Bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulching film as well as preparation method and application thereof

Abstract

The invention discloses a bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulching film as well as a preparation method and application thereof, and belongs to the technical field of agricultural mulching materials. According to the mulching film, bamboo pulp paper is used as a base material, and a water-based PHA inner stable coating on a soil attaching surface and a PHA extrusion film layer on a wind and rain facing surface are firmly combined by utilizing a'same-family wet-to-heat 'glue-free composite process. The problems that a traditional paper film is poor in weather resistance and a biodegradable plastic film is prone to premature senility are solved. Compared with products in the market, the scheme abandons an adhesive and a fluorine-containing auxiliary agent which hinder degradation, and the tear-grade strength of the fiber can be realized only by homeotropic interface anchoring; in addition, the blocking and soil moisture preservation effects superior to those of a traditional thick coating can be achieved with less PHA dosage, and the water absorption is remarkably reduced; the material has excellent mechanical adaptability and photo-thermal adjusting function, is completely mineralized after being buried into soil, and really realizes perfect unification of high performance and full environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of agricultural covering materials technology, and particularly relates to bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film, its preparation method and uses. Background Technology

[0002] Polyethylene mulch film is widely used to increase and stabilize agricultural yields, but it is difficult to recycle, and the accumulation of residual film and microplastics poses ecological risks. Pure thermoplastic biodegradable plastic films such as polybutylene adipate terephthalate (PBAT), polylactic acid (PLA), and polyhydroxyalkanoates (PHA) have degradation potential, but they are prone to premature aging and breakage in long seasons, strong winds and rain, and mechanical erosion. Pure paper-based mulch film has insufficient water resistance and tear resistance, and poor compatibility with mechanical film laying equipment.

[0003] It is known that PHA-paper lamination primarily targets the packaging field. For example, US6322899B1 and WO1999001278A1 apply PHA to paper or paperboard through extrusion coating, but do not address requirements related to soil mulch, wet-to-heat composite windows, or fiber tear failure. WO2001 / 21881A2 discloses a technology for coating PHA emulsion onto paper, but this still falls under the packaging category. US2022 / 0033158A1 uses a water-dispersed nanosheet barrier layer, which differs from the present invention's avoidance of restrictions on nanosheets and independent adhesive layers. WO2025 / 073274A1 relates to PHA waterborne coatings, but does not mention integration with paper-based wet-to-heat composites or overall soil mineralization indicators. The reports published by Dubaicheng, such as CN120026524A, CN120250392A, and CN120192646A, describe water-based systems containing polyvinyl alcohol (PVA) or PBAT for use in paper-based barrier packaging. These differ fundamentally from the combination of "PHA, no independent adhesive layer, soil mulch film scenario, and composite window" specified in this invention. Even combining the water-based primer layer superimposed with a nanosheet barrier layer from US2022 / 0033158A1 with the extrusion coating approach from US6322899B1, the resulting structure still relies on nanosheets or non-isotropic interlayer adhesion. In contrast, this invention specifies "PHA double-sided" and "no independent adhesive and wet-to-heat composite window," and provides control of the entire mulch film according to the 24-month mineralization index and fiber tearing failure mode of ISO17556.

[0004] In summary, current technologies still lack an agricultural mulch film structure and preparation window that can simultaneously meet the requirements of "long-season weather resistance and mechanical laying compatibility of paper-based film," "high-strength homogeneous interface bonding without independent adhesives," "significant barrier and reduced water absorption with low PHA dosage," and "ultimate aerobic mineralization within 24 months after plowing into the soil." Therefore, it is necessary to propose a double-sided composite mulch film based on bamboo pulp paper and PHA homogeneous materials and its preparation method to solve problems such as poor weather resistance of paper films, premature aging of biodegradable plastic films, and incompatibility of paper-plastic interfaces. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film, its preparation method and uses, so as to solve the problems of difficult recycling of mulch film, poor weather resistance of paper mulch film and premature aging of biodegradable plastic film in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] Bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film, its preparation method and uses, wherein the mulch film comprises a paper base layer mainly composed of bamboo pulp, and the paper base layer includes a soil-facing side and a wind-facing side;

[0008] The basis weight of the paper substrate is 25–300 g / m², for example, 25 g / m², 30 g / m², 35 g / m², 50 g / m², 80 g / m², 100 g / m², 120 g / m², 150 g / m², 160 g / m², 200 g / m², 220 g / m², 250 g / m², 280 g / m², or 300 g / m², and the proportion of bamboo pulp to the total mass of pulp fibers in the paper substrate is ≥50 wt%, for example, 50 wt%, 55 wt%, 60 wt%, 65 wt%. The pulp comprises 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, or 100wt%; the pulp contains long fibers and short fibers in a mass ratio of 30:70 to 70:30, for example 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, or 70:30, and the pulp contains 0.2–1.0wt%, for example 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, or 0.6wt%. The paper substrate comprises 0.8 wt%, 0.9 wt%, or 1.0 wt% bamboo-based microfibrillated cellulose (CNF), bamboo-based nanocellulose (CNC), or a mixture thereof; the long fibers are selected from bamboo long fibers or softwood pulp, and the short fibers are selected from hardwood pulp or bamboo short fibers; the air permeability and smoothness of the paper substrate meet the following requirements: Beck smoothness is 80–600s, for example, 80s, 100s, 150s, 180s, 200s, 210s, 220s, 260s, 300s, 400s, 500s. Or 600s, the air permeability of Guri is 50–600s / 100mL, for example 50s / 100mL, 80s / 100mL, 100s / 100mL, 120s / 100mL, 150s / 100mL, 160s / 100mL, 180s / 100mL, 200s / 100mL, 240s / 100mL, 300s / 100mL, 320s / 100mL, 400s / 100mL, 500s / 100mL or 600s / 100mL;

[0009] When the paper base layer is an ultralight paper with a basis weight of 25–50 g / m², a 10–35% creping treatment, such as 10%, 15%, 20%, 22%, 25%, 30%, or 35%, is applied, and / or a 2–6 g / m², such as 2 g / m², 3 g / m², 4 g / m², 5 g / m², or 6 g / m², is implemented for water-based PHA infiltration to improve mechanical lay-up compatibility; when the paper base layer is a heavy paper with a basis weight of 160–300 g / m², a micro- The micro-cuts or edge stitching have a single cut length of 0.5–1.5 mm, such as 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm or 1.5 mm, a pitch of 5–20 mm, such as 5 mm, 8 mm, 10 mm, 15 mm or 20 mm, 50–200 stitches per meter, such as 50, 100, 150 or 200 stitches, and a total area percentage of ≤0.5%, such as 0.1%, 0.2%, 0.3% or 0.5%.

[0010] The paper base layer has a homologous water-based PHA barrier coating on its surface. The dry coating amount of the barrier coating is 5–25 g / m², for example, 5 g / m², 6 g / m², 8 g / m², 9 g / m², 10 g / m², 12 g / m², 15 g / m², 18 g / m², 20 g / m², 22 g / m², or 25 g / m². This barrier coating is derived from a homologous internally stable emulsion, and the particle size D of the emulsion is... 50 The thickness is 0.15–2.0 μm, for example 0.15 μm, 0.20 μm, 0.25 μm, 0.30 μm, 0.50 μm, 0.80 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, or 2.0 μm, and the zeta potential is -25 to -45 mV, for example -25 mV, -28 mV, -30 mV, -32 mV, -35 mV, -38 mV, -40 mV, -42 mV, or -45 mV. The polymer solids in the barrier coating consist only of polyhydroxyalkanoates and have a purity ≥97 wt%, for example 97 wt%, 98 wt%, 99 wt%, or 100 wt%. The Cobb coating applied to the soil surface... 60 The value decreases by ≥30% compared to the uncoated paper surface, for example, 30%, 33.3%, 35%, 40%, 50%, 60%, or 70%; when the basis weight of the paper base is >25 and ≤160 g / m², the Cobb coating value decreases by ≥30%, for example, 30%, 33.3%, 35%, 40%, 50%, 60%, or 70%; 60 Value ≤30g / m², for example 30g / m², 28g / m², 26g / m², 25g / m², 24g / m², 23g / m², or 20g / m²; when the basis weight of the paper base layer is >160 and ≤300g / m², the Cobb coating... 60 Value ≤ 40g / m², for example 40g / m², 38g / m², 35g / m², 32g / m² or 30g / m²;

[0011] The paper substrate has a thermoplastic PHA extruded film layer on its windward side. The thickness of the extruded film layer is 20–80 μm, for example, 20 μm, 25 μm, 28 μm, 30 μm, 33 μm, 35 μm, 40 μm, 45 μm, 50 μm, 60 μm, 70 μm, or 80 μm. The extruded film layer is a multilayer co-extruded structure, comprising a PHA-grafted anhydride compatibility layer with a thickness of 1–10 μm, for example, 1 μm, 2 μm, 3 μm, 5 μm, 8 μm, or 10 μm, attached to the windward side of the paper substrate, and a functional layer with a thickness of 20–70 μm, for example, 20 μm, 25 μm, 27 μm, 30 μm, 32 μm, 35 μm, 40 μm, 50 μm, 60 μm, or 70 μm, disposed outside the compatibility layer. The functional layer is a PHA homogeneous blend structure.

[0012] Before being laminated with the extruded film layer, the windward surface of the paper substrate is subjected to corona or plasma activation treatment with an equivalent treatment energy ≥0.8kJ / m², such as 0.8kJ / m², 0.9kJ / m², 1.0kJ / m², 1.2kJ / m² or 1.5kJ / m², and a surface tension ≥38mN / m, such as 38mN / m, 39mN / m, 40mN / m, 41mN / m, 42mN / m or 44mN / m.

[0013] After the coating on the substrate is dried to an outlet paper temperature ≤55℃, it is stored for ≤2 hours (e.g., 0.5h, 1.0h, 1.5h, or 2.0h) in an environment with a temperature of 20–30℃ (e.g., 20℃, 22℃, 25℃, 28℃, or 30℃) and a relative humidity of 40%–60% (e.g., 40%, 45%, 50%, 55%, or 60%), and then wet-heat bonded with the wind-facing surface. This results in a 180° peel strength at the paper-film interface ≥1.5N / 25mm (e.g., 1.5N / 25mm, 1.6N / 25mm, 1.8N / 25mm, 2.0N / 25mm, 2.1N / 25mm, 2.2N / 25mm, 2.3N / 25mm, or 2.5N / 25mm), with the failure mode being fiber tearing. Furthermore, after aging at 40℃ for 7 days, it still meets the aforementioned strength and failure mode requirements.

[0014] The water vapor transmission rate (WVTR) of the whole film is tested according to ASTM E96 / E96M-24a standard Procedure B under conditions of 38°C and 90% RH, and is 50-75% lower than that of uncoated paper, for example, 50%, 55%, 60%, 65%, 66%, 68%, 70%, 72%, or 75%; the biodegradability of the overcoating layer in aerobic soil for 24 months according to ISO 17556 standard is ≥90%, for example, 90%, 92%, 95%, 96%, or 98%; the barrier coating and the extruded film layer are made of PHA family materials; the windward extruded film layer is directly bonded to the paper base layer, and the resin of the windward extruded film layer is only a PHA family material.

[0015] The extruded film layer is selected from one of black opaque film, white foamed film, or natural-colored film; when it is black opaque film, it contains 0.5–1.0 wt% of low polycyclic aromatic hydrocarbon carbon-based pigment; when it is white foamed film, it contains 0.1–2.0 wt% of white inorganic pigment and is obtained by carbon dioxide foaming, with a carbon dioxide injection pressure of 5–7 MPa, a foaming temperature of 150–165°C, and a draw ratio of 1.4–1.8; when it is natural-colored film, no pigment is added.

[0016] The functional layer is selected from one or more combinations of the following: a blend of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) containing 5–12 mol%, for example 5 mol%, 8 mol%, 10 mol%, or 12 mol% of 3-hydroxyhexanoate units and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBV) containing 8–20 mol%, for example 8 mol%, 10 mol%, 12 mol%, 15 mol%, or 20 mol% of 3-hydroxyvalerate units, wherein the mass ratio of PHBHHx to PHBV is 30:70 to 90:10; or a blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) containing 20–40 mol%, for example 20 mol%, 25 mol%, 30 mol%, 35 mol%, or 40 mol% of 4-hydroxybutyrate units. A blend of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) containing 8–20 mol%, for example 8 mol%, 10 mol%, 12 mol%, 15 mol%, or 20 mol%, 3-hydroxyvalerate units, wherein the mass ratio of P34HB to PHBV is 30:70 to 90:10; a blend of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) wherein the mass ratio of PHB to PHBV is 30:70 to 90:10; the above mass ratio can be 30:70 to 90:10, for example 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, or 90:10;

[0017] The polyhydroxy fatty acid ester may also include homologous blends or grafted modifiers, wherein the grafting groups of the grafted modifiers are selected from acid anhydrides or epoxy functional groups.

