PHA-based barrier-pore synergistic potted seedling cups suitable for natural composting disposal, their preparation method and application

Abstract

This invention discloses a PHA-based barrier porous synergistic potted seedling cup suitable for natural composting, its preparation method, and its applications, belonging to the fields of biodegradable polymer materials, horticultural container structural engineering, and natural composting technology. Addressing the industry pain point that existing biodegradable containers struggle to balance wet-state durability with composting degradation speed, this solution innovatively constructs an asymmetric gradient structure with a loose outer layer and a hydrophilic inner layer. The outer layer employs highly efficient bio-based barrier technology, requiring only a very low addition amount to form a dense protective layer, achieving superior water control performance and structural strength comparable to petrochemical plastics. The inner layer features a specially designed hydrophilic porous system that actively absorbs water in the composting environment, triggering microporous disintegration, significantly improving microbial colonization efficiency and guiding root penetration, overcoming the technical barrier of difficult degradation of high-barrier materials. This product is fully biodegradable and fluorine-free and safe, perfectly achieving a balance between robust reliability during use and rapid return to nature after disposal, possessing broad application prospects.

Description

Technical Field

[0001] This invention belongs to the fields of biodegradable polymer materials, horticultural container structural engineering and natural composting disposal technology, specifically involving a PHA-based barrier porous synergistic potted seedling cup suitable for natural composting disposal, its preparation method and application. Background Technology

[0002] Gardening containers such as seedling cups, nutrient cups, and plug trays are in high demand in the fields of flower and grass seedling cultivation, vegetable seedling cultivation, and forestry seedling cultivation. Traditional seedling cups are mostly made of petrochemical-based general-purpose plastics such as polypropylene (PP) and polyethylene (PE), which have advantages such as high strength, dimensional stability, mature processing, and low cost. However, after use, these containers are usually covered with substrate, stains, and agricultural residues, resulting in high recycling and cleaning costs, a broken recycling chain, and a high risk of generating large amounts of difficult-to-manage solid waste, putting pressure on the ecological environment.

[0003] To reduce plastic waste, alternatives such as molded pulp pots, natural fiber pots, starch-based pots, and some biodegradable plastic pots have emerged in the market. However, in actual seedling production, transportation, and retail scenarios, these alternatives generally present irreconcilable engineering contradictions. Firstly, there is the issue of wet strength decay during the seedling stage and failure during transport and stacking. Under prolonged watering and high humidity conditions, or during stacking and transportation, these materials are prone to softening, deformation, cracking, or collapse, severely impacting the reliability of automated potting, mechanical handling, and shelf display. Secondly, increased sidewall seepage and evaporation lead to additional irrigation burdens. Water migration and ineffective evaporation along the sidewalls of porous or absorbent materials significantly increase the frequency and amount of water needed for replenishment, increasing management costs. Furthermore, there is a difficult trade-off between root penetration, disintegration during the treatment period, and reliability during the seedling stage. If the container walls are too dense, while reliable during the seedling stage, root penetration is difficult and disintegration during the treatment period is slow; if they are too porous, seedlings are prone to premature failure. Finally, there is the issue of adaptability to natural composting conditions. Natural composting, which is home, community, or farm composting, has large fluctuations in temperature, humidity, and oxygen supply levels, with a relatively low average temperature and significant differences in management intensity. This results in many materials that are only suitable for industrial composting environments degrading slowly, taking a long time, or having uncontrollable residual time in natural composting.

[0004] Polyhydroxyalkanoate (PHA) polymers are a class of thermoplastic biodegradable materials synthesized by microorganisms. They possess excellent biocompatibility and full biodegradability potential, and can be molded using processes such as injection molding, making them promising for applications in horticultural containers. Common PHA materials include poly(3-hydroxybutyric acid) (PHB), poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) (P34HB), poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) (PHBH), and medium- and long-chain PHAs. However, PHA materials are sensitive to moisture and thermal history, and are prone to thermal degradation during melt processing, leading to a decrease in molecular weight and performance fluctuations. Furthermore, using excessively strong barrier systems to achieve effective water control during the seedling stage often hinders the entry of moisture and microorganisms under natural composting conditions, thus slowing down the disintegration and degradation initiation during the disposal phase. In existing publicly available technologies, some technical approaches attempt to obtain water resistance by combining fiber substrates with surface barrier treatments, or by using organic solvents or aqueous dispersions for coating. However, these methods have problems such as complex processes, high costs, or potential environmental risks.

[0005] Therefore, there is an urgent need for an engineered solution that can exhibit water control capabilities and mechanical strength close to those of traditional plastic containers during the seedling stage, while actively initiating porosimetry and pyrolysis during the natural composting process to accelerate disintegration and degradation, and meeting stringent environmental compliance requirements. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a PHA-based barrier pore-forming synergistic potted seedling cup suitable for natural composting disposal, as well as its preparation method and application.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a PHA-based barrier-porous synergistic potted seedling cup suitable for natural composting, comprising a cup body having sidewalls and a bottom, and the cup body comprising a cup body matrix formed by thermoplastic injection molding. The sidewalls, along their thickness direction, include an outer barrier region on the outer surface and an inner porous structure region on the inner surface. The outer barrier region and the inner porous structure region are layered or have a compositional gradient structure, and both are thermoplastic PHA-based composite materials. The outer barrier region is made of the outer barrier composite material, which, by mass, comprises: a PHA polymer and a biodegradable hydrophobic barrier component, wherein the biodegradable hydrophobic barrier component comprises 0.2 parts to 8 parts by mass, specifically 0.2 parts, 0.5 parts, 1.0 parts, 2.0 parts, 3.0 parts, 4.0 parts, 5.0 parts, 6.0 parts, 7.0 parts, and 8.0 parts. The inner porous structure region is made of an inner porous composite material, which comprises, by mass parts, a PHA polymer and a hydrophilic porous component, wherein the hydrophilic porous component comprises 6 to 28 parts by mass, specifically 6, 7, 8, 10, 12, 15, 18, 19, 20, 22, 25, or 28 parts. The equivalent thickness of the outer barrier region is 0.02 mm to 0.20 mm, specifically 0.02 mm, 0.03 mm, 0.05 mm, 0.06 mm, 0.08 mm, 0.09 mm, 0.10 mm, 0.12 mm, 0.15 mm, 0.18 mm, or 0.20 mm. When the outer barrier region is formed by melt coating and bonding with the cup body substrate, the outer barrier region is located on the outside of the cup body substrate, and an interface transition layer is provided between the outer barrier region and the inner porous structure region. The thickness of the interface transition layer is 0.01mm to 0.30mm, specifically 0.01mm, 0.03mm, 0.05mm, 0.08mm, 0.10mm, 0.15mm, 0.20mm, 0.25mm, 0.30mm, etc.

[0009] The total fluoride content of the seedling cups is characterized by the total fluoride result measured according to IEC 62321-3-2:2020, which is <5 mg / kg on a dry basis, and the detection limit of the total fluoride determination method is 5 mg / kg.

[0010] The outer barrier composite material and / or the inner porous composite material further include a flexible modifying component, a reinforcing or filling component, a reaction compatibilizer or chain extender component, and / or auxiliaries. The flexible modifying component is formed by the condensation polymerization of a diacid component and a diol component or by the ring-opening polymerization of a lactone monomer, wherein the lactone monomer is selected from one or both of ε-caprolactone and lactide. The reinforcing or filling component is selected from natural fibers, mineral fillers, or combinations thereof. The reaction compatibilizer or chain extender component is selected from epoxy-containing polyfunctional compounds, anhydride-containing compatibilizers, isocyanate-containing chain extenders, carbodiimide stabilizers, or combinations thereof. The auxiliaries are selected from lubricants, antioxidants, heat stabilizers, UV stabilizers, nucleating agents, plasticizers, processing aids, colorants, antistatic agents, flame retardants, antibacterial agents, or combinations thereof.

[0011] When the sidewall has a composition gradient structure, the mass fraction of the outer barrier composite material and the inner porous composite material changes continuously in the thickness direction, so that the mass fraction of the outer barrier composite material in the outer barrier region is greater than the mass fraction of the inner porous composite material, and the mass fraction of the inner porous composite material in the inner porous structure region is greater than the mass fraction of the outer barrier composite material.

[0012] The outer barrier region is a semi-continuous barrier molten coating formed on the outer surface of the sidewall. The semi-continuous barrier molten coating has at least one uncoated discontinuous area on the outer surface of the sidewall along the circumferential or axial direction. The semi-continuous barrier molten coating is formed by melting and coating the outer barrier composite material and then cooling it. The melting and coating is performed by melt extrusion coating or melt scraping coating, using the melt of the outer barrier composite material as the coating medium.

[0013] The sidewall is provided with guide root weak lines extending along the axial direction of the cup body. These guide root weak lines are crack-initiating structures formed by thinning grooves, indentations, scribing lines, or micro-perforations. Furthermore, the outer barrier region is discontinuous, strip-shaped, microporous, or thinned in the area corresponding to the guide root weak lines. The bottom of the cup is provided with drainage holes and / or pre-cracked guide root structures, wherein the number of drainage holes is at least one, and the pre-cracked guide root structure is a pre-crack line structure disposed on the bottom of the cup.

[0014] When the outer barrier region is formed by melt coating and bonding with the cup matrix, the interface transition layer contains a PHA polymer and a reaction compatibilizer or chain extender component.

[0015] The PHA polymer is selected from short-chain PHA, medium- and long-chain PHA, or copolymers between monomers forming short-chain and medium- and long-chain PHA. The short-chain PHA is selected from one or more combinations of poly(3-hydroxybutyric acid) (PHB), poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) (PHBV), and poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) (P34HB). The medium- and long-chain PHA is selected from one or more combinations of poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), poly(3-hydroxynonanoate), poly(3-hydroxydecanoate), poly(3-hydroxyundecanoate), poly(3-hydroxydodecanoate), poly(3-hydroxytridecanoate), poly(3-hydroxytetradecanoate), poly(3-hydroxypentadecanoate), and poly(3-hydroxyhexadecanoate). The molar content of the 3-hydroxyvalerate structural unit in the PHBV is 2 mol% to 25 mol%, specifically 2 mol%, 3 mol%, 5 mol%, 8 mol%, 10 mol%, 12 mol%, 15 mol%, 18 mol%, 20 mol%, 22 mol%, 25 mol%, etc.

