Parallel composite self-crimping polyester staple fiber using recycled polyester as raw material, preparation method and system

Abstract

The present invention relates to the field of recycled polyester spinning technology, and more particularly to a parallel composite self-crimping polyester staple fiber made from recycled polyester, as well as a preparation method and production system thereof. This method utilizes polyester bottle flakes as a high-viscosity component and polyester foam as a low-viscosity component. Based on the establishment of a raw material viscosity database, the raw materials are proportioned to achieve intelligent, coarse viscosity adjustment. An online viscosity tester is then installed between the secondary filter and the box. Based on the measured melt viscosity, the melt viscosity is precisely adjusted by adding a chain extender and / or adjusting the shear rate of the melt stirring box, thereby stabilizing the melt viscosity difference. This ensures stable product quality and improves production efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of recycled polyester spinning, in particular to a parallel composite self-crimping polyester staple fiber using recycled polyester as a raw material, and a preparation method and a production system thereof. Background Art

[0002] Currently, polyester staple fibers are widely used as filling materials in the textile industry. Three-dimensional hollow polyester staple fibers, in particular, are popular in clothing, toys, pillows, quilts, and other areas due to their excellent warmth retention and resilience. With the development of product diversity, polyester staple fibers are beginning to penetrate into the home furnishing sector as a filling material, serving as an alternative to sponge and latex cotton in mattresses, cushions, sofas, and other applications. This requires the fiber to possess excellent resilience to meet product comfort requirements.

[0003] Parallel composite fibers, produced from recycled polyester, utilize the differential shrinkage and stress between the two parallel components to form a three-dimensional spiral crimp structure. Compared to conventional single-component three-dimensional crimps, parallel composite fibers exhibit high crimping and high elastic recovery. Mixing parallel composite polyester fibers with low-melting-point staple fibers to produce nonwoven fabrics or rigid cotton offers high comfort, making them a viable alternative to latex and sponges, and are widely used in home furnishings.

[0004] Currently, recycled polyester spinning primarily uses polyester bottle flakes and polyester foam. Polyester bottle flakes generally have a higher viscosity than polyester foam. Utilizing the viscosity difference of recycled polyester, the production of parallel composite fibers offers low raw material costs, melt-spinnability, long-lasting elasticity, and complies with a circular green economy. For example, the applicant's Chinese invention patent application (publication number: CN106319656A, publication date: January 11, 2017) discloses a method for preparing two-component parallel composite fibers. The method comprises the following steps: 1) drying the recycled polyester raw material; 2) feeding the dried polyester into two sets of screw extruders. After melting in the screws, the first melt passes through a secondary filter and enters a spinning manifold. The second melt passes through a primary filter and enters a liquid-phase conditioning and viscosity adjustment device. The viscosity-enhanced melt then passes through a secondary filter and enters a spinning manifold. The two melts are metered by respective component metering pumps installed in the spinning manifold before entering a composite spinning assembly for spinning. 3) The fibers are then cooled by annular air, oiled, dropped into a barrel, drawn, shaped, and cut to produce the parallel composite polyester staple fibers.

[0005] However, the production of parallel composite fibers from recycled polyester is prone to problems such as unstable curl, large batch-to-batch fluctuations, and low production efficiency. This is mainly due to the wide variety of recycled polyester sources, the large viscosity fluctuations between batches, and the rapid thermal degradation of recycled polyester, especially polyester foam, during melting. This leads to unstable viscosity differences between parallel components, resulting in unstable product resilience. Producing high-quality and stable parallel composite fibers from recycled polyester has long been a technical challenge for the industry.

