Paper pulp-based hydroxyethyl cellulose antibacterial composite film as well as preparation method and application thereof

Abstract

The invention relates to a paper pulp-based hydroxyethyl cellulose antibacterial composite film as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) preparing paper pulp-based hydroxyethyl cellulose; (2) preparing a peppermint essential oil nano-emulsion; and (3) preparing the paper pulp-based hydroxyethyl cellulose antibacterial composite film. The average thickness of the paper pulp based hydroxyethyl cellulose antibacterial composite film provided by the invention is 0.205 + / -0.017 mm, and the density is 0.59 + / -0.05 g / cm < 3 >. Hydroxyl in paper pulp base HEC and carboxyl and hydroxyl of SA form a multiple hydrogen bond network; pO is used as a hydrophobic plasticizer and generates interfacial tension with a hydrophilic SA / HEC matrix, and tiny liquid drops or agglomerates are easily formed in the film forming process; ca < 2 + > and carboxylate radicals in SA form ionic bonds through electrostatic interaction to generate a calcium alginate gel network, so that the tensile strength of the paper pulp-based hydroxyethyl cellulose antibacterial composite film reaches 6.1 MPa, the water vapor permeability is 5.32 * 10 <-10 > g.m <-1 >. S <-1 >. Pa <-1 >, and the paper pulp-based hydroxyethyl cellulose antibacterial composite film has a remarkable inhibition effect on growth of penicillium oxalicum.

Description

Technical Field

[0001] The invention relates to a pulp-based hydroxyethyl cellulose antibacterial composite film and a preparation method and application thereof, belonging to the technical field of cellulose antibacterial composite films. Background Art

[0002] Traditional petroleum-based packaging materials can effectively block the permeation of gases such as oxygen, moisture, and carbon dioxide, thereby extending the shelf life of food. However, these materials are non-biodegradable, and long-term use not only causes many health problems but also exacerbates environmental pollution. This dual environmental and health crisis has forced the academic community to explore biodegradable alternative materials, among which cellulose has become a research focus due to its advantageous reserves and CO2-neutral cycle characteristics. Utilizing renewable resources such as cellulose to develop environmentally friendly packaging materials can help reduce dependence on petroleum-based plastics, thereby alleviating environmental pressures. Unfortunately, cellulose itself lacks antimicrobial activity, which limits its application in antimicrobial packaging.

[0003] Hydroxyethyl cellulose (HEC) is an important cellulose derivative that is hydrophilic, odorless, and non-toxic. It also possesses excellent film-forming properties, biodegradability, and biocompatibility, making it widely used in the pharmaceutical, food, and cosmetic industries. Currently, the conventional preparation process for hydroxyethyl cellulose uses cotton cellulose as the raw material and adopts a slurry process system. However, cotton is an important textile raw material with a high market price. In recent years, the price of refined cotton has continued to rise, and the supply of raw materials has been unstable. As a result, the production cost of hydroxyethyl cellulose has remained high. As a result, people have increasingly focused their attention on the development and utilization of other celluloses.

[0004] Despite its numerous advantages, hydroxyethyl cellulose (HEC) still has some limitations in practical applications. For example, its poor toughness, ductility, and load-bearing capacity restrict its use as a single material. Furthermore, HEC's inherent antimicrobial properties struggle to meet the demands of practical applications. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides a pulp-based hydroxyethyl cellulose antibacterial composite film and a preparation method and application thereof.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for preparing a pulp-based hydroxyethyl cellulose antibacterial composite film comprises the following steps:

[0008] (1) crushing, alkalizing, etherifying, neutralizing, cross-linking, washing and drying the pulp raw material to obtain pulp-based hydroxyethyl cellulose;

[0009] (2) adding a surfactant to peppermint essential oil (PO) and mixing uniformly to obtain a mixed system; then injecting the mixed system into deionized water, shaking and mixing, and homogenizing to obtain a peppermint essential oil nanoemulsion;

[0010] (3) Add pulp-based hydroxyethyl cellulose, peppermint essential oil nanoemulsion and glycerol to the sodium alginate (SA) solution, mix well to obtain a mixed solution; inject the mixed solution into a mold, dry at 55-65°C for 10-15 hours to obtain a composite film; spray the CaCl2 solution evenly on the surface of the composite film, dry at 20-30°C and 20-30% RH for 5-10 hours to obtain a pulp-based hydroxyethyl cellulose antibacterial composite film.

[0011] According to the present invention, preferably, in step (1), the pulp is dissolving pulp, broadleaf pulp, coniferous pulp or reed pulp.

[0012] According to a preferred embodiment of the present invention, in step (1), the preparation method of the pulp-based hydroxyethyl cellulose is as follows:

[0013] a. Soaking the pulp sheet in deionized water at a solid-liquid ratio of 1:15 for 24 hours, then deflocculently disintegrating the fibers and balancing the fibers to a moisture content of 8-10%, and crushing the pulp to obtain pulp;

[0014] b. In a reaction kettle, the dispersion medium, alkali solution and the pulp obtained in step a are uniformly mixed, and alkalized at 18-22° C. for 60-80 min. During the alkalization process, an inerting treatment is simultaneously performed, vacuuming to -0.05 MPa, and then filling with nitrogen to 0.2 MPa, and repeating this process 4 times to obtain alkalized pulp;

[0015] c. Continue to add ethylene oxide to the alkalized pulp obtained in step b and pressurize it to 0.32 MPa, stir for 5-15 minutes, react at 55-65° C. for 60-70 minutes, heat to 75-85° C. and continue to react for 70-90 minutes, cool to 40-45° C., add nitric acid, neutralize for 10-15 minutes, then add glyoxal, and cross-link for 5-15 minutes; finally, wash twice with acetone and dry at 55-65° C. for 5-8 hours to obtain pulp-based hydroxyethyl cellulose.

[0016] Further preferably, in step b, the dispersion medium is prepared by mixing tert-butanol, isopropanol and water in a mass ratio of 50:38:12.

[0017] Further preferably, in step b, the alkali solution is prepared by mixing the dispersion medium and sodium hydroxide in a mass ratio of 80:6.

[0018] Further preferably, in step b, the mass ratio of the dispersion medium, alkali solution and pulp is 120:86:10.

[0019] Further preferably, in step c, the mass ratio of the ethylene oxide to the alkalized pulp is (1-1.1):1; the mass ratio of the glyoxal to ethylene oxide is (3-5):(100-110); the mass concentration of the nitric acid is 35-45%, and the mass ratio of nitric acid to ethylene oxide is (220-240):(100-110).

[0020] Preferably, according to the present invention, in step (2), the mass volume ratio of the peppermint essential oil, surfactant and deionized water is (1-4) mL: (0.1-0.6) g: (2-8) mL.

[0021] Further preferably, the mass volume ratio of the peppermint essential oil, surfactant and deionized water is 2.4 mL:0.36 g:5 mL; and the surfactant is Tween 80.

[0022] According to the preferred embodiment of the present invention, in step (2), the oscillation mixing and homogenization are: first placing the mixture in a vortex shaker for 2 to 5 minutes; and then using an ultrasonic device at 40kHz and 650W to continue homogenization for 10 to 20 minutes.

