Environment-friendly MPP cable protection pipe and preparation method thereof

Abstract

The invention relates to an environment-friendly MPP cable protection tube based on regenerated polypropylene and plant fibers. The environment-friendly MPP cable protection tube comprises 50-80 parts of regenerated polypropylene rPP; 10 to 30 parts of plant fiber; 3 to 10 parts of a compatilizer; 5 to 15 parts of a toughening agent; 0.5 to 2 parts of a heat stabilizer; 1-3 parts of a lubricant; 0.3 to 1 part of an antioxidant; the plant fibers are one or more of wood powder, bamboo powder, rice hull powder or bagasse powder; the compatilizer is maleic anhydride grafted polypropylene, an ethylene-acrylate-maleic anhydride terpolymer or a titanate coupling agent; or a compound compatilizer; the flexibilizer is a polyolefin elastomer, a styrene-butadiene-styrene block copolymer or an ethylene-vinyl acetate copolymer; or a compound toughening agent; the heat stabilizer is a composite stable system and comprises a main antioxidant and an auxiliary antioxidant; the lubricant comprises an inner lubricant and an outer lubricant; the antioxidant is a thioester auxiliary antioxidant or a ternary synergistic stable system formed by hindered phenol, phosphite ester and thioester. The invention also discloses a corresponding preparation method.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a pipe for the protection of power and communication cables and its preparation method, particularly an environmentally friendly modified polypropylene (MPP) cable protection pipe based on recycled polypropylene (rPP) and plant fibers and its preparation method. Background Technology

[0002] MPP (Modified Polypropylene) cable protection pipes are widely used in urban power grid construction and renovation, municipal engineering construction, and other fields due to their excellent high temperature resistance, external pressure resistance, insulation performance, flexibility, and environmental friendliness. Traditional MPP pipes are mainly made of virgin polypropylene (PP) as the base resin, with the addition of toughening agents, fillers, and other modifying materials.

[0003] However, with increasing environmental awareness and the advancement of the "dual carbon" goal, reducing plastic pollution and carbon emissions has become an inevitable requirement for industrial development. The extensive use of virgin plastics not only consumes petroleum resources, but also generates high carbon emissions during its production process. On the other hand, large quantities of plant fiber waste (such as wood flour, bamboo flour, rice husks, and bagasse) generated by agriculture and the food industry are typically incinerated or landfilled, resulting in resource waste and environmental pollution.

[0004] Combining recycled polypropylene (rPP) with plant fibers to prepare composite materials theoretically achieves both resource recycling and cost reduction. However, this technological approach faces numerous technical challenges:

[0005] (1) Poor compatibility: Plant fiber surface is rich in hydroxyl groups, which are hydrophilic substances, while rPP is a non-polar hydrophobic polymer. The interfacial bonding force between the two is weak, which leads to a decrease in the mechanical properties of the composite material.

[0006] (2) Poor dispersibility: Plant fibers tend to agglomerate in the rPP matrix, forming stress concentration points, which affects the uniformity and stability of the material.

[0007] (3) Poor thermal stability: Plant fibers are prone to thermal degradation at processing temperatures, which leads to darkening of the material color and deterioration of its performance.

[0008] (4) rPP performance fluctuates greatly: the source of recycled materials is complex, the performance is unstable, and it may contain impurities and degradation products. It is difficult to meet the requirements of national standards (such as GB / T 20218, CJ / T 458, etc.) when directly used in cable protection pipes with high performance requirements.

[0009] Therefore, developing a method that can effectively solve the above problems and produce high-performance, high-value-added, environmentally friendly MPP pipes has important practical significance and economic value. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fibers, as well as its preparation method. This protection pipe not only meets relevant national standards and achieves high-value utilization of waste resources, but also solves the key technical problems of poor compatibility and dispersibility between rPP and plant fibers through a unique formula and process design.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] The first aspect of this invention is to provide an environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber, comprising the following parts of raw materials:

[0013] Recycled polypropylene (rPP): 50-80 parts; plant fiber: 10-30 parts; compatibilizer: 3-10 parts; toughening agent: 5-15 parts; heat stabilizer: 0.5-2 parts; lubricant: 1-3 parts; antioxidant: 0.3-1 parts.