[0006] The applicant applied for a Chinese invention patent application (publication number: CN109693905A, publication date: 2019-04-30), which discloses an intelligent distribution and mixing system and method for polyester recycled materials. The system includes a storage bin, a distribution pipeline, a batching bin and a host computer. Each storage bin stores a single type of recycled material. The distribution pipeline includes a feed pipeline, which connects the discharge port of each storage bin and the feeding port of the batching bin. The batching bin is used to hold the mixed recycled material. The host computer includes a discharge calculation module and a distribution control module. The discharge calculation module is used to obtain the required types of recycled materials and calculate the amount of each type of recycled material based on the production formula and production plan, and then calculate the theoretical discharge speed of the corresponding storage bin based on the bulk density of the recycled material in the corresponding storage bin. The distribution control module is used to adjust the discharge speed of the corresponding storage bin and the feed speed of the feed pipeline based on the calculated theoretical discharge speed, so that the required recycled materials are fed into the batching bin at the same time for mixing. The system and method realize automatic control of the classification, storage and transportation of recycled materials. However, the patent does not disclose the method for intelligent control of polyester recycled materials.

[0007] Separately, the applicant has filed a Chinese invention patent application (publication number: CN109693905A, publication date: April 30, 2019) disclosing a method, equipment, control device, and readable carrier medium for the intelligent production of colored recycled low-melting-point fibers that utilize the color of waste polyester textiles in situ. This method establishes a color matching database for colored polyester foam, performs multi-dimensional in-situ color matching on the polyester foam, and monitors the melt color in real time online. Masterbatch addition via a dynamic mixer enables online color matching and color correction, achieving color differences between finished fibers within 3-4 levels or higher. This method achieves online color matching and color correction for colored recycled low-melting-point fibers. Summary of the Invention

[0008] In response to the deficiencies in the prior art, the present invention provides a method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as a raw material. The method uses polyester bottle flakes as a high-viscosity component and polyester foam as a low-viscosity component. Based on the establishment of a raw material viscosity database, the raw materials are proportioned to achieve intelligent coarse adjustment of viscosity. An online viscosity tester is then installed between the secondary filter and the box body. Based on the measured melt viscosity, the melt viscosity is precisely adjusted by adding a chain extender and / or adjusting the shear rate of the melt stirring box to stabilize the melt viscosity difference, thereby ensuring stable product quality and improving production efficiency.

[0009] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0010] A method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as raw material comprises the following steps:

[0011] 1) Polyester bottle flakes are used as high-viscosity component raw materials, and polyester foam is used as low-viscosity component raw materials;

[0012] 2) Send the prepared raw materials into the continuous drying system to dry them;

[0013] 3) The dried polyester bottle flakes and polyester foam are respectively fed into the screw for melting and filtered in the first filter. The filtered melt enters the melt box for mixing and stirring, and then is pumped into the second filter by the melt gear pump. The filtered melt enters the spinning box. The high and low viscosity melts are respectively fed into the parallel composite spinneret assembly through the respective component metering pumps for parallel composite spinning to produce the spun fiber;

[0014] 4) The spun fibers are then drawn, crimped, cut / relaxed and heat-set, and then relaxed and heat-set / cut to prepare regenerated parallel composite polyester staple fibers;

[0015] The method further includes:

[0016] In step 1), all batches of incoming polyester flakes and polyester foam are sampled, the raw material viscosity is tested, and a basic database is established. Based on the raw material viscosity database, the raw materials are batched according to the product viscosity requirements. The intelligent distribution and mixing system for polyester recycled materials is used for batching. The viscosity of the high-viscosity component polyester flakes is not less than 0.63 dL / g, and the viscosity of the low-viscosity component polyester foam is not less than 0.48 dL / g.

[0017] In step 3), an online viscosity tester is installed between the secondary filter and the box. Based on the measured melt viscosity, the melt viscosity is adjusted by adding a chain extender and / or adjusting the shear rate of the melt stirring box to stabilize the melt viscosity difference. The viscosity difference between the two melts is controlled to be 0.03 to 0.15 dL / g.

[0018] Preferably, the ingredients in step 1) are designed according to the specific viscosities of the high and low viscosity components of the product and the established viscosity database of different batches of products. The raw materials of the same component are selected in the following manner: the portion with a viscosity higher than the set viscosity accounts for 30-60%, the portion with a viscosity close to the set viscosity accounts for 20-40%, and the portion with a viscosity lower than the set viscosity accounts for 10-30%. Based on this, the high and low viscosity components are dosed separately.

