Preparation method of polyester / spandex elastic composite fiber and application of polyester / spandex elastic composite fiber in synthetic leather

Abstract

The invention discloses a preparation method of a polyester / spandex elastic composite fiber and application of the polyester / spandex elastic composite fiber to synthetic leather. The preparation method comprises the following steps: preparing spandex particles, adding acrylamide into the spandex particles for grafting modification to obtain modified spandex particles, melting the modified spandex particles to obtain a spandex melt, and melting the polyester particles to form a polyester melt; the spandex melt and the polyester melt are extruded through the same spinneret orifice, and the polyester particle spandex elastic composite fiber is obtained; acrylamide interacts with an original molecular chain, so that the number and length of grafted chain segments are moderate, and when external force or temperature changes, spandex and polyester molecular chains can be effectively guided to be in coordinated orientation arrangement, proper cross-linking points are formed to transmit stress, the molecular chains are orderly arranged to improve the orientation degree, and polyester and spandex are consistent in heat shrinkage behavior; the shrinkage rate difference between the fibers is reduced, the effect that the fibers are curled unevenly when being heated and bent is reduced, the thermal shrinkage rate difference of the synthetic leather at high temperature is reduced, and the dimensional stability is improved.

Description

Technical Field

[0001] The present invention relates to a method for preparing composite fibers, in particular to a method for preparing polyester / spandex elastic composite fibers and application thereof in synthetic leather. Background Art

[0002] With the continuous development of the synthetic leather industry, performance requirements are increasing, especially in terms of heat resistance, dimensional stability, appearance and feel. Traditional synthetic leather is prone to problems such as uneven fiber curling and surface wrinkling when heated. This not only affects the product's appearance quality but also limits its promotion and use in high-end applications such as automotive interiors and high-end footwear.

[0003] When synthetic leather is made from polyester and spandex, polyester fiber is widely used in the production of synthetic leather due to its advantages such as high strength, good wear resistance, and strong chemical resistance. However, polyester has a relatively high thermal shrinkage rate and is prone to shrinkage and deformation in high-temperature environments, resulting in poor dimensional stability of the synthetic leather. Spandex is an elastomeric fiber with excellent elasticity and flexibility, which can impart good elasticity and comfort to synthetic leather. However, due to its molecular structure, spandex also has a high thermal shrinkage rate and its thermal shrinkage behavior does not match that of polyester. This makes it prone to uneven fiber curling during the production and use of synthetic leather, affecting the overall performance and quality of the synthetic leather.

[0004] While various methods exist for producing composite fibers of polyester and spandex, there are still deficiencies in minimizing the difference in thermal shrinkage between the two. Composite fibers produced by some methods exhibit inconsistent shrinkage behavior between the polyester and spandex when heated, leading to uneven fiber curling, wrinkles, and deformation on the surface of synthetic leather, affecting the appearance and dimensional stability of the synthetic leather. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a preparation method of a polyester / spandex elastic composite fiber and application of the composite fiber in synthetic leather.

[0006] To achieve the above-mentioned object, the technical solution adopted by the present invention is: a method for preparing a polyester / spandex elastic composite fiber and its application in synthetic leather, comprising:

[0007] S1. Reacting isocyanate, polyol, and ethylenediamine at a mass ratio of 1-5:1-5:1-3 at 80° C. for 3 h to obtain spandex particles;

[0008] S2. Dissolve the spandex particles in dimethylformamide at 50–60°C and stir for 2 h to obtain a swollen spandex solution;

[0009] S3, mixing the swollen spandex solution with a 5-20% acrylamide solution, washing the mixture with ethanol and water alternately three times, and vacuum drying to obtain modified spandex particles;

[0010] S4, melting the modified spandex particles at 200-210° C. for 4-6 hours to obtain a spandex melt, and vacuum drying the polyester particles at 120-140° C. for 4-6 hours and melting them to form a polyester melt;

[0011] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0012] In a preferred embodiment of the present invention, in step S1, the isocyanate is diphenylmethane-4,4'-diisocyanate, and the polyol is polytetramethylene ether glycol, and the molecular weight thereof is 1000-2000.

[0013] In a preferred embodiment of the present invention, the mass ratio of spandex particles to dimethylformamide in step S2 is 1:6-10, the dissolution process is carried out under nitrogen protection, and the stirring speed gradient is controlled to be 100-200 rpm.

[0014] In a preferred embodiment of the present invention, in step S3, the acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate in a dimethylacetamide solvent in a mass ratio of 5-20:0.1-1:79-94.9, and stirring for 20-30 minutes until completely dissolved to obtain an acrylamide solution.

