A method for preparing UV-resistant recycled lunch box polypropylene fiber

Abstract

The invention relates to a method for preparing an anti-ultraviolet recycled lunch box polypropylene fiber, and the preparation steps are as follows: (1) melt blending the recycled lunch box polypropylene and hindered phenol monomer (3,5-di-tert-butyl-4-hydroxyphenylpropionic acid), and after the reaction, the melt is subjected to twin-screw extrusion granulation; (2) the particles obtained in step (1) are subjected to twin-screw reactive blending extrusion granulation with initiator dibenzoyl peroxide and aliphatic ring secondary amine olefin monomer to obtain spinning slices; (3) the spinning slices are subjected to melt spinning to obtain the anti-ultraviolet recycled lunch box polypropylene fiber; the anti-ultraviolet recycled lunch box polypropylene fiber has a breaking strength of 2.85-3.66 cN / dtex, an elongation at break of 23-27%, and a breaking strength retention rate of 97-98%, 93-95% and 85-90% after ultraviolet irradiation for 12h, 24h and 72h, respectively. The invention effectively solves the problem that it is difficult to recycle and reuse waste lunch box polypropylene and the product added value is low.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling polypropylene plastic products and relates to a method for preparing UV-resistant recycled lunch box polypropylene fibers. Background Art

[0002] As the online food delivery market grows, more than 100 million disposable lunch boxes are consumed every day, generating a large amount of waste. Disposable lunch boxes are mostly made of polypropylene (PP) plastic. Because they are difficult to handle and wash, have low recycling prices, high recycling costs and low added value, most of them are incinerated or landfilled, causing serious impacts on the environment.

[0003] At present, the main way to recycle and reuse polypropylene plastic products is to blend them with new materials or other materials to make woven bags, composite flooring and low-end daily plastic products. In recent years, preparing waste polypropylene into polypropylene fibers has gradually become a new direction to solve the recycling and reuse of polypropylene. Patent CN201110095807 discloses a direct spinning process for regenerated polypropylene fibers, which specifically includes washing and exhausting pre-treatment of the raw materials, filtering through a filter device, spinning and cooling, oiling and stretching to obtain fibers, but the raw materials targeted in this patent are generally conventional waste polypropylene plastics. However, the existing products prepared by recycling waste polypropylene have poor product performance, low added value, and lack of functional waste polypropylene products.

[0004] There are several obvious differences between waste lunch box polypropylene and conventional waste polypropylene. Because waste lunch box polypropylene has been in contact with the oil in food for a long time, some of it will penetrate into the amorphous area of ​​polypropylene. In addition, in order to improve melt flow, the polypropylene raw materials used to make lunch boxes are often prepared by hydrogen adjustment during polymerization. Therefore, there will be more residual C=C double bonds in the waste lunch box polypropylene. Some of the residual C=C double bonds are further oxidized and introduced into oxygen-containing groups during the use and recycling of lunch boxes. The mechanical properties of the products recycled and reused by lunch box polypropylene are poor through simple water washing and purification operations, and the strength is low and the toughness is insufficient. The literature (Research on the Performance of Glass Fiber Reinforced Recycled Lunch Box Polypropylene [J]. Renewable Resources and Circular Economy, 2021, 14 (10): 28-31) discloses a glass fiber reinforced lunch box polypropylene resin material, which improves the mechanical properties of the resin material by blending glass fibers, but the resin system is not suitable for melt spinning.

[0005] Therefore, it is of great significance to study a preparation method of recycled lunch box polypropylene fiber suitable for melt spinning and with good mechanical properties, so as to solve the problem of difficulty in recycling and reusing waste lunch box polypropylene and low product added value. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a method for preparing UV-resistant recycled lunch box polypropylene fiber, by utilizing the groups on the main chain of lunch box polypropylene and the small fatty acid molecules remaining in the lunch box, respectively introducing hindered phenol antioxidant structures and secondary amine structures to prepare polypropylene fibers. When the fiber is irradiated with ultraviolet light, the hindered phenol structure captures free radicals to produce a chemical cross-linked structure, while at the same time, the anhydride structure of the hindered phenol fatty acid structure is connected to the secondary amine structure connected to the main chain through hydrogen bonds. Therefore, the fatty acid anti-ultraviolet additive (i.e., the reaction product of the residual fatty acid molecules in the lunch box and the hindered phenol monomer) in the entire system is physically cross-linked with the main chain (such as Figure 3 As shown in the figure, the migration rate of the additive is effectively reduced, and finally the mechanical strength of the fiber can be maintained to the greatest extent after ultraviolet light irradiation, thereby solving the problem of difficult recycling and reuse of polypropylene in waste lunch boxes and low added value of the product.

