Modification method of PET plastic and application of modified PET plastic in asphalt modification

Abstract

The invention discloses a modification method of PET plastic and application of the modified PET plastic in asphalt modification, and relates to the technical field of road engineering materials. The PET modification method comprises the following steps: (1) carrying out microwave radiation treatment on PET to realize PET depolymerization so as to obtain a PET oligomer; (2) carrying out grafting reaction on soybean oil and the PET oligomer to obtain grafted modified PET; the condition of microwave radiation treatment is normal pressure, the radiation frequency is 2.45 GHz, and the radiation temperature is 200-300 DEG C. According to the invention, PET is depolymerized by using a microwave depolymerization technology, efficient depolymerization of PET can be realized in an extremely short time of 2-10 min under a normal pressure condition, then the microwave depolymerized PET is subjected to graft modification by using soybean oil as a raw material, the waste soybean oil can be used as a raw material, resource utilization of the waste soybean oil is realized, and the problems of phase splitting and performance degradation of a PET modified asphalt material are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of road engineering materials, and particularly to a method for modifying PET plastics and the application of modified PET plastics in asphalt modification. Background Art

[0002] Polyethylene terephthalate (PET) is a polymer material widely used in the plastic packaging and textile industries. Due to its good mechanical properties, chemical corrosion resistance, and thermal stability, PET plastics are widely used in the manufacture of products such as beverage bottles, food containers, and textile fibers. However, the high molecular weight and polar structure of PET make it difficult to be effectively recycled in waste treatment, and at the same time, its poor compatibility with non-polar asphalt materials makes it difficult to be directly applied to the field of asphalt modification.

[0003] In road construction, asphalt is a key component of pavement materials, and its mechanical properties and durability are crucial for improving the service life of roads. To improve the performance of asphalt, researchers have tried to improve its rheological, viscoelastic, and anti-aging properties through modifiers. Traditional asphalt modifiers include polymers (such as SBS, SBR, etc.), rubber powder, etc. However, these materials usually have problems such as high price, unstable modification effect, and environmental pollution. Therefore, people's exploration of alternative materials has been continuously deepened. With the improvement of environmental awareness and the progress of resource recovery technology, more and more research focuses on how to apply waste PET plastics to asphalt modification to achieve waste resource utilization. However, the complex molecular structure of PET plastics, especially their high molecular weight and polar molecular chains, make their compatibility with asphalt poor.

[0004] The high molecular weight of PET comes from its long-chain polymerization structure, which endows PET plastics with good mechanical strength and heat resistance, but at the same time increases the difficulty of material decomposition. In traditional PET degradation technologies, pyrolysis, chemical depolymerization, or biodegradation are often used. However, these methods usually require long reaction times and high energy consumption, and may produce harmful by-products, making it difficult to achieve large-scale application. In addition, the compatibility problem of PET materials in asphalt is also a key challenge in the application of PET-modified asphalt. Asphalt is a complex non-polar compound, mainly composed of saturates, aromatics, resins, and asphaltenes, with weak polarity. Therefore, PET with strong polarity is not easily dispersed in asphalt and is prone to phase separation. This phase separation not only affects the uniformity of modified asphalt but also leads to the deterioration of material properties during high temperature or storage. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for modifying PET plastics and the application of modified PET plastics in asphalt modification to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a PET modification method based on microwave depolymerization and soybean oil grafting, comprising the following steps:

[0008] (1) Subject PET to microwave radiation treatment to achieve the depolymerization of PET and obtain PET oligomers;

[0009] (2) Carry out a grafting reaction between soybean oil and the PET oligomers to obtain graft-modified PET;

[0010] The conditions of the microwave radiation treatment are normal pressure, a radiation frequency of 2.45 GHz, and a radiation temperature of 200 - 300 °C.

[0011] As a further preference of the present invention, during the radiation process, the microwave output power is 600 - 800 w, and the time of the microwave radiation treatment is 2 - 10 min.

[0012] As a further preference of the present invention, the molecular weight of the PET oligomers is 4000 Da - 5000 Da.