[0015] In a preferred embodiment of the present invention, in step S3, the specific steps of mixing the swollen spandex solution with the acrylamide solution are as follows: S31, pouring the swollen spandex solution into a three-necked flask, heating it to 70±1°C, adding the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5-1 L / min, maintaining the temperature at 70°C, stirring at a speed of 200 rpm, and reacting for 4 hours;

[0016] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution.

[0017] In a preferred embodiment of the present invention, in step S3, the washing process involves washing the reaction solution alternately with ethanol and deionized water three times to remove unreacted acrylamide, and vacuum drying is performed at 50° C. for 4 hours to obtain modified spandex particles.

[0018] In a preferred embodiment of the present invention, in step S4, the spandex is melted using a twin-screw extruder with a set temperature of 200-210°C, a screw speed of 50-100 rpm, and a melt pressure of 10-15 MPa; the polyester is melted using a single-screw extruder with a set temperature of 280-290°C, a screw speed of 80-120 rpm, and a melt pressure of 15-25 MPa.

[0019] In a preferred embodiment of the present invention, the vacuum degassing system is turned on during the melting process, the vacuum degree is maintained at -0.06 to -0.08 MPa, and the degassing time is not less than 30% of the total melting time.

[0020] In a preferred embodiment of the present invention, coaxial composite spinning is adopted in step S5, the volume ratio of spandex melt to polyester melt is 1:2-3, the spinning temperature range is 250-270°C, and the winding speed is 3000-3500 m / min.

[0021] The invention discloses an application of polyester / spandex elastic composite fiber in synthetic leather. The composite fiber is a polyester particle spandex elastic composite fiber prepared by any method. The composite fiber is processed into a synthetic leather base fabric through a wet web forming, hot pressing and biaxial stretching process. The stretching temperature is 110-130°C, the longitudinal stretching ratio is 3-4:1, and the transverse stretching ratio is 2-3:1.

[0022] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0023] (1) Spandex particles are prepared, and acrylamide is added to the spandex particles for grafting modification to obtain modified spandex particles. The modified spandex particles are melted to obtain a spandex melt, and the polyester particles are melted to form a polyester melt; the spandex melt and the polyester melt are extruded through the same spinneret to obtain a polyester particle spandex elastic composite fiber; acrylamide interacts with the original molecular chain to make the number and length of the grafted chain segments moderate, which can effectively guide the spandex and polyester molecular chains to coordinate and arrange in an orientation when external force or temperature changes, form suitable cross-linking points to transmit stress, and allow the molecular chains to be arranged in an orderly manner to improve the orientation degree, so that the polyester and spandex have consistent shrinkage behavior when heated; at the same time, the acrylamide chain segments form hydrogen bonds with the polyester molecular chains to construct a tight network structure, so that the molecular chains of the two move in coordination when heated, reducing the shrinkage inconsistency caused by the difference in flexibility; compared with the existing technology, the shrinkage rate difference between the fibers is reduced, the effect of uneven curling when the fibers are bent when heated is reduced, the difference in thermal shrinkage rate of the synthetic leather at high temperature is reduced, and the dimensional stability is improved.

[0024] (2) By adjusting the mass ratio of isocyanate, polyol and ethylenediamine, the ratio of hard segments to soft segments constituting spandex is changed, and the ratio of hard segments is increased to a reasonable value; the number of active groups in the spandex molecular chain is increased, which complements the reaction activity of the acrylamide grafted chain segment, promotes the chemical cross-linking reaction between spandex and polyester, and combines the physical interaction of acrylamide to form a strong interface bonding system; at the same time, the hard segments are conducive to orientation arrangement when subjected to force, restrict random movement, strengthen the synergistic orientation effect, make the interface molecular chains arranged tightly and regularly, and reduce the difference in thermal shrinkage rate; compared with the existing technology, the shrinkage rate difference between fibers is further reduced, and the effect of uneven curling of fibers when bent under heat is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0026] Figure 1 is a flow chart of a preferred embodiment of the present invention; DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0029] like Figure 1 As shown, a method for preparing a polyester / spandex elastic composite fiber and its application in synthetic leather include:

[0030] S1. Reacting isocyanate, polyol, and ethylenediamine at a mass ratio of 1-5:1-5:1-3 at 80° C. for 3 h to obtain spandex particles;

[0031] S2. Dissolve the spandex particles in dimethylformamide at 50–60°C and stir for 2 h to obtain a swollen spandex solution;

[0032] S3, mixing the swollen spandex solution with a 5-20% acrylamide solution, washing the mixture with ethanol and water alternately three times, and vacuum drying to obtain modified spandex particles;

[0033] S4, melting the modified spandex particles at 200-210° C. for 4-6 hours to obtain a spandex melt, and vacuum drying the polyester particles at 120-140° C. for 4-6 hours and melting them to form a polyester melt;

[0034] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0035] Specifically, the structure of spandex is generally composed of soft segments (flexible segments) and hard segments (rigid segments); in step S1, isocyanate contains a highly reactive -NCO group, which can react with a hydroxyl group (-OH) or an amino group (-NH2) to form a carbamate bond (-NH-COO-) or a urea bond (-NH-CO-NH-), and this highly bonded carbamate bond or urea bond forms a hard segment.

