Polyester core material and preparation method thereof, wind turbine blade skin and wind turbine blade

Abstract

The present application provides a polyester core material and a preparation method thereof, a wind turbine blade skin, and a wind turbine blade. The polyester core material includes a modified polyester, wherein the modified polyester material introduces a chain segment of bisphenol A diglycidyl ether and a chain segment of methyltetrahydrophthalic acid into a PET material, and the molar ratio of the chain segment of bisphenol A diglycidyl ether to the chain segment of ethylene glycol is controlled to be 1:(10-50). A higher content of rigid structure groups and a greater spatial internal resistance can be introduced into the PET material, so that its number average molecular weight and molecular weight distribution are within a suitable range, and the modified polyester molecules are difficult to move, thereby simultaneously improving the heat resistance and mechanical properties of the PET.

Description

Technical Field

[0001] The present application belongs to the technical field of polyester materials, and specifically relates to a polyester core material and a preparation method thereof, a wind turbine blade skin, and a wind turbine blade. Background Art

[0002] Polyethylene terephthalate (PET) core material is primarily made by mixing PET resin with a blowing agent and foaming it. The performance of PET core material depends primarily on the properties of the PET resin used. PET resin is inexpensive, exhibits low abrasion resistance, high hardness, is non-toxic, exhibits excellent weather and chemical resistance, has low water absorption, and is resistant to weak acids and organic solvents. It is one of the most cost-effective plastic resins, hence its widespread use.

[0003] However, the heat resistance and mechanical properties of PET resins are less than ideal, and it is particularly difficult to obtain PET resins with both good heat resistance and mechanical properties. Although there are methods to modify PET resins by increasing the molecular weight of PET or introducing functional additives, these methods still fail to effectively achieve both heat resistance and mechanical properties, such as tensile strength and yield strength. Summary of the Invention

[0004] The present application provides a polyester core material and a preparation method thereof, a wind turbine blade skin and a wind turbine blade, aiming to simultaneously improve the heat resistance and mechanical properties of the polyester core material.

[0005] In a first aspect, the present application provides a polyester core material, comprising a modified polyester, wherein the modified polyester comprises segments represented by the following formulas 1, 2, 3, and 4:

[0006]

[0007]

[0008] The segment represented by formula 1 is connected to the segment represented by formula 3 or formula 4; the segment represented by formula 4 is connected to the segment represented by formula 1 or formula 2; the molar ratio of the segment represented by formula 1 to that represented by formula 2 is 1:(10-50).

[0009] In a feasible embodiment of the first aspect of the present application, the modified polyester satisfies at least one of the following conditions:

[0010] a. The molar ratio of the chain segments represented by formula 4 to formula 3 is 1:(10-50);

[0011] b. The ratio of the total molar amount of the segments represented by Formula 1 and Formula 2 to the total molar amount of the segments represented by Formula 3 and Formula 4 is 1:(0.6 to 2), optionally 1:(1.0 to 1.5);

[0012] c. The weight of the chain segments represented by Formula 1 and Formula 4 accounts for 1% to 20% of the total weight of the modified polyester.

[0013] In a feasible embodiment of the first aspect of the present application, the modified polyester satisfies at least one of the following conditions:

[0014] d. The number average molecular weight of the modified polyester is 20,000Da to 30,000Da;

[0015] e. The molecular weight distribution of the modified polyester is 1.5 to 2.2;

[0016] f. The hydroxyl value of the modified polyester is 50 mgKOH / g to 150 mgKOH / g.

[0017] In a feasible embodiment of the first aspect of the present application, the melt viscosity of the modified polyester is 250 Pa·s to 520 Pa·s; and / or the heat deformation temperature of the modified polyester is 100°C to 120°C.

[0018] In a feasible embodiment of the first aspect of the present application, the ultimate tensile strength of the modified polyester is 40 MPa to 55 MPa; and / or the yield strength of the modified polyester is 35 MPa to 50 MPa.

[0019] In a feasible embodiment of the first aspect of the present application, the polyester core material also includes a foaming agent, and the mass ratio of the modified polyester to the foaming agent is 1:(0.2~0.8); optionally, the foaming agent includes one or more of azodicarbonamide, azobisisobutyronitrile and azodiacetate.