[0014] Preferably, the plant fiber is one or more of wood flour, bamboo flour, rice husk flour or sugarcane bagasse flour, with a particle size of 100-400 mesh.

[0015] Preferably, the compatibilizer is one or more of maleic anhydride-grafted polypropylene, ethylene-acrylate-maleic anhydride terpolymer, or titanate coupling agent.

[0016] Preferably, the compatibilizer is a compound compatibilizer, comprising: maleic anhydride-grafted polypropylene as the main compatibilizer, supplemented by ethylene-acrylate-maleic anhydride terpolymer, and 0.5%-1% titanate coupling agent added during the plant fiber pretreatment stage; wherein, the maleic anhydride-grafted polypropylene accounts for 60%-80% of the total compatibilizer, the ethylene-acrylate-maleic anhydride terpolymer accounts for 20%-40% of the total compatibilizer, and the amount of titanate coupling agent added is determined based on the quality of the plant fiber.

[0017] Preferably, the toughening agent is one or more of polyolefin elastomer, styrene-butadiene-styrene block copolymer, or ethylene-vinyl acetate copolymer.

[0018] Preferably, the toughening agent is a compound toughening agent, comprising: a polyolefin elastomer as the main toughening phase, and a small amount of ethylene-vinyl acetate copolymer with high VA content; wherein the polyolefin elastomer as the main toughening phase accounts for 70%-90% of the total toughening agent, and the ethylene-vinyl acetate copolymer accounts for 10%-30% of the total toughening agent.

[0019] Preferably, the heat stabilizer is a composite stabilizing system, comprising: a primary antioxidant and a secondary antioxidant; wherein the primary antioxidant is a hindered phenol, and the secondary antioxidant is a phosphite; the mixing ratio of the two is 1:1 to 1:2; the hindered phenol is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and the phosphite is tris(2,4-di-tert-butylphenyl)phosphite.

[0020] Preferably, the lubricant includes an internal lubricant and an external lubricant to achieve both internal and external lubrication; the internal lubricant is calcium stearate, and the external lubricant is polyethylene wax or Fischer-Tropsch wax.

[0021] Preferably, the antioxidant is a thioester-based auxiliary antioxidant, specifically dilauryl thiodipropionate or distearate thiodipropionate; or, the antioxidant is a ternary synergistic stabilizing system formed by hindered phenols, phosphites, and thioesters.

[0022] A second aspect of the present invention is to provide a method for preparing an environmentally friendly MPP cable protection tube as described in the first aspect, comprising the following steps:

[0023] S1, Prepare the raw materials according to the first aspect;

[0024] S2, pretreatment of plant fibers, including: drying plant fibers at 80-120℃ for 2-4 hours to reduce their moisture content to less than 1%; then surface treatment of the dried plant fibers with a silane coupling agent solution, followed by drying again;

[0025] S3, pretreatment of recycled polypropylene rPP, including screening, cleaning and granulation of recycled polypropylene rPP to ensure its purity and uniformity.

[0026] S4, after high-speed mixing of all raw materials, pretreated plant fiber and recycled polypropylene rPP, a premix is ​​obtained, including: adding pretreated plant fiber, rPP, compatibilizer, toughening agent, heat stabilizer, lubricant and antioxidant into a high-speed mixer and mixing at 80-110℃ for 5-10 minutes to obtain the premix.

