High-strength and high-toughness chemical fertilizer packaging bag and preparation process thereof

Abstract

The application discloses a high-strength and high-toughness chemical fertilizer packaging bag and a preparation process thereof, and relates to the technical field of high polymer materials. The packaging bag prepared by the application is a five-layer co-extrusion blow molding film structure, and comprises, from outside to inside, a surface layer, a secondary surface layer, a core layer, a secondary inner layer and an inner layer in sequence, and an interface layer with rigidity and flexibility, a multi-dimensional physical cross-linking network and a dynamic reversible bond self-repairing structure are constructed, so that the problems of easy agglomeration of inorganic fillers, insufficient chemical corrosion resistance and weak interlayer adhesion are effectively improved. The packaging bag has high tensile strength, high puncture toughness and excellent environmental stress cracking resistance, and is suitable for high-strength packaging of various chemical fertilizers.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a high-strength, high-toughness fertilizer packaging bag and its preparation process. Background Technology

[0002] Heavy-duty packaging bags, as a primary packaging form for solid chemical products, are widely used in the packaging and transportation of bulk materials such as fertilizers, synthetic resins, and catalysts. With the development of the fertilizer industry and the improvement of packaging automation, the performance requirements for packaging bags are becoming increasingly stringent. During use and distribution, fertilizer packaging bags not only need to withstand the impact of filling, the static pressure of stacking, and the effects of drops, tearing, and punctures during handling, but also require long-term direct contact with fertilizers. Fertilizers have complex compositions, often containing nitrogen, phosphorus, potassium salts, and various trace elements. Some fertilizer particles are sharp, highly hygroscopic, and may release corrosive acidic or alkaline small molecules in humid environments. This necessitates that packaging materials possess high strength and toughness, as well as excellent resistance to environmental stress cracking and chemical corrosion.

[0003] Currently, heavy-duty packaging film materials are mainly resin-based, prepared through multi-layer co-extrusion blow molding. To improve the mechanical properties of packaging films, existing technologies often employ blends of metallocene polyethylene and high-density polyethylene, or add inorganic rigid particles for filler modification. For example, Chinese patent CN114573893B discloses a composite material for the middle layer of a heavy-duty packaging film, which enhances film strength by adding inorganic fillers such as nano-sized talc, silica, and titanium dioxide. However, the interfacial compatibility between inorganic fillers and the polyolefin matrix may be poor, and simple physical blending can easily lead to filler agglomeration, forming stress concentration points that may become the initiation point for material failure. Chinese patent CN117183517B improves puncture resistance by adding nano-organic montmorillonite and nano-silica sol to the polyethylene matrix, but there may be competitive compatibilization effects between different nanoparticles, making dispersion difficult to guarantee, and the feasibility of the sol morphology in high-temperature extrusion processing is questionable.

[0004] In recent years, some studies have attempted to use biodegradable polyester materials as the core layer of packaging films, aiming to improve mechanical properties while also considering environmental protection. Polybutylene terephthalate (PET) has attracted widespread attention due to its good flexibility and processing performance, while polylactic acid (PLA) is used as a reinforcing component due to its high modulus and rigidity. However, polyester materials still face technical challenges in practical applications. On the one hand, PET and PLA have poor compatibility, and simple blending easily leads to phase separation, forming a distinct two-phase interface that becomes a stress concentration point under stress, making it difficult to achieve an effective balance between rigidity and toughness. On the other hand, the hydrolytic properties of some polyester materials mean that in the potentially humid environment of fertilizer packaging and when exposed to acidic or alkaline substances, ester bonds are prone to hydrolytic breakage, leading to accelerated deterioration of material properties.

[0005] Regarding the problem of chemical corrosion in fertilizer packaging, existing technologies have not yet proposed effective solutions or improvements. On the one hand, polyolefin materials themselves have limited tolerance to polar substances and are prone to environmental stress cracking when in contact with electrolyte solutions for a long time. On the other hand, polar layer materials introduced to improve barrier performance, such as nylon and ethylene-vinyl alcohol copolymers, can improve gas barrier properties, but their adhesion to the polyolefin layer is weak, making them prone to delamination failure under fertilizer corrosion and transportation stress. Chinese patent CN115891358B uses a five-layer co-extrusion structure to achieve light-shielding and UV protection through a black masterbatch interlayer, but it does not address improvements in chemical corrosion resistance. Chinese patent CN108925327A adds rare earth compounds to agricultural mulch films to improve optical properties, but such highly reactive components may react with fertilizer components in a fertilizer environment, accelerating material aging.

[0006] Furthermore, existing technologies suffer from functional overlap and interface defects in multilayer structural designs. The functional positioning of the outer layer, sub-outer layer, core layer, sub-inner layer, and inner layer is ambiguous, and the significant differences in melt flow rates between layers lead to mismatched processing rheological behavior, making the film prone to microphase separation or insufficient interlayer bonding. While Chinese patent CN116970234A introduces antistatic reinforcing masterbatch into the outer layer, its "cavitation reinforcement" theory does not conform to conventional understanding of polymer reinforcement mechanisms, and the interface defect problem caused by the stacking of various inorganic fillers remains unresolved.

[0007] In summary, developing a fertilizer packaging bag that combines high strength, high toughness, excellent resistance to environmental stress cracking, long-term resistance to chemical corrosion, strong interlayer bonding, and good processing performance remains a pressing technical problem to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to provide a high-strength, high-toughness fertilizer packaging bag and its preparation process to solve the problems mentioned in the background art.