[0018] The weather-facing surface is a black opaque film or a white foamed film; when the weather-facing surface is a black opaque film, the low-polycyclic aromatic hydrocarbon carbon-based pigment used is selected from furnace black, channel black, thermal cracking black, or acetylene black, and the total amount of pigment is ≤1.0wt%, for example 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, or 1.0wt%, and the transmittance T at 600nm is such that... 600 ≤3%, for example, 0.5%, 0.8%, 1.0%, 1.5%, 2.0%, or 3.0%; when the windward side is a white foamed film, the closed-cell volume fraction is 15–40%, for example, 15%, 20%, 25%, 30%, 35%, or 40%, and the visible light integrated reflectance R 400–700≥70%, for example 70%, 72%, 75%, 80% or 85%, and the white foamed film further contains 0.1–2.0 wt%, for example 0.1 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.5 wt% or 2.0 wt% of white inorganic pigment, said pigment being selected from one or more of titanium dioxide, calcium carbonate or talc.

[0019] The anhydride monomer used for grafting the compatibility layer is selected from one or more of maleic anhydride, itaconic anhydride, succinic anhydride, fumaric anhydride or maleic anhydride, and the apparent acid value of the grafted material is 3–15 mg KOH / g, for example 3 mg KOH / g, 5 mg KOH / g, 6 mg KOH / g, 8 mg KOH / g, 10 mg KOH / g, 12 mg KOH / g or 15 mg KOH / g.

[0020] The bio-based carbon content of the polymer solids is ≥90%, for example, 90%, 92%, 94%, 95%, 96% or 98%; the total amount of non-polymer additives in the barrier coating and the extruded film is ≤3.0wt%, for example, 0.5wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 2.0wt% or 3.0wt%, and the additives are selected from one or more of plasticizers, antioxidants, slip agents or processing aids, and do not change the limitation that the polymer solids are PHA.

[0021] The coating on the soil surface has a biodegradability of ≥90% (e.g., 90%, 92%, or 95%) in aerobic soil at 25–30°C for 90 days, according to ISO 17556 standard. The sample used to test the biodegradability is the coating body obtained by forming a film on a non-absorbent inert substrate and peeling off the coating on the soil surface.

[0022] The coating on the soil surface is derived from a homologous internally stable emulsion, primarily composed of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and containing 10–20 wt% (e.g., 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt%) of PHA oligomers and 2–5 wt% (e.g., 2 wt%, 3 wt%, 4 wt%, or 5 wt%) of PHA grafted anhydride half-esters based on polymer solids. The number-average molecular weight of the PHA oligomers is 3–8 kDa, e.g., 3 kDa, 4 kDa, 5 kDa, 6 kDa, or 8 kDa. The half-ester is partially neutralized by one of sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, triethanolamine, or 2-amino-2-methyl-1-propanol, with an apparent acid value of 3–10 mg KOH / g, e.g., 3 mg KOH / g, 5 mg KOH / g, 6 mg KOH / g, etc. KOH / g, 8 mg KOH / g or 10 mg KOH / g, with a degree of neutralization of 20–45%, such as 20%, 25%, 30%, 35%, 40% or 45%; and a dry coating weight of 5–12 g / m², such as 5 g / m², 8 g / m², 10 g / m² or 12 g / m².

[0023] After being accelerated to age at 40°C for 7 days, the paper-film interface retains ≥90% of the 180° peel strength, for example, 90%, 92% or 95%, and the failure mode is fiber tearing.

[0024] When the windward side is a white foamed film, the white foamed film is obtained by carbon dioxide foaming. The carbon dioxide injection pressure is 5–7 MPa, for example, 5.0 MPa, 5.5 MPa, 5.8 MPa, 6.0 MPa, 6.5 MPa or 7.0 MPa; the foaming temperature is 150–165℃, for example, 150℃, 155℃, 160℃ or 165℃; the draw ratio is 1.4–1.8, for example, 1.4, 1.5, 1.6 or 1.8; the average pore size is 5–30 μm, for example, 5 μm, 10 μm, 12 μm, 15 μm, 20 μm, 25 μm or 30 μm; and the closed-cell volume fraction is 15–40%, for example, 15%, 20%, 25%, 30%, 35% or 40%.

[0025] The ash content of the paper base layer is ≤2.0wt%, for example 0.5wt%, 1.0wt%, 1.2wt%, 1.3wt%, 1.4wt%, or 2.0wt%), and the added surfactant is ≤0.5wt%, for example 0wt%, 0.1wt%, 0.2wt%, or 0.5wt%; the inner diameter of the mulch film roll is 76mm, the width is 800–1800mm, for example 800mm, 1000mm, 1200mm, 1400mm, 1500mm, or 1800mm, the roll length is 200–1000m, for example 200m, 400m, 500m, 800m, or 1000m, and the maximum roll weight is ≤110kg, for example 75kg, 80kg, 90kg, 100kg, or 110kg.

[0026] The total organic fluorine in the barrier coating, each layer of the extruded film, and the entire sample was not detected, with a detection limit of ≤5 mg / kg.

[0027] A method for preparing the mulch film as described above includes the following steps:

[0028] Step 1. Papermaking: Add bamboo-based microfibrillated cellulose, bamboo-based nanocellulose, or a mixture of both to the refined pulp and mix thoroughly. Form a paper base with a basis weight of 25–300 g / m², such as 25 g / m², 30 g / m², 35 g / m², 50 g / m², 80 g / m², 100 g / m², 120 g / m², 150 g / m², 200 g / m², or 300 g / m², using bamboo pulp as the main component. Adjust the paper surface to a Beck smoothness of 80–600 s. For example, 80s, 150s, 200s, 300s or 600s, and Gurry air permeability of 50–600s / 100mL, such as 50s / 100mL, 120s / 100mL, 160s / 100mL, 320s / 100mL or 600s / 100mL, are used to obtain the paper base layer; when the basis weight is 25–50g / m², creping and / or PHA infiltration are performed; when the basis weight is 160–300g / m², micro-cutting or edge creasing is performed.

[0029] Step 2. Emulsion acquisition: PHA grafted anhydride is obtained by reactive extrusion, hydrolyzed, and partially neutralized to form PHA grafted anhydride hemiester salt; PHA melt at 160–180°C, for example, 160°C, 165°C, 170°C, 175°C, or 180°C, is metered and pumped into an 85–95°C, for example, 85°C, 90°C, at a rate of 0.5–1.5 L / min, for example, 0.5 L / min, 0.8 L / min, 1.0 L / min, 1.2 L / min, or 1.5 L / min. A rotor-stator emulsifier with a hot water side at 0°C or 95°C performs high-shear emulsification at speeds of 5000–15000 r / min, for example, 5000 r / min, 8000 r / min, 10000 r / min, 12000 r / min or 15000 r / min, to obtain a homologous internally stable emulsion; the homologous internally stable emulsion has a solids content of 35–45 wt%, for example, 35 wt%, 38 wt%, 40 wt%, 42 wt% or 45 wt%), D 50 The viscosity ranges from 0.15 to 2.0 μm, for example, 0.15 μm, 0.20 μm, 0.50 μm, 1.0 μm or 2.0 μm; the zeta potential ranges from -25 to -45 mV, for example, -25 mV, -30 mV, -32 mV, -40 mV or -45 mV; the pH ranges from 6.5 to 8.0, for example, 6.5, 7.0, 7.2, 7.5 or 8.0; the pH ranges from 25 °C; and the viscosity ranges from 50 to 400 mPa·s, for example, 50 mPa·s, 100 mPa·s, 180 mPa·s, 200 mPa·s, 300 mPa·s or 400 mPa·s.

[0030] Step 3. Coating the soil-attached surface: Apply the homologous internally stable emulsion obtained in Step 2 to the soil-attached surface of the paper base obtained in Step 1. Control the dry coating amount to 5–25 g / m², for example, 5 g / m², 8 g / m², 10 g / m², 12 g / m² or 25 g / m². Dry it in stages at 80℃, 95℃ and 110–115℃, for example, 110℃, 112℃ or 115℃, until the exit paper temperature is ≤55℃, for example, 40℃, 45℃, 50℃ or 55℃, to obtain the coating on the soil-attached surface.

[0031] Step 4. Preparation of PHA extrusion film raw materials for the windward side. The extrusion film raw materials include PHA grafted anhydride compatibility layer granules and functional layer granules. When preparing the PHA grafted anhydride compatibility layer granules, dry polyhydroxyalkanoate powder is used as the compatibility layer raw material base. 0.5wt% to 2.0wt%, for example, 0.5wt%, 0.8wt%, 1.0wt%, 1.5wt%, or 2.0wt%, of anhydride monomer and 0.05wt% to 0.2wt%, for example, 0.05wt%, 0.1wt%, 0.15wt%, or 0.2wt%, of initiator are added by weight. The reaction extrusion is carried out in a twin-screw extruder at 170℃ to 185℃, for example, 170℃, 175℃, 180℃, or 185℃. The granules are then underwater chopped and dried to obtain an apparent acid value corresponding to the grafting rate of 3–15 mg KOH / g, for example, 3 mg KOH / g, 5 mg KOH / g, or 10 mg KOH / g. PHA grafted anhydride compatibility layer granules with KOH / g, 12mg KOH / g or 15mg KOH / g; when preparing granules for functional layers, dry PHA homologous resins are mixed in the aforementioned proportions as functional layer raw materials, and color masterbatch or nucleating agent is added as needed. The mixture is melt-blended and extruded in a twin-screw extruder at a temperature of 160°C to 180°C, for example 160°C, 165°C, 170°C, 175°C or 180°C, then pelletized and dried to obtain granules for functional layers.

[0032] Step 5. Activation and Coating of the Weather-Facing Surface: After the coating on the substrate in Step 3 is dried to an exit paper temperature ≤55℃, the weather-facing surface of the paper substrate is subjected to corona or plasma treatment for ≤2 hours within an environment with a temperature of 20–30℃ and a relative humidity of 40%–60% until the equivalent treatment energy is ≥0.8kJ / m² and the surface tension is ≥38mN / m, for example, 38mN / m, 40mN / m, or 4... 2mN / m, using the PHA grafted anhydride compatibility layer granules prepared in step 4 and the functional layer granules, the film is extruded and coated at a melt temperature of 160–185°C, for example, 160°C, 165°C, 170°C, 175°C, 180°C, or 185°C, to a thickness of 20–80 μm, for example, 20 μm, 30 μm, 33 μm, 35 μm, 40 μm, 50 μm, or 80 μm, to obtain an extruded film layer on the windward side, and then bonded to the paper base layer. The weather-facing side is laminated to obtain a double-sided composite semi-finished product. The lamination conditions are as follows: cooling roller temperature 15–25℃, for example 15℃, 18℃, 20℃, 22℃ or 25℃; pressing line pressure 0.2–0.5MPa, for example 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa; linear speed 30–120m / min, for example 30m / min, 50m / min, 80m / min, 95m / min, 100m / min or 120m / min; resin is dried at 60–70℃, for example 60℃, 65℃ or 70℃ for 4–8h, for example 4h, 6h or 8h, with a moisture content ≤0.02wt%, for example 0.01wt% or 0.02wt%; during multilayer co-extrusion, the temperature difference between each melt is ≤15℃, for example 5℃, 10℃ or 15℃; the activation standard is a surface tension ≥38mN / m.

[0033] Step 6. Wet-heat composite and curing: The double-sided composite semi-finished product obtained in step 5 is cured at a temperature of 20–30℃, such as 20℃, 22℃, 25℃, 28℃ or 30℃ and a relative humidity of 40%–60%, such as 40%, 45%, 50%, 55% or 60%, for ≥24h and then cut, such as after 24h, 48h or 72h, to obtain the bamboo pulp paper PHA double-sided composite soil biodegradable agricultural mulch film.

[0034] Based on the aforementioned uses of mulch film in farmland mulching cultivation, it is used for shading, weed suppression, moisture retention, and temperature regulation; after crop harvesting, it is plowed into the soil, and the barrier coating and the extruded film layer have a biodegradability of ≥90% within 24 months according to ISO 17556 standard.

[0035] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0036] Excellent interfacial bonding strength and weather resistance: This invention utilizes the molecular affinity of homologous PHA materials through a "homologous wet-to-heat" composite process, combined with specific activation energy and composite timing window, to achieve high-strength bonding between the paper base and the film layer without adhesives. It also features high peel strength and an ideal failure mode of fiber tearing, solving the problems of easy delamination and poor water resistance in traditional paper-plastic interfaces.

[0037] All bio-based and environmentally friendly: All components of the mulch film of this invention (bamboo pulp paper, PHA coating, PHA extruded film) are all bio-based, with high bio-based carbon content, and do not contain petroleum-based or slow-degrading components such as polyvinyl alcohol and polybutylene adipate, nor fluorine and harmful surfactants. After being plowed into the soil, it can be completely biodegraded into water and carbon dioxide, avoiding microplastic accumulation and soil pollution.

