Method for preparing antibacterial film from biomass heat treatment waste liquid

Abstract

The invention discloses a method for preparing an antibacterial film from biomass heat treatment waste liquid, and relates to the technical field of biological energy sources, material technologies and packaging films, 1, the method comprises the following steps: S1, adding a biomass raw material into a solvent for heat treatment, carrying out solid-liquid separation after the treatment is finished, and collecting liquid to obtain the biomass heat treatment waste liquid; s2, removing an organic solvent in the biomass heat treatment waste liquid to obtain a reaction liquid; and S3, mixing the reaction liquid with a film-forming substrate to obtain a film-forming liquid, preparing a film crude product from the film-forming liquid through a tape casting method, and drying to obtain the antibacterial film. The liquid waste generated by biomass heat treatment and the high-molecular polymer are used for preparing the film material with mechanical properties and water resistance, and high-level oxidation resistance and antibacterial properties are maintained, so that the application range of the film in the application fields of food preservation and the like is remarkably widened, and the film material has a good application prospect in the fields of food preservation and the like. The realization of a zero-waste biomass utilization method is also effectively promoted.

Description

Technical Field

[0001] The invention relates to the fields of bioenergy, material technology and packaging films, and in particular to a method for preparing an antibacterial film from waste liquid from thermal treatment of biomass. Background Art

[0002] As the consumption of agricultural and forestry biomass waste continues to rise worldwide, the amount of waste generated has also increased dramatically, which not only causes a huge waste of biomass energy, but also imposes a heavy burden on the environment. There are many types of agricultural and forestry waste, including but not limited to crop residues, fruit and vegetable waste, leaves, roots, branches, etc. They are rich in functional groups such as phenolic hydroxyl groups, carboxylic acid groups, alkoxy groups, and contain a variety of nutrients and bioactive substances such as polysaccharides, flavonoids, alkaloids, etc., so they have extremely high recycling potential.

[0003] Biomass thermal treatment is a commonly used biomass conversion method, which has shown great prospects in promoting the transformation of agricultural and forestry wastes into high-value-added functional materials, especially in the field of recycling of biomass resources. However, although the biomass thermal treatment process may consume a large amount of solvent resources and produce corresponding thermal treatment waste liquid, the current research focus is mostly on the development and application of the main product carbonization material, while the accompanying solvent products are often treated as by-products or waste liquids, and their potential utilization value is seriously underestimated. Summary of the invention

[0004] In response to the technical problems existing in the prior art, the present invention aims to provide a method for preparing antibacterial film based on waste liquid from thermal treatment of agricultural and forestry waste biomass, which can significantly improve the safety and quality of packaging products, and achieve the reduction of agricultural and forestry organic waste and high-value resource utilization.

[0005] A method for preparing an antibacterial film from biomass thermal treatment waste liquid comprises the following steps:

[0006] S1: adding the biomass raw material into a solvent for heat treatment, performing solid-liquid separation after the treatment, and collecting the liquid to obtain biomass heat treatment waste liquid;

[0007] S2: removing the organic solvent from the biomass thermal treatment waste liquid to obtain a reaction liquid;

[0008] S3: mixing the reaction solution with a film-forming substrate to obtain a film-forming solution, preparing a film crude product by a casting method using the film-forming solution, and obtaining an antibacterial film after drying.

[0009] Furthermore, in step S3, a plasticizer is added to the film-forming solution, and the amount of the plasticizer added is 10 to 50% of the mass of the film-forming substrate.

[0010] Furthermore, the mass ratio of the biomass raw material to the solvent is 1:2-20, the heat treatment temperature is 100-250° C., and the time is 2-24 hours.

[0011] Furthermore, the solvent is at least one of water, an aqueous solution, ethanol, methanol, ethylene glycol, and glycerol, and the aqueous solution is an acidic aqueous solution or an alkaline aqueous solution.

[0012] Furthermore, the film-forming substrate is at least one of starch, guar gum, carrageenan, pectin, gelatin, sodium alginate, chitosan, cellulose, and bacterial cellulose nanofibers.

[0013] Furthermore, the mass ratio of the film-forming substrate to the reaction liquid is 1:7-40.

