Field of the Invention

This invention relates to the use of an additive for reducing the preparation time of preparing a polymer- modified bitumen composition.

Background of the Invention

Bitumen is used as a binder in road asphalt

mixtures, and has developed continually to meet ever- increasing performance demands from road building constructors . In general bitumen performs well in road asphalt, but increasingly heavy traffic loads and high traffic volume have led to the wear of many roads through rutting and cracking of the surface.

In their article entitled "Polymer modification of bitumen: Advances and challenges", published in May 2014 in the European Polymer Journal, volume 54, pages 18-38,

J. Zhu et al . describe the modification of bitumen with polymers . By polymer modification of bitumen is herein understood to mean the incorporation of polymers in bitumen, for example by mechanical mixing or by chemical reaction. According to J. Zhu et al . polymer

modification is reported to lead to improved properties, such as higher stiffness at high temperatures, a higher cracking resistance at low temperatures, a better moisture resistance and/or a longer fatigue life. J. Zhu et al, however, indicated that in addition to the reported advantages, researchers also encountered various challenges, including high costs and poor storage stability .

WO2015/170739 describes an asphalt composition used for e.g. road surfacing containing 0.5 to 20 parts mass of a block copolymer and 100 parts mass of asphalt. The block copolymer comprises a polymer block (A) containing 20-60% mass vinyl aromatic monomer units as main

component, and copolymer block (B) containing conjugated diene monomer units and vinyl aromatic monomer units.

The content of copolymer block (A) in the block copolymer is 10-40% mass. The hydrogenation rate of double bonds in the conjugated diene monomer units of the block copolymer is 40-100%.

It would be an advancement in the art to provide a process for producing a polymer-modified bitumen that allows for a significant reduction in the preparation time of the polymer-modified bitumen as well as obtaining a high softening point, whilst maintaining good storage stability, good road application properties and good rutting and cracking properties.

Summary of the Invention

According to the present invention there is provided the use of an additive for reducing the preparation time of a polymer-modified bitumen composition in a process which comprises blending:

(a) from 0.5 to 5 wt%, by weight of the polymer-modified bitumen composition, of a fully or partially hydrogenated block copolymer;

(b) from 85.0 wt% to 99.4 wt%, based on the total weight of the polymer-modified bitumen composition, of a bitumen component ;

(c) from 0.1 to 10 wt%, by weight of the polymer-modified bitumen composition, of an additive selected from (i) polyphosphoric acid, (ii) a flux component selected from aromatic, naphthenic or paraffinic flux oils, and petroleum extracts, and mixtures thereof; and (iii) mixtures of (i) and (ii); and (d) optionally one or more additional components.

The use of the additive described herein

surprisingly leads to a reduction in the time taken to prepare a polymer-modified bitumen using the process described herein.

Brief Description of the Drawings

Figure 1 is a plot of the results shown in Table 1 Figure 2 is a plot of the results shown in Table 2 Figure 3 is a plot of the results shown in Table 3 Figure 4 is a plot of the results shown in Table 4.

Detailed Description of the Invention

The process herein comprises blending together components (a) , (b) , (c) and optionally (d) .

Component (a) is a fully or partially hydrogenated block copolymer. In the process herein, the fully or partially hydrogenated block copolymer is used at a level of from 0.5 to 5 wt%, by weight of the polymer-modified bitumen composition. Preferably, the block copolymer is present in an amount of from 1 wt% to 5 wt%, preferably from 1.5 wt% to 4 wt%, even more preferably from 2 wt% to

3.5 wt%, by weight of the polymer-modified bitumen composition .

The block copolymer for use herein preferably comprises at least one polymer block derived from a vinyl aromatic hydrocarbon monomer and at least one polymer block derived from a conjugated diene monomer. The block copolymer may be linear or radial, symmetric or

asymmetric, and may have a structure represented by the formula A-B, A-B-A, B-A-B, A-B-A-B etc. wherein A is the polymer block of a vinyl aromatic hydrocarbon and B is polymer block of a conjugated diene. The block copolymer preferably contains up to 40% by weight of vinyl aromatic hydrocarbon, more preferably from 30 to 40% by weight of vinyl aromatic hydrocarbon.

The vinyl aromatic hydrocarbon is preferably styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene , 1 , 3-dimethylstyrene, a-methylstyrene, vinylnaphthalene or vinylanthracene, most preferably styrene. Mixtures of vinyl aromatic hydrocarbons may be used.

The conjugated diene preferably has from 4 to 8 carbon atoms, and is more preferably selected from 1,3- butadiene, 2-methyl-l, 3-butadiene (isoprene), 2,3- dimethyl-1, 3-butadiene, 1 , 3-pentadiene , and 1,3- hexadiene . Most preferably the conjugated diene is 1,3- butadiene or isoprene. Mixtures of conjugated dienes may be used.