[0016] The biodegradable hydrophobic barrier component is selected from natural resin derivatives, waxes, plant oil derivatives, aliphatic esters, aliphatic amides, biodegradable hydrophobic polyester waxes, or combinations thereof. The natural resin derivatives include one or more of rosin and its derivatives, and damar resin. The waxes include one or more of carnauba wax, beeswax, rice bran wax, and candelilla wax. The plant oil derivatives include one or more of hydrogenated vegetable oils and castor oil derivatives. The aliphatic esters include one or more of esters formed from fatty acids and polyols, and esters formed from fatty alcohols and fatty acids. The aliphatic amides include one or more of fatty acid amides. The biodegradable hydrophobic polyester wax is a hydrophobic polyester wax formed by the condensation polymerization of aliphatic diacids and aliphatic diols.

[0017] The hydrophilic porous component is selected from thermoplastic starch (TPS) and its derivatives, water-soluble polysaccharides, water-soluble cellulose derivatives, water-soluble oligomers, water-soluble inorganic salts, or combinations thereof. The hydrophilic porous component in the internal porous composite material includes 0.2 to 8 parts of a natural composting promoting component, specifically 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0 parts. The natural composting promoting component is included as part of the mass fraction of the hydrophilic porous component. The natural composting promoting component is selected from monosaccharides, disaccharides, oligosaccharides, starch hydrolysates, amino acids, peptides, organic acid salts, or combinations thereof. The organic acid salt includes one or more of lactate, citrate, and acetate. When the internally porous composite material includes a reinforcing or filler component, the reinforcing or filler component is selected from natural fibers, mineral fillers, or combinations thereof. When the reinforcing or filler component contains natural fibers, the average length of the natural fibers is 0.1 mm to 0.8 mm, specifically 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, etc.

[0018] When the sidewall has a layered structure, the equivalent thickness of the outer barrier region is the arithmetic mean of the thickness of the outer barrier region obtained by microscopic measurement of the sidewall cross-section at at least three measurement points along the circumference and axial direction of the sidewall. Alternatively, when the outer barrier region is a semi-continuous barrier molten coating with discontinuous areas, the equivalent thickness of the outer barrier region is the equivalent thickness obtained by dividing the unit area mass increment by the density of the coating material, wherein the unit area is the total area of ​​the outer surface of the sidewall and includes the discontinuous areas, the unit area mass increment is the difference in unit area mass of the sample before and after coating, and the density of the coating material is the density at 23°C. The ratio of the equivalent thickness of the outer barrier region to the total thickness of the sidewall is 4% to 20%, specifically 4%, 5%, 8%, 10%, 10.91%, 12%, 13.33%, 13.85%, 15%, 16.67%, 17.14%, 18%, 20%, etc., and the ratio of the equivalent thickness of the outer barrier region to the thickness of the inner porous structure region is 1:4 to 1:20, specifically 1:4, 1:4.83, 1:5, 1:6, 1:6.22, 1:6.5, 1:8, 1:8.17, 1:9, 1:10, 1:12, 1:15, 1:18, 1:20, etc. The static water droplet contact angle of the outer surface of the outer barrier region, measured according to GB / T 30693-2014 at 25°C and 50% relative humidity, is 95° to 120°, specifically 95°, 96°, 98°, 100°, 102°, 105°, 106°, 108°, 110°, 112°, 115°, 118°, 120°, etc., and the static water droplet contact angle of the inner surface of the inner porous structure region, measured according to GB / T30693-2014 at 25°C and 50% relative humidity, is 40° to 80°, specifically 40°, 42°, 45°, 50°, 55°, 58°, 60°, 62°, 65°, 68°, 70°, 75°, 78°, 80°, etc.

[0019] The outer barrier composite material comprises, by weight, 60 to 95 parts of PHA polymer, specifically 60, 65, 70, 75, 80, 82, 85, 88, 90, and 95 parts; 0.2 to 8 parts of biodegradable hydrophobic barrier component, specifically 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0 parts; and 0 to 1 part of hydrophilic porous component, specifically 0 parts. 2 parts, 0.5 parts, 0.8 parts, 1.0 parts, etc.; flexible modification components 0 parts to 25 parts, specifically 0 parts, 5 parts, 10 parts, 12 parts, 15 parts, 20 parts, 25 parts, etc.; reinforcement or filler components 0 parts to 20 parts, specifically 0 parts, 1.0 parts, 2.0 parts, 4.0 parts, 5.0 parts, 6.0 parts, 10 parts, 12 parts, 15 parts, 20 parts, etc.; additives 0 parts to 10 parts, specifically 0 parts, 0.5 parts, 1.0 parts, 2.0 parts, 5.0 parts, 8.0 parts, 10 parts, etc. The internally porous composite material comprises, by weight, 40 to 90 parts of PHA polymer, specifically 40, 50, 55, 60, 65, 65.2, 70, 80, and 90 parts; 0 to 1 part of biodegradable hydrophobic barrier component, specifically 0, 0.2, 0.5, 0.8, and 1.0 parts; 6 to 28 parts of hydrophilic porous component, specifically 6, 7, 10, 12, 15, 18, 19, 20, 25, and 28 parts; and 0 to 20 parts of reinforcing or filler component, specifically 0, ... 0.5 parts, 2.0 parts, 2.5 parts, 3.0 parts, 5.0 parts, 5.2 parts, 10 parts, 15 parts, 20 parts, etc.; flexible modification components 0 parts to 30 parts, specifically 0 parts, 10 parts, 15 parts, 18 parts, 20 parts, 25 parts, 30 parts, etc.; reaction compatibilizers or chain extenders 0 parts to 3 parts, specifically 0 parts, 1.0 parts, 1.1 parts, 1.5 parts, 2.0 parts, 2.1 parts, 3.0 parts, etc.; additives 0 parts to 10 parts, specifically 0 parts, 0.3 parts, 0.5 parts, 0.55 parts, 0.8 parts, 0.9 parts, 1.0 parts, 5.0 parts, 10 parts, etc.

[0020] The present invention also provides a method for preparing the above-mentioned seedling cup, comprising the following steps.

[0021] Step 1. Dry the PHA polymer in a vacuum drying oven until the moisture content is ≤0.025wt%, specifically 0.005wt%, 0.01wt%, 0.015wt%, 0.02wt%, 0.025wt%, etc., where the moisture content is expressed as a mass percentage and determined using a Karl Fischer moisture titrator; dry the hydrophilic porous component, biodegradable hydrophobic barrier component, reinforcing or filler component, flexible modification component, reaction compatibilizer or chain extender component, and auxiliaries separately until their moisture content is ≤0.4wt%, specifically 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, etc., and seal them after cooling to obtain the dried raw material.

[0022] Step 2. Add the dried raw materials obtained in Step 1 to a twin-screw extruder for melt blending and granulation to obtain outer barrier composite material granules and inner porous composite material granules.

[0023] Step 3. Feed the outer barrier composite material granules and the inner porous composite material granules obtained in Step 2 into an injection molding machine, and use one of the following methods: co-injection molding, two-material injection molding, in-mold melt coating combined molding, external melt coating combined molding, or single-layer gradient molding, so that the outer barrier area and the inner porous structure area are formed on the sidewall to obtain the cup body.

[0024] Step 4. Cool and shape the cup obtained in step 3 inside or outside the mold and then demold it to obtain the seedling cup.

[0025] In steps 2 and 3, the melting residence time is ≤3 min, specifically 0.5 min, 1.0 min, 1.5 min, 2.0 min, 2.5 min, 3.0 min, etc. The melting residence time is the average melting residence time, calculated as the ratio of the effective melt volume of the equipment to the actual mass flow rate. When step 3 uses melt coating combined with molding, the melt coating is performed by melt extrusion coating or melt scraping coating, using the melt of the outer barrier composite material as the coating medium.

[0026] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0027] Gradient barrier synergistic water control performance: This invention constructs an asymmetric gradient structure on the sidewall with a dense hydrophobic barrier on the outside and a hydrophilic porous layer on the inside. The outer PHA-based barrier layer (containing natural wax, rosin ester, etc.) effectively cuts off the capillary migration and ineffective evaporation of water outward, while the inner hydrophilic porous layer maintains the water continuity between the substrate and the cup wall interface, thus achieving excellent water retention performance during the seedling stage. The daily water replenishment frequency is comparable to that of traditional PP containers.

[0028] The active disintegration mechanism of natural composting: Unlike traditional single barrier materials that are difficult to degrade under mild composting conditions, the hydrophilic porous components (such as TPS, sodium citrate, etc.) on the inside of this invention rapidly absorb water, swell or dissolve in the early stage of composting, forming a large number of microporous channels inside the cup wall. This significantly increases the attachment area and colonization depth of microorganisms, thereby actively initiating the breakage and disintegration of the material from the inside out, ensuring rapid degradation under natural composting conditions (low temperature, humidity fluctuations).

[0029] Root growth directional guidance function: The porous structure on the inner side wall softens or forms micropores when moist, which can induce the roots to pierce outward and grow. Combined with the pre-set root guide weak line structure on the outer side, it effectively avoids the "root rolling" phenomenon common in traditional containers, and significantly improves the transplant survival rate and seedling recovery speed.

[0030] Excellent wet mechanical strength: Despite the introduction of hydrophilic components, the seedling cup of the present invention can still maintain high compressive strength and drop resistance under long-term humid conditions through the protection of the outer dense layer and the regulation of the PHA matrix crystal structure, meeting the engineering requirements of frequent handling and stacking in automated seedling facilities.