[0020] The second aspect of the present application provides a method for preparing the polyester core material provided in the first aspect of the present application, comprising:

[0021] Providing a degradation product of a pultruded plate material for a wind turbine blade, wherein the degradation product of the pultruded plate material for a wind turbine blade comprises components of the chain segments shown in Formulas 1 and 4;

[0022] The degradation product of the wind turbine blade pultruded sheet is mixed with terephthalic acid and ethylene glycol to obtain a modified polyester;

[0023] The modified polyester and the foaming agent are mixed and expanded to obtain a polyester core material.

[0024] In a feasible embodiment of the second aspect of the present application, in the step of providing a degradation product of a wind turbine blade pultruded plate, wherein the degradation product of the wind turbine blade pultruded plate includes components of the chain segments represented by Formulas 1 and 4, the hydroxyl value of the degradation product of the wind turbine blade pultruded plate is 300 mg KOH / g to 400 mg KOH / g.

[0025] In a feasible implementation manner of the second aspect of the present application, in the step of mixing the degradation products of the wind turbine blade pultruded sheet with terephthalic acid and ethylene glycol to obtain modified polyester, the degradation products of the wind turbine blade pultruded sheet are reacted with terephthalic acid and ethylene glycol in an inert atmosphere and a vacuum degree of 0Pa to 10Pa at 240°C to 300°C for 5h to 12h to obtain modified polyester.

[0026] In a feasible embodiment of the second aspect of the present application, the step of mixing the modified polyester and the foaming agent and expanding them to obtain a polyester core material includes mixing and stirring the modified polyester and the foaming agent in a mass ratio of 1:(0.2 to 0.8), stirring for 2 hours to 10 hours in a nitrogen atmosphere at 240°C to 260°C, and cooling to room temperature to set to obtain a PET core material.

[0027] A third aspect of the present application provides a wind turbine blade skin, comprising the polyester core material provided in the first aspect of the present application.

[0028] A fourth aspect of the present application provides a wind turbine blade, comprising the wind turbine blade skin provided by the third aspect of the present application.

[0029] The polyester core material of the present application includes modified polyester, wherein the modified polyester material uses a component including the chain segment shown in the above formula 1 (for example, a degradation product of bisphenol A diglycidyl ether containing terminal hydroxyl groups obtained by hydrolysis of wind turbine blade pultrusion resin) to replace part of ethylene glycol, and a component including the chain segment shown in the above formula 4 (for example, methyltetrahydrophthalic acid containing carboxyl groups obtained by hydrolysis of wind turbine blade pultrusion resin) to replace part of terephthalic acid. The chain segments shown in the above formulas 1 and 4 are introduced into the PET material (the chain segments shown in formulas 2 and 3) through the condensation reaction of hydroxyl groups and carboxyl groups. A higher content of rigid structure groups and greater spatial internal resistance can be introduced into the PET material, making it difficult for the modified polyester molecules to move, thereby simultaneously improving the heat resistance and mechanical properties of PET.

[0030] Furthermore, the present application controls the molar ratio of the chain segments shown in Formula 1 and Formula 2 to 1:(10-50), thereby making the PET material less susceptible to degradation, so that its number average molecular weight, molecular weight distribution, and hydroxyl value are within a suitable range, thereby improving the problems of decreased number average molecular weight, wide molecular weight distribution, and decreased viscosity of the PET material, and at the same time improving the heat resistance and mechanical properties of PET. DETAILED DESCRIPTION

[0031] In order to make the invention purpose, technical solution and beneficial technical effect of this application clearer, this application is further described in detail with reference to the following embodiments. It should be understood that the embodiments described in this specification are only for explaining this application and are not intended to limit this application.

[0032] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value can serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0033] In the description herein, when a composition is described as containing, comprising or including specific components, or when a process is described as containing, comprising or including specific process steps, it is intended that the composition of the present application also consists essentially of or consists of the components, and the process of the present application also consists essentially of or consists of the process steps.

[0034] The use of the terms "including," "comprising," "containing," and "having" should generally be construed as open ended and non-limiting unless expressly stated otherwise.

[0035] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number themselves, and “a variety” in “one or more” means more than two.

[0036] The above summary of the invention of this application is not intended to describe every disclosed embodiment or every implementation in this application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, the enumeration is intended only as a representative group and should not be construed as exhaustive.

[0037] The inventors have discovered that PET's properties can be improved by increasing its molecular weight, such as by introducing chain extenders to diversify its branches, or by adding other resins or functional additives. However, these methods have limited effectiveness. Furthermore, since chain extension is typically performed on the original PET molecular weight, it can easily result in an excessively large molecular weight distribution, at least 3 or 4 or more. This large molecular weight distribution of PET results in high viscosity and a low glass transition temperature, limiting improvements in mechanical properties and heat resistance.