[0027] S5, based on the premix, melt blending and granulation includes: feeding the premix into a twin-screw extruder for melt blending, extrusion, cooling, and pelletizing to obtain composite modified material particles; wherein the processing temperature of the twin-screw extruder is: zone 1 160-170℃, zone 2 170-180℃, zone 3 180-190℃, zone 4 190-200℃, and die head 200-210℃; the screw speed of the twin-screw extruder is 200-400 rpm;

[0028] S6, Pipe forming based on the composite modified material particles: The composite modified material particles are fed into a single screw extrusion pipe production line, and after melting, extrusion, sizing, cooling, traction and cutting, the environmentally friendly MPP cable protection pipe is obtained. The pipe forming temperature is controlled at 190-210℃.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) Environmental protection and resource recycling: Using recycled polypropylene and waste plant fiber as the main raw materials, the dependence on virgin plastics has been greatly reduced, and the high-value utilization of solid waste has been realized, which is in line with the green and low-carbon development concept.

[0031] (2) Excellent comprehensive performance: The plant fiber is surface-treated with a silane coupling agent and a highly efficient compatibilizer (such as PP-g-MAH) is selected, which significantly improves the interfacial compatibility between the plant fiber and the rPP matrix and enhances the interfacial adhesion, thereby effectively overcoming the problem of decreased mechanical properties caused by the addition of plant fiber. With the addition of toughening agent and stabilizer system, the final product can meet or even exceed the national standard requirements for MPP cable protection pipes in terms of ring stiffness, impact resistance and heat resistance.

[0032] (3) Good processability: Through optimized formulation and step-by-step heating process, the plant fiber is well dispersed in the matrix, avoiding thermal degradation and scorching during processing, and ensuring production stability and pipe surface quality.

[0033] (4) Cost advantage: The raw material cost is significantly lower than that of traditional virgin PP-based MPP pipes, giving it a strong market competitiveness. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the specific embodiments or related technologies of the present invention, the drawings used in the description of the specific embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 A process flow diagram illustrating the preparation method of the environmentally friendly MPP cable protection pipe provided in this embodiment of the invention. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0037] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] Example 1

[0040] This embodiment provides an environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber, comprising the following parts of raw materials:

[0041] Recycled polypropylene (rPP): 50-80 parts; plant fiber: 10-30 parts; compatibilizer: 3-10 parts; toughening agent: 5-15 parts; heat stabilizer: 0.5-2 parts; lubricant: 1-3 parts; antioxidant: 0.3-1 parts.

[0042] In a preferred embodiment, the plant fiber is one or more of wood flour, bamboo flour, rice husk flour or sugarcane bagasse flour, with a particle size of 100-400 mesh.

[0043] In a preferred embodiment, the compatibilizer is one or more of maleic anhydride-grafted polypropylene (PP-g-MAH), ethylene-acrylate-maleic anhydride terpolymer, or titanate coupling agent.

[0044] (1) Maleic anhydride-grafted polypropylene (PP-g-MAH) is a technology that achieves a responsive effect based on the principle of "like dissolves like" and chemical reactivity. The main chain of PP-g-MAH is polypropylene, which has excellent chemical compatibility with the matrix recycled polypropylene (rPP), ensuring that it is well dispersed and anchored in the rPP matrix. The grafted maleic anhydride (MAH) functional groups are strongly electrophilic groups, which can undergo esterification reactions or form strong hydrogen bonds with the abundant hydroxyl groups (-OH) on the surface of plant fibers at high temperatures during melt blending. This is equivalent to building countless "molecular bridges" between the polar plant fibers and the non-polar rPP, fundamentally changing the properties of the interface and upgrading the physical "point contact" to a chemical "bonding". When directly blended, the interfacial adhesion between plant fibers and rPP is extremely weak, which is the weakest link in the material. The introduction of maleic anhydride-grafted polypropylene (PP-g-MAH) significantly improves the interfacial bonding strength through chemical bonding, thereby effectively transferring externally applied stress from the matrix to the fiber and fully leveraging the reinforcing potential of plant fibers.

