Method for preparing water reducing agent based on PET degradation product

Abstract

The invention belongs to the technical field of preparation of water reducing agents, and particularly relates to a method for preparing a water reducing agent based on a PET degradation product. The preparation method comprises the following steps: mixing PET (Polyethylene Terephthalate), EG (Ethylene Glycol) and stannous chloride, and carrying out degradation reaction to obtain PTA-EG; mixing the PTA-EG with a polymerization inhibitor, adding AA and HEA, finally adding a catalyst, and heating for partial esterification reaction to obtain a PEA mixed solution; finally, mixing TPEG, water and PEA mixed liquid to obtain a reaction system, and dropwise adding the material A and the material B to obtain the water reducing agent after dropwise adding is completed. When the prepared water reducing agent is used for preparing concrete, the prepared concrete is relatively good in fluidity, slump and strength, the water reducing rate of the water reducing agent can reach 28%, and in the preparation process of the water reducing agent, no technological wastewater or waste gas is generated, so that the water reducing agent is a green and environment-friendly material.

Description

Technical Field

[0001] The present invention belongs to the technical field of water reducing agent preparation, and more specifically relates to a method for preparing a water reducing agent based on PET degradation products. Background Art

[0002] Water reducing agents are very important external additives in concrete. Especially the third-generation polycarboxylate water reducing agents have an increasing market share due to their excellent performance, environmental friendliness, and greenness. With the development of the construction industry, more requirements are now placed on concrete, and traditional concrete can no longer meet the needs of the new era. Therefore, a new high-performance polycarboxylate water reducing agent needs to be synthesized.

[0003] The first problem in preparing high-performance polycarboxylate water reducing agents is the production of raw materials. Currently, only a few companies have the ability to synthesize polyether macromonomers of qualified quality. The use of a large number of unqualified polyether macromonomers results in uneven quality of the produced polycarboxylate water reducing agents. Then there is the rising price of raw materials and the excessively high cost, which hinders the application of polycarboxylate water reducing agents and seriously hinders the research and development of polycarboxylate water reducing agents.

[0004] There is a large difference between the theoretically studied functions of polycarboxylate water reducing agents and their actual applications. Because the actual performance of polycarboxylate water reducing agents is also closely related to the temperature, climate, etc. at that time. It is easy in theory, but it is difficult to meet the requirements in actual applications. The differences in polyether macromonomers, the mixing ratios of various monomers, the side chain density and length will all affect the performance of polycarboxylate water reducing agents.

[0005] At the same time, polycarboxylate water reducing agents are not necessarily suitable for all cements, and there are still certain limitations in the use of polycarboxylate water reducing agents. There are also problems in the construction application process of the synthesized polycarboxylate water reducing agents, such as the influence of the viscosity of concrete and the slump problem. Especially in concrete materials with a low water-cement ratio, when the state of the concrete is more appropriate, problems such as high viscosity and difficult construction will occur. There is also incomplete theoretical analysis, especially the complex organic synthesis process, including main reactions, side reactions, as well as main products and by-products, and there is a lack of understanding of its reaction mechanism. The performance of water reducing agents is also affected by factors such as the weather, temperature, humidity, and gel materials on site, and there may be a large difference from the data measured in the laboratory. Therefore, how to provide a method for preparing a water reducing agent based on PET degradation products to solve the above technical problems has become a difficult problem that needs to be overcome by those skilled in the art. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a water reducing agent based on PET degradation products to solve the problems existing in the above prior art.

[0007] To achieve the above purpose, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention: Provide a method for preparing a water reducing agent based on PET degradation products, and the steps include:

[0009] After mixing PET (polyethylene terephthalate), EG (ethylene glycol) and stannous chloride, carry out a degradation reaction to obtain PTA-EG (a mixture of terephthalic acid, ethylene glycol, and terephthalic acid-ethylene glycol oligomers);

[0010] After mixing the PTA-EG and the inhibitor, then add AA (acrylic acid) and HEA (2-hydroxyethyl acrylate), and finally add a catalyst, and heat to carry out a partial esterification reaction to obtain a PEA mixture (a polyester acrylate functional monomer);

[0011] Mix TPEG (isopentenyl alcohol polyoxyethylene ether), water and the above-mentioned PEA mixture to obtain a reaction system, and then dropwise add Material A and Material B. After the dropping is completed, obtain the water reducing agent;

[0012] Material A is composed of AA and water; Material B includes a chain transfer agent and an initiator.

[0013] It should be noted that the partial esterification reaction specifically refers to controlling the degree of esterification through the setting of experimental parameters to ensure that the product has good water solubility.

[0014] Further, the mass ratio of PET to ethylene glycol is 1:2-6.

[0015] Optionally, the mass ratio of PET to ethylene glycol is 1:5.

