Degradable packaging material capable of controlling release rate of fertilizer nutrients and preparation method of degradable packaging material

Abstract

The invention discloses a degradable packaging material capable of controlling the release rate of fertilizer nutrients and a preparation method of the degradable packaging material, and relates to the technical field of agricultural packaging. The material is composed of a base material layer, a slow-release regulation and control layer and a degradation promotion layer, the base material layer provides mechanical support and barrier property, the slow-release regulation and control layer realizes accurate release of nutrients, and the inner surface of the degradation promotion layer is loaded with lipase and carboxymethyl cellulose sodium or a polyvinyl alcohol binder to accelerate degradation. The preparation adopts a multi-layer co-extrusion blow molding blank making and enzyme solution spraying post-treatment process, and the steps are clear and controllable. The material is adjustable in nutrient release, degradable and residue-free after use, suitable for various crop fertilization scenes, capable of improving the fertilizer utilization rate and reducing environmental pollution, and remarkable in practical value, and the mechanical property meets the packaging and transportation requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of agricultural packaging and eco-friendly materials, and particularly relates to a packaging material capable of controlling the release rate of fertilizer nutrients and degradable, and a preparation method thereof. BACKGROUND

[0002] In the field of agricultural production, fertilizer is a key production material for ensuring crop growth and improving yield, and its application effect is closely related to the application method. Traditional fertilizers are mostly applied by direct spreading or simple wrapping, however, direct spreading can cause the fertilizer to be exposed to the air, and the nutrients are easy to volatilize and lose; simple wrapping is difficult to control the release rate of nutrients, which seriously affects the utilization efficiency of fertilizer, and also causes adverse effects on the ecological environment.

[0003] From the perspective of fertilizer utilization efficiency, after the application of traditional fertilizers, they are easily affected by natural environmental factors such as rainwater erosion, soil leaching, and microbial decomposition, resulting in rapid release of nutrients in a short period of time. According to relevant data, the utilization rate of traditional nitrogen fertilizer is usually only 30-40%, the utilization rate of phosphorus fertilizer is lower, only 10-25%, and the utilization rate of potassium fertilizer is about 35-50%. A large amount of nutrients that are not absorbed and utilized by crops are lost to the environment, not only causing serious resource waste and increasing the cost of agricultural production, but also causing a series of environmental problems. For example, the lost nitrogen, phosphorus and other nutrients entering the water body can cause water eutrophication and blue-green algae bloom, and destroy the ecological balance of the water body; entering the atmosphere can form greenhouse gases and exacerbate global warming.

[0004] In order to solve the problem of too fast release of nutrients in traditional fertilizers, slow-release fertilizers have emerged. Slow-release fertilizers can control the release rate of nutrients by special treatment of fertilizers, so as to match the nutrient demand of crops at different growth stages, thereby improving the utilization efficiency of fertilizers. At present, the common slow-release fertilizers on the market mainly achieve the slow-release effect by coating one or more layers of slow-release materials on the surface of fertilizer particles, and these slow-release materials include high molecular polymers, sulfur, minerals, etc. Among them, high molecular polymers are widely used in the preparation of slow-release fertilizers due to their good slow-release performance.

[0005] However, most of the existing high molecular slow-release materials are not degradable. These non-degradable slow-release materials will gradually accumulate in the soil, destroy the soil structure, cause soil compaction, affect the air permeability and water permeability of the soil, and thus have adverse effects on the growth of crops. At the same time, with the continuous development of agricultural production, the accumulation of non-degradable materials in the soil will become more and more serious, and the harm to the ecological environment will also increase.

[0006] To solve the problem of degradation of slow-release materials, researchers have conducted a lot of research and developed some degradable slow-release materials. For example, slow-release materials prepared from natural polymer materials such as starch and cellulose have good biodegradability. However, these natural polymer slow-release materials usually have poor mechanical properties and unstable slow-release effect. In actual application, they are easily affected by external environmental factors and are prone to premature degradation or rupture, resulting in premature release of fertilizer nutrients and failing to meet the nutrient needs of crops throughout the growth cycle.

[0007] In addition, some synthetic degradable polymer materials, such as polylactic acid and polycaprolactone, are also used to prepare slow-release fertilizer packaging materials. These synthetic degradable polymer materials have good mechanical properties and slow-release performance, but their degradation rate is usually difficult to control. Under different soil environmental conditions, such as temperature, humidity, and pH value, the degradation rate differs greatly, resulting in unstable slow-release effect. Moreover, the production cost of these synthetic degradable polymer materials is relatively high, and their large-scale application is limited to a certain extent.

[0008] In addition, the existing slow-release fertilizer packaging materials also have deficiencies in the precision of controlling the release rate of fertilizer nutrients. Different crops have different nutrient demand and demand rate at different growth stages, and the existing packaging materials are difficult to accurately control the release rate of fertilizer nutrients according to specific crop varieties and growth environments. Often, the release rate of fertilizer nutrients does not match the nutrient demand of crops, resulting in insufficient nutrient supply during the peak demand period of crops, affecting the growth and yield of crops, or excessive release of nutrients during the off-season of crop nutrient demand, causing nutrient loss and environmental pollution.

[0009] In summary, the current fertilizer packaging materials on the market still have many problems in slow-release performance, degradability, mechanical properties, and slow-release precision, and cannot meet the needs of agricultural production for efficient, environmentally friendly, and precise fertilization. Therefore, it is of great practical significance and broad application prospect to develop a packaging material with good nutrient release rate control performance, degradability, excellent mechanical properties, and the ability to accurately control the release rate of fertilizer nutrients, as well as a preparation method thereof.

[0010] The disclosure of the above background art content is only used to assist in understanding the inventive concept and technical solutions of the present application, and it does not necessarily belong to the prior art of the present patent application. In the absence of explicit evidence that the above content has been disclosed before the filing date of the present patent application, the above background art should not be used to evaluate the novelty and inventiveness of the present application. SUMMARY

[0011] The present application aims to provide a packaging material capable of controlling the release rate of fertilizer nutrients and degradable, and a preparation method thereof, to solve the technical problems of the prior art, i.e., the release rate of fertilizer nutrients is difficult to accurately control, the packaging material is not degradable or the degradation period does not match the nutrient release period, the mechanical properties of the material cannot meet the packaging and transportation requirements, and the environmental protection and functionality are difficult to balance.

[0012] To achieve the above technical purposes, the present application adopts the following technical solutions:

[0013] A packaging material capable of controlling the release rate of fertilizer nutrients and degradable, which is composed of a base material layer, a slow-release control layer and a degradation promotion layer, and the composition of each layer is as follows in terms of mass fraction:

[0014] The base material layer is composed of the following components: polybutylene adipate terephthalate 40-60 parts, polylactic acid 20-30 parts, propylene oxide modified starch 10-20 parts, tributyl citrate 3-8 parts, maleic anhydride grafted polyolefin 2-5 parts, and hindered phenolic antioxidant 1010 0.5-2 parts;

[0015] The slow-release control layer is composed of the following components: polyvinyl alcohol 30-50 parts, organic modified montmorillonite 5-15 parts, chitosan 10-20 parts, nano-silicon dioxide 2-8 parts, and glutaraldehyde 1-3 parts;

[0016] The degradation promotion layer is composed of the following components: polybutylene succinate 40-60 parts, starch 20-30 parts, and calcium stearate 1-3 parts;

[0017] The inner surface of the degradation promotion layer is loaded with lipase 5-10 parts and 1-3% of an environmentally friendly adhesive, which is sodium hydroxymethyl cellulose or polyvinyl alcohol.

[0018] Preferably, in the base material layer, the degree of substitution of propylene oxide modified starch is 0.3-0.5, and the grafting rate of maleic anhydride grafted polyolefin is 1.5-3%.

[0019] Preferably, in the slow-release control layer, the organic modified montmorillonite is modified with cetyltrimethylammonium bromide, and the interlayer spacing of the modified montmorillonite is 2.5-3.5 nm; the polymerization degree of polyvinyl alcohol is 1700-2000, and the alcoholysis degree is 88-99%.

[0020] Preferably, in the degradation promotion layer, the starch is corn starch or potato starch, and the particle size of the starch is 50-100 μm; the enzyme activity of the lipase is 10000-20000 U / g.

