Preparation method of fluorine-free waterproof bio-based nylon composite fabric capable of closed-loop recycling

Abstract

The application discloses a preparation method of a fluorine-free waterproof bio-based nylon composite fabric capable of closed-loop recycling, and comprises the following steps: (1) long carbon chain copolyamide hot melt adhesive preparation: long carbon chain dibasic acid, bio-based dibasic amine and auxiliary dibasic acid are added into a reaction bottle, a predetermined amount of a catalyst and an antioxidant are added into the reaction flask, and the dimeric acid polyamide is synthesized by adopting a multi-stage temperature rising program under a nitrogen atmosphere; and the long carbon chain copolyamide hot melt adhesive is obtained after cooling treatment; (2) fabric waterproof finishing; (3) the long carbon chain copolyamide hot melt adhesive is formed into regular glue points on the surface of the fabric by a hot melt adhesive point sticking process, and the other side of the glue points is attached to a nylon fabric or a nylon film. The application develops a bio-based composite fabric which is suitable for textile and garment, firm in adhesion, washable, fluorine-free, environmentally friendly and capable of closed-loop recycling, and has important industrial value and practical significance.

Description

Technical Field

[0001] This invention belongs to the field of textile fabrics, and specifically relates to a method for preparing a fluorine-free, waterproof, bio-based nylon composite fabric that can be recycled in a closed loop. Background Technology

[0002] Currently, bio-based nylon composites are widely used in high-end apparel and outdoor products due to their environmentally friendly properties. However, to meet environmental protection and waterproof performance requirements, the industry generally uses fluorine-free waterproofing agents to treat bio-based nylon. But it has been found that existing fluorine-free waterproofing finishing processes generally have technical defects: the surface energy of nylon fabric treated with fluorine-free waterproofing agents drops sharply to below 20 mN / m, resulting in a highly hydrophobic and inert surface. Traditional polyurethane (PU) hot melt adhesives or ordinary polyamide hot melt adhesives cannot effectively wet and spread on this surface, leading to a significant decrease in the peel strength of the composite fabric and making it prone to delamination. At the same time, existing bio-based nylon composite fabrics often incorporate non-polyamide components such as polyolefins (PO) and thermoplastic polyurethanes (TPU) as adhesives or film materials. Due to chemical incompatibility, waste composite fabrics must undergo complex physical sorting during recycling, making direct melt blending impossible, resulting in high recycling costs and a heavy environmental burden. Therefore, there is currently no bio-based composite fabric that can simultaneously meet the requirements of fluorine-free waterproofing, high composite strength, water resistance, and overall closed-loop recyclability. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a fluorine-free, waterproof, bio-based nylon composite fabric that can be recycled in a closed loop. In view of the deficiencies in the prior art, this invention develops a bio-based composite fabric that is suitable for textiles and clothing, has strong adhesion, is washable, fluorine-free, environmentally friendly, and can be recycled in a closed loop.

[0004] To solve the above technical problems, the following technical solution is adopted:

[0005] A method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric, characterized by comprising the following steps:

[0006] (1) Preparation of long carbon chain copolyamide hot melt adhesive: Long carbon chain dicarboxylic acid, bio-based diamine and auxiliary dicarboxylic acid were added to the reaction flask, and a predetermined amount of catalyst and antioxidant were added to the reaction flask; then, the reaction flask was degassed and repeatedly purged with nitrogen three times during the reaction to obtain a nitrogen atmosphere; dimer acid polyamide was synthesized by multi-stage heating program; after cooling treatment, long carbon chain copolyamide hot melt adhesive was obtained;

[0007] (2) Waterproof finishing of fabric: Immerse the fabric in the waterproof working solution, with a pick-up rate of 70%~80%, and bake at 150-170℃ for 60-90 seconds;

[0008] (3) The prepared long carbon chain copolyamide hot melt adhesive is heated to 105°C and melted by a hot melt machine. Regular adhesive dots are formed on the fabric surface by hot melt adhesive dotting process, and nylon fabric or nylon film is attached to the other side of the adhesive dots.

[0009] After optimization, in step (1), the long-chain dicarboxylic acid is sebacic acid (C12), the bio-based diamine is bio-based pentanediamine, and the auxiliary dicarboxylic acid (C12) is dodecanoic acid or adipic acid.

