High-strength degradable straw paper mulch, and preparation method and application thereof

Abstract

This invention relates to a high-strength biodegradable straw paper mulch film, its preparation method, and its application. The method involves: dissociating straw mechanical pulp and preparing a pulp suspension; sequentially treating the pulp suspension with cationic starch, dialdehyde starch, and amylopectin to obtain a treated pulp; and sequentially subjecting the treated pulp to paper forming, pressing dewatering, and hot pressing to obtain a high-strength biodegradable straw paper mulch film. This invention, through the development of a starch-based composite wet-strength agent (composed of cationic starch, dialdehyde starch, and amylopectin in a specific order) and optimization of the heat treatment process, ultimately produces an environmentally friendly straw fiber mulch film with high dry and wet strength, good water resistance, and full biodegradability, effectively meeting agricultural mulch requirements.

Description

Technical Field

[0001] This invention belongs to the technical field of agricultural environmental protection materials and efficient utilization of biomass resources, and particularly relates to a high-strength biodegradable straw paper mulch film, its preparation method and application. Background Technology

[0002] Mulching technology is a crucial agronomic measure in modern agriculture, effectively conserving moisture, increasing soil temperature, and suppressing weeds, playing an irreplaceable role in improving crop yield and quality. However, the widely used traditional polyethylene (PE) plastic mulch film is non-degradable. These difficult-to-degrade film residues damage soil aggregate structure, hinder root development and water and fertilizer transport, leading to a decline in soil fertility. Measurements show that when the residual mulch film reaches 4 kg / acre, crop yield reduction can exceed 10%.

[0003] To address this challenge, developing environmentally friendly and fully biodegradable alternative mulch films has become an urgent need in the field of sustainable agricultural development. Among these, straw fiber mulch films made from crop straw are highly favored due to their renewable, widely available, low-cost, and fully biodegradable raw material characteristics. This technology not only achieves high-value resource utilization of agricultural waste (straw) and reduces environmental pollution caused by straw burning at the source, but also perfectly aligns with the development concept of green circular agriculture. Straw-derived mulch films can achieve a green closed loop of "straw recycling - mulch film production - field application - degradation and return to the field," with a degradation cycle that can be precisely controlled from 40 to 180 days and can be matched to different crop growth cycles.

[0004] However, the practical application of straw-based paper mulch film still faces a key technical bottleneck: insufficient mechanical strength, especially insufficient wet strength. After irrigation or rainfall in farmland, ordinary straw fiber mulch film with insufficient wet strength will quickly absorb water and soften, resulting in deformation, cracking, or even disintegration. Its wet strength is often only about 30% of its dry strength, thus losing its physical protection function for soil and crops, which greatly limits its application effect and scope.

[0005] To improve wet strength, researchers often add wet-strength agents. However, existing mainstream wet-strength technologies have the following significant drawbacks in green agriculture: 1. High risk of chemical pollution: Traditional wet-strength agents such as urea-formaldehyde resin (UF) and melamine-formaldehyde resin (MF) release formaldehyde during production and degradation (the free formaldehyde content in UF can reach 1.5-3.0%). Formaldehyde is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC), posing a potential threat to the soil environment, crop quality, and the health of operators, which runs counter to the original intention of environmentally friendly mulch films. Even some new synthetic resins, such as polyamide epichlorohydrin (PAE), although formaldehyde-free, may produce organochlorides (such as 1,3-dichloro-2-propanol) during their preparation, which have potential carcinogenicity and environmental persistence. Moreover, their biodegradability is poor, and the degradation cycle can take several years or more, which cannot match the degradation cycle of straw mulch films. 2. The Dilemma of Balancing Cost and Performance: While some high-efficiency synthetic wet strength agents (such as PAE) can achieve 20%-40% of the dry strength of paper, their cost is high (market price approximately 20,000-30,000 RMB / ton). Applying them to the already cost-sensitive agricultural sector would significantly increase the price of straw mulch film, making it uncompetitive in the market. Studies have shown that when the wet strength agent content exceeds 1.5% (absolute dry pulp), the cost of straw mulch film will increase significantly. 3. Limited Performance of Natural Products: Single natural polymeric wet strength agents, such as modified starch, while environmentally friendly and non-toxic, have limited strengthening effects. Studies have shown that using cationic starch alone (1% addition) can only increase the wet-to-dry strength ratio to 10-15%; while dialdehyde starch, although it can provide a certain wet strength by forming a cross-linked structure with cellulose (wet strength retention rate of approximately 15-20%), its reaction efficiency is greatly affected by pH and temperature, its performance is unstable in complex field environments, and excessive addition (>2%) will significantly increase the brittleness of the paper mulch film. 4. Impact on other key properties of mulch film: Many wet-strength agents, while increasing wet strength, sacrifice the air permeability and flexibility of the mulch film. For example, after adding certain resin-based wet-strength agents, the air permeability of the mulch film can be reduced to about 60% of that without the addition, affecting crop root respiration. At the same time, the brittleness of the paper mulch film increases, making it prone to breakage during mechanical laying, causing inconvenience in practical applications.

[0006] Therefore, developing a green enhancement technology that is efficient, non-toxic, low-cost, and compatible with the degradation cycle of straw paper mulch film is the key to breaking through its application bottlenecks and promoting its large-scale industrial application.

[0007] In summary, it is essential to provide a high-strength biodegradable straw paper mulch film, its preparation method, and its application. Summary of the Invention

[0008] To address the limitations of existing technologies in modifying straw fiber mulch films with wet-strength agents, the lack of diverse market offerings, and environmental unfriendliness leading to low strength and brittleness, this invention provides a high-strength biodegradable straw paper mulch film, its preparation method, and its applications. This invention develops a starch-based composite wet-strength agent (composed of cationic starch, dialdehyde starch, and amylopectin in a specific order) and optimizes the application process (optimizing the heat treatment process). This results in an environmentally friendly straw fiber mulch film (straw paper mulch film) with high dry and wet strength, good water resistance, and full biodegradability. This effectively meets agricultural coverage requirements while ensuring its environmental friendliness and economic feasibility throughout its entire life cycle, providing a novel technical solution for completely resolving "white pollution" in farmland.

[0009] The present invention provides a method for preparing a high-strength biodegradable straw paper mulch film in a first aspect, the method comprising the following steps: (1) The straw mechanical pulp is dissociated and prepared into a pulp suspension; (2) The pulp suspension was sequentially treated with cationic starch, dialdehyde starch and amylopectin to obtain treated pulp; (3) The pulp is subjected to paper forming, pressing and dewatering and hot pressing in sequence to obtain high-strength biodegradable straw paper film.

[0010] Preferably, in step (1): the dissociation is performed at a speed of 1000~1500 rpm for 10~15 min; the pulp suspension uses water as a dispersant; and / or the concentration of the pulp suspension is 2~5 wt%.