[0036] Specifically, in step S1, the polyol is polytetramethylene ether glycol (PTMEG), whose ether bond (-O-) imparts high elasticity and hydrolysis resistance. The polyol contains long-chain molecules with terminal hydroxyl groups (-OH). Because the ether bond between polytetramethylene ether glycol and isocyanate is non-polar or low-polar, the molecular chain is relatively flexible and can react with isocyanate to form a soft segment, which determines the elasticity, flexibility and low-temperature performance.

[0037] Ethylenediamine contains diamino groups (-NH2), which can react with isocyanate to form urea bonds (-NH-CO-NH-), significantly increasing the hard segment ratio and intermolecular hydrogen bond density, improving strength, modulus and heat resistance. It can also act as a short-chain extender to make the hard segment tighter and increase fiber resilience.

[0038] More specifically, the isocyanate here is diphenylmethane-4,4'-diisocyanate, which is sourced from BASF ( M20S), the polyol is polytetramethylene ether glycol (PTMEG), which is sourced from BASF ( 1000, 2000), ethylenediamine is from Huntsman ( EDR-148).

[0039] Specifically, in step S1, the steps for synthesizing spandex particles are as follows: in a three-necked flask protected by dry nitrogen, diphenylmethane-4,4'-diisocyanate (BASF M20S), polytetramethylene ether glycol (PTMEG, BASF 2000, molecular weight 2000±50), ethylenediamine (Huntsman EDR-148), maintaining the reaction temperature at 80±1°C and mechanically stirring at 200 rpm for 3 hours. After the reaction, the product was quenched and pulverized with liquid nitrogen to obtain spandex particles with a particle size of 200-400 μm.

[0040] In step S2, the specific steps are as follows: adding dimethylformamide solvent (DMF) to a dry three-necked flask, adding spandex particles to the dimethylformamide in a mass ratio of 1-1.5:10, controlling the temperature to 50-60°C, stirring while adding, adjusting the stirring speed from 100 rpm to 200 rpm, and continuing the reaction for 2 hours under nitrogen protection, the solution gradually changes from turbid to uniform transparent or slightly turbid colloid, and the swelling is completed to obtain a swollen spandex solution.

[0041] In step S2, dimethylformamide is sourced from BASF, Germany. DMF (>99.9%).

[0042] Specifically, in step S3, the acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in a DMAC (dimethylacetamide) solvent in a mass ratio of 5-20:0.1-1:79-94.9, and stirring for 20-30 minutes until completely dissolved to obtain an acrylamide solution.

[0043] Specifically, in step S3, the specific steps of mixing the swollen spandex solution with the acrylamide solution are as follows: S31, pouring the swollen spandex solution into a three-necked flask, heating it to 70±1°C, adding the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5-1 L / min, maintaining the temperature at 70°C, stirring at a speed of 200 rpm, and reacting for 4 hours;

[0044] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution.

[0045] In step S3, the reaction solution is washed alternately with ethanol and deionized water for three times to remove unreacted acrylamide and homopolymer, and vacuum drying is performed at 50° C. for 4 hours to obtain modified spandex particles.

[0046] In step S3, acrylamide is derived from Mitsubishi Chemical of Japan. -100 (≥99.5%).

[0047] In step S4, the specific steps of melting the modified spandex particles and polyester particles are as follows:

[0048] The modified spandex pellets were added to a twin-screw extruder, the temperature was set to 200-210°C (zone temperature control: feeding zone 190°C, melting zone 205°C, die head 210°C), the screw speed was 50-100 rpm, and the melt pressure was 10-15 MPa for 5 hours to obtain a spandex melt; the polyester pellets were added to a single-screw extruder, the temperature was set to 280-290°C (zone temperature control: feeding zone 270°C, melting zone 285°C, die head 290°C), the screw speed was 80-120 rpm, and the melt pressure was 15-25 MPa for 5 hours to obtain a polyester melt;

[0049] More specifically, during the melting process, vacuum degassing (-0.06 MPa to -0.08 MPa) is turned on, and the degassing time accounts for 35% of the total melting time, so as to remove volatile components in the melt.

