Agricultural waste biomass-based degradable mulching film and preparation method thereof

Abstract

The application discloses an agricultural waste biomass-based degradable mulch film and a preparation method thereof, and particularly relates to the fields of biomass resource utilization and low-energy processing. The mulch film is composed of PLA 20-50%, PBAT 35-65%, agricultural waste biomass functional powder 5-25%, reactive compatibilizer 0.5-4.0%, chain extender 0.05-1.0%, and bio-based lubrication / rheological adjustment component 0.1-1.5%, and the sum of the mass fractions of the components is 100%. The application realizes low-energy continuous preparation by replacing high-temperature drying with mechanical dehydration and low-grade heat drying, replacing wet treatment with dry surface regulation, and replacing a repeated melting route with one-step extrusion film blowing. Compared with a traditional route, the comprehensive power consumption per unit mass is reduced by 20-35%, the tensile strength of the mulch film is greater than or equal to 25 MPa, and the elongation at break is greater than or equal to 280%, so that the mulch film has the advantages of resource utilization, degradability and low-carbon manufacturing.

Description

Technical Field

[0001] This invention relates to the field of biomass resource utilization and low-energy processing technology, and more specifically, to a biodegradable agricultural waste biomass-based mulch film and its preparation method. Background Technology

[0002] With the increasing prominence of residual pollution problems from polyethylene mulch films, biodegradable mulch films have become an important alternative to traditional PE mulch films. Polylactic acid (PLA) and polybutylene adipate / terephthalate (PBAT) are currently the most widely used biodegradable polyester materials. PBAT has excellent flexibility and ductility, while PLA provides high rigidity and transparency. Blends of these two materials are widely used in the preparation of biodegradable mulch films. Meanwhile, introducing agricultural waste biomass (such as crop straw, vegetable residues, and horticultural pruning materials) as functional fillers into biodegradable mulch film systems can not only reduce the amount of petroleum-based or bio-based polyesters used, but also provide a high-value-added pathway for the resource utilization of waste biomass, while enriching the biodegradability of the mulch film.

[0003] Patent application publication number CN208081437U discloses a biodegradable mulch film and its preparation method, which adjusts the degradation rate by adding starch or plant fiber powder to a PLA / PBAT matrix. Furthermore, existing technologies have also reported on surface modification of biomass fillers using methods such as alkali treatment and silane coupling modification to improve their interfacial compatibility with polyester matrices.

[0004] However, the above technical solutions still have many shortcomings in practical application, mainly in the following aspects:

[0005] First, agricultural waste biomass (such as water chestnut leaves, rice straw, vegetable residues, etc.) usually has a high initial moisture content (wet basis moisture content can reach 60%-85%). In order to process it into powder and blend it with polyester, existing technologies often require high-temperature drying (usually at 80-105℃) or even multiple drying processes. This process not only consumes a lot of heat energy, but may also cause partial thermal degradation of fiber components and agglomeration of powder particles, which in turn affects the subsequent dispersion effect in the matrix.

[0006] Secondly, to improve the interfacial bonding between hydrophilic biomass fillers and hydrophobic polyester matrices, many technical approaches employ multi-step pretreatment processes such as wet alkali treatment, water washing and neutralization, and secondary drying. While these processes improve interfacial compatibility to some extent, they also introduce additional environmental burdens such as reagent consumption, industrial water usage, and wastewater treatment, which contradicts the low-carbon goal of utilizing agricultural waste biomass resources.

[0007] Third, current conventional biodegradable mulch film preparation processes mostly employ a two-step route of blending and granulation followed by secondary blown film production. This involves first melting and blending the components in a twin-screw extruder and granulating them, then re-melting the resulting granules in a single-screw extruder before blown film production. While this route facilitates material homogenization and process control, the two melting processes significantly increase the power consumption per unit product. Furthermore, PLA is prone to hydrolysis and thermal degradation under repeated thermal history, leading to a decrease in molecular weight and weakened melt strength, which in turn affects the stability of the blown film bubble and the mechanical properties of the film.

