Polylactic acid fabric dyeing method

Abstract

The invention discloses a method for dyeing a polylactic acid fabric. The method comprises the following steps: S1, modifying the polylactic acid fabric by using a modifier; s2, blending deionized water and sodium carbonate to prepare a dissolving solution; s3, coffee grounds are added into the dissolving solution in the step S2 to be fully soaked, suction filtration is performed after extraction, and a coffee grounds extracting solution is obtained; s4, selecting a mordant and performing pre-complexing on the mordant and the coffee residue extracting solution in the step S3 to form a mixed solution; s5, dyeing the polylactic acid fabric modified in the step S1 and the mixed solution in the step S4; s6, the mordant is added again for secondary mordanting, the technological process is simple and environmentally friendly, and the dyeing color depth of the polylactic acid fabric can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of textile printing and dyeing technology, and specifically to a method for dyeing polylactic acid fabrics. Background Technology

[0002] Polylactic acid (PLA) is a biodegradable polyester material produced by fermentation from renewable biomass resources such as corn and cassava. It has good mechanical properties, biocompatibility, and processability, and its application in the textile field is becoming increasingly widespread. However, PLA fabrics are characterized by strong hydrophobicity and high crystallinity, which leads to poor dyeing performance. Conventional dyes are difficult to achieve good dyeing effects on it, and the color depth and color fastness are not ideal.

[0003] Plant dyeing, as an environmentally friendly dyeing method, has received increasing attention in recent years. Coffee grounds, a large amount of waste generated during coffee processing, contain abundant natural pigments, such as caffeine, chlorogenic acid, and other polyphenols, and have the potential to be used as natural dyes. However, there is currently little research on using coffee grounds to dye polylactic acid (PLA) fabrics, and the dyeing depth is insufficient, making it difficult to meet practical application needs. Existing technologies for improving PLA fabric dyeing methods either involve complex processes and high costs, or cause some environmental pollution, which is not conducive to sustainable development. Therefore, developing a simple, environmentally friendly method that can effectively improve the color depth of PLA fabric dyeing is of great practical significance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for dyeing polylactic acid (PLA) fabrics that is simple, environmentally friendly, and can effectively improve the color depth of PLA fabrics.

[0005] A method for dyeing polylactic acid fabrics according to the present invention includes the following steps: S1: Modify polylactic acid fabrics using a modifier; S2: A solution is prepared by mixing deionized water and sodium carbonate. S3: Add coffee grounds to the solution in step S2 and soak them thoroughly. After extraction, filter to obtain coffee grounds extract. S4: Select a mordant and pre-complex it with the coffee grounds extract from step S3 to form a mixture; S5: Dye the polylactic acid fabric modified in step S1 with the mixture in step S4; S6: Add mordant again for secondary mordation.

[0006] Throughout the process, coffee grounds extract is used in combination with mordants to mordine polylactic acid fabrics. This method is simple and environmentally friendly, allowing for the reuse of coffee grounds. Furthermore, the secondary mordating process can effectively improve the depth of the dyed color.

[0007] Furthermore, the modifier is selected as a cationic modifier.

[0008] Furthermore, the cationic modifier includes one of quaternary ammonium salt compounds and chitosan derivatives.

[0009] Furthermore, the mordant includes one of aluminum sulfate, ferrous sulfate, and rare earth elements.

[0010] Furthermore, the pH value of the mixture in step S4 is between 4 and 5.

[0011] Furthermore, the coffee extract includes natural pigments.

[0012] Furthermore, the natural pigments include melanoidins. Attached Figure Description

[0013] Figure 1 The image shows the dyeing result after using the polylactic acid fabric dyeing method described in this invention.

[0014] Figure 2 The image shows the staining results after using the method described in Comparative Example 1.

[0015] Figure 3 The image shows the staining results after using the method described in Comparative Example 2.

[0016] Figure 4 The image shows the staining results after using the method described in Comparative Example 3. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0018] Combination Figure 1 This invention illustrates a method for dyeing polylactic acid fabrics, comprising the steps of: S1: Modify polylactic acid fabrics using a modifier; S2: A solution is prepared by mixing deionized water and sodium carbonate. S3: Add coffee grounds to the solution in step S2 and soak them thoroughly. After extraction, filter to obtain coffee grounds extract. S4: Select a mordant and pre-complex it with the coffee grounds extract from step S3 to form a mixture; S5: Dye the polylactic acid fabric modified in step S1 with the mixture in step S4; S6: Add mordant again for secondary mordation.