[0021] The present application also provides a preparation method of a packaging material capable of controlling the release rate of fertilizer nutrients and degradable, which comprises the following steps:

[0022] S1: preparing the substrate layer master batch, weighing the raw materials according to the composition of the substrate layer, and obtaining the substrate layer master batch through high-speed mixing and double-screw extrusion granulation;

[0023] S2: preparing the slow-release control layer master batch, weighing the raw materials according to the composition of the slow-release control layer, and obtaining the slow-release control layer master batch through dissolution, mixing, cross-linking reaction, spray drying, and single-screw extrusion granulation;

[0024] S3: preparing the degradation promotion layer master batch, weighing the raw materials according to the composition of the degradation promotion layer, and obtaining the degradation promotion layer master batch through high-speed mixing and double-screw extrusion granulation;

[0025] S4: multi-layer co-extrusion blow molding, adding the master batches of each layer prepared in steps S1, S2, and S3 into a multi-layer co-extrusion blow molding machine, and obtaining a three-layer composite packaging film without enzymes through melt extrusion, compounding, blowing, and shaping; after heat sealing and cutting, a packaging material blank is obtained through the bag-making process;

[0026] S5: enzyme loading post-treatment, applying an enzyme solution to the inner surface of the degradation promotion layer of the packaging bag blank, and after low-temperature drying treatment, a packaging material directly used for fertilizer packaging is obtained.

[0027] Preferably, in step S1, high-speed mixing is divided into two steps: in the first step, polybutylene adipate-terephthalate, polylactic acid, and antioxidant 1010 are mixed at 80-90°C and 800-1000 r / min for 5-10 min; in the second step, modified starch, tributyl citrate, and maleic anhydride grafted polyolefin are added to the mixture of the first step, and mixed at 90-100°C and 1000-1200 r / min for 10-15 min; the temperature for double-screw extrusion granulation is 160-180°C, and the screw rotation speed is 200-250 r / min.

[0028] Preferably, in step S2, polyvinyl alcohol is dissolved by stirring at 80-90°C to form a water solution with a mass concentration of 10-15%; organic modified montmorillonite and nano-silicon dioxide are dispersed at a rotation speed of 600-800 r / min for 30-40 min; chitosan is dissolved in a 1-2% acetic acid aqueous solution to form a chitosan solution with a mass concentration of 5-8%; the polyvinyl alcohol aqueous solution, the dispersion of montmorillonite and nano-silicon dioxide, and the chitosan solution are mixed uniformly, and glutaraldehyde is added for cross-linking reaction at 60-70°C for 1-2 h; the cross-linked material is subjected to spray drying, and the inlet temperature for spray drying is 120-140°C; the dried powder is granulated through a single-screw extruder, and the granulation temperature is 180-200°C, and the screw rotation speed is 150-200 r / min.

[0029] Preferably, in the step S3, the high-speed mixing is mixing the polybutylene succinate, starch and calcium stearate at 90-110℃ and a rotation speed of 900-1100r / min for 10-15min; the temperature for the double-screw extrusion granulation is 150-170℃, and the screw rotation speed is 180-220r / min.

[0030] Preferably, in the step S4, the temperature of each section of the multi-layer co-extrusion blow molding machine is set as follows: the section for melting the base material layer master batch is 165-185℃, the section for melting the slow-release control layer master batch is 185-205℃, the section for melting the degradation promotion layer master batch is 155-175℃, and the die temperature is 170-190℃; the screw rotation speed is 220-260r / min for the base material layer, 160-200r / min for the slow-release control layer, and 190-230r / min for the degradation promotion layer, the blow ratio is 1.5-2.5, the pulling speed is 2-5m / min, and the prepared packaging material film thickness is 50-150μm.

[0031] Preferably, the specific operation of the step S5 comprises:

[0032] (1) Preparing an enzyme solution: dissolving or dispersing lipase in water containing 1-3% sodium hydroxymethyl cellulose or polyvinyl alcohol to form a uniform suspension / solution;

[0033] (2) Spraying treatment: keeping the bag opening of the packaging bag blank open, and using a spraying device to uniformly spray the enzyme solution on the inner surface of the degradation promotion layer under a spraying pressure of 0.2-0.5MPa;

[0034] (3) Low-temperature drying: drying in a circulating hot air at 40-50℃ for 15-30min to obtain a packaging material that can be directly used for fertilizer packaging.

[0035] Through the specific processing technology, especially the way of adding lipase in the low-temperature zone when preparing the degradation promotion layer, the bioactivity of the degradation promotion layer is ensured to be retained in the processing process, so that the final product has the characteristics of efficient degradation.

[0036] The beneficial effects of the present application compared with the prior art include:

[0037] I. Precise and controllable nutrient release rate, matching the fertilizer demand law of different crops in the whole growth period

[0038] The packaging material of the prior art is mostly single barrier layer or simple coating, the nutrient release rate regulation mechanism is single, the nutrient release rate is fixed, and the fertilizer supply cannot be matched with the differentiated fertilizer demand of different crops, and the problem of disconnection between fertilizer supply and demand is prone to occur. The present application constructs a multi-mechanism synergistic controlled release system through a slow-release regulation layer. The swelling rate of polyvinyl alcohol can be set by the degree of polymerization and alcoholysis degree, the organic modified montmorillonite delays nutrient diffusion, the crosslinking reaction of chitosan and glutaraldehyde controls the permeation resistance, and the nano-silicon dioxide smooth release curve. By adjusting the raw material ratio, the slow-release rate can be flexibly changed, which can not only meet the concentrated fertilizer supply demand of short growth period crops such as vegetables, but also adapt to the sustained fertilizer supply demand of long growth period crops such as fruit trees, and realize the on-demand fertilizer supply.

[0039] II. Degradable and period-matched, no soil residue risk

[0040] The prior art often faces the contradiction between degradability and slow-release performance: natural polymer materials degrade too quickly, and synthetic polymer materials degrade slowly and may leave residues. The three-layer structure of the present application all selects completely biodegradable raw materials, and the degradation products are harmless substances. The degradation rate of each layer is precisely regulated by raw material ratio and lipase, ensuring that the material structure is stable during the growth period of crops, and after the release of fertilizer nutrients, the lipase catalyzes the hydrolysis of polyester, and the starch promotes microbial degradation, so that the material degrades within 2-3 months, which is highly matched with the nutrient release period, eliminating the risk of soil residue.

[0041] III. Balanced mechanical properties, meeting all scene requirements

[0042] The mechanical properties of the packaging material of the prior art have short boards: natural starch materials are poor in impact resistance and easy to break, pure synthetic polymer materials are brittle and easy to break, and multi-layer materials may also peel between layers. The substrate layer of the present application realizes soft-rigid complementation through polybutylene adipate-terephthalate and polylactic acid, the modified starch and the compatibilizer improve the compatibility, and the plasticizer balances the flexibility; the nano-silicon dioxide of the slow-release regulation layer fills the voids, the degradation promotion layer and the other layers form good interface bonding, effectively preventing peeling, so that the material has sufficient tensile strength, impact resistance and abrasion resistance, and is suitable for packaging, transportation and field application in all scenes.

[0043] IV. Raw materials are environmentally friendly and non-toxic, ensuring ecology and safety

[0044] Some materials of the prior art use harmful raw materials, such as phthalate plasticizers, which are easy to migrate and harmful to the human body, and additives containing heavy metals, which can damage the soil. The raw material system of the present application follows the principle of environmental protection and non-toxicity, the plasticizer is selected to be degradable and non-migratory, the degradation product of the compatibilizer is harmless, the antioxidant is used in small amount and is stable, and the lipase is a natural biological enzyme and can promote microbial activity. All raw materials have passed toxicity detection and meet the agricultural environmental protection standards, and will not harm the soil, crops and human body in the whole life cycle from production, use to degradation.

[0045] V. The preparation process is compatible, can be produced on a large scale and the cost is controllable

[0046] The prior art has complex and special preparation processes, requires special equipment, harsh conditions, or scarce raw materials, resulting in difficulty in large-scale production and high cost. The present application adopts the mature multi-layer co-extrusion blow molding process in the plastic packaging industry, and existing enterprises can produce by adjusting equipment parameters without the need to purchase new equipment. The raw materials used are common varieties, the supply chain is mature and the cost is stable, and the cost can be reduced by replacing part of the synthetic polyester with modified starch. The preparation of each layer of master batch is a standardized process, which can be produced continuously, has high efficiency and low energy consumption, and is convenient for large-scale agricultural promotion. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a structural diagram of the packaging material base material layer, slow-release control layer and degradation promotion layer;

[0048] Figure 2 is a research and development scene diagram of the packaging material of the present application;

[0049] Figure 3 is a packaging fertilizer on-site diagram of the packaging material of the present application;

[0050] Figure 4 is a product diagram of the fertilizer packaged by the packaging material of the present application;

[0051] Figure 5 is a sample diagram of the nutrient release comparison test of the packaged fertilizer of the present application;

[0052] Figure 6 is a fertilizer application test on-site diagram of the present application.

[0053] In the figure: 1, base material layer; 2, slow-release control layer; 3, degradation promotion layer. DETAILED DESCRIPTION

[0054] The present application will be further described in detail below in conjunction with specific embodiments. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope of the present application and its applications.