[0007] To achieve the above object, the scheme adopted by the present invention is as follows:

[0008] A method for preparing UV-resistant recycled lunch box polypropylene fiber comprises the following steps:

[0009] (1) melt blending the cleaned recycled lunch box polypropylene and hindered phenol monomer in a reactor, the reactor is kept in dry nitrogen circulation, the reaction time is 3 hours, and the system is vacuumed for 30 minutes after the reaction is completed. After the melt blending reaction, the melt is subjected to twin-screw extrusion granulation;

[0010] (2) the particles obtained in step (1) are reactively blended and extruded by a twin-screw extruder with an initiator, dibenzoyl peroxide (BPO), and an aliphatic ring secondary amine olefin monomer to obtain spinning chips;

[0011] (3) melt-spinning the spun slices to obtain the UV-resistant recycled lunch box polypropylene fiber;

[0012] The hindered phenol monomer is 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid;

[0013] The breaking strength of the anti-UV recycled lunch box polypropylene fiber is 2.85-3.66 cN / dtex, the breaking elongation is 23-27%, and the breaking strength retention rates after UV irradiation for 12h, 24h and 72h are 97-98%, 93-95% and 85-90% respectively.

[0014] The small fatty acid molecules remaining in the recycled lunch box polypropylene will cause the fiber to break during the spinning process. The present invention obtains the required anhydride structure by modifying the residual fatty acid molecules in the lunch box with the hindered phenol monomer, thereby realizing the beneficial utilization of the small fatty acid molecules, and then avoids the cross-linking between the hindered phenols and affecting the fluidity of the polypropylene through the hydrogen bond between the anhydride structure and the secondary amine structure. Finally, while effectively reducing the mobility of the auxiliary agent, the mechanical strength of the fiber can still be maintained to the greatest extent after ultraviolet light irradiation.

[0015] As the preferred technical solution:

[0016] According to the preparation method of the UV-resistant recycled lunch box polypropylene fiber as described above, the melt index of the recycled lunch box polypropylene is 30-50 g / 10 min (the melt index is tested with reference to GB / T 3682.1-2018 standard, and the test conditions are temperature 230°C and load 2.16 kg).

[0017] According to the preparation method of the UV-resistant recycled lunch box polypropylene fiber, the content of fatty acid substances is measured by dissolution titration to obtain the content of -COOH, and the mass fraction of -COOH groups in the recycled lunch box polypropylene is 0.02-0.5wt%.

[0018] In the preparation method of the above-mentioned anti-ultraviolet recycled lunch box polypropylene fiber, the aliphatic ring-containing secondary amine olefin monomer is preferably a six-membered aliphatic ring structure. The long-chain alkane secondary amine structure is relatively flexible and easy to entangle between branches, which will reduce the ability of the secondary amine structure to generate hydrogen bonds with the structure of the auxiliary agent; the six-membered aromatic ring has too much steric hindrance, which will significantly increase the melt viscosity and is not suitable for the requirements of melt spinning.

[0019] In the method for preparing the UV-resistant recycled lunch box polypropylene fiber as described above, the amount of hindered phenol monomer added in step (1) is 0.15 to 3.7 wt % of the recycled lunch box polypropylene.

[0020] In the method for preparing the UV-resistant recycled lunch box polypropylene fiber as described above, the temperature of melt blending in step (1) is 200-220°C, and the temperature of the twin screw is 210°C.

[0021] In the method for preparing the UV-resistant recycled polypropylene fiber for lunch boxes as described above, the amount of the aliphatic ring secondary amine olefin monomer added in step (2) is 0.5-2.5wt% of the recycled polypropylene for lunch boxes, and the amount of the initiator dibenzoyl peroxide added is 0.05-0.1wt% of the recycled polypropylene for lunch boxes.