[0009] The purpose of this invention is to provide a high-strength, high-toughness fertilizer packaging bag and its preparation process. By constructing a multi-layer composite structure based on rigid-flexible interface compatibilization, multi-dimensional physical cross-linking network, and dynamic reversible bond self-healing, a polyester-based heavy-duty packaging film with high tensile strength, high puncture toughness, excellent environmental stress cracking resistance, and long-term corrosion resistance is prepared. This solves the technical problems of existing polyolefin packaging films in the background art when dealing with sharp and corrosive fertilizers, such as easy agglomeration of inorganic fillers leading to interface defects, lack of targeted chemical protection design, insufficient interlayer adhesion of multi-layer structure leading to delamination, and difficulty in balancing physical strength and corrosion resistance.

[0010] In a first aspect, the present invention provides a high-strength and high-toughness fertilizer packaging bag, comprising a five-layer co-extruded blown film structure, which, from the outside to the inside, includes a surface layer, a sub-surface layer, a core layer, a sub-inner layer, and an inner layer.

[0011] As a preferred embodiment of the present invention, the surface layer comprises the following raw materials in parts by weight: Metallocene linear low-density polyethylene has a melt flow rate (MFR, 2.16 kg, 190℃) of 1.8-2.2 g / 10 min and a density of 0.916-0.920 g / cm³. 3 The dosage is 60-80 servings; Low-density polyethylene has an MFR of 0.7-0.9 g / 10 min and a density of 0.922-0.925 g / cm³. 3 The dosage is 10-25 servings; Anti-blocking masterbatch, the effective component is 5-8 wt% synthetic silica, the carrier is low-density polyethylene, and the dosage is 3-8 parts; Smooth masterbatch, with 4-6 wt% erucamide as the active ingredient and low-density polyethylene as the carrier, and a dosage of 2-5 parts; The light stabilizer masterbatch contains 8-12 wt% of UV-944 hindered amine light stabilizer as the active ingredient, and the carrier is linear low-density polyethylene, with a dosage of 2-4 parts.

[0012] As a preferred embodiment of the present invention, the subsurface layer comprises the following raw materials in parts by weight: Linear low-density polyethylene, with an MFR of 0.9-1.1 g / 10 min and a density of 0.916-0.920 g / cm³. 3 The dosage is 50-70 servings; High-density polyethylene (HDPE) has an MFR of 0.2-0.4 g / 10 min and a density of 0.952-0.956 g / cm³. 3 The dosage is 30-45 servings; High-density polyethylene grafted with maleic anhydride, with a grafting rate of 0.8-1.2% and a dosage of 4-7 parts; Ethylene-octene copolymer grafted with glycidyl methacrylate, with a grafting rate of 0.8-1.2%, and an amount of 1-3 parts; Antioxidant masterbatch, the effective component is a compound of antioxidant 1010 and antioxidant 168 (mass ratio 1:1) with an effective component of 8-12 wt%, the carrier is linear low-density polyethylene, and the dosage is 1-2 parts.

[0013] As a preferred embodiment of the present invention, the core layer comprises the following raw materials by weight: Polybutylene terephthalate (PET) has a melt flow rate (MFR, 2.16 kg, 190 °C) of 2-5 g / 10 min and a density of 1.20-1.26 g / cm³. 3 The dosage is 40-55 servings; Polylactic acid (PLA) has a melt flow rate (MFR, 2.16 kg, 190 °C) of 3-8 g / 10 min and a density of 1.24-1.26 g / cm³. 3 The dosage is 15-25 servings; Polylactic acid grafted with maleic anhydride, with a grafting rate of 0.8-1.2%, and a dosage of 2-4 parts; Ethylene-octene copolymer grafted with glycidyl methacrylate, with a grafting rate of 0.8-1.2% and an amount of 5-8 parts; Magnesium-aluminum base layer dihydroxy composite metal oxide, surface treated with sodium stearate, with a sheet diameter of 100-300 nm, and a dosage of 5-8 parts; Hydrophobically modified cellulose nanofibers, used in amounts of 2-4 parts; Polyurethane prepolymer, dosage: 0.5-2 parts; Antioxidant 1010, dosage: 0.1-0.2 parts; Antioxidant 168, dosage: 0.1-0.2 parts; Zinc stearate, dosage: 0.3-0.5 parts.

[0014] As a preferred embodiment of the present invention, the innermost layer comprises the following raw materials by weight: Linear low-density polyethylene, with an MFR of 0.9-1.1 g / 10 min and a density of 0.916-0.920 g / cm³. 3 The dosage is 70-90 servings; Metallocene linear low-density polyethylene has an MFR of 0.9-1.1 g / 10 min and a density of 0.916-0.920 g / cm³. 3 The dosage is 10-20 portions; High-density polyethylene grafted with maleic anhydride, with a grafting rate of 0.8-1.2% and a dosage of 3-5 parts; The slip masterbatch contains 4-6 wt% erucamide as the active ingredient and linear low-density polyethylene as the carrier, with a dosage of 1-3 parts.

[0015] As a preferred embodiment of the present invention, the inner layer comprises the following raw materials by weight: Metallocene linear low-density polyethylene has an MFR of 1.4-1.6 g / 10 min and a density of 0.914-0.918 g / cm³. 3 The dosage is 60-80 servings; Very low density polyethylene (VLDPE) has an MFR of 0.8-1.2 g / 10 min and a density of 0.895-0.905 g / cm³. 3 The dosage is 20-30 servings; Polyolefin elastomers with a molecular weight filtration rate (MFR) of 0.8-1.2 g / 10 min and a density of 0.865-0.875 g / cm³. 3 The dosage is 5-10 portions; Antistatic masterbatch, the effective component is 15-25wt% ethoxylated alkylamine, the carrier is linear low-density polyethylene, and the dosage is 0.5-1.5 parts; The open-ended, smooth masterbatch contains 3-6 wt% erucamide and 3-6 wt% synthetic silica compound as active ingredients, with linear low-density polyethylene as the carrier, and the dosage is 3-5 parts.

