Chitosan-based environment-friendly sponge with improved antibacterial durability and wet strength and preparation method thereof

Abstract

The application discloses an environment-friendly sponge based on chitosan with improved antibacterial durability and wet strength and a preparation method thereof, relates to the technical field of natural polysaccharide materials, and belongs to the patent classification C08L5 / 00. The method comprises the following steps: grafting glycidyltrimethylammonium chloride onto chitosan to obtain cationized chitosan containing permanent cations, compounding the cationized chitosan with unmodified chitosan, polyvinyl alcohol and mechanically microfibrillated cellulose, cross-linking the mixture at low density by using glycerol diglycidyl ether, and preparing the sponge through freezing and thawing and freeze-drying. The application realizes durable antibacterial property in a neutral environment by using the fixed cationic structure, and improves the wet strength by limiting the molecular chain slip through the cross-linking network; meanwhile, the introduced polyvinyl alcohol and microfibrillated cellulose form a 'flexible continuous phase-rigid fiber skeleton' synergistic bearing structure, compensate for the occupation of the wet strength covalent network points by cationization, and solve the process coupling problem.

Description

Technical Field

[0001] This invention relates to the field of natural polysaccharide materials technology, belonging to patent classification number C08L5 / 00, specifically to a chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength, and its preparation method. Background Technology

[0002] Chitosan is a natural polymer obtained by the deacetylation of chitin. It is relatively abundant and has good film-forming properties, water absorption, and biodegradability. After freezing and drying, chitosan solutions can form an interconnected porous structure, making them suitable for preparing environmentally friendly sponges for liquid absorption, cleaning, filtration, and cushioning.

[0003] The antibacterial ability of chitosan is mainly related to the positively charged amino groups on its molecular chain. In a slightly acidic environment, chitosan amino groups are easily protonated and exhibit a certain antibacterial effect. When the environment is close to neutral, the degree of protonation of the amino groups decreases, the positive charge density on the sponge surface decreases accordingly, and the antibacterial effect easily weakens. If the antibacterial function depends on unfixed small molecules, these substances may gradually migrate out during repeated water absorption, squeezing, and washing of the sponge, making it difficult for the material to maintain stable antibacterial ability over a long period. Therefore, it is necessary to construct a fixed antibacterial structure on the chitosan molecular chain that is independent of environmental acidity and does not easily migrate with water.

[0004] When chitosan sponges absorb water, water molecules enter the pore walls and increase the distance between molecular chains, weakening the original hydrogen bonds and chain entanglement. Under pressure, the water-absorbing chitosan chains are prone to slippage, leading to softening of the pore walls, pore collapse, and decreased sponge resilience. Simply increasing the dry hardness of the sponge cannot fundamentally solve this problem; it is necessary to establish a stable load-bearing network within the pore walls while preserving the sponge's necessary porosity, water absorption capacity, and deformation ability.

[0005] In improving antibacterial durability, permanent cationic groups need to be immobilized onto the chitosan molecular chain. This process occupies some of the primary amino groups in chitosan. On the other hand, primary amino groups are important reaction sites for subsequent construction of wet-strength covalent networks. As the degree of cationization increases, the number of primary amino groups available for wet-strength network formation decreases, potentially leading to insufficient effective covalent network sites. This is the only process coupling problem arising from the antibacterial durability treatment's interaction with the wet-strength treatment.

[0006] Therefore, the technical problem to be solved by this invention is how to construct a permanent cationic antibacterial structure in chitosan sponge that is not easily migrated, under the premise of mild reaction conditions and without causing thermal degradation of chitosan, so as to improve the antibacterial retention ability of the material in a neutral environment and after repeated washing; at the same time, to establish a stable wet-state support network, thereby improving the compressive strength and structural retention ability of the sponge after water absorption; and to solve the problem of the reduction of subsequent effective covalent sites caused by cationization treatment by using a compensating support structure that does not depend on the primary amino groups of chitosan. Summary of the Invention

[0007] The purpose of this invention is to provide a chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength, and a method for preparing the same, so as to solve the technical problems mentioned in the background.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength includes the following steps: (1) Chitosan was subjected to a ring-opening grafting reaction with glycidyltrimethylammonium chloride, and after purification, cationic chitosan containing hydroxypropyltrimethylammonium side groups was obtained. (2) The cationic chitosan, unmodified chitosan, polyvinyl alcohol and mechanically microfibrillated cellulose are dispersed in an acidic aqueous phase to obtain a sponge precursor solution; (3) Add glycerol diglycidyl ether to the sponge precursor solution to allow the residual primary amino groups in the cationic chitosan and unmodified chitosan to undergo ring-opening crosslinking with the epoxy groups of glycerol diglycidyl ether to obtain a crosslinked gel. (4) The cross-linked gel is subjected to freeze-thaw treatment, and then neutralized, washed, frozen and freeze-dried in sequence to obtain the chitosan-based environmentally friendly sponge.

