Bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulching film and its preparation method and use

Abstract

The application discloses a bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulching film and a preparation method and application thereof, and belongs to the technical field of agricultural mulching materials. The film takes bamboo pulp paper as a base material, and firmly combines a water-based PHA inner stabilizing coating on a soil sticking surface with a PHA extruded film layer on a wind and rain facing surface by using a "same group wetting to heat" glue-free composite process. The application solves the problems of poor weather resistance of traditional paper films and early decay of biodegradable plastic films. Compared with market products, the scheme discloses the following advantages. First, the scheme discards the glue and fluorine-containing additives that hinder degradation, and realizes fiber tearing level strength only by anchoring the same group interface. Second, the scheme can achieve a barrier and soil conservation effect better than a traditional thick coating with less PHA, and significantly reduces water absorption. Third, the scheme has excellent mechanical adaptability and light and heat regulation functions, and is completely mineralized after entering the soil, thereby truly realizing the perfect unity of high performance and full environmental protection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of agricultural mulching materials, and particularly relates to a bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulching film and a preparation method and application thereof. BACKGROUND

[0002] Polyethylene mulching films are widely used in agriculture to increase and stabilize yield, but recycling is difficult, and the accumulation of residual films and microplastics poses an ecological risk. Pure thermoplastic degradable plastic films such as polybutylene adipate terephthalate (PBAT), polylactic acid (PLA), and polyhydroxyalkanoate (PHA) have degradation potential, but they are prone to early decay and rupture in long-season, strong wind and rain, and mechanical scouring scenarios. Pure paper-based films are not resistant to water and tearing, and have poor compatibility with mechanical mulching equipment.

[0003] It is known that PHA-paper lamination is mainly directed to the packaging field. For example, US6322899B1 and WO1999001278A1 add PHA to paper or paperboard by extrusion coating, but do not involve soil mulching films, wet-against-hot composite windows, or fiber tear failure requirements. WO2001 / 21881A2 discloses a technology of coating PHA emulsion on the surface of paper, but it still belongs to the packaging scenario. US2022 / 0033158A1 uses a water-dispersed nanosheet barrier layer, which is different from the avoidance and limitation of nanosheets and independent adhesive layers in the present application. WO2025 / 073274A1 relates to a PHA water-based coating, and there is no combination of paper-based "wet-against-hot" integrated composite and soil mineralization indicators. Duobai City discloses CN120026524A, CN120250392A, and CN120192646A, which report water-based systems containing polyvinyl alcohol (PVA) or PBAT and are used for paper-based barrier packaging, which is essentially different from the combination limitation of the present application "PHA, no independent adhesive layer, soil mulching film scenario, and composite window". Even if the water-based primer of US2022 / 0033158A1 is combined with the nanosheet barrier layer and the extrusion coating idea of US6322899B1, the resulting structure still relies on nanosheets or non-homologous interlayer adhesion. Unlike this, the present application limits "PHA double-sided" and "no independent adhesive and wet-against-hot composite window", and gives the 24-month mineralization indicators of the whole mulching film according to ISO17556 and the fiber tear failure mode control.

[0004] In summary, the prior art still lacks an agricultural mulching film structure and preparation window that can simultaneously meet the requirements of "paper-based long-season weather resistance and mechanical laying adaptation", "high-strength homologous interface bonding without independent adhesive", "significant barrier and water reduction with lower PHA dosage", and "whole piece achieving ultimate aerobic mineralization within 24 months after turning into soil". Therefore, it is necessary to propose a double-sided composite mulching film based on bamboo pulp paper and PHA homologous materials and a preparation method thereof to solve the problems of poor weather resistance of paper films, early decay of biodegradable plastic films, and difficulty in compatibility of paper-plastic interfaces. SUMMARY

[0005] The present application aims to overcome the deficiencies of the prior art, and provides a bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulching film, a preparation method and use thereof, so as to solve the problems of difficult recycling of the mulching film, poor weather resistance of the paper mulching film, and early decay of the biodegradable plastic film in the prior art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] The bamboo pulp paper-PHA double-sided composite soil biodegradable agricultural mulching film, the preparation method and use thereof, wherein the mulching film comprises a paper-based layer taking bamboo pulp as the main body, and the paper-based layer comprises a soil-adhering surface and a wind-and-rain-facing surface.

[0008] The paper-based layer has 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, 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 in the total mass of the pulp fibers of the paper-based layer is ≥ 50 wt%, such as 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or 100 wt%; the pulp contains long fibers and short fibers in a mass ratio of 30:70 to 70:30, such as 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, or 70:30, and the pulp contains 0.2-1.0 wt% of bamboo-based microfibrillated cellulose (CNF), bamboo-based nanocellulose (CNC), or a mixture of the two, such as 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.8 wt%, 0.9 wt%, or 1.0 wt%; the long fibers are selected from bamboo long fibers or conifer pulp, and the short fibers are selected from broadleaf pulp or bamboo short fibers; the air permeability and smoothness of the paper-based layer meet the following requirements: the Bekk smoothness is 80-600 s, such as 80 s, 100 s, 150 s, 180 s, 200 s, 210 s, 220 s, 260 s, 300 s, 400 s, 500 s, or 600 s, and the Gurley air permeability is 50-600 s / 100 mL, such as 50 s / 100 mL, 80 s / 100 mL, 100 s / 100 mL, 120 s / 100 mL, 150 s / 100 mL, 160 s / 100 mL, 180 s / 100 mL, 200 s / 100 mL, 240 s / 100 mL, 300 s / 100 mL, 320 s / 100 mL, 400 s / 100 mL, 500 s / 100 mL, or 600 s / 100 mL;

[0009] When the paper base layer basis weight is 25-50 g / m2of ultra-light paper, 10-35%, such as 10%, 15%, 20%, 22%, 25%, 30% or 35% of creping treatment and / or 2-6 g / m2, such as 2 g / m2, 3 g / m2, 4 g / m2, 5 g / m2or 6 g / m2of aqueous PHA internal penetration are adopted to improve mechanical laying adaptability; when the paper base layer basis weight is 160-300 g / m2of thick paper, micro-slits or edge lines are provided, the micro-slits have a single slit 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 per meter, such as 50, 100, 150 or 200, and a total area ratio of ≤0.5%, such as 0.1%, 0.2%, 0.3% or 0.5%.

[0010] The soil side of the paper base layer is provided with a homologous aqueous PHA barrier coating, the dry coating amount of the barrier coating is 5-25 g / m2, such as 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 / m2or 25 g / m2, which is derived from a homologous internal emulsion, the particle size D 50 of the emulsion is 0.15-2.0 μm, such as 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, such as -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 of polyhydroxyalkanoate only and the purity is ≥97 wt%, such as 97 wt%, 98 wt%, 99 wt% or 100 wt%, the Cobb 60 value of the soil side after coating is reduced by ≥30%, such as 30%, 33.3%, 35%, 40%, 50%, 60% or 70% compared with the uncoated paper side; when the paper base layer basis weight is >25 and ≤160 g / m2, the Cobb 60 value after coating is ≤30 g / m2, such as 30 g / m2, 28 g / m2, 26 g / m2, 25 g / m2, 24 g / m2, 23 g / m2or 20 g / m2; when the paper base layer basis weight is >160 and ≤300 g / m2, the Cobb 60 value after coating is ≤40 g / m2, such as 40 g / m2, 38 g / m2, 35 g / m2, 32 g / m2or 30 g / m2;

[0011] The windward rain face of the paper base layer is provided with a thermoplastic PHA extrusion film layer, the thickness of the extrusion 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 extrusion film layer is a multilayer co-extrusion structure, comprising a PHA grafted anhydride compatible layer with a thickness of 1-10 μm, for example 1 μm, 2 μm, 3 μm, 5 μm, 8 μm or 10 μm, which is arranged close to the windward rain face of the paper base layer, 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, which is arranged outside the compatible layer; the functional layer is a PHA homologous blend structure;

[0012] The windward rain face of the paper base layer is provided with a thermoplastic PHA extrusion film layer, the thickness of the extrusion 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 extrusion film layer is a multilayer co-extrusion structure, comprising a PHA grafted anhydride compatible layer with a thickness of 1-10 μm, for example 1 μm, 2 μm, 3 μm, 5 μm, 8 μm or 10 μm, which is arranged close to the windward rain face of the paper base layer, 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, which is arranged outside the compatible layer; the functional layer is a PHA homologous blend structure;

[0013] The coating on the soil side is dried to an outlet paper temperature ≤55℃, and then the windward rain face is subjected to wet-heat lamination in an environment with a temperature of 20-30℃, for example 20℃, 22℃, 25℃, 28℃ or 30℃, and a relative humidity of 40%-60%, for example 40%, 45%, 50%, 55% or 60%, for a time of ≤2h, for example 0.5h, 1.0h, 1.5h or 2.0h, so that the 180° peel strength of the paper-film interface is ≥1.5N / 25mm, for example 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, and the failure mode is fiber tearing, and after aging at 40℃ for 7 days, the above strength and failure mode requirements are still met;

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

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

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

[0017] The polyhydroxyalkanoate can further comprise a homologous blend or a graft modification, the graft modification having a grafting group selected from an anhydride or an epoxy functional group.

[0018] The windward rain face is a black, non-reflective film or a white, foamed film; when the windward rain face is a black, non-reflective film, the low polycyclic aromatic carbon-based pigments used are selected from furnace black, channel black, thermal black, or acetylene black, the total amount of pigments being < 1.0 wt%, such as 0.1 wt%, 0.2 wt%, 0.5 wt%, 0.8 wt%, or 1.0 wt%, and such that the light transmittance T 600 at 600 nm is < 3%, such as 0.5%, 0.8%, 1.0%, 1.5%, 2.0%, or 3.0%; when the windward rain face is a white, foamed film, the closed cell volume fraction is 15-40%, such as 15%, 20%, 25%, 30%, 35%, or 40%, and the visible light integral 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 a white inorganic pigment selected from one or more of titanium dioxide, calcium carbonate or talc.