[0038] Excellent agronomic performance: The double-sided PHA composite structure design endows the mulch film with excellent barrier properties (Cobb). 60 It significantly reduces soil moisture content and has excellent weed control capabilities. The black formula effectively blocks light and suppresses weeds, while the white foaming formula reflects light and cools the soil, meeting the planting needs of different crops.

[0039] Excellent adaptability to mechanical laying: Targeted treatments such as wrinkling, internal seepage, or micro-cutting are adopted for paper base layers with different basis weights, which significantly improves the flexibility and stress release capacity of the mulch film, enabling it to adapt to mechanized laying operations and reducing the breakage rate. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the microstructure of the bamboo pulp paper-PHA composite biodegradable agricultural mulch film described in this invention.

[0041] In the figure, 1-homologous waterborne PHA barrier coating; 2-paper base layer; 3-PHA grafted anhydride compatibility layer; 4-functional layer. Detailed Implementation

[0042] 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.

[0043] In this specification, "covering layer," "whole film," and "whole sample" all refer to the overall composite mulch film structure, including the bamboo pulp paper base layer, the water-based PHA barrier coating on the soil-facing surface, and the thermoplastic PHA extruded film layer on the windward side. The water-based PHA barrier coating on the soil-facing surface is derived from a similar internally stabilized emulsion, and the resin in the extruded film layer on the windward side is only a PHA-related material, without polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), or polyvinyl alcohol (PVA). The "equivalent treatment energy" mentioned in this specification refers to the energy actually received per unit area of ​​the substrate surface during corona or plasma treatment, calculated based on the effective power of the equipment, the treatment width, and the linear velocity, expressed in kJ / m². The "wet-to-thermal lamination" described in this specification refers to the following: after the water-based PHA coating on the soil surface is dried in stages to an outlet paper temperature of ≤55℃, it is stored in an environment of 20–30℃ and 40%–60% RH for ≤2 hours. During this time window, the windward side is activated and lamination is completed using a PHA melt coating method at 160–185℃. This allows the paper / film interface to form a high-strength interfacial bond under the combined effect of molecular affinity of homologous materials and wetting and spreading of the activated surface.

[0044] Figure 1 The microstructure of the bamboo pulp paper-PHA composite biodegradable agricultural mulch film of the present invention is shown. The structure has a paper base layer 2 reinforced with bamboo-based cellulose as the main skeleton. The soil-facing side is anchored by a specific emulsion to form a dense homologous water-based PHA barrier coating 1 to achieve efficient moisture retention and significantly reduce water absorption. The windward side is composited with a multi-layer co-extruded thermoplastic PHA film. The core is a thin PHA-grafted anhydride compatible layer 3 tightly attached to the paper base layer. It uses active groups to form a high-strength interface bond with the paper base layer 2 under a specific glue-free "wet-to-heat" composite process, thereby solving the weather resistance problem. The outermost functional layer 4 undertakes the functions of shading and weed suppression or reflecting and regulating temperature according to agronomic needs. The entire mulch film can ultimately achieve complete soil biomineralization.

[0045] Main reagents and raw materials:

[0046] Table 1. Main reagent and raw material names, product models and manufacturers:

[0047]

[0048] Main analytical and testing instruments:

[0049] Table 2: Main Equipment Names, Product Models, and Manufacturers:

[0050]

[0051] Main testing standards and methods:

[0052] ISO 17556:2019 Plastics in soil: Determination of ultimate aerobic biodegradability by measuring oxygen demand or carbon dioxide production;

[0053] GB / T 1540-2002: Determination of water absorbency of paper and paperboard using the Cobb method. (Specific Cobb method details...) 60 The test method is as follows: After equilibration for 24 hours in a constant temperature and humidity environment (23±1℃, 50±2% RH), a circular sample with a diameter of 125mm is cut and its initial mass is recorded as m1 (g). The sample is placed on the metal cylinder base of the Cobb tester, ensuring that the surface in contact with the soil is facing upwards (i.e., the surface in contact with water is the surface of the coating to be tested), and is tightly fixed with a metal pressure ring. 100mL of distilled water is quickly poured into the cylinder and the timing is started simultaneously. At 45s, the water in the cylinder is poured out; at 60s, the pressure ring is immediately released and the sample is removed. The wet side is placed on standard absorbent paper, and then covered with another sheet of standard absorbent paper. A 10kg standard metal pressure roller is used to roll the sample back and forth once within 4s. The sample is then removed and its mass after absorbing water is immediately recorded as m2 (g). Calculation formula: Cobb 60 =(m2-m1)×100, unit: g / m²;

[0054] ASTM E96 / E96M-24a (Procedure B, 38°C, 90% RH): Test method for water vapor permeability of materials;

[0055] GB / T 2790-1995: Determination of 180° peel strength of adhesives;

[0056] GB / T 455-2002: Determination of tear strength of paper and paperboard (Elmendorf method);

[0057] ASTM D5748-95(2019): Standard test method for resistance to puncture of films and sheets;

[0058] ASTM D1003-21: Standard test method for haze and transmittance of transparent plastics (integrating sphere);

[0059] ISO 5627:1995 Determination of Beck smoothness of paper and paperboard;

[0060] ISO 5636-5:2013 Paper and paperboard – Determination of air permeability – Part 5: Gully method;

[0061] ISO 16620-2:2019 Plastics - Bio-based content - Part 2: Determination of bio-based carbon content;

[0062] ISO 22412:2025 Determination of particle size by dynamic light scattering (DLS);

[0063] ISO 13099-1:2012 / ISO 13099-2:2025 General rules for determination of electrophoretic light scattering zeta potential;

[0064] EN 14582:2016 Oxygen bomb combustion - Ion chromatography for the determination of halogens (for total organic fluorine TOF);

[0065] DIN 38409-59:2022-10 Determination of adsorbable organic fluorine (AOF);

[0066] ISO 4590:2016 Foamed plastics—Determination of open and closed cell ratios (for closed cell volume fraction);

[0067] ASTM D792-20: Determination of density and relative density of plastics (immersion method, for density / Archimedes method traceability);

[0068] ISO 2144:2019 Paper, paperboard and pulp—Determination of ash content (for paper base layer ash);

[0069] ISO 2114:2000 (or equivalent) Plastics and resins—Determination of partial and total acid values ​​(for acid value determination).

[0070] Example:

[0071] General preparation process for PHA oligomers:

[0072] Step 1. Weigh PHBV powder or a blend of PHBV and P34HB in a mass ratio of 1:2, mix evenly, and then vacuum dry at 60℃ to 70℃ for 4 to 8 hours to obtain dried PHA-based raw material.

[0073] Step 2. Add the dried PHA-based raw material obtained in Step 1 to a twin-screw extruder with a high-shear screw combination of 3 to 5 kneading blocks, and continuously melt-shear for 3 to 8 minutes under conditions of 190°C to 200°C, screw speed of 150 r / min to 250 r / min and nitrogen protection, and extrude into strips to obtain melt-sheared PHA extruded strips.

[0074] Step 3. Cool and pulverize the PHA extruded strip obtained in Step 2 to a particle size ≤ 2 mm; take samples and determine the number-average molecular weight Mn using gel permeation chromatography (GPC). By adjusting the melt shear time (3 to 8 minutes), screw speed (150 r / min to 250 r / min), and extrusion temperature (190°C to 200°C) in Step 2, Mn is controlled within the range of 3 kDa to 8 kDa, for example, 5 kDa, to obtain PHA oligomers.

[0075] General preparation process of PHA-grafted anhydride and PHA-grafted anhydride half ester salt:

[0076] Step 1. Preparation of PHA-grafted anhydride. Take polyhydroxyalkanoate powder, i.e., PHA resin, such as PHBV, P34HB, or a blend of both, and add 0.5wt% to 2.0wt% of anhydride monomer and 0.05wt% to 0.2wt% of dicumyl peroxide by weight of the total mixture. The anhydride monomer is selected from one or more of maleic anhydride, itaconic anhydride, succinic anhydride, fumaric anhydride, or maleic anhydride. The material is melt-extruded in a ZSK 26mc twin-screw reactive extruder at 180℃ to 185℃ to obtain PHA-grafted anhydride.

[0077] Step 2. Preparation of PHA grafted anhydride half-ester salt. The PHA grafted anhydride obtained in Step 1 is added to a reaction vessel containing deionized water. According to the target apparent acid value of 3 mg KOH / g to 10 mg KOH / g and the degree of neutralization of 20% to 45%, one of sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, triethanolamine or 2-amino-2-methyl-1-propanol is added for partial neutralization and hydrolysis. The reaction is stirred at 60℃ to 80℃ for 1 hour to 3 hours. After cooling, PHA grafted anhydride half-ester salt is obtained.

[0078] General preparation process of plastic film:

[0079] Step 1. Papermaking. Add bamboo-based microfibrillated cellulose, bamboo-based nanocellulose, or a mixture of both to the refined pulp and mix thoroughly. Use bamboo pulp as the main component for papermaking. Control the basis weight of the paper base at 25 g / m² to 300 g / m², and adjust the paper surface properties to achieve a Beck smoothness of 80 s to 600 s and a Gurry air permeability of 50 s / 100 mL to 600 s / 100 mL to obtain the paper base.

[0080] Step 2. Emulsion Acquisition. In the emulsion system, the PHA grafted anhydride half-ester salt prepared according to the general process described above is pre-dissolved or dispersed in hot water at 85°C to 95°C to obtain the stabilizer aqueous phase; according to the target solid content of 35wt% to 45wt%, the mass flow rate ratio of the polyhydroxyalkanoate melt to the stabilizer aqueous phase is controlled at 35:65 to 45:55 (for example, when the target solid content is 40wt%, the mass flow rate of the aqueous phase is 1.5 times the mass flow rate of the melt); the polyhydroxyalkanoate melt is heated to 160°C to 180°C. The ester melt is metered and pumped into the side rotor-stator emulsifier at a flow rate of 0.5 L / min to 1.5 L / min through the side inlet. It undergoes high-shear emulsification with the stabilizer aqueous phase at a speed of 5000 r / min to 15000 r / min for 10 to 60 seconds, maintaining the emulsifier outlet temperature at 80°C to 95°C. After discharge, the emulsion is cooled to 30°C to 40°C and filtered (80 mesh to 200 mesh) to remove large particles, yielding a solid content of 35 wt% to 45 wt% and a particle size D. 50 Internally stable emulsions of the same family with a size of 0.15 μm to 2.0 μm, a zeta potential of -25 mV to -45 mV, a pH of 6.5 to 8.0, and a viscosity of 50 mPa·s to 400 mPa·s at 25 °C.

[0081] Step 3. Coating the soil-attached surface. Apply the homologous internally stable emulsion obtained in Step 2 to the soil-attached surface of the paper base obtained in Step 1, controlling the dry coating amount to be 5g / m² to 25g / m², and dry it in stages at temperatures of 80℃, 95℃ and 110℃ to 115℃ until the exit paper temperature is ≤55℃, to obtain the coating on the soil-attached surface.

[0082] Step 4. Preparation of PHA extrusion film raw materials for the windward side. The extrusion film raw materials include PHA-grafted anhydride compatibility layer granules and functional layer granules. When preparing the PHA-grafted anhydride compatibility layer granules, dry polyhydroxyalkanoate powder, such as PHBV or P34HB, is used as the compatibility layer raw material base. 0.5wt% to 2.0wt% of anhydride monomers, such as maleic anhydride, and 0.05wt% to 0.2wt% of initiator, such as dicumyl peroxide, are added by weight. The mixture is reacted and extruded in a twin-screw extruder at 170°C to 185°C, then pelletized underwater and dried to obtain an apparent acid value of 3–15 mg corresponding to the grafting rate. PHA grafted anhydride compatibility layer granules with KOH / g are prepared as follows: When preparing granules for the functional layer, dried PHA homologous resins, such as PHBHHx and PHBV or P34HB and PHBV, are mixed in the proportions described in this invention as raw materials for the functional layer. Color masterbatch, such as carbon black concentrate, or nucleating agent, such as talc, is added as needed. The mixture is then melt-blended and extruded in a twin-screw extruder at 160°C to 180°C, granulated, and dried to obtain granules for the functional layer.

[0083] Step 5. Activation and lamination of the wind-facing surface: After the coating on the substrate in Step 3 is dried to an exit paper temperature ≤55℃, the wind-facing surface is subjected to corona or plasma treatment for ≤2 hours at a temperature of 20–30℃ and a relative humidity of 40%–60% until the equivalent treatment energy is ≥0.8kJ / m² and the surface tension is ≥38mN / m. The PHA grafted anhydride compatibility layer granules prepared in Step 4 and the functional layer granules are then melt-treated at 160–185℃. The extrusion coating process forms a 20–80 μm thick extruded film layer on the windward side, which is then laminated with the windward side of the paper base layer to obtain a double-sided composite semi-finished product. The coating conditions are: cooling roller temperature 15–25℃, pressing line pressure 0.2–0.5 MPa, and line speed 30–120 m / min; the resin is dried at 60–70℃ for 4–8 h with a moisture content ≤0.02 wt%; the temperature difference between each melt during multilayer co-extrusion is ≤15℃; and the activation standard is ≥38 mN / m.