[0055] A packaging material for controlling the nutrient release rate of fertilizer and being degradable, which is composed of a base material layer, a slow-release control layer and a degradation promotion layer, and the composition of each layer is as follows in terms of mass fraction:

[0056] The base material layer is composed of the following components: polybutylene adipate-terephthalate 40-60 parts, polylactic acid 20-30 parts, propylene oxide modified starch 10-20 parts, tributyl citrate 3-8 parts, maleic anhydride grafted polyolefin 2-5 parts, and hindered phenolic antioxidant 1010 0.5-2 parts;

[0057] The slow-release control layer is composed of the following components: polyvinyl alcohol 30-50 parts, organic modified montmorillonite 5-15 parts, chitosan 10-20 parts, nano-silicon dioxide 2-8 parts, and glutaraldehyde 1-3 parts.

[0058] The degradation promotion layer is composed of the following components: polybutylene succinate 40-60 parts, starch 20-30 parts, and calcium stearate 1-3 parts.

[0059] In the substrate layer, the degree of substitution of the propylene oxide modified starch is 0.3-0.5, and the grafting rate of the maleic anhydride grafted polyolefin is 1.5%-3%.

[0060] In the slow-release control layer, the organic modified montmorillonite is modified by cetyltrimethylammonium bromide, and the interlayer spacing of the modified montmorillonite is 2.5-3.5 nm; the degree of polymerization of the polyvinyl alcohol is 1700-2000, and the alcoholysis degree is 88-99%.

[0061] In the degradation promotion layer, the starch is corn starch or potato starch, and the particle size of the starch is 50-100 mu m; the enzyme activity of the lipase is 10000-20000 U / g. Figure 1 The structure diagram of the packaging material substrate layer, the slow-release control layer and the degradation promotion layer is shown in

[0062] The inner surface of the degradation promotion layer is loaded with 5-10 parts of lipase and 1-3% of an environmentally friendly adhesive, and the environmentally friendly adhesive is sodium hydroxymethyl cellulose or polyvinyl alcohol.

[0063] The application also provides a preparation method of the packaging material capable of controlling the release rate of fertilizer nutrients and being degradable, comprising the following steps:

[0064] The preparation of the packaging material of the application needs to rely on standardized research and development scenes, and the research and development scene is as shown in Figure 2

[0065] S1: preparing a substrate layer master batch, weighing raw materials according to the composition of the substrate layer, and obtaining the substrate layer master batch through high-speed mixing and double-screw extrusion granulation;

[0066] S2: preparing a slow-release control layer master batch, weighing raw materials according to the composition of the slow-release control layer, and obtaining the slow-release control layer master batch through dissolution, mixing, crosslinking reaction, spray drying and single-screw extrusion granulation;

[0067] S3: preparing a degradation promotion layer master batch, weighing raw materials according to the composition of the degradation promotion layer, and obtaining the degradation promotion layer master batch through high-speed mixing and double-screw extrusion granulation;

[0068] ​S4: multilayer co-extrusion blow molding, the prepared each layer of the master batch in step S1, S2, S3 is added into a multilayer co-extrusion blow molding machine, and a three-layer composite packaging film without enzyme is obtained through melt extrusion, compounding, blowing and shaping, and the film is subjected to a bag-making process of heat sealing and cutting to obtain a packaging material blank;

[0069] S5: enzyme loading post-treatment, the enzyme solution is applied to the inner surface of the degradation promoting layer of the packaging bag blank, and after low-temperature drying treatment, a packaging material directly used for fertilizer packaging is obtained.

[0070] In the step S1, the high-speed mixing is divided into two steps: in the first step, polybutylene adipate-terephthalate, polylactic acid and antioxidant 1010 are mixed at 80-90℃ and 800-1000r / min for 5-10min; in the second step, modified starch, tributyl citrate and maleic anhydride grafted polyolefin are added to the mixture of the first step, and mixed at 90-100℃ and 1000-1200r / min for 10-15min; the temperature for double-screw extrusion granulation is 160-180℃, and the screw rotation speed is 200-250r / min.

[0071] In the step S2, polyvinyl alcohol is dissolved at 80-90℃ to form a water solution with a mass concentration of 10-15%; organic modified montmorillonite and nano-silicon dioxide are dispersed at a rotation speed of 600-800r / min for 30-40min; chitosan is dissolved in 1-2% acetic acid aqueous solution to form a chitosan solution with a mass concentration of 5-8%; the polyvinyl alcohol aqueous solution, the dispersion of montmorillonite and nano-silicon dioxide, and the chitosan solution are mixed uniformly, and then glutaraldehyde is added, and the crosslinking reaction is carried out at 60-70℃ for 1-2h; the crosslinked material is subjected to spray drying, and the inlet temperature of the spray drying is 120-140℃; the dried powder is granulated by a single-screw extruder, and the granulation temperature is 180-200℃, and the screw rotation speed is 150-200r / min.

[0072] In the step S3, the high-speed mixing is as follows: polybutylene succinate, starch and calcium stearate are mixed at 90-110℃ and a rotation speed of 900-1100r / min for 10-15min; the temperature for double-screw extrusion granulation is 150-170℃, and the screw rotation speed is 180-220r / min.

[0073] The temperature of each section of the multi-layer co-extrusion blow molding machine in the step S4 is set as follows: the section for melting the base material layer master batch is 165-185 DEG C, the section for melting the slow-release control layer master batch is 185-205 DEG C, the section for melting the degradation promotion layer master batch is 155-175 DEG C, and the die temperature is 170-190 DEG C; the screw rotation speed is 220-260 r / min for the base material layer, 160-200 r / min for the slow-release control layer, and 190-230 r / min for the degradation promotion layer, the blow-up ratio is 1.5-2.5, and the pulling speed is 2-5 m / min; and the prepared packaging material film has a thickness of 50-150 mu m.

[0074] The specific operation of the step S5 includes:

[0075] (1) Preparing an enzyme solution: dissolving or dispersing lipase in water containing 1-3% sodium hydroxymethyl cellulose or polyvinyl alcohol to form a uniform suspension / solution;

[0076] (2) Spraying treatment: keeping the bag opening of the packaging bag blank open, and using a spraying device to uniformly spray the enzyme solution on the inner surface of the degradation promotion layer under a spraying pressure of 0.2-0.5 MPa;

[0077] (3) Low-temperature drying: drying in a circulating hot air at 40-50 DEG C for 15-30 min to obtain a packaging material which can be directly used for fertilizer packaging.

[0078] The technical principle of the application is as follows:

[0079] I. Base material layer: synergistic mechanism of raw materials for structural support and basic barrier

[0080] The base material layer forms a soft-rigid complementary system with polybutylene adipate terephthalate and polylactic acid, the polybutylene adipate terephthalate provides impact resistance to avoid damage during packaging and transportation, and the polylactic acid ensures stiffness to ensure stable shape after filling the fertilizer. The propylene oxide modified starch reduces hydrophilicity through hydroxyl ether bonds to avoid swelling in a humid environment, and its branched structure can also form hydrogen bonds with the ester groups of the polyester, cooperate with the esterification reaction of the maleic anhydride grafted polyolefin, and improve the three-phase compatibility, solving the problem of mechanical decline caused by traditional starch addition. The tributyl citrate inserts between molecular chains to weaken the force, balance flexibility and rigidity; the antioxidant 1010 captures free radicals during processing to prevent oxidative degradation of the polyester and prolong the storage life.

[0081] II. Slow-release control layer: multi-mechanism raw material synergistic mechanism for precise controlled release

[0082] The core of the slow-release regulation layer is a synergistic controlled release of "swelling-barrier-adsorption". Polyvinyl alcohol swells in water to form water channels, and the pore size is controlled by the crosslinking degree of glutaraldehyde; the organic modified montmorillonite forms a lamellar barrier, prolongs the nutrient diffusion path, and simultaneously adsorbs cations; the porous structure of chitosan assists in adsorbing nutrients, and the degradation products can also promote microbial activity; nanosilica fills the gaps, not only improving the mechanical strength, but also serving as a nutrient storage library to smooth the release curve. The four synergistically achieve low release at the beginning, stable release in the middle, and slow release at the end, matching the crop fertilizer demand law.

[0083] III. Degradation promotion layer: synergistic mechanism of raw materials with fast degradation after function

[0084] The degradation promotion layer uses polybutylene succinate as a carrier to ensure the stability of the structure during the slow-release period. Starch increases the specific surface area, providing nutrients for microorganisms and promoting their reproduction; lipase specifically catalyzes the hydrolysis of polyester ester bonds, forming a double acceleration with microbial degradation. Calcium stearate improves processing fluidity, avoiding overheating due to friction of raw materials, and its calcium ions can also activate lipase activity. The three synergistically achieve material stability during the slow-release period, rapid degradation 2-3 months after nutrient release, and no soil residue.

