Novel biodegradable film and preparation method thereof

Abstract

The invention belongs to the field of agricultural films, and relates to a novel biodegradable film and a preparation method thereof. The biodegradable film is prepared from the following components: plant stalk powder, sodium alginate and glycerol. The biodegradable thin film is biodegradable; pretreatment is avoided by a simple mixing process, and energy consumption and production cost are reduced; the film with the optimized ratio can reach a relatively high ultraviolet ray blocking rate; seed germination can be promoted, and excellent mechanical and thermal properties are achieved; life cycle evaluation shows that the influence on the environment is lower than that of a polyethylene film.

Description

Technical Field

[0001] The present invention belongs to the field of agricultural films and relates to a novel biodegradable film and a preparation method thereof. Background Art

[0002] In recent years, significant progress has been made in the development of degradable packaging materials extracted from waste biomass, especially in the field of degradable agricultural films. These films rapidly degrade in the soil after use, effectively preventing the long-term accumulation of plastic waste and alleviating the "white pollution" caused by traditional plastic films. In addition, they contribute to promoting soil health and enhancing agricultural sustainability. However, due to the complex and diverse composition of raw materials, producing biodegradable films from waste biomass remains challenging, often requiring expensive and energy-intensive processes. Traditional methods, such as chemical extraction, have been found to reduce biomass utilization efficiency, consume large amounts of solvents, and cause significant environmental impacts. Moreover, these processes require substantial energy and water inputs, which may undermine the environmental benefits of the final product. Addressing these challenges requires the development of simpler and more sustainable production methods to reduce energy consumption and minimize the environmental burden.

[0003] Physical blending technology has emerged as a promising solution to these challenges. This method avoids complex extraction steps, significantly reduces energy consumption, and lowers production costs, providing an innovative approach for the effective utilization of agricultural waste such as plant straw to produce biodegradable films. Among various biopolymers, sodium alginate, a natural polysaccharide, has received extensive attention due to its biodegradability, non-toxicity, and biocompatibility, making it an ideal candidate for preparing biodegradable films. However, films produced from pure sodium alginate often exhibit insufficient mechanical strength and high sensitivity to environmental conditions such as humidity, limiting their direct application in agriculture. This highlights the necessity of addressing these limitations by enhancing performance.

[0004] To improve the functional properties of sodium alginate films, waste biomass extracts such as tea polyphenols, lignin, and cellulose nanocrystals have been used in the prior art to enhance characteristics such as mechanical strength. Although these strategies have shown potential, they require additional extraction steps, thereby increasing energy consumption, chemical use, and production costs. These increased complexities not only limit the scalability of these methods but also reduce resource utilization efficiency. In addition, studies on sodium alginate-based blend films have shown significant performance variations, with the maximum tensile strength ranging from as low as 0.1 MPa to as high as 160 MPa. This variability is largely attributed to differences in experimental conditions such as the molecular weight of sodium alginate, solution concentration, stirring parameters, and the volume of the film solution applied per unit area. These inconsistencies hinder the standardization of performance comparisons and the establishment of clear experimental guidelines for optimizing sodium alginate-based films. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a novel biodegradable film. Specifically, the present invention provides a biodegradable film based on a composite system of plant stalk powder and sodium alginate and a preparation method thereof.

[0006] The components of the biodegradable film include: plant stalk powder, sodium alginate, and glycerol.

[0007] Preferably, the mass ratio of the plant stalk powder to the sodium alginate is 10% - 50%:50% - 90%; based on the total mass of the plant stalk powder and the sodium alginate, the addition amount of the glycerol is 30% - 50% (w / w); the total solid concentration of the plant stalk powder and the sodium alginate in the film-forming solution is 20 - 50 g / L (excluding glycerol).

[0008] Preferably, the mass ratio of the plant stalk powder to the sodium alginate is 20% - 40%:60% - 80%, more preferably 25% - 35%:65% - 75%, more preferably 28% - 32%:68% - 72%, and further preferably 30%:70%.

[0009] Preferably, based on the total mass of the plant stalk powder and the sodium alginate, the addition amount of the glycerol is 30% - 45% (w / w), more preferably 30% - 40% (w / w), more preferably 35% - 40% (w / w), and further preferably 40% (w / w).

[0010] Preferably, the total solid concentration of the plant stalk powder and the sodium alginate in the film-forming solution is 30 - 40 g / L, more preferably 30 - 35 g / L, and further preferably 30 g / L.

[0011] In a specific embodiment, the raw material ratio and the film-forming solution concentration of the biodegradable film are set as follows: the mass ratio of the plant stalk powder to the sodium alginate is 30%:70% (i.e., 30 wt% of the plant stalk powder and 70 wt% of the sodium alginate are fully mixed to form a solid base system for film formation); the addition amount of the glycerol is 40% (w / w) of the total mass of the solid (i.e., if 30 g of the solid is used, 12 g of glycerol is added as a plasticizer); the solid concentration of the film-forming solution is 30 g / L (i.e., 30 g of the mixed solid (9 g of the plant stalk powder and 21 g of the sodium alginate) is dissolved or dispersed in 1 L of water to prepare the film-forming solution, and then glycerol is added for homogenization treatment).

[0012] The solvent of the film-forming solution is water (such as deionized water).

[0013] The film-forming solution refers to a solution obtained by mixing the plant stalk powder and the sodium alginate in water.

[0014] The total solid concentration in the film solution refers to the total mass of plant stalk powder and sodium alginate contained in a unit volume of the film solution, usually expressed in grams per liter (g / L), excluding the mass of glycerol.

[0015] Preferably, the plant stalk is selected from: tomato stalk (tomato straw).

[0016] Preferably, the plant stalk is not chemically treated.

[0017] Preferably, the plant stalk powder is obtained by drying, pulverizing, and passing through a 60-mesh sieve of the raw material plant stalk.

[0018] Preferably, the sodium alginate has M:G = 1:1, Mw = 90000 - 10000, and viscosity = 200 ± 20 mPa·s.

[0019] Preferably, the biodegradable film has a tensile strength greater than 5 MPa, an elongation at break greater than 10%, a water vapor permeability less than 2×10-12 g cm-1 Pa-1, and an ultraviolet blocking efficiency greater than 90%.

[0020] Preferably, the biodegradable film degrades at least 50% in the soil in 20 days.

[0021] In addition, the present invention provides a method for preparing the biodegradable film, which includes the following steps:

[0022] Add sodium alginate to water (for example, deionized water), heat and stir (for example, with a magnetic stirrer) until completely dissolved; then add plant stalk powder and stir; then add glycerol and stir to obtain a solution; evenly distribute the solution into a mold, remove surface bubbles, dry (for example, in an oven at 40°C), and then gently lift the film along the edge to obtain the film.

[0023] The beneficial effects of the present invention are as follows: (1) A completely biodegradable covering film is made of plant stalk powder and sodium alginate. (2) The simple mixing process avoids pretreatment and reduces energy consumption and production costs. (3) The film after optimizing the ratio (the plant stalk powder accounts for 30% of the solid components, the solid concentration of the film solution is 30 g / L, and the glycerol addition amount is 40% of the solid mass) can achieve a relatively high ultraviolet blocking rate. (4) The film promotes seed germination and has excellent mechanical and thermal properties. (5) Life cycle assessment shows that the impact on the environment is lower than that of polyethylene film. Description of the Drawings

[0024] Figure 1 Are the appearance and SEM images of biodegradable films with different formulations.