[0038] In view of this, the present application provides a polyester core material and a preparation method thereof, a wind turbine blade skin and a wind turbine blade, aiming to simultaneously improve the heat resistance and mechanical properties of the PET core material.

[0039] In an embodiment of the first aspect of the present application, a polyester core material is provided, comprising a modified polyester, wherein the modified polyester comprises segments represented by the following formulas 1, 2, 3, and 4:

[0040]

[0041] The segment represented by formula 1 is connected to the segment represented by formula 3 or formula 4; the segment represented by formula 4 is connected to the segment represented by formula 1 or formula 2; the molar ratio of the segment represented by formula 1 to that represented by formula 2 is 1:(10-50).

[0042] The polyester core material of the present application includes a modified polyester and a foaming agent, wherein the modified polyester material uses a component including the chain segment shown in the above formula 1 (for example, a degradation product of bisphenol A diglycidyl ether containing terminal hydroxyl groups obtained by hydrolysis of a wind turbine blade pultrusion resin) to replace part of the ethylene glycol, and a component including the chain segment shown in the above formula 4 (for example, methyltetrahydrophthalic acid containing carboxyl groups obtained by hydrolysis of a wind turbine blade pultrusion resin) to replace part of the terephthalic acid. The chain segments shown in the above formulas 1 and 4 are introduced into the PET material (the chain segments shown in formulas 2 and 3) through the condensation reaction of hydroxyl groups and carboxyl groups, and a higher content of rigid structure groups and greater spatial internal resistance can be introduced into the PET material, making it difficult for the modified polyester molecules to move, thereby simultaneously improving the heat resistance and mechanical properties of the PET.

[0043] Furthermore, the present application controls the molar ratio of the chain segments shown in Formula 1 and Formula 2 to 1:(10-50), thereby making the PET material less susceptible to degradation, so that its number average molecular weight, molecular weight distribution, and hydroxyl value are within a suitable range, thereby improving the problems of decreased number average molecular weight, wide molecular weight distribution, and decreased viscosity of the PET material, and at the same time improving the heat resistance and mechanical properties of PET.

[0044] Furthermore, this application involves modifying the PET material at the front end of its production process, partially replacing ethylene glycol and phthalic acid. This avoids chain extension on the original PET molecular weight, which results in a wide molecular weight distribution, thereby further improving the thermal resistance and mechanical properties of PET. For example, there are methods that modify the PET material at the back end after its production. This method is prone to a wide molecular weight distribution, often compromising the mechanical properties and thermal stability of the PET material, resulting in limited improvement.

[0045] At the same time, since the present application introduces a plurality of benzene rings with hydrophobic groups, the water resistance of the modified PET material can be enhanced to improve the comprehensive performance of the PET resin.

[0046] For example, the chain segments shown in Formula 1, Formula 2, Formula 3 and Formula 4 in the modified polyester can be connected in a manner that is one or more of Formula 1-Formula 3-Formula 2-Formula 4, Formula 1-Formula 3-Formula 4-Formula 2, Formula 1-Formula 4-Formula 3-Formula 2, Formula 1-Formula 4-Formula 2-Formula 3, Formula 1-Formula 3-Formula 1-Formula 4-Formula 2, Formula 1-Formula 3-Formula 2-Formula 3-Formula 4 and Formula 2-Formula 4-Formula 2-Formula 3-Formula 1-Formula 3. For example, the reaction formula of the modified polyester can be as follows

[0047] As shown in formula 5.

[0048]

[0049] The raw materials of the chain segments represented by Formula 1, Formula 2, Formula 3 and Formula 4 in the polyester core material in the present application can be recycled wind turbine blade-related materials, such as wind turbine blade pultruded plates, wind turbine blade skins, or can be from other materials.

[0050] For example, the substances comprising the chain segments represented by Formula 1 and Formula 4 in the polyester material of the present application can both be derived from degradation products of thermosetting resins in recycled wind turbine blade pultruded plates. For example, they can be derived from degradation products of bisphenol A diglycidyl ethers containing terminal hydroxyl groups and methyltetrahydrophthalic acid, respectively.