[0009] Preferably, the degree of deacetylation of the chitosan used in step (1) is 85% to 92%, and the weight-average molecular weight is 80,000 to 150,000.

[0010] Preferably, in step (1), the molar ratio of glycidyltrimethylammonium chloride active ingredient to the primary amino group of chitosan is 0.40 to 0.50; The ring-opening grafting reaction is carried out in an aqueous phase with pH 5.7–5.9. First, 60% of the total amount of glycidyltrimethylammonium chloride is added, and the reaction is carried out at 53–57°C for 1.5–2.5 h. Then, the remaining 40% is added, and the reaction is carried out at 63–67°C for 6–8 h.

[0011] Preferably, the reaction product of step (1) is washed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa, and then washed with an aqueous acetic acid solution of 0.1% to 0.3% by mass for no less than 6 dialysis volumes, and then precipitated with ethanol and dried under vacuum at 40 to 45°C.

[0012] Preferably, in step (2), the sum of the dry basis mass of cationic chitosan and unmodified chitosan is 100 parts by mass, wherein the cationic chitosan is 35-45 parts by mass, the unmodified chitosan is 55-65 parts by mass, the polyvinyl alcohol is 35-45 parts by mass, and the mechanically microfibrillated cellulose is 8-12 parts by mass.

[0013] Preferably, the polyvinyl alcohol is PVA-1799; the mechanically microfibrillated cellulose is low-charge mechanically microfibrillated cellulose with a carboxyl content of not more than 0.3 mmol / g. The polyvinyl alcohol is pre-prepared into a 10% aqueous solution, dissolved at 92-95°C and then cooled to no higher than 35°C; The mechanically microfibrillated cellulose is added in the form of an aqueous dispersion with a mass fraction of 2% to 5%.

[0014] Preferably, the total solids content of the sponge precursor solution obtained in step (2) is 5% to 8%, and the pH is 6.0 to 6.2.

[0015] Preferably, the diglycidyl ether used in step (3) is a water-soluble diglycidyl ether with an epoxy functionality of 2. The amount of glycerol diglycidyl ether added satisfies the requirement that the molar ratio of the epoxy functional group to the residual primary amino functional group in the sponge precursor solution is 0.15 to 0.25.

[0016] Preferably, the mass of the glycerol diglycidyl ether is determined according to the following formula: m GDGE =R×n NH2 ×EEW / 1000; In the formula, m GDGE The mass of glycerol diglycidyl ether is expressed in grams; R is the molar ratio of the epoxy functional group to the residual primary amino functional group; n NH2 The amount of substance of the residual primary amino functional group is expressed in mmol; EEW is the epoxy equivalent of the glycerol diglycidyl ether used, expressed in g / eq.

[0017] A chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength is prepared by the method described above.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. The trimethylammonium side groups in cationic chitosan possess a permanent positive charge that does not significantly change with environmental pH, allowing the sponge to maintain a high surface cation density even in near-neutral usage environments. When bacteria come into contact with the sponge's pore walls, the charge balance on the cell surface and cell membrane permeability are disrupted. Because the cationic antibacterial structure is fixed to the chitosan molecular chains and further constrained by the overall sponge network, it is less likely to migrate out during water absorption, squeezing, and repeated washing. Therefore, it slows down the decline of antibacterial function with increased use, improving the sponge's antibacterial durability.

[0019] 2. The low-density covalent network formed by diglycidyl ethers of glycerol can limit the movement range of chitosan molecular chains after water absorption, reducing chain segment untangling and relative slippage within the pore walls. When the sponge is compressed, the external force can be transmitted to surrounding chain segments through stable connection points in the pore walls, reducing pore wall rupture and pore collapse caused by stress concentration. The number of cross-linking points is controlled according to the residual primary amine content, which improves the wet compression load-bearing capacity without making the pore walls excessively dense, thus balancing the sponge's water absorption capacity, flexibility, and wet resilience.