[0084] Step 6. Maturation and Slitting: The double-sided composite semi-finished product obtained in Step 5 is matured at a temperature of 20–30℃ and a relative humidity of 40%–60% for ≥24 hours and then slitted to obtain the bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film.

[0085] Example 1: Preparation of a conventional main double-sided black film.

[0086] The basis weight of the paper substrate is 80 g / m², and its fiber composition is 45 wt% bamboo long fibers, 30 wt% bamboo short fibers, and 25 wt% broadleaf pulp short fibers. Bamboo pulp fibers account for 75 wt% of the total, and long fibers account for 45 wt%. The pulp contains 0.4 wt% bamboo-based nanocellulose by oven-dry weight. The substrate has a Beck smoothness of 220 s and a Gurley air permeability of 180 s / 100 mL.

[0087] Layer B1, the surface layer for bonding to the soil, is coated with a homologous internally stabilized emulsion at a dry coating weight of 12 g / m², applied in two coats of 6 g / m² each. The drying temperature for the final coat is increased from 110°C to 115°C, while the paper exit temperature remains controlled at ≤55°C to ensure a dense film. The main polyhydroxyalkanoate component of this homologous internally stabilized emulsion is a blend of P34HB and PHBV in a 2:1 mass ratio. P34HB contains approximately 30 mol% of 4HB units, and PHBV contains approximately 20 mol% of 3HV units. The oligomer used was PHBV oligomer, prepared by vacuum drying PHBV powder at 60℃ for 4 hours, followed by melt shearing at 195℃ and 200 r / min for 5 minutes in a twin-screw extruder, with a Mn content of 5 kDa. The emulsion stabilizer used was PHBV-grafted maleic anhydride half-ester salt, prepared by reacting PHBV powder with 1.0 wt% maleic anhydride and 0.1 wt% dicumyl peroxide at 182℃ and extruding, with an apparent acid value of 6 mg KOH / g. The emulsion was then neutralized with sodium hydroxide at 70℃ for 2 hours, achieving a neutralization degree of 30%. Based on polymer solids, the emulsion contained 15 wt% PHBV oligomer and 3 wt% PHBV-grafted maleic anhydride half-ester salt.

[0088] The B2 layer, serving as the wind-facing surface, is a multi-layer co-extruded structure with a total thickness of 35 μm. It comprises a 3 μm thick PHA-grafted anhydride compatibility layer and a 32 μm thick functional layer. The functional layer uses a blend of PHBHHx and PHBV at a mass ratio of 70:30, and adds furnace black at a total amount of 0.8 wt% (dry basis) of the film layer. The carbon black is added in the form of PHA-based concentrate.

[0089] The mulch film roll produced in this embodiment has an inner diameter of 76mm, a width of 1200mm, a roll length of 500m, and a maximum single roll weight of approximately 80kg and ≤110kg.

[0090] Example 2: Preparation of an ultralight short-season mulch film for greenhouse applications.

[0091] The basis weight of the paper substrate is 35 g / m², and the fiber composition is 35 wt% bamboo long fibers, 30 wt% bamboo short fibers, and 35 wt% broadleaf pulp short fibers. Bamboo pulp fibers account for 65 wt% of the total, and long fibers account for 35 wt%. The pulp contains 0.4 wt% bamboo-based nanocellulose by oven-dry weight. The substrate has a Beck smoothness of 150 s and a Gurley air permeability of 120 s / 100 mL. The paper is treated with a micro-creaming process, and the creasing rate is calculated as the ratio of the difference in strip length before and after creasing to the length before creasing; the creasing rate is 22%.

[0092] Layer B1 uses the same formulation and preparation parameters as in Example 1. The internal infiltration treatment is carried out by sizing machine / immersion-extrusion method to allow the same family of internally stable emulsion to enter the interior of the paper base layer, and the dry basis internal infiltration amount is controlled to be 3g / m². Then, a surface coating method is used to coat another 9g / m², so that the total dry coating amount is 12g / m².

[0093] Layer B2 is a multi-layer co-extruded structure with a total thickness of 30 μm, comprising a 3 μm thick PHA-grafted anhydride compatibility layer and a 27 μm thick functional layer. The composition of the functional layer is the same as in Example 1, with PHA-based concentrate added as carbon black. The surface tension of the activated weather-facing surface is controlled at 40 mN / m.

[0094] The mulch film roll produced in this embodiment has an inner diameter of 76mm, a width of 1400mm, a roll length of 800m, and a maximum single roll weight of approximately 90kg and ≤110kg.

[0095] Example 3: Preparation of a thick, long-lasting white reflective mulch film.

[0096] The basis weight of the paper substrate is 200 g / m², and the fiber composition is 50 wt% bamboo long fibers, 35 wt% bamboo short fibers, and 15 wt% softwood pulp long fibers. Bamboo pulp fibers account for 85 wt% of the total, and long fibers account for 65 wt%. The pulp contains 0.4 wt% bamboo-based nanocellulose by oven-dry weight. The paper substrate has a Beck smoothness of 260s and a Gurley air permeability of 320s / 100mL. The paper surface is incorporating micro-slits, each 1 mm long with a pitch of 10 mm, translating to approximately 100 slits per meter. The total area of ​​the micro-slits is ≤0.5%.

[0097] Layer B1 uses a homologous internally stable emulsion with the same formulation and preparation parameters as in Example 1, with a dry coating amount of 8 g / m².

[0098] Layer B2 is a multilayer co-extruded white film with a total thickness of 40 μm, comprising a 5 μm compatibility layer and a 35 μm functional layer. The compatibility layer was prepared by adding 0.8 wt% maleic anhydride and 0.08 wt% dicumyl peroxide by weight, resulting in an apparent acid value of 5 mg KOH / g after reaction extrusion. The functional layer is a blend of PHBHHx and PHBV (60:40 mass ratio) with 1.0 wt% calcium carbonate added, followed by carbon dioxide foaming. The foaming process parameters were: CO2 injection pressure 6.0 MPa, foaming temperature 160 °C, and draw ratio 1.6. The resulting film has an average pore size of approximately 15 μm and a closed-cell volume fraction of 32%.

[0099] The mulch film roll produced in this embodiment has an inner diameter of 76mm, a width of 1000mm, a roll length of 400m, and a maximum single roll weight of approximately 100kg and ≤110kg.

[0100] Example 4: Preparation of a whole-piece mulch film that can be rapidly mineralized when applied to soil surface.

[0101] The basis weight of the paper substrate is 80 g / m², and the fiber composition is 50 wt% bamboo long fibers, 25 wt% bamboo short fibers, and 25 wt% broadleaf pulp short fibers. Bamboo pulp fibers account for 75 wt% of the total, and long fibers account for 50 wt%. The pulp contains 0.4 wt% bamboo-based nanocellulose on an oven-dry basis. The paper substrate has a Beck smoothness of 200 s and a Gurley air permeability of 160 s / 100 mL.

[0102] The main polyhydroxyalkanoate (PHA) ester used in the B1 layer is a blend of P34HB and PHBV in a 2:1 mass ratio, where P34HB contains approximately 30 mol% of 4HB units and PHBV contains approximately 20 mol% of 3HV units. The oligomer used is a blend of PHBV and P34HB in a 1:2 mass ratio, prepared by mixing and drying PHBV and P34HB, followed by melt shearing at 195°C and 200 r / min for 5 min, with a Mn of 5 kDa. The emulsion stabilizer used is PHBV grafted maleic anhydride hemiester salt, prepared using the same parameters as in Example 1. Based on polymer solids, the emulsion contains 15 wt% PHA oligomer and 3 wt% PHBV grafted maleic anhydride hemiester salt. The emulsion properties exhibit D... 50 The particle size is 0.20 μm, the solid content is 40 wt%, the zeta potential is -32 mV, the pH value is 7.2, and the viscosity is 180 mPa·s. The coating process uses three coats, with a total dry coating weight of 10 g / m², and the coating weights of each coat are 3 g / m², 3 g / m², and 4 g / m², respectively.

[0103] Layer B2 consists of a 30 μm thick functional layer and a 3 μm thick PHA-grafted anhydride compatibility layer, for a total thickness of 33 μm. The functional layer is a blend of PHBV and PHBHHx in a mass ratio of 30:70. The compatibility layer is prepared by adding 1.5 wt% maleic anhydride and 0.15 wt% dicumyl peroxide during preparation, resulting in a graft with an apparent acid value of 8 mg KOH / g, without the addition of color masterbatch.

[0104] The mulch film roll produced in this embodiment has an inner diameter of 76mm, a width of 1200mm, a roll length of 500m, and a maximum single roll weight of approximately 75kg and ≤110kg.

[0105] Example 5: Preparation of a reflectance-enhancing microbubble white film.

[0106] The basis weight of the paper substrate is 120 g / m², and the fiber composition is 40 wt% bamboo long fibers, 30 wt% bamboo short fibers, and 30 wt% broadleaf pulp short fibers. Bamboo pulp fibers account for 70 wt% of the total, and long fibers account for 40 wt%. The pulp contains 0.4 wt% bamboo-based nanocellulose on an oven-dry basis. The paper substrate has a Beck smoothness of 210 s and a Gurley air permeability of 240 s / 100 mL.

[0107] Layer B1 uses a homologous internally stable emulsion with the same formulation and preparation parameters as in Example 1, with a dry coating amount of 10 g / m².

[0108] Layer B2 is a co-extruded white film of 28 μm thickness, co-extruded from a 50:50 mass ratio blend of PHBHHx and PHBV, including a 3 μm compatibility layer. The film is treated with carbon dioxide foaming and contains 0.5 wt% titanium dioxide (dry basis). The foaming process parameters are: CO2 injection pressure 5.8 MPa, foaming temperature 160 °C, and draw ratio 1.6. The arithmetic mean of 50 randomly measured pore sizes from cross-section slices is 12 μm, and the closed-cell volume fraction, determined according to ISO 4590:2016, is 28%.

[0109] The mulch film roll produced in this embodiment has an inner diameter of 76mm, a width of 1200mm, a roll length of 400m, and a maximum single roll weight of approximately 80kg and ≤110kg.

[0110] Example 6: Preparation of a mulch film based on a blend of P34HB and PHBV.

[0111] The basis weight of the paper substrate is 100 g / m², and the fiber composition is 35 wt% bamboo long fibers, 25 wt% bamboo short fibers, and 40 wt% broadleaf pulp short fibers. Bamboo pulp fibers account for 60 wt% of the total, while long fibers account for 35 wt%. The pulp contains 0.4 wt% bamboo-based nanocellulose by oven-dry weight. The substrate has a Beck smoothness of 180 s and a Gurley air permeability of 150 s / 100 mL.

[0112] Layer B1 uses a homologous internally stable emulsion with the same formulation and preparation parameters as in Example 1, with a dry coating amount of 10 g / m².

[0113] Layer B2 is a multilayer co-extruded structure with a total thickness of 35 μm, comprising a 3 μm thick PHA-grafted anhydride compatible layer and a 32 μm thick functional layer. The functional layer is a blend of P34HB and PHBV in a mass ratio of 60:40, where P34HB contains 30 mol% of 4HB units and PHBV contains 20 mol% of 3HV units. The weather-facing surface is black by adding carbon black concentrate with PHA as a carrier; the total pigment content is 0.8 wt% of the film's dry basis.

[0114] The mulch film roll produced in this embodiment has an inner diameter of 76mm, a width of 1200mm, a roll length of 450m, and a maximum single roll weight of approximately 80kg and ≤110kg.

[0115] Comparative example:

[0116] Comparative Example 1: An ultralight, wrinkle-free, and non-seepage-free mulch film is provided. Its preparation process is the same as in Example 2, except that the paper base layer is not wrinkled, and the B1 layer is not subjected to an infiltration process; only surface coating is performed, with a dry coating amount of 12 g / m². The inner diameter, width, and roll length of the mulch film roll are consistent with those of Example 2, i.e., inner diameter 76 mm, width 1400 mm, roll length 800 m, and the maximum weight of a single roll is approximately 90 kg and ≤110 kg.

[0117] Comparative Example 2: This comparative example provides a thick, heavy mulch film without micro-slits or edge seams. Its preparation process is the same as in Example 3, except that the paper base layer does not have micro-slits or edge seams. The inner diameter, width, and roll length of the mulch film roll are consistent with those of Example 3, i.e., inner diameter 76mm, width 1000mm, roll length 400m, and maximum single roll weight approximately 100kg and ≤110kg.

[0118] Comparative Example 3: A composite mulch film with an adhesive layer is provided. Its preparation process is the same as in Example 1, except that an acrylic pressure-sensitive adhesive layer with a dry weight of 6 g / m², model Dow PS-2000, is introduced between layers B1 and B2. The inner diameter, width, and roll length of the mulch film roll are consistent with those of Example 1, i.e., inner diameter 76 mm, width 1200 mm, roll length 500 m, and maximum single roll weight approximately 80 kg and ≤110 kg.

