Method for preparing a milk protein modified regenerated cellulose fiber

Abstract

The application discloses a preparation method of milk protein modified regenerated cellulose fiber, and relates to the technical field of cellulose fiber, and the method comprises the following steps: preparing pre-crosslinking activated microspheres by pre-crosslinking and spray drying of milk casein through a microorganism transglutaminase; then, a water-soluble oxidation-reduction initiation system is used to graft and polymerize cationic monomers and epoxy functional monomers onto the surface of the microspheres to obtain grafted functionalized milk protein; viscose spinning stock solution is added into the grafted functionalized milk protein and an epoxy type crosslinking auxiliary agent, and then short-time low-temperature mixing and vacuum degassing are carried out, and finally, composite fiber is obtained through wet spinning, coagulation forming and post-processing. The obtained fiber has excellent mechanical properties, antibacterial durability and antistatic property.

Description

Technical Field

[0001] This invention relates to the field of cellulose fiber technology, and specifically to a method for preparing milk protein-modified regenerated cellulose fiber. Background Technology

[0002] Milk protein fiber is a regenerated protein fiber made from milk casein through blending or graft copolymerization with polymers and then spinning. It has advantages such as soft hand feel, good breathability, and good skin-friendliness, and has broad application prospects in the fields of high-end clothing, home textiles and functional textiles.

[0003] Currently, the preparation of milk protein-cellulose composite fibers mainly employs the blending spinning method. For example, Chinese patent CN102260933B discloses a milk protein blended regenerated cellulose fiber and its preparation process. The technical solution involves: pulverizing milk casein at low temperature to 0.5–0.8 micrometers, dissolving it in a 10% alkaline solution (40–45°C) with a ketose crosslinking agent (such as 1,3-dihydroxyacetone) to obtain a milk protein spinning solution, then blending it with a viscose spinning solution, and finally wet spinning to obtain the composite fiber. This process uses ketoses as crosslinking agents, achieving partial crosslinking of protein and cellulose through the Maillard reaction, thus reducing protein dissolution in alkaline systems.

[0004] However, this existing technology has the following technical drawbacks:

[0005] (1) The problem of protein alkaline degradation has not been effectively solved.

[0006] CN102260933B describes directly dissolving milk casein in a 10% alkaline solution (pH>13). This highly alkaline environment leads to severe alkaline degradation of the milk casein. Under these alkaline conditions, peptide bonds in the protein molecular chain hydrolyze and break, significantly reducing the molecular weight and partially degrading into low-molecular-weight peptides or even amino acids. These degradation products are largely lost during subsequent spinning and washing processes, resulting in a significant decrease in protein retention in the fiber. This not only wastes protein raw materials but also contaminates the coagulation bath and washing water, increasing the burden on environmental treatment.

[0007] (2) Poor protein dispersibility affects fiber mechanical properties.

[0008] CN102260933B uses a physical pulverization method to process casein to the micron level (0.5–0.8 μm). However, the pulverized casein particles are hydrophobic and easily aggregate in viscose solution, making uniform dispersion difficult. Aggregated protein particles form stress concentration points during spinning, leading to a decrease in fiber breaking strength. In this patented embodiment, after adding 5% milk protein solution, the dry breaking strength of viscose filament decreased from 2.10 cN / dtex to 1.90 cN / dtex, a decrease of 9.5%; the dry breaking strength of viscose staple fiber decreased from 2.08 cN / dtex to 2.01 cN / dtex. This indicates that protein addition has a significant negative impact on fiber mechanical properties.

[0009] (3) Limited cross-linking efficiency and insufficient functional durability

[0010] CN102260933B uses ketose (1,3-dihydroxyacetone) as a cross-linking agent. Its cross-linking mechanism relies on the Maillard reaction, which is slow and inefficient in alkaline environments. Relying solely on a small amount of ketose (0.5–3% by weight of the alkaline solution) is insufficient to achieve adequate cross-linking between proteins and cellulose, leading to the gradual loss of protein from the fiber during subsequent washing, thus compromising the durability of antibacterial and skin-friendly functions. This patent does not provide any data regarding wash resistance.

[0011] To address the aforementioned issues, there are existing reports of pre-grafting modification of milk casein. For example, casein is grafted and copolymerized with acrylic monomers to improve its compatibility in viscose solutions. However, conventional graft polymerization often uses oil-soluble initiators (such as azobisisobutyronitrile), which have low initiation efficiency and high homopolymer formation in water-organic mixed solvent systems. Furthermore, the grafting sites are mainly located at the ends of protein molecular chains, resulting in a low grafting rate (typically <25%) and limited protection of proteins in alkaline systems.