[0016] As a preferred embodiment of the present invention, the method for preparing the polyurethane prepolymer specifically includes the following steps: Polytetramethylene ether glycol was dehydrated at 100-110℃ and under a vacuum of -0.08 to -0.1 MPa for 1-2 hours, and then cooled to 70-80℃. Under nitrogen protection, isophorone diisocyanate was added, and the mixture was heated to 80-85℃ and reacted for 2-3 hours. Dibutyltin dilaurate was added, followed by bis(2-hydroxyethyl) disulfide, and the mixture was reacted again at 80-85℃ for 1-2 hours to obtain a polyurethane prepolymer, which was then kept at 60-80℃ for later use. The mass ratio of polytetramethylene ether diol, isophorone diisocyanate, dibutyltin dilaurate, and bis(2-hydroxyethyl) disulfide is 100:(93.5-102.5):(0.05-0.15):(24.5-30.5).

[0017] As a preferred embodiment of the present invention, the polytetramethylene ether diol has a molecular weight of 2000.

[0018] As a preferred embodiment of the present invention, the sodium stearate surface treatment process for the magnesium-aluminum base layer dihydroxy composite metal oxide specifically includes the following steps: The MgAl-LDO bimetallic composite oxide was dispersed in anhydrous ethanol, sodium stearate was added, and ultrasonic dispersion was carried out at 50-60℃ for 30-60 min. After filtration, the filter cake was washed with anhydrous ethanol 2-3 times, vacuum dried at 60-80℃ to constant weight, ground and sieved for later use. The mass ratio of the MgAl-LDO bimetallic composite oxide, anhydrous ethanol, and sodium stearate is (5-10):(90-95):(0.15-0.5).

[0019] As a preferred embodiment of the present invention, the method for preparing the hydrophobically modified cellulose nanocrystals specifically includes the following steps: Cellulose nanocrystals were dispersed in an aqueous ethanol solution, the pH was adjusted to 4.5-5.5 with acetic acid, KH570 silane coupling agent was added, and the mixture was ultrasonically reacted at 40-50℃ for 2-4 hours. The reaction product was centrifuged, washed 3-5 times with anhydrous ethanol, and vacuum dried at 50-60℃ to constant weight to obtain hydrophobic modified cellulose nanocrystals. The mass ratio of the cellulose nanocrystals, the ethanol aqueous solution, and the KH570 silane coupling agent is (2-5):(95-98):(0.1-0.5). The average length of the cellulose nanocrystals is 100-300 nm, and the aspect ratio is greater than 50. The ethanol aqueous solution contains 90-95% ethanol by mass.

[0020] As a preferred embodiment of the present invention, the thickness of the surface layer, sub-surface layer, core layer, sub-inner layer, and inner layer as a percentage of the total thickness of the film are respectively: 8-12%, 10-15%, 50-60%, 10-15%, and 8-12%.

[0021] As a preferred embodiment of the present invention, the average particle size of the synthetic silica in the anti-blocking masterbatch is 3-6 μm; and the purity of the erucamide in the slip masterbatch is greater than 98%.

[0022] As a preferred embodiment of the present invention, the carrier resin of the antioxidant masterbatch, antistatic masterbatch, and open slip masterbatch is linear low-density polyethylene, and the difference between its MFR and the MFR of the main linear low-density polyethylene or metallocene linear low-density polyethylene in the corresponding layer does not exceed 0.5 g / 10 min.

[0023] A second aspect of the present invention provides a process for preparing a high-strength, high-toughness fertilizer packaging bag, comprising the following steps: S1. Preparation of core layer hybrid filler-compensator masterbatch: Weigh magnesium aluminum base layer dihydroxy composite metal oxide and cellulose nanocrystals according to the formula, add them to a high-speed mixer, and mix at 60-80℃ for 8-12 min; then add ethylene-octene copolymer grafted with glycidyl methacrylate and polylactic acid grafted with maleic anhydride according to the formula, and continue mixing for 4-6 min to obtain a pre-dispersed mixture; melt-blend extrusion granulation of the pre-dispersed mixture through a co-rotating parallel twin-screw extruder, with the extruder temperature set as follows from the feed port to the die head: 120-130℃, 130-140℃, 140-150℃, 145-155℃, respectively, with a die head temperature of 150-160℃ and a screw speed of 200-400 rpm to obtain the core layer hybrid filler-compensator masterbatch; S2. Add the core layer hybrid filler-compensator masterbatch obtained in step S1, the formulated amounts of polybutylene terephthalate-adipate, polylactic acid, antioxidant 1010, antioxidant 168, and zinc stearate to a low-speed mixer and mix for 5-8 minutes. During the mixing process, spray the polyurethane prepolymer into the mixer in a mist and continue mixing for 3-5 minutes to obtain the final core layer blend. S3. Add the raw materials of the surface layer, sub-surface layer, sub-inner layer and inner layer to their respective high-speed mixers according to the formula amount, mix for 5-8 minutes to obtain the blends of each layer. S4. The final core layer blend obtained in step S2 and the surface layer, sub-surface layer, sub-inner layer, and inner layer blends obtained in step S3 are respectively fed into the five extruders corresponding to the five-layer co-extrusion blown film unit. The heating section temperature of the surface layer, sub-surface layer, sub-inner layer, and inner layer extruders is set to 160-200℃, the heating section temperature of the core layer extruder is set to 130-160℃, and the die head temperature is set to 190-200℃. The molten material is extruded after converging in the die head to form a tube blank. The film bubble is cooled and shaped using a dual-air-outlet air ring and a film bubble internal cooling system. The air ring temperature is 8-15℃, the blow-up ratio is controlled at (2.5-3.5):1, and the traction speed is adjusted according to the target film thickness. After cooling and shaping, the film bubble is folded by a herringbone plate, pulled by traction rollers, corona treated, trimmed, and wound up to obtain a high-strength and high-toughness fertilizer packaging bag.

