Method for dyeing polylactic acid fibers and polylactic acid colored yarn

Abstract

This invention provides a method for dyeing polylactic acid (PLA) fibers and PLA colored filaments. The dyeing process involves first blending PLA chips, mixed auxiliaries, and modified starch in a predetermined ratio in a specific order, heating and melting the mixture, then extruding and spinning it through a spinneret. After stretching and heat setting, PLA fiber precursors are obtained. Next, the PLA fiber precursors are dyed at a predetermined temperature in a dye bath containing a predetermined mass concentration of disperse dye to obtain PLA colored filaments. This invention, through the synergistic effect of a specific melt spinning process, mixed auxiliaries, and modified starch, ultimately yields brightly colored, high-strength PLA colored filaments. The operation is simple, achieving a deep dyeing effect at a relatively low dyeing temperature, which helps reduce the strength loss of PLA fibers during high-temperature dyeing. The spinning and dyeing processes do not damage the molecular chain structure of PLA, resulting in PLA colored filaments with good strength and flexibility. The dyeing process requires fewer auxiliaries, and the residual liquor pollution after dyeing is minimal.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid dyeing technology, and more particularly to a method for dyeing polylactic acid fibers and polylactic acid colored yarn. Background Technology

[0002] Polylactic acid (PLA) fiber is made from starches such as corn and wheat, which are fermented and converted into lactic acid, then polymerized and melt-spun. After disposal, PLA products can be decomposed into water and carbon dioxide by microorganisms under natural conditions, without disrupting the ecological balance. Therefore, PLA fiber is considered one of the most promising new materials of the 21st century.

[0003] Polylactic acid (PLA) used in polylactic acid (PLA) fiber spinning is mainly produced by polymerizing L-lactic acid. PLA fibers are not heat-resistant and are considered temperature-sensitive. However, textile dyeing processes require the addition of dyes and other chemicals, followed by high-temperature treatment. Since PLA fibers are not heat-resistant, high-temperature dyeing processes can easily damage their properties. Therefore, it is difficult to increase the dyeing depth of PLA fibers by raising the dyeing temperature. In the textile industry, consumers place great importance on the style and color of products; therefore, the production of brightly colored PLA fibers has attracted widespread attention from researchers.

[0004] Patent application CN201711279891.9 discloses a colored polylactic acid (PLA) fiber filament. This filament is made by mixing PLA chips and color masterbatch, melting the mixture, extruding it through a spinneret, and then stretching and heat-treating it to obtain colored PLA fiber filaments. The cross-section of the filament fibers is circular or rectangular. This method directly melts and blends color masterbatch with PLA chips. During spinning, masterbatch particles (especially those incompatible with the PLA melt spinning solution) become embedded between the fibers, reducing fiber continuity and affecting fiber strength. Simultaneously, it accelerates the degradation of the PLA fiber filaments, leading to problems during storage and use.

[0005] In view of this, it is necessary to design an improved dyeing method for polylactic acid fibers and polylactic acid colored yarns to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a dyeing method for polylactic acid (PLA) fibers and PLA colored yarns. The dyeing process first involves blending PLA chips, mixed auxiliaries, and modified starch in a specific order, followed by melt spinning to obtain PLA fiber precursors with a special structure. Then, the PLA fiber precursors are placed in a dye bath for dyeing. Under the synergistic effect of a specific melt spinning process, mixed auxiliaries, and modified starch, brightly colored and high-strength PLA colored yarns are finally obtained.

[0007] To achieve the above-mentioned objective, the present invention provides a method for dyeing polylactic acid fibers, comprising the following steps:

[0008] S1. Polylactic acid chips and mixed auxiliaries are mixed in a preset ratio, then modified starch is added and mixed again. After heating and melting, the mixture is extruded and spun through a spinneret. After stretching and heat setting, polylactic acid fiber filaments are obtained.

[0009] S2. The polylactic acid fiber filaments obtained in step S1 are dyed in a dye bath containing a preset mass concentration of disperse dye at a preset temperature to obtain polylactic acid colored filaments.