[0019] Preferably, the viscosity of the high-viscosity component polyester bottle flakes is 0.63-0.80 dL / g, the viscosity of the low-viscosity component polyester foam is 0.50-0.65 dL / g, the viscosity difference between the two melts is controlled at 0.05-0.12 dL / g, and the melt viscosity difference fluctuation is controlled at ±0.01 dL / g.

[0020] Preferably, in step 3), an online viscosity tester monitors the melt viscosity in real time. Based on the measured viscosity data, the amount of chain extender added is controlled by adjusting the frequency of the chain extender addition gear pump. The chain extender is added into the screw along with the raw materials to increase the melt viscosity. The online viscosity tester adjusts the shear rate of the melt stirring box based on the measured viscosity data to reduce the melt viscosity.

[0021] Preferably, the chain extender is a mixture of one or more of 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), pyromellitic dianhydride (PMDA), 2,4'-toluene diisocyanate (TDI), phthalic anhydride (PA), 2,2'-bis(2-bisoxazoline), glycidyl ester type epoxy resin, and glycidyl ether type epoxy resin, and the added amount of the chain extender is 0.01% to 0.3%.

[0022] Preferably, in the continuous drying system in step 2), the pre-crystallization temperature is 140-170°C, and the pre-crystallization air volume is 300-700m 3 / h, drying temperature is 80~130℃, drying air volume is 300~700m 3 / h, drying air dew point ≤-50℃, polyester moisture content ≤80ppm after drying.

[0023] Preferably, the melt box has a stirring function, and the purpose of melt blending is achieved by stirring. At the same time, by adjusting the stirring shear rate, the melt viscosity is reduced, thereby achieving the purpose of controlling the viscosity.

[0024] Preferably, the step 3) adopts a two-stage filtration method, both of which use reverse osmosis filtration devices, and the filters are automatically flushed by reverse osmosis.

[0025] Preferably, the parallel spinneret assembly in step 3) adopts a "C"-shaped spinneret hole.

[0026] Furthermore, the present invention also discloses a production system of the method described, which includes a polyester bottle flake silo, a polyester foam material silo, a silo batching system, a continuous drying system, a melting screw, a primary filtration system, a secondary filtration system, a parallel composite spinning box, a spinning assembly and a control system, wherein the polyester bottle flake silo and the polyester foam material silo are respectively provided with multiple silos for storing different batches of polyester bottle flakes and polyester foam materials; different batches of polyester bottle flakes and polyester foam materials are sampled, the raw material viscosity is tested, and a basic database is established. According to the product viscosity requirements, the control system batches the raw materials based on the raw material viscosity database, and selects a polyester recycled material intelligent distribution and mixing system for batching; an online viscosity tester is installed between the secondary filter and the spinning box, and a melt stirring box is provided between the primary filtration system and the secondary filtration system, and a chain extender adding device is provided at the front end of the continuous drying system; the online viscosity tester is connected to the control system, and the control system adjusts the melt viscosity by adding a chain extender and / or adjusting the shear rate of the melt stirring box according to the measured melt viscosity to stabilize the melt viscosity difference.

[0027] Furthermore, the present invention also discloses the method for preparing parallel composite self-curling polyester staple fibers.

[0028] The present invention utilizes the aforementioned technical solution, using polyester bottle flakes as the high-viscosity component and polyester foam as the low-viscosity component. Based on the establishment of a raw material viscosity database, the raw materials are proportioned to achieve intelligent, coarse viscosity adjustment. An online viscosity tester is then installed between the secondary filter and the housing. Based on the measured melt viscosity, the melt viscosity is precisely adjusted by adding a chain extender and / or adjusting the shear rate of the melt mixing chamber to stabilize the melt viscosity difference, thereby ensuring stable product quality and improving production efficiency. The regenerated parallel composite polyester staple fibers produced by the present invention can be used in filling, automotive interiors, and home interiors.