[0024] It should be noted that the high-strength, high-toughness fertilizer packaging bag provided by this invention achieves its performance improvement through a multi-layer composite structure and the synergistic design of each layer's materials. The surface layer is a blend of high melt index metallocene linear low-density polyethylene and low-density polyethylene, with added slip agents and anti-blocking agents, which helps to provide good printability and a certain degree of weather resistance while ensuring the film's opening properties. The second surface layer incorporates a high proportion of high-density polyethylene grafted with maleic anhydride and ethylene-octene copolymer grafted with glycidyl methacrylate. The rigidity of the high-density polyethylene helps to improve the film's tensile yield strength and creep resistance, providing skeletal support for the overall structure. The introduction of the two grafted polymers helps to improve the interfacial compatibility between the high-density polyethylene and other layers. The core layer is the core functional layer, designed to construct a network structure that combines physical reinforcement and chemical protection through the interaction of multiple components. In this system, polybutylene terephthalate (PET) and polylactic acid (PLA) are blended as the matrix. The flexible segments of PET provide toughness, while the rigid segments of PLA provide strength, forming a matrix framework that combines rigidity and flexibility. Surface-treated magnesium-aluminum layered dihydroxy composite metal oxides and hydrophobically modified cellulose nanofibers interact through hydrogen bonds to form a hybrid system. The rigidity of the cellulose nanofibers helps to further improve the modulus, while the layered structure of the magnesium-aluminum layered dihydroxy composite metal oxides can extend the permeation path of gases and corrosive media. Simultaneously, its anion exchange capacity facilitates adsorption and permeation. The filler contains corrosive anions; ethylene-octene copolymer grafted with glycidyl methacrylate and polylactic acid grafted with maleic anhydride is used as a compatibilizer. The epoxy groups of glycidyl methacrylate can react with the hydroxyl groups on the filler surface and the end groups of polylactic acid, while the maleic anhydride groups are compatible with polybutylene terephthalate. Together, they form a flexible interface layer between the filler and the matrix, which helps with stress transfer and buffers internal stress; the polyurethane prepolymer containing disulfide bonds introduces dynamic reversible covalent bonds. When the film is subjected to minor damage or under the thermal action of the heat sealing process, the disulfide bonds can undergo an exchange reaction, which helps to repair micro-cracks or defects. The inner layer, as a transition layer between the core layer and the inner layer, is made of linear low-density polyethylene with a high melt index and metallocene linear low-density polyethylene, with the addition of an appropriate amount of high-density polyethylene grafted with maleic anhydride, which helps to ensure interlayer adhesion. The inner layer, as a heat-sealing layer, is made of a blend of low melt index, low density metallocene linear low-density polyethylene, ultra-low density polyethylene, and polyolefin elastomer. This helps to reduce the heat-sealing initiation temperature and improve the heat-sealing strength. At the same time, the addition of antistatic agents helps to reduce electrostatic adsorption during the filling of powder fertilizers.Overall, through its multi-scale structural design, this packaging bag exhibits high tensile strength, puncture resistance, and impact resistance on a macroscopic scale. When subjected to external forces, the rigid filler can induce crazing to absorb energy, the flexible interface layer can prevent crazing from developing into cracks, the layered filler can deflect crack propagation paths, and the dynamic disulfide bonds can repair early micro-damage. When in contact with fertilizers, the anchoring of polar small molecules by the interface layer, the adsorption of corrosive ions by the magnesium-aluminum layered dihydroxy composite metal oxide, and the blocking of the permeation path by the dense filler network work together to help delay the performance degradation of the material in a chemical environment, demonstrating good resistance to environmental stress cracking.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention introduces surface-treated magnesium-aluminum layered dihydroxy composite metal oxide and cellulose nanofibers into the core layer. The two form a hybrid network through hydrogen bonds and are uniformly dispersed in the matrix. The rigid whiskers are used to improve the tensile strength and modulus of the film, and the barrier effect of the layered dihydroxy composite metal oxide is used to extend the penetration path of corrosive media. At the same time, its anion exchange capacity can adsorb and passivate the corrosive ions that penetrate in, thereby improving the film's resistance to environmental stress cracking in fertilizer packaging environment.

[0026] (2) The present invention uses a blend of polybutylene terephthalate and polylactic acid as the matrix in the core layer to achieve a synergy between flexibility and rigidity. At the same time, ethylene-octene copolymer grafted with glycidyl methacrylate and polylactic acid grafted with maleic anhydride are used as compatibilizers. The glycidyl methacrylate groups can react with the hydroxyl groups on the filler surface and the polylactic acid end groups, while the maleic anhydride groups are compatible with polybutylene terephthalate. The two work together to build a stable interface layer between the filler and the matrix, which effectively improves the dispersibility of inorganic fillers and enhances the puncture resistance and impact toughness of the film.

[0027] (3) By introducing polyurethane prepolymer into the core layer, the reversible reaction of disulfide bonds can repair microcracks or defects generated in the early stages of processing and use when the film is subjected to minor damage or heat during the heat sealing process, thereby reducing the formation of stress concentration points and improving the long-term durability and service reliability of the film.

[0028] (4) The present invention designs a five-layer co-extrusion structure to enable the functions of each layer to work together. The core layer provides core reinforcement and protection, the sub-surface layer provides rigid skeleton support, and the inner layer ensures heat sealing performance, thus achieving high strength, high toughness and chemical corrosion resistance at the same time.

[0029] (5) The high-strength and high-toughness fertilizer packaging bag prepared by the present invention is made of polyester core layer and other polyethylene core layers. Since the core layer material belongs to the category of degradable materials, it is also easy to recycle or compost. Detailed Implementation

[0030] 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.