[0012] On the other hand, the viscose wet spinning process itself has extremely strict requirements on the pH value and stability of the spinning solution. When modified proteins are directly added to a strongly alkaline viscose solution (pH>13), even after grafting modification, the proteins still face varying degrees of risk of alkaline degradation. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a method for preparing milk protein modified regenerated cellulose fiber, which can effectively inhibit the alkaline degradation of milk casein, improve its dispersion stability in viscose solution, and enhance the mechanical properties and functional durability of the fiber, in order to address the shortcomings of the existing technology.

[0014] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0015] A method for preparing milk protein-modified regenerated cellulose fiber, characterized by comprising the following steps:

[0016] A: Milk casein was subjected to a pre-crosslinking reaction under the action of microbial transglutaminase. After the enzyme activity was terminated, it was spray-dried to obtain pre-crosslinked activated milk protein microspheres with an average particle size of 1-5 μm and a crosslinking degree of 30-40%.

[0017] The degree of crosslinking was determined by the TNBS (2,4,6-trinitrobenzenesulfonic acid) method and calculated by the reduction rate of free amino groups in the protein before and after the reaction. The formula is: degree of crosslinking (%) = (1 - free amino content after reaction / free amino content before reaction) × 100%.

[0018] B: Pre-crosslinked activated milk protein microspheres were dispersed in a mixed solvent of phosphate buffer and ethanol at pH 6.5–7.5. Cationic monomers and epoxy functional monomers were added, and in-situ grafting polymerization was carried out in a water-soluble redox initiation system. After the reaction, the homopolymer was removed by purification to obtain grafted functionalized milk protein with a grafting rate of 35–50%.

[0019] C: Adjust the viscose spinning solution to pH 9.5–10.2 with 0.1–0.5 mol / L disodium hydrogen phosphate-citric acid buffer and cool to 15–18°C. Add grafted functionalized milk protein and epoxy crosslinking agent, mix thoroughly, and obtain the mixed solution after vacuum degassing. Maintain the pH of the system at 9.5–10.2 during mixing, and the mixing time should not exceed 30 min to inhibit protein degradation by alkali.

[0020] The vacuum degassing process is carried out at 15–18°C and pH 9.5–10.2, with a degassing time not exceeding 20 minutes. During the degassing process, an inert gas (nitrogen) is continuously introduced to maintain pH stability. The total mixing and degassing time is controlled within 50 minutes, thereby further reducing the risk of protein exposure in an alkaline environment.

[0021] D: The mixed solution is fed into an acidic coagulation bath through wet spinning, and after stretching and coagulation, nascent fibers are obtained.

[0022] E: The nascent fibers are sequentially washed with hot water, neutralized and washed, desulfurized, washed with water, oiled and dried to obtain milk protein-cellulose composite fibers.

[0023] Preferably, the amount of microbial transglutaminase added in step A is 5-12 U / g milk casein, the pre-crosslinking reaction temperature is 35-45℃, and the reaction time is 1-2 h; the enzyme activity is terminated by heating in a water bath at 75-80℃ for 15-20 min, the spray drying inlet air temperature is 170-190℃, and the outlet air temperature is 70-80℃.

[0024] Preferably, the cationic monomer in step B is methacryloyloxyethyltrimethylammonium chloride, and its addition amount is 8-15 wt% of the milk cheese weight; the epoxy functional monomer is glycidyl methacrylate, and its addition amount is 3-6 wt% of the milk cheese weight; the volume ratio of phosphate buffer to ethanol in the mixed solvent is 8.5:1.5-9:1, and the concentration of phosphate buffer is 20-30 mM.

[0025] Preferably, the initiation system in step B is a water-soluble redox initiation system, specifically ammonium persulfate and sodium bisulfite in a molar ratio of 1:1, which are prepared into aqueous solutions with a concentration of 2-3 wt% and added sequentially or simultaneously, with a total addition amount of 0.8-1.5 wt% of the total mass of the cationic monomer and the epoxy functional monomer; the graft polymerization reaction temperature is 40-50℃, the reaction time is 2-3 h, and nitrogen protection is used during the reaction to reduce the formation of homopolymer.

[0026] Preferably, the homopolymer removal method in step B includes the following steps:

[0027] After the reaction is terminated, the graft polymerization reaction solution is cooled to 20-25°C, and 3-5 times the volume of 90-95% ethanol is added to the system. The mixture is stirred for 10-15 minutes to allow the homopolymer to fully dissolve in the alcohol phase, while the grafted functionalized milk protein forms a dispersed precipitate.

[0028] Place the mixture in a high-speed centrifuge and centrifuge at 8000-10000 rpm for 15-20 minutes at 20-25°C to allow the grafted functionalized milk protein microspheres to settle to the bottom of the centrifuge tube.

