Root-guiding full-biodegradable tree planting bag based on hybrid material modification and application

Abstract

The application relates to the technical field of forestry seedling raising and ecological restoration, and discloses a root guiding type full-biodegradable tree planting bag based on hybrid material modification and application, the tree planting bag is an integrally injection molded structure, the inner wall is provided with vertical root guiding edges, and the bottom is provided with a cross-shaped easy-to-crack line; the tree planting bag is longitudinally divided into an upper structure area and a lower degradation promoting area. The upper part is composed of PBAT / PLA and hybrid materials and has high strength and weather resistance; the lower part is composed of PBAT / PPC, hybrid materials and plant fibers and has moisture absorption and rapid degradation characteristics. The hybrid material is a composite in which nano-hydroxyapatite grows in situ on the surface of attapulgite. Through the synergy of the longitudinal gradient material and the physical root guiding structure, long-term shape retention during seedling raising and rapid disintegration of the bottom after planting are realized, the problems of seedling taproot and degradation lag are solved, the degradation products can adjust the pH value of the rhizosphere soil and provide phosphorus and calcium nutrition, and the afforestation survival rate is improved.

Description

Technical Field

[0001] This invention relates to the field of forestry seedling cultivation and ecological restoration technology, specifically to root-guided fully biodegradable planting bags based on hybrid material modification and their applications. Background Technology

[0002] With the rapid development of modern forestry seedling cultivation technology, container seedling cultivation has gradually replaced traditional bare-root seedling afforestation due to its advantages such as high survival rate and no seasonal restrictions. Traditional seedling containers are mostly made of non-degradable plastics such as polyethylene (PE), which must be removed from the containers during planting. This not only increases labor costs but also easily damages the seedling roots. Furthermore, incomplete recycling of discarded plastic bags can easily cause serious white pollution. Therefore, developing fully biodegradable planting bags has become an inevitable trend in the industry.

[0003] However, existing fully biodegradable seedling containers still face technical bottlenecks in practical applications. Firstly, current biodegradable planting bags typically employ homogeneous material formulations and structural designs, making it difficult to balance the conflict between shape retention during the seedling stage and the degradation rate after planting. To meet the requirements for handling, UV resistance, and hydrolysis resistance during the long seedling stage (6 to 12 months), the material must possess high mechanical strength and stability. However, this results in an excessively long degradation induction period after planting, preventing rapid disintegration during critical growth stages and thus creating mechanical constraints that limit root extension into the surrounding soil. Conversely, if rapid degradation is prioritized, premature damage due to leaching or sunlight during the seedling stage is highly likely, failing to meet the requirements of intensive production.

[0004] Secondly, the smooth inner walls of conventional cylindrical planting bags lack effective physical guidance structures, easily inducing lateral roots to grow spirally along the bag walls, forming root tangles (commonly known as root entanglement). Even when using biodegradable materials, in the early stages of planting before the materials have undergone substantial degradation, the integrity of the bottom of the bag will still prevent the taproot from penetrating deeper into the soil, leading to a significant slow-growth period or stunted growth after afforestation, severely impacting initial growth.

[0005] Furthermore, commonly used biodegradable polyester materials (such as polylactic acid (PLA) and polybutylene adipate / terephthalate (PBAT)) mainly undergo ester bond hydrolysis during degradation, producing a large number of carboxyl-terminated or acidic intermediates (such as lactic acid monomers). The localized accumulation of these acidic substances around the roots leads to a decrease in rhizosphere soil pH, not only poisoning young roots but also affecting soil microbial activity and nutrient availability. Existing biodegradable material formulations mostly focus on molding and processing performance, lacking self-regulating mechanisms for the acidity and alkalinity of degradation products and functions for improving soil nutrition. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a root-guided, fully biodegradable planting bag based on hybrid material modification and its application. This solves the problems of existing biodegradable seedling containers, which are difficult to balance maintaining the shape of seedlings during the seedling stage with quickly breaking open the bag after planting to release root constraints, easily causing root entrapment in seedlings, and causing rhizosphere soil acidification due to polyester degradation products.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a root-guided, fully biodegradable planting bag based on hybrid material modification, employing the following technical solution: A root-guided, fully biodegradable planting bag based on hybrid material modification, wherein the planting bag is an integrally injection-molded bottomed cylindrical structure with vertical root-guiding ridges on the inner wall and a crack-prone line at the bottom. The planting bag is longitudinally composed of an upper structural zone and a lower descending zone, and both the upper structural zone and the lower descending zone are made from raw materials comprising the following parts by weight: Raw materials for the upper structural region: 50-65 parts of poly(butylene adipate) / poly(terephthalate); 20-30 parts of polylactic acid; 5-10 parts of attapulgite / hydroxyapatite hybrid material; 0.5-1.0 parts of anti-hydrolysis agent; 0.2-0.5 parts of ultraviolet absorber; Raw materials for the lower descending zone: 25-40 parts of poly(butylene adipate / terephthalate); 20-35 parts of polypropylene carbonate; 20-30 parts of attapulgite / hydroxyapatite hybrid material; 10-20 parts of plant fiber; 1-2 parts of hydrophilic agent.

[0008] By adopting the above technical solution, this invention utilizes polymer material modification technology and biomimetic structural design to resolve the contradiction between the shape retention of existing biodegradable seedling containers during the seedling stage and the degradation rate after transplanting. Its specific mechanism of action is as follows: Vertical gradient material distribution enables time and air conditioning control for functional zoning: Upper structure area: By introducing polylactic acid to provide high rigidity support, combined with anti-hydrolysis agent and ultraviolet absorber, a stable structure that can withstand light, leaching and external physical impact is formed, ensuring that the above-ground part of the bag does not break or deform during the 6-12 month seedling cycle, meeting the mechanized operation requirements of container seedling cultivation.