[0011] Preferably, in step (2): the cationic starch is tertiary amine cationic starch and / or quaternary ammonium cationic starch; the amount of cationic starch used is 1-5% of the oven-dry weight of the straw mechanical pulp, preferably 3-5%; and / or the cationic starch treatment time is 10-15 min.

[0012] Preferably, in step (2): before the dialdehyde starch treatment, the pH of the system is adjusted to 4-6, preferably 4.5-5.5, preferably using citric acid solution for pH adjustment; the amount of dialdehyde starch is 1-5% of the oven-dry weight of the straw mechanical pulp, preferably 2-3.5%; and / or the dialdehyde starch treatment time is 15-20 min.

[0013] Preferably, in step (2): the amylopectin is waxy corn starch and / or glutinous rice starch; the amount of amylopectin used is 5-12% of the oven-dry weight of the straw mechanical pulp, preferably 7-10%; and / or the amylopectin treatment time is 20-30 min.

[0014] Preferably, in step (3): the treated pulp is subjected to paper forming to obtain a dryness of 15-30% and a basis weight of 85-100 g / m³. 2 The wet paper pages.

[0015] Preferably, in step (3): the pressing and dehydration is performed at 0.2~0.4MPa for 2~5 minutes.

[0016] Preferably, in step (3): the pressure of the hot pressing treatment is 0.2~0.5MPa, the temperature is 80~120℃ (preferably 90~105℃), the time is 5~30min, and the rate of heating to the hot pressing treatment temperature is 3~8℃ / min.

[0017] In a second aspect, the present invention provides a high-strength biodegradable straw paper mulch film prepared by the preparation method described in the first aspect of the present invention.

[0018] In a third aspect, the present invention provides the application of high-strength biodegradable straw paper mulch film prepared by the preparation method described in the first aspect of the present invention in the agricultural field.

[0019] This invention innovatively employs a cationic starch-dialdehyde starch-branched starch composite wet strength agent system (combined in a specific order) and combines it with a directional heat treatment process (hot pressing), significantly improving the overall performance of straw paper mulch film. It achieves a good balance between high strength, high water resistance, and controllable degradation. Compared with existing technologies, the high-strength biodegradable straw paper mulch film prepared by this invention has at least the following beneficial effects: (1) Significant synergistic effect of composite wet strength agent: This invention found that the three types of starch exert a synergistic strengthening effect through functional complementarity. Cationic starch enhances fiber bonding through electrostatic interaction; dialdehyde starch forms water-resistant covalent crosslinks with fibers; amylopectin acts as a polymer skeleton to fill pores and enhance film-forming properties. After hot pressing, the three together construct a stable network structure, making the dry tensile index of straw paper mulch film ≥15 N·m / g, wet tensile index ≥6 N·m / g, and burst strength index ≥3.5 kPa·m 2 / g.

[0020] (2) Outstanding water resistance and moisture retention performance: The water contact angle of the paper mulch film surface is ≥105°, exhibiting a lotus leaf-like hydrophobic effect, effectively delaying water diffusion; the bulk phase impermeability is greatly improved, with a water absorption rate of ≤50% in 2 hours, which can maintain structural integrity under irrigation and rainfall conditions and reduce soil moisture evaporation.

[0021] (3) Environmentally friendly and highly applicable: No formaldehyde resin or other harmful chemical crosslinking agents are used in the entire preparation process, and the product has excellent environmental compatibility; its comprehensive mechanical and water resistance properties meet the requirements of agricultural machinery laying and soil covering operations, and it has both agricultural applicability and green sustainability. Attached Figure Description

[0022] Figure 1 This is a comparison of the dry tensile strength properties of the straw paper mulch films prepared in Examples 1-4 and Comparative Examples 1-3 of the present invention; Figure 2 This is a comparison of the wet tensile strength properties of the straw paper mulch films prepared in Examples 1-4 and Comparative Examples 1-3 of the present invention; Figure 3 This is a comparison of the bursting strength performance of the straw paper mulch films prepared in Examples 1-4 and Comparative Examples 1-3 of the present invention; Figure 4 This is the infrared spectrum of the straw paper mulch film prepared in Example 3 of the present invention; Figure 5 These are XRD comparison images of the straw paper mulch films prepared in Example 1 and Comparative Example 2 of this invention; Figure 5 The results can be compared with the crystallinity of straw paper mulch film. The crystallinity of straw paper mulch film prepared by this invention is greatly increased (Cl=48.13%). Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] The present invention provides a method for preparing a high-strength biodegradable straw paper mulch film (abbreviated as straw paper mulch film) in a first aspect, the method comprising the following steps: (1) The straw mechanical pulp is dissociated and prepared into a pulp suspension; specifically, step (1) is as follows: the dry straw mechanical pulp is placed in a standard pulp dissociator, water is added to adjust the pulp concentration to 4~8wt%, and dissociated at a speed of 1000~1500rpm for 10-15 minutes until the fibers are fully dispersed and there are no visible lumps. Then the pulp is transferred to a mixing tank, continuously stirred and water is slowly added to adjust the pulp concentration to 2~4wt% to ensure that the fibers are uniformly suspended and to avoid sedimentation or concentration stratification, so as to obtain the pulp suspension. (2) The pulp suspension is sequentially treated with cationic starch, dialdehyde starch, and amylopectin to obtain treated pulp; specifically, step (2) is, for example, adding cationic starch to the pulp suspension and stirring for 10-15 min, then adding dialdehyde starch and stirring for 15-20 min, and then adding amylopectin and stirring for 20-30 min; in this invention, unless otherwise specified, the stirring speed involved is, for example, 600-1500 rpm; the key to step (2) of this invention is that the cationic starch, dialdehyde starch, and amylopectin are added in a specific order to form a material with significant A composite wet-strength system exhibiting synergistic effects; this sequence is not directly deducible from conventional experience, but was determined by the inventors through extensive inventive experiments; the inventors discovered that the initial cationic starch treatment allows its cationic groups to preferentially adsorb onto the negatively charged fiber surface via electrostatic interactions, providing "anchoring points" for subsequent components. This prevents the addition of anionic or neutral starches (such as dialdehyde starch and amylopectin) from hindering adsorption, ensuring the "anchoring" effect and initially enhancing inter-fiber bonding; subsequently, dialdehyde starch treatment allows it to undergo irreversible covalent cross-linking with the hydroxyl groups of cellulose under suitable acidic conditions, forming hemiacetal and acetal structures. This is key to providing durable, water-resistant strength. The final amylopectin treatment avoids the steric hindrance of amylopectin affecting the effective contact and reaction between the first two starches and the fiber, allowing it to primarily function as a filler and film-forming agent. It acts mainly as a polymer filler and film-forming agent, filling the pores between fibers and gelatinizing after heat treatment to form a continuous film covering the fiber network, collectively improving dry strength and impermeability. Through this specific sequential treatment, the adsorption, cross-linking, and film-forming processes of the three starches on the fiber surface are fully utilized, producing a synergistic reinforcing effect significantly superior to any other addition order, thus achieving a comprehensive combination of high wet strength, high dry strength, and good water resistance. Performance improvement is achieved, but changing the order of addition will lead to a significant decrease in the mechanical properties of straw paper mulch film. This invention does not specifically limit the cationic starch, dialdehyde starch, and amylopectin. Those skilled in the art can make conventional choices, using products that can be purchased directly or synthesized by existing methods. For example, in some specific embodiments of this invention, the cationic starch is quaternary ammonium cationic starch, the amylopectin is waxy corn starch, the CAS number of the quaternary ammonium cationic starch used is 56780-58-6, the CAS number of the dialdehyde starch is 9047-50-1, and the CAS number of the waxy corn starch is 9005-25-8. (3) The treated pulp is subjected to paper forming, pressing and dewatering and hot pressing in sequence to obtain a high-strength biodegradable straw paper mulch film; In this invention, preferably, after the hot pressing is completed, the pressure is maintained and the hot-pressed paper is cooled to room temperature to finally obtain the finished product, that is, a high-strength biodegradable straw paper mulch film; The key to step (3) of this invention is that directional heat treatment (hot pressing) is carried out, which is fundamentally different from the simple "hot air drying" in the prior art. Hot air drying is only for the purpose of removing moisture, the temperature is usually low (<80℃), and there is no pressure or Low pressure is insufficient to effectively promote starch gelatinization and deep cross-linking with fibers. This invention places the wet paper sheet after pressing and dehydration in a hot press for hot pressing, which helps the starch to flow and distribute better among the fibers after gelatinization. Heat provides energy for the complete gelatinization of amylopectin and the thorough completion of the cross-linking reaction between dialdehyde starch and fiber / starch. If only ordinary hot air drying is performed, the starch will not be fully gelatinized and cross-linked, and the effect of the composite wet strength agent will be greatly reduced. It is expected that the wet strength can only reach less than 50% of that of hot pressing, and the water resistance will be poor.