[0014] Furthermore, the drying temperature is 30-60° C., and the drying time is 5-72 hours.

[0015] Furthermore, the step S3 also includes the following operation: adding auxiliary antibacterial active ingredients to the film-forming liquid, wherein the auxiliary antibacterial active ingredients are at least one of nano zinc oxide, nano silver, and essential oil, and the mass ratio of the auxiliary antibacterial ingredients to the film-forming substrate is 1 to 5:8.

[0016] Furthermore, the film-forming substrate is a composition of sodium alginate and bacterial cellulose nanofibers, and the mass ratio of the sodium alginate to the bacterial cellulose nanofibers is 5:1-5.

[0017] Furthermore, the biomass raw materials and the processing method thereof are as follows: drying the lignocellulosic materials at 60-120° C. and then crushing them through a 40-200 mesh sieve; the lignocellulosic materials are passion fruit peels, pomegranate peels, mangosteen shells, banana peels, mango peels, longan shells, mango leaves, tea leaves and other agricultural and forestry biomass and biomass waste.

[0018] The present invention has the following beneficial effects:

[0019] 1. The present invention aims at the liquid products that are often neglected and discarded during the thermal treatment of biomass, and proposes to utilize them in a high-value manner for the preparation of antibacterial packaging films. This not only achieves the efficient utilization and reduced treatment of agricultural biomass waste, but also the biomass thermal treatment waste liquid product has significant antibacterial and antioxidant activity, showing potential application value in the fields of biomedicine, food preservation, etc., effectively promoting the realization of zero-waste biomass utilization methods.

[0020] 2. The present invention prepares a film with excellent mechanical properties and water resistance by combining the waste liquid product of biomass thermal treatment with a hydrophilic high molecular polymer. The film maintains good antioxidant and antibacterial activity, and after the introduction of auxiliary antibacterial active ingredients such as zinc oxide nanoparticles, the synergistic effect of the two further enhances its ultraviolet light protection and moisture-proof properties, thereby broadening the application scenarios in outdoor packaging materials, food preservation and other fields. At the same time, through the actual application verification of the fruit preservation test, the film effectively extends the shelf life of the fruit, fully proving its application prospects as a functional additive in the field of packaging films. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 These are the moisture content (a), tensile strength (b) and elongation at break (c) results of the ASB antibacterial films prepared in Examples 4 to 7 of the present invention.

[0023] Figure 2 These are the mechanical properties and water vapor transmission rate results of the ZASB antibacterial films prepared in Examples 8 to 11 of the present invention.

[0024] Figure 3 The antibacterial effects (a, b, c) of the ZASB antibacterial films prepared in Examples 8 to 11 of the present invention, and the cytotoxicity (d) results of the ZASB antibacterial films prepared in Examples 10 to 12 and the SB film prepared in Comparative Example 2 are shown.

[0025] Figure 4 These are scanning electron microscope images of the surface (A-D) and cross-sectional (a-d) morphologies of the ZASB antibacterial films prepared in Examples 8-11 of the present invention.

[0026] Figure 5 The distribution and mass percentage of zinc element in the ZASB antibacterial films prepared in Examples 8 to 11 of the present invention.

[0027] Figure 6 The results of the ZASB antibacterial films prepared in Examples 10 and 11 of the present invention in the strawberry preservation application experiment include the appearance (a), weight loss rate (b), decay rate (c), pH value (d) and malondialdehyde content (e) of the strawberries. Among them, the values ​​represented by different letters (a to c) in the statistical graph are significantly different (p<0.05). DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] A method for preparing an antibacterial film from biomass thermal treatment waste liquid comprises the following steps:

[0030] S1: adding the biomass raw material into a solvent for heat treatment, performing solid-liquid separation after the treatment, and collecting the liquid to obtain biomass heat treatment waste liquid;

[0031] S2: removing the organic solvent from the biomass thermal treatment waste liquid to obtain a reaction liquid;

[0032] S3: mixing the reaction solution with a film-forming substrate to obtain a film-forming solution, preparing a film crude product by a casting method using the film-forming solution, and obtaining an antibacterial film after drying.