[0020] 3. When increasing the fixed cationic structure to obtain long-lasting antibacterial ability, some of the chitosan primary amino groups are occupied, which reduces the number of wet-strength covalent networks that can be formed subsequently. When there are insufficient covalent networks, although the sponge can be formed, chain segment slippage is still prone to occur after the pore walls absorb water. This is a process coupling problem that this solution needs to solve. To compensate for the reduced covalent networks, this solution introduces PVA-1799 and low-charge mechanical microfibrillated cellulose as two independent load-bearing skeleton materials: PVA forms continuously distributed microcrystalline connection points and chain entanglement structures during freeze-thaw processes, which can bridge adjacent pore walls and provide flexible and continuous force transmission channels for the sponge; low-charge mechanical microfibrillated cellulose has a high aspect ratio and good wet dimensional stability, which can form a rigid fiber force transmission skeleton inside the pore walls, limiting the slippage, creep, and excessive swelling of PVA and chitosan chains after water absorption. Meanwhile, PVA can fill the gaps between adjacent microfibers, improving the continuity of microfibrillated cellulose distribution in the pore walls and reducing local fiber aggregation and interfacial detachment. Microfibrillated cellulose, in turn, provides support for the continuous PVA phase, preventing significant deformation of the PVA network under long-term immersion and repeated pressure. Together, they form a synergistic load-bearing structure of "flexible continuous phase - rigid fiber skeleton," allowing external forces to be dispersed and transmitted over a wider range, thus compensating for the wet load-bearing gap caused by the reduction of covalent network points without further consuming chitosan primary amines. Attached Figure Description

[0021] Figure 1 This is a low-magnification SEM image of the chitosan-based environmentally friendly sponge prepared in Example 1 of the present invention.

[0022] Figure 2This is a high-magnification SEM image of the chitosan-based environmentally friendly sponge prepared in Example 1 of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0024] A method for preparing a chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength includes the following steps: 10.00 g of chitosan with a degree of deacetylation of 85% and a weight-average molecular weight of 80,000 was added to a solution composed of 4.00 g glacial acetic acid and 496.00 g deionized water, and stirred at 25 °C for 6 h until completely dissolved. The pH was slowly adjusted to 5.7 using 1 mol / L sodium hydroxide solution. Based on a molar ratio of glycidyltrimethylammonium chloride to available primary amino groups of chitosan of 0.40, 4.40 g of a 70% glycidyltrimethylammonium chloride aqueous solution was weighed. 2.64 g was added first, and the reaction was carried out at 53 °C for 2.5 h; then the remaining 1.76 g was added within 30 min, and the temperature was raised to 63 °C to continue the reaction for 8 h.

[0025] The reaction solution was cooled to 25°C and washed with a 0.1% acetic acid aqueous solution for 6 dialysis volumes using an ultrafiltration membrane with a molecular weight cutoff of 10 kDa. The retentate was concentrated to approximately 100 mL, and 3 times its volume of 95% ethanol was added to precipitate cationic chitosan. The precipitate was then filtered and dried under vacuum at 40°C.

[0026] Weigh 3.50 g of the above-mentioned cationic chitosan and 6.50 g of unmodified chitosan, add them to 350.00 g of 0.8% acetic acid aqueous solution, and stir at 25°C until completely dissolved. Concentrate the chitosan solution under reduced pressure at a temperature not exceeding 35°C to a total mass of approximately 127.75 g.

[0027] Separately, 3.50 g of PVA-1799 was added to 31.50 g of deionized water and stirred at 92 °C for 60 min until completely dissolved, then cooled to 35 °C. 16.00 g of a 5% (w / w) aqueous dispersion of low-charge mechanically microfibrillated cellulose was taken, containing 0.80 g of dry microfibrillated cellulose with a carboxyl content of 0.30 mmol / g. The PVA solution and microfibrillated cellulose dispersion were sequentially added to the concentrated chitosan solution, dispersed under high shear for 8 min, slowly adjusted to pH 6.0, and degassed under vacuum for 10 min to obtain a sponge precursor solution with a total solids content of approximately 8%.

[0028] The total amount of residual primary amino functional groups in the precursor solution was determined to be 43.0 mmol. Glyceryl diglycidyl ether (GDGE) (epoxy equivalent of 105 g / eq) was selected. The molar ratio of epoxy functional groups to residual primary amino functional groups was set to 0.15, therefore the amount of GDGE used was: m GDGE =0.15×43×10⁵ / 1000=0.677g 0.677 g of GDGE was prepared into a 10% (w / w) fresh aqueous solution. The precursor solution was slowly added over 45 min at 20 °C. After stirring for another 15 min, the solution was poured into a mold, and the liquid layer thickness was controlled to be 10 mm. The solution was kept at 38 °C for 18 h to obtain a cross-linked gel.