[0019] The anhydride monomer for grafting the compatibilization layer is selected from one or more of maleic anhydride, itaconic anhydride, succinic anhydride, fumaric anhydride or maleic anhydride, the graft of which has an apparent acid value of 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 polymer solid has a biobased carbon content of ≥ 90%, for example 90%, 92%, 94%, 95%, 96% or 98%; the barrier coating has a total amount of non-polymeric auxiliaries of ≤ 3.0 wt%, for example 0.5 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 2.0 wt% or 3.0 wt%, the auxiliaries being selected from one or more of plasticizers, antioxidants, slip agents or processing aids, without changing the definition of the polymer solid being PHA.

[0021] The coating on the soil-facing side has a biodegradability of ≥ 90%, for example 90%, 92% or 95%, in 25 - 30 °C, aerobic soil for 90 days according to ISO 17556 standard, the sample for testing the biodegradability being a coating body made of the coating on the soil-facing side film-formed on a non-absorbing inert substrate and peeled off.

[0022] The coating on the soil-facing side originates from a homo-internal emulsion with poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) as the main body and contains 10-20 wt%, such as 10 wt%, 12 wt%, 15 wt%, 18 wt% or 20 wt% of PHA oligomers based on the polymer solids and 2-5 wt%, such as 2 wt%, 3 wt%, 4 wt% or 5 wt% of PHA grafted anhydride half-ester salt based on the polymer solids; the number average molecular weight of the PHA oligomers is 3-8 kDa, such as 3 kDa, 4 kDa, 5 kDa, 6 kDa or 8 kDa; the half-ester salt is partially neutralized by one of sodium hydroxide, potassium hydroxide, aqueous ammonia, monoethanolamine, diethanolamine, triethanolamine or 2-amino-2-methyl-1-propanol, with an apparent acid value of 3-10 mg KOH / g, such as 3 mg KOH / g, 5 mg KOH / g, 6 mg KOH / g, 8 mg KOH / g or 10 mg KOH / g, and a neutralization degree of 20-45%, such as 20%, 25%, 30%, 35%, 40% or 45%; the dry coating amount of the coating is 5-12 g / m2, such as 5 g / m2, 8 g / m2, 10 g / m2or 12 g / m2.

[0023] After 7 days of accelerated aging at 40°C, the retention rate of the 180° peeling strength at the interface of the paper and the film is ≥ 90%, such as 90%, 92% or 95%, and the failure mode is fiber tearing.

[0024] When the windward rain-facing 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, such as 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°C, such as 150°C, 155°C, 160°C or 165°C, the draw ratio is 1.4-1.8, such as 1.4, 1.5, 1.6 or 1.8, the average pore size is 5-30 μm, such as 5 μm, 10 μm, 12 μm, 15 μm, 20 μm, 25 μm or 30 μm, and the closed pore volume fraction is 15-40%, such as 15%, 20%, 25%, 30%, 35% or 40%.

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

[0026] The barrier coating has no detectable total organic fluorine with each layer of the extruded film layer and the whole sample, with detection limit ≤5mg / kg.

[0027] A method for preparing the mulch as described above, comprising the following steps:

[0028] Step 1. Papermaking, adding bamboo-based microfibrillated cellulose, bamboo-based nanocellulose or mixture of the two to the paper pulp after pulping and mixing uniformly, taking bamboo pulp as the main body to form a paper base layer with basis weight of 25-300g / m², such as 25g / m², 30g / m², 35g / m², 50g / m², 80g / m², 100g / m², 120g / m², 150g / m², 200g / m² or 300g / m², and adjusting the paper surface to Beck smoothness of 80-600s, such as 80s, 150s, 200s, 300s or 600s, Gurley air permeability of 50-600s / 100mL, such as 50s / 100mL, 120s / 100mL, 160s / 100mL, 320s / 100mL or 600s / 100mL, to obtain the paper base layer; when the basis weight is 25-50g / m², perform creping treatment and / or PHA internal penetration; when the basis weight is 160-300g / m², perform micro-slit or edge line pressing treatment;

[0029] Step 2. Emulsion obtaining, PHA grafted anhydride by reaction extrusion, hydrolysis and partial neutralization to form PHA grafted anhydride half ester salt; PHA melt at 160-180℃, for example 160℃, 165℃, 170℃, 175℃ or 180℃, is metered at 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, into a hot water side rotor-stator emulsifier at 85-95℃, for example 85℃, 90℃ or 95℃, for high shear emulsification at a rotational speed 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 stable emulsion; the solid content of the homologous stable emulsion is 35-45 wt%, for example 35 wt%, 38 wt%, 40 wt%, 42 wt% or 45 wt%, the D 50 0.15-2.0 μm, for example 0.15 μm, 0.20 μm, 0.50 μm, 1.0 μm or 2.0 μm, the zeta potential is -25 to -45 mV, for example -25 mV, -30 mV, -32 mV, -40 mV or -45 mV, the pH is 6.5-8.0, for example 6.5, 7.0, 7.2, 7.5 or 8.0, the viscosity at 25℃ is 50-400 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. Top side coating, the homologous stable emulsion obtained in step 2 is coated onto the top side of the paper base layer obtained in step 1, the dry coating amount is controlled at 5-25 g / m², for example 5 g / m², 8 g / m², 10 g / m², 12 g / m² or 25 g / m², and is sequentially dried in stages at 80℃, 95℃ and 110-115℃, for example 110℃, 112℃ or 115℃, to an outlet paper temperature ≤55℃, for example 40℃, 45℃, 50℃ or 55℃, to obtain a coating on the top side;

[0031] Step 4. Windward rain-facing PHA extruded film raw material preparation, the extruded film raw material includes PHA grafted anhydride compatilizer layer pellets and functional layer pellets, when preparing the PHA grafted anhydride compatilizer layer pellets, taking dry polyhydroxyaliphatic acid ester powder as the compatilizer layer raw material base material, adding 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, carrying out reactive extrusion in a twin-screw extruder at a temperature of 170°C to 185°C, for example 170°C, 175°C, 180°C or 185°C, underwater pelletizing and drying, to obtain PHA grafted anhydride compatilizer layer pellets with a corresponding apparent acid value of 3-15mg KOH / g, for example 3mg KOH / g, 5mg KOH / g, 10mg KOH / g, 12mg KOH / g or 15mg KOH / g; when preparing the functional layer pellets, mixing dry PHA homologous resin as the functional layer raw material in the aforementioned proportions, and adding color masterbatch or nucleating agent as needed, carrying out melt blending extrusion 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, pelletizing and drying, to obtain functional layer pellets.

[0032] Step 5. Windward rain face activation and coating, after the coating on the earth face in step 3 is dried to an outlet paper temperature ≤55℃, the windward rain face surface of the paper base layer is subjected to corona or plasma treatment within a time window of ≤2h at a temperature of 20-30℃ and a relative humidity of 40%-60%, to an equivalent treatment energy ≥0.8kJ / m² and a surface tension ≥38mN / m, for example 38mN / m, 40mN / m or 42mN / m, using the PHA grafted anhydride compatible layer pellets prepared in step 4 and the functional layer pellets to extrusion coat a 20-80μm, for example 20μm, 30μm, 33μm, 35μm, 40μm, 50μm or 80μm, extrusion film layer at a melt temperature of 160-185℃, for example 160℃, 165℃, 170℃, 175℃, 180℃ or 185℃, to complete the compounding of the windward rain face extrusion film layer with the windward rain face of the paper base layer, to obtain a double-sided compounded semi-finished product; the coating conditions are a cooling roller temperature of 15-25℃, for example 15℃, 18℃, 20℃, 22℃ or 25℃, a pressure of 0.2-0.5MPa, for example 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa, and a line speed of 30-120m / min, for example 30m / min, 50m / min, 80m / min, 95m / min, 100m / min or 120m / min; the 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 of ≤0.02wt%, for example 0.01wt% or 0.02wt%; the temperature difference between the melts is ≤15℃, for example 5℃, 10℃ or 15℃; and the activation criterion is a surface tension ≥38mN / m;

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

[0034] According to the use of the aforementioned mulch film in agricultural field cultivation, for light blocking and weed suppression, soil conservation and temperature regulation; after the crops are harvested, the mulch film is plowed into the soil, and the barrier coating and the extrusion film layer have a biodegradation of ≥90% in 24 months according to the ISO 17556 standard.

[0035] Compared with the prior art, the use of the present application can obtain the following significant beneficial effects:

[0036] Excellent interface bonding strength and weather resistance: the application realizes high-strength bonding of paper base and film layer without adhesive by using the molecular affinity of homologous PHA material, combining specific activation energy and compounding time window through the "homologous wet-heat" compounding process, the peeling strength is high and the failure mode is ideal fiber tearing, solving the problem of easy delamination and poor water resistance of traditional paper-plastic interface.

[0037] Full biobased and environmentally friendly: all components of the mulch film (bamboo pulp paper, PHA coating, PHA extruded film) are fully biobased, with high biobased carbon content, and do not contain polyvinyl alcohol, polybutylene adipate-terephthalate and other petroleum-based or slow-degrading components, do not contain fluorine and harmful surfactants, can be completely biodegraded into water and carbon dioxide after plowing into the soil, avoiding microplastic accumulation and soil pollution.

[0038] Excellent agronomic performance: through the design of double-sided PHA composite structure, the mulch film is endowed with excellent barrier property (Cobb 60 value is greatly reduced), soil conservation ability and weed inhibition function. The black formula can efficiently block light and inhibit weeds, and the white foamed formula can reflect heat and reduce temperature, meeting the planting needs of different crops.

[0039] Good mechanical laying adaptability: targeted treatment such as wrinkling, internal infiltration or micro-slit is adopted for paper base layers of different basis weight, which significantly improves the flexibility and stress release ability of the mulch film, making it able to adapt to mechanical laying operation and reducing the damage rate. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The figure is a schematic diagram of the microstructure cross-section of the bamboo pulp paper-PHA composite biodegradable agricultural mulch film described in the application.

[0041] In the figure, 1 is a homologous water-based PHA barrier coating; 2 is a paper base layer; 3 is a PHA grafted anhydride compatible layer; and 4 is a functional layer. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with specific examples. It should be understood that the specific examples described here are only used to explain the application and not to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included within the protection scope of the application. Unless otherwise specified, the raw materials used in the examples are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, the performance test methods are carried out according to the standards described in the summary of the invention.