The block copolymer is fully or partially

hydrogenated which means that all or a certain percentage of the double bonds in the conjugated diene moieties are hydrogenated. Preferably the block copolymer is from 40 to 100 wt% hydrogenated, more preferably 40 to 99.5 wt% hydrogenated, even more preferably from 50 to 90 wt% hydrogenated, and especially from 60 to 90 wt%

hydrogenated .

Examples of suitable fully or partially hydrogenated block copolymers for use herein include a fully or partially hydrogenated styrene-/3-isoprene polymer (SEP), a fully or partially hydrogenated styrene-/3-isoprene-/3- styrene polymer (SEPS) , a fully or partially hydrogenated styrene-isoprene-styrene polymer (SIS) , a fully or partially hydrogenated styrene-/3-butadiene-/3-styrene copolymer (SEBS) , and a fully or partially hydrogenated styrene-/3-isoprene/butadiene-/3-styrene copolymer (SEEPS) .

In a preferred embodiment herein, the block copolymer comprises a polymer block (A) comprising vinyl aromatic monomer units as main component, and copolymer block (B) comprising conjugated diene monomer units and vinyl aromatic monomer units, wherein the content of the vinyl aromatic monomer units in the block copolymer is in the range from 20 to 60 mass%, the content of the copolymer block (A) in the block copolymer is in the range from 10 to 40 mass% and the hydrogenation rate of double bonds in the conjugated diene monomer units of the block copolymer is in the range from 40 to 100%, preferably in the range from 50 to 90%, more preferably in the range from 60 to 90%. Polymers of this type are disclosed in

WO2015/170739, incorporated herein by reference in its entirety .

In a preferred embodiment herein, the conjugated diene monomers units of the block copolymer comprise (a) conjugated diene monomer units derived from 1,2-bonds and/or 3,4-bonds and (b) conjugated diene monomer units derived from 1,4-bonds, and if the total content of conjugated monomer diene units is taken to be 100 mass%, the content of alkenyl monomer units (al) obtained by hydrogenating the conjugated diene monomer units (a) is in the range from 10 to 50 mass%, the content of alkenyl monomer units (bl) obtained by hydrogenating the

conjugated diene monomer units (b) is in the range from 0 to 80 mass%, and the total content of unhydrogenated conjugated diene monomers units (a2) following

hydrogenation and unhydrogenated conjugated diene monomer units (b2) following hydrogenation is in the range from 0 to 90 massl.

Preferably, the content of conjugated diene monomer units (a) derived from 1,2-bonds and/or 3,4-bonds is in the range from 10 to 50 mass% relative to the total content of the conjugated diene monomer of the block copolymer . The weight average molecular weight of the block copolymer for use herein is preferably in the range of from 50, 000 to 300, 000.

In a preferred embodiment herein the block copolymer has at least one type of functional group selected from hydroxyl groups, acid anhydride groups, epoxy groups, amino groups, amide groups, silanol groups and

alkoxysilane groups .

Component (b) is a bitumen component. The bitumen component used in the process of the present invention may be a residue from the distillation of crude oil, a cracked residue, naturally occurring bitumen or a blend of various bitumen types. Examples of bitumen that may be conveniently used in the present invention include distillation or "straight run" bitumen, precipitation bitumen, e.g. propane bitumen, oxidized or blown bitumen, naphthenic bitumen, paraffinic bitumen or mixtures thereof .

Various grades of bitumen may be used in the process of producing the polymer-modified bitumen described herein, such as, for example, 35/50, 50/70, 60/70,

70/100, 80/100, 100/150, 160/220 grades.

The bitumen component is present in the polymer- modified bitumen composition at a level of from 85 wt% to 99.4 wt%, preferably from 90 wt% to 95 wt%, based on the total weight of the polymer-modified bitumen.

Component (c) is an additive selected from (i) polyphosphoric acid, (ii) a flux component selected from aromatic, naphthenic or paraffinic flux oils, petroleum extracts, and mixtures thereof; and (iii) mixtures of (i) and (ii) .

Component (c) is used at a level of from 0.1 wt% to 10 wt%, preferably from 0.1 wt% to 5 wt%, more preferably from 0.5 wt% to 5 wt%, and even more preferably from 0.5 to 2 wt%, by weight of the polymer-modified bitumen composition .

Polyphosphoric acid (PPA) is a polymeric product of thermal dehydration and polycondensation of

orthophosphoric acid ( H3PO4 ) . Besides orthophosphoric forms, it contains a mixture of polymeric forms whose content increases with increasing acid concentration. Commercially available PPA is a mixture of linear polyacids of general formula H _n +2PnC>3n+i, wherein n≥2.

Those acids are produced either from the dehydration of H3P O4 at high temperatures or by heating P2O5 dispersed in H3P O4 . In the latter method, longer chains are obtained. Polyphosphoric acid is highly hydroscopic and easily hydrolyses in moist air. Its viscosity and physical form at room temperature depends on the content of P2O5.