[0010] After optimization, in step (1), the catalyst is sodium phosphite and the antioxidant is a hindered phenolic antioxidant.

[0011] After optimization, step (1), the multi-stage heating program, includes:

[0012] a. In the first stage, the reaction time is 1 hour under nitrogen protection at 120℃ to ensure complete melting of the material;

[0013] b. In the second stage, the reaction temperature is 180℃, and the reaction is kept at a constant temperature for 6 hours to form an amide prepolymer.

[0014] c. The reaction temperature in the third stage is 220℃, and the reaction time is 2 hours to obtain dimer acid polyamide.

[0015] After optimization, after obtaining dimer acid polyamide, the temperature is reduced to 160°C, and the dimer acid polyamide is poured into a PTFE mold and cooled to room temperature to obtain long carbon chain copolyamide hot melt adhesive.

[0016] After optimization, in step (2), a polyurethane-acrylic modified fluorine-free waterproofing agent is used to prepare a waterproofing working solution with a concentration of 20-40 g / L.

[0017] After optimization, in step (2), the surface energy of the treated fabric is controlled to be 28-35mN / m and the waterproof rating is 4.5-5 by adjusting the waterproof finishing process parameters.

[0018] After optimization, in step (2), a non-contact padding device is used to pad the fabric. The non-contact padding device includes a frame, an immersion tank, a roller mechanism, and a non-contact auxiliary mechanism. The immersion tank is filled with a waterproof working liquid for immersing the fabric. The roller mechanism includes an upper roller, a middle roller, and a lower roller, which work together to press the impregnated fabric. The non-contact auxiliary mechanism includes an immersion component and a feeding component. The immersion component is used to carry the fabric into the waterproof working liquid, and the feeding component is used to feed the impregnated fabric to the lower roller to complete the pressing operation.

[0019] After optimization, the impregnation assembly includes a mounting frame, a lifting cylinder, a guide rod, and a fabric clamp. The piston rod of the lifting cylinder and the guide rod both pass through the mounting frame from top to bottom and are connected as a single unit via a connecting plate. A connecting rod is connected to the lower end of both the piston rod and the guide rod. The connecting rod extends towards the impregnation tank and is connected to a fabric clamp at its end. The fabric clamp includes a first electromagnet, a second electromagnet, a first back plate, and a second back plate. A limiting rod is connected between the first back plate and the second back plate, and the limiting rod passes through and guides the first electromagnet and the second electromagnet. The first electromagnet is connected to the first back plate by a first spring, and the second electromagnet is connected to the second back plate by a second spring. The lower end of the first electromagnet is connected to a left clamping plate, and the lower end of the second electromagnet is connected to a right clamping plate. When energized, the first electromagnet and the second electromagnet attract each other, causing the left clamping plate and the right clamping plate to clamp together. When de-energized, the first electromagnet returns to its original position under the action of the first spring, and the second electromagnet returns to its original position under the action of the second spring, causing the left clamping plate and the right clamping plate to open.

[0020] After optimization, the feeding assembly includes a transverse lead screw module and a fabric pusher. The transverse lead screw module has two sets of supports connected to the left and right supports of the frame, respectively. The transverse lead screw module is used to drive the impregnation assembly to move laterally and transport the impregnated fabric to the lower roller position. The fabric pusher includes a fabric pusher guide roller, a push rod, a movable arm, a control rod, and a push-pull guide rail. The push-pull guide rail is connected to the left and right supports and is used to connect the push rod. The rear end of the push rod is connected to the control rod, and the front end of the push rod is hinged to the movable arm. The movable arm is connected to the fabric pusher guide roller, which is a rotatable structure. By pushing the fabric pusher guide roller, the fabric is laid flat on the lower roller.

[0021] The above technical solution has the following beneficial effects:

[0022] 1. The composite fabric of this invention is an overall polyamide compatible system. That is, the bio-based fabric, long-chain copolyamide hot melt adhesive, and nylon membrane have good chemical compatibility. Therefore, when recycling waste composite fabrics, there is no need to separate or sort the layers; they can be directly recycled and regenerated through crushing, melt blending, and extrusion granulation to achieve closed-loop recycling.