[0085] IV. Interlayer synergy: overall performance breakthrough of three-layer structure

[0086] In terms of barrier synergy, the substrate layer slows down the entry of water to avoid the rapid swelling of the slow-release regulation layer; the slow-release regulation layer reduces the contact of fertilizer with other layers to avoid interference with degradation. In terms of degradation synergy, the three layers match the degradation period, and the rapid degradation of the degradation promotion layer drives the overall decomposition. In terms of mechanical synergy, the substrate layer provides support, and the slow-release regulation layer and the degradation promotion layer prevent peeling through interfacial bonding, ensuring the structural integrity of the packaging in all scenarios.

[0087] In summary, the three-layer structure breaks through the contradictions of traditional technology through raw material and interlayer synergy, achieving the optimal comprehensive performance of mechanics, controlled release, and degradation.

[0088] In order to make the present disclosure more complete, the following will be described by more specific examples. In the specific implementation process, the packaging material encapsulates the fertilizer on site as shown in Figure 3 .

[0089] Example 1:

[0090] A packaging material for controlling the release rate of fertilizer nutrients and being degradable, composed of a substrate layer, a slow-release regulation layer, and a degradation promotion layer, the composition of each layer is as follows in mass fraction:

[0091] The substrate layer is composed of the following components: polybutylene adipate-terephthalate 40 parts, polylactic acid 20 parts, propylene oxide modified starch 10 parts, tributyl citrate 3 parts, maleic anhydride grafted polyolefin 2 parts, and hindered phenolic antioxidant 1010 0.5 parts;

[0092] The slow-release control layer is composed of the following components: 30 parts of polyvinyl alcohol, 5 parts of organically modified montmorillonite, 10 parts of chitosan, 2 parts of nano-silicon dioxide, and 1 part of glutaraldehyde;

[0093] The degradation promotion layer is composed of the following components: 40 parts of polybutylene succinate, 20 parts of starch, and 1 part of calcium stearate.

[0094] In the substrate layer, the degree of substitution of the propylene oxide modified starch is 0.3, and the grafting rate of the maleic anhydride grafted polyolefin is 1.5%.

[0095] In the slow-release control layer, the organically modified montmorillonite is modified with cetyltrimethylammonium bromide, and the interlayer spacing of the modified montmorillonite is 2.5 nm; the degree of polymerization of the polyvinyl alcohol is 1700, and the alcoholysis degree is 88%.

[0096] In the degradation promotion layer, the starch is corn starch, and the particle size of the starch is 50 μm; the enzyme activity of the lipase is 10,000 U / g.

[0097] The inner surface of the degradation promotion layer is loaded with 5 parts of lipase and 1% of an environmentally friendly adhesive, which is sodium hydroxymethyl cellulose.

[0098] A preparation method of a packaging material capable of controlling the release rate of fertilizer nutrients and degrading, comprising the following steps:

[0099] S1: preparing a substrate layer master batch, weighing the raw materials according to the composition of the substrate layer, and obtaining the substrate layer master batch through high-speed mixing and double-screw extrusion granulation;

[0100] S2: preparing a slow-release control layer master batch, weighing the raw materials according to the composition of the slow-release control layer, and obtaining the slow-release control layer master batch through dissolution, mixing, crosslinking reaction, spray drying, and single-screw extrusion granulation;

[0101] S3: preparing a degradation promotion layer master batch, weighing the raw materials according to the composition of the degradation promotion layer, and obtaining the degradation promotion layer master batch through high-speed mixing and double-screw extrusion granulation;

[0102] S4: multi-layer co-extrusion blow molding, adding the master batches of each layer prepared in steps S1, S2, and S3 into a multi-layer co-extrusion blow molding machine, and obtaining a three-layer composite packaging film without enzyme through melting extrusion, compounding, blowing, and setting; after the film is subjected to a bag-making process of heat sealing and cutting, a packaging material blank is obtained;

[0103] S5: enzyme loading post-treatment, applying an enzyme solution to the inner surface of the degradation promotion layer of the packaging material blank, and after low-temperature drying treatment, a packaging material directly used for fertilizer packaging is obtained.

[0104] In the step S1, the high-speed mixing is divided into two steps: in the first step, the polybutylene adipate terephthalate, polylactic acid and antioxidant 1010 are mixed at 80℃ and 800r / min for 5min; in the second step, the propylene oxide modified starch, tributyl citrate and maleic anhydride grafted polyolefin are added to the mixture of the first step, and mixed at 90℃ and 1000r / min for 10min; the temperature for the double-screw extrusion granulation is 160℃, and the screw speed is 200r / min.

[0105] In the step S2, the polyvinyl alcohol is dissolved in water at 80℃ to form a 10% aqueous solution; the organically modified montmorillonite and nano-silica are dispersed at 600r / min for 30min; the chitosan is dissolved in 1% acetic acid aqueous solution to form a 5% chitosan solution; the polyvinyl alcohol aqueous solution, the dispersion of the montmorillonite and nano-silica, and the chitosan solution are mixed uniformly, and then glutaraldehyde is added, and the cross-linking reaction is carried out at 60℃ for 1h; the cross-linked material is subjected to spray drying, and the inlet temperature for the spray drying is 120℃; the dried powder is granulated by a single-screw extruder, and the granulation temperature is 180℃ and the screw speed is 150r / min.

[0106] In the step S3, the high-speed mixing is carried out by mixing the polybutylene succinate, starch and calcium stearate at 90℃ and 900r / min for 15min; the temperature for the double-screw extrusion granulation is 150℃, and the screw speed is 180r / min.

[0107] In the step S4, the temperature of each section of the multi-layer co-extrusion blowing machine is set as follows: the substrate layer is 165℃, the slow-release control layer is 185℃, the degradation promotion layer is 155℃, and the die head is 170℃; the screw speed is 220r / min for the substrate layer, 160r / min for the slow-release control layer, and 190r / min for the degradation promotion layer; the blowing ratio is 1.5, and the pulling speed is 2m / min; the prepared packaging material film has a thickness of 50μm.

[0108] The specific operation of the step S5 includes: (1) preparing an enzyme solution: dissolving or dispersing lipase in water containing 1% sodium hydroxymethyl cellulose to form a uniform suspension; (2) spray treatment: keeping the bag opening of the packaging material blank open, and using a spraying device to uniformly spray the enzyme solution on the inner surface of the degradation promotion layer under a spraying pressure of 0.2MPa; (3) low-temperature drying: drying in a circulating hot air at 40℃ for 30min to obtain a packaging material which can be directly used for fertilizer packaging.

[0109] Example 2:

[0110] A kind of control fertilizer nutrient release rate and degradable packaging material, by substrate layer, slow-release control layer and degradation promotion layer, the composition of each layer is as follows by mass fraction:

[0111] Substrate layer: polybutylene adipate terephthalate 50 parts, polylactic acid 25 parts, propylene oxide modified starch 15 parts, tributyl citrate 5 parts, maleic anhydride grafted polyolefin 3 parts, hindered phenolic antioxidant 1010 is 1 part;

[0112] Slow-release control layer: polyvinyl alcohol 40 parts, organic modified montmorillonite 10 parts, chitosan 15 parts, nano silicon dioxide 5 parts, glutaraldehyde 2 parts;

[0113] Degradation promotion layer: polybutylene succinate 50 parts, starch 25 parts, calcium stearate 2 parts.

[0114] In the substrate layer, the degree of substitution of propylene oxide modified starch is 0.4, and the grafting rate of maleic anhydride grafted polyolefin is 2%.

[0115] In the slow-release control layer, the organic modified montmorillonite is modified by cetyltrimethylammonium bromide, and the interlayer spacing of the modified montmorillonite is 3.0 nm;The degree of polymerization of polyvinyl alcohol is 1800, and the alcoholysis degree is 92%.

[0116] In the degradation promotion layer, the starch is potato starch, and the particle size of the starch is 70 μm;The enzyme activity of the lipase is 15000 U / g.

[0117] The inner surface of the degradation promotion layer is loaded with lipase 7 parts and 2% of environmentally friendly adhesive, and the environmentally friendly adhesive is polyvinyl alcohol.

[0118] A preparation method of a packaging material for controlling the release rate of fertilizer nutrients and degradable, comprising the following steps:

[0119] S1: preparing a substrate layer master batch, weighing the raw materials according to the composition of the substrate layer, and obtaining by high-speed mixing and double-screw extrusion granulation;

[0120] S2: preparing a slow-release control layer master batch, weighing the raw materials according to the composition of the slow-release control layer, and obtaining by dissolving, mixing, crosslinking reaction, spray drying and single-screw extrusion granulation;

[0121] S3: preparing a degradation promotion layer master batch, weighing the raw materials according to the composition of the degradation promotion layer, and obtaining by high-speed mixing and double-screw extrusion granulation;

[0122] S4: multi-layer co-extrusion blow molding, adding each layer master batch into a multi-layer co-extrusion blow molding machine, and obtaining a three-layer composite packaging film without enzyme by melting extrusion, compounding, blowing and setting;The film is cut after heat sealing and bag making process;Obtain the packaging material blank;

[0123] S5: After enzyme loading, the enzyme solution is applied to the inner surface of the degradation promoting layer of the packaging material blank, and after low-temperature drying treatment, the packaging material directly used for fertilizer packaging is obtained.