[0023] Preferably, according to the present invention, in step (3), the mass volume ratio of the sodium alginate solution, pulp-based hydroxyethyl cellulose, peppermint essential oil nanoemulsion and glycerol is (20-30) mL: (0.2-1) g: (6-9) g: (0.5-1.5) mL; and the concentration of the sodium alginate solution is 20-30 mg / mL.

[0024] Further preferably, the mass volume ratio of the sodium alginate solution, pulp-based hydroxyethyl cellulose, peppermint essential oil nanoemulsion and glycerol is 25 mL:0.6 g:7.5 g:1 mL; the concentration of the sodium alginate solution is 24 mg / mL, which is obtained by dispersing 600 mg of sodium alginate in 25 mL of deionized water and continuously stirring with a magnetic stirrer at 800 rpm in an oil bath at 90±1°C until completely dissolved.

[0025] According to the preferred embodiment of the present invention, in step (3), the concentration of the CaCl2 solution is 1.5-2.5%; the spraying parameters are 60-65cm 2 Spray 2mL.

[0026] Further preferably, the concentration of the CaCl2 solution is 2%; the spraying parameter is 63.62cm 2 Spray 2mL.

[0027] A pulp-based hydroxyethyl cellulose antibacterial composite film is prepared according to the method.

[0028] Application of the pulp-based hydroxyethyl cellulose antibacterial composite film in the field of cling film.

[0029] The technical features of the present invention are as follows:

[0030] The present invention first prepares pulp-based HEC based on pulp raw materials, and then uses the casting method to construct a pulp-based HEC / sodium alginate (SA) / peppermint essential oil (PO) / calcium chloride (CaCl2) quaternary composite system: first, SA is introduced as a co-base material. Its molecular chain is rich in hydroxyl / carboxyl groups, which can achieve performance regulation and complement HEC - the former enhances hydrophilicity and degradability, and the latter improves film-forming stability. More importantly, the function is upgraded by loading PO: the active ingredients such as L-menthol in PO can not only synergistically enhance the antibacterial effect, but also give the composite film antioxidant properties, forming a multiple preservation mechanism. Finally, CaCl2 is added as a cross-linking agent, Ca 2+ It reacts with the carboxylate in SA to form bridges between different alginate chains, promoting the reorganization of SA polymer chains into a denser structure in water, reducing the water solubility of the film and extending its life in water.

[0031] Beneficial effects of the present invention:

[0032] 1. The present invention uses pulp as raw material to prepare pulp-based hydroxyethyl cellulose. First, the cellulose content in the pulp is more than 70%, with few impurities, high efficiency of the etherification reaction (with ethylene oxide), and easier control of the degree of substitution of the product. Secondly, the global annual output of pulp exceeds 100 million tons, the raw material supply is sufficient, and the large-scale production system is mature, which can ensure the continuity of hydroxyethyl cellulose production. Moreover, the price of pulp is significantly lower than that of cotton fiber, and is not affected by fluctuations in demand in the textile industry. It is low-cost and sustainable. By selecting different types of pulp, products with different viscosities, dissolution rates, and rheological properties can be customized to meet diverse needs; good biocompatibility; excellent solubility and thickening properties.

[0033] 2. The average thickness of the pulp-based hydroxyethyl cellulose antibacterial composite film provided by the present invention is 0.205±0.017mm and the density is 0.59±0.05g / cm 3 The hydroxyl groups in the pulp-based HEC form a multiple hydrogen bond network with the carboxyl and hydroxyl groups of SA; PO, as a hydrophobic plasticizer, generates interfacial tension with the hydrophilic SA / HEC matrix, which easily forms tiny droplets or agglomerates during the film formation process; Ca 2+ The ionic bonds were formed with the carboxyl groups in SA through electrostatic interaction to generate a calcium alginate gel network, which made the tensile strength of the pulp-based hydroxyethyl cellulose antibacterial composite film reach 6.1 MPa and the water vapor permeability was 5.32×10 -10 g·m -1 ·s -1 ·Pa -1, and has a significant inhibitory effect on the growth of Penicillium oxalicum.

[0034] 3. The preparation method provided by the present invention is simple to operate, low in cost, has good film uniformity, and can flexibly control the film structure and performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The morphology of the pulp raw material used in Example 1 and the prepared pulp-based hydroxyethyl cellulose.

[0036] Figure 2 Component analysis of broadleaf pulp 1, broadleaf pulp 2, coniferous pulp 1, coniferous pulp 2, coniferous pulp 3 and reed pulp used in Example 2.

[0037] Figure 3 The moisture content of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0038] Figure 4 The ash content of the pulp-based hydroxyethyl cellulose prepared in Example 2 is:

[0039] Figure 5 This is the pH value of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0040] Figure 6 The viscosity of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0041] Figure 7 The light transmittance of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0042] Figure 8 This is the bioenzyme stability of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0043] Figure 9 FTIR spectra of the pulp raw material used in Example 2 and the pulp-based hydroxyethyl cellulose prepared.

[0044] In the figure, (a) is pulp raw material; (b) is pulp-based hydroxyethyl cellulose.

[0045] Figure 10 This is the TGA spectrum of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0046] Figure 11 This is the DSC spectrum of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0047] Figure 12 This is the XRD pattern of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0048] Figure 13 FTIR spectra of composite membranes of different configurations of Example 3 and Comparative Examples 1 to 3.

[0049] Figure 14 The XRD patterns of the composite films of Example 3 and Comparative Examples 1 to 3 with different configurations are shown.

[0050] Figure 15 The SEM images of the plane and cross-section of the composite membranes of different configurations of Example 3 and Comparative Examples 1 to 3 are as follows;

[0051] In the figure, a and b are the planar and cross-sectional SEM images of SA; c and d are the planar and cross-sectional SEM images of HEC / SA; e and f are the planar and cross-sectional SEM images of HEC / SA / PO; g and h are the planar and cross-sectional SEM images of HEC / SA / PO / CaCl2.

[0052] Figure 16 The AFM images of the plane and three-dimensional composite films of different configurations of Example 3 and Comparative Examples 1 to 3 are as follows;

[0053] In the figure, a is SA; b is HEC / SA; c is HEC / SA / PO; d is HEC / SA / PO / CaCl2.

[0054] Figure 17 The figures are actual pictures of composite membranes of different configurations of Example 3 and Comparative Examples 1 to 3;

[0055] In the figure, a is SA; b is HEC / SA; c is HEC / SA / PO; d is HEC / SA / PO / CaCl2.

[0056] Figure 18 The mechanical properties of the composite films of Example 3 and Comparative Examples 1 to 3 with different configurations are shown.

[0057] Figure 19 This is the growth inhibition of Penicillium oxalicum by the pulp-based hydroxyethyl cellulose antibacterial composite film (HEC / SA / PO / CaCl2) prepared in Example 3.

[0058] Figure 20 These are the appearance pictures of cherries in the CK, CM, and HSPC groups after 0, 3, and 7 days of storage.

[0059] Figure 21 These are the appearance pictures of strawberries in the CK, CM, and HSPC groups after 0, 3, and 7 days of storage.

[0060] Figure 22 The weight loss rate changes of cherries and strawberries;

[0061] In the picture, (a) Cherries (casting method) (b) Strawberries (coating method). DETAILED DESCRIPTION

[0062] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0063] The reagents and equipment involved in the present invention are all conventional products and can be obtained commercially.

