WO2001030911A1

WO2001030911A1 - Asphalt composition comprising polymeric mdi

Info

Publication number: WO2001030911A1
Application number: PCT/EP2000/009555
Authority: WO
Inventors: Berend Eling; Norman Washington Keane
Original assignee: Huntsman International Llc
Priority date: 1999-10-25
Filing date: 2000-09-29
Publication date: 2001-05-03
Also published as: AU7910300A

Abstract

The invention relates to an asphalt composition comprising, by weight based on the total weight of the composition, about 1 to 8 %, of a polymeric MDI, where the polymeric MDI has a functionality of at least 2.5. The invention also relates to a process for preparing said asphalt composition.

Description

ASPHALT COMPOSITION COMPRISING POLYMERIC MDI.

The instant invention provides an asphalt composition comprising polymeric MDI as asphalt modifier.

Asphalts that are modified by added binders are known for years. There is still a need in the asphalt industry, however, for improved asphalts. In part this is because currently known polymer-modified asphalts have a number of deficiencies. These include susceptibility to for instance permanent deformation (rutting), flexural fatigue, moisture damage (stripping) and low temperature thermally-induced cracking.

The article "Urethane-Modified Asphalt for Pavement Overlays/Wearing Courses for Road Applications", Sendijaveric et al, Polyurethane 1995, September 26-29, 1995, discloses various modified asphalts. The study was partly focused on the potentially large use for fly ash. This study was carried out with asphalts modified with PAPI27 (a polymeric MDI having a functionality of 2.7) and with a prepolymer based on said PAPI27 and on polybutadiene polyol. The minimum content was 10% by weight.

Thus, the prior art teaches relatively high amounts of polymeric MDI in the modified asphalt compositions. This, however, has several drawbacks: high costs and MDI vapours which may be released when applying the modified hot asphalt mix. MDI vapours can be harmful and may raise safety, health and environmental concerns.

The invention is based on the surprising effect that the amount of a specific polymeric MDI can be below 5% by weight, while still imparting good properties to the final asphalt composition.

Thus, the instant invention provides an asphalt composition comprising, by weight based on the total weight of the composition, about 1 to 8%, preferably about 2 to 5%, especially about the stoichiometric amount, of a polymeric MDI, where the polymeric MDI has a functionality of at least 2.5, preferably at least 2.6.

The polymeric MDI is known in the art. It is polymethylene-polyphenylene polyisocyanate, and is also referred to as polyarylene polyisocyanate or polyphenylmethane polyisocyanate, PAPI. It can comprise varying amounts of the standard isomers, i.e. the 4,4'-, 2,4'- and 2,2'-isomers. It can also comprise modified variants containing carbodiimide, uretonimine, isocyanurate, urethane, aliphanate, urea or biuret groups. This will be referred to in the following as pMDI. The isocyanate functionality of the pMDI is one key feature of the invention. This functionality is to be at least 2.5, preferably at least 2.6.

Without wishing to be bound by a theory, applicant believes that the pMDI can react with the phenolic, carboxylic, anhydride and pyrrolic groups of the asphalt, which are NCO-reactive groups. What is formed is a covalently linked polymer gel/network that was found to reduce the plastic flow of the asphalt at elevated temperatures, i.e. about 60°C or more.

It is in fact possible to determine an "equivalent weight" of NCO-reactive groups in the asphalt. Experimentally this can be determined by preparing asphalt-polymeric MDI blends with increasing amounts of polymeric MDI. The stoichiometric amount of MDI for the selected asphalt could be defined as that amount MDI that is present in the sample that contains the highest concentration of MDI and in which all the NCO groups have reacted.

The presence of unreacted isocyanate (NCO) groups in the asphalt could, for instance, be detected by Infra Red measurements. From this amount the equivalent weight of the asphalt can be calculated. This equivalent weight varies as a function of the kind and nature of the asphalt; examples of asphalt equivalent weight are about 2000-10.000. In the case the "stoichiometric" amount of pMDI (with an NCO value of 30.6) amounts to about

3.6 weight %, this leads to an estimated equivalent weight of about 3800. This value for the "stoichiometric" amount, however, varies as a function of the equivalent weight of the asphalt (which itself varies as a function of the asphalt).

The formation of the product MDI-asphalt of the present invention can be measured by an increase in the product's viscosity, but more preferably dynamic mechanical analysis (DMA) is used to measure the product properties.