[0025] Figure 2 Are the mechanical properties of biodegradable films with different formulations.

[0026] Figure 3 Water contact angles of biodegradable films with different formulations.

[0027] Figure 4 Solubility, swelling, and water vapor permeability of biodegradable films with different formulations.

[0028] Figure 5 UV-visible light transmittance of biodegradable films with different formulations.

[0029] Figure 6 FTIR spectra of biodegradable films with different formulations.

[0030] Figure 7 Thermogravimetric analysis of biodegradable films with different formulations.

[0031] Figure 8 Rheological property analysis of pure sodium alginate film solution and biodegradable film solution.

[0032] Figure 9 Degradation and seed germination experiments.

[0033] Figure 10 Life cycle assessment of polyethylene mulch film and biodegradable film.

[0034] Figure 11 Scanning electron microscopy (SEM) images of tomato stem powder.

[0035] Figure 12 X-ray diffraction (XRD) patterns of tomato straw powder.

[0036] Figure 13 Particle size distribution map of tomato straw powder. Detailed implementation manners

[0037] The present invention will be described below by way of examples, but the present invention is not limited thereto.

[0038] The following terms, such as "tomato straw" and "tomato stem", have the same meaning. The following terms, such as "vegetable stem", "straw", and "plant stem", have the same meaning. The following terms, such as "film", "mulch film", "covering film", and "biodegradable film (BDF)", have the same meaning.

[0039] The present invention optimizes the application of agricultural waste, such as tomato straw powder and sodium alginate, in the development of biodegradable films by precisely controlling the preparation parameters. The research focused on systematically studying the effects of key factors such as straw addition amount, film solution concentration, and glycerol plasticizer content on the physical and chemical properties of the films. Notably, an innovative blending preparation method was proposed, eliminating the energy consumption and environmental pollution caused by traditional solvent extraction methods. This preparation method not only improves the mechanical strength, water resistance, and biodegradability of the films but also ensures their suitability for sustainable agricultural applications. By comprehensively optimizing the preparation method, the present invention significantly improves the economic feasibility of the films while enhancing their environmental sustainability. The present invention provides a cost-effective and practical solution for agricultural waste stabilization, bridging the gap between waste management and the development of high-performance biodegradable films and contributing to the development of sustainable agricultural practices.

[0040] Biodegradable mulch films (plastic films) are key to reducing agricultural plastic pollution; however, current production methods often rely on complex and expensive chemical processes. The present invention proposes an innovative and environmentally friendly method to develop fully biodegradable mulch films using untreated plant stems and sodium alginate through a simple mixing method. By eliminating the need for pretreatment, this process significantly reduces energy consumption and maximizes the utilization of agricultural waste. The optimized film formulation (30% plant stems, 3 g / 100 mL film solution concentration, 40% glycerol) has good mechanical and barrier properties, including tensile strength (greater than 5 MPa), elongation at break (greater than 10%), water vapor permeability (less than 2×10-12 g cm-1 Pa-1 s-1), and UV blocking efficiency (greater than 90%). Rheological analysis shows that the addition of vegetable stems affects the viscosity of the film-forming solution, improving the processing and application properties. In addition, compared with traditional polyethylene films, the films of the present invention degrade at least 50% in soil within 20 days, showing superior environmental sustainability. Life cycle assessment confirms that the biodegradable films of the present invention significantly reduce environmental impacts, supporting their potential for widespread adoption in sustainable agricultural practices. The present invention provides a scalable and cost-effective strategy for converting agricultural residues into high-performance biodegradable films, addressing the need for sustainable solutions in the fields of agriculture and environmental protection.

[0041] 1. Materials

[0042] Sodium alginate (chemically pure; M:G = 1:1, Mw = 90000 - 10000, viscosity = 200 ± 20 mPa·s), Shanghai Macklin Biochemical Co., Ltd. Tomato stems, from a farm in the suburbs of Tianjin.

[0043] The tomato stem powder used in this example is as Figures 11 - 13 shown. Figure 11It is a scanning electron microscope (SEM) image of tomato stem powder. Figure 12 It is an X-ray diffraction (XRD) pattern of tomato straw powder. Figure 13 It is a particle size distribution diagram of tomato straw powder.

[0044] 2. Preparation of composite film (thin film) of tomato stem powder and sodium alginate

[0045] (1) Fabrication of the thin film: Dry, grind the tomato stems, and sieve through a 60-mesh sieve for standby. Weigh the sodium alginate powder, add it to deionized water, and then heat and stir with a magnetic stirrer until completely dissolved. After 15 minutes, add the tomato stem powder, stir and mix, mix for another 15 minutes, and then add the plasticizer glycerol. Stir the mixture for another 30 minutes to prepare the thin film solution. Distribute the thin film solution evenly in the mold, with an addition amount of 0.23 g / m 2 . Remove the surface bubbles and dry the thin film in an oven at 40 °C. Finally, gently peel the dried thin film along the edges.

[0046] (2) Experimental variables: The formulation of the thin film solution is controlled by three key variables: the mass ratio of plant stem powder to sodium alginate (S), the solid concentration of the film solution (C), and the addition amount of glycerol (G). In the experimental design, only one variable is changed each time, and the other two remain unchanged, as described below:

[0047] (1) Mass ratio of plant stem powder to sodium alginate (S, w / w): This parameter represents the mass percentage ratio between the plant stem powder and sodium alginate. For example, 30:70 means that 30% of the total solid mass is plant stem and 70% is sodium alginate. During the test of this parameter, the film solution concentration is fixed at 3% (w / v), and the glycerol addition amount is 1.2% (w / v), which is equivalent to 40% of the total solid mass. The tested mass ratios of plant stem powder to sodium alginate include: 0:10, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, and 80:20.

[0048] (2) Solid concentration of the film solution (C, % w / v): The solid concentration refers to the total mass of plant stem powder and sodium alginate (excluding glycerol) in every 100 mL of the solution. For example, 3% (w / v) means that there are 3 g of solids in 100 mL of the aqueous solution. In the experiment of this parameter, the stem content is fixed at 30% of the total solid mass, and the glycerol addition ratio is 40%. The tested film solution concentrations include: 2%, 3%, 4%, 5%, and 6% (w / v).

[0049] (3) Glycerol addition amount (G, mass percentage based on the total solid mass): Glycerol is added as a plasticizer, and its addition amount is calculated based on the total mass of the plant stalks and sodium alginate solids, rather than the total amount of the solution. This addition amount is expressed as the percentage of the glycerol mass in the total solid mass. For example, when the total solid mass is 3 g, a 40% glycerol addition amount corresponds to 1.2 g of glycerol. In this set of experiments, the content of the plant stalk powder and the concentration of the film solution were fixed at 30% and 3% (w / v) respectively, and the tested glycerol addition amounts included: 0%, 10%, 20%, 30%, 40% and 50% (w / w).