[0043] In the specification, "cover layer", "whole film" and "whole piece of sample" all refer to the whole composite mulch film structure including the bamboo pulp paper base layer, the water-based PHA barrier coating on the soil side, and the thermoplastic PHA extruded film layer on the windward and rainy side; the water-based PHA barrier coating on the soil side is derived from the same family of emulsion, and the extruded film layer resin on the windward and rainy side is only the PHA material of the same family, without polylactic acid (PLA), polybutylene adipate terephthalate (PBAT) and polyvinyl alcohol (PVA). In the specification, "equivalent treatment energy" refers to the actual energy received per unit area of the substrate surface during the process of corona or plasma treatment, which is calculated based on the effective power of the equipment, the processing width and the line speed, and the unit is kJ / m². In the specification, "wet-to-hot compounding" refers to: after the water-based PHA coating on the soil side is dried in sections to an outlet paper temperature ≤55°C, the windward and rainy side is activated and compounded by using a PHA melt showering film method at 160-185°C within a time window of ≤2h in an environment of 20-30°C and 40%-60% RH, so that the paper / film interface forms a high-strength interface bonding under the combined action of molecular affinity of the same family material 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 application is shown, which has a paper base layer 2 containing bamboo-based cellulose reinforcement as the main skeleton, a dense water-based PHA barrier coating 1 of the same family on the soil side formed by specific emulsion penetration anchoring to achieve efficient soil conservation and significantly reduce water absorption, and a multi-layer co-extruded thermoplastic PHA film on the windward and rainy side, wherein the thin layer of PHA grafted anhydride compatibility layer 3 close to the paper base is the core key, which forms a high-strength interface bonding with the paper base layer 2 at the fiber tearing level in a specific glue-free "wet-to-hot" compounding process by using active groups, thereby solving the weather resistance problem, and the outermost functional layer 4 undertakes the functions of light blocking and weed inhibition or reflection and temperature adjustment according to the agronomic requirements, and the whole piece of mulch film can finally be completely soil biomineralized.

[0045] Main reagents and raw materials:

[0046] Table 1: Main reagent and raw material name, product model and manufacturer:

[0047]

[0048] Main analysis and detection instruments:

[0049] Table 2: Main equipment name, product model and manufacturer:

[0050]

[0051] Main test standards and methods:

[0052] ISO 17556:2019 Determination of ultimate aerobic biodegradability of plastics by determination of oxygen demand or carbon dioxide production;

[0053] GB / T 1540-2002: Determination of water absorption of paper and board Cobb method, specific Cobb 60 The test method is as follows: After equilibration for 24 hours in a constant temperature and humidity environment (23±1℃, 50±2% RH), cut a circular sample with a diameter of 125 mm, and weigh its initial mass, denoted as m1(g). Place the sample on the metal cylinder base of the Cobb tester, ensuring that the soil side faces up (i.e., the water contact surface is the coating surface to be tested), and tightly secure it with a metal compression ring. Quickly inject 100 mL of distilled water into the cylinder and simultaneously start the timer. At 45 s, pour out the water in the cylinder; at 60 s, immediately remove the compression ring and take out the sample, place it wet side down on a standard blotter paper, cover it with another standard blotter paper, and use a 10 kg standard metal compression roller to roll back and forth once within 4 s. Take out the sample and immediately weigh its water absorption mass, denoted as m2(g). The calculation formula is: Cobb 60 =(m2-m1)×100, unit g / m²;

[0054] ASTM E96 / E96M-24a (Procedure B, 38℃, 90% RH): Standard Test Methods for Water Vapor Transmission Rate of Materials;

[0055] GB / T 2790-1995: Determination of Adhesives 180° Peel Strength;

[0056] GB / T 455-2002: Determination of Tearing Strength of Paper and Paperboard (Elmendorf Method);

[0057] ASTM D5748-95 (2019): Standard Test Methods for Puncture Resistance of Membranes and Sheeting;

[0058] ASTM D1003-21: Standard Test Methods for Haze and Luminous Transmittance of Transparent Plastics (Integrating Sphere);

[0059] ISO 5627:1995 Determination of the Bekk smoothness of paper and board;

[0060] ISO 5636-5:2013 Determination of the air permeance of paper and board - Part 5: Gurley 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 Electrophoretic light scattering zeta potential determination - General rules;

[0064] EN 14582:2016 Oxygen bomb combustion - Ion chromatography 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 content (for closed cell volume fraction);

[0067] ASTM D792-20:Standard Test Methods for Density, Relative Density, and API Gravity of Petroleum Liquids (immersion method for density / Archimedes method for gravity traceability);

[0068] ISO 2144:2019 Paper, board and pulp - Determination of ash content (for paper-based layer ash content);

[0069] ISO 2114:2000 (or equivalent standard) Plastics and resins - Determination of acid value and total acid value (for acid value determination).

[0070] Examples:

[0071] General preparation procedure of PHA oligomer:

[0072] Step 1. Weigh PHBV powder or a blend of PHBV and P34HB with a mass ratio of 1:2, mix uniformly, and then vacuum dry at 60°C to 70°C for 4 hours 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, continuously melt shear at 190°C to 200°C, screw speed 150 r / min to 250 r / min, and nitrogen protection for 3 minutes to 8 minutes, and extrude into a strip to obtain a melt-sheared PHA extruded strip.

[0074] Step 3. Cool and crush the PHA extruded strip obtained in Step 2 to a particle size of ≤2 mm; take a sample and use gel permeation chromatography (GPC) to determine the number average molecular weight Mn. Adjust the melt-shearing time (3 minutes to 8 minutes), screw speed (150 r / min to 250 r / min), and extrusion temperature (190°C to 200°C) of Step 2 to control Mn in the range of 3 kDa to 8 kDa, for example 5 kDa, to obtain a PHA oligomer.

[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 the two, and add 0.5wt% to 2.0wt% of anhydride monomer and 0.05wt% to 0.2wt% of dicumyl peroxide based on the total mass of the 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-reactive extruded in a ZSK 26mc twin-screw reactive extruder at 180°C to 185°C 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 placed in a reaction kettle containing deionized water, and one of sodium hydroxide, potassium hydroxide, aqueous ammonia, monoethanolamine, diethanolamine, triethanolamine or 2-amino-2-methyl-1-propanol is added to partially neutralize and hydrolyze according to the requirements of the target apparent acid value of 3mg KOH / g to 10mg KOH / g and the neutralization degree of 20% to 45%, and stirred at 60°C to 80°C for 1 hour to 3 hours. After cooling, the PHA grafted anhydride half ester salt is obtained.

[0078] General preparation process of mulch film:

[0079] Step 1. Papermaking. Bamboo-based microfibrillated cellulose, bamboo-based nanocellulose or a mixture of the two are added to the pulp after refining and mixed uniformly, and the paper base layer is made by taking bamboo pulp as the main body, with the basis weight of the paper base layer controlled at 25g / m² to 300g / m², and the paper surface properties adjusted to achieve a Bekk smoothness of 80s to 600s and a Gurley air permeability of 50s / 100mL to 600s / 100mL, to obtain the paper base layer.

[0080] Step 2. Emulsion preparation. In the emulsification system, the PHA grafted anhydride half-ester salt prepared according to the general procedure above is pre-dissolved or dispersed in hot water at 85-95°C to obtain the stabilizer water phase; the mass flow ratio of the polyhydroxyalkanoate melt to the stabilizer water phase is controlled to be 35:65-45:55 (for example, when the target solid content is 40wt%, the water phase mass flow is 1.5 times the melt mass flow) to meet the requirement of 35-45wt% solid content; the polyhydroxyalkanoate melt at 160-180°C is metered into the side rotor-stator emulsifier at a flow rate of 0.5-1.5L / min by the side feed pump, and high shear emulsification is carried out with the stabilizer water phase at a rotation speed of 5000-15000r / min for 10-60s, so that the emulsifier outlet temperature is maintained at 80-95°C; after the emulsion is discharged, it is cooled to 30-40°C and filtered (80-200 mesh) to remove large particles, to obtain an intra-family stable emulsion with a solid content of 35-45wt%, a particle size D 50 0.15-2.0μm, a zeta potential of -25 to -45mV, a pH value of 6.5-8.0, and a viscosity of 50-400mPa·s at 25°C.

[0081] Step 3. Clay side coating. The intra-family stable emulsion obtained in step 2 is coated onto the clay side of the paper base layer obtained in step 1, and the dry coating amount is controlled to be 5-25g / m², and the coating is sequentially dried in stages at temperatures of 80°C, 95°C, and 110-115°C to an outlet paper temperature ≤55°C, to obtain a coating on the clay side.

[0082] Step 4. Preparation of PHA extruded film raw material for the windward rain side, which includes PHA grafted anhydride compatible layer granules and functional layer granules; to prepare the PHA grafted anhydride compatible layer granules, dry polyhydroxyalkanoate powder such as PHBV or P34HB is taken as the compatible layer raw material substrate, 0.5-2.0wt% of anhydride monomer such as maleic anhydride and 0.05-0.2wt% of initiator such as dicumyl peroxide are added based on the total mass, and reaction extrusion is carried out in a twin-screw extruder at 170-185°C, underwater pelletization is carried out, and drying is carried out, to obtain PHA grafted anhydride compatible layer granules with an apparent acid value corresponding to a grafting rate of 3-15mg KOH / g; to prepare the functional layer granules, dry PHA homologous resin such as PHBHHx and PHBV or P34HB and PHBV are mixed in the proportions described in the present application as the functional layer raw material, and color masterbatch such as carbon black concentrate or nucleating agent such as talc is added as needed, and melt blending extrusion is carried out in a twin-screw extruder at 160-180°C, pelletization is carried out, and drying is carried out, to obtain the functional layer granules.