[0064] Example 1. Preparation of pulp-based hydroxyethyl cellulose

[0065] A method for preparing dissolving pulp-based hydroxyethyl cellulose is as follows:

[0066] a. Tear the dissolving pulp sheet into sheets, soak them in deionized water at a solid-liquid ratio of 1:15 for 24 hours (25°C) to swell the fibers; then use a PFI refiner to gradually deflagrate the fibers, equilibrate them to a moisture content of 8-10% in a humidity-controlled air drying oven at 30% RH ± 3%, and finally use a wall breaker to crush them to obtain pulp;

[0067] b. In a reactor, uniformly mix the dispersion medium, alkali solution, and the pulp obtained in step a, open the cooling water of the reactor, start stirring, and alkalize at 20° C. for 70 minutes. During the alkalization process, perform an inerting treatment simultaneously, evacuate to -0.05 MPa, and then fill with nitrogen to 0.2 MPa, repeating this process 4 times to obtain alkalized pulp;

[0068] The dispersion medium is prepared by mixing tert-butyl alcohol, isopropyl alcohol and water in a mass ratio of 50:38:12.

[0069] The preparation method of alkali solution is as follows: in a reactor, a dispersion medium and caustic soda (NaOH) are mixed in a mass ratio of 80:6, stirring is started, and the jacket steam is turned on to increase the temperature. When the temperature reaches 45°C, heating is stopped and timing is started. The mixture is stirred for 30 minutes, and cooling water is turned on to cool the mixture to 20°C. The preparation is completed.

[0070] c. Ethylene oxide (EO) was further added to the alkalized pulp obtained in step b and the pressure was increased to 0.32 MPa. The mixture was stirred for 10 min, reacted at 60° C. for 60 min, heated to 80° C. and reacted for 90 min. The mixture was cooled to 42° C. and 40% nitric acid (HNO 3 ) was added. The mixture was neutralized for 15 min, and then 5 g of glyoxal was added and cross-linked for 10 min. The mixture was washed twice with acetone and dried at 60° C. for 6 h to obtain pulp-based hydroxyethyl cellulose, which was designated as HEC1.

[0071] According to the same method, hydroxyethyl cellulose was prepared using broadleaf pulp 1, broadleaf pulp 2, coniferous pulp 1, coniferous pulp 2, coniferous pulp 3 and reed pulp as raw materials to obtain another 6 different pulp-based hydroxyethyl celluloses, which were respectively recorded as HEC2, HEC3, HEC4, HEC5, HEC6 and HEC7.

[0072] Among them, broadleaf pulp 1 is made from eucalyptus and acacia; broadleaf pulp 2 is made from hybrid eucalyptus; coniferous pulp 1 is made from Siberian fir, Siberian spruce and Siberian pine; coniferous pulp 2 is made from Douglas pine; coniferous pulp 3 is made from radiata pine, southern pine, spruce and fir.

[0073] When preparing hydroxyethyl cellulose using coniferous pulp 1 and 3, steps a and b are exactly the same, and the difference in step c is: react at 60°C for 70 minutes, heat to 85°C and continue to react for 70 minutes, cool to 42°C, add nitric acid (HNO3) with a mass concentration of 42% for neutralization, and cross-link with 3g of glyoxal.

[0074] In the above method, the specific amount of each reagent is shown in Table 1 below.

[0075] Table 1. Specific dosage of drugs in the preparation process of pulp-based hydroxyethyl cellulose

[0076]

[0077] The morphology of the pulp raw material and the pulp-based hydroxyethyl cellulose prepared in this embodiment is as follows: Figure 1 shown.

[0078] Depend on Figure 1 Dissolving pulp is highly purified, with a high cellulose content, few impurities, and a smooth fiber surface. Broadleaf pulps 1-2 have shorter, thinner fibers with a smoother surface. Coniferous pulps 1-3 have longer, thicker fibers with a rougher surface and thicker fiber walls. Reed pulp has shorter, thinner fibers with looser arrangement and a lower overall density. All seven pulp-based hydroxyethyl celluloses are yellow, granular solids with irregular shapes and slightly rough surfaces.

[0079] Example 2: Analysis of Pulp-Based Hydroxyethyl Cellulose

[0080] 1. Since the core of the synthesis of pulp-based hydroxyethyl cellulose lies in the etherification reaction between cellulose in the pulp and ethylene oxide, the cellulose content in each pulp has a decisive influence on the product preparation. Therefore, the dissolving pulp and broadleaf pulp used in Example 1

[0081] The components of broadleaf pulp 1, broadleaf pulp 2, coniferous pulp 1, coniferous pulp 2, coniferous pulp 3 and reed pulp were compared and analyzed. The results are as follows: Figure 2 shown.

[0082] Depend on Figure 2 As can be seen, the proportions of cellulose, hemicellulose, and lignin in different pulps vary significantly. Notably, dissolving pulp leads the pack with 83.27% cellulose, highlighting its significant advantage as a high-quality raw material. Reed pulp, on the other hand, exhibits a higher content of impurities, with hemicellulose at 14.2% and lignin at 3.92%. The cellulose content of all seven selected pulps exceeds 68%, with softwood pulp 2 and hardwood pulp 2 closely following dissolving pulp at 77.93% and 73.26%, respectively.

[0083] 2. The moisture content of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 was calculated according to the formula. The relative standard deviation (RSD) of three parallel experiments was controlled at ≤0.5% (n=3). The results are as follows: Figure 3 shown.

[0084] The formula is:

[0085] Where W1 represents the sample weight (g); W2 represents the weight of the weighing bottle after drying (g); W3 represents the weight of the weighing bottle and sample after drying (g).

[0086] Depend on Figure 3 It can be seen that the moisture contents of HEC1, HEC2, HEC3, HEC4, HEC5, HEC6 and HEC7 are 5.1%, 4.5%, 6.3%, 5.8%, 5.9%, 4.2% and 4.3% respectively.

[0087] 3. The ash contents of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 were quantitatively calculated by high-temperature ashing method. The results are as follows: Figure 4 shown.

[0088] Depend on Figure 4 It can be seen that the ash values of HEC1, HEC2, HEC3, HEC4, HEC5, HEC6 and HEC7 are 17.88%, 17.43%, 17.89%, 20.92%, 17.90%, 21.38% and 23.42% respectively.

[0089] 4. 1.00 g of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 were accurately weighed and prepared into a 1% by mass aqueous dispersion (dissolution temperature 25°C, magnetic stirring 30 min). The acid-base properties of the solution were characterized using a three-point calibrated precision pH meter (accuracy ±0.01). The parallelism control standard was set to relative standard deviation RSD ≤ 0.8% (n = 3). The results were as follows: Figure 5 As shown,

[0090] Depend on Figure 5It can be seen that the pH values of HEC1-HEC7 are 3.39, 3.40, 3.13, 3.17, 3.48, 3.71, and 4.54, respectively.

[0091] 5. Accurately weigh 1.00 g of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 and prepare aqueous dispersions with mass fractions of 1% and 2% (dissolution temperature 25°C, magnetic stirring 30 min). The viscosity characteristics of the solutions were characterized by a rotational viscometer system. The experiment adopted a stepwise concentration design (mass concentration of 1% and 2%). The results are as follows: Figure 6 shown.