[0050] 3. Characteristics

[0051] (1) Mechanical properties: To determine the tensile strength (TS) and elongation at break (EAB) of the film, a micro-controlled electronic universal testing machine (model: LD23.503) from Force Control (Shanghai) Scientific Instrument Co., Ltd. was used, equipped with a BSA-XS-50kgP sensor (capacity of 50 kg, sensitivity of 1.9995 mV / V). The film was cut into strips with dimensions of 20×80 mm and tested at a speed of 15 mm / s, controlled by LAB testing software and data processing was carried out.

[0052] (2) Solubility and swelling: The pre-dried composite film sample (Φ = 10 cm) was weighed and immersed in 50 mL of deionized water at room temperature for 24 hours. The insoluble film residue was filtered off and dried at 105 °C for 24 hours to obtain dry, insoluble sample fragments. The film solubility (%) is defined by the following formula 1:

[0053]

[0054] Where: W0 is: the weight before the sample is immersed; W f is: the final dry weight of the insoluble components after immersion.

[0055] To evaluate the water absorption capacity of the film, each sample was first dried to a constant weight and then immersed in water for 24 hours. After immersion, the film was weighed to determine the mass increase. The calculation method of the water absorption rate is shown in the following formula 2:

[0056]

[0057] Where, W0 is: the dry weight; Wt is: the weight after water absorption.

[0058] (3) Water vapor permeability (WVP): The internal humidity of the sealed box was adjusted to be constant at 75% using saturated brine. The film was fixed onto a beaker containing anhydrous calcium chloride (5 cm in diameter), then sealed and placed in the sealed box for 24 hours. Then the weight increase of the anhydrous calcium chloride was measured. The calculation method of WVP (g·m / m 2 ) is shown in the following formula 3:

[0059]

[0060] In the formula, Δg is the weight change of the WVP cup (g); L is the average film thickness (m); t is the time (s); A is the permeation area of the film (m 2 ); ΔP is the partial vapor pressure difference between the entire film (Pa).

[0061] (4) Water contact angle: The static contact angle of the sample was measured using a MODERPGX contact angle meter produced by Fiber System AB (Sweden), and the data and images were analyzed and stored using the attached PGX+ software.

[0062] (5) Microstructural characteristics: The structure of the film was analyzed in the range of 600 - 4000 cm-1 using Fourier transform infrared spectroscopy (FTIR, Thermo Fisher Scientific iS20). The morphology of the film was observed using a scanning electron microscope (SEM, TESCAN MIRA LMS, Czech Republic). The optical properties of the film, including the absorption spectrum and transmittance, were measured using a UV-visible spectrophotometer (Hitachi UH4150, Japan). Thermogravimetric analysis (TGA) of the film was performed using a Mettler TGA2 (Switzerland). Approximately 10 mg of the sample was heated at a rate of 30 - 600 °C under a nitrogen flow of 50 cm / min, and the DTG was calculated using the central finite difference method.

[0063] (6) Biodegradability: The biodegradable film (BDF) of the present invention was buried 3 cm deep in the soil, and its degradation was photographed. The contour of the degraded film was traced, and the film area was calculated using AutoCAD to evaluate the degree of degradation.

[0064] (7) Seed germination test: Three groups were set up: one group was covered with the biodegradable film (BDF) of the present invention, one group was covered with a commercially available polyethylene film (PEF), and one group was an uncovered control group (NF). Each group had three flower pots. These flower pots were 15 cm in diameter and 25 cm in height, and each flower pot was filled with 1 kg of farm soil and 100 mL of water. Then, 30 Chinese cabbage seeds were evenly sown on the soil surface of each flower pot to form a seed layer, and then 1 cm of soil was covered. The germination rate of the seeds in each flower pot was recorded.

[0065] (8) Life cycle analysis: The life cycle assessment (LCA) of the biodegradable film (BDF) of the present invention was carried out using SimaPro 9.5 and compared with the traditional polyethylene film (PEF) to quantify the environmental impact and energy requirements of the two films. This assessment identified the main factors contributing to environmental impact (Xiong et al., 2024). The input data included raw materials, energy, and transportation consumption. In contrast, the output data included the gases, solids, and liquids emitted to the environmental system throughout the system life cycle, which covered all material and energy inputs and outputs of the two films "from cradle to grave" (Hao et al., 2024). The impact assessment methods used were ReCiPe 2016 v1.1 midpoint, hierarchist perspective, and IPCC GWP 100.

[0066] The life cycles of BDF and PEF can be divided into four stages: raw material production, product manufacturing, product use, and waste management. In the raw material production stage, the life cycle inventory data for cultivating seaweed and preparing sodium alginate were sourced from (Chiew et al., 2022), and the remaining data were from the Ecoinvent 3 database. In the product manufacturing stage, the BDF production data included the chemicals and energy consumption used in this experimental protocol, while the PE film manufacturing data were sourced from (Tan et al., 2023). The consumption of energy and resources involved in the use stage of the film was negligible and was thus considered ignorable. In the waste management stage, it was assumed that BDF was 100% in-situ biodegradable in soil, and the degradation scenario was modeled as "home composting", with 0.79 kg of peat added per kg of compost product as a soil conditioner (Hermann et al., 2011). For the treatment method of PEF, please refer to (Tan et al., 2023), where 30% of the film was collected and incinerated for power generation, and the rest remained in the soil. The electricity generated from incineration was stored and transmitted to the power grid and customers, and the remaining film in the soil was simulated in the case of an open landfill. In the transportation stage, medium-sized trucks (16 - 32 tons, 6 euros) were used as the standard transportation method. Such trucks are suitable for most common typical situations, and their emission standards and load capacities are quite clear (Xiong et al., 2024).

[0067] Results and discussion

[0068] 1. Appearance and microstructure

[0069] The method of adding fillers to improve film properties is widely used and usually involves nanoparticles or extracted homogeneous materials, with a small addition ratio to ensure uniform distribution within the film. However, the present invention innovatively uses untreated vegetable stem powder as a filler material. Compared with traditional nanomaterials and homogeneous fillers, the composition of stem powder is more complex and the particles are larger. When using untreated plant stem powder as a raw material, this poses a greater challenge to the uniformity and integrity of the film.

[0070] Figure 1 Appearance and SEM images of biodegradable films with different formulations. Among them, a shows the external morphology of the films with different proportions of plant stalk powder; b shows the external morphology of the films with different film solution concentrations; c shows the external morphology of the films with different glycerol contents; d shows the SEM images of the films with different proportions of plant stalk powder; e shows the SEM images of the films with different film solution concentrations; f shows the SEM images of the films with different glycerol contents. Among them, "S" represents the proportion of plant stalk powder (0 - 80% w / w), "C" represents the film solution concentration (2 - 6 g / 100 mL), and "G" represents the glycerol addition ratio (0 - 50%). For example, "S30C3G40" represents one configuration of the combination of three variables.