[0119] Comparative Example 4: A mulch film using a PHA and PVA blended aqueous dispersion is provided. Its preparation process is the same as in Example 1, except that layer B1 uses a PHA and polyvinyl alcohol blended aqueous dispersion with a mass ratio of 80:20, a solid content of 40 wt%, and a dry coating weight of 12 g / m². Layer B2 and the paper base layer are the same as in Example 1. The inner diameter, width, and roll length of the mulch film roll are consistent with Example 1, i.e., inner diameter 76 mm, width 1200 mm, roll length 500 m, and a maximum single roll weight of approximately 80 kg and ≤110 kg.

[0120] Comparative Example 5: A black film with a low-PAH carbon-based pigment content below a specified range is provided. Its preparation process is the same as in Example 1, except that the total amount of low-PAH carbon-based pigment in the B2 functional layer is only 0.2 wt% of the film's dry basis. The total thickness of the B2 layer and the multi-layer co-extrusion structure are the same as in Example 1, and the remaining process conditions are consistent. The inner diameter, width, and roll length of the film roll are consistent with Example 1, i.e., inner diameter 76 mm, width 1200 mm, roll length 500 m, and maximum single roll weight approximately 80 kg and ≤110 kg.

[0121] Comparative Example 6: A white foamed film with a closed-cell volume fraction and pore structure deviating from the defined range was provided. Its preparation process was the same as in Example 3, except that the carbon dioxide foaming conditions were adjusted to: CO2 injection pressure 4.0 MPa, foaming temperature 145°C, and draw ratio 1.2. Under the same titanium dioxide addition and total thickness, the resulting white foamed film had an average pore size of approximately 35 μm and a closed-cell volume fraction of approximately 12%. The coating formulations on the remaining paper base and soil-attached surface were consistent with those in Example 3. The inner diameter, width, and roll length of the mulch film were consistent with those in Example 3, i.e., inner diameter 76 mm, width 1000 mm, roll length 400 m, and a maximum single roll weight of approximately 100 kg and ≤110 kg.

[0122] Comparative Example 7: A mulch film with emulsion particle size and zeta potential deviation from the window was provided. Its preparation process was the same as in Example 4, except that the emulsification shear strength was significantly reduced in step 2, the rotation speed was adjusted to 3000 r / min, the neutralization degree of PHBV-grafted maleic anhydride half-ester salt was controlled at 10%, and the neutralization reaction time was shortened to 0.5 h. The resulting PHA emulsion particle size D... 50 The micrometer diameter is approximately 2.5 μm, the zeta potential is approximately -15 mV with an absolute value less than 25 mV, and the viscosity at 25°C is approximately 30 mPa·s. This emulsion was used as the B1 layer coating, with a dry coating weight of 10 g / m², and the remaining process conditions were the same as in Example 4. The inner diameter, width, and roll length of the mulch film were consistent with those in Example 4, namely an inner diameter of 76 mm, a width of 1200 mm, a roll length of 500 m, and a maximum single roll weight of approximately 75 kg and ≤110 kg.

[0123] Comparative Example 8: A composite mulch film with activation energy and surface tension lower than that of the window is provided. Its preparation process is the same as in Example 1, except that in step 4, the corona treatment applies only an equivalent treatment energy of 0.4 kJ / m², resulting in a surface tension of 35 mN / m on the windward side. The same wet-to-heat lamination sequence (1 hour) and subsequent curing conditions as in Example 1 are used, with the remaining paper base and coating formulations remaining consistent. The inner diameter, width, and roll length of the mulch film roll are consistent with Example 1, i.e., inner diameter 76 mm, width 1200 mm, roll length 500 m, and a maximum single roll weight of approximately 80 kg and ≤110 kg.

[0124] Application example:

[0125] Application Example 1: Mechanical and physical properties of plastic film.

[0126] Experimental Description: This application example aims to systematically evaluate the overall mechanical strength, optical properties, and key barrier properties of the mulch film samples prepared in Examples 1–6 and Comparative Examples 1–8.

[0127] The preparation conditions for all samples were strictly controlled: the windward B2 layer was activated by corona or plasma treatment to an equivalent treatment energy of 0.8–1.2 kJ / m² and a surface tension (wetting tension) of 38–42 mN / m (determined by the dyne ink method: when drop-coated with dyne inks of 38, 40, and 42 mN / m respectively, continuous spreading within 2 seconds and no shrinkage within 10 seconds were considered to have reached this level of wetting tension). The coating temperature was set at 170–175℃, the cooling roller temperature was controlled at 20℃, the composite linear pressure was 0.3 MPa, and the linear speed was 95 m / min. The "wet-to-heat" lamination was completed within a 1-hour time window after the B1 layer was coated and dried, and a curing treatment of ≥48 hours was carried out at room temperature.

[0128] Mechanical performance testing was conducted using a universal testing machine, strictly following GB / T 2790-1995 standards for 180° peel strength testing (sample width 25mm, tensile speed 300mm / min); puncture resistance was tested according to ASTM D5748-95 (2019); tear strength was measured according to GB / T 455-2002, specifically in the longitudinal (MD) and transverse (TD) directions. Regarding optical performance, the transmittance (T) of the black mulch film at 600nm was measured using a spectrophotometer. 600 For white mulch film, the integrated reflectance in the visible light region (400–700 nm) was measured using an integrating sphere. The WVTR reduction was calculated relative to uncoated base paper, based on ASTM E96 / E96M-24a (Procedure B, 38°C, 90% RH). All laboratory tests were performed after equilibration for 24 hours in a constant temperature and humidity environment (23±1°C, 50±2% RH), and each data point represents the average of five independent tests with recorded standard deviation.

[0129] Field laying and integrity evaluation: The plastic film was mechanically laid in the same plot using a plastic film laying machine, and no less than 3 replicate plots were set up for each sample. Table 4 defines “Number of film breaks ( / 100m)” as the number of through holes or through cracks that occur every 100m of mulch laid and require manual repair; “Number of downtime ( / ha)” as the number of times the equipment must be stopped due to mulch film damage, deviation, or breakage, calculated per hectare; “Laying qualification rate (%)” is calculated based on laying length, with the qualification criteria being continuous coverage, intact edge soil compaction, and no through holes; “7-day edge curling (%)” is the percentage of edge curling length to the total measured edge length, calculated on the 7th day after covering; and “Field integrity (120d, 5-point scale)” is scored as follows: 5 points = no through cracks / no delamination within 120d; 4 points = slight edge damage but no through cracks; 3 points = localized through cracks but damaged area <5%; 2 points = through cracks or delamination causing damaged area of ​​5%–20%; 1 point = through cracks or delamination causing damaged area >20% or inability to maintain coverage function.

[0130] Table 3. Mechanical, optical, and barrier properties of plastic film:

[0131]

[0132] Table 4. Data on the water absorption and field laying performance of plastic film:

[0133]

[0134] Note: The contact angle of the soil-contacting surface was measured using a contact angle measuring instrument. Deionized water was used as the test solution, with a drop volume of 3 μL. Five locations were randomly selected on the soil-contacting surface of the sample under the conditions of 23±1℃ and 50±2% RH. The static contact angle 5 seconds after the drop was added was recorded and the average value was taken.

[0135] Analysis: The experimental results show that Examples 1–6 exhibit excellent performance in terms of mechanical strength, interfacial bonding, and field applicability. In particular, the peel strength is consistently above 1.5 N / 25 mm, and the failure mode is the ideal "fiber tearing," indicating a strong integrated structure between the PHA extruded film layer and the bamboo pulp paper base layer. In contrast, the comparative examples have significant defects: Comparative Example 1 did not perform creping treatment on the ultralight paper, resulting in insufficient elongation, a significant increase in the number of film breaks and machine shutdowns, and a drop in the laying qualification rate to 88%; Comparative Example 2's heavy paper lacked micro-cut stress release, leading to severe edge warping; Comparative Example 3 introduced a pressure-sensitive adhesive layer, which, although initially bonded well, was prone to adhesive layer creep or internal breakage in humid and hot soil environments, resulting in a low field integrity score; Comparative Example 4 used a PHA / PVA blend, and due to the hydrophilicity of PVA, the interfacial bonding decreased after moisture absorption, exhibiting a mixed failure mode.

[0136] The comparative data further revealed the impact of key parameters: Comparative Example 5 reduced the amount of opaque pigment, and although the mechanical properties were not damaged, the light transmittance surged to 15.4%, which will seriously affect the weed suppression effect; Comparative Example 6 had improper foaming process control, resulting in low closed-cell rate and reflectivity of only 45%, failing to achieve the expected cooling and light enhancement; Comparative Example 7 had emulsion particle size and potential deviating from the window, resulting in poor coating film formation, with the 180° peel strength dropping to 1.3N / 25mm and being interfacial peeling; Comparative Example 8 had insufficient activation energy, low surface tension, and extremely poor interfacial bonding (1.1N / 25mm), making it extremely easy to delaminate in the field. In summary, this invention successfully solved the interfacial compatibility and weather resistance problems between paper base and PHA film layer through strict material selection and process window control (such as wet-to-heat composite, emulsion parameters, and activation energy).

[0137] Application Example 2: Cobb coating on soil surface 60 Verification of the decrease.

[0138] Experimental Description: This application example specifically verifies the effect of the PHA barrier coating on improving the water absorption of paper substrates. Paper substrates corresponding to Examples 1–6 and Comparative Examples 1–8 were selected for the experiment, and tests were conducted strictly according to GB / T 1540 "Determination of Water Absorption of Paper and Paperboard - Cobb Method". The test consisted of three stages: the first stage tested the uncoated base paper; the second stage tested the paper sample with only the B1 coating; and the third stage (mainly for reference) tested the entire composite. 100 mL of distilled water was used in the test, with a contact time of 60 seconds (Cobb). 60 The test area was 100 cm². The focus was on examining the reduction in water absorption (percentage reduction) between the coated and uncoated surfaces to evaluate the film-forming density and sealing ability of the water-based PHA emulsion on the paper fiber surface. Five samples were cut from each sample for parallel testing. The results were calculated as the arithmetic mean and standard deviation. The test environment was controlled at 23±1℃ and 50±2% relative humidity.

[0139] Table 5 Cobb coating on soil surface 60 Decrease data:

[0140]

[0141] Analysis: Experimental data show that Examples 1–6, by using particle size D 50 Cobb's internally stable PHA emulsions, with a thickness of 0.15–2.0 μm and a zeta potential of -25 to -45 mV, can effectively penetrate and cover the fiber pores on the paper surface. 60The value reduction was consistently above 30%, reaching a maximum of 35.0%. This indicates that the specific emulsion formed a continuous and dense hydrophobic layer on the paper surface, effectively blocking the rapid penetration of moisture into the paper matrix. Although Comparative Examples 1, 2, 3, 5, 6, and 8 differed in other structures or processes, their B1 layer coating formulations or processes were essentially the same as (or minimally affected by) the corresponding examples; therefore, their Cobb coating... 60 The decline has also remained at a normal level of around 30%.

[0142] However, a significant anomaly was observed in the data for proportion 7, with its Cobb... 60 The decrease was only 12.1%. This is because the emulsion used in Comparative Example 7 had excessively large particle size and a low absolute value of zeta potential (-15mV), resulting in poor emulsion stability, easy flocculation, and the inability of large particles to effectively fill the micropores on the paper surface, leading to discontinuous or defective film formation and thus ineffective moisture barrier. Comparative Example 4 used a PHA / PVA blend system. Due to the high hydrophilicity of the PVA component, the overall hydrophobicity of the coating decreased, and Cobb... 60 The reduction was slightly less than 30%. This result strongly demonstrates the importance of the PHA emulsion particle size and potential parameters specified in this invention for constructing an efficient soil-adhering barrier layer, which is directly related to the film's tolerance in moist soil environments.

[0143] Application Example 3: Rapid mineralization of the coating body on the soil surface.

[0144] Experimental Description: This application example aims to evaluate the biodegradability of the soil-attached PHA barrier coating as a standalone material in a soil environment. The experiment was conducted according to ISO 17556:2019, "Plastics in soil – Determination of ultimate aerobic biodegradability by determination of oxygen demand or carbon dioxide production". First, the B1 layer coating solutions of Examples 1–6 and Comparative Examples 1–8 were coated onto an inert PET substrate, dried to form a film, and carefully peeled off to obtain pure coating samples. The soil was sourced from topsoil from a major crop-growing area, sieved through a 2mm sieve, and its moisture content adjusted to 40%–60% of maximum water holding capacity. After peeling, the samples were cut into fragments ≤5mm × 5mm and thoroughly mixed with soil that had passed through a 2mm sieve and had its moisture content adjusted to 40%–60% of maximum water holding capacity. The mixture was then prepared according to the dry basis mass of the soil (m). 土壤 With the dry basis mass m of the sample 样品The samples were packed into sealed respirometer reaction flasks at a ratio of 100:1 to 200:1 and incubated in the dark at 25–28°C. The carbon dioxide concentration in the headspace of the reaction flasks was continuously monitored using an aerobic CO2 respirometer system. The cumulative CO2 release was converted to mineralization after subtracting the amount from the control soil. Biodegradability was calculated according to ISO 17556 as "cumulative CO2 release / theoretical CO2 release × 100%", where the theoretical CO2 release was obtained by converting the total organic carbon content of the sample. Microcrystalline cellulose was used as the reference material, and the control soil was used as the standard. The experiment lasted 180 days, with a focus on recording the biodegradability at 90 and 180 days. The half-life was calculated based on the mineralization curve fitting. Three parallel samples were set up for each group, and the average value and standard deviation were recorded.