[0051] Vigorously developing renewable energy, reducing fossil energy consumption, and building a green and low-carbon energy system are important measures to control global warming and achieve carbon emission reduction targets. Wind turbine blades, as the key core components of wind turbines to capture wind energy, are leading the development of wind turbines towards high power and large-scale. Among them, wind turbine blade pultruded plates usually use continuous fibers (such as glass fibers and carbon fibers) as reinforcing materials. Through resin matrix impregnation, they obtain higher mechanical properties than vacuum infusion molding processes, especially the compression performance in the 0° direction can be increased by nearly doubled. The application of pultruded plates makes the design and manufacture of ultra-large wind turbine blades possible.

[0052] Pultruded boards are typically made from thermosetting resins and glass or carbon fiber yarns through a pultrusion process. Literature reports [Dissolution of epoxy thermosets via mild alcoholysis: the mechanism and kinetics study.], [Recycling of Epoxy Thermoset and Composites via GoodSolvent Assisted and Small Molecules Participated Exchange Reactions], and [Bonafide upcycling strategy of anhydride cured epoxy and reutilization of decomposed dual monomers into multipurpose applications, Lin Shao, Yu-Chung Chang, Baoming Zhao, Xinyan Yan, Brian J. Bliss, Ming-en Fei, Chenhao Yu, Jinwen Zhang, Chemical Engineering Journal, Volume 464, 2023, 142735] indicate that anhydride-cured epoxy resins, which have a similar structure to pultruded resins, can be degraded using alkaline hydrolysis, theoretically enabling the separation of fibers and resin in pultruded boards. However, the high-value utilization of wind turbine blade degradation products, such as bisphenol A diglycidyl ether and methyltetrahydrophthalic acid, remains a technical bottleneck for this technology. Therefore, developing high-value applications for pultruded board degradation resin products is a key challenge facing the alkaline hydrolysis degradation solution for pultruded board.

[0053] The inventors analyzed that the reasons why the degradation products of wind turbine blade pultruded sheets, including degradation products of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid, have not been utilized in a high-value manner may be: 1) wind turbine blade pultruded sheets are currently a relatively cutting-edge technical field, and the degradation of wind turbine blade pultruded sheets is even more cutting-edge. In addition, the cost of degrading wind turbine blade pultruded sheets is high, and the economic efficiency is poor, resulting in less research data; 2) the content of epoxy resin in wind turbine blade pultruded sheets is relatively low, with a mass content of only about 10% to 20%, making it difficult to be utilized in a high-value manner; 3) the composition of the degradation products of wind turbine blade pultruded sheets is complex, and it is difficult to find a suitable parameter, range or standard to evaluate whether they can be utilized; 4) due to the complexity of the degradation products and the almost no past research data, whether they can generate application value by adding them to other materials is a blank technical field and is difficult.

[0054] The present application overcomes the defect that the degradation products of thermosetting resins in wind turbine blade pultruded plates are difficult to be utilized in a high-value manner by controlling the hydroxyl value of the degradation products of the wind turbine blade pultruded plates within a suitable range, for example, 300 mg KOH / g to 400 mg KOH / g. The degradation products of thermosetting resins in wind turbine blade pultruded plates, such as bisphenol A diglycidyl ether degradation products and methyltetrahydrophthalic acid, are successfully introduced into PET materials. The wind turbine blade pultruded plates are combined with PET materials for application, which not only realizes the high-value application of the degradation products of the wind turbine blade pultruded plates, but also comprehensively improves the performance of the PET material, for example, simultaneously improves the heat resistance and mechanical strength of the PET material, and has high application value.

[0055] Furthermore, the present application can control the amount of bisphenol A diglycidyl ether degradation products and methyltetrahydrophthalic acid introduced, for example, the percentage of the weight of the chain segments contained therein to the total weight of the modified PET material is within a suitable range, for example, the molar ratio of the segments shown in Formula 4 to Formula 3, the ratio of the total molar amount of the segments shown in Formulas 1 and 2 to the total molar amount of the segments shown in Formulas 3 and 4, so as to affect the terminal carboxyl group content and the ester group content in the modified polyester, so that the content of both is lower, thereby further improving the mechanical properties, thermal stability and water resistance of PET.

[0056] For example, in some embodiments, the modified polyester satisfies at least one of the following conditions:

[0057] a. The molar ratio of the chain segments represented by formula 4 to formula 3 is 1:(10-50);

[0058] b. The ratio of the total molar amount of the segments represented by Formula 1 and Formula 2 to the total molar amount of the segments represented by Formula 3 and Formula 4 is 1:(0.6 to 2), optionally 1:(1.0 to 1.5);

[0059] c. The weight of the chain segments represented by Formula 1 and Formula 4 accounts for 1% to 20% of the total weight of the modified polyester.

