WO2000005303A1

WO2000005303A1 - Composition containing bitumen and polymer coated mineral particles, and process for the preparation of polymer coated mineral particles

Info

Publication number: WO2000005303A1
Application number: PCT/NL1999/000451
Authority: WO
Inventors: Marcellus Cornelis Maria Van Der Sanden; Wilhelmus Gerardus Marie Bruls; Mathijs Joseph Maria Gerardus Kisters
Original assignee: Dsm N.V.
Priority date: 1998-07-20
Filing date: 1999-07-14
Publication date: 2000-02-03
Also published as: NL1009695C2; AU5070499A

Abstract

Composition containing bitumen and mineral particles, which particles have been provided with a polymer coating, the composition containing mineral particles with a particle diameter ∫ 63 νm, which particles have been provided with a polymer coating, which coating has been applied onto the particles from an aqueous solution of a polymer, which polymer in the solution contains monomer units containing carboxylate anions.

Description

COMPOSITION CONTAINING BITUMEN AND POLYMER COATED MINERAL PARTICLES,AND PROCESS FOR THE PREPARATION OF POLYMER COATED MINERAL PARTICLES

0

The invention relates to a composition containing bitumen and mineral particles, which particles are provided with a polymer coating.

Such compositions can be used for instance 5 in asphalt and roofing materials. Asphalt is normally composed of mineral particles of different diameters which are enveloped and bonded together by a bituminous binder. The greater part of the particles constitutes a mineral skeleton. Bitumen keeps the skeleton together 0 and fills up at least part of the cavities between the particles. Bitumen can be modified or non-modified. The mineral skeleton provides much of the load-bearing capacity of the asphalt .

Bitumens are highly viscous liquids or 5 solid substances which mainly consist of hydrocarbons or hydrocarbon derivatives and which are almost completely soluble in carbon disulphide. Natural as well as factory-made bitumen can be used for the composition according to the invention. 0 Mineral particles can be subdivided according to particle diameter. Particles having a diameter mainly larger than 2 mm are classified as 'stones' or 'gravel'. Particles having a diameter mainly between 63 μm and 2 mm are classified as 'sand' . Particles having a diameter mainly smaller than 63 μm are classified as 'filler'. Examples of mineral particles with a variety of diameters are rubble, gravel, sand and combinations of these. A mixture of bitumen and filler is called a

'mortar' . Mortar is used to fill the mineral skeleton. Mortar can fill up completely or partially the hollow space within the skeleton or can be present in such a quantity that skeleton components are squeezed apart. In the latter case the mixture is called 'overfilled asphalt'. In overfilled asphalt the material used to fill up the hollow space must also have a load bearing capacity. The properties of a mortar are determined by, among other factors, the ratio between the amount of bitumen and the amount of filler, the type of bitumen and the type of filler, and by the presence of any additives .

US patent 5,219,901 (W.J. Burke), 15.06.1993, column 2, lines 38-45, describes a composition comprising bitumen and mineral particles, which particles are provided with a polymer coating. Said composition contains particles of a variety of diameters, which particles are provided with a coating of an organic polymer of a high molecular weight, which polymer is soluble in organic solvents, but insoluble in water. The coating is applied by contacting the particles with an emulsion of the polymer diluted with water, decanting the excess of emulsion and then drying the particles. Next, the particles are mixed with molten bitumen.

The known composition has the drawback that its application results in asphalt which may exhibit rut formation relatively soon. The invention aims to provide a composition which does not present said drawback or only to a much lesser extent. This aim is achieved due to the composition according to the invention being characterized in that the composition contains mineral particles with a particle diameter of less than 63 μm, which particles are provided with a polymer coating, which coating has been applied onto the particles from an aqueous solution of a polymer, which polymer in the solution contains monomer units which contain carboxylate anions. In the present text a 'coating' is understood to be a layer which covers at least part of the particle surface.

Japanese patent specification JP-A-62079268 does disclose a composition which contains bitumen and a water-soluble copolyτner, but it teaches that the addition of the copolymer is effected by mixing the copolymer with the bitumen. It does not mention a solution of the polymer, nor the application of a coating of the polymer onto mineral particles of a particle diameter of less than 63 μm. Also, the composition described in JP-A-62079268 is more sensitive to rut formation than the composition according to the invention.

