Preparation method of pH-responsive core-shell microsphere emulsion

Abstract

The invention discloses a preparation method of a pH-responsive core-shell microsphere emulsion. The preparation method comprises the following steps: S1, preparing a polystyrene emulsion; s2, uniformly mixing a spiropyran monomer, butyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, an emulsifier and water to form a pre-emulsion; s3, dropwise adding the pre-emulsion into the polystyrene emulsion according to the mass ratio of the polystyrene emulsion to the pre-emulsion of 1: (0.2-0.5), preserving heat at 65 DEG C for 1 hour, preserving heat at 75 DEG C for 1 hour, preserving heat at 85 DEG C for 4 hours, and cooling to room temperature to obtain the core-shell microsphere emulsion. The core-shell microspheres prepared by the preparation method disclosed by the invention are good in washability and have a wider adjustable pH response range.

Description

Technical Field

[0001] This invention relates to the field of textile materials, and more particularly to a method for preparing a pH-responsive core-shell microsphere emulsion. Background Technology

[0002] Denim fabric, a pillar textile with an annual global consumption exceeding 5 billion meters, has long been limited in its printing process by high-energy-consuming heat transfer technology (operating temperature > 150℃) and static pattern representation. Although cold transfer printing technology (operating temperature ≤ 45℃) has gradually matured in recent years, the lack of functional ink systems severely restricts its development. The application of existing color-changing materials in the denim field faces three major technical barriers: First, while traditional spiropyran-based color-changing agents possess pH-responsive characteristics, when directly incorporated into the ink system, the aggregation effect caused by molecular-level dispersion (particle size > 500nm) not only results in a high inkjet printing head clogging rate of up to 23% (EPSON printhead test data), but also leads to a sharp deterioration in wash resistance due to the lack of a protective mechanism—according to the AATCC 61-2020 standard test, the color difference ΔE decreases by > 30% after 20 accelerated washes, failing to meet commercial-grade durability requirements (industry standards require resistance to 50 washes). Secondly, the color-changing threshold of existing pH-responsive materials is fixed within a narrow range, typically pH 5.0-6.5, which cannot adapt to the diverse needs of human sweat pH fluctuations (pH 4.5-7.5) and environmental monitoring. For example, the acrylic / spiropyran copolymer disclosed in patent CN101704921A has a relatively fixed response threshold, mainly concentrated in a specific narrow pH range, making it difficult to flexibly cope with complex acid-base changes. According to a 2023 report in the Textile Research Journal, 91% of smart printed fabrics worldwide were discontinued due to uncontrollable color-changing performance. Therefore, there is an urgent need for a core-shell microsphere emulsion with good wash resistance and a wide adjustable pH response range. Summary of the Invention

[0003] The objective of this invention is achieved through the following technical solution: A method for preparing a pH-responsive core-shell microsphere emulsion includes the following steps: S1. Preparation of polystyrene emulsion; S2. Mix spiropyran monomer, butyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, emulsifier and water evenly to form a pre-emulsion. The mass ratio of spiropyran monomer, butyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, emulsifier and water is 45:18:(3.14-23.58):0.3:0.6:300. S3. Add the pre-emulsion dropwise to the polystyrene emulsion. The mass ratio of the polystyrene emulsion to the pre-emulsion is 1:(0.2-0.5). After the addition is complete, keep the temperature at 65°C for 1 hour, at 75°C for 1 hour, at 85°C for 4 hours, and then cool to room temperature to obtain the core-shell microsphere emulsion.

[0004] Preferably, the polystyrene in step S1 is prepared by mixing water, emulsifier, and sodium bicarbonate, then purging with nitrogen to remove oxygen, adding styrene monomer, heating to 70°C, adding potassium persulfate aqueous solution, and stirring for 6 hours. The mass ratio of water, emulsifier, sodium bicarbonate, styrene monomer, and potassium persulfate aqueous solution is 1200:2.4:1.2:150:30.36, and the potassium persulfate aqueous solution is prepared by dissolving 0.36g of potassium persulfate in 30g of water.