[0092] Depend on Figure 6 It can be seen that HEC5 made from coniferous pulp 2 exhibits significant non-Newtonian fluid properties: the viscosity of its 2% solution reaches 368 mPa·s, which is 1372% higher than that of the 1% solution (25 mPa·s), and 951% higher than that of the lowest-performing HEC1 (2% solution = 35 mPa·s).

[0093] 6. Accurately weigh 1.00 g of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 and prepare a 2% by mass aqueous dispersion (dissolution temperature 25°C, magnetic stirring 30 min). The optical transparency of the dispersion is determined by spectrophotometry at 590 nm. The results are as follows: Figure 7 shown.

[0094] Depend on Figure 7 It can be seen that the transmittance of HEC1-7 shows significant differences: HEC4 made from coniferous pulp 1 shows the best optical properties, with a transmittance of 92.7%. In contrast, the transmittance of HEC7 drops sharply to 27.8%.

[0095] 7. The enzymatic hydrolysis resistance of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 was determined by the enzymatic hydrolysis-viscosity degradation method. The specific method is as follows: the initial viscosity of a 1% HEC aqueous solution is measured at 25±0.2°C, and then a freshly prepared cellulase solution is added. The reaction is kept at 25±0.5°C for 24 hours and then the viscosity after degradation is measured. The results are shown in FIG. Figure 8 shown.

[0096] Depend on Figure 8 The 24h bioenzyme stability of HEC1-7 showed significant heterogeneity (16.45%-37.23%). Among them, HEC1 and HEC7 showed the best resistance to enzymatic degradation, with stability reaching 37.23% and 37.20% respectively, which was 125% higher than the least stable HEC5 (16.45%).

[0097] 8. The pulp raw materials used in Example 1 and the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 were subjected to infrared spectroscopy (FTIR) analysis to determine their functional groups. The results are as follows: Figure 9 shown.

[0098] Depend on Figure 9 It can be seen that the pulp raw materials used in Example 1 and the 7 pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 have a relative humidity of 3660-3040 cm -1 The hydroxyl group absorption peak of the derivative changes from 3340 cm to 4360 cm. -1 Move to 3385cm -1 This red shift phenomenon originates from the reconstruction of the intermolecular hydrogen bond network caused by hydroxyethyl substitution, which quantitatively confirms the regulatory effect of etherification reaction on the supramolecular structure of cellulose.

[0099] 9. Thermogravimetric analysis (TGA) of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 was performed. The results are as follows: Figure 10 shown.

[0100] The thermogravimetric analysis (TGA) includes three stages: (1) initial desorption stage (30-100°C); (2) main chain depolymerization stage (200-330°C); and (3) carbonization stage (>330°C).

[0101] Depend on Figure 10 During the initial desorption phase, the sample experienced a slight loss of approximately 0.4% in mass. This is because hydroxyethyl cellulose is a hydrophilic cellulose ether that readily absorbs moisture from the environment. As the temperature rises, the adsorbed moisture in the hydroxyethyl cellulose begins to evaporate. As the temperature rises further, the moisture evaporates completely, and the sample mass stabilizes.

[0102] 10. The thermal transition behaviors of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 were analyzed by DSC. The results are as follows: Figure 11 shown.

[0103] Depend on Figure 11 It can be seen that HEC1-7 presents characteristic endothermic peaks in the range of 131.12-135.65℃. The appearance of these endothermic peaks indicates that the hydroxyethyl molecules in hydroxyethyl cellulose are semi-melted during the heating process.

[0104] 11. XRD analysis was performed on the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1. The results are as follows: Figure 12 shown.

[0105] Depend on Figure 12It can be seen that the original pulp raw material presents a typical cellulose I-type structure, and its characteristic diffraction peak is located at The hydroxyethylation reaction significantly reconstructed the supramolecular structure of cellulose: the modified product showed broadened diffuse diffraction peaks at 2θ=10.4° and 20.8°, which were significantly shifted and merged with the characteristic peaks of cellulose type II. The crystallinity was changed to 25.77%, 12.24%, 3.82%, 7.06%, 1.20%, 2.95% and 16.36%, respectively. This indicates that the crystallinity of cellulose decreased significantly after the etherification reaction with ethylene oxide.

[0106] Based on the above data, it can be found that the 2% aqueous solution of HEC5 (derived from coniferous pulp 2) has the best shear thinning properties, with a zero-shear viscosity of 368mPa·s (25°C), a 951% increase from the lowest value (HEC1 = 35mPa·s). The light transmittance of HEC4 (derived from coniferous pulp 1) reaches 92.7% ± 0.5%. This shows that HEC derived from pulps of different sources has potential applications in medical dressings (high light transmittance), oilfield thickening (high viscosity), and low-cost building material additives.

[0107] Example 3: Preparation of pulp-based hydroxyethyl cellulose antibacterial composite film

[0108] A method for preparing a pulp-based hydroxyethyl cellulose antibacterial composite film comprises the following steps:

[0109] (1) According to the method described in Example 1, the pulp raw material was crushed, alkalized, etherified, neutralized, cross-linked, washed and dried to obtain 7 types of pulp-based hydroxyethyl cellulose (HEC1-7);

[0110] (2) 0.36 g of a surfactant was added to 2.4 mL of peppermint essential oil (PO) and mixed uniformly to form a surfactant monolayer coating structure to obtain a mixed system; the mixed system was then injected into 5 mL of deionized water and placed in a vortex oscillator for 3 min to form a coarse emulsion; the coarse emulsion was then homogenized using an ultrasonic instrument (40 kHz, 650 W) for 15 min to obtain a more uniform and stable emulsion system, thereby obtaining a peppermint essential oil nanoemulsion;

[0111] (3) 0.6 g of sodium alginate (SA) was dispersed in 25 mL of deionized water and continuously stirred magnetically (800 rpm) in an oil bath at 90 °C until completely dissolved to obtain a sodium alginate solution; then, 0.6 g of pulp-based hydroxyethyl cellulose, 7.5 g of peppermint essential oil nanoemulsion and 1 mL of glycerol were added to the sodium alginate solution and mixed evenly to obtain a mixed solution; 20 g of the mixed solution was injected into a 9 cm polytetrafluoroethylene mold and dried in a 60 °C forced air drying oven for 12 h to obtain a composite membrane; 2 mL of 2% CaCl2 solution was evenly sprayed on the surface of the composite membrane and dried at 25 °C and 25% RH for 8 h to obtain a pulp-based hydroxyethyl cellulose antibacterial composite membrane (HEC / SA / PO / CaCl2).

[0112] Example 4

[0113] A method for preparing a pulp-based hydroxyethyl cellulose antibacterial composite film comprises the following steps:

[0114] (1) According to the method described in Example 1, the pulp raw material was crushed, alkalized, etherified, neutralized, cross-linked, washed and dried to obtain 7 types of pulp-based hydroxyethyl cellulose (HEC1-7);

[0115] (2) 0.18 g of a surfactant was added to 1.2 mL of peppermint essential oil (PO) and mixed uniformly to form a surfactant monolayer coating structure to obtain a mixed system; the mixed system was then injected into 5 mL of deionized water and placed in a vortex oscillator for 3 min to form a coarse emulsion; the coarse emulsion was then homogenized using an ultrasonic instrument (40 kHz, 650 W) for 15 min to obtain a more uniform and stable emulsion system, thereby obtaining a peppermint essential oil nanoemulsion;

[0116] (3) 0.6 g of sodium alginate (SA) was dispersed in 25 mL of deionized water and continuously stirred magnetically (800 rpm) in a 90 °C oil bath until completely dissolved to obtain a sodium alginate solution; then 0.6 g of pulp-based hydroxyethyl cellulose, 6.25 g of peppermint essential oil nanoemulsion and 1 mL of glycerol were added to the sodium alginate solution and mixed evenly to obtain a mixed solution; 20 g of the mixed solution was injected into a 9 cm polytetrafluoroethylene mold and dried in a 60 °C forced air drying oven for 12 h to obtain a composite membrane; 2 mL of 2% CaCl2 solution was evenly sprayed on the surface of the composite membrane and dried at 25 °C and 25% RH for 8 h to obtain a pulp-based hydroxyethyl cellulose antibacterial composite membrane.