[0083] Step 5. Compound the windward rain surface activation with the lamination film. After the coating on the earth surface in step 3 is dried to an outlet paper temperature ≤55℃, the windward rain surface is subjected to corona or plasma treatment in a temperature of 20-30℃ and relative humidity of 40%-60% for a time window of ≤2h, to an equivalent treatment energy ≥0.8kJ / m² and a surface tension ≥38mN / m. The PHA grafted anhydride compatible layer pellets prepared in step 4 and the functional layer pellets are extruded into a lamination film with a thickness of 20-80μm at a melt temperature of 160-185℃, and the windward rain surface extruded film layer is compounded with the paper base layer windward rain surface to obtain a double-sided compounded semi-finished product; the lamination film conditions are a cooling roller temperature of 15-25℃, a pressure of 0.2-0.5MPa, and a line speed of 30-120m / min; the resin is dried at 60-70℃ for 4-8h, with a water content ≤0.02wt%; the temperature difference of each melt in multi-layer co-extrusion is ≤15℃; and the activation criterion is a surface tension ≥38mN / m.

[0084] Step 6. Curing and slitting. After the double-sided compounded semi-finished product obtained in step 5 is cured for ≥24h in an environment with a temperature of 20-30℃ and a relative humidity of 40%-60%, it is slitted to obtain the bamboo pulp paper-PHA double-sided compounded soil biodegradable agricultural mulching film.

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

[0086] The basis weight of the paper base layer is 80g / m², and the fiber composition is 45wt% bamboo long fiber, 30wt% bamboo short fiber, and 25wt% broadleaf pulp short fiber. The total proportion of bamboo pulp fiber is 75wt%, and the total proportion of long fiber is 45wt%. The paper pulp contains 0.4wt% of bamboo-based nanocellulose in absolute dry mass. The Bekk smoothness of the paper base layer is 220s, and the Gurley air permeability is 180s / 100mL.

[0087] The B1 layer as the earth-contacting surface was coated with a self-stable emulsion in the same family, with a dry coating amount of 12 g / m2, and two passes of coating, 6 g / m2for each pass. The dry end temperature of the last pass of coating was increased from 110°C to 115°C, and the paper outlet temperature was still controlled at ≤55°C to ensure a dense film. The main polyhydroxyalkanoate of the self-stable emulsion in the same family was a blend of P34HB and PHBV, with a mass ratio of 2:1, wherein P34HB contained about 30 mol% 4HB units and PHBV contained about 20 mol% 3HV units. The oligomer used was PHBV oligomer, which was prepared by vacuum drying PHBV powder at 60°C for 4 h, melting and shearing in a twin-screw extruder at 195°C and 200 r / min for 5 min, with Mn of 5 kDa. The emulsion stabilizer used was PHBV grafted maleic anhydride half ester salt, which was prepared by reacting PHBV powder with 1.0 wt% maleic anhydride and 0.1 wt% dicumyl peroxide at 182°C, with an apparent acid value of 6 mg KOH / g, and then neutralizing with sodium hydroxide at 70°C for 2 h, with a neutralization degree of 30%. Based on the solid content of the polymer, the emulsion contained 15 wt% PHBV oligomer and 3 wt% PHBV grafted maleic anhydride half ester salt.

[0088] The B2 layer as the wind and rain-facing surface was a multi-layer co-extrusion structure with a total thickness of 35 μm, including a PHA grafted anhydride compatibility layer with a thickness of 3 μm and a functional layer with a thickness of 32 μm. The functional layer used a blend of PHBHHx and PHBV with a mass ratio of 70:30, and added a total amount of 0.8 wt% of the dry base of the film layer of furnace carbon black, which was added in the form of a PHA-based concentrate.

[0089] The film roll prepared in this example had an inner diameter of 76 mm, a width of 1200 mm, a roll length of 500 m, and a maximum roll weight of about 80 kg and ≤110 kg per roll.

[0090] Example 2: Preparation of an ultra-light short-season mulch film for greenhouse scenarios.

[0091] The basis weight of the paper base layer was 35 g / m2, and the fiber composition was 35 wt% bamboo long fibers, 30 wt% bamboo short fibers, and 35 wt% broadleaf pulp short fibers. The total proportion of bamboo pulp fibers was 65 wt%, and the total proportion of long fibers was 35 wt%. The paper pulp contained 0.4 wt% of bamboo-based nanocellulose based on the dry mass. The Bekk smoothness of the paper base layer was 150 s, and the Gurley air permeability was 120 s / 100 mL. The paper was treated with a micro-creping process for creping, and the creping rate was calculated based on the length difference of the sample belt before and after creping and the length before creping. The creping rate was 22%.

[0092] B1 layer adopts the same formulation and preparation parameters as Example 1, and the internal penetration treatment is to make the same family internal stable emulsion into the paper base layer by means of gluing machine / impregnation-extrusion, and the dry base internal penetration amount is controlled to be 3 g / m2; then 9 g / m2 of surface coating is applied to make the total dry coating amount to be 12 g / m2.

[0093] B2 layer is a multi-layer co-extrusion structure with a total thickness of 30 pm, including a PHA grafted anhydride compatible layer with a thickness of 3 pm and a functional layer with a thickness of 27 pm. The material composition of the functional layer is the same as that of Example 1, and carbon black is added in the form of PHA-based concentrate. The surface tension of the windward rain-activated surface is controlled to be 40 mN / m.

[0094] The mulch film coiled material prepared in this example has an inner diameter of 76 mm, a width of 1400 mm, a coil length of 800 m, and a maximum single coil weight of about 90 kg and ≤110 kg.

[0095] Example 3: Preparation of a thick and heavy long-season white film reflective mulch film.

[0096] The basis weight of the paper base layer is 200 g / m2, and the fiber composition is 50 wt% bamboo long fiber, 35 wt% bamboo short fiber and 15 wt% coniferous pulp long fiber. The total proportion of bamboo pulp fiber is 85 wt%, and the total proportion of long fiber is 65 wt%. The paper pulp contains 0.4 wt% of bamboo-based nanocellulose in absolute dry mass. The Bekk smoothness of the paper base layer is 260 s, and the Gurley air permeability is 320 s / 100 mL. The paper surface is provided with micro-slits, with a single slit length of 1 mm, a pitch of 10 mm, a conversion of about 100 strips per meter, and a total micro-slit area proportion of ≤0.5%.

[0097] B1 layer adopts the same formulation and preparation parameters as Example 1, and the internal penetration treatment is to make the same family internal stable emulsion into the paper base layer by means of gluing machine / impregnation-extrusion, and the dry base internal penetration amount is controlled to be 3 g / m2; then 9 g / m2 of surface coating is applied to make the total dry coating amount to be 12 g / m².

[0098] B2 layer is a multi-layer co-extrusion white film with a total thickness of 40 pm, including a compatible layer of 5 pm and a functional layer of 35 pm. During the preparation of the compatible layer, 0.8 wt% of maleic anhydride and 0.08 wt% of dicumyl peroxide are added based on the total mass, and the apparent acid value after reaction and extrusion is 5 mg KOH / g. The functional layer is a PHBHHx and PHBV blend with a mass ratio of 60:40, with the addition of 1.0 wt% calcium carbonate, and is treated by carbon dioxide foaming. The foaming process parameters are CO2 injection pressure 6.0 MPa, foaming temperature 160°C, and draw ratio 1.6. The average pore size of the obtained film layer is about 15 pm, and the closed pore volume fraction is 32%.

[0099] The mulch film coiled material prepared in this example has an inner diameter of 76 mm, a width of 1000 mm, a coil length of 400 m, and a maximum single coil weight of about 100 kg and ≤110 kg.

[0100] Example 4: Preparation of a whole piece of mulch film which can be quickly mineralized on the soil surface.

[0101] The basis weight of the paper-based layer is 80 g / m², and the fiber composition is 50 wt% long bamboo fibers, 25 wt% short bamboo fibers, and 25 wt% short broadleaf pulp fibers. The total proportion of bamboo pulp fibers is 75 wt%, and the total proportion of long fibers is 50 wt%. The paper pulp contains 0.4 wt% of bamboo-based nanocellulose based on the dry mass. The Bek smoothness of the paper-based layer is 200 s, and the Gurley air permeability is 160 s / 100 mL.

[0102] The main polyhydroxyalkanoate of the same family in-situ emulsion used in B1 layer is a blend of P34HB and PHBV with a mass ratio of 2:1, wherein P34HB contains about 30 mol% of 4HB units, and PHBV contains about 20 mol% of 3HV units. The oligomer used is a PHBV and P34HB blend oligomer with a mass ratio of 1:2, which is prepared by mixing dry PHBV and P34HB, then melt shearing at 195℃, 200r / min for 5min, Mn is 5kDa. The emulsion stabilizer used is PHBV grafted maleic anhydride half ester salt, and the preparation parameters are the same as in Example 1. The emulsion contains 15wt% PHA oligomer and 3wt% PHBV grafted maleic anhydride half ester salt, calculated based on the solid content of the polymer. The emulsion properties are D 50 The particle size is 0.20μm, the solid content is 40wt%, the zeta potential is-32mV, the pH value is 7.2, and the viscosity is 180mPa·s. The coating process adopts three coating, and the total dry coating amount is 10g / m², and the coating amount of each coating is 3g / m², 3g / m² and 4g / m² respectively.

[0103] B2 layer is composed of a 30μm thick functional layer and a 3μm thick PHA grafted anhydride compatible layer, with a total thickness of 33μm. The functional layer uses a PHBV and PHBHHx blend with a mass ratio of 30:70. The compatible layer uses PHA grafted maleic anhydride with an apparent acid value of 8mg KOH / g of graft, obtained by adding 1.5wt% of maleic anhydride and 0.15wt% of dicumyl peroxide based on the total mass during preparation, without adding color masterbatch.

[0104] The mulch film roll prepared in this example has an inner diameter of 76mm, a width of 1200mm, a roll length of 500m, and a maximum roll weight of about 75kg and ≤110kg per roll.

[0105] Example 5: Preparation of a micro-foamed white film with enhanced reflection.

[0106] The paper base layer has a basis weight of 120 g / m2, and a fiber composition of 40 wt% long bamboo fibers, 30 wt% short bamboo fibers, and 30 wt% short broadleaf pulp fibers. The total proportion of bamboo pulp fibers is 70 wt%, and the total proportion of long fibers is 40 wt%. The paper pulp contains 0.4 wt% of bamboo-based nanocellulose based on the absolute dry mass. The Bekk smoothness of the paper base layer is 210 s, and the Gurley air permeability is 240 s / 100 mL.

[0107] The B1 layer uses the same formulation and preparation parameters as in Example 1, and the dry coating amount is 10 g / m2.