[0045] (2) The ethylene-acrylate-maleic anhydride terpolymer forms a flexible interface layer design. The molecular chains of the terpolymer are more flexible and longer than those of maleic anhydride-grafted polypropylene (PP-g-MAH). Its acrylate segments provide excellent flexibility and elasticity. When used in conjunction with maleic anhydride-grafted polypropylene (PP-g-MAH), its long molecular chains can better wrap and entangle plant fibers, forming a flexible, energy-absorbing transition layer in the interface region. Although maleic anhydride-grafted polypropylene (PP-g-MAH) alone improves the bonding strength, the interface is too rigid and prone to brittle fracture under impact. After introducing the flexible terpolymer, the flexible interface layer can effectively absorb and disperse impact energy, passivate crack tips, and enable the material to have both high strength and better toughness.

[0046] (3) Titanate coupling agents are used for surface pretreatment and to reduce polarity. One end of the titanate coupling agent molecule can react chemically with the hydroxyl groups on the surface of plant fibers, while the long-chain organic groups at the other end are compatible with the polypropylene matrix. This process “coats” and “modifies” the surface of the fiber before it is mixed into the polymer matrix, which significantly reduces the surface polarity and hygroscopicity of the plant fiber.

[0047] Plant fibers are highly hygroscopic, and the water vapor generated at high processing temperatures can cause pores in the finished product and accelerate polymer degradation. Pretreatment with titanate not only improves the wettability between the fiber and the polymer but also fundamentally suppresses the "moisture" problem during processing, thereby improving product quality and processing stability.

[0048] A more preferred compatibilizer formulation is: using maleic anhydride-grafted polypropylene (PP-g-MAH) as the main compatibilizer (accounting for 60%-80% of the total compatibilizer), supplemented with ethylene-acrylate-maleic anhydride terpolymer (20%-40%), and adding 0.5%-1% titanate coupling agent (based on the quality of plant fiber) during the plant fiber pretreatment stage.

[0049] The synergistic combination of the above three compatibilizers results in:

[0050] (1) Significantly improved interfacial strength. While PP-g-MAH alone can improve the interface, the composite system of "PP-g-MAH + flexible terpolymer" produces a strong and tough interfacial structure. The tensile and flexural strength of the composite material are further increased by 15%-25% compared with the system using a single compatibilizer. In addition, the impact strength does not decrease due to excessive interfacial strength, but rather increases significantly due to the presence of the flexible layer.

[0051] (2) Improved processing fluidity and product appearance. Pretreatment with titanate greatly improves the dispersibility of plant fibers in the melt, reduces the viscosity of the system, increases melt fluidity, reduces injection or extrusion pressure, and decreases energy consumption. The surface finish of the product is significantly improved, and defects such as surface roughness and porosity caused by fiber agglomeration or moisture are basically eliminated.

[0052] (3) Improved long-term resistance to damp heat aging. The coating of plant fibers with titanate and the strong interfacial bonding reduce the channels for water intrusion, resulting in a reduction of the water absorption rate of the composite material by more than 50%. In this embodiment, an accelerated aging test at 80℃ / 95%RH was conducted, and the experiment confirmed that the mechanical property retention rate was much higher than that of the untreated or single compatibilizer system, which greatly extended the service life of this environmentally friendly material in humid environments (such as underground cable protection pipes).

[0053] In a preferred embodiment, the toughening agent is one or more of polyolefin elastomer (POE), styrene-butadiene-styrene block copolymer (SBS), or ethylene-vinyl acetate copolymer (EVA).

[0054] (1) Polyolefin elastomers (POEs) have good compatibility and form an "island structure" for toughening: Polyolefin elastomers (POEs) are copolymers of ethylene and α-olefins. Their molecular structure is highly similar to that of polypropylene, thus they have excellent compatibility with the matrix of recycled polypropylene rPP. They can be uniformly dispersed in the continuous phase ("sea phase") of recycled polypropylene rPP in micron-sized particles ("island phase"). The efficient toughening mechanism of polyolefin elastomers (POEs) is that when the material is subjected to impact, these uniformly distributed, soft POE particles act as stress concentration points, which can induce a large number of crazes and shear bands in the surrounding rPP matrix. This process absorbs a large amount of impact energy. At the same time, the POE particles themselves can terminate the propagation of crazes through their own deformation and cavitation, preventing them from developing into destructive cracks. This is the most classic and efficient elastomer toughening mechanism.