[0033] Furthermore, in step S3, a plasticizer is added to the film-forming solution, and the amount of the plasticizer added is 10 to 50% of the mass of the film-forming substrate.

[0034] Furthermore, the mass ratio of the biomass raw material to the solvent is 1:2-20, the heat treatment temperature is 100-250° C., and the time is 2-24 hours.

[0035] Furthermore, the solvent is at least one of water, an aqueous solution, ethanol, methanol, ethylene glycol, and glycerol, and the aqueous solution is an acidic aqueous solution or an alkaline aqueous solution.

[0036] Furthermore, the film-forming substrate is at least one of starch, guar gum, carrageenan, pectin, gelatin, sodium alginate, chitosan, cellulose, and bacterial cellulose nanofibers.

[0037] Furthermore, the mass ratio of the film-forming substrate to the reaction liquid is 1:7-40.

[0038] Furthermore, the drying temperature is 30-60° C., and the drying time is 5-72 hours.

[0039] Furthermore, the step S3 also includes the following operation: adding auxiliary antibacterial active ingredients to the film-forming liquid, wherein the auxiliary antibacterial active ingredients are at least one of nano zinc oxide, nano silver, and essential oil, and the mass ratio of the auxiliary antibacterial ingredients to the film-forming substrate is 1 to 5:8.

[0040] Furthermore, the film-forming substrate is a composition of sodium alginate and bacterial cellulose nanofibers, and the mass ratio of the sodium alginate to the bacterial cellulose nanofibers is 5:1-5.

[0041] Furthermore, the biomass raw materials and the processing method thereof are as follows: drying the lignocellulosic materials at 60-120° C. and then crushing them through a 40-200 mesh sieve; the lignocellulosic materials are passion fruit peels, pomegranate peels, mangosteen shells, banana peels, mango peels, longan shells, mango leaves, tea leaves and other agricultural and forestry biomass and biomass waste.

[0042] Example 1

[0043] Preparation of banana peel biomass thermal treatment waste liquid: Dry the banana peel in an oven at 105°C overnight, grind it and pass it through a 60-mesh sieve to obtain banana peel powder. Add 500g of banana peel powder and 2000g of water to a thermal treatment reactor, heat it to 200°C, and store it for 12h. After cooling to room temperature, the reaction mixture is filtered, and the liquid phase is filtered through a 0.22μm filter membrane to obtain biomass thermal treatment waste liquid. Since it does not contain an organic solvent, the product is reaction liquid A, which is stored in a 4°C refrigerator away from light for future use.

[0044] Example 2

[0045] Preparation of passion fruit peel biomass thermal treatment waste liquid: The passion fruit shell was dried in an oven at 60°C overnight, then ground and passed through a 40-mesh sieve to obtain passion fruit shell powder. 500g of passion fruit shell powder and 1000g of ethanol were added to a heat treatment reactor, heated to 150°C, and stored for 24h. After cooling to room temperature, the reaction mixture was filtered, and the liquid phase was filtered through a 0.22μm filter membrane to obtain biomass thermal treatment waste liquid, which was then rotary evaporated to recover the ethanol therein. The remaining liquid without organic solvent was the reaction liquid B, which was stored in a 4°C refrigerator away from light for standby use.

[0046] Example 3

[0047] Preparation of mangosteen shell biomass thermal treatment waste liquid: The mangosteen shell was dried overnight at 120°C in an oven, then ground and passed through a 200-mesh sieve to obtain mangosteen shell powder. 500g of mangosteen shell powder and 10,000g of ethanol aqueous solution (the mass ratio of ethanol to water in the solvent is 1:1) were added to the thermal treatment reactor, heated to 250°C, and stored for 2h. After cooling to room temperature, the reaction mixture was filtered, and the liquid phase was filtered through a 0.22μm filter membrane to obtain biomass thermal treatment waste liquid, which was then subjected to rotary evaporation to recover the ethanol therein. The remaining liquid without organic solvent was the reaction liquid C, which was stored in a 4°C refrigerator away from light for standby use. .