[0124] In the step S1, the high-speed mixing is divided into two steps: in the first step, polybutylene adipate-terephthalate, polylactic acid and antioxidant 1010 are mixed at 85℃ and 900r / min for 7min; in the second step, propylene oxide modified starch, butyl citrate and maleic anhydride grafted polyolefin are added to the mixture of the first step, and mixed at 95℃ and 1100r / min for 12min; the temperature for double-screw extrusion granulation is 170℃, and the screw speed is 220r / min.

[0125] In the step S2, polyvinyl alcohol is dissolved at 85℃ to form a water solution with a mass concentration of 12%; organic modified montmorillonite and nano-silicon dioxide are dispersed at 700r / min for 35min; chitosan is dissolved in 1.5% acetic acid aqueous solution to form a chitosan solution with a mass concentration of 6%; the polyvinyl alcohol aqueous solution, the dispersion of montmorillonite and nano-silicon dioxide, and the chitosan solution are mixed uniformly, and then glutaraldehyde is added, and the cross-linking reaction is carried out at 65℃ for 1.5h; the cross-linked material is subjected to spray drying, and the inlet temperature of the spray drying is 130℃; the dried powder is granulated by a single-screw extruder, and the granulation temperature is 190℃ and the screw speed is 170r / min.

[0126] In the step S3, the high-speed mixing is carried out as follows: polybutylene succinate, starch and calcium stearate are mixed at 100℃ and 1000r / min for 12min; the temperature for double-screw extrusion granulation is 160℃, and the screw speed is 200r / min.

[0127] In the step S4, the temperature of each section of the multi-layer co-extrusion blowing machine is set as follows: the substrate layer is 175℃, the slow-release control layer is 195℃, the degradation promoting layer is 165℃, and the die head is 180℃; the screw speed is: the substrate layer is 240r / min, the slow-release control layer is 180r / min, and the degradation promoting layer is 210r / min; the blowing ratio is 2.0, and the pulling speed is 3.5m / min; the prepared packaging material film has a thickness of 100μm.

[0128] The specific operation of the step S5 includes: (1) preparing an enzyme solution: dissolving or dispersing lipase in water containing 2% polyvinyl alcohol to form a uniform suspension; (2) spray treatment: keeping the bag opening of the packaging material blank open, and using a spray device to uniformly spray the enzyme solution on the inner surface of the degradation promoting layer under a spraying pressure of 0.3MPa; (3) low-temperature drying: drying in a circulating hot air at 45℃ for 22min to obtain the packaging material directly used for fertilizer packaging.

[0129] Embodiment 3

[0130] A kind of control fertilizer nutrient release rate and degradable packaging material, by substrate layer, slow-release control layer and degradation promotion layer, the composition of each layer is as follows by mass fraction component:

[0131] Substrate layer: polybutylene adipate-terephthalate 55 parts, polylactic acid 28 parts, propylene oxide modified starch 18 parts, tributyl citrate 6 parts, maleic anhydride grafted polyolefin 4 parts, hindered phenolic antioxidant 1010 is 1.5 parts;

[0132] Slow-release control layer: polyvinyl alcohol 45 parts, organic modified montmorillonite 12 parts, chitosan 18 parts, nano silicon dioxide 6 parts, glutaraldehyde 2.5 parts;

[0133] Degradation promotion layer: polybutylene succinate 55 parts, starch 28 parts, calcium stearate 2.5 parts.

[0134] In the substrate layer, the degree of substitution of propylene oxide modified starch is 0.45, and the grafting rate of maleic anhydride grafted polyolefin is 2.5%.

[0135] In the slow-release control layer, the organic modified montmorillonite is modified by cetyltrimethylammonium bromide, and the interlayer spacing of the modified montmorillonite is 3.2 nm;The degree of polymerization of the polyvinyl alcohol is 1900, and the alcoholysis degree is 95%.

[0136] In the degradation promotion layer, the starch is corn starch, and the particle size of the starch is 80 μm;The enzyme activity of the lipase is 18000 U / g.

[0137] The inner surface of the degradation promotion layer is loaded with lipase 8 parts and 2% of environmentally friendly adhesive, and the environmentally friendly adhesive is sodium hydroxymethyl cellulose.

[0138] A preparation method of a control fertilizer nutrient release rate and degradable packaging material, comprising the following steps:

[0139] S1: preparing a substrate layer master batch, weighing the raw materials according to the composition of the substrate layer, and obtaining by high-speed mixing and double-screw extrusion granulation;

[0140] S2: preparing a slow-release control layer master batch, weighing the raw materials according to the composition of the slow-release control layer, and obtaining by dissolving, mixing, crosslinking reaction, spray drying and single-screw extrusion granulation;

[0141] S3: preparing a degradation promotion layer master batch, weighing the raw materials according to the composition of the degradation promotion layer, and obtaining by high-speed mixing and double-screw extrusion granulation;

[0142] S4: multilayer co-extrusion blow molding, adding each layer of master batch into the multilayer co-extrusion blow molding machine respectively, obtaining the three-layer composite packaging film without enzyme through melt extrusion, compounding, blowing and shaping, and obtaining the packaging material blank through the bag-making process of heat sealing and cutting;

[0143] S5: enzyme loading post-processing, applying the enzyme solution to the inner surface of the degradation promoting layer of the packaging material blank, and after low-temperature drying treatment, it is the packaging material that can be directly used for fertilizer packaging.

[0144] In the step S1, the high-speed mixing is divided into two steps: in the first step, polybutylene adipate-terephthalate, polylactic acid and antioxidant 1010 are mixed at 88℃ and a rotation speed of 950r / min for 8min; in the second step, propylene oxide modified starch, butyl citrate and maleic anhydride grafted polyolefin are added to the mixture of the first step, and mixed at 98℃ and a rotation speed of 1150r / min for 13min; the temperature for double-screw extrusion granulation is 175℃, and the screw rotation speed is 230r / min.

[0145] In the step S2, polyvinyl alcohol is dissolved in water to form an aqueous solution with a mass concentration of 14% at 88℃; organic modified montmorillonite and nano-silicon dioxide are dispersed at a rotation speed of 750r / min for 38min; chitosan is dissolved in 1.8% acetic acid aqueous solution to form a solution with a mass concentration of 7%; the polyvinyl alcohol aqueous solution, the dispersion of montmorillonite and nano-silicon dioxide, and the chitosan solution are mixed uniformly, and then glutaraldehyde is added, and the crosslinking reaction is carried out at 68℃ for 1.8h; the crosslinked material is subjected to spray drying, and the inlet temperature of spray drying is 135℃; the dried powder is granulated by a single-screw extruder, and the granulation temperature is 195℃ and the screw rotation speed is 180r / min.

[0146] In the step S3, the high-speed mixing is as follows: polybutylene succinate, starch and calcium stearate are mixed at 105℃ and a rotation speed of 1050r / min for 11min; the temperature for double-screw extrusion granulation is 165℃, and the screw rotation speed is 210r / min.

[0147] In the step S4, the temperature of each section of the multilayer co-extrusion blow molding machine is set as follows: the base material layer is 180℃, the slow-release control layer is 200℃, the degradation promoting layer is 170℃, and the die head is 185℃; the screw rotation speed is 250r / min for the base material layer, 190r / min for the slow-release control layer, and 220r / min for the degradation promoting layer; the blowing ratio is 2.2, and the pulling speed is 3m / min; the prepared packaging material film has a thickness of 120μm.

[0148] The specific operation of the step S5 includes: (1) preparing an enzyme solution: dissolving or dispersing lipase in water containing 2% sodium hydroxymethyl cellulose to form a uniform suspension; (2) spray treatment: keeping the bag opening of the packaging material blank open, using a spraying device to uniformly spray the enzyme solution on the inner surface of the degradation promoting layer under a spraying pressure of 0.4 MPa; (3) low-temperature drying: drying in a circulating hot air at 48℃ for 18 min to obtain a packaging material which can be directly used for fertilizer packaging.

