A method for controlling the crystal structure of PET and its application

Abstract

This invention discloses a method for regulating the crystal structure of PET and its application. The method involves first melting the PET product to be recycled at a temperature above 250°C, then transferring it to a crystallization temperature of 200-240°C for at least 1 minute. Through high-temperature isothermal crystallization, the size of the amorphous region between the crystals of the PET product to be recycled is increased. This allows PET-degrading enzymes to partially enter the amorphous region between the crystals and degrade a portion of the PET molecular chain segments inside the spherulites.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a method for regulating the crystal structure of PET and its application. Background Technology

[0002] Polyethylene terephthalate (PET) is widely used in food packaging and textiles due to its excellent thermal stability, mechanical properties, chemical resistance, and safety (non-toxicity). However, PET products are difficult to degrade naturally, making them a significant source of plastic pollution. Therefore, how to efficiently recycle and reuse PET products is a critical issue that urgently needs to be addressed.

[0003] Enzymatic degradation, as a low-energy-consumption and high-yield PET recycling strategy, has attracted much attention in recent years. PET-degrading enzymes can act on the lactone bonds in the PET molecular chain, causing PET to break down and depolymerize. The recovered terephthalic acid (TPA) monomer can then be used as a monomer to resynthesize PET, achieving recycling. Currently, dozens of PET-degrading enzymes have been discovered and extracted in the field of enzyme structural biology, and their degradation efficiency has been improved through genetic modification. The most active PET-degrading enzyme can almost completely degrade amorphous PET within 3.3 hours.

[0004] However, existing bio-enzymes still face challenges in degrading highly crystalline PET products (especially those with a crystallinity higher than 20%). To improve the degradation efficiency of bio-enzymes on PET crystalline regions, researchers have attempted to regulate the microstructure of PET. Currently, common structural regulation methods include the following:

[0005] Chemical modification: This method alters the molecular structure of PET by introducing specific chemical groups. For example, copolymerization modification introduces flexible segments or functional groups, which can improve certain properties of PET to some extent. However, chemical modification is complex, costly, and may affect the original excellent properties of PET, such as thermal stability and mechanical properties. Furthermore, the modification process may introduce new environmental problems, hindering large-scale applications.

[0006] Physical blending: PET is blended with other polymers or additives. This method can adjust the properties of PET to some extent, but the compatibility of the blend is a major challenge. Poor compatibility can lead to phase separation, resulting in uneven material properties and affecting the overall performance of PET products. It also fails to effectively improve the degradation ability of biological enzymes on its crystalline regions.

[0007] Traditional heat treatment methods (such as annealing) involve annealing PET products within a certain temperature range to alter their crystalline structure. However, traditional annealing has a limited temperature range and fails to address the control of PET flake spacing, resulting in limited effectiveness in enhancing the wetting of bio-enzymes in the crystalline regions and failing to fully meet the requirements for promoting the bio-enzymatic degradation of highly crystalline PET.

[0008] In summary, existing methods for regulating the structure of PET products have many shortcomings, and there is an urgent need for a more effective regulation method to improve the degradation efficiency of PET products by biological enzymes and achieve the green recycling of PET products. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for controlling the crystal structure of PET and its application.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] In a first aspect, the present invention proposes a method for controlling the crystal structure of PET, the method comprising:

[0012] The PET products to be recycled are first melted at a temperature above 250°C, and then transferred to a temperature of 200~240°C for at least 1 minute to crystallize.

[0013] Preferably, the process also includes post-treatment of the crystallized product, which includes natural cooling at room temperature.

[0014] Preferably, the melting temperature is 270°C and the melting time is 3 minutes.

[0015] Preferably, the crystallization temperature is 230°C and the crystallization time is 1-60 min.

[0016] Preferably, the crystallinity of the PET article is higher than 20%.