[0048] Example 4

[0049] Preparation of ASB (i.e., containing reaction solution A, SA and BCNFs) film: bacterial cellulose nanofibers (BCNFs) were added to 1.0% sodium alginate (SA) solution to prepare a mixed solution of SA and BCNFs, wherein the mass ratio of SA to BCNFs was 5:5, and 10 g of reaction solution A prepared in Example 1 was added to 70 g of the mixed solution. A film was obtained by casting: 10-ASB antibacterial film.

[0050] Example 5

[0051] Different from Example 5, the mass ratio of SA to BCNFs is 5:1, the addition amount of reaction solution A is adjusted from 10 g to 20 g, and 0.042 g of glycerol is added to the mixed solution as a plasticizer, and the obtained film is 20-ASB antibacterial film.

[0052] Example 6

[0053] Different from Example 5, the mass ratio of SA to BCNFs is 5:2, the addition amount of reaction solution A is adjusted from 10 g to 30 g, and the addition amount of glycerol is adjusted from 0.042 g to 0.098 g, and the obtained film is 30-ASB antibacterial film.

[0054] Example 7

[0055] Different from Example 5, the mass ratio of SA to BCNFs is 5:3, the addition amount of reaction solution A is adjusted from 10 g to 40 g, and the addition amount of glycerol is adjusted from 0.042 g to 0.448 g, and the obtained film is a 40-ASB antibacterial film.

[0056] Example 8

[0057] Preparation of ZASB (i.e., containing ZnO-NPs, reaction solution A, SA and BCNFs) film: bacterial cellulose nanofibers (BCNFs) were added to 1.0% sodium alginate (SA) solution to prepare a mixed solution of SA and BCNFs, wherein the mass ratio of SA to BCNFs was 5:3, and 0.2% nano zinc oxide (ZnO-NPs) was added to the mixed solution as an auxiliary antibacterial active ingredient according to the mass ratio. The mixed suspension was then homogenized 3 times at 1000 bar to uniformly disperse the ZnO-NPs. 20 g of reaction solution A prepared in Example 1 was added to 70 g of the mixed solution, and 0.336 g of glycerol was added as a plasticizer. A film was obtained by a casting method: 0.2-ZASB antibacterial film.

[0058] Example 9

[0059] Different from Example 14, the addition amount of ZnO-NPs was adjusted from 0.2% to 0.5%, and the obtained film was a 0.5-ZASB antibacterial film.

[0060] Example 10

[0061] The only difference from Example 14 is that the addition amount of ZnO-NPs is adjusted from 0.2% to 1.0%, and the obtained film is a 1.0-ZASB antibacterial film.

[0062] Embodiment 11

[0063] Different from Example 14, the addition amount of ZnO-NPs was adjusted from 0.2% to 0.0% (ie, no ZnO-NPs were added), and the obtained film was a 0.0-ZASB antibacterial film.

[0064] Comparative Example 1

[0065] Blank control group: Compared with Example 1, the only difference is that biomass such as banana peel, passion fruit peel, and mangosteen shell is not added, and the other operations are completely the same.

[0066] Comparative Example 2

[0067] SB (i.e., containing SA and BCNFs components) film control group: Different from Example 4, no ZnO-NPs and reaction solution A were added, and only water in an amount equal to that of reaction solution A was added, and the prepared film was a SB film.

[0068] Comparative Example 3

[0069] ZSB (i.e., containing ZnO-NPs, SA and BCNFs components) film control group: The only difference from Example 8 is that the reaction solution A is not added, and only water in an amount equal to that of the reaction solution A is added, and the prepared film is a ZSB film.

[0070] The specific experimental conditions of each embodiment and comparative example are shown in Table 1:

[0071] Table 1 List of experimental conditions corresponding to each embodiment and comparative example

[0072]

[0073] Test Case

[0074] (1) Test methods for physical and chemical properties of banana peel reaction solution A

[0075] Antibacterial activity test: The Oxford cup method was used to test the antibacterial activity of the reaction solution A. 7 CFU / mL) were inoculated into LB solid medium and maintained at 37°C for 8 h. The growth of bacteria was observed and the diameter of the inhibitory bacteria was recorded. The results were photographed using a gel imager (Champ Gel 7000, Beijing, China).

