Cellulose-based controllable degradation agricultural mulching film and preparation method thereof

Abstract

The present application relates to the technical field of degradable material, and discloses a cellulose-based controllable degradation agricultural mulching film and a preparation method thereof, the agricultural mulching film is made of 19.7-31.8 parts of acid composite powder, 65.29-72.88 parts of premixed polyester particles and 4.0-8.0 parts of epoxy soybean oil, wherein the acid composite powder is dispersed in a polyester phase provided by the premixed polyester particles. In the preparation, the acid composite powder and a first part of the premixed polyester particles are melt-mixed through a main feeding port to obtain activated material, the remaining premixed polyester particles are added through a side feeding port to obtain a regulated melt, then the epoxy soybean oil is injected to form a closed melt, and the agricultural mulching film is obtained through vacuum exhaust, granulation, drying, film blowing and winding. According to the present application, the initial water absorption is delayed by hydrophobic sealing, and the polyester phase hydrolytic degradation is promoted by the release of the acid component in the later stage, so that the obtained agricultural mulching film has controllable degradation characteristics and is suitable for agricultural covering scenes.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials technology, specifically to a cellulose-based controllable biodegradable agricultural mulch film and its preparation method. Background Technology

[0002] Agricultural mulch film, as a basic agricultural production material, plays a role in warming the soil, conserving moisture, and suppressing weeds, thus providing some support for increasing the yield of winter wheat, corn, and other crops in arid regions. However, due to the long-term, high-intensity laying and difficulty in recycling traditional mulch film, large amounts of residual film easily accumulate in farmland. These non-degradable residues affect soil aggregate structure and hinder the downward development of crop roots. Therefore, finding degradable alternatives from the source of the material has become an important direction for alleviating the problem of residual mulch film accumulation in farmland.

[0003] Degradable polymeric materials were subsequently introduced into the production of agricultural mulch films. Cellulose-based materials, in particular, use naturally occurring plant fiber macromolecules as a matrix. Their macromolecular chains can gradually participate in the biodegradation process in the soil environment, thus gaining practical application. For agricultural applications, these alternative products typically need to exhibit controllable degradation characteristics. That is, agricultural mulch films must maintain basic structural support and moisture isolation throughout the entire growth cycle of crops such as winter wheat and corn. After the mulching stage, the residual film mixed into the soil needs to respond to changes in the external environment and accelerate its depolymerization rate, thereby achieving a balance between initial usage requirements and subsequent natural decomposition.

[0004] Existing composite mulches containing cellulose matrix still have limitations in actual laying and degradation stages. Cellulose materials are highly hydrophilic, making the film susceptible to external moisture intrusion in the early stages of use. After absorbing moisture, it easily induces early hydrolysis within the matrix, causing the mulch to lose its supporting strength prematurely or even break, making it difficult to meet the requirements of long-term crop coverage. When the film enters the waste stage, the residual film lacks the triggering conditions to promote ester bond breakage, mainly relying on the slow action of the external environment. The long polymer chain depolymerization cycle is long, and the degradation process is difficult to control. In addition, in the early extrusion and mixing stage, the mixture containing easily degradable components is prone to premature chain breakage under prolonged heating and shearing, causing fluctuations in melt viscosity and adversely affecting continuous blown film production operations.

[0005] Therefore, this invention proposes a cellulose-based controllable degradable agricultural mulch film and its preparation method to overcome the shortcomings of the prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a cellulose-based controllable degradable agricultural mulch film and its preparation method. This solves the problems of existing agricultural mulch films made from cellulose-based matrices being susceptible to spontaneous hydrolysis due to soil moisture intrusion in the early stages of use, resulting in loss of performance. Furthermore, these films lack an internal catalytic chain-breaking mechanism after the mulching cycle ends, making it difficult to form a decomposition process with a controllable degradation rate in the natural environment. Additionally, the early chain-breaking during the extrusion and mixing stage can cause fluctuations in melt viscosity, affecting continuous blown film production.

[0007] To address the above problems, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a cellulose-based controllable degradable agricultural mulch film, employing the following technical solution:

[0009] A cellulose-based controlled-degradable agricultural mulch film, made from raw materials comprising the following parts by weight:

[0010] Acidic composite powder: 19.7–31.8 parts;

[0011] Premixed polyester granules: 65.29–72.88 parts;

[0012] Epoxidized soybean oil: 4.0–8.0 parts;

[0013] The acidic composite powder is dispersed in the polyester phase provided by the premixed polyester particles, and is used to release acidic components and promote the hydrolytic degradation of the polyester phase after moisture enters; the premixed polyester particles are used to provide polyester melt support during melt processing and to regulate the hydrolysis resistance of the polyester phase; the epoxidized soybean oil is used to undergo a ring-opening addition reaction with the terminal carboxyl groups in the polyester phase to form a hydrophobic closed structure.

[0014] By adopting the above technical solution, the present invention achieves the following beneficial effects by controlling the early structural stability and later chain breaking process of the thin film through the synergistic reaction between raw materials:

[0015] During the mixing and melt processing stage, premixed polyester granules are heated and melted to form a continuous polyester matrix, with acidic composite powder dispersed within it. As processing progresses and subsequent film formation occurs, the epoxy groups in the epoxidized soybean oil undergo ring-opening addition reactions with the carboxyl groups at the ends of the polyester molecular chains, transforming the originally hydrophilic terminal carboxyl groups and allowing long-chain fatty acid structures to attach to the molecular ends, forming a hydrophobic closed structure inside and outside the film. In the initial stage of actual use, this hydrophobic structure delays the penetration of external moisture into the film, reducing the probability of early depolymerization and breakage due to excessive water absorption, and helping to maintain physical support during the covering period. In the middle and later stages of film use, environmental moisture slowly penetrates and comes into contact with the acidic composite powder through long-term exposure. The acidic composite powder releases acidic components and lowers the pH value of the surrounding environment, thereby producing acid-catalyzed hydrolysis of the ester bonds on the polyester backbone, causing the long chains to gradually depolymerize and break, shortening the natural retention period of film residues. Through the initial hydrophobic sealing between the components and the subsequent release of acidic components, a staged regulation of the polyester chain breaking rate is achieved.

[0016] Preferably, it is made from raw materials comprising the following parts by weight:

[0017] The acidic composite powder: 25.75 parts;

[0018] The premixed polyester granules: 69.08 parts;

[0019] The epoxidized soybean oil: 6.0 parts.

[0020] By adopting the above technical solution, the number of hydrophobic reactive groups inside the film is matched with the potential for acidic substance release under the above ratio. The epoxy groups provided by 6.0 parts of epoxidized soybean oil are used to consume the excess terminal carboxyl groups in the polyester matrix and reduce the outward migration and diffusion of free oil components; at the same time, 25.75 parts of acidic composite powder release acidic components after moisture intrusion in the later stage to promote the main chain breakage, and at this dosage, it is not easy to cause obvious unintended degradation during early processing and melting.

[0021] Preferably, the acidic composite powder is made from components comprising the following parts by weight:

[0022] Microcrystalline cellulose: 15.0–23.0 parts, alkali lignin: 3.0–5.0 parts, anhydrous citric acid: 1.5–3.0 parts, sodium phytate: 0.2–0.8 parts;

[0023] The premixed polyester granules are made from the following components in parts by weight: dicumyl peroxide: 0.04-0.08 parts, triallyl isocyanurate: 0.15-0.45 parts, polycarbodiimide: 0.10-0.35 parts, and polybutylene terephthalate-adipate: 65.0-72.0 parts.

[0024] By employing the above technical solution, microcrystalline cellulose and alkali lignin serve as the basic matrix to support anhydrous citric acid and sodium phytate. Anhydrous citric acid dissociates upon contact with water, providing hydrogen ions as the primary acid release source, while sodium phytate assists in regulating the dissociation and release rhythm of hydrogen ions. Microcrystalline cellulose provides the necessary physical framework for the powder. Alkali lignin, with its macromolecular properties, helps improve the dispersion of the acidic composite powder in the polyester phase, corresponding to a higher basic respiration rate and shorter fragmentation time under subsequent soil contact conditions. Dicumyl peroxide, upon thermal cracking, releases free radicals that abstract hydrogen atoms from the polybutylene terephthalate (PET) molecular chain to form macromolecular active centers. These centers then combine with triallyl isocyanurate containing double bonds to undergo moderate branching crosslinking, thereby compensating for the decrease in melt carrying capacity caused by processing degradation. The polycarbodiimide in the formulation reacts with the terminal carboxyl groups and acidic active groups generated during processing through the carbodiimide functional group, reducing the catalytic hydrolysis effect of acidic components on the polyester backbone in the early stage of processing, so that the resulting film can take into account both the rheological properties of film formation and the controllability of the life cycle.