[0050] Furthermore, in step S5, a coaxial composite spinning assembly (spinneret aperture 0.25 mm, aspect ratio 3:1) was used, the volume ratio of spandex to polyester melt was controlled to 1:2.5, the spinning temperature was 260°C, and the winding speed was 3200 m / min to obtain a composite fiber with a fineness of 75 dtex / 24f.

[0051] Example 1:

[0052] S1. Reacting isocyanate, polyol, and ethylenediamine at a mass ratio of 3:1:2 at 80° C. for 3 h to obtain spandex particles;

[0053] S2. Add dimethylformamide solvent (DMF) to a dry three-necked flask, add spandex particles to dimethylformamide at a mass ratio of 1-1.5:10, control the temperature to 55°C, stir while adding, adjust the stirring speed from 100 rpm to 200 rpm, and continue the reaction under nitrogen protection for 2 hours. The solution gradually changes from turbid to uniform transparent or slightly turbid colloid, and swelling is completed to obtain a swollen spandex solution.

[0054] S31. Pour the swollen spandex solution into a three-necked flask, raise the temperature to 70±1°C, add the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5–1 L / min, maintain the temperature at 70°C, stir at 200 rpm, and react for 4 hours;

[0055] The acrylamide solution was prepared by dissolving acrylamide and ammonium persulfate (APS) in water at a mass ratio of 12:0.8:87.2, and stirring for 30 minutes until the acrylamide solution was completely dissolved.

[0056] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution; wash the reaction solution three times with ethanol and deionized water alternately to remove unreacted acrylamide and homopolymer, and vacuum dry it at 50° C. for 4 hours to obtain modified spandex particles.

[0057] S4, melting the modified spandex particles at 205° C. for 5 h to obtain a spandex melt, and vacuum drying the polyester particles at 130° C. for 5 h and melting them to form a polyester melt;

[0058] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0059] Comparative Example 1: The difference is:

[0060] The acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in water at a mass ratio of 5:0.1:94.9, stirring for 20-30 minutes until the acrylamide solution is completely dissolved.

[0061] The specific steps are: S1, reacting isocyanate, polyol and ethylenediamine at a mass ratio of 3:1:2 at 80°C for 3 hours to obtain spandex particles;

[0062] S2. Add dimethylformamide solvent (DMF) to a dry three-necked flask, add spandex particles to dimethylformamide at a mass ratio of 1-1.5:10, control the temperature to 55°C, stir while adding, adjust the stirring speed from 100 rpm to 200 rpm, and continue the reaction under nitrogen protection for 2 hours. The solution gradually changes from turbid to uniform transparent or slightly turbid colloid, and swelling is completed to obtain a swollen spandex solution.

[0063] S31. Pour the swollen spandex solution into a three-necked flask, raise the temperature to 70±1°C, add the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5–1 L / min, maintain the temperature at 70°C, stir at 200 rpm, and react for 4 hours;

[0064] The acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in water at a mass ratio of 5:0.1:94.9, stirring for 20-30 minutes until the acrylamide solution is completely dissolved.

[0065] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution; wash the reaction solution three times with ethanol and deionized water alternately to remove unreacted acrylamide and homopolymer, and vacuum dry it at 50° C. for 4 hours to obtain modified spandex particles.

[0066] S4, melting the modified spandex particles at 205° C. for 5 h to obtain a spandex melt, and vacuum drying the polyester particles at 130° C. for 5 h and melting them to form a polyester melt;

[0067] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0068] Comparative Example 2: The difference is:

[0069] The acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in water in a mass ratio of 8:0.3:91.7, stirring for 20-30 minutes until the acrylamide solution is completely dissolved.

[0070] The specific steps are: S1, reacting isocyanate, polyol and ethylenediamine at a mass ratio of 3:1:2 at 80°C for 3 hours to obtain spandex particles;

[0071] S2. Add dimethylformamide solvent (DMF) to a dry three-necked flask, add spandex particles to dimethylformamide at a mass ratio of 1-1.5:10, control the temperature to 55°C, stir while adding, adjust the stirring speed from 100 rpm to 200 rpm, and continue the reaction under nitrogen protection for 2 hours. The solution gradually changes from turbid to uniform transparent or slightly turbid colloid, and swelling is completed to obtain a swollen spandex solution.

[0072] S31. Pour the swollen spandex solution into a three-necked flask, raise the temperature to 70±1°C, add the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5–1 L / min, maintain the temperature at 70°C, stir at 200 rpm, and react for 4 hours;

[0073] The acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in water in a mass ratio of 8:0.3:91.7, stirring for 20-30 minutes until the acrylamide solution is completely dissolved.

