Composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier and preparation method thereof

Abstract

The invention discloses a composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier and a preparation method thereof, and belongs to the technical field of asphalt modifiers. The preparation method comprises the following steps: 1) preparing a pre-emulsion; 2) SBR emulsion pretreatment; (3) carrying out in-situ polymerization reaction; (4) post-treatment pre-stabilization; the invention discloses a preparation method of a composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier.The composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier.The composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier has the advantages that high-temperature rutting resistance and low-temperature crack resistance of asphalt can be improved, and temperature-sensitive response can be realized so that the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier is applicable to road service temperature ranges.

Description

Technical Field

[0001] The present invention belongs to the technical field of asphalt modifiers, and particularly relates to a composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier and a preparation method thereof. Background Art

[0002] As a core material of modern transportation infrastructure, the performance optimization of asphalt pavement has always been a research focus in the field of road engineering. Styrene-butadiene rubber (SBR) modified asphalt is widely used because it improves the ductility, crack resistance and other properties of asphalt. However, with the complexity of traffic loads and the frequent occurrence of extreme climates, the inherent defects of traditional SBR modified asphalt have gradually emerged. The dynamic shear modulus of existing SBR modified asphalt at high temperatures (60°C) is generally lower than 1.5 KPa, resulting in insufficient rutting resistance and difficulty in meeting the durability requirements of heavy-duty traffic pavements; at the same time, its low-temperature ductility (-20°C elongation ≤ 25 cm) cannot effectively relieve the shrinkage stress in cold regions and is prone to cause low-temperature cracking of the pavement; due to the polarity difference between the SBR modifier and the asphalt matrix, phase separation is likely to occur, and delamination and segregation phenomena occur during long-term storage, resulting in a decrease in the homogeneity and performance consistency of the modified asphalt. This defect not only increases the difficulty of construction quality control, but also causes early pavement diseases due to material performance fluctuations, significantly shortening the service life of the road; traditional SBR modified asphalt is a static performance regulation material and cannot dynamically adjust its mechanical behavior according to environmental temperature changes. In regions with significant day-night temperature differences or drastic seasonal climate fluctuations, the material is difficult to adaptively match the temperature stress changes, exacerbating the accumulation of fatigue damage in the pavement structure and limiting its application potential in intelligent road scenarios.

[0003] In summary, developing a new type of modified asphalt system with both high- and low-temperature synergistic enhancement, stable storage and environmental adaptability functions has become an urgent need to break through the technical bottleneck of road materials and achieve long-life intelligent pavements. Summary of the Invention

[0004] The present invention provides a composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier and a preparation method thereof. The asphalt modifier can improve the high-temperature rutting resistance and low-temperature crack resistance of asphalt, and can achieve temperature-sensitive response to be applicable to the road service temperature range.

[0005] In the first aspect, a preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier is disclosed, including the following steps: 1) Preparation of the pre-emulsion: Dissolve 5-20 parts by weight of N-isopropylacrylamide monomer, 0.1-1 part by weight of cross-linking agent N,N'-methylenebisacrylamide, and 1-3 parts by weight of emulsifier in water accounting for 50-70% of the total mass of the pre-emulsion, and stir until completely dissolved to form a transparent pre-emulsion; 2) Pretreatment of SBR emulsion: Add water to dilute the solid content of 100 parts by weight of SBR emulsion to 20%-30%, and adjust the pH of the SBR emulsion to 8-9; 3) In-situ polymerization reaction: Drop the pre-emulsion into the SBR emulsion after pretreatment, continuously stir, maintain the temperature at 25-30°C, add 0.5-2 parts by weight of initiator, raise the temperature to 60-70°C, initiate free radical polymerization, and carry out the constant temperature reaction for 4-6 h; 4) Post-treatment pre-stabilization: Cool to room temperature to terminate the polymerization reaction, centrifuge to remove unreacted monomers, add emulsifier to the centrifuged product, and adjust the pH to 8-9 to obtain SBR / PNIPAM composite emulsion; 5) Preparation of carbon nanotube dispersion: First, acidify the carbon nanotubes, and then shear and disperse 0.5-5 parts by weight of the acidified carbon nanotubes in water. The mass fraction of the acidified carbon nanotubes is 5-10%; 6) Mechanically blend the carbon nanotube dispersion with the SBR / PNIPAM composite emulsion to produce a composite modified thermosensitive styrene-butadiene rubber asphalt modifier.