The composition according to the invention is preferably prepared with factory-made penetration bitumen. The polymer coating of the particles with a diameter < 63 μm has preferably been applied from an aqueous solution of a polymer, which polymer comprises monomer units which contain carboxylic acid groups and/or anhydride groups or a salt thereof. Mixtures of such polymers can also be used.

The polymer coating of the particles with a diameter < 63 μm has preferably been applied from an aqueous solution characterized in that the polymer in the aqueous solution comprises at least 10 mol% monomer units which contain carboxylate anions . Even more preferably the aqueous solution comprises a polymer which contains at least 20 mol%, even more preferably at least 30 mol% monomer units which contain carboxylate anions . Examples of polymers that can be used in the aqueous solution are water-soluble styrene maleic anhydride copolymer, water-soluble isobutylene maleic anhydride copolymer, polyacrylic acid and water- soluble salts of such polymers. Preferably a coating has been applied onto the particles from an aqueous solution of polyacrylic acid or an aqueous solution of a copolymer of styrene and maleic anhydride, preferably a copolymer of styrene and maleic anhydride which contains at least 30 mol% maleic anhydride monomer units.

By 'water-soluble polymers' in this text are understood polymers which dissolve in an aqueous medium, which aqueous medium may be neutral and/or acid and/or basic. By preference, copolymers containing maleic anhydride monomer units dissolved in an aqueous solution of an alkali hydroxide are used.

The molecular weight of the polymer which in the solution contains monomer units which contain carboxylate anions can vary from for instance 1000 g/mol to for instance 500,000 g/mol .

By preference the particles having a diameter of less than 63 μm have been provided with a coating from an aqueous solution of between 0.25 and 5 wt . % polymer, relative to the weight of the dry particles. Even more preferably, the particles have been provided with a coating from an aqueous solution of between 1 and 2.5 wt . % polymer, relative to the weight of the dry particles.

It is possible for the composition according to the invention to be prepared in the form of a mortar.

In a preferred embodiment of the composition according to the invention it is characterized in that the composition contains mineral particles of which at least 75% have a diameter of less than 63 μm. Fillers used in asphalt compositions generally have to meet requirements in respect of the particle size distribution. Thus, in the Netherlands it is required that at least 75% of the filler particles have a diameter of < 63 μm and at least 85% a diameter of < 90 μm. Preferably the mineral particles in the composition according to the invention therefore have a particle size distribution which satisfies the requirements for an aggregate for asphalt, both before and after application of the coating. All fillers known for application in bitumen can be used in the composition according to the invention. Examples of fillers are rock meal, fly ash, lime hydrate, lime rock meal. Preferably, fly ash or lime rock meal or a mixture of these is used.

It is also possible for the composition according to the invention to be prepared in the form of an asphalt. Besides mineral particles with a particle diameter < 63 μm, which particles have been provided with a polymer coating, which coating has been applied onto the particles from an aqueous solution of a polymer, which polymer in the solution contains monomer units containing carboxylate anions, the composition then comprises particles with a particle diameter > 63 μm, which particles are either provided or not provided with the polymer coating.

In a preferred embodiment the composition according to the invention is characterized in that it contains an elastomer and/or a thermoplast, capable of reducing the susceptibility to cracking. It is as such a known fact that bitumen is less susceptible to cracking and rut formation if such elastomers or thermoplasts have been added to the bitumen, but with application of the composition according to the invention much smaller amounts of the elastomer or the thermoplast are already sufficient to obtain better properties than with the known compositions. Examples of such elastomers used in bitumen are styrene butadiene (SB) copolymers or styrene butadiene random (SBR) copolymer or styrene butadiene styrene (SBS) block copolymers, styrene isoprene styrene (SIS) block copolymers or ethene propene diene terpolymer (EPDM) . Examples of such thermoplasts are atactic polypropene (aPP) , ethene vinyl acetate (EVA) copolymers and polyethene (PE) . The elastomers or the thermoplasts are usually added in the form of powder or granulate, resulting in a physical mixture. The composition according to the invention preferably contains SBS, aPP or EVA. The amount of SBS contained in the composition according to the invention preferably is between 0.5 and 3.5 wt . % relative to the amount of bitumen. The amount of EVA contained in the composition according to the invention preferably is between 0.5 and 4 wt . % relative to the amount of bitumen. The amount of aPP contained in the composition according to the invention preferably is between 2.5 and 10 wt.%, more preferably between 4 and 6 wt.%, relative to the amount of bitumen. By using a composition according to the invention in the preparation of for instance asphalt to which a thermoplast or an elastomer is added, a considerable saving on the costs of elastomers and/or thermoplasts can be achieved. The invention also relates to a process for the preparation of the particles provided with the polymer coating as used in the composition according to the invention. The process is characterized in that mineral particles having a particle diameter < 63 μm are contacted with an aqueous solution of a polymer, which polymer in the solution contains monomer units which contain carboxylate anions, after which the aqueous solvent is removed. The resulting particles are provided with the polymer coating.