[0025] This invention innovatively proposes a method for preparing high-strength biodegradable straw paper mulch film using straw fiber as the base material. This method is based on a starch composite wet-strength agent (composed of cationic starch, dialdehyde starch, and amylopectin in a specific order) and an optimized heat treatment process. The innovation of this method lies in abandoning traditional synthetic wet-strength agents such as PAE, and using only bio-based starch components. Through the synergistic effect of "cationic starch adsorption and anchoring - dialdehyde starch cross-linking - amylopectin filling for film formation," combined with a directional heat treatment process (hot pressing), the covalent cross-linking reaction is further promoted to achieve complete results. The aim is to increase the wet-to-dry strength ratio of the straw paper mulch film to over 35%, while ensuring its environmental friendliness and economic feasibility throughout its entire life cycle, providing a novel technical solution for completely solving "white pollution" in farmland. Although there are reports of using starch as a wet-strength agent in existing technologies, starch usually needs to be compounded with other traditional wet-strength agents. For example, CN108824073A uses cationic starch in combination with PAE resin, which has limited reinforcing effect and poses environmental risks. In contrast, this invention provides a fully bio-based, multi-component synergistic composite wet strength system and its supporting process, which fundamentally solves one or more problems of existing technologies for modifying wet strength agents for straw fiber mulch films, such as limited market variety, environmental unfriendliness leading to low strength and easy breakage of straw fiber mulch films.

[0026] In this invention, the composite wet-strength agent exhibits significant synergistic effects: This invention reveals that the three types of starch exert synergistic reinforcing effects through functional complementarity; cationic starch enhances fiber bonding through electrostatic interactions; dialdehyde starch forms water-resistant covalent crosslinks with fibers; and amylopectin acts as a polymer backbone, filling pores and enhancing film-forming properties. After hot-pressing, the three components together construct a stable network structure, resulting in a dry tensile index ≥15 N·m / g, a wet tensile index ≥6 N·m / g, and a burst strength index ≥3.5 kPa·m for the straw paper mulch film. 2 / g; In this invention, the high-strength biodegradable straw paper mulch film exhibits outstanding water resistance and moisture retention: the water contact angle on the surface of the mulch film is ≥105°, exhibiting a lotus leaf-like hydrophobic effect, effectively delaying water diffusion; the bulk impermeability is significantly improved, with a 2-hour water absorption rate ≤50%, enabling it to maintain structural integrity under irrigation and rainfall conditions and reduce soil moisture evaporation; In this invention, the high-strength biodegradable straw paper mulch film is environmentally friendly and highly applicable: the entire preparation process does not use formaldehyde-based resins or other harmful chemical crosslinking agents, resulting in excellent environmental compatibility; its comprehensive mechanical and water resistance properties meet the requirements for agricultural machinery laying and soil covering operations, combining agricultural applicability with green sustainability.

[0027] According to some preferred embodiments, in step (1): the dissociation is performed at a speed of 1000~1500 rpm (e.g., 1000, 1100, 1200, 1300, 1400 or 1500 rpm) for 10~15 min (e.g., 10, 11, 12, 13, 14 or 15 min); the pulp suspension uses water as a dispersant; and / or the concentration of the pulp suspension is 2~5 wt% (e.g., 2, 3, 4 or 5 wt%); in this invention, the concentration of the pulp suspension refers to the mass percentage of solids contained in the pulp suspension.

[0028] According to some preferred embodiments, in step (2): the cationic starch is tertiary amine cationic starch and / or quaternary ammonium cationic starch; in this invention, for example, tertiary amine cationic starch and / or quaternary ammonium cationic starch with a degree of substitution of 0.02 to 0.05 can be selected; the amount of cationic starch used is 1 to 5% (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%) of the oven-dry mass of straw mechanical pulp, preferably 3 to 5% (e.g., 3%, 3.5%, 4%, 4.5% or 5%); in this invention, the oven-dry mass of straw mechanical pulp refers to the mass of straw mechanical pulp after complete removal of moisture; and / or the cationic starch treatment time is 10 to 15 min (e.g., 10, 11, 12, 13, 14 or 15 min); in this invention, when performing cationic starch treatment, the cationic starch is added in the form of a cationic starch dispersion, the cationic starch dispersion uses water as a dispersant, and the mass fraction of cationic starch in the cationic starch dispersion is 8 to 12%.