[0019] Throughout the process, coffee grounds extract is used in combination with mordants to mordine polylactic acid fabrics. This method is simple and environmentally friendly, allowing for the reuse of coffee grounds. Furthermore, the secondary mordating process can effectively improve the depth of the dyed color.

[0020] Cationic modifiers were selected as the modifiers.

[0021] Cationic modifiers include one of the following: quaternary ammonium salt compounds and chitosan derivatives.

[0022] Mordants include one of aluminum sulfate, ferrous sulfate, or rare earth elements.

[0023] The pH value of the mixture in step S4 is between 4 and 5.

[0024] Coffee extract contains natural pigments.

[0025] Natural pigments include melanoidins.

[0026] Natural pigments also include at least one of carotenoids and lutein.

[0027] It is worth noting that cationic modifiers can be used to treat polylactic acid fabrics. These cationic modifiers can include quaternary ammonium salts, chitosan derivatives, etc.

[0028] Example 1 Polylactic acid (PLA) fabrics are immersed in a solution containing a cationic modifier. PLA is a weakly polar biodegradable polymer with a surface that is typically neutral or weakly negatively charged. Natural pigments in coffee grounds (such as melanoidins and carotenoids) often contain polar groups (such as hydroxyl and carboxyl groups), which readily dissociate into negatively charged ions in aqueous solutions. After treatment with cationic modifiers (such as quaternary ammonium salts and chitosan derivatives), a large number of positively charged groups (such as quaternary ammonium cations and amino cations) are introduced onto the surface of the PLA fabric, making the fabric surface positively charged. Based on the electrostatic principle of "like charges repel, unlike charges attract," a strong electrostatic attraction occurs between the positively charged fabric surface and the negatively charged natural pigments, significantly increasing the initial adsorption of dye on the fabric surface, thereby improving dyeing efficiency and reducing dye waste.

[0029] The cationic modifier concentration is 1-5 g / L, the bath ratio is 1:10-1:50, and the treatment is carried out at 50-80℃ for 30-60 min. Through cationic modification, the charge properties of the polylactic acid fabric surface are changed to make it positively charged, thereby increasing the adsorption affinity for natural dyes from coffee grounds.

[0030] It is worth noting that the liquor ratio refers to the ratio of the mass of polylactic acid fabric to the mass of cationic modifier.

[0031] After drying the coffee grounds, water is used as the extraction solvent with a solid-liquid ratio of 1:10 to 1:50 and sodium carbonate dosage of 5-20 g / L. The extraction is carried out at 80-100℃ for 1-3 hours. After extraction, the mixture is filtered to obtain coffee grounds extract, which contains the natural pigments from the coffee grounds.

[0032] A mordant is selected to pre-complex with coffee grounds extract. The mordant can be aluminum sulfate, ferrous sulfate, rare earth elements, etc. The mordant and coffee grounds extract are mixed in a certain proportion, with the mass ratio of the mordant to the pigment in the coffee grounds extract being 1:3-1:5. The pH value is adjusted to 4-5, and the mixture is stirred and complexed at 30-50℃ for 20-40 minutes to form a mixed solution. The polylactic acid fabric that has undergone cationic modification pretreatment is placed in a dye bath containing a pre-complexed mixture for dyeing. The bath ratio is 1:10-1:50, and the dyeing is carried out at 90-98℃ for 60-90 minutes. During this process, the mixture is adsorbed and fixed on the surface of the polylactic acid fabric.

[0033] After dyeing, a second mordant is added to the dye bath for mordating. The amount of the second mordant is 2%-5% of the fabric weight. The treatment is carried out at 70-90℃ for 20-30 minutes. This second mordating further promotes the bonding between the dye and the fabric, enhancing color depth and color fastness. The results are as follows: Figure 1 As shown.

[0034] Using coffee grounds as a dye source reduces the use of chemically synthesized dyes and lowers environmental pollution. At the same time, most of the cationic modifiers and mordants used in the dyeing process are environmentally friendly substances, which meet the requirements of sustainable development.

[0035] The present invention also includes the extraction of coffee grounds pigment. 20g of dried coffee grounds and 2g of sodium carbonate are added to 400 mL of distilled water, and the mixture is extracted in a constant temperature water bath at 95°C for 90 min. After cooling to room temperature, the mixture is filtered and the volume is adjusted to 500 mL to obtain a coffee grounds pigment solution with a mass concentration of 20g / L.