[0017] Secondly, this invention proposes a method for improving the bio-enzymatic degradation efficiency of PET, comprising:

[0018] By using the above method to regulate PET products, PET products with regulated crystal structure are obtained;

[0019] PET products with regulated crystal structure are used as substrates for PET bioenzymes.

[0020] The beneficial effects of this invention are at least as follows:

[0021] This invention proposes to expand the intercrystalline spacing of PET sheets through high-temperature isothermal crystallization, which exposes the amorphous regions within the spherulites more effectively, providing more favorable conditions for enzyme action on the PET molecular chains and promoting the degradation of PET molecular chain segments inside the spherulites.

[0022] The PET substrate preparation process of this invention is relatively simple and easy to implement, involving only conventional steps such as melting, isothermal crystallization, and natural cooling, without the need for complex equipment or cumbersome processes. Furthermore, by precisely controlling process parameters such as melting temperature, crystallization temperature, and crystallization time, the PET crystal structure can be effectively regulated, exhibiting high controllability and repeatability. This makes the method easier to operate and promote in practical production and applications, facilitating large-scale processing of PET products, improving recycling efficiency, and reducing processing costs.

[0023] This invention provides a method for promoting the bio-enzymatic degradation of PET products, which facilitates the recycling of PET. The degradation product, terephthalic acid (TPA) monomer, can be used as a polymerization monomer to resynthesize PET, forming a closed-loop cycle. This not only reduces dependence on primary petroleum resources and lowers energy consumption and carbon emissions during PET production, but also improves resource utilization, aligning with the concept of sustainable development and playing a significant role in promoting the green circular economy of the PET industry. Attached Figure Description

[0024] Figure 1 Crystallinity data for PET substrates prepared in comparative examples and Examples 1-3.

[0025] Figure 2 The data shows the dimensions of the amorphous regions between the crystallites of the PET substrates prepared in comparative examples and Examples 1-3.

[0026] Figure 3 This is a comparative data set showing the ratio of spherulite mass in the PET substrates prepared in the comparative examples and Examples 1-3 to the ratio of the remaining PET substrate mass after degradation. Detailed Implementation

[0027] The embodiments and examples of the present invention will be described in detail below. However, those skilled in the art will understand that the following embodiments and examples are for illustrative purposes only and should not be considered as limiting the scope of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specified, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0028] It should be noted that:

[0029] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0030] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0031] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0032] As is known from the background art, existing methods for controlling the structure of PET products have many shortcomings. Therefore, this invention provides a more effective control method to improve the degradation efficiency of PET products by bio-enzymes, thereby achieving the green recycling of PET products. The inventors discovered that semi-crystalline PET products consist of μm-sized spherulites and amorphous regions between the spherulites, with the spherulites containing nm-sized lamellar crystals and amorphous regions between them. During bio-enzyme degradation, the amorphous regions between the spherulites are more easily degraded, while the spherulites themselves are more difficult to degrade. This is the main reason why highly crystalline PET products are difficult to degrade. From a molecular level, both the bio-enzyme and the amorphous regions between PET lamellar crystals are nm-sized, and their size matching relationship may be a key factor restricting the enzyme's degradation of the crystalline regions of PET. Therefore, the bio-enzyme degradation efficiency can be promoted by controlling the microstructure of PET.

[0033] Therefore, in one aspect, at least one embodiment provides a method for controlling the crystal structure of PET, the method comprising:

[0034] First, the PET products to be recycled undergo high-temperature melting treatment. This step aims to completely melt the PET products, eliminating their original crystalline structure and providing a uniform melt state for the subsequent isothermal crystallization process. The melting temperature is above 250°C, typically but not limiting, for example, 250°C, 260°C, 265°C, 270°C, 275°C, 280°C, or 285°C. The melting time is at least 1 minute, typically but not limiting, for example, 2 minutes, 3 minutes, 4 minutes, 5 minutes, or 6 minutes.