[0009] Lower Degradation Zone: Utilizing the easily hydrolyzed ester bonds in the polypropylene carbonate molecular chain, combined with a high content of plant fibers and hydrophilic agents, it rapidly absorbs moisture and swells after planting, initiating bulk degradation. The high-content attapulgite / hydroxyapatite hybrid material acts as microscopic defect points, further accelerating the matrix disintegration process, thereby achieving rapid attenuation of physical strength in the early stages of planting and relieving the roots from constraint.

[0010] Physical structure guides root configuration: The vertical root-guiding ridges on the inner wall alter the growth trajectory of lateral roots after contact with the wall, forcing them to grow downwards and effectively avoiding the root entanglement and knotting common in container seedlings. The easily crackable line at the bottom, combined with the rapid degradation properties of the lower material, allows the taproot to break through the bottom of the bag through its own growth expansion force in the early stages of planting, achieving unimpeded soil growth.

[0011] Preferably, the vertical guide root ridges are distributed from top to bottom along the generatrix direction on the inner wall of the bag, with a quantity of 12-16 ridges, and the cross-section is arc-shaped with a radius of 1.5-3.0 mm and a height of 1.0-2.5 mm; the crackable lines are distributed in a cross shape at the bottom of the bag, and the wall thickness is 30%-50% of the normal wall thickness of the bag.

[0012] By adopting the above technical solution, the vertical root guide ridges of the specified dimensions provide sufficient physical obstruction and guidance. If the height is too low, it cannot effectively prevent lateral roots from spiraling laterally; if the height is too high, it will affect the integrity of the root ball. The bottom cross-shaped cracking line creates stress concentration through localized thinning design, ensuring that the planting bag will preferentially rupture from the bottom when subjected to internal root growth pressure or external soil pressure. Combined with the degradation of the underlying material, this achieves a synergistic effect of physical structural damage and chemical degradation and disintegration.

[0013] Preferably, the attapulgite / hydroxyapatite hybrid material has a microstructure in which nano-hydroxyapatite crystals are grown in situ on the surface and pores of the attapulgite rod crystals; the preparation method of the attapulgite / hydroxyapatite hybrid material includes the following steps: dispersing attapulgite that has been acid-activated and calcined in water, adding a calcium source for adsorption, then adding a phosphorus source, adjusting the pH value to 10-11, and carrying out a hydrothermal reaction at a temperature of 140-180℃ for 6-12 hours, and obtaining the product after washing, drying and pulverizing.

[0014] By adopting the above technical solution, a unique inorganic hybrid enhancement and chemical buffering system was constructed, and its innovative mechanism includes: In-situ growth and nano-reinforcement: Attapulgite undergoes acid activation and calcination to remove pore impurities and expose more active silanol sites. Under hydrothermal conditions, these sites induce calcium ion adsorption and act as nucleation centers, enabling nano-hydroxyapatite crystals to grow in situ on the rod-like surface and within the pores of the attapulgite. This chemically bonded hybrid structure exhibits stronger interfacial bonding than simple physical mixing, and can act as rigid particles to enhance the tensile strength and modulus of the polymer matrix.

[0015] Self-regulating mechanism of degradation environment: Polyester materials (PBAT, PLA, PPC) generate terminal carboxyl groups during degradation, leading to localized acidification of the rhizosphere soil, which in turn inhibits plant growth. In the hybrid material prepared in this invention, nano-sized hydroxyapatite possesses high specific surface area and reactivity, enabling it to slowly release calcium and phosphate ions in neutral or acidic environments, neutralizing the acidic degradation products. This in-situ buffering effect not only stabilizes the rhizosphere pH but also delays the excessively rapid auto-accelerated degradation of polymers caused by acid catalysis, making the degradation process more controllable.

[0016] Preferably, the acid activation treatment of the attapulgite is: treating it with a hydrochloric acid solution with a mass fraction of 10%-15% at 60-80°C for 2-4 hours; the calcination treatment is: calcining at 400-500°C for 2 hours.

[0017] By adopting the above technical solution, acid activation conditions can open up the pores of attapulgite and increase its specific surface area without destroying its crystal framework structure; moderate calcination treatment removes structural water and organic impurities, improves its stability as a carrier, and provides the best matrix for the uniform loading of hydroxyapatite in the future.

[0018] Preferably, the plant fiber is selected from bamboo powder or wood powder, with a particle size distribution D50 of 15-25 μm; the hydrophilic agent is polyethylene glycol; the anti-hydrolysis agent is polycarbodiimide; and the ultraviolet absorber is 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole.

[0019] By employing the above technical solution, micron-sized plant fibers and polyethylene glycol construct a moisture-absorbing channel in the lower settling zone. The water absorption and expansion of the plant fibers create microcracks, promoting the entry of moisture and microorganisms into the material. Polycarbodiimide in the upper structural region can capture carboxyl groups generated by polyester hydrolysis, preventing autocatalytic hydrolysis. Combined with a UV absorber, this extends the service life of the upper material in open-air seedling environments.

[0020] Preferably, the attapulgite / hydroxyapatite hybrid material and plant fiber in the lower settling zone raw material are pre-melted and blended with a portion of poly(adipate adipate / butylene terephthalate) at 125°C-140°C to prepare a pre-dispersed masterbatch, which is then mixed with the remaining raw material. During the preparation of the pre-dispersed masterbatch, the weight of poly(adipate adipate / butylene terephthalate) participating in the melt blending is 30%-40% of the total weight of poly(adipate adipate / butylene terephthalate) in the lower settling zone raw material. The extrusion granulation temperature of the lower settling zone raw material is 125-140°C, and the extrusion granulation temperature of the upper structural zone raw material is 160-175°C.