[0008] Fourth, as the proportion of biomass fillers increases, the melt viscosity of the blend system often rises significantly, leading to increased extrusion torque, a narrower processing window, and a higher likelihood of problems such as uneven film thickness, film breakage, or increased scrap rates. Some companies raise the processing temperature to maintain processability, but this further accelerates the thermal degradation of PLA / PBAT and increases energy consumption, creating a vicious cycle of sacrificing energy consumption and performance for processing.

[0009] In summary, the existing technology for preparing biodegradable agricultural waste-based mulch films urgently needs a systematic, low-energy solution that can integrate raw material pretreatment, interface control, blending process, and energy management. Summary of the Invention

[0010] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a biodegradable mulch film based on agricultural waste and its preparation method. The technical problem to be solved by the present invention is: how to reduce wet processing, reduce the number of repeated meltings and control the processing power consumption per unit mass of mulch film while taking into account the film formation stability, basic performance of farmland cover and subsequent degradability in the existing preparation process of biodegradable mulch film based on agricultural waste.

[0011] To achieve the above objectives, the present invention provides the following technical solution: a biodegradable mulch film based on agricultural waste biomass, comprising the following components by mass fraction: PLA 20%-50%, PBAT 35%-65%, agricultural waste biomass functional powder 5%-25%, reactive compatibilizer 0.5%-4.0%, chain extender 0.05%-1.0%, and bio-based lubricant / rheology modifier 0.1%-1.5%, wherein the sum of the mass fractions of each component is 100%, and the thickness of the mulch film is 8-20 μm.

[0012] In a preferred embodiment, the agricultural waste biomass functional powder is water chestnut leaf powder, rice straw powder, wheat straw powder, corn stalk powder, vegetable leaf powder, horticultural pruning material powder, or a combination thereof, with a particle size of 80-200 mesh, preferably 100-160 mesh; the moisture content of the powder before entering the extruder is not higher than 2.5 wt%, preferably not higher than 1.5 wt%.

[0013] In a preferred embodiment, the reactive compatibilizer is an epoxidized vegetable oil, an epoxy functional polymer, a maleic anhydride-grafted biodegradable polyester, or a combination thereof; the chain extender is a multifunctional epoxy chain extender, a carbodiimide chain extender, or a combination thereof; and the bio-based lubricant / rheology modifier is a fatty acid ester, a vegetable oil-based lubricant, or a biodegradable wax.

[0014] This invention also includes a method for preparing a biodegradable agricultural waste-based mulch film, comprising the following steps:

[0015] S1. Raw material sorting and pre-dehydration: Agricultural waste biomass is sheared or coarsely crushed after removing mud, sand and obvious impurities; raw materials with high initial moisture content are mechanically dehydrated by pressing, centrifugation or natural drainage to reduce the moisture content to 50%-70%;

[0016] S2. Low-grade thermal drying and refining: The pre-dehydrated raw materials are dried naturally, by solar-assisted drying, by heat pump low-temperature drying, or by industrial waste heat until the moisture content is no higher than 2.5 wt%; the drying temperature is controlled at 40-65℃ to avoid high-temperature long-term processing; then the powder is crushed and sieved to obtain the target particle size.

[0017] S3. Dry reactive surface conditioning: Add reactive compatibilizer and / or bio-based lubricating components at 0.5-5 wt% of the biomass powder mass, and carry out dry coating in a high-speed mixer or kneader to ensure that the compatibilizing components are evenly distributed on the powder surface; this step does not involve large-scale water washing or secondary wet neutralization.

[0018] S4. Online metering blending: PLA, PBAT, dry-controlled biomass powder and chain extender are fed into the twin-screw extrusion system through loss-in-weight or volumetric feeding devices; the feed ratio of each component is controlled by online metering.