[0060] In this application, the PET material is modified at the front end. The resulting modified PET material has a number average molecular weight of 20,000 to 30,000 Da, with a narrow molecular weight distribution of 1.5 to 2.2. The low hydroxyl value can enhance the heat resistance and mechanical properties of the modified polyester, such as tensile strength and yield strength. Furthermore, the water resistance, curing speed, hardness, and mechanical properties of the PET material can be improved.

[0061] For example, in some embodiments, the modified polyester satisfies at least one of the following conditions:

[0062] d. The number average molecular weight of the modified polyester is 20,000Da to 30,000Da, optionally 25,000Da to 29,000Da;

[0063] e. The molecular weight distribution of the modified polyester is 1.5 to 2.2;

[0064] f. The hydroxyl value of the modified polyester is 50 mgKOH / g to 150 mgKOH / g.

[0065] The modified PET material of the present application has excellent heat resistance. For example, in some embodiments, the modified polyester has a melt viscosity of 250 Pa·s to 520 Pa·s; and / or a heat deformation temperature of 100°C to 120°C, optionally 109°C to 120°C.

[0066] The modified PET material of the present application not only has excellent heat resistance but also high mechanical strength. For example, in some embodiments, the modified polyester has an ultimate tensile strength of 40 MPa to 55 MPa, optionally 43 MPa to 55 MPa; and / or a yield strength of 35 MPa to 50 MPa, optionally 36 MPa to 50 MPa.

[0067] In some embodiments, the polyester core material further includes a foaming agent, and the mass ratio of the modified polyester to the foaming agent is 1:(0.2-0.8); optionally, the foaming agent includes one or more of azodicarbonamide, azobisisobutyronitrile and azodiacetate.

[0068] In an embodiment of the second aspect of the present application, a method for preparing the polyester core material provided in the first aspect of the present application is provided, comprising:

[0069] Providing degradation products of a pultruded plate material for a wind turbine blade, wherein the degradation products of the pultruded plate material for a wind turbine blade include components having structures shown in Formula 1 and Formula 4 respectively;

[0070] The degradation product of the wind turbine blade pultruded sheet is mixed with terephthalic acid and ethylene glycol to obtain a modified polyester;

[0071] The modified polyester and the foaming agent are mixed and expanded to obtain a polyester core material.

[0072] The inventors discovered that when the hydroxyl value of the degradation products of the wind turbine blade pultruded sheet is controlled within a certain range, such as within the range of 300 mg KOH / g to 400 mg KOH / g, the degradation products of the thermosetting resin in the wind turbine blade pultruded sheet, such as bisphenol A diglycidyl ether degradation products and methyltetrahydrophthalic acid, can be introduced into the PET material to improve the heat resistance and mechanical strength of the PET material, thereby realizing the high-value application of the degradation products of the wind turbine blade pultruded sheet.

[0073] In some embodiments, in the step of providing a degradation product of a wind turbine blade pultruded plate, wherein the degradation product of the wind turbine blade pultruded plate includes components having structures represented by Formula 1 and Formula 4, respectively, the degradation product of the wind turbine blade pultruded plate has a hydroxyl value of 300 mg KOH / g to 400 mg KOH / g.

[0074] In some embodiments, the step of mixing the degradation products of the wind turbine blade pultruded sheet with terephthalic acid and ethylene glycol to obtain the modified polyester includes the step of conducting a polycondensation reaction of the degradation products of the wind turbine blade pultruded sheet with terephthalic acid and ethylene glycol in an inert atmosphere and a vacuum degree of 0Pa to 10Pa at 240°C to 300°C for 5h to 12h to obtain the modified polyester.

[0075] In some embodiments, the step of mixing the modified polyester and the foaming agent and expanding them to obtain a polyester core material includes mixing and stirring the modified polyester and the foaming agent in a mass ratio of 1:(0.2-0.8), stirring for 2h-10h in a nitrogen atmosphere at 240°C-260°C, and cooling to room temperature to set the shape to obtain a PET core material.

[0076] In an embodiment of the third aspect of the present application, a wind turbine blade skin is provided, comprising the polyester core material provided in the first aspect of the present application.

[0077] In an embodiment of the fourth aspect of the present application, a wind turbine blade skin is provided, comprising the wind turbine blade skin provided by the third aspect of the present application.