[0031] Preparation Example 1 The preparation method of polyurethane prepolymer specifically includes the following steps: Polytetramethylene ether glycol with a molecular weight of 2000 was dehydrated at 105°C and under a vacuum of -0.09 MPa for 2 hours, and then cooled to 75°C. Isophorone diisocyanate was added under nitrogen protection, and the mixture was heated to 80°C and reacted for 3 hours. Dibutyltin dilaurate was added, followed by bis(2-hydroxyethyl) disulfide, and the reaction was continued at 85°C for 1 hour to obtain a polyurethane prepolymer, which was then kept at 70°C for later use. The mass ratio of polytetramethylene ether diol, isophorone diisocyanate, dibutyltin dilaurate, and bis(2-hydroxyethyl) disulfide is 100:98:0.1:27.5.

[0032] Preparation Example 2 The sodium stearate surface treatment process for magnesium-aluminum base layer dihydroxy composite metal oxides specifically includes the following steps: The MgAl-LDO bimetallic composite oxide was dispersed in anhydrous ethanol, sodium stearate was added, and the mixture was ultrasonically dispersed at 55℃ for 45 min. The mixture was then filtered, the filter cake was washed three times with anhydrous ethanol, vacuum dried at 70℃ to constant weight, ground and sieved for later use. The MgAl-LDO bimetallic composite oxide was purchased from Xi'an Ruixi Biotechnology Co., Ltd.

[0033] The mass ratio of the MgAl-LDO bimetallic composite oxide, anhydrous ethanol, and sodium stearate is 7.5:92.5:0.33.

[0034] Preparation Example 3 The preparation method of hydrophobically modified cellulose nanocrystals specifically includes the following steps: Cellulose nanocrystals were dispersed in an aqueous ethanol solution with a mass fraction of 95%, the pH was adjusted to 5 with acetic acid, KH570 silane coupling agent was added, and the reaction was carried out by sonication at 45°C for 3 hours. The reaction product was centrifuged, washed 4 times with anhydrous ethanol, and dried under vacuum at 55°C to constant weight to obtain hydrophobic modified cellulose nanocrystals. The mass ratio of the cellulose nanocrystals, the aqueous ethanol solution, and the KH570 silane coupling agent is 3.5:96.5:0.3. Example

[0035] A high-strength and high-toughness fertilizer packaging bag has a five-layer co-extruded blown film structure, which includes, from the outside to the inside, an outer layer, a sub-outer layer, a core layer, a sub-inner layer, and an inner layer.

[0036] The surface layer comprises the following raw materials by weight: 70 parts of metallocene linear low-density polyethylene; 17.5 parts of low-density polyethylene; 5.5 parts of anti-blocking masterbatch; 3.5 parts of smooth masterbatch; Three parts of light stabilizer masterbatch.

[0037] The subsurface layer comprises the following raw materials by weight: 60 parts of linear low-density polyethylene; 37.5 parts of high-density polyethylene; 5.5 parts of high-density polyethylene grafted with maleic anhydride; Two parts of ethylene-octene copolymer grafted with glycidyl methacrylate; 1.5 parts antioxidant masterbatch.

[0038] As a preferred embodiment of the present invention, the core layer comprises the following raw materials by weight: 47.5 parts of polybutylene terephthalate-adipate; 10 parts polylactic acid; Three parts of polylactic acid grafted with maleic anhydride; 6.5 parts of ethylene-octene copolymer grafted with glycidyl methacrylate; 6.5 parts of magnesium-aluminum base layered dihydroxy composite metal oxide; Three parts of hydrophobically modified cellulose nanofibers; 1.3 parts of polyurethane prepolymer; Antioxidant 1010 0.15 parts; Antioxidant 168, 0.15 parts; 0.4 parts of zinc stearate.

[0039] The innermost layer comprises the following raw materials by weight: 80 parts of linear low-density polyethylene; 15 parts of metallocene linear low-density polyethylene; Four parts of maleic anhydride were grafted onto high-density polyethylene. Two parts of smooth masterbatch.

[0040] The inner layer comprises the following raw materials by weight: 70 parts of metallocene linear low-density polyethylene; 25 parts of very low density polyethylene; 7.5 parts of polyolefin elastomer; 1 part antistatic masterbatch; Four parts of open-ended, smooth masterbatch.

[0041] The percentages of the thickness of the surface layer, sub-surface layer, core layer, sub-inner layer, and inner layer relative to the total thickness of the film are 10%, 12.5%, 55%, 12.5%, and 10%, respectively.