[0031] Strict ecological and environmental safety: The entire formula system of this invention does not contain organic fluorine additives, the total organic fluorine content of the product is <5mg / kg, and all components are biodegradable materials. After natural composting, there are no microplastics or toxic substances left, which fully meet the strict environmental protection standards of ecological agriculture and green horticulture. Attached Figure Description

[0032] Figure 1 This is a schematic cross-sectional view of the PHA-based barrier pore-forming synergistic potted seedling cup suitable for natural composting, as described in this invention.

[0033] In the figure, 1-cup body; 2-outer barrier zone; 3-weak line of the guide root; 4-inner porous structure zone; 5-pre-cracked guide root structure; 6-drainage hole. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0035] Figure 1This is a cross-sectional structural diagram of the PHA-based seedling cup described in this invention in its use state. It clearly shows that the sidewall of the cup body 1 has significant layered characteristics along the thickness direction, including an outer barrier zone 2 located near the outer surface area, which has a water barrier function, and an inner porous structure zone 4 located near the inner surface area, which is used to contain the substrate and guide root growth. In addition, the outer surface of the sidewall is provided with axially extending root guide weak lines 3 to assist the sidewall cracking. The bottom center of the cup is provided with a drainage hole 6 to remove excess water, and a radial pre-splitting root guide structure 5 is set around the drainage hole to facilitate root penetration into the bottom of the cup.

[0036] In the examples and comparative examples of this specification, unless otherwise stated, "parts by mass" refers to the relative mass parts of each component after drying, calculated as dry solids; wherein, the water content of the PHA polymer is ≤0.025wt%, and the water content of the other components is ≤0.4wt%, and the water content is determined by Karl Fischer titration.

[0037] The reagents and raw materials used in the embodiments and application examples of this invention are shown in Table 1.

[0038] Table 1. Main reagent and raw material names, product models / specifications, and manufacturers:

[0039]

[0040] The main analytical and detection instruments used in the embodiments and application examples of this invention are shown in Table 2.

[0041] Table 2 mainly analyzes the names, models, and manufacturers of the testing instruments:

[0042]

[0043] The main test standards used in the embodiments and application examples of this invention are shown in Table 3.

[0044] Table 3. Main Test Items and Test Standard Numbers:

[0045]

[0046] General preparation process of thermoplastic starch (TPS):

[0047] Step 1. Spread food-grade corn starch evenly on a stainless steel tray and place it in an electric heating drying oven. Dry it at 110℃ for 24 hours to remove moisture. After cooling, weigh 70kg of dried corn starch and 30kg of glycerin and put them into a high-speed mixer. Mix them at 1500r / min for 15min to obtain a starch-glycerin premix.

[0048] Step 2. Add the starch-glycerol premix obtained in Step 1 to the main feed port of the twin-screw extruder. Set the temperatures of each zone of the extruder to 90℃, 120℃, 135℃, 140℃, 135℃, and 125℃ respectively, and the screw speed to 220 r / min. After the material is melt-plasticized, extruded into strands, air-cooled and dried, and pelletized, TPS is obtained.

[0049] General preparation process for simulated compost substrate:

[0050] Step 1. Collect well-rotted compost, dried pine sawdust, fresh rabbit manure, and waste cabbage leaves. Crush them separately using a pulverizer and pass them through a 5mm mesh screen. Add them to a horizontal mixer in a mass ratio of 2:1:1:1 and mix for 30 minutes to obtain a basic solid mixture.

[0051] Step 2. Determine the carbon-nitrogen ratio and moisture content of the basic solid mixture obtained in Step 1. Adjust the carbon-nitrogen ratio to 25:1 by adding urea and adjust the moisture content to 58% by spraying deionized water. After mixing evenly, let it stand at room temperature for 24 hours to obtain the simulated compost substrate.

[0052] Terminology Explanation: "Natural composting" as used in this specification refers to a composting process conducted under natural ventilation conditions, primarily through pile turning for oxygen supply, and in a non-closed reactor environment, where temperature, humidity, and oxygen supply fluctuate over time. This specification uses the pile test conditions described in Example 3 to representatively evaluate the disintegration behavior under the aforementioned natural composting disposal scenario. "Equivalent thickness" as used in this specification refers to: when the sidewall has a layered structure, it is the arithmetic mean of the corresponding layer thicknesses obtained through microscopic measurements of the sidewall cross-section at at least three measurement points along the circumference and axial direction of the sidewall; when the outer barrier region is a semi-continuous barrier molten coating, it is the equivalent thickness obtained by dividing the increase in mass per unit area of ​​the sample before and after coating by the density of the coating material at 23°C, where the unit area is the total area of ​​the outer surface of the sidewall and includes discontinuous regions. When the sidewall has a composition gradient structure, the outer barrier region is defined as the region in the thickness direction where the mass fraction of the outer barrier composite material is greater than that of the inner porous composite material, and the inner porous structure region is defined as the region in the thickness direction where the mass fraction of the inner porous composite material is greater than that of the outer barrier composite material. The boundary between the two is where the mass fractions of the two composite materials are equal.

[0053] Example:

[0054] In the following embodiments, the outer barrier composite material is used to form the outer barrier region (or to form a semi-continuous barrier molten coating), and the inner porous composite material is used to form the inner porous structure region; each formulation is in parts by weight.

[0055] General preparation process for seedling cups (applicable to Examples 1-12, unless otherwise stated):

[0056] Step 1 (Drying): Place the PHA polymer in a vacuum drying oven and dry at 60°C for 8 hours until the moisture content is ≤0.025wt%. The moisture content is determined using a Karl Fischer moisture titrator. Place the hydrophilic porous component, biodegradable hydrophobic barrier component, reinforcing or filler component, flexible modification component, reaction compatibilizer or chain extender component, and auxiliaries in a forced-air drying oven and dry at 50°C for 4 hours until the moisture content is ≤0.4wt%. After cooling, seal and store for later use to obtain the dried raw material package.

[0057] Step 2 (Twin-screw blending and granulation): A twin-screw extruder is used for melt blending. The temperatures of each zone of the extruder are set sequentially to 140℃, 155℃, 165℃, 170℃, 170℃, and 165℃. The screw speed is set to 200 r / min, and the vacuum degree at the vacuum exhaust port is set to -0.08 MPa. The dried raw material package is melt-blended and extruded and granulated according to the outer barrier formulation and the inner porousing formulation, respectively, to obtain outer barrier composite material granules and inner porous composite material granules.

[0058] Step 3 (Injection Molding / Co-injection Molding): The temperatures of each zone of the injection molding machine barrel are set to 150℃, 165℃, 170℃, and 170℃ respectively, and the mold temperature is set to 40℃. Except for Example 6 and corresponding examples 5-8, co-injection molding is used to form an outer barrier area and an inner porous structure area on the sidewall of the outer barrier composite material particles and the inner porous composite material particles. When a coating bonding structure is used, the cup body substrate is molded by injection molding to form the inner porous structure area, and the cup body injection molded part is obtained.

[0059] Step 4 (Coating and Bonding Molding): For seedling cups with a coating and bonding structure (Example 6 and corresponding proportions 5-8), melt-coating and bonding molding is performed within 30 seconds after the injection molding of the cup body. The melt-coating and bonding molding process includes the following steps:

[0060] A PHA-type polymer was melt-mixed with a compatibilizer or chain extender to form an interfacial transition layer melt. The PHA-type polymer was PHBV, and the compatibilizer or chain extender was epoxy chain extender ADR-4468, with a mass ratio of 100:1.0. The interfacial transition layer melt was coated onto the outer surface of the sidewall using a melt-coating method to form an interfacial transition layer. In Example 6, the interfacial transition layer scraper gap was set to 0.05 mm; in Comparative Example 7, the scraper gap was set to 0.005 mm; and in Comparative Example 8, the scraper gap was set to 0.35 mm. After the interfacial transition layer was coated, it was cooled for 30 seconds under 20°C cooling air conditions.

[0061] Subsequently, the outer barrier composite material particles are melted to obtain an outer barrier composite material melt. Using this outer barrier composite material melt as a coating medium, an outer barrier molten coating is formed on the outer surface of the sidewall using a melt-coating method. When the cup sidewall has a weak guide root line, no coating is applied to the strip-shaped area (1.0 mm wide) corresponding to the weak guide root line, so that the outer barrier molten coating forms an intermittent structure in the strip-shaped area, thereby obtaining a semi-continuous barrier molten coating. In Example 6, the outer barrier molten coating scraper gap is set to 0.08 mm, in Comparative Example 5, the outer barrier molten coating scraper gap is set to 0.015 mm, and in Comparative Example 6, the outer barrier molten coating scraper gap is set to 0.45 mm. After the outer barrier molten coating is formed, it is immediately cooled for 60 seconds under a cooling air condition at 20°C to obtain a coated and bonded cup.

[0062] Step 5 (Cooling, Demolding, and Humidification): The in-mold cooling time is set to 20s. After demolding, the cup is placed in an environment of 23℃ for 24h. When the coating bonding structure is not used, the cup body obtained in Step 3 above is used as the sample. When the coating bonding structure is used, the coated bonding cup body obtained in Step 4 above is used as the sample to obtain the seedling cup sample to be tested.

[0063] Step 6: Method for determining the equivalent thickness of the outer barrier region: When the sidewall is a layered structure, select 3 measurement points along the circumference and axial direction of the sidewall, prepare a sidewall cross-section, and measure the thickness of the outer barrier region using a cross-section micro-measurement system. Take the arithmetic mean as the equivalent thickness. When the outer barrier region is a semi-continuous barrier molten coating, take the total area of ​​the outer surface of the sidewall (including the uncoated discontinuous area) as the unit area, measure the difference in mass per unit area of ​​the sample before and after coating as the mass increment per unit area, and divide the mass increment per unit area by the density of the coating material at 23℃ to obtain the equivalent thickness. The density of the coating material is the density measured at 23℃ according to GB / T 1033.1-2008.