[0025] Preferably, the preparation method of the acidic composite powder includes the following steps:

[0026] (1) The microcrystalline cellulose and the alkali lignin are put into a mixer with a sealed cover, and nitrogen gas with a purity of 99.9% at a pressure of 0.02 to 0.05 MPa is introduced into the mixer for purging for 1 to 3 minutes to obtain deoxygenated mixed powder.

[0027] (2) Add the anhydrous citric acid and the sodium phytate to the deoxygenated mixed powder, and under the condition of continuous introduction of nitrogen gas with a purity of 99.9% at 0.02-0.05 MPa, set the rotation speed to 300-500 r / min and stir continuously for 3-5 min to obtain the primary premixed powder;

[0028] (3) Increase the speed of the mixer containing the primary premixed powder to 1000-1500 r / min and continue stirring for 7-10 min to obtain the acidic composite powder.

[0029] By employing the above technical solution, nitrogen purging removes oxygen and moisture from the gaps between the mixed materials, preventing anhydrous citric acid from agglomerating due to moisture absorption to some extent. Initial mixing at low speeds allows the acid-releasing components to adhere to the matrix surface. As the speed increases to high speeds, the shear force and frictional heat applied by the equipment promote the dispersion of anhydrous citric acid and sodium phytate in microcrystalline cellulose and alkali lignin. This mixing process helps improve the uniformity of acidic component distribution in the powder, reducing the occurrence of premature water absorption or chain breakage in the early stages of film use due to localized enrichment of acidic particles.

[0030] Preferably, the method for preparing the premixed polyester granules includes the following steps:

[0031] (1) The dicumyl peroxide, the triallyl isocyanurate and the polycarbodiimide are put into a stirring tank, the rotation speed is set to 50-100 r / min, the ambient temperature is set to 20-25℃, and the stirring is continued for 1-3 min to obtain the mixed additive;

[0032] (2) Add the polybutylene terephthalate-adipate to the mixing vessel containing the mixing additive, maintain the ambient temperature at 20-25°C, set the stirring speed at 50-100 r / min, and continue stirring for 5-8 min to obtain the premixed polyester particles.

[0033] By adopting the above technical solution, the room-temperature multi-stage mixing of additives avoids the early failure of heat-sensitive components. The initiator, crosslinking agent, and anti-hydrolysis component are mixed at room temperature first, allowing trace amounts of liquid and powder additives to reach a premixed state before being incorporated into the main polyester particles. Maintaining a room-temperature environment inhibits the early decomposition of dicumyl peroxide and the premature reaction of polycarbodiimide. Through stepwise dispersion, the additives and polyester particles are fully premixed, ensuring that the chemical reactions in each region tend to be balanced when the material is heated and extruded, thus helping to maintain the uniformity of the melt rheological state.

[0034] Secondly, the present invention provides a method for preparing a cellulose-based controllable degradable agricultural mulch film, which adopts the following technical solution:

[0035] A method for preparing a cellulose-based controllable degradable agricultural mulch film includes the following steps:

[0036] S1: The acidic composite powder and 50% of the total weight of the premixed polyester particles are added together to the main feed port of a co-rotating twin-screw extruder for melt mixing to obtain activated material;

[0037] S2: The remaining 50% of the total weight of the premixed polyester granules is added through the side feed port of the co-rotating twin-screw extruder and mixed with the activated material to obtain a controlled melt;

[0038] S3: Inject the epoxidized soybean oil into the controlled melt to complete the hydrophobic sealing reaction and obtain the sealed melt;

[0039] S4: The closed melt is subjected to vacuum degassing, extrusion pelletizing and drying to obtain modified masterbatch;

[0040] S5: The modified masterbatch obtained in step S4 is blown into film and then wound up to obtain the agricultural mulch film.

[0041] By adopting the above technical solution, this preparation method mainly uses multi-stage feeding and stepped melt temperature control for material compounding. The acidic composite powder and the first part of premixed polyester granules are mixed and heated first. Relying on the shearing action provided within the twin-screw extruder barrel, the powdery components are gradually dispersed in the polyester phase, resulting in a pre-dispersed activated material. As the material is conveyed forward, the remaining premixed polyester granules are added through the side feed port. This operation replenishes the polyester components with a shorter thermal shear history and promotes a moderate branching reaction under the action of the initiator and triallyl isocyanurate, thereby partially compensating for the chain breakage loss caused by the heating of the macromolecular chains in the early stage. In the later stage of extrusion, epoxidized soybean oil is injected in liquid form and penetrates into the melt, undergoing a ring-opening addition reaction to convert some terminal carboxyl groups. The segmented feeding method disperses the heating process of easily degradable materials, avoids the pre-processing hydrolysis that is easily caused by one-time long-term mixing of acidic powder and all resin, reduces the tendency for melt viscosity fluctuations due to early chain breakage, maintains the processing stability of the final melt to a certain extent, and facilitates continuous blown film formation.

[0042] Preferably, in step S1, the temperature of the melt mixing is 145–155°C;

[0043] In step S2, the temperature at which the activated material is blended with the remaining 50% of the total weight of the premixed polyester particles is 165–175°C.

[0044] By adopting the above technical solution, the lower initial mixing temperature at the main feed inlet keeps some polyester in a moderately molten state to support the powder. The lower heat input helps to slow down the premature release of acidic substances and suppress the initial tendency of autocatalytic degradation. When entering the later blending zone, by increasing the barrel temperature, the plasticizing endothermic requirements of the newly mixed polyester particles are met, and the necessary heat energy is also provided for the reaction of peroxide cracking to generate free radicals and polycarbodiimide. This method of controlling the temperature difference between the front and back stages allows the chemical reactions at different stages to be activated in the corresponding temperature ranges, and the final melt rheological state is closer to the conditions required for blown film forming.

[0045] Preferably, in step S3, the epoxidized soybean oil is injected into the controlled melt via a liquid metering pump, the pumping pressure of the liquid metering pump is 0.50 to 1.0 MPa, and the set barrel temperature of the hydrophobic closed reaction is 160 to 165°C.

[0046] By employing the above technical solution, the presence of melt back pressure inside the barrel allows for pressure injection using a metering pump, enabling epoxidized soybean oil to penetrate the high-viscosity polyester matrix more effectively. Combined with a localized barrel temperature of 160–165°C, the epoxy groups obtain the activation conditions required for ring-opening addition, thus reacting with the terminal carboxyl groups. This results in less free oil components remaining on the material surface, reducing the likelihood of membrane tube slippage or oil precipitation during subsequent blown film stages.

[0047] Preferably, in step S4, the vacuum degree of the vacuum exhaust is set to -0.095MPa to -0.08MPa, the drying is carried out in a fluidized bed drying chamber, the drying temperature is 60 to 70°C, and the moisture content of the modified masterbatch is 200 to 450ppm.

[0048] By adopting the above technical solution, the negative pressure suction during the extrusion process is mainly used to remove small molecule volatiles and free moisture generated in the early heating reaction. After pelleting, the material is dried in a fluidized bed of hot air, allowing the moisture on the particle surface to be removed relatively evenly. Controlling the final moisture content of the modified masterbatch within the range of 200–450 ppm is mainly to reduce the risk of excessive residual water inducing polyester chain breakage during secondary heating and blown film production, which helps to maintain the stability of the film's appearance quality.

[0049] Preferably, in step S5, the set die temperature of the blown film is 150-155°C, and the blow-up ratio of the blown film is 2.0-2.5.

[0050] By adopting the above technical solution, the die temperature set during blown film forming is adapted to the actual melt flowability of the modified masterbatch, which helps maintain the uniformity of film thickness during extrusion and reduces the occurrence of film bubble instability and skewing. By controlling the blow-up ratio at 2.0 to 2.5, the polymer chains are moderately stretched in the radial and traction directions, resulting in oriented alignment. This structural change improves the physical strength required for the film during actual laying to a certain extent.