[0016] Further, the dosage of stannous chloride is 0.1 wt.% - 0.6 wt.% of the sum of the masses of PET and ethylene glycol.

[0017] Optionally, the dosage of stannous chloride is 0.4 wt.% of the sum of the masses of PET and ethylene glycol.

[0018] Further, the temperature of the degradation reaction is 140-180 °C, and the time is 6-14 h.

[0019] Optionally, the temperature of the degradation reaction is 160 °C, and the time is 12 h.

[0020] Further, the mass ratio of PTA-EG to AA is 1:1-3.

[0021] Optionally, the mass ratio of PTA-EG to AA is 1:1.5.

[0022] Further, the mass ratio of PTA-EG to HEA is 1-2.5:1.

[0023] Optionally, the mass ratio of the PTA-EG to the HEA is 1:1.

[0024] Furthermore, the catalyst includes at least one of concentrated sulfuric acid, concentrated hydrochloric acid, and phosphotungstic acid.

[0025] Furthermore, the addition amount of the catalyst is 0.2-1.2% of the sum of the masses of the PTA-EG, AA, and HEA.

[0026] Optionally, the addition amount of the catalyst is 1.0% of the sum of the masses of the PTA-EG, AA, and HEA.

[0027] Furthermore, the inhibitor includes at least one of hydroquinone, phenothiazine, and hydroquinone monomethyl ether.

[0028] Furthermore, the addition amount of the inhibitor is 0.8-1.0 wt.% of the sum of the masses of the PTA-EG, AA, and HEA.

[0029] Optionally, the addition amount of the inhibitor is 1.0% of the sum of the masses of the PTA-EG, AA, and HEA.

[0030] Furthermore, the temperature for carrying out the partial esterification reaction by heating is 110-130 °C, and the time is 5-7 h.

[0031] Furthermore, the acid-ether ratio of AA to TPEG in the A material is 2-4.5:1.

[0032] Optionally, the acid-ether ratio of AA to TPEG in the A material is 4:1.

[0033] Furthermore, the mass ratio of the TPEG, water, and PEA mixture is 100:100:0-2.5, and the mass of the PEA mixture is not 0.

[0034] Optionally, the mass ratio of the TPEG, water, and PEA mixture is 100:100:2.

[0035] Furthermore, the chain transfer agent includes at least one of ethylene glycol bis(3-mercaptopropionate), ethylene glycol mercaptoacetate, mercaptopropionic acid, mercaptoacetic acid, and mercaptoethanol.

[0036] Furthermore, the dosage of the chain transfer agent is 0.5-0.9% of the mass of the TPEG.

[0037] Optionally, the dosage of the chain transfer agent is 0.7% of the mass of the TPEG.

[0038] Further, the initiator includes at least one of ammonium persulfate, potassium persulfate, hydrogen peroxide / Vc, sodium persulfate, ammonium persulfate / Vc, and potassium persulfate / Vc.

[0039] Among them, hydrogen peroxide / Vc, ammonium persulfate / Vc, and potassium persulfate / Vc are initiator systems.

[0040] Further, the dosage of the initiator is 0.6 - 1.4% of the mass of the TPEG.

[0041] Optionally, the dosage of the initiator is 1% of the mass of the TPEG.

[0042] Further, the temperature for dropping the A material and the B material is 70 - 90°C, and the time is 60 - 150 min.

[0043] Optionally, the temperature for dropping the A material and the B material is 80°C, and the time is 120 min.

[0044] The second technical solution of the present invention: Provide a water reducer prepared by the above method.

[0045] The third technical solution of the present invention: Provide an application of the above water reducer in the preparation of concrete.

[0046] The present invention discloses the following technical effects:

[0047] The present invention recycles waste PET, uses ethylene glycol as a solvent, and obtains PTA-EG through catalytic degradation. The mixed solution of PTA-EG is used for esterification synthesis of functional monomers, and then the functional monomers are used to replace part of the macromonomers to synthesize a water reducer. When used in the preparation of concrete, the fluidity, slump, and strength of the prepared concrete are relatively good. The water reduction rate of the water reducer can reach 28%, and during the preparation of the water reducer, no process wastewater and waste gas are generated, which is a green and environmentally friendly material. Description of the Drawings

[0048] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0049] Figure 1 Shows the effect of temperature on the alcoholysis rate.

[0050] Figure 2 Shows the effect of time on the alcoholysis rate.

[0051] Figure 3 Shows the effect of the dosage of stannous chloride on the alcoholysis rate.

[0052] Figure 4Effect of mass ratio of PET plastic to ethylene glycol on alcoholysis rate.

[0053] Figure 5 Effect of mass ratio of PTA-EG to AA on PEA solution.

[0054] Figure 6 Effect of mass ratio of HEA to PTA-EG on PEA solution.