[0010] As a further improvement of the present invention, in step S1, the mixed additive accounts for 1%-20% of the mass of the polylactic acid chips; and the modified starch accounts for 1%-10% of the mass of the polylactic acid chips.

[0011] As a further improvement of the present invention, the mixed additive includes a first additive, a second additive, and a third additive, wherein the mass ratio of the first additive, the second additive, and the third additive is 70%-85%:5%-15%:5%-15%.

[0012] As a further improvement of the present invention, in step S1, the heating and melting temperature is 180-250℃, the spinning speed is 1000-3000m / min, the draw ratio is 1-2 times, and the heat setting temperature is 100-150℃.

[0013] As a further improvement of the present invention, in step S2, the preset mass concentration of the disperse dye is 1%-3%, the dyeing temperature is 80-120℃, and the heating rate is 0.5-2℃ / min.

[0014] As a further improvement of the present invention, the staining time is 10-100 min and the pH of the staining solution is 4-6.

[0015] As a further improvement of the present invention, the first auxiliary agent includes one or more of quaternary ammonium salt, dodecyl phenyl ether, and sodium hexadecyl-N-dimethylaminoacetate; the second auxiliary agent includes one or more of sodium phosphate and potassium phosphate; the third auxiliary agent includes one or more of ammonium chloride, calcium carbonate, and sodium carbonate; and the modified starch includes one or more of thermoplastic starch, esterified starch, and porous starch.

[0016] As a further improvement of the present invention, the disperse dye includes one or more of disperse blue, disperse red, and disperse yellow.

[0017] As a further improvement to the present invention, the following steps are also included:

[0018] S3. Soap the polylactic acid colored filaments obtained in step S2 at 50-100℃ for 10-30 minutes.

[0019] The present invention also provides a polylactic acid colored filament, which is obtained by dyeing polylactic acid fibers using the dyeing method described above.

[0020] The beneficial effects of this invention are:

[0021] (1) The dyeing method of polylactic acid fiber provided by the present invention firstly mixes polylactic acid chips, mixed auxiliaries and modified starch in a specific order, so that the mixed auxiliaries and modified starch are embedded in the amorphous region of polylactic acid. After melt spinning, stretching and heat setting, the mixed auxiliaries and modified starch are uniformly and firmly embedded in the pores of the fiber filament and the gaps between the polylactic acid molecular chains. At the same time, the mixed auxiliaries and modified starch are bonded to the active groups in polylactic acid to obtain polylactic acid fiber filament with a special structure. Next, the polylactic acid (PLA) fiber filaments are dyed in a dye bath. As the dyeing temperature increases, the third auxiliary agent, through its foaming and swelling effect, expands the gaps between the PLA molecular chains in the PLA fiber filaments, providing favorable conditions for the disperse dye to smoothly enter the gaps between the PLA molecular chains. The first and second auxiliary agents in the PLA fiber filaments work synergistically to improve the dispersion of the disperse dye in the PLA fiber, making it easier for the disperse dye to be evenly dispersed in the PLA fiber. At the same time, the second auxiliary agent can effectively increase the adhesion between the disperse dye and the PLA fiber, improving both dyeing uniformity and color fastness. Meanwhile, the presence of modified starch further improves the dyeing performance of PLA. Under the synergistic effect of a specific melt spinning process, mixed auxiliary agents, and modified starch, brightly colored and high-strength PLA filaments are finally obtained.

[0022] (2) The polylactic acid fiber dyeing method provided by this invention is simple to operate and can achieve a deep dyeing effect at a relatively low dyeing temperature, which helps to reduce the strength loss of polylactic acid fibers during high-temperature dyeing. The spinning and dyeing processes do not damage the molecular chain structure of polylactic acid, and the resulting polylactic acid colored yarn has good strength and flexibility. Fewer auxiliaries are required during the dyeing process, and the residual liquor pollution after dyeing is small. Compared with dyeing methods that do not add mixed auxiliaries and modified starch, or add mixed auxiliaries and modified starch to the dye liquor, the dyeing depth of this invention is better. Attached Figure Description

[0023] Figure 1 a is a schematic diagram of the structure of polylactic acid fiber precursor obtained by step S1 of the dyeing method for polylactic acid fiber provided by the present invention; 1b is a schematic diagram of the structure of polylactic acid colored fiber obtained by step S2.