[0023] 2. By precisely controlling the surface energy of the fluorine-free waterproof fabric to 28~35 mN / m and matching it with a long carbon chain PA hot melt adhesive with a surface energy of 30~35 mN / m, good wetting and spreading of the adhesive layer on the fluorine-free surface is achieved, and the peel strength of the composite fabric is significantly improved, reaching 4.5~6.5 N / cm.

[0024] 3. The compatible system and special hot melt adhesive give the composite fabric good moisture and heat resistance, and the peel strength retention rate is ≥85% after 20 washes. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings:

[0026] Figure 1 This is a schematic diagram of a non-contact impregnation equipment.

[0027] Figure 2 This is a schematic diagram of the rolling mill mechanism;

[0028] Figure 3 This is a schematic diagram of the non-contact auxiliary mechanism;

[0029] Figure 4 This is a schematic diagram of the impregnation assembly;

[0030] Figure 5 This is a schematic diagram of the fabric clamp.

[0031] Figure 6 This is a schematic diagram of the fabric pusher.

[0032] Figure 7 This is a schematic diagram of the hinge connection between the push rod and the movable arm.

[0033] The attached figures are labeled as follows: frame 1, left support 11, right support 12, pallet 13, roller mechanism 2, upper roller 21, middle roller 22, lower roller 23, non-contact auxiliary mechanism 3, impregnation tank 4, impregnation assembly 5, lifting cylinder 51, piston rod 52, guide rod 53, mounting frame 54, connecting rod 55, fabric clamp 56, first electromagnet 561, first back plate 562, first spring 563, second electromagnet 564, second back plate 565, second spring 566, left clamping plate 567, right clamping plate 568, limit rod 569, rubber pad 570, fabric pusher 6, push-pull guide rail 61, control rod 62, push rod 63, stop block 631, fabric pusher guide roller 64, movable arm 65, and lead screw module 7. Detailed Implementation

[0034] The present invention aims to develop a bio-based composite fabric suitable for textiles and clothing, which is strong, washable, fluorine-free, environmentally friendly, and recyclable in a closed loop.

[0035] I. The technical solution of the present invention will be described in detail below with reference to specific embodiments:

[0036] Example 1

[0037] (1) Preparation of long-chain copolyamide hot melt adhesive: 46 parts of sebacic acid (C10), 34 parts of bio-based pentanediamine, and 9 parts of dodecanoic acid (C12) were added to the reaction flask. 0.07 parts of sodium phosphite and 0.13 parts of hindered phenolic antioxidant were added to the reaction flask. Subsequently, the reaction flask was degassed, and nitrogen was repeatedly purged three times during the reaction to obtain a nitrogen atmosphere. Dimeric acid polyamide was synthesized using a multi-stage heating program: a) The first stage was carried out at 120℃ under nitrogen protection for 1 hour to allow the materials to melt completely; b) The second stage was carried out at 180℃ for 6 hours to form an amide prepolymer; c) The third stage was carried out at 220℃ for 2 hours to obtain dimeric acid polyamide. Then the temperature was lowered to 160℃, and the dimeric acid polyamide was poured into a PTFE mold and cooled to room temperature to obtain long-chain copolyamide hot melt adhesive.

[0038] (2) Waterproofing of fabric: A polyurethane-acrylic modified fluorine-free waterproofing agent was prepared into a working solution with a concentration of 30 g / L. The fabric was immersed in the waterproof working solution and padded with a padded rate of 75%, and then baked at 160℃ for 80 seconds.

[0039] (3) The prepared long carbon chain PA hot melt adhesive is heated to 105°C and melted by a hot melt machine. Regular adhesive dots are formed on the fabric surface by hot melt adhesive dotting process, and nylon fabric or nylon film is attached to the other side of the adhesive dots.

[0040] Example 2

[0041] (1) Preparation of long-chain copolyamide hot melt adhesive: 44 parts of sebacic acid (C10), 33 parts of bio-based pentanediamine, and 11 parts of dodecanoic acid (C12) were added to the reaction flask. 0.06 parts of sodium phosphite and 0.12 parts of hindered phenolic antioxidant were added to the reaction flask. Subsequently, the reaction flask was degassed and repeatedly purged with nitrogen three times during the reaction to obtain a nitrogen atmosphere. Dimeric acid polyamide was synthesized using a multi-stage heating program: a) The first stage was carried out at 120℃ under nitrogen protection for 1 hour to allow the materials to melt completely; b) The second stage was carried out at 180℃ for 6 hours to form an amide prepolymer; c) The third stage was carried out at 220℃ for 2 hours to obtain dimeric acid polyamide. Then the temperature was lowered to 160℃, and the dimeric acid polyamide was poured into a PTFE mold and cooled to room temperature to obtain long-chain copolyamide hot melt adhesive.