[0064] Step 6a: Method for determining the thickness of the interface transition layer and the thickness of the composition gradient transition zone: When the seedling cup is a coated composite structure, three measurement points are selected along the circumferential and axial directions of the sidewall to prepare a sidewall cross-section. The interface transition layer boundary is identified between the outer barrier zone and the inner porous structure zone using a cross-sectional micro-measurement system, and the thickness of the interface transition layer is measured. The arithmetic mean is taken as the thickness of the interface transition layer. When the seedling cup is a composition gradient structure, three measurement points are selected along the circumferential and axial directions of the sidewall to prepare a sidewall cross-section. The continuous change zone of the transition area between the outer barrier composite material and the inner porous composite material in the thickness direction is identified using a cross-sectional micro-measurement system, and the thickness of the continuous change zone is measured. The arithmetic mean is taken as the thickness of the composition gradient transition zone.

[0065] Step 7: Calculation and Control of Melting Residence Time: The average melting residence time is calculated as the ratio of the effective melt volume of the equipment to the actual mass flow rate. The calculation formula is t=V eff ×ρ / Q m Where t is the average melting residence time, and V eff Q is the effective melt volume of the equipment, ρ is the melt density, and Q is the effective melt volume of the equipment. m The actual mass flow rate; during the preparation of the example, t was controlled to be ≤3 min during the melt processing in steps 2 and 3 to obtain the average melt residence time t.

[0066] Example 1:

[0067] External barrier composite material formulation (parts by weight): 60 parts PHBV, 25 parts PBAT, 8 parts pentaerythritol rosin ester, 6 parts talc, 0.5 parts antioxidant compound, and 0.6 parts lubricant.

[0068] The formulation of the internally porous composite material (parts by weight) is as follows: 40 parts PHBV, 30 parts PBAT, 28 parts TPS, and 2.1 parts epoxy chain extender.

[0069] Example 2:

[0070] External barrier composite material formulation (parts by weight): 95 parts PHBV, 0.2 parts carnauba wax, 4.0 parts talc, 0.5 parts antioxidant compound, and 0.35 parts lubricant.

[0071] The formulation of the internally porous composite material (parts by weight) is as follows: 90 parts PHBV, 6 parts maltodextrin, 0.5 parts chopped cellulose fibers, 2.5 parts talc, 0.55 parts antioxidant compound, and 0.5 parts lubricant.

[0072] Example 3:

[0073] External barrier composite material formulation (parts by weight): 80 parts PHBV, 15 parts PBAT, 3 parts pentaerythritol rosin ester, 1.0 part talc, 0.55 parts antioxidant compound, and 0.5 parts lubricant.

[0074] The formulation of the internally porous composite material (parts by weight) is as follows: 65.2 parts PHBV, 15 parts PBAT, 15 parts TPS, and 5 parts chopped cellulose fibers.

[0075] Example 4:

[0076] External barrier composite material formulation (parts by weight): 70 parts P34HB, 20 parts PBAT, 5 parts beeswax, 4.0 parts talc, 0.5 parts antioxidant compound, and 0.55 parts lubricant.

[0077] The formulation of the internally porous composite material (parts by weight) is as follows: 50 parts P34HB, 25 parts PBAT, 20 parts TPS, and 5.2 parts talc.

[0078] Example 5:

[0079] External barrier composite material formulation (parts by weight): 85 parts PHBV, 10 parts PBAT, 4 parts glyceryl monostearate, 0.55 parts antioxidant compound, and 0.5 parts lubricant.

[0080] The formulation of the internally porous composite material (parts by weight) is as follows: 60 parts PHBV, 20 parts PBAT, 12 parts CMC, 1.1 parts epoxy chain extender, and 7 parts maltodextrin.

[0081] Example 6:

[0082] External barrier composite material formulation (parts by weight): 88 parts PHBV, 12 parts PBAT, 6 parts pentaerythritol rosin ester, 1.0 part carnauba wax, 0.5 parts maltodextrin, 12 parts talc, 0.8 parts antioxidant compound, and 0.9 parts lubricant.

[0083] The formulation of the internally porous composite material (parts by weight) is as follows: 55 parts PHBV, 18 parts PBAT, 19 parts TPS, 6 parts CMC, 2 parts maltodextrin, 5 parts talc, 0.8 parts beeswax, 1.5 parts epoxy chain extender, 0.8 parts antioxidant compound, and 0.9 parts lubricant.

[0084] Example 7:

[0085] External barrier composite material formulation (parts by weight): 60 parts PHBH, 25 parts PBAT, 8 parts carnauba wax, 6 parts talc, 0.5 parts antioxidant compound, and 0.5 parts lubricant.

[0086] The formulation of the internally porous composite material (parts by weight) is as follows: 40 parts PHBH, 30 parts PBAT, 28 parts TPS, and 2.0 parts epoxy chain extender.

[0087] Injection molding / coating process control: control the equivalent thickness of the outer barrier zone to 0.20mm.

[0088] Example 8:

[0089] External barrier composite material formulation (parts by weight): 95 parts PHBV, 0.2 parts pentaerythritol rosin ester, 2 parts talc, 0.3 parts antioxidant compound, and 0.3 parts lubricant.

[0090] The formulation of the internally porous composite material (parts by weight) is as follows: 90 parts PHBV, 6 parts maltodextrin, 2 parts talc, 0.3 parts antioxidant compound, and 0.3 parts lubricant.

[0091] Injection molding / coating process control: control the equivalent thickness of the outer barrier zone to 0.02mm.

[0092] Example 9:

[0093] External barrier composite material formulation (parts by weight): 90 parts PHB, 5 parts PBAT, 4 parts carnauba wax, 0.5 parts talc, 0.5 parts antioxidant compound, and 0.5 parts lubricant.

[0094] The formulation of the internally porous composite material (parts by weight) is as follows: 70 parts PHB, 10 parts PBAT, 15 parts TPS, 3 parts chopped cellulose fibers, 1.0 part epoxy chain extender, and 0.5 parts lubricant.

[0095] Note: This example verifies the applicability of short-chain PHA homopolymers (PHB).

[0096] Example 10:

[0097] External barrier composite material formulation (parts by weight): 82 parts PHBV, 12 parts PBAT, 3 parts oleamide, 2 parts hydrogenated vegetable oil, 1.0 part talc, 0.6 parts antioxidant compound, and 0.4 parts lubricant.

[0098] The formulation of the internally porous composite material (parts by weight) is as follows: 65 parts PHBV, 15 parts PBAT, 18 parts TPS, and 2 parts maltodextrin.

[0099] Note: This embodiment verifies the effectiveness of fatty acid amides and plant oil derivatives as biodegradable hydrophobic barrier components.

[0100] Example 11:

[0101] External barrier composite material formulation (parts by weight): 85 parts PHBH, 10 parts PBAT, 4 parts beeswax, 0.5 parts antioxidant compound, and 0.5 parts lubricant.

[0102] The formulation of the internally porous composite material (parts by weight) is as follows: 70 parts PHBH, 10 parts PBAT, 8 parts sodium citrate, 10 parts TPS, 1.5 parts talc, and 0.5 parts antioxidant compound.

[0103] Note: This example verifies the effect of organic acid salt (sodium citrate) as a hydrophilic pore-forming component.

[0104] Example 12:

[0105] The formulation (parts by weight) of the outer barrier composite material is the same as that in Example 3.

[0106] The formulation (parts by weight) of the internally porous composite material is the same as that in Example 3.

[0107] Process Description: A two-material co-injection molding process is adopted. By controlling the convergence and flow of the two melts in the mold cavity, no obvious switching interface is set during the injection process. Instead, by adjusting the injection rate curve, a composition gradient transition zone is formed at the contact interface between the outer barrier composite material and the inner porous composite material. The thickness of the composition gradient transition zone is measured to be 0.15 mm in step 6a, thus preparing a seedling cup with a composition gradient structure.

[0108] Comparative example:

[0109] Table 4 summarizes the structural and formulation characteristics of the examples and comparative examples.

[0110] Comparative Example 1: A single-layer cup body was injection molded using only the internally porous composite material from Example 3.

[0111] Comparative Example 2: A single-layer cup body was injection molded using only the outer barrier composite material from Example 3.

[0112] Comparative Example 3: The outer barrier composite material and the inner porous composite material from Example 3 were physically blended at a mass ratio of 1:4 and then injection molded into a single-layer cup.

[0113] Comparative Example 4: PP injection molding of a single-layer cup body.

[0114] Comparative Example 5: The formulation of Example 6 was used, but the thickness of the outer barrier layer was 0.015 mm.

[0115] Comparative Example 6: The formulation of Example 6 was used, but the thickness of the outer barrier layer was 0.45 mm.

[0116] Comparative Example 7: The formulation of Example 6 was used, and the thickness of the interface transition layer was 0.005 mm.

[0117] Comparative Example 8: The formulation of Example 6 was used, and the thickness of the interface transition layer was 0.35 mm.

[0118] Comparative Example 9 (Method Control): The same sample as in Example 6 was used, but the detection limit was set to 10 mg / kg.

[0119] Comparative Example 10:

[0120] External barrier composite material formulation (parts by weight): 70 parts PHBV, 14 parts PBAT, 15 parts carnauba wax, 0.5 parts antioxidant compound, and 0.5 parts lubricant.

[0121] Formulation of the internally porous composite material: same as in Example 3.

[0122] Note: To verify the effect of excessive external barrier components (>8 parts).

[0123] Comparative Example 11:

[0124] External barrier composite material formulation: same as in Example 3.

[0125] Internally porous composite material formulation (parts by weight): 80 parts PHBV, 15 parts PBAT, 3 parts TPS, and 2 parts chopped cellulose fibers.

[0126] Note: This study verifies the effect of insufficient (<6 parts) hydrophilic porous components on the inner side.

[0127] Comparative Example 12:

[0128] External barrier composite material formulation: same as in Example 3.

[0129] Internally porous composite material formulation (parts by weight): 40 parts PHBV, 20 parts PBAT, and 40 parts TPS.