[0029] Discard the supernatant, add phosphate buffer solution with pH 6.5-7.5 to the precipitate, stir gently to reconstitute, and repeat the above "ethanol extraction-centrifugation" steps 2-3 times (add phosphate buffer solution with pH 6.5-7.5 to the precipitate at 1 / 2 the volume of the original reaction solution) to avoid increasing the subsequent centrifugation load by using too much buffer solution, or causing the precipitate to not be fully reconstituted due to insufficient buffer solution.

[0030] After the final centrifugation, the bottom precipitate was collected and freeze-dried under vacuum (temperature -50 to -40℃, vacuum degree ≤0.05MPa) to obtain high-purity grafted functionalized milk protein.

[0031] Preferably, the amount of grafted functionalized milk protein added in step C is 6-10 wt% of the dry weight of cellulose in the viscose spinning solution; the epoxy crosslinking aid is polyethylene glycol diglycidyl ether with a number average molecular weight of 1000-1500, and the amount added is 0.8-1.2 wt% of the grafted functionalized milk protein.

[0032] Preferably, the viscose spinning solution in step C has a cellulose content of 9.0–10.0 wt%, a cooling rate of 1–2 °C / min, a mixing temperature of 14–16 °C, and a stirring speed of 400–600 rpm.

[0033] Preferably, the sulfuric acid concentration in the acidic coagulation bath in step D is 45–60 g / L, and the temperature is 30–40 °C.

[0034] Preferably, the coagulation bath in step D further comprises: 250-300 g / L sodium sulfate and 5-10 g / L zinc sulfate.

[0035] Preferably, in step D, the diameter of the spinneret orifice in wet spinning is 0.08–0.10 mm, the extrusion speed is 6–10 m / min, the stretching ratio is 1.5–1.8 times, and the stretching method adopts two-stage stretching, wherein the first-stage stretching ratio is 1.2–1.3 times and the second-stage stretching ratio is 1.2–1.3 times.

[0036] Preferably, in step E, the neutralization washing uses an acetic acid solution with a concentration of 1-2 g / L to adjust the pH to 6.5-7.5, the washing temperature is 40-50°C, and the washing time is 15-20 min; the desulfurization uses a sodium sulfite solution with a concentration of 2.0-3.0 g / L, the temperature is 50-60°C, and the desulfurization time is 20-30 min.

[0037] Preferably, the oiling in step E uses a non-ionic fiber oiling agent with an oiling rate of 0.8–1.2 wt%; the drying temperature is 80–90 °C; and the drying time is 30–40 min.

[0038] Preferably, the drying in step E is carried out in stages, with the first stage drying at 60-70°C for 15-25 minutes and the second stage drying at 80-90°C for 5-15 minutes, in order to avoid fiber deformation.

[0039] Preferably, the obtained milk protein-cellulose composite fiber has the following characteristics:

[0040] Dry fracture strength ≥ 2.2 cN / dtex;

[0041] The inhibition rate against Staphylococcus aureus is ≥95%;

[0042] After 20 standard water washes, the antibacterial retention rate is ≥85%;

[0043] Volume resistivity ≤ 5 × 10 10 Ω·cm;

[0044] Protein retention rate in the fiber (relative to the theoretical amount of protein added in the spinning solution, dried basis) ≥ 70%.

[0045] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0046] 1. Pre-crosslinked microspheres improve the overall stability of the protein structure. Pre-crosslinking reduces the exposure of protein chain ends, thus lowering the alkaline hydrolysis rate. Graft polymerization introduces active groups onto the microsphere surface. pH adjustment reduces the alkalinity of the mixture from >13 to 9.5–10.2, significantly reducing the protein alkaline degradation rate. Epoxy crosslinking aids form chemical crosslinks between the protein and cellulose, covalently fixing the protein to the fiber matrix. The synergistic effect of these four factors achieves highly efficient protein retention during spinning and post-processing, increasing the protein retention rate in the fiber to ≥70% (relative to the theoretical amount of protein added to the spinning solution, dried basis).

[0047] 2. The pre-crosslinked microspheres (1–5 μm) have a uniform particle size distribution and a moderate crosslinking ratio (30–40%), ensuring stable dispersion in the viscose solution and avoiding stress concentration caused by large particle agglomeration. The cationic and epoxy groups introduced by graft polymerization enhance the interfacial bonding between the protein microspheres and the cellulose matrix. Secondary stretching (total ratio 1.5–1.8 times) ensures full orientation of the fiber molecular chains while preventing the protein microspheres from detaching due to severe stretching. These three factors work synergistically, making protein addition a reinforcing rather than weakening factor for the fiber. The dry breaking strength of the milk protein-cellulose composite fiber of this invention is ≥2.2 cN / dtex.