[0042] (2) Waterproofing of fabric: A polyurethane-acrylic modified fluorine-free waterproofing agent was prepared into a working solution with a concentration of 30 g / L. The fabric was immersed in the waterproof working solution and padded with a padded rate of 75%, and then baked at 160℃ for 80 seconds.

[0043] (3) The prepared long carbon chain PA hot melt adhesive is heated to 105°C and melted by a hot melt machine. Regular adhesive dots are formed on the fabric surface by hot melt adhesive dotting process, and nylon fabric or nylon film is attached to the other side of the adhesive dots.

[0044] Example 3

[0045] (1) Preparation of long-chain copolyamide hot melt adhesive: 48 parts of sebacic acid (C10), 33 parts of bio-based pentanediamine, and 7 parts of dodecanoic acid (C12) were added to the reaction flask. 0.08 parts of sodium phosphite and 0.15 parts of hindered phenolic antioxidant were added to the reaction flask. Subsequently, the reaction flask was degassed and repeatedly purged with nitrogen three times during the reaction to obtain a nitrogen atmosphere. Dimeric acid polyamide was synthesized using a multi-stage heating program: a) The first stage was carried out at 120℃ under nitrogen protection for 1 hour to allow the materials to melt completely; b) The second stage was carried out at 180℃ for 6 hours to form an amide prepolymer; c) The third stage was carried out at 220℃ for 2 hours to obtain dimeric acid polyamide. Then the temperature was lowered to 160℃, and the dimeric acid polyamide was poured into a PTFE mold and cooled to room temperature to obtain long-chain copolyamide hot melt adhesive.

[0046] (2) Waterproofing of fabric: A polyurethane-acrylic modified fluorine-free waterproofing agent was prepared into a working solution with a concentration of 30 g / L. The fabric was immersed in the waterproof working solution and padded with a padded rate of 75%, and then baked at 160℃ for 80 seconds.

[0047] (3) The prepared long carbon chain PA hot melt adhesive is heated to 105°C and melted by a hot melt machine. Regular adhesive dots are formed on the fabric surface by hot melt adhesive dotting process, and nylon fabric or nylon film is attached to the other side of the adhesive dots.

[0048] Compare with Example 1

[0049] The difference from Example 1 is that a common polyamide adhesive is used instead of the long carbon chain copolyamide hot melt adhesive. The common polyamide adhesive is BT-PA90 type copolyamide hot melt adhesive from Zhejiang Bangtai New Material Co., Ltd.

[0050] Example 4

[0051] Unlike Example 1, a working solution with a concentration of 20 g / L was prepared.

[0052] Example 5

[0053] Unlike Example 1, a working solution with a concentration of 40 g / L was prepared.

[0054] Compare with Example 6

[0055] Unlike Example 1, a working solution with a concentration of 10 g / L was prepared.

[0056] Compare with Example 7

[0057] Unlike Example 1, a working solution with a concentration of 50 g / L was prepared.

[0058] II. Performance testing of the above embodiments and control examples.

[0059] 1. The effect of the dosage of fluorine-free waterproofing agent on the surface energy of fabrics is shown in Table 1.

[0060] Table 1

[0061] Dosage of fluorine-free waterproofing agent (g / L) Contact angle (°) Surface energy (mN / m) Waterproof rating (level) Is it easy to glue together? Compare with Example 6 10 105 36 Level 3 easy Example 4 20 112 32 Level 4-5 easy Example 1 30 118 30 Level 5 relatively easy Example 5 40 124 28 Level 5 critical Compare with Example 7 50 130 24 Level 5 Cannot stick

[0062] The preferred fabric surface energy is 28–35 mN / m, corresponding to a fluorine-free waterproofing agent dosage of 20–40 g / L.