[0051] This invention provides a cellulose-based controllable degradable agricultural mulch film and its preparation method. It has the following beneficial effects:

[0052] 1. The epoxy groups in epoxidized soybean oil undergo ring-opening addition with the terminal carboxyl groups of the polyester, incorporating the long-chain fatty acid structure into the material. This molecular-level transformation, along with the reaction of the anti-hydrolysis components with the terminal carboxyl groups and acidic active groups, forms a closed structure with hydrophobic characteristics within the matrix. For materials containing cellulose-based components, the rate of inward penetration of external moisture is thus restrained, inhibiting to some extent the unintended depolymerization of agricultural mulch film in the early stages of installation. This maintains the physical support required during the mulching period while also providing a necessary time window for the material to enter the controlled degradation stage later.

[0053] 2. Through the physical framework constructed by microcrystalline cellulose, anhydrous citric acid undergoes slow dissociation after absorbing environmental moisture over a long period. The released hydrogen ions then act as a catalyst, producing an acid-catalyzed hydrolysis effect on the ester bonds within the continuous phase, promoting the depolymerization and breakage of long polymer chains. This embedded catalytic chain-splitting mechanism provides an internal promoting factor for the decomposition of discarded agricultural mulch film in the soil, improving the relatively slow natural decomposition of ordinary ester macromolecules. This allows the residual fragments containing cellulose-based components to exhibit a controllable degradation trend, helping to shorten the environmental retention time of polymer residues.

[0054] 3. In the melt extrusion stage, stepped temperature control and multi-stage side-feeding processes pre-disperse the heat-sensitive acid-releasing powder and some of the resin. Through staggered melting, supplemented by a moderate branching reaction generated by a crosslinking agent, the chain breakage damage to polyester macromolecules caused by processing heat is partially repaired. The segmented compounding operation disperses the high-heat and shear processes experienced by the internal components, reducing the probability of rapid hydrolysis of cellulose-based active materials induced in the barrel. The uniformity of the melt rheological state is thus maintained, which not only meets the operational requirements of continuous blown agricultural mulch film production but also provides a processing foundation for the stable performance of its controllable degradation properties. Attached Figure Description

[0055] Figure 1 This is a flowchart of the preparation method of the cellulose-based controllable degradable agricultural mulch film of the present invention. Detailed Implementation

[0056] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] The main raw materials and reagents used in the following preparation examples, examples, comparative examples and test examples are as follows. Unless otherwise specified, all reagents are commercially available analytical grade or higher grade products.

[0058] Polybutylene terephthalate (PET), CAS No. 55231-08-8, is a random copolyester copolymerized from terephthalic acid, adipic acid, and 1,4-butanediol. The repeating units are arranged randomly. The weight-average molecular weight is 90,000 to 130,000, the melt flow rate is 3.0 g / 10 min to 5.0 g / 10 min (under test conditions of 190 °C and 2.16 kg), and the density is 1.20 g / cm³. 3 Up to 1.26 g / cm 3 .

[0059] Microcrystalline cellulose, CAS number 9004-34-6, has an average particle size distribution between 40 μm and 60 μm.

[0060] Alkali lignin, CAS No. 8068-05-1, weight average molecular weight of 5000 to 10000, ash content greater than 0 wt% and less than or equal to 2.0 wt%.

[0061] Anhydrous citric acid, CAS number 77-92-9. Sodium phytate, CAS number 14306-25-3.

[0062] Polycarbodiimide contains N=C=N functional groups, is a brown powder, and has a softening point of 70°C to 80°C.

[0063] Epoxidized soybean oil, CAS number 8013-07-8, with an epoxy value of 6.0% to 7.5%.

[0064] Dicumyl peroxide, CAS number 80-43-3.

[0065] Triallyl isocyanurate, CAS number 1025-15-6.

[0066] Preparation Example 1:

[0067] This preparation example provides a method for preparing acidic composite powder, including the following steps:

[0068] Step 1: Add 19.0 parts by weight of microcrystalline cellulose and 4.0 parts by weight of alkali lignin into a mixer with a sealed lid. Purge the mixer with nitrogen gas of 99.9% purity at a pressure of 0.035 MPa for 2 minutes to obtain deoxygenated mixed powder.

[0069] Step 2: Add 2.25 parts by weight of anhydrous citric acid and 0.50 parts by weight of sodium phytate to the deoxygenated mixed powder obtained in Step 1. Under the condition of continuous introduction of nitrogen gas with a purity of 99.9% at 0.035 MPa, turn on the stirring function, set the speed to 400 r / min, and stir continuously for 4 min to obtain the primary premixed powder.

[0070] Step 3: Increase the speed of the mixer containing the primary premixed powder obtained in Step 2 to 1250 r / min, continue stirring for 8 minutes, stop the machine and discharge the material to obtain acidic composite powder.

[0071] Preparation Example 2:

[0072] This preparation example provides a method for preparing acidic composite powder, including the following steps:

[0073] Step 1: Add 15.0 parts by weight of microcrystalline cellulose and 3.0 parts by weight of alkali lignin into a mixer with a sealed lid. Purge the mixer with nitrogen gas of 99.9% purity at a pressure of 0.02 MPa for 1 minute to obtain deoxygenated mixed powder.

[0074] Step 2: Add 1.5 parts by weight of anhydrous citric acid and 0.20 parts by weight of sodium phytate to the deoxygenated mixed powder obtained in Step 1. Under the condition of continuous introduction of nitrogen gas with a purity of 99.9% at 0.02 MPa, turn on the stirring function, set the speed to 300 r / min, and stir continuously for 3 min to obtain the primary premixed powder.

[0075] Step 3: Increase the speed of the mixer containing the primary premixed powder obtained in Step 2 to 1000 r / min, continue stirring for 7 minutes, stop the machine and discharge the material to obtain acidic composite powder.

[0076] Preparation Example 3:

[0077] This preparation example provides a method for preparing acidic composite powder, including the following steps:

[0078] Step 1: Add 23.0 parts by weight of microcrystalline cellulose and 5.0 parts by weight of alkali lignin into a mixer with a sealed lid. Purge the mixer with nitrogen gas of 99.9% purity at a pressure of 0.05 MPa for 3 minutes to obtain deoxygenated mixed powder.

[0079] Step 2: Add 3.0 parts by weight of anhydrous citric acid and 0.80 parts by weight of sodium phytate to the deoxygenated mixed powder obtained in Step 1. Under the condition of continuous introduction of nitrogen gas with a purity of 99.9% at 0.05 MPa, turn on the stirring function, set the speed to 500 r / min, and stir continuously for 5 min to obtain the primary premixed powder.

[0080] Step 3: Increase the speed of the mixer containing the primary premixed powder obtained in Step 2 to 1500 r / min, continue stirring for 10 min, stop the machine and discharge the material to obtain acidic composite powder.

[0081] Preparation Example 4:

[0082] This preparation example provides a method for preparing premixed polyester pellets, including the following steps:

[0083] Step 1: Add 0.06 parts by weight of dicumyl peroxide, 0.30 parts by weight of triallyl isocyanurate and 0.22 parts by weight of polycarbodiimide into a stirred tank, turn on the stirring function, set the speed to 75 r / min, set the ambient temperature to 22℃, and stir continuously for 2 minutes to obtain the mixed additive.

[0084] Step 2: Add 68.5 parts by weight of polybutylene terephthalate-adipate to the mixing vessel containing the mixed additives obtained in Step 1, maintain the ambient temperature at 22°C, set the stirring speed to 75 r / min, continue stirring for 6 min, stop the machine and discharge the material to obtain premixed polyester granules.

[0085] Preparation Example 5:

[0086] This preparation example provides a method for preparing premixed polyester pellets, including the following steps:

[0087] Step 1: Add 0.04 parts by weight of dicumyl peroxide, 0.15 parts by weight of triallyl isocyanurate and 0.10 parts by weight of polycarbodiimide into a stirred tank, turn on the stirring function, set the speed to 50 r / min, set the ambient temperature to 20℃, and stir continuously for 1 min to obtain the mixed additive.

