RU2838477C1 - Method of producing polymer-bitumen binder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the production of modified road bitumen, specifically to the technology of preparing a polymer-bitumen binder with the introduction of carbon nanofibres, and can be used for production of high-quality and climatic universal hot and cast asphalt mixes. Disclosed is a method of producing a polymer-bitumen binder, which involves premixing petroleum-based mineral oil as a plasticising additive with a butadiene-styrene thermoplastic elastomer as a modifier at a temperature of over 200°C for 45-50 minutes. Further, the obtained melt is introduced into commercial bitumen of BND 50/70 grade in the following ratio, wt. %: plasticiser 8, butadiene-styrene thermoplastic elastomer 1.5-6, bitumen BND 86-90.5 with mixing and duration of 20 minutes. Ready sample of polymer-bitumen binder (PBB 60) is settled for a day with protection from moisture, then the obtained mixture is heated to temperature of 150°C, carbon nanofibres are added for 10-15 minutes to form a homogeneous mixture at the following ratio of components, wt.%: PBB bitumen – 97-99, carbon nanofibres – 1-3, and settled for a day.

EFFECT: improving rheological properties of oil bitumen, such as temperature characteristics and hardness.

1 cl, 3 tbl, 5 ex

Description

The invention relates to the production of modified road bitumens, namely to the technology of preparing a polymer-bitumen binder with the addition of carbon nanofiber and can be used to produce high-quality and climatically universal hot and cast asphalt concrete mixtures.

In the process of preparing all asphalt concretes, the key role is played by the quality of the mineral (bitumen) binder, its content in the mixture, and rheological properties. Depending on the quality of the bitumen binder, it is possible to add polymer modifiers, plasticizers, and carbon materials to improve the commercial performance of not only petroleum bitumen, but also asphalt concrete mixtures.

An invention is known in which modified bitumen is obtained on the basis of residual bitumen from deep vacuum distillation, in which a copolymer is added as a surfactant and a viscosity-lowering agent as a plasticizing additive. In this case, the copolymer is synthesized from allyl ether of polyalkylene glycol, a block of unsaturated dicarboxylic acid and a block of aromatic vinyl compound, and the viscosity-lowering agent is industrial oil. All the components described above are dispersed in specified proportions in specialized colloid mills. Modified bitumen contains petroleum bitumen of direct distillation of oil (A1) in an amount of 25 to 70 wt. %, a viscosity-lowering agent (B), which is industrial oil, in an amount of 20 to 65 wt. % and a copolymer (C) in an amount of 0.5 to 7 wt. %. The copolymer (C) contains a structural block of allyl ether of polyalkylene glycol (cl), a block of unsaturated dicarboxylic acid and/or its anhydride (c2) and a block of aromatic vinyl compound (c3). The molar ratio of the blocks is approximately 1:1:1 (patent RU 2442808).

The disadvantages of this invention are the high consumption of technical oil to reduce viscosity, and, consequently, the increased cost of bitumen, as well as the complexity and high cost of producing copolymers.

There is an invention in which a polymer-bitumen binder is obtained by mixing in a mixer all components of the composition (bitumen 86-89% by weight, SBS polymer 2.5-5% by weight, industrial oil 5.5-7.5% by weight, TFA 1-3% by weight), fed in the calculated amount, with subsequent passage of the composition through a colloid mill into a second mixer. Then this process is repeated. The temperature of PBB preparation should not exceed 160°C, and the duration of the PBB production process should not exceed 60 minutes. The invention concerns a polymer-bitumen binder containing bitumen, a polymer - butadiene-styrene thermoplastic elastomer, a plasticizer - industrial oil and a high-molecular surfactant, containing heavy fatty acids (HFA) as a high-molecular surfactant (RU 2297990).

The disadvantage of this method is the use of industrial oil, which negatively affects the adhesive properties of the binder to the mineral components contained in asphalt concrete, which leads to a deterioration in the performance characteristics of asphalt concrete, for example, low resistance to cracking.

A method for preparing a polymer-bitumen binder is known, which includes introducing a thermoplastic elastomer, a plasticizer into bitumen heated to 165-175°C, and mixing. The binder additionally contains a nitrogen-containing surfactant in an amount of 0.5-2.0% of the bitumen weight with the following sequence of binder preparation: the nitrogen-containing surfactant is introduced into the bitumen or, if it is solid, semi-solid or pasty, it is mixed with a portion of the plasticizer until a liquid mixture is obtained and introduced into the bitumen in this form, then the thermoplastic elastomer is introduced in granulated form with subsequent mixing, after which the plasticizer or the remaining portion thereof is introduced and mixed until a homogeneous state is obtained (patent RU 2152964).