[0145] Table 6. Degradation performance data of the coating bulk:

[0146]

[0147] Analysis: The degradation test results clearly demonstrate the absolute advantage of the all-PHA system of this invention in terms of environmental friendliness. The coatings of Examples 1–6 all exhibited a biodegradability exceeding 90% within 90 days, with a half-life controlled within 30 days, demonstrating an extremely rapid mineralization rate. This is attributed to PHA, as a naturally microbially synthesized polyester, which has a large number of specific degrading bacteria in the soil. Furthermore, the PHA oligomers and grafted anhydride half-esters introduced into the formulation further promote microbial attachment and hydrolysis initiation. Although Comparative Examples 1, 2, and 5–8 have defects in physical structure or processing technology (such as emulsion instability and different pigment contents), the chemical nature of their coatings is still mainly PHA. Therefore, their degradation performance is comparable to the examples and all meet the biodegradation requirements.

[0148] However, Comparative Example 3 used acrylic pressure-sensitive adhesive as the bonding layer, and its degradation rate in the bulk was only 25.4% after 90 days, severely hindering the overall mineralization process of the mulch film and demonstrating the unsuitability of traditional synthetic adhesives in biodegradable agricultural mulch films. Comparative Example 4 introduced PVA. Although PVA is water-soluble, its biomineralization rate in the soil environment is much slower than that of PHA, and it may form a partially interpenetrating network with PHA, hindering enzyme attack, resulting in a degradation rate of only 66.1% after 90 days and an extended half-life of 51 days. These data fully demonstrate that abandoning non-homologous adhesives and slow-degrading components such as PVA, and adhering to the pure component design of PHA, is the key to ensuring that the mulch film can quickly and thoroughly return to the natural cycle after being tilled into the soil.

[0149] Application Example 4: Time Series and Platform Statistics of Whole Film Mineralization.

[0150] Experimental Description: This application example simulates the actual degradation of the mulch film after it is tilled into the soil, conducting a long-term biodegradation test on the entire composite mulch film. Samples were randomly cut from the finished rolls of the Examples 1–6 and Comparative Examples 1–8. The samples were pre-cooled in liquid nitrogen or at -40°C and then freeze-pulverized, or sheared to prepare fragments with a maximum characteristic size ≤5mm. The fragments were then mixed evenly to ensure that the proportions of each layer were consistent with the finished product. The samples were then processed according to the dry soil mass m. 土壤 With the dry basis mass m of the sample 样品 The biodegradation ratio was 100:1 to 200:1, and the samples were placed in respirometer reaction bottles. Testing was conducted according to ISO 17556 standards in an aerobic soil environment for 24 months (720 days). The cumulative biodegradation rate was recorded at 90, 180, 360, 540, and 720 days; the plateau criterion was set as "cumulative mineralization increase of less than 5% in the most recent 30 days." This experiment aimed to verify whether the entire membrane could achieve complete mineralization (≥90%) under long-term soil burial conditions, and the influence of different structures and components on degradation kinetics. Each sample group was tested in triplicate, and data are expressed as mean ± standard deviation.

[0151] Table 7 Time series data of whole membrane biodegradation:

[0152]

[0153] Analysis: Whole-film degradation data show that Examples 1–6 all achieved over 90% biodegradability within 24 months, and entered or approached the degradation plateau around 540 days, demonstrating the reliability of this technology in achieving complete biodegradation. Although Comparative Examples 5–8 have serious defects in product functionality (such as light blocking, reflection, and interfacial adhesion), their materials are essentially still all PHA components or contain very small amounts of inert impurities (such as low-content pigments). Therefore, their final biomineralization capacity at the chemical level is not fundamentally affected, and they can ultimately achieve a 90% degradation index.

[0154] In contrast, Comparative Examples 1 and 2, due to improper physical structure design (lack of wrinkling or micro-slits), resulted in the mulch film being difficult to break down and disperse in the soil, having a small specific surface area, and making it difficult for microorganisms to colonize. Therefore, the degradation rate was significantly delayed, with a degradation rate of only 85%–87% after 24 months. The problems with Comparative Examples 3 and 4 were more fundamental: the adhesive layer in Comparative Example 3 was not only difficult to degrade itself, but also blocked microbial attacks on the paper base and PHA film layer, resulting in a final degradation rate of only 75%; Comparative Example 4, limited by the slow degradation characteristics of PVA and the structural inhomogeneity caused by poor compatibility, also failed to meet the standard. This result profoundly reveals the dual influence of "material chemical composition" and "physical structure design" on the degradation performance of mulch film: chemical composition determines "whether it can degrade," while physical structure (such as micro-slits and good interfacial dispersion) determines "the rate of degradation." This invention achieves a perfect unity of the two through a complete PHA composition and optimized physical structure design.

[0155] Application Example 5: Activation energy and timing window for sample dimension verification of the interface.

[0156] Experimental Description: This application example aims to verify the key influence of activation energy and lamination time on interfacial bonding strength in the "wet-to-heat" lamination process, serving as the basis for establishing the process window of this invention. Two comparative conditions were designed: Condition A represents the "inside the window" process, where the equivalent activation energy on the windward side is ≥0.8 kJ / m², and lamination is completed within 1 hour after drying layer B1; Condition B represents the "outside the window" process, where although the activation energy meets the standard (0.8 kJ / m²), the lamination time is delayed to 3 hours. The initial 180° peel strength and failure modes of samples from Examples 1–6 and Comparative Examples 1–8 were tested, and then tested again after accelerated aging at 40°C for 7 days. Failure modes were categorized as "fiber tearing" (ideal mode, indicating interfacial strength higher than paper strength) and "interfacial peeling" (failure mode, indicating insufficient interfacial adhesion). Each set of data represents the average of 5 parallel samples.

[0157] Table 8: Verification data for the interface window:

[0158]

[0159] Analysis: The results of this experiment conclusively demonstrate that "activation energy" and "recombination time" are the two core variables determining the bonding quality of the PHA-paper substrate interface. Examples 1–6 all achieved the ideal "fiber tearing" mode under condition A (within the window), and the strength retention rate after aging was extremely high (>90%), indicating that the polar functional groups on the PHA film surface (generated by activation) and the active sites on the paper substrate coating surface (in a semi-molten / incompletely crystalline state) underwent effective chemical or physical anchoring. However, once condition B (over-time recombination) was entered, the surface activity decreased significantly due to the cooling and crystallization of the B1 coating. Even with sufficient activation energy, effective intermolecular entanglement could not be formed, leading to a sharp drop in interfacial strength and a transition to "interfacial peeling."

[0160] The data from Comparative Examples 7 and 8 are particularly crucial: Comparative Example 7, due to its excessively large emulsion particle size and low absolute potential value, exhibited low coating cohesion and numerous surface defects, failing to achieve effective adhesion even within window A, resulting in interfacial delamination. Comparative Example 8, on the other hand, suffered from insufficient activation energy (<0.8 kJ / m²), leading to excessively low surface tension on the windward side, preventing the coating from wetting and spreading on the soil-attached surface, resulting in extremely low interfacial strength (<1.2 N / 25 mm) regardless of the time sequence. The failure modes (internal breakage of the adhesive layer, mixed failure) of Comparative Examples 3 and 4 further confirmed the inherent disadvantage of non-homogeneous systems in terms of interfacial consistency. In summary, only by strictly adhering to the activation energy (≥0.8 kJ / m²) and wet-to-heat time sequence (≤2 h) specified in this invention, combined with high-quality homogeneous emulsions, can an aging-resistant, high-strength, fully biodegradable composite interface be constructed.

[0161] Application Example 6: Field moisture retention and soil temperature measurement.

[0162] Experimental Description: This application example aims to quantitatively evaluate the soil water retention capacity and soil temperature regulation effect of bamboo pulp paper PHA double-sided composite mulch film under actual field mulching conditions. The experimental site was set up in an agricultural demonstration base with typical climatic characteristics and homogeneous soil texture. A randomized block design was used, with four replicate plots for each treatment, each plot area being 20 square meters. A TDR soil moisture sensor (TEROS 12) and a high-precision thermocouple temperature probe were vertically buried 10 cm below the soil surface under the mulch film in the center of each plot. A bare-field control group was also included. Using an automatic data acquisition system, soil volumetric water content (θv) and soil temperature changes were continuously recorded at 30-minute intervals from day 1 to day 14 after mulching. Data from day 14 (the stabilization period) were selected for statistical analysis to calculate the increase in soil moisture content relative to bare land, the daily amplitude of soil temperature, and the difference in daytime average temperature relative to bare land. The results are expressed as the arithmetic mean and standard deviation of the four replicates to comprehensively evaluate the agronomic performance of the mulch film.

[0163] Table 9. Soil moisture retention and ground temperature data:

[0164]

[0165] Analysis: The data on moisture retention and temperature regulation reveal the crucial regulatory role of the physical structure integrity of the mulch film and the quality of the barrier coating on the microclimate of farmland. Examples 1 to 6 all demonstrated excellent moisture retention effects, increasing the volumetric moisture content by 6.3% to 9.0% compared to bare land. This is mainly attributed to the effective sealing of the paper pores by the PHA barrier coating on the soil-facing side, combined with the extruded film layer on the windward side, forming a double water-locking barrier. In terms of temperature regulation, the black mulch film (Examples 1, 2, and 6) showed a significant warming effect, while the white foamed mulch film (Examples 3 and 5) significantly reduced the daily soil temperature amplitude (only 5.8 to 6.1°C) through its high reflectivity, playing a role in "stabilizing the temperature and cooling the soil," making it suitable for heat-sensitive crops.

[0166] The comparative data reflect the negative impacts of different defects. Comparative Examples 7 and 8, due to poor interfacial bonding or suboptimal coating quality, failed to effectively block water vapor permeation, or the mulch film showed delamination and damage in the early stages of field application, resulting in a significant decrease in moisture retention capacity, with Δθv only +4.1% to +4.4%. Comparative Example 5, due to excessively low carbon black content, increased light transmittance, leading to more direct solar radiation heating of the soil, resulting in a daily soil temperature fluctuation of up to 11.2℃ and an excessive increase in average daytime temperature, potentially causing heat damage to crop roots and excessive water evaporation. Comparative Example 6, due to its low foaming closed-cell rate, suffered a significant reduction in heat insulation performance and failed to achieve the expected temperature stabilization effect. In conclusion, only double-sided composite mulch films with good interfacial bonding, dense coatings, and reasonable optical design can achieve optimal allocation of water and heat resources.

[0167] Application Example 7: Weed Suppression Effect (Weed Count).

[0168] Experimental Description: This application example aims to evaluate the inhibitory effect of different mulch film structures on weed growth under real-world field cultivation conditions. The experimental site was a single plot with a high and evenly distributed weed population, in loam soil with moderate fertility. After crop planting and mulching, a randomized block design was used, with three fixed quadrats of 1 square meter each in each treatment plot. For 30 days after mulching, the number of weeds growing through or breaking through the mulch film within the quadrats was regularly observed and recorded. This test not only examines the optical shading performance of the mulch film (e.g., light transmittance of black mulch film, reflectance of white mulch film) but also indirectly reflects the physical integrity of the mulch film, as mechanical damage often provides an entry point for weeds. To ensure statistical significance, each example and comparative example had four replicate plots. The final results were recorded as the cumulative number of weeds emerging over 30 days, expressed as mean ± standard deviation, and outlier data were investigated and analyzed.

[0169] Table 10: Data on grass production over 30 days:

[0170]

[0171] Analysis: The experimental results showed a significant differential distribution, profoundly revealing the dual determining role of the optical properties and physical integrity of the mulch film on its weed-suppressing effect. Examples 1, 2, and 6, as black opaque mulch films, had a T... 600 With extremely low light transmittance (less than 1%), it effectively cuts off the light source required for weed photosynthesis. Furthermore, its excellent physical strength (such as the fiber tearing failure mode in Example 1) prevents weeds from breaking through, resulting in extremely low weed numbers, only 4 to 8 plants / m². Examples 3 and 5 use white reflective mulch. Although the light transmittance is higher than that of the black mulch, its high reflectivity and good coverage still keep weeds within an acceptable range (17 to 25 plants / m²).