[0024] Figure 2 a is a physical image of the polylactic acid colored filament prepared in Comparative Example 5 of this invention; Figure 2 b is a physical image of the polylactic acid colored filament prepared in Comparative Example 16 of this invention; Figure 2 c is a physical image of the polylactic acid colored filament prepared in Example 1 of this invention.

[0025] Figure 3 a is a schematic diagram of the structure of polylactic acid fiber precursor obtained in step S1 of Comparative Examples 5 and 16 of the present invention; 3b is a schematic diagram of the structure of polylactic acid colored filament obtained in step S2 of Comparative Example 16; 3c is a schematic diagram of the structure of polylactic acid colored filament obtained in step S2 of Comparative Example 5. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0028] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0029] Please see Figures 1 to 3 As shown, the present invention provides a method for dyeing polylactic acid fibers, comprising the following steps:

[0030] S1. Preparation of polylactic acid fiber precursor:

[0031] Polylactic acid (PLA) chips and additives are blended in a predetermined ratio, followed by the addition of modified starch. After heating and melting, the mixture is extruded through a spinneret and spun into PLA fiber filaments. These filaments are then drawn and heat-set to obtain PLA fiber precursors. Specifically, the melting temperature is 180-250℃, the spinning speed is 1000-3000 m / min, the drawing ratio is 1-2 times, and the heat-setting temperature is 100-150℃.

[0032] The mixed additives account for 1%-20% of the mass of polylactic acid (PLA) chips; the modified starch accounts for 1%-10% of the mass of the PLA chips. The mixed additives include a first additive, a second additive, and a third additive, with the mass ratio of the first additive, the second additive, and the third additive being 70%-85%: 5%-15%: 5%-15%.

[0033] Specifically, the first adjuvant includes one or more of quaternary ammonium salts, dodecyl phenyl ether, and sodium hexadecyl-N-dimethylaminoacetate.

[0034] The second adjuvant includes one or more of sodium phosphate and potassium phosphate.

[0035] The third auxiliary agent includes one or more of ammonium chloride, calcium carbonate, and sodium carbonate.

[0036] Modified starch includes one or more of thermoplastic starch, esterified starch, and porous starch.

[0037] In this process, polylactic acid (PLA) chips and a blending agent are first mixed to achieve a more uniform mixture. Then, modified starch is added and blended again. The heating and melting process further promotes the uniform dispersion of the modified starch, ensuring all three are evenly dispersed in the molten spinning solution. Because the blending agent and modified starch have very small molecular structures and are easily soluble in the molten spinning solution, while quaternary ammonium salts and secondary auxiliaries, although not soluble in the molten spinning solution, have very small particle sizes (compared to disperse dyes) and will not damage the PLA molecular chain structure. The blending agent and modified starch are embedded in the amorphous region of PLA. After extrusion through a spinneret, a preliminary spinning stream is formed. After stretching and heat setting, the spinning stream uniformly and firmly embeds the blending agent and modified starch into the pores of the fiber precursor and the gaps between PLA molecular chains. Simultaneously, the blending agent and modified starch bond with the active groups in PLA, resulting in a final product. Figure 1 The polylactic acid fiber precursor with the special structure shown in figure a.

[0038] S2. Staining:

[0039] The polylactic acid fiber filaments obtained in step S1 are dyed in a dye bath containing a predetermined mass concentration of disperse dye at a predetermined temperature to obtain polylactic acid colored filaments.

[0040] Specifically, the preset mass concentration of the disperse dye is 1%-3%, the dyeing temperature is 80-120℃, the heating rate is 0.5-2℃ / min, the dyeing time is 10-100min, and the pH of the dye solution is 4-6. The disperse dyes include one or more of disperse blue, disperse red, and disperse yellow.