A disadvantage of the invention is the use of expensive surfactants to improve the adhesive properties and facilitate the process of preparing the polymer-bitumen binder.

The closest to the proposed invention is the method for producing a polymer-bitumen binder described in patent No. 2211846. According to the invention, molten bitumen of BND grades is mixed with a butadiene-styrene thermoplastic elastomer of linear, star-shaped or tree-like structure, filled with a mixture of ionol and phosphite NF, with orthophosphoric acid, with technical carbon and polymer adhesive additives, which are polymers of the structure: polystyrene or polybutadiene, or polystyrene - polyisoprene with a total molecular weight of 2-60 thousand and terminal polar functional groups.

The disadvantages of this method are the complex system of preparing PBB using a large number of additional components with separate preparation of mixtures of ionol, phosphite and orthophosphoric acid, the use of extremely expensive additives - carbon black and polymer adhesive additives, as well as a slightly increased plasticity range of binders.

The technical problem of the invention is the development of a method for obtaining a composition of a modified polymer-bitumen binder that eliminates the above-mentioned disadvantages, with the achievement of the following technical result: an increase in the rheological properties of petroleum bitumen (temperature characteristics and its hardness).

The specified technical result is achieved by the fact that in the method for producing a polymer-bitumen binder based on bitumen, a plasticizing additive and a polymer modifier, according to the invention, a petroleum-based mineral oil is pre-mixed as a plasticizing additive with a butadiene-styrene thermoplastic elastomer as a modifier at a temperature above 200°C for 45-50 minutes, then the resulting melt is introduced into commercial bitumen of the BND 50/70 brand in the ratio: plasticizer 8 wt. %: polymer modifier 1.5-6 wt. %: BND bitumen 86-90.5 wt. % with stirring and for a duration of 20 minutes, the finished sample of the polymer-bitumen binder (PBB 60) is settled for 24 hours while protecting it from moisture. Then the resulting mixture is heated to a temperature of 150°C and carbon nanofibers are added to it over the course of 10-15 minutes until a homogeneous mixture is formed, with the following ratio of components: PBB bitumen 97-99 wt.%: carbon nanofibers - 1-3 wt.% and left to settle for 24 hours.

Substandard commercial bitumen grade BND 50/70 is used as a basis for the preparation of modified bitumen. Table 1 shows that the bitumen sample fully meets the requirements of GOST 33133-2014 for its grade.

Table 1

Indicator Values for the studied sample of bitumen grade BND
50/70 GOST requirements
33133-2014 for BND
50/70 Needle penetration depth, 0.1 mm (at 25.0°C) 68.7 51-70 Softening temperature
by ring and ball, °C 53.3 not less than 51 Stretchability, cm (at 25.0°C) 84.8 not less than 60 Brittleness temperature, °C -19 no higher than -16 Plasticity range, °C 72.3 not standardized

A petroleum-based mineral oil was used as a plasticizing additive. During modification, the optimal oil concentration was determined first. A series of tests established the optimal plasticizer content (8% of the total bitumen mass), which allows for a significant increase in the brittleness temperature reserve, without significantly lowering the softening temperature, reducing extensibility and increasing the depth of needle penetration.

After identifying the optimal concentration of plasticizer in bitumen, polymer-oil melts were produced. In the total mass, the effect on the quality of the binder was tested from 1.5 to 6% by weight of butadiene-styrene thermoplastic elastomer (SBS polymer) (also from the total mass of the sample) while maintaining the plasticizer content at 8% by weight. During the addition of SBS, the softening and needle penetration depth indicators constantly increased, and the brittleness temperature and extensibility of the bitumen also decreased.

The best indicators are demonstrated by bitumen with the addition of 6% by weight of SBS, while the introduction of a larger amount of polymer leads to the process of polymer destruction, all values correspond to the requirements of GOST R 52056-2003 for the grade of bitumen PBB 60. Table 2 presents comparative results.

Carbon nanofibers obtained by catalytic cracking of methane are used.

Carbon nanofibers were introduced into the finished model sample in an amount of 1 to 3% by weight. As a result of mixing the obtained PBB with carbon material, it was possible to increase the hardness, heat resistance and frost resistance of bitumen, but at the same time its plasticity was not critically reduced. The results are presented in Table 3.