[0071] During the experiment, the appearance and microstructure of the films under different parameters (plant stalk powder addition ratio, film solution concentration, and glycerol addition amount) were observed using a scanning electron microscope (SEM). The film made of pure sodium alginate has a high viscosity and tends to adhere to itself or other objects, resulting in film damage. Adding 10% of plant stalk powder significantly reduces this viscosity. As the addition ratio of plant stalk powder increases, the color of the film gradually darkens, and the SEM images show that the amount of plant stalk powder gradually increases. After adding 30% of plant stalk powder, the film shows better uniformity and integrity. When 50% of plant stalk powder is added, the accumulation of plant stalk powder can be seen on the film surface, which is further confirmed by scanning electron microscopy imaging. When the addition amount of plant stalk powder reaches 70%, the film surface is covered with a large amount of plant stalk powder, and particles fall off during the folding process, making the surface texture rough. This indicates that adding a higher proportion of untreated plant stalk powder poses a challenge to uniform distribution and affects the overall structure and performance of the film. The maximum addition amount of plant stalk powder during film formation reaches 80%, but it is also close to the maximum bearing capacity of sodium alginate, demonstrating the feasibility of using more economical and easily available waste plant stalk powder as a filler to replace more expensive film-forming substances such as sodium alginate.

[0072] In addition, the increase in film solution concentration significantly affects the physical properties of the film. As the concentration increases, due to the increase in solid content, the film darkens and hardens, resulting in greater internal stress. When the concentration is 2 g / 100 mL, the film can only form a continuous and complete structure, but due to its thin thickness, it is prone to tearing and damage during manual processing. At 3 g / 100 mL, the thickness and strength of the film are improved, enhancing its durability and mechanical stability. When the sodium alginate concentration reaches 6 g / 100 mL, due to the high internal stress of the concentrated film solution, the film hardens and curls during drying, facilitating processing and use. The SEM images also show the tight integration between the stalk particles and sodium alginate.

[0073] The addition of glycerol as a plasticizer significantly affects the flexibility and surface properties of the film. Films without glycerol or with only 10% glycerol added show obvious brittleness, cannot be folded, and have visible cracks on the surface. When the glycerol content reaches 20%, the flexibility of the film is improved, but there are still fine cracks on the surface. However, when the glycerol content exceeds 50%, an oily phenomenon begins to appear on the film surface, affecting the structural stability and appearance of the film.

[0074] 2. Mechanical properties

[0075] Mechanical properties are key indicators for evaluating the performance of the film and directly affect its practical applicability. Figure 2 For the mechanical properties of biodegradable films with different formulations. Among them, a is the stress-strain curve of films with different proportions of plant stalk powder; b is the stress-strain curve of films with different glycerol contents; c is the stress-strain curve of films with different film solution concentrations; d is the relationship between the maximum stress (TS) and elongation at break (EAB) and the proportion of plant stalk powder; e is the relationship between the maximum stress (TS) and elongation at break (EAB) and the glycerol content; f is the relationship between the maximum stress (TS) and elongation at break (EAB) and the film solution concentration.

[0076] As the content of plant stalk powder increases, the stress-strain curve gradually becomes flatter, indicating that the fibrous structure of plant stalk powder helps to disperse stress, increase the toughness of the material, and keep the film intact under higher strain. However, with the addition of plant stalk powder, the maximum tensile strength decreases significantly. The maximum tensile strength of pure sodium alginate film is 12.25 MPa. When the plant stalk content reaches 80%, the tensile strength decreases to 0.86 MPa. This phenomenon shows that the increase in the content of plant stalk powder reduces the structural integrity and load-bearing capacity of the film. This may be due to the relatively high proportion of plant stalk powder, resulting in uneven internal structure and affecting its mechanical strength. The change trend of elongation at break increases from 11.89% at 0% content to 28.59% at 30% content and decreases to 2.44% at 80% content. At low to medium stalk contents (0 - 30%), the ductility of the film is enhanced, probably because the fibers of plant stalk powder reduce the adhesiveness of the sodium alginate network, enabling the film to be further stretched without breaking (Kepekci et al., 2024). However, when the content of plant stalk powder exceeds 40%, the excessive filling amount will damage the basic structure of the film, significantly reducing its extensibility and overall mechanical properties.

[0077] The concentration of the film-forming solution also significantly affects its mechanical properties. The TS and EAB of the film increase and then decrease with the change of the film-forming solution concentration. At a relatively low film-forming solution concentration (2 g / 100 mL), the film exhibits a relatively low maximum tensile strength (about 4.42 MPa), which may be because, at such a low concentration, the interaction between the sodium alginate molecular chains is not sufficient to form enough cross-linking points, resulting in a relatively loose material structure that cannot effectively resist external stress. When the solution concentration increases to 3 g / 100 mL, the maximum tensile strength and elongation at break increase to 6.80 MPa and 28.59%, respectively, indicating that at 3 g / 100 mL, the interaction between the sodium alginate molecules and the handle fibers is sufficient to produce a relatively stable cross-linking network, enabling the film to have a certain degree of flexibility and plasticity while maintaining its structural integrity. Further increasing the solution concentration to 4 g / 100 mL and 5 g / 100 mL, the TS decreases slightly but remains stable. Therefore, a liquid with a concentration of 3 - 4 g / 100 mL can provide the best mechanical properties. Higher concentrations increase the production cost without increasing the mechanical strength. The influence law of the film-forming solution concentration on the mechanical properties is consistent with the previous research results on sodium alginate-montmorillonite clay, sodium alginate-chitosan, and sodium alginate-starch films. With the increase of the film-forming solution concentration, mechanical properties such as the tensile strength and elongation at break show a corresponding increasing trend, which may be due to the fact that the higher the concentration, the denser the molecular arrangement in the film, resulting in a more uniform structure and an increase in its overall strength. However, the excessive cross-linking of sodium alginate molecules makes the film more rigid and brittle, while the increase in the solid content increases the internal stress and reduces the deformation ability during the stretching process (Casariiego et al., 2009; Chung et al., 2010; Olivas and Barbosa-Cánovas, 2008).

[0078] The addition of glycerol as a plasticizer also significantly affects the mechanical properties of the films. The unevenness of the curves is very noticeable at low glycerol additions. Films with low glycerol content (0–20%) exhibit a lack of strain, indicating extreme brittleness, little flexibility, and easy fracture with minimal deformation. The sudden drop in the curves also indicates the sudden appearance of cracks in the films due to the rapid development of microcracks and stress concentrations. Although these films have large maximum stresses, they are not suitable for production applications. Adding glycerol from 20–40% results in higher strains but lower stresses, consistent with research on the effects of glycerol on film stress (Olivas and Barbasa-Canovas, 2008). With increasing glycerol content, the curves exhibit smoother characteristics, indicating a more uniform distribution of stress during loading. The improved continuity of the internal structure is attributed to the fact that glycerol, a large polar molecule, forms hydrogen bonds with the alginate molecules when added to the membrane solution, weakening the interactions between the alginate molecules and leading to changes in the film's flexibility (Hammann & Schmid, 2014; Sharma et al., 2022). With the addition of 40% glycerol, the film maintained its flexibility without becoming overly greasy. The elongation decreased with the addition of more glycerol, likely due to a significant reduction in inter- and intramolecular segregation / bleeding within the alginate network (Gao et al., 2017). Furthermore, with the addition of additional glycerol, the curve gradually exhibited a buffering phenomenon near fracture (the curve did not break abruptly but rather buffered for a period before decreasing), indicating that the material experienced a plastic deformation phase before fracture, improving its safety and adaptability in practical applications.