[0036] Comparative Example 1 Comparative Example 1 uses coffee grounds dye for direct dyeing. 1g of polylactic acid fabric is added to a 20g / L coffee grounds dye solution (liquid ratio 1:50), the pH is adjusted to 3-9, the dyeing temperature is set to 60-98℃, and the dyeing time is 15-90 min. The fabric is then removed, washed with water, soaped, washed with water again, and air-dried. The dyeing results are as follows. Figure 2 As shown.

[0037] As can be seen from the above, Example 1, based on the use of coffee grounds, also modified the polylactic acid fabric and combined it with multiple mordant dyeing processes, achieving an effect far exceeding that of Comparative Example 1, which directly used coffee grounds pigment for dyeing.

[0038] Comparative Example 2 Comparative Example 2 uses coffee grounds pigment for direct dyeing combined with mordant. 1g of polylactic acid fabric is put into a 3% mordant solution (potassium aluminum sulfate, ferrous sulfate, lanthanum chloride) at a liquor ratio of 1:50 and mordated at 80℃ for 30min. After removal, it is put into a 20g / L coffee grounds pigment dyeing solution and dyed under the optimal direct dyeing conditions. After removal, it is washed with water, soaped, washed with water, and dried.

[0039] Comparative Example 3 In Comparative Example 3, polylactic acid (PLA) fabric was first modified with a cationic modifier, and then dyed with coffee grounds pigment. The PLA fabric was immersed in a solution containing the cationic modifier (concentration 1-5 g / L, liquor ratio 1:10-1:50) at 50-80℃ for 30-60 minutes. The modified PLA fabric was then immersed in a 20 g / L coffee grounds pigment dye bath (liquid ratio 1:50), with the pH adjusted to 3-9. The dyeing temperature was set at 60-98℃ for 15-90 minutes. The fabric was then removed, washed with water, soaped, washed again, and dried. The dyeing results are shown below. Figure 4 As shown.

[0040] Combination Figures 1 to 4 The dyeing results of Example 1 are deeper. The method used in this invention is that cationic modification makes the surface of polylactic acid fabric positively charged, increasing the adsorption sites for coffee grounds dye. Pre-complex mordant dyeing forms a stable dye-mordant complex, which improves the binding force of dye molecules to the fabric. Secondary mordant dyeing further strengthens the binding of dye to fabric. The three work together to significantly improve the dyeing depth. Using coffee grounds as a dye source reduces the use of chemically synthesized dyes and lowers environmental pollution. At the same time, most of the cationic modifiers and mordants used in the dyeing process are environmentally friendly substances, which meet the requirements of sustainable development. Through a unique process, the dye bonds more firmly with the fabric, and the dyed polylactic acid fabric performs well in terms of color fastness to rubbing and washing, meeting the needs of actual use.

[0041] Based on the above embodiments and several comparative examples, this invention also conducted an experiment on the effect of the amount of modifier solution on the color characteristic values ​​of polylactic acid fabrics. The amount of modifier BS was set to 0-10 g / L, the pH of the solution was adjusted to 9, the liquor ratio was 1:50, the treatment temperature was 80℃, and the treatment time was 30 min. The modified polylactic acid fabrics were dyed according to method 1.2.3. The effect of the amount of modifier on the color characteristic values ​​of the fabrics is shown in Table 1 below: Dosage / g / L K / S value L* a* b* c* ho 0 0.87 78.41 3.34 12.97 78.41 89.36 0.5 0.95 75.00 3.35 13.64 75.01 89.27 1 1.14 72.93 3.78 14.04 72.94 89.10 3 1.38 70.54 4.23 15.27 70.55 88.88 5 1.47 70.07 4.37 15.79 70.09 88.80 7 1.49 70.04 4.40 15.82 70.06 88.78 10 1.48 70.06 4.39 15.81 70.08 88.79 Table 1. Effect of BS modifier dosage on color characteristic values ​​of polylactic acid fabrics The K / S value is a key indicator of the color of dyed fabrics. It is used to quantify the depth of color and the concentration of dye on the fabric surface. The larger the K / S value, the higher the dye concentration and the darker the color on the fabric surface; conversely, the smaller the K / S value, the lighter the color. L* represents the lightness value, a* represents the color shift in the red-green direction, b* represents the color shift in the yellow-blue direction, c* represents the vividness or saturation of the color. The larger the c* value, the more vivid and intense the color. ho represents the hue angle of the color.

