High-strength polyester fiber reinforced polyethylene composite plastic grid

Abstract

The application discloses a high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid, which comprises a copolymerized PET fiber inner layer and a wrapped protective layer. The raw material of the protective layer comprises double-modified basalt fiber, polyethylene, maleic anhydride grafted polyethylene and ethylene-vinyl acetate copolymer. The preparation steps of the composite fiber-plastic grid comprise the following steps: preparing the copolymerized PET fiber from diisopropyl tartrate, terephthalic acid and ethylene glycol; reacting catechin with 4-trifluoromethylbenzoic acid to obtain catechin ester, mixing the basalt fiber with the catechin ester and triethylenetetramine, and treating the mixture with ultraviolet light to obtain modified basalt fiber; reacting the modified basalt fiber with isocyanuric acid triglycidyl ester to obtain double-modified basalt fiber; and finally, co-extruding to obtain the composite fiber-plastic grid. The grid prepared by the application has high interfacial bonding strength, good stress transfer efficiency, excellent anti-creep performance, low-temperature impact resistance, processing fluidity and weather resistance.

Description

Technical Field

[0001] This invention belongs to the field of fiber-plastic grid technology, and particularly relates to a high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid. Background Technology

[0002] Geogrids, as an important foundation reinforcement material, are widely used in soft soil treatment, slope reinforcement, dam protection, road widening, and pile-supported reinforced embankments in highways, railways, airports, and water conservancy projects. Currently, polymer materials such as polypropylene (PP), polyethylene (PE), and polyester (PET) are the main matrix materials for preparing geogrids. Among them, polyethylene shows broad application prospects in the field of geogrids due to its excellent chemical corrosion resistance, good low-temperature toughness, and significant cost advantages.

[0003] However, the crystal evolution and crystallization behavior of polyethylene during processing are extremely complex, which brings significant technical challenges to its application in geogrid materials. Specifically, while higher crystallinity helps improve the tensile strength and modulus of the material, it often leads to a decrease in toughness and elongation at break; conversely, if crystallinity is reduced or toughening components are introduced to improve toughness, tensile strength will deteriorate significantly. This inherent conflict between strength and toughness makes it difficult for traditional polyethylene geogrids to simultaneously meet the dual requirements of high strength and large deformation conditions (such as soft soil subgrades and high embankment slopes) for the material's mechanical properties.

[0004] Furthermore, the low interfacial friction coefficient between a single polyethylene geogrid and the soil, coupled with insufficient long-term creep performance, restricts its widespread application in deep reinforcement scenarios. To overcome these limitations, existing technologies have attempted to prepare composite geogrids by combining glass fiber or polyester fiber with plastics. However, problems such as weak interfacial bonding between the fiber and the polyethylene matrix, easy delamination, and uneven fiber dispersion still exist, making it difficult to fully utilize the reinforcing effect of the fibers.

[0005] Currently, two improved composite geogrids have been applied in engineering practice. One is a high-toughness polyester yarn bundled geogrid. This material bundles high-toughness, high-modulus polyester yarns into strands and covers them with a PE sheath for protection. It can also be composited with high-strength fibers such as glass fiber, carbon fiber, basalt fiber, aramid fiber, or polyester fiber, forming a fiber-plastic composite strip structure through a specialized process. The strips are arranged in an orderly longitudinal and transverse pattern into a mesh, and welded at the intersections to enhance overall stability. This geogrid features high strength, low creep deformation, good durability and weather resistance, and is suitable for projects such as high-speed railways, soft soil embankments of highways, road-bridge transition sections, embankment widening, and airport slopes in rainy areas. In pile-supported reinforced embankments, it can increase pile spacing and reduce the number of piles used, thereby reducing construction costs. Secondly, there is steel-plastic geogrid. This material is made by blending high-strength steel wire (or other fibers) with polyethylene and additives after special treatment, and forming a composite high-strength tensile strip through extrusion. The surface has a rough embossed texture, forming a high-strength reinforced geotextile. This geogrid combines the high strength of steel wire with the corrosion resistance of polyethylene. It has high strength and low creep, which can enhance the interlocking and locking effect between reinforced bearing surfaces, improve the bearing capacity of the foundation, and control lateral displacement. Compared with traditional geogrids, steel-plastic geogrids have advantages such as high strength, high bearing capacity, corrosion resistance, aging resistance, high friction coefficient, uniform mesh size, convenient construction, and long service life. It is more suitable for harsh environments such as deep-sea operations and embankment reinforcement, as well as for embankment and roadbed reinforcement, slope protection, tunnel wall reinforcement, and places requiring long-term foundation reinforcement such as large airports, parking lots, and docks.

[0006] While the aforementioned composite geogrids exhibit certain advantages in specific applications, they still have shortcomings in areas such as interfacial bonding strength, stress transfer efficiency, long-term creep resistance, low-temperature impact resistance, and processing fluidity. Therefore, developing a composite fiber-plastic geogrid that combines high strength, high toughness, low creep, and excellent soil-material synergy is of significant engineering application value. Summary of the Invention

[0007] To address the above issues and overcome the shortcomings of existing technologies, the present invention adopts the following technical solution: The present invention provides a high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid, comprising an inner layer and a protective layer wrapping the inner layer; the composite fiber-plastic grid is prepared through the following steps:

[0008] (1) Synthesis of copolymer PET: Diisopropyl tartrate, terephthalic acid and ethylene glycol are added to a reaction vessel, and tetrabutyl titanate is added as a catalyst. Polycondensation reaction is carried out under nitrogen protection to obtain copolymer PET. Then, copolymer PET fibers are obtained by melt spinning, stretching, shaping and cutting.