[0079] 3. Water contact angle

[0080] Next, the present inventors studied the hydrophobicity of the film surface. Figure 3 Water contact angles of biodegradable films with different formulations. a represents the change in water contact angle with varying plant stem powder ratios; b represents the change in water contact angle with varying film solution concentrations; and c represents the change in water contact angle with varying glycerol addition levels.

[0081] As can be seen from a, adding only 10% of the stems can significantly improve the hydrophobicity of the film, and the water contact angle of the control pure sodium alginate film increased from 46.15° to a significant level. This change is mainly due to the fact that the non-polar components in the stems reduce the interaction between the film surface and water molecules (Zhang et al., 2022). As the stem content increases from 10% to 40%, the contact angle gradually increases, reaching a peak of 89.28° at a stem content of 40%, after which the increase in hydrophobicity tends to saturate. However, when the stem content exceeds 50%, the contact angle of water begins to decrease, which may be because the excessive amount of stems destroys the uniformity of the film surface and affects the integrity of its structure.

[0082] Then, the present inventors investigated the effects of the film solution concentration and glycerol addition amount on hydrophobicity. As the film solution concentration increased from 2 g / 100 mL to 4 g / 100 mL, the water contact angle of the thin film gradually increased from 65.84° to a maximum of 89.28°. This increase may be because a higher concentration led to closer molecular cross-linking, reducing the number of hydrogen groups on the surface available for forming hydrogen bonds with water molecules. Although many studies have shown that the excessive hydroxyl groups in glycerol reduce the water contact angle (Sharma et al., 2022), in this study, as the glycerol addition amount increased from 0 to 40%, the maximum water contact angle reached 87.07°. However, increasing the glycerol amount to 50% slightly decreased the water contact angle, which may be due to a small amount of glycerol increasing the distance between molecules, thus weakening the interaction between hydroxyl groups and water molecules, while the hydroxyl groups in glycerol form hydrogen bonds with sodium alginate, masking the active sites on the surface. Excessive glycerol would cause the film surface to be too soft or uneven, affecting its hydrophobicity (Gao et al., 2017).

[0083] 4. Solubility, Swelling Degree, and Water Vapor Permeability

[0084] For agricultural films, water solubility contributes to natural degradation, although too high solubility may shorten the service life. The ability to swell helps retain moisture, while excessive swelling may damage the film structure. Reducing the water vapor permeability helps maintain soil moisture. This part of the study investigated the effects of different variables on the solubility, swelling property, and water vapor permeability (WVP) of the films. Figure 4 The solubility, swelling property, and water vapor permeability of biodegradable films with different formulations are shown. Among them, a shows the solubility and swelling property of films with different plant stalk powder ratios within 24 hours; b shows the solubility and swelling property of films with different film solution concentrations within 24 hours; c shows the solubility and swelling property of films with different glycerol contents within 24 hours; d shows the water vapor permeability of films with different plant stalk powder ratios; e shows the water vapor permeability of films with different film solution concentrations; f shows the water vapor permeability of films with different glycerol contents.

[0085] The results showed that as the content of plant stalk powder increased, its water solubility and swelling degree decreased significantly, which was due to the insolubility of plant stalk powder in water and its minimum water absorption rate. Therefore, it can be predicted that adding plant stalk powder reduces the water solubility and swelling ability of the film, indicating that it can improve the water stability of sodium alginate films. However, the WVP increased with the increase in stalk content, damaging the structural integrity of the film and allowing steam to permeate through the film faster. Therefore, it is necessary to find a balance between water stability and structural integrity, and an acceptable plant stalk content level is 20 - 30%.

[0086] As the concentration of the film-forming solution increased, both the water solubility and swelling degree of the film decreased, which might be due to the formation of a stronger and more robust network at higher concentrations (Avella et al., 2007; Zhang et al., 2023). However, the increase in the WVP value might be because the higher concentration in the film generated more free volume, reducing the barrier performance of the film (Yang et al., 2024), or because the alginate with a lower concentration had a higher swelling property, so the initial moisture was absorbed, resulting in a lower WVP value at lower concentrations (Jost et al., 2014). In the previous water contact angle tests, the inventors observed that when the concentration of the film-forming solution was 4 g / 100 mL, the contact angle of water increased by about 15 degrees compared with the previous results. However, the analysis of this study showed that increasing the film-forming solution concentration from 3 g / 100 mL to 4 g / 100 mL did not significantly improve the water stability or vapor barrier performance of the film. Therefore, considering that using less raw materials can reduce the environmental impact, a film-forming solution concentration of 3 g / 100 mL is still the best choice.

[0087] When the glycerol content was 0 - 30%, the brittleness of the film led to surface cracking, which was not suitable for WVP testing. The works of Olivas and Barbosa-Cánovas (Olivas and Barbosa-Cánovas, 2008) also showed that the film without a plasticizer was too brittle and might exhibit microcracks that increased the WVP value. With the addition of glycerol, the WVP of the film decreased, which might be due to the interaction between glycerol and sodium alginate preventing the permeation of water vapor (Al-Hassan, 2024). However, when the glycerol content reached 50%, the WVP value increased slightly, which might be due to the excessive glycerol increasing the free volume and moisture content of the film, significantly improving the permeability to oxygen and water vapor (Jost et al., 2014). In fact, the effect of glycerol addition on the water stability of the film was far less significant than its effect on the mechanical properties. Therefore, adding 40% glycerol was the most suitable considering mechanical properties as a priority. These results indicated that optimizing the film formulation was the key to regulating the vapor barrier performance and water stability of the film.

[0088] 5. Ultraviolet-visible spectroscopy

[0089] The low ultraviolet transmittance in the film plays a crucial role in preventing the growth of weeds under agricultural covers (Cai et al., 2024). Figure 5 The ultraviolet-visible transmittance of biodegradable films with different formulations is shown. Among them, a shows the ultraviolet-visible spectra of films with different proportions of plant stalk powder; b shows the ultraviolet-visible spectra of films with different film-forming solution concentrations; c shows the ultraviolet-visible spectra of films with different glycerol contents.

[0090] Generally, the light transmittance of the film increases with the increase in wavelength but generally decreases with the increase in the content of plant stalk powder, film solution concentration, and glycerol content. The film with 0% plant stalk content (pure sodium alginate) has the highest light transmittance, indicating that the ultraviolet shielding effect of a single sodium alginate film is poor (Abdul Aziz and Salama, 2022). However, with the increase in the content of plant stalk powder, the light transmittance decreases significantly. In the short wavelength range (200 - 400 nm), adding 10% plant stalks can achieve an average ultraviolet blocking rate of 87.8%, while adding 30% plant stalks can effectively block most ultraviolet light, with an average blocking rate of 98.5%. This enhanced ultraviolet blocking ability is mainly attributed to the lignin molecules in the plant stalk powder. The rich aromatic ring structure and p-π conjugation of phenolic hydroxyl and carbonyl groups in these molecules absorb significant ultraviolet light (Wang Shujie et al., et al., 2024). The increase in film solution concentration and glycerol content also enhances the ultraviolet shielding effect of the film, but the effect is smaller, which is consistent with previous research results (Cazon et al., 2020; Ren et al., 2022; Yang et al., 2024), indicating that the main source of ultraviolet shielding in the film is the addition of plant stalk powder. In the long wavelength range (400 - 800 nm), the light transmittance increases with the increase in wavelength, indicating that the film allows more visible light to pass through, which is beneficial for ensuring the light required for crop photosynthesis (Wang et al., 2023). Therefore, compared with the method of extracting lignin from biomass to enhance ultraviolet shielding, directly adding 30% untreated plant stalks to the film is sufficient to provide excellent ultraviolet shielding performance, thus eliminating the need for specialized lignin extraction. This method simplifies the production process while maintaining the effective shielding ability of the film.