[0021] By adopting the above technical solutions, the problem of difficult dispersion of high-filler inorganic powders and plant fibers in a polymer matrix was solved using a masterbatch process. The low-temperature extrusion process avoids the thermal degradation and carbonization of plant fibers during processing, while preserving the thermosensitive properties of PPC, ensuring that the intrinsic degradation performance of the material is not damaged during processing. Pre-dispersion ensures the uniform distribution of the hybrid material in the matrix, thereby guaranteeing the uniformity of mechanical properties and the stability of degradation behavior.

[0022] Preferably, the tree planting bag is prepared using a two-component injection molding process, and a non-layered interface fusion structure is formed between the upper structural area and the lower settling area; wherein, the injection melt temperature forming the lower settling area is 135-150℃, the injection melt temperature forming the upper structural area is 155-170℃, and the melt of the upper structural area remelts and bonds with the contact interface of the lower settling area within the mold.

[0023] By employing the above technical solution, two-component injection molding technology was used to achieve the integrated molding of two different formulation materials. Through precise control of the temperature difference and injection sequence of the two melts, the heat from the upper high-temperature melt caused the interface of the lower material, which had been injected first and partially cooled, to remelt, achieving mutual diffusion and entanglement of molecular chains. This interface fusion structure eliminates macroscopic layering interfaces, ensuring the overall structural integrity of the planting bag during transportation and use, and preventing breakage along the interface during use.

[0024] Preferably, the melt flow rate of the poly(butylene adipate) / terephthalate is 3 g / 10 min to 5 g / 10 min; the melt flow rate of the polylactic acid is 6 g / 10 min to 10 g / 10 min; and the melt flow rate of the polypropylene carbonate is 10 g / 10 min to 15 g / 10 min.

[0025] By adopting the above technical solution, the melt flow rate of each component is limited, which ensures the rheological matching of different polymers during blending, which is beneficial to the stability of the phase structure. At the same time, it also ensures that the melt can smoothly fill the complex mold cavity (such as the root ridge structure) during the two-component injection molding process and obtain a good interface welding effect.

[0026] Secondly, this invention provides an application of a root-guided, fully biodegradable planting bag based on hybrid material modification, employing the following technical solution: An application of a root-guided, fully biodegradable planting bag based on hybrid material modification in forestry seedling cultivation and soil improvement involves planting seedlings in the planting bag for cultivation, and then directly planting the seedlings and planting bags together in the soil when the seedlings are ready for transplanting. After the planting bag degrades, the attapulgite / hydroxyapatite hybrid material contained in it remains in situ in the root zone soil to regulate the soil pH and release phosphorus and calcium nutrients.

[0027] By adopting the above technical solution, this application achieves integrated seedling cultivation and afforestation in forestry, avoiding root damage and plastic pollution caused by traditional bag-removal planting. More importantly, this application utilizes the ecological functions of the degraded planting bag material: pH environment improvement: The attapulgite / hydroxyapatite hybrid material remaining in the soil can continuously neutralize the acidic byproducts of polyester degradation and the acidic soil environment by utilizing the weak alkalinity and ion exchange capacity of hydroxyapatite, thus maintaining the pH value of the rhizosphere soil within a range suitable for plant growth.

[0028] Slow-release nutrients: As the inorganic components in the hybrid material gradually dissociate, essential nutrients such as calcium and phosphorus are slowly released, improving the fertility of the root zone microenvironment and promoting rapid recovery and long-term growth of seedlings after planting.

[0029] This invention provides a root-guided, fully biodegradable planting bag based on hybrid material modification and its application. It has the following beneficial effects: 1. This invention constructs a longitudinal gradient material structure through a two-component injection molding process. The upper structural area uses polylactic acid reinforcement and hydrolysis-resistant modified formula to ensure the mechanical strength and integrity of the bag in the open environment during the 6-12 month seedling period, meeting the needs of intensive handling. The lower descending zone introduces easily hydrolyzable polypropylene carbonate and hydrophilic plant fibers, so that after the planting bag is planted in the soil, the bottom area can preferentially disintegrate rapidly through moisture absorption, swelling and microbial erosion. This effectively solves the technical contradiction of traditional biodegradable containers that degrade too early and cannot protect seedlings or degrade too slowly and restrict the root system.

[0030] 2. This invention, by setting vertical root-guiding ridges on the inner wall and a cross-shaped easy-crack line at the bottom, forcibly alters the growth trajectory of lateral roots through physical structure, guiding the horizontally coiled roots to grow downwards, thus eliminating the root tangling problem commonly found in container seedlings. The stress concentration design of the easy-crack line at the bottom, combined with the rapid degradation characteristics of the lower material, creates a synergistic effect, ensuring that the main root of the seedling can break through the limitations of the bag bottom using its own growth expansion force in the early stages of planting, achieving seamless connection between the root system and the surrounding soil, thereby improving the survival rate of afforestation and the initial growth.