[0006] Preferably, the initiator is ammonium persulfate and the emulsifier is sodium dodecyl sulfate.

[0007] Preferably, ammonia water or sodium hydroxide solution is used to adjust the pH in steps 2) and 4).

[0008] Preferably, the stirring speed in step 1) is 500-1000 rpm, and the continuous stirring speed in step 3) is 300-500 rpm.

[0009] Preferably, the free radical polymerization reaction in step 3) is carried out under nitrogen protection, and the stirring speed of the free radical polymerization reaction is 200-300 rpm.

[0010] Preferably, the addition amount of the emulsifier in step 4) is 0.5-1% of the total mass of the centrifuged product.

[0011] Preferably, in step 5), concentrated sulfuric acid and concentrated nitric acid are used for acidification, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is (1-3):1. The ratio of carbon nanotubes to the mixed acid is 1 g:(100-200) mL. The specific acidification method is as follows: Add the carbon nanotubes to the acid, ultrasonically disperse them evenly, stir and react, pour the reaction solution into an ice-water mixture for dilution, terminate the reaction, filter by suction, wash and dry the filter cake to obtain the acidified carbon nanotubes.

[0012] Preferably, the shear rate of the mechanical blending in step 6) is ≥1000 s -1 .

[0013] In a second aspect, a composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier prepared by the described preparation method is disclosed.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. Through the synergistic effect of molecular structure design and functional components, the present invention regulates the lower critical solution temperature (LCST) of the temperature-sensitive polymer to 25 - 35 °C, which matches the actual service temperature range of the road. When the ambient temperature exceeds the LCST, a reversible phase change occurs inside the material, dynamically enhancing the high-temperature deformation resistance ability; when the temperature decreases, the material returns to a flexible state to release the low-temperature shrinkage stress. This characteristic endows the asphalt with an "intelligent response" function, enabling it to adapt to the diurnal temperature difference and seasonal climate change, significantly reducing the fatigue damage caused by temperature fluctuations on the road surface, and extending the service life.

[0015] 2. The present invention introduces a nano-reinforcing phase and an interpenetrating network structure of flexible chain segments, significantly improving the mechanical properties of asphalt at extreme temperatures: the dynamic shear modulus at 60 °C is increased to ≥3.0 KPa, effectively resisting the flow deformation caused by heavy traffic and continuous high temperature; the ductility at -30 °C reaches ≥35 cm, tolerating the shrinkage stress in extremely cold environments and inhibiting the propagation of microcracks.

[0016] 3. The present invention constructs a three-dimensional nano-reinforcing network through directionally dispersed carbon nanotubes. The high modulus property of CNTs significantly improves the rutting resistance and fatigue resistance of asphalt; the ultra-high thermal conductivity of CNTs quickly transfers the environmental temperature change to the temperature-sensitive component, shortening the phase change response time.

[0017] 4. The present invention uses an aqueous emulsion system to replace the traditional organic solvent process, achieving environmental friendliness throughout the process. Description of the Drawings

[0018] Figure 1 It is a differential scanning calorimetry test chart of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier prepared in Example 1 of the present invention. Detailed Embodiments

[0019] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions will be clearly and completely described below in conjunction with the embodiments of the present invention. The parts used in the embodiments and comparative examples are in weight parts unless otherwise specified.