[0074] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution; wash the reaction solution three times with ethanol and deionized water alternately to remove unreacted acrylamide and homopolymer, and vacuum dry it at 50° C. for 4 hours to obtain modified spandex particles.

[0075] S4, melting the modified spandex particles at 205° C. for 5 h to obtain a spandex melt, and vacuum drying the polyester particles at 130° C. for 5 h and melting them to form a polyester melt;

[0076] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0077] Comparative Example 3: The difference is:

[0078] The acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in water in a mass ratio of 16:0.6:83.4, stirring for 20-30 minutes until the acrylamide solution is completely dissolved.

[0079] The specific steps are:

[0080] S1. Reacting isocyanate, polyol, and ethylenediamine at a mass ratio of 3:1:2 at 80° C. for 3 h to obtain spandex particles;

[0081] S2. Add dimethylformamide solvent (DMF) to a dry three-necked flask, add spandex particles to dimethylformamide at a mass ratio of 1-1.5:10, control the temperature to 55°C, stir while adding, adjust the stirring speed from 100 rpm to 200 rpm, and continue the reaction under nitrogen protection for 2 hours. The solution gradually changes from turbid to uniform transparent or slightly turbid colloid, and swelling is completed to obtain a swollen spandex solution.

[0082] S31. Pour the swollen spandex solution into a three-necked flask, raise the temperature to 70±1°C, add the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5–1 L / min, maintain the temperature at 70°C, stir at 200 rpm, and react for 4 hours;

[0083] The acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in water in a mass ratio of 16:0.6:83.4, stirring for 20-30 minutes until the acrylamide solution is completely dissolved.

[0084] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution; wash the reaction solution three times with ethanol and deionized water alternately to remove unreacted acrylamide and homopolymer, and vacuum dry it at 50° C. for 4 hours to obtain modified spandex particles.

[0085] S4, melting the modified spandex particles at 205° C. for 5 h to obtain a spandex melt, and vacuum drying the polyester particles at 130° C. for 5 h and melting them to form a polyester melt;

[0086] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0087] Comparative Example 4: The difference is:

[0088] The acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in water at a mass ratio of 20:1:79, stirring for 20-30 minutes until the acrylamide solution is completely dissolved.

[0089] The specific steps are:

[0090] S1. Reacting isocyanate, polyol, and ethylenediamine at a mass ratio of 3:1:2 at 80° C. for 3 h to obtain spandex particles;

[0091] S2. Add dimethylformamide solvent (DMF) to a dry three-necked flask, add spandex particles to dimethylformamide at a mass ratio of 1-1.5:10, control the temperature to 55°C, stir while adding, adjust the stirring speed from 100 rpm to 200 rpm, and continue the reaction under nitrogen protection for 2 hours. The solution gradually changes from turbid to uniform transparent or slightly turbid colloid, and swelling is completed to obtain a swollen spandex solution.

[0092] S31. Pour the swollen spandex solution into a three-necked flask, raise the temperature to 70±1°C, add the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5–1 L / min, maintain the temperature at 70°C, stir at 200 rpm, and react for 4 hours;

[0093] The acrylamide solution is prepared by dissolving acrylamide and ammonium persulfate (APS) in water at a mass ratio of 20:1:79, stirring for 20-30 minutes until the acrylamide solution is completely dissolved.

[0094] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution; wash the reaction solution three times with ethanol and deionized water alternately to remove unreacted acrylamide and homopolymer, and vacuum dry it at 50° C. for 4 hours to obtain modified spandex particles.

[0095] S4, melting the modified spandex particles at 205° C. for 5 h to obtain a spandex melt, and vacuum drying the polyester particles at 130° C. for 5 h and melting them to form a polyester melt;

[0096] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0097] Comparative Example 5: The difference is: S1, isocyanate, polyol and ethylenediamine are reacted at a mass ratio of 2:1:1 at 80°C for 3 hours to obtain spandex particles;

[0098] The specific steps are: S1, reacting isocyanate, polyol and ethylenediamine at a mass ratio of 2:1:1 at 80°C for 3 hours to obtain spandex particles;

[0099] S2. Add dimethylformamide solvent (DMF) to a dry three-necked flask, add spandex particles to dimethylformamide at a mass ratio of 1-1.5:10, control the temperature to 55°C, stir while adding, adjust the stirring speed from 100 rpm to 200 rpm, and continue the reaction under nitrogen protection for 2 hours. The solution gradually changes from turbid to uniform transparent or slightly turbid colloid, and swelling is completed to obtain a swollen spandex solution.