[0088] Step 2: Add 65.0 parts by weight of polybutylene terephthalate adipate to the mixing vessel containing the mixed additives obtained in Step 1, maintain the ambient temperature at 20°C, set the stirring speed to 50 r / min, continue stirring for 5 min, stop the machine and discharge the material to obtain premixed polyester granules.

[0089] Preparation Example 6:

[0090] This preparation example provides a method for preparing premixed polyester pellets, including the following steps:

[0091] Step 1: Add 0.08 parts by weight of dicumyl peroxide, 0.45 parts by weight of triallyl isocyanurate and 0.35 parts by weight of polycarbodiimide into a stirred tank, turn on the stirring function, set the speed to 100 r / min, set the ambient temperature to 25℃, and stir continuously for 3 minutes to obtain the mixed additive.

[0092] Step 2: Add 72.0 parts by weight of polybutylene terephthalate-adipate to the mixing vessel containing the mixed additives obtained in Step 1, maintain the ambient temperature at 25°C, set the stirring speed to 100 r / min, and continue stirring for 8 minutes. Then stop the machine and discharge the material to obtain premixed polyester granules.

[0093] Reference Figure 1 Examples 1 to 3 below provide a method for preparing a cellulose-based controllable degradable agricultural mulch film. The preparation method includes the following steps: S1: adding acidic composite powder and a portion of premixed polyester particles together and performing melt mixing and activation; S2: adding the remaining premixed polyester particles and extruding and controlling; S3: injecting epoxidized soybean oil and extruding and sealing; S4: vacuum degassing, pelletizing and drying; S5: blowing the modified masterbatch into film and winding it up.

[0094] Example 1:

[0095] This embodiment provides a method for preparing a cellulose-based controllable degradable agricultural mulch film, including the following steps:

[0096] S1: 25.75 parts by weight of acidic composite powder obtained in Preparation Example 1 and 34.54 parts by weight of premixed polyester granules obtained in Preparation Example 4 were fed into the main feed port of a co-rotating twin-screw extruder with an aspect ratio of 40. The materials were melt-mixed in the melt-mixing and dispersing section consisting of Zone 1 to Zone 3. The barrel temperature of this section was set to 150°C. The materials then passed through the high-shear kneading blocks arranged from the end of Zone 3 to the front of Zone 4. Under the support of the polyester melt, the acidic composite powder was dispersed in the polyester phase to obtain activated materials.

[0097] S2: The remaining 34.54 parts by weight of premixed polyester granules obtained in Preparation Example 4 are added through the first side feed port in Zone 4 and mixed with the activated material in step S1. The barrel temperature of Zone 4 is set to 170°C. The remaining premixed polyester granules are further melted and mixed with the activated material. The initiator decomposes to promote free radical bridging. At the same time, the anti-hydrolysis agent reacts with the terminal carboxyl groups and acidic active groups generated during processing and inhibits the catalytic hydrolysis of the polyester backbone by the acidic components, thus obtaining a controlled melt.

[0098] S3: 6.0 parts by weight of epoxidized soybean oil are injected into the controlled melt of step S2 through a liquid metering pump at a pumping pressure of 0.75 MPa via the second side feed port located in zone 5. The barrel temperature of zones 5 to 7 is set at 162°C. Zone 5 is used for the injection and initial dispersion of epoxidized soybean oil, zone 6 is used for continued mixing and promoting the ring-opening addition reaction of epoxy groups and the remaining terminal carboxyl groups, and zone 7 is used to complete the hydrophobic sealing reaction and transport the material to the front end of the vacuum exhaust port to obtain a sealed melt.

[0099] S4: Start the vacuum exhaust port set between the end of zone 7 and zone 8, and set the vacuum degree to -0.09MPa to remove small molecule water and volatiles generated in the reaction. Send the closed melt obtained in step S3 into the homogenization zone inside zone 8 for homogenization treatment, then extrude it through the die and perform water ring pelleting, and then send it into the fluidized bed dryer to dry at 65°C until the moisture content drops to 300ppm to obtain the modified masterbatch.

[0100] S5: Add the modified masterbatch obtained in step S4 into a single-screw blown film machine, set the die temperature to 152℃, adjust the air volume of the air ring to control the blowing ratio to 2.2, and after the film is pulled upward to cool and flatten, it is wound into a roll by a winding machine to obtain agricultural mulch film.

[0101] Example 2:

[0102] This embodiment provides a method for preparing a cellulose-based controllable degradable agricultural mulch film, including the following steps:

[0103] S1: 19.7 parts by weight of acidic composite powder obtained in Preparation Example 2 and 32.645 parts by weight of premixed polyester granules obtained in Preparation Example 5 were fed into the main feed port of a co-rotating twin-screw extruder with an aspect ratio of 36. The materials were melt-mixed in the melt-mixing and dispersing section consisting of Zone 1 to Zone 3. The barrel temperature of this section was set to 145°C. The materials then passed through the high-shear kneading blocks arranged from the end of Zone 3 to the front of Zone 4. Under the support of the polyester melt, the acidic composite powder was dispersed in the polyester phase to obtain activated materials.

[0104] S2: The remaining 32.645 parts by weight of premixed polyester granules obtained in Preparation Example 5 are added through the first side feed port in Zone 4 and mixed with the activated material in step S1. The barrel temperature of Zone 4 is set to 165°C. The remaining premixed polyester granules are further melted and mixed with the activated material. The initiator decomposes to promote free radical bridging. At the same time, the anti-hydrolysis agent reacts with the terminal carboxyl groups and acidic active groups generated during processing and inhibits the catalytic hydrolysis of the polyester backbone by the acidic components, thus obtaining a controlled melt.

[0105] S3: 4.0 parts by weight of epoxidized soybean oil are injected into the controlled melt of step S2 through a liquid metering pump at a pumping pressure of 0.50 MPa via the second side feed port located in zone 5. The barrel temperature of zones 5 to 7 is set at 160°C. Zone 5 is used for the injection and initial dispersion of epoxidized soybean oil, zone 6 is used for continued mixing and promoting the ring-opening addition reaction of epoxy groups and the remaining terminal carboxyl groups, and zone 7 is used to complete the hydrophobic sealing reaction and transport the material to the front end of the vacuum exhaust port to obtain a sealed melt.

[0106] S4: At the vacuum exhaust port set between the end of zone 7 and zone 8, the vacuum is turned on and the vacuum degree is set to -0.08MPa to remove small molecule water and volatiles generated in the reaction. The closed melt obtained in step S3 is sent to the homogenization zone inside zone 8 for homogenization treatment, then extruded through a die and granulated by water ring cutting. It is then sent to a fluidized bed dryer and dried at 60°C until the moisture content drops to 450ppm to obtain modified masterbatch.

[0107] S5: Add the modified masterbatch obtained in step S4 into a single-screw blown film machine, set the die temperature to 150℃, adjust the air volume of the air ring to control the blowing ratio to 2.0, and after the film is pulled upward to cool and flatten, it is wound into a roller by a winding machine to obtain agricultural mulch film.

[0108] Example 3:

[0109] This embodiment provides a method for preparing a cellulose-based controllable degradable agricultural mulch film, including the following steps:

[0110] S1: 31.8 parts by weight of acidic composite powder obtained in Preparation Example 3 and 36.44 parts by weight of premixed polyester granules obtained in Preparation Example 6 were fed into the main feed port of a co-rotating twin-screw extruder with an aspect ratio of 44. The materials were melt-mixed in the melt-mixing and dispersion section consisting of Zone 1 to Zone 3. The barrel temperature of this section was set to 155°C. The materials then passed through the high-shear kneading blocks arranged from the end of Zone 3 to the front of Zone 4. Under the support of the polyester melt, the acidic composite powder was dispersed in the polyester phase to obtain activated materials.

[0111] S2: The remaining 36.44 parts by weight of premixed polyester granules obtained in Preparation Example 6 are added through the first side feed port in Zone 4 and mixed with the activated material in step S1. The barrel temperature of Zone 4 is set to 175°C. The remaining premixed polyester granules are further melted and mixed with the activated material. The initiator decomposes to promote free radical bridging. At the same time, the anti-hydrolysis agent reacts with the terminal carboxyl groups and acidic active groups generated during processing and inhibits the catalytic hydrolysis of the polyester backbone by the acidic components, thus obtaining a controlled melt.