[0055] Figure 7 Effect of catalyst dosage on PEA solution.

[0056] Figure 8 Effect of acid-ether ratio on performance of water reducer.

[0057] Figure 9 Effect of dosage of PEA mixture on performance of water reducer.

[0058] Figure 10 Effect of dosage of chain transfer agent on performance of water reducer.

[0059] Figure 11 Effect of initiator dosage on performance of water reducer.

[0060] Figure 12 Effect of reaction temperature on performance of water reducer.

[0061] Figure 13 Effect of reaction time on performance of water reducer.

[0062] Figure 14 Infrared spectrum of PTA-EG.

[0063] Figure 15 Infrared spectrum of water reducer.

[0064] Figure 16 TGA curve of PTA-EG. Detailed implementation manners

[0065] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation manners of the present invention.

[0066] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, 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 may be independently included or excluded from the range.

[0067] 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 only preferred methods and materials are described in this invention, any methods and materials similar or equivalent to those described herein can 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 the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0068] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0069] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0070] It should be noted that those aspects not described in detail in this invention are all conventional operation means in the art and are not the focus of this invention.

[0071] In the specific embodiments of this invention, room temperature and normal temperature both refer to 20 - 30 °C.

[0072] The raw materials and reagents used in the specific embodiments of this invention are all commercially available products. Among them, TPEG with a molecular weight of 2500 is provided by Nanjing Yangzi Chemical Factory; AA with a molecular weight of 72.06 is provided by Zhengzhou Paini Chemical Reagent Factory; 3 - M with a molecular weight of 106.14 is provided by Qingdao Ruisi High - Molecular Materials Co., Ltd.; EG with a molecular weight of 62.08 is provided by Nantong Petrochemical Co., Ltd.

[0073] Example 1

[0074] The preparation steps of PTA - EG include:

[0075] Mix PET plastic, ethylene glycol and stannous chloride, and react at 160 °C for 12 h to obtain PTA - EG;

[0076] Among them, the mass ratio of PET plastic to ethylene glycol is 1:5, and the dosage of stannous chloride is 0.4% of the sum of the masses of PET plastic and ethylene glycol.

[0077] Example 2

[0078] Compared with Example 1, the only difference is that the reaction temperature is 140 °C, 150 °C, 170 °C or 180 °C.

[0079] Example 3

[0080] Compared with Example 1, the only difference is that the reaction time is 6 h, 8 h, 10 h or 14 h.

[0081] Example 4

[0082] Compared with Example 1, the only difference is that the dosage of stannous chloride is 0.1%, 0.2%, 0.3%, 0.5% or 0.6% of the sum of the masses of PET plastic and ethylene glycol.

[0083] Example 5

[0084] Compared with Example 1, the only difference is that the mass ratio of PET plastic to ethylene glycol is 1:2, 1:3, 1:4 or 1:6.

[0085] Test Example 1

[0086] For the methods of preparing PTA-EG in Examples 1-5, the alcoholysis rate was calculated. After the reaction was completed, the reaction solution was filtered. Subsequently, the filter paper was dried to remove the white insoluble substances on the filter paper, and its mass was weighed. The obtained solution was a mixed solution of terephthalic acid and ethylene glycol. The calculation formula of the alcoholysis rate is shown in Equation (1).

[0087]

[0088] Among them, the polyester input amount is the mass of PET, and the particles not passing through the filter paper are the mass of the white insoluble substances.

[0089] Figure 1 Shows the effect of temperature on the alcoholysis rate (Examples 1 and 2). It can be seen from the figure that the alcoholysis rate gradually increases with the increase of temperature. The alcoholysis reaction is an endothermic reaction and requires a relatively high activation energy. When the temperature is below 160 °C, the alcoholysis rate is relatively low. When the reaction temperature exceeds 160 °C, the alcoholysis reaction rate increases rapidly, and the alcoholysis rate obviously increases. This is because, with the increase of temperature, the molecular movement becomes more intense, increasing the collision chance between molecules. Therefore, as the temperature increases, the reaction between ethylene glycol and PET becomes simpler, and the alcoholysis rate can reach 93%. Theoretically speaking, for an endothermic reaction, the higher the temperature, the faster the reaction rate. However, the reaction temperature is not the higher the better. Too high a temperature will cause ethylene glycol to volatilize, the condensation and reflux speed of ethylene glycol to slow down, and the alcoholysis reaction rate to also slow down. Therefore, the alcoholysis rate slightly decreases after exceeding 160 °C.