[0130] Note: To verify the effect of excessive (>28 parts) of the inner hydrophilic porous component.

[0131] Table 4 summarizes the structural and formulation characteristics of the examples and comparative examples:

[0132]

[0133] Note: For coated structures, the thickness of the inner porous structure region is the sum of the thickness of the inner porous structure region and the thickness of the interface transition layer; the thickness of the interface transition layer is characterized by the arithmetic mean obtained by the cross-sectional microscopy measurement described in step 6a, and is separately noted in the "Key Formulation / Structural Features" column; the outer / inner thickness ratio of Comparative Examples 1-4 is not applicable because the equivalent thickness of the outer barrier region is 0.00 mm.

[0134] Application example:

[0135] Application Example 1: Water control performance test during seedling stage.

[0136] Experiment Description: This experiment was conducted in an intelligent artificial climate chamber to simulate the differences in water retention capacity of different seedling cup structures during actual seedling cultivation. The climate chamber's light cycle was set to 14 hours of light / 10 hours of darkness, the light intensity was set to 20,000 Lux, the internal temperature was set to 25℃, the relative humidity was set to 60%, and the internal air circulation speed was maintained at 0.5 m / s. Ten seedling cup samples from each group were selected and uniformly filled with a peat, perlite, and vermiculite substrate mixed in a volume ratio of 2:1:1. Initially, water was added to the substrate until the maximum water holding capacity was reached, and the free water was drained off under gravity for 30 minutes. Using a time-domain reflectometry (TDR) soil moisture sensor (volume water content measurement accuracy of 1%), the probe was vertically inserted into the geometric center of the substrate at a depth of 5 cm. The sensor was connected to a data acquisition unit, and multiplexers were used to achieve automatic polling and data acquisition of multiple samples, with the data acquisition frequency set to once every 30 minutes. The experiment set the water replenishment threshold at a substrate volumetric water content (VWC) of 60% and the target VWC at 80%. Water was replenished by slowly adding deionized water dropwise from the rim of the container. The amount of water replenished each time was calibrated using a weighing method (analytical balance reading accuracy 0.001g). The total number of water replenishments over a 15-day culture period was recorded, and the average daily replenishment frequency was calculated. This indicator directly reflects the water barrier efficiency of the container.

[0137] Table 5. Results of water control performance test during the seedling stage:

[0138]

[0139] Note: Comparative Example 9 is a methodological comparison and is not applicable to this physical performance test.

[0140] Results Analysis: According to the experimental data in Table 5, the average daily watering frequency for all sample examples was controlled between 0.5 and 0.9 times / day. Examples 6, 7, and 10 showed the best performance, with an average daily watering frequency of only 0.5 times / day, comparable to the traditional PP material (Comparative Example 4) (relative increase of 0%). This indicates that a reasonable outer barrier layer design, especially the use of melt coating or the addition of highly efficient biodegradable hydrophobic barrier components (such as oleic acid amide and hydrogenated vegetable oil in Example 10), can effectively cut off the migration path of water to the sidewalls. Example 8, due to the outer barrier layer thickness being at the lower limit of the design (0.02 mm), had a slightly higher watering frequency (0.9 times / day), but it was still within the acceptable range for horticultural operations. Example 9 used a PHB homopolymer matrix, and thanks to the material's high crystallinity and barrier properties, it achieved good water control even with a relatively thin coating.

[0141] In contrast, Comparative Example 1, with its single-layer hydrophilic porous structure and lack of a barrier layer, exhibited extremely rapid water evaporation, requiring a water replenishment frequency of up to 1.5 times / day, 200% higher than PP. Comparative Example 3, employing a simple physical blend, also showed poor water control (1.1 times / day) due to the hydrophilic component forming through channels within the matrix. Comparative Example 5 demonstrated that an outer barrier layer thickness <0.02mm (only 0.015mm) could not form an effective dense barrier, leading to a surge in water replenishment frequency to 1.2 times / day. Notably, Comparative Example 12, due to a severe excess of the inner hydrophilic porous component (40 parts), resulted in excessive water absorption on the inner wall, accelerating water conduction and evaporation, with a water replenishment frequency reaching 1.1 times / day, nearing the point of failure. While Comparative Examples 10 (excessive barrier agent) and 6 (excessively thick barrier layer) demonstrated excellent water control, as shown in subsequent application examples, this comes at the cost of other properties.

[0142] Application Example 2: Surface wettability and water vapor transmission rate (WVTR) test.

[0143] Experimental Description: This experiment quantitatively characterizes the surface energy and overall barrier properties of different areas of the sidewall of the seedling cup using static water droplet contact angle and WVTR. Surface wettability testing was conducted at 25℃ and 50% relative humidity using a contact angle meter. The test liquid was deionized water, and the droplet volume was precisely controlled to 4 μL. Five flat points were randomly selected on both the outer and inner surfaces of the sample for testing. After the droplet fell and remained still for 3 seconds, a screenshot was taken, and the arithmetic mean of the left and right contact angles was recorded. WVTR testing was performed using a PERMATRAN-W 3 / 34 (MOCON) water vapor transmission rate meter, employing the infrared sensor method, and following ASTM F1249-25. After axially splitting the sidewall of the seedling cup, the middle area of ​​the sidewall was taken and flattened using a flatbed hot press at 80℃, a hot pressing pressure of 0.5 MPa, and a hot pressing time of 60 s. The sample was then cooled at room temperature for 60 s. The thickness of the flattened sample was measured with a micrometer and recorded. The specimens were then cut according to the PERMATRAN-W 3 / 34 test chamber fixture requirements and clamped between the test chambers to achieve an effective test area of ​​50.0 cm². The test temperature was set to 38°C, the relative humidity on the wet side to 90%, and dry nitrogen was introduced on the dry side as the carrier gas. The WVTR readings were taken after stabilization, with the stability criterion being a difference of ≤5% between two consecutive WVTR readings. Three parallel samples were tested for each group, and the arithmetic mean was taken.

[0144] Table 6. Surface wettability and WVTR test results:

[0145]

[0146] Results Analysis: As shown in Table 6, the samples of this invention successfully constructed a functional gradient structure of "hydrophobic on the outside and hydrophilic on the inside". The outer surface contact angle of all embodiments was between 96° and 118°, exhibiting significant hydrophobicity and effectively blocking the wetting and penetration of external liquid water. Among them, the outer surface contact angle of Examples 7 and 10 exceeded 110°, and the WVTR was as low as 35 and 40 g / m²·24h, respectively, demonstrating the contribution of high content of barrier components or specific hydrophobic additives (such as amides) to improving barrier performance. The inner surface contact angle was generally controlled between 42° and 78°. In particular, in Example 11, the inner surface contact angle decreased to 45° after the introduction of sodium citrate. This hydrophilic surface is beneficial for maintaining the continuity of moisture between the substrate and the cup wall during the seedling stage, and for accelerating the attachment and colonization of microorganisms through water absorption and swelling during the composting stage.

[0147] In contrast, Comparative Example 1, with its hydrophilic materials both inside and out, had a contact angle of only 58° and a WVTR as high as 320 g / m²·24h, indicating almost no moisture barrier capability. Comparative Example 3, while showing slight improvement with its blended structure, still had an outer surface contact angle of only 85°, failing to meet the hydrophobic standard (>90°), and its WVTR remained as high as 150 g / m²·24h. Comparative Example 5 further confirmed that an excessively thin barrier layer (0.015 mm) could not provide sufficient surface coverage, resulting in a low outer surface contact angle (92°) and high moisture permeability. Comparative Example 10, with the addition of excessive wax (15 parts), while exhibiting an extremely hydrophobic outer surface (125°) and excellent barrier properties, could lead to surface precipitation and whitening due to these extreme surface properties. Comparative Example 12 had an extremely low inner surface contact angle (35°), indicating excessive hygroscopicity, causing the overall WVTR to actually increase to 110 g / m²·24h, thus disrupting the overall barrier system.

[0148] Application Example 3: Disintegration performance test under simulated composting conditions.

[0149] Experimental Description: This experiment used aerobic composting to evaluate the disintegration rate of seedling cups under natural composting conditions. The compost substrate consisted of well-rotted compost, sawdust, rabbit manure, and waste vegetable leaves mixed in a mass ratio of 2:1:1:1, with the initial carbon-to-nitrogen ratio (C / N) adjusted to 25:1 and the moisture content controlled at 58%. The seedling cup samples were buried 30 cm deep in the center of the compost pile. Each sample was wrapped in a 2 mm mesh bag for easy recovery and positioning. The compost pile was maintained in an aerobic state through natural ventilation, with oxygen supply and homogenization achieved by manual turning once daily. The initial total mass of the pile was 50 kg, and the pile's geometric dimensions were 0.80 m × 0.80 m × 0.60 m. The temperature at the center of the reactor was continuously monitored using a temperature recorder, and the daily average temperature at the center of the reactor during the test was 58℃. The moisture content was retested every 3 days using the drying method according to ISO 11465:2025. Specifically, a 20.0g sample was taken from the center of the reactor and dried in a 105℃ forced-air drying oven for 24 hours until constant weight was achieved (the difference between two consecutive weighings ≤ 0.001g). The moisture content was calculated as w = (m0 - m1) / m0 × 100%, and the moisture content was corrected to 58% by spraying deionized water. The experimental period was 12 weeks.

[0150] Before the experiment, samples of seedling cups from the same batch were pre-dried to constant weight in a 45℃ forced-air drying oven (the difference between two consecutive weighings ≤ 0.001g), and the initial dry weight m was recorded. 初始 The sample was placed in a nylon mesh bag and buried in the compost pile. At the end of the experiment, the mesh bag was carefully removed, and the attached compost substrate and microbial film were rinsed off with a low-pressure water stream. Then, it was dried in a 45℃ forced-air drying oven to constant weight (the difference between two consecutive weighings ≤ 0.001g). The final dry weight m was recorded. 最终 The mass loss rate (disintegration rate) is calculated as η = (m 初始 -m 最终 ) / m 初始 The results were calculated at 100% and the macroscopic morphological changes of the samples were observed and recorded.

