Nano-composite chain extender with core-shell structure as well as preparation method and application of nano-composite chain extender

Abstract

The invention provides a nano-composite chain extender with a core-shell structure as well as a preparation method and application of the nano-composite chain extender. The preparation method of the nano-composite chain extender comprises the following steps: (1) dispersing TiO2 nano-particles in a trihydroxymethyl aminomethane buffer solution, then adding dopamine hydrochloride, and carrying out polymerization reaction to form a polydopamine coating layer on the TiO2 nano-particles, so as to obtain modified titanium dioxide; and (2) mixing the modified titanium dioxide, styrene-glycidyl methacrylate and an acrylate monomer, adding an initiator, and reacting to obtain the nano composite chain extender with the core-shell structure. The prepared nano-composite chain extender is applied to PET recovery treatment, broken molecular chains of the recovered PET can be repaired, the intrinsic viscosity of regenerated PET is improved to be close to the original PET level, the tensile strength of the prepared regenerated polyester fiber can be improved to 80-95 MPa, the elongation at break is improved by 20-30%, and the prepared regenerated polyester fiber has the advantages of being high in mechanical strength, good in mechanical property and good in mechanical property. And an efficient and environment-friendly solution is provided for the application of the regenerated PET in the fields of high-performance textiles, engineering plastics and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of PET recycling, and particularly to a nano-composite chain extender with a core-shell structure, a preparation method thereof, and an application thereof. Background Art

[0002] With the global emphasis on sustainable development and circular economy, the research and development of recycled polyester fibers has become a hot issue in the textile and materials fields. However, during the multiple reprocessing of recycled PET, thermal oxidative degradation and hydrolysis reactions are likely to occur, resulting in problems such as molecular chain breakage, an increase in the content of terminal carboxyl groups, and a decrease in molecular weight, seriously weakening the mechanical properties and processing stability of the fibers.

[0003] Traditionally, small molecule chain extenders are used to repair PET molecular chains, such as oxazoline-based or epoxy-based chemicals, but there are the following defects. Firstly, small molecule chain extenders are prone to volatilization or have poor compatibility with the PET matrix and are difficult to disperse uniformly, resulting in insufficient reaction sites. Secondly, the chain extender is prone to decomposition during high-temperature processing, triggering side reactions and causing gelation or yellowing phenomena. In recent years, nano-particle modified chain extenders have attracted attention due to their high specific surface area and designability. For example, titanium dioxide nano-particles have excellent photocatalytic activity and stability, but their surface has strong hydrophilicity, is prone to agglomeration in a water-transporting polymer matrix, and has insufficient chemical binding force with PET end groups, resulting in interfacial defects. In the prior art, silane coupling agents or surface grafting modification are usually used to improve the dispersibility, but the process is complex, and the modified layer is prone to peeling off during melt processing.

[0004] Based on this, there is an urgent need for a new type of nano-composite chain extender that can not only efficiently repair PET molecular chains but also has excellent dispersibility, thermal stability, and multifunctional characteristics to meet the requirements of high-performance and high-value utilization of recycled polyester fibers. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] In view of the deficiencies of the prior art, the present invention provides a nano-composite chain extender with a core-shell structure, a preparation method thereof, and an application thereof, solving the problems raised in the above background art.

[0007] (2) Technical Solutions

[0008] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0009] According to the first aspect of the present invention, a preparation method of a nano-composite chain extender with a core-shell structure is provided, including the following steps:

[0010] (1) Disperse TiO2 nanoparticles in tris (hydroxymethyl) aminomethane buffer solution, then add dopamine hydrochloride, and carry out a polymerization reaction to form a polydopamine coating layer on the TiO2 nanoparticles to obtain modified titanium dioxide;

[0011] (2) Mix the modified titanium dioxide, styrene-glycidyl methacrylate and acrylate monomer, add an initiator, and react to obtain a nano-composite chain extender with a core-shell structure.

[0012] In this application, dopamine hydrochloride forms strong coordination bonds with the TiO2 surface through catechol and amino groups. At the same time, its hydrophobic surface improves the compatibility with the PET matrix, reduces the agglomeration of nanoparticles. The thickness of the polydopamine coating layer formed on the TiO2 nanoparticles is 5-15 nm. By regulating the thickness of the polydopamine coating layer, the rigid support of the TiO2 core can be retained, and covalent bonding can occur between the amino or quinone groups remaining on the surface and the epoxy groups of the shell copolymer, enabling a stable chemical connection between the core and the shell.