[0005] Preferably, the emulsifier in both steps S1 and S2 is sodium dodecyl sulfate.

[0006] Preferably, the mass ratio of polystyrene emulsion to pre-emulsion is 1:(0.3-0.4).

[0007] Preferably, the dripping rate of the pre-emulsion in step S3 is 0.5 ml / min.

[0008] Preferably, in step S2, the mass ratio of spiropyran monomer, butyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, emulsifier, and water is 45:18:(8.6-23.6):0.3:0.6:300.

[0009] 7. The method for preparing pH-responsive core-shell microsphere emulsion according to claim 3, characterized in that, after cooling to room temperature in step S3, the core-shell microsphere emulsion is passed through a 200-mesh sieve.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention forms a spiropyran-dimethylaminoethyl methacrylate copolymer soft shell on the surface of a polystyrene hard core by using a gradient temperature polymerization process: 65°C low-speed polymerization, 75°C for core-shell growth, and 85°C for crosslinking and curing. The resulting core-shell structured microspheres exhibit good wash resistance and have an adjustable pH response threshold range. Detailed Implementation

[0011] To make the technical problems solved by this invention, the technical solutions adopted, and the technical effects achieved clearer, the technical solutions of the embodiments of this invention will be described in further detail below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Example

[0012] This embodiment provides a method for preparing a pH-responsive core-shell microsphere emulsion, comprising the following steps: S1. Preparation of polystyrene emulsion: Mix 1200ml of water, 2.4g of sodium dodecyl sulfate and 1.2g of sodium bicarbonate, then bubble with nitrogen for 30min to completely remove oxygen. Add 150g of styrene monomer, heat to 70℃ and add potassium persulfate aqueous solution (0.36g of potassium persulfate dissolved in 30g of water). Stir and react for 6h to obtain polystyrene emulsion. S2. Mix 45g of spiropyran monomer, 18g of butyl acrylate, 3.14g of dimethylaminoethyl methacrylate, 0.3g of ethylene glycol dimethacrylate, 0.6g of sodium dodecyl sulfate and 300g of water evenly to form a pre-emulsion. S3. Add the pre-emulsion dropwise to the polystyrene emulsion at a rate of 0.5 ml / min. The mass ratio of the polystyrene emulsion to the pre-emulsion is 1:0.4. After the addition is complete, keep the mixture at 65°C for 1 hour, at 75°C for 1 hour, and at 85°C for 4 hours. Then cool it to room temperature to obtain the core-shell microsphere emulsion, which is then passed through a 200-mesh sieve. Example

[0013] This embodiment is similar to Example 1, except that the amount of dimethylaminoethyl methacrylate used is 8.64g. Example

[0014] This embodiment is similar to Example 1, except that the amount of dimethylaminoethyl methacrylate used is 15.72g. Example

[0015] This embodiment is similar to Example 1, except that the amount of dimethylaminoethyl methacrylate used is 23.58g. Example

[0016] This embodiment is similar to Embodiment 3, except that the mass ratio of polystyrene emulsion to pre-emulsion is 1:0.2. Example

[0017] This embodiment is similar to Embodiment 3, except that the mass ratio of polystyrene emulsion to pre-emulsion is 1:0.3. Example

[0018] This embodiment is similar to Embodiment 3, except that the mass ratio of polystyrene emulsion to pre-emulsion is 1:0.5.

[0019] Comparative Example 1 This comparative example provides a method for synthesizing spiropyran color changer by continuous dropwise addition. 50g of styrene, 5g of acrylic acid, 2g of spiropyran monomer, 0.5g of divinylbenzene, 0.1g of sodium persulfate and 200g of water are added to a reaction vessel and reacted at a constant temperature of 75℃ for 4h. Sodium persulfate is diluted and dissolved with 8.3g of water and then added dropwise to the reaction vessel.