[0108] The B2 layer uses a PHBHHx and PHBV blend with a mass ratio of 50:50, and the co-extruded film has a thickness of 28 μm, including a 3 μm compatible layer. The film layer is treated by carbon dioxide foaming, and 0.5 wt% of titanium dioxide based on the dry base is added. 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 pore diameters randomly measured on a cross-section slice is 12 μm, and the closed cell volume fraction measured according to the ISO 4590:2016 standard is 28%.

[0109] The film roll prepared in this example has an inner diameter of 76 mm, a width of 1200 mm, a roll length of 400 m, and a maximum roll weight of about 80 kg and ≤110 kg per roll.

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

[0111] The paper base layer has a basis weight of 100 g / m2, and a fiber composition of 35 wt% long bamboo fibers, 25 wt% short bamboo fibers, and 40 wt% short broadleaf pulp fibers. The total proportion of bamboo pulp fibers is 60 wt%, and the total proportion of long fibers is 35 wt%. The paper pulp contains 0.4 wt% of bamboo-based nanocellulose based on the absolute dry mass. The Bekk smoothness of the paper base layer is 180 s, and the Gurley air permeability is 150 s / 100 mL.

[0112] The B1 layer uses the same formulation and preparation parameters as in Example 1, and the dry coating amount is 10 g / m2.

[0113] The B2 layer is a multi-layer co-extruded structure with a total thickness of 35 μm, including a 3 μm PHA grafted anhydride compatible layer and a 32 μm functional layer. The functional layer is a blend of P34HB and PHBV with a mass ratio of 60:40, wherein P34HB contains 30 mol% of 4HB units and PHBV contains 20 mol% of 3HV units. The windward rain surface is black by adding a concentrated carbon black material with PHA as a carrier, and the total amount of pigment is 0.8 wt% of the dry base of the film layer.

[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 mulch film with low amount of low polycyclic aromatic carbon-based pigments in black film is provided. The preparation process is the same as Example 1, except that the total amount of low polycyclic aromatic carbon-based pigments in the functional layer of B2 is only 0.2 wt% of the dry basis of the film layer. The total thickness of B2 layer and the multi-layer co-extrusion structure are the same as Example 1, and the remaining process conditions remain the same. The inner diameter, width and length of the mulch film roll are the same as Example 1, i.e. inner diameter 76 mm, width 1200 mm, length 500 m, the maximum roll weight of a single roll is about 80 kg and ≤ 110 kg.

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

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

[0123] Comparative Example 8: A composite mulch film with activation energy and surface tension lower than the window is provided. The preparation process is the same as Example 1, except that in step 4, the corona treatment is only applied with an equivalent treatment energy of 0.4 kJ / m², so that the surface tension of the windward rain surface is 35 mN / m. The same wet-to-hot composite timing of 1 hour and subsequent curing conditions as in Example 1 are adopted, and the remaining paper base layer and coating formula remain the same. The inner diameter, width and length of the mulch film roll are the same as Example 1, i.e. inner diameter 76 mm, width 1200 mm, length 500 m, the maximum roll weight of a single roll is about 80 kg and ≤ 110 kg.

[0124] Application Example:

[0125] Application Example 1: Mechanical and Physical Properties of Mulch Films

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

[0127] The preparation conditions of all samples are strictly controlled: the windward rain surface B2 layer is treated by corona or plasma activation 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 da Vinci ink method: 38, 40, 42 mN / m da Vinci ink is dropped and spread continuously within 2 s and does not retract within 10 s, which is determined to reach the level of wetting tension), the coating temperature is set to 170-175°C, the cooling roller temperature is controlled at 20°C, the composite line pressure is 0.3 MPa, and the line speed is 95 m / min. The "wet-to-hot" compounding is completed within 1 h of the B1 layer coating and drying, and the aging treatment is carried out at room temperature for ≥48 h.

[0128] Mechanical property testing uses a universal material testing machine, and strictly follows GB / T 2790-1995 standard for 180° peeling strength test (sample width 25 mm, tensile speed 300 mm / min); puncture resistance is tested according to ASTM D5748-95(2019); tear resistance is determined according to GB / T 455-2002 for longitudinal (MD) and transverse (TD) directions respectively. In terms of optical properties, the transmittance (T 600 ) of black mulch film is measured at 600 nm using a spectrophotometer, and the integral reflectance in the visible region (400-700 nm) is measured using an integrating sphere. The WVTR reduction is calculated based on ASTM E96 / E96M-24a (Procedure B, 38°C, 90% RH), relative to the change of the uncoated base paper. All laboratory tests are carried out after 24 h of equilibration in a constant temperature and humidity environment (23±1°C, 50±2% RH), and each data point is the average of 5 independent tests with standard deviation recorded.

[0129] Field laying and integrity evaluation: The mulching machine was used to lay the mulch film in the same field, and each sample was set up not less than 3 repeated plots. The "times of broken film per 100m" in Table 4 refers to the times of through hole or through crack that need to be repaired by hand during laying per 100m; the "times of stop machine per ha" refers to the times of machine stop for processing due to film damage, deviation or breakage, which is calculated per hectare; the "qualified rate of laying (%) " is calculated according to the laying length, and the qualified criterion is continuous coverage, complete edge soil pressing and no through hole; the "7d edge lifting (%) " is the percentage of the edge lifting length on the total length of the measured edge on the 7th day after covering; the "field integrity (120d, 5-point system)" scoring standard is: 5 points = no through crack / no delamination within 120d; 4 points = slight edge damage but no through crack; 3 points = local through crack but damaged area < 5%; 2 points = through crack or delamination leading to damaged area of 5%-20%; 1 point = through crack or delamination leading to damaged area > 20% or unable to maintain the covering function.

[0130] Table 3: Mechanical, optical and barrier properties data of mulch film

[0131]

[0132] Table 4: Water absorption and field laying performance data of mulch film

[0133]

[0134] Note: The contact angle of the soil surface was measured by a contact angle measuring instrument, deionized water was used as the test liquid, the droplet volume was 3 μL, and 5 positions were randomly selected on the soil surface of the sample under the condition of 23±1 ℃, 50±2% RH for testing, the static contact angle after 5s of droplet addition was taken and the average value was taken.

[0135] Analysis: From the experimental results, it can be seen that Examples 1-6 all perform excellently in mechanical strength, interfacial bonding force and field applicability, especially the peeling strength is stable at above 1.5 N / 25mm, and the failure mode is ideal "fiber tearing", which indicates that a firm integrated structure is formed between the PHA extruded film layer and the bamboo pulp paper base layer. In contrast, the comparative examples have obvious defects: Comparative Example 1 does not have the corrugated treatment of the ultra-light paper, which leads to insufficient extensibility, significantly increased times of broken film and stop machine, and the qualified rate of laying is reduced to 88%; Comparative Example 2 has heavy paper lacking of micro-slit stress release, which leads to serious edge lifting; Comparative Example 3 introduces a pressure-sensitive adhesive layer, although the initial adhesion is acceptable, but the adhesive layer is prone to creep or internal breakage in the humid and hot soil environment, resulting in lower field integrity score; Comparative Example 4 uses PHA / PVA blend, due to the hydrophilicity of PVA, the interfacial bonding force decreases after moisture absorption, showing a mixed failure mode.

[0136] The comparative example data further reveals the influence of key parameters: Comparative Example 5 reduces the shading pigment, although the mechanical properties are not affected, but the light transmittance increases to 15.4%, which will seriously affect the weed control effect; Comparative Example 6 has improper foaming process control, low closed cell rate, and reflectivity of only 45%, which cannot achieve the expected cooling and light enhancement; the emulsion particle size and potential of Comparative Example 7 deviate from the window, resulting in poor coating film-forming property, 180° peeling strength reduced to 1.3 N / 25 mm and interfacial peeling; Comparative Example 8 has insufficient activation energy, low surface tension, and poor interfacial bonding (1.1 N / 25 mm), which is prone to delamination in the field. In summary, the present application successfully solves the interface compatibility and weather resistance problems of the paper base and the PHA film layer through strict material selection and process window control (such as wet-heat compounding, emulsion parameters, and activation energy).

[0137] Application Example 2: Cobb's earth surface coating 60 Drop verification.

[0138] Experimental explanation: This application example is specifically designed to verify the improvement effect of the earth surface PHA barrier coating on the water absorption of the paper base. The paper base layers corresponding to Examples 1-6 and Comparative Examples 1-8 are selected for testing, and the test is strictly carried out according to the GB / T 1540 "Determination of Water Absorption of Paper and Paperboard by Cobb Method" standard. The test is divided into three stages: the first stage tests the uncoated base paper, the second stage tests the paper sample after coating only B1 layer, and the third stage (mainly for reference) can test the whole after compounding. 100 mL of distilled water is used for testing, the contact time is 60 seconds (Cobb 60 ), and the test area is 100 cm². The water absorption reduction amplitude (percentage of reduction) of "after coating" relative to "uncoated" is mainly investigated to evaluate the film-forming density and sealing ability of the water-based PHA emulsion on the surface of the paper fibers. Five test samples are cut from each sample for parallel testing, and the arithmetic mean value is taken and the standard deviation is calculated. The test environment temperature is controlled at 23±1℃, and the relative humidity is 50±2%.

