Technical Field The present invention relates to a modified bituminous mixture comprising only polyurethane synthesized through a polymerization reaction using waste polyethylene terephthalate (PET) and/or comprising the polyurethane together with Styrene-Butadiene- Styrene tri-block copolymer, as well as to a preparation method thereof. Prior Art

Bitumen is a petroleum residue obtained as a bottom product of distillation units following the processing of crude oil and separating the contained light hydrocarbons therefrom by means of distillation methods. Bitumen, the bottom product of vacuum distillation units of refineries, is a hydrocarbon with high molecular weight. Bitumen contains sulfurous compounds and high amounts of heteroatoms and has high viscosity.

Bitumen, having a very wide range of utility, is particularly used in asphalt pavements and in making roofs and papers waterproof. Around 85% of bitumen produced is used in asphalt compositions employed in the pavement of roads and serves as a binder in asphalt mixtures. The amount of bitumen in asphalt mixtures is 4 to 7%, but is still the most important agent determining the performance of an asphalt pavement due to its binding properties. However, bitumen with a substantial role in asphalt compositions as pointed out above, fails in fulfilling ideal high-performance criteria applicable to bridges, crossroads, and highways where extreme hot or colt climates are prevalent. As a result of bitumen, acting as a binder, failing to show the expected performance, some problems are encountered in the form of heat- and fatigue-induced cracks or rutting in asphalt pavements. The number of vehicles used worldwide increases year by year as a function of human population and as a result of this, more deformations are encountered on highways. Almost yearly, asphalt pavements are renewed and maintenance-repair works are done, leading to economic problems. In this context, the production and use of high-performance bituminous materials gain importance and become a necessity.

On the other hand, waste plastics have become a fast-growing problem with the increasing use of plastics. The PET plastic, in turn, is one of the plastic products produced and used in rather high amounts based on its easy production procedures and low costs. For this reason, many works are being done for the recycling of waste PETs and for their use in different areas. L. Bartolome et al. studied various reaction conditions applicable to the chemical recycling of PET and the resulting products from these reactions (L. Bartolome, Recent Developments in the Chemical Recycling of PET, Material Recycling - Trends and Perspectives). The direct use of PET in the form of waste without recycling is also known from the prior art. In a work conducted by Abdelaziz Mahrez and Mohammed Rehan Karim, the influence of incorporation of PET wastes into bitumen at 2-4-6-8% using a high-speed mixer was researched (Abdelaziz Mahrez et al., Rheological evaluation of Bituminous Binder Modified with Waste Plastic Material). When a search is made in the prior art in terms of solving these problems, it is seen that bituminous products are modified using various additives, for use in regions requiring high-performance asphalt properties. In such efforts aiming at achieving more durable asphalt products using high-performance modified bitumen, it is seen that bitumen is modified particularly with a styrene-butadiene-styrene (SBS) polymer additive. Jiqing Zhu et al. reviewed the state of art of polymer-modified bitumen and summarized the data regarding polymer-modified bitumen. For instance, the patent no. US6759454B2 describes a bituminous composition for use in asphalt, roof, insulation and pipe linings, containing 0.5-25% of SBS copolymer. The patent US5371 121A, in turn, describes the use of bitumen comprising 0.015-0.075% by mass of sulfur and an SBS polymer additive in hot-mixture asphalt applications. However, SBS is a relatively expensive polymeric additive. The use of this material increases the costs. Therefore, there is a need for reducing the amount of SBS used in bitumen modifications and for novel low-cost high- performance polymeric additives. Brief Description of Invention

A process is developed according to the present invention to synthesize polyurethane through a polymerization reaction of a diisocyanate monomer, diol monomer and a chain extender, the process comprising the steps of adding MDI as an isocyanate monomer into a reactor having a mechanical mixer; adding into the MDI-containing reactor BHET monomers, as a diol monomer, obtained through recycling reactions from waste PET products; following the addition of BHET monomers into the reactor, adding butanediol as a chain extender so that the polymerization reaction is initiated; and following the completion of the polymerization reaction, obtaining polyurethane suitable for use as an additive in modified bituminous mixtures.