[0031] 3. This invention utilizes an in-situ hydrothermal synthesis method to produce an attapulgite / hydroxyapatite hybrid material. Leveraging the high reactivity and acid-base buffering capacity of nano-hydroxyapatite, it effectively neutralizes acidic end products generated during the degradation of polyester materials (PBAT, PLA, PPC), preventing localized acidification of the root zone soil. Simultaneously, this hybrid material, acting as an inorganic carrier, slowly releases nutrients such as calcium and phosphorus during degradation, achieving a dual ecological effect of improving soil physicochemical properties and promoting seedling establishment and recovery. Attached Figure Description

[0032] Figure 1 This is a three-dimensional structural schematic diagram of the present invention; Figure 2 This is a schematic diagram of the internal structure of the planting bag of the present invention.

[0033] Among them, 1. Bag body; 2. Vertical guide root edge; 3. Easily cracked line; 4. Upper structural area; 5. Lower descending area. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments and comparative examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing an attapulgite / hydroxyapatite (ATP-HAP) hybrid material.

[0036] 100g of raw attapulgite powder was dispersed in 1000mL of 12% hydrochloric acid solution and mechanically stirred for 3 hours in a constant temperature water bath at 70℃. The solution was then filtered and washed with deionized water until the pH of the filtrate was 7.0. It was then dried in an oven at 105℃ for 12 hours and then placed in a muffle furnace and calcined at 450℃ for 2 hours to obtain pretreated attapulgite.

[0037] Take 50g of the pretreated attapulgite clay and disperse it in 800mL of deionized water, then ultrasonically disperse for 30 minutes to prepare a suspension. Weigh calcium nitrate tetrahydrate and diammonium hydrogen phosphate according to a Ca / P molar ratio of 1.67. First, dissolve 39.4g of calcium nitrate tetrahydrate in 200mL of deionized water and add it to the above suspension, stirring and adsorbing for 1 hour. Then, dissolve 13.2g of diammonium hydrogen phosphate in 100mL of deionized water and slowly add it dropwise to the mixed system. After the addition is complete, adjust the pH of the system to 10.5 using 1mol / L sodium hydroxide solution.

[0038] The above mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor, sealed, and placed in an oven for hydrothermal reaction at 160°C for 9 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The product was centrifuged, washed three times with deionized water and once with anhydrous ethanol, dried in a vacuum drying oven at 80°C for 12 hours, and finally pulverized using an air jet mill to obtain the ATP-HAP hybrid material described in Example 1, with a BET specific surface area of ​​132 m². 2 / g.

[0039] Preparation Example 2: This preparation example provides a method for preparing an attapulgite / hydroxyapatite (ATP-HAP) hybrid material.

[0040] 100g of attapulgite powder was dispersed in 1000mL of 10% hydrochloric acid solution and mechanically stirred for 2 hours in a constant temperature water bath at 60℃. The subsequent washing and drying steps were the same as in Preparation Example 1. Then, it was placed in a muffle furnace and calcined at 400℃ for 2 hours to obtain pretreated attapulgite.

[0041] Take 50g of the pretreated attapulgite clay and disperse it in 800mL of deionized water, then ultrasonically disperse for 30 minutes. The amount of chemical reagents (calcium nitrate tetrahydrate and diammonium hydrogen phosphate) added and the pH adjustment steps are the same as in Preparation Example 1.

[0042] The mixture was transferred to a high-pressure reactor and subjected to a hydrothermal reaction at 140°C for 6 hours. The post-processing steps were the same as in Preparation Example 1, yielding the ATP-HAP hybrid material described in Preparation Example 2, with a BET specific surface area of ​​125 m². 2 / g.

[0043] Preparation Example 3: This preparation example provides a method for preparing an attapulgite / hydroxyapatite (ATP-HAP) hybrid material.

[0044] 100g of raw attapulgite powder was dispersed in 1000mL of 15% hydrochloric acid solution and mechanically stirred and activated for 4 hours in a constant temperature water bath at 80℃. The subsequent washing and drying steps were the same as in Preparation Example 1. Then, it was placed in a muffle furnace and calcined at 500℃ for 2 hours to obtain pretreated attapulgite.

[0045] Take 50g of the pretreated attapulgite clay and disperse it in 800mL of deionized water, then ultrasonically disperse for 30 minutes. The amount of chemical reagents (calcium nitrate tetrahydrate and diammonium hydrogen phosphate) added and the pH adjustment steps are the same as in Preparation Example 1.

[0046] The mixture was transferred to a high-pressure reactor and subjected to a hydrothermal reaction at 180°C for 12 hours. The post-processing steps were the same as in Preparation Example 1, yielding the ATP-HAP hybrid material described in Preparation Example 3, with a BET specific surface area of ​​138 m². 2 / g.

[0047] Examples 1-4: Example 1: This example provides a root-guided, fully biodegradable planting bag (Φ15cm×H20cm) modified with hybrid materials, including the following steps: (1) Preparation of special granules for the lower descending zone: Weigh 30 parts of PBAT, 30 parts of PPC, 25 parts of the ATP-HAP hybrid material prepared in Preparation Example 1, 15 parts of bamboo powder, and 1.5 parts of polyethylene glycol (PEG-4000) by weight. First, dry all raw materials under vacuum at 75°C for 8 hours.

[0048] The process employs a masterbatch production method: First, a total amount of ATP-HAP hybrid material, a total amount of bamboo powder, and 10 parts of PBAT resin are mixed and fed into a twin-screw extruder. The extrusion temperature is set to 135℃, and the mixture is melt-blended and extruded to granulate, yielding a high-concentration pre-dispersed masterbatch. Subsequently, this pre-dispersed masterbatch is mixed evenly with the remaining 20 parts of PBAT, 30 parts of PPC, and 1.5 parts of polyethylene glycol, and then extruded again through a twin-screw extruder at 140℃ to granulate, obtaining granules specifically for the lower settling zone.