The viscous and elastic properties of an asphalt are important performance indicators. Dynamic mechanical analysis properties are determined using a dynamic mechanical analyzer (DMA), for example, a RDA II Dynamic Analyzer (from Rheometrics Inc.). This instrument resolves the viscous and elastic nature of asphalt samples tested at various temperatures and shear rates. DMA involves the application of a periodically varying (oscillatory) stain or stress. The ratio of the peak stress to the peak strain is defined as the complex modulus (G*), which is a measure to the overall resistance of a material to deformation. The in-phase component of G* is defined as the storage modulus (G') and the out-of-phase component as the loss modulus (G"). G' describes the amount of energy stored and released elastically in each oscillation, while G" describes the average energy dissipation rate that is associated with viscous effects. The difference between the stress and strain in an oscillatory deformation is defined as phase angle (delta). Delta is a measure of the viscoelastic character of the material. If delta equals 90°, then the binder can be considered to be purely viscous in nature and, vice versa, a delta of 0° represents an ideal elastic solid. In the SHRP (strategic highway research program, USA) binder specification, a G*-based rheology parameter, GVsin delta at 10 rad/sec, has been selected to measure the contribution of a binder to rutting performance. High G*/sin delta values were found to correlate with high rutting resistance (L.H. Lewandowski, Rubber Chem. Techn., 67, 447 (1994)). According to the SHRP binder specification, a minimum value of rheological G*/sin delta should be 1 kPa at 60°C for the binder to be considered as pavement mix. The criterion suggests that the binder should have both high complex modulus and elasticity at the maximum pavement temperatures.

When added to the asphalt (the continuous, non asphaltene, phase thereof), the pMDI will act as a modifier. At 60°C, the G* value will increase by about 2-5 times, when compared to an unmodified asphalt. At the same temperature, the delta value will decrease from about 85° to about 55°, when compared to an unmodified asphalt, evidencing a change in the rheological behavior from liquid-like to visco-elastic. The average strength of the aggregate mix (5% asphalt, 95% stone) in the Marshall stability test (ASTM 1559) increases by a factor of 1.25. Finally, at that temperature, the rheological and mechanical properties are similar to those obtained with a 3% SBS modified asphalt.

When added to the asphalt, the NCO group of the pMDI will react relatively quickly, in about less than 60 minutes, at the temperature of about 135°C. Thus, since the storage temperature for hot asphalt is 120-150°C, i.e. around this value of 135°C, it makes it possible to mix the pMDI just before use. Thus, at the time the composition is applied to the desired site, the pMDI will have completely reacted.

The present invention allows in-line blending and affords improved adhesion to substrates. The instant invention thus allows not using high processing temperature and refusion that are mandatory in case of SBS block copolymers.

Operating at an amount of about stoichiometric value (of about 2.7%) brings the additional benefit that substantially all the NCO groups will be consumed by the reaction, thus avoiding any release of MDI vapours in the atmosphere, finally enhancing the safety, health and environment of the workers. The asphalt used in the instant invention is any asphalt known and generally covers any bituminous compound. It can be any of the materials referred to as bitumen or asphalt, e.g. distillate, blown, high vacuum and cut-back bitumen, and also e.g. asphalt concrete, cast asphalt, asphalt mastic and natural asphalt. For example, a directly distilled asphalt can be used, having, for example, a penetration of 80/100 or 180/220. For example, the asphalt can be free of fly ash.

The asphalt compositions of the invention will be used as any classical asphalt compositions of the prior art. The asphalt compositions of the invention will notably be useful for the production of: - paints and coatings, particularly for waterproofing,

- mastics for filling joints and sealing cracks

- grouts and hot-poured surfaces for surfacing of roads, aerodromes, sports grounds, etc.

- in admixture with stone to provide aggregates (comprising about 5-20% of modified asphalt) - hot coatings for surfacing as above

- surface coatings for surfacing as above

- generally speaking as "hot mix"

The instant compositions may also be used as the asphalt part of emulsions, the water reacting with the NCO groups that could have remained, thus rendering the final emulsion completely free of NCO group, and thus fully meets the safety, health and environment requirements.

The present invention also provides a process for making the composition, which comprises mixing the asphalt and the pMDI at a temperature comprised between 120 and 150°C, for a sufficient time, for example between 1 and 120 minutes, preferably between 10 and 60 minutes.

The following examples illustrate the invention without limiting it. Examples

Preparation of the samples:

100 g of an asphalt with penetration rate 85-100 (1/lOmm) from Trumbull Owens Corning (three different batches, bxl, bx2 and bx3) was put into a metal container and was heated up in an oil batch to 135 °C. To this a given amount polymeric MDI with an average functionality (fn) of 2.7 and an NCO value of 30.6% is added at once whilst stirring with an over head stirrer and reacted for 30 minutes. The sample container is subsequently taken out of the oil bath and cooled down to room temperature. The sample is at least stored at room temperature for a week before it is submitted for further testing. In this way sample nr 2, 4, 5, 6, 7, 9 and 10 have been prepared.