[0172] In contrast, Comparative Examples 1 and 2, lacking wrinkle-like or micro-slit designs, exhibited poor weather resistance in the field, resulting in large-scale cracking of the mulch film. This allowed weeds to proliferate rapidly through the cracks, with weed numbers reaching 42 to 60 plants / m². The most typical example is Comparative Example 5. Although its physical structure was intact, the insufficient addition of low-PAH carbon-based pigments (only 0.2 wt%) resulted in a light transmittance as high as 15.4%, allowing direct sunlight to reach the soil surface. Weed photosynthesis was not inhibited, leading to a surge in weed numbers to 65 plants / m², completely negating its weed-control function. Comparative Example 6 suffered from a collapsed foam structure, resulting in weak light scattering and decreased physical strength, leading to a higher weed number. Comparative Examples 7 and 8, due to poor interfacial bonding (interfacial delamination), were prone to delamination and damage under wind, rain, and soil stress, creating entry points for weed growth. This clearly demonstrates that excellent weed-suppressing function must be based on the synergistic combination of extremely low light transmittance and high physical integrity.

[0173] Application Example 8: Determination of bio-based carbon content in cover layers.

[0174] Experimental Description: This application example is based on the international standard ISO 16620 2 2019, "Plastics – Bio-based content – ​​Part 2: Determination of bio-based carbon content," aiming to quantitatively evaluate the biomass origin of mulch film products, a core indicator for measuring their low-carbon and environmentally friendly value. Test samples were taken from the cover layer of the mulch film (including the paper base, coating, and extruded film layers). The samples were converted into carbon dioxide through combustion, and the carbon-14 isotope abundance was determined using accelerator mass spectrometry (AMS) or liquid scintillation counting (LSC). Since carbon-14 in petroleum-based materials has completely decayed, while the carbon-14 abundance in bio-based materials is consistent with the atmospheric environment, the percentage of bio-based carbon in the total carbon can be accurately calculated. To ensure the representativeness of the results, the test results were calculated as a weighted average based on the dry basis mass of each component of the cover layer. Each sample was measured in triplicate, and the results were rounded to one decimal place, with the standard deviation recorded.

[0175] Table 11 Bio-based carbon content data of the overburden layer:

[0176]

[0177] Analysis: The test data strongly demonstrates the superiority of the fully bio-based technical route of this invention. The bio-based carbon content of Examples 1-6 is consistently above 95.0%, reaching a maximum of 96.7%. This is because the bamboo pulp paper base layer (derived from bamboo), PHA coating, and film layer (derived from microbial fermentation) used in this invention are all 100% bio-based materials, containing only trace amounts of inorganic additives or mineral fillers (such as calcium carbonate and talc), achieving true sourcing from nature.

[0178] Conversely, Comparative Example 3 introduced petroleum-based acrylic pressure-sensitive adhesive as the bonding layer. Although the adhesive layer was very thin, its extremely high carbon content and complete absence of carbon-14 significantly reduced the overall bio-based content to 82.1%. Comparative Example 4 used polyvinyl alcohol (PVA). Currently, most commercially available PVA is synthesized from petroleum-based ethylene or natural gas, which are fossil-derived, thus its bio-based content also decreased to 86.5%. Although Comparative Examples 5, 6, 7, and 8 had defects in physical properties or processing technology, their chemical raw material composition did not deviate from the main framework of PHA and pulp (Comparative Example 5 even slightly increased the proportion due to the reduction of carbon black), so their bio-based carbon content remained at a high level of over 95%. This high bio-based content not only aligns with global environmental themes but also ensures that the products of mulch film degradation do not release paleogeological carbon into the soil, maintaining the balance of the modern carbon cycle.

[0179] Application Example 9: Detection of total organic fluorine and AOF.

[0180] Experimental Description: To investigate the presence of persistent organic pollutants (PFAS) and other fluorinated chemicals in the mulch film, this application example performs total organic fluoride (TOF) testing according to EN 14582:2016 and adsorbable organic fluoride (AOF) testing on the water extract according to DIN 38409-59:2022-10. For the TOF test, the entire sample and each layer of material were cut into fragments ≤5mm. m0 (g) of the sample was weighed and placed in an oxygen bomb combustion apparatus for combustion under oxygen-enriched conditions. The combustion products were absorbed according to EN 14582 and prepared as the test solution. The fluoride ion content was determined using ion chromatography and the TOF (mg / kg) was calculated. The detection limit, calculated based on the sample weight and the volume of the absorption liquid, was ≤5 mg / kg.

[0181] For AOF testing, m1 (g) of sample fragments was weighed and added to V (mL) of ultrapure water. The mixture was extracted by shaking at 23±2℃ for 2 hours, and then filtered to obtain the aqueous extract. The aqueous extract was subjected to activated carbon adsorption, washing, combustion, and ion chromatography determination of fluoride ions according to DIN 38409-59 to obtain the AOF concentration of the extract. This concentration was then converted to the sample AOF (mg / kg) using V and m1. Each sample was tested in triplicate, and the detection limit was calculated using the same conversion method to be ≤5 mg / kg.

[0182] Table 12 Total Organic Fluorines and AOF Data:

[0183]

[0184] Analysis: The test results showed that the total organic fluorine (TOF) and adsorbable organic fluorine (AOF) levels in all samples, including all examples and comparative examples, were below the detection limit (5 mg / kg), meaning they were deemed undetectable. This result has significant environmental implications. Fluorinated surfactants or fluoropolymers are often used in traditional oil-proof and paper-proof packaging or certain high-performance agricultural films to enhance barrier properties and weather resistance, but this poses a permanent PFAS pollution risk to the soil.

[0185] This invention, through technological innovation, utilizes the excellent crystallinity and hydrophobic properties of PHA material, combined with the high density of bamboo pulp paper, to achieve superior waterproof and barrier effects (as described above with Cobb) without adding any fluorine-containing additives. 60 (As shown in the data). Even the comparative samples, although their physical properties did not meet the standards, still followed the fluorine-free principle in their formulation design and therefore did not contain fluorine. This confirms that the product of this invention is a truly fluorine-free material. After the mulch film completes its life cycle, its degradation during tilling into the soil will not lead to the accumulation of fluorides in the soil and groundwater, completely eliminating the potential threat of this emerging pollutant to the agricultural ecosystem and meeting the most stringent soil protection regulations.

[0186] Application Example 10: Calculation of total amount of non-polymer additives.

[0187] Experimental Description: This application example aims to accurately determine the total amount of non-polymer components (i.e., auxiliary chemicals without biodegradable framework function) in the mulch film through formulation traceability and calculation. Based on the detailed production feed sheets of each example and comparative example, the dry basis mass percentage of all additives was identified and calculated. The statistical scope covers all functional additives used in the B1 coating and B2 extruded film layers, including but not limited to plasticizers, antioxidants, nucleating agents, slip agents, dispersants, and inorganic fillers (such as calcium carbonate, titanium dioxide, carbon black, etc.). According to the present invention and environmental design concept, this total amount is strictly controlled (≤3.0 wt%) to prevent excessive small molecule additives from migrating into the soil and causing secondary salinization or toxic effects. The results are listed separately as weighted percentages for each layer and the overall cover layer.

[0188] Table 13 Data on total non-polymer additives:

[0189]

[0190] Analysis: The results show that, except for Comparative Example 3 (which was not included in the routine statistics due to the presence of an unremovable adhesive layer), the total amount of non-polymer additives in all samples was strictly controlled below 3.0 wt%, with most examples controlled at an extremely low level of 1.1 wt% to 1.3 wt%. This reflects the principle of simplification in the formulation design of this invention: relying mainly on the excellent properties of the PHA polymer itself (such as crystallinity, barrier properties, and mechanical strength) to meet application requirements, rather than relying on a large amount of chemical additives.

[0191] Comparative Example 5, due to the reduced amount of carbon black pigment, had a slightly lower B2 layer and total additive content (1.0 wt%), but this directly led to a loss of its shading performance. Comparative Example 4, although containing PVA dispersant, saw its total content rise slightly to 1.4 wt%, but remained within the controllable range. This low-additive design has dual benefits: on the one hand, it maximizes the proportion of biodegradable carbon sources in the mulch film, providing a pure food source for soil microorganisms; on the other hand, it greatly reduces the risk of accumulation of unknown chemicals or recalcitrant small molecules in the soil, ensuring that the farmland soil maintains healthy physicochemical properties even after years of continuous use and degradation, meeting the requirements of sustainable development in ecological agriculture.

[0192] Application Example 11: Compliance between paper ash content and added surfactants.

[0193] Experimental Description: This application example primarily tests the purity of the paper base layer and the introduction of surfactants in the coating system to verify whether the product meets the design intent of "natural and harmless". Paper ash content testing was conducted according to ISO 2144 2019, "Determination of ash content in paper, paperboard and pulp". The paper sample was ignited in a high-temperature muffle furnace at 525°C to constant weight, and the mass of residual inorganic matter was weighed to assess whether excessive amounts of inorganic fillers such as talc or kaolin were added to the pulp. The determination of added surfactants was based on the B1 layer coating liquid formulation, focusing on whether traditional emulsifiers such as alkylphenol polyoxyethylene ethers, which are harmful to aquatic organisms, were used. The testing scope covered all examples and comparative examples. Each sample was taken three times, and the average value and standard deviation were calculated to ensure the accuracy and traceability of the data.

[0194] Table 14 Data on paper ash content and added surfactants:

[0195]

[0196] Analysis: Test results show that the ash content of the paper in Examples 1-6 is between 1.2 wt% and 1.4 wt%, far below the upper limit of 2.0 wt%. This indicates that the bamboo pulp paper base layer selected in this invention is mainly composed of plant cellulose, without reducing costs by filling a large amount of inorganic minerals, thus ensuring the paper's strength retention rate in humid environments and its soil permeability after degradation.

[0197] More importantly, the content of added surfactants in all examples and most comparative examples (except Comparative Example 4) was 0. This is because one of the core technologies of this invention is the use of "homogeneous internally stable emulsions," which utilize the self-emulsifying function of PHA-grafted anhydride half-ester salts to stabilize the system, completely eliminating the need for added sodium dodecyl sulfate (SDS) or polyoxyethylene ether-based added surfactants that must be added in traditional emulsion polymerization. Only in Comparative Example 4, due to the introduction of the PVA system, a dispersant was required to maintain stability, and 0.5 wt% of added surfactant was detected. Achieving zero surfactant not only avoids foaming problems and improves the density of the coated film, but also eliminates the potential interference of surfactants on soil microbial cell membranes, ensuring the safety and health of the soil micro-ecosystem from the source.

[0198] Experimental Results and Analysis:

[0199] Based on the systematic test data of the above application examples 1-11, the bamboo pulp paper PHA double-sided composite soil biodegradable agricultural mulch film of the present invention has shown significant advantages in terms of mechanical strength, agronomic function, environmental friendliness and biodegradability. It has successfully overcome the technical bottlenecks of traditional paper mulch film being easily damaged, pure biodegradable plastic film being prone to premature aging and paper-plastic composite film having poor interface compatibility.

[0200] First, the "homogeneous wet-heat" composite process is the core key to constructing a high-strength interface. Data from Application Examples 1 and 5 show that Examples 1–6, by precisely coupling the surface activation (equivalent energy ≥0.8kJ / m²) of the PHA extruded film layer on the windward side with the semi-molten state of the PHA coating on the soil side (≤2h after drying), achieved physical entanglement and chemical anchoring of the two homogeneous materials at the molecular chain level. Their 180° peel strength was generally higher than 1.5N / 25mm, and the failure mode was the ideal "fiber tearing," with a strength retention rate exceeding 90% after aging at 40℃ for 7 days. Conversely, Comparative Example 3, while introducing acrylic pressure-sensitive adhesive, exhibited initial tack, but poor resistance to wet-heat aging, leading to internal cracking of the adhesive layer; Comparative Example 8 suffered from insufficient activation energy (low surface tension), Comparative Example 7 had coating defects due to large emulsion particle size, and Application Example 5 experienced excessively long composite time outside the "window," all resulting in a sharp drop in interfacial strength and interfacial delamination. This confirms that the process window defined in this invention is a necessary condition for achieving adhesive-free high-strength composites.

[0201] Secondly, the PHA's fully bio-based component design ensures complete biomineralization and environmental safety. Data from Application Examples 3, 4, 8, 9, and 10 form a complete chain of evidence: the sample samples not only have a bio-based carbon content exceeding 95% but also contain no total organic fluorine (TOF / AOF < 5 mg / kg) and have extremely low levels of non-polymer additives. In terms of degradation performance, the coating half-life on the soil surface is as short as 25–30 days, and the entire film achieves a biodegradation rate exceeding 90% within 24 months. In contrast, the adhesive layer in Comparative Example 3 hindered degradation (only 75% after 24 months), and the PVA component in Comparative Example 4 slowed down the mineralization rate. This indicates that abandoning non-homogeneous adhesives and petroleum-based / slow-degrading modifiers is the fundamental way to achieve the transition of mulch film from "disintegration" to "complete mineralization."