[0013] As a further preference of the present invention, the grafting reaction is carried out at 120 - 180 °C, and the time of the grafting reaction is 1 - 3 h.

[0014] As a further preference of the present invention, the carboxyl content in the soybean oil is 1% - 10%.

[0015] As a further preference of the present invention, the soybean oil is waste soybean oil after treatment, and the treatment includes the steps of water washing, filtration, dehydration, and acid treatment.

[0016] As a further preference of the present invention, the temperature of the acid treatment is 60 °C to 80 °C.

[0017] As a further preference of the present invention, the pretreatment of the waste soybean oil specifically includes the following steps:

[0018] a. Water washing: Mix water and waste soybean oil, stir evenly and then let it stand for stratification, separate the aqueous phase, and repeat the washing multiple times;

[0019] b. Filtration: After water washing, carry out multi-stage filtration. First, remove large particle impurities through a coarse filter screen, and then remove fine impurities with a fine filter screen;

[0020] c. Dehydration: Heat the filtered waste soybean oil to 60 °C to 80 °C and maintain for a certain time to remove moisture.

[0021] d. Acid treatment: The waste soybean oil after washing, filtering, and dehydration is subjected to acid treatment. The waste soybean oil is heated to 60°C - 80°C, and an aqueous solution of an acid with a concentration of 30 - 50 wt% is added for acid treatment. The temperature is controlled at 60°C - 80°C, and the acid treatment time is 30 - 60 min. The aqueous solution of the acid accounts for 1% - 15% of the mass of the waste soybean oil.

[0022] As a further preference of the present invention, in the graft modification treatment, the depolymerized PET and the pretreated soybean oil are mixed in a mass ratio of 1:1.

[0023] As a further preference of the present invention, after the graft reaction is completed, acetone is used to wash the unreacted waste soybean oil.

[0024] The acids that can be selected for the acid treatment include phosphoric acid (H 3 PO 4 ), hydrochloric acid (HCl), oxalic acid (H 2 C 2 O 4 ), and sulfuric acid (H 2 SO 4 ). The present invention preferably uses mild oxalic acid to perform acid treatment on the waste soybean oil to effectively remove impurities, reduce the risk of oil emulsification, improve the treatment effect and the stability of subsequent applications.

[0025] The second technical solution of the present invention is to provide a modified PET material, which is prepared by the above modification method.

[0026] The third technical solution of the present invention is to provide a modified asphalt, which is obtained by mixing the above modified PET material with matrix asphalt.

[0027] As a further preference of the present invention, the mixing mass ratio of the modified PET material to the matrix asphalt is 3% to 10%.

[0028] The present invention discloses the following technical effects:

[0029] The present invention uses microwave depolymerization technology to depolymerize PET, which can achieve efficient depolymerization of PET in an extremely short time of 2 - 10 min under atmospheric pressure conditions. The reaction process is rapid and the energy utilization rate is high, avoiding the problems of high energy consumption and long reaction time of traditional pyrolysis methods.

[0030] The present invention uses soybean oil as a raw material to graft-modify the microwave-depolymerized PET. The waste soybean oil raw material can be used, realizing its resource utilization, effectively improving the polarity problem of PET, making it more suitable for application in asphalt modification materials, and having the remarkable characteristics of economy and environmental protection. The modified PET material of the present invention shows excellent storage stability in asphalt, and can effectively solve the phase separation and performance degradation problems of PET-modified asphalt materials.

[0031] The PET-modified asphalt material based on microwave depolymerization and graft modification with waste soybean oil of the present invention has a wide application prospect in the related fields of road construction. It can improve the road performance while promoting the resource utilization of waste plastics and waste oils, and has important economic and environmental significance. Brief Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is the segregation index of the PET-doped modified asphalt of the control group and each treatment group of the present invention.

[0034] Figure 2 It is the comparison of the modifier distribution in the modified asphalt samples under different test conditions of the present invention. Detailed Embodiments

[0035] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0036] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0037] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to those documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0038] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this invention are merely exemplary.

[0039] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0040] It should be noted that the aspects not described in detail in this invention are all conventional operating means in the art and are not the focus of this invention.