[0151] Table 7. Results of simulated compost disintegration rate test over 12 weeks:

[0152]

[0153] Note: Comparative Example 9 is a methodological control and is not applicable to this test.

[0154] Results Analysis: According to the experimental results in Table 7, all samples from the examples achieved good disintegration during the 12-week composting cycle, with disintegration rates ranging from 78% to 98%. Example 11 achieved a disintegration rate as high as 96%, mainly attributed to sodium citrate in the inner layer formulation. As a water-soluble salt, it rapidly dissolved and was lost in the early stages of composting, leaving a large number of porous structures inside the cup wall, greatly increasing the contact area for microorganisms. Although Example 9 used a PHB matrix with high crystallinity and relatively slow degradation, it still achieved a disintegration rate of 85% thanks to the design of the internal porous structure, demonstrating the effectiveness of the layering strategy for recalcitrant matrices.

[0155] The comparative test results highlight the regulatory role of material structure design on degradation behavior. Comparative Example 4 (PP), as a non-degradable control, had a disintegration rate of 0%. Comparative Example 2, with its hydrophobic barrier material inside and out, made it difficult for moisture and microorganisms to penetrate, resulting in a disintegration rate of only 45%. Comparative Example 6, due to its excessively thick outer barrier layer (0.45 mm), severely hindered the initiation of degradation of the internal material, resulting in a disintegration rate as low as 55%, with noticeable residue. Although the matrix of Comparative Example 10 was biodegradable, the excessive addition of wax (15 parts) formed a dense hydrophobic barrier, reducing the disintegration rate to 70%. Conversely, Comparative Example 11, lacking sufficient hydrophilic porous components in its inner layer (only 3 parts), could not form effective biodegradation channels, resulting in a disintegration rate of only 60%. Although Comparative Examples 1 and 12 had extremely high disintegration rates, combined with the results of Application Example 1, they showed a risk of failure during the seedling stage, failing to meet the usage requirements. This fully demonstrates that only within a specific formulation ratio and structural thickness range can a balance be achieved between durability during the seedling stage and ease of decomposition during composting.

[0156] Application Example 4: Environmental safety and total fluoride testing.

[0157] Experimental Description: This experiment verifies the ecological safety of the seedling cup samples, focusing on the detection of total fluoride (TF) content, and using the TF results as a conservative characterization of total organic fluoride (TOF). Since the formulation system of this invention does not add inorganic fluoride salts or fluorine-containing mineral additives, and does not introduce fluorine-containing processing aids, the TF results measured by combustion-ion chromatography can be used as a conservative characterization of TOF. Before testing, the seedling cup samples were frozen in liquid nitrogen for 15 minutes to make them brittle, then pulverized using an ultracentrifuge grinder and passed through a 100-mesh sieve to ensure uniform particle size <150μm. 50.0 mg of the prepared powder sample was weighed and placed in a quartz boat, then fed into a combustion furnace-ion chromatography system (AQF-IC). The combustion program was set as follows: injection zone temperature 400℃, combustion zone temperature 1000℃, high-purity oxygen flow rate 400 mL / min, and water vapor flow rate 200 mL / min, to ensure that the fluorine-containing substances in the sample were completely converted to hydrogen fluoride. The gas produced by combustion was absorbed by an absorbent solution, which was a 20.0 mL absorbent solution obtained by mixing 2.0 mL of hydrogen peroxide solution (30 wt%) with 18.0 mL of deionized water. The absorbent solution was diluted to 20.0 mL, filtered through a 0.22 μm filter membrane, and then injected into an ion chromatograph. An anion exchange column was used, with potassium hydroxide solution as the eluent, employing isocratic elution at 5 mmol / L and a flow rate of 1.0 mL / min. A suppressed conductivity detector was used to detect the fluoride ion concentration.

[0158] A series of standard curves with fluoride ion standard solutions of 0.01 mg / L, 0.02 mg / L, 0.05 mg / L, 0.10 mg / L, and 0.20 mg / L were prepared. For every 10 samples, one blank and one midpoint standard solution (0.05 mg / L) were inserted for drift correction.

[0159] Total fluoride (TF, in mg / kg) is calculated using the following formula: TF = C × V / m, where C is the fluoride ion concentration in the absorbent (mg / L), V is the volume of the absorbent (L), and m is the sample mass (kg). According to IEC 62321-3-2:2020, the method detection limit (LOD) is set at 5 mg / kg; when the TF measurement result is lower than the LOD, it is considered undetectable and can be used as a conservative characterization result for TOF.

[0160] Table 8 Total Fluorine (TF) Test Results:

[0161]

[0162] Results Analysis: The test results (Table 8) show that the total organic fluorine content of all 12 example samples and most comparative sample samples was below the method detection limit of 5 mg / kg, and was judged as "not detected". This indicates that under the condition that the detection limit of combustion-ion chromatography is 5 mg / kg, the total organic fluorine of the PHA matrix resin, biodegradable hydrophobic barrier components (such as natural wax, rosin ester, vegetable oil derivatives), hydrophilic porosilicate components, and all processing aids selected in this invention was not detected. In particular, Example 10 introduced novel aids such as oleamide and hydrogenated vegetable oil, and the total organic fluorine was also not detected under the above detection limit conditions, demonstrating good environmental safety. Comparative Example 9, as a method control, although its determination result was not detected, because its detection method's detection limit was set at 10 mg / kg, which is higher than the preferred standard of 5 mg / kg in this invention, the risk of trace residues in the range of 5-10 mg / kg could not be ruled out, and it could not meet the extremely high requirements of this invention for environmental safety.

[0163] Application Example 5: Mechanical properties and stacking reliability testing during the seedling stage.

[0164] Experimental Description: This experiment verifies the mechanical strength of the seedling cups under moist conditions and their resistance to drop during transportation, ensuring that they meet the requirements for engineering applications.

[0165] Test 1 (Wet Compressive Strength): Following the loading method and speed settings in GB / T 1041-2008, the seedling cup samples were completely immersed in deionized water at 25℃ for 24 hours. After removal, the surface water was immediately blotted dry with filter paper. The sample was placed upright in the center of the pressure plate of the universal testing machine, with the pressure plate descent speed set to 10 mm / min. The instantaneous load (N) at which the cup body underwent 5 mm axial deformation was recorded. The average value of 5 samples in each test group was taken.

[0166] Test 2 (Drop Breakage Rate): Simulating a real-world handling scenario, seedling cups were filled with a standard mixed substrate with a moisture content of 60%, and the total weight was uniformly adjusted to 250.0g. A drop tester (PDT-80) was used to perform free drops with the bottom facing down. The drop height was set to 1.0 meter, and the drop surface was a hard, flat cement floor; each sample was dropped once. The cups were observed for visible cracks, breakage, or severe deformation that caused substrate spillage. 20 samples were tested in each group, and the percentage of broken samples out of the total was calculated as the breakage rate.

[0167] Table 9. Mechanical properties and stack reliability test results:

[0168]

[0169] Results Analysis: According to Table 9, the example samples exhibited excellent wet mechanical properties. Example 9 (PHB-based) showed extremely high wet strength (65 N), attributed to the high rigidity of PHB. Although its drop breakage rate (10%) was slightly higher than the more tough PBAT-modified group, it was still within an acceptable range. Example 4 (P34HB-based) achieved a 0% drop breakage rate due to the excellent toughness of the material itself. Overall, the example samples maintained a load-bearing capacity of over 45 N after water absorption, and the breakage rate was controlled within 15%, which can meet the stacking and handling requirements in automated seedling facilities.

[0170] Comparative data reveal the drawbacks of pursuing a single performance characteristic. Comparative Examples 1 and 12, due to their high content of hydrophilic porous components (40 parts for the entire layer and 40 parts for the inner layer, respectively), experienced severe softening after water absorption, with wet loads of only 25 N and 20 N, respectively, and extremely high drop breakage rates (40%-60%), making them prone to collapse or breakage in practical use. While Comparative Example 10 exhibited good barrier properties, the excessive low-molecular-weight wax (15 parts) disrupted the continuous phase of the polymer matrix, leading to brittleness, a decrease in mechanical strength to 45 N, and an increase in drop breakage rate to 20%. Comparative Examples 2 and 6, although possessing excellent mechanical properties (similar to PP), did so at the expense of disintegration resistance.

[0171] Application Example 6: Root system guidance function verification.

[0172] Experiment Description: This experiment selected the "Provence" tomato variety, known for its vigorous growth and well-developed root system, as the test plant to verify the guiding effect of the seedling cup structure on the root system. The seedling substrate consisted of a 3:1 mixture of imported peat and perlite. During the seedling stage, the greenhouse daytime temperature was set at 27℃, the nighttime temperature at 19℃, and the relative humidity at 65%. A tidal irrigation system was used, watering every 3 days and applying Hoagland nutrient solution every 7 days. Four root-guiding weak lines extending axially along the sidewall of the seedling cup were designed. These weak lines were molded thinning groove structures with a width of 0.6mm, a depth of 0.15mm, and a circumferential angle of 90° between the grooves. The outer barrier zone corresponding to the thinning groove formed a locally discontinuous or thinned structure, preferentially inducing cracks and guiding root penetration. Four drainage holes, each 2.0 mm in diameter, are provided at the bottom of the cup. In another embodiment, no drainage holes are provided at the bottom of the cup, or a pre-splitting root-guiding structure is further provided on top of the drainage holes. The pre-splitting root-guiding structure is a pre-splitting line structure set at the bottom of the cup. The pre-splitting line structure is a cross-shaped or grid-shaped thinned line with a line width of 0.6 mm and a line depth of 0.15 mm. Tomatoes were planted in each group of seedling cups, and all samples were observed on day 25. The criteria for root penetration were: the root tip was visibly able to penetrate the sidewall and extend to a length of 2 mm on the outside, or the root system opened the pre-set cracks and was exposed to the air. For samples that did not penetrate, the cup was carefully dissected, and the presence of root coiling (root rolling) on ​​the inner wall of the cup was observed and recorded. 20 plants were tested in each group.