[0019] S5, One-step reactive extrusion blown film: The melt blending, reactive compressing, melt pressure stabilization and blown film forming are completed on the same continuous production line without intermediate granulation and remelting; the processing temperature is 125-165℃, the screw speed is 80-220rpm, the blow-up ratio is 1.5-3.5, and the traction speed is adjusted online according to the film thickness;

[0020] S6. Energy consumption feedback control: Collects extruder main unit current, torque, energy consumption of each temperature zone, melt pressure, membrane bubble oscillation amplitude and scrap rate; when torque, melt pressure or membrane bubble fluctuation exceeds the preset threshold, it is adjusted by reducing the instantaneous biomass feed rate, adjusting the screw speed or temperature zone.

[0021] S7. Winding and Quality Control: Cool, pull and wind the formed mulch film to obtain a biodegradable agricultural mulch film with a thickness of 8-20μm; test the film thickness uniformity, tensile properties, tear properties, light transmittance and water vapor transmission properties.

[0022] In a preferred embodiment, the drying endpoint in step S2 is controlled in real time by an online moisture detector. When the moisture content of the powder drops to a set value (not higher than 2.5 wt%), the drying process automatically stops or the powder is switched to a heat preservation and standby state to avoid over-drying.

[0023] In a preferred embodiment, the preset threshold in step S6 is: when the torque fluctuates by more than ±15% relative to the reference value, the melt pressure fluctuates by more than ±10%, and the membrane bubble oscillation amplitude exceeds ±8% of the membrane bubble diameter, the adjustment mechanism is triggered, and the adjustment priority is as follows: adjusting the biomass feed rate, adjusting the screw speed, and adjusting the temperature zone.

[0024] The technical effects and advantages of this invention are as follows:

[0025] 1. This invention replaces traditional high-temperature drying or multiple drying processes by combining mechanical dehydration with low-grade thermal drying at 40-65℃, thereby reducing the heat energy consumption in the pretreatment of agricultural waste biomass and avoiding fiber thermal degradation and powder agglomeration caused by high-temperature treatment. The dry reaction-type surface conditioning step does not use a large amount of water washing and secondary wet neutralization, eliminating the burden of reagent consumption and waste liquid treatment, and effectively reducing the energy and water consumption of the pretreatment stage.

[0026] 2. This invention integrates melt blending, reactive compatibilization, and blown film forming into a single continuous production line through online continuous metering, integrated reactive extrusion, and direct blown film forming processes. This eliminates intermediate granulation and secondary melting steps, which not only avoids the thermal degradation and molecular weight reduction of PLA / PBAT under repeated thermal history and reduces the processing power consumption per unit product, but also shortens the production process and reduces material handling and equipment occupation.

[0027] 3. This invention, through the synergistic effect of reactive compatibilizers, chain extenders, and bio-based lubricating / rheology modifiers, effectively improves the interfacial bonding force between hydrophilic biomass powder and hydrophobic PLA / PBAT matrix while increasing the proportion of biomass fillers, reducing stress concentration points and membrane defects caused by filler agglomeration; at the same time, the lubricating / rheology modifiers reduce the melt viscosity and extrusion resistance of the blend system, and reduce the film breakage rate and scrap rate under high filler ratios;

[0028] 4. This invention establishes an energy consumption feedback control mechanism with clear threshold criteria by collecting key process parameters such as host current, torque, energy consumption in each temperature zone, melt pressure, membrane bubble oscillation amplitude, and scrap rate online. This implements the low energy consumption target at the level of recordable, comparable, and reproducible engineering parameters, providing a quantitative basis for subsequent carbon-energy flow evaluation and continuous process optimization. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] This invention provides a biodegradable agricultural waste-based mulch film and its preparation method, comprising PLA, PBAT, water chestnut leaf functional powder, reactive compatibilizer, chain extender, and bio-based lubricating / rheology regulating components;

[0032] Specifically, in this embodiment (by mass percentage): PLA 34.5%, PBAT 52.0%, water chestnut leaf powder (120 mesh) 10.0%, epoxidized soybean oil (reactive compatibilizer) 2.0%, multifunctional epoxy chain extender 0.5%, and fatty acid ester lubricant 1.0%.