[0117] Example 5

[0118] A method for preparing a pulp-based hydroxyethyl cellulose antibacterial composite film comprises the following steps:

[0119] (1) According to the method described in Example 1, the pulp raw material was crushed, alkalized, etherified, neutralized, cross-linked, washed and dried to obtain 7 types of pulp-based hydroxyethyl cellulose (HEC1-7);

[0120] (2) 0.54 g of a surfactant was added to 3.6 mL of peppermint essential oil (PO) and mixed uniformly to form a surfactant monolayer coating structure to obtain a mixed system; the mixed system was then injected into 5 mL of deionized water and placed in a vortex oscillator for 3 min to form a coarse emulsion; the coarse emulsion was then homogenized using an ultrasonic instrument (40 kHz, 650 W) for 15 min to obtain a more uniform and stable emulsion system, thereby obtaining a peppermint essential oil nanoemulsion;

[0121] (3) 0.6 g of sodium alginate (SA) was dispersed in 25 mL of deionized water and continuously stirred magnetically (800 rpm) in a 90 °C oil bath until completely dissolved to obtain a sodium alginate solution; then 0.6 g of pulp-based hydroxyethyl cellulose, 8.74 g of peppermint essential oil nanoemulsion and 1 mL of glycerol were added to the sodium alginate solution and mixed evenly to obtain a mixed solution; 20 g of the mixed solution was injected into a 9 cm polytetrafluoroethylene mold and dried in a 60 °C forced air drying oven for 12 h to obtain a composite membrane; 2 mL of 2% CaCl2 solution was evenly sprayed on the surface of the composite membrane and dried at 25 °C and 25% RH for 8 h to obtain a pulp-based hydroxyethyl cellulose antibacterial composite membrane.

[0122] Comparative Example 1

[0123] A method for preparing an antibacterial film comprises the following steps:

[0124] 0.6 g of sodium alginate (SA) was dispersed in 25 mL of deionized water and continuously stirred with magnetic stirring (800 rpm) in a 90°C oil bath until completely dissolved to obtain a sodium alginate solution. Then, 1 mL of glycerol was added to the sodium alginate solution and mixed evenly. 20 g of the sodium alginate solution was injected into a 9 cm polytetrafluoroethylene mold and dried in a 60°C forced air drying oven for 12 h to obtain an antibacterial film (SA).

[0125] Comparative Example 2

[0126] A method for preparing an antibacterial composite film comprises the following steps:

[0127] 0.6 g of sodium alginate (SA) was dispersed in 25 mL of deionized water and continuously stirred with magnetic stirring (800 rpm) in a 90 °C oil bath until completely dissolved to obtain a sodium alginate solution; then, 0.6 g of pulp-based hydroxyethyl cellulose and 1 mL of glycerol were added to the sodium alginate solution and mixed evenly to obtain a mixed solution; 20 g of the mixed solution was injected into a 9 cm polytetrafluoroethylene mold and dried in a 60 °C forced air drying oven for 12 h to obtain an antibacterial composite film (HEC / SA).

[0128] Comparative Example 3

[0129] A method for preparing an antibacterial composite film comprises the following steps:

[0130] 0.6 g of sodium alginate (SA) was dispersed in 25 mL of deionized water and continuously stirred magnetically (800 rpm) in an oil bath at 90 °C until completely dissolved to obtain a sodium alginate solution; then, 0.6 g of pulp-based hydroxyethyl cellulose, 7.5 g of peppermint essential oil nanoemulsion and 1 mL of glycerol were added to the sodium alginate solution and mixed evenly to obtain a mixed solution; 20 g of the mixed solution was injected into a 9 cm polytetrafluoroethylene mold and dried in a 60 °C forced air drying oven for 12 h to obtain an antibacterial composite film (HEC / SA / PO).

[0131] Test example

[0132] 1. The HEC / SA / PO / CaCl2 antibacterial composite film, SA antibacterial film, HEC / SA antibacterial composite film and HEC / SA / PO antibacterial composite film prepared in Example 3 and Comparative Examples 1 to 3 were subjected to infrared spectroscopy (FTIR) analysis. The results are as follows: Figure 13 shown.

[0133] Depend on Figure 13 It can be seen that the FT-IR spectra of the four composite films show different characteristics. -1 The absorption peak in the range corresponds to the stretching vibration of hydroxyl (-OH). After SA is compounded with pulp-based HEC, the peak changes from 3276 cm -1 Displacement to 3319cm -1 and the strength becomes weaker. -1 、2882cm -1 The positions correspond to CH asymmetric stretching vibration and CH symmetric stretching vibration respectively; 1607cm -1 The peak at 1412 cm corresponds to the asymmetric stretching vibration of carboxylate (-COO-); -1 The peak at 1027 cm mainly corresponds to the symmetrical stretching vibration of carboxylate (-COO-); -1 The peaks at 300 nm correspond to the stretching vibration of ether bonds (COC). The presence of these peaks confirms the cross-linking reaction between SA, pulp-based HEC, PO, and CaCl2.

[0134] 2. X-ray diffraction analysis (XRD) was performed on the HEC / SA / PO / CaCl2 antibacterial composite film, SA antibacterial film, HEC / SA antibacterial composite film and HEC / SA / PO antibacterial composite film prepared in Example 3 and Comparative Examples 1 to 3. The results are as follows: Figure 14 shown.

[0135] Depend on Figure 14 The pure SA film exhibits a single, broadened diffraction peak at 2θ = 20.56°, indicating an amorphous structure. The introduction of pulp-based HEC increases the half-width of this diffraction peak and shifts it to a higher angle of 21.28°. This structural evolution stems from the strong hydrogen bond network formed between the HEC molecules and the SA chains, significantly enhancing interactions within the polymer matrix. This enhanced intermolecular force promotes structural reorganization within the film, leading to an increase in locally ordered regions and lattice distortion, which in turn causes a positive shift in the Bragg diffraction angle and a broadening of the diffraction peak.

[0136] 3. The HEC / SA / PO / CaCl2 antibacterial composite membrane, SA antibacterial membrane, HEC / SA antibacterial composite membrane and HEC / SA / PO antibacterial composite membrane prepared in Example 3 and Comparative Examples 1 to 3 were studied using a scanning electron microscope (SEM). The SEM images of the plane and cross-section are shown in FIG. Figure 15 shown.

