 h(168 h), % 2(4) IS: 8887 maximum Particle charge +ve IS: 8887 Test on Residue: Residue by evaporation, % minimum 60 IS: 8887 Penetration at 25° C./100 g/5 s 40-100 IS: 1203 Ductility at 27° C., cm, minimum 50 IS: 1208 Softening point, in ° C., minimum 57 IS: 1205 Elastic recovery*, %, minimum 50 IS: 15462 Solubility in tri-chloroethylene, %, 97 IS: 1216 minimum *Elastic recovery is tested for Torsional Elastic Recovery as per Appendix 8 of IRC: 81, the minimum value shall be 20%.

(35) Table 3 describes the some of the typical properties of the PMB developed using varying % of SBS and softer grade bitumen only, while Table 4 describes softening point of the residue of the PMBE obtained using the PMB. The PMB thus obtained was stable but PMBE formed out of this intermediate PMB was not cost effective. Moreover, the resulting PMBE did not show any remarkable improvement in the softening point parameter.

(36) TABLE-US-00003 TABLE 3 Blend properties of SBS and VG10 (Softer Grade Bitumen) Properties of PMB developed using SBS and Softer Grade Bitumen VG10 3% SBS 3.5% SBS 4% SBS 5% SBS 6% SBS Properties in VG-10 in VG-10 in VG-10 in VG-10 in VG-10 Softening 59.5 61 62 64.5 67 point, Deg C., min Elastic 70 71 73 75 77 Recovery, % min

(37) TABLE-US-00004 TABLE 4 Softening Point property of Residue of PMBE developed using SBS and Softer Grade Bitumen (VG10) Properties of Residue of PMBE developed using SBS and Softer Grade Bitumen VG10 3% SBS 3.5% SBS 4% SBS 5% SBS 6% SBS Properties in VG-10 in VG-10 in VG-10 in VG-10 in VG-10 Softening 53 53 54 56 59 point, Deg C., min

(38) Table 5 describes the properties of the PMB developed using varying % of SBS together with harder grade and softer grade bitumen prepared based on the co-solubilization process as disclosed in the present invention, wherein harder and softer grades bitumen are co-added. Table 6 describes the typical softening point of residue properties of the PMBE obtained using the PMB. The tables indicated that the PMB obtained by the process of co-solubilization and the PMBE prepared subsequently showed higher softening point. The PMBE thus obtained showed improved properties of the residue after emulsion breaking as required for micro-surfacing.

(39) TABLE-US-00005 TABLE 5 Blend properties of PMB developed using Co-solubilization Properties of PMB developed using co-solubilization 3% SBS 3.5% SBS 4% SBS 4.5% SBS 5% SBS in VG10 + in VG10 + in VG10 + in VG10 + in VG10 + Properties VG30 VG30 VG30 VG30 VG30 Softening 62 64 70 81 90 point, Deg C., min Elastic 70 72 76 81 87 Recovery, % min

(40) TABLE-US-00006 TABLE 6 Blend properties of PMBE developed using PMB obtained by co-solubilization process Properties of Residue of PMBE developed using co-solubilization 3.5% SBS in 3.5% SBS in 3.5% SBS in VG10 + VG30 VG10 + VG30 VG10 + VG30 PMB (63%) + 3% SKO + PMB (63%) + 3% SKO + PMB (63%) + 3% SKO + Properties 1.2% Rodhaval CS6 1.2% Redicote 500 1.2% Polyram L920 Softening point, 61 60 62 Deg C., min