[0033] The preparation method of this embodiment includes the following steps:

[0034] S1. Raw material sorting and pre-dehydration: After removing mud, sand and obvious impurities from fresh water bamboo leaves, cut them into 3-5cm sections and mechanically dehydrate them using a screw press, reducing the moisture content from the initial approximately 78% to approximately 62%.

[0035] S2. Low-grade heat drying and refining: The pre-dehydrated water chestnut leaves are dried at 55±3℃ using a heat pump low-temperature drying equipment to a moisture content of 1.2%, and then sieved by a hammer mill and a vibrating screen to obtain 120-mesh powder;

[0036] S3. Dry reaction type surface conditioning: Add 3.0wt% of epoxidized soybean oil according to the mass of water chestnut leaf powder, and mix in a high-speed mixer at 800rpm for 8min to make the compatibilizer evenly coat the powder surface.

[0037] S4. Online metering blending: Each component is fed into the twin-screw extruder in a set ratio through a loss-in-weight feeder;

[0038] S5, One-step reactive extrusion blown film: Melt blending, reactive compatibilization and blown film forming are completed on the same twin-screw extrusion blown film production line. The processing temperature is set as follows: feeding section 135℃, melting section 150℃, homogenization section 160℃, die head 155℃, screw speed 150 rpm, blow-up ratio 2.5, and traction speed is adjusted online according to the target film thickness (12μm).

[0039] S6. Energy consumption feedback control: Real-time acquisition of extruder main unit current and torque, with steady-state operating parameters under standard formula (biomass powder content of 0%) as the benchmark. When the torque fluctuates more than ±15% from the benchmark value, the adjustment is made by reducing the biomass feed amount by 5%-10%.

[0040] S7. Winding and Quality Control: The formed mulch film is cooled by the wind ring, pulled and wound up, and the film thickness uniformity (within ±0.5μm), tensile strength (longitudinal ≥25MPa), and elongation at break (longitudinal ≥300%) are tested.

[0041] Through this embodiment, the overall power consumption per unit mass of mulch film is reduced by about 28% compared with the traditional blending granulation-secondary blown film route, the film thickness uniformity is good, and the mechanical properties during the mulching period meet the requirements of crop coverage.

[0042] Example 2:

[0043] This invention provides a biodegradable agricultural waste-based mulch film and its preparation method.

[0044] Specifically, in this embodiment (by mass percentage): PLA 30.0%, PBAT 50.5%, water chestnut leaf powder (100 mesh) 15.0%, maleic anhydride grafted PBAT (reactive compatibilizer) 3.0%, carbodiimide chain extender 0.5%, and vegetable oil-based lubricant 1.0%.

[0045] The preparation method in this embodiment is the same as in Example 1, except that the low-grade thermal drying adopts a combination of solar-assisted drying and heat pump (solar energy during the day, and heat pump at night and on cloudy or rainy days), the drying temperature is controlled at 50±2℃, and the final moisture content of the powder is 1.0%. In the dry reaction-type surface conditioning, maleic anhydride-grafted PBAT is added at 4.5wt% of the mass of the water chestnut leaf powder, and the mixing time is 10min.

[0046] The one-step reactive extrusion blown film parameters in this embodiment are: processing temperature 130-160℃, screw speed 120rpm, blow-up ratio 2.8, and target film thickness 15μm. The energy consumption feedback control threshold is the same as in Example 1.

[0047] In this embodiment, the biomass powder substitution ratio is increased to 15%, the amount of resin used is reduced, and the cost of raw materials per unit mass of mulch film is further reduced; the overall power consumption is reduced by about 32% compared with the traditional route, the film bubble stability is good, and no film breakage occurs.

[0048] Example 3:

[0049] This invention provides a biodegradable agricultural waste-based mulch film and its preparation method.

[0050] Specifically, in this embodiment (by mass percentage): PLA 38.0%, PBAT 48.5%, water chestnut leaf powder (160 mesh) 8.0%, epoxidized linseed oil (reactive compatibilizer) 3.0%, multifunctional epoxy chain extender 0.5%, and biodegradable wax lubricant / rheology modifier 2.0%.