[0090] Figure 2Effect of time on alcoholysis rate (Examples 1 and 3). As can be seen from the figure, at the beginning of the reaction, the rate of the alcoholysis reaction has been increasing, and the alcoholysis rate shows a linear increase. The alcoholysis rate can reach about 65% when the reaction time is 8 h. After 10 h, a certain amount of the solution was taken to check whether it could dissolve in water, and it was found that most of it dissolved in water. After another 0.5 h, it was found that almost all of it dissolved in water. At 12 h, the alcoholysis rate could reach about 91%. However, since this reaction is reversible, the alcoholysis rate began to decrease after 12 h. Therefore, the best alcoholysis time is 12 h.

[0091] Figure 3 Effect of the amount of stannous chloride (catalyst) on alcoholysis rate (Examples 1 and 4). As can be seen from the figure, the alcoholysis rate increases significantly with the increase in the amount of catalyst. When the amount of catalyst reaches 0.4% of the sum of the masses of PET plastic and ethylene glycol, the alcoholysis rate reaches 93%. Then, when the amount of catalyst is further increased, the alcoholysis rate does not show a significant increase. Therefore, the optimal amount of catalyst is 0.4% of the sum of the masses of PET plastic and ethylene glycol.

[0092] Figure 4 Effect of the mass ratio of PET plastic to ethylene glycol (material ratio) on alcoholysis rate (Examples 1 and 5). As can be seen from the figure, when the mass ratio of ethylene glycol to PET is 3, the measured alcoholysis rate is 50%. When the material ratio increases from 2 to 5, the alcoholysis rate of the polyester material increases significantly. When the input amount of ethylene glycol is further increased, the alcoholysis rate hardly changes. Therefore, a more suitable input amount of ethylene glycol is about 5 times the mass of the polyester, that is, the mass ratio of PET plastic to ethylene glycol is 1:5.

[0093] Example 6

[0094] The preparation steps of the PEA mixture include:

[0095] After mixing the PTA-EG prepared in Example 1 and the polymerization inhibitor (hydroquinone / phenothiazine, mass ratio 9:1), AA and HEA (2-hydroxyethyl acrylate) were added, and finally the catalyst (concentrated sulfuric acid) was added. A partial esterification reaction was carried out at 110 - 120 °C for 5 h to obtain the PEA mixture;

[0096] Among them, the mass ratio of PTA-EG to AA is 1:1.5, the mass ratio of PTA-EG to HEA is 1:1, the amount of the catalyst is 0.8% of the sum of the masses of PTA-EG, AA and HEA, and the amount of the polymerization inhibitor is 1.0% of the sum of the masses of PTA-EG, AA and HEA.

[0097] Example 7

[0098] Compared with Example 6, the difference is only that the mass ratio of PTA-EG to AA is 1:1, 1:2, 1:2.5 or 1:3.

[0099] Example 8

[0100] Compared with Example 6, the difference is only that the mass ratio of HEA to PTA-EG is 1:1.5, 1:2 or 1:2.5.

[0101] Example 9

[0102] Compared with Example 6, the difference is only that the addition amount of the catalyst is 0.2%, 0.4%, 0.6%, 1.0% or 1.2% of the sum of the masses of PTA-EG, AA and HEA.

[0103] Test Example 2

[0104] The methods of Examples 6-9 were compared, and the results are as Figures 5 - 7 shown.

[0105] Esterification rate detection:

[0106] Step 1: Take out 1-2 ml of a certain amount of the reaction mixture sample and place it in a dry and clean conical flask.

[0107] Step 2: Extract the unreacted acid or alcohol.

[0108] Step 3: Titration: For the unreacted acid, add a few drops of phenolphthalein indicator to the conical flask and titrate with a standard base solution (such as 0.1 mol / L sodium hydroxide solution) until the solution color changes from colorless to pink and the color remains unchanged for 30 seconds. For the unreacted alcohol, add a few drops of methyl orange indicator to the conical flask and titrate with a standard acid solution (such as 0.1 mol / L hydrochloric acid solution) until the solution color changes from yellow to orange and the color remains unchanged for 30 seconds.

[0109] Step 4: Calculate the number of moles of the unreacted acid or alcohol according to the volume and concentration of the standard solution consumed during the titration.

[0110] Step 5: Esterification rate (%) = [(number of moles of initial acid or alcohol - number of moles of unreacted acid or alcohol) / number of moles of initial acid or alcohol] × 100%.

[0111] Figure 5The influence of the mass ratio of PTA-EG to AA on the PEA solution. As can be seen from the figure, with the increase in the amount of AA used, the esterification rate of PEA shows an increasing trend. When the mass ratio of PTA-EG to AA is 1:1.5, the partial conversion rate of PTA-EG is relatively high. When the ratio increases to 1:3, the conversion rate in the early stage is already very high. After 6 hours of reaction, it is basically completely converted. Extending the time has no obvious effect, and the product is insoluble in water. In order for the subsequent reaction to proceed normally, it is necessary to control the partial conversion of PTA-EG. Therefore, the mass ratio of PTA-EG to AA is 1:1.5, and the reaction time is 5 hours.