[0020] Example 1 The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier includes the following steps: 1) Preparation of pre-emulsion: Dissolve 5 parts of N-isopropylacrylamide monomer, 0.1 part of N,N'-methylenebisacrylamide, and 1 part of emulsifier sodium dodecyl sulfate in water accounting for 60% of the total mass of the pre-emulsion, stir until completely dissolved, with a stirring speed of 800 rpm, to form a transparent pre-emulsion; 2) Pretreatment of SBR emulsion: Add water to dilute the solid content of the SBR emulsion to 25%, and adjust the pH of the SBR emulsion to 8 using ammonia water; 3) In-situ polymerization reaction: Drop the pre-emulsion in step 1) into 100 parts of the pretreated SBR emulsion, continuously stir, with a stirring speed of 400 rpm, maintain the temperature at 28 °C, add 0.5 part of initiator ammonium persulfate, heat up to 65 °C, under nitrogen protection, initiate free radical polymerization, with a stirring speed of 250 rpm for the free radical polymerization reaction, and carry out the constant temperature reaction for 5 h; 4) Post-treatment pre-stabilization: Cool to room temperature to terminate the polymerization reaction, centrifuge to remove unreacted monomers, add emulsifier sodium dodecyl sulfate to the centrifuged product, with the addition amount of the emulsifier being 0.8% of the total mass of the centrifuged product, adjust the pH to 8 using ammonia water to obtain the SBR / PNIPAM composite emulsion; 5) Preparation of carbon nanotube dispersion: First, perform acidification treatment on carbon nanotubes. Add carbon nanotubes to a mixed acid of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1. The mass-volume ratio of carbon nanotubes to the mixed acid is 1 g:100 mL, ultrasonically disperse for 30 min (power 200 W), and then magnetically stir (500 rpm) in a 60 °C water bath for 4 h. Slowly pour the reaction solution into an ice-water mixture for dilution to terminate the reaction. Use a vacuum filtration device to filter, and repeatedly wash the filter cake with deionized water until the filtrate is neutral (pH≈7). Place the washed carbon nanotubes in a 60 °C vacuum oven to dry for 24 h to obtain acidified carbon nanotube powder.

[0021] Then, shear-disperse 0.5 part of the acidified carbon nanotubes in water, with the mass fraction of the acidified carbon nanotubes being 8%; 6) Mechanically blend the carbon nanotube dispersion with the SBR / PNIPAM composite emulsion, with a shear rate of 2000 s -1 to produce a composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier, and conduct DSC testing on it as Figure 1 shown. The absorption peak is at 25 - 35 °C, and its lower critical solution temperature (LCST) is 25 - 35 °C. The material has a temperature-sensitive effect at the use temperature of 25 - 35 °C.

[0022] Example 2 The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier described above includes the following steps: 1) Preparation of the pre-emulsion: Dissolve 10 parts of N-isopropylacrylamide monomer, 0.5 part of N,N'-methylenebisacrylamide, and 2 parts of emulsifier sodium dodecyl sulfate in water accounting for 50% of the total mass of the pre-emulsion, stir until completely dissolved, with a stirring speed of 500 rpm, to form a transparent pre-emulsion; 2) Pretreatment of the SBR emulsion: Add water to dilute the solid content of the SBR emulsion to 20%, and adjust the pH of the SBR emulsion to 9 using sodium hydroxide solution; 3) In-situ polymerization reaction: Drop the pre-emulsion obtained in step 1) into 100 parts of the pretreated SBR emulsion, continuously stir, with a stirring speed of 300 rpm, maintain the temperature at 25 °C, add 1 part of initiator ammonium persulfate, raise the temperature to 60 °C, under nitrogen protection, initiate free radical polymerization, with a stirring speed of 200 rpm for the free radical polymerization reaction, and carry out the constant temperature reaction for 6 h; 4) Post-treatment for pre-stabilization: Cool to room temperature to terminate the polymerization reaction, centrifuge to remove unreacted monomers, add emulsifier sodium dodecyl sulfate to the centrifuged product, with the addition amount of the emulsifier being 0.5% of the total mass of the centrifuged product, adjust the pH to 9 using sodium hydroxide solution to obtain the SBR / PNIPAM composite emulsion; 5) Preparation of the carbon nanotube dispersion: First, perform acidification treatment on the carbon nanotubes. Add the carbon nanotubes to a mixed acid of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 1:1, with a mass-volume ratio of carbon nanotubes to the mixed acid of 1 g:200 mL, ultrasonically disperse for 30 min (power 200 W), and then magnetically stir (500 rpm) in a 60 °C water bath for 5 h. Slowly pour the reaction solution into an ice-water mixture for dilution to terminate the reaction. Use a vacuum filtration device for filtration, and repeatedly wash the filter cake with deionized water until the filtrate is neutral (pH≈7). Place the washed carbon nanotubes in a 60 °C vacuum oven for drying for 24 h to obtain acidified carbon nanotube powder, and then shear disperse 3 parts of the acidified carbon nanotubes in water, with the mass fraction of the acidified carbon nanotubes being 5%; 6) Mechanically blend the carbon nanotube dispersion with the SBR / PNIPAM composite emulsion, with a shear rate of 2000 s -1 to prepare the composite modified thermosensitive styrene-butadiene rubber asphalt modifier.