[0137] Depend on Figure 15 It can be seen that the pure SA membrane has a typical glassy homogeneous structure, its surface presents atomic-level smooth features, and the cross section shows a dense and defect-free cross-sectional morphology. In sharp contrast, the surface of the HEC / SA / PO / CaCl2 antibacterial composite membrane shows nanoscale roughness structural discontinuities, and the cross section shows through pores with a pore size distribution of 16 to 20 μm. The appearance of irregular pores may be related to the intervention and diffusion of oil droplets in the membrane network and the uneven distribution of cross-linking points between CaCl2 and SA. The appearance of the pore structure can improve the air permeability of the membrane, thereby enhancing the food preservation effect. In addition, the pore structure can provide more release channels for PO, enabling it to be released more evenly and continuously, and exerting better antibacterial and preservation effects. The transformation of the topological structure of the HEC / SA / PO / CaCl2 membrane can be attributed to the synergistic effect between the four components: PO is dispersed in the membrane matrix through physical action to provide antibacterial properties; HEC enhances membrane stability by binding to SA through hydrogen bonds; CaCl2 2+ The cross-linking effect occurs by binding to the carboxylate groups on the SA molecular chain, building three-dimensional cross-linking points in the polymer network. This process promotes the conformational reconstruction of the polymer chain, ultimately forming a bicontinuous phase structure with open pore characteristics.

[0138] 4. The HEC / SA / PO / CaCl2 antibacterial composite films, SA antibacterial films, HEC / SA antibacterial composite films, and HEC / SA / PO antibacterial composite films prepared in Example 3 and Comparative Examples 1 to 3 were characterized (thickness, density, and surface roughness) using a micrometer. The evaluation results of the thickness, density, and surface roughness are shown in Table 2.

[0139] The atomic force microscopy (AFM) two-dimensional (planar) morphology maps and three-dimensional (stereoscopic) topological reconstruction results of the HEC / SA / PO / CaCl2 antibacterial composite film, SA antibacterial film, HEC / SA antibacterial composite film and HEC / SA / PO antibacterial composite film prepared in Example 3 and Comparative Examples 1 to 3 are shown in FIG. Figure 16 As shown in the actual picture Figure 17 shown.

[0140] Table 2. Evaluation of thickness, density, and surface roughness of composite films with different configurations

[0141]

[0142] From Table 2 and Figure 16 It can be seen that with the sequential introduction of pulp-based HEC, PO, and CaCl2, the root mean square roughness (Rq) and average roughness (Ra) of the composite membranes show a significant synergistic growth trend, with their values increasing from the subnanometer smoothness of the pure SA membrane (Ra = 4.31nm) to the nanoscale roughness characteristics of the quaternary composite system (Ra = 56.5nm). This morphological evolution can be attributed to the intermolecular interaction dynamics of the multicomponent system: the hydroxyl groups in the HEC molecules form multiple hydrogen bond networks with the carboxyl and hydroxyl groups of the SA, triggering local gelation differences in the polymer chains, leading to microphase separation of the HEC / SA binary system and the formation of topological fluctuations; PO, as a hydrophobic plasticizer, generates interfacial tension with the hydrophilic SA / HEC matrix, easily forming tiny droplets or agglomerates during the film formation process, resulting in increased surface roughness, thereby increasing the Rq and Ra values; the CaCl2 in the 2+ The carboxyl groups in SA form ionic bonds through electrostatic interactions, forming a calcium alginate gel network. During the cross-linking process, localized uneven gelation causes tiny particles or bumps to appear on the membrane surface, increasing the surface roughness, which is consistent with the SEM results.

[0143] From Table 2 and Figure 17It can be seen that the film thickness gradually increases with the addition of pulp-based HEC and PO, and slightly decreases with the addition of CaCl2. Pulp-based HEC, as a high-viscosity water-soluble polymer, significantly increases the solution viscosity and reduces the fluidity after being added to the SA solution, resulting in more material deposition on the substrate and increasing the film thickness; at the same time, the hydrogen bonding between pulp-based HEC and SA fills the gaps between SA molecular chains, making the membrane structure denser. The addition of PO increases the solid content of the film, resulting in an increase in thickness. At the same time, the diffusion of oil droplets in the membrane network forms pores, further reducing the density, which is consistent with existing research. The addition of CaCl2 reduces the film thickness, which is due to the solubilization effect of CaCl2 in the cross-linking solution; while the increase in density is due to the cross-linking network formed by CaCl2 and SA. Statistical analysis shows that the average thickness of the HEC / SA / PO / CaCl2 antibacterial composite film is 0.205±0.017mm and the density is 0.59±0.05g / cm 3 The composite film has a transparent and uniform structure, and the thickness variation is controlled within the specified range (±0.5mm), indicating good thickness uniformity. Therefore, the effect of film thickness on mechanical strength, light transmittance, barrier properties and other properties can be ignored.

[0144] 5. The mechanical properties of the HEC / SA / PO / CaCl2 antibacterial composite film, SA antibacterial film, HEC / SA antibacterial composite film and HEC / SA / PO antibacterial composite film prepared in Example 3 and Comparative Examples 1 to 3 were measured. Figure 18 shown.

[0145] Determination method: The tensile properties of the composite film were tested using a universal testing machine Instron 5963 (Instron, USA). The film was cut into rectangles of 50 mm × 10 mm and tested at a speed of 30 mm / min. Figure 18 It can be seen that the tensile strength of the HEC / SA / PO / CaCl2 composite membrane is the largest, which is 6.1MPa. The SA molecular chains form a strong network structure through hydrogen bonds and ionic interactions, which gives the material higher rigidity, but also leads to poor ductility. After the addition of pulp-based HEC, the strong interaction between the SA molecular chains is destroyed, the flexibility of the membrane is improved, but the strength is reduced. The addition of peppermint essential oil weakens the interaction between pulp-based HEC and SA molecular chains; at the same time, the irregular distribution of peppermint essential oil and its hydrophobicity form a microporous structure in the membrane, further enhancing the flexibility of the membrane. The addition of CaCl2 greatly improves the tensile strength of the HEC / SA / PO / CaCl2 composite membrane, which is mainly attributed to the cross-linking effect of CaCl2 and SA. The SA molecular chain is composed of β-D-mannuronic acid (M) and α-L-guluronic acid (G) units. When the CaCl2 solution comes into contact with SA, Ca 2+It will cross-link with the carboxylate on the SA molecular chain. 2+ It can combine with the carboxylate groups on the two G units to form stable crosslinking points. At the same time, the pulp-based HEC molecular chains hydrogen bond with the SA molecular chains to further enhance the mechanical properties of the film. This multiple interaction optimizes the mechanical properties of the composite film, making it both flexible and ductile, and with high tensile strength.

[0146] 6. The water vapor transmission rates (WVP) of the HEC / SA / PO / CaCl2 antibacterial composite films, SA antibacterial films, HEC / SA antibacterial composite films and HEC / SA / PO antibacterial composite films prepared in Example 3 and Comparative Examples 1 to 3 were determined.

[0147] Determination method: Use a micrometer to measure the thickness of the composite film at 6 random positions with an accuracy of 0.001mm. First, at the cup mouth area of 4.9cm 2 Add approximately 2.0 g of anhydrous calcium chloride (0% RH) to a 10 mL beaker. Then, place a circular film approximately 30 mm in diameter on top of the 10 mL beaker and seal it with vaseline. Finally, weigh the beaker and place it in an environment at 20°C and 80% RH. Reweigh the beaker every hour until the weight gain remains constant (relative deviation < 0.05).