[0112] Figure 6 The influence of the mass ratio of HEA to PTA-EG on the PEA solution. As can be seen from the figure, with the increase in the mass ratio of HEA to PTA-EG, the esterification rate of PEA shows an increasing trend. When the mass ratio of HEA to PTA-EG is 1:1, the partial conversion rate of PTA-EG is relatively high. As the ratio increases, the product begins to stratify, the product is insoluble in water, and the esterification rate is relatively high. In order for the subsequent reaction to proceed normally, it is necessary to control the partial conversion of PTA-EG. Therefore, the mass ratio of HEA to PTA-EG is 1:1, and the reaction time is 5 hours.

[0113] Figure 7 The influence of the addition amount of the catalyst on the PEA solution. As can be seen from the figure, with the increase in the amount of the catalyst used, the catalytic effect is enhanced, the reaction rate is increased, and the esterification rate of the product is increased. When the amount exceeds 1%, the side reactions increase, the reactants are consumed, and the esterification rate of the product is reduced. Therefore, the optimal amount is controlled at 0.8%.

[0114] Example 10

[0115] The preparation steps of the water reducer include:

[0116] After mixing TPEG and water evenly, add the PEA mixed solution prepared in Example 6, stir until completely dissolved, and then dropwise add Material A and Material B at 80°C. Use a peristaltic pump to control the dropping rates of Material A and Material B. The dropping time (reaction time) is 2 / 2.5 h. After the reaction, a water reducer (polycarboxylate water reducer, hereinafter referred to as water reducer) is obtained;

[0117] Among them, Material A is composed of AA and water, and the concentration of AA is 50%; Material B is a chain transfer agent (3-M) and an initiator (hydrogen peroxide / Vc); the acid-ether ratio of AA to TPEG is 4:1; the dosage of the chain transfer agent is 0.7% of the mass of TPEG; the dosage of the initiator is 1% of the mass of TPEG; the mass ratio of TPEG, water and the PEA mixed solution is 100:100:2.

[0118] Example 11

[0119] Compared with Example 10, the only difference is that the acid-ether ratio of AA and TPEG is 2:1, 2.5:1, 3:1, 3.5:1 or 4.5:1.

[0120] Example 12

[0121] Compared with Example 10, the only difference is that the mass ratio of the mixture of TPEG, water and PEA is 100:100:0, 100:100:0.5, 100:100:1.0, 100:100:1.5 or 100:100:2.5.

[0122] Example 13

[0123] Compared with Example 10, the only difference is that the dosage of the chain transfer agent is 0.5%, 0.6%, 0.8% or 0.9% of the mass of TPEG.

[0124] Example 14

[0125] Compared with Example 10, the only difference is that the dosage of the initiator is 0.6%, 0.8%, 1.2% or 1.4% of the mass of TPEG.

[0126] Example 15

[0127] Compared with Example 10, the only difference is that the A material and the B material are added dropwise under the conditions of 70 °C, 75 °C, 85 °C or 90 °C.

[0128] Example 16

[0129] Compared with Example 10, the only difference is that the dropping time (reaction time) is 60 min, 80 min, 100 min or 140 min.

[0130] Test Example 3

[0131] The water reducer prepared in Examples 10 - 16 was supplemented with water to a solid content of 40%. Subsequently, the mixing pot was wetted with a wet towel, 300 g of cement was weighed, and then the water reducer with a solid content of 40% and 87 g of water were added. Stirring was carried out in a neat paste mixer. After the stirring was completed, the paste was immediately poured into a conical mold, and the excess paste on the mold was scraped off with a trowel. Then the mold was slowly lifted vertically upward, and its diameter was measured. The experimental operation should be slow to measure the fluidity of the cement paste more accurately, and the change in the performance of the water reducer was reflected by the fluidity of the cement paste.

[0132] Figure 8Effect of acid-ether ratio on the performance of water reducer (Examples 10 and 11). As can be seen from the figure, the fluidity of cement paste first increases and then decreases with the increase of acid-ether ratio. Different acid-ether ratios are closely related to the density of the side chains of polycarboxylate water reducer molecules. Acrylic acid also provides the main chain for the water reducer, and the carboxyl groups on it can adsorb cement, which can greatly affect the fluidity of cement paste. When the acid-ether ratio is low, the number of carboxylic acid groups is small, resulting in slow adsorption of polycarboxylate water reducer on cement particles and poor dispersibility of cement paste. Other reasons may include that when the amount of acrylic acid is small, the main chain of polycarboxylate water reducer molecules will change, and the most important thing is that the anchoring groups will decrease, and fewer polycarboxylate water reducer molecules are adsorbed on cement particles, which will also lead to poor fluidity of cement paste. With the increase of acid-ether ratio, the fluidity of cement paste also increases. There are other reasons, such as the increase of acrylic acid, the increase of carboxyl groups, the increase of the density of anionic charges, and the enhancement of the repulsion between cement surface particles. When this ratio gradually increases, the long side chain density of pentaerythritol polyoxyethylene ether is large enough to provide a large steric hindrance effect, making the fluidity of cement paste better. However, when this ratio exceeds 4:1, the long side chain density of pentaerythritol polyoxyethylene ether on the main chain decreases, the steric hindrance effect decreases, and the fluidity of cement paste becomes poor. Therefore, the optimal acid-ether ratio is determined to be 4:1.