[0023] Example 3 The preparation method of the composite modified thermosensitive styrene-butadiene rubber asphalt modifier includes the following steps: 1) Preparation of the pre-emulsion: Dissolve 20 parts of N-isopropylacrylamide monomer, 1 part of N,N'-methylenebisacrylamide, and 3 parts of emulsifier sodium dodecyl sulfate in water accounting for 70% of the total mass of the pre-emulsion, stir until completely dissolved, with a stirring speed of 1000 rpm, to form a transparent pre-emulsion; 2) Pretreatment of SBR emulsion: Add water to dilute the solid content of the SBR emulsion to 30%, and adjust the pH of the SBR emulsion to 9 with sodium hydroxide; 3) In-situ polymerization reaction: Drop the pre-emulsion prepared in step 1) into 100 parts of the pretreated SBR emulsion, continuously stir at a stirring speed of 500 rpm, maintain the temperature at 30 °C, add 2 parts of initiator ammonium persulfate, heat up to 70 °C, and start free radical polymerization under nitrogen protection. The stirring speed of the free radical polymerization reaction is 300 rpm, and keep the temperature constant for 4 h; 4) Post-treatment and pre-stabilization: Cool to room temperature to terminate the polymerization reaction, centrifuge to remove unreacted monomers, add emulsifier sodium dodecyl sulfate to the centrifuged product, and the addition amount of the emulsifier is 1% of the total mass of the centrifuged product. Adjust the pH to 9 with sodium hydroxide to obtain the SBR / PNIPAM composite emulsion; 5) Preparation of carbon nanotube dispersion: First, acidify the carbon nanotubes. Add the carbon nanotubes to a mixed acid of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 2:1. The mass-volume ratio of the carbon nanotubes to the mixed acid is 1 g:150 mL. Ultrasonically disperse for 30 min (power 200 W), and then stir magnetically (500 rpm) in a 60 °C water bath for 6 h. Slowly pour the reaction solution into an ice-water mixture for dilution to terminate the reaction. Use a vacuum filtration device to filter, and wash the filter cake with deionized water repeatedly until the filtrate is neutral (pH≈7). Place the washed carbon nanotubes in a 60 °C vacuum oven and dry for 24 h to obtain acidified carbon nanotube powder. Then, shear and disperse 5 parts of the acidified carbon nanotubes in water, and the mass fraction of the acidified carbon nanotubes is 10%; 6) Mechanically blend the carbon nanotube dispersion with the SBR / PNIPAM composite emulsion, and the shear rate of the mechanical blending is 2000 s -1 , and a composite modified thermosensitive styrene-butadiene rubber asphalt modifier is prepared.

[0024] Comparative Example 1 Modify with a commercially available SBR asphalt modifier, purchased from Tianjin Kangzewei Technology Co., Ltd.

[0025] Comparative Example 2 Different from Example 1, in this comparative example, step 2) for the pretreatment of the SBR emulsion is not included, and the commercially available SBR emulsion is directly used in step 3). The remaining preparation methods and steps are the same as those in Example 1.