Samples 2, 4, 5, 6, 7, 9 and 10 have been submitted to infra red measurements using FTIR equipped with a standard 'split-pea' accessory. In none of the samples an adsorption at 2270 cm^"1, assigned to isocyanate (e.g. NCO), was detected. Samples prepared from asphalt Bx. 2 and 4.0 weight % polymeric MDI and of Bx. 3 and 4.0 weight % of polymeric MDI, however, showed in both cases a clear absorption at 2270 cm^"1, indicating the presence of unreacted isocyanate in these two samples. Measurement of the dynamic viscoelastic properties:

The dynamic viscoelastic properties of asphalts and isocyanate modified asphalts were measured using a RDA II Dynamic Analyzer (from Rheometrics, Inc) at a frequency of 10 radians per second and 10% stain. The measurements were carried out in the temperature range from 25 to 90°C with a temperature ramp of 1 °C per minute. A sample was placed between parallel plates with a diameter of 25 mm and a gap of approximately 1.7 mm. The values of G*, delta and G*/sin delta given in the Tables 1, 2 and 4 are measured at 60°C. The DMA results of the three batches of asphalt (samples 1, 3 and 8) and that of the polymeric MDI modified asphalts (samples 2, 4, 5, 6, 7, 9 and 10) are given in Table 1.

Table 1 : The DMA results of asphalts and asphalts modified with polymeric MDI sample Bx. Nr. amount (wt%) G* at 60°C delta at 60°C G*/sin delta at

Nr. (kPa) 60°C (kPa)

1 1 0 1.7 84 1.7

2 1 2.7 17.8 61 20.4

3 2 0 5.5 81 5.5

4 2 0.9 5 73 5.3

5 2 1.8 7.5 70 7.9

6 2 2.7 13 67 14.1

7 2 3.6 20 58 23.6

8 3 0 1.3 78 1.3

9 3 2.7 7.8 67 8.5

10 3 3.6 26.7 58 31.6 Sample 1 and 2 have been aged using the rolling thin film oven test according to ASTM D2872. After aging these samples have been assessed on their dynamic visco elastic behavior using the DMA. The results are given in Table 2.

Table 2: The DMA results of aged asphalt and MDI modified asphalt

sample Nr., aged G* at 60°C (kPa) delta at 60°C G*/sin delta at

60°C (kPa)

1 6.4 81 6.5

2 22.5 63 25.3

Marshall stability tests were performed on the unmodified asphalt of sample nr.1 (e.g. asphalt Bx. 1) and of the MDI modified asphalt sample nr.2 (e.g. asphalt bx. 1 that was modified with 2.7 weight % polymeric MDI) according to ASTM D-1559. Test specimens were prepared with 5.0, 5.5 and 6.0 weight % binder utilizing gravel (grade AA20). At each concentration 3 samples were prepared and the results were averaged. The experimental error amounted to less then 10 %. The results are given in Table 3.

Table 3 : Marshall stability results of concrete mixes

asphalt binder in concrete asphalt sample asphalt sample mix (wt%) nr.1 (kg) nr.2 (kg)

5 550 800 5.5 750 850

6 700 850

Comparative examples: Each of the three batches of asphalt were modified with SBS block-copolymer

(Vector 241 lp, from 'DEXCO POLYMERS', styrene/butadiene ratio 30/70). This modifier was added at a 3.0 weight % addition. The additive was added to the asphalt in a similar manner as described above for the preparation of MDI modified asphalts with this difference that the temperature was raised, according to the suppliers recommendation, to 160°C. This to melt the crystalline polymer. In this way samples 11, 12 and 13 have been prepared. The DMA results of the SBS modified asphalts are given in Table 4.

Table 4: The DMA results of asphalts modified with SBS

sample Bx. Nr. amount (wt%) G* at 60°C delta at 60°C GVsin delta at

Nr. (kPa) 60°C (kPa)

11 1 3 20.4 64 23

12 2 3 8 58 9.4

13 3 3 6 65 6.6

Marshall stability tests were performed on the SBS modified asphalts of sample nr.l l (e.g. asphalt Bx. 1 with 3 weight % of Vector 241 lp) according to ASTM D-1559. Test specimens were prepared with 5.0, 5.5 and 6.0 weight % binder utilizing gravel (grade AA20). The results are given in Table 5.

Table 5: Marshall results of concrete mixes using SBS modifier

asphalt binder in concrete mix asphalt sample nr.11 (kg) (wt%)

5 950 5.5 800

Claims

Claims:

1. An asphalt composition comprising, by weight based on the total weight of the composition, about 1 to 8%, of a polymeric MDI, where the polymeric MDI has a functionality of at least 2.5.

2. The asphalt composition of claim 1 , comprising about 2 to 5% of the polymeric MDI.

3. The asphalt composition of claim 1, comprising about the stoichiometric amount of the polymeric MDI.

4. The asphalt composition of claims 1-3, where the pMDI has a functionality of at least 2.6.

5. A process for preparing the asphalt composition of claims 1-4, comprising the step of mixing the asphalt and the pMDI at a temperature of about 120-150°C, for a sufficient time.