[0100] S31. Pour the swollen spandex solution into a three-necked flask, raise the temperature to 70±1°C, add the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5–1 L / min, maintain the temperature at 70°C, stir at 200 rpm, and react for 4 hours;

[0101] The acrylamide solution was prepared by dissolving acrylamide and ammonium persulfate (APS) in water at a mass ratio of 12:0.8:87.2, and stirring for 30 minutes until the acrylamide solution was completely dissolved.

[0102] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution; wash the reaction solution three times with ethanol and deionized water alternately to remove unreacted acrylamide and homopolymer, and vacuum dry it at 50° C. for 4 hours to obtain modified spandex particles.

[0103] S4, melting the modified spandex particles at 205° C. for 5 h to obtain a spandex melt, and vacuum drying the polyester particles at 130° C. for 5 h and melting them to form a polyester melt;

[0104] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0105] Comparative Example 6: The difference is: S1, isocyanate, polyol and ethylenediamine are reacted at a mass ratio of 4:1:1 at 80°C for 3 hours to obtain spandex particles;

[0106] The specific steps are as follows: S1, reacting isocyanate, polyol and ethylenediamine at a mass ratio of 4:1:1 at 80°C for 3 hours to obtain spandex particles;

[0107] S2. Add dimethylformamide solvent (DMF) to a dry three-necked flask, add spandex particles to dimethylformamide at a mass ratio of 1-1.5:10, control the temperature to 55°C, stir while adding, adjust the stirring speed from 100 rpm to 200 rpm, and continue the reaction under nitrogen protection for 2 hours. The solution gradually changes from turbid to uniform transparent or slightly turbid colloid, and swelling is completed to obtain a swollen spandex solution.

[0108] S31. Pour the swollen spandex solution into a three-necked flask, raise the temperature to 70±1°C, add the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5–1 L / min, maintain the temperature at 70°C, stir at 200 rpm, and react for 4 hours;

[0109] The acrylamide solution was prepared by dissolving acrylamide and ammonium persulfate (APS) in water at a mass ratio of 12:0.8:87.2, and stirring for 30 minutes until the acrylamide solution was completely dissolved.

[0110] S32. Add hydroquinone to the spandex solution reacted in S31 at a mass ratio of 1:0.1 to obtain a reaction solution; wash the reaction solution three times with ethanol and deionized water alternately to remove unreacted acrylamide and homopolymer, and vacuum dry it at 50° C. for 4 hours to obtain modified spandex particles.

[0111] S4, melting the modified spandex particles at 205° C. for 5 h to obtain a spandex melt, and vacuum drying the polyester particles at 130° C. for 5 h and melting them to form a polyester melt;

[0112] S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

[0113] Test Example 1:

[0114] The polyester spandex elastic composite fibers prepared in Example 1 and Comparative Examples 1-6 were cut into appropriate lengths (10 mm), placed in a high shear disperser, and an appropriate amount of water (the mass ratio of fiber to water was 1:10) was added. The fibers were dispersed at a speed of 3000-5000 rpm for 25 minutes to form a uniform fiber suspension. The fiber suspension was poured into the papermaking trough of a wet papermaking machine, and the equipment was started to allow the fibers to settle evenly on the papermaking net to form a wet non-woven fabric. The wet non-woven fabric was carefully transferred to an oven and dried at 75° C. for 3 hours to remove moisture to obtain a dry non-woven fabric. The dried non-woven fabric was placed in a mold of a flat vulcanizer, the temperature was set to 200° C., the pressure was 10 MPa, and hot pressing was performed for 10 minutes to form a synthetic leather blank. The synthetic leather blank was placed on a stretching and setting machine and stretched in the longitudinal and transverse directions at a temperature of 110° C., with a longitudinal stretching ratio of 4 times and a transverse stretching ratio of 3 times. The temperature was maintained for 15 minutes after stretching to obtain synthetic leather.