[0035] Next, the molten PET product is rapidly transferred to a high-temperature crystallization process. During this process, the PET molecular chains begin to rearrange and crystallize. By precisely controlling the crystallization temperature and time, the interlamellar spacing can be regulated. The crystallization temperature is typically 200–240°C, but not limited to, for example, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, or 240°C. The crystallization time is at least 1 minute, but not limited to, for example, 1 minute, 4 minutes, 5 minutes, 16 minutes, 30 minutes, 45 minutes, or 60 minutes.

[0036] In a preferred embodiment, the crystallized product is further subjected to post-processing, which includes natural cooling at room temperature to allow the PET product to finally form a state with a specific crystal structure, thereby obtaining a PET substrate for bioenzymatic degradation.

[0037] On the other hand, at least one embodiment provides a method for improving the bio-enzymatic degradation efficiency of PET, comprising:

[0038] By using the above method to regulate PET products, PET products with regulated crystal structure are obtained;

[0039] PET products with regulated crystal structure are used as substrates for PET bioenzymes.

[0040] The following will describe in detail some typical embodiments that embody the features and advantages of the present invention. It should be understood that the present invention can have many variations in different embodiments, all of which do not depart from the scope of the present invention. Furthermore, the descriptions and illustrations herein are for illustrative purposes only and are not intended to limit the present invention.

[0041] The PET products used in the following examples are manufactured by Goodfellow in the UK and have a thickness of 0.25 mm.

[0042] Example 1

[0043] The PET products to be recycled were melted at 260°C for 3 minutes and then transferred to 230°C for 4 minutes to crystallize. After that, they were allowed to cool naturally at room temperature to obtain PET substrates for bio-enzymatic degradation.

[0044] Take 10 mg of the above PET substrate and add 50 nL of FAST-PETase-N212A / N277A enzyme (5 μg / mL) to form a 1 mL mixture. Place the mixture in a 50 mM glycine, pH 9.0 buffer solution for degradation testing at 50 °C. The product amount was determined and analyzed by high-performance liquid chromatography (HPLC) every 24 h. The analytical column was an InertSustain C18 column (4.6 × 250 mm, 5 μm), the mobile phase was methanol / phosphate (20 mM, pH 2.5), the flow rate was 1 mL / min, the detection wavelength was 254 nm, the elution conditions were 0–15 min, and the methanol linear gradient was 35%–70%.

[0045] Example 2

[0046] The PET products to be recycled were melted at 270°C for 3 minutes and then transferred to 235°C for 16 minutes to crystallize. After that, they were allowed to cool naturally at room temperature to obtain PET substrates for bio-enzymatic degradation.

[0047] Take 10 mg of the above PET substrate and add 50 nL of FAST-PETase-N212A / N277A enzyme (5 μg / mL) to form a 1 mL mixture. Place the mixture in a 50 mM glycine, pH 9.0 buffer solution for degradation testing at 50 °C. The product amount was determined and analyzed by high-performance liquid chromatography (HPLC) every 24 h. The analytical column was an InertSustain C18 column (4.6 × 250 mm, 5 μm), the mobile phase was methanol / phosphate (20 mM, pH 2.5), the flow rate was 1 mL / min, the detection wavelength was 254 nm, the elution conditions were 0–15 min, and the methanol linear gradient was 35%–70%.

[0048] Example 3

[0049] The PET products to be recycled were melted at 285°C for 3 minutes and then transferred to 240°C for 60 minutes to crystallize. After that, they were allowed to cool naturally at room temperature to obtain PET substrates for bio-enzymatic degradation.

[0050] Take 10 mg of the above PET substrate and add 50 nL of FAST-PETase-N212A / N277A enzyme (5 μg / mL) to form a 1 mL mixture. Place the mixture in a 50 mM glycine, pH 9.0 buffer solution for degradation testing at 50 °C. The product amount was determined and analyzed by high-performance liquid chromatography (HPLC) every 24 h. The analytical column was an InertSustain C18 column (4.6 × 250 mm, 5 μm), the mobile phase was methanol / phosphate (20 mM, pH 2.5), the flow rate was 1 mL / min, the detection wavelength was 254 nm, the elution conditions were 0–15 min, and the methanol linear gradient was 35%–70%.