[0029] The method of the present invention has the following advantages:

[0030] 1) The parallel composite polyester staple fibers produced using polyester bottle flakes and polyester foam as raw materials have better elastic recovery properties than conventional single-component three-dimensional crimped fibers and can be used in the field of home filling to replace sponges and latex cotton.

[0031] 2) By combining ingredients with chain extenders to increase viscosity and stirring to reduce viscosity, the melt viscosity is stabilized, overcoming the technical difficulty of large viscosity fluctuations in recycled polyester. The stable viscosity difference ensures stable product quality.

[0032] 3) A two-stage filtration device is used to effectively remove melt impurities, stabilize melt quality, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1The present invention is a flow chart of the pre-spinning process of a parallel composite self-crimping polyester staple fiber using recycled polyester as raw material. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] like Figure 1 The system is a production system for parallel composite self-crimping polyester staple fibers using recycled polyester as raw material. The system includes a polyester bottle flake silo, a polyester foam silo, a silo batching system, a continuous drying system, a melting screw, a primary filtration system, a secondary filtration system, a parallel composite spinning box, a spinning assembly, and a control system. The polyester bottle flake silo and the polyester foam silo are each provided with multiple silos for storing different batches of polyester bottle flakes and polyester foam. Different batches of polyester bottle flakes and polyester foam are sampled, the raw material viscosity is tested, and a basic database is established. According to the product viscosity requirements, the control system batches the raw materials based on the raw material viscosity database, and a polyester recycled material intelligent distribution and mixing system is selected for the batching. The polyester recycled material intelligent distribution and mixing system adopts the polyester recycled material intelligent distribution and mixing system and method of Ningbo Dafa Chemical Fiber Co., Ltd. (publication number: CN109693905A, publication date: 2019-04-30) to achieve automatic batching and uniform mixing of each component.

[0036] like Figure 1 As shown, an online viscosity tester is installed between the secondary filter and the spinning box, and a melt stirring box is provided between the primary filtration system and the secondary filtration system, which has a stirring effect. The purpose of melt blending is achieved by stirring, and the melt viscosity is reduced by adjusting the stirring shear rate to achieve the purpose of controlling the viscosity; a chain extender adding device is provided at the front end of the continuous drying system, and the amount of chain extender added is controlled by frequency regulation of the chain extender adding gear pump. The chain extender is added into the screw along with the raw materials to increase the melt viscosity; the online viscosity tester is connected to the control system, and the control system adjusts the melt viscosity by adding chain extender and / or adjusting the shear rate of the melt stirring box according to the measured melt viscosity to stabilize the melt viscosity difference.

[0037] Example 1

[0038] A 3D (3.3dtex)*32mm parallel composite self-crimped polyester staple fiber. This product is used for clothing filling and imitation down. The product is required to be smooth and have good resilience.

[0039] 1) The viscosity requirements of this product are 0.65-0.68 dL / g for the high-viscosity part and 0.58-0.62 dL / g for the low-viscosity part. The viscosity difference is controlled within 0.05-0.08 dL / g, and the viscosity difference fluctuation is controlled within ±0.01 dL / g. According to the viscosity basic database, the polyester bottle flakes and polyester foam materials are mixed, as shown in Table 1.

[0040] Table 1 Raw material formula

[0041]

[0042] 2) According to the raw material formula, the "intelligent distribution and mixing system and method for polyester recycled materials" is used to mix and feed the raw materials, and the mixed raw materials are dried. The pre-crystallization temperature is 160℃, the pre-crystallization air volume is 500m3 / h, the drying temperature is 110℃, and the drying air volume is 600m 3 / h, drying air dew point -60℃, moisture content of polyester after drying 70ppm;

[0043] 3) The dried raw materials are melted by a screw extruder and fed into a primary filter. After filtration, the melt enters a melt mixing tank, where it is mixed evenly and then pumped through a melt pump to a secondary filter for filtration. The filtered melt then enters a spinning manifold for spinning. The chain extender dosage and stirring speed in the mixing tank are adjusted based on the viscosity measured by an online viscosity tester, as shown in Table 2. The chain extender selected is at least one of 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), pyromellitic dianhydride (PMDA), 2,4'-toluene diisocyanate (TDI), phthalic anhydride (PA), 2,2'-bis(2-bisoxazoline), a glycidyl ester epoxy resin, or a glycidyl ether epoxy resin.