[0009] (2) Preparation of double-modified basalt fiber: Catechin and 4-trifluoromethylbenzoic acid were dissolved in anhydrous dichloromethane, EDC and DMAP were added, and the mixture was stirred at room temperature for 12 h. The catechin ester was purified by column chromatography. The catechin ester was dissolved in deionized water with triethylenetetramine, and the pH was adjusted to 8.5 with sodium bicarbonate. Short-cut basalt fiber was added, and after irradiation with ultraviolet light, the fiber was removed, washed with deionized water, and then vacuum dried to obtain modified basalt fiber. The modified basalt fiber was dispersed in an ethanol solution containing triglycidyl isocyanurate and reacted at 55-65℃ for 3-8 h. After washing and drying, double-modified basalt fiber was obtained.

[0010] (3) Co-extrusion of composite fiber-plastic grid: Copolymer PET fiber is used as the inner core material. Double-modified basalt fiber, polyethylene, maleic anhydride grafted polyethylene and ethylene-vinyl acetate copolymer are mixed evenly according to the mass parts and used as the raw material for the protective layer. The mixture is extruded through a co-extrusion mold, cooled and shaped, and then pulled and cut to obtain a high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid.

[0011] This invention utilizes diisopropyl tartrate units introduced into the inner layer of copolymerized PET to form flexible ester bond side groups in the molecular chain, reducing the regularity of the PET chain segments and increasing the density of polar groups. This allows for stronger interfacial interactions between the PET and the anhydride groups in maleic anhydride-grafted polyethylene. The maleic anhydride-grafted polyethylene and ethylene-vinyl acetate copolymer in the outer layer act as compatibilizers, and their anhydride groups can undergo esterification or amidation reactions with the terminal hydroxyl or carboxyl groups of the copolymerized PET, forming in-situ covalent bonds during co-extrusion. This enhances the interfacial bonding between the inner fiber layer and the outer protective layer. The peel strength and shear resistance between the fibers are improved. The surface of the double-modified basalt fiber is subjected to UV-induced polymerization of catechin trifluoromethyl benzoate and triethylenetetramine to form a dopamine-like structure. This structure is rich in catechol and amino active sites, which can undergo ring-opening addition with the epoxy groups in triglycidyl isocyanurate and then graft onto the polyethylene matrix. At the same time, the residual catechol groups can form hydrogen bonds or π-π stacking interactions with the ester groups in the copolymer PET to construct a three-dimensional stress transfer network, ensuring that the load is uniformly and efficiently distributed and transferred in the grid structure.

[0012] The grid prepared by this invention has long-term weather resistance. The introduction of diisopropyl tartrate in the inner layer of copolymer PET increases the steric hindrance of the macromolecular chain, inhibits the hydrolysis reaction kinetics of ester bonds in humid and hot environments, and improves durability. The 4-trifluoromethyl benzoate structure grafted on the surface of the double-modified basalt fiber in the outer layer contains a strongly hydrophobic trifluoromethyl group. Catechins themselves have the ability to capture free radicals and chelate metal ions, which can neutralize reactive oxygen species generated by ultraviolet light or thermal oxidation and delay the oxidative degradation of polyethylene matrix. The triazine ring structure in triglycidyl isocyanate has excellent chemical and thermal stability. The above mechanisms work synergistically to enable the grid to maintain its mechanical properties and structural integrity even when it is in long-term service in humid, acid rain, salt spray or chemically contaminated soil.

[0013] Polymer materials are prone to creep deformation under sustained loads, leading to the failure of the grid's support or reinforcement function. This invention employs a soft-rigid composite structure formed by high-modulus, low-creep, dual-modified basalt fibers and copolymerized PET fibers. The elastic modulus of basalt fibers is much higher than that of polyethylene and PET. During co-extrusion, they are axially oriented and distributed in the outer layer, effectively embedding a continuous rigid skeleton within the polyethylene matrix. When the grid is subjected to long-term tensile loads, the basalt fibers bear most of the stress first, limiting the slippage and rearrangement of the polyethylene molecular chains. Simultaneously, the copolymerized PET fibers, as the main load-bearing element in the inner layer, have branching points formed by diisopropyl tartrate units in their molecular chains that hinder the oriented crystallization of chain segments along the direction of stress, thus delaying the onset of accelerated creep. Furthermore, the cross-linked interface layer formed by the reaction of maleic anhydride-grafted polyethylene with the epoxy groups on the surface of the dual-modified basalt fibers further inhibits the relative slippage between the fibers and the matrix. The above structure reduces the creep strain rate of the grid and prolongs the long-term creep fracture time, making it particularly suitable for engineering scenarios that require decades of stability, such as slope reinforcement and soft soil treatment.

[0014] Traditional PET / polyethylene composite grids are prone to brittle fracture at low temperatures. This invention utilizes the flexible side chains of diisopropyl tartrate in copolymerized PET to lower the glass transition temperature, giving the inner fiber layer a certain degree of toughness at low temperatures. The vinyl acetate segments of EVA in the outer layer act as an elastomer dispersion phase, effectively absorbing impact energy and inducing crazing, thus preventing crack propagation. The organic layer (a polymer of catechin derivatives and triethylenetetramine) on the surface of the double-modified basalt fibers possesses a certain degree of deformability, acting as a stress buffer layer at the fiber-matrix interface to prevent stress concentration caused by direct contact between rigid fibers and the matrix. Therefore, this grid maintains high impact toughness and bending flexibility in low-temperature environments such as cold-region roads and permafrost foundations, facilitating transportation, laying, and adapting to uneven foundation settlement.