[0022] In the method for preparing the UV-resistant recycled lunch box polypropylene fiber as described above, the temperature of the twin-screw reactive blending in step (2) is 200-220°C.

[0023] In the method for preparing the UV-resistant recycled lunch box polypropylene fiber as described above, the spinning temperature in step (3) is 220-230°C, the spinning speed is 1500-2500 m / min, and after melt spinning, the fiber is oiled and bundled and subjected to hot roller heat stretching treatment, the temperature of the first roller is 80-90°C, and the temperature of the second roller is 120-130°C.

[0024] The mechanism of the present invention is as follows:

[0025] In order to solve the problem that the recycling of waste lunch box polypropylene is difficult and the product added value is low, the present invention introduces hindered phenol antioxidant structure and secondary amine structure respectively by using the groups on the main chain of lunch box polypropylene and the fatty acid small molecules remaining in the lunch box, firstly reacts the fatty acid molecules with the hindered phenol monomer, and then reacts the secondary amine olefin monomer of the six-membered aliphatic ring structure with the recycled lunch box polypropylene to prepare the fiber. When the fiber is irradiated with ultraviolet light, the hindered phenol structure captures free radicals to produce a chemical cross-linking structure, and at the same time, the anhydride structure in the hindered phenol fatty acid structure obtained by the reaction of the residual fatty acid molecules of the lunch box with the hindered phenol monomer is connected to the secondary amine structure connected to the main chain through hydrogen bonds. Therefore, the fatty acid anti-UV additive (i.e., the reaction product of residual fatty acid molecules in the lunch box and hindered phenol monomers) in the entire system is physically cross-linked with the main chain, which effectively reduces the mobility of the additive, and ultimately achieves that the mechanical strength of the fiber can still be maintained to the greatest extent after ultraviolet light irradiation (if the secondary amine structure is not introduced, after ultraviolet irradiation, only the additives react with each other, and there is no connection with the main chain, so it is easy to migrate; but by introducing secondary amine groups, the reaction of the additives after ultraviolet irradiation can produce physical cross-linking through hydrogen bonds).

[0026] Beneficial Effects

[0027] (1) The preparation method of the UV-resistant recycled lunch box polypropylene fiber of the present invention effectively solves the problem that the recycling and reuse of waste lunch box polypropylene is difficult and the product added value is low;

[0028] (2) The method for preparing an anti-ultraviolet recycled lunch box polypropylene fiber of the present invention utilizes the structural characteristics of waste lunch box polypropylene, makes full use of the existing groups and residual grease in the lunch box, and introduces anti-ultraviolet groups into the main chain structure of the recycled lunch box polypropylene;

[0029] (3) The method for preparing the UV-resistant recycled lunch box polypropylene fiber of the present invention can achieve long-lasting UV-resistant performance of polypropylene through a two-step reaction of the melt, and the preparation method is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the mechanism of action of anti-ultraviolet recycled lunch box polypropylene fiber;

[0031] Figure 2 It is the reaction between the residual fatty acid molecules of the lunch box and the hindered phenol monomer;

[0032] Figure 3 Schematic diagram of the physical cross-linking structure formed by fatty acid anti-UV additives. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0034] The present invention adopts the following testing method:

[0035] (1) Breaking strength: GB / T 14344-2022 was used, with the gauge length controlled at 500 mm and the tensile rate at 500 mm / min to test the breaking strength of the UV-resistant recycled lunch box polypropylene fiber;

[0036] (2) Elongation at break: GB / T 14344-2022 was used, with the gauge length controlled at 500 mm and the tensile rate at 500 mm / min to test the elongation at break of the UV-resistant recycled lunch box polypropylene fiber.