[0044] Table 2 Viscosity control parameters

[0045] distinguish Chain extender content (wt%) Stirring speed (rpm) High viscosity components 0 30～40 Low viscosity component 0.1～0.2 10

[0046] 4) The two polyester melts are metered by their respective metering pumps and then enter the spinneret composite assembly. The melts ejected from the spinneret of the composite assembly are cooled, oiled, bundled, drawn, crimped, shaped, cut, and packaged to obtain 3D (3.3 dtex) * 32 mm parallel composite self-crimped polyester staple fibers. The physical properties of the fibers are shown in Table 9.

[0047] Example 2

[0048] A 3D (3.3dtex)*64mm parallel composite self-crimped polyester staple fiber. This product is used in mattresses and imitation latex cotton. The product is required to be smooth and have good resilience.

[0049] 1) The viscosity requirements of this product are as follows: the viscosity of the high-viscosity part is required to be 0.70~0.73dL / g, the viscosity of the low-viscosity part is required to be 0.55~0.58dL / g, the viscosity difference is controlled at 0.1~0.15dL / g, and the viscosity difference fluctuation is controlled at ±0.01dL / g. According to the viscosity basic database, the polyester bottle flakes and polyester foam materials are mixed, as shown in Table 3.

[0050] Table 3 Raw material formula

[0051]

[0052] 2) According to the raw material formula, the "intelligent distribution and mixing system and method for polyester recycled materials" is used to mix and feed the raw materials, and the mixed raw materials are dried. The pre-crystallization temperature is 160℃, the pre-crystallization air volume is 500m3 / h, the drying temperature is 110℃, and the drying air volume is 600m 3 / h, drying air dew point -60℃, moisture content of polyester after drying 60ppm;

[0053] 3) The dried raw materials are melted by a screw extruder and fed into a primary filter. After filtration, the melt enters a melt mixing tank, where it is mixed evenly and then pumped through a melt pump to a secondary filter for filtration. The filtered melt then enters a spinning manifold for spinning. The chain extender dosage and stirring speed in the mixing tank are adjusted based on the viscosity measured by an online viscosity tester, as shown in Table 4. The chain extender selected is at least one of 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), pyromellitic dianhydride (PMDA), 2,4'-toluene diisocyanate (TDI), phthalic anhydride (PA), 2,2'-bis(2-bisoxazoline), a glycidyl ester epoxy resin, or a glycidyl ether epoxy resin.

[0054] Table 4 Viscosity control parameters

[0055] distinguish Chain extender content (wt%) Stirring speed (rpm) High viscosity components 0 10 Low viscosity component 0.05～0.15 10

[0056] 4) The two polyester melts are metered by their respective metering pumps and then enter the spinneret composite assembly. The melts ejected from the spinneret of the composite assembly are cooled, oiled, bundled, drawn, crimped, shaped, cut, and packaged to obtain 3D (3.3 dtex) * 64 mm parallel composite self-crimped polyester staple fibers. The physical properties of the fibers are shown in Table 9.

[0057] The regenerated parallel composite self-crimping staple fibers and conventional single-component three-dimensional crimped polyester staple fibers prepared above were mixed with low-melting-point fibers and needle-punched into 800 gsm non-woven fabrics. After 80,000 compression tests, the performance comparison is shown in Table 5.