[0076] Antioxidant test: 0.1 mL of reaction solution A was added to 5 mL of DPPH-ethanol solution (40 μg / mL), and then reacted for 0.5 h in the dark. The absorbance of the reaction mixture was measured at a wavelength of 517 nm using UV-visible spectrophotometry (UH-5300, HITACHI, Japan). Pure water was used as a blank control group, and ascorbic acid solution of the same concentration was used as a positive control. EC was also measured. 50 (mg / mL).

[0077] Total phenol content test: The total phenol content was determined by the Folin phenol colorimetric method. 1 mL of reaction solution A was added to 5 mL of 10% (v / v) Folin phenol reagent, and 4 mL of Na2CO3 solution (7.5 wt%) was added after 3 to 8 minutes. Water was added to the mixed solution to adjust the volume to 25 mL. After reacting at room temperature in the dark for 2.5 hours, the absorbance of the reaction mixture was determined at 765 nm by UV-visible spectrophotometry. The total phenol content in reaction solution A was quantified using a calibration curve.

[0078] Gas chromatography-mass spectrometry (GC-MS) test: 50 μL of reaction solution A-pyridine solution (10 mg / mL) was transferred to a glass sample bottle, and then 10 μL (2 mg / mL) of ethyl decanoate was added as an internal standard. Finally, 50 μL of BSTFA was added and incubated at 70°C for 1 h for silanization reaction. Analysis method: DB-5MS column (Agilent, J&W Scientific, 30m×0.25mm×0.25μm), injection temperature was 250°C, split ratio was 10:1, carrier gas was high purity helium, and flow rate was 1.00mL / min. The temperature was initially maintained at 70°C for 2 min, then increased to 320°C for 15 min, and the heating rate was 8°C / min.

[0079] (2) Test methods for the physical and chemical properties of ASB antibacterial films

[0080] Moisture content test: Cut the ASB film into squares (2 cm × 2 cm), use a balance to accurately weigh and record the initial mass W0, dry the ASB film at 80 °C overnight, accurately weigh its mass W1, and calculate the moisture content of the ASB film using the weight loss method.

[0081] Mechanical properties test: A universal testing machine (AI-7000-SJ, GOTECH, China) was used to test the tensile strength (TS) and elongation at break (EAB) at a test rate of 5 mm / min.

[0082] (3) Test methods for the physical and chemical properties of ZASB antibacterial films

[0083] Mechanical properties test: A universal testing machine (AI-7000-SJ, GOTECH, China) was used to test the tensile strength (TS) and elongation at break (EAB) at a test rate of 5 mm / min.

[0084] Water vapor transmission rate (WVTR) test: The water vapor transmission rate (WVTR) was measured using a water vapor transmission instrument (GBPI, AUTO W806, Guangzhou, China) with 20 mL of water (23°C, 10% RH) in the permeation cup. The WVTR was calculated using the weight loss method.

[0085] Antibacterial test: The film was cut into a disk with a diameter of 6 mm, placed on the surface of LB solid medium, and incubated at 37 ° C for 8 h. Finally, the diameter of the inhibition zone was recorded.

[0086] Cytotoxicity: The film (1.5 mm in diameter) was immersed in deionized water for 12 h. Then 10 μL of the film-immersion solution was directly contacted with L02 cells (1×10 5 CFU / mL). After culturing for 24 hours, the culture medium of all wells was removed and 100 μL of 10% (v / v) CCK-8 solution was added. After culturing for 4 hours, the ultraviolet absorbance of the sample was measured at 450 nm.

[0087] Scanning electron microscopy (SEM) test: The distribution of zinc in the ZASB antibacterial film was analyzed using SEM-EDS analysis (Phenom Pro, Thermo, USA) at an accelerating voltage of 5 kV.

[0088] Application method for strawberry preservation: Select strawberries of similar size, uniform maturity, and no fungal infection and physical damage, and divide them into three groups: (1) control group, (2) 0.0-ZASB antimicrobial film, and (3) 1.0-ZASB antimicrobial film. Each box contains 5 strawberries and is wrapped with film. The strawberry samples are tested every two days during the 8-day storage period (24°C, 35% RH).