[0026] Comparative Example 3 Different from Example 1, in this comparative example, "0.1 part of N,N'-methylenebisacrylamide" is replaced with 2 parts of sulfur, and the remaining preparation methods and steps are the same as those in Example 1.

[0027] Comparative Example 4 Different from Example 1, the addition amount of the initiator in step 3) is 2.5 parts, and the remaining preparation methods and steps are the same as those in Example 1. An excessive amount of initiator will decompose to generate too many free radicals, increasing side reactions, generating short-chain polymers or branched structures, deteriorating the mechanical properties of the modifier and the stability of the emulsion; at the same time, it will cause too high a grafting rate of PNIPAM and SBR, forming a rigid network, weakening the thermosensitivity; it will also oxidize the surface functional groups of CNTs, reducing the conductivity.

[0028] Comparative Example 5 The preparation method of the asphalt modifier described includes the following steps: 1) Preparation of the pre-emulsion: Dissolve 5 parts of N-isopropylacrylamide monomer, 0.1 part of N,N'-methylenebisacrylamide, and 1 part of emulsifier sodium dodecyl sulfate in water accounting for 60% of the total mass of the pre-emulsion, stir until completely dissolved, and the stirring speed is 800 rpm to form a transparent pre-emulsion; 2) Pretreatment of the SBR emulsion: Add water to dilute the solid content of the SBR emulsion to 25%, and use ammonia water to adjust the pH of the SBR emulsion to 8; 3) In-situ polymerization reaction: Drop the pre-emulsion in step 1) into 100 parts of the pretreated SBR emulsion, continuously stir, the stirring speed is 400 rpm, maintain the temperature at 28 °C, add 0.5 part of initiator ammonium persulfate, raise the temperature to 65 °C, under nitrogen protection, initiate free radical polymerization, and the stirring speed of the free radical polymerization reaction is 250 rpm, and react at a constant temperature for 5 h; 4) Post-treatment pre-stabilization: Cool to room temperature to terminate the polymerization reaction, centrifuge to remove unreacted monomers, add emulsifier sodium dodecyl sulfate to the centrifuged product, and the addition amount of the emulsifier is 0.8% of the total mass of the centrifuged product, and adjust the pH to 8 with ammonia water to obtain the SBR / PNIPAM composite emulsion.

[0029] Comparative Example 6 Different from Example 1, in step 1) of this comparative example, the stirring speed is 450 rpm, and the remaining preparation methods and steps are the same as those in Example 1. When preparing the pre-emulsion, too low a rotation speed will result in insufficient shear force, uneven dispersion of the emulsifier, poor stability of the emulsion, and uneven subsequent polymerization reaction. In terms of performance impact, it will deteriorate the mechanical properties of the modifier and weaken the thermosensitivity.

[0030] Comparative Example 7 Different from Example 1, in this comparative example, step 3) is as follows: The pre-emulsion in step 1) is added dropwise to 100 parts of the pretreated SBR emulsion, and continuous stirring is carried out at a stirring speed of 400 rpm while maintaining the temperature at 28 °C. 0.5 part of ammonium persulfate as the initiator is added, and the temperature is raised to 75 °C. Under nitrogen protection, free radical polymerization is initiated, and the stirring speed of the free radical polymerization reaction is 250 rpm, and the reaction is carried out at a constant temperature for 5 h. The remaining preparation methods and steps are the same as those in Example 1.

[0031] If the reaction temperature is too high, PNIPAM will aggregate hydrophobically in advance, resulting in a decrease in compatibility and the disappearance of thermosensitivity; at the same time, high temperature accelerates the free radical reaction, forming an over-crosslinked rigid network, and the ductility at low temperature decreases; the surface functional groups of carbon nanotubes are also oxidized, resulting in a decrease in conductivity.