[0037] Example 1

[0038] A method for preparing UV-resistant recycled lunch box polypropylene fiber comprises the following steps:

[0039] (1) Raw material preparation: recycled polypropylene for lunch boxes with a melt index of 45 g / 10 min, the mass fraction of -COOH groups in the recycled polypropylene for lunch boxes is 0.1 wt%; the chemical structure is The aliphatic ring secondary amine olefin monomer, wherein R2 is 4; 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid; initiator dibenzoyl peroxide;

[0040] (2) melt blending the recycled lunch box polypropylene and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid in a reactor at 210° C., the reactor is kept in dry nitrogen circulation, the reaction time is 3 hours, and after the reaction is completed, the system is evacuated and maintained for 30 minutes, and then the melt is subjected to twin-screw extrusion granulation at 210° C.;

[0041] The amount of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid added is 0.74wt% of the recycled polypropylene for lunch boxes. The fatty acid molecules remaining in the recycled polypropylene for lunch boxes react with 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid to form Figure 2 As shown;

[0042] (3) at 210° C., the particles obtained in step (2) are reactively blended and extruded with an initiator, dibenzoyl peroxide, and an aliphatic ring secondary amine olefin monomer by a twin-screw extruder to obtain spinning chips;

[0043] The amount of the aliphatic ring secondary amine olefin monomer added is 1.2wt% of the recycled polypropylene for the lunch box, and the amount of the initiator dibenzoyl peroxide added is 0.07wt% of the recycled polypropylene for the lunch box;

[0044] (4) melt-spinning the spun fiber obtained in step (3) at a temperature of 225° C. and a spinning speed of 2000 m / min, and after melt spinning, oiling and bundling the spun fiber and performing hot roller heat stretching treatment, wherein the temperature of the first roller is 85° C. and the temperature of the second roller is 125° C., to obtain UV-resistant recycled lunch box polypropylene fiber, such as Figure 1 As shown;

[0045] The breaking strength of the prepared UV-resistant recycled lunch box polypropylene fiber is 3.34 cN / dtex, the breaking elongation is 27%, and the breaking strength retention rates after UV irradiation for 12h, 24h and 72h are 98%, 95% and 88% respectively.

[0046] Example 2

[0047] A method for preparing UV-resistant recycled lunch box polypropylene fiber comprises the following steps:

[0048] (1) Raw material preparation: recycled polypropylene for lunch boxes with a melt index of 30 g / 10 min, the mass fraction of -COOH groups in the recycled polypropylene for lunch boxes is 0.02 wt%; the chemical structure is The aliphatic ring secondary amine olefin monomer, wherein R1 is 3; 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid; initiator dibenzoyl peroxide;

[0049] (2) melt blending the recycled lunch box polypropylene and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid in a reactor at 220° C., the reactor is kept in dry nitrogen circulation, the reaction time is 3 h, and after the reaction is completed, the system is evacuated and maintained for 30 min, and then the melt is subjected to twin-screw extrusion granulation at 210° C.;

[0050] The amount of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid added is 0.15wt% of the recycled lunch box polypropylene;

[0051] (3) at 220° C., the particles obtained in step (2) are reactively blended and extruded with an initiator, dibenzoyl peroxide, and an aliphatic ring secondary amine olefin monomer by a twin-screw extruder to obtain spinning chips;

[0052] The amount of the aliphatic ring secondary amine olefin monomer added is 0.5wt% of the recycled polypropylene for the lunch box, and the amount of the initiator dibenzoyl peroxide added is 0.05wt% of the recycled polypropylene for the lunch box;

[0053] (4) melt-spinning the spun fiber obtained in step (3) at a temperature of 230° C. and a spinning speed of 1500 m / min, applying oil to the spun fiber after melt spinning, bundling the spun fiber, and performing hot roller heat stretching treatment, wherein the temperature of the first roller is 90° C. and the temperature of the second roller is 130° C., thereby obtaining UV-resistant recycled lunch box polypropylene fiber;

[0054] The breaking strength of the prepared UV-resistant recycled lunch box polypropylene fiber is 3.66 cN / dtex, the breaking elongation is 26%, and the breaking strength retention rates after UV irradiation for 12h, 24h and 72h are 97%, 95% and 90% respectively.