[0115] The synthetic leathers of Example 1 and Comparative Examples 1-6 were cut into 50 mm pieces, laid flat on a glass plate, and fixed with dilute glue to prepare test samples. Each group of samples had no fewer than 30 pieces, and each test sample was marked with its original length using a marking method that could be identified under a microscope. The samples were placed in a heat shrinkage tester and treated at different temperatures (80°C, 100°C, 120°C, and 140°C) for 10 minutes. After the treatment, the samples were removed and cooled to room temperature. The length of the leather fibers after shrinkage was measured using a microscope and the data was recorded. The heat shrinkage of each sample at different temperatures was calculated according to the formula, and the average value of multiple fibers was taken. The formula is as follows:

[0116] As shown in Table 1;

[0117] Table 1

[0118]

[0119]

[0120] As can be seen from the data in Table 1, the difference in thermal shrinkage at each temperature point in Example 1 is smaller than that in Comparative Examples 1-4. The reason is that in Example 1, the 12% acrylamide concentration makes the number and length of the grafted segments just right. When subjected to external forces (such as stretching, heat treatment, etc.), these segments can effectively guide the spandex and polyester molecular chains to coordinate their orientation. Example 1 can form suitable cross-linking points between the molecular chains. These cross-linking points can effectively transmit stress when subjected to external forces, so that the molecular segments are arranged in an orderly manner according to the direction of the external force. This orderly arrangement improves the orientation of the entire composite fiber, making the shrinkage behavior of polyester and spandex more consistent when heated; and in Example 1, the acrylamide segments and polyester molecular chains maintain interaction by forming hydrogen bonds. These interactions form a tighter network structure between the molecular chains, allowing the polyester and spandex molecular chains to better coordinate movement when heated. The acrylamide segments increase the flexibility of the spandex molecular chains to a certain extent, enabling them to better cooperate with the polyester molecular chains when heated, reducing the shrinkage inconsistency caused by differences in flexibility.

[0121] In Comparative Examples 1-2, however, the acrylamide concentration is too low, resulting in a limited number of segments grafted onto the spandex molecular chains. These small amounts of grafted segments are unable to effectively guide the spandex and polyester molecular chains into adequate orientation. When subjected to external forces or temperature changes, the movement of the spandex molecular segments is relatively disordered, failing to form a good coordinated movement with the polyester molecular segments, resulting in inconsistent shrinkage behavior. Furthermore, the lower concentration of acrylamide forms fewer grafted segments, failing to establish sufficient interaction between the polyester and spandex molecular chains. Due to the lack of sufficient connection points, the polyester and spandex molecular chains tend to move independently according to their own characteristics when heated, failing to achieve effective force transmission and coordinated shrinkage, resulting in an increased difference in thermal shrinkage. In Comparative Examples 3-4, where the acrylamide concentration is too high, the large number of grafted segments increases entanglement between the molecular segments. These entangled segments restrict the movement of the spandex molecular segments, making them relatively rigid. This mismatch with the kinematic properties of polyester molecular segments means that when heated, polyester segments can move and contract relatively freely, while spandex segments are too entangled to contract synchronously. Furthermore, the excessive number of grafted segments easily forms stress concentration points at the polyester-spandex interface. When subjected to external forces or temperature fluctuations, these stress concentration points lead to localized deformation and uneven shrinkage, disrupting the overall coordination of the polyester and spandex segments and causing a significant difference in thermal shrinkage.

[0122] As can be seen from the data in Table 1, the difference in thermal shrinkage at each temperature point in Example 1 is less than that in Comparative Examples 5-6. This is because Example 1 increases the proportion of hard segments in the spandex and adjusts it to a reasonable ratio. At this ratio, the number of reactive groups available for reaction in the resulting spandex molecular chains increases, complementing the reactivity of the acrylamide grafted segments and jointly promoting the chemical crosslinking reaction between the spandex and polyester. This chemical crosslinking, combined with the physical interaction of acrylamide, forms a more powerful interfacial binding system. Simultaneously, the hard segments in the spandex molecular chains are more easily oriented along the direction of the external force when subjected to an external force. The presence of the hard segments also restricts the random motion of the spandex molecular chains, making their movement more orderly. When combined with the guiding effect of acrylamide, the orderly arrangement and orientation of the hard segments further enhances the synergistic orientation effect between the spandex and polyester molecular chains, making the molecular chains at the interface more tightly arranged and regular, reducing the difference in thermal shrinkage between the spandex and polyester, and thus reducing the effect of uneven fiber curling.

[0123] In Comparative Example 5, the proportion of hard segments is relatively small, while the proportion of soft segments is relatively large, resulting in excessive flexibility of the spandex molecular chain. When subjected to external forces or temperature changes, the molecular segments are prone to significant movement and deformation, making it difficult for the molecular segments to maintain an orderly arrangement and consistent shrinkage behavior when heated. Furthermore, because they are too flexible, it is difficult for the molecular segments to form an effective orientation through external forces or self-interaction. The acrylamide segments cannot find suitable "anchor points" within the flexible spandex molecular chains to guide the molecular chain's orientation and limit its excessive movement, resulting in poor modification results and an inability to effectively reduce the difference in thermal shrinkage. In Comparative Example 6, the proportion of hard segments is relatively large, resulting in excessive rigidity of the spandex molecular chain. The rigid structure of the hard segments limits the molecular segments' mobility, restricting the spandex molecular chain's shrinkage behavior when heated, which is inconsistent with the shrinkage characteristics of the polyester molecular chain. The acrylamide segments cannot effectively optimize the molecular chain's arrangement and movement on the rigid spandex molecular chain, effectively guiding the molecular chain's orientation and limiting its excessive movement. This results in unsatisfactory modification results and a large difference in thermal shrinkage.