To implement the claimed method, before preparing the polymer-bitumen binder, the effect of a pure plasticizing additive on the properties of bitumen is determined (how the characteristics change depending on the amount of plasticizing additive added). A bitumen sample is mixed with a plasticizing additive, after which the required tests are carried out. After identifying the optimal amount of plasticizing additive, "plasticizer: polymer" melts are prepared. A polymer modifier is added to the plasticizing additive at a temperature above 200°C with constant stirring for 45-50 minutes. The finished melt is mixed with pure bitumen for 20 minutes until a homogeneous binder is obtained, after which the resulting PBB is left to settle for 24 hours, protecting it from moisture, and tests are carried out, comparing the result with the requirements of GOST R 52056-2003. The prepared PBB is heated to a temperature of 150°C and carbon nanofibers are mixed into it for 10-15 minutes until a homogeneous mixture is formed and, after the bitumen has settled for 24 hours, tests are carried out again to determine changes in the characteristics.

The method according to the invention is illustrated by examples.

Example 1

- BND bitumen (94% wt.);

- mineral oil (3% by weight);

- SBS polymer (3% wt.).

In order to prevent a significant drop in softening and hardness indices, as well as to save on the plasticizing additive and polymer modifier, their minimum contents were taken. However, since mineral oil is not a specialized plasticizer, when the polymer was added to the plasticizing additive at a temperature of 205°C, the polymer was subjected to destruction (thermal decomposition). Reducing the temperature to 190°C did not allow the polymer to melt.

Example 2

- BND bitumen (84.5% wt.);

- mineral oil (8% by weight);

- SBS polymer (7.5% wt.).

To increase frost-resistant properties and subsequent restoration of penetration and softening after dilution of bitumen with plasticizer, the maximum available amount of polymer was taken. With a slight decrease in temperature to 190 ° C, the polymer did not dissolve completely, partially remaining as sediment in the container. Repeated increase in temperature to 200 ° C led to the onset of destructive processes and combustion of the polymer, which indicates the impossibility of introducing a large amount of SBS in mineral oil. At the same time, an increase in the oil content can greatly increase the cost of future PBB, and, despite a significant increase in frost resistance, adhesion, hardness and heat resistance of bitumen will decrease.

Example 3

- BND bitumen (86% wt.);

- mineral oil (8% by weight);

- SBS polymer (6% wt.).

According to example 3, a sample is obtained that is similar in its properties to PBB 60 (Table 2).

Example 4

- BND bitumen (90.5% wt.);

- mineral oil (8% by weight);

- SBS polymer (1.5% wt.).

The given ratio of components made it possible to melt the polymer in the plasticizer at a temperature above 205°C without thermal decomposition of SBS, however, after introducing the resulting melt into bitumen, the softening temperature of the latter decreased significantly and the expected decrease in the brittleness temperature was not achieved.

With a decrease in the SBS content in bitumen, the softening index decreases from 60.1°C (at 6%) to 51.8°C (at 1.5%). The brittleness of bitumen decreases from -24°C (at 6%) to -20°C (at 1.5%). The extensibility and needle penetration depth also decrease from 50.6 cm (at 6%) to 67.2 cm (at 1.5%) and from 82.4 (at 6%) to 90.5 (at 1.5%), respectively.

Example 5

- PBB bitumen (97% by weight);

- carbon nanofibers (3% by weight).

The resulting PBB bitumen is heated to 150°C and carbon nanofibers are mixed into it for 10-15 minutes until a homogeneous mixture is formed. Afterwards, the resulting sample is left to settle for 24 hours.

With an increase in the nanofiber content in the obtained PBB sample, the thermal and frost-resistant properties of bitumen increase, its hardness increases, and its extensibility decreases (Table 3).

Thus, modified road bitumen is obtained with the preparation of a polymer-bitumen binder grade 60 on its basis, followed by the introduction of carbon nanofibers into it, which leads to a sharp improvement in the rheological characteristics of the binder, such as: softening temperature, brittleness temperature and hardness of the material, which can allow the use of the obtained bitumen in the preparation of high-quality hot and cast asphalt concrete mixtures.

Claims (1)

A method for producing a polymer-bitumen binder, including introducing a thermoplastic elastomer and a plasticizing additive into bitumen, characterized in that petroleum-based mineral oil is pre-mixed as a plasticizing additive with styrene-butadiene thermoplastic elastomer as a modifier at a temperature above 200°C for 45-50 min, then the resulting melt is introduced into commercial bitumen of the BND 50/70 brand in a ratio, wt.%: plasticizer 8, styrene-butadiene thermoplastic elastomer 1.5-6, BND 86-90.5 bitumen with stirring and for 20 min, the finished sample of the polymer-bitumen binder (PBB 60) is left to settle for 24 hours while protecting it from moisture, then the resulting mixture is heated to a temperature of 150°C, carbon nanofibers are added to it for 10-15 min until formation homogeneous mixture with the following ratio of components, wt.%: bitumen PBB 97-99, carbon nanofibers 1-3, settled for 24 hours.