[0091] 6. FTIR Analysis

[0092] Figure 6 Figure shows the FTIR spectra of biodegradable films with different formulations. Among them, a shows the FTIR spectra of films with different proportions of plant stalk powder; b shows the FTIR spectra of films with different film solution concentrations; c shows the FTIR spectra of films with different glycerol contents.

[0093] One -OH stretching vibration peak appears in the range of 3000 - 3600 cm⁻¹, mainly from glycerol and sodium alginate (Zhou et al., 2022). The peak is broad and intense, indicating the formation of polymers. The peak intensity of sodium alginate and glycerol at -1 increases with the increase of sodium alginate, indicating that the contribution of glycerol and sodium alginate to the -OH group is more significant. In contrast, the contribution of plant stalk powder is less significant. The characteristic absorption peak at 2900 cm⁻¹ is related to the vibration of the alkyl functional group CH bond produced by small molecules (X. Zhang et al., 2024), mainly contributed by glycerol. At 1730 cm⁻¹, an absorption peak was detected only in pure plant stalks and films containing 80% plant stalks, which is due to the stretching vibration of the ester carbonyl group in plant stalks (Lazdovica et al., 2017; Nesic et al., 2023). In addition, the peaks at 1610 and 1410 cm⁻¹ correspond to the asymmetric and symmetric stretching vibrations of the COO⁻ group, mainly from sodium alginate (Choi et al., 2022; Zhou et al., 2022). The latter is related to the vibration of C - OH in the pyranose ring of sodium alginate (Wang Shujie, et al., 2024) or related to guluronic acid (Paula et al., 2015). The peak at 930 cm⁻¹ corresponds to the stretching of C - O - C in 3,6 - anhydrogalactose (Paula et al., 2015). The absorption band near 850 cm⁻¹ is related to the C - H bond in glucuronic acid in alginate (Villanueva et al., 2023), while 815 cm⁻¹ is related to polyguluronic acid (Mollah et al., 2023). The infrared spectra of plant stalk powder and sodium alginate show main absorption peaks similar to their respective spectra, and no new characteristic peaks appear, indicating that the interaction between them is mainly physical (Liu et al., 2024).

[0094] 7. Thermal analysis

[0095] Figure 7 Figure shows the thermogravimetric analysis of biodegradable films with different formulations. Among them, a shows the TG curves of films with different proportions of plant stalk powder; b shows the DTG curves of films with different proportions of plant stalk powder; c shows the TG curves of films with different film solution concentrations; d shows the DTG curves of films with different film solution concentrations; e shows the TG curves of films with different glycerol contents; f shows the DTG curves of films with different glycerol contents.

[0096] In the temperature range of 30 - 130 °C, all samples showed significant mass loss, mainly due to the evaporation of water and the breaking of intra- and intermolecular hydrogen bonds (Rashid et al., 2024). Between 130 and approximately 275 °C, an obvious peak appeared, which was related to the decomposition and volatilization of sodium alginate, possibly due to the dehydration, depolymerization of protonated carboxyl groups, and oxidation of macromolecules (Cao et al., 2024; Soazo et al., 2015). With the increase in the proportion of plant stalk powder, this peak gradually decreased, indicating that the addition of plant stalk powder improved the thermal stability of the material. Similar to past work (Liu et al., 2024), the introduction of CCN improved the thermal stability of the film. In this study, the lignocellulose fibers in the plant stalk powder also played a similar role. As the temperature further increased to the range of 275 - 350 °C, the decomposition of the stalk began to dominate, mainly due to the pyrolysis reactions of hemicellulose, cellulose, and lignin (Zhang et al., 2020; X. Zhang et al., 2024). In this temperature range, the sample with 80% plant stalk powder content showed the most significant peak on the DTG curve, which was consistent with the thermal decomposition characteristics of cellulose and lignin. In contrast, the thermal decomposition of pure sodium alginate and samples with lower plant stalk powder content mainly occurred at lower temperatures. Therefore, the addition of plant stalk powder had a positive effect on the thermal stability and decomposition kinetics of sodium alginate films.

[0097] The change in the concentration of the film solution had little effect on the thermal loss temperature, but the proportion of mass loss in different stages was different. In the initial stage (30 - approximately 130 °C), the film solution with a lower concentration showed more significant mass loss due to the evaporation of water. In contrast, the material with a higher concentration had better thermal stability due to its denser molecular structure. In the main thermal decomposition stage, from approximately 140 - 280 °C, the mass loss of the low-concentration film was significantly higher than that of the high-concentration film, indicating that the thermal decomposition process of the latter was delayed. In the high-temperature range of 280 - 800 °C, the mass loss of the high-concentration film was greater, indicating that the high-concentration film did not decompose rapidly at lower temperatures due to its dense structure.

[0098] With the addition of glycerol, the peak temperature of water release in the film below 100 °C decreased, probably because the preferential interaction between glycerol and alginate expelled some water, and the remaining bound water was released at a higher temperature (110 - 130 °C). Films containing plasticizers generally had a lower thermal degradation temperature, indicating that the addition of glycerol reduced the thermal stability of sodium alginate films, and the residual mass decreased with the increase in glycerol content, which was consistent with the previous research results (Avella et al., 2007; Gao et al., 2017).

[0099] Based on the above research results and considering factors such as the mechanical strength, ductility, water stability, and UV-blocking performance of the film, the inventors selected a formulation containing 30% vegetable stalks, a film solution concentration of 3 g / 100 mL, and 40% glycerol added (S30C3G40) for performance testing. The tensile strength (TS) of this formulation was 7 MPa, the elongation at break (EAB) was 29%, the water vapor permeability (WVP) was 1.88E-12 g / cmPas, and the average UV-blocking rate was 98.5%, which is comparable to the films prepared using complex extraction processes or other additives reported in past studies. Summarize the performance data of sodium alginate composite films in previous studies, including tensile strength, elongation at break, and water vapor permeability. These data indicate that the films developed in this study are competitive in multiple key performance indicators.

[0100] 8. Measurement of Rheological Properties of Film-Forming Solution

[0101] Rheological properties are important research tools for understanding and optimizing the behavior of materials during film formation. Analyzing the rheological response of the film solution under different shear conditions and temperatures can predict its performance during actual processing. This analysis helps to adjust the formulation and process parameters, thereby improving the uniformity and application performance of the film. In this study, a pure sodium alginate film solution (SA) with a concentration of 2.1 g / 100 mL and a film solution containing straw (2.1 g / 100 mL sodium alginate and 0.9 g / 100 mL plant stalks) (BDF) were prepared while keeping the sodium alginate concentration constant. Rheological tests were conducted on these two film solutions to study the effect of straw addition on the viscosity, shear-thinning performance, and viscoelasticity of the film solution. Figure 8 Rheological property analysis of pure sodium alginate film solution and biodegradable film solution.