[0041] In the embodiments of this invention, waste soybean oil is used to graft-modify the PET material after microwave radiation depolymerization, and the modified PET material is used for the modification treatment of asphalt to improve the stability of asphalt.

[0042] Example 1

[0043] (1) Microwave depolymerization of PET plastic fragments:

[0044] The recycled PET plastics are sorted and cleaned to remove surface residues, and the washed PET plastics are crushed by a crusher and then dried to remove residual moisture.

[0045] According to the standard of 30 g per portion of PET fragments, 5 portions are weighed respectively as treatment groups 1 - 4 and the control group. Among them, the control group is not subjected to microwave radiation treatment (as it is), and treatment groups 1 - 4 are subjected to microwave radiation at a frequency of 2.45 GHz (the microwave radiation temperature is 200 - 300 °C, and the molecular weight of the PET oligomer after microwave depolymerization is 4000 Da - 5000 Da). Specifically:

[0046] Treatment group 1: The microwave output power is 600 w for 5 min; Treatment group 2: The microwave output power is 600 w for 10 min; Treatment group 3: The microwave output power is 800 w for 5 min; Treatment group 4: The microwave output power is 800 w for 10 min.

[0047] (2) Pretreatment of waste soybean oil:

[0048] a. Washing: Mix water and waste soybean oil, stir evenly, let stand and separate, separate the water phase, and repeat the washing several times;

[0049] b. Filtration: After washing, multi-stage filtration is performed, first using a coarse filter to remove large particles of impurities, and then using a fine filter to remove fine impurities;

[0050] c. Dehydration: Heat the filtered waste soybean oil to 80°C to remove moisture.

[0051] d. Acidification treatment: The washed, filtered and dehydrated waste soybean oil was heated to 80°C, and 50wt% oxalic acid (H 2 C 2 O 4 ) aqueous solution, the temperature is controlled at 80°C, the amount of oxalic acid aqueous solution added is 10% of the mass of the waste soybean oil, the acid treatment time is 3h, until the pH of the lower aqueous phase reaches 3.5. Finally, the upper oil layer is collected to remove free fatty acids, colloids and other impurities, and improve the purity and stability of the oil.

[0052] (3) Graft modification treatment:

[0053] The waste soybean oil pretreated in step (2) and the PET products under five different test conditions in step (1) were mixed at 180°C in a ratio of 1:1 and reacted for 60 minutes. After the reaction was completed, the mixture was cooled to room temperature and the precipitate was suspended in 500 mL of acetone to wash away the excess unreacted waste soybean oil. After filtering and separating the product, the precipitate was placed in 250 mL of acetone for secondary washing. After washing, the product was filtered and retained, and placed in a tray and spread flat, and dried in an oven at 160°C for 1 hour to obtain grafted modified PET. The grafted modified PET products after drying were ground to a particle size of 0.3-0.6 mm for subsequent preparation of modified asphalt.

[0054] (4) Preparation of PET modified asphalt:

[0055] Weigh 15g of the grafted modified PET ground in step (3) respectively, and heat a certain amount of matrix asphalt in a 150°C oven to liquefy it. Weigh 300g of the material while it is flowing, transfer it to a heating table for preheating, and evenly add the 15g of grafted modified PET to the 300g matrix asphalt to ensure that the grafted modified plastic accounts for 5%. Use a temperature-controlled high-speed shearing machine, with a shearing control temperature of 160°C, a shearing rate of 4000r / min, and a shearing time of 60min to ensure that the grafted modified PET material is fully dispersed in the asphalt matrix to form a uniform composite material, namely PET modified asphalt.

[0056] The storage stability experiment was conducted on the prepared PET modified asphalt, and a dynamic rheological shear instrument was used to test the rutting factor and fatigue factor. Furthermore, the segregation index was calculated to comprehensively evaluate the performance comparison of the PET modified asphalt prepared by the present invention with unmodified asphalt and conventional PET modified asphalt in terms of high-temperature performance, compatibility, and storage stability.