[0048] 3. The methacryloyloxyethyltrimethylammonium chloride introduced by graft polymerization is a quaternary ammonium salt cationic monomer. Its positive charge can interact electrostatically with the bacterial cell membrane, disrupting the cell structure and thus achieving antibacterial properties. This antibacterial group is covalently grafted onto the surface of the protein microspheres, rather than through simple physical blending, resulting in excellent wash resistance. The pre-crosslinked microspheres and graft functionalization together ensure the uniform distribution and strong binding of the antibacterial group within the fiber. The composite fiber of this invention exhibits an antibacterial rate of ≥95% against Staphylococcus aureus, and retains ≥85% of the antibacterial rate after 20 standard water washes, achieving durable antibacterial function.

[0049] 4. The grafted methacryloyloxyethyltrimethylammonium chloride is a cationic polyelectrolyte. Its quaternary ammonium salt structure exhibits hygroscopicity and ionic conductivity, effectively reducing the surface resistance of the fiber. This antistatic and antibacterial function originates from the same functional monomer, achieving multi-functional integration and simplifying the formulation system. The volume resistivity of the composite fiber of this invention is ≤5×10⁻⁶. 10 Ω·cm effectively solves the problem of static electricity during textile processing and use.

[0050] 5. In this invention, the viscose solution is adjusted to pH 9.5–10.2 using disodium hydrogen phosphate-citric acid buffer and cooled to 15–18°C, with a mixing time not exceeding 30 minutes. This significantly reduces protein alkaline degradation while ensuring spinnability. Through the synergistic effect of short-duration low-temperature mixing and pH adjustment, protein protection and the spinning process are compatible.

[0051] 6. This invention optimizes the coagulation bath composition (45-60 g / L sulfuric acid, 250-300 g / L sodium sulfate, 5-10 g / L zinc sulfate), spinneret diameter (0.08-0.10 mm), extrusion speed (6-10 m / min), and two-stage stretching process (total ratio 1.5-1.8 times) for composite spinning solutions containing protein microspheres. This ensures the stability of the spinning process and the uniformity of the fiber structure, achieving high-quality spinning of the protein-cellulose composite system.

[0052] 7. This invention uses segmented drying (first stage 60-70℃ / 15-25min, second stage 80-90℃ / 5-15min) instead of constant temperature high-temperature drying. The low-temperature long-time first stage drying removes most of the free water, and the high-temperature short-time second stage drying completely removes the bound water. This ensures drying efficiency and reduces the risk of protein thermal denaturation and uneven fiber shrinkage, avoiding structural deformation and protein thermal damage caused by rapid water loss from the fiber surface. Detailed Implementation

[0053] The present invention will be further illustrated below with reference to the embodiments. Example 1

[0054] A method for preparing milk protein-modified regenerated cellulose fiber includes the following steps:

[0055] A: Preparation of pre-crosslinked activated milk protein microspheres

[0056] 100g of milk casein was added to a reaction vessel, along with 5U / g of microbial transglutaminase (total enzyme activity 500U). The reaction temperature was 35℃, and the reaction time was 1 hour. After the pre-crosslinking reaction, the reaction solution was heated in a 75℃ water bath for 20 minutes to terminate enzyme activity. Subsequently, spray drying was performed with an inlet air temperature of 170℃, an outlet air temperature of 70℃, a feed solution of deionized water at a concentration of 5wt%, and an atomizer speed of 25000rpm, yielding pre-crosslinked activated milk protein microspheres with an average particle size of 1μm and a crosslinking degree of 30%.

[0057] B: Preparation of grafted functionalized milk protein

[0058] 100 g of the pre-crosslinked activated milk protein microspheres obtained in step A were dispersed in a mixed solvent of phosphate buffer (20 mM) and ethanol at pH 6.5 (buffer:ethanol volume ratio 8.5:1.5). 8 g of methacryloyloxyethyltrimethylammonium chloride and 3 g of glycidyl methacrylate were added. Ammonium persulfate and sodium bisulfite were each prepared into 2 wt% aqueous solutions at a molar ratio of 1:1 and added separately. The total amount added was 0.8 wt% of the total mass of methacryloyloxyethyltrimethylammonium chloride and glycidyl methacrylate. The graft polymerization reaction was carried out at 40 °C for 2 h, with nitrogen gas purging during the reaction.

[0059] After the reaction was terminated, the homopolymer was removed by purification to obtain grafted functionalized milk protein with a grafting rate of 35%.

[0060] C: Preparation of the mixed stock solution

[0061] A viscose spinning solution (9.0 wt% cellulose A) was prepared and adjusted to pH 9.5 using 0.1 mol / L disodium hydrogen phosphate-citric acid buffer. The solution was then cooled to 15°C (cooling rate 1°C / min). Grafted functionalized milk protein obtained in step B (6 wt% of the dry weight of cellulose in the viscose spinning solution) was added, along with polyethylene glycol diglycidyl ether (0.8 wt% of the grafted functionalized milk protein) with a number average molecular weight of 1000. The mixture was stirred at 14°C for 30 min at 400 rpm, maintaining pH 9.5 throughout the mixing process. After homogeneous mixing, the solution was degassed under vacuum to obtain the mixed stock solution.