[0041] like Figure 1As shown in b, during this process, with the increase of dyeing temperature, due to the presence of mixed auxiliaries and modified starch in the polylactic acid (PLA) fiber filament, on the one hand, the third auxiliary agent, through its own foaming and swelling effect, expands the gaps between PLA molecular chains in the PLA fiber filament, causing the PLA fiber filament to swell and providing favorable conditions for the disperse dye to smoothly enter the gaps between PLA molecular chains. As the PLA fiber filament swells, the molecular orientation of the mixed auxiliaries and modified starch bonded to the side chains of the PLA fiber molecules changes, further increasing the gaps between PLA molecular chains under the synergistic effect of various substances, making it easier for the disperse dye to enter the interior of the PLA fiber. On the other hand, the first and second auxiliary agents in the PLA fiber filament work together to improve the dispersion of the disperse dye in the PLA fiber, making it easier for the disperse dye to be evenly dispersed in the PLA fiber. At the same time, the second auxiliary agent can effectively increase the adhesion between the disperse dye and the PLA fiber, making the disperse dye firmly bonded to the interior of the PLA molecular chains, thereby improving the dyeing uniformity and color fastness. Furthermore, the presence of modified starch further enhances the dyeing properties of polylactic acid, ultimately yielding results such as... Figure 1 b shows brightly colored, high-strength polylactic acid colored yarn.

[0042] S3. Soap wash:

[0043] The polylactic acid colored yarn obtained in step S2 is placed in a soaping solution and soaped at 50-100℃ for 10-30 minutes to remove excess dye and further improve color fastness and color brightness. This process has virtually no impact on the structure of the polylactic acid colored yarn.

[0044] The soaping solution includes sodium hydrosulfite and soda ash, with a sodium hydrosulfite concentration of 2 g / L and a soda ash concentration of 1 g / L. The solvent used is water.

[0045] The present invention also provides a polylactic acid colored filament, which is obtained by dyeing polylactic acid fibers using the above-mentioned dyeing method.

[0046] The present invention will now be described in detail through specific embodiments.

[0047] Example 1

[0048] A method for dyeing polylactic acid fibers, comprising the following steps:

[0049] S1. Preparation of polylactic acid fiber precursor:

[0050] Polylactic acid (PLA) chips and additives were mixed in a predetermined ratio for 10 minutes, followed by the addition of modified starch and further mixing. The mixture was then heated to melt, extruded through a spinneret, and spun into PLA fiber filaments. After stretching and heat setting, PLA fiber precursors were obtained. Specifically, the melting temperature was 200°C, the spinning speed was 2000 m / min, the stretching ratio was 1, and the heat setting temperature was 125°C.

[0051] The mixed additives comprise 10% of the mass of the polylactic acid (PLA) chips, and the modified starch comprises 5% of the mass of the PLA chips. The mixed additives include a first additive, a second additive, and a third additive, with a mass ratio of 80%:10%:10%.

[0052] Specifically, the first auxiliary agent is dodecylbenzene ether; the second auxiliary agent is sodium phosphate; the third auxiliary agent is ammonium chloride; and the modified starch is thermoplastic starch.

[0053] S2. Staining:

[0054] The polylactic acid fiber filaments obtained in step S1 are dyed in a dye bath containing a predetermined mass concentration of disperse dye at a predetermined temperature to obtain polylactic acid colored filaments.

[0055] Specifically, the preset mass concentration of the disperse dye is 2%, the dyeing temperature is 100℃, the heating rate is 1.5℃ / min, the dyeing time is 50min, and the pH of the dye solution is 5. The disperse dye is disperse blue.

[0056] S3. Soap wash:

[0057] The polylactic acid (PLA) colored yarn obtained in step S2 was placed in a soaping solution and soaped at 80°C for 20 minutes to remove excess dye, further improving color fastness and color brightness, ultimately yielding a deep blue PLA colored yarn. A photograph of the obtained PLA colored yarn is shown below. Figure 2 As shown in c (the diameter of the polylactic acid colored filament is 60μm), to further clarify the color of the polylactic acid colored filament, the left side shows a further magnified view of the color of the polylactic acid colored filament.

[0058] The soaping solution specifically includes sodium hydrosulfite and soda ash, with a sodium hydrosulfite concentration of 2 g / L and a soda ash concentration of 1 g / L. The solvent used is water.