[0063] 2. Surface energies of different hot melt adhesives are shown in Table 2.

[0064] Types of adhesives Surface energy (mN / m) Can it wet fluorine-free surfaces? Compare with Example 1 Ordinary PA glue 42 cannot Example 1 Long-chain PA adhesive 1 30 able Example 2 Long-chain PA adhesive 2 32 able Example 3 Long-chain PA adhesive 3 35 able

[0065] The preferred surface energy of the hot melt adhesive is 30–35 mN / m.

[0066] 3. The effect of surface energy matching on peel strength is shown in Table 3.

[0067] Fabric surface energy (mN / m) Surface energy of hot melt adhesive (mN / m) Peel strength (N / cm) Peel strength retention rate after 20 water washes (%) result 24 32 1.2 50 Unqualified 28 30 4.8 85 qualified 32 32 6.5 90 excellent 35 35 5.2 87 good 40 42 2.1 55 Difference

[0068] It is evident that both waterproofing and peel strength can only be achieved when the surface energy of the fabric is 28–35 mN / m and the surface energy of the hot melt adhesive is 30–35 mN / m.

[0069] Since long-chain copolyamide hot melt adhesive and bio-based fabrics both belong to the polyamide compatible system, the composite fabric of this invention can be directly crushed, melt-blended and granulated after being discarded, without the need to separate the layers, thus achieving closed-loop recycling and reuse, which meets the requirements of green and low-carbon development of textiles and clothing.

[0070] III. The above embodiments use a non-contact padding device for padding. This non-contact padding device is suitable for laboratory use and is used for padding small-sized fabrics. It includes a frame 1, an impregnation tank 4, a roller mechanism 2, and a non-contact auxiliary mechanism 3. The frame 1 is equipped with an impregnation tank 4, which is used to fill the waterproof working liquid to facilitate the impregnation of the fabric. The upper end of the frame 1 is equipped with a roller mechanism 2, which is a conventional three-roller type, including an upper roller 21, a middle roller 22, and a lower roller 23. The three rollers work together to press the impregnated fabric. In addition, the three rollers can be arranged in a certain gradient, that is, the lower roller 23 is closest to the non-contact auxiliary mechanism 3, and the upper roller 21 is furthest away from the non-contact auxiliary mechanism 3.

[0071] The non-contact auxiliary mechanism 3 includes an impregnation assembly 5 and a feeding assembly. The impregnation assembly 5 is used to carry the fabric into the waterproof working fluid for automated impregnation of the fabric. The feeding assembly is used to feed the impregnated fabric to the lower roller 23 to complete the pressing operation.

[0072] The impregnation assembly 5 includes a mounting frame 54, a lifting cylinder 51, guide rods 53, and a fabric clamp 56. The upper end of the mounting frame 54 is equipped with a lifting cylinder 51. The piston rod 52 of the lifting cylinder 51 passes through the mounting frame 54 downwards, and a connecting rod 55 is connected to the lower end of the piston rod 52. There are two guide rods 53, located on the left and right sides of the lifting cylinder 51. The guide rods 53 also pass through the mounting frame 54 from top to bottom, and a connecting rod 55 is also connected to their lower ends. The piston rod 52 and the two guide rods 53 are connected into an integrated structure by a connecting plate (not shown in the figure). Under the drive of the lifting cylinder 51, the guide rods 53 can follow the lifting and lowering, playing a guiding role and improving stability. The connecting rod 55 extends in the direction of the impregnation tank 4, that is, its outer end is located above the impregnation tank 4, and a fabric clamp 56 is connected to this end. There are three fabric clamps 56, which together clamp the fabric. The fabric clamp 56 includes a first electromagnet 561, a second electromagnet 564, a first back plate 562 and a second back plate 565. A limiting rod 569 is connected between the first back plate 562 and the second back plate 565. The limiting rod 569 passes through and guides the first electromagnet 561 and the second electromagnet 564, so that the first electromagnet 561 and the second electromagnet 564 move forward or backward along the limiting rod 569. A first spring 563 connects the first electromagnet 561 to the first back plate 562, and a second spring 566 connects the second electromagnet 564 to the second back plate 565. A left clamping plate 567 is connected to the lower end of the first electromagnet 561, and a right clamping plate 568 is connected to the lower end of the second electromagnet 564. When energized, the first electromagnet 561 and the second electromagnet 564 attract each other, causing the left clamping plate 567 and the right clamping plate 568 to clamp each other. At this time, the first spring 563 and the second spring 566 are in a stretched state. When de-energized, the first electromagnet 561 returns to its original position under the action of the rebound force of the first spring 563, and the second electromagnet 564 returns to its original position under the action of the second spring 566. The left clamping plate 567 and the right clamping plate 568 open, releasing the fabric.