[0042] A process for preparing a high-strength, high-toughness fertilizer packaging bag includes the following steps: S1. Preparation of core layer hybrid filler-compensator masterbatch: Weigh magnesium aluminum base layer dihydroxy composite metal oxide and cellulose nanocrystals according to the formula amount, add them to a high-speed mixer, and mix at 70℃ for 10 min; then add ethylene-octene copolymer grafted with glycidyl methacrylate and polylactic acid grafted with maleic anhydride according to the formula amount, and continue mixing for 5 min to obtain a pre-dispersed mixture; melt-blend extrusion granulation of the pre-dispersed mixture through a co-rotating parallel twin-screw extruder, with the extruder temperature set as follows from the feed port to the die head: 125℃, 135℃, 145℃, 150℃, die head temperature 155℃, screw speed 300 rpm to obtain core layer hybrid filler-compensator masterbatch; S2. Add the core layer hybrid filler-compensator masterbatch obtained in step S1, the formulated amounts of polybutylene terephthalate-adipate, polylactic acid, antioxidant 1010, antioxidant 168, and zinc stearate to a low-speed mixer and mix for 6 minutes. During the mixing process, spray the polyurethane prepolymer prepared and kept at a temperature in step S2 into the mixer in a mist and continue mixing for 4 minutes to obtain the final core layer blend. S3. Add the raw materials of the surface layer, sub-surface layer, sub-inner layer and inner layer to their respective high-speed mixers according to the formula amount, mix for 6 minutes to obtain the blends of each layer. S4. The final core layer blend obtained in step S2 and the surface layer, sub-surface layer, sub-inner layer, and inner layer blend obtained in step S3 are respectively fed into the five extruders corresponding to the five-layer co-extrusion blown film unit. The heating section temperature of the surface layer, sub-surface layer, sub-inner layer, and inner layer extruders is set to 160-200℃, the heating section temperature of the core layer extruder is set to 130-160℃, and the die head temperature is set to 190-200℃. The molten material is extruded after converging in the die head to form a tube blank. The film bubble is cooled and shaped using a dual-air-outlet air ring and a film bubble internal cooling system. The air ring temperature is 12℃, the blow-up ratio is controlled at 3:1, and the traction speed is adjusted according to the target film thickness. After cooling and shaping, the film bubble is folded by a herringbone plate, pulled by traction rollers, and then corona treated, trimmed, and wound to obtain a high-strength and high-toughness fertilizer packaging bag.

[0043] In this embodiment, some of the raw materials used are the same as those obtained in Preparation Examples 1-3, and the other examples are the same. Example

[0044] A high-strength and high-toughness fertilizer packaging bag has a five-layer co-extruded blown film structure, which includes, from the outside to the inside, an outer layer, a sub-outer layer, a core layer, a sub-inner layer, and an inner layer.

[0045] The surface layer comprises the following raw materials by weight: 60 parts of metallocene linear low-density polyethylene; 10 parts of low-density polyethylene; 3 parts of anti-blocking masterbatch; 2 parts of smooth masterbatch; Two parts of light stabilizer masterbatch.

[0046] The subsurface layer comprises the following raw materials by weight: 50 parts of linear low-density polyethylene; 30 parts high-density polyethylene; Four parts of maleic anhydride were grafted onto high-density polyethylene. One part of ethylene-octene copolymer grafted with glycidyl methacrylate; One part of antioxidant masterbatch.

[0047] As a preferred embodiment of the present invention, the core layer comprises the following raw materials by weight: 40 parts of polybutylene terephthalate-adipate; 15 parts polylactic acid; Two parts of polylactic acid grafted with maleic anhydride; 5 parts of ethylene-octene copolymer grafted with glycidyl methacrylate; Five parts of magnesium-aluminum base layered dihydroxy composite metal oxide; Two parts of hydrophobically modified cellulose nanofibers; 0.5 parts of polyurethane prepolymer; Antioxidant 1010, 0.1 parts; Antioxidant 168, 0.1 parts; 0.3 parts zinc stearate.

[0048] The innermost layer comprises the following raw materials by weight: 70 parts of linear low-density polyethylene; 10 parts of metallocene linear low-density polyethylene; Three parts of maleic anhydride were grafted onto high-density polyethylene. 1 part of smooth masterbatch.

[0049] The inner layer comprises the following raw materials by weight: 60 parts of metallocene linear low-density polyethylene; 20 parts of very low density polyethylene; 5 parts of polyolefin elastomer; 0.5 parts of antistatic masterbatch; Three parts of open-ended, smooth masterbatch.

[0050] The percentages of the thickness of the surface layer, sub-surface layer, core layer, sub-inner layer, and inner layer relative to the total thickness of the film are 10%, 12.5%, 55%, 12.5%, and 10%, respectively.

[0051] The preparation process is the same as in Example 1. Example

[0052] A high-strength and high-toughness fertilizer packaging bag has a five-layer co-extruded blown film structure, which includes, from the outside to the inside, an outer layer, a sub-outer layer, a core layer, a sub-inner layer, and an inner layer.

[0053] The surface layer comprises the following raw materials by weight: 80 parts of metallocene linear low-density polyethylene; 25 parts of low-density polyethylene; 8 parts of anti-blocking masterbatch; 5 parts of smooth masterbatch; Four parts of light stabilizer masterbatch.

[0054] The subsurface layer comprises the following raw materials by weight: 70 parts of linear low-density polyethylene; 45 parts high-density polyethylene; 7 parts of high-density polyethylene grafted with maleic anhydride; Three parts of ethylene-octene copolymer grafted with glycidyl methacrylate; Two parts of antioxidant masterbatch.

[0055] As a preferred embodiment of the present invention, the core layer comprises the following raw materials by weight: 55 parts of polybutylene terephthalate-adipate; 25 parts polylactic acid; 4 parts of polylactic acid grafted with maleic anhydride; 8 parts of ethylene-octene copolymer grafted with glycidyl methacrylate; Eight parts of magnesium-aluminum base layered dihydroxy composite metal oxide; Four parts of hydrophobically modified cellulose nanocrystals; Two parts of polyurethane prepolymer; Antioxidant 1010, 0.2 parts; Antioxidant 168, 0.2 parts; 0.5 parts zinc stearate.

[0056] The innermost layer comprises the following raw materials by weight: 90 parts of linear low-density polyethylene; 20 parts of metallocene linear low-density polyethylene; 5 parts of maleic anhydride grafted onto high-density polyethylene; 3 parts of smooth masterbatch.

[0057] The inner layer comprises the following raw materials by weight: 80 parts of metallocene linear low-density polyethylene; 30 parts of very low density polyethylene; 10 parts of polyolefin elastomer; 1.5 parts of antistatic masterbatch; Five parts of open-ended, smooth masterbatch.