[0173] Table 10: Root system guidance function test results:

[0174]

[0175] Results Analysis: Table 10 shows that the sample samples from the examples generally exhibited excellent root guidance function, with root penetration rates ranging from 80% to 100%. This indicates that the porous structure on the inner side softens or forms micropores upon contact with water, effectively inducing outward root growth and preventing coiling within the cup wall. In particular, in Example 11, the physical pores left after the sodium citrate dissolved became natural channels for the roots, achieving a penetration rate of 100%.

[0176] The results of the comparative examples were highly polarized. Comparative Examples 2 and 4 (PP), due to their dense, hard sidewalls and lack of inducing structures, showed a 0% root penetration rate and severe root curling, which would significantly impact the seedling recovery rate after transplanting. Comparative Example 6, with its excessively thick wall (0.45 mm), struggled to allow roots to penetrate, resulting in a penetration rate of only 10%. Comparative Example 11 revealed the consequences of insufficient internal porosity (3 parts), making it difficult for roots to find a breakthrough point, with a penetration rate of only 30% and noticeable root curling. Conversely, while Comparative Examples 1 and 12 showed high penetration rates (100%), this was because the cups softened and disintegrated prematurely, losing their basic function as containers.

[0177] Application Example 7: Verification of processing parameters.

[0178] Experimental Description: Example 3 was selected as the representative test object in this experiment because this formulation covers the core PHA matrix (PHBV) of this invention and typical modified components (PBAT, rosin ester, and inorganic filler), and the mass fractions of each component are within the typical range of protection of this invention, thus objectively reflecting the general rheological behavior and mechanical response characteristics of the material system described in this invention during thermal processing. It should be noted that since the sensitivity of PHA polymers (including PHB, PHBV, P34HB, etc.) to thermal history is an intrinsic characteristic determined by their molecular backbone structure, and not limited to specific formulations, the melt residence time and performance degradation laws derived from Example 3 are universal and applicable to all formulation systems described in this invention.

[0179] The experiment involved preparing standard tensile specimens on a precision injection molding machine. The average residence time of the melt in the barrel was precisely controlled by manually adjusting the temperature distribution of the injection molding barrel, back pressure, and screw speed. Three residence time gradients were set: 1 minute (rapid molding), 3 minutes (upper limit of standard process), and 5 minutes (overtime process). The injection mold temperature was controlled at 40℃. The prepared specimens were conditioned for 48 hours at 23℃ and 50% relative humidity. Subsequently, the melt mass flow rate (MFR, test conditions 190℃ / 2.16kg) of the material was tested according to GB / T 3682.1-2018, and the tensile strength was tested according to GB / T 1040.1-2025 and GB / T 1040.2-2022 (test speed 50mm / min). An abnormally high MFR value usually indicates severe thermal degradation and breakage of the polymer molecular chains.

[0180] Table 11 Effect of different melting residence times on the properties of the materials formulated in Example 3:

[0181]

[0182] Results Analysis: Experimental data clearly show that when the melt residence time is controlled within 3 minutes, the thermal degradation of PHA is within a controllable range, and the mechanical property retention rate is above 90%. Once the residence time is extended to 5 minutes, the MFR surges to 18.5 g / 10 min, indicating severe molecular chain breakage, with the tensile strength nearly halved (16.2 MPa), resulting in brittle and easily broken injection-molded cups. This fully verifies that limiting the "average melt residence time to ≤3 minutes" in this invention is crucial for ensuring product quality.

[0183] Experimental Results and Analysis:

[0184] This invention comprehensively validates the structural design, formulation components, and process parameters of PHA-based seedling cups through systematic experiments in Examples 1-12 and Comparative Examples 1-12. By comprehensively applying the test data from Examples 1-7, the experimental results reveal the significant advantages of the "outer barrier-inner pore-forming" asymmetric gradient structure in resolving the core contradiction between "durability during the seedling stage" and "degradability during disposal" in biodegradable horticultural containers.

[0185] Synergistic Effect Analysis of Asymmetric Gradient Structure on Moisture Management: The results of Application Example 1 (water control performance) and Application Example 2 (surface wettability) confirm that the synergistic effect of the outer barrier region and the inner porous structure region is the key to achieving excellent water control performance. The water droplet contact angles on the outer surface of the example samples remained within the highly hydrophobic range of 95°–120°, and the water volume per unit temperature (WVTR) was controlled within a suitable range of 35–85 g / m²·24h. This resulted in the daily water replenishment frequency (0.5–0.9 times / day) of the example samples being on par with that of traditional petrochemical-based PP containers (Comparative Example 4, 0.5 times / day). In contrast, Comparative Example 1 (single-layer hydrophilic), lacking an outer barrier layer, experienced excessively rapid water loss, with the water replenishment frequency surging by 200%. Simultaneously, the hydrophilicity of the inner porous region (contact angle 40°–80°) ensured the hydraulic continuity of the matrix-cup wall interface, avoiding "crevice drought" caused by interfacial hydrophobicity.

[0186] The regulatory mechanism of component content and structural thickness on degradation behavior: Data from Example 3 (simulated compost disintegration) shows that the degradation mechanism of this invention is significantly proactive. In Example 11, sodium citrate was introduced as a natural composting promoter, utilizing its rapid water solubility to form interconnected pores inside the cup wall, resulting in a disintegration rate as high as 96%. Trend analysis of the influence of changes in the content of the detailed numerical examples on the experimental results:

[0187] The effect of the thickness of the outer barrier layer: Experimental data revealed a clear performance balance point within the barrier layer thickness range of 0.02 mm to 0.20 mm. When the thickness was near the lower limit (e.g., 0.02 mm in Example 8), although the disintegration rate was extremely high (98%), the daily water replenishment frequency increased slightly (0.9 times / day). When the thickness increased to the upper limit (e.g., 0.20 mm in Example 7), the barrier performance reached its optimal level (0.5 times / day for water replenishment), but the disintegration rate decreased (78%). Once this range was exceeded, as in Comparative Example 6 (0.45 mm), the disintegration rate plummeted to 55%, resulting in severe residue; while below this range, as in Comparative Example 5 (0.015 mm), the barrier function was lost.

[0188] Effect of the content of the biodegradable hydrophobic barrier component: This component exhibits a modifying effect in the range of 0.2 parts to 8 parts. Appropriate addition (such as 5 parts of total barrier component in Example 10) can improve hydrophobicity without affecting the continuity of the matrix; however, when the content is too high and exceeds the range (such as 15 parts of wax in Comparative Example 10), the material undergoes phase separation, resulting in increased brittleness (wet load drops to 45 N) and hinders degradation (disintegration rate 70%).

[0189] Effect of hydrophilic porous component content: This component played a role in promoting disintegration initiation in the range of 6 to 28 parts. The degradation rate showed a positive correlation with the increase of content, but when the content was below the lower limit (e.g., comparative example 11, 3 parts), the degradation initiation was slow (disintegration rate 60%); when the content exceeded the upper limit (e.g., comparative example 12, 40 parts), the material absorbed too much moisture, resulting in a decrease in mechanical properties during the seedling stage (wet load only 20 N).

[0190] Engineering verification of root guidance and mechanical reliability: Application Example 6 confirms that the internal porous structure, combined with the weak root guide line, achieves a root penetration rate of 80%–100%, completely solving the root curling problem caused by PP containers (0% penetration rate) and fully hydrophobic PHA containers (Comparative Example 2, 0% penetration rate). Application Example 5 further demonstrates that, despite the introduction of hydrophilic components, thanks to the protection of the outer dense layer and reasonable control of PHA matrix crystallization (such as the PHB matrix in Example 9), the seedling cup of this invention can still maintain a compressive load of over 45N and a drop breakage rate of less than 15% under wet conditions, meeting the strength requirements of automated seedling cultivation. In addition, the process window of "melt residence time ≤ 3 min" determined in Application Example 7 effectively avoids the thermal degradation of PHA, ensuring the stability of product performance.

[0191] In summary, by precisely controlling the formulation components and molding structure of PHA-based composite materials, this invention has successfully constructed a seedling container that integrates "high-efficiency barrier, active disintegration, root induction, and environmental safety," providing a high-performance and completely environmentally friendly solution to replace traditional petrochemical plastic containers.

[0192] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, or improvements made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A PHA-based, barrier-apertured, co-cubling, potting cup suitable for natural compost disposal comprising a cup body, characterised in that, The cup body has side walls and a bottom, and the cup body includes a cup body base obtained by thermoplastic injection molding; The sidewall includes an outer barrier region on the outer surface and an inner porous structure region on the inner surface along the thickness direction. The outer barrier region and the inner porous structure region are layered structures or compositional gradient structures, and both the outer barrier region and the inner porous structure region are thermoplastic polyhydroxy fatty acid ester-based composite materials. The outer barrier region is made of an outer barrier composite material, which comprises, by mass, a polyhydroxyalkanoate polymer and a biodegradable hydrophobic barrier component, wherein the biodegradable hydrophobic barrier component comprises 0.2 to 8 parts by mass. The internally porous structure region is made of an internally porous composite material, which comprises, by mass, a polyhydroxyalkanoate polymer and a hydrophilic porous component, and the hydrophilic porous component is in the range of 6 to 28 parts by mass. The equivalent thickness of the outer barrier region is 0.02 mm to 0.20 mm; When the outer barrier region is formed by melt coating and bonding with the cup body substrate, the outer barrier region is located on the outside of the cup body substrate, and an interface transition layer is provided between the outer barrier region and the inner porous structure region, the thickness of the interface transition layer being 0.01mm to 0.30mm.

2. The PHA-based, barrier-apertured, co-potted, and simultaneously natural compostable cup of claim 1, wherein: The total fluoride content of the seedling cup is characterized by the total fluoride result measured according to IEC 62321-3-2:2020, which is <5 mg / kg on a dry basis, and the detection limit of the method for determining the total fluoride content is 5 mg / kg.