[0073] The impregnation assembly 5 enables automated fabric impregnation. First, the first electromagnet 561 and the second electromagnet 564 are energized, and the three fabric clamps 56 clamp the fabric. Then, the lifting cylinder 51 is activated, lowering the fabric and immersing it in the working solution. After impregnation, the lifting cylinder 51 rises, lifting the impregnated fabric back to its original position. This invention achieves non-contact fabric impregnation by using the impregnation assembly 5, improving impregnation safety and avoiding human contact that could affect the impregnation effect. Furthermore, it simplifies manual operation and reduces the probability of misoperation.

[0074] The left clamping plate 567 and the right clamping plate 568 have a certain length, so that when the fabric is impregnated, the first electromagnet 561 and the second electromagnet 564 do not come into contact with the working fluid. The specific length can be adapted to the actual working conditions. In addition, the inner sides of the left clamping plate 567 and the right clamping plate 568 are provided with rubber pads 570, which can avoid the problem of insufficient clamping force due to the left clamping plate 567 and the right clamping plate 568 being too long, and can also reduce clamping damage to the fabric.

[0075] The feeding assembly includes a transverse lead screw module 7 and a fabric pusher 6. The transverse lead screw module 7 has two sets of left brackets 11 and right brackets 12 respectively installed on the frame 1. The two sets of transverse lead screw modules 7 are connected and drive the mounting frame 54 of the impregnation assembly 5 to move transversely, thereby driving the fabric clamped by the fabric clamp 56 to move transversely and directionally to the position of the lower roller 23. When the transverse movement is in place, the first electromagnet 561 and the second electromagnet 564 are de-energized, the fabric clamp 56 releases the fabric, and the fabric remains on the lower roller 23 to complete the pressing operation, achieving a non-contact impregnation operation. To ensure the stability of the transverse movement, the left bracket 11 and the right bracket 12 are connected to a support plate 13. The support plate 13 is used to support the mounting frame 54, and the support plate 13 is equipped with a guide rail (not shown in the figure). The bottom of the mounting frame 54 is equipped with a guide rail groove (not shown in the figure). The transverse movement is guided by the connection between the guide rail and the guide rail groove.

[0076] The fabric pusher 6 includes a fabric pusher roller 64, a push rod 63, a movable arm 65, a control rod 62, and a push-pull guide rail 61. The push-pull guide rail 61 is connected to the left support 11 and the right support 12. The push rod 63 is connected to the push rod 63, which can move back and forth under the guidance of the push-pull guide rail 61. The rear end of the push rod 63 is connected to the control rod 62, which can push and pull the push rod 63. The front end of the push rod 63 is hinged to the movable arm 65, and a stop block 631 is provided at the lower end of the hinge position. The stop block 631 is used to prevent the movable arm 65 from flipping downward, so that the movable arm 65 can only flip upward. The movable arm 65 is connected to the fabric pusher roller 64, which is a rotatable structure. When the push rod 63 is pushed forward step by step, the fabric pusher roller 64 gradually moves upward on the lower roller 23, thereby spreading the fabric on the lower roller 23 and avoiding problems such as folding and wrinkling.

[0077] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric, characterized in that... The following steps are included: (1) Preparation of long carbon chain copolyamide hot melt adhesive: long carbon chain dicarboxylic acid, bio-based diamine and auxiliary dicarboxylic acid are added to the reaction flask, and a predetermined amount of catalyst and antioxidant are added to the reaction flask; then, the reaction flask is degassed and repeatedly purged with nitrogen three times during the reaction to obtain a nitrogen atmosphere; dimer acid polyamide is synthesized by multi-stage heating program; after cooling treatment, long carbon chain copolyamide hot melt adhesive is obtained; (2) Waterproof finishing of fabric: the fabric is immersed in waterproof working liquid with a roll-off rate of 70%~80%, and baked at 150-170℃ for 60-90 seconds; (3) the prepared long carbon chain copolyamide hot melt adhesive is heated to 105℃ by a hot melt machine and regular adhesive dots are formed on the surface of the fabric by hot melt adhesive dotting process, and nylon fabric or nylon film is attached to the other side of the adhesive dots.

2. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 1, characterized in that: In step (1), the long-chain dicarboxylic acid is sebacic acid, the bio-based diamine is bio-based pentanediamine, and the auxiliary dicarboxylic acid is dodecanoic acid or adipic acid.

3. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 1, characterized in that: In step (1), the catalyst is sodium phosphite and the antioxidant is a hindered phenolic antioxidant.

4. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 1, characterized in that: The step (1), the multi-stage heating process includes: a) the first stage is at 120°C under nitrogen protection for 1 hour to allow the material to melt completely; b) the second stage is at 180°C for 6 hours to form an amide prepolymer; c) the third stage is at 220°C for 2 hours to obtain dimer acid polyamide.

5. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 1, characterized in that: After obtaining the dimer acid polyamide, the temperature is lowered to 160°C, and the dimer acid polyamide is poured into a PTFE mold and cooled to room temperature to obtain a long carbon chain copolyamide hot melt adhesive.

6. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 1, characterized in that: In step (2), a polyurethane-acrylic modified fluorine-free waterproofing agent is used to prepare a waterproofing working solution with a concentration of 20-40 g / L.

7. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 1, characterized in that: In step (2), the surface energy of the treated fabric is controlled to be 28-35 mN / m and the waterproof rating is 4.5-5 by adjusting the waterproof finishing process parameters.

8. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 1, characterized in that: In step (2), a non-contact padding device is used to pad the fabric. The non-contact padding device includes a frame, an immersion tank, a roller mechanism, and a non-contact auxiliary mechanism. The immersion tank is filled with a waterproof working liquid for immersing the fabric. The roller mechanism includes an upper roller, a middle roller, and a lower roller, which work together to press the impregnated fabric. The non-contact auxiliary mechanism includes an immersion component and a feeding component. The immersion component is used to carry the fabric into the waterproof working liquid, and the feeding component is used to feed the impregnated fabric to the lower roller to complete the pressing operation.

9. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 8, characterized in that: The impregnation assembly includes a mounting frame, a lifting cylinder, a guide rod, and a fabric clamp. The piston rod of the lifting cylinder and the guide rod both pass through the mounting frame from top to bottom and are connected as a single unit via a connecting plate. A connecting rod is connected to the lower end of both the piston rod and the guide rod. The connecting rod extends towards the impregnation tank and is connected to a fabric clamp at its end. The fabric clamp includes a first electromagnet, a second electromagnet, a first back plate, and a second back plate. A limiting rod is connected between the first back plate and the second back plate, passing through and guiding the first electromagnet and the second electromagnet. A first spring connects the first electromagnet to the first back plate, and a second spring connects the second electromagnet to the second back plate. A left clamp is connected to the lower end of the first electromagnet, and a right clamp is connected to the lower end of the second electromagnet. When energized, the first and second electromagnets attract each other, causing the left and right clamps to clamp together. When de-energized, the first electromagnet returns to its original position under the action of the first spring, and the second electromagnet returns to its original position under the action of the second spring, causing the left and right clamps to open.

10. The method for preparing a closed-loop recyclable fluorine-free waterproof bio-based nylon composite fabric according to claim 9, characterized in that: The feeding assembly includes a transverse lead screw module and a fabric pusher. The transverse lead screw module has two sets of components connected to the left and right supports of the frame, respectively. The transverse lead screw module is used to drive the impregnation assembly to move laterally and transport the impregnated fabric to the lower roller position. The fabric pusher includes a fabric pusher guide roller, a push rod, a movable arm, a control rod, and a push-pull guide rail. The push-pull guide rail is connected to the left and right supports and is used to connect the push rod. The rear end of the push rod is connected to the control rod, and the front end of the push rod is hinged to the movable arm. The movable arm is connected to the fabric pusher guide roller, and the fabric pusher guide roller has a rotatable structure. By pushing the fabric guide roller, the fabric is laid flat on the lower roller.

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