A method for preparing a modified bituminous mixture is also developed according to the present invention using the polyurethane as an additive obtained through said polyurethane synthesis process, the method comprising the steps of fluidizing bitumen as the main component of the mixture at 130-140°C; transferring the fluidized bitumen into a mechanical mixer running at 120 rpm stirring speed; producing a polyurethane-bitumen mixture by adding polyurethane, in hot form, obtained through said polyurethane synthesis process to bitumen in said mixer while stirring process continues; stirring this mixture for a predetermined time at a predetermined stirring speed to obtain a homogeneous polyurethane-bitumen mixture; following the completion of the stirring process, obtaining a homogeneous polyurethane-added modified bituminous mixture.

According to the present invention, also a method for adding SBS to bitumen comprising the polyurethane additive obtained through said method is developed, this method comprising the steps of adding a 10% amount of the total of additive to be added, each at 3-minute intervals, to the fluidized polyurethane-added bitumen at 135°C using a mechanical mixer at 400 rpm speed and preparing the bitumen modified with polyurethane and SBS.

The present invention also discloses a modified bituminous mixture obtained according to said methods, the mixture comprising polyurethane synthesized through polymerization reaction using BHET monomers, as a diol monomer, obtained through a recycling reaction of waste PET products, MDI as a diisocyanate monomer, and butanediol as a chain extender. The whole methods developed according to the present invention provide an enhancement in the performance and durability of bitumen used in improving the properties of asphalt, wherein either only the polyurethane that is synthesized through the synthesis process according to the present invention is added to bitumen, or SBS and said polyurethane are added together to bitumen. By virtue of using polyurethane alone or together with SBS, the use of SBS having a tonnage price more than that of bitumen is reduced so that a method is developed with more reduced costs. Additionally, by virtue of using polyurethane obtained through the recycling of waste PET, a product is achieved which is not only of low-cost, but also is environment friendly. Thus, by providing bitumen with the polyurethane additive obtained through the overall methods developed according to the present invention, modified bitumen/asphalt products are achieved having lower cost, higher quality as compared to pure bitumen and asphalt in terms of quality/performance/strength, and an increased production volume.

Object of Invention

The object of the present invention is to develop a low-cost, environment frienly and high- performance modified bituminous mixture and a production method thereof, for use in asphalt pavements, aiming to prevent heat- and fatigue-induced crack- and rutting-related problems in asphalt pavements.

Another object of the present invention is to develop a polyurethane synthesis process providing the synthesis of polyurethanes to be used as an additive in modified bituminous mixtures.

A further object of the present invention is to develop a modified bituminous mixture and a preparation method thereof, wherein polyethylene terephthalate (PET) emerging as a waste in plastic production plants is made use of and an alternative field of use is created for waste PET.

Still a further object of the present invention is to develop a modified bituminous mixture and a preparation method thereof, wherein a more environmental friendly modified mixture is obtained as a result of utilizing polyurethane synthesized from waste PET. Still another object of the present invention is to develop a product and a preparation method thereof, enabling to use a relatively reduced amount of SBS in bitumen by using polyurethane synthesized from waste PET together with SBS, and thus enhancing the performance of the resulting product.

Yet another object of the present invention is to develop a modified bituminous mixture and a preparation method thereof, reducing the costs of asphalt production without reducing the performance of asphalt.

Description of Invention

Bitumen is obtained from the processing of crude oil and used mainly in asphalt production. On the other hand, because of both extreme hot or cold climates, and the invariably increasing number of vehicles, the performance of bitumen produced and therefore of asphalts comprising bitumen are not satisfactory and they fail to show the required durability. Deformed asphalt pavements have to be renewed regularly and/or subjected to maintenance-repair works, this causing both environmental and economic burdens. Reinforced modified bituminous mixtures are produced in the art to solve these problems. In the modified mixtures produced is used styrene-butadiene-styrene (SBS) as an additive, but this polymeric additive is quite expensive and increases the costs. In order to solve this problem, a synthesis process for polyurethane suitable for use as an additive in bituminous mixtures, as well as a modified bituminous mixture and a preparation method thereof have been developed, said mixture comprising the synthesized polyurethane and enhancing the performance of asphalt without increasing the production cost thereof.