[0015] Further, in step (1), the molar ratio of diisopropyl tartrate, terephthalic acid, and ethylene glycol is 1:4~10:8~12, and the amount of tetrabutyl titanate is 0.03%~0.08% of the total mass of the three monomers.

[0016] Further, in step (1), the polycondensation reaction temperature is 270~280℃, the vacuum degree is less than 100Pa, and the time is 2.5~3.5h; the stretching is water bath stretching, the stretching temperature is 75~85℃, and the stretching ratio is 3.0~4.0 times.

[0017] Further, in step (2), the molar ratio of catechin, 4-trifluoromethylbenzoic acid, EDC and DMAP is 1:1.1~1.3:1.0~1.3:0.1~0.15, the ultraviolet light irradiation power is 250~350W, and the irradiation time is 3~5h.

[0018] Furthermore, the mass ratio of the catechin ester, triethylenetetramine, and chopped basalt fiber is 1.5~2:0.8~1.2:10~15.

[0019] Further, in step (2), the mass ratio of the modified basalt fiber to triglycidyl isocyanurate is 8~10:2~5, and the volume fraction of the ethanol solution is 50%~70%.

[0020] Further, the outer layer raw materials mentioned in step (3) are as follows by mass: 10-20 parts of double-modified basalt fiber, 65-75 parts of polyethylene, 3-8 parts of maleic anhydride-grafted polyethylene, and 8-12 parts of ethylene-vinyl acetate copolymer.

[0021] Furthermore, the polyethylene mentioned in step (3) is high-density polyethylene with a melt index of 1.5~2.5 g / 10 min (190℃ / 2.16 kg).

[0022] Furthermore, the grafting rate of the maleic anhydride-grafted polyethylene in step (3) is 4.5% to 6.0%.

[0023] Furthermore, in step (3), the inner layer temperature during co-extrusion is 260~270℃ and the outer layer temperature is 190~200℃.

[0024] The synergistic use of maleic anhydride-grafted polyethylene and ethylene-vinyl acetate copolymer in the outer layer formulation of this invention significantly improves the melt processing performance of high-filler systems (containing basalt fibers). The polar anhydride groups of maleic anhydride-grafted polyethylene interact strongly with the amino, hydroxyl, or epoxy groups on the surface of the double-modified basalt fibers, promoting fiber wetting and dispersion in the polyethylene melt and preventing fiber agglomeration. The low melt viscosity of EVA reduces the shear viscosity of the blend system, improving melt flowability. The basalt fiber surface after UV prepolymerization treatment exhibits dopamine-like adhesiveness, further assisting in rapid bonding of the fiber to the matrix during melt blending, shortening the processing cycle, and reducing energy consumption.

[0025] The material system of this invention also exhibits certain flame-retardant potential. The triazine ring in triglycidyl isocyanate promotes char formation at high temperatures, creating a dense carbonized layer that isolates oxygen and heat. Simultaneously, basalt fiber, as an inorganic material, is non-flammable and has low thermal conductivity; its uniform distribution acts as a physical heat insulation barrier. The aromatic structure in copolymerized PET shrinks upon exposure to fire, reducing dripping. These mechanisms collectively endow the grid with the ability to delay ignition, suppress flame spread, and self-extinguish when encountering fire or high-temperature heat sources, thus improving fire safety in engineering applications.

[0026] The beneficial effects of this invention are:

[0027] The composite fiber-plastic grid prepared by this invention has excellent interfacial bonding strength and stress transfer efficiency, resistance to damp heat aging and chemical corrosion, creep resistance and long-term service stability, good low-temperature impact resistance and flexibility, processing fluidity and fiber dispersion uniformity, as well as fire resistance and flame retardancy.

[0028] Specifically, the diisopropyl tartrate side groups in the copolymerized PET increase polarity, undergoing esterification / amidation reactions with maleic anhydride-grafted polyethylene to form a chemically bonded interface. The dopamine-like structure on the surface of the double-modified basalt fiber reacts with the epoxy groups of triglycidyl isocyanate, while simultaneously forming hydrogen bonds or π-π interactions with the copolymerized PET, constructing a three-dimensional stress transfer network that evenly distributes the load. The diisopropyl tartrate in the copolymerized PET increases steric hindrance, inhibiting ester bond hydrolysis. The trifluoromethyl group on the surface of the double-modified basalt fiber imparts hydrophobic properties to the interface, preventing the penetration of water molecules and corrosive ions. Catechins capture free radicals, delaying oxidative degradation, while the triazine ring structure enhances acid and alkali resistance, ensuring long-term service stability. The high-modulus double-modified basalt fiber forms a rigid skeleton in the outer layer, bearing long-term tensile loads and restricting polyethylene molecular chain slippage. The branched structure in the inner layer of the copolymerized PET hinders chain segment orientation rearrangement, and the cross-linked interface layer inhibits... The relative slippage between the fiber and the matrix reduces the creep strain rate and prolongs the creep rupture time. The flexible side chains of diisopropyl tartrate in the copolymerized PET lower the glass transition temperature, giving the inner layer low-temperature toughness. The outer ethylene-vinyl acetate copolymer acts as an elastic dispersed phase to absorb impact energy. The organic buffer layer on the surface of the double-modified basalt fiber avoids stress concentration, allowing the grid to maintain its impact resistance and flexibility in cold regions. The polar groups of maleic anhydride-grafted polyethylene form a strong interaction with the surface of the double-modified basalt fiber, promoting fiber wetting and dispersion and preventing agglomeration. The ethylene-vinyl acetate copolymer reduces the melt viscosity of the blend system and improves flowability. In addition, the dopamine-like adhesion of the fiber surface ensures that the co-extrusion forms a uniform concentric structure and reduces energy consumption. The triazine ring in triglycidyl isocyanate promotes high-temperature charring, forming a heat-insulating carbon layer. The basalt fiber, as an inorganic filler, physically blocks heat, synergistically giving the grid the ability to delay ignition and self-extinguish. Attached Figure Description

[0029] Figure 1 This is a diagram showing the interface bonding strength test results of the present invention;

[0030] Figure 2 The figure shows the test results of the resistance to damp heat aging of this invention.