[0029] The cross-linked gel was kept at -18℃ for 12 hours, then thawed at 23℃ for 5 hours, and this operation was repeated twice. Then, the gel was immersed in approximately 375 mL of a 65% ethanol aqueous solution containing 0.15 mol / L sodium hydroxide at a dry gel-to-neutralization liquid volume ratio of 1 g:25 mL, and neutralized at 20℃ for 2.5 hours. The gel was washed twice with 65% ethanol aqueous solution, and then washed with deionized water until the pH of the washing solution was 6.8–7.5 and the extractable epoxy compounds were below the detection limit. The washed gel was frozen at -40℃ for 12 hours, and then freeze-dried for 24 hours under cold trap conditions of -50℃ and a pressure not exceeding 50 Pa to obtain chitosan-based environmentally friendly sponge. Example 2

[0030] A method for preparing a chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength includes the following steps: 10.00 g of chitosan with a degree of deacetylation of 90% and a weight-average molecular weight of 110,000 was added to a solution composed of 4.00 g glacial acetic acid and 496.00 g deionized water, and stirred at 25 °C for 6 h until completely dissolved. The pH was slowly adjusted to 5.8 using 1 mol / L sodium hydroxide solution. Based on a molar ratio of glycidyltrimethylammonium chloride to available primary amino groups of chitosan of 0.45, 5.30 g of a 70% glycidyltrimethylammonium chloride aqueous solution was weighed. 3.18 g was added first, and the reaction was carried out at 55 °C for 2 h; then the remaining 2.12 g was added over 30 min, and the temperature was raised to 65 °C to continue the reaction for 7 h.

[0031] The reaction solution was cooled to 25°C and washed with a 0.2% (w / w) aqueous acetic acid solution for 7 dialysis volumes using an ultrafiltration membrane with a molecular weight cutoff of 10 kDa. The retentate was concentrated to approximately 100 mL, and 3.5 times its volume of 95% ethanol was added to precipitate cationic chitosan. The precipitate was then filtered and dried under vacuum at 42°C.

[0032] Weigh 4.00 g of the above-mentioned cationic chitosan and 6.00 g of unmodified chitosan, add them to 320.00 g of 0.9% acetic acid aqueous solution, and stir at 25°C until completely dissolved. Concentrate the chitosan solution under reduced pressure at a temperature not exceeding 35°C to a total mass of approximately 162.20 g.

[0033] Separately, 4.00 g of PVA-1799 was added to 36.00 g of deionized water and stirred at 93 °C for 60 min until completely dissolved, then cooled to 32 °C. 28.57 g of a 3.5% (w / w) aqueous dispersion of low-charge mechanically microfibrillated cellulose was taken, containing 1.00 g of dry microfibrillated cellulose with a carboxyl content of 0.20 mmol / g. The PVA solution and microfibrillated cellulose dispersion were sequentially added to the concentrated chitosan solution, dispersed under high shear for 11 min, slowly adjusted to pH 6.1, and degassed under vacuum for 10 min to obtain a sponge precursor solution with a total solids content of approximately 6.5%.

[0034] The total amount of residual primary amino functional groups in the precursor solution was determined to be 44.5 mmol. Glyceryl diglycidyl ether (GDGE) (epoxy equivalent of 110 g / eq) was selected. The molar ratio of epoxy functional groups to residual primary amino functional groups was set to 0.20, therefore the amount of GDGE used was: m GDGE =0.2×44.5×110 / 1000=0.979g 0.979 g of GDGE was prepared into a fresh aqueous solution with a mass fraction of 10%. The precursor solution was added at 25 °C over 38 min. After stirring for another 12 min, the solution was poured into a mold, and the liquid layer thickness was controlled to be 15 mm. The solution was kept at 40 °C for 15 h to obtain a cross-linked gel.

[0035] The cross-linked gel was kept at -20℃ for 10 h, then thawed at 25℃ for 4 h, and this operation was repeated 3 times. Then, the gel was immersed in approximately 480 mL of a 70% ethanol aqueous solution containing 0.20 mol / L sodium hydroxide at a dry gel-to-neutralization liquid volume ratio of 1 g:30 mL, and neutralized at 25℃ for 2 h. The gel was washed twice with 70% ethanol aqueous solution, and then washed with deionized water until the pH of the washing solution was 6.8–7.5 and the extractable epoxy compounds were below the detection limit. The washed gel was frozen at -45℃ for 14 h, and then freeze-dried for 30 h under cold trap conditions of -55℃ and a pressure not exceeding 40 Pa to obtain chitosan-based environmentally friendly sponge. Example 3

[0036] A method for preparing a chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength includes the following steps: 10.00 g of chitosan with a degree of deacetylation of 92% and a weight-average molecular weight of 150,000 was added to a solution composed of 4.00 g glacial acetic acid and 496.00 g deionized water, and stirred at 25 °C for 6 h until completely dissolved. The pH was slowly adjusted to 5.9 using 1 mol / L sodium hydroxide solution. Based on a molar ratio of glycidyltrimethylammonium chloride to available primary amino groups of chitosan of 0.50, 6.06 g of a 70% glycidyltrimethylammonium chloride aqueous solution was weighed. 3.64 g was added first, and the reaction was carried out at 57 °C for 1.5 h; then the remaining 2.42 g was added over 30 min, and the temperature was raised to 67 °C to continue the reaction for 6 h.