Any items produced as a result of any commercial activity and left around after use are classified as "waste", wherein polyethylene terephthalate (PET) is similarly a waste material occurring in huge amounts as a result of producing and using plastic products being left around following its use. According to the present invention, a polyurethane synthesis process has been developed wherein waste polyethylene terephthalate (PET) is utilized. In the process developed, waste PET products are subjected to a recycling reaction through a glycolysis reaction to result in Bis-Hydroxyethyl terephthalate (BHET) monomers. Then, according to the present invention, polyurethane is synthesized for use as an additive in modified bituminous mixtures through a polymerization reaction of diisocyanate monomer, diol monomer, and chain extender, wherein BHET obtained as a result of the recycling reaction is used in the form of diol monomer. By virtue of this polyurethane synthesis process developed, BHET monomers obtained through recycling reactions of Waste PET are reacted with a diisocyanate, preferably 4,4'-Methylene diphenyl diisocyanate (MDI), through a polymerization reaction, and as a result of this reaction, polyurethane for use as a bitumen additive is synthesized. In addition, a method is developed for preparing modified bitumen comprising polyurethane synthesized according to the present invention preferably along with SBS, wherein homogeneous and easily-applicable modified bituminous mixtures are prepared by adding polyurethane alone or preferably adding polyurethane together with SBS to bitumen. According to the present invention, both alternative fields of use are provided for waste plastics, and improvements are made in asphalt quality without increasing its production costs. In the synthesis process of polyurethane developed according to the present invention, Bis-Hydroxyethyl Terephthalate (BHET) monomers are synthesized from waste Polyethylene Terephthalate (PET) through a recycling reaction. The stage of synthesizing BHET monomers preferably comprises the steps of washing waste PET products, which are gathered in collection areas where wastes resulting from production processes of plastic products are collected, with a predetermined amount of water to free PET products from impurities; drying the washed waste PET products; turning the dried waste PET products into scrap PET, preferably of a size of 1cmx1cm, suitable for use in the recycling reactions of waste PET products; loading the scrap PETs preferably into a glass-made, preferably three-neck reactor in which the recycling reaction is to be carried out; adding Ethylene Glycol into the reactor to which scrap PETs were loaded to carry out the recycling reaction; conducting the recycling reaction in the presence of at least one catalyst (preferably zinc acetate catalyst) preferably at a temperature from 195 to 200°C for preferably 3 hours; following the completion of the recycling reaction, obtaining a product comprising monomeric His-Hydroxyethyl Terephthalate (BHET), ethylene glycol and impurities (long-chain oligomers and unreacted scrap PET); in order to purify the obtained product from said impurities, washing it with a predetermined amount of water; taking into a first container the fractions (long-chain oligomers and unreacted scrap PET) from the washed product, which make up impurities in the product by remaining water- insoluble; after separating the fraction forming impurities from the product, taking the remaining BHET monomers and ethylene glycol into a second container; crystallizing the BHET monomers by helding the remaining BHET monomers and ethylene glycol in the second container in a cooler at +4 to +6°C preferably for 24 hours; generating a phase separation with the crystallized BHET monomers sinking to the bottom in ethylene glycol; filtering the sunk BHET monomers to separate them from ethylene glycol; obtaining BHET monomers suitable for use in polyurethane reactions by purifying BHET monomer crystals obtained after filtration from the whole ethylene glycol.

The polyurethane suitable for use as an additive in modified bituminous mixtures developed according to the present invention is synthesized through the polymerization reaction of diisocyanate monomer, diol monomer and chain extender, this synthesis process comprising the steps of adding 4,4'-methylene diphenyl diisocyanate (MDI) in melt form preferably at 80°C, as the isocyanate monomer, to a reactor (preferably a batch reactor) comprising preferably a top mechanical mixer; adding preferably dropwise into the MDI-containing reactor the BHET monomers in melt form preferably at 1 10°C, as the diol monomer, obtained from said waste polyethylene terephthalate (PET) products; following the addition of BHET into the reactor, adding butanediol as the chain extender so that the polymerization reaction is initiated; following the completion of the polymerization reaction preferably under a nitrogen blanket, obtaining polyurethane suitable for use as an additive in modified bituminous mixtures.

In a representative embodiment of the polyurethane synthesis process developed according to the present invention, BHET, butanediol and MDI are added to said reactor preferably in a mass proportion of 1 :1 :8 (BHET:Butanediol:MDI).

In an alternative embodiment of the polyurethane synthesis process developed according to the present invention, the polymerization reaction is conducted in the presence of at least one catalyst. The addition of catalyst depends on the conditions of the polymerization reaction and on the reactivities of the monomers added.