[0051] Comparative Example

[0052] The PET products to be recycled were annealed at 110°C for 24 hours and then allowed to cool naturally at room temperature to obtain PET substrates for bio-enzymatic degradation.

[0053] Take 10 mg of the above PET substrate and add 50 nL of FAST-PETase-N212A / N277A enzyme (5 μg / mL) to form a 1 mL mixture. Place the mixture in a 50 mM glycine, pH 9.0 buffer solution for degradation testing at 50 °C. The product amount was determined and analyzed by high-performance liquid chromatography (HPLC) every 24 h. The analytical column was an InertSustain C18 column (4.6 × 250 mm, 5 μm), the mobile phase was methanol / phosphate (20 mM, pH 2.5), the flow rate was 1 mL / min, the detection wavelength was 254 nm, the elution conditions were 0–15 min, and the methanol linear gradient was 35%–70%.

[0054] By comparing various data during the degradation process of Examples 1-3 and the Comparative Example, such as changes in crystallinity, changes in the size of amorphous regions between lamellar crystals, changes in the mass ratio of spherulites, and the remaining mass ratio of PET substrate after degradation, etc. (e.g.) Figure 1-3 As shown in the figure, the significant effect of the method of the present invention in promoting the bio-enzymatic degradation of PET products can be clearly seen. The cold crystallization sample (comparative example) has a crystallinity of over 20% ( Figure 1 and smaller interlamellar amorphous region size ( Figure 2 After degradation, the remaining mass ratio of the PET substrate is much greater than the mass ratio of the internal spherulites. Figure 3 This indicates that the degrading enzyme cannot penetrate the spherulites to achieve degradation; while the high-temperature isothermal crystallized samples (Examples 1-3), even with a crystallinity higher than 20%, ( Figure 1 ), due to its significantly increased size of the amorphous region between lamellar crystals ( Figure 2After degradation, the remaining mass ratio of the PET substrate is still less than the mass ratio of the spherulites. Figure 3 This indicates that the degrading enzyme can enter the interior of the spherulites and degrade the amorphous regions therein. Therefore, the isothermal crystallization treatment method of the present invention can effectively regulate the PET crystal structure, improve the wetting ability of the bio-enzyme in the crystal region, and thus significantly improve the bio-enzymatic degradation efficiency of highly crystalline PET products, providing a more advantageous solution for the recycling of PET products.

[0055] In summary, this invention increases the size of the amorphous region between PET flakes from ~6 nm to ~12 nm through isothermal crystallization at 200~240℃. This allows PET-degrading enzymes with a size of approximately 5 nm to partially enter the amorphous region between the flakes and degrade a portion of the PET molecular chain segments within the spherulites. This method reveals a "size-matching" mechanism for the infiltration of bioenzymes within spherulites and can therefore guide further research into bioenzymatic degradation methods for PET products.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the bio-enzymatic degradation efficiency of PET, characterized in that, The method includes: The PET products to be recycled are first melted at a temperature above 250°C, then transferred to a temperature of 200-240°C for crystallization for at least 1 minute, and then allowed to cool naturally at room temperature to obtain PET products with regulated crystal structure. The selection of crystallization temperature and time is based on increasing the interlamellar spacing of the obtained PET products and exposing the amorphous regions within the spherulites more effectively. PET products with regulated crystal structure are used as substrates for PET bio-enzymatic degradation.

2. The method according to claim 1, characterized in that, The melting temperature is 270℃ and the melting time is 3 minutes.

3. The method according to claim 1, characterized in that, The crystallization temperature is 230℃, and the crystallization time is 1-60 min.

4. The method according to claim 1, characterized in that, The crystallinity of the PET product is higher than 20%.

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