[0089] Experimental results analysis

[0090] (1) Physicochemical properties of banana peel reaction solution A

[0091] Table 2 Properties of Banana Peel Reaction Solution A

[0092]

[0093] Table 2 lists in detail several key physical and chemical properties of banana peel reaction solution A, specifically covering parameters such as its antibacterial effect on specific bacteria, total phenol content, pH value, and solid content.

[0094] In terms of antibacterial performance, the inhibitory effect of reaction solution A on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was evaluated by the Oxford cup method. The experimental results showed that reaction solution A exhibited significant inhibitory effects on both of the above bacteria, with the diameter of the inhibition zone for E. coli being 18.71±1.3396mm and the diameter of the inhibition zone for Staphylococcus aureus being 22.22±0.6158mm.

[0095] In terms of antioxidant performance, the DPPH method was used to determine the antioxidant activity of reaction solution A. When the concentration of reaction solution A was 20 mg / mL, its DPPH free radical scavenging rate reached 87.51%; while the DPPH free radical scavenging rate of reaction solution A stock solution was as high as 95.29%, and its half effective concentration (EC 50 ) was 1.37 mg / mL. In addition, the total phenol content in reaction solution A was further determined by Folin phenol colorimetry, and the result was 1.8597±0.0007 mg (GAE) / mL, which further confirmed that reaction solution A had good antioxidant capacity.

[0096] Finally, the composition of reaction solution A was analyzed in depth using gas chromatography-mass spectrometry (GC-MS). The results showed that reaction solution A mainly contained organic acids (accounting for 23.88%), alcohols (accounting for 18.74%) and amino acids (accounting for 16.92%). At the same time, three phenolic substances were also detected in reaction solution A, namely pyrogallol, guaiacol and probucol. The discovery of these components provides a basis for the in-depth understanding and application of banana peel biomass thermal treatment wastewater.

[0097] (2) Physical and chemical properties of ASB antibacterial film

[0098] In terms of moisture content, compared with the SB antibacterial film prepared in Comparative Example 2, the ASB antibacterial films prepared in Examples 4 to 7 showed a significant increase in moisture content (see Figure 1 a) This improvement is attributed to the rich hydrophilic components in the biomass thermal treatment wastewater, which gives the ASB film excellent water absorption performance. This feature gives the ASB film a significant advantage in applications that require efficient moisture retention or moisture regulation.

[0099] In terms of mechanical properties, although the tensile strength (TS) of the ASB film decreased compared with the SB film, its elongation at break (EAB) showed a unique change trend. In particular, when the amount of biomass thermal treatment waste liquid added was 20 g, the EAB of the ASB film reached a peak of 20%, and then fell slightly (see Figure 1b&c). This change is also due to the hydrophilic substances in the wastewater from the thermal treatment of biomass, which make the ASB film easy to absorb water, thereby weakening the intermolecular forces between the polymer chains (such as SA and BCNFs) inside the film and enhancing the mobility of the chain segments. Although the reduction of TS may pose a challenge in some applications with high strength requirements, the increase of EAB provides the ASB film with good flexibility and ductility.

[0100] (3) Physical and chemical properties of ZASB antibacterial film

[0101] In terms of mechanical properties, the ZASB antibacterial films prepared in Examples 8 to 11 showed certain differences compared with Comparative Example 3 (ZSB film). Specifically, the tensile strength (TS) of the 0.0-ZASB antibacterial film prepared in Example 11 (i.e., the ZASB antibacterial film without the addition of ZnO-NPs) was 10.31 MPa, which was lower than that of the SB film without the addition of active substance biomass thermal treatment wastewater (Comparative Example 2). Figure 2 and Figure 1 ). This result shows that although the addition of biomass thermal treatment wastewater can improve the interaction within the film, excessive addition or improper ratio may weaken the mechanical properties of the film, resulting in phase separation and decreased mechanical properties. However, when ZnO-NPs were added, the TS of the ZASB antibacterial film increased, which was due to the rigidity of ZnO-NPs, which enhanced the mechanical strength of the film. However, it should be noted that the addition of ZnO-NPs also led to a decrease in the elongation at break (EAB) of the film, which was due to the fact that ZnO-NPs, as rigid nanoparticles, limited the ductility of the film.