The process is preferably characterized in that the mass obtained after removal of the solvent is ground and screened to particles having a diameter _< 63 μm. The advantage of this is that after being prepared and screened the particles again have a particle size distribution which meets the particle size requirement which for instance in the Netherlands is imposed for an aggregate for asphalt .

Removal of the aqueous solvent can be effected in several ways, for instance by evaporation or by filtration.

In a preferred embodiment of the process for the preparation of the particles provided with the polymer coating the solvent is removed by evaporation. This offers the advantage that all the polymer that was present in the aqueous solution adheres very well to the particles having a diameter < 63 μm and so a very good asphalt can be obtained.

The composition according to the invention can be obtained by mixing with bitumen, with stirring and heating, particles obtained by the process for the preparation of particles provided with a polymer coating.

The invention will be illustrated by means of examples, without being restricted thereto.

Examples and Comparative Experiments

Example I

To 16.8 ml of a potassium hydroxide solution (KOH solution) in a beaker, which solution was prepared from 45 g KOH in 55 g demineralized water, were added 20 g of a copolymer containing 34 mol% maleic anhydride monomer units and 66 mol% styrene monomer units (SMA; Stapron S (TM) SZ34080 from DSM, The Netherlands, molecular weight 80,000 g/mol) and the solution thus obtained was made up with demineralized water to a total weight of 100 g. Then the solution was heated and stirring was continued at a temperature of 80 to 90 °C until the polymer was dissolved completely. Next, a dilution was prepared by making up 14.3 g of the polymer solution with demineralized water to a total weight of 100 g. 100 g Wigro 60k (a filler supplied by interswijksche Steen- en Kalkgroeve B.V., The Netherlands, typically composed of 65-75 mass% limestone meal and 25-35 mass% lime hydrate; bitumen number (min-max) = 56-62) with a diameter of less than 63 μm were contacted with 10 ml of the diluted polymer solution (2 wt% SMA relative to the dry filler) , after which another 20 ml demineralized water were added. This was followed by stirring with a spatula until a thick paste was obtained. The beaker containing the paste was dried in a stove at a temperature of 80 to 90 °C under a nitrogen atmosphere. The cake that formed in the drying process was ground in a ball mill to particles with a diameter of less than 63 μm. A mixture of bitumen (Esso 80/100, penetration index 80/100, from Esso in The Netherlands) and the coated filler particles (50/50 volume parts) was heated to 150 °C in a steel mixing cup. The mixture was stirred manually with a spatula until it had a homogeneous aspect and then for at least another three minutes . The mortar thus obtained (bitumen + coated filler) was poured into a mould with a diameter of 15 mm and a height of 2.3 mm. A weight of about 3 kg was kept on the mould for 5 minutes in order to compact the mortar. Then the mould was placed in a refrigerator. The cooled mortar was easily released from the mould.

The viscoelastic behaviour (the dynamic modulus as a function of the frequency) of the mortar shaped by means of the mould was determined as described under "Rheological measurements" using a rheometer, type RMS800, manufactured by Rheometrics . This was done with application of flat plate geometry, with flat plates of a diameter of 15 mm. The plates were heated to 50 °C . The deformation was 0.2%. The results of the measurements are presented in Table 1.

Comparative Experiment A

100 g Wigro 60k (an aggregate supplied by

Winterswijksche Steen- en Kalkgroeve B.V., The Netherlands) with a diameter of less than 63 μm were mixed with bitumen (type Esso 80/100) as described in example I .