[0037] The reaction solution was cooled to 25°C and washed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa for eight dialysis volumes using a 0.3% (w / w) aqueous acetic acid solution. The retentate was concentrated to approximately 100 mL, and four times its volume of 95% ethanol was added to precipitate cationic chitosan. The precipitate was then filtered and dried under vacuum at 45°C.

[0038] Weigh 4.50 g of the above-mentioned cationic chitosan and 5.50 g of unmodified chitosan, add them to 280.00 g of a 1.0% (w / w) aqueous acetic acid solution, and stir at 25 °C until completely dissolved. Concentrate the chitosan solution under reduced pressure at a temperature not exceeding 35 °C to a total mass of approximately 209.00 g.

[0039] Separately, 4.50 g of PVA-1799 was added to 40.50 g of deionized water and stirred at 95 °C for 60 min until completely dissolved, then cooled to 30 °C. 60.00 g of a 2% (w / w) aqueous dispersion of low-charge mechanically microfibrillated cellulose was taken, containing 1.20 g of dry microfibrillated cellulose with a carboxyl content of 0.10 mmol / g. The PVA solution and microfibrillated cellulose dispersion were sequentially added to the concentrated chitosan solution, dispersed under high shear for 15 min, slowly adjusted to pH 6.2, and degassed under vacuum for 10 min to obtain a sponge precursor solution with a total solids content of approximately 5%.

[0040] The total amount of residual primary amino functional groups in the precursor solution was determined to be 43.5 mmol. Glyceryl diglycidyl ether (GDGE) (epoxy equivalent 115 g / eq) was selected. The molar ratio of epoxy functional groups to residual primary amino functional groups was set at 0.25, therefore the amount of GDGE used was: m GDGE =0.25×43.5×115 / 1000=1.251g 1.251 g of GDGE was prepared into a fresh aqueous solution with a mass fraction of 10%. The precursor solution was added at 30 °C over 30 min. After stirring for another 10 min, the solution was poured into a mold, and the liquid layer thickness was controlled to be 20 mm. The solution was kept at 42 °C for 12 h to obtain a cross-linked gel.

[0041] The cross-linked gel was kept at -22℃ for 8 hours, then thawed at 27℃ for 3 hours, and this operation was repeated 4 times. Then, the gel was immersed in approximately 595 mL of a 75% ethanol aqueous solution containing 0.25 mol / L sodium hydroxide at a dry gel-to-neutralization liquid volume ratio of 1 g:35 mL, and neutralized at 30℃ for 1.5 hours. The gel was washed twice with 75% ethanol aqueous solution, and then washed with deionized water until the pH of the washing solution was 6.8–7.5 and the extractable epoxy compounds were below the detection limit. The washed gel was frozen at -50℃ for 16 hours and freeze-dried for 36 hours under cold trap conditions of -60℃ and a pressure not exceeding 30 Pa to obtain chitosan-based environmentally friendly sponge.

[0042] Comparative Example 1: Compared with Example 1, no GTMAC grafting treatment of chitosan was performed, and all the cationic chitosan in Example 1 was replaced with unmodified chitosan of equal dry basis weight. The other raw material types, polyvinyl alcohol dosage, low charge mechanical microfibrillated cellulose dosage, total solid content of precursor solution and preparation conditions were the same as in Example 1.

[0043] Comparative Example 2: Compared with Example 1, benzalkonium chloride was physically added to the precursor solution so that the amount of quaternary ammonium functional group provided by the added benzalkonium chloride was the same as the amount of quaternary ammonium functional group contained in the cationic chitosan in Example 1, so as to compare the antibacterial durability of covalently fixed quaternary ammonium groups and free quaternary ammonium salts.

[0044] Comparative Example 3: Compared with Example 1, no diglycidyl ether was added during the wet strength modification process. The precursor solution was directly kept at 38°C for 18 hours and then subjected to freeze-thaw treatment. The other operating conditions were the same as in Example 1.

[0045] Comparative Example 4: Compared with Example 1, PVA-1799 was not added during the construction of the synergistic support skeleton. Only 0.80g of low-charge mechanical microfibrillated cellulose was retained, and the total solid content of the precursor liquid was kept at 8% by adjusting the water volume. The amount of other raw materials and operating conditions were the same as in Example 1.