[0102] In terms of water vapor transmission rate (WVTR), ZASB antibacterial film also showed significant differences compared with the control. Figure 1 and Figure 2 Data comparison shows that the WVTR of the SB film prepared in Comparative Example 2 is 1385.95 g / (m 2 ·24h), the WVTR of the 0.0-ZASB antibacterial film prepared in Example 11 decreased slightly to 1338.86 g / (m 2 ·24h). However, after adding ZnO-NPs, the WVTR value of ZASB antibacterial film decreased significantly, which was mainly attributed to the blocking effect of ZnO-NPs on water diffusion, making the water diffusion path tortuous. This result shows that the addition of ZnO-NPs can effectively reduce the water vapor permeability of the film and improve the barrier properties of the film.

[0103] In terms of antibacterial properties, ZASB antibacterial film also shows obvious advantages compared with the control. Figure 3As shown in a, when only biomass thermal treatment wastewater is added, the antibacterial ability of the film is average (Example 11, 0.0-ZASB group). Similarly, when only ZnO-NPs are added (Comparative Example 3, ZSB group), the antibacterial ability of the ZSB film is better. When biomass thermal treatment wastewater and ZnO-NPs are added at the same time, the antibacterial ability of the ZASB antibacterial film is greatly improved, and the inhibition zone gradually increases with the increase of ZnO-NPs. In particular, when the addition amount of ZnO-NPs is ≥0.5%, the ZASB antibacterial film has good antibacterial activity ( Figure 3 b&c). This result indicates that there is a synergistic antibacterial effect between biomass thermal treatment wastewater and ZnO-NPs.

[0104] In terms of cytotoxicity, the L02 cells in each example of ZASB showed good viability, with a cell proliferation rate of more than 80% ( Figure 3 d). This result indicates that the ZASB antimicrobial film has good biocompatibility and is safe for use in food preservation packaging.

[0105] The results of scanning electron microscopy (SEM) showed that the white particles uniformly distributed on the surface of the ZASB antibacterial film were zinc oxide nanoparticles (ZnO-NPs). Figure 4 As shown in the figure, the microstructure of the ZASB antibacterial film showed good integrity, and no obvious holes or cracks were observed on the surface of the film, which showed that the addition of ZnO-NPs did not damage the microstructure of the film, but may help to enhance the density and stability of the film. Furthermore, the content of Zn atoms in the film was determined by energy spectrum analysis and other methods. Figure 5 As shown in the figure, with the increase of the amount of ZnO-NPs added, the content of Zn atoms shows a gradually increasing trend. At the same time, it can be seen from the SEM image that the white particles (ZnO-NPs) are evenly distributed in the film without obvious agglomeration or aggregation. This good dispersion helps ZnO-NPs to fully exert its functional role, such as improving the mechanical properties, barrier properties and antibacterial properties of the film.

[0106] In terms of strawberry preservation, ZASB antibacterial film also shows significant effects. Figure 6The experimental results shown in the figure show that the degree of damage to strawberries in the 1.0-ZASB group (Example 10) is significantly lower than that in the control group and the 0.0-ZASB group (Example 11). After 8 days of storage, the weight loss rate, degree of decay, pH, and malondialdehyde content of the strawberries in the 1.0-ZASB group are better than those in the control group and the 0.0-ZASB group (Example 11). These results all show that the 1.0-ZASB antibacterial film can effectively extend the shelf life of strawberries and reduce the loss of nutrients in strawberries. Compared with the control group or other packaging materials, the ZASB antibacterial film shows obvious advantages in preserving strawberries.

[0107] In summary, the biomass thermal treatment waste liquid product obtained from agricultural biomass waste including banana peels through thermal treatment technology showed significant antibacterial activity. At the same time, it also had extremely high antioxidant activity, and its DPPH free radical scavenging ability reached 95.29%.

[0108] When the waste liquid product of biomass thermal treatment is combined with sodium alginate (SA) and bacterial cellulose nanofibers (BCNFs) composite film substrate to make ASB antibacterial film, it not only has excellent mechanical properties, but also shows good water resistance and antioxidant capacity. In addition, the film also has excellent antibacterial activity. The cytotoxicity test results further confirmed the safety of the antibacterial film, which is non-cytotoxic and suitable for food packaging and other fields.