[0148] The water vapor transmission rates of SA, HEC / SA, HEC / SA / PO, and HEC / SA / PO / CaCl2 composite films were 4.78×10 -10 g·m -1 ·s -1 ·Pa -1 , 4.84×10 -10 g·m -1 ·s -1 ·Pa -1 , 7.77×10 -10 g·m -1 ·s -1 ·Pa -1 , 5.32×10 -10 g·m -1 ·s -1 ·Pa -1 .

[0149] From the above results, it can be seen that pulp-based HEC and SA are both hydrophilic polymer materials with strong hygroscopicity, which makes the composite membrane have a higher WVP value. In the HEC / SA / PO composite membrane, due to the irregular distribution of PO and its hydrophobic nature, a pore structure is formed in the membrane, which increases the diffusion path of water vapor molecules, thereby significantly improving the WVP value. However, in the HEC / SA / PO / CaCl2 antibacterial composite membrane, the introduction of CaCl2 through CaCl2 2+ The cross-linking reaction with the carboxylate groups in the SA molecular chain enhanced the interaction force between the molecular chains, reduced the hydrophilicity and free volume of the composite membrane, and effectively hindered the diffusion of water molecules, so the WVP value was reduced.

[0150] 7. The antibacterial properties of the pulp-based hydroxyethyl cellulose antibacterial composite film (HEC / SA / PO / CaCl2) prepared in Example 3 were evaluated using Penicillium oxalicum. The results are shown in FIG. Figure 19 shown.

[0151] The specific method is as follows: Penicillium oxalicum was inoculated onto a potato dextrose agar (PDA) slant medium and incubated at 30°C for 5 days. Subsequently, mycelium and spores were gently scraped off and dissolved in sterile saline. 100 μL of the saline solution was spread onto a PDA plate and incubated at 30°C for 48 hours to form a bacterial cake with a diameter of 1.3 ± 0.02 cm. Next, 50 μL of CaCl₂ and 500 μL of HEC / SA / PO₂ membrane solution were evenly spread onto the PDA plate, and a bacterial cake was placed in the center of each plate, designated the HEC / SA / PO / CaCl₂ composite membrane group. A blank PDA solid medium was used as a blank control. Both groups were incubated in a 30°C incubator for 48 hours, and the growth of Penicillium oxalicum was observed.

[0152] Depend on Figure 19 In the blank control group, Penicillium oxalicum formed colonies with a diameter of 1.54±0.02 cm (including bacterial cake) after 24 hours of culture on PDA medium. After 48 hours, hyphae and conidia significantly expanded on the surface of the culture medium. In sharp contrast, the HEC / SA / PO / CaCl2 composite film group exhibited a significant antibacterial effect: after 48 hours of culture, hyphae growth and conidia formation were completely inhibited, and no obvious colonies were observed in the culture medium.

[0153] This remarkable antimicrobial performance may stem from a dual synergistic mechanism: ① Compounds present in PO, such as menthol, menthone, 1,8-cineole, β-pinene, limonene, and β-caryophyllene, possess potent antimicrobial activity. Furthermore, the hydrophobicity of PO damages the phospholipid membranes of fungal cells. ② Cross-linking between CaCl2 and SA inhibits fungal activity by disrupting fungal physiological functions and preventing biofilm formation. Experimental results demonstrated that the HEC / SA / PO / CaCl2 antimicrobial composite film effectively inhibited the growth and spore formation of Penicillium oxalicum, demonstrating its potential application in food preservation and antimicrobial applications.

[0154] 8. Evaluation of preservation performance

[0155] ①, using cherries as samples, the preservation performance of the pulp-based hydroxyethyl cellulose antibacterial composite film (HEC / SA / PO / CaCl2) prepared in Example 3 was evaluated. The results are as follows: Figure 20 shown.

[0156] The specific method is as follows:

[0157] All cherries were randomly divided into three groups: the control group (CK), which was not subjected to any preservation treatment; the commercial film group (CM), which used commercially available PE preservative film; and the composite film group (HSPC), which used HEC / SA / PO / CaCl2 composite film.

[0158] Each group of cherries was sterilized with sodium hypochlorite solution and then placed in a 6-cm diameter glass Petri dish. The CK group received no preservative treatment; the CM group was sealed with commercially available PE plastic wrap; and the HSPC group was sealed with a 9-cm diameter circular film made by casting the HEC / SA / PO / CaCl2 composite film of the present invention. All groups were stored at room temperature (25±1°C), and changes in their appearance were recorded daily.

[0159] Depend on Figure 20As can be seen, the cherries in the CK group wilted and developed wrinkled skins after seven days of storage. This was primarily due to the lack of external protection, which resulted in significant water loss through transpiration. Furthermore, exposure to air made the cherries susceptible to microbial infection, accelerating spoilage and water loss. While the CM group reduced water evaporation to some extent, the limited permeability and adhesion of the plastic wrap prevented complete water and gas exchange, resulting in limited preservation. The HEC / SA / PO / CaCl2 antimicrobial composite film group achieved the best preservation results. This is due to the excellent film-forming properties and density of the composite film formed by the pulp-based HEC and SA, which effectively reduced water evaporation, regulated gas exchange, and slowed fruit respiration. Furthermore, the addition of PO imparted antimicrobial and antioxidant properties to the composite film, further inhibiting microbial growth and oxidative deterioration of the fruit. Therefore, the HEC / SA / PO / CaCl2 antimicrobial composite film significantly extended the shelf life of cherries through multiple preservation mechanisms, preserving their appearance and quality.

[0160] ②, using strawberries as samples, the preservation performance of the pulp-based hydroxyethyl cellulose antibacterial composite film (HEC / SA / PO / CaCl2) prepared in Example 3 was evaluated. The results are as follows: Figure 21 shown.

[0161] All strawberries were disinfected with sodium hypochlorite solution and then randomly divided into three groups: the CK group, which was not subjected to any preservation treatment; the CM group, which was sealed with PE film around the whole fruit; and the HSPC group: a liquid coating method was used, in which the disinfected strawberries were first immersed in HEC / SA / PO film-forming liquid for 60 seconds, air-dried at room temperature, and then evenly sprayed with CaCl2 solution, and air-dried a second time to form a composite film layer.

[0162] All groups were stored at room temperature (25±1°C), and the changes in apparent morphology were recorded daily.

[0163] Depend on Figure 21 As can be seen, strawberries in the CK group developed severe mold after 7 days of storage, indicating that unprotected strawberries are highly susceptible to microbial infection and rapid spoilage. While the CM group slowed the spoilage process over the same period, significant mold spots still appeared, indicating limited antibacterial efficacy. In contrast, strawberries in the HSPC group showed no signs of decay during storage and minimal weight change, demonstrating excellent preservation. Compared to the CK and CM groups, strawberries in the HSPC group showed significantly suppressed mold growth, demonstrating the significant antibacterial properties of the HEC / SA / PO / CaCl2 antibacterial composite film of the present invention. This preservation performance may be due to the dense barrier structure formed by the pulp-based HEC and SA, which blocks the intrusion of external microorganisms and reduces water loss. These experimental results demonstrate that the HEC / SA / PO / CaCl2 antibacterial composite film not only effectively inhibits mold growth but also significantly extends the postharvest life of strawberries, making it a promising antibacterial and fresh-keeping material.