[0055] Example 3

[0056] A method for preparing UV-resistant recycled lunch box polypropylene fiber comprises the following steps:

[0057] (1) Raw material preparation: recycled polypropylene for lunch boxes with a melt index of 50 g / 10 min, the mass fraction of -COOH groups in the recycled polypropylene for lunch boxes is 0.5 wt%; the chemical structure is The secondary amine-containing aliphatic ring olefin monomer, wherein R2 is 5; 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid; initiator dibenzoyl peroxide;

[0058] (2) melt blending the recycled lunch box polypropylene and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid in a reactor at 200° C., the reactor is kept in dry nitrogen circulation, the reaction time is 3 hours, and after the reaction is completed, the system is evacuated for 30 minutes, and then the melt is subjected to twin-screw extrusion granulation at 210° C.;

[0059] Among them, the addition amount of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid is 3.7wt% of the recycled lunch box polypropylene;

[0060] (3) at 200° C., the particles obtained in step (2) are reactively blended and extruded with an initiator, dibenzoyl peroxide, and an aliphatic ring secondary amine olefin monomer by a twin-screw extruder to obtain spinning chips;

[0061] The amount of the aliphatic ring secondary amine olefin monomer added is 2.5wt% of the recycled polypropylene for the lunch box, and the amount of the initiator dibenzoyl peroxide added is 0.1wt% of the recycled polypropylene for the lunch box;

[0062] (4) melt-spinning the spun fiber obtained in step (3) at a temperature of 220° C. and a spinning speed of 2500 m / min, applying oil to the spun fiber after melt spinning, bundling the spun fiber, and performing hot roller heat stretching treatment, wherein the temperature of the first roller is 80° C. and the temperature of the second roller is 120° C., thereby obtaining UV-resistant recycled lunch box polypropylene fiber;

[0063] The breaking strength of the prepared UV-resistant recycled lunch box polypropylene fiber is 2.85 cN / dtex, the breaking elongation is 23%, and the breaking strength retention rates after UV irradiation for 12h, 24h and 72h are 98%, 93% and 85% respectively.

Claims

1. A method for preparing UV-resistant recycled lunch box polypropylene fiber, characterized in that The steps include: (1) melt-blending the recycled lunch box polypropylene with hindered phenol monomers, and then subjecting the melt to twin-screw extrusion granulation after the reaction; (2) the particles obtained in step (1) are reactively blended with dibenzoyl peroxide as an initiator and an aliphatic ring secondary amine olefin monomer by a twin-screw extrusion granulation to obtain spinning chips; (3) melt-spinning the spun slices to obtain the UV-resistant recycled lunch box polypropylene fiber; The mass fraction of -COOH groups in the recycled lunch box polypropylene is 0.02 to 0.5 wt%; The hindered phenol monomer is 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid; The chemical formula of the aliphatic ring secondary amine olefin monomer is Wherein, R1 is 3, and R2 is 4 or 5; The breaking strength of the anti-UV recycled lunch box polypropylene fiber is 2.85-3.66 cN / dtex, the breaking elongation is 23-27%, and the breaking strength retention rates after UV irradiation for 12h, 24h and 72h are 97-98%, 93-95% and 85-90% respectively.

2. The method for preparing a UV-resistant recycled lunch box polypropylene fiber according to claim 1, characterized in that: The melt index of recycled lunch box polypropylene is 30-50g / 10min.

3. The method for preparing a UV-resistant recycled lunch box polypropylene fiber according to claim 1, characterized in that: The amount of hindered phenol monomer added in step (1) is 0.15 to 3.7 wt % of the recycled lunch box polypropylene.

4. The method for preparing a UV-resistant recycled lunch box polypropylene fiber according to claim 1, characterized in that: In step (1), the temperature of melt blending is 200-220°C, and the temperature of the twin screw is 210°C.

5. The method for preparing a UV-resistant recycled lunch box polypropylene fiber according to claim 1, characterized in that: In step (2), the amount of the aliphatic ring secondary amine olefin monomer added is 0.5-2.5wt% of the recycled polypropylene for lunch boxes, and the amount of the initiator dibenzoyl peroxide added is 0.05-0.1wt% of the recycled polypropylene for lunch boxes.

6. The method for preparing the UV-resistant recycled lunch box polypropylene fiber according to claim 1, characterized in that: The temperature of the twin-screw reactive blending in step (2) is 200-220°C.

7. The method for preparing the UV-resistant recycled lunch box polypropylene fiber according to claim 1, characterized in that: In step (3), the spinning temperature is 220-230°C, the spinning speed is 1500-2500 m / min, and after melt spinning, the fibers are oiled and bundled and subjected to hot roller heat stretching treatment. The temperature of the first roller is 80-90°C, and the temperature of the second roller is 120-130°C.

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