[0058] The percentages of the thickness of the surface layer, sub-surface layer, core layer, sub-inner layer, and inner layer relative to the total thickness of the film are 10%, 12.5%, 55%, 12.5%, and 10%, respectively.

[0059] The preparation process is the same as in Example 1.

[0060] Comparative Example 1 The difference between this comparative example and Example 1 is that the polyurethane prepolymer prepared in Preparation Example 1 was not added to the core layer, while the remaining components and preparation process are the same as in Example 1.

[0061] Comparative Example 2 The difference between this comparative example and Example 1 is that the core layer does not contain the sodium stearate-surface-treated magnesium-aluminum base layer dihydroxy composite metal oxide prepared in Example 2, while the remaining components and preparation process are the same as in Example 1.

[0062] Comparative Example 3 The difference between this comparative example and Example 1 is that the hydrophobic modified cellulose nanocrystals prepared in Example 3 were not added to the core layer, while the remaining components and preparation process are the same as in Example 1.

[0063] test: I. Tensile property testing The test was conducted in accordance with GB / T 1040.3-2006 Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets. The specimen was a long strip with a width of 15 mm, an initial clamping distance of 50 mm, and a tensile speed of 500 mm / min. The longitudinal and transverse tensile strengths and nominal strain at break of the film were tested respectively.

[0064] II. Puncture Resistance Test The test was conducted according to the method specified in Appendix C of GB / T 10004-2008 Plastic Composite Films and Bags for Packaging - Dry Lamination and Extrusion Lamination. A sample holder with a diameter of 50 mm was used, the puncture needle diameter was 1.0 mm, the tip curvature radius was 0.5 mm, and the puncture speed was 50 mm / min. The maximum force value during the puncture process was recorded as the puncture strength, in N.

[0065] III. Dart Impact Performance Test The test was conducted according to GB / T 9639.1-2008 Test method for impact resistance of plastic films and sheets - Free-falling dart method - Part 1: Step method, using method A, with a dart diameter of 38 mm. The impact mass of the film at a 50% breakage rate was measured in g.

[0066] IV. Environmental stress cracking resistance test The test was conducted according to GB / T 1842-2008, "Environmental Stress Cracking Test Method for Polyethylene Plastics," with the following adjustments: A rectangular strip of 38mm × 13mm was cut longitudinally from the film sample. A 19mm long scratch was made along the longitudinal direction in the middle of the sample. The scratched sample was bent and placed in a sample holder, then immersed in a test tube containing a 10% urea aqueous solution (pH=8) and a 10% ammonium chloride aqueous solution (pH=5). The test tube was placed in a constant temperature water bath at 50±0.5℃. The time when cracks appeared in the sample was recorded. Ten samples were tested in each group. The time when the failure rate reached 50% was calculated and denoted as F. 50 Value, in h.

[0067] V. Summary of Results Table 1 Example 1 34.2 28.6 813 756 13.8 285 165 Example 2 32.8 27.4 794 732 13.2 270 152 Example 3 33.5 28.1 805 745 13.5 278 158 Comparative Example 1 29.6 25.2 757 711 11.4 238 112 Comparative Example 2 26.8 23.1 682 634 9.8 215 78 Comparative Example 3 27.3 23.8 710 657 10.2 220 86 VI. Discussion of Results As shown in Table 1, the high-strength, high-toughness fertilizer packaging bags prepared in Examples 1-3 of this invention possess excellent comprehensive mechanical properties and resistance to environmental stress cracking. Compared with Comparative Example 1, the examples, while maintaining high tensile strength and puncture strength, significantly extended the environmental stress cracking time, indicating that the introduction of polyurethane prepolymer helps repair microscopic defects generated during processing and use, reduces stress concentration, and thus improves the service life of the material in chemical media environments. Compared with Comparative Example 2, all mechanical property indicators of the examples were significantly improved, indicating that the magnesium-aluminum layered dihydroxy composite metal oxide treated with sodium stearate was effectively dispersed in the matrix, and its layered structure had a physical barrier effect on crack propagation and corrosive media penetration. Compared with Comparative Example 3, the tensile strength and puncture strength of the examples were significantly improved, indicating that the hydrophobically modified cellulose nanocrystals formed a rigid skeleton in the matrix, which worked synergistically with the layered dihydroxy composite metal oxide to achieve a balance between rigidity and toughness. The performance differences between Examples 1-3 were small, indicating that the technical solution of this invention has good stability and repeatability.

[0068] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0069] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the scope defined by the invention, and all such modifications and additions should fall within the protection scope of the present invention.

Claims

1. A high-strength, high-toughness fertilizer packaging bag, characterized in that: It includes a five-layer co-extruded blown film structure, which, from the outside to the inside, consists of a surface layer, a sub-surface layer, a core layer, a sub-inner layer, and an inner layer. The percentages of the thickness of the surface layer, sub-surface layer, core layer, sub-inner layer, and inner layer relative to the total film thickness are, respectively: 8-12%, 10-15%, 50-60%, 10-15%, and 8-12%. The core layer comprises the following raw materials by weight: 40-55 parts of polybutylene terephthalate-adipate; 15-25 parts of polylactic acid; 2-4 parts of polylactic acid grafted with maleic anhydride; 5-8 parts of ethylene-octene copolymer grafted with glycidyl methacrylate; 5-8 parts of magnesium-aluminum base layered dihydroxy composite metal oxide; 2-4 parts of hydrophobically modified cellulose nanofibers; 0.5-2 parts of polyurethane prepolymer; Antioxidant 1010: 0.1-0.2 parts; Antioxidant 168, 0.1-0.2 parts; 0.3-0.5 parts of zinc stearate.