[0029] According to some preferred embodiments, in step (2): before performing the dialdehyde starch treatment, the pH of the system is first adjusted to 4-6 (e.g., 4, 4.5, 5, 5.5 or 6), preferably 4.5-5.5 (e.g., 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4 or 5.5), preferably using a citric acid solution (citric acid aqueous solution); preferably, the dialdehyde starch is added for treatment after the pH of the system is adjusted to 4-6. This provides the optimal pH environment for the cross-linking reaction of dialdehyde starch. This acidic environment is the most suitable pH range for the subsequent cross-linking reaction between dialdehyde starch and fiber, ensuring maximum cross-linking efficiency. If the pH is too high (e.g., pH > 7.0), the cross-linking reaction is slow and inefficient, while if the pH is too low (e.g., pH < 3.5), it may cause hydrolysis of cellulose chains and damage fiber strength. This invention does not impose specific limitations on the concentration and amount of citric acid solution. Those skilled in the art can make conventional selections to adjust the pH of the system to the target range.

[0030] According to some preferred embodiments, the aldehyde content of the dialdehyde starch is ≥90%.

[0031] According to some preferred embodiments, in step (2), the amount of the dialdehyde starch is 1-5% (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%) of the oven-dry weight of the straw mechanical pulp, preferably 2-3.5% (e.g., 2%, 2.5%, 3%, or 3.5%). In this invention, it is preferred that the amount of the dialdehyde starch is 1-5% of the oven-dry weight of the straw mechanical pulp. This invention has found that if the amount added is too small (e.g., <1%), it will cause adverse reactions. Insufficient crosslinking points result in insignificant wet strength; excessive addition (>5%) leads to brittle paper and reduced flexibility; and / or the treatment time of the dialdehyde starch is 15-20 min (e.g., 15, 16, 17, 18, 19, or 20 min); in this invention, during the dialdehyde starch treatment, the dialdehyde starch is added in the form of a dialdehyde starch dispersion, the dialdehyde starch dispersion uses water as a dispersant, and the mass fraction of dialdehyde starch in the dialdehyde starch dispersion is 15-18%.

[0032] According to some preferred embodiments, in step (2): the amylopectin is waxy corn starch and / or glutinous rice starch; the amount of amylopectin used is 5-12% (e.g., 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5% or 12%) of the oven-dry weight of the straw mechanical pulp, preferably 7-10% (e.g., 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%); in this invention, it is preferred that the amount of amylopectin used is equal to the oven-dry weight of the straw mechanical pulp. The mass fraction of amylopectin is 5-12%. This invention has found that if the amount added is too small (<5%), the filling effect is poor; if it is too large (>12%), the slurry is too viscous, affecting the uniformity of the molding and increasing costs; and / or the amylopectin treatment time is 20-30 min (e.g., 20, 25, or 30 min) to ensure that all components are fully mixed and to promote cross-linking between fiber and starch. In this invention, during amylopectin treatment, the amylopectin is added in the form of an amylopectin dispersion, the amylopectin dispersion uses water as a dispersant, and the mass fraction of amylopectin in the amylopectin dispersion is 8-12%.

[0033] According to some preferred embodiments, in step (3): the treated pulp is subjected to paper forming to obtain a dryness of 15-30% and a basis weight of 85-100 g / m³. 2 The wet paper sheet; specifically, for example, the treated pulp is injected into a paper forming machine and a vacuum filter is turned on to dewater and form the paper sheet, resulting in a dryness of 20±2% and a basis weight of 95±5 g / m³. 2 The wet paper pages.

[0034] According to some preferred embodiments, in step (3): the pressing and dewatering is performed at 0.2~0.4MPa for 2~5 minutes; specifically, for example, the wet paper sheet obtained from paper forming is transferred to the pressing device and pressed at 0.3MPa pressure for 3 minutes to further dewater while improving the interfiber bonding force, resulting in a basis weight of 85~100g / m³. 2 A wet paper sheet of uniform thickness; in this invention, the pressing and dehydration is carried out at room temperature (e.g., 15~35°C).

[0035] According to some preferred embodiments, in step (3): the pressure of the hot pressing treatment is 0.2~0.5MPa, the temperature is 80~120℃ (preferably 90~105℃), the time is 5~30min, and the rate of heating to the hot pressing treatment temperature is 3~8℃ / min, which promotes the starch to fully gelatinize and form a stable cross-linked structure with the fiber; the present invention preferably performs hot pressing treatment for 5~30min at a pressure of 0.2-0.5MPa and a programmed heating rate of 3-8℃ / min to 80-120℃ (preferably 90-105℃), and the pressure helps to better integrate the starch with the fiber after gelatinization. The heat provides energy for the complete gelatinization of amylopectin and the thorough cross-linking reaction between dialdehyde starch and fiber / starch. In the hot pressing process of this invention, the pressure is preferably controlled within the range of 0.2~0.5MPa. This invention has found that if the pressure is too low, the viscosity of the gelatinized starch is high, making it difficult to fully penetrate and flow between fibers, resulting in insufficient contact between dialdehyde starch and fiber / starch, incomplete cross-linking reaction, and ultimately weak internal bonding, high porosity, and insufficient compaction of the material. This leads to a decrease in the wet strength of the formed straw paper film and makes it prone to defects such as warping or interlayer delamination. Conversely, if the pressure is too high, the gelatinized starch will be squeezed out of the fiber structure, destroying the expected component ratio and resulting in insufficient internal binder. At the same time, excessive pressure will cause the fiber structure to collapse and the pores to be over-compressed, thereby affecting the toughness and structural stability of the material. In addition, excessive pressure may hinder the normal migration and discharge of moisture during the hot pressing process, resulting in uneven distribution of internal moisture content. After cooling, problems such as bulging and cracking may occur, and it may also cause local excessive cross-linking or thermal degradation, leading to a reduction in material performance.

[0036] According to some preferred embodiments, after hot pressing in step (3), the high-strength biodegradable straw paper mulch film is naturally cooled to room temperature under a pressure of 0.2~0.5MPa to obtain the high-strength biodegradable straw paper mulch film. In this invention, it is preferable to continue to maintain a pressure of 0.2~0.5MPa during the natural cooling process after hot pressing. The continuous pressure can further promote the uniform and stable formation of the cross-linked network, which is ultimately beneficial to improving the dry tensile strength, wet tensile strength and burst resistance of the obtained straw paper mulch film.

[0037] In a second aspect, the present invention provides a high-strength biodegradable straw paper mulch film prepared by the preparation method described in the first aspect of the present invention.

[0038] In a third aspect, the present invention provides the application of high-strength biodegradable straw paper mulch film prepared by the preparation method described in the first aspect of the present invention in the agricultural field.

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, all raw materials used in the embodiments and comparative examples of the present invention can be obtained commercially or synthesized by existing methods; the cationic starch, dialdehyde starch, and amylopectin used in the following embodiments and comparative examples are the same.

[0040] Example 1 ① Place the dried rice straw mechanical pulp in a standard pulp deionizer, add deionized water to adjust the pulp concentration to 5wt%, deionize at 1200rpm for 10 minutes, then transfer the pulp to a mixing tank, continue stirring and slowly add deionized water to adjust the pulp concentration to 2.5wt%, and obtain a uniformly dispersed pulp suspension.