[0013] Preferably, in step (1), the particle size of the TiO2 nanoparticles is 20-50 nm;

[0014] The pH of the tris (hydroxymethyl) aminomethane buffer solution is 8.5-9.0.

[0015] Preferably, in step (1), the addition amount of dopamine hydrochloride is 0.5-2.0% of the TiO2 nanoparticles;

[0016] The temperature of the polymerization reaction is 40-60 °C, and the time is 12-24 h.

[0017] Preferably, in step (2), the mass ratio of the modified titanium dioxide, styrene-glycidyl methacrylate and acrylate monomer is 1-3: 3-5: 1;

[0018] The addition amount of the initiator is 0.5-1.5% of the acrylate monomer;

[0019] The acrylate monomer is selected from at least one of methyl methacrylate and butyl acrylate;

[0020] The initiator is selected from potassium persulfate or ammonium persulfate.

[0021] Preferably, in step (2), the temperature of the reaction is 75-85 °C, and the time is 6-8 h.

[0022] According to the second aspect of the present invention, there is provided a nano-composite chain extender obtained by the above preparation method. The nano-composite chain extender includes a shell layer and a core layer. The shell layer is a styrene-glycidyl methacrylate-acrylate copolymer, and the core layer is titanium dioxide.

[0023] Preferably, the particle size of the nano-composite chain extender is 80 - 150 nm, and the shell thickness accounts for 30 - 40% of the total diameter of the nano-composite chain extender particles.

[0024] According to the third aspect of the present invention, a method for preparing recycled polyester fiber is provided. The above-mentioned nano-composite chain extender with a core-shell structure is mixed with recycled PET fragments, and then an antioxidant, a hydrolysis inhibitor, and a lubricant are added. Through co-blending and spinning by a twin-screw extruder under a partition temperature and a high-shear screw configuration, the recycled polyester fiber is obtained.

[0025] In this application, the epoxy groups in the shell of the nano-composite chain extender undergo a ring-opening reaction with the terminal carboxyl or terminal hydroxyl groups of recycled PET, directly repairing the broken PET molecular chains, improving the intrinsic viscosity and the chain entanglement density. The acrylate segments in the shell form a physical cross-linking network with the PET molecular chains through van der Waals forces and chain segment interpenetration, enhancing the interfacial stress transfer efficiency and inhibiting crack propagation. The TiO2 nano-core is uniformly dispersed in the PET matrix as a rigid filler, and hinders the molecular chain slip through the "pinning effect", improving the tensile strength. At the same time, the shell on the surface of the TiO2 nano-core can prevent the direct exposure of TiO2 and prevent its photocatalytic activity from causing PET degradation.

[0026] Preferably, the mass of the nano-composite chain extender is 0.3 - 2.0% of the mass of the recycled PET fragments;

[0027] The total addition amount of the antioxidant, the hydrolysis inhibitor, and the lubricant is 0.5 - 2.0% of the mass of the recycled PET fragments. Among them, the mass ratio of the antioxidant, the hydrolysis inhibitor, and the lubricant is 3 - 5:2 - 4:1.

[0028] Specifically, the antioxidant is selected from the hindered phenol antioxidant 168 and the phosphite antioxidant 626. Among them, the mass ratio of the hindered phenol antioxidant 168 to the phosphite antioxidant 626 is 1 - 2:1;

[0029] The hydrolysis inhibitor is selected from at least one of polycarbodiimide, benzotriazole derivatives, and triallyl cyanurate;

[0030] The lubricant is selected from at least one of calcium stearate, polyethylene wax, and ethylene bis-stearamide.

[0031] Preferably, the process parameters of the twin-screw extruder are: the temperature of the first zone is 255 - 265 °C, the temperature of the second zone is 265 - 275 °C, the temperature of the third zone is 270 - 280 °C, the temperature of the die head is 275 - 285 °C, the screw speed is 200 - 350 r / min, and the vacuum degree is ≤ -0.08 MPa.