[0164] Calculate the weight loss rate changes of the above two groups of experiments (cherries and strawberries), the results are as follows Figure 22 The calculation formula is:

[0165]

[0166] Where W0 represents the initial weight of cherries and strawberries; W represents the weight of cherries and strawberries on each sampling day.

[0167] Depend on Figure 22 The results showed that cherries coated with the HEC / SA / PO / CaCl2 antibacterial composite film and strawberries treated with the coating exhibited the lowest weight loss rates (7-day cumulative weight loss of 23.6±0.9% and 6.9±0.7%, respectively), which were 12.6% and 22.5% lower than those in the CM group (27.0±1.2% and 8.9±0.8%) and 29.3% and 42.5% lower than those in the CK group (33.4±2.0% and 12.0±2.6%), respectively. This difference was mainly attributed to the moisturizing and antibacterial properties of the plastic wrap. Although commercially available PE plastic wrap can block water loss to a certain extent, it lacks antibacterial properties and has limited preservation effects. In contrast, the cherries and strawberries in the CK group had the highest weight loss rates due to their direct exposure to air, rapid water evaporation, and susceptibility to microbial contamination. In summary, the HEC / SA / PO / CaCl2 antibacterial composite film significantly improves the preservation of cherries and strawberries by combining moisturizing and antibacterial functions, providing a better solution for fruit preservation.

[0168] The 7-day cumulative weight loss of cherries (23.6±0.9%) was significantly higher than that of strawberries (6.9±0.7%). This difference stems from differences in their epidermal structure, water evaporation rate, and preservation methods. Strawberries have a natural waxy layer and dense seed structure on their epidermal surface. This biological barrier not only effectively reduces water evaporation but also, to a certain extent, blocks the invasion of external microorganisms, thereby reducing metabolic losses. Cherries, on the other hand, have a smoother epidermal surface and lack a similar protective layer. Their pore distribution and epidermal permeability are higher, making water loss more likely through transpiration. Furthermore, strawberries are preserved by coating. The pulp-based HEC and SA film adheres tightly to the surface, further reducing water evaporation. The antibacterial properties of peppermint essential oil also delay spoilage. Cherries, on the other hand, are preserved by covering them. There is a gap between the plastic wrap and the cherry surface, which cannot completely prevent water loss. Furthermore, cherries themselves have a higher water content, making them more susceptible to weight loss through transpiration. Therefore, under the same storage days and temperature conditions, the overall weight loss rate of cherries is higher than that of strawberries.

[0169] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a pulp-based hydroxyethyl cellulose antibacterial composite film, characterized in that: The steps are as follows: (1) crushing, alkalizing, etherifying and neutralizing, cross-linking, washing and drying the pulp raw material to obtain pulp-based hydroxyethyl cellulose; (2) adding a surfactant to the peppermint essential oil and mixing uniformly to obtain a mixed system; then injecting the mixed system into deionized water, shaking and mixing, and homogenizing to obtain a peppermint essential oil nanoemulsion; (3) Adding pulp-based hydroxyethyl cellulose, peppermint essential oil nanoemulsion and glycerol to the sodium alginate solution, mixing evenly to obtain a mixed solution; injecting the mixed solution into a mold, and drying at 55-65°C for 10-15 hours to obtain a composite film; spraying CaCl2 solution evenly on the surface of the composite film, and drying at 20-30°C and 20-30% RH for 5-10 hours to obtain a pulp-based hydroxyethyl cellulose antibacterial composite film.

2. The preparation method according to claim 1, wherein The pulp is dissolving pulp, broadleaf pulp, coniferous pulp or reed pulp.

3. The preparation method according to claim 1, wherein In step (1), the preparation method of the pulp-based hydroxyethyl cellulose is as follows: a. Soaking the pulp sheet in deionized water at a solid-liquid ratio of 1:15 for 24 hours, then deflocculently disintegrating the fibers and balancing the fibers to a moisture content of 8-10%, and crushing the pulp to obtain pulp; b. In a reaction kettle, the dispersion medium, alkali solution and the pulp obtained in step a are uniformly mixed, and alkalized at 18-22° C. for 60-80 min. During the alkalization process, an inerting treatment is simultaneously performed, vacuuming to -0.05 MPa, and then filling with nitrogen to 0.2 MPa, and repeating this process 4 times to obtain alkalized pulp; c. Continue to add ethylene oxide to the alkalized pulp obtained in step b and pressurize it to 0.32 MPa, stir for 5-15 minutes, react at 55-65° C. for 60-70 minutes, heat to 75-85° C. and continue to react for 70-90 minutes, cool to 40-45° C., add nitric acid, neutralize for 10-15 minutes, then add glyoxal, and cross-link for 5-15 minutes; finally, wash twice with acetone and dry at 55-65° C. for 5-8 hours to obtain pulp-based hydroxyethyl cellulose.

4. The preparation method according to claim 3, wherein In step b, the dispersion medium is prepared by mixing tert-butyl alcohol, isopropyl alcohol and water in a mass ratio of 50:38:12; the alkali solution is prepared by mixing the dispersion medium and sodium hydroxide in a mass ratio of 80:6; and the mass ratio of the dispersion medium, alkali solution and pulp is 120:86:

10.

5. The preparation method according to claim 3, wherein In step c, the mass ratio of the ethylene oxide to the alkalized pulp is (1-1.1):1; the mass ratio of the glyoxal to the ethylene oxide is (3-5):(100-110); the mass concentration of the nitric acid is 35-45%, and the mass ratio of nitric acid to ethylene oxide is (220-240):(100-110).

6. The preparation method according to claim 3, wherein In step (2), the mass volume ratio of the peppermint essential oil, surfactant and deionized water is (1-4) mL: (0.1-0.6) g: (2-8) mL; Further preferably, the mass volume ratio of the peppermint essential oil, surfactant and deionized water is 2.4 mL:0.36 g:5 mL; and the surfactant is Tween 80.

7. The preparation method according to claim 3, wherein In step (3), the mass volume ratio of the sodium alginate solution, pulp-based hydroxyethyl cellulose, peppermint essential oil nanoemulsion and glycerol is (20-30) mL: (0.2-1) g: (6-9) g: (0.5-1.5) mL; the concentration of the sodium alginate solution is 20-30 mg / mL; Further preferably, the mass volume ratio of the sodium alginate solution, pulp-based hydroxyethyl cellulose, peppermint essential oil nanoemulsion and glycerol is 25 mL:0.6 g:7.5 g:1 mL; the concentration of the sodium alginate solution is 24 mg / mL, which is obtained by dispersing 600 mg of sodium alginate in 25 mL of deionized water and continuously stirring with a magnetic stirrer at 800 rpm in an oil bath at 90±1°C until completely dissolved.

8. The preparation method according to claim 3, wherein In step (3), the concentration of the CaCl2 solution is 1.5-2.5%; the spraying parameter is 60-65cm 2 Spray 2mL; Further preferably, the concentration of the CaCl2 solution is 2%; the spraying parameter is 63.62cm 2 Spray 2mL.

9. A pulp-based hydroxyethyl cellulose antibacterial composite film, characterized in that: The invention is prepared according to the method according to any one of claims 1 to 8.

10. Use of the pulp-based hydroxyethyl cellulose antibacterial composite film according to claim 9 in the field of fresh-keeping film.

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