[0112] S3: 8.0 parts by weight of epoxidized soybean oil are injected into the controlled melt of step S2 through a liquid metering pump at a pumping pressure of 1.0 MPa via the second side feed port located in zone 5. The barrel temperature of zones 5 to 7 is set at 165°C. Zone 5 is used for the injection and initial dispersion of epoxidized soybean oil, zone 6 is used for continued mixing and promoting the ring-opening addition reaction of epoxy groups and the remaining terminal carboxyl groups, and zone 7 is used to complete the hydrophobic sealing reaction and transport the material to the front end of the vacuum exhaust port to obtain a sealed melt.

[0113] S4: Start the vacuum exhaust port set between the end of zone 7 and zone 8, and set the vacuum degree to -0.095MPa to remove small molecule water and volatiles generated in the reaction. Send the closed melt obtained in step S3 into the homogenization zone inside zone 8 for homogenization treatment, then extrude it through the die and perform water ring pelleting, and then send it into the fluidized bed dryer to dry at 70°C until the moisture content drops to 200ppm to obtain the modified masterbatch.

[0114] S5: Add the modified masterbatch obtained in step S4 into a single-screw blown film machine, set the die temperature to 155℃, adjust the air volume of the air ring to control the blowing ratio to 2.5, and after the film is pulled upward to cool and flatten, it is wound into a roll by a winding machine to obtain agricultural mulch film.

[0115] In a preferred embodiment, the co-rotating twin-screw extruder of Examples 1 to 3 has a length-to-diameter ratio of 36 to 44, and is sequentially provided with a main feed inlet, a first zone, a second zone, a third zone, a fourth zone, a fifth zone, a sixth zone, a seventh zone, an eighth zone, and a die head along the material conveying direction; the main feed inlet is located in the first zone; zones 1 to 3 constitute a melt mixing and dispersion section; a strong shear kneading block is arranged from the end of the third zone to the front of the fourth zone; a first side feed inlet is located in the fourth zone; a second side feed inlet is located in the fifth zone; zones 5 to 7 constitute a liquid additive dispersion and hydrophobic sealing reaction section, wherein the fifth zone is used for the injection and initial dispersion of epoxidized soybean oil, the sixth zone is used for continued mixing and ring-opening addition reaction, and the seventh zone is used for sealing the post-reaction conveying and melt stabilization before vacuum exhaust; a vacuum exhaust port is provided between the end of the seventh zone and the eighth zone; the interior of the eighth zone is a homogenization zone.

[0116] In a preferred embodiment, in Examples 1 to 3 above, the average particle size of the modified masterbatch obtained after water ring pelleting in step S4 is 2.0 mm to 4.0 mm.

[0117] Comparative Example 1:

[0118] Compared with Example 1, the difference is that in step two of preparation Example 1, 2.25 parts by weight of anhydrous citric acid and 0.50 parts by weight of sodium phytate were not added, and the amount of microcrystalline cellulose added was adjusted from 19.0 parts by weight to 21.75 parts by weight; that is, the oxygen-deoxidizing mixed powder in step one was directly stirred under the same conditions until the end of step three, and the rest were the same.

[0119] Comparative Example 2:

[0120] Compared with Example 1, the difference is that step S2 and step S1 are combined. That is, instead of adding the remaining premixed polyester granules through the first side feed port, 69.08 parts by weight of premixed polyester granules and 25.75 parts by weight of acidic composite powder are premixed and then added all at once through the main feed port of the co-rotating twin-screw extruder. The rest are the same.

[0121] Comparative Example 3:

[0122] Compared with Example 1, the difference is that 0.22 parts by weight of polycarbodiimide was not added in step one of preparation Example 4, and the amount of polybutylene terephthalate added in step two of preparation Example 4 was adjusted from 68.5 parts by weight to 68.72 parts by weight, while the rest were the same.

[0123] Comparative Example 4:

[0124] Compared with Example 1, the difference is that the injection of epoxidized soybean oil and the hydrophobic sealing reaction operation in step S3 were not performed, that is, epoxidized soybean oil was not injected into the controlled melt through the second side feed port; at the same time, the amount of polybutylene terephthalate added in step two of Preparation Example 4 was adjusted from 68.5 parts by weight to 74.5 parts by weight, so that the total amount of premixed polyester particles in Comparative Example 4 was adjusted to 75.08 parts by weight; in step S1, 37.54 parts by weight of premixed polyester particles were fed together with the acidic composite powder, and in step S2, the remaining 37.54 parts by weight of premixed polyester particles were added through the first side feed port; the controlled melt was still conveyed backward according to the temperature conditions of zones 5 to 7 in Example 1, and the rest were the same.

[0125] Comparative Example 5:

[0126] Compared with Example 1, the difference is that 4.0 parts by weight of alkali lignin were not added in step one of preparation Example 1, and the amount of microcrystalline cellulose added was increased from 19.0 parts by weight to 23.0 parts by weight to make up the total amount, so that the acidic composite powder used in step S1 does not contain lignin components, and the rest are the same.

[0127] Test Example 1:

[0128] Experimental steps:

[0129] 1. Accurately weigh the acidic composite powders prepared according to Preparation Example 1, Preparation Example 2, and Preparation Example 3, respectively. Three parallel samples are set up for each preparation example, with 0.50 g weighed for each parallel sample. Divide the above acidic composite powders into three test groups, designated as Preparation Example 1 Group, Preparation Example 2 Group, and Preparation Example 3 Group, respectively. Place each parallel sample into a beaker containing 200 mL of neutral deionized water. The initial pH of the neutral deionized water is 7.02 ± 0.02, and the water temperature is controlled at 25.0 ± 0.5℃. Turn on the thermostatic magnetic stirrer and set the stirring speed to 150 r / min. Using a calibrated high-precision portable pH meter, continuous immersion tests were conducted on the water in the corresponding beakers for each parallel sample. The pH values ​​of the water were recorded at immersion times of 5 min, 15 min, 30 min, 60 min, 120 min, and 240 min. After each recording, the pH electrode was removed from the corresponding beaker, rinsed with deionized water, dried, and then the beaker was kept immersed under the same temperature and stirring conditions until the next test time point for recording. The arithmetic mean of the test results of three parallel samples at the same time point for each test group was used to evaluate the pH change of the acidic composite powder under water contact conditions.

[0130] 2. Accurately weigh the modified masterbatches prepared according to Examples 1, 2, 3, and Comparative Example 4. Three parallel samples are prepared for each example or comparative example, with each parallel sample weighing 20.00 g. Divide the modified masterbatches into four test groups, designated as Example 1 group, Example 2 group, Example 3 group, and Comparative Example 4 group. Dry each parallel sample in an 80℃ forced-air drying oven until constant weight, recording the mass after drying as the initial mass W0. Then, place each parallel sample in a constant-temperature water bath containing 500 mL of deionized water, maintaining the water temperature at 30.0 ± 0.5℃. On days 1, 3, 7, 14, 21, and 28, parallel samples of the same group were continuously removed and weighed. Each parallel sample was removed from its corresponding constant-temperature water bath, and the surface of the masterbatch was gently wiped with absorbent paper to remove any remaining free moisture. The immediate mass was then measured using a precision balance and recorded as Wt at the corresponding time point. Except for the sample weighed on day 28, which was not returned to the bath, the parallel samples were returned to the original constant-temperature water bath after weighing at each of the other time points to continue soaking until the next test time point. The mass water absorption rate at different time points was calculated using the formula: Mass Water Absorption Rate = (Wt - W0) / W0 × 100%. The arithmetic mean of the test results of three parallel samples at the same time point for each test group was used to evaluate the water absorption change of the modified masterbatch under water immersion conditions.

[0131] The experimental results are shown in Tables 1 and 2.