[0139] Table 5: Cobb's earth surface coating 60 Drop data:

[0140]

[0141] Analysis: The experimental data shows that Examples 1-6 can effectively penetrate and cover the fiber pores on the surface of the paper by using the same family stable PHA emulsion with particle size D 50 of 0.15-2.0 μm and ζ potential of -25 to -45 mV, Cobb 60The Cobb value reduction rate is stable at more than 30%, and the highest is 35.0%. This shows that the specific emulsion forms a continuous and dense hydrophobic layer on the surface of the paper, effectively blocking the rapid penetration of water into the paper base. Although Comparative Examples 1, 2, 3, 5, 6 and 8 are different in other structures or processes, their B1 layer coating formula or process is basically the same (or has little effect) as the corresponding examples, so their Cobb 60 The Cobb value reduction rate is stable at more than 30%, and the highest is 35.0%. This shows that the specific emulsion forms a continuous and dense hydrophobic layer on the surface of the paper, effectively blocking the rapid penetration of water into the paper base. Although Comparative Examples 1, 2, 3, 5, 6 and 8 are different in other structures or processes, their B1 layer coating formula or process is basically the same (or has little effect) as the corresponding examples, so their Cobb

[0142] However, the data of Comparative Example 7 is significantly abnormal, and the Cobb 60 The Cobb value reduction rate is stable at more than 30%, and the highest is 35.0%. This shows that the specific emulsion forms a continuous and dense hydrophobic layer on the surface of the paper, effectively blocking the rapid penetration of water into the paper base. Although Comparative Examples 1, 2, 3, 5, 6 and 8 are different in other structures or processes, their B1 layer coating formula or process is basically the same (or has little effect) as the corresponding examples, so their Cobb 60 The Cobb value reduction rate is stable at more than 30%, and the highest is 35.0%. This shows that the specific emulsion forms a continuous and dense hydrophobic layer on the surface of the paper, effectively blocking the rapid penetration of water into the paper base. Although Comparative Examples 1, 2, 3, 5, 6 and 8 are different in other structures or processes, their B1 layer coating formula or process is basically the same (or has little effect) as the corresponding examples, so their Cobb

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

[0144] Experimental explanation: This application example aims to evaluate the biodegradation performance of the PHA barrier coating on the soil surface as an independent material in the soil environment. The experiment is carried out according to the ISO 17556:2019 standard "Determination of ultimate aerobic biodegradation of plastics in soil by determination of oxygen demand or carbon dioxide production". First, the B1 layer coating liquid of Examples 1-6 and Comparative Examples 1-8 is coated on an inert PET substrate, and after drying and film forming, it is carefully peeled off to obtain a pure coating body sample. The soil is derived from the surface soil of the main crop planting area, sieved through a 2mm sieve, and the moisture content is adjusted to 40%-60% of the maximum water holding capacity. After peeling off the sample, cut it into fragments with a size of ≤5mm×5mm and mix it thoroughly with soil that has been sieved through a 2mm sieve and adjusted to a moisture content of 40%-60% of the maximum water holding capacity, and then add the soil to the soil with a dry basis mass m 土壤 The sample dry basis mass m 样品The ratio of 100:1 to 200:1 was loaded into a sealed respirometer reaction bottle, and incubated in the dark at 25-28°C; the headspace carbon dioxide concentration of the reaction bottle was continuously monitored using an aerobic CO2 respirometer system, and the cumulative carbon dioxide release was converted into mineralization degree after deducting the blank soil. The biodegradation degree was calculated according to "cumulative CO2 release amount / theoretical CO2 release amount x 100%" in ISO 17556, wherein the theoretical CO2 release amount was obtained by converting the total organic carbon content of the sample. Microcrystalline cellulose was used as a reference material, and the blank soil was used as a control. The experiment lasted for 180 days, and the biodegradation degree at 90 days and 180 days was recorded, and the half-life was calculated according to the fitting of the mineralization curve. Three parallel samples were set in each group, and the average value was taken and the standard deviation was recorded.

[0145] Table 6: Coating body degradation performance data:

[0146]

[0147] Analysis: The degradation test results clearly show the absolute advantage of the full-PHA system of the present application in environmental friendliness. The biodegradation degree of the coating body of Examples 1-6 is more than 90% within 90 days, and the half-life is controlled within 30 days, showing an extremely fast mineralization rate. This is due to the fact that PHA is a naturally synthesized polyester by microorganisms, and there are a large number of specific degradation bacteria in the soil, and the introduction of PHA oligomers and grafted anhydride half ester salt in the formula further promotes the attachment and hydrolysis of microorganisms. Although Comparative Examples 1, 2 and 5-8 have defects in physical structure or processing technology (such as unstable emulsion, different pigment content, etc.), the chemical nature of their coating bodies is still mainly PHA, so their body degradation performance is comparable to that of the examples, and can meet the biodegradation requirements.

[0148] However, Comparative Example 3 uses acrylic pressure-sensitive adhesive as the adhesive layer, and the degradation degree of its body is only 25.4% at 90 days, which seriously hinders the overall mineralization process of the mulch film, showing the inapplicability of traditional synthetic adhesives in biodegradable agricultural mulch films. Comparative Example 4 introduces PVA, although PVA is water-soluble, but its biomineralization rate in soil environment is much slower than PHA, and it may form part of the interpenetrating network with PHA to hinder enzyme attack, resulting in a 90-day degradation degree of only 66.1% and a half-life of 51 days. These data fully prove that abandoning non-consanguineous adhesives and slow-degrading components such as PVA and adhering to the pure component design of PHA are the key to ensuring that the mulch film can quickly and completely return to the natural cycle after being plowed into the soil.

[0149] Application Example 4: Whole film mineralization time sequence and platform statistics.

[0150] Experimental instruction: This application example simulates the actual degradation of mulching film after ploughing into the soil, and tests the long-term biodegradation of the whole composite mulching film. Randomly cut samples from the finished coiled material of Examples 1-6 and Comparative Examples 1-8, pre-cool the samples in liquid nitrogen or at -40°C, then freeze and crush them, or use shearing method to prepare fragments with a maximum characteristic size of ≤5 mm, and mix them uniformly to ensure that the proportion of each layer component is consistent with the finished product; according to the ratio of soil dry basis mass m 土壤 to sample dry basis mass m 样品 of 100:1 to 200:1, fill the respirometer reaction bottle, and test the continuous monitoring in aerobic soil environment for 24 months (720 days) according to ISO 17556 standard. Record the cumulative biodegradation degree at 90 days, 180 days, 360 days, 540 days and 720 days; the plateau criterion is set as "the cumulative mineralization degree in the last 30 days increases by less than 5%". This experiment aims to verify whether the whole film can achieve complete mineralization (≥90%) under long-term soil burial conditions, and the influence of different structures and components on degradation kinetics. Each group of samples is set with 3 replicates, and the data is represented as mean ± standard deviation.

[0151] Table 7 Whole film biodegradation time series data:

[0152]

[0153] Analysis: The whole film degradation data shows that Examples 1-6 all achieve a biodegradation degree of more than 90% within 24 months, and enter or approach the degradation plateau around 540 days, proving the reliability of this technical solution in achieving complete biodegradation. Although Comparative Examples 5-8 have serious defects in product functionality (such as light shielding, reflection, and interface adhesion), since the materials in each layer are still essentially all PHA components or contain very small amounts of inert impurities (such as low content of pigments), the ultimate biomineralization ability at the chemical level is not fundamentally affected, and ultimately also achieves a degradation index of 90%.

[0154] In contrast, Comparative Example 1 and Comparative Example 2 were physically designed improperly (lack of creping or micro-slit), making it difficult for the mulch film to break and disperse in the soil, with a small specific surface area, and it was difficult for microorganisms to colonize, so the degradation rate was significantly lagging behind, and the degradation degree was only 85%-87% in 24 months. The problem of Comparative Example 3 and Comparative Example 4 is more fundamental: the adhesive layer in Comparative Example 3 is not only difficult to degrade itself, but also blocks the attack of microorganisms on the paper base and the PHA film layer, resulting in a final degradation degree of only 75%; Comparative Example 4 is also unable to meet the standard due to the slow degradation characteristics of PVA and the uneven structure caused by poor compatibility. This result reveals the dual influence of "material chemical composition" and "physical structure design" on the degradation performance of the mulch film: the chemical composition determines "whether it can be degraded", and the physical structure (such as micro-slit, good interface dispersion) determines "how fast it is degraded". The present application realizes the perfect unity of the two through the full PHA component and the optimized physical structure design.

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

[0156] Experimental explanation: This application example aims to verify the key influence of activation energy and compounding time sequence on the interface bonding strength in the "wet-heat" compounding process, which is the basis for establishing the process window of the present application. Two comparison conditions are designed: condition A represents the "in-window" process, that is, the equivalent activation energy of the windward and leeward surfaces is ≥0.8 kJ / m², and the compounding is completed within 1 h after the B1 layer is dried; condition B represents the "out-of-window" process, that is, although the activation energy meets the standard (0.8 kJ / m²), the compounding time sequence is delayed to 3 h. The initial 180° peeling strength and failure mode of the samples of Examples 1-6 and Comparative Examples 1-8 are tested, and after 7 days of accelerated aging at 40°C, the test is performed again. The failure mode is divided into "fiber tearing" (ideal mode, indicating that the interface strength is higher than the paper strength) and "interface peeling" (failure mode, indicating that the interface adhesion is insufficient). Each group of data is the average value of 5 parallel samples.

[0157] Table 8 Interface window verification data:

[0158]

[0159] Analysis: The experimental results have convincingly proved that the "activation energy" and "complexation timing" are the two core variables that determine the quality of the PHA-paper-based interface bonding. Examples 1-6 all achieve the ideal "fiber tearing" mode under condition A (within the window), and the strength retention rate after aging is extremely high (>90%), which indicates that the polar functional groups on the surface of the PHA film layer (generated by activation) and the active sites on the surface of the paper-based coating layer (in a semi-melted / uncrystallized state) have effectively chemically or physically anchored. However, once it enters condition B (overlapping timing), due to the B1 coating cooling and crystallizing solidification, the surface activity is greatly reduced, even if the activation energy is sufficient, it is also impossible to form effective intermolecular entanglement, resulting in a sharp drop in interface strength and turning into "interface peeling".

[0160] The data of Comparative Examples 7 and 8 are particularly crucial: Comparative Example 7 cannot achieve effective adhesion even within window A due to the excessively large emulsion particle size and low absolute value of zeta potential, low cohesion of the coating layer and many surface defects, which directly manifests as interface peeling; Comparative Example 8 is because the activation energy is insufficient (<0.8 kJ / m²), the surface tension of the windward rain face is too low, and it cannot wet and spread on the coating layer on the soil side, resulting in extremely low interface strength (<1.2 N / 25 mm) regardless of the timing. The failure modes (inner layer breakage, mixed breakage) of Comparative Examples 3 and 4 further confirm the natural disadvantage of non-homologous systems in interface consistency. In summary, only by strictly following the activation energy (≥0.8 kJ / m²) and wet-against-hot timing (≤2 h) defined in the present application, combined with high-quality homologous emulsion, can a full-biodegradable composite interface with aging resistance and high strength be constructed.