[0059] Examples 2-5 and Comparative Examples 1-5

[0060] A method for dyeing polylactic acid fibers, which differs from Example 1 in that the proportions of the mixed auxiliaries and modified starch in step S1 are different, while the rest is roughly the same as in Example 1, and will not be repeated here.

[0061] The polylactic acid colored yarns obtained in Examples 1-5 and Comparative Examples 1-5 were woven into dyed fabrics and their performance was tested. The results are shown in Table 1.

[0062] The K / S value test is conducted using a colorimeter under conditions of D65 light source, 10° viewing angle, 10mm colorimetric aperture, including specular light and 100% UV light filtering. Ten different locations on each dyed sample are tested, and the average value is taken.

[0063] The strength test is specifically conducted as follows: referring to GB / T 3916, "Determination of breaking strength and elongation at break of single yarn in packaged textiles (CRE method)," the breaking strength of the sample is tested under the conditions of a spacing length of (50±2) mm, a tensile speed of 50 mm / min, and a pretension of 2.0 cN / tex, and the average value of the strength is taken.

[0064] The degradation performance test was conducted as follows: the woven dyed fabric was cut into 2cm × 2cm pieces and weighed W0; then the sample was placed in a sodium hydroxide solution with a pH of 9 and left for 30 days, after which it was removed, dried, and weighed W. t Calculate the mass loss rate W L The specific formula is as follows:

[0065]

[0066] Table 1. Properties of the dyed fabrics obtained in Examples 1-5 and Comparative Examples 1-5

[0067]

[0068] As shown in Table 1, the data from Examples 1-3 and Comparative Examples 1-2 indicate that with the increase of the mixed auxiliary agent content, the K / S value of the dyed fabric gradually increases, while the strength and mass loss rate gradually decrease. Similarly, the data from Examples 1, 4-5, and Comparative Examples 3-4 show that with the increase of the modified starch content, the K / S value and mass loss rate of the dyed fabric gradually increase, while the strength gradually decreases. This is mainly because changes in the content of both the mixed auxiliary agent and the modified starch affect the structure of the resulting polylactic acid (PLA) fiber filament, thus affecting the penetration of dye into the PLA fiber filament and further impacting the structure and properties of the PLA colored filament. When the addition of mixed auxiliary agent or modified starch is too high or too low, the performance of the resulting PLA colored filament is poor; the mixed auxiliary agent has a greater impact on the K / S value, strength, and mass loss rate of the fabric compared to modified starch.

[0069] The data from Comparative Example 5 show that when neither the mixed auxiliaries nor the modified starch are added simultaneously, the K / S value of the fabric decreases significantly, while the mass loss rate increases markedly. This indicates that not only does the dyeing performance deteriorate, but the fabric stability also worsens. Therefore, the addition of the mixed auxiliaries and modified starch can delay the degradation of polylactic acid dyed yarn and improve its stability. The preparation process of Comparative Example 5 first yielded the following... Figure 3The polylactic acid fiber filament shown in step a is then dyed with the dye from step S2 to obtain the following result: Figure 3 The polylactic acid colored filament shown in c is compared to Figure 1 b, Figure 3 The dye distribution inside the polylactic acid colored filament in c is significantly less. Meanwhile, a physical image of the polylactic acid colored filament prepared in Comparative Example 5 is shown below. Figure 2 As shown in a, by Figure 2 As can be seen from a, the polylactic acid colored filament prepared in Comparative Example 5 has a lighter color.

[0070] Examples 6-8 and Comparative Examples 6-8

[0071] A method for dyeing polylactic acid fibers differs from Example 1 in that the mass ratio of the first auxiliary agent, the second auxiliary agent, and the third auxiliary agent in the mixed auxiliaries in step S1 is different. Otherwise, it is largely the same as Example 1 and will not be described again here.

[0072] The polylactic acid colored yarns obtained in Examples 6-8 and Comparative Examples 6-8 were woven into dyed fabrics and their performance was tested. The results are shown in Table 2.