[0132] Table 1: Test data on pH changes in water during the soaking of acidic compound powder

[0133] Preparation Example 1 7.02 4.45 3.91 3.62 3.48 3.41 3.38 Preparation Example 2 7.01 4.88 4.35 4.08 3.92 3.86 3.84 Preparation Example 3 7.03 4.12 3.63 3.35 3.21 3.15 3.12

[0134] Table 2: Test data on water absorption rate of modified masterbatch at different soaking times (unit: %)

[0135] Example 1 0.12 0.35 0.78 1.65 3.42 6.18 Example 2 0.18 0.48 1.05 2.12 4.35 7.64 Example 3 0.08 0.22 0.54 1.18 2.64 4.95 Comparative Example 4 0.65 1.84 3.92 6.85 10.42 14.88

[0136] Test conclusion:

[0137] According to the data in Tables 1 and 2, the acidic composite powder can lower the pH value of water under water contact conditions. The modified masterbatches obtained in Examples 1 to 3 have a lower water absorption rate in the early stage of water immersion than Comparative Example 4. As can be observed from Table 1, in the early stage of deionized water immersion, i.e., from 0 min to 30 min, the pH value of the water corresponding to Preparation Group 1, Preparation Group 2, and Preparation Group 3 all decreased; in the period from 60 min to 240 min, the decrease in pH value decreased and gradually tended to stabilize, with the pH value at 240 min ranging from 3.12 to 3.84.

[0138] The above results indicate that the acidic composite powder, with anhydrous citric acid as the main acidic component and sodium phytate as the auxiliary regulating component, can release acidic components and regulate the pH value of water under water contact conditions. Among them, the pH value of preparation group 3 is lower than that of preparation groups 1 and 2, while the pH value of preparation group 2 is relatively higher. This order of change basically corresponds to the changes in the amount of anhydrous citric acid and sodium phytate added in each preparation example.

[0139] Meanwhile, as shown in Table 2, the water absorption rates of Comparative Example 4 were 0.65%, 1.84%, and 3.92% on days 1, 3, and 7, respectively, and 14.88% on day 28. The water absorption rates of Examples 1 to 3 ranged from 0.08% to 1.05% from day 1 to day 7, which was lower than that of Comparative Example 4 under the same soaking time. From day 14 to day 28, the water absorption rates of Examples 1 to 3 increased with prolonged soaking time, and the water absorption rate on day 28 ranged from 4.95% to 7.64%.

[0140] The above results indicate that after epoxidized soybean oil is involved in the extrusion sealing process, the water absorption of the modified masterbatch decreases in the early stage of water immersion; however, as the soaking time increases, the modified masterbatch still exhibits a gradual increase in water absorption. This characteristic corresponds to the design requirement of agricultural mulch film to maintain a low water absorption rate in the early stage and gradually allow water to enter in the later stage.

[0141] Test Example 2:

[0142] Experimental steps:

[0143] 1. Take 500g of each of the modified masterbatches prepared according to step S4 of Examples 1 to 3, Comparative Examples 2 and 3. Divide the modified masterbatches into five test groups, designated as Example 1 group, Example 2 group, Example 3 group, Comparative Example 2 group, and Comparative Example 3 group. Place the five test groups in a forced-air drying oven and dry at 80°C for 4 hours. After drying, take samples from each test group and test them using a melt flow rate meter; the test temperature is 190°C and the load is 2.16kg. Each test group is tested in parallel 5 times, and the test results are recorded and the arithmetic mean is calculated to evaluate the change in melt mass flow rate of different modified masterbatches.

[0144] 2. Take 30 kg of each of the modified masterbatches prepared according to step S4 of Examples 1 to 3, Comparative Examples 2 and 3. Divide the modified masterbatches into five test groups, denoted as the Example 1 blown film group, Example 2 blown film group, Example 3 blown film group, Comparative Example 2 blown film group, and Comparative Example 3 blown film group. Add the five test groups to a single-screw blown film machine and test them under the same blown film conditions. Set the die temperature to 152°C, the blow-up ratio to 2.2, and keep the other traction, cooling, and winding conditions consistent. During the continuous extrusion blown film process for 4 hours, record the die pressure fluctuation range, which is the difference between the maximum and minimum die pressure readings within 4 hours. At the same time, count the number of film bubble ruptures that occur within 4 hours. One film bubble rupture is counted when the film bubble becomes unstable and needs to be re-pulled and bubbled. After a film bubble rupture occurs, re-pulling and bubble formation are carried out, and the test continues until the cumulative test time reaches 4 hours. The above test is used to evaluate the continuous film formation stability of different test objects.

[0145] The experimental results are shown in Tables 3 and 4.

[0146] Table 3: Test data on melt mass flow rate of modified masterbatch

[0147] Example 1 Group 3.56 Example 2 group 4.14 Example 3 Group 3.21 Comparative Example 2 0.85 Comparative Example 3 Groups 7.58

[0148] Table 4: Stability test data of modified masterbatch in continuous blown film production

[0149] Example 1: Blown Film Assembly 0 0.32 Example 2: Blown Film Assembly 1 0.45 Example 3: Blown Film Assembly 0 0.38 Comparative Example 2: Blown Film Group 17 3.65 Comparative Example 3: Blown Film Group 7 1.16

[0150] Test conclusion:

[0151] According to the data in Tables 3 and 4, the segmented feeding method and the addition of polycarbodiimide correspond to the changes in melt flow rate and continuous blown film stability of the modified masterbatch. Table 3 shows that the melt flow rate of the modified masterbatch obtained in Examples 1 to 3 ranges from 3.21 g / 10 min to 4.14 g / 10 min, which is close to the melt flow rate range of the polybutylene terephthalate (PET) raw material used. Comparative Example 2 did not use a segmented feeding method; instead, the premixed polyester granules and acidic composite powder were premixed and added all at once through the main feed port. Its melt flow rate was 0.85 g / 10 min, lower than that of Examples 1 to 3. Comparative Example 3 did not add polycarbodiimide, and its melt flow rate was 7.58 g / 10 min, higher than that of Examples 1 to 3.

[0152] The above results show that the segmented feeding method and the addition of polycarbodiimide are beneficial to keeping the melt mass flow rate of the modified masterbatch within a relatively stable range.

[0153] Based on the data in Table 4, during the continuous 4-hour blown film test, the number of film bubble ruptures in the blown film groups of Examples 1 to 3 ranged from 0 to 1, and the die pressure fluctuation ranged from 0.32 MPa to 0.45 MPa, indicating a relatively stable continuous blown film process. In Comparative Example 2, the number of film bubble ruptures was 17, and the die pressure fluctuation range was 3.65 MPa; in Comparative Example 3, the number of film bubble ruptures was 7, and the die pressure fluctuation range was 1.16 MPa, both higher than those in Examples 1 to 3.

[0154] The above test data show that the segmented feeding method and polycarbodiimide addition method used in Examples 1 to 3 correspond to a lower number of film bubble ruptures and a smaller range of die pressure fluctuations; the test results of Comparative Examples 2 and 3 show that the continuous blown film stability of their modified masterbatch decreased under the same blown film conditions.

[0155] Test Example 3:

[0156] Experimental steps:

[0157] 1. Agricultural mulch films prepared according to the methods of Examples 1 to 3, Comparative Examples 3 and 4 were cut into circular test samples that could cover the opening of PVC cylindrical soil column containers. The test samples of each group were of the same size. The above films were divided into five groups of test objects, which were designated as the Example 1 mulch film group, Example 2 mulch film group, Example 3 mulch film group, Comparative Example 3 mulch film group and Comparative Example 4 mulch film group. PVC cylindrical soil column containers of the same specifications were prepared, with an inner diameter of 20 cm and a height of 30 cm. Three parallel soil column containers were set up for each group of test objects. 4.0 kg of dried homogeneous soil from a dryland corn experimental field was weighed, and 1.0 kg of deionized water was added in several sprays and mixed evenly to obtain moist soil with an initial moisture content of 1.0 kg; the initial moisture content, calculated as the proportion of the added water mass to the total mass of the moist soil, was 20.0%. The moist soil was then layered and filled into the corresponding PVC cylindrical soil column containers and compacted in layers to ensure that the filling and compaction conditions of each parallel soil column container were consistent.