[0062] D: Wet spinning

[0063] The mixed solution was wet-spun into an acidic coagulation bath. The coagulation bath consisted of 45 g / L sulfuric acid, 250 g / L sodium sulfate, and 5 g / L zinc sulfate, at a temperature of 30°C. The spinneret diameter was 0.08 mm, the extrusion speed was 6 m / min, and a two-stage stretching process was used: a first-stage stretching ratio of 1.2 times and a second-stage stretching ratio of 1.25 times (total stretching ratio of 1.5 times). After stretching and coagulation, nascent fibers were obtained.

[0064] E: Post-processing

[0065] The nascent fibers were sequentially subjected to hot water washing, neutralization washing (pH adjusted to 6.5 with 1 g / L acetic acid solution, 40℃, 15 min), desulfurization (2.0 g / L sodium sulfite solution, 50℃, 20 min), water washing, oiling (non-ionic fiber oiling agent, oiling rate 0.8 wt%), and drying (first stage 60℃, 25 min; second stage 80℃, 5 min, total drying time 30 min) to obtain milk protein-cellulose composite fibers.

[0066] The properties of the obtained composite fiber are as follows: dry breaking strength 2.2 cN / dtex (GB / T 14337-2008); antibacterial rate against Staphylococcus aureus 95% (GB / T 20944.3-2008); antibacterial retention rate after 20 standard water washes 85% (FZ / T 73023-2006, water washing conditions refer to GB / T 8629); volume resistivity 5×10⁻⁶. 10 Ω·cm (FZ / T 50015-2015, the sample was tested after equilibration at 20℃ and 65% RH for 24h); protein retention rate 70% (GB / T 2910.4-2022 sodium hypochlorite method). Example 2

[0067] A method for preparing milk protein-modified regenerated cellulose fiber includes the following steps:

[0068] A: Preparation of pre-crosslinked activated milk protein microspheres

[0069] 100g of milk casein was added to a reaction vessel, along with 8.5U / g of microbial transglutaminase (total enzyme activity 850U). The reaction temperature was 40℃, and the reaction time was 1.5h. After the pre-crosslinking reaction was completed, the reaction solution was heated in a 78℃ water bath for 17min to terminate enzyme activity. Subsequently, spray drying was performed with an inlet air temperature of 180℃, an outlet air temperature of 75℃, a feed concentration of 8wt%, and an atomizer speed of 20000rpm, yielding pre-crosslinked activated milk protein microspheres with an average particle size of 3μm and a crosslinking degree of 35%.

[0070] B: Preparation of grafted functionalized milk protein

[0071] 100 g of the pre-crosslinked activated milk protein microspheres obtained in step A were dispersed in a mixed solvent of phosphate buffer (25 mM) and ethanol at pH 7.0 (buffer:ethanol volume ratio 8.75:1.25). 11.5 g of methacryloyloxyethyltrimethylammonium chloride and 4.5 g of glycidyl methacrylate were added. Ammonium persulfate and sodium bisulfite were prepared separately into 2.5 wt% aqueous solutions at a molar ratio of 1:1 and added simultaneously. The total amount added was 1.15 wt% of the total mass of methacryloyloxyethyltrimethylammonium chloride and glycidyl methacrylate. The graft polymerization reaction was carried out at 45 °C for 2.5 h, with nitrogen gas purging during the reaction.

[0072] After the reaction was terminated, the homopolymer was removed by purification to obtain grafted functionalized milk protein with a grafting rate of 42.5%.

[0073] C: Preparation of the mixed stock solution

[0074] A viscose spinning solution (9.5 wt% cellulose methyl ester) was prepared and adjusted to pH 10 using 0.3 mol / L disodium hydrogen phosphate-citric acid buffer. The solution was then cooled to 16.5°C (cooling rate 1.5°C / min). Grafted functionalized milk protein (8 wt% of the dry weight of cellulose in the viscose spinning solution) and polyethylene glycol diglycidyl ether (1.0 wt% of the grafted functionalized milk protein) with a number average molecular weight of 1250 were added. The mixture was stirred at 15°C for 500 rpm for 20 min, maintaining pH 10 throughout the mixing process. After mixing, the solution was transferred to a vacuum degassing tank, where the temperature was controlled at 16 ± 1°C and maintained constant temperature using a jacket cooling system. A vacuum pump was activated, and a small amount of nitrogen gas (0.1 L / min) was simultaneously introduced below the liquid surface to maintain the pH within the range of 9.5–10.0. Degassing was performed for 15 min. The total mixing and degassing time was 35 min. After degassing, a uniform mixed stock solution is obtained.