[0046] Comparative Example 5: Compared with Example 1, no low-charge mechanical microfibrillated cellulose was added during the construction of the synergistic support skeleton. Only 3.50g of PVA-1799 was retained, and the total solid content of the precursor liquid was kept at 8% by adjusting the water volume. The amount of other raw materials and operating conditions were the same as in Example 1.

[0047] Comparative Example 6: Compared with Example 1, PVA-1799 and low-charge mechanical microfibrillated cellulose were omitted in the construction process of the synergistic support framework, and the total solid content of the precursor liquid containing only chitosan component was kept at 8% by adjusting the water volume. The amount of other raw materials and operating conditions were the same as in Example 1.

[0048] Comparative Example 7: Compared with Example 1, the cross-linked gel did not undergo a freeze-thaw cycle of "freezing at -18°C and thawing at 23°C". Instead, it was directly neutralized, washed, finally frozen and freeze-dried after cross-linking was completed. The amount of other raw materials and operating conditions were the same as in Example 1.

[0049] Comparative Example 8: Compared with Example 1, TEMPO oxidized cellulose nanofibers with a carboxyl content of 0.30 mmol / g and an isobaric weight were used to replace low-charge mechanical microfibrillated cellulose with a carboxyl content of 1.0 mmol / g. The amounts of other raw materials and operating conditions were the same as in Example 1.

[0050] Comparative Example 9: Compared with Example 1, the molar ratio of epoxy functional group to residual primary amine functional group was reduced from 0.15 to 0.10, and the amount of GDGE was recalculated based on the residual primary amine test value and GDGE epoxy equivalent. The amounts of other raw materials and operating conditions were the same as in Example 1.

[0051] Comparative Example 10: Compared with Example 1, the molar ratio of epoxy functional group to residual primary amine functional group was increased from 0.15 to 0.30, and the amount of GDGE was recalculated based on the residual primary amine test value and GDGE epoxy equivalent. The amounts of other raw materials and operating conditions were the same as in Example 1.

[0052] Performance testing 1. Washability and Antibacterial Performance Test: The sample and a 2.0 g / L neutral phosphate-free standard detergent were placed in a washing container at a mass ratio of 1:100. The mixture was washed at 40±2℃ and 150 r / min with shaking for 15 min. Then, it was rinsed three times with an equal volume of deionized water for 5 min each time. Finally, it was dried at 40℃ to constant weight. One complete washing, rinsing, and drying process was recorded as one washing cycle. Unwashed, 20-cycle, and 50-cycle washing samples were used independently. The washed sponge was cut into small pieces with sides of approximately 5 mm. 0.75±0.05 g of each piece was placed in a 250 mL sterile conical flask, and 70 mL of a 2.0×10⁻⁶ standard detergent was added to each flask. 5 CFU / mL *Escherichia coli* CMCC(B)44102 bacterial suspension or *Staphylococcus aureus* CMCC(B)26003 bacterial suspension were contacted at 24±1℃ and 150 r / min for 18±1 h with shaking. After contact, the sustained antibacterial effect of the quaternary ammonium group was terminated using lecithin-polysorbate 80 neutralization solution with verified neutralization efficacy. Bacteria adhering to the well walls were thoroughly washed away by shaking, and after serial dilution, plates were cultured for counting. A bacterial suspension without sponge was used as a blank control under the same culture conditions. The antibacterial rate was calculated as R = (Nc - Ns) / Nc × 100%, where Nc is the viable count in the blank control and Ns is the viable count in the treated sample.

[0053] 2. Equilibrium water absorption ratio test: The sample was cut into 30mm×30mm×10mm pieces and dried to constant weight under vacuum at 40℃. The dry mass m0 was measured with a weighing accuracy of 0.001g. The sample was then completely immersed in deionized water at 23±2℃ and compressed underwater to 50% of its original thickness before being released. This process was repeated five times to remove air from the pores. The sample was then soaked for another 24 hours. After removal, the sample was placed on a stainless steel mesh to drain naturally for 60 seconds without compression, and the wet mass m1 was immediately measured. The 24-hour equilibrium water absorption ratio was calculated using Q=(m1-m0) / m0, in g / g.

[0054] 3. Dry and Wet 50% Compressive Stress and Wet Strength Retention Rate Tests: Samples were cut into 50mm × 50mm × 10mm pieces. Dry samples were tested directly after standard environmental conditioning. Wet samples were immersed in deionized water at 23±2℃ for 24 hours, then gently patted to remove surface free water, and the test was completed within 2 minutes. A universal testing machine equipped with parallel pressure plates was used, with a contact preload of 0.1N, compressed to 50% strain at a speed of 10mm / min and held for 60s. The load F at the end of the holding period was recorded. 50 According to σ 50 =F 50 / A0 is used to calculate the 50% compressive stress, where A0 is the initial compression area of ​​the specimen; the wet strength retention rate is calculated as K = σwet / σdry × 100%. Independent specimens are used for dry and wet tests.