[0078] The present application can first obtain degradation products by degrading discarded wind turbine blade pultruded sheets, then control the hydroxyl value of the degradation products within a certain range, and apply the high-value degradation products of the wind turbine blade pultruded sheets to PET to obtain a PET core material with excellent heat resistance and mechanical properties. The PET core material can then be prepared into a wind turbine blade skin, and the wind turbine blade skin can be further assembled into a wind turbine blade, thereby realizing the long-term recycling of wind turbine blade materials and effectively integrating the resources of wind turbine blades. This is of great significance to environmental protection, production costs, and resource utilization, and is conducive to sustainable development.

[0079] Example

[0080] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0081] Example 1

[0082] This embodiment provides a method for preparing a modified PET core material, comprising: obtaining degradation products of a pultruded wind turbine blade sheet having a hydroxyl value of ˜350 mg KOH / g, wherein the degradation products include degradation products of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid, and subjecting the degradation products of the pultruded wind turbine blade sheet to a polycondensation reaction with terephthalic acid and ethylene glycol in an inert atmosphere and a vacuum of 10 Pa at 300° C. for 5 hours to obtain a modified PET resin.

[0083] The molar ratio of bisphenol A diglycidyl ether to ethylene glycol is controlled to be 1:30, the molar ratio of methyltetrahydrophthalic acid to terephthalic acid is controlled to be 1:25, the ratio of the total molar amount of bisphenol A diglycidyl ether and ethylene glycol to the total molar amount of methyltetrahydrophthalic acid and terephthalic acid is controlled to be 1:1, and the weight of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid accounts for 8% of the total weight of the modified PET resin.

[0084] The modified PET resin and azodicarbonamide were mixed at a mass ratio of 1:0.5, stirred at 250° C. for 4 h in a nitrogen atmosphere, and cooled to room temperature to set, thereby obtaining a PET core material.

[0085] Examples 2 to 8

[0086] Example 2, compared with Example 1, mainly differs in that the molar ratio of methyltetrahydrophthalic acid to terephthalic acid is changed to 1:50, other conditions such as the molar ratio of bisphenol A diglycidyl ether to ethylene glycol is 1:30, the ratio of the total molar amount of bisphenol A diglycidyl ether and ethylene glycol to the total molar amount of methyltetrahydrophthalic acid and terephthalic acid is 1:1, and the weight percentage of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid to the total weight of the modified PET resin is adaptively adjusted.

[0087] Example 3, compared with Example 1, mainly differs in that the molar ratio of methyltetrahydrophthalic acid to terephthalic acid is changed to 1:10, other conditions such as the molar ratio of bisphenol A diglycidyl ether to ethylene glycol is 1:30, the ratio of the total molar amount of bisphenol A diglycidyl ether and ethylene glycol to the total molar amount of methyltetrahydrophthalic acid and terephthalic acid is 1:1, and the weight percentage of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid to the total weight of the modified PET resin is adaptively adjusted.

[0088] Example 4, compared with Example 1, mainly differs in that the weight of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid is changed to 20% of the total weight of the modified polyester, and other conditions such as the molar ratio of bisphenol A diglycidyl ether to ethylene glycol is 1:30, the ratio of the total molar amount of bisphenol A diglycidyl ether and ethylene glycol to the total molar amount of methyltetrahydrophthalic acid and terephthalic acid is 1:1, and the molar ratio of methyltetrahydrophthalic acid to terephthalic acid is adaptively adjusted.

[0089] Example 5, compared with Example 1, the main difference is that the ratio of the total molar amount of bisphenol A diglycidyl ether and ethylene glycol to the total molar amount of methyltetrahydrophthalic acid and terephthalic acid is changed to 1:1.5, and the other conditions are that the molar ratio of bisphenol A diglycidyl ether to ethylene glycol is 1:30, the molar ratio of methyltetrahydrophthalic acid to terephthalic acid is 1:25, and the weight percentage of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid to the total weight of the modified PET resin is adaptively changed.

[0090] Example 6, compared with Example 1, the main difference is that the ratio of the total molar amount of bisphenol A diglycidyl ether and ethylene glycol to the total molar amount of methyltetrahydrophthalic acid and terephthalic acid is changed to 1:0.67, and the other conditions are that the molar ratio of bisphenol A diglycidyl ether to ethylene glycol is 1:30, the molar ratio of methyltetrahydrophthalic acid to terephthalic acid is 1:25, and the weight percentage of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid to the total weight of the modified PET resin is adaptively changed.