[0058] Table 5 Comparison of nonwoven fabric properties

[0059] distinguish Patented products Conventional one-component three-dimensional curling products Element 85% patented products + 15% low melting point 85% conventional products + 15% low melting point 40% indentation hardness (N) 45.6 40.1 Thickness loss rate (%) 15.8 20.5 Hardness loss rate (%) 33.7 40.2

[0060] Example 3

[0061] A 20D (22.2dtex)*64mm parallel composite self-crimped polyester staple fiber. This product is used for car seat cushions to replace sponge and requires good resilience and high hardness.

[0062] 1) The viscosity requirements of this product are 0.66-0.70dL / g for the high-viscosity part and 0.55-0.58dL / g for the low-viscosity part. The viscosity difference is controlled within 0.06-0.08dL / g, and the viscosity difference fluctuation is controlled within ±0.01 dL / g. According to the viscosity basic database, the polyester bottle flakes and polyester foam materials are mixed, as shown in Table 6.

[0063] Table 6 Raw material formula

[0064]

[0065] 2) According to the raw material formula, the "intelligent distribution and mixing system and method for polyester recycled materials" is used to mix and feed the raw materials, and the mixed raw materials are dried. The pre-crystallization temperature is 160℃, the pre-crystallization air volume is 500m3 / h, the drying temperature is 110℃, and the drying air volume is 600m 3 / h, drying air dew point -60℃, moisture content of polyester after drying 70ppm;

[0066] 3) The dried raw materials are melted by a screw extruder and fed into a primary filter. After filtration, the melt enters a melt mixing tank, where it is mixed evenly and then pumped through a melt pump to a secondary filter for filtration. The filtered melt then enters a spinning manifold for spinning. The chain extender dosage and stirring speed in the mixing tank are adjusted based on the viscosity measured by an online viscosity tester, as shown in Table 7. The chain extender selected is at least one of 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), pyromellitic dianhydride (PMDA), 2,4'-toluene diisocyanate (TDI), phthalic anhydride (PA), 2,2'-bis(2-bisoxazoline), a glycidyl ester epoxy resin, or a glycidyl ether epoxy resin.

[0067] Table 7 Viscosity control parameters

[0068] distinguish Chain extender content (wt%) Stirring speed (rpm) High viscosity components 0 20～30 Low viscosity component 0.03～0.1 10

[0069] 4) The two polyester melts are metered by their respective metering pumps and then enter the spinneret composite assembly. The melts ejected from the spinneret of the composite assembly are cooled, oiled, bundled, drawn, crimped, shaped, cut, and packaged to obtain 20D (22.2 dtex) * 64 mm parallel composite self-crimped polyester staple fibers. The physical properties of the fibers are shown in Table 9.

[0070] The regenerated parallel composite self-crimping staple fibers and conventional single-component three-dimensional curled polyester staple fibers prepared above were mixed with low-melting-point fibers to make hard cotton. The 40% indentation hardness of the hard cotton was tested, and the performance comparison is shown in Table 8.

[0071] Table 8 Comparison of hardness of hard cotton

[0072] Serial number formula Hardness (N) formula Hardness (N) 1 Low melting point fiber: patented composite fiber = 30:70 172 Low melting point fiber: conventional fiber = 30:70 160 2 Low melting point fiber: patented composite fiber = 35:65 165 Low melting point fiber: conventional fiber = 35:65 152 3 Low melting point fiber: patented composite fiber = 40:60 150 Low melting point fiber: conventional fiber = 40:60 135

[0073] Table 9 Comparison of fiber physical properties

[0074] distinguish type Number of curls (pcs / 25mm) Defect content (mg / 100g) Bulkiness V1 (cm3 / g) Fill power V2 (cm3 / g) Fill power V3 (cm3 / g) Elastic recovery rate (%) Example 1 silicon 5.5 32 201 54 172 80 Regular 3D*32mm silicon 3.5 65 190 40 151 74 Example 2 silicon 8 32 165 58 142 79 Regular 3D*64mm silicon 4.5 82 198 48 162 76 Example 3 silicon 4.5 258 192 53 158 76 Regular 20D*64mm silicon 4 635 187 50 150 73