[0158] 2. During the soil filling process of the aforementioned soil column containers, sensor mounting holes are pre-drilled on the side wall of each PVC cylindrical soil column container at a depth of 10cm below the soil surface. The probe of a high-precision soil temperature sensor is horizontally inserted into the soil column container through the mounting hole, ensuring the probe is 10cm below the soil surface. The sensor wire is led out through the mounting hole, and the mounting hole is sealed with sealant. Test samples from the five test objects are placed on the surface of the corresponding soil column containers, and the edges are sealed with rubber rings. All soil column containers are placed in an artificial climate chamber, with a daytime temperature of 25℃, a nighttime temperature of 15℃, and a light cycle of 12h / 12h. The total mass of each soil column container at the start of the experiment is recorded as the initial total mass of the soil column containers. On the 10th, 20th, 30th, and 40th days after the start of the experiment, the same batch of soil column containers is weighed as a whole, and the total mass of the soil column containers at the corresponding time point is recorded. After each weighing, the corresponding soil column containers are returned to the artificial climate chamber to continue the experiment until the next test time point. Soil moisture loss rate was calculated using the formula: Soil moisture loss rate = (Total mass of initial soil column container - Total mass of soil column container at test time point) / 1.0 kg × 100%. The arithmetic mean of the test results of 3 parallel soil column containers was taken for each test object.

[0159] 3. Starting from the 30th day after the start of the experiment, the soil temperature data at a depth of 10cm inside each soil column container was continuously recorded for 5 days using the aforementioned high-precision soil temperature sensor, with the recording period ending at the corresponding time on the 35th day. The recording interval was 1 hour. The arithmetic mean of all temperature data obtained for each soil column container within the 5-day recording period was calculated to obtain the average soil temperature corresponding to that soil column container. The difference between the highest and lowest soil temperatures recorded for each soil column container each day was calculated to obtain the daily temperature difference, and the arithmetic mean of the daily temperature differences over 5 days was calculated to obtain the average daily temperature difference corresponding to that soil column container. The arithmetic mean of the test results of 3 parallel soil column containers for each test object was used to evaluate the soil temperature changes under different cover conditions for different test objects.

[0160] The experimental results are shown in Tables 5 and 6.

[0161] Table 5: Soil water loss rate test data under different mulch film covering conditions (unit: %)

[0162] Example 1: Mulch Film Group 3.12 7.45 11.23 14.86 Example 2: Mulch Film Group 4.05 8.21 12.64 16.32 Example 3: Mulch Film Group 2.87 6.18 9.77 13.54 Comparative Example 3: Mulch Film Group 8.64 17.52 26.83 35.14 Comparative Example 4: Mulch Film Group 6.71 14.36 21.45 28.97

[0163] Table 6: Soil temperature test data under different plastic film mulching conditions (test period: 5 consecutive days starting from day 30)

[0164] Example 1: Mulch Film Group 21.6 3.4 Example 2: Mulch Film Group 21.2 3.7 Example 3: Mulch Film Group 22.1 3.1 Comparative Example 3: Mulch Film Group 17.8 6.8 Comparative Example 4: Mulch Film Group 18.5 5.9

[0165] Test conclusion:

[0166] According to the data in Table 5, the soil moisture loss rates of the mulch film groups in Examples 1 to 3 from day 10 to day 40 were all lower than those in Comparative Example 3 and Comparative Example 4. Specifically, the soil moisture loss rates of the mulch film groups in Examples 1 to 3 on day 40 ranged from 13.54% to 16.32%; while the soil moisture loss rates of the mulch film groups in Comparative Example 3 and Comparative Example 4 on day 40 were 35.14% and 28.97%, respectively.

[0167] The above results indicate that, under the same test conditions, the soil column corresponding to the agricultural mulch film obtained in Examples 1 to 3 had a lower water loss rate after covering. The test results of the mulch film group in Comparative Example 3 correspond to its preparation conditions without the addition of polycarbodiimide; the test results of the mulch film group in Comparative Example 4 correspond to its preparation conditions without epoxidized soybean oil hydrophobic sealing treatment.

[0168] According to the data in Table 6, the average soil temperature of the mulch film groups in Examples 1 to 3 ranged from 21.2℃ to 22.1℃ during the test period, and the average daily temperature difference ranged from 3.1℃ to 3.7℃. The average soil temperatures of the mulch film groups in Comparative Example 3 and Comparative Example 4 were 17.8℃ and 18.5℃, respectively, and the average daily temperature differences were 6.8℃ and 5.9℃, respectively.

[0169] The above results indicate that, under the same artificial climate chamber test conditions, the average soil temperature and average daily temperature difference after agricultural mulch film covering in Examples 1 to 3 were higher. Combined with the data in Tables 5 and 6, the hydrophobic sealing treatment with epoxidized soybean oil and the addition of polycarbodiimide correspond to the lower soil moisture loss rate, higher average soil temperature, and smaller average daily temperature difference after agricultural mulch film covering.

[0170] Test Example 4:

[0171] Experimental steps:

[0172] 1. Agricultural mulch films prepared according to Examples 1 to 3, Comparative Examples 1 and 5 were selected. Comparative Example 2 had a high number of film bubble ruptures during continuous film blowing, making it difficult to consistently obtain test samples that met the dimensional integrity requirements of this test; therefore, it was not included in this test. The above five groups of agricultural mulch films were cut into 10cm × 10cm test samples, and the initial mass of each test sample was recorded. The test samples were divided into groups: Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 5. Fifteen parallel samples were prepared for each test subject, with three parallel samples each corresponding to day 30, day 60, day 90, day 120, and day 150. A test chamber containing soil from a dryland winter wheat experimental field was prepared, with the soil moisture content controlled at 25.0% and the temperature maintained at 25.0℃. The test samples of each group were buried horizontally 5cm below the soil surface. On days 30, 60, 90, 120, and 150 of the burial test, three parallel samples corresponding to each time point were collected. This sampling was destructive; the samples were not returned to the soil after collection. The collected test samples were rinsed with deionized water to remove surface soil, dried in a 40℃ vacuum drying oven for 24 hours, and then weighed. The residual mass was recorded. The residual mass percentage was calculated using the formula: Residual Mass Percentage = (Residual Mass / Initial Mass) × 100%. The arithmetic mean of the test results of three parallel samples at the same time point was taken for each test group.

[0173] 2. On day 120 of the soil burial experiment, during the removal of residual mass test samples on day 120, soil samples within a 1cm radius around three parallel samples from each test group were collected and mixed thoroughly to obtain the mixed soil sample for that group. Three 10g subsamples were weighed from each mixed soil sample group and placed in a sealed wide-mouth bottle. A small glass cup containing 10.0mL of 0.1mol / L sodium hydroxide absorbent solution was suspended inside the bottle. A blank control bottle without soil sample was also prepared. The wide-mouth bottles were placed in a 25℃ constant temperature incubator and incubated for 24 hours. After incubation, the small glass cup containing the absorbent solution was removed, excess barium chloride solution was added to precipitate carbonate ions, and then titrated with 0.1mol / L hydrochloric acid standard solution, using phenolphthalein as an indicator. The moisture content of another mixed soil sample from the same batch was determined, and the soil dry weight was calculated. The mass of carbon dioxide released by the soil during the closed incubation period was calculated by subtracting the volume of hydrochloric acid standard solution consumed by the blank control from that consumed by the soil subsample. This mass was then divided by the soil dry weight and incubation time to calculate the soil basal respiration rate, expressed in mgCO2 / (kg·h). In this step, the arithmetic mean of the test results of three parallel soil subsamples for each test group was taken.

[0174] 3. To reduce the impact of frequent soil disturbance on the aforementioned residual quality test, a separate test chamber was set up for observing the macroscopic fragmentation time. A test chamber containing soil from a winter wheat experimental field in a dryland area was prepared, with the soil moisture content controlled at 25.0% and the temperature maintained at 25.0℃. Test samples cut to 10cm × 10cm from Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 5 were horizontally buried 5cm below the soil surface. For each test subject, 25 parallel observation samples were buried in the observation chamber. Starting from 90 days after burial, one corresponding sample was randomly excavated from the observation chamber every 3 days for observation. During observation, the size of the membrane fragments was measured with a ruler. The sampled fragments were discarded and not returned to the soil. When a sample from a certain test subject showed macroscopic fragmentation, and the projected area of ​​all identifiable fragments in that sample was less than 2cm², the test was considered complete. 2 At that time, record the corresponding number of days of burial. For this group of test subjects, the plastic film should be broken to a thickness of <2cm. 2 Number of days required; if the test subject still does not meet the above-mentioned fracture judgment conditions when observed on the 150th day, it is recorded as >150 days.

[0175] The experimental results are shown in Tables 7 and 8.