[0041] ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 10 min. Then adjust the pH of the system to 5.0 with citric acid aqueous solution, add dialdehyde starch dispersion and stir for 15 min. Finally, add amylopectin dispersion and continue stirring for 20 min to obtain the treated pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch. The cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of cationic starch dispersion used is such that the quaternary ammonium cationic starch... The amount of amylopectin used is 4% of the oven-dry weight of the rice straw mechanical pulp; the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of dialdehyde starch dispersion used is such that the amount of dialdehyde starch is 2% of the oven-dry weight of the rice straw mechanical pulp; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of amylopectin dispersion used is such that the amount of waxy corn starch is 8% of the oven-dry weight of the rice straw mechanical pulp.

[0042] ③ The treated pulp is injected into the paper forming machine and the vacuum filter is turned on to dewater and form the paper, resulting in a dryness of 25% and a basis weight of 90 g / m³. 2The wet paper sheet is then pressed and dehydrated in a press device at a pressure of 0.3 MPa for 3 minutes to preliminarily shape it, thus obtaining the pressed wet paper sheet.

[0043] ④ Place the pressed wet paper sheet obtained in step ③ in a hot press device, raise the temperature to 95°C at a programmed rate of 5°C / min under a pressure of 0.3MPa, and hot press at 95°C for 25 minutes. After the hot pressing is completed, allow it to cool naturally to room temperature while maintaining a pressure of 0.3MPa, and take it out to obtain a high-strength biodegradable straw paper film.

[0044] Performance testing: The dry tensile index of the high-strength biodegradable straw paper mulch film prepared in this embodiment was measured to be 16.1 N·m / g, the wet tensile index to be 6.5 N·m / g, and the bursting index (bursting strength) to be 4.8 kPa·m. 2 With a water contact angle of 107° and a water absorption rate of 45% after 2 hours, it possesses excellent mechanical properties, water resistance, and moisture retention.

[0045] Example 2 ① Place the dried corn stalk mechanical pulp in a standard pulp deionizer, add deionized water to adjust the pulp concentration to 5wt%, deionize at 1300rpm for 12 minutes, then transfer the pulp to a mixing tank, continue stirring and slowly add deionized water to adjust the pulp concentration to 2.8wt%, and obtain a uniformly dispersed pulp suspension.

[0046] ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 12 min. Then adjust the pH of the system to 4.8 with citric acid aqueous solution, add dialdehyde starch dispersion and stir for 18 min. Finally, add amylopectin dispersion and continue stirring for 25 min to obtain the treated pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch. The cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of cationic starch dispersion used is such that the quaternary ammonium cationic starch... The amount of amylopectin used is 5% of the oven-dry weight of the corn stalk mechanical pulp; the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of the dialdehyde starch dispersion is such that the amount of dialdehyde starch is 3% of the oven-dry weight of the corn stalk mechanical pulp; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of the amylopectin dispersion is such that the amount of waxy corn starch is 9% of the oven-dry weight of the corn stalk mechanical pulp.

[0047] ③ The treated pulp is injected into the paper forming machine and the vacuum filter is turned on to dewater and form the paper, resulting in a dryness of 26% and a basis weight of 92 g / m³. 2The wet paper sheet is then pressed and dehydrated in a press device at a pressure of 0.35 MPa for 4 minutes to preliminarily shape it, thus obtaining the pressed wet paper sheet.

[0048] ④ Place the pressed wet paper sheet obtained in step ③ in a hot press device, raise the temperature to 98°C at a programmed rate of 5°C / min under a pressure of 0.35MPa, and hot press at 98°C for 28 minutes. After the hot pressing is completed, allow it to cool naturally to room temperature while maintaining a pressure of 0.35MPa, and take it out to obtain a high-strength biodegradable straw paper film.

[0049] Performance testing: The dry tensile index of the high-strength biodegradable straw paper mulch film prepared in this embodiment was measured to be 16.8 N·m / g, the wet tensile index was 6.9 N·m / g, and the bursting index (bursting strength) was 4.7 kPa·m. 2 With a water contact angle of 109° and a water absorption rate of 42% after 2 hours, it has excellent mechanical properties, water resistance, and moisture retention.

[0050] Example 3 ① Place the dried cotton stalk mechanical pulp in a standard pulp deionizer, add deionized water to adjust the pulp concentration to 5wt%, deionize at 1400rpm for 15 minutes, then transfer the pulp to a mixing tank, continue stirring and slowly add deionized water to adjust the pulp concentration to 3.0wt%, and obtain a uniformly dispersed pulp suspension.

[0051] ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 15 min. Then adjust the pH of the system to 4.6 with citric acid aqueous solution, add dialdehyde starch dispersion and stir for 20 min. Finally, add amylopectin dispersion and continue stirring for 30 min to obtain the treated pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch. The cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of cationic starch dispersion used is such that the quaternary ammonium cationic starch... The amount of amylopectin used is 4.5% of the oven-dry weight of the cotton stalk mechanical pulp; the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of dialdehyde starch dispersion is such that the amount of dialdehyde starch is 3.5% of the oven-dry weight of the cotton stalk mechanical pulp; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of amylopectin dispersion is such that the amount of waxy corn starch is 9.5% of the oven-dry weight of the cotton stalk mechanical pulp.

[0052] ③ The treated pulp is injected into the paper forming machine and the vacuum filter is turned on to dewater and form the paper sheet, resulting in a dryness of 28% and a basis weight of 95 g / m³. 2The wet paper sheet is then pressed and dehydrated in a press device at a pressure of 0.4 MPa for 5 minutes to preliminarily shape it, thus obtaining the pressed wet paper sheet.

[0053] ④ Place the pressed wet paper sheet obtained in step ③ in a hot press device, raise the temperature to 100℃ at a programmed rate of 5℃ / min under a pressure of 0.4MPa, and hot press at 100℃ for 30 minutes. After the hot pressing is completed, allow it to cool naturally to room temperature while maintaining a pressure of 0.4MPa, and take it out to obtain a high-strength biodegradable straw paper mulch film.

[0054] Performance testing: The dry tensile index of the high-strength biodegradable straw paper mulch film prepared in this embodiment was measured to be 17.5 N·m / g, the wet tensile index was 7.2 N·m / g, and the bursting index (bursting strength) was 5.0 kPa·m. 2 / g, with a water contact angle of 110° and a water absorption rate of 40% in 2 hours. The cotton stalk paper mulch film exhibits optimal comprehensive performance, and its fiber structure characteristics give the finished product higher mechanical strength and better water resistance.

[0055] Example 4 ① Mix dried rice straw mechanical pulp, dried corn straw mechanical pulp, and dried cotton stalk mechanical pulp in a mass ratio of 1:1:1 and place them in a standard pulp decontaminator. Add deionized water to adjust the pulp concentration to 5wt% and decontaminate at 1350rpm for 14 minutes. Then transfer the pulp to a mixing tank, continue stirring and slowly add deionized water to adjust the pulp concentration to 2.8wt% to obtain a uniformly dispersed pulp suspension.