The viscoelastic behaviour of the mortar thus obtained was determined as described under example I. The results of the measurements are presented in

Table I. Comparative Experiment B

8.82 g bitumen (Esso 80/100 (penetration index 80/100) from Esso, The Netherlands) were heated to 180-190 °C, which caused the bitumen to melt. 0.18 g SMA containing 34 mol% maleic anhydride monomer units and 66 mol% styrene monomer units (molar weight 80,000 g/mol) was added to the molten bitumen with stirring with a blade stirrer. After about 45 minutes the SMA had melted. Stirring was continued for at least 1 hour. Then Wigro 60 K (without polymer coating) was added to the bitumen/SMA mixture at 150 °C (50/50 volume parts) . The mixture was stirred manually with a spatula until it had a homogeneous aspect and then for at least another three minutes . The mortar thus obtained was poured into a mould with a diameter of 15 mm and a height of 2.3 mm. A weight of about 3 kg was kept on the mould for 5 minutes in order to compact the mortar. Then the mould was placed in a refrigerator. The cooled mortar was easily released from the mould. The viscoelastic behaviour of the mortar thus formed was determined as described under example 1. The results of the measurements are presented in Table 1.

Example II

A mixture of bitumen and Stamyroid (TM) 43C (a mixture of atactic polypropene with a minor amount of isotactic polypropene) from DSM, The Netherlands, was prepared by combining 0.5 part by weight of Stamyroid 43C and 10 parts by weight of bitumen (Esso 80/100) in a steel mixing cup at room temperature. The mixture was heated with stirring to a temperature of 190 °C . When the Stamyroid was dispersed homogeneously in the bitumen, stirring was continued for at least 1 hour. In portions of about 10 g the mass was poured into aluminium trays and stored in the refrigerator.

A mortar was prepared as described in Example I, but instead of pure bitumen the above- described mixture of bitumen and Stamyroid C was used. The mixture of 50/50 parts by volume of the coated filler particles (2 wt.% SMA polymer on the dry filler particles) and bitumen/Stamyroid 43C was heated to 150°C in a steel mixing cup. The mixture was stirred manually with a spatula until it had a homogeneous aspect and then for at least another three minutes . The mortar (of polymer-coated filler and bitumen/Stamyroid 43C) thus obtained was poured into a mould with a diameter of 15 mm and a height of 2.3 mm. A weight of about 3 kg was kept on the mould for 5 minutes in order to compact the mortar. Then the mould was placed in a refrigerator. The cooled mortar was easily released from the mould.

The viscoelastic behaviour of the mortar thus formed was determined as described under example 1. The results of the measurements are presented in Table 1.

Comparative Experiment C Analogously to the procedure described in

Example II a mortar was prepared. However, instead of filler particles with a polymer coating, filler particles without a polymer coating were used.

The mortar thus obtained was poured into a mould with a diameter of 15 mm and a height of 2.3 mm. A weight of about 3 kg was kept on the mould for 5 minutes in order to compact the mortar. Then the mould was placed in a refrigerator. The cooled mortar was easily released from the mould. The viscoelastic behaviour of the mortar thus formed was determined as described under example 1. The results of the measurements are presented in Table 1.

Comparative Experiment D

Analogously to the procedure described in

Comparative Experiment C a mortar was prepared.

However, instead of a mixture of 0.5 part by weight of Stamyroid 43C and 10 parts by weight of bitumen (Esso

80/100) , a mixture of 1 part by weight of Stamyroid and

10 parts by weight of bitumen was used.

The mortar thus obtained was poured into a mould with a diameter of 15 mm and a height of 2.3 mm. A weight of about 3 kg was kept on the mould for 5 minutes in order to compact the mortar. Then the mould was placed in a refrigerator. The cooled mortar was easily released from the mould.

The viscoelastic behaviour of the mortar thus formed was determined as described under example

1. The results of the measurements are presented in

Table 1.

Rheological measurements The viscoelastic behaviour of the various mortars was determined with the aid of a rheometer, type RMS800, manufactured by Rheometrics . This was done with application of flat plate geometry, with flat plates of a diameter of 15 mm. The plates were heated to 50 °C. The deformation was 0.2%.

For a comparison of the rut formation behaviour of the compositions containing bitumen and a fraction of inorganic parts, for each composition the lowest temperature was determined at which G* / sin (5) > 10 kPa, with a measurement frequency of 1.6 Hz (10 rad/s) . This method was developed specially for rheological measurements on mortars and is described in "Effect of filler aggregate on Rheological Properties of Mastic", by Molenaar, Voskuilen and Bothmer, published in Proc . Int. RILEM Symp., 5th (1997), 101- 108. The higher the measured temperature, the less susceptible the composition is to rut formation. The results of the measurements on the mortar compositions according to Examples I and II and Comparative Experiments A to D are presented in Table 1.