[0032] Comparative Example 8 Different from Example 1, in this comparative example, step 3) is as follows: The pre-emulsion in step 1) is added dropwise to 100 parts of the pretreated SBR emulsion, and continuous stirring is carried out at a stirring speed of 400 rpm while maintaining the temperature at 28 °C. 0.5 part of ammonium persulfate as the initiator is added, and the temperature is raised to 65 °C. Under nitrogen protection, free radical polymerization is initiated, and the stirring speed of the free radical polymerization reaction is 350 rpm, and the reaction is carried out at a constant temperature for 5 h. The remaining preparation methods and steps are the same as those in Example 1. Too fast stirring speed will reduce the stability of the emulsion. At the same time, the shear force of high-speed stirring destroys the dynamic cross-linked structure of the thermosensitive polymer, resulting in a decrease in thermosensitivity; it will also reduce the aspect ratio of carbon nanotubes and decrease the conductivity.

[0033] The segregation rates of the asphalt modifiers obtained in the examples and comparative examples were measured. The specific test standard was "ASTM D6930 Test Methods for Synthetic Rubber Latices", and the test results are shown in Table 1.

[0034] Table 1 Segregation rate test results of asphalt modifiers obtained in examples and comparative examples

[0035] The asphalt modifiers obtained in the examples and comparative examples were used to make asphalt. The specific production method was as follows: The asphalt modifiers prepared in the examples and comparative examples were added according to 5% of the weight of the emulsified asphalt, and stirred at 200 rpm for 5 min to obtain the modified emulsified asphalt, which was used for road construction. The performance of the obtained modified emulsified asphalt was tested, and the test results are shown in Table 2.

[0036] Table 2 Related performance tests of asphalt made from asphalt modifiers obtained in examples and comparative examples

[0037] The test methods and standards used for the performance tests in Table 2 are as follows: Dynamic shear modulus: "JTG E20-2011 (T0628-2011) Asphalt Rheological Property Test"; Low temperature ductility: "ASTM D113 Standard Test Method for Ductility of Asphalt Materials"; Elastic recovery: "GB / T 4508 Determination Method for Elastic Recovery of Asphalt"; Resistivity: "ASTM D257 Standard Test Method for DC Resistance or Conductivity of Insulating Materials"; Rate of change of modulus in response to temperature: "ASTM D7175 Standard Test Method for Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer".

[0038] Compared with Example 1, in Comparative Example 1, a conventional asphalt modifier was used, there was no temperature-sensitive dynamic crosslinking, the physical properties were low, there was no temperature-sensitive response, the thermal conductivity was poor, and the latex stability was poor.

[0039] In Comparative Example 2, since the initiator decomposes more efficiently in an alkaline environment and the emulsion is not pretreated, the monomer conversion rate will be low; too high solid content will make the system viscosity large, resulting in uneven polymerization, poor compatibility, temperature-sensitive failure, and large segregation rate at the same time.

[0040] In Comparative Example 3, when using conventional sulfur, the crosslinking agent cannot form a permanent covalent crosslinking network at low temperature, and cannot respond to temperature changes to achieve dynamic bond breakage and recombination. Sulfur crosslinking requires high-temperature vulcanization (160-180 °C), with high energy consumption and possible damage to temperature-sensitive components.

[0041] In Comparative Example 4, adding an excessive amount of initiator will decompose to generate too many free radicals, increasing side reactions, generating short-chain polymers or branched structures, resulting in a decrease in the mechanical properties of the modifier and poor latex stability; at the same time, it will cause too high grafting rate of PNIPAM and SBR, forming a rigid network, weakening the temperature sensitivity; it will also oxidize the surface functional groups of CNTs, reducing the conductivity.

[0042] In Comparative Example 5, the unique nanostructure of carbon nanotubes can effectively improve the thermal conductivity of the material, accelerate the temperature-sensitive response; at the same time improve the mechanical properties. Without the modification and addition of carbon nanotubes, the mechanical properties and temperature sensitivity decrease.

[0043] In Comparative Example 6, when preparing the pre-emulsion liquid, the rotation speed is too low, resulting in insufficient shear force, uneven dispersion of the emulsifier, poor stability of the emulsion, and uneven subsequent polymerization reaction. In terms of performance impact, it will cause a decrease in the mechanical properties of the modifier and a weakening of the temperature sensitivity.

