HRP960560A2 - Bitumen compositions and a process for their preparation - Google Patents

Description

The present invention relates to bitumen mixtures, a process for their preparation and their use in asphalt mixtures for use on roads.

Bitumen is used as a binding agent in road asphalt mixtures and is constantly being developed to meet the ever-increasing demands of road construction. In general, bitumen is well maintained in road asphalt, but the increase in heavy goods traffic has led to premature wear of many roads through rutting and cracking of the surface. A crack is a serious damage in an asphalt road because it allows water to reach the lower layers of the road surface, where it causes rapid deterioration and accelerates the need for premature repairs. Increasing the bitumen content in asphalt and the use of a softer grade of bitumen improves the cracking resistance of the asphalt at low temperatures, but increases the risk of increasing the formation of ruts at higher temperatures, because the mixture is effectively softer. Conversely, rutting resistance can be improved by reducing the amount of bitumen in the asphalt mixture or by using a harder grade of bitumen at the expense of cracking resistance, as the mixture becomes less flexible.

It will be clear from the above that it would be very advantageous to discover a hard bitumen mixture that would meet today's cracking resistance requirements, that is, a bitumen mixture that has both good properties at low temperatures and good resistance to rutting at high temperatures.

It is known that the properties of bitumen at low temperatures can be improved by mixing them with a polymer. However, when this modification is applied to hard bitumens, incompatibility between bitumen and polymer is generally observed, resulting in little or no improvement in low temperature properties and relatively poor aging behavior.

Furthermore, it is known to prepare industrial and roofing bitumens by subjecting the bitumen/polymer mixture to the usual oxidation process. These bitumen mixtures, however, as it turned out, are not suitable for road applications, due to their high softening point and relatively high penetration.

The aim of the present invention is to provide a bitumen mixture suitable for filling on roads, which has good properties at low temperatures and resistance to rutting at high temperatures, and additionally improved aging behavior.

Surprisingly, it has now been found that such a bitumen mixture can be prepared by subjecting a certain bitumen mixture to an oxidation process.

Accordingly, the present invention relates to a process for the preparation of a bitumen mixture which comprises oxidizing the mixture with some oxygen-containing gas, which mixture comprises bitumen having a penetration (penetration) of less than 300 dmm (as measured by ASTM D 5 at 25°C ) and thermoplastic rubber that is present in an amount of less than 5%, based on the total mixture.

Suitably, the thermoplastic rubber is present in an amount of less than 3% by weight, preferably in the range of 1 to 3% by weight, based on the total mixture.

The bitumen used in the current process has a penetration (penetration) of less than 300 dmm (as measured by ASTM D 5 at 25°C).

Suitably, the bitumen has a penetration (penetration) of less than 250 dmm, preferably less than 200 dmm (as measured by ASTM D 5 at 25°C).

The oxidation was carried out with a gas containing oxygen, such as air or pure oxygen. Air is preferably used.

Conveniently, the process of the present invention is carried out at a temperature in the range of 200 to 280°C. Preferably, the process according to the present invention is carried out at temperatures ranging from 210 to 260°C, more preferably from 230 to 250°C. The process according to the present invention can be carried out at ambient pressure or elevated pressure. However, it will normally be carried out at ambient pressure.

Conveniently, the present process is carried out over a time period of less than 4 hours, preferably less than 3 hours, more preferably less than 2.5 hours.

The compound includes thermoplastic rubber. The mixture may include one or more different types of thermoplastic rubber. More preferably, however, only one type of thermoplastic rubber is used.

Although a wide variety of thermoplastic rubbers may be conveniently used in accordance with the present invention, preferred thermoplastic rubbers include optionally hydrogenated block copolymers comprising at least two terminal poly(monovinylaromatic hydrocarbon) blocks and at least one central poly(conjugated diene) block.

Preferably, the components of the block copolymer are selected from the group consisting of those of the formula A(BA)m or (AB)nX, where A represents a predominantly poly(monovinylaromatic hydrocarbon) block, where B represents a predominantly poly(conjugated diene) block, where X represents the residue of a multivalent binding agent and where n represents an integer ≥ 1, preferably ≥ 2, and m represents an integer ≥ 1, preferably m is 1.