[0031] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0032] 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. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are all purchased from commercial channels.

[0035] Example 1

[0036] A high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid includes an inner layer and a protective layer wrapped around the inner layer; the composite fiber-plastic grid is prepared by the following steps:

[0037] (1) Synthesis of copolymer PET: Diisopropyl tartrate, terephthalic acid, and ethylene glycol were added to a reactor in a molar ratio of 1:4:8. Tetrabutyl titanate catalyst was added at 0.03% of the total mass of the three monomers. Polycondensation reaction was carried out under nitrogen protection at a temperature of 270°C, a vacuum degree of less than 100 Pa, and a time of 2.5 h to obtain copolymer PET. Then, copolymer PET fibers were obtained by melt spinning, stretching, shaping, and cutting. The stretching was water bath stretching at a temperature of 75°C and a stretching ratio of 3.0 times.

[0038] (2) Preparation of double-modified basalt fiber: Catechin and 4-trifluoromethylbenzoic acid, EDC and DMAP were dissolved in anhydrous dichloromethane at a molar ratio of 1:1.1:1.0:0.1, and EDC and DMAP were added. The mixture was stirred at room temperature for 12 h and purified by column chromatography to obtain catechin ester. The catechin ester was dissolved in deionized water at a mass ratio of catechin ester, triethylenetetramine and chopped basalt fiber of 1.5:0.8:10. In the process of adjusting the pH to 8.5 with sodium bicarbonate, short-cut basalt fibers were added and irradiated with ultraviolet light at a power of 250W for 3 hours. The fibers were then removed, washed with deionized water, and vacuum dried to obtain modified basalt fibers. The modified basalt fibers were dispersed in an ethanol solution containing 50% triglycidyl isocyanurate at a mass ratio of 8:2, reacted at 55°C for 3 hours, washed and dried to obtain double-modified basalt fibers.

[0039] (3) Co-extrusion of composite fiber-plastic grid: Copolymer PET fiber is used as the inner core material. 10 parts of double-modified basalt fiber, 65 parts of polyethylene, 3 parts of maleic anhydride-grafted polyethylene, and 8 parts of ethylene-vinyl acetate copolymer are mixed evenly according to the mass ratio as the protective layer raw material. The mixture is extruded through a co-extrusion die, cooled and shaped, and then traction-cut to obtain a high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid. The polyethylene is high-density polyethylene with a melt index of 1.5 g / 10 min (190℃ / 2.16 kg). The grafting rate of the maleic anhydride-grafted polyethylene is 4.5%. The inner layer temperature is 260℃ and the outer layer temperature is 190℃ during co-extrusion.

[0040] Example 2

[0041] A high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid includes an inner layer and a protective layer wrapped around the inner layer; the composite fiber-plastic grid is prepared by the following steps:

[0042] (1) Synthesis of copolymer PET: Diisopropyl tartrate, terephthalic acid, and ethylene glycol were added to a reactor in a molar ratio of 1:10:12. Tetrabutyl titanate catalyst was added at 0.08% of the total mass of the three monomers. Polycondensation reaction was carried out under nitrogen protection at a temperature of 280°C, a vacuum degree of less than 100 Pa, and a time of 3.5 h to obtain copolymer PET. Then, copolymer PET fibers were obtained by melt spinning, stretching, shaping, and cutting. The stretching was carried out by water bath stretching at a temperature of 85°C and a stretching ratio of 4.0 times.

[0043] (2) Preparation of double-modified basalt fiber: Catechin and 4-trifluoromethylbenzoic acid, EDC and DMAP were dissolved in anhydrous dichloromethane at a molar ratio of 1:1.3:1.3:0.15. EDC and DMAP were added, and the mixture was stirred at room temperature for 12 h. The catechin ester was purified by column chromatography. The catechin ester and triethylenetetramine were dissolved in deionized water at a mass ratio of 2:1.2:15. The pH was adjusted to 8.5 with sodium bicarbonate, and short-cut basalt fibers were added. After irradiation with ultraviolet light (350W for 5 hours), the fibers were removed, washed with deionized water, and then vacuum dried to obtain modified basalt fibers. The modified basalt fibers were dispersed in an ethanol solution containing 70% triglycidyl isocyanurate at a mass ratio of 10:5, reacted at 65°C for 8 hours, washed and dried to obtain double-modified basalt fibers.

[0044] (3) Co-extrusion of composite fiber-plastic grid: Copolymer PET fiber is used as the inner core material. 20 parts of double-modified basalt fiber, 75 parts of polyethylene, 8 parts of maleic anhydride-grafted polyethylene, and 12 parts of ethylene-vinyl acetate copolymer are mixed evenly according to the mass ratio as the protective layer raw material. The mixture is extruded through a co-extrusion die, cooled and shaped, and then pulled and cut to obtain a high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid. The polyethylene is high-density polyethylene with a melt index of 2.5 g / 10 min (190℃ / 2.16 kg). The grafting rate of the maleic anhydride-grafted polyethylene is 6.0%. The inner layer temperature is 270℃ and the outer layer temperature is 200℃ during co-extrusion.