[0109] Furthermore, when the waste liquid product of biomass thermal treatment and zinc oxide nanoparticles (ZnO-NPs) were added to sodium alginate and bacterial cellulose nanofibers to prepare the ZASB antibacterial film, the two showed obvious synergistic antibacterial effects. The prepared 1.0-ZASB antibacterial film not only maintained good mechanical properties, but also had excellent ultraviolet light protection and moisture resistance. At the same time, the film also showed a high antioxidant effect and good antibacterial activity against Escherichia coli and Staphylococcus aureus.

[0110] In addition, the results of the fruit preservation test show that the biomass thermal treatment waste liquid film prepared by the present invention can effectively delay the ripening process of the fruit, thereby extending the shelf life of the fruit, confirming the potential application prospects of biomass thermal treatment waste liquid products as functional ingredients in packaging films.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an antibacterial film from biomass thermal treatment wastewater, characterized in that: The following steps are involved: S1: adding the biomass raw material into a solvent for heat treatment, performing solid-liquid separation after the treatment, and collecting the liquid to obtain biomass heat treatment waste liquid; S2: removing the organic solvent from the biomass thermal treatment waste liquid to obtain a reaction liquid; S3: mixing the reaction solution with a film-forming substrate to obtain a film-forming solution, preparing a film crude product by a casting method using the film-forming solution, and obtaining an antibacterial film after drying.

2. The method for preparing an antibacterial film from biomass thermal treatment wastewater according to claim 1, characterized in that: In the step S3, a plasticizer is added to the film-forming solution, and the amount of the plasticizer added is 5-40% of the mass of the film-forming substrate.

3. The method for preparing an antibacterial film from biomass thermal treatment wastewater according to claim 1, characterized in that: The mass ratio of the biomass raw material to the solvent is 1:2-20, the heat treatment temperature is 100-250° C., and the time is 2-24 hours.

4. The method for preparing an antibacterial film from biomass thermal treatment wastewater according to claim 1, characterized in that: The solvent is at least one of water, an aqueous solution, ethanol, methanol, ethylene glycol, and glycerol, and the aqueous solution is an acidic aqueous solution or an alkaline aqueous solution.

5. The method for preparing an antibacterial film from biomass thermal treatment wastewater according to claim 1, characterized in that: The film-forming substrate is at least one of starch, guar gum, carrageenan, pectin, gelatin, sodium alginate, chitosan, cellulose, and bacterial cellulose nanofibers.

6. The method for preparing an antibacterial film from biomass thermal treatment wastewater according to claim 1, characterized in that: The mass ratio of the film-forming substrate to the reaction solution is 1:7-40.

7. The method for preparing an antibacterial film from biomass thermal treatment wastewater according to claim 1, characterized in that: The drying temperature is 30-60° C. and the drying time is 5-72 hours.

8. The method for preparing an antibacterial film from biomass thermal treatment wastewater according to claim 1 or 2, characterized in that: The step S3 also includes the following operation: adding auxiliary antibacterial active ingredients to the film-forming liquid, wherein the auxiliary antibacterial active ingredients are at least one of nano zinc oxide, nano silver, and essential oil, and the mass ratio of the auxiliary antibacterial ingredients to the film-forming substrate is 1 to 5:

8.

9. The method for preparing an antibacterial film from biomass thermal treatment wastewater according to claim 5, characterized in that: The film-forming substrate is a composition of sodium alginate and bacterial cellulose nanofibers, and the mass ratio of the sodium alginate to the bacterial cellulose nanofibers is 5:1-5.

10. The method for preparing antibacterial film from biomass thermal treatment wastewater according to claim 1, characterized in that: The biomass raw material and the processing method thereof are as follows: drying the lignocellulose material at 60-120° C. and then crushing the material through a 40-200 mesh sieve; the lignocellulose material is passion fruit peel, pomegranate peel, mangosteen shell, banana peel, mango peel, longan shell, mango leaf, tea and other agricultural and forestry biomass and biomass waste.

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