Preferable A blocks are predominantly poly(styrene) blocks and B blocks are predominantly poly(butadiene) or poly(isoprene). Multivalent binding agents used include those commonly known in the art.

By the term "predominantly" it was meant that blocks A and B, respectively, can mainly originate from monovinyl aromatic hydrocarbon monomers and conjugated diene monomers, which monomers can be mixed with other structurally appropriate or inappropriate comonomers, for example, monovinyl aromatic hydrocarbon monomer as the main ingredient and a small amount (up to 10%) of other monomers or butadiene mixed with isoprene or with a small amount of styrene.

More preferably, the copolymers contain pure poly(styrene), pure poly(isoprene) or pure poly(butadiene) blocks, of which the poly(isoprene) or poly(butadiene) blocks can be selectively hydrogeminated to a maximum residual ethylenic unsaturation of 20% and preferably less of 5%. The most preferably used block copolymer has the structure ABA, where A has an apparent molecular weight of 3,000 to 100,000, and preferably of 5,000 to 40,000, and B has an apparent molecular weight of 10,000 to 250,000 and preferably of 40,000 to 200,000. Originally prepared poly(conjugated diene) blocks usually contain from 5 to 50 mol% vinyl groups, formed from 1,2 polymerization relative to the conjugated diene molecules, and preferably a vinyl content of 10 to 25%.

The complete block copolymer to be used according to the present invention normally contains the polymerized vinyl aromatic monomer in an amount of from 10 to 60% by weight and preferably from 15 to 45% by weight.

The apparent molecular weight of the total block copolymer will normally be in the range of 15,000 to 350,000 and preferably in the range of 40,000 to 250,000.

Examples of suitable pure block copolymers include KRATON G-1651, KRATON G-1654, KRATON G-1657, KRATON G-1650, KRATON G-1701, KRATON D-1101, KRATON d-1102, KRATON D-1107, KRATON D-lll, KRATON D-1116, KRATON D-1117, KRATON D-1118, KRATON D-1122, KRATON D-1135X, KRATON D-1184, KRATON D-1144X, KRATON D-1300X, KRATON D-4141 and KRATON D-4158 (KRATON is a trade name).

Bitumen can be crude oil distillation residue, cracked residue, crude oil oxidation residue or crude oil distillation residue or crude oil extracts, bitumen obtained from propane bitumen, butane bitumen, peutane bitumen or mixtures thereof. Other suitable bitumens include mixtures of the above bitumens with fillers (diluents) such as petroleum extracts, for example, aromatic extracts, distillates or residues.

Suitably, the applied bitumen has a softening point in the range of 35 to 65°C, preferably in the range of 42 to 58°C (as measured by ASTM D 36).

One of the most surprising and beneficial aspects of the present process is that now very attractive bitumen mixtures can be prepared under mild conditions without the need for the presence of a bitumen oxidation catalyst. Therefore, the process according to the present invention is conveniently carried out in the absence of a bitumen oxidation catalyst.

The tennoplastic rubbers mentioned above are preferably non-vulcanized thermoplastic rubbers. The use of unvulcanized thermoplastic rubbers in accordance with the present invention has the advantage that attractive bitumen mixtures can be prepared without the need for the presence of a vulcanizing agent. Therefore, the present process can be carried out in the absence of a vulcanizing agent.

As the skilled person will understand, the mixture of bitumen and thermoplastic rubber is superheated before undergoing the oxidation process. The mixture of bitumen and thermoplastic rubber is normally overheated so as to establish the initial temperature of the mixture in the range of 160 to 220°C.

The present invention further provides a bitumen mixture according to any of the methods described hereinbefore.

Such a bitumen mixture conveniently has a penetration (penetration) of less than 100 dmm, preferably less than 75 dmm (as measured by ASTM D 5 at 25°C) and a softening point in the range of 60 to 90°C, preferably in the range of 65 to 75°C (as measured by ASTM D 36), and contains less than 5% by weight, preferably less than 3% by weight, and more preferably 1 to 3% by weight of any of the aforementioned thermoplastic rubbers, based on the total bitumen mixture. Such a bitumen mixture is very attractive because it shows good properties at low temperatures and good resistance to rutting at high temperatures.