[0075] D: Wet spinning

[0076] The mixed solution was wet-spun into an acidic coagulation bath. The coagulation bath composition was: sulfuric acid 52.5 g / L, sodium sulfate 275 g / L, and zinc sulfate 7.5 g / L, at a temperature of 35℃. The spinneret diameter was 0.09 mm, the extrusion speed was 8 m / min, and a two-stage stretching process was adopted: the first-stage stretching ratio was 1.25 times, the second-stage stretching ratio was 1.28 times (total stretching ratio 1.6 times). After stretching and coagulation, nascent fibers were obtained.

[0077] E: Post-processing

[0078] The nascent fibers were sequentially subjected to hot water washing, neutralization washing (pH adjusted to 7.0 with 1.5 g / L acetic acid solution, 45℃, 17.5 min), desulfurization (2.5 g / L sodium sulfite solution, 55℃, 25 min), water washing, oiling (non-ionic fiber oiling agent, oiling rate 1.0 wt%), and drying (first stage 65℃, 20 min; second stage 85℃, 10 min, total drying time 30 min) to obtain milk protein-cellulose composite fibers.

[0079] The properties of the obtained composite fiber are as follows: dry breaking strength 2.35 cN / dtex; antibacterial rate against Staphylococcus aureus 95%; antibacterial retention rate after 20 standard water washes 85%; volume resistivity 4 × 10⁻⁶. 10 Ω·cm; protein retention rate 75%. Example 3

[0080] A method for preparing milk protein-modified regenerated cellulose fiber includes the following steps:

[0081] A: Preparation of pre-crosslinked activated milk protein microspheres

[0082] 100g of milk casein was added to a reaction vessel, along with 12U / g of microbial transglutaminase (total enzyme activity 1200U). The reaction temperature was 45℃, and the reaction time was 2 hours. After the pre-crosslinking reaction was completed, the reaction solution was heated in an 80℃ water bath for 15 minutes to terminate enzyme activity. Subsequently, spray drying was performed with an inlet air temperature of 190℃, an outlet air temperature of 80℃, a feed concentration of 12wt%, and an atomizer speed of 15000rpm, yielding pre-crosslinked activated milk protein microspheres with an average particle size of 5μm and a crosslinking degree of 40%.

[0083] B: Preparation of grafted functionalized milk protein

[0084] 100 g of the pre-crosslinked activated milk protein microspheres obtained in step A were dispersed in a mixed solvent of phosphate buffer (30 mM) and ethanol at pH 7.5 (buffer:ethanol volume ratio 9:1). 15 g of methacryloyloxyethyltrimethylammonium chloride and 6 g of glycidyl methacrylate were added. Ammonium persulfate and sodium bisulfite were each prepared into 3 wt% aqueous solutions at a molar ratio of 1:1. The total amount added was 1.5 wt% of the total mass of methacryloyloxyethyltrimethylammonium chloride and glycidyl methacrylate. The graft polymerization reaction was carried out at 50 °C for 3 h, with nitrogen gas purging during the reaction.

[0085] After the reaction was terminated, the homopolymer was removed by purification to obtain grafted functionalized milk protein with a grafting rate of 50%.

[0086] C: Preparation of the mixed stock solution

[0087] A viscose spinning solution (10.0 wt% cellulose methyl ester) was prepared and adjusted to pH 10.2 using 0.5 mol / L disodium hydrogen phosphate-citric acid buffer. The solution was then cooled to 18°C ​​(cooling rate 2°C / min). Grafted functionalized milk protein (10 wt% of the dry weight of cellulose in the viscose spinning solution) and polyethylene glycol diglycidyl ether (1.2 wt% of the grafted functionalized milk protein) with a number average molecular weight of 1500 were added. The mixture was stirred at 16°C for 15 min at 600 rpm, maintaining pH 10.2 throughout the mixing process. After homogeneous mixing, the solution was degassed under vacuum to obtain the mixed stock solution.

[0088] D: Wet spinning

[0089] The mixed solution was wet-spun into an acidic coagulation bath. The coagulation bath consisted of 60 g / L sulfuric acid, 300 g / L sodium sulfate, and 10 g / L zinc sulfate, at a temperature of 40°C. The spinneret diameter was 0.10 mm, the extrusion speed was 10 m / min, and a two-stage stretching process was used: a first-stage stretching ratio of 1.3 times and a second-stage stretching ratio of 1.3 times (total stretching ratio of 1.69 times). After stretching and coagulation, nascent fibers were obtained.