[0161] Application Example 6: Field Soil Moisture Preservation and Ground Temperature Measurement

[0162] Experimental Description: The purpose of this application example is to quantitatively evaluate the soil water retention capacity and ground temperature regulation effect of bamboo pulp paper PHA double-sided composite mulch under actual field covering conditions. The test site is located in an agricultural demonstration base with typical climate characteristics, and the soil texture is uniform. Randomized block arrangement method is used, and 4 repeated plots are set for each treatment, with a plot area of 20 square meters. In the central mulch covering row of each plot, a TDR soil moisture sensor (TEROS 12) and a high-precision thermocouple temperature probe are vertically buried at a depth of 10 centimeters below the soil surface, and a bare ground control group is set. Using an automatic data acquisition system, the soil volume water content (θv) and ground temperature change data from the 1st to the 14th day after covering are recorded at 30-minute intervals. The data on the 14th day (stable covering period) are selected for statistical analysis to calculate the soil water content improvement value relative to bare ground, ground temperature daily amplitude, and diurnal mean temperature difference relative to bare ground. The data results are expressed as the arithmetic mean and standard deviation of the 4 repeats to comprehensively evaluate the agronomic performance of the mulch.

[0163] Table 9 Soil Moisture Preservation and Ground Temperature Data:

[0164]

[0165] Analysis: The data of soil moisture conservation and temperature regulation reveal the key roles of the physical structure integrity and barrier coating quality of the mulch film in regulating the microclimate of farmland. All of Examples 1 to 6 exhibit excellent soil moisture conservation effect, with the volumetric water content increased by 6.3% to 9.0% relative to the bare soil. This is mainly attributed to the effective blocking of the paper pores by the barrier coating of PHA on the soil-contacting surface, combined with the extrusion of the film layer on the windward and rainward surface, forming a double barrier to lock water. In terms of temperature regulation, the black mulch films (Examples 1, 2 and 6) exhibit a significant warming effect, while the white foamed mulch films (Examples 3 and 5) significantly reduce the daily amplitude of soil temperature (only 5.8 to 6.1°C) through high reflectivity, playing a role of "temperature-stabilizing and cool ground", which is suitable for heat-sensitive crops.

[0166] The data of the comparative examples reflect the negative effects of different defects. Comparative Examples 7 and 8 have poor interfacial bonding or poor coating film quality, resulting in the failure to effectively block the water vapor transmission path, or the mulch film is damaged and layered in the early stage in the field, and the soil moisture conservation ability is significantly reduced, with Δθv of only +4.1% to +4.4%. Comparative Example 5 has too low a content of carbon black, and the light transmittance is increased, resulting in more direct heating of the soil by solar radiation, with a daily amplitude of soil temperature of 11.2°C, and the daytime average temperature is increased too much, which may cause heat damage to the crop roots and excessive evaporation of water. Comparative Example 6 has low foaming and low closed cell rate, and the heat insulation performance is greatly reduced, failing to achieve the expected temperature stabilization effect. In summary, only the double-sided composite mulch film with good interfacial bonding, dense coating and reasonable optical design can achieve the optimal allocation of water and heat resources.

[0167] Application Example 7: Weed suppression effect (emergence number).

[0168] Experimental description: This application example aims to evaluate the weed growth inhibition ability of different structure mulch films in the real field cultivation environment. The test site is selected in the same test plot with high and uniform weed base, and the soil type is loam with medium fertility. After the crops are planted and covered with mulch film, a random block design is adopted, and 3 fixed 1 square meter sample frames are drawn in each treatment plot. Within 30 days after covering, the number of weeds growing through or breaking through the mulch film in the sample frame is observed and recorded regularly. This test not only examines the optical shielding performance of the mulch film (such as the light transmittance of black mulch film and the reflectivity of white mulch film), but also indirectly reflects the physical integrity of the mulch film, because the mechanical damage is often the window for weeds to break through. In order to ensure the statistical significance of the data, 4 repeated plots are set for each example and comparative example, and the final result is recorded as the cumulative emergence number within 30 days, expressed as mean ± standard deviation, and abnormal data is analyzed.

[0169] Table 10: Thirty-day emergence data

[0170]

[0171] Analysis: The experimental results show a significant differential distribution, which reveals the dual role of mulch optical performance and physical integrity in weed control. Examples 1, 2 and 6, as black opaque mulch, have a T 600 The low transmittance (less than 1%) effectively cuts off the light source required for weed photosynthesis, and its excellent physical strength (such as the fiber tear failure mode of Example 1) prevents weeds from breaking through, so the emergence is very low, only 4 to 8 plants / m2. Examples 3 and 5 are white reflective mulch, although the transmittance is higher than that of black film, but with high reflectivity and good coverage, the weeds are still controlled within an acceptable range (17 to 25 plants / m2).

[0172] In contrast, Comparative Example 1 and Comparative Example 2, due to the lack of corrugated or micro-slit design, have poor field weather resistance, and the mulch cracks in large areas, leading to the growth of weeds from the cracks, with an emergence of 42 to 60 plants / m2. Most typically, Comparative Example 5, although the physical structure is intact, due to the insufficient amount of low polycyclic aromatic carbon-based pigment additive (only 0.2 wt%), the transmittance is as high as 15.4%, leading to direct sunlight on the soil surface, and the weed photosynthesis is not inhibited, the emergence is as high as 65 plants / m2, completely losing the weed control function. Comparative Example 6 has a foamed structure that collapses, weak light scattering ability, and decreased physical strength, resulting in a higher emergence. Comparative Examples 7 and 8 are because of poor interfacial adhesion (interfacial peeling), which is easy to delaminate and break under wind and rain and soil stress, forming a breakthrough for weed growth. This fully illustrates that excellent weed control function must be based on the synergistic cooperation of extremely low transmittance and high physical integrity.

[0173] Application Example 8: Determination of the bio-based carbon content of the cover layer

[0174] Experimental instruction: This application example is based on the international standard ISO 16620-2 2019 "Plastics - Determination of bio-based content - Part 2: Determination of bio-based carbon content", aiming to quantitatively evaluate the biomass source attribute of the mulch film product, which is the core indicator to measure its low-carbon and environmentally friendly value. The test sample is taken from the cover layer of the mulch film (including the paper-based layer, the coating layer and the extruded film layer), the sample is converted into carbon dioxide by burning, and the abundance of carbon 14 isotope in it is determined by using accelerator mass spectrometry (AMS) or liquid scintillation counting method (LSC). Since the carbon 14 in petroleum-based materials has completely decayed, and the carbon 14 abundance in bio-based materials is consistent with the atmospheric environment, the percentage of bio-based carbon in total carbon can be accurately calculated. In order to ensure the representativeness of the results, the test results are weighted and averaged according to the dry basis mass of each component of the cover layer, each sample is tested in parallel for 3 times, the results are kept to one decimal place and the standard deviation is recorded.

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

[0176]

[0177] Analysis: The test data strongly proves the superiority of the full bio-based technical route of the present application. The bio-based carbon content of examples 1-6 is stable at 95.0% or above, with the highest being 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 the present application are all 100% bio-based materials, containing only trace amounts of inorganic additives or mineral fillers (such as calcium carbonate, talc), achieving truly taking from nature.

[0178] On the contrary, comparative example 3 introduces petroleum-based acrylic pressure-sensitive adhesive as the adhesive layer, although the adhesive layer is very thin, but due to its very high carbon content and complete absence of carbon 14, it significantly reduces the overall bio-based content to 82.1%. Comparative example 4 uses polyvinyl alcohol (PVA), which is currently synthesized from petroleum-based ethylene or natural gas, and belongs to fossil sources, so its bio-based content is also reduced to 86.5%. Although comparative examples 5, 6, 7 and 8 have defects in physical properties or processing technology, their chemical raw material composition does not deviate from the main framework of PHA and paper pulp (comparative example 5 even slightly improves the proportion by reducing carbon black), so their bio-based carbon content still remains at a high level of more than 95%. This high bio-based content feature not only meets the global environmental theme, but also ensures that the product after degradation of the mulch film does not release ancient geological carbon to the soil, maintaining the balance of modern carbon cycle.

[0179] Application example 9: Total organic fluorine and AOF detection.

[0180] Experimental instructions: In order to investigate whether the mulch contains persistent organic pollutants (PFAS) and other fluorine-containing chemicals, the present application carries out total organic fluorine (TOF) detection according to EN 14582:2016, and adsorbable organic fluorine (AOF) detection on water extract according to DIN 38409-59:2022-10. During TOF testing, the whole sample and each layered material are cut into ≤5mm fragments, and m0(g) of the sample is weighed and placed in an oxygen bomb combustion device for combustion under oxygen-rich conditions. The combustion products are absorbed according to EN 14582 and prepared into a test solution, and the fluorine ion content is determined by ion chromatography to obtain the TOF (mg / kg) of the sample. The detection limit is converted to ≤5mg / kg based on the sample weight and the volume of the absorption liquid.

[0181] During AOF testing, m1(g) of sample fragments is weighed and added to V(mL) of ultrapure water, and the mixture is shaken and extracted for 2h at 23±2℃. The water extract is obtained by filtration. The water extract is subjected to activated carbon adsorption, washing, combustion and ion chromatography according to DIN 38409-59 to determine the AOF concentration of the extract. The AOF (mg / kg) of the sample is converted based on V and m1. Each sample is tested in triplicate, and the detection limit is converted to ≤5mg / kg by the same conversion method.

[0182] Table 12 Total organic fluorine and AOF data:

[0183]

[0184] Analysis: The test results show that the total organic fluorine (TOF) and adsorbable organic fluorine (AOF) of all samples including all examples and comparative examples are below the detection limit (5mg / kg), i.e. not detected. This result has important environmental significance. In traditional oil and paper resistant packaging or some high-performance agricultural films, fluorine-containing surfactants or fluorine-containing polymers are often used to improve barrier properties and weather resistance, but this may cause permanent PFAS pollution risk to the soil.