[0073] Table 2. Properties of the dyed fabrics obtained in Examples 6-8 and Comparative Examples 6-8

[0074]

[0075]

[0076] Table 2 shows that, within a certain range, the K / S value, strength, and mass loss rate of the dyed fabric fluctuate within a certain range as the mass ratio of the first, second, and third auxiliary agents in the mixed auxiliaries changes. When none of the first, second, or third auxiliary agents are added, the performance of the dyed fabric decreases. This indicates that only through the synergistic effect of the first, second, and third auxiliary agents can a polylactic acid fiber precursor with excellent structure be obtained, thereby yielding high-performance polylactic acid colored yarn.

[0077] Examples 9-10 and Comparative Examples 9-10

[0078] A method for dyeing polylactic acid fibers, which differs from Example 1 in that the heating and melting temperature in step S1 is different, but the rest is roughly the same as Example 1, and will not be described again here.

[0079] The polylactic acid colored filaments obtained in Examples 9-10 and Comparative Examples 9-10 were woven into dyed fabrics and their performance was tested. The results are shown in Table 3.

[0080] Table 3. Properties of the dyed fabrics obtained in Examples 9-10 and Comparative Examples 9-10

[0081]

[0082] As shown in Table 3, when the heating and melting temperature is lower than the melting temperature of polylactic acid (Comparative Example 9), the K / S value and strength of the resulting dyed fabric are significantly lower, and the mass loss rate is higher. This is mainly because the polylactic acid is not mixed evenly with the mixed auxiliaries and modified starch at this time.

[0083] As the heating and melting temperature increases (above the melting temperature of polylactic acid), the K / S value and strength of the dyed fabric gradually increase, the mass loss rate gradually decreases, and the performance of the dyed fabric is improved.

[0084] When the heating and melting temperature is too high, the K / S value and strength of the dyed fabric are significantly lower. This is mainly because the high temperature will damage the structure of polylactic acid, mixed auxiliaries and modified starch, thereby affecting the performance of the dyed fabric.

[0085] Example 11 and Comparative Example 11

[0086] A method for dyeing polylactic acid fibers, which differs from Example 1 in that the stretching ratio in step S1 is different, but the rest is roughly the same as Example 1, and will not be described again here.

[0087] The polylactic acid colored filaments obtained in Example 11 and Comparative Example 11 were woven into dyed fabrics and their performance was tested. The results are shown in Table 4.

[0088] Table 4. Properties of the dyed fabrics obtained in Example 11 and Comparative Example 11

[0089]

[0090] As shown in Table 4, with the increase of the draw ratio, the crystallinity and orientation of the obtained polylactic acid fiber filaments are higher, which affects the process of dye entering the fiber interior, resulting in a decrease in the K / S value and strength of polylactic acid colored filaments and dyed fabrics, and a decrease in the mass loss rate.

[0091] Examples 12-13 and Comparative Examples 12-13

[0092] A method for dyeing polylactic acid fibers, which differs from Example 1 in that the dyeing temperature in step S2 is different, but the rest is roughly the same as Example 1, and will not be described again here.

[0093] The polylactic acid colored yarns obtained in Examples 12-13 and Comparative Examples 12-13 were woven into dyed fabrics and their performance was tested. The results are shown in Table 5.

[0094] Table 5. Properties of the dyed fabrics obtained in Examples 12-13 and Comparative Examples 12-13

[0095]

[0096]

[0097] As shown in Table 5, the higher the dyeing temperature, the higher the K / S value and mass loss rate of the dyed fabric, and the lower the strength. This is mainly because when the dyeing temperature is too high, it will damage the structure of the polylactic acid fiber filament, thereby affecting the performance of the polylactic acid colored filament and the dyed fabric.

[0098] Examples 14-15 and Comparative Examples 14-15

[0099] A method for dyeing polylactic acid fibers, which differs from Example 1 in that the dyeing time in step S2 is different, but the rest is roughly the same as Example 1, and will not be described again here.

[0100] The polylactic acid colored yarns obtained in Examples 14-15 and Comparative Examples 14-15 were woven into dyed fabrics and their performance was tested. The results are shown in Table 6.