[0045] Example 3

[0046] A high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid includes an inner layer and a protective layer wrapped around the inner layer; the composite fiber-plastic grid is prepared by the following steps:

[0047] (1) Synthesis of copolymer PET: Diisopropyl tartrate, terephthalic acid, and ethylene glycol were added to a reactor in a molar ratio of 1:7:10. Tetrabutyl titanate catalyst was added at 0.055% of the total mass of the three monomers. Polycondensation reaction was carried out under nitrogen protection at a temperature of 275°C, a vacuum degree of less than 100 Pa, and a time of 3 hours to obtain copolymer PET. Then, copolymer PET fibers were obtained by melt spinning, stretching, shaping, and cutting. The stretching was carried out by water bath stretching at a temperature of 80°C and a stretching ratio of 3.5 times.

[0048] (2) Preparation of double-modified basalt fiber: Catechin and 4-trifluoromethylbenzoic acid, EDC and DMAP were dissolved in anhydrous dichloromethane at a molar ratio of 1:1.2:1.2:0.12, and EDC and DMAP were added. The mixture was stirred at room temperature for 12 h and purified by column chromatography to obtain catechin ester. The catechin ester was then dissolved in deionized water at a mass ratio of catechin ester, triethylenetetramine and chopped basalt fiber of 1.75:1.0:12.5. In a process where the pH was adjusted to 8.5 with sodium bicarbonate, short-cut basalt fibers were added and irradiated with ultraviolet light (300W for 4 hours). The fibers were then removed, washed with deionized water, and vacuum dried to obtain modified basalt fibers. The modified basalt fibers were dispersed in an ethanol solution containing 60% triglycidyl isocyanurate at a mass ratio of 9:3.5, reacted at 60°C for 5.5 hours, washed, and dried to obtain double-modified basalt fibers.

[0049] (3) Co-extrusion of composite fiber-plastic grid: Copolymer PET fiber is used as the inner core material. 15 parts of double-modified basalt fiber, 70 parts of polyethylene, 5.5 parts of maleic anhydride-grafted polyethylene, and 10 parts of ethylene-vinyl acetate copolymer are mixed evenly according to the mass ratio as the protective layer raw material. The mixture is extruded through a co-extrusion die, cooled and shaped, and then traction-cut to obtain a high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid. The polyethylene is high-density polyethylene with a melt index of 2.0 g / 10 min (190℃ / 2.16 kg). The grafting rate of the maleic anhydride-grafted polyethylene is 5.25%. The inner layer temperature is 265℃ and the outer layer temperature is 195℃ during co-extrusion.

[0050] Comparative Example 1

[0051] A polyester fiber reinforced polyethylene composite fiber-plastic grid includes an inner layer and a protective layer wrapped around the inner layer; the composite fiber-plastic grid is prepared by the following steps:

[0052] (1) Synthesis of ordinary PET: Terephthalic acid and ethylene glycol were added to a reaction vessel at a molar ratio of 1:1.2. Tetrabutyl titanate catalyst was added at 0.05% of the total mass of the two monomers. Polycondensation reaction was carried out under nitrogen protection at a reaction temperature of 275°C, a vacuum degree of less than 100 Pa, and a time of 3 hours to obtain ordinary PET. Then, ordinary PET fibers were obtained by melt spinning, stretching, shaping, and cutting. The stretching was water bath stretching at a stretching temperature of 80°C and a stretching ratio of 3.5 times.

[0053] (2) Preparation of double-modified basalt fiber: Same as in Example 1;

[0054] (3) Co-extrusion of composite fiber plastic grid: ordinary PET fiber is used as the inner core material, and the rest is the same as in Example 1.

[0055] Comparative Example 2

[0056] A high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid includes an inner layer and a protective layer wrapped around the inner layer; the composite fiber-plastic grid is prepared by the following steps:

[0057] (1) Synthesis of copolymerized PET: Same as in Example 1;

[0058] (2) Preparation of unmodified basalt fiber: Take short-cut basalt fiber, wash it with deionized water, and vacuum dry it to obtain unmodified basalt fiber;

[0059] (3) Co-extrusion of composite fiber plastic grid: Copolymer PET fiber is used as the inner core material. 10 parts of unmodified basalt fiber, 65 parts of polyethylene, 3 parts of maleic anhydride grafted polyethylene and 8 parts of ethylene-vinyl acetate copolymer are mixed evenly according to the mass ratio as the raw material of the protective layer. The rest is the same as in Example 1.

[0060] Comparative Example 3

[0061] A high-strength polyester fiber-reinforced polyethylene composite fiber-plastic grid includes an inner layer and a protective layer wrapped around the inner layer; the composite fiber-plastic grid is prepared by the following steps:

[0062] (1) Synthesis of copolymerized PET: Same as in Example 1;

[0063] (2) Preparation of double-modified basalt fiber: Same as in Example 1;

[0064] (3) Co-extrusion of composite fiber plastic grid: Copolymer PET fiber is used as the inner core material. 10 parts of double-modified basalt fiber, 76 parts of polyethylene (to make up for the missing maleic anhydride grafted polyethylene and EVA parts), 0 parts of maleic anhydride grafted polyethylene and 0 parts of ethylene-vinyl acetate copolymer are mixed evenly according to the mass ratio as the raw material of the protective layer. The rest is the same as in Example 1.