Polyphosphoric acid is available in various grades, for example, concentrations of 105, 110 and 114% H3P O4 are used (the % exceeds 100% since it reflects the

calculation of H3P O4 concentration on the base of P2O5 content in the inorganic polymer) . 105%, 110% and 114% H3P O4 is equivalent to 75.9%, 79.8% and 82.6% P2O5, respectively.

The flux component (ii) for use herein is selected from aromatic, naphthenic or paraffinic flux oils, petroleum extracts, e.g. aromatic extracts, distillates or residues, mineral derived or synthetic base oils, and vegetable oils. Specific examples of suitable flux components include bright stock furfuryl extract (BFE) , Fischer-Tropsch derived base oils such as HVI 160B supplied by Shell, lubricating base oils such as re- refined SN150 supplied by Whelan Refining Limited, Sneyd Hill, Burslem, Stoke-on-Trent, ST6 2DZ, UK and Vivatec 500 (a refined solvent mineral oil) supplied by H&R group, and De-asphalted cylinder oil (DACO) .

Preferred flux components for use herein are SN150 (from Whelan Refining Limited) and HVI 160B (from Shell) . Shell HVI 160B is a paraffinic base oil with good oxidation stability and high viscosity/temperature behaviour. HVI 160B is classified as a Group I base stock slate within the API/ATIEL Guidelines. SN150 is a Group I base oil.

When additive component (c) is a flux component, a preferred level of flux component is from 0.5 to 10 wt%, by weight of the polymer-modified bitumen composition.

In a preferred embodiment herein, component (c) is polyphosphoric acid. A preferred level of polyphosphoric acid is 0.5 to 5 wt%, by weight of the polymer-modified bitumen composition.

The polymer-modified bitumen composition may also comprise one or more additional components (d) suitable for use in a bitumen formulation. Such additional components are well known to those skilled in the art and include, for example, waxes, anti-stripping agents, viscosity modifiers, penetration correctors (for example, Gilsonite) , softening agents, process oils, GTL oils, aromatic oils, paraffinic oils, and petroleum

distillates, and the like.

During preparation of the polymer-modified bitumen composition, high shear mixing is preferably used for blending of components (a) , (b) , (c) and optionally (d) . As used herein, the term "high shear mixing" means mixing at a speed from 1500 to 6000, preferably 3000 to 6000, even more preferably from 4000 to 6000 rpm. Preferably, high shear mixing involves the use of a Silverson high shear mixer. The use of an additive component (c) enables a reduction in the time taken for the production of a polymer-modified bitumen using the process described herein. Preferably, the time taken to produce the polymer-modified bitumen is reduced by at least 30%, preferably at least 50%, more preferably at least 60%, even more preferably at least 70%, especially at least 80%, compared with the time taken to produce a polymer- modified bitumen in an analogous process which doesn't include the use of an additive component (c) .

In a preferred embodiment, the blending of components (a) , (b) , (c) and optionally (d) in the process herein is carried out at a temperature of less than 180°C,

preferably less than 170°C, more preferably less than 165°C. The use of additive (c) enables the process of preparing the polymer-modified bitumen composition to be carried out at a lower temperature compared to the temperature used in an analogous process which does not use additive (c) .

The softening point of the polymer-modified bitumen is preferably 60°C or greater, more preferably 70°C or greater, even more preferably 80°C or greater, especially 90°C or greater.

The final polymer-modified bitumen composition should meet the desired polymer-modified bitumen specification.

The final polymer-modified bitumen composition produced herein can be used as a binder in an asphalt composition for road paving applications.

The invention is further illustrated by the following non-limiting examples.

Examples

Various polymer-modified bitumen compositions were produced by blending a bitumen component, a polymer and polyphosphoric acid using a Silverson high shear mixer.

The bitumen grades used were 60/70 (from Bahrain Petroleum Company), 60/70 (from Shell Eastern Petroleum Limited), 80/100, and 70/100. The polymer was a

partially hydrogenated polymer as disclosed and prepared in WO2015/170739.

Tables 1 to 4 set out the grades of bitumen and the levels of each component, as well as mixing times, mixing temperatures and softening points measured at various intervals in the production process. For each of the polymer-modified bitumen compositions produced, the softening points were measured at various intervals (mixing times) using the EN 1427-2015 test method. The polymer-modified bitumen compositions are deemed to be stable when the change in softening point stabilizes. Table 1

Table 2

Table 3

Table 4

Figure 1 is a plot of the softening point against the mixing time results shown in Table 1.

Figure 2 is a plot of the softening point against the mixing time results shown in Table 2

Figure 3 is a plot of the softening point against the mixing time results shown in Table 3

Figure 4 is a plot of the softening point against the mixing time results shown in Table 4.

In Figures 1-4, "HP" means "hydrogenated polymer". Discussion

The results shown in Tables 1-4 and Figures 1-4 show that the use of PPA helps to significantly reduce the time taken to make a stable polymer-modified bitumen composition comprising a partially hydrogenated polymer.