[0101] Table 6. Properties of the dyed fabrics obtained in Examples 14-15 and Comparative Examples 14-15

[0102]

[0103] As shown in Table 6, with the increase of dyeing time, the K / S value and mass loss rate of the dyed fabric gradually increase, while the strength gradually decreases. This indicates that as the polylactic acid fiber filament is immersed in the dye bath for a longer time, the structure of the polylactic acid fiber filament will be damaged to a certain extent, thereby affecting the performance of polylactic acid filament and dyed fabric.

[0104] Comparative Example 16

[0105] A method for dyeing polylactic acid fibers, compared with Example 1, differs in that, in step S1, no mixing agent or modified starch is added during melt spinning; instead, the mixing agent and modified starch are added to the dye in step S2. The rest is largely the same as in Example 1 and will not be repeated here. At this point, the following is obtained: Figure 3 The polylactic acid fiber filament shown in figure a is then dyed with a dye containing mixed auxiliaries and modified starch added in step S2 to obtain the following result: Figure 3 The polylactic acid colored filament shown in b, compared to Figure 1 b, Figure 3 The distribution of mixed auxiliaries, modified starch, and dyes inside polylactic acid colored fibers (b) is significantly less.

[0106] Meanwhile, a physical image of the polylactic acid colored filament prepared in Comparative Example 16 is shown below. Figure 2 As shown in b, by Figure 2As can be seen from b, the color of the polylactic acid colored filament prepared in Comparative Example 16 is significantly lighter than that of the polylactic acid colored filament prepared in Example 1.

[0107] Comparative Example 17

[0108] A method for dyeing polylactic acid fibers differs from Example 1 in that, in the melt spinning process of step S1, polylactic acid chips, mixed auxiliaries, modified starch, and disperse blue are directly blended, and step S2, dyeing in the dye bath, is not performed. The rest is roughly the same as in Example 1 and will not be described again here.

[0109] Comparative Example 18

[0110] A method for dyeing polylactic acid fibers differs from Example 1 in that, in the melt spinning process of step S1, polylactic acid chips and disperse blue are directly blended (without adding mixing aids and modified starch), and step S2, dyeing in the dye bath, is not performed. The rest is roughly the same as in Example 1 and will not be described again here.

[0111] Comparative Example 19

[0112] A method for dyeing polylactic acid fibers, which differs from Example 1 in that, in step S1, polylactic acid chips, mixing auxiliaries, and modified starch are directly mixed together. The rest is roughly the same as in Example 1 and will not be described again here.

[0113] Comparative Example 20

[0114] A method for dyeing polylactic acid fibers, which differs from Example 1 in that, in the melt spinning process of step S1, the mixing agent and modified starch are replaced with a large-molecule poly(dihydroxyethyl terephthalate) resin containing sodium 1,3-dicarboxybenzenesulfonate. The polylactic acid chips and the poly(dihydroxyethyl terephthalate) resin containing sodium 1,3-dicarboxybenzenesulfonate are directly blended. The rest is roughly the same as in Example 1 and will not be described in detail here.

[0115] Comparative Example 21

[0116] A method for dyeing polylactic acid fibers, which differs from Example 1 in that, in the melt spinning process of step S1, modified starch is replaced with polybutylene succinate, while the rest is largely the same as in Example 1, and will not be repeated here.

[0117] The polylactic acid colored filaments obtained in Comparative Examples 16-21 were woven into dyed fabrics and their performance was tested. The results are shown in Table 7.

[0118] Table 7 shows the properties of the dyed fabrics obtained in Comparative Examples 16-21.

[0119] Example K / S value Strength σ (MPa) Quality loss rate WL (%) Example 1 24 56.5 12.1 Comparative Example 16 13 58.5 14.9 Comparative Example 17 27 20.2 17.2 Comparative Example 18 28 23.1 19.2 Comparative Example 19 17 41.2 15.1 Comparative Example 20 15 46.2 10.5 Comparative Example 21 14 48.9 9.8

[0120] As can be seen from the data of Comparative Example 16 in Table 7, the K / S value of the dyed fabric obtained by directly adding the mixed auxiliaries and modified starch to the dyeing liquor is much smaller than that obtained by adding the mixed auxiliaries and modified starch during melt spinning.