[0056] ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 13 min. Then adjust the pH of the system to 4.7 with citric acid aqueous solution, add dialdehyde starch dispersion and stir for 18 min. Finally, add amylopectin dispersion and continue stirring for 28 min to obtain the treated pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch. The cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of cationic starch dispersion used is such that the amount of quaternary ammonium cationic starch is... The amount of the dialdehyde starch dispersion is 4.2% of the sum of the oven-dry weights of the three mechanical pulps in step ①; the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of the dialdehyde starch dispersion is such that the amount of the dialdehyde starch is 3.2% of the sum of the oven-dry weights of the three mechanical pulps in step ①; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of the amylopectin dispersion is such that the amount of the waxy corn starch is 9.2% of the sum of the oven-dry weights of the three mechanical pulps in step ①.

[0057] ③ The treated pulp is injected into the paper forming machine and the vacuum filter is turned on to dewater and form the paper sheet, resulting in a dryness of 27% and a basis weight of 93 g / m³. 2 The wet paper sheet is then pressed and dehydrated in a press device at a pressure of 0.38 MPa for 4.5 minutes to preliminarily shape it, thus obtaining the pressed wet paper sheet.

[0058] ④ Place the pressed wet paper sheet obtained in step ③ in a hot press device, raise the temperature to 99°C at a programmed rate of 5°C / min under a pressure of 0.38MPa, and hot press at 99°C for 28 minutes. After the hot pressing is completed, allow it to cool naturally to room temperature while maintaining a pressure of 0.38MPa, and take it out to obtain a high-strength biodegradable straw paper film.

[0059] Performance testing: The dry tensile index of the high-strength biodegradable straw paper mulch film prepared in this embodiment was measured to be 17.2 N·m / g, the wet tensile index was 7.0 N·m / g, and the bursting index (bursting strength) was 4.9 kPa·m. 2 / g, with a water contact angle of 109° and a water absorption rate of 41% in 2 hours. In this embodiment, the mixed straw paper mulch film combines the advantages of various straw raw materials, significantly reducing raw material costs while ensuring performance, and exhibiting good performance stability and process adaptability.

[0060] Example 5 Example 5 is basically the same as Example 1, except that: ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 10 min. Then adjust the pH of the system to 3.5 with citric acid aqueous solution, add dialdehyde starch dispersion and stir for 15 min. Finally, add amylopectin dispersion and continue stirring for 20 min to obtain the treated pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch. The cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of cationic starch dispersion used is such that the quaternary ammonium cationic starch... The amount of starch used is 4% of the oven-dry weight of the rice straw mechanical pulp; the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of the dialdehyde starch dispersion is such that the amount of dialdehyde starch is 0.8% of the oven-dry weight of the rice straw mechanical pulp; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of the amylopectin dispersion is such that the amount of waxy corn starch is 4% of the oven-dry weight of the rice straw mechanical pulp.

[0061] Performance testing: The dry tensile index of the high-strength biodegradable straw paper mulch film prepared in this embodiment was measured to be 9.5 N·m / g, and the wet tensile index was 2.8 N·m / g.

[0062] Example 6 Example 6 is basically the same as Example 1, except that: ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 10 minutes, then add dialdehyde starch dispersion and stir for 15 minutes, and finally add amylopectin dispersion and continue stirring for 20 minutes to obtain the treated pulp; wherein, the cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch, and the cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch, and the amount of cationic starch dispersion used is such that the amount of quaternary ammonium cationic starch is equal to the amount of rice The dry weight of the straw mechanical pulp is 4%; the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of the dialdehyde starch dispersion is such that the amount of dialdehyde starch is 6% of the dry weight of the rice straw mechanical pulp; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of the amylopectin dispersion is such that the amount of waxy corn starch is 13% of the dry weight of the rice straw mechanical pulp.

[0063] Performance testing: The dry tensile index of the high-strength biodegradable straw paper mulch film prepared in this embodiment was measured to be 12.8 N·m / g, and the wet tensile index was 3.5 N·m / g.

[0064] Example 7 Example 7 is basically the same as Example 1, except that: ④ Place the pressed wet paper sheet obtained in step ③ in a hot press device, raise the temperature to 95°C at a programmed rate of 5°C / min under a pressure of 0.3MPa, and hot press at 95°C for 25 minutes. After the hot pressing is completed, release the pressure and allow it to cool naturally to room temperature. Take it out to obtain a high-strength biodegradable straw paper mulch film.

[0065] Performance testing: The dry tensile index of the high-strength biodegradable straw paper mulch film prepared in this embodiment was measured to be 14.9 N·m / g, and the wet tensile index was 5.5 N·m / g.

[0066] Comparative Example 1 This comparative example provides a plastic mulch film, manufactured by Zhejiang Jialemi Horticulture Technology Co., Ltd.; model: PBAT biodegradable plastic.

[0067] The dry tensile index of the plastic mulch film was measured to be 15 N·m / g, the wet tensile index to be 8 N·m / g, and the bursting index to be 4.0 kPa·m. 2 / g, with a water contact angle of 90°.

[0068] Comparative Example 2 The preparation of the straw paper mulch in this comparative example is as follows: Dry rice straw mechanical pulp is prepared and dissociated. The dissociated pulp is then formed using a paper machine. After hot air drying to remove excess moisture, the final straw paper mulch is obtained.

[0069] The dry tensile index of the straw-paper mulch film in this comparative example was measured to be 2 N·m / g, the wet tensile index to be 0.5 N·m / g, and the bursting index to be 2.5 kPa·m. 2 / g, water contact angle is 95°, and water absorption rate is 60% after 2 hours.

[0070] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that: ② Add polyamide epichlorohydrin resin wet strength agent (PAE wet strength agent) to the pulp suspension obtained in step ① and stir continuously for 45 minutes to obtain the treated pulp; wherein, the amount of polyamide epichlorohydrin resin wet strength agent (PAE wet strength agent) is 4% of the oven-dry weight of the rice straw mechanical pulp.

[0071] The dry tensile index of the straw-paper mulch film in this comparative example was measured to be 8 N·m / g, the wet tensile index to be 4.2 N·m / g, and the bursting index to be 3.9 kPa·m. 2 / g, water contact angle is 95°, and water absorption rate is 55% after 2 hours.

[0072] Comparative Example 4 ①The steps are the same as in Example 1.

[0073] ② The pulp suspension is injected into the paper forming machine and the vacuum filter is turned on to dewater and form the paper sheet, resulting in a dryness of 25% and a basis weight of 90 g / m³. 2 The wet paper sheet is then pressed and dehydrated in a press device at a pressure of 0.3 MPa for 3 minutes to preliminarily shape it, thus obtaining the pressed wet paper sheet.