Fillers such as carbon black, silicon or calcium carbonate, stabilizers, antioxidants, pigments and solvents are known to be useful in bituminous mixtures and can be incorporated into the mixtures of this invention at concentrations designed in the art.

The present invention still further relates to the use of a bitumen mixture as hereinbefore described in an asphalt mixture for road applications.

The present invention will now be illustrated in terms of the following Examples.

Examples

Example 1

The prepared mixture was based on bitumen with a penetration (penetration) of 100 (as measured by ASTM D 5 at 25°), industrially made bitumen which is prepared by distillation from crude oil. The bitumen had a penetration index of 0.5 and a softening point of 44°C (as measured by ASTM D 36).. To this bitumen was added 2% by weight of block copolymer, based on the total mixture. The block copolymer used was a hydrogenated polystyrene-polybutadiene-polystyrene block copolymer with a polystyrene content of 30% and an average molecular weight of 103,000 as measured by GPC with a polystyrene standard. The ethylene unsaturation of the polymer was reduced to less than 1% of the original unsaturation after hydrogenation.

The mixture was prepared by mixing bitumen and block copolymer at a temperature of 180°C. After that, the preheated mixture thus obtained was oxidized with air in an oxidation vessel at a temperature of 220°C for 2 hours. The main properties of the oxidized bitumen mixture are shown in Table 1.

Example 2

A comparative oxidation procedure was carried out in a similar manner as described in Example 1, except that thermoplastic rubber was not added to the bitumen. The main properties of the oxidized bitumen mixture are shown in Table 1.

The resulting bitumen mixture was subjected to the Rollmg Thin film Oven Test (ASTM method D 2572). The main properties of the bitumen mixture after this aging test are shown in the lower part of Table 1.

Example 3

A comparative oxidation procedure was carried out in a similar manner as described in Example 1, except that the block copolymer was added to the bitumen after the bitumen had been oxidized. The main properties of the oxidized bitumen mixture are shown in Table 1.

Example 4

The oxidation process was carried out in a similar manner as described in Example 1, except that 1% by weight of the block copolymer was added to the bitumen, based on the total mixture. The main properties of the oxidized bitumen mixture are shown in Table 1. The main properties of the bitumen mixture after undergoing the RTFOT aging test are shown in the lower part of Table 1.

From the results shown in Table 1, it will be clear that the process of the present invention (Examples 1 and 4) can produce a hard bitumen mixture having attractive elasticity at low temperatures, as shown by the Fraas breaking point (as measured by IP 80). , while procedures that fall outside the present invention (Examples 2 and 3) yielded less attractive hard bitumen products. Moreover, as will be clear from Examples 2 and 4, the present bitumen mixture is more stable to thermal oxidation.

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Claims (8)

1. A process for the preparation of a bituminous mixture, characterized by the fact that it includes the oxidation of the mixture with some gas containing oxygen and which mixture includes bitumen having a penetration (penetration) of less than 300 dmm (as measured by ASTM D 5 at 25°C) and thermoplastic gum that is present in an amount of less than 3% by weight, based on the total mixture. 2. The method according to claim 1, characterized in that the mixture is oxidized with air. 3. The method according to any one of claims 1 or 2, characterized in that the applied temperature is in the range of 210 to 260°C. 4. The method according to any one of claims 1-3, characterized in that the thermoplastic rubber comprises an optionally hydrogenated block copolymer comprising at least two terminal poly(monovinylaromatic hydrocarbon) blocks and at least one central poly(conjugated diene) block. 5. The method according to claim 4, characterized in that the block copolymer has the formula A(BA)m or (AB)nX, where A represents a block of predominantly poly(monovinyl-aromatic hydrocarbon) and where B represents a block of predominantly poly(conjugated diene ), where X represents the residue of a multivalent binding agent and where n is an integer ≥ 1 and m is some integer ≥ 1. 6. The method according to claim 5, characterized in that the A blocks are predominantly poly(styrene) blocks and the B blocks are predominantly poly(butadiene) blocks or poly(isoprene) blocks. 7. A mixture of bitumen, indicated by the fact that it was obtained with the process defined in any of claims 1-6. 8. The use of the bitumen mixture as defined in claim 7, characterized in that it is applied in mixtures for asphalting roads.