[0044] In Comparative Example 7, too high reaction temperature will cause PNIPAM to aggregate hydrophobically in advance, resulting in a decrease in compatibility and disappearance of temperature sensitivity; at the same time, high temperature accelerates the free radical reaction, forming an over-crosslinked rigid network, and the low temperature ductility decreases; the surface functional groups of carbon nanotubes are also oxidized, and the conductivity decreases.

[0045] In Comparative Example 8, too fast stirring speed will reduce the stability of the emulsion. At the same time, the shear force of high-speed stirring will destroy the dynamic cross-linked structure of the thermosensitive polymer, resulting in a decrease in thermosensitivity; it will also reduce the aspect ratio of carbon nanotubes and decrease the conductivity.

Claims

1. Preparation method of composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier, characterized in that, It includes the following steps: 1) Preparation of the pre-emulsion: Dissolve 5-20 parts by weight of N-isopropylacrylamide monomer, 0.1-1 part by weight of cross-linking agent N,N'-methylenebisacrylamide, and 1-3 parts by weight of emulsifier in water accounting for 50-70% of the total mass of the pre-emulsion, and stir until completely dissolved to form a transparent pre-emulsion; 2) Pretreatment of SBR emulsion: Add water to dilute the solid content of 100 parts by weight of SBR emulsion to 20%-30%, and adjust the pH of the SBR emulsion to 8-9; 3) In-situ polymerization reaction: Drop the pre-emulsion into the SBR emulsion after pretreatment, continuously stir, maintain the temperature at 25-30 °C, add 0.5-2 parts by weight of initiator, raise the temperature to 60-70 °C, initiate free radical polymerization, and carry out the constant temperature reaction for 4-6 h; 4) Post-treatment and pre-stabilization: Cool to room temperature to terminate the polymerization reaction, centrifuge to remove unreacted monomers, add emulsifier to the centrifuged product, and adjust the pH to 8-9 to obtain an SBR / PNIPAM composite emulsion; 5) Preparation of carbon nanotube dispersion: First, perform acidification treatment on carbon nanotubes, and then shear and disperse 0.5-5 parts by weight of acidified carbon nanotubes in water, and the mass fraction of acidified carbon nanotubes is 5-10%; 6) Mechanically blend the carbon nanotube dispersion with the SBR / PNIPAM composite emulsion to produce a composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier.

2. The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier according to claim 1, characterized in that, The initiator is ammonium persulfate, and the emulsifier is sodium dodecyl sulfate.

3. The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier according to claim 1, characterized in that, In step 2) and step 4), ammonia water or sodium hydroxide solution is used to adjust the pH.

4. The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier according to claim 1, characterized in that, In step 1), the stirring speed is 500-1000 rpm, and in step 3), the continuous stirring speed is 300-500 rpm.

5. The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier according to claim 1, characterized in that, The free radical polymerization reaction in step 3) is carried out under nitrogen protection, and the stirring speed of the free radical polymerization reaction is 200-300 rpm.

6. The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier according to claim 1, characterized in that, In step 4), the addition amount of the emulsifier is 0.5-1% of the total mass of the centrifuged product.

7. The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier according to claim 1, characterized in that, In step 5), the acidification uses concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is (1-3):

1. The ratio of carbon nanotubes to the mixed acid is 1 g:(100-200) mL. The specific acidification method is: Add carbon nanotubes to the acid, ultrasonically disperse evenly, stir and react, pour the reaction solution into an ice-water mixture for dilution, terminate the reaction, filter by suction, wash and dry the filter cake to obtain acidified carbon nanotubes.

8. The preparation method of the composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier according to claim 3, characterized in that, The shear rate of mechanical blending in step 6) ≥ 1000 s -1 .

9. A composite modified temperature-sensitive styrene-butadiene rubber asphalt modifier prepared by the preparation method according to any one of claims 1-8.

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