[0057] 1. Rutting factor and fatigue factor test:

[0058] First, the PET modified asphalt after shearing in the example was poured into an aluminum tube with a diameter of 25 mm and a length of 140 mm. Then the aluminum tube was tightly sealed and vertically placed in a bracket inside the oven at a temperature of 163 °C for 48 hours. Then, the aluminum tube was immediately placed in a refrigerator at -18 °C for 6 hours. After the sample became hard due to freezing, each tube of the sample was cut into 3 equal parts (top, middle, and bottom), and the samples inside the top and bottom were extracted and placed in aluminum boxes with a diameter of 30 mm for storage. Then, the samples at the top and bottom were placed in an oven at 150 °C for 30 min to liquefy and drop the samples for rutting factor and fatigue factor tests.

[0059] Using a dynamic rheological shear instrument with a 25 mm spindle, at 64 °C, set the frequency to 10 rad / s and the strain value to 12%, measure the complex shear modulus G* and phase angle δ at the top and bottom of five kinds of modified asphalt, and calculate the rutting factor (Equation 1); using a dynamic shear rheometer with an 8 mm spindle, at 25 °C, set the frequency to 10 rad / s and the strain value to 12%, measure the complex shear modulus G* and phase angle δ at the top and bottom of five kinds of modified asphalt, and calculate the fatigue factor (Equation 2).

[0060]

[0061] Fatigue factor = G * ·sinδ (2)

[0062] In Equation (1) and Equation (2), G* is the complex shear modulus, which represents the total resistance of the material during repeated shear deformation, including the elastic (recoverable) part and the viscous (non-recoverable) part; δ is the phase angle, which represents the relative index of the number of recoverable and non-recoverable deformations.

[0063] According to Formula 1 and Formula 2, the calculation results of the rutting factor and fatigue factor obtained from the complex modulus and phase angle at 64 °C and 25 °C tested by the dynamic shear rheometer are respectively summarized in Table 1 and Table 2.

[0064] Table 1 Calculation results of rutting factor at 64 °C

[0065]

[0066]

[0067] Table 2 Calculation Results of Fatigue Factor at 25°C

[0068]

[0069] It can be seen that the calculated rutting factor and fatigue factor values are both larger at the bottom and smaller at the top. After the storage stability test of PET modified asphalt, due to the higher density of the PET modifier than that of the base asphalt, PET deposits at the bottom. The rutting factor represents the high-temperature rutting resistance of asphalt materials. The larger the rutting factor, the stronger the rutting resistance of the asphalt material. The fact that the bottom value is greater than the top value indicates that the modified asphalt at the bottom has stronger rutting resistance at high temperatures. The fatigue factor represents the medium-temperature fatigue resistance of asphalt materials. The larger the fatigue factor, the stronger the fatigue resistance of the asphalt material. The fact that the bottom value is greater than the top value indicates that the modified asphalt at the bottom has stronger fatigue resistance at medium temperatures.

[0070] Analyze the compatibility of PET modified asphalt according to the segregation index (Equation (3) or Equation (4)).

[0071]

[0072] In Equation (3) and Equation (4), SI is the storage stability index for evaluating PET modified asphalt, (G* / sinδ) is the rutting factor, and (G*·sinδ) is the fatigue factor. Calculate the segregation index according to the rutting factor and the fatigue factor respectively. The results of the storage stability index of PET modified asphalt are as Figure 1 shown.

[0073] 2. Stability Test:

[0074] Figure 1 is the segregation index of the control group and PET-doped modified asphalt in each treatment group. The smaller the segregation index, the better the storage stability of the modified asphalt.

[0075] Calculated by Equation (3), the segregation index of the PET modified asphalt without microwave depolymerization is 61%. For the sample with a microwave output power of 600 w and a microwave exposure time of 5 min, the segregation index is 45%. For the sample with a microwave output power of 600 w and a microwave exposure time of 10 min, the segregation index is 31%. For the sample with a microwave output power of 800 w and a microwave exposure time of 5 min, the segregation index is 15%. For the sample with a microwave output power of 800 w and a microwave exposure time of 10 min, the segregation index is 7%.