[0074] ③ The pressed wet paper sheet obtained in step ② is placed in a hot press device and heated to 95°C at a programmed temperature of 5°C / min under a pressure of 0.3MPa. It is then hot-pressed at 95°C for 25 minutes. After the hot pressing is completed, it is naturally cooled to room temperature while maintaining a pressure of 0.3MPa to obtain a high-strength biodegradable straw paper mulch film.

[0075] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 2.1 N·m / g, and the wet tensile index was 0.5 N·m / g.

[0076] Comparative Example 5 Comparative Example 5 is basically the same as Example 1, except that: Step ② is as follows: Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 10 minutes to obtain the treated pulp; wherein, the cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch, the cationic starch dispersion contains 10wt% quaternary ammonium cationic starch, and the amount of cationic starch dispersion is such that the amount of quaternary ammonium cationic starch is 4% of the oven-dry weight of the rice straw mechanical pulp.

[0077] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 4.5 N·m / g, the wet tensile index was 1.2 N·m / g, and the bursting index (bursting strength) was 2.9 kPa·m. 2 / g, with a water absorption rate of 57% after 2 hours. The data of the straw paper mulch film prepared in this comparative example are significantly lower than those in Example 1, which proves the necessity of the ternary composite system and the limited effect of adding a single cationic starch.

[0078] Comparative Example 6 Comparative Example 6 is basically the same as Example 1, except that: ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 10 min. Then adjust the pH of the system to 5.0 with citric acid aqueous solution and add dialdehyde starch dispersion and stir for 15 min to obtain the treated pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch. The cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of cationic starch dispersion is such that the amount of quaternary ammonium cationic starch is 4% of the oven-dry weight of the rice straw mechanical pulp. The dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1. The amount of dialdehyde starch dispersion is such that the amount of dialdehyde starch is 2% of the oven-dry weight of the rice straw mechanical pulp.

[0079] The dry tensile index of the straw paper mulch film in this comparative example was measured to be 7.3 N·m / g, and the wet tensile index was 3.8 N·m / g.

[0080] This comparative example uses a composite wet strength agent of 4% cationic starch + 2% dialdehyde starch. Although the crosslinking of dialdehyde starch contributes significantly to wet strength compared to adding only 4% cationic starch as a wet strength agent, the dry strength, wet strength and toughness are still far inferior to the ternary composite wet strength agent system in this invention.

[0081] Comparative Example 7 Comparative Example 7 is basically the same as Example 1, except that: ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 10 min, then add amylopectin dispersion and continue stirring for 20 min to obtain the treated pulp; wherein, the cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch, the cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch, and the amount of cationic starch dispersion is such that the amount of quaternary ammonium cationic starch is 4% of the oven-dry weight of the rice straw mechanical pulp; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of amylopectin dispersion is such that the amount of waxy corn starch is 8% of the oven-dry weight of the rice straw mechanical pulp.

[0082] Performance testing: The dry tensile index of the straw paper film prepared in this comparative example was measured to be 14.0 N·m / g, and the wet tensile index was 2.5 N·m / g. This comparative example shows that amylopectin significantly improves dry strength, but lacks cross-linking and has poor wet strength.

[0083] Comparative Example 8 Comparative Example 8 is basically the same as Example 1, except that: ② Adjust the pH of the pulp suspension obtained in step ① to 5.0 with citric acid aqueous solution, add the dialdehyde starch dispersion and stir for 15 min, then add the amylopectin dispersion and continue stirring for 20 min to obtain the treated pulp; wherein, the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of the dialdehyde starch dispersion is such that the amount of the dialdehyde starch is 2% of the oven-dry weight of the rice straw mechanical pulp; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of the amylopectin dispersion is such that the amount of the waxy corn starch is 8% of the oven-dry weight of the rice straw mechanical pulp.

[0084] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 10.8 N·m / g, and the wet tensile index was 4.8 N·m / g.

[0085] Comparative Example 9 Comparative Example 9 is basically the same as Example 1, except that: ② Add amylopectin dispersion to the pulp suspension obtained in step ① and stir continuously for 20 minutes. Then adjust the pH of the system to 5.0 with citric acid aqueous solution, add dialdehyde starch dispersion and stir for 15 minutes. Finally, add cationic starch dispersion and continue stirring for 10 minutes to obtain the treated pulp. The amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1. The amount of amylopectin dispersion used is such that the amount of waxy corn starch is 8% of the oven-dry weight of the rice straw mechanical pulp. The dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1. The amount of the dialdehyde starch dispersion is such that the amount of dialdehyde starch is 2% of the oven-dry weight of the rice straw mechanical pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch. The cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of the cationic starch dispersion is such that the amount of quaternary ammonium cationic starch is 4% of the oven-dry weight of the rice straw mechanical pulp.

[0086] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 12.0 N·m / g, and the wet tensile index was 3.9 N·m / g.

[0087] Comparative Example 10 Comparative Example 10 is basically the same as Example 1, except that: ② Add amylopectin dispersion to the pulp suspension obtained in step ① and stir continuously for 20 minutes. Then add cationic starch dispersion and continue stirring for 10 minutes. Finally, adjust the pH of the system to 5.0 with citric acid aqueous solution, then add dialdehyde starch dispersion and stir for 15 minutes to obtain the treated pulp. The amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1. The amount of amylopectin dispersion used is such that the amount of waxy corn starch is 8% of the oven-dry weight of the rice straw mechanical pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch, and the cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of the cationic starch dispersion is such that the amount of quaternary ammonium cationic starch is 4% of the oven-dry weight of the rice straw mechanical pulp. The dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1. The amount of the dialdehyde starch dispersion is such that the amount of dialdehyde starch is 2% of the oven-dry weight of the rice straw mechanical pulp.

[0088] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 12.0 N·m / g, and the wet tensile index was 4.0 N·m / g.

[0089] Comparative Example 11 Comparative Example 11 is basically the same as Example 1, except that: ② Add cationic starch dispersion to the pulp suspension obtained in step ① and stir continuously for 10 min. Then add amylopectin dispersion and continue stirring for 20 min. Finally, adjust the pH of the system to 5.0 with citric acid aqueous solution, then add dialdehyde starch dispersion and stir for 15 min to obtain the treated pulp. The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch. The cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of cationic starch dispersion used is such that the quaternary ammonium cationic starch... The amount of amylopectin used is 4% of the oven-dry weight of the rice straw mechanical pulp; the amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of the amylopectin dispersion is such that the amount of waxy corn starch is 8% of the oven-dry weight of the rice straw mechanical pulp; the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of the dialdehyde starch dispersion is such that the amount of dialdehyde starch is 2% of the oven-dry weight of the rice straw mechanical pulp.

[0090] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 14.5 N·m / g, and the wet tensile index was 4.5 N·m / g.