[0121] Meanwhile, data from Comparative Examples 17-19 show that direct one-pot blending (referring to the blending of the three raw materials or the blending of the raw materials and disperse dyes together) results in significantly poorer performance of polylactic acid colored yarns. Although the K / S values ​​of Comparative Examples 17-18 are higher than those of Example 1, the uniformity of dyeing is relatively poor.

[0122] The data from Comparative Examples 20-21 show that when the mixed additives and modified starch are replaced with sodium 1,3-dicarboxybenzenesulfonate poly(hydroxyethyl terephthalate) resin, or when the modified starch is replaced with polybutylene succinate, the performance of the resulting polylactic acid colored filaments is significantly worse. This further illustrates that specific additives and polylactic acid chips need to be blended together to achieve excellent results.

[0123] In summary, this invention provides a method for dyeing polylactic acid (PLA) fibers and PLA colored filaments. The dyeing process first involves blending PLA chips, mixed auxiliaries, and modified starch in a specific order, followed by melt spinning to obtain PLA fiber precursors with a special structure. These precursors are then placed in a dye bath for dyeing. Through the synergistic effect of the specific melt spinning process, mixed auxiliaries, and modified starch, brightly colored and high-strength PLA filaments are ultimately obtained. The method is simple to operate, achieving a deep dyeing effect at relatively low dyeing temperatures, which helps reduce the strength loss of PLA fibers during high-temperature dyeing. The spinning and dyeing processes do not damage the molecular chain structure of PLA, resulting in PLA colored filaments with good strength and flexibility. The dyeing process requires fewer auxiliaries, and the residual liquor pollution after dyeing is minimal.

[0124] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for dyeing polylactic acid fibers, characterized in that, Includes the following steps: S1. Polylactic acid (PLA) chips and a mixed auxiliaries are blended in a predetermined ratio, followed by the addition of modified starch and blending. After heating and melting, the mixture is extruded through a spinneret and spun into filaments. After stretching and heat setting, PLA fiber precursors are obtained. The mixed auxiliaries account for 1%-20% of the mass of the PLA chips; the modified starch accounts for 1%-10% of the mass of the PLA chips. The mixed auxiliaries include a first auxiliary, a second auxiliary, and a third auxiliary, with a mass ratio of 70%-85%:5%-15%:5%-15%. The first auxiliary includes one or more of quaternary ammonium salts, dodecylbenzene ether, and sodium hexadecyl-N-dimethylaminoacetate. The second auxiliary includes one or more of sodium phosphate and potassium phosphate. The third auxiliary includes one or more of ammonium chloride, calcium carbonate, and sodium carbonate. The modified starch includes one or more of thermoplastic starch, esterified starch, and porous starch. S2. The polylactic acid fiber filaments obtained in step S1 are dyed in a dye bath containing a preset mass concentration of disperse dye at a preset temperature to obtain polylactic acid colored filaments.

2. The dyeing method for polylactic acid fibers according to claim 1, characterized in that, In step S1, the heating and melting temperature is 180-250℃, the spinning speed is 1000-3000m / min, the draw ratio is 1-2 times, and the heat setting temperature is 100-150℃.

3. The dyeing method for polylactic acid fibers according to claim 1, characterized in that, In step S2, the preset mass concentration of the disperse dye is 1%-3%, the dyeing temperature is 80-120℃, and the heating rate is 0.5-2℃ / min.

4. The dyeing method for polylactic acid fibers according to claim 3, characterized in that, The staining time is 10-100 minutes, and the pH of the staining solution is 4-6.

5. The dyeing method for polylactic acid fibers according to claim 3, characterized in that, The disperse dyes include one or more of disperse blue, disperse red, and disperse yellow.

6. The dyeing method for polylactic acid fibers according to claim 1, characterized in that, It also includes the following steps: S3. Soap the polylactic acid colored filaments obtained in step S2 at 50-100℃ for 10-30 minutes.

7. A polylactic acid colored filament, characterized in that: The polylactic acid fiber was dyed using the dyeing method described in any one of claims 1-6.

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