In the polyurethane synthesis process developed according to the present invention, BHET monomers obtained from recycling reactions are used directly in the polyurethane synthesis reactions. Thus, the source of diols required for use in polyurethane synthesis is obtained from Waste PETs so that a reduction is achieved in the costs of polyurethane synthesis. Also a method for preparing a modified bituminous mixture is developed according to the present invention using the polyurethane obtained through said polyurethane synthesis process as an additive, the method comprising the steps of fluidizing bitumen, as the main component of the mixture, preferably at 135°C; transferring the fluidized bitumen into a mechanical mixer preferably running at 120 rpm stirring speed; obtaining a polyurethane- bitumen mixture by adding polyurethane, in hot form, obtained through said polyurethane synthesis process to bitumen in said mixer while stirring process continues; stirring further this mixture for a predetermined time (preferably 60 minutes) at a predetermined stirring speed (preferably 500 rpm) to obtain a homogeneous polyurethane-bitumen mixture; and following the completion of the stirring process, obtaining a homogeneous polyurethane- added modified bituminous mixture.

In the method of preparing modified bituminous mixture according to the present invention, the polyurethane is added to hot fluidized bitumen so that both a homogeneous distribution of polyurethane is ensured and energy is saved by eliminating extra heating costs. Apart from the method according to the present invention, due to cooling down of the polyurethane following its synthesis, a material is obtained which is hard and does not soften under high temperatures. Here, no softening or melting is observed after synthesized polyurethane is left in a drying oven at 140-160°C; however structural degradation is seen after exposure to heat for a long period of time. It is also seen here that when such solid polyurethane is used in bitumen at 180°C, it remains in the form of hard particles. These results, in turn, show that synthesized polyurethane produces a stronger bond structure as it is cooled down and a duromeric polymer structure is obtained. Therefore, in order to be able to prepare synthesized polyurethane and bituminous mixtures homogeneously, the method has been developed so that bitumen is added in a hot and fluidized form following the synthesis, and it has been concluded that the results indicated cannot be obtained when it is stepped out of this method. The properties achieved when synthesized polyurethane according to the present method was added into bitumen in various proportions are given in Table 1.

Table 1. Properties of Modified Bitumen Comprising Increasing Proportions of Synthesized Polyurethane Additive Bitumen Bitumen Bitumen

Bitumen with 3% with 5% with 7%

Bitumen

PURE with synthesize synthesi synthesize with 3%

BITUM 4.5% d zed d

SBS EN SBS polyuretha polyuret polyuretha additive

additive ne hane ne

additive additive additive

Softening point,

48.2 51.9 62.0 52 52 51

°C

DSR

(Dynamic Shear 66 70.1 77.4 70.6 72.3 69.7

Rheometer), °C

Elastic

5.4 47.25 82.3 14 7.8 9.3

Recovery, %

When the results in Table 1 are reviewed, it can be seen that when the synthesized polyurethane is added to bitumen, the properties of bitumen are improved as compared to pure bitumen, and that when 3% is added, it provides the same improvement that was achieved by adding 3% SBS additive. On the other hand, no effect was seen when the amount of added synthesized polyurethane was increased above 3%. It is assumed here that there may be subgroups in bitumen with which polyurethane reacts with, and that all these subgroups reacts with 3% polyurethane additive and that any more polyurethane additive exceeding this proportion cannot make any further improvement that is observed in bitumen. For this reason, it is concluded that the amount of synthesized polyurethane that can be added to bitumen is restricted to 3%, and that using this proportion provides similar improvements both in DSR and softening point to that provided by 3% SBS.

In a preferred embodiment of the method for preparing a polyurethane-added modified bituminous mixture developed according to the present invention, the method also comprises the steps of adding a predetermined amount of SBS, preferably divided into 10 equal portions, preferably each at 3-minute intervals, preferably at 180°C, into the obtained polyurethane-added modified bituminous mixture using a mechanical mixer running at 400 rpm; following the addition of SBS, obtaining a polyurethane- and SBS- added modified bituminous mixture; stirring further this mixture for a predetermined amount of time (preferably 60 minutes) at a predetermined stirring speed (preferably 400 rpm) to obtain a homogeneous polyurethane- and SBS-added modified bituminous mixture; following the completion of the stirring step, obtaining a homogeneous polyurethane- and SBS-added modified bituminous mixture.

The present invention also discloses a modified bituminous mixture obtained according to said methods, the mixture comprising polyurethane synthesized through a polymerization reaction using BHET monomers, as a diol monomer, obtained through a recycling reaction of waste PET products, MDI as a diisocyanate monomer, and butanediol as a chain extender.