[0065] Results Analysis

[0066] Test Example 1: Interface Bond Strength Test

[0067] (1) Test objective: To verify the interfacial bonding strength between the inner copolymer PET layer and the outer protective layer, and between the double-modified basalt fiber and the polyethylene matrix in this invention. Test results are shown in […]. Figure 1 .

[0068] (2) Test standard: Refer to GB / T 2790-1995 "Test method for 180° peel strength of adhesives, flexible materials versus rigid materials".

[0069] (3) Detailed testing process:

[0070] Sampling: Five samples with a width of 25 mm and a length of 200 mm were cut from the composite fiber plastic grid strips of Examples 1-3 and Comparative Examples 1-3 along the length direction.

[0071] Pretreatment: All samples were placed at a temperature of 23±2℃ and a relative humidity of 50±5% for 24 hours.

[0072] Layering preparation: At one end of the sample, use a sharp blade to separate the inner copolymer PET fiber bundle from the outer protective layer for about 50 mm to form the peeling start section.

[0073] Fixture installation: Clamp the separated inner fiber bundles onto the upper fixture of the testing machine, clamp the outer protective layer onto the lower fixture, keep the sample vertical, and set the initial peeling angle to 180°.

[0074] Test parameters: peeling speed set to 100 mm / min, sampling frequency 50 Hz, and test ambient temperature 23 ± 2 ℃.

[0075] Test procedure: Start the testing machine and record the peel force as a function of peel distance. The effective peel distance should be no less than 100 mm. The average value of the stable peel force range for each sample is taken as the peel force of that sample.

[0076] Calculation: Peel strength (N / mm) = Average peel force (N) / Sample width (25mm).

[0077] from Figure 1 It can be seen that the peel strength of Examples 1-3 is above 8.7 N / mm, while that of Comparative Example 1 is only 3.24 N / mm. This is because Comparative Example 1 uses ordinary PET fibers, whose molecular chains are regular and have low polarity, making it impossible to undergo esterification / amidation reactions with maleic anhydride-grafted polyethylene. The interface relies solely on physical intercalation, resulting in weak bonding. Comparative Example 2 has the lowest peel strength because the surface of the unmodified basalt fibers lacks active groups, resulting in no chemical bonding or hydrogen bonding with the polyethylene matrix. The fibers are easily pulled out directly during the peeling process. Comparative Example 3 lacks maleic anhydride-grafted polyethylene and EVA, resulting in no compatibilizer at the interface, poor compatibility between the inner PET layer and the outer PE layer, and poor fiber dispersion.

[0078] Test Example 2: Resistance to Damp Heat Aging (Double 85 Test)

[0079] (1) Test objective: To verify the long-term durability of this invention against hydrolysis and oxidation under humid and hot conditions. Test results are shown below. Figure 2 .

[0080] (2) Test standard: Refer to the damp heat aging section of GB / T 2573-2008 "Test Method for Aging of Glass Fiber Reinforced Plastics".

[0081] (3) Detailed testing process:

[0082] Sampling: Tensile specimens were cut from the grid strips of Examples 1-3 and Comparative Examples 1-3, referring to the tensile specimen dimensions in GB / T 17689-2017. For each sample, 40 specimens were prepared (5 specimens each for 0, 7, 14, 21 and 28 days).

[0083] Initial performance test: Take 5 samples in each group and test their longitudinal tensile strength at a speed of 50 mm / min using a universal testing machine under the conditions of 23±2℃ and 50±5%RH. Take the average value as the initial strength.

[0084] Humid heat aging conditions: The remaining samples were placed in a constant temperature and humidity chamber, with the temperature set at 85±2℃ and the relative humidity at 85±5%.

[0085] Aging treatment: After aging for 7, 14, 21 and 28 days respectively, the corresponding group of samples were taken out and placed at room temperature for 24 hours to regain moisture.

[0086] Post-aging test: The tensile strength of the aged specimens was tested using the same method as the initial test.

[0087] Strength retention rate calculation: Strength retention rate (%) = (Average tensile strength after aging / Initial average tensile strength) × 100%.

[0088] from Figure 2 As can be seen, after 28 days, all examples exhibited excellent resistance to damp heat aging. Example 3 showed a retention rate of 83.2%, while Comparative Example 1 only achieved 52.3%. Comparative Example 1 used ordinary PET, which lacks the steric hindrance protection of diisopropyl tartrate in its molecular chain. The ester bonds are easily hydrolyzed and broken under damp heat, leading to a decrease in strength. Comparative Example 2 used unmodified basalt fiber, which lacks a trifluoromethyl hydrophobic layer on its surface. Water molecules can penetrate along the fiber-matrix interface, accelerating aging, resulting in a retention rate of 61.9%. Comparative Example 3, lacking maleic anhydride-grafted polyethylene and EVA, had voids at the interface, allowing water molecules to penetrate more easily, resulting in a retention rate of 55.8%.

[0089] Test Example 3: Long-term creep resistance test

[0090] (1) Test objective: To verify the dimensional stability and long-term service capability of the present invention under continuous load. The test results are shown in Table 1.

[0091] (2) Test standard: Refer to GB / T 11546.1-2008 "Determination of creep properties of plastics - Part 1: Tensile creep".

[0092] (3) Detailed testing process:

[0093] Sampling: Tensile creep specimens with an effective gauge length of 100 mm and a width of 25 mm were cut from the grid strips of Examples 1-3 and Comparative Examples 1-3, with 5 specimens per group.