[0149] The packaging material prepared in Example 3 can be used for packaging fertilizer to form a controlled-release fertilizer product with stable morphology and good sealing performance, which can adapt to common packaging forms such as bagging and roll film in agricultural production, and the product is as shown in Figure 4

[0150] Example 4:

[0151] A kind of controllable fertilizer nutrient release rate and degradable packaging material, which is composed of substrate layer, slow-release control layer and degradation promoting layer, and the composition of each layer is as follows in mass fraction:

[0152] The substrate layer: polybutylene adipate terephthalate 60 parts, polylactic acid 30 parts, propylene oxide modified starch 20 parts, tributyl citrate 8 parts, maleic anhydride grafted polyolefin 5 parts, and hindered phenolic antioxidant 1010 2 parts;

[0153] The slow-release control layer: polyvinyl alcohol 50 parts, organic modified montmorillonite 15 parts, chitosan 20 parts, nano silicon dioxide 8 parts, and glutaraldehyde 3 parts;

[0154] The degradation promoting layer: polybutylene succinate 60 parts, starch 30 parts, and calcium stearate 3 parts.

[0155] In the substrate layer, the degree of substitution of propylene oxide modified starch is 0.5, and the grafting rate of maleic anhydride grafted polyolefin is 3%.

[0156] In the slow-release control layer, the organic modified montmorillonite is modified by cetyltrimethylammonium bromide, and the interlayer spacing of the modified montmorillonite is 3.5 nm; the degree of polymerization of the polyvinyl alcohol is 2000, and the alcoholysis degree is 99%.

[0157] In the degradation promoting layer, the starch is potato starch, and the particle size of the starch is 100 μm; the enzyme activity of the lipase is 20000 U / g.

[0158] The inner surface of the degradation promoting layer is loaded with 10 parts of lipase and 3% of an environmentally friendly adhesive, and the environmentally friendly adhesive is polyvinyl alcohol.

[0159] A preparation method of a controllable fertilizer nutrient release rate and degradable packaging material, comprising the following steps:​

[0160] S1: preparing the base layer master batch, weighing the raw materials according to the composition of the base layer, and obtaining by high-speed mixing and double-screw extrusion granulation;

[0161] S2: preparing the slow-release control layer master batch, weighing the raw materials according to the composition of the slow-release control layer, and obtaining by dissolving, mixing, cross-linking reaction, spray drying, and single-screw extrusion granulation;

[0162] S3: preparing the degradation promotion layer master batch, weighing the raw materials according to the composition of the degradation promotion layer, and obtaining by high-speed mixing and double-screw extrusion granulation;

[0163] S4: multi-layer co-extrusion blow molding, adding each layer master batch into a multi-layer co-extrusion blow molding machine, and obtaining an enzyme-free three-layer composite packaging film by melt extrusion, compounding, blowing, and shaping. After heat sealing and cutting, a packaging material blank is obtained;

[0164] S5: enzyme loading post-processing, applying an enzyme solution to the inner surface of the degradation promotion layer of the packaging material blank, and after low-temperature drying treatment, a packaging material directly used for fertilizer packaging is obtained;

[0165] In step S1, high-speed mixing is divided into two steps: in the first step, polybutylene adipate-terephthalate, polylactic acid, and antioxidant 1010 are mixed at 90℃ and a rotation speed of 1000r / min for 10min; in the second step, propylene oxide modified starch, butyl citrate, and maleic anhydride grafted polyolefin are added to the mixture of the first step, and mixed at 100℃ and a rotation speed of 1200r / min for 15min; the temperature for double-screw extrusion granulation is 180℃, and the screw rotation speed is 250r / min.

[0166] S2: preparing the slow-release control layer master batch, weighing the raw materials according to the composition of the slow-release control layer, and obtaining by dissolving, mixing, cross-linking reaction, spray drying, and single-screw extrusion granulation;

[0167] In step S2, polyvinyl alcohol is dissolved by stirring at 90℃ to form a water solution with a mass concentration of 15%; organic modified montmorillonite and nano-silicon dioxide are dispersed at a rotation speed of 800r / min for 40min; chitosan is dissolved in a 2% acetic acid aqueous solution to form a solution with a mass concentration of 8%; the polyvinyl alcohol aqueous solution, the dispersion of montmorillonite and nano-silicon dioxide, and the chitosan solution are uniformly mixed, and glutaraldehyde is added, and cross-linking reaction is carried out at 70℃ for 2h; the cross-linked material is subjected to spray drying, and the inlet temperature of spray drying is 140℃; the dried powder is granulated by a single-screw extruder, and the granulation temperature is 200℃ and the screw rotation speed is 200r / min.

[0168] The high-speed mixing in the step S3 is mixing polybutylene succinate, starch and calcium stearate at 110°C and a rotation speed of 1100 r / min for 10 min; the temperature for double-screw extrusion granulation is 170°C, and the screw rotation speed is 220 r / min.

[0169] In the step S4, the temperature of each section of the multi-layer co-extrusion blowing machine is set as follows: 185°C for the substrate layer, 205°C for the slow-release control layer, 175°C for the degradation promotion layer, and 190°C for the die; the screw rotation speed is 260 r / min for the substrate layer, 200 r / min for the slow-release control layer, and 230 r / min for the degradation promotion layer; the blowing ratio is 2.5, and the pulling speed is 5 m / min; and the prepared packaging material film has a thickness of 150 μm.

[0170] The specific operation of the step S5 includes the following steps: (1) preparing an enzyme solution: dissolving or dispersing lipase in water containing 3% polyvinyl alcohol to form a uniform suspension; (2) spray treatment: keeping the bag opening of the packaging material blank open, and using a spraying device to uniformly spray the enzyme solution on the inner surface of the degradation promotion layer under a spraying pressure of 0.5 MPa; and (3) low-temperature drying: drying in a circulating hot air at 50°C for 15 min to obtain a packaging material that can be directly used for fertilizer packaging.

[0171] Comparative Example 1: Fertilizer packaging material lacking propylene oxide modified starch

[0172] Core difference: referring to the formula and process of Example 3, only the propylene oxide modified starch in the substrate layer is deleted, and the rest of the raw material composition and process parameters are completely consistent.

[0173] Comparative Example 2: Fertilizer packaging material lacking organic modified montmorillonite

[0174] Core difference: referring to the formula and process of Example 3, only the organic modified montmorillonite in the slow-release control layer is deleted, and the rest of the raw material composition and process parameters are completely consistent.

[0175] Comparative Example 3: Fertilizer packaging material lacking lipase loading

[0176] Core difference: referring to the formula and process of Example 3, the lipase loaded on the inner surface of the degradation promotion layer is deleted, and the rest of the raw material composition and process parameters are completely consistent.

[0177] Single-factor experiment:

[0178] Five key process parameters affecting the core performance of the material are selected for single-factor experiment, other parameters are fixed (referring to Example 3), only the target parameter is changed, and the test index is tensile strength (MPa), nutrient release period (month), and 6-month degradation rate (%); the optimal parameters of each experiment and the analysis are as follows:

[0179] Experiment 1: Substrate layer double screw extrusion temperature

[0180] The process is basically the same as that of the optimal embodiment 3, except that the substrate layer double screw extrusion temperature is set at 165°C, 170°C, 175°C, 180°C, and 185°C respectively. The results are shown in Table 1.

[0181]

[0182] Conclusion analysis: In this experiment, the optimal value of the substrate layer double screw extrusion temperature is 180°C. When the temperature is lower than 175°C, the polybutylene adipate terephthalate and polylactic acid are not fully melted, the molecular chain entanglement degree is low, the tensile strength, barrier property and degradation rate gradually increase with the increase of temperature; when the temperature is 175°C, the raw materials are fully melted, there is no risk of thermal degradation, and the performance can meet the actual demand; when the temperature is 180°C, the raw materials are more fully melted, the tensile strength, nutrient release period and degradation rate are the most optimal; when the temperature is 185°C, the polylactic acid is thermally degraded, the molecular chain is broken, the tensile strength drops sharply, the degradation rate decreases due to the abnormal increase of crystallinity, and the practicality decreases.

[0183] Experiment 2: Crosslinking reaction temperature of slow-release control layer

[0184] The process is basically the same as that of the optimal embodiment 3, except that the crosslinking reaction temperature of the slow-release control layer is set at 60°C, 65°C, 70°C, 75°C, and 80°C respectively. The results are shown in Table 2.

[0185]

[0186] Conclusion analysis: In this experiment, the optimal value of the crosslinking reaction temperature of the slow-release control layer is 70°C. When the temperature is lower than 70°C, the crosslinking reaction of glutaraldehyde with polyvinyl alcohol and chitosan is not complete, the pore size of the network structure is large, the nutrient release period is short, and the tensile strength is low; when the temperature is 70°C, the crosslinking reaction is sufficient and not excessive, the pore size of the network structure is uniform, the tensile strength, nutrient release period and degradation rate are all optimal; when the temperature is higher than 70°C, the crosslinking reaction is excessive, the pore size of the network structure is reduced, the fertilizer nutrient release resistance is increased, the nutrient release period is too long, the tensile strength and degradation rate are decreased, and it does not meet the functional requirements.