[0091] Example 7, compared with Example 1, is mainly different in that the degradation product of the wind turbine blade pultruded plate having a hydroxyl value of ˜500 mg KOH / g is used in the preparation method.

[0092] Example 8, compared with Example 1, mainly differs in that, in the preparation method, commercial PET pellets are used instead of terephthalic acid and ethylene glycol, and then degradation products of wind turbine blade pultruded sheets with a hydroxyl value of ~350 mg KOH / g are added for modification to obtain a modified PET material.

[0093] Comparative Examples 1 to 3

[0094] Comparative Example 1 is different from Example 1 in that only the chain segment shown in Formula 1 and bisphenol A diglycidyl ether are introduced into the modified PET resin.

[0095] Comparative Example 2, compared with Example 1, is mainly different in that only the chain segment shown in Formula 4 and methyltetrahydrophthalic acid are introduced into the modified PET resin.

[0096] Comparative Example 3, compared with Example 1, the main difference is that the molar ratio of bisphenol A diglycidyl ether to ethylene glycol in the modified PET resin is changed to 1:55, the other conditions are that the molar ratio of methyltetrahydrophthalic acid to terephthalic acid is 1:25, the ratio of the total molar amount of bisphenol A diglycidyl ether and ethylene glycol to the total molar amount of methyltetrahydrophthalic acid and terephthalic acid is 1:1, and the mass percentage of the weight of bisphenol A diglycidyl ether and methyltetrahydrophthalic acid to the total weight of the modified PET resin is adaptively changed.

[0097] The properties of the modified PET resins prepared in the examples and comparative examples were tested, and the test results are shown in Tables 1 and 2 below.

[0098] Measurement method

[0099] Number average molecular weight: determined according to ASTM D5296 / ASTM D6226.

[0100] Molecular weight distribution: refer to ASTM D5296 / ASTM D6226 standards.

[0101] Hydroxyl value: refer to ASTM D4274 standard.

[0102] Melt viscosity: measured in accordance with ASTM D3835 / ISO 11443.

[0103] Heat distortion temperature: refer to ASTM D648 standard.

[0104] Ultimate tensile strength: Refer to ISO 527 standard.

[0105] Yield strength: Refer to ISO 527 standard.

[0106] Table 1 Physical and chemical property test data of PET resin in various embodiments and comparative examples

[0107]

[0108]

[0109] Table 2 Test data of heat resistance and mechanical properties of PET resin in various embodiments and comparative examples

[0110]

[0111] As can be seen from Tables 1 and 2, the modified PET resin of the present application examples obtained samples with excellent heat resistance and mechanical properties by introducing the chain segments represented by Formula 1 and Formula 4 and controlling the ratio of the introduced amounts. Among them, Comparative Examples 1 and 2 did not simultaneously introduce the chain segments represented by Formula 1 and Formula 2, and the heat resistance and mechanical strength were reduced, especially the heat deformation temperature, ultimate tensile strength, and yield strength. Although Comparative Example 3 introduced the chain segments represented by Formula 1 and Formula 2, the introduction amount of the chain segment represented by Formula 1 was small and the ethylene glycol was high, which may lead to poor polymerization reaction of the PET material, a decrease in the number average molecular weight, an increase in the molecular distribution, and a significant decrease in both heat resistance and mechanical properties. This shows that the introduction of the chain segments represented by Formula 1 and Formula 4 and the ratio of the introduced amounts are very important for improving the heat resistance and mechanical properties of the modified PET resin.

[0112] In addition, the inventors have also found through experimental research that the amount of the chain segment shown in Formula 4, the total amount of the chain segments shown in Formulas 1 and 4, the total amount of the chain segments shown in Formulas 1 and 2, and the total amount of the chain segments shown in Formulas 3 and 4 can be controlled to further improve the heat resistance and mechanical properties of PET. As can be seen from Examples 1 to 3, the increase in the amount of the chain segment shown in Formula 4 can increase the rigid groups in the polymer molecular structure, thereby improving the heat resistance and mechanical properties. As can be seen from Examples 1, 4 to 6, the proportion of the total amount of the chain segments shown in Formulas 1 and 4, the proportion of the total amount of the chain segments shown in Formulas 1 and 2 to the total amount of the chain segments shown in Formulas 3 and 4 can be controlled within a suitable range, and the number average molecular weight, molecular weight distribution, and hydroxyl value of the modified polyester can be controlled within a suitable range, thereby increasing the number average molecular weight, reducing the molecular weight distribution, and further improving the performance of PET.