[0049] (2) Preparation of special granules for the upper structure region: Weigh 58 parts of PBAT, 25 parts of PLA, 8 parts of the ATP-HAP hybrid material prepared in Preparation Example 1, 0.8 parts of polycarbodiimide, and 0.3 parts of UV absorber UV-326 by weight. The raw material drying conditions are the same as above.

[0050] Mix all the above components evenly, feed them into a twin-screw extruder, set the extrusion temperature to 165℃, and then cut them into pellets by water cooling to obtain special pellets for the upper structure zone.

[0051] (3) Two-component injection molding: A two-component injection molding machine equipped with a rotary table is used. The first cavity of the mold corresponds to the complete bag shape. Its inner wall is provided with 14 vertical guide root ridges running along the generatrix direction (the cross-section is arc-shaped, with a radius of R=2.0mm and a height of H=1.5mm). The bottom is provided with a cross-shaped protrusion to form a crack line (the thickness at this point is 40% of the normal wall thickness of the bag); the second cavity only corresponds to the upper 2 / 3 area of ​​the bag.

[0052] Step 1: Add the special granules for the lower settling zone to the first injection unit (Unit A), and control the barrel temperature within the range of 135-150℃. Inject the melt into the first cavity, filling approximately 1 / 3 of the cavity volume (covering the bottom and lower sidewalls), and hold the pressure while cooling to solidify the surface.

[0053] Step 2: The moving mold rotates the core and the already formed lower part 180° to the second cavity position. Special granules for the upper structural area are added to the second injection unit (Unit B), controlling the barrel temperature within the range of 155-170℃. The melt is injected into the second cavity to fill the remaining space, utilizing the higher temperature of the melt in Unit B to remelt the interface. After pressure holding, cooling, and ejection, the planting bag is obtained.

[0054] Example 2: This example provides a root-guided, fully biodegradable planting bag based on hybrid material modification, including the following steps: (1) Preparation of special granules for the lower settling zone: Weigh 40 parts PBAT, 20 parts PPC, 30 parts ATP-HAP hybrid material prepared in Preparation Example 2, 10 parts bamboo powder, and 1.0 part polyethylene glycol by weight. The preparation process is the same as in Example 1, except that the extrusion temperature of the masterbatch preparation is adjusted to 140°C and the final granulation temperature is adjusted to 145°C.

[0055] (2) Preparation of special granules for the upper structure region: Weigh 50 parts of PBAT, 30 parts of PLA, 10 parts of ATP-HAP hybrid material prepared in Preparation Example 2, 1.0 part of polycarbodiimide, and 0.5 parts of UV absorber UV-326 by weight. The preparation process is the same as in Example 1, and the extrusion temperature is set to 170℃.

[0056] (3) Two-component injection molding: The mold structure parameters are adjusted as follows: vertical guide root radius R=3.0mm, height H=2.5mm, and the thickness of the bottom crack line is 50% of the normal wall thickness of the bag.

[0057] Step 1: Add the lower part of the material to Unit A, set the barrel temperature to 140-150℃, and injection mold the lower area.

[0058] Step 2: After the mold rotates, the upper material is added to unit B, and the barrel temperature is set to 160-170℃ for injection molding of the upper area. After pressure holding, cooling, and ejection, the planting bag is obtained.

[0059] Example 3: This example provides a root-guided, fully biodegradable planting bag based on hybrid material modification, including the following steps: (1) Preparation of special granules for the lower settling zone: By weight, weigh 25 parts PBAT, 35 parts PPC, 20 parts ATP-HAP hybrid material obtained in Preparation Example 3, 20 parts bamboo powder, and 2.0 parts polyethylene glycol. The preparation process is the same as in Example 1, except that the extrusion temperature for masterbatch preparation is adjusted to 125℃ and the final granulation temperature is adjusted to 135℃. (2) Preparation of special granules for the upper structure region: By weight, weigh 65 parts of PBAT, 20 parts of PLA, 5 parts of ATP-HAP hybrid material prepared in Preparation Example 3, 0.5 parts of polycarbodiimide, and 0.2 parts of UV absorber UV-326. The preparation process is the same as in Example 1, and the extrusion temperature is set to 160℃.

[0060] (3) Two-component injection molding: The mold structure parameters are adjusted as follows: vertical guide root radius R=1.5mm, height H=1.0mm, and bottom crack line thickness is 30% of the normal wall thickness of the bag.

[0061] Step 1: Add the lower part of the material to Unit A, set the barrel temperature to 135-145℃, and injection mold the lower area.

[0062] Step 2: After the mold rotates, the upper material is added to unit B, and the barrel temperature is set to 155-165℃ for injection molding of the upper area. After pressure holding, cooling, and ejection, the planting bag is obtained.

[0063] Example 4: This example provides a root-guided, fully biodegradable planting bag based on hybrid material modification, including the following steps: (1) Preparation of special granules for the lower descending zone: Weigh out 35 parts of PBAT, 25 parts of PPC, 28 parts of the ATP-HAP hybrid material prepared in Example 1, 12 parts of bamboo powder, and 1.2 parts of polyethylene glycol by weight. The preparation process is the same as in Example 1.

[0064] (2) Preparation of special granules for the upper structure region: Weigh 55 parts of PBAT, 28 parts of PLA, 6 parts of the ATP-HAP hybrid material prepared in Example 1, 0.6 parts of polycarbodiimide, and 0.4 parts of UV absorber UV-326 by weight. The preparation process is the same as in Example 1.

[0065] (3) Two-component injection molding: The mold structure is the same as in Example 1 (guide root edge R=2.0mm, H=1.5mm). The injection molding process temperature parameters are the same as in Example 1. After holding pressure, cooling, and ejection, the planting bag is obtained.