In exemplary embodiments of the method for preparing modified bitumen according to the present invention, polyurethane-added or polyurethane- and SBS-added modified bituminous mixture comprises 3% or less than 3% (preferably 3%) by weight of hot polyurethane obtained according to the present method, and 3% or less than 3% (preferably 3%) by weight of preferably solid, powder-form SBS. The test results and performance classification, according to the standards TS EN 12591 and ASSHTO MP1 , of modified bitumens prepared in exemplary embodiments of the present invention are given in Table 2.

Table 2. Test results of Additive-Free and Modified Bitumens according to Standards EN 12591 and ASSTHO MP1

Softening TS EN

°C 48.2 51.9 62.0 52.1 61.2 Point 1427

Elastic TS EN

% 5.4 47.3 82.3 14 81.75 Recovery 13398

Thin film

TS EN

Heating Test - + + + + +

12607-1

(RT-FOT)

Change in

- % 0.18 0.16 0.14 0.28 0.22 Mass

Retained TS EN

% 74 74 64 76 73 Penetration 1426

Softening

TS EN

Point after °C 52.4 58.5 62.9 55.4 66

1427

RT-FOT

Softening

Point - °C 4.2 6.6 0.9 3.4 4.2 Increase

TS EN

Flash Point °C 382.8 332 328 336 336

ISO 2592

TS EN

Viscosity cP 382.8 729 1 192 460.9 1 182

12595

TS EN

Elastic recovery % 5.4 47.3 85.3 14 81.8

13398

Dynamic

Shear TS EN 66 70.1 77.4 70.6 79

°C

Rheometer 14770

SUPE (DSR)

RPAV DSR After TS EN

°C 64.1 74.3 78.2 76.1 77.5 E RT-FOT 14770

Pressurized TS EN

- + + + + + Aging (PAV) 14769

DSR After TS EN

°C 25.7 19 25.2 26.5 20.3 PAV 14770 Bending

Beam TS EN

°C -22 -16 -16 -22 -16 Rheometer 14771

Test (BBR)

70-

Performance Class 64-22 76-16 70-22 76-16

16

It can be seen in Table 2 that the performance class of polyurethane- and SBS-added modified bitumens prepared according to the present invention shows an enhancement as compared to pure bitumen. However, the performance class provided with 4.5% SBS additive is now provided with less SBS in the presence of polyurethane (3% SBS + 3% polyurethane). Additionally, the use of SBS together with the developed polyurethane additive provides a synergistic effect on the elastic recovery, showing a higher increase as compared to when the additives are used alone. Numerically, elastic recovery values of 47.3% and 14% are achieved respectively when 3% SBS and 3% Polyurethane are used alone. However, when the same proportions of SBS and polyurethane are used together, the elastic recovery is determined as 81.8%. Furthermore, the developed polyurethane additive does not increase the viscosity property, which effects the stirring and compacting temperatures of bitumen in asphalt applications, as high as it is increased by SBS, and when it is used together with SBS, it ensures the same performance as compared to 4.5% SBS additive, but results in an ease of processability at a lower viscosity.

The effect of developed polyurethane on the performance of bitumen is again seen in Table 2 with the performance results of modified bitumens with individual SBS (3%) and polyurethane (3%) additives at the same proportion. While polyurethane additive ensures the same high-temperature performance enhancement (increase from 64 to 70) in bitumen as it is ensured by SBS, it does not negatively affect the low-temperature performance of bitumen as SBS does (SBS lowers it from -22 to -16, but it keeps it at -22). Thus, when compared with the use of SBS at the same proportion, it can be stated that the developed polyurethane additive provides better results in the cold-climate performance of bitumen as compared to SBS. So, it is seen that the performance enhancement provided in bitumen when the developed polyurethane and SBS are used together can now be provided with the developed polyurethane additive. The whole methods developed according to the present invention provide an enhancement in the performance and durability of bitumen used in asphalt applications, wherein either only the polyurethane that is synthesized through the synthesis process according to the present invention is added to bitumen, or SBS and said polyurethane are added together to bitumen. By virtue of using polyurethane together with SBS, the use of SBS which is purchased from abroad, increases the current account deficit and has a tonnage price more than that of bitumen is reduced so that a method is developed with more reduced costs. Additionally, by virtue of using polyurethane obtained through the recycling of waste PET, a product is achieved which is not only of low-cost, but also is environment friendly. Thus, by providing bitumen with the polyurethane additive obtained through the overall methods developed according to the present invention, modified bitumen/asphalt products are achieved having lower cost, higher quality as compared to pure bitumen and asphalt in terms of quality/performance/strength, and an increased production volume.