[0076] First, compared with the PET modified asphalt without microwave depolymerization, the segregation index of the PET modified asphalt after microwave depolymerization is significantly reduced, which can significantly improve the storage stability of the modified asphalt. Secondly, the segregation index has a linear relationship with the microwave output power and the microwave exposure time. The optimal microwave treatment conditions can be obtained as a microwave output power of 800 w and a microwave exposure time of 10 min. Similarly, the segregation index calculated by formula (4) is consistent with the above.

[0077] 3. Compatibility test:

[0078] The distribution of PET plastics in the top and bottom samples of five modified asphalts was observed by a dark-field fluorescence microscope:

[0079] The modified asphalt sample was heated and liquefied and dropped onto the center of a glass slide, then covered with a glass slide and evenly pressed into a thin layer. After the modified asphalt sample cooled to room temperature, a purple excitation light source with a wavelength of 435 mm was used, and a high-resolution camera and an optoelectronic image acquisition system were used to obtain two images. The comparison of the modifier distribution in the modified asphalt samples under different test conditions is shown in Figure 2 .

[0080] When observing the PET modified asphalt by a dark-field fluorescence microscope, the distribution state of the modifier in the asphalt can be intuitively seen. The modifier PET will emit obvious fluorescence, while the asphalt itself does not emit light. First, for the PET modified asphalt (as-received) without microwave depolymerization, the modifier PET obviously forms large aggregates or uneven distribution in the asphalt, indicating poor compatibility. For the sample with a microwave output power of 600 w and a microwave exposure time of 5 min, the top shows a chain-like shape and the bottom shows a lump-like shape, and there is partial aggregation of the modifier. Similarly, for the two types of samples with a microwave output power of 600 w and 800 w and a microwave exposure time of 5 min, there is also lump-like aggregation of the modifier, but it is improved compared with the above samples. For the sample with a microwave output power of 800 w and a microwave exposure time of 10 min, the PET particles at the top and bottom are smaller and have better dispersibility, and can be more evenly distributed in the asphalt, thus improving the compatibility.

[0081] The present invention can achieve the efficient depolymerization of PET within an extremely short time of 2 - 10 min under normal pressure conditions, significantly improving the degradation efficiency. Moreover, the present invention uses the treated waste soybean oil to graft-modify the PET after microwave depolymerization, which can effectively improve the phase separation and performance degradation problems during the storage of traditional PET modified asphalt. The present invention follows the concept of environmental protection and recycling, uses waste PET plastics and waste soybean oil, not only reduces the plastic pollution and waste oil disposal problems, but also provides high-performance modified asphalt materials for road construction, with significant environmental and economic benefits.

[0082] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A PET modification method based on microwave depolymerization and soybean oil grafting, characterized in that: The following steps are involved: (1) subjecting PET to microwave radiation treatment to achieve PET depolymerization to obtain PET oligomers; (2) performing a grafting reaction on the soybean oil and the PET oligomer to obtain a grafted modified PET; The microwave radiation treatment is carried out under normal pressure, a radiation frequency of 2.45 GHz and a radiation temperature of 200-300°C.

2. The PET modification method according to claim 1, characterized in that: The molecular weight of the PET oligomer is 4000Da-5000Da.

3. The PET modification method according to claim 1, characterized in that: The microwave radiation treatment time is 2-10 min.

4. The PET modification method according to claim 1, characterized in that: The grafting reaction is carried out at 120-180° C., and the grafting reaction time is 1-3 hours.

5. The PET modification method according to claim 1, characterized in that: The carboxyl content in the soybean oil is 1%-10%.

6. The PET modification method according to claim 1, characterized in that: The soybean oil is waste soybean oil that has been processed, and the processing includes the steps of water washing, filtering, dehydration and acid treatment.

7. The PET modification method according to claim 6, characterized in that: The temperature of the acid treatment is 60°C to 80°C.

8. A modified PET material, characterized in that: The modified product is prepared by the modification method according to any one of claims 1 to 7.

9. A modified asphalt, characterized in that: The modified PET material according to claim 8 is mixed with base asphalt to obtain the obtained product.

10. The modified asphalt according to claim 9, characterized in that The mixing mass ratio of the modified PET material to the base asphalt is 3% to 10%.

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