[0032] (III) Beneficial effects

[0033] The present invention provides a nano-composite chain extender with a core-shell structure, a preparation method thereof and an application. It has the following beneficial effects:

[0034] (1) In the nano-composite chain extender with a core-shell structure provided by this solution, the styrene-glycidyl methacrylate (GMA) copolymer shell layer of the core-shell chain extender is rich in epoxy groups, which can undergo efficient ring-opening reactions with the terminal carboxyl groups (-COOH) and terminal hydroxyl groups (-OH) of recycled PET during melt processing to directly repair the broken molecular chains. The polydopamine in the core layer is combined with TiO2 through Ti-O coordination bonds and is covalently linked to the copolymer in the shell layer through amino / quinone groups to form a rigid core-flexible shell structure.

[0035] (2) In the preparation method of recycled polyester fiber provided by this solution, the prepared nano-composite chain extender is used. The glycidyl methacrylate in the shell layer of the nano-composite chain extender undergoes a ring-opening reaction with the terminal carboxyl groups of PET through epoxy groups to directly repair the molecular chain breakage caused by degradation, increasing the intrinsic viscosity of recycled PET to 0.95 - 1.1 dL / g, making it close to the level of virgin PET. The core layer in the nano-composite chain extender hinders the slippage of PET molecular chains through the "pinning effect" to increase the tensile modulus. The flexible copolymer shell layer forms a "chemical bond + physical crosslinking" dual interface through epoxy chemical bonding and physical entanglement of acrylate segments, increasing the tensile strength of the recycled polyester fiber to 80 - 95 MPa and the elongation at break by 20 - 30%. Description of the Drawings

[0036] Figure 1 XRD diagram of a nano-composite chain extender provided in Example 1 of the present invention;

[0037] Figure 2 SEM schematic diagram of a nano-composite chain extender provided in Example 1 of the present invention;

[0038] Figure 3 SEM schematic diagram of a recycled polyester fiber provided by the present invention. Detailed Embodiments

[0039] In order to better illustrate and elaborate the content of the present invention, the following will be described in detail with specific examples.

[0040] Example 1

[0041] A preparation method of a nano-composite chain extender with a core-shell structure is obtained through the following preparation method:

[0042] Preparation of modified titanium dioxide (TiO2@PDA): 100 g of titanium dioxide nanoparticles with a particle size of 30 nm were dispersed in 1 L of tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.8, and then 1 g of dopamine hydrochloride was added. The mixture was stirred and reacted at 50 °C for 18 h, followed by centrifugation, washing, and drying to obtain modified titanium dioxide, where the thickness of the polydopamine coating layer was approximately 10 nm;

[0043] Preparation of nano composite chain extender: 100 g of modified titanium dioxide, 150 g of styrene-glycidyl methacrylate, and 70 g of methyl methacrylate were mixed, and 1 g of potassium persulfate was added. The mixture was subjected to suspension polymerization at 80 °C for 7 h to obtain a nano composite chain extender with a core-shell structure.

[0044] The structure of the nano composite chain extender prepared in this example is as Figure 1 and Figure 2 shown. The core layer of the nano composite chain extender is modified titanium dioxide coated with polydopamine, and the shell layer is a copolymer of styrene-glycidyl methacrylate-acrylate. The particle size of the nano composite chain extender is approximately 100 nm, and the proportion of the shell layer thickness is 35%.

[0045] Example 2

[0046] The preparation method of this example is the same as that of Example 1, except that the addition amount of dopamine hydrochloride is 2 g, and the thickness of the polydopamine coating layer on the surface of the obtained modified titanium dioxide is 15 nm; the particle size of the prepared nano composite chain extender is approximately 100 nm, and the proportion of the shell layer thickness is 40%.

[0047] Example 3

[0048] The preparation method of this example is the same as that of Example 1, except that the addition amount of dopamine hydrochloride is 0.5 g, and the thickness of the polydopamine coating layer on the surface of the obtained modified titanium dioxide is 8 nm. The particle size of the prepared nano composite chain extender is approximately 80 nm, and the proportion of the shell layer thickness is 30%.

[0049] Comparative Example 1

[0050] A preparation method of a nano composite chain extender includes the following steps:

[0051] 100 g of titanium dioxide nanoparticles with a particle size of 30 nm, 60 g of styrene-glycidyl methacrylate, and 15 g of methyl acrylate were mixed, and 0.2 g of potassium persulfate was added. The mixture was subjected to suspension polymerization at 80 °C for 7 h to obtain a nano composite chain extender, and the prepared nano composite chain extender could not form a complete core-shell structure.