[0020] Comparative Example 2 10g of spiropyran methacrylate, 2g of acrylic acid and 0.2g of azobisisobutyronitrile were reacted at 70°C for 8h in a mixed solvent consisting of 30g of toluene and 10g of ethanol. The reaction product was poured into n-hexane to precipitate and then dried to obtain a purple solid color-changing agent.

[0021] The core-shell microsphere emulsions or color-changing agents of Examples 1-7 and Comparative Examples 1-2 were formulated into transfer inks, wherein 720g of core-shell microsphere emulsion / color-changing agent (25% solid content), 375g of aqueous polyurethane PU-326, 192g of propylene glycol methyl ether, 12Gbyk-349 and 701g of deionized water were used to obtain blue ink.

[0022] The denim fabric was treated with 5g / L of amylase at 50℃ for 20 minutes, followed by cold transfer printing with blue ink at a pressure of 5kg / cm. 2 The transfer temperature was 40℃, the transfer time was 30s, and the humidity was 65%RH.

[0023] The denim fabrics of Example 3 and Comparative Document 1 were tested for color development response speed at pH 6.5→7.0 and fading response speed at pH 7.0→6.5 during the alkali→acid transition, as well as stability cycling and microsphere shedding rates. The results are shown in Table 1.

[0024] The stability cycle test steps are as follows: 1. Testing equipment: Customized pH switching device.

[0025] 2. Cyclic procedure: Acid treatment: pH 5.0 buffer × 30s; Alkali treatment: pH 8.0 buffer × 30s.

[0026] 3. Performance Monitoring: ΔE value is measured every 50 cycles (CIE Lab); Termination condition: ΔE decay > 30%. 4. Failure determination: Disappearance of characteristic peaks in the ultraviolet spectrum (absorbance at 580nm <0.1).

[0027] Microsphere shedding rate test: 40±2℃, 0.15% soap solution, 45min / time, equivalent to 50 household washes.

[0028] Sample preparation: The fabric was sprayed with gold after washing (thickness 5nm).

[0029] Electron microscopy observation: 5000x images were captured using a Hitachi SU8010 SEM (5kV, WD=8mm).

[0030] Image analysis: ImageJ software was used to count the number of microspheres per unit area (100 μm²).

[0031] The formula for the shedding rate is: Shedding rate = [1 - (Nn / N0)] × 100%; where N0 is the number of microspheres per unit area before washing, and Nn is the number of microspheres per unit area after washing n times.

[0032]

[0033] The actual color change threshold of the core-shell microspheres in the denim fabrics tested in Examples 1-4 was established. With the other components remaining constant, a linear regression equation was established with the mass of dimethylaminoethyl methacrylate as the independent variable and the theoretical color change threshold as the dependent variable: pH = 0.216X + 3.553, R² = 0.991. This linear regression equation showed good fit in the pH range of 4-8.5. The results are shown in Table 2.

[0034]

[0035] Due to defects in the synthesis process, Comparative Example 1 showed uneven protonation enrichment on the surface of the microspheres. XPS testing revealed a protonation concentration ratio of 1:8 between the surface and interior of the microspheres, leading to a corresponding threshold drift. The actual color-changing thresholds for the two batches of color-changing agents synthesized in Comparative Example 1 were as follows: For the first batch, after multiple measurements, the actual color-changing threshold fluctuated between 6.3 and 7.1, with a unilateral fluctuation of 0.4. For the second batch, the actual color-changing threshold fluctuated between 5.8 and 6.7, with a unilateral fluctuation of 0.5. In contrast, the color-changing thresholds of Examples 1-4 were stable, without any problem of uneven protonation distribution. Furthermore, the regression equation established in this invention deviated from the actual color-changing threshold by no more than 0.2, allowing for precise adjustment of the core-shell microsphere composition within the applicable range of the linear regression equation and the pH range of human sweat to suit different scenarios.

[0036] After the denim fabrics of Examples 3 and 5-7 were subjected to 50 soap washes, the ΔE value decay, microsphere shedding rate, microsphere breakage rate and bending stiffness were tested. The ΔE value decay test method was similar to the stability cycle test, and the results are shown in Table 3.