[0090] E: Post-processing

[0091] The nascent fibers were sequentially subjected to hot water washing, neutralization washing (pH adjusted to 7.5 with 2 g / L acetic acid solution, 50℃, 20 min), desulfurization (3.0 g / L sodium sulfite solution, 60℃, 30 min), water washing, oiling (non-ionic fiber oiling agent, oiling rate 1.2 wt%), and drying (first stage 70℃, 15 min; second stage 90℃, 15 min, total drying time 30 min) to obtain milk protein-cellulose composite fibers.

[0092] The properties of the prepared composite fiber are as follows: dry breaking strength 2.40 cN / dtex; antibacterial rate against Staphylococcus aureus 96%; antibacterial retention rate after 20 standard water washes 86%; volume resistivity 3.5 × 10⁻⁶. 10 Ω·cm; protein retention rate 78%. Example 4

[0093] The homopolymer removal method in step B of Example 2 includes the following steps:

[0094] The graft polymerization reaction solution was cooled to 22±2℃, and 4 times its volume of 95% ethanol was slowly added under stirring, with the addition time controlled at 10-15 min. After the addition was complete, stirring was continued for 12.5 min to allow the DMC (methacryloyloxyethyltrimethylammonium chloride) homopolymer, GMA (glycidyl methacrylate) homopolymer, and DMC-GMA copolymer generated in the system to fully dissolve in the alcohol phase, while the grafted functionalized milk protein formed a dispersed precipitate in the high concentration of ethanol due to the hydrophobic GMA segments grafted on its surface.

[0095] The mixture was transferred to a tube centrifuge and centrifuged at 9000 rpm for 17.5 min at 22°C. After centrifugation, the grafted functionalized milk protein microspheres settled to the bottom of the centrifuge tube.

[0096] Discard the supernatant, add half the initial reaction volume of pH 7.0, 25 mM phosphate buffer to the bottom precipitate, and gently stir with a magnetic stirrer for 5–10 min to fully redissolve the precipitate. Repeat the above "ethanol extraction-centrifugation" operation twice.

[0097] After the third centrifugation, the bottom precipitate was collected, spread evenly in a stainless steel freeze-drying tray, and placed in a vacuum freeze dryer. Freeze-drying conditions: pre-freezing at -40℃ for 2 hours, primary drying at -30℃ (0.04 MPa vacuum) for 12 hours, secondary drying at -25℃ (0.03 MPa vacuum) for 6 hours, and final drying at 20℃ for 2 hours. The resulting product was powdered grafted functionalized milk protein (grafting rate 42.5%). Comparative Example 1

[0098] Step A is omitted, and graft polymerization in step B is carried out directly using uncrosslinked milk casein (physically pulverized to an average particle size of 3 μm). The remaining steps are exactly the same as in Example 2.

[0099] Results: During the grafting polymerization in step B, the uncrosslinked milk casein had poor solubility in the reaction system, with a grafting rate of only 22%. The final composite fiber had a protein retention rate of only 45%, a dry breaking strength of 1.85 cN / dtex, an antibacterial rate of 68% against Staphylococcus aureus, and an antibacterial retention rate of 52% after 20 washes. Comparative Example 2

[0100] Step B is omitted, and the pre-crosslinked activated milk protein microspheres obtained in step A are directly used for mixing in step C. The remaining steps are the same as in Example 2.

[0101] Results: During the mixing process in step C, the ungrafted pre-crosslinked microspheres showed poor dispersion and significant aggregation in the viscose solution. The final composite fiber exhibited a dry breaking strength of 1.78 cN / dtex, a protein retention rate of 52%, an antibacterial rate against Staphylococcus aureus of 32% (due to weak antibacterial activity derived solely from the protein itself), and a volume resistivity of 8 × 10⁻⁶. 10 Ω·cm. Comparative Example 3

[0102] The pH adjustment step in step C is omitted, and the viscose spinning solution (pH>13) is directly mixed with the grafted functionalized milk protein. The remaining steps are the same as in Example 2.

[0103] Results: Grafted functionalized milk protein underwent significant alkaline degradation in a strongly alkaline environment, resulting in a darker color in the mixture (due to intensified Maillard reaction) and protein flocculation during spinning. The final composite fiber exhibited a protein retention rate of only 38%, a dry breaking strength of 1.92 cN / dtex, a 72% inhibition rate against Staphylococcus aureus, and a 55% retention rate of the inhibition rate after 20 washes. Comparative Example 4

[0104] Ungrafted pre-crosslinked activated milk protein microspheres (obtained in step A) were physically blended with methacryloyloxyethyltrimethylammonium chloride in the same proportion as in Example 2, without undergoing the grafting polymerization reaction in step B, and were directly used for mixing in step C. The remaining steps were the same as in Example 2.