[0042] As shown in Table 1, the modifier BS can improve the apparent color depth of polylactic acid (PLA) fabrics dyed with coffee grounds pigment, and increase the K / S value of the fabric. When the modifier BS is in the range of 0-5 g / L, the higher the amount of modifier BS, the higher the K / S value, a*, and b* of the fabric, while c* decreases. This indicates that after coffee grounds dyeing, the yellow and red light on the surface of the modified PLA fabric increases, the color brightness decreases, and the ho value changes relatively little, indicating that the hue of the color does not change much. When the amount of modifier BS is 5 g / L, the depth of the dyed fabric increases by nearly 70%. After exceeding 5 g / L, the change in color depth and other characteristic values ​​is very small. Therefore, the preferred amount of modifier BS is 5 g / L.

[0043] Based on this, the present invention also conducted an experiment on the effect of the pH value of the modifier solution on the color characteristic values ​​of polylactic acid fabrics. The dosage of modifier BS was set at 5 g / L, the pH of the solution was adjusted to 3-11, the liquor ratio was 1:50, the treatment temperature was 80℃, and the treatment time was 30 min. The effect of the pH value of the modifier solution on the color characteristic values ​​of the fabric is shown in Table 2. PH K / S value L* a* b* c* ho 3 0.97 74.78 3.37 13.69 74.79 89.26 5 1.00 74.60 3.47 13.91 74.61 89.23 7 1.03 74.16 3.63 14.12 74.17 89.20 9 1.47 70.07 4.37 15.79 70.09 88.80 11 1.30 71.28 4.03 14.99 71.29 88.96 Table 2. Effect of pH value of modifier solution on color properties of polylactic acid fabrics. As can be seen from Table 2, under acidic and neutral conditions, the K / S value of modified polylactic acid fabrics only increased by 11.5%-18% compared with that of unmodified polylactic acid fabrics. This is mainly because polylactic acid has very little negative charge on its surface, and the amount of cationic modifier BS adsorbed by electrostatic adsorption is also limited. Furthermore, the amount of coffee grounds pigment adsorbed during dyeing is not much higher than that of unmodified fabrics. When the solution pH=9, the K / S value increases by 70%, and a* and b* also increase significantly. Under alkaline conditions, a large number of carboxyl groups on the polylactic acid surface dissociate into -COO (formate ions), resulting in a sharp increase in negative charge density. This significantly enhances the electrostatic attraction with the cationic modifier, leading to a substantial increase in the amount of modifier adsorbed and a significant increase in the amount of coffee grounds pigment bound. As the alkalinity of the solution increases, the K / S value of the dyed polylactic acid fabric decreases. Polylactic acid fabrics have poor alkali resistance, and the fibers undergo hydrolysis, reducing the strength of the fabric. At the same time, strong alkali may also affect the activity of the modifier BS. All these factors combined result in the K / S value of the dyed fabric being lower at pH=11 than at pH=9. Therefore, the optimal pH value for the solution during modification treatment is 9.

[0044] Based on this, the present invention also conducted an experiment on the effect of modification treatment temperature on the color characteristic values ​​of polylactic acid fabrics. The dosage of modifier BS was set to 5 g / L, the pH of the solution was adjusted to 9, the liquor ratio was 1:50, the treatment temperature was 40-80℃, and the treatment time was 30 min. The effect of modification treatment temperature on the color characteristic values ​​of the fabric is shown in Table 3. Temperature / °C K / S value L* a* b* c* ho 40 1.06 73.87 3.66 13.91 73.88 89.18 50 1.23 71.85 3.98 14.74 71.86 89.02 60 1.35 70.75 4.14 15.14 70.76 88.91 70 1.41 70.25 4.28 15.30 70.26 88.85 80 1.47 70.07 4.37 15.79 70.09 88.80 Table 3 Effect of modification treatment temperature on color properties of polylactic acid fabrics As shown in Table 3, when the modification temperature increases from 40℃ to 80℃, the K / S value, a*, and b* of the dyed polylactic acid fabric all increase. The temperature increase promotes the swelling of polylactic acid fibers. The more the modifier BS is adsorbed, the higher the positive charge density on the fiber surface, the more coffee grounds pigment is bound, the darker the apparent color, and the lower L*. As the modification temperature increases, the yellow and red hues of the dyed fabric become more obvious. The ho does not change much, indicating that the hue is relatively stable.