[0094] Test conditions: Temperature set at 23±1℃, relative humidity at 50±5%.

[0095] Loading stress: A constant creep stress of 25% of the initial tensile strength of the grid was used. For each sample, the loading force was calculated based on the initial strength in Test Example 2.

[0096] Test procedure: Install the specimen and the extensometer within the gauge length; apply a constant stress at a rate of 2 mm / min to the set stress; continuously record the strain change over time at the following time points: 1 min, 10 min, 30 min, 1 h, 2 h, 5 h, 10 h, 24 h, 48 h, 72 h, 100 h, 200 h, 500 h, 1000 h. The test lasts for 1000 h.

[0097] Data processing: Plot the creep strain-time curve. Calculate the creep strain at 100h and 1000h.

[0098] Table 1 Comparison of Long-Term Creep Resistance Test Results

[0099] sample 100h creep strain (%) 1000h creep strain (%) Does it break within 1000 hours? Example 1 0.85 1.52 no Example 2 0.82 1.48 no Example 3 0.78 1.41 no Comparative Example 1 1.65 3.88 no Comparative Example 2 2.10 5.24 no Comparative Example 3 2.35 6.10 no

[0100] As shown in Table 1, the 1000-hour creep of Comparative Examples 2 and 3 is significantly higher than that of Examples 1-3. In Comparative Example 2, the unmodified basalt fiber has no chemical bond with the matrix, and under long-term stress, the fiber slips from the matrix, failing to effectively bear the stress. In Comparative Example 3, there is no compatibilizer, resulting in a poor interface between the inner PET layer and the outer PE layer, low stress transfer efficiency, and large creep of the polyethylene matrix itself. In Comparative Example 1, the regular molecular chains of ordinary PET are prone to orientation rearrangement, leading to relatively large creep. In this invention, the triglycidyl isocyanate grafted onto the surface of the double-modified basalt fiber forms a cross-linked interface layer with maleic anhydride grafted onto polyethylene, preventing slippage between the fiber and the matrix. The branched structure in the copolymerized PET hinders chain rearrangement, thus resulting in smaller creep strain.

[0101] Test Example 4: Low Temperature Impact Resistance Test

[0102] (1) Test objective: To verify the impact toughness and flexibility of the present invention in a low-temperature environment. The test results are shown in Table 2.

[0103] (2) Test standard: Refer to GB / T 1843-2008 "Determination of impact strength of plastic cantilever beam". Because the grid is strip-shaped, it needs to be made into a standard impact test strip.

[0104] (4) Detailed testing process:

[0105] Sampling and Sample Preparation: The outer protective layer material of the grid in Examples 1-3 and Comparative Examples 1-2 was made into standard strips of 80mm×10mm×4mm by injection molding or pressing, with 10 strips per group. A V-shaped notch (notch depth 2mm, root radius 0.25mm) was machined in the middle of the strips using a notch sample preparation machine.

[0106] Low temperature treatment: Place the sample in a low temperature chamber, set the temperature to -30±1℃, and keep it at that temperature for 4 hours.

[0107] Impact test: Quickly remove the specimen (within 5 seconds) and place it on the cantilever beam impact testing machine. Select an impact pendulum energy of 2.75 J and an impact velocity of 3.46 m / s. Record the impact energy absorbed by each specimen (kJ / m²).

[0108] Observe the damage pattern: record the shape of the gap cross section.

[0109] Table 2 Comparison of Low Temperature Impact Resistance Test Results

[0110] sample Impact strength at -30℃ (kJ / m²) Forms of destruction Example 1 18.6±1.2 Tough fracture, with whitening Example 2 19.2±1.1 Tough fracture, with whitening Example 3 20.5±0.9 Tough fracture, with whitening Comparative Example 1 8.3±1.5 Brittle fracture, flat Comparative Example 2 12.4±1.4 Semi-brittle, with slight whitening Comparative Example 3 5.8±1.3 Brittle fracture, flat

[0111] Table 2 shows that Comparative Example 3 has the lowest low-temperature impact strength because its outer layer contains only polyethylene and basalt fiber, without EVA elastomer toughening or an interfacial buffer layer. At low temperatures, the polyethylene molecular chains freeze, and cracks easily propagate rapidly along the fiber-matrix interface. In Comparative Example 1, the ordinary PET inner layer lacks flexible side chains, resulting in high low-temperature brittleness. Comparative Example 2, due to the absence of an organic buffer layer on the fiber surface, although providing some reinforcement, exhibits significant interfacial stress concentration, resulting in semi-brittle fracture. In this invention, the diisopropyl tartrate side group of the copolymerized PET lowers the glass transition temperature of PET; the outer EVA acts as an elastomer dispersion phase to absorb impact energy; and the dopamine-like organic layer on the surface of the double-modified basalt fiber acts as a stress buffer layer, preventing rigid stress concentration.

[0112] Test Example 5: Flame Retardant Performance Test

[0113] (1) Test objective: To verify the flame retardant performance of the present invention. The test results are shown in Table 3.

[0114] (2) Test standard: Refer to GB / T 2408-2008 "Determination of the flammability of plastics by horizontal and vertical methods".

[0115] (3) Detailed testing process:

[0116] Sampling: 130mm×13mm×3mm strip samples were made from the outer protective layer material of the grid in Examples 1-3 and Comparative Examples 1-3, with 5 strips in each group.

[0117] Pretreatment: Place at 23±2℃ and 50±5%RH for 48 hours.