[0102] Among them, a and b describe the viscosity and stress response as functions of the shear rate of the two solutions. a shows the shear viscosity of the two solutions; b shows the stress of the two solutions. Both samples exhibit typical shear-thinning behavior: as the shear rate increases from 0.1 s-1 to 100 s-1, the apparent viscosity gradually decreases while the shear stress gradually increases. This phenomenon may be due to the reduction of physical interactions or structural disruption between adjacent polymer chains during shear (Shi et al., 2023). The Herschel-Bulkley model was used to mathematically describe this flow behavior, and the model fitting was good, with correlation coefficients of 0.9994 and 0.9986, respectively. Both solutions exhibit non-Newtonian shear-thinning behavior, with the flow behavior index (n) less than 1, and the BDF solution shows a more pronounced shear-thinning effect. As the shear rate increases, it is sufficient to overcome Brownian motion, and the emulsion droplets are arranged more orderly along the flow field, reducing the flow resistance and viscosity (Xu et al., 2023). The consistency coefficient (K) is a measure of viscosity, and the BDF solution is significantly higher than the SA solution, indicating that the addition of plant stalks significantly increases the viscosity of the solution. This increase is due to the fact that plant stalk fibers enhance the internal friction and resistance within the solution, thus requiring a greater flow force. In addition, both solutions exhibit a yield stress (τ0) close to zero, which indicates that theoretically, these materials can flow with little applied stress, facilitating applications that are easy to handle and flow under low-shear conditions. However, the BDF solution shows more significant variability in yield stress measurements, which may reflect the heterogeneity of the samples or experimental condition fluctuations due to the incorporation of plant stalks.

[0103] Among them, c and d describe the rheological properties of the frequency sweep. c shows G′, G″, and tanδ of the frequency sweep BDF; d shows G′, G″, and tanδ of the frequency sweep SA. The storage modulus (G′) and loss modulus (G″) increase with the increase of angular frequency (ω), showing frequency dependence. The dependence of G′ and G″ on ω can be characterized by the most common classification to describe the properties of the dispersion system: dilute solution, entangled network (or concentrated solution), weak gel, and strong gel. At lower frequencies, the viscous response dominates, G″ > G′ and tanδ > 1; at higher frequencies, the elastic response dominates, G′ > G″ and tanδ < 1. This viscoelastic behavior indicates a concentrated solution or entangled network (Huang et al., 2016). At relatively low frequencies, due to the longer oscillation period, the polymer chains in the film solution can be significantly unraveled, and the loss modulus G″ dominates, reflecting the viscous response of the material to the applied deformation. In contrast, at relatively high frequencies, the oscillation rate exceeds the time scale of molecular rearrangement, resulting in the entanglement coupling between polymer chains and the temporary bonding within the gel network, effectively knotting (Li et al., 2020). The formation of this structure makes the storage modulus G′ dominate the response of the material, forming a temporary three-dimensional network structure, enhancing the elastic properties of the material, enabling effective shape recovery and resistance to external deformation.

[0104] Among them, e and f show the viscoelastic behavior of the material at different temperatures. e shows the viscoelastic behavior of BDF at different temperatures; f shows the viscoelastic behavior of SA at different temperatures. The storage modulus curve of the SA solution shows obvious fluctuations, probably because the viscosity and modulus of the sample are low, making it unstable under the load strain, but its trend and range can still be analyzed. For these two materials, the loss modulus (G’) is always more significant than the storage modulus (G’), and the tanδ value remains above 1, indicating that viscous deformation always exceeds elastic deformation. Comparing the rheological data of the BDF solution and the SA solution, BDF shows higher storage and loss moduli, indicating its superior viscoelastic properties, that is, it shows higher elastic and viscous responses under external stress. This is due to high molecular weight polymers or the inclusion of straw fibers, which increases the internal friction and resistance in the BDF solution. As the temperature increases, the storage modulus and loss modulus of both the BDF and SA groups show a downward trend, which is usually related to the weakening of the intermolecular interactions between polymers in the solution. For example, as the temperature increases, these structures increase the thermal motion of molecules, relatively reducing the intermolecular attraction, thereby reducing the overall viscoelastic properties of the solution (Xu et al., 2023). Physicochemically, this phenomenon is related to the thermal softening behavior of polymers, that is, the elevated temperature weakens the internal secondary binding forces, making the polymer chains slide past each other more easily. Specifically, compared with the loss modulus, the more significant decrease in the storage modulus indicates that the elastic response decreases more significantly than the energy dissipation, usually meaning a decrease in the structural integrity or cross-linking density at higher temperatures, resulting in a decrease in the elastic recovery ability.

[0105] The rheological property analysis provides profound insights into the film-forming ability of this solution. The shear-thinning property indicates that although during processing such as stirring or coating, the viscosity is appropriately reduced to facilitate flow and form a uniform layer, over-stirring must be avoided to prevent the viscosity from dropping too low, which may affect the quality of the film. In addition, the temperature sensitivity of the film solution indicates that controlling the appropriate temperature during the drying and curing processes is crucial for maintaining the appropriate viscosity and ensuring the structural stability and uniformity of the film after drying. The addition of plant stalk powder increases the internal friction and resistance in the film solution, which is crucial for maintaining a high viscosity and controlling the morphology and quality of the film material. In addition, the film solution containing plant stalk powder has high viscosity and viscoelasticity, enabling it to absorb impacts more effectively under dynamic loads and quickly recover to its original state, improving the stability and fault tolerance during production and storage. The change in temperature affects both of these film solutions, demonstrating their thermal stability and softening behavior, further clarifying the positive impact of the plant stalk additive on thermal management and stability throughout the processing and application stages.

[0106] 9. Evaluation of the Seed Germination and Biodegradation Properties of the BDF Film

[0107] The present inventor selected a BDF film with parameters of S30C3G40 for the seed germination and film degradation experiments. Figure 9 For the degradation and seed germination experiments. Among them, a shows the time-lapse photos of BDF degradation; b shows the contour tracing of the film edge of BDF degradation; c shows the scatter plot of the number of days of the reduced film area of BDF degradation. The treatment types for seed germination analysis are PEF, BDF, and NF; among them: d is the daily germination progress; e is the daily germination count; f is the cumulative germination of each treatment type within three days. d, e, and f were used to evaluate the effect of different covering methods (covered with BDF) on the seed germination rate using a pot experiment.