[0075] The above is a description of the embodiments of the present invention. The above description of the disclosed embodiments will enable professionals in the field to implement or use the present invention. Various modifications to these embodiments will be apparent to professionals in the field. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as raw material, comprising the following steps: 1) Polyester bottle flakes are used as high-viscosity component raw materials, and polyester foam is used as low-viscosity component raw materials; 2) Send the prepared raw materials into the continuous drying system to dry them; 3) The dried polyester bottle flakes and polyester foam are respectively fed into the screw for melting and filtered in the first filter. The filtered melt enters the melt box for mixing and stirring, and then is pumped into the second filter by the melt gear pump. The filtered melt enters the spinning box. The high and low viscosity melts are respectively fed into the parallel composite spinneret assembly through the respective component metering pumps for parallel composite spinning to produce the spun fiber; 4) The spun fibers are then drawn, curled, cut, relaxed, and heat-set to produce regenerated parallel composite polyester staple fibers; Characterized in that the method further comprises: In step 1), all batches of incoming polyester flakes and polyester foam are sampled, the raw material viscosity is tested, and a basic database is established. Based on the raw material viscosity database and the product viscosity requirements, the raw materials are batched. A polyester recycled material intelligent distribution and mixing system is used for batching. The viscosity of the high-viscosity component polyester flakes is 0.63-0.80 dL / g, and the viscosity of the low-viscosity component polyester foam is 0.50-0.65 dL / g. The batching is designed based on the specific viscosities of the high and low viscosity components of the product and the established viscosity database of different batches of products. The raw materials of the same component are selected in the following manner: the portion with a viscosity higher than the set value accounts for 30-60%, the portion with a viscosity close to the set value accounts for 20-40%, and the portion with a viscosity lower than the set value accounts for 10-30%. Based on this, the high and low viscosity components are batched separately. In step 3), an online viscosity tester is installed between the secondary filter and the spinning manifold. The online viscosity tester monitors the melt viscosity in real time. Based on the measured viscosity data, the amount of chain extender added is controlled by frequency regulation of the chain extender addition gear pump. The amount of chain extender added is 0.01% to 0.3%. The chain extender is added into the screw along with the raw materials to increase the melt viscosity. The online viscosity tester adjusts the shear rate of the melt stirring box based on the measured viscosity data to reduce the melt viscosity. The viscosity difference between the two melts is controlled to be 0.03 to 0.15 dL / g.

2. The method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as raw material according to claim 1, characterized in that: The viscosity difference between the two melts is controlled within the range of 0.05 to 0.12 dL / g, and the fluctuation of the melt viscosity difference is controlled within ±0.01 dL / g.

3. The method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as raw material according to claim 1, characterized in that: The chain extender is a mixture of one or more of 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), pyromellitic dianhydride (PMDA), 2,4'-toluene diisocyanate (TDI), phthalic anhydride, 2,2'-bis(2-bisoxazoline), glycidyl ester type epoxy resin, and glycidyl ether type epoxy resin.

4. The method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as raw material according to claim 1, characterized in that: In step 2), the continuous drying system has a pre-crystallization temperature of 140-170°C and a pre-crystallization air volume of 300-700m 3 / h, drying temperature is 80~130℃, drying air volume is 300~700m 3 / h, drying air dew point ≤-50℃, polyester moisture content ≤80ppm after drying.

5. The method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as raw material according to claim 1, characterized in that: The melt box has a stirring effect, which achieves the purpose of melt blending by stirring. At the same time, by adjusting the stirring shear rate, the melt viscosity is reduced to achieve the purpose of controlling viscosity.

6. The method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as raw material according to claim 1, characterized in that: The step 3) adopts a two-stage filtration method, both of which use reverse osmosis filtration devices, and the filters are automatically flushed by reverse osmosis.

7. The method for preparing parallel composite self-crimping polyester staple fibers using recycled polyester as raw material according to claim 1, characterized in that: The parallel spinneret assembly in step 3) adopts a "C"-shaped spinneret hole.

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