[0118] Vertical burning test:

[0119] The sample is held vertically in the fixture, with the lower end 10 mm from the Bunsen burner nozzle.

[0120] Adjust the height of the Bunsen burner flame to 20±2mm and the height of the blue inner flame to 10±1mm.

[0121] Apply flame for 10 seconds and record the burning time t1 of the sample after the first application of flame (the burning time after the flame is removed).

[0122] After the flame is extinguished, the flame is immediately applied again for 10 seconds. The second burning time t2 and the flaming burning time t3 of the sample after the second flame is removed are recorded (i.e., t2 is the continuous burning time after the second application, and t3 is the burning time without scorching. The standard usually records t1, t2 and whether there is dripping ignition of cotton).

[0123] Record whether the drippings ignite the absorbent cotton underneath.

[0124] Grading determination: Classify according to the standard into V-0, V-1, and V-2.

[0125] Table 3 Comparison of Flame Retardant Performance Test Results

[0126] sample t1 (s) t2 (s) The dripping cotton ignited Flame retardant rating Example 1 2.5 6.2 no V-0 Example 2 2.3 5.8 no V-0 Example 3 1.8 4.5 no V-0 Comparative Example 1 7.5 14.2 yes V-2 Comparative Example 2 7.2 12.5 yes V-2 Comparative Example 3 4.6 8.0 yes V-1

[0127] As shown in Table 3, in the embodiments of the present invention, the triglycidyl isocyanurate grafted on the surface of the double-modified basalt fiber promotes cross-linking into carbon at high temperature, forming a dense carbon layer to isolate oxygen and heat; the basalt fiber acts as an inorganic filler to further provide physical insulation; the aromatic structure in the copolymer PET shrinks when exposed to fire, reducing molten droplets.

[0128] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0129] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid, characterized in that: The composite fiber-plastic grid comprises an inner layer and a protective layer encasing the inner layer; the composite fiber-plastic grid is prepared by the following steps: (1) Synthesis of copolymer PET: Diisopropyl tartrate, terephthalic acid and ethylene glycol are added to a reaction vessel, and tetrabutyl titanate is added as a catalyst. Polycondensation reaction is carried out under nitrogen protection to obtain copolymer PET. Then, copolymer PET fibers are obtained by melt spinning, stretching, shaping and cutting. (2) Preparation of double-modified basalt fiber: Catechin and 4-trifluoromethylbenzoic acid were dissolved in anhydrous dichloromethane, EDC and DMAP were added, and the mixture was stirred at room temperature for 12 h. The catechin ester was purified by column chromatography. The catechin ester was dissolved in deionized water with triethylenetetramine, and the pH was adjusted to 8.5 with sodium bicarbonate. Short-cut basalt fiber was added, and after irradiation with ultraviolet light, the fiber was removed, washed with deionized water, and then vacuum dried to obtain modified basalt fiber. Modified basalt fibers were dispersed in an ethanol solution containing triglycidyl isocyanurate and reacted at 55-65°C for 3-8 hours. After washing and drying, double-modified basalt fibers were obtained. (3) Co-extrusion of composite fiber-plastic grid: Copolymer PET fiber is used as the inner core material. Double-modified basalt fiber, polyethylene, maleic anhydride grafted polyethylene and ethylene-vinyl acetate copolymer are mixed evenly according to the mass parts and used as the raw material for the protective layer. The mixture is extruded through a co-extrusion mold, cooled and shaped, and then pulled and cut to obtain a high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid.

2. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 1, characterized in that: In step (1), the molar ratio of diisopropyl tartrate, terephthalic acid, and ethylene glycol is 1:4~10:8~12, and the amount of tetrabutyl titanate is 0.03%~0.08% of the total mass of the three monomers.

3. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 2, characterized in that: The polycondensation reaction temperature in step (1) is 270~280℃, the vacuum degree is less than 100Pa, and the time is 2.5~3.5h; the stretching is water bath stretching, the stretching temperature is 75~85℃, and the stretching ratio is 3.0~4.0 times.

4. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 3, characterized in that: In step (2), the molar ratio of catechin, 4-trifluoromethylbenzoic acid, EDC and DMAP is 1:1.1~1.3:1.0~1.3:0.1~0.15, the ultraviolet light irradiation power is 250~350W, and the irradiation time is 3~5h.

5. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 4, characterized in that: The mass ratio of the catechin ester, triethylenetetramine, and chopped basalt fiber is 1.5~2:0.8~1.2:10~15.

6. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 5, characterized in that: In step (2), the mass ratio of the modified basalt fiber to triglycidyl isocyanurate is 8~10:2~5, and the volume fraction of the ethanol solution is 50%~70%.

7. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 6, characterized in that: The outer layer raw materials mentioned in step (3) are as follows by mass parts: 10-20 parts of double-modified basalt fiber, 65-75 parts of polyethylene, 3-8 parts of maleic anhydride grafted polyethylene, and 8-12 parts of ethylene-vinyl acetate copolymer.

8. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 7, characterized in that: The polyethylene mentioned in step (3) is high-density polyethylene with a melt index of 1.5~2.5g / 10min (190℃ / 2.16kg).

9. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 8, characterized in that: The grafting rate of maleic anhydride-grafted polyethylene in step (3) is 4.5% to 6.0%.

10. The high-strength polyester fiber reinforced polyethylene composite fiber-plastic grid according to claim 9, characterized in that: In step (3), the inner layer temperature during co-extrusion is 260~270℃ and the outer layer temperature is 190~200℃.

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