[0066] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that the ATP-HAP hybrid material prepared in Preparation Example 1 in the formulation of the lower descending zone and the upper structural zone is completely replaced with an equal part by weight of commercially available 1250 mesh heavy calcium carbonate powder, while the other raw material types, ratios, preparation processes and injection mold structural parameters are the same.

[0067] Comparative Example 2: Compared with Example 1, the difference is that the inner surface of the side wall of the first cavity of the injection mold is a smooth cylindrical surface and does not have a vertical guide root ridge structure; and the thickness of the bottom of the first cavity is uniform and does not have a cross-shaped easy-crack line structure; the rest of the raw material formula and injection molding process parameters are the same.

[0068] Comparative Example 3: Compared with Example 1, the difference is that the entire tree planting bag is made of the special granules for the upper structure area described in Example 1. The specific process is as follows: using a single-component injection molding machine, the special granules for the upper structure area are melted and injected in one go to fill the mold cavity with the root guide ridge and crack-prone line structure, without longitudinal gradient material distribution; the other mold structure parameters are the same.

[0069] Comparative Example 4: Compared with Example 1, the difference lies in that the preparation step of the pre-dispersed masterbatch was omitted when preparing the special granules for the lower settling zone. Specifically, PBAT, PPC, the ATP-HAP hybrid material obtained in Example 1, bamboo powder, and polyethylene glycol were directly mixed uniformly in the weight proportions described in Example 1, and fed into a twin-screw extruder for extrusion granulation at 140°C; the remaining raw material formulation, top material preparation, and two-component injection molding process were all the same.

[0070] Comparative Example 5: Compared to Example 1, the difference lies in that the ATP-HAP hybrid material obtained in Preparation Example 1 is replaced with a physical mixture of attapulgite powder and nano-hydroxyapatite powder in equal parts by weight. The mass ratio of attapulgite to hydroxyapatite in this physical mixture is consistent with the theoretical composition ratio of the final product in Preparation Example 1; the remaining raw material formulations, preparation processes, and mold structures are all the same.

[0071] Test Example 1-2: Test Example 1: Basic Physical and Mechanical Properties and In Vitro Simulated Degradation Performance Test This test case aims to verify the basic material properties of the planting bags prepared in Examples 1-4 and their degradation behavior under simulated conditions, so as to evaluate whether they meet the basic requirements of maintaining shape during the seedling stage and degradation after being planted in the soil.

[0072] Experimental methods: Tensile property testing (for the upper structural area): Standard dumbbell-shaped specimens (compliant with GB / T1040.2-2006 standard, type 1A) were cut from the upper structural area of ​​the planting bags prepared in Examples 1-4. Tensile tests were performed at room temperature using a universal testing machine at a tensile rate of 50 mm / min. Tensile strength and elongation at break were recorded. Five parallel specimens were tested in each group, and the average value was taken.

[0073] Water absorption test (for the lower settling zone): A 50mm × 50mm square sample was cut from the lower settling zone of the planting bag and tested according to GB / T1034-2008 standard. The sample was dried at 80℃ to constant weight (denoted as ). Then immerse it in deionized water at 23°C for 24 hours. After removing it, blot the surface moisture with filter paper and weigh it immediately (record as ). The formula for calculating water absorption rate is: .

[0074] (3) Soil degradation weight loss rate test (for the lower settling zone): To simulate the natural soil environment, a landfill substrate was prepared by mixing humus, sand, and organic fertilizer in a ratio of 5:3:2, maintaining a moisture content of 40%-50%, and adjusting the pH value to 6.8-7.2. The samples from the lower settling zone (dried to constant weight, denoted as...) were... The substrate was buried to a depth of 10 cm, and the ambient temperature was controlled at 25±2℃. It was removed on days 30, 60, and 90, respectively. The surface soil was washed off, ultrasonically cleaned, and vacuum dried to constant weight (denoted as ). The formula for calculating the weightlessness rate is: .

[0075] Test results: Table 1. Summary of basic physical properties and degradation data of planting bag materials in Examples 1-4

[0076] Results analysis: According to Table 1 and appendix Figure 1 and attached Figure 2 The data analysis is as follows: The mechanical strength meets the requirements for seedling cultivation. The tensile strength of the upper structural region in Examples 1-4 all exceeds 35 MPa, with Example 2 reaching 55.8 MPa due to its higher PLA and ATP-HAP content. This indicates that the ATP-HAP hybrid material acts as a rigid particle reinforcement in the PBAT / PLA matrix, and the hybrid material prepared by the in-situ hydrothermal method has good interface bonding with the matrix, effectively bearing stress and ensuring that the planting bags have sufficient physical support during the 6-12 month seedling cultivation period, preventing damage or deformation.

[0077] The regulation mechanism of water absorption rate and degradation rate shows a clear positive correlation between the water absorption rate and the degradation weight loss rate in the lower degradation zone. Example 3, containing a high proportion of PPC and bamboo powder, exhibited a water absorption rate of nearly 8% in 24 hours and a weight loss rate as high as 76.3% in 90 days. This is because the ester bonds in the PPC molecular chain are easily hydrolyzed, and combined with the hygroscopic swelling effect of bamboo powder and the hydrophilic surface of the ATP-HAP hybrid material, interconnected water transport channels are constructed within the material, accelerating the bulk degradation of the matrix. Conversely, the formulation of Example 2, with its high PLA content, hinders water penetration and exhibits a slower degradation rate.