[0052] Comparative Example 2

[0053] A preparation method of a nano composite chain extender, comprising the following steps:

[0054] Preparation of modified titanium dioxide (TiO2@PDA): Disperse 100 g of titanium dioxide nanoparticles with a particle size of 30 nm in 1 L of tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.8, then add 1 g of dopamine hydrochloride, stir and react at 50 °C for 18 h, centrifuge, wash and dry to obtain modified titanium dioxide, wherein the thickness of the polydopamine coating layer is about 10 nm;

[0055] Preparation of the nano composite chain extender: Mix 100 g of modified titanium dioxide, 100 g of styrene-glycidyl methacrylate and 33 g of methyl methacrylate, wherein the mass ratio of styrene-glycidyl methacrylate to methyl methacrylate is 2:1, add 0.5 g of potassium persulfate, and carry out suspension polymerization reaction at 80 °C for 7 h to obtain a nano composite chain extender with a core-shell structure.

[0056] Application Example 1

[0057] Mix 1 kg of recycled PET fragments with a limiting viscosity of 0.68 dL / g and 10 g of the nano composite chain extender prepared in Example 1, then add 2 g of a mixture of hindered phenol antioxidant 168 and phosphite antioxidant 626, 1 g of carbodiimide and 1 g of calcium stearate, and carry out co-blending spinning through a twin-screw extruder under a sectional temperature and a high-shear screw configuration, wherein the temperature of the first zone of the twin-screw extruder is 260 °C, the temperature of the second zone is 270 °C, the temperature of the third zone is 275 °C, the temperature of the die head is 280 °C, the screw speed is 300 rpm, and the vacuum degree is -0.09 MPa to obtain recycled polyester fibers. The cross-sectional view of the recycled polyester fibers is as shown in Figure 3 shown. It can be seen that the nano composite chain extender is uniformly dispersed inside the PET fibers, and the fibers prepared therefrom have significantly enhanced comprehensive properties such as thermal properties.

[0058] Application Example 2

[0059] The preparation method of this application example is the same as that of Application Example 1, except that the nano composite chain extender prepared in Example 2 is used.

[0060] Application Example 3

[0061] The preparation method of this application example is the same as that of Application Example 1, except that the nano composite chain extender prepared in Example 3 is used.

[0062] Comparative Application Example 1

[0063] The preparation method of this comparative application example is the same as that of Application Example 1, except that the nano composite chain extender prepared in Comparative Example 1 is used.

[0064] Comparative Application Example 2

[0065] The preparation method of this comparative application example is the same as that of Application Example 1, except that the nano-composite chain extender prepared in Comparative Example 2 is used.

[0066] Comparative Application Example 3

[0067] In this comparative application example, 10 g of epoxy chain extender ADR-4370 was mixed with 1 kg of recycled PET chips, and then 2 g of a mixture of hindered phenol antioxidant 168 and phosphite antioxidant 626, 1 g of carbodiimide and 1 g of calcium stearate were added. The mixture was melt-spun by a twin-screw extruder under a zoned temperature and a high-shear screw configuration. The temperature of the first zone of the twin-screw extruder was 260 °C, the temperature of the second zone was 270 °C, the temperature of the third zone was 275 °C, the head temperature was 280 °C, the screw speed was 300 rpm, and the vacuum degree was -0.09 MPa, obtaining recycled polyester fibers.

[0068] Comparative Application Example 4

[0069] The preparation method of this comparative application example is the same as that of the application example, except that the temperature of the first zone of the twin-screw extruder is 240 °C and the head temperature is 260 °C.

[0070] The recycled polyester fibers prepared in Application Examples 1 to 3 and Comparative Application Examples 1 to 4 were respectively subjected to performance tests, and the intrinsic viscosity, tensile strength, and elongation at break of the recycled polyester fibers were respectively measured, as shown in Table 1.