[0133] Figure 9 Effect of the dosage of PEA mixture on the performance of water reducer (Examples 10 and 12). As can be seen from the figure, the fluidity of cement paste first increases and then decreases with the increase of the mass of PEA mixture. When no PEA mixture is added, the maximum fluidity of cement paste is 180 mm. As a modifier, PEA mixture can improve the fluidity of cement paste, and the effect is good. The hydrophilicity of ethylene glycol and terephthalic acid is very strong. When they come into contact with water, they will fully blend, improving the dispersibility of cement paste. Moreover, ethylene glycol and terephthalic acid will form free radicals and graft copolymerize onto the side chains of water reducer molecules, increasing the length of the molecular chain, thereby affecting its fluidity. When the mass ratio of TPEG, water and PEA mixture is 100:100:2, the fluidity of cement paste reaches the maximum. Therefore, the mass ratio of TPEG, water and PEA mixture is preferably 100:100:2.

[0134] Figure 10Effect of the dosage of chain transfer agent on the performance of water reducer (Examples 10 and 13). As can be seen from the figure, with the increase of the dosage of chain transfer agent, the fluidity of cement paste first increases and then decreases. Especially when the dosage of chain transfer agent increases from 0.6% to 0.7%, the increase in the fluidity of cement paste is particularly obvious. During the synthesis of water reducer molecules, the chain transfer agent is used to adjust the molecular weight of the water reducer. When its dosage is relatively low, the molecular weight of the water reducer is relatively large, which makes it difficult for its structure to unfold between cement particles, reducing the adsorption on the surface of cement particles, thus resulting in a decrease in the fluidity of cement. When the dosage of chain transfer agent exceeds 0.7%, the free radical polymerization reaction in the solution is not easy to proceed, and the conversion rate of the reaction system is relatively low, so the fluidity of cement paste decreases. Therefore, about 0.7% of chain transfer agent is selected to synthesize excellent water reducer.

[0135] Figure 11 Effect of the dosage of initiator on the performance of water reducer (Examples 10 and 14). As can be seen from the figure, the fluidity of cement paste is closely related to the dosage of initiator. When the dosage of initiator is relatively low, the reaction rate is slow, so the fluidity of cement paste is relatively poor. With the increase of the dosage of initiator, the fluidity of cement paste first increases and then decreases. The reason for the increase in the fluidity of cement paste is that the initiator generates a lot of free radicals, which accelerates the polymerization rate. When the dosage of initiator increases to 1.0%, the fluidity of the paste is nearly 260 mm. However, when the dosage of initiator is too high, the phenomenon of explosive polymerization may occur, which also leads to poor dispersion performance of the water reducer and wastes raw materials. Therefore, the dosage of initiator is preferably 1.0%.

[0136] Figure 12 Effect of reaction temperature on the performance of water reducer (Examples 10 and 15). As can be seen from the figure, when the temperature is relatively low, the water reducer can still be initiated at this temperature. However, due to the relatively low reaction temperature, the rate of chain initiation of the redox system is slow, and the monomer dissolves slowly, so the reaction cannot be fully initiated. When the temperature slowly rises, from 70 °C to 80 °C, the rate of chain initiation of the redox system is synchronized with the reaction consumption rate, and the reaction in the solution is in a relatively balanced state, and the reaction efficiency is relatively high. But when the reaction temperature exceeds 80 °C, the decomposition rate of the initiation system is fast, resulting in a sharp decrease in the number of initiators, thus leading to an unreasonable molecular weight distribution of the water reducer and a decrease in the fluidity of cement paste. Therefore, the most suitable reaction temperature is 80 °C.