2. The high-strength, high-toughness fertilizer packaging bag according to claim 1, characterized in that: The surface layer comprises the following raw materials by weight: 60-80 parts of metallocene linear low-density polyethylene; 10-25 parts of low-density polyethylene; The dosage of anti-blocking masterbatch is 3-8 parts; 2-5 parts of smooth masterbatch; 2-4 parts of light stabilizer masterbatch.

3. The high-strength, high-toughness fertilizer packaging bag according to claim 1, characterized in that: The subsurface layer comprises the following raw materials by weight: 50-70 parts of linear low-density polyethylene; 30-45 parts of high-density polyethylene; 4-7 parts of high-density polyethylene grafted with maleic anhydride; 1-3 parts of ethylene-octene copolymer grafted with glycidyl methacrylate; 1-2 parts antioxidant masterbatch.

4. The high-strength, high-toughness fertilizer packaging bag according to claim 1, characterized in that: The preparation method of the polyurethane prepolymer specifically includes the following steps: Polytetramethylene ether glycol was dehydrated at 100-110℃ and under a vacuum of -0.08 to -0.1 MPa for 1-2 hours, and then cooled to 70-80℃. Under nitrogen protection, isophorone diisocyanate was added, and the mixture was heated to 80-85℃ and reacted for 2-3 hours. Dibutyltin dilaurate was added, followed by bis(2-hydroxyethyl) disulfide, and the mixture was reacted again at 80-85℃ for 1-2 hours to obtain a polyurethane prepolymer, which was then kept at 60-80℃ for later use.

5. The high-strength, high-toughness fertilizer packaging bag according to claim 4, characterized in that: The mass ratio of polytetramethylene ether diol, isophorone diisocyanate, dibutyltin dilaurate, and bis(2-hydroxyethyl) disulfide is 100:(93.5-102.5):(0.05-0.15):(24.5-30.5).

6. The high-strength, high-toughness fertilizer packaging bag according to claim 1, characterized in that: The surface of the magnesium-aluminum base layer dihydroxy composite metal oxide is treated with sodium stearate. The specific treatment process includes: Disperse the MgAl-LDO bimetallic composite oxide in anhydrous ethanol, add sodium stearate, and ultrasonically disperse at 50-60℃ for 30-60 min; filter, wash the filter cake 2-3 times with anhydrous ethanol, vacuum dry at 60-80℃ to constant weight, grind and sieve for later use.

7. The high-strength, high-toughness fertilizer packaging bag according to claim 6, characterized in that: The mass ratio of the MgAl-LDO bimetallic composite oxide, anhydrous ethanol, and sodium stearate is (5-10):(90-95):(0.15-0.5).

8. The high-strength, high-toughness fertilizer packaging bag according to claim 1, characterized in that: The innermost layer comprises the following raw materials by weight: 70-90 parts of linear low-density polyethylene; 10-20 parts of metallocene linear low-density polyethylene; 3-5 parts of maleic anhydride grafted onto high-density polyethylene; 1-3 parts of smooth masterbatch.

9. The high-strength, high-toughness fertilizer packaging bag according to claim 1, characterized in that: The inner layer comprises the following raw materials by weight: 60-80 parts of metallocene linear low-density polyethylene; 20-30 parts of very low density polyethylene; 5-10 parts of polyolefin elastomer; 0.5-1.5 parts of antistatic masterbatch; 3-5 parts of open-ended, smooth masterbatch.

10. A manufacturing process for a high-strength, high-toughness fertilizer packaging bag as described in any one of claims 1-9, characterized in that: Includes the following steps: S1. Preparation of core layer hybrid filler-compensator masterbatch: Weigh magnesium aluminum base layer dihydroxy composite metal oxide and cellulose nanocrystals according to the formula, add them to a high-speed mixer, and mix at 60-80℃ for 8-12 min; then add ethylene-octene copolymer grafted with glycidyl methacrylate and polylactic acid grafted with maleic anhydride according to the formula, and continue mixing for 4-6 min to obtain a pre-dispersed mixture; melt-blend extrusion granulation of the pre-dispersed mixture through a co-rotating parallel twin-screw extruder, with the extruder temperature set as follows from the feed port to the die head: 120-130℃, 130-140℃, 140-150℃, 145-155℃, respectively, with a die head temperature of 150-160℃ and a screw speed of 200-400 rpm to obtain the core layer hybrid filler-compensator masterbatch; S2. Add the core layer hybrid filler-compensator masterbatch obtained in step S1, the formulated amounts of polybutylene terephthalate-adipate, polylactic acid, antioxidant 1010, antioxidant 168, and zinc stearate to a low-speed mixer and mix for 5-8 minutes. During the mixing process, spray the polyurethane prepolymer into the mixer in a mist and continue mixing for 3-5 minutes to obtain the final core layer blend. S3. Add the raw materials of the surface layer, sub-surface layer, sub-inner layer and inner layer to their respective high-speed mixers according to the formula amount, mix for 5-8 minutes to obtain the blends of each layer. S4. The final core layer blend obtained in step S2 and the surface layer, sub-surface layer, sub-inner layer, and inner layer blends obtained in step S3 are respectively fed into the five extruders corresponding to the five-layer co-extrusion blown film unit. The heating section temperature of the surface layer, sub-surface layer, sub-inner layer, and inner layer extruders is set to 160-200℃, the heating section temperature of the core layer extruder is set to 130-160℃, and the die head temperature is set to 190-200℃. The molten material is extruded after converging in the die head to form a tube blank. The film bubble is cooled and shaped using a dual-air-outlet air ring and a film bubble internal cooling system. The air ring temperature is 8-15℃, the blow-up ratio is controlled at (2.5-3.5):1, and the traction speed is adjusted according to the target film thickness. After cooling and shaping, the film bubble is folded by a herringbone plate, pulled by traction rollers, corona treated, trimmed, and wound up to obtain a high-strength and high-toughness fertilizer packaging bag.