[0105] Results: Methacryloxyethyltrimethylammonium chloride was largely lost during subsequent washing, and the antibacterial rate of the fiber against Staphylococcus aureus was only 48%. After 20 washes, the antibacterial retention rate dropped to 21%. Comparative Example 5

[0106] The epoxy crosslinking aid (polyethylene glycol diglycidyl ether) in step C is omitted, and the remaining steps are the same as in Example 2.

[0107] Results: The protein retention rate of the resulting composite fiber decreased to 57%, the dry breaking strength decreased to 2.05 cN / dtex, the antibacterial rate against Staphylococcus aureus was 93% (after the first wash), and the antibacterial retention rate decreased to 73% after 20 washes.

[0108] It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing milk protein-modified regenerated cellulose fiber, characterized in that... Includes the following steps: A: Milk casein was pre-crosslinked under the action of microbial transglutaminase. After terminating the enzyme activity, it was spray-dried to obtain pre-crosslinked activated milk protein microspheres. B: Pre-crosslinked activated milk protein microspheres were dispersed in a mixed solvent of phosphate buffer and ethanol at pH 6.5–7.

5. Cationic monomers and epoxy functional monomers were added, and in-situ grafting polymerization was carried out in a water-soluble redox initiation system. After the reaction, the homopolymer was purified to remove the polymer and the grafted functionalized milk protein was obtained. C: Adjust the viscose spinning solution to pH 9.5-10.2 with disodium hydrogen phosphate-citric acid buffer and cool it to 15-18℃. Add grafted functionalized milk protein and epoxy crosslinking agent, mix evenly, and obtain the mixed solution after vacuum degassing. D: The mixed solution is fed into an acidic coagulation bath through wet spinning, and after stretching and coagulation, nascent fibers are obtained. E: The nascent fibers are sequentially washed with hot water, neutralized and washed, desulfurized, washed with water, oiled and dried to obtain milk protein-cellulose composite fibers.

2. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that: The amount of microbial transglutaminase added in step A is 5-12 U / g milk casein, the pre-crosslinking reaction temperature is 35-45℃, and the reaction time is 1-2h; the enzyme activity is terminated by heating in a water bath at 75-80℃ for 15-20min, the spray drying inlet air temperature is 170-190℃, and the outlet air temperature is 70-80℃.

3. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that: In step B, the cationic monomer is methacryloyloxyethyltrimethylammonium chloride, and its addition amount is 8-15 wt% of the milk cheese weight; the epoxy functional monomer is glycidyl methacrylate, and its addition amount is 3-6 wt% of the milk cheese weight; the volume ratio of phosphate buffer to ethanol in the mixed solvent is 8.5:1.5-9:1, and the concentration of phosphate buffer is 20-30 mM.

4. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that: The initiation system described in step B is a water-soluble redox initiation system, specifically ammonium persulfate and sodium bisulfite in a molar ratio of 1:1, which are prepared into aqueous solutions with a concentration of 2-3 wt% and added sequentially or simultaneously. The total amount added is 0.8-1.5 wt% of the total mass of the cationic monomer and the epoxy functional monomer. The graft polymerization reaction temperature is 40-50℃, and the reaction time is 2-3 h.

5. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that: In step C, the amount of grafted functionalized milk protein added is 6-10 wt% of the dry weight of cellulose in the viscose spinning solution; the epoxy crosslinking aid is polyethylene glycol diglycidyl ether, and the amount added is 0.8-1.2 wt% of the grafted functionalized milk protein.

6. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that: The viscose spinning solution in step C has a cellulose content of 9.0–10.0 wt%, a cooling rate of 1–2 °C / min, a mixing temperature of 14–16 °C, and a stirring speed of 400–600 rpm.

7. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that, In step D, the sulfuric acid concentration in the acidic coagulation bath is 45–60 g / L, and the temperature is 30–40 °C.

8. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that: In step E, the neutralization washing uses an acetic acid solution with a concentration of 1-2 g / L to adjust the pH to 6.5-7.5, the washing temperature is 40-50℃, and the washing time is 15-20 min; the desulfurization uses a sodium sulfite solution with a concentration of 2.0-3.0 g / L, the temperature is 50-60℃, and the desulfurization time is 20-30 min.

9. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that: In step E, the oiling agent used is a non-ionic fiber oiling agent with an oiling rate of 0.8–1.2 wt%; the drying temperature is 80–90 °C and the drying time is 30–40 min.

10. The method for preparing milk protein-modified regenerated cellulose fiber as described in claim 1, characterized in that, The obtained milk protein-cellulose composite fiber has the following characteristics: Dry fracture strength ≥ 2.2 cN / dtex; The inhibition rate against Staphylococcus aureus is ≥95%; After 20 standard water washes, the antibacterial retention rate is ≥85%; Volume resistivity ≤ 5 × 10 10 Ω·cm; Compared to the amount of spinning solution added, the protein retention rate in milk protein-cellulose composite fiber is ≥70%.