[0137] Figure 13Effect of reaction time on the performance of water reducing agent (Examples 10 and 16). As can be seen from the figure, the fluidity of cement paste first increases and then decreases with the increase of time. When the reaction time is short, the concentration of material A and material B in the three-necked flask increases rapidly, which will lead to a relatively fast speed of aqueous solution free radical copolymerization reaction, and then lead to an increase in the viscosity of the water reducing agent. Acrylic acid will also self-polymerize, and only a part of the added acrylic acid participates in the copolymerization reaction, and the synergistic effect will become weaker, affecting the molecular weight of the polycarboxylate water reducing agent, thus affecting the fluidity of the cement paste. When the reaction time exceeds 2.5 h, all acrylic acid participates in the copolymerization reaction, and the reaction rates of material A and material B are also appropriate, and the synergistic effect of functional groups is exerted to the extreme, so the fluidity of the cement paste is also improved. Therefore, the best synthesis time for the water reducing agent is 2 / 2.5 h.

[0138] Test Example 4

[0139] The PTA-EG prepared in Example 1 and the water reducing agent prepared in Example 10 were dried in an oven to obtain the corresponding solid particles. The solid particles were crushed and placed at the aperture, and the solid particles were pressed, and then scanning was started for data processing and ATR correction to obtain an infrared spectrogram, and then functional group analysis was carried out. The results are as Figure 14 and Figure 15 shown.

[0140] Figure 14 is the infrared spectrogram of PTA-EG. As can be seen from the figure, the characteristic peak at 3305 cm -1 is related to the stretching vibration of O-H, and the characteristic peaks at 2938 cm -1 and 2874 cm -1 are related to the stretching vibration of C-H. The characteristic peak at 1718 cm -1 is related to the stretching vibration of C=O. The characteristic peaks at 1081 cm -1 and 1036 cm -1 are related to hydroxyl groups, and the characteristic peak at 859 cm -1 is related to the deformation vibration of C-H (para-disubstituted).

[0141] Figure 15 is the infrared spectrogram of the water reducing agent. As can be seen from the figure, the characteristic peaks at 3439 cm -1 and 2882 cm -1 are related to the stretching vibration of O-H. The characteristic peak at 1728 cm -1 is related to the stretching vibration of C=O. The characteristic peak at 1340 cm -1 is related to the stretching vibration of C-O. The characteristic peak at 955 cm -1 is related to the out-of-plane deformation vibration of O-H. The characteristic peak at 843 cm -1 is related to the deformation vibration of C-H (para-disubstituted).

[0142] Test Example 5

[0143] Concrete fluidity, slump and strength test:

[0144] Concrete fluidity refers to the property that the concrete mixture can flow under its own weight or mechanical vibration, and can flow evenly and densely to fill the formwork, which reflects the consistency of the concrete mixture and its ability to fill the formwork. Table 1 shows the composition of the concrete.

[0145] Table 1 Composition of C30 Concrete (g)

[0146]

[0147] The water reducer (solid content 40%) prepared in Example 10 was compared with the same type of water reducer in terms of concrete spread, slump and compressive strength. Specifically:

[0148] The concrete raw materials were mixed evenly according to the above ratio, the water reducer aqueous solution was added and stirred evenly, and then it was poured into the slump cone. Then the slump cone was lifted vertically and steadily, and the concrete at the bottom of the slump was removed. The time of this process is very short. After lifting the slump cone, the height difference between the height of the slump cone and the highest point of the concrete surface and the diameter of the concrete were measured with a ruler, and the slump value and spread of the concrete were obtained as shown in Table 2, and the strength was shown in Table 3.

[0149] Among them, the water reducers were 6C water-reducing type water reducer, denoted as PCE1; compound water reducer (adding 0.1% sodium gluconate), denoted as PCE2; slow-release water reducer, denoted as PCE3; water reducer prepared in Example 10 (solid content 40%), denoted as PCE4.

[0150] Table 2 Concrete Spread and Slump Test

[0151]

[0152] Table 3 Concrete Strength Test

[0153]

[0154] Test Example 6

[0155] Viscosity test:

[0156] Viscosity is a very important factor in measuring the molecular weight of water reducers. First, the Ubbelohde viscometer and the beaker should be cleaned, and an appropriate large rotor should be replaced. Then the water reducer is poured into the beaker so that the rotor is completely immersed in the solution, and stirring is started. Different rotation speeds are adjusted to test the viscosity. The rotation speed adjusted in this experiment is 20 rpm, and the test is repeated twice.

[0157] Viscosity tests were conducted on the high water-reducing type (grade 6C high water-reducing) and PCE4 water-reducing agents, and the test results are shown in Table 4.

[0158] Table 4 Viscosity Test

[0159]

[0160] Test Example 7

[0161] Gel Permeation Chromatography Detection

[0162] GPC molecular weight test is an analytical method used to determine the molecular weight of polymers, also known as gel permeation chromatography. In the field of polymer science and engineering, the molecular weight and molecular weight distribution of polymers are very important parameters, which directly affect the properties and uses of polymers. Therefore, accurately determining the molecular weight of polymers is crucial. In this case, the molecular weight of the water-reducing agent synthesized in Example 10 was tested.