[0108] The results showed that germination started on the 3rd day for all treatments and was completed on the 6th day. After most seeds germinated on the 3rd day, the film was removed, and the germination number, total germination rate, and the ratio of the germination rate on the third day to the total number of germinations were recorded on the 4th, 5th, and 6th days. The respective total germination rates for PEF, BDF, and the film-free group were 94.4%, 94.4%, and 91.1%, with no significant differences, indicating that the differences in total germination rates were mainly due to the seeds themselves and errors during sowing, as all materials were free of ecotoxic substances. The germination rates of PEF, BDF, and the film-free group on the first day were 85.9%, 85.0%, and 75.5% respectively. The germination rate of the seeds covered with the BDF film on the first day was similar to that of w and significantly higher than that of the uncovered seeds. The film-free group had a higher germination rate on the 5th day (delayed by 1 day compared to the film-covered group), indicating that the BDF film was as effective as the traditional covering film in promoting seed growth. a, b, and c show the degradation process of the BDF film within 20 days. Since the film covered a large amount of soil, it was difficult to evaluate the degree of weight degradation. Therefore, the change in the film area was used to measure the degradation process. As the degradation time increased, the area of the film gradually decreased, and the degradation process could be visually observed through comparison charts. The reduction in the first three days was due to film dehydration. The area of the film buried in the soil decreased by 45% on the 20th day. Compared with the film area on the soil surface, it remained almost unchanged during the same period, indicating that the film had good degradability in the soil, and the film degradation rate on the soil surface was slower. As the burial time extended, the film gradually became harder but maintained a high flexibility, indicating that the film had good usability and good degradation performance at the same time.

[0109] 10. Life cycle analysis

[0110] The LCA analysis method was used to compare the environmental impacts of BDF films and PEF films. Figure 10Life cycle assessment of polyethylene film (PEF) and biodegradable film (BDF). Among them, a shows the impacts of different life cycle stages (transportation, forming, material, end - of - life) of PEF on different environmental indicators; b shows the impacts of different life cycle stages (transportation, forming, material, end - of - life) of BDF on different environmental indicators; c shows the comparative impacts of BDF and PEF; d shows the comparison of carbon emissions of BDF and PEF at each life cycle stage. The environmental impacts of these two types of films are concentrated in three categories: marine ecotoxicity, freshwater ecotoxicity, and freshwater eutrophication. a and b respectively show the normalization results of PEF film and BDF film, indicating that the significant environmental impacts of PEF film occur at the end of its life cycle, especially at the end - of - life stage. Discarded old films in the soil can damage the soil structure and have an adverse impact on terrestrial and aquatic systems (Brodhagen et al., 2015). Therefore, recycling PEF film plays a crucial role in reducing white blood cell pollution. In contrast, the environmental impacts of BDF film mainly come from the extraction process of sodium alginate. Extracting sodium alginate from seaweed requires a large amount of electricity and chemicals, acids and alkalis, which makes it a more important contributor to the environmental impacts of these films (Borgio et al., 2023), and this is further verified in d. The model of the present invention uses the life cycle inventory results of sodium alginate extraction (Chiew et al., 2022) and compares them with previous research results (Ayala et al., 2023; Rashid et al., 2024), all of which highlight the substantial environmental impacts of the sodium alginate extraction process. In addition, b and d also show that the biodegradable film of the present invention, which skips the high - energy extraction step and directly uses plant stalk waste, has less environmental impact. The other impacts of BDF film are very small, mainly because they degrade naturally in the soil, do not require additional waste management or energy consumption, and do not produce secondary pollutants. In addition, once the degradable film degrades, it can also be used as a soil conditioner, which explains the negative value shown at the end - of - life of BDF film in d. Generally speaking, the alginate - based biodegradable film is more environmentally friendly than 0.01 mm polyethylene and significantly reduces the environmental impact.

[0111] Conclusion

[0112] The present invention proposes a novel biodegradable film and its preparation method. The preparation method is simple and environmentally friendly, using untreated plant stalk powder and sodium alginate to develop a completely biodegradable covering film. By eliminating the need for pretreatment, this method significantly reduces energy consumption while maximizing the utilization of waste vegetable stalks. The optimized film formulation exhibits excellent properties, including a tensile strength of 7 MPa, an elongation at break of 29%, an ultraviolet protection efficiency of 98.5%, biodegradability, and a soil degradation rate of 50% at 20 days. These findings indicate that the biodegradable film developed by the present invention has great promise in reducing the environmental footprint associated with traditional polyethylene films. In addition, adding plant stalks can improve the rheological properties of the film-forming solution, enhancing its processing and application properties. Life cycle assessment further confirms that this method significantly reduces the environmental impact compared to traditional plastic films, highlighting its potential for wider application in sustainable agriculture. Future research should focus on further improving the film's properties to meet various agricultural needs, scaling up the production process, and evaluating the long-term effects on soil health and crop productivity. These advancements will enhance the practicality and applicability of the biodegradable covering film, supporting sustainable agricultural practices and environmental protection. In summary, the present invention provides a viable approach to converting agricultural residues into high-value, environmentally friendly products, making a meaningful contribution to the pursuit of sustainable agricultural systems.

[0113] Based on the above description of the invention content, those skilled in the art can comprehensively apply the present invention, and all identical principles or similar modifications should be regarded as included within the scope of the present invention.

Claims

1. A biodegradable film comprising: Plant stalk powder, sodium alginate, and glycerol.

2. The biodegradable film according to claim 1, wherein the mass ratio of the plant stalk powder to sodium alginate is 10% - 50%: 50% - 90%; based on the total mass of the plant stalk powder and sodium alginate, the addition amount of glycerol is 30% - 50%; the total solid concentration of the plant stalk powder and sodium alginate in the film solution is 20 - 50 g / L.

3. The biodegradable film according to claim 2, wherein the mass ratio of the plant stalk powder to sodium alginate is 20% - 40%: 60% - 80%, preferably 25% - 35%: 65% - 75%, further preferably 28% - 32%: 68% - 72%, and further preferably 30%: 70%.

4. The biodegradable film according to claim 2, wherein based on the total mass of the plant stalk powder and sodium alginate, the addition amount of glycerol is 30% - 45%, preferably 30% - 40%, further preferably 35% - 40%, and further preferably 40%.

5. The biodegradable film according to claim 2, wherein the total solid concentration of the plant stalk powder and sodium alginate in the film solution is 30 - 40 g / L, preferably 30 - 35 g / L, and further preferably 30 g / L.

6. The biodegradable film according to claim 1, wherein the mass ratio of the plant stalk powder to sodium alginate is 30%: 70%; based on the total mass of the plant stalk powder and sodium alginate, the addition amount of glycerol is 40%; the solid concentration of the film solution is 30 g / L.

7. The biodegradable film according to claim 1, wherein the plant stalk is selected from: tomato stalk; preferably, the plant stalk is not chemically treated; preferably, the plant stalk powder is obtained by drying, pulverizing, and passing through a 60 - mesh sieve of the raw material plant stalk; the sodium alginate has M:G = 1:1, Mw = 90000 - 100000, and viscosity = 200 ± 20 mPa·s.

8. The biodegradable film according to claim 1, wherein the tensile strength of the biodegradable film is greater than 5 MPa, the elongation at break is greater than 10%, the water vapor permeability is less than 2×10 - 12 g·cm - 1·Pa - 1, and the ultraviolet blocking efficiency is greater than 90%.

9. The biodegradable film according to claim 1, wherein the biodegradable film degrades at least 50% in soil in 20 days.

10. The preparation method of the biodegradable film according to claim 1, comprising the following steps: Adding sodium alginate into water, heating and stirring until completely dissolved; then adding plant stalk powder and stirring; then adding glycerol and stirring to obtain a solution; uniformly distributing the solution into a mold, removing surface bubbles, and drying to obtain the product.

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