[0124] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing polyester / spandex elastic composite fiber, characterized in that: include: S1. Reacting isocyanate, polyol, and ethylenediamine at a mass ratio of 1-5:1-5:1-3 at 80° C. for 3 h to obtain spandex particles; S2. Dissolve the spandex particles in dimethylformamide at 50–60°C and stir for 2 h to obtain a swollen spandex solution; S3, mixing the swollen spandex solution with a 5-20% acrylamide solution, washing the mixture with ethanol and water alternately three times, and vacuum drying to obtain modified spandex particles; S4, melting the modified spandex particles at 200-210° C. for 4-6 hours to obtain a spandex melt, and vacuum drying the polyester particles at 120-140° C. for 4-6 hours and melting them to form a polyester melt; S5. Extruding the spandex melt and the polyester melt through the same spinneret hole to obtain polyester particle spandex elastic composite fibers.

2. The method for preparing a polyester / spandex elastic composite fiber according to claim 1, characterized in that: In step S1, the isocyanate is diphenylmethane-4,4'-diisocyanate, and the polyol is polytetramethylene ether glycol, and the molecular weight thereof is 1000-2000.

3. The method for preparing a polyester / spandex elastic composite fiber according to claim 1, wherein: In step S2, the mass ratio of spandex particles to dimethylformamide is 1:6-10, the dissolution process is carried out under nitrogen protection, and the stirring speed gradient is controlled to be 100-200 rpm.

4. The method for preparing a polyester / spandex elastic composite fiber according to claim 1, wherein: In step S3, the acrylamide solution is prepared in the following steps: according to a mass ratio of 5-20: 0.1-1:79-94.9 Dissolve acrylamide and ammonium persulfate in dimethylacetamide solvent and stir for 20-30 minutes until completely dissolved to obtain acrylamide solution.

5. The method for preparing a polyester / spandex elastic composite fiber according to claim 1, characterized in that: In step S3, the specific steps of mixing the swollen spandex solution with the acrylamide solution are as follows: S31. Pour the swollen spandex solution into a three-necked flask, raise the temperature to 70±1°C, add the acrylamide solution dropwise for 30 minutes under nitrogen protection at a flow rate of 0.5–1 L / min, maintain the temperature at 70°C, stir at 200 rpm, and react for 4 hours; S32. Add hydroquinone to the spandex solution obtained by reaction in S31 at a mass ratio of 1:0.1 to obtain a reaction solution.

6. The method for preparing a polyester / spandex elastic composite fiber according to claim 1, characterized in that: In step S3, the reaction solution is washed alternately with ethanol and deionized water for three times to remove unreacted acrylamide, and vacuum drying is performed at 50° C. for 4 hours to obtain modified spandex particles.

7. The method for preparing a polyester / spandex elastic composite fiber according to claim 1, characterized in that: In step S4, the spandex is melted using a twin-screw extruder with a set temperature of 200-210° C., a screw speed of 50-100 rpm, and a melt pressure of 10-15 MPa; the polyester is melted using a single-screw extruder with a set temperature of 280-290° C., a screw speed of 80-120 rpm, and a melt pressure of 15-25 MPa.

8. The method for preparing a polyester / spandex elastic composite fiber according to claim 7, characterized in that: During the melting process, the vacuum degassing system is turned on, the vacuum degree is maintained at -0.06 to -0.08 MPa, and the degassing time is not less than 30% of the total melting time.

9. The method for preparing a polyester / spandex elastic composite fiber according to claim 1, characterized in that: In step S5, coaxial composite spinning is adopted, the volume ratio of spandex melt to polyester melt is 1:2-3, the spinning temperature range is 250-270° C., and the winding speed is 3000-3500 m / min.

10. Use of a polyester / spandex elastic composite fiber in synthetic leather, wherein the composite fiber is a polyester granular spandex elastic composite fiber prepared by the method according to any one of claims 1 to 9, characterized in that: The composite fiber is wet-laid, hot-pressed and biaxially stretched to form a synthetic leather base fabric at a stretching temperature of 110-130° C., a longitudinal stretching ratio of 3-4:1 and a transverse stretching ratio of 2-3:1.

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