[0163] The molecular weight of the water-reducing agent prepared in Example 10 was tested, and the test results of the number-average molecular weight (Mn), peak molecular weight (Mp), and weight-average molecular weight (Mw) are shown in Table 5.

[0164] Table 5 Gel Permeation Chromatography Detection

[0165]

[0166] Table 5 results show that the peak molecular weight of PCE4 is 32029, the number-average molecular weight is 24756, and the weight-average molecular weight is 45973. The ratio of the weight-average molecular weight to the number-average molecular weight is 1.9, indicating that the molecular weight distribution of the synthesized water-reducing agent is relatively uniform.

[0167] Test Example 8

[0168] PTA-EG Thermogravimetric Analysis

[0169] Thermogravimetric analysis is a method for measuring the relationship between the mass of a substance and temperature or time under programmed temperature control. When the substance being measured sublimates, vaporizes, decomposes to release gas, or loses crystal water during heating, the mass of the substance being measured will change. By analyzing the thermogravimetric curve, we can know what changes have occurred to the substance being measured. Thermogravimetric analysis tests were conducted on the PTA-EG prepared in Example 1.

[0170] 8.717 mg of the sample was placed in the machine, and the temperature range for heating was 30 - 800 °C with a heating rate of 20 °C / min. The thermogravimetric image is as Figure 16 shown.

[0171] Figure 16The TGA curve of PTA-EG is shown in the figure. It can be seen that there are two weight loss stages for PTA-EG. The first weight loss occurs from 128°C to 405°C, and the mass of the substance decreases from 8.57 g to 6.81 g, which is due to the sublimation of terephthalic acid resulting in mass reduction. The second weight loss occurs from 470°C to 700°C, and the curve becomes stable after 700°C.

[0172] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0173] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a water reducing agent based on PET degradation products, characterized in that the steps Comprising: Mix PET, ethylene glycol and stannous chloride, and then carry out a degradation reaction to obtain PTA-EG; Mix the PTA-EG and inhibitor, then add AA and HEA, and finally add a catalyst, and heat to carry out a partial esterification reaction to obtain a PEA mixture; Mix TPEG, water and the PEA mixture to obtain a reaction system, and then dropwise add Material A and Material B, and obtain the water reducing agent after the dropping is completed; Material A is composed of AA and water; Material B includes a chain transfer agent and an initiator.

2. The method according to claim 1, wherein The dosage of stannous chloride is 0.1 wt.% - 0.6 wt.% of the sum of the masses of PET and ethylene glycol; and / or, the temperature of the degradation reaction is 140 - 180 °C, and the time is 6 - 14 h.

3. The method according to claim 1, wherein The mass ratio of PTA-EG to HEA is 1 - 2.5:1; and / or, the mass ratio of PTA-EG to AA is 1:1 - 3.

4. The method according to claim 1, wherein The catalyst includes at least one of concentrated sulfuric acid, concentrated hydrochloric acid and phosphotungstic acid; and / or, the addition amount of the catalyst is 0.2 - 1.2% of the sum of the masses of PTA-EG, AA and HEA.

5. The method according to claim 1, characterized in that, The inhibitor includes at least one of hydroquinone, phenothiazine and methyl hydroquinone; and / or, the addition amount of the inhibitor is 0.8 - 1.0 wt.% of the sum of the masses of PTA-EG, AA and HEA.

6. The method according to claim 1, wherein The temperature for heating to carry out the partial esterification reaction is 110 - 130 °C, and the time is 5 - 7 h.

7. The method according to claim 1, wherein The acid-ether ratio of AA in Material A to TPEG is 2 - 4.5:1; and / or, the mass ratio of TPEG, water and the PEA mixture is 100:100:0 - 2.5, and the mass of the PEA mixture is not 0.

8. The method according to claim 1, characterized in that, The chain transfer agent includes at least one of ethylene glycol bis(3-mercaptopropionate), ethylene glycol mercaptoacetate, mercaptopropionic acid, mercaptoacetic acid and mercaptoethanol; and / or, the dosage of the chain transfer agent is 0.5 - 0.9% of the mass of TPEG; and / or, the initiator includes at least one of ammonium persulfate, potassium persulfate, hydrogen peroxide / Vc, sodium persulfate, ammonium persulfate / Vc and potassium persulfate / Vc; and / or, the dosage of the initiator is 0.6 - 1.4% of the mass of TPEG; and / or, the temperature for dropping Material A and Material B is 70 - 90 °C, and the time is 60 - 150 min.

9. A water reducing agent, characterized in that, The water reducing agent is prepared by the method according to any one of claims 1 - 8.

10. Use of the water reducing agent according to claim 9 in the preparation of concrete.

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