[0051] The preparation method in this embodiment is the same as in Example 1, except that the low-grade heat drying uses waste heat from the factory (waste heat from the circulating cooling water of a nearby thermal power plant, with a water temperature of about 60°C) to heat the drying air through a heat exchanger. The drying temperature is controlled at 60±2°C, and the final moisture content of the powder is 1.5%. In the dry reactive surface conditioning, epoxidized linseed oil and biodegradable wax components are added simultaneously and kneaded at a low speed of 60 rpm for 15 minutes in a kneader.

[0052] The one-step reactive extrusion blown film parameters in this embodiment are: processing temperature 135-165℃, screw speed 180rpm, blow-up ratio 2.2, and target film thickness 10μm. This formulation and process setting focuses on film formation stability and widening the low-temperature processing window, making it suitable for applications requiring thinner films.

[0053] Through this embodiment, the processing temperature is controlled within 165°C, which effectively avoids the thermal degradation of PLA / PBAT at excessively high temperatures. The membrane bubble has excellent stability, the scrap rate is controlled below 2%, and the comprehensive power consumption per unit mass of mulch film is reduced by about 25%.

[0054] Example 4:

[0055] This invention provides a biodegradable agricultural waste-based mulch film and its preparation method.

[0056] The difference between this embodiment and Example 1 is that rice straw powder (140 mesh) is used instead of water chestnut leaf powder in the functional powder of agricultural waste biomass. The remaining components and proportions are the same as in Example 1. The preparation method is the same as in Example 1, with a low-grade heat drying temperature of 58±2℃ and a final powder moisture content of 1.3%. The results show that after dry reactive surface conditioning, rice straw powder can also form a good interfacial bond with the PLA / PBAT matrix. The blown film process is stable, and the mechanical properties and thickness uniformity of the resulting mulch film are comparable to those of Example 1. The overall power consumption per unit mass is reduced by approximately 26%.

[0057] Example 5:

[0058] This invention provides a biodegradable agricultural waste-based mulch film and its preparation method.

[0059] The difference between this embodiment and embodiment 1 is that in step S6 energy consumption feedback control, when the melt pressure fluctuation exceeds ±10% or the membrane bubble oscillation amplitude exceeds ±8% of the membrane bubble diameter, the biomass feed rate is adjusted first (reduced by 5%-15%). If the feed rate still exceeds the standard after adjustment, the screw speed (increase or decrease by 10-30 rpm) and the temperature zone (increase or decrease by 2-5℃) are adjusted in sequence.

[0060] The biodegradable agricultural waste biomass-based mulch films prepared in Examples 1-5 above were used to evaluate their processing energy consumption, mechanical properties, and film thickness uniformity. At least five samples were tested in each group, and the average value was taken to obtain the following data:

[0061]

[0062] As shown in the table above, the mulch films provided by the embodiments of the present invention, while reducing the comprehensive power consumption per unit mass by 25%-32% compared to the traditional method, achieve a longitudinal tensile strength of 25-30 MPa, a longitudinal elongation at break of 295%-340%, and a film thickness deviation controlled within ±0.5 μm, all meeting the requirements for agricultural mulch films. Among them, Example 3 shows the best performance in terms of film-forming stability and mechanical properties, while Example 2 has the most significant effect in terms of energy saving and consumption reduction.

[0063] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A biodegradable mulch film based on agricultural waste, characterized in that: It is composed of the following components by mass fraction: PLA 20%-50%, PBAT 35%-65%, agricultural waste biomass functional powder 5%-25%, reactive compatibilizer 0.5%-4.0%, chain extender 0.05%-1.0%, and bio-based lubricant / rheology modifier 0.1%-1.5%, with the sum of the mass fractions of all components being 100%. The agricultural waste biomass functional powder is obtained through mechanical pre-dehydration, low-grade thermal drying at 40-65℃, pulverization and sieving, and dry reactive surface conditioning, without the use of large-scale water washing and secondary wet neutralization; The thickness of the mulch film is 8-20 μm.