[0055] 4. Wet Cyclic Thickness Recovery Rate Test: This indicator refers to the evaluation method of thickness recovery after compression in GB / T 6669-2008, and the cyclic test conditions are established according to the wet use state of the sponge. A 50mm×50mm×10mm sample is immersed in deionized water at 23±2℃ for 24h, and the initial thickness h0 is measured under a contact pressure of 0.2kPa. Then, it is compressed from zero strain to 50% strain at a speed of 10mm / min in a water bath compression fixture, held for 10s, unloaded, and allowed to recover in water for 60s. This process is repeated 10 times. After the 10th unloading, the sample is placed in water for 5min to recover, and the recovered thickness h is measured under the same contact pressure. r According to H=h r / h0×100% calculates the wet thickness recovery rate after 10 cycles.

[0056] 5. Open Porosity Test: Since existing standards for foamed plastic porosity are not entirely applicable to swellable hydrophilic chitosan sponges, the anhydrous ethanol displacement method is used for laboratory determination. The dried sample to constant weight is cut into 20mm × 20mm × 10mm pieces. Anhydrous ethanol of volume V1 is added to a graduated cylinder, completely submerging the sample below the ethanol surface. The sample is then degassed under a vacuum of -0.08MPa for 20 minutes, and allowed to stand for 10 minutes after returning to normal pressure. The total volume of the sample and ethanol, V2, is recorded. The sample that has absorbed the ethanol is removed without further compression, and the remaining ethanol volume, V3, is recorded. If a metal mesh is used to fix the sample, the mesh volume should be deducted from the blank test. The open porosity is calculated as P = (V1 - V3) / (V2 - V3) × 100%.

[0057] Table 1:

[0058] Comparative Example 1, which did not undergo chitosan cationization, showed significantly lower antibacterial rates both before and after washing compared to Example 1, indicating that fixing cation sites is the main factor in improving antibacterial activity. Comparative Example 2, which used the physical addition of benzalkonium chloride, achieved an antibacterial rate of over 99% before washing, but this decreased to 52.7% and 57.6% after 50 washes, respectively. This suggests that while free antibacterial components can achieve high initial antibacterial rates, they are prone to migration during continuous washing. In contrast, the antibacterial groups in the examples are part of the chitosan molecular structure. The washing process mainly causes surface abrasion and the migration of a small amount of soluble matter, without causing concentrated loss of the antibacterial components, thus resulting in a slower decline in antibacterial performance.

[0059] The wet mechanical results showed that the wet 50% compressive stress, wet strength retention rate, and cyclic thickness recovery rate of Example 1 were 24.8 kPa, 64.2%, and 87.0%, respectively, while those of Comparative Example 3 (without GDGE) were 14.8 kPa, 34.9%, and 67.2%, respectively. This indicates that without stable network constraints, the sponge is prone to pore wall softening and irreversible collapse after water absorption. Comparative Example 9 had a relatively low crosslinking agent equivalent, with a wet compressive stress of only 19.0 kPa. Although Comparative Example 10 had a wet compressive stress of 29.1 kPa and a wet strength retention rate of 72.6%, its water absorption ratio, porosity, and cyclic thickness recovery rate decreased to 14.8 g / g, 85.9%, and 80.1%, respectively. Therefore, simply increasing the degree of crosslinking can improve the load-bearing capacity during a single compression, but it will reduce the deformation recovery capacity of the liquid absorption space and pore walls, and it cannot be concluded that the overall performance is improved simultaneously.

[0060] Example 1 and Comparative Examples 4-6 constitute a two-factor control of PVA and low-charge mechanical microfibrillated cellulose. Comparative Example 6, containing neither PVA nor cellulose, had a wet compressive stress of 13.5 kPa; Comparative Example 4, retaining only low-charge mechanical microfibrillated cellulose, had a stress of 17.4 kPa; and Comparative Example 5, retaining only PVA, had a stress of 19.2 kPa. A simple summation of the two individual contributions yielded an expected value of 23.1 kPa, while Example 1 reached 24.8 kPa, exceeding the summed reference value by 1.7 kPa. Using the same method, Example 1 showed a wet strength retention rate 5.6 percentage points higher than the summed reference value, and a wet thickness recovery rate after 10 cycles 1.3 percentage points higher than the summed reference value, demonstrating a positive interaction trend. This interaction stems from the different functions performed by the two materials. PVA forms a continuous, flexible hydrophilic phase within the pore walls and creates reversible physical constraint points through freeze-thaw cycles, enabling the pore walls to deform under pressure and disperse localized stress. Low-charge mechanically microfibrillated cellulose, in the form of long, thin fibers, bridges adjacent pore walls, limiting slippage and crack propagation in the wet state. When both are present, the flexible continuous phase buffers strain, while the fibrous skeleton transfers load and inhibits creep, thus compensating for the reduced number of primary amino groups that can participate in subsequent network fixation after chitosan cationization and the wet softening problem caused by increased hydrophilicity. Due to the low surface charge of the cellulose used, its shielding effect on fixed cation sites is weak; in Comparative Example 8, the use of high-carboxyl cellulose nanofibers resulted in a decrease in both antibacterial rate and porosity, further demonstrating that controlling the fiber surface charge is beneficial for balancing structural reinforcement and effective exposure of antibacterial sites.