[0037] Microsphere breakage rate test: Microsphere shedding rate test: 40±2℃, 0.15% soap solution, 45min / time, equivalent to 50 household washes.

[0038] Under a laser confocal microscope, the number of microspheres before and after water washing was counted, and the microsphere breakage rate was calculated.

[0039]

[0040] Example 5 exhibits poor wash resistance, while Examples 3, 6, and 7 demonstrate good wash resistance. However, Example 7 has relatively stiff bending rigidity, i.e., a stiffer hand feel. Overall, Examples 3 and 6 offer good wash resistance while maintaining a soft denim fabric.

[0041] Comparative Example 3 The scheme of Comparative Example 3 is similar to that of Example 3, except that the ethylene glycol dimethacrylate in the example is replaced with trimethylolpropane trimethacrylate in this comparative example.

[0042] Comparative Example 4 The scheme of Comparative Example 4 is similar to that of Example 3, except that the ethylene glycol dimethacrylate in the example is replaced with hexanediol diacrylate in this comparative example.

[0043] The microsphere rupture rate of Example 3 and Comparative Examples 3-4 was tested, and the results are shown in Table 4.

[0044]

[0045] Comparative Example 3 used trimethylolpropane trimethacrylate trifunctional crosslinking agent, which resulted in excessive crosslinking, causing the microspheres to become brittle and easily break during washing. Comparative Example 4 used hexanediol diacrylate, forming flexible long chains, but with insufficient shear resistance, causing the microspheres to easily break during washing.

[0046] The above embodiments are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a pH-responsive core-shell microspheres emulsion, characterized in that , comprising the following steps: S1, preparing a polystyrene emulsion; S2, uniformly mixing a spiropyran monomer, butyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, an emulsifier and water to form a pre-emulsion, the mass ratio of the spiropyran monomer, butyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, the emulsifier and water being 45:18: (3.14-23.58):0.3:0.6:300; S3, adding the pre-emulsion to the polystyrene emulsion, the mass ratio of the polystyrene emulsion to the pre-emulsion being 1: (0.2-0.5), and after the addition is completed, keeping the temperature at 65°C for 1h, 75°C for 1h, and 85°C for 4h, and then cooling to room temperature to obtain the core-shell microsphere emulsion.

2. The method for preparing the pH-responsive core-shell microsphere emulsion according to claim 1, characterized in that, The polystyrene in step S1 is prepared by mixing water, an emulsifier and sodium bicarbonate, removing oxygen by nitrogen bubbling, adding styrene monomers, heating to 70°C and adding an aqueous potassium persulfate solution, and stirring for 6h, the mass ratio of the water, the emulsifier, sodium bicarbonate, styrene monomers, and the aqueous potassium persulfate solution being 1200:2.4:1.2:150:30.36, and the aqueous potassium persulfate solution being 0.36g of potassium persulfate dissolved in 30g of water.

3. The method for preparing the pH-responsive core-shell microsphere emulsion according to claim 2, characterized in that, The emulsifiers in steps S1 and S2 are both sodium dodecyl sulfate.

4. The method for preparing the pH-responsive core-shell microsphere emulsion according to claim 3, characterized in that, The mass ratio of the polystyrene emulsion to the pre-emulsion is 1: (0.3-0.4).

5. The method for preparing the pH-responsive core-shell microsphere emulsion according to claim 4, characterized in that, The dropwise addition speed of the pre-emulsion in step S3 is 0.5ml / min.

6. The method for preparing the pH-responsive core-shell microsphere emulsion according to claim 5, characterized in that, The mass ratio of the spiropyran monomer, butyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, the emulsifier and water in step S2 is 45:18: (8.6-23.6):0.3:0.6:

300.

7. The method for preparing the pH-responsive core-shell microsphere emulsion according to claim 3, characterized in that, After cooling to room temperature in step S3, the core-shell microsphere emulsion is passed through a 200-mesh screen.

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