[0078] Comparing the data from Examples 1, 2, and 3 regarding the designability of degradation behavior, it is evident that by adjusting the ratio of PBAT / PLA / PPC and the filler content in the formulation, the degradation cycle of the material can be adjusted within a wide range (90-day weight loss rate covering a range of 33.7% to 76.3%). The degradation curve of Example 1 (30 days 12.8% -> 90 days 54.1%) shows a clear accelerating trend, which meets the growth requirements of protecting the root system in the early stage of seedling planting and rapidly disintegrating to make way in the later stage. The above results confirm the feasibility of the vertical gradient functionalization scheme achieved by the present invention through component regulation. Test Example 2: Comprehensive Evaluation of Seedling Root Morphology Regulation and Planting Growth Effect This test case compares and examines the effects of planting bags prepared in each embodiment and the comparative example on the root system structure of seedlings, the ability to break through the bags after planting, and the improvement effect on the soil microenvironment in the root zone under actual seedling cultivation and afforestation scenarios.

[0079] Experimental methods: The seedling cultivation and planting experiment used tissue-cultured eucalyptus (Eucalyptus robusta) seedlings with uniform growth as test plants. The seedling substrate was a mixture of yellow soil, peat moss, and carbonized rice husks in a volume ratio of 6:3:1, with an initial pH of 5.5-5.8 (acidic soil environment). Planting bags prepared in Examples 1-4 and Comparative Examples 1-5 were used for soil-filled seedling cultivation, with 100 bags per treatment. Conventional water and fertilizer management was applied, and the seedling cultivation period was 8 months. After the seedling cultivation period, the seedlings, along with the planting bags, were directly planted in the afforestation experimental site. The planting hole dimensions were 30cm × 30cm × 30cm, with a plant spacing of 2m × 3m.

[0080] The root knot index (root entanglement rate) was determined at the end of the seedling stage (before transplanting). Ten seedlings were randomly selected from each group, and the planting bags were carefully cut open. The root morphology on the surface of the root ball was observed. If the taproot or lateral root with a diameter >1mm bent and coiled at an angle exceeding 90 degrees on the inner wall of the bag, it was recorded as root entanglement. The proportion of seedlings with root entanglement was calculated.

[0081] Bottom penetration rate was measured 4 weeks after planting. Ten seedlings were randomly dug up from each group, and the interaction between the root system and the bottom of the bag was observed. The number of seedlings whose taproots successfully broke through the crack line at the bottom of the bag and penetrated into the surrounding soil was counted, and the penetration rate was calculated.

[0082] Growth and soil pH monitoring: Six months after planting, seedling height was measured, and the net increase in height since planting was calculated. Simultaneously, rhizosphere soil within a 5cm radius around the roots was collected (excluding undegraded plastic fragments), air-dried, sieved, and its pH was determined using a potentiometry method to evaluate the effect of material degradation products on improving acidic soil.

[0083] Test results: Table 2. Test data on the application effects of eucalyptus seedling cultivation and planting in each embodiment and comparative example.

[0084] Results analysis: Based on the material structure design mechanism and the measured data in Table 2, the analysis is as follows: Comparing the data from Example 1 and Comparative Example 2, which show the decisive role of physical structure in root system configuration, under the premise of completely identical material formulations, Example 1 had a root trapping rate of only 4.2%, while Comparative Example 2, with its smooth inner wall and no root-guiding ridges, had a root trapping rate as high as 78.6%. The data indicates that the vertical root-guiding ridges on the inner wall effectively altered the growth trajectory of lateral roots after contact with the wall, forcibly guiding them downwards. Simultaneously, Example 1's high bottom penetration rate of 93.5% verified the synergistic effect of the bottom cross-shaped cracking line and the lower root-promoting material, ensuring that the taproot could quickly break through the limitations in the early stages of planting. In contrast, Comparative Example 2, due to the lack of physical guidance and bottom stress concentration points, resulted in severe root coiling within the bag and a low bottom penetration rate, leading to significant stunted growth after planting and a lower increase in plant height compared to the Example 1 group.

[0085] The gradient material distribution addresses the contradiction of degradation timing. Comparative Example 3 used a homogeneous high-strength material (formula in the upper structural zone). Although it maintained good shape during the seedling stage, the bottom penetration rate was only 12.8% four weeks after transplanting. This indicates that a single material cannot simultaneously meet the strength requirements during the seedling stage and the need for rapid bag breaking after transplanting, resulting in long-term root confinement and severely inhibiting the growth of the above-ground parts (the lowest increase in plant height, only 48.2 cm). Examples 1-4, through a longitudinal gradient design, successfully achieved spatial separation of shape preservation and bag breaking functions by utilizing the rapid disintegration characteristics of the lower PPC and high-ATP-HAP content.

[0086] The chemical modification and soil improvement advantages of hybrid materials: In terms of soil improvement, the rhizosphere soil pH of Example 1 increased to 7.12 (neutral), while that of Comparative Example 1 using calcium carbonate filling was only 6.15, and that of Comparative Example 5 using physically mixed ATP / HAP was 6.53. This difference reveals the unique mechanism of in-situ hydrothermal synthesis of ATP-HAP hybrid materials: First, the degradation process of PBAT / PLA produces carboxyl termini, leading to local soil acidification. HAP (hydroxyapatite) has excellent acid-base buffering capacity, but simple physical mixing (Comparative Example 5) or ordinary calcium carbonate (Comparative Example 1) tends to agglomerate in the polymer matrix, resulting in a small specific surface area and limited reactivity.