[0061] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength, characterized in that, Includes the following steps: (1) Chitosan was subjected to a ring-opening grafting reaction with glycidyltrimethylammonium chloride, and after purification, cationic chitosan containing hydroxypropyltrimethylammonium side groups was obtained. (2) The cationic chitosan, unmodified chitosan, polyvinyl alcohol and mechanically microfibrillated cellulose are dispersed in an acidic aqueous phase to obtain a sponge precursor solution; (3) Add glycerol diglycidyl ether to the sponge precursor solution to allow the residual primary amino groups in the cationic chitosan and unmodified chitosan to undergo ring-opening crosslinking with the epoxy groups of glycerol diglycidyl ether to obtain a crosslinked gel. (4) The cross-linked gel is subjected to freeze-thaw treatment, and then neutralized, washed, frozen and freeze-dried in sequence to obtain the chitosan-based environmentally friendly sponge.

2. The preparation method according to claim 1, characterized in that, The degree of deacetylation of the chitosan used in step (1) is 85% to 92%, and the weight-average molecular weight is 80,000 to 150,000.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the molar ratio of glycidyltrimethylammonium chloride active ingredient to chitosan primary amino group is 0.40 to 0.50; The ring-opening grafting reaction is carried out in an aqueous phase with pH 5.7–5.

9. First, 60% of the total amount of glycidyltrimethylammonium chloride is added, and the reaction is carried out at 53–57°C for 1.5–2.5 h. Then, the remaining 40% is added, and the reaction is carried out at 63–67°C for 6–8 h.

4. The preparation method according to claim 3, characterized in that, The reaction product of step (1) was washed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa for no less than 6 dialysis volumes using an aqueous acetic acid solution with a mass fraction of 0.1% to 0.3%, and then precipitated with ethanol and dried under vacuum at 40 to 45°C.

5. The preparation method according to claim 1, characterized in that, In step (2), the sum of the dry basis mass of cationic chitosan and unmodified chitosan is 100 parts by mass, wherein the cationic chitosan is 35-45 parts by mass, the unmodified chitosan is 55-65 parts by mass, the polyvinyl alcohol is 35-45 parts by mass, and the mechanically microfibrillated cellulose is 8-12 parts by mass.

6. The preparation method according to claim 5, characterized in that, The polyvinyl alcohol is PVA-1799; the mechanically microfibrillated cellulose is low-charge mechanically microfibrillated cellulose with a carboxyl content of not more than 0.3 mmol / g; The polyvinyl alcohol is pre-prepared into a 10% aqueous solution, dissolved at 92-95°C and then cooled to no higher than 35°C; The mechanically microfibrillated cellulose is added in the form of an aqueous dispersion with a mass fraction of 2% to 5%.

7. The preparation method according to claim 5 or 6, characterized in that, The total solids content of the sponge precursor solution obtained in step (2) is 5% to 8%, and the pH is 6.0 to 6.

2.

8. The preparation method according to claim 1, characterized in that, The diglycidyl ether used in step (3) is a water-soluble diglycidyl ether with an epoxy functionality of 2; The amount of glycerol diglycidyl ether added satisfies the requirement that the molar ratio of the epoxy functional group to the residual primary amino functional group in the sponge precursor solution is 0.15 to 0.

25.

9. The preparation method according to claim 8, characterized in that, The mass of the diglycidyl ether is determined according to the following formula: m GDGE =R×n NH2 ×EEW / 1000; In the formula, m GDGE The mass of glycerol diglycidyl ether is expressed in grams. R is the molar ratio of the epoxy functional group to the residual primary amine functional group; n NH2 The amount of substance of the residual primary amino functional group is expressed in mmol; EEW is the epoxy equivalent of the glycerol diglycidyl ether used, expressed in g / eq.

10. A chitosan-based environmentally friendly sponge with improved antibacterial durability and wet strength, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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