[0071] Table 1

[0072]

[0073]

[0074] According to the data in Table 1, it can be seen that without coating TiO2, the performance will decrease significantly due to agglomeration. By modifying TiO2 with PDA coating, the dispersibility and interfacial bonding ability are improved, and thus the intrinsic viscosity and tensile properties of the prepared recycled polyester fibers can reach the level of virgin PET; changing the shell monomer ratio of the nano-composite chain extender results in insufficient epoxy group density and a significant decrease in chain extension efficiency; compared with traditional small molecule chain extenders, the core-shell structured chain extender prepared in this example has high chain extension ability; when the temperature of the twin-screw process is insufficient, the PET is not fully melted and the chain extension reaction is not sufficient, resulting in a decrease in the intrinsic viscosity of the recycled polyester fibers.

[0075] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a nano-composite chain extender with a core-shell structure, characterized in that: It includes the following steps: (1) Dispersing TiO2 nanoparticles in tris(hydroxymethyl)aminomethane buffer solution, adding dopamine hydrochloride, and carrying out a polymerization reaction to form a polydopamine coating layer on the TiO2 nanoparticles to obtain modified titanium dioxide; (2) Mixing the modified titanium dioxide, styrene-glycidyl methacrylate, and acrylate monomer, adding an initiator, and reacting to obtain a nano-composite chain extender with a core-shell structure.

2. The preparation method of a nano composite chain extender with a core-shell structure according to claim 1, characterized in that: In step (1), the particle size of the TiO2 nanoparticles is 20 - 50 nm; The pH of the tris(hydroxymethyl)aminomethane buffer solution is 8.5 - 9.

0.

3. The preparation method of a nano-composite chain extender with a core-shell structure according to claim 1, characterized in that: In step (1), the addition amount of dopamine hydrochloride is 0.5 - 2.0% of the TiO2 nanoparticles; The temperature of the polymerization reaction is 40 - 60 °C, and the time is 12 - 24 h.

4. The preparation method of a nano-composite chain extender with a core-shell structure according to claim 1, characterized in that: In step (2), the mass ratio of the modified titanium dioxide, styrene-glycidyl methacrylate, and acrylate monomer is 1 - 3:3 - 5:1; The addition amount of the initiator is 0.5 - 1.5% of the acrylate monomer; The acrylate monomer is selected from at least one of methyl methacrylate and butyl acrylate; The initiator is selected from potassium persulfate or ammonium persulfate.

5. The preparation method of a nano-composite chain extender with a core-shell structure according to claim 1, characterized in that: In step (2), the temperature of the reaction is 75 - 85 °C, and the time is 6 - 8 h.

6. A nano-composite chain extender obtained by the preparation method according to any one of claims 1 to 5, characterized in that: The nano-composite chain extender includes a shell layer and a core layer. The shell layer is a styrene-glycidyl methacrylate-acrylate copolymer, and the core layer is titanium dioxide.

7. The nano-composite chain extender with a core-shell structure according to claim 6, characterized in that: The particle size of the nano-composite chain extender is 80 - 150 nm, and the shell layer thickness accounts for 30 - 40% of the total diameter of the nano-composite chain extender particles.

8. A method for preparing regenerated polyester fiber, characterized in that: Mixing the nano-composite chain extender obtained by the preparation method according to any one of claims 1 to 5 or the nano-composite chain extender according to claim 6 or 7 with recycled PET fragments, adding an antioxidant, a hydrolysis-resistant agent, and a lubricant, and carrying out co-blending spinning through a twin-screw extruder under a partition temperature and a high-shear screw configuration to obtain the recycled polyester fiber.

9. The preparation method of a regenerated polyester fiber according to claim 8, characterized in that: The mass of the nano-composite chain extender is 0.3 - 2.0% of the recycled PET fragments; The total addition amount of the antioxidant, the hydrolysis-resistant agent, and the lubricant is 0.5 - 2.0% of the recycled PET fragments. Among them, the mass ratio of the antioxidant, the hydrolysis-resistant agent, and the lubricant is 3 - 5:2 - 4:

1.

10. The preparation method of a regenerated polyester fiber according to claim 8, characterized in that: The process parameters of the twin-screw extruder are: the temperature of the first zone is 255 - 265 °C, the temperature of the second zone is 265 - 275 °C, the temperature of the third zone is 270 - 280 °C, the temperature of the die head is 275 - 285 °C, the screw speed is 200 - 350 r / min, and the vacuum degree is ≤ -0.08 MPa.

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