TABLE 1

Comparison of the temperatures found for Comparative Experiment A and for Comparative Experiment B shows that the direct addition of SMA to bitumen results in a higher temperature at which G* / sin (<3) > 10 kPa. This means that composition A is less resistant to rut formation than composition B. However, from a comparison of the results of Comparative Experiments A and B and Example I it clearly appears that the composition which contains particles with a diameter < 63 μm with SMA in the coating applied is even less susceptible to rut formation. Comparison of the temperatures found for Comparative Experiment C and Comparative Experiment D reveals that the addition of twice as much Stamyroid C43 to the bitumen results in a higher temperature at which G* / sin (5) > 10 kPa . This means that composition D has much more resistance to rut formation than composition C. However, from a comparison of the results of Comparative Experiments C and D and Example

II it clearly appears that the composition containing polymer-coated particles with a diameter < 63 μm is still less susceptible to rut formation.

Claims

C A I M

1. Composition containing bitumen and mineral particles, which particles have been provided with a polymer coating, characterized in that the composition contains mineral particles with a particle diameter < 63 ╬╝m, which particles have been provided with a polymer coating, which coating has been applied onto the particles from an aqueous solution of a polymer, which polymer in the solution contains monomer units containing carboxylate anions .

2. Composition according to Claim 1, characterized in that the polymer coating of the particles with a diameter < 63 ╬╝m has been applied from an aqueous solution of a polymer, which polymer comprises monomer units which contain carboxylic acid groups and/or anhydride groups or a salt thereof.

3. Composition according to either one of Claims 1-2, characterized in that the polymer in the aqueous solution contains at least 10 mol% monomer units containing carboxylate anions .

4. Composition according to either one of Claims 1-2, characterized in that the polymer in the aqueous solution contains at least 20 mol% monomer units containing carboxylate anions.

5. Composition according to any one of Claims 1-4, characterized in that the coating on the particles has been applied from an aqueous solution of polyacrylic acid or an aqueous solution of a copolymer of styrene and maleic anhydride.

6. Composition according to any one of Claims 1-5, characterized in that copolymers containing maleic 00/05303 - i fi -

anhydride monomer units have been dissolved in an aqueous solution of an alkali hydroxide.

7. Composition according to any one of Claims 1-6, characterized in that the coating on the particles with a diameter of less than 63 ╬╝m has been applied from an aqueous solution of from 0.25 to 5 wt.% polymer, relative to the weight of the dry particles .

8. Composition according to any one of Claims 1-6, characterized in that the coating on the particles with a diameter of less than 63 ╬╝m has been applied from an aqueous solution of from 1 to 2.5 wt.% polymer, relative to the weight of the dry particles .

9. Composition according to any one of Claims 1-8, characterized in that the composition contains mineral particles of which at least 75% have a diameter of less than 63 ╬╝m.

10. Composition according to any one of Claims 1-9, characterized in that fly ash or limestone meal or a mixture thereof is used for the mineral particles having a diameter < 63 ╬╝m.

11. Composition according to any one of Claims 1-10, characterized in that the composition contains an elastomer and/or a thermoplast.

12. Composition according to Claim 11, characterized in that the composition contains SBS, aPP or EVA.

13. Composition according to Claim 12, characterized in that the amount of SBS which the composition contains is from 0.5 to 3.5 wt.%, relative to the amount of bitumen.

14. Composition according to Claim 12, characterized in that the amount of EVA which the composition contains is from 0.5 to 4 wt.%, relative to the amount of bitumen.

15. Composition according to Claim 12, characterized in that the amount of aPP which the composition contains is from 2.5 to 10 wt.%, relative to the amount of bitumen.

16. Composition according to Claim 12, characterized in that the amount of aPP which the composition contains is from 4 to 6 wt.%, relative to the amount of bitumen.

17. Process for the preparation of particles provided with the polymer coating as used in the composition according to any one of Claims 1-16, characterized in that mineral particles having a particle diameter < 63 ╬╝m are contacted with an aqueous solution of a polymer, which polymer in the solution contains monomer units which contain carboxylate anions, after which the aqueous solvent is removed.

18. Process according to Claim 17, characterized in that characterized in that the mass obtained after removal of the solvent is ground and screened to particles having a diameter < 63 ╬╝m.

19. Process according to either one of Claims 17-18, characterized in that the solvent is removed by evaporation.

20. Application of particles provided with a polymer coating according to any one of Claims 17-19 in a composition containing bitumen.