3. The PHA-based, barrier-apertured, co-potted, and natural compostable cup of claim 1, wherein: The outer barrier composite material and / or the inner porous composite material further include flexible modification components, reinforcing or filler components, reaction compatibilizers or chain extenders and / or additives; The flexible modification component is formed by the condensation polymerization of a diacid component and a diol component or by the ring-opening polymerization of a lactone monomer, wherein the lactone monomer is selected from one or both of ε-caprolactone and lactide. The reinforcing or filler components are selected from natural fibers, mineral fillers, or combinations thereof; The reaction compatibilizer or chain extender is selected from polyfunctional compounds containing epoxy groups, compatibilizers containing acid anhydride groups, chain extenders containing isocyanate groups, carbodiimide stabilizers, or combinations thereof. The additives are selected from lubricants, antioxidants, heat stabilizers, ultraviolet stabilizers, nucleating agents, plasticizers, processing aids, colorants, antistatic agents, flame retardants, antibacterial agents, or combinations thereof.

4. The PHA-based, barrier-apertured, co-potted, and natural compostable cup of claim 1, wherein: When the sidewall has a composition gradient structure, the mass fraction of the outer barrier composite material and the inner porous composite material changes continuously in the thickness direction, so that the mass fraction of the outer barrier composite material in the outer barrier region is greater than the mass fraction of the inner porous composite material, and the mass fraction of the inner porous composite material in the inner porous structure region is greater than the mass fraction of the outer barrier composite material.

5. The PHA-based, barrier-apertured, co-potted, and natural compostable cup of claim 1, wherein: The outer barrier region is a semi-continuous barrier molten coating formed on the outer surface of the sidewall, and the semi-continuous barrier molten coating has at least one uncoated discontinuous area on the outer surface of the sidewall along the circumferential or axial direction. The semi-continuous barrier molten coating is formed by molten coating of the outer barrier composite material followed by cooling, and the molten coating is performed by molten extrusion coating or molten scraping coating, with the melt of the outer barrier composite material as the coating medium.

6. The PHA-based barrier-porous synergistic potted seedling cup suitable for natural composting as described in claim 1, characterized in that: The sidewall is provided with a guide root weak line extending along the axial direction of the cup body. The guide root weak line is a crack initiation structure formed by thinning groove, indentation, scribing or micro-perforation. Furthermore, the outer barrier region is an intermittent, strip-shaped, microporous, or thinned structure in the area corresponding to the weak line of the guide root; The bottom of the cup is provided with a drainage hole and / or a pre-cracked guide root structure, wherein the number of drainage holes is at least one, and the pre-cracked guide root structure is a pre-cracked line structure provided on the bottom of the cup.

7. The PHA-based barrier-porous synergistic potted seedling cup suitable for natural composting as described in claim 1, characterized in that: When the outer barrier region is formed by melt coating and bonding with the cup matrix, the interface transition layer comprises a polyhydroxy fatty acid ester polymer and a reaction compatibilizer or chain extender component.

8. The PHA-based barrier-porous synergistic potted seedling cup suitable for natural composting as described in claim 1, characterized in that: The polyhydroxyalkanoate polymer is selected from short-chain polyhydroxyalkanoates, medium- and long-chain polyhydroxyalkanoates, or copolymers between monomers that form short-chain and medium- and long-chain polyhydroxyalkanoates. The short-chain polyhydroxy fatty acid ester is selected from one or more combinations of poly(3-hydroxybutyric acid), poly(3-hydroxybutyric acid-co-3-hydroxyvalerate), and poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid). The medium- and long-chain polyhydroxy fatty acid esters are selected from one or more combinations of poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), poly(3-hydroxynonanoate), poly(3-hydroxydecanoate), poly(3-hydroxyundecanoate), poly(3-hydroxydodecanoate), poly(3-hydroxytridecanoate), poly(3-hydroxytetradecanoate), poly(3-hydroxypentadecanoate), and poly(3-hydroxypentadecanoate). The molar content of 3-hydroxyvalerate structural units in the poly-3-hydroxybutyric acid-co-3-hydroxyvalerate is 2 mol% to 25 mol.

9. The PHA-based barrier-porous synergistic potted seedling cup suitable for natural composting as described in claim 1, characterized in that: The biodegradable hydrophobic barrier component is selected from natural resin derivatives, waxes, plant oil derivatives, aliphatic esters, aliphatic amides, biodegradable hydrophobic polyester waxes, or combinations thereof; The natural resin derivatives mentioned therein include one or more of rosin and its derivatives, and dammar resin; The waxes include one or more of carnauba wax, rice bran wax, candelilla wax, and beeswax; The plant oil derivatives include one or more of hydrogenated vegetable oils and castor oil derivatives; The aliphatic esters include one or more of the following: esters formed from fatty acids and polyols, and esters formed from fatty alcohols and fatty acids. The aliphatic amides include one or more fatty acid amides; The biodegradable hydrophobic polyester wax is a hydrophobic polyester wax formed by the condensation polymerization of aliphatic dicarboxylic acid and aliphatic diol.

10. The PHA-based barrier-pore synergistic potted seedling cup suitable for natural composting as described in claim 1, characterized in that: The hydrophilic porous component is selected from thermoplastic starch and its derivatives, water-soluble polysaccharides, water-soluble cellulose derivatives, water-soluble oligomers, water-soluble inorganic salts or combinations thereof; The hydrophilic porous component in the internal porous composite material includes 0.2 to 8 parts of a natural composting promoting component. The natural composting promoting component is included in the mass fraction of the hydrophilic porous component as part of the hydrophilic porous component. The natural composting promoting component is selected from monosaccharides, disaccharides, oligosaccharides, starch hydrolysates, amino acids, peptides, organic acid salts or combinations thereof. The organic acid salts include one or more of lactate, citrate, and acetate. When the internally porous composite material includes a reinforcing or filler component, the reinforcing or filler component is selected from natural fibers, mineral fillers, or combinations thereof, and when the reinforcing or filler component contains natural fibers, the average length of the natural fibers is 0.1 mm to 0.8 mm.

11. The PHA-based barrier-pore synergistic potted seedling cup suitable for natural composting as described in claim 1, characterized in that: When the sidewall is a layered structure, the equivalent thickness of the outer barrier zone is the arithmetic mean of the thickness of the outer barrier zone obtained by microscopic measurement of the sidewall cross section at at least three measurement points along the circumferential and axial directions of the sidewall. Alternatively, when the outer barrier region is a semi-continuous barrier molten coating with discontinuous areas, the equivalent thickness of the outer barrier region is the equivalent thickness obtained by dividing the unit area mass increment by the coating material density, wherein the unit area is the total area of ​​the outer surface of the sidewall and includes the discontinuous areas, the unit area mass increment is the difference in unit area mass of the sample before and after coating, and the coating material density is the density at 23°C. The ratio of the equivalent thickness of the outer barrier region to the total thickness of the sidewall is 4% to 20%, and the ratio of the equivalent thickness of the outer barrier region to the thickness of the inner porous structure region is 1:4 to 1:

20. The static water droplet contact angle of the outer surface of the outer barrier region, measured according to GB / T 30693-2014 at 25°C and 50% relative humidity, is 95° to 120°, and the static water droplet contact angle of the inner surface of the inner porous structure region, measured according to GB / T 30693-2014 at 25°C and 50% relative humidity, is 40° to 80°.

12. The PHA-based barrier-pore synergistic potted seedling cup suitable for natural composting as described in claim 1, characterized in that: The outer barrier composite material comprises, by weight, 60 to 95 parts of polyhydroxy fatty acid ester polymer, 0.2 to 8 parts of biodegradable hydrophobic barrier component, 0 to 1 part of hydrophilic porous component, 0 to 25 parts of flexible modification component, 0 to 20 parts of reinforcing or filler component, and 0 to 10 parts of additives. The internally porous composite material comprises, by weight, 40 to 90 parts of polyhydroxyalkanoate polymer, 0 to 1 part of biodegradable hydrophobic barrier component, 6 to 28 parts of hydrophilic porous component, 0 to 20 parts of reinforcing or filler component, 0 to 30 parts of flexible modification component, 0 to 3 parts of reaction compatibilizer or chain extender component, and 0 to 10 parts of additives.

13. A method for preparing a PHA-based barrier-pore synergistic potted seedling cup suitable for natural composting disposal according to claim 1, characterized in that, The preparation method includes the following steps: Step 1. Dry the polyhydroxyalkanoate polymer in a vacuum drying oven until the moisture content is ≤0.025wt%, which is expressed as a mass percentage and determined using a Karl Fischer moisture titrator; dry the hydrophilic porous component, biodegradable hydrophobic barrier component, reinforcing or filler component, flexible modification component, reaction compatibilizer or chain extender component and auxiliaries separately until their moisture content is ≤0.4wt%, cool and seal for later use to obtain the dried raw material; Step 2. Add the dried raw materials obtained in Step 1 to a twin-screw extruder for melt blending and granulation to obtain outer barrier composite material granules and inner porous composite material granules. Step 3. Feed the outer barrier composite material granules and the inner porous composite material granules obtained in Step 2 into an injection molding machine, and use one of the following methods: co-injection molding, two-material injection molding, in-mold melt coating combined molding, external melt coating combined molding, or single-layer gradient molding, so that the outer barrier area and the inner porous structure area are formed on the sidewall to obtain the cup body; Step 4. Cool and shape the cup obtained in step 3 inside or outside the mold and then demold it to obtain the seedling cup; In steps 2 and 3, the melting residence time is ≤3min. The melting residence time is the average melting residence time, which is calculated as the ratio of the effective melt volume of the equipment to the actual mass flow rate. When step 3 uses melt coating combined molding, the melt coating is performed by melt extrusion coating or melt scraping coating, using the melt of the outer barrier composite material as the coating medium.

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