[0187] Experiment 3: Mixing total time of degradation promotion layer

[0188] The process is basically the same as that of the optimal embodiment 3, except that the mixing total time of the degradation promotion layer is set at 10 min, 12 min, 14 min, 16 min, and 18 min respectively. The results are shown in Table 3.

[0189]

[0190] Conclusion analysis: In this experiment, the optimal value of the total mixing time of the degradation promotion layer is 14 min. When the mixing time is less than 14 min, the lipase and polybutylene succinate, starch are not evenly dispersed, the degradation rate and tensile strength are low; when the mixing time is 14 min, the raw materials are evenly dispersed, the lipase wrapping effect is good, the tensile strength is optimal, the degradation rate is the highest, and the nutrient release period is stable; when the mixing time is higher than 14 min, excessive mixing leads to starch granule fragmentation and raw material thermal oxidation, and the tensile strength and degradation rate decrease, which has no practical optimization significance.

[0191] Experiment 4: Multi-layer co-extrusion blowing ratio

[0192] The process is basically the same as the optimal embodiment 3, except that the multi-layer co-extrusion blowing ratio is set to 1.8, 2.0, 2.2, 2.4, and 2.6, respectively. The results are shown in Table 4.

[0193]

[0194] Conclusion analysis: In this experiment, the optimal value of the multi-layer co-extrusion blowing ratio is 2.4. When the blowing ratio is less than 2.2, the film orientation degree is low, the molecular chain arrangement is disordered, the tensile strength and degradation rate are low, and the thickness uniformity is poor; when the blowing ratio is 2.2, the performance is balanced and suitable for industrial production; when the blowing ratio is 2.4, the film orientation degree is further optimized, the tensile strength and degradation rate are optimal, and the nutrient release period is suitable for demand; when the blowing ratio is 2.6, the film is over-stretched, the thickness drops sharply and micro-holes are prone to occur, the tensile strength and degradation rate decrease significantly, and the practicality is insufficient.

[0195] Experiment 5: Spray drying temperature of slow-release control layer

[0196] The process is basically the same as the optimal embodiment 3, except that the spray drying temperature of the slow-release control layer is set to 125℃, 130℃, 135℃, 140℃, and 145℃, respectively. The results are shown in Table 5.

[0197]

[0198] Conclusion analysis: In this experiment, the optimal value of the spray drying temperature of the slow-release control layer is 135℃. When the temperature is lower than 135℃, the slow-release control layer powder has high moisture content, and the extrusion is prone to produce bubbles, the tensile strength is low, and the nutrient release period is short; when the temperature is 135℃, the powder moisture content is appropriate, there are no bubble defects, the tensile strength, nutrient release period, and degradation rate are optimal; when the temperature is higher than 135℃, the powder is prone to agglomeration due to excessive drying, and the tensile strength and degradation rate decrease, which affects the stability of subsequent processing.

[0199] From the single factor experiment, the optimal parameters of experiments 1-5 are: extrusion temperature 180℃, crosslinking reaction temperature of slow-release control layer 70℃, total mixing time of degradation promotion layer 14min, multi-layer co-extrusion blow ratio 2.4, and spray drying temperature of slow-release control layer 135℃.

[0200] Performance index detection test and data comparison and analysis:

[0201] (I) Detection index and method

[0202] Tensile strength: tested according to GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: test conditions for films and sheets".

[0203] Nutrient release period: the time required for the fertilizer nutrient release rate to reach 90% was monitored by soil burial method.

[0204] Degradation rate: tested according to GB / T19277.1-2025 "Determination of ultimate aerobic biodegradation capacity of materials under controlled composting conditions - Part 1: general method" for 6 months degradation rate.

[0205] Impact strength: tested according to GB / T1043.1-2008 "Determination of impact properties of plastics - Part 1: non- instrumented impact test".

[0206] (II) Test results

[0207] The test sample includes four examples and three comparative examples. The test results are shown in Table 6.

[0208]

[0209] (III) Data comparison and theoretical analysis

[0210] Tensile strength comparison: the tensile strength of examples 1-4 is 28.5-31.2 MPa, among which the tensile strength of example 3 is optimal (31.2 MPa); the tensile strength of comparative example 1 (lacking propylene oxide modified starch) is only 21.3 MPa, which is significantly lower than all examples, and the tensile strength of comparative example 2 (lacking organic modified montmorillonite) and comparative example 3 (lacking lipase) is 29.8 MPa and 30.5 MPa respectively, which is slightly lower than example 3 but higher than comparative example 1. Theoretical analysis: propylene oxide modified starch can form hydrogen bonds with the ester groups of polybutylene adipate terephthalate and polylactic acid in the substrate layer through branched chain structure, and at the same time improve the compatibility of natural starch and synthetic polyester, and after the absence of the component, the interfacial bonding force in the substrate layer is greatly reduced, and obvious interface defects appear, resulting in a sharp drop in tensile strength; while the organic modified montmorillonite mainly acts on the barrier and controlled release of the slow-release control layer, and the lipase mainly acts on the degradation acceleration of the degradation promotion layer, both of which have little effect on the overall tensile strength, so the tensile strength decreases limitedly after the absence of the latter. This proves that propylene oxide modified starch is the key raw material to ensure the mechanical properties of the substrate layer, and the present application effectively improves the material structure stability through the synergy of the raw material and other components, meeting the creative requirements of raw material combination.

[0211] Impact strength comparison: the impact strength of examples 1-4 is 4.2-4.8 kJ / m 2 , and example 3 is optimal (4.8 kJ / m 2 ); the impact strength of comparative example 1 is only 3.0 kJ / m 2 , which is much lower than the examples, and the impact strength of comparative example 2 and comparative example 3 is 4.4 kJ / m 2 and 4.5 kJ / m 2 , respectively, which is less different from the examples. Theoretical analysis: impact performance depends on the flexibility and structural integrity of the substrate layer, and propylene oxide modified starch can reduce the hydrophilicity of starch to avoid the swelling of the substrate layer due to moisture absorption, and reduce the brittleness of the material, and the absence of the substrate layer is prone to micro-cracks due to moisture intrusion, and the cracks quickly expand when impacted, resulting in a decrease in impact strength; organic modified montmorillonite and lipase do not directly affect the flexibility of the material, so the impact performance does not change significantly after the absence of the latter. This further verifies the core role of propylene oxide modified starch in the flexibility-rigidity balance of the substrate layer, and embodies the pertinence and rationality of the raw material selection of the present application.

[0212] Nutrient release period comparison: the nutrient release period of examples 1-4 is 4.2-5.0 months, example 3 (4.8 months) is suitable for most crop growth periods and is the best overall; the nutrient release period of comparative example 2 (lacking organic modified montmorillonite) is only 2.6 months, which is much shorter than examples, and comparative example 1 (3.8 months) and comparative example 3 (4.7 months) are lower and close to example 3, respectively. Theoretical analysis: after the organic modified montmorillonite is modified by cetyltrimethylammonium bromide, the interlayer spacing is expanded to 2.5-3.5 nm, which can form a lamellar barrier structure in the slow-release control layer, prolong the diffusion path of the fertilizer solution, and double the nutrient release by interlayer charge adsorption of cations. After the lack of this component, the slow-release control layer only relies on the swelling of polyvinyl alcohol and the adsorption of chitosan, and the controlled release capacity is greatly weakened, resulting in a sharp reduction in the nutrient release period. Propylene oxide modified starch does not directly participate in controlled release, and the lack of it only slightly shortens the nutrient release period due to the slight decrease in the barrier property of the substrate. Lipase has no direct relationship with the slow-release process, and the lack of it has little effect on the nutrient release period. The nutrient release comparison test sample after the packaging material is packaged with the fertilizer is shown in Figure 5 .

[0213] Degradation rate comparison: the 6-month degradation rate of examples 1-4 is 89.6-91.3%, and example 3 is the best (91.3%); the degradation rate of comparative example 3 (lacking lipase) is only 68.9%, which is much lower than examples, and comparative example 1 (83.5%) and comparative example 2 (90.2%) are lower than example 3 but higher than comparative example 3. Theoretical analysis: lipase can specifically catalyze the hydrolysis of ester bonds in polyester materials, forming a double degradation mechanism based on the promotion of starch microbial reproduction. After the lack of it, only microbial degradation of starch is relied on, and the degradation rate is greatly slowed down, and polyester components such as polybutylene succinate cannot be quickly decomposed, resulting in a significant decrease in the 6-month degradation rate. Although propylene oxide modified starch can be decomposed by microorganisms, it is not the core driving force for degradation promotion, and the lack of it only slightly reduces the degradation rate. Organic modified montmorillonite can be absorbed by soil with the degradation of the whole material and does not affect the degradation efficiency, so the lack of it has no obvious effect on the degradation rate. This proves that lipase is the key raw material for realizing the rapid degradation of the material after function, and the present application solves the traditional problem of mismatching between slow-release and degradation period through the synergy of the raw material and starch, which embodies the technological progress.