[0176] Table 7: Test data on the percentage of residual plastic film mass in soil burial tests (unit: %)

[0177] Example 1 Group 98.2 95.1 68.4 31.5 8.2 Example 2 group 97.5 94.6 62.1 28.7 6.4 Example 3 Group 99.1 96.8 75.2 42.6 11.3 Comparative Example 1 98.1 94.3 86.7 76.4 68.5 Comparative Example 5 Groups 98.5 94.2 71.3 45.2 22.8

[0178] Table 8: Test data on the time of plastic film breakage and the basic respiration intensity of the surrounding soil

[0179] Example 1 Group 114 4.12 Example 2 group 108 4.56 Example 3 Group 123 3.85 Comparative Example 1 ＞150 1.85 Comparative Example 5 Groups 135 2.15

[0180] Test conclusion:

[0181] According to the data in Tables 7 and 8, the residual mass percentage of Examples 1 to 3 decreased with the extension of burial time, and the decrease was greater between day 90 and day 150; the decrease in the residual mass percentage of Comparative Example 1 was relatively smaller. As shown in Table 7, the residual mass percentage of Examples 1 to 3 was in the range of 97.5% to 99.1% on day 30, and in the range of 94.6% to 96.8% on day 60; between day 90 and day 120, the residual mass percentage decreased from the range of 62.1% to 75.2% to the range of 28.7% to 42.6%; and on day 150, the residual mass percentage was in the range of 6.4% to 11.3%. The residual mass percentage of Comparative Example 1 on day 150 was 68.5%, which was higher than that of Examples 1 to 3.

[0182] The above results indicate that the residual mass of the agricultural mulch film obtained in Examples 1 to 3 changed little in the early stage of soil burial, but the rate of decrease in residual mass increased in the middle and late stages. The residual mass percentage of Comparative Example 1, which did not contain anhydrous citric acid and sodium phytate, decreased more slowly during the test period, and was still higher than that of Examples 1 to 3 on day 150.

[0183] Based on the data in Table 8, the basal respiration intensity of the surrounding soil in Examples 1 to 3 was between 3.85 mg CO2 / (kg·h) and 4.56 mg CO2 / (kg·h) on day 120, and the mulch film was broken to a depth of <2 cm. 2 The required number of days ranged from 108 to 123 days. In the five comparative groups without added lignin, the basal respiration rate of the surrounding soil on day 120 was 2.15 mg CO2 / (kg·h), and the mulch film was broken to a depth of <2 cm. 2 The required number of days was 135 days, and the residual mass percentage on day 150 was 22.8%, which was higher than the residual mass percentage on day 150 for Examples 1 to 3.

[0184] The results above indicate that, under the test conditions, the addition of lignin components corresponds to higher basal respiration intensity of the surrounding soil, shorter mulch film breakage time, and lower residual mass percentage at day 150.

[0185] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these specific embodiments are for illustrative purposes only and should not be construed as limiting the scope of protection of the present invention. Without departing from the concept of the present invention, those skilled in the art can make appropriate adjustments, substitutions, combinations, or equivalent changes to the above-described types of raw materials, raw material ratios, process steps, process parameters, and testing conditions. All equivalent substitutions, conventional improvements, or modifications that do not substantially alter the technical effects of the present invention made based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A cellulose-based controllable biodegradable agricultural mulch film, characterized in that, Made from the following ingredients in parts by weight: Acidic composite powder: 19.7–31.8 parts; Premixed polyester granules: 65.29–72.88 parts; Epoxidized soybean oil: 4.0–8.0 parts; The acidic composite powder is dispersed in the polyester phase provided by the premixed polyester particles, and is used to release acidic components and promote the hydrolytic degradation of the polyester phase after moisture enters; the premixed polyester particles are used to provide polyester melt support during melt processing and to regulate the hydrolysis resistance of the polyester phase; the epoxidized soybean oil is used to undergo a ring-opening addition reaction with the terminal carboxyl groups in the polyester phase to form a hydrophobic closed structure.

2. The cellulose-based controllable degradable agricultural mulch film according to claim 1, characterized in that, Made from the following ingredients in parts by weight: The acidic composite powder: 25.75 parts; The premixed polyester granules: 69.08 parts; The epoxidized soybean oil: 6.0 parts.

3. The cellulose-based controllable degradable agricultural mulch film according to claim 1, characterized in that, The acidic composite powder is made from components comprising the following parts by weight: Microcrystalline cellulose: 15.0–23.0 parts, alkali lignin: 3.0–5.0 parts, anhydrous citric acid: 1.5–3.0 parts, sodium phytate: 0.2–0.8 parts; The premixed polyester granules are made from the following components in parts by weight: dicumyl peroxide: 0.04-0.08 parts, triallyl isocyanurate: 0.15-0.45 parts, polycarbodiimide: 0.10-0.35 parts, and polybutylene terephthalate-adipate: 65.0-72.0 parts.

4. The cellulose-based controllable degradable agricultural mulch film according to claim 3, characterized in that, The preparation method of the acidic composite powder includes the following steps: (1) The microcrystalline cellulose and the alkali lignin are put into a mixer with a sealed cover, and nitrogen gas with a purity of 99.9% at a pressure of 0.02 to 0.05 MPa is introduced into the mixer for purging for 1 to 3 minutes to obtain deoxygenated mixed powder. (2) Add the anhydrous citric acid and the sodium phytate to the deoxygenated mixed powder, and under the condition of continuous introduction of nitrogen gas with a purity of 99.9% at 0.02-0.05 MPa, set the rotation speed to 300-500 r / min and stir continuously for 3-5 min to obtain the primary premixed powder; (3) Increase the speed of the mixer containing the primary premixed powder to 1000-1500 r / min and continue stirring for 7-10 min to obtain the acidic composite powder.

5. The cellulose-based controllable degradable agricultural mulch film according to claim 3, characterized in that, The method for preparing the premixed polyester granules includes the following steps: (1) The dicumyl peroxide, the triallyl isocyanurate and the polycarbodiimide are put into a stirring tank, the rotation speed is set to 50-100 r / min, the ambient temperature is set to 20-25℃, and the stirring is continued for 1-3 min to obtain the mixed additive; (2) Add the polybutylene terephthalate-adipate to the mixing vessel containing the mixing additive, maintain the ambient temperature at 20-25°C, set the stirring speed at 50-100 r / min, and continue stirring for 5-8 min to obtain the premixed polyester particles.

6. A method for preparing a cellulose-based controllable degradable agricultural mulch film as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1: The acidic composite powder and 50% of the total weight of the premixed polyester particles are added together to the main feed port of a co-rotating twin-screw extruder for melt mixing to obtain activated material; S2: The remaining 50% of the total weight of the premixed polyester granules is added through the side feed port of the co-rotating twin-screw extruder and mixed with the activated material to obtain a controlled melt; S3: Inject the epoxidized soybean oil into the controlled melt to complete the hydrophobic sealing reaction and obtain the sealed melt; S4: The closed melt is subjected to vacuum degassing, extrusion pelletizing and drying to obtain modified masterbatch; S5: The modified masterbatch obtained in step S4 is blown into film and then wound up to obtain the agricultural mulch film.

7. The method for preparing cellulose-based controllable degradable agricultural mulch film according to claim 6, characterized in that, In step S1, the temperature of the melt mixing is 145–155°C; In step S2, the temperature at which the activated material is blended with the remaining 50% of the total weight of the premixed polyester particles is 165–175°C.

8. The method for preparing cellulose-based controllable degradable agricultural mulch film according to claim 6, characterized in that, In step S3, the epoxidized soybean oil is injected into the controlled melt through a liquid metering pump. The pumping pressure of the liquid metering pump is 0.50 to 1.0 MPa, and the set barrel temperature of the hydrophobic closed reaction is 160 to 165°C.

9. The method for preparing cellulose-based controllable degradable agricultural mulch film according to claim 6, characterized in that, In step S4, the vacuum degree of the vacuum exhaust is set to -0.095MPa to -0.08MPa, the drying is carried out in a fluidized bed drying chamber, the drying temperature is 60 to 70°C, and the moisture content of the modified masterbatch is 200 to 450ppm.

10. The method for preparing cellulose-based controllable degradable agricultural mulch film according to claim 6, characterized in that, In step S5, the set die temperature of the blown film is 150-155°C, and the blow-up ratio of the blown film is 2.0-2.5.

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