Claims

1. A polyester core material, characterized in that: The polyester core material includes modified polyester, wherein the modified polyester includes segments shown in the following formulas 1, 2, 3 and 4: The segment represented by Formula 1 is connected to the segment represented by Formula 3 or Formula 4; the segment represented by Formula 4 is connected to the segment represented by Formula 1 or Formula 2; The molar ratio of the chain segments represented by Formula 1 to Formula 2 is 1:(10-50); The molar ratio of the chain segments represented by Formula 4 to those represented by Formula 3 is 1:(10-50); The number average molecular weight of the modified polyester is 20,000 Da to 30,000 Da.

2. The polyester core material according to claim 1, characterized in that The modified polyester satisfies at least one of the following characteristics: a. The ratio of the total molar amount of the segments represented by Formula 1 and Formula 2 to the total molar amount of the segments represented by Formula 3 and Formula 4 is 1:(0.6 to 2); b. The weight of the chain segments represented by Formula 1 and Formula 4 accounts for 1% to 20% of the total weight of the modified polyester.

3. The polyester core material according to claim 2, characterized in that: The ratio of the total molar amount of the segments represented by Formula 1 and Formula 2 to the total molar amount of the segments represented by Formula 3 and Formula 4 is 1:(1.0-1.5).

4. The polyester core material according to claim 1, characterized in that The modified polyester satisfies at least one of the following characteristics: c. The molecular weight distribution of the modified polyester is 1.5 to 2.2; d. The hydroxyl value of the modified polyester is 50 mgKOH / g to 150 mgKOH / g.

5. The polyester core material according to claim 1, characterized in that The melt viscosity of the modified polyester is 250 Pa·s to 520 Pa·s.

6. The polyester core material according to claim 1, characterized in that The heat deformation temperature of the modified polyester is 100° C. to 120° C.

7. The polyester core material according to claim 1, characterized in that: The ultimate tensile strength of the modified polyester is 40 MPa to 55 MPa.

8. The polyester core material according to claim 1, characterized in that The yield strength of the modified polyester is 35 MPa to 50 MPa.

9. The polyester core material according to claim 1, characterized in that: The polyester core material also includes a foaming agent, and the mass ratio of the modified polyester to the foaming agent is 1:(0.2-0.8).

10. The polyester core material according to claim 9, characterized in that: The foaming agent includes one or more of azodicarbonamide, azobisisobutyronitrile and azodiacetate.

11. The method for preparing a polyester core material according to any one of claims 1 to 10, wherein: include: Providing a degradation product of a wind turbine blade pultruded plate, wherein the degradation product of the wind turbine blade pultruded plate comprises components of the chain segments represented by Formula 1 and Formula 4; allowing the degradation product of the wind turbine blade pultruded plate to react with terephthalic acid and ethylene glycol to obtain a modified polyester; The modified polyester and a foaming agent are mixed and expanded to obtain the polyester core material.

12. The method for preparing a polyester core material according to claim 11, characterized in that: In the step of providing a degradation product of a wind turbine blade pultruded plate, wherein the degradation product of the wind turbine blade pultruded plate includes components of the chain segments represented by Formula 1 and Formula 4, the hydroxyl value of the degradation product of the wind turbine blade pultruded plate is 300 mg KOH / g to 400 mg KOH / g.

13. The method for preparing a polyester core material according to claim 11, characterized in that: The step of mixing the degradation product of the wind turbine blade pultruded sheet with terephthalic acid and ethylene glycol to obtain the modified polyester includes reacting the degradation product of the wind turbine blade pultruded sheet with terephthalic acid and ethylene glycol in an inert atmosphere and a vacuum degree of 0Pa to 10Pa at 240°C to 300°C for 5h to 12h to obtain the modified polyester.

14. The method for preparing a polyester core material according to claim 11, wherein: The step of mixing the modified polyester and the foaming agent and expanding them to obtain the polyester core material includes mixing and stirring the modified polyester and the foaming agent in a mass ratio of 1:(0.2-0.8), stirring for 2h-10h under a nitrogen atmosphere at 240°C-260°C, and cooling to room temperature to set the shape to obtain the polyester core material.

15. A wind turbine blade skin, characterized in that: The invention comprises the polyester core material according to any one of claims 1 to 10.

16. A wind turbine blade, characterized in that: Including the wind turbine blade skin according to claim 15.

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