[0087] Second, in Example 1, ATP is used as a nanocarrier to uniformly disperse HAP nanocrystals, increasing their contact area with acidic degradation products, thereby more efficiently neutralizing acidic substances and stabilizing the pH environment in the root zone.

[0088] Furthermore, comparing Example 1 with Comparative Example 4 (without masterbatch process), the plant height increase and penetration rate data of Comparative Example 4 fluctuated significantly and were generally lower, confirming the necessity of masterbatch process for the performance stability of high-filler composite materials. Uneven dispersion can lead to a decrease in local mechanical properties or uncontrollable degradation of the material, affecting the final application effect.

Claims

1. A root-guided, fully biodegradable planting bag based on hybrid material modification, characterized in that, The planting bag is a one-piece injection-molded cylindrical structure with a bottom. It has vertical root guide ridges (2) on the inner wall and easy-crack lines (3) at the bottom. The planting bag is composed of an upper structural area (4) and a lower descending area (5) in the longitudinal direction. The upper structural area (4) and the lower descending area (5) are made of raw materials containing the following parts by weight: Upper structural region (4) raw materials: 50-65 parts of poly(adipic acid) / butylene terephthalate; 20-30 parts of polylactic acid; 5-10 parts of attapulgite / hydroxyapatite hybrid material; 0.5-1.0 parts of anti-hydrolysis agent; 0.2-0.5 parts of ultraviolet absorber; Lower descending zone (5) Raw materials: 25-40 parts of poly(butylene adipate / terephthalate); 20-35 parts of polypropylene carbonate; 20-30 parts of attapulgite / hydroxyapatite hybrid material; 10-20 parts of plant fiber; 1-2 parts of hydrophilic agent.

2. The root-guided, fully biodegradable planting bag based on hybrid material modification according to claim 1, characterized in that, The vertical guide root ridges (2) are distributed from top to bottom along the generatrix direction on the inner wall of the bag body (1), with a quantity of 12-16 ridges. The cross-section is arc-shaped with a radius of 1.5-3.0 mm and a height of 1.0-2.5 mm. The easily cracked line (3) is distributed in a cross shape at the bottom of the bag body (1), and the wall thickness is 30%-50% of the normal wall thickness of the bag body (1).

3. The root-guided, fully biodegradable planting bag based on hybrid material modification according to claim 1, characterized in that, The preparation method of the attapulgite / hydroxyapatite hybrid material includes the following steps: Attapulgite clay that has been acid-activated and calcined is dispersed in water, and a calcium source is added for adsorption, followed by the addition of a phosphorus source. The pH value is adjusted to 10-11, and a hydrothermal reaction is carried out at 140-180℃ for 6-12 hours. The product is then washed, dried, and pulverized to obtain the final product.

4. The root-guided, fully biodegradable planting bag based on hybrid material modification according to claim 3, characterized in that, The acid activation treatment of the attapulgite clay is as follows: using a hydrochloric acid solution with a mass fraction of 10%-15% to treat it at 60-80℃ for 2-4 hours; The calcination treatment is as follows: calcination at 400-500℃ for 2 hours.

5. The root-guided, fully biodegradable planting bag based on hybrid material modification according to claim 1, characterized in that, The plant fiber is selected from bamboo powder or wood powder, and the particle size distribution D50 is 15-25μm. The hydrophilic agent is polyethylene glycol; The anti-hydrolysis agent is polycarbodiimide; The ultraviolet absorber is 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole.

6. The root-guided, fully biodegradable planting bag based on hybrid material modification according to claim 1, characterized in that, The attapulgite / hydroxyapatite hybrid material and plant fiber in the lower descending zone (5) are pre-blended with a portion of poly(adipic acid) / butylene terephthalate at 125℃-140℃ to form a pre-dispersed masterbatch, which is then mixed with the remaining raw materials.

7. The root-guided, fully biodegradable planting bag based on hybrid material modification according to claim 1, characterized in that, The injection melt temperature for forming the lower settling zone (5) of the tree planting bag is 135-150℃, and the injection melt temperature for forming the upper structural zone (4) is 155-170℃. The melt of the upper structural zone (4) undergoes remelting and bonding with the contact interface between the lower settling zone (5) and the mold.

8. The root-guided, fully biodegradable planting bag based on hybrid material modification according to claim 1, characterized in that, The melt mass flow rate of the poly(butylene adipate / terephthalate) is 3 g / 10 min to 5 g / 10 min. The melt mass flow rate of the polylactic acid is 6 g / 10 min to 10 g / 10 min; The melt flow rate of the polypropylene carbonate is 10 g / 10 min to 15 g / 10 min.

9. The root-guided, fully biodegradable planting bag based on hybrid material modification according to claim 6, characterized in that, In the preparation of the pre-dispersed masterbatch, the weight of poly(adipate adipate / butyl terephthalate) participating in the melt blending is 30%-40% of the total weight of poly(adipate adipate / butyl terephthalate) in the raw materials of the lower settling zone (5); The extrusion granulation temperature of the raw material in the lower settling zone (5) is 125-140℃; The extrusion granulation temperature of the raw material in the upper structural region (4) is 160-175℃.

10. The application of root-guided, fully biodegradable planting bags based on hybrid material modification, characterized in that, The application of the root-guided fully biodegradable planting bag based on hybrid material modification as described in any of claims 1-9 in forestry seedling cultivation and soil improvement involves planting seedlings in the planting bag for cultivation, and then directly planting the seedlings and planting bags together in the soil when the seedlings are ready for transplanting. After the tree planting bags degrade, the attapulgite / hydroxyapatite hybrid material they contain remains in situ in the root zone soil to regulate soil pH and release phosphorus and calcium nutrients.

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