[0091] Comparative Example 12 Comparative Example 12 is basically the same as Example 1, except that: ② After adjusting the pH of the pulp suspension obtained in step ① to 5.0 with citric acid aqueous solution, add the dialdehyde starch dispersion and stir for 15 min, then add the cationic starch dispersion and continue stirring for 10 min, and finally add the amylopectin dispersion and continue stirring for 20 min to obtain the treated pulp; wherein, the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of the dialdehyde starch dispersion is such that the amount of dialdehyde starch is 2% of the oven-dry weight of the rice straw mechanical pulp; The cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch, and the cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch. The amount of the cationic starch dispersion is such that the amount of quaternary ammonium cationic starch is 4% of the oven-dry weight of the rice straw mechanical pulp. The amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of the amylopectin dispersion is such that the amount of waxy corn starch is 8% of the oven-dry weight of the rice straw mechanical pulp.

[0092] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 14.2 N·m / g, and the wet tensile index was 4.8 N·m / g.

[0093] Comparative Example 13 Comparative Example 13 is basically the same as Example 1, except that: ② After adjusting the pH of the pulp suspension obtained in step ① to 5.0 with citric acid aqueous solution, add the dialdehyde starch dispersion and stir for 15 min, then add the amylopectin dispersion and continue stirring for 20 min, and finally add the cationic starch dispersion and continue stirring for 10 min to obtain the treated pulp; wherein, the dialdehyde starch dispersion is formed by uniformly dispersing water and dialdehyde starch (aldehyde content 92%) at a mass ratio of 5:1, and the amount of the dialdehyde starch dispersion is such that the amount of dialdehyde starch is 2% of the oven-dry weight of the rice straw mechanical pulp; The amylopectin dispersion is formed by uniformly dispersing water and waxy corn starch at a mass ratio of 10:1, and the amount of the amylopectin dispersion is such that the amount of waxy corn starch is 8% of the oven-dry weight of the rice straw mechanical pulp; the cationic starch dispersion is formed by uniformly dispersing water and quaternary ammonium cationic starch, and the cationic starch dispersion contains 10 wt% quaternary ammonium cationic starch, and the amount of the cationic starch dispersion is such that the amount of quaternary ammonium cationic starch is 4% of the oven-dry weight of the rice straw mechanical pulp.

[0094] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 11.5 N·m / g, and the wet tensile index was 5.0 N·m / g.

[0095] Comparing Comparative Examples 9-13 with Example 1, it can be seen that changing the order of adding cationic starch, dialdehyde starch, and amylopectin has a significant impact on the mechanical properties of the final straw paper mulch film. The present invention uses a specific order of adding cationic starch, dialdehyde starch, and amylopectin to form a composite wet strength system with a significant synergistic effect. If the order of addition is changed, the mechanical properties of the straw paper mulch film will decrease significantly.

[0096] Comparative Example 14 Comparative Example 14 is basically the same as Example 1, except that: ④ The pressed wet paper sheet obtained in step ③ is dried in hot air at 95℃ for 25 minutes, and then naturally cooled to room temperature to obtain straw paper mulch film.

[0097] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 10.0 N·m / g, and the wet tensile index was 2.0 N·m / g. This comparative example illustrates that the hot pressing process of the present invention has a crucial impact on the performance of the straw paper mulch film.

[0098] Comparative Example 15 Comparative Example 15 provides a biodegradable paper mulch film according to Example 3 of CN108824073A.

[0099] Performance testing: The dry tensile index of the straw paper mulch film prepared in this comparative example was measured to be 9.5 N·m / g, and the wet tensile index was 2.0 N·m / g.

[0100] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-strength biodegradable straw paper mulch film, characterized in that, The method includes the following steps: (1) The straw mechanical pulp is dissociated and prepared into a pulp suspension; (2) The pulp suspension is sequentially treated with cationic starch, dialdehyde starch and amylopectin to obtain treated pulp; the cationic starch is quaternary ammonium cationic starch; the amylopectin is waxy corn starch; (3) The pulp is subjected to paper forming, pressing and dewatering and hot pressing in sequence to obtain high-strength biodegradable straw paper film.

2. The preparation method according to claim 1, characterized in that, In step (1): The dissociation is performed at a rotation speed of 1000~1500 rpm for 10~15 minutes; The pulp suspension uses water as a dispersant; The concentration of the pulp suspension is 2-5 wt%.

3. The preparation method according to claim 1, characterized in that, In step (2): The amount of cationic starch used is 1-5% of the oven-dry weight of the straw mechanical pulp; and / or The cationic starch treatment time is 10-15 minutes.

4. The preparation method according to claim 3, characterized in that, In step (2): The amount of cationic starch used is 3-5% of the oven-dry weight of the straw mechanical pulp.

5. The preparation method according to claim 1, characterized in that, In step (2): Before performing the dialdehyde starch treatment, the pH of the system should be adjusted to 4-6. The amount of the dialdehyde starch used is 1-5% of the oven-dry weight of the straw mechanical pulp; The treatment time for the dialdehyde starch is 15-20 minutes.

6. The preparation method according to claim 5, characterized in that, In step (2): Before performing the dialdehyde starch treatment, the pH of the system should be adjusted to 4.5-5.

5.

7. The preparation method according to claim 5, characterized in that: pH adjustment was performed using citric acid solution.

8. The preparation method according to claim 5, characterized in that, In step (2): The amount of the dialdehyde starch used is 2 to 3.5% of the oven-dry weight of the straw mechanical pulp.

9. The preparation method according to claim 1, characterized in that, In step (2): The amount of amylopectin used is 5-12% of the oven-dry weight of the straw mechanical pulp; and / or The amylopectin treatment time is 20-30 minutes.

10. The preparation method according to claim 9, characterized in that, In step (2): The amount of amylopectin used is 7-10% of the oven-dry weight of the straw mechanical pulp.

11. The preparation method according to claim 1, characterized in that, In step (3): The treated pulp is then used for paper forming to obtain paper sheets with a dryness of 15-30% and a basis weight of 85-100 g / m³. 2 The wet paper pages.

12. The preparation method according to claim 1, characterized in that, In step (3): The pressing and dehydration process involves pressing and dehydrating at 0.2~0.4MPa for 2~5 minutes.

13. The preparation method according to claim 1, characterized in that, In step (3): The hot pressing process is carried out at a pressure of 0.2~0.5MPa, a temperature of 80~120℃, a time of 5~30min, and a heating rate of 3~8℃ / min to the hot pressing temperature.

14. The preparation method according to claim 13, characterized in that, In step (3): The hot pressing temperature is 90~105℃.

15. A high-strength biodegradable straw paper mulch film prepared by any one of claims 1 to 14.

16. The application of high-strength biodegradable straw paper mulch film prepared by any one of claims 1 to 14 in the agricultural field.

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