[0185] Through technical innovation, the present application utilizes the excellent crystallization performance and hydrophobic characteristics of PHA materials, and the high density of bamboo pulp paper, to achieve excellent water resistance and barrier effect (as shown in the aforementioned Cobb 60 Data) without adding any fluorine-containing additives. Even the comparative sample, although its physical properties do not meet the standards, also follows the fluorine-free principle in formulation design, and therefore does not contain fluorine. This confirms that the product of the present application is a true fluorine-free material, and after the end of the life cycle of the mulch, plowing into the soil for degradation will not cause the accumulation of fluoride in the soil and groundwater, completely eliminating the potential threat of such emerging pollutants to the agricultural ecosystem, and meeting the most stringent soil protection regulations.

[0186] Application Example 10: Non-polymer additive total amount accounting.

[0187] Experimental explanation: The purpose of this application example is to accurately calculate the total amount of non-polymer components (i.e. auxiliary chemicals without biodegradable backbone function) in the mulch film through formula tracing and accounting. According to the detailed production input sheet of each example and comparative example, the dry basis mass proportion of all additives is identified and calculated. The statistical range covers all functional additives used in B1 coating and B2 extruded film layer, 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 invention and the environmental protection design concept, the total amount has a strict upper limit control (≤3.0wt%), in order to prevent excessive small molecule additives from migrating to the soil and causing secondary salinization or toxicity effects. The results are listed as the weighted percentage of each layer and the overall mulch layer.

[0188] Table 13 Non-polymer additive total amount data:

[0189]

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

[0191] Comparative Example 5 has a slightly lower B2 layer and overall additive content (1.0wt%) due to the reduction of carbon black pigment, but this also directly leads to the loss of light shielding performance. Although Comparative Example 4 contains PVA dispersant, the total amount increases to 1.4wt%, but it is still within the control range. This low additive design has double benefits: on the one hand, it maximizes the proportion of biodegradable carbon source 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 difficult-to-degrade small molecules in the soil, ensuring that the soil in the farmland remains healthy in physical and chemical properties after continuous use and degradation of the mulch film, meeting the sustainable development requirements of ecological agriculture.

[0192] Application Example 11: Paper ash content and added surfactant compliance.

[0193] Experimental instructions: This application example mainly detects the purity of the paper base layer and the introduction of surfactants in the coating system to verify whether the product meets the design intention of "natural and harmless". The paper ash content test is carried out according to ISO 2144 2019 "Determination of ash in paper, paperboard and pulp", the paper sample is burned in a high temperature muffle furnace at 525℃ to constant weight, and the mass of residual inorganic matter is weighed to evaluate whether excessive talc or kaolin and other inorganic fillers are added in the pulp. The determination of additional surfactants is based on the B1 layer coating liquid formula, which focuses on whether alkyl phenol polyoxyethylene ether and other traditional emulsifiers harmful to aquatic organisms are used. The detection range covers all examples and comparative examples, each sample is taken 3 times, the average value and standard deviation are calculated to ensure the accuracy and traceability of the data.

[0194] Table 14 Paper ash and additional surfactant data:

[0195]

[0196] Analysis: The test results show that the paper ash content of examples 1-6 is between 1.2wt% and 1.4wt%, which is much lower than the upper limit of 2.0wt%. This indicates that the bamboo pulp paper base layer selected by the present application is mainly composed of plant cellulose, without filling a large amount of inorganic minerals to reduce cost, so as to ensure the strength retention rate of paper in wet environment and the soil permeability after degradation.

[0197] More importantly, the additional surfactant content of all examples and most comparative examples (except comparative example 4) is 0. This is because one of the core technologies of the present application is to use "homologous internal emulsion", which uses the self-emulsifying function of PHA grafted anhydride half ester salt to stabilize the system, completely abandoning the sodium dodecyl sulfate (SDS) or polyoxyethylene ether additional surfactant which must be added in traditional emulsion polymerization. Only comparative example 4, due to the introduction of PVA system, must rely on dispersant to maintain stability, and 0.5wt% of additional surfactant is detected. The realization of zero surfactant not only avoids the problem of foam and improves the compactness of coating film, but also eliminates the potential interference of surfactant to soil microbial cell membrane, which ensures the safety and health of soil microbial 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 PHA double-sided composite soil biodegradable agricultural mulching film described in the present application has shown significant superiority in mechanical strength, agronomic function, environmental friendliness and biodegradation characteristics, and has successfully overcome the technical bottlenecks of traditional paper mulch easy to break, pure biodegradable plastic film easy to early decline and paper-plastic composite film difficult to be compatible.

[0200] Firstly, the "homogeneous wet-to-hot" composite process is the core key to building a high-strength interface. The data of application example 1 and application example 5 show that by activating the surface of the windward rain-facing PHA extruded film layer (equivalent energy ≥0.8 kJ / m²) and accurately coupling the semi-melted state of the soil-facing PHA coating (≤2 h after drying), embodiments 1-6 realize physical entanglement and chemical anchoring of the two layers of homogeneous materials at the molecular chain level. The 180° peeling strength is generally higher than 1.5 N / 25 mm, and the failure mode is ideal "fiber tearing", and the strength retention rate is more than 90% after 40°C aging for 7 days. In contrast, although the introduction of acrylic pressure-sensitive adhesive in Comparative Example 3 has initial adhesion, it has poor wet heat aging resistance, leading to internal rupture of the adhesive layer; Comparative Example 8 has insufficient activation energy (low surface tension), and Comparative Example 7 has large emulsion particle size leading to coating defects, and the "window outside" in application example 5, all of which result in a sharp drop in interface strength and interface peeling. This confirms that the process window defined in the present application is a necessary condition for realizing high-strength composite without adhesives.

[0201] Secondly, the all-bio-based component design of PHA ensures complete biomineralization and environmental safety. The data of application example 3, application example 4, application example 8, application example 9 and application example 10 form a complete evidence chain: the bio-based carbon content of the embodiment samples is as high as 95% or more, and there is no total organic fluorine (TOF / AOF <5 mg / kg), and the non-polymer additive is extremely low. In terms of degradation performance, the coating on the soil-facing surface has a half-life of 25-30 days, and the entire film has a biodegradation rate of more than 90% within 24 months. In contrast, the adhesive layer in Comparative Example 3 hinders degradation (only 75% in 24 months), and the PVA component in Comparative Example 4 slows down the mineralization rate. This shows that abandoning non-homogeneous adhesives and petroleum-based / slow-degrading modifiers is the fundamental way to realize the transition of mulch from "disintegration" to "complete mineralization".

[0202] Thirdly, the fine regulation of physical structure determines the field applicability and agronomic effect. Application example 1, application example 6 and application example 7 show that the creping treatment of ultra-light paper (embodiment 2) and the micro-slit design of thick paper (embodiment 3) significantly improve the mechanical laying qualification rate and reduce the edge lifting, while Comparative Example 1 and Comparative Example 2 lack these treatments and exhibit serious field adaptability problems. In terms of functional regulation, the black formula of embodiment 1, embodiment 2 and embodiment 6 achieves extremely low light transmittance (<1%) and excellent weed suppression effect (<8 plants / m²), while Comparative Example 5 fails to suppress weeds due to insufficient pigment, resulting in high light transmittance; the white foaming structure of embodiment 3 and embodiment 5 achieves high reflectivity and temperature stabilization effect, while the failure of foaming in Comparative Example 6 leads to functional loss.

[0203] Finally, the precise definition of the aqueous emulsion parameters guarantees the film quality of the barrier coating. The data of Application Example 2 show that only the emulsions (Examples 1-6) with the specific range of particle size (0.15-0.25 pm) and zeta potential (-25 to -45 mV) can form a dense coating on the paper substrate, which significantly reduces the Cobb 60 value (>30%) and endows the mulch film with excellent soil conservation ability (Application Example 6). The comparative example 7 deviates from this window and cannot effectively form a film, which directly leads to the failure of the barrier and the collapse of the interfacial strength.

[0204] In summary, the present application successfully prepares a new agricultural mulch film with high strength, excellent agronomic function and complete biodegradability through the synergistic innovation of the microstructure design of the bamboo pulp paper substrate layer, the interfacial modification of the homologous PHA aqueous emulsion and the wet-against-hot non-adhesive compounding process.

[0205] Those skilled in the art should understand that the above examples are only exemplary and are not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement, etc. of the technical solutions of the present application within the spirit and principles of the present application shall be included in the protection scope of the present application.

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 infiltrated with water-based PHA after creping treatment; 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 homologous internally stable emulsion is prepared by the following method: PHA grafted anhydride is obtained by 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 the homologous internally stable emulsion; The homologous internally stable emulsion has a solid content of 35–45 wt%, a pH of 6.5–8.0, and a viscosity of 50–400 mPa·s at 25°C. 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 the extruded film layer is black opaque film, it contains 0.5–1.0 wt% of low polycyclic aromatic hydrocarbon carbon-based pigment; when the extruded film layer 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 the extruded film layer 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 then implement PHA infiltration. When the basis weight is 160–300 g / m², perform micro-cutting or edge creasing treatment. Step 2. Coating the soil surface: Apply the same family of internally stabilized emulsion 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 3. 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% of anhydride monomer and 0.05wt% to 0.2wt% of initiator are added by weight. The mixture is reacted and extruded in a twin-screw extruder at 170℃ to 185℃, then underwater pelletized 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 used to prepare functional layer granules. Dry PHA homologous resins are used as functional layer raw materials, wherein the functional layer raw materials are selected from one or more of the following combinations: a mass ratio of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) of 30:70 to 90:10; or a mass ratio of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) of 30:70 to 90:10; or a mass ratio of poly(3-hydroxybutyrate) to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) of 30:70 to 90:

10. Color masterbatch or nucleating agents are added as needed. The mixture is melt-blended and extruded in a twin-screw extruder at 160°C to 180°C, then pelletized and dried to obtain functional layer granules. Step 4. Activation and lamination of the windward side: After the coating on the substrate in Step 2 is dried to an exit paper temperature ≤55℃, it is stored in an environment with a temperature of 20–30℃ and a relative humidity of 40%–60% for ≤2 hours. During this time window, the windward side of the paper substrate is subjected to corona or plasma treatment 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 3 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 5. Maturation and Slitting: The double-sided composite semi-finished product obtained in Step 4 is matured at a temperature of 20–30℃ and a relative humidity of 40%–60% for ≥24 hours and then slid 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.

Images