[0045] Based on this, the present invention also conducted an experiment on the effect of modification treatment time on the color characteristic values ​​of polylactic acid fabrics. The dosage of modifier BS was set to 5 g / L, the pH of the solution was adjusted to 9, the liquor ratio was 1:50, the treatment temperature was 40-80℃, and the treatment time was 30 min. The effect of modification treatment temperature on the color characteristic values ​​of the fabric is shown in Table 4. Time / min K / S value L* a* b* c* ho 5 1.05 73.93 3.63 13.87 73.94 89.19 10 1.20 72.13 3.87 14.54 72.14 89.05 15 1.33 70.82 4.10 14.88 70.83 88.92 20 1.42 70.16 4.29 15.32 70.17 88.84 30 1.47 70.07 4.37 15.79 70.09 88.80 Table 4. Effect of modification treatment time on color property values ​​of polylactic acid fabrics As shown in Table 4, with the extension of modification treatment time, the K / S value, a*, and b* of the dyed polylactic acid fabric all increased. In the first 20 minutes of modification treatment, the color depth increased relatively quickly, and the increase slowed down after 20-30 minutes. This is mainly because the active reaction sites on the fiber surface gradually became saturated, the modifier could no longer bind in large quantities, the number of cationic sites tended to stabilize, and the rate of increase in pigment dyeing slowed down. Therefore, the optimal modification treatment time is 30 minutes.

[0046] Based on this, the preferred embodiment of the dyeing method for polylactic acid fabric provided by the present invention is as follows: the polylactic acid fabric is immersed in a solution containing a cationic modifier, and after treatment with the modifier BS, the surface of the fabric is positively charged. The concentration of the modifier BS is 5 g / L, the pH is 9, the bath ratio is 1:10-1:50, and the treatment is carried out at 40-80℃ for 30 min. After drying the coffee grounds, water is used as the extraction solvent with a solid-liquid ratio of 1:10 to 1:50 and sodium carbonate dosage of 5-20 g / L. The extraction is carried out at 80-100℃ for 1-3 hours. After extraction, the mixture is filtered to obtain coffee grounds extract, which contains the natural pigments from the coffee grounds.

[0047] A mordant is selected to pre-complex with coffee grounds extract. The mordant can be aluminum sulfate, ferrous sulfate, rare earth elements, etc. The mordant and coffee grounds extract are mixed in a certain proportion, with the mass ratio of the mordant to the pigment in the coffee grounds extract being 1:3-1:5. The pH value is adjusted to 4-5, and the mixture is stirred and complexed at 30-50℃ for 20-40 minutes to form a mixed solution. The polylactic acid fabric that has undergone cationic modification pretreatment is placed in a dye bath containing a pre-complexed mixture for dyeing. The bath ratio is 1:10-1:50, and the dyeing is carried out at 90-98℃ for 60-90 minutes. During this process, the mixture is adsorbed and fixed on the surface of the polylactic acid fabric.

[0048] After dyeing, a mordant is added to the dye bath for secondary mordating. The amount of secondary mordant is 2%-5% of the fabric mass. The treatment is carried out at 70-90℃ for 20-30 minutes. Secondary mordating further promotes the bonding between the dye and the fabric, and enhances the color depth and color fastness.

[0049] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for dyeing polylactic acid fabrics, characterized in that, Including the following steps: S1: Modify polylactic acid fabrics using a modifier; S2: A solution is prepared by mixing deionized water and sodium carbonate. S3: Add coffee grounds to the solution in step S2 and soak them thoroughly. After extraction, filter to obtain coffee grounds extract. S4: Select a mordant and pre-complex it with the coffee grounds extract from step S3 to form a mixture; S5: Dye the polylactic acid fabric modified in step S1 with the mixture in step S4; S6: Add mordant again for secondary mordation.

2. The polylactic acid fabric dyeing method according to claim 1, characterized in that, The modifier is a cationic modifier.

3. The polylactic acid fabric dyeing method according to claim 2, characterized in that, The cationic modifier includes one of quaternary ammonium salt compounds and chitosan derivatives.

4. The polylactic acid fabric dyeing method according to claim 1, characterized in that, The mordant includes one of aluminum sulfate, ferrous sulfate, and rare earth elements.

5. The polylactic acid fabric dyeing method according to claim 1, characterized in that, The pH value of the mixture in step S4 is between 4 and 5.

6. The polylactic acid fabric dyeing method according to claim 1, characterized in that, The coffee extract contains natural pigments.

7. The polylactic acid fabric dyeing method according to claim 6, characterized in that, The natural pigments include melanoidins.

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