[0202] Furthermore, the refined control of the physical structure determines the field applicability and agronomic effects. Application Examples 1, 6, and 7 show that the creping treatment for ultralight paper (Example 2) and the micro-cutting design for heavy paper (Example 3) significantly improved the mechanical laying qualification rate and reduced edge curling, while Comparative Examples 1 and 2, lacking these treatments, exhibited serious field adaptability problems. In terms of functional control, the black formulations of Examples 1, 2, and 6 achieved extremely low light transmittance (<1%) and excellent weed suppression effect (<8 plants / m²), while Comparative Example 5 suffered from high light transmittance and weed control failure due to insufficient pigment; the white foamed structures of Examples 3 and 5 achieved high reflectivity and temperature stability, while the foaming failure of Comparative Example 6 resulted in functional loss.

[0203] Finally, the precise definition of the parameters of the aqueous emulsion ensured the film quality of the barrier coating. Application Example 2 data shows that only internally stable emulsions of the same family (Examples 1–6) with particle size (0.15–0.25 μm) and zeta potential (-25 to -45 mV) within a specific range can form a dense coating on the paper substrate, enabling Cobb... 60 The value decreased significantly (>30%) and endowed the mulch film with excellent moisture retention capacity (Application Example 6). Comparative Example 7, which deviated from this window, could not form a film effectively, directly leading to barrier failure and the collapse of interfacial strength.

[0204] In summary, this invention has successfully prepared a novel agricultural mulch film that combines high strength, excellent agronomic functions, and complete biodegradability through the synergistic innovation of microstructure design of bamboo pulp paper base layer, interface modification of PHA waterborne emulsion of the same family, and wet-to-heat adhesive-free composite process.

[0205] 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, improvements, etc., 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 bamboo pulp paper-PHA double-sided composite soil-biodegradable agricultural mulch film, characterized in that, The biodegradable agricultural mulch film comprises a paper base layer mainly composed of bamboo pulp, and the paper base layer includes a soil-facing side and a wind-facing side; The basis weight of the paper base layer is 25–300 g / m², and the proportion of bamboo pulp to the total mass of pulp fibers in the paper base layer is ≥50 wt%; and the pulp contains bamboo-based microfibrillated cellulose, bamboo-based nanocellulose, or a mixture of the two. When the paper base layer is ultralight paper with a basis weight of 25–50 g / m², it is wrinkled and / or infiltrated with water-based PHA; when the paper base layer is heavy paper with a basis weight of 160–300 g / m², it is provided with micro-cuts or edge pressing lines. The paper base layer has a homologous water-based PHA barrier coating on its surface, which is derived from a homologous internally stable emulsion, and the particle size D of the emulsion is... 50 The thickness is 0.15–2.0 μm and the zeta potential is -25 to -45 mV. The polymer solids in the barrier coating consist only of polyhydroxyalkanoates with a purity ≥97 wt%. The paper substrate has a thermoplastic PHA extruded film layer on its wind-facing surface. The extruded film layer is a multi-layer co-extrusion structure, comprising a PHA-grafted anhydride compatibility layer disposed in close contact with the wind-facing surface of the paper substrate and a functional layer disposed on the outside of the compatibility layer; the functional layer is a PHA homogeneous blend structure. The extruded film layer is selected from one of black opaque film, white foamed film, or natural-colored film; when it is black opaque film, it contains 0.5–1.0 wt% of low polycyclic aromatic hydrocarbon carbon-based pigment; when it is white foamed film, it contains 0.1–2.0 wt% of white inorganic pigment and is obtained by carbon dioxide foaming, with a carbon dioxide injection pressure of 5–7 MPa, a foaming temperature of 150–165°C, and a draw ratio of 1.4–1.8; when it is natural-colored film, no pigment is added. Before being laminated with the extruded film layer, the wind-facing surface of the paper substrate is subjected to corona or plasma activation treatment with an equivalent treatment energy ≥0.8kJ / m² and a surface tension ≥38mN / m. The extruded film layer on the windward side is directly bonded to the paper base layer, and the resin of the extruded film layer on the windward side is only a material of the PHA family.

2. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, The pulp comprises long fibers and short fibers in a mass ratio of 30:70 to 70:

30. The long fibers are selected from bamboo long fibers or softwood pulp, and the short fibers are selected from hardwood pulp or bamboo short fibers. The pulp contains 0.2–1.0 wt% bamboo-based microfibrillated cellulose, bamboo-based nanocellulose, or a mixture thereof. The paper base has a Beck smoothness of 80–600 s and a Gurley air permeability of 50–600 s / 100 mL.

3. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, When the paper base is ultralight paper, the wrinkling rate of the wrinkling treatment is 10–35%, and the water-based PHA infiltration amount is 2–6 g / m²; when the paper base is heavy paper, the single slit length of the micro-cut is 0.5–1.5 mm, the pitch is 5–20 mm, there are 50–200 slits per meter, and the total area ratio is ≤0.5%.

4. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, The dry coating amount of the barrier coating is 5–25 g / m²; the Cobb coating applied to the soil surface 60 The value decreases by ≥30% compared to the uncoated paper surface; when the basis weight of the paper base is >25 and ≤160 g / m², the Cobb coating value decreases by ≥30%. 60 Value ≤30g / m²; when the basis weight of the paper base layer is >160 and ≤300g / m², after coating, Cobb 60 Value ≤40g / m²; The 180° peel strength of the paper base layer and the extruded film layer interface is ≥1.5N / 25mm, the failure mode is fiber tearing, and it still meets the aforementioned strength and failure mode requirements after aging at 40°C for 7 days.

5. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, The thickness of the extruded film layer is 20–80 μm; the thickness of the compatibility layer is 1–10 μm; and the thickness of the functional layer is 20–70 μm. The functional layer is selected from one or more combinations of the following: a blend of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) containing 5–12 mol% of 3-hydroxyhexanoate units and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) containing 8–20 mol% of 3-hydroxyvalerate units; a blend of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) containing 20–40 mol% of 4-hydroxybutyrate units and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) containing 8–20 mol% of 3-hydroxyvalerate units; and a blend of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate). The polyhydroxy fatty acid ester comprises homologous blends or grafted modifiers, wherein the grafting groups of the grafted modifiers are selected from acid anhydrides or epoxy functional groups.

6. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, When the weather-facing surface is a black opaque film, the low-polycyclic aromatic hydrocarbon carbon-based pigment used is selected from furnace black, channel black, thermal cracking black, or acetylene black, and the transmittance T at 600 nm is [not specified]. 600 ≤3%; when the windward surface is a white foamed film, the closed-cell volume fraction is 15–40%, and the visible light integrated reflectance R 400–700 ≥70%, and the white inorganic pigment is selected from one or more of titanium dioxide, calcium carbonate or talc.

7. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, The anhydride monomers used for grafting the compatibility layer are selected from one or more of maleic anhydride, itaconic anhydride, succinic anhydride, fumaric anhydride, or maleic anhydride, and the apparent acid value of the grafted material is 3–15 mg KOH / g.

8. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, The bio-based carbon content of the polymer solids is ≥90%; the total amount of non-polymer additives in the barrier coating and the extruded film is ≤3.0wt%, and the additives are selected from one or more of plasticizers, antioxidants, slip agents or processing aids, without changing the limitation that the polymer solids are PHA.

9. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, The ash content of the paper base layer is ≤2.0wt%, and the added surfactant is ≤0.5wt%. The inner diameter of the mulch film roll is 76mm, the width is 800–1800mm, the roll length is 200–1000m, and the maximum roll weight is ≤110kg. The total organic fluorine in the barrier coating, the extruded film layer, and the whole sample was not detected, and the detection limit was ≤5mg / kg. The water vapor transmission rate of the whole film was tested according to ASTM E96 / E96M-24a standard Procedure B under 38℃ and 90% RH conditions, and it decreased by 50–75% compared with uncoated paper. The biodegradability of the coating on the soil surface is ≥90% according to ISO 17556 standard at 25–30℃ in aerobic soil for 90 days. The sample used to test the biodegradability is the coating body obtained by forming and peeling the coating on the soil surface onto a non-absorbent inert substrate. The biodegradability of the covering layer is ≥90% according to ISO 17556 standard in aerobic soil for 24 months.

10. The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, The coating on the soil surface is derived from a homologous internally stable emulsion, mainly composed of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and contains 10–20 wt% PHA oligomer and 2–5 wt% PHA grafted anhydride half-ester salt based on polymer solids; the number average molecular weight of the PHA oligomer is 3–8 kDa; the half-ester salt is partially neutralized by one of sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, triethanolamine or 2-amino-2-methyl-1-propanol, with an apparent acid value of 3–10 mg KOH / g and a degree of neutralization of 20–45%; the dry coating weight is 5–12 g / m².

11. A method for preparing a bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1, characterized in that, Includes the following steps: Step 1. Papermaking: Add bamboo-based microfibrillated cellulose, bamboo-based nanocellulose, or a mixture of both to the refined pulp and mix thoroughly. Use bamboo pulp as the main body to form a paper base with a basis weight of 25–300 g / m². Adjust the paper surface to a Beck smoothness of 80–600 s and a Guillier air permeability of 50–600 s / 100 mL to obtain the paper base. When the basis weight is 25–50 g / m², perform creping treatment and / or PHA infiltration; when the basis weight is 160–300 g / m², perform micro-cutting or edge creasing treatment. Step 2. Emulsion acquisition: PHA grafted anhydride is obtained through reactive extrusion, hydrolyzed, and partially neutralized to form PHA grafted anhydride hemiester salt; PHA melt at 160–180℃ is metered and pumped into a rotor-stator emulsifier on the hot water side at 85–95℃ at a speed of 0.5–1.5 L / min, and subjected to high-shear emulsification at a speed of 5000–15000 r / min to obtain a homologous internally stable emulsion; the solid content of the homologous internally stable emulsion is 35–45 wt%, D 50 Its viscosity is 0.15–2.0 μm, its zeta potential is -25 to -45 mV, its pH is 6.5–8.0, and its viscosity at 25 °C is 50–400 mPa·s. Step 3. Coating the soil surface: Apply the homologous internally stable emulsion obtained in Step 2 to the soil surface of the paper base obtained in Step 1, control the dry coating amount to 5–25 g / m², and dry it in stages at 80℃, 95℃ and 110–115℃ until the exit paper temperature is ≤55℃ to obtain the coating on the soil surface. Step 4. Preparation of PHA extrusion film raw materials for the windward side, wherein the extrusion film raw materials include PHA grafted anhydride compatibility layer granules and functional layer granules. When preparing the PHA grafted anhydride compatibility layer granules, dry polyhydroxyalkanoate powder is used as the compatibility layer raw material base. 0.5wt% to 2.0wt% of anhydride monomer and 0.05wt% to 0.2wt% of initiator are added by weight. The mixture is then reacted and extruded in a twin-screw extruder at 170°C to 185°C, granulated underwater, and dried to obtain PHA grafted anhydride compatibility layer granules with an apparent acid value of 3–15 mg KOH / g corresponding to the grafting rate. When preparing the functional layer granules, dry PHA homologous resins are mixed according to the proportions described in claim 2 as the functional layer raw materials, and color masterbatch or nucleating agents are added as needed. The mixture is then melt-blended and extruded in a twin-screw extruder at 160°C to 180°C, granulated, and dried to obtain the functional layer granules. Step 5. Activation and lamination of the windward side: After the coating on the substrate in Step 3 is dried to an exit paper temperature ≤55℃, the surface of the windward side of the paper substrate is subjected to corona or plasma treatment for ≤2 hours at a temperature of 20–30℃ and a relative humidity of 40%–60% until the equivalent treatment energy is ≥0.8kJ / m² and the surface tension is ≥38mN / m. The PHA grafted anhydride compatibility layer granules prepared in Step 4 and the functional layer granules are then melted at 160–100 kJ / m. The film is extruded and coated at 85℃ to form a 20–80 μm thick extruded film layer on the windward side, and then laminated with the windward side of the paper base layer to obtain a double-sided composite semi-finished product. The coating conditions are: cooling roller temperature 15–25℃, pressing line pressure 0.2–0.5 MPa, and line speed 30–120 m / min; the resin is dried at 60–70℃ for 4–8 h with a moisture content ≤0.02 wt%; the temperature difference between each melt during multilayer co-extrusion is ≤15℃; the activation standard is ≥38 mN / m. Step 6. Maturation and Slitting: The double-sided composite semi-finished product obtained in Step 5 is matured at a temperature of 20–30℃ and a relative humidity of 40%–60% for ≥24 hours and then slitted to obtain the bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film.

12. The use of the bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulch film according to claim 1 in farmland mulching cultivation, characterized in that, Used for shading, weed suppression, moisture retention, and temperature regulation; after crop harvest, it is plowed into the soil, and the barrier coating and the extruded film layer have a biodegradability of ≥90% in 24 months according to ISO 17556 standard.

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