2. The biodegradable agricultural waste-based mulch film according to claim 1, characterized in that: The agricultural waste biomass functional powder is water chestnut leaf powder, rice straw powder, wheat straw powder, corn stalk powder, vegetable leaf powder, horticultural pruning material powder, or a combination thereof, with a particle size of 80-200 mesh; the moisture content of the powder before entering the extruder is not higher than 2.5 wt%; the reactive compatibilizer is one or more of epoxidized vegetable oil, epoxy functional polymer, and maleic anhydride-grafted biodegradable polyester; the chain extender is a multifunctional epoxy chain extender or a carbodiimide chain extender; the bio-based lubricant / rheology modifier is a fatty acid ester, a vegetable oil-based lubricant, or a biodegradable wax.

3. A method for preparing the biodegradable agricultural waste-based mulch film according to any one of claims 1-2, characterized in that, Includes the following steps: S1. Raw material sorting and pre-dehydration: Agricultural waste biomass is sheared or coarsely crushed after removing mud, sand and impurities; mechanical dehydration is carried out by pressing, centrifugation or natural drainage. S2. Low-grade thermal drying and refining: The pre-dehydrated raw materials are dried naturally, by solar-assisted drying, by heat pump low-temperature drying, or by industrial waste heat until the moisture content is no higher than 2.5 wt%, and the drying temperature is controlled at 40-65℃; then they are crushed and sieved to obtain powder of the target particle size. S3. Dry reactive surface conditioning: Add reactive compatibilizer and / or bio-based lubricating components at 0.5-5 wt% of the biomass powder mass, and carry out dry coating in a high-speed mixer or kneader; S4. Online metering blending: Each component is fed into the twin-screw extrusion system through a loss-in-weight or volumetric feeding device, and the feed ratio is controlled by online metering. S5, One-step reactive extrusion blown film: The melt blending, reactive compressing, melt pressure stabilization and blown film forming are completed on the same continuous production line without intermediate granulation and remelting; the processing temperature is 125-165℃, the screw speed is 80-220rpm, and the blow-up ratio is 1.5-3.5; S6. Energy consumption feedback control: Collects extruder main unit current, torque, energy consumption of each temperature zone, melt pressure, membrane bubble oscillation amplitude and scrap rate; when torque, melt pressure or membrane bubble fluctuation exceeds the preset threshold, it is adjusted by reducing the instantaneous biomass feed rate, adjusting the screw speed or temperature zone. S7. Winding and Quality Control: Cool, pull and wind the formed mulch film to obtain a biodegradable agricultural mulch film with a thickness of 8-20μm.

4. The method for preparing a biodegradable agricultural waste-based mulch film according to claim 3, characterized in that: In step S2, the drying endpoint is controlled in real time by an online moisture detector. When the moisture content of the powder drops to no more than 2.5 wt%, the drying will automatically stop or the powder will be put into a heat preservation state for use. In step S3, the dry reaction-type surface conditioning does not use water washing or secondary wet neutralization treatment.

5. The method for preparing a biodegradable agricultural waste-based mulch film according to claim 3, characterized in that: In step S6, the preset thresholds are: when the torque fluctuates by more than ±15% relative to the reference value, the melt pressure fluctuates by more than ±10%, and the membrane bubble oscillation amplitude exceeds ±8% of the membrane bubble diameter, the adjustment mechanism is triggered. The adjustment priorities are: adjusting the biomass feed rate, adjusting the screw speed, and adjusting the temperature zone.

6. The method for preparing a biodegradable agricultural waste-based mulch film according to claim 3, characterized in that: In step S5, the one-step reactive extrusion blown film is achieved using a twin-screw extrusion blown film machine, a single-screw online mixing blown film machine, or a composite extrusion device with a side feeding and vacuum degassing module.

7. The method for preparing a biodegradable agricultural waste-based mulch film according to claim 3, characterized in that: In step S2, the particle size of the agricultural waste biomass powder is 100-160 mesh, and the moisture content of the powder before entering the extruder is not higher than 1.5 wt%; in step S5, the processing temperature is 130-160℃, the screw speed is 100-180 rpm, and the blow-up ratio is 2.0-3.0.

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