[0214] Comprehensive performance analysis: comparative examples 1-3 all have obvious performance short boards due to the lack of a single key raw material: comparative example 1 lacks propylene oxide modified starch, and the mechanical properties are severely insufficient; comparative example 2 lacks organic modified montmorillonite, and the slow-release function is invalid; comparative example 3 lacks lipase, and the degradation efficiency is sharply reduced; and example 3 realizes the comprehensive optimal performance of tensile strength 31.2 MPa, impact strength 4.8 kJ / m 2 , nutrient release period 4.8 months, and 6-month degradation rate 91.3% through the synergy of the three key raw materials and other components, without obvious short boards.

[0215] The controlled release fertilizer prepared by the packaging material of the present application needs to be further verified for practical application value through field fertilization test. In the test, different groups are set to observe the nutrient absorption and growth of crops, so as to evaluate the fertilizer utilization rate and environmental adaptability. The field fertilization test site diagram of the fertilizer packaged by the packaging material is shown in Figure 6 .

[0216] The above is a further detailed description of the present application in combination with the preferred embodiments. It cannot be considered that the specific implementation of the present application is limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, they can make several substitutions or modifications to the described embodiments without departing from the concept of the present application, and these substitutions or modifications shall be considered to belong to the protection scope of the present application.

[0217] Although the present application and its advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made without departing from the spirit and scope of the present application. In addition, the scope of application of the present application is not limited to the specific embodiments of the processes, methods and steps described in the specification. From the disclosure of the present application, those skilled in the art will easily utilize existing or later developed processes, methods or steps which substantially perform the same function or achieve the same result as the corresponding embodiments described herein. Therefore, the appended claims are intended to include these processes, methods or steps.

Claims

1. A biodegradable packaging material that controls the release rate of fertilizer nutrients, characterized in that, It consists of a substrate layer, a sustained-release regulating layer, and a degradation promoting layer. The composition of the raw materials in each layer by mass parts is as follows: The substrate layer is composed of the following components: 40-60 parts of polybutylene adipate-terephthalate, 20-30 parts of polylactic acid, 10-20 parts of propylene oxide modified starch, 3-8 parts of tributyl citrate, 2-5 parts of maleic anhydride grafted polyolefin, and 0.5-2 parts of hindered phenolic antioxidant 1010. The sustained-release control layer is composed of the following components: 30-50 parts of polyvinyl alcohol, 5-15 parts of organically modified montmorillonite, 10-20 parts of chitosan, 2-8 parts of nano-silica, and 1-3 parts of glutaraldehyde. The degradation promoting layer is composed of the following components: 40-60 parts of polybutylene succinate, 20-30 parts of starch, and 1-3 parts of calcium stearate. The inner surface of the degradation promoting layer is loaded with 5-10 parts of lipase and 1%-3% of an environmentally friendly binder, wherein the environmentally friendly binder is sodium hydroxymethyl cellulose or polyvinyl alcohol.

2. The packaging material for controlling fertilizer nutrient release rate and being biodegradable according to claim 1, characterized in that, In the substrate layer, the degree of substitution of the propylene oxide-modified starch is 0.3-0.5, and the grafting rate of the maleic anhydride-grafted polyolefin is 1.5-3%.

3. The packaging material for controlling fertilizer nutrient release rate and being biodegradable according to claim 1, characterized in that, In the controlled-release layer, the organically modified montmorillonite is modified with hexadecyltrimethylammonium bromide, and the interlayer spacing of the modified montmorillonite is 2.5-3.5 nm; the degree of polymerization of the polyvinyl alcohol is 1700-2000, and the degree of alcoholysis is 88-99%.

4. The packaging material for controlling fertilizer nutrient release rate and being biodegradable according to claim 1, characterized in that, In the degradation promoting layer, the starch is corn starch or potato starch with a particle size range of 50-100μm; the lipase activity is 10000-20000U / g.

5. A method for preparing a biodegradable packaging material that controls the release rate of fertilizer nutrients as described in any one of claims 1-4, characterized in that, Includes the following steps: S1: Prepare substrate layer masterbatch by weighing raw materials according to the composition of the substrate layer, and obtaining substrate layer masterbatch by high-speed mixing and twin-screw extrusion granulation. S2: Prepare the masterbatch for the slow-release control layer. Weigh the raw materials according to the composition of the slow-release control layer, and obtain the masterbatch for the slow-release control layer by dissolving, mixing, cross-linking reaction, spray drying, and single-screw extrusion granulation. S3: Prepare degradation promoting layer masterbatch. Weigh the raw materials according to the composition of the degradation promoting layer, and obtain the degradation promoting layer masterbatch by high-speed mixing and twin-screw extrusion granulation. S4: Multilayer co-extrusion blow molding. The masterbatches obtained in steps S1, S2 and S3 are added to the corresponding hoppers of the multilayer co-extrusion blow molding machine. After melt extrusion, compounding, blowing, and cooling, an enzyme-free three-layer composite packaging film is obtained. The film is then heat-sealed and cut into a bag-making process to obtain a packaging material blank. S5: Enzyme loading post-treatment, the enzyme solution is applied to the inner surface of the degradation promotion layer of the packaging bag blank, and after low-temperature drying, it becomes a packaging material that can be directly used for fertilizer encapsulation.

6. The method for preparing a biodegradable packaging material with controlled fertilizer nutrient release rate according to claim 5, characterized in that, In step S1, the high-speed mixing is performed in two steps: The first step involves mixing polybutylene adipate terephthalate, polylactic acid, and antioxidant 1010 at 80-90°C and 800-1000 rpm for 5-10 minutes. The second step involves adding propylene oxide-modified starch, tributyl citrate, and maleic anhydride-grafted polyolefin to the mixture from the first step, and mixing at 90-100°C and 1000-1200 rpm for 10-15 minutes. The twin-screw extrusion granulation temperature is 160-180°C, and the screw speed is 200-250 rpm.

7. The method for preparing a biodegradable packaging material with controlled fertilizer nutrient release rate according to claim 5, characterized in that, Step S2 includes: Polyvinyl alcohol is stirred and dissolved at 80-90℃ to form an aqueous solution with a mass concentration of 10-15%; organic modified montmorillonite and nano silica are dispersed at a speed of 600-800 r / min for 30-40 min; chitosan is dissolved in an aqueous solution of acetic acid with a mass concentration of 1-2% to form a chitosan solution with a mass concentration of 5-8%. After the polyvinyl alcohol aqueous solution, the dispersion of montmorillonite and nano silica, and the chitosan solution are mixed evenly, glutaraldehyde is added, and a crosslinking reaction is carried out at 60-70℃ for 1-2 hours. The cross-linked material is spray-dried at an inlet temperature of 120-140℃; the dried powder is then granulated using a single-screw extruder at a granulation temperature of 180-200℃ and a screw speed of 150-200 r / min.

8. The method for preparing a biodegradable packaging material with controlled fertilizer nutrient release rate according to claim 5, characterized in that, In step S3, the high-speed mixing is as follows: polybutylene succinate, starch and calcium stearate are mixed at 90-110℃ and 900-1100 r / min for 10-15 min; the twin-screw extrusion granulation temperature is 150-170℃ and the screw speed is 180-220 r / min.

9. The method for preparing a biodegradable packaging material with controlled fertilizer nutrient release rate according to claim 5, characterized in that, In step S4, the processing parameters of the multi-layer co-extrusion blow molding machine are as follows: temperature settings for each section: 165-185℃ for the section used to melt the substrate layer masterbatch, 185-205℃ for the section used to melt the slow-release control layer masterbatch, 155-175℃ for the section used to melt the degradation promotion layer masterbatch, and 170-190℃ for the die head temperature; screw speed: 220-260 r / min for the corresponding substrate layer, 160-200 r / min for the corresponding slow-release control layer, and 190-230 r / min for the corresponding degradation promotion layer; blow-up ratio: 1.5-2.5; traction speed: 2-5 m / min; and the thickness of the resulting packaging material film is 50-150 μm.

10. The method for preparing a biodegradable packaging material with controlled fertilizer nutrient release rate according to claim 5, characterized in that, The specific operations of step S5 include: (1) Preparation of enzyme solution: Dissolve or disperse lipase in water containing 1-3% sodium hydroxymethyl cellulose or polyvinyl alcohol to form a uniform suspension / solution; (2) Spraying treatment: Keep the bag opening of the packaging bag blank open, and use a spraying device to spray the enzyme solution evenly on the inner surface of its degradation promotion layer at a spraying pressure of 0.2-0.5MPa; (3) Low temperature drying: After drying in circulating hot air at 40-50℃ for 15-30 minutes, packaging materials that can be directly used for fertilizer packaging are obtained.

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