[0055] (2) Styrene-butadiene-styrene block copolymer (SBS) was chosen because of the synergistic effect of rigid and elastic particles. The polystyrene (PS) hard segments in SBS are glassy micro-regions at room temperature, which can act as reinforcing points, providing a certain degree of rigidity and modulus. The polybutadiene (PB) soft segments provide elasticity. Under specific ratios, SBS can achieve a balance between toughening and minimal loss of rigidity.

[0056] (3) As a preferred embodiment, the ethylene-vinyl acetate copolymer (EVA) is particularly a high-VA-content ethylene-vinyl acetate copolymer (EVA). EVA exhibits polarity matching and interfacial compatibilization; the vinyl acetate (VA) segments in the ethylene-vinyl acetate copolymer (EVA) are polar, which gives it a certain affinity for polar plant fibers. When used in combination with POE, the ethylene-vinyl acetate copolymer (EVA) tends to distribute at the interface between the plant fibers and the POE / rPP matrix, further strengthening interfacial adhesion, and especially improving the toughness loss that may be caused by the addition of plant fibers. It plays a dual role as a "toughening agent" and a "compatibility agent."

[0057] A more preferred formulation for toughening agents is to use polyolefin elastomer (POE) as the main toughening phase (accounting for 70%-90% of the total toughening agent) and to compound a small amount of ethylene-vinyl acetate copolymer (EVA) with high VA content (10%-30%).

[0058] The compounding of toughening agents achieved the following technical effects:

[0059] (1) Good low-temperature toughness: In low-temperature environments of 0℃ or even -20℃, the notched impact strength of the simply supported beam of the composite material can maintain more than 80% of that at room temperature, which is far superior to the system without toughening or using other toughening agents (such as EPDM). This is crucial for buried cable protection pipes to cope with the severe cold in winter, and effectively avoids protection failure caused by brittle fracture.

[0060] (2) Optimized rigidity-toughness balance: By compounding POE with a small amount of EVA, the impact strength is significantly improved (reaching 3-5 times that of the pure rPP / plant fiber system), while the decrease in the flexural modulus and tensile strength of the material is controlled to a minimum (<15%). This excellent rigidity-toughness balance ensures that the protective pipe has good impact resistance and foundation settlement resistance, while still maintaining sufficient ring stiffness to withstand soil pressure and is not easily flattened.

[0061] (3) Improve processing stability: POE has a narrow molecular weight distribution and controllable branching degree. Its melt strength is high, which helps to maintain the stability of the pipe wall during extrusion molding and prevent sagging or deformation, making the produced protective pipe more accurate in size and more uniform in wall thickness.

[0062] As a preferred embodiment, the heat stabilizer is a composite stabilization system, comprising: a primary antioxidant and a secondary antioxidant; wherein the primary antioxidant is a hindered phenol and the secondary antioxidant is a phosphite; the mixing ratio of the two is 1:1 to 1:2.

[0063] In this embodiment, the hindered phenol is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010); the phosphite is tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168).

[0064] The composite stabilizing system heat stabilizer was added in this embodiment because the recycled polypropylene (rPP) has undergone one processing aging, and its molecular chain has more weaknesses, requiring stronger stabilization protection.

[0065] (1) Hindered phenols (antioxidant 1010) are used as chain terminators. During thermo-oxidative aging, polymers generate free radicals (R·, ROO·), which are autocatalytic chain reactions. Hindered phenolic antioxidants provide active hydrogen atoms to quickly capture and eliminate the generated peroxy free radicals (ROO·), converting them into stable hydroxyl compounds, thereby interrupting the propagation of the chain reaction. They are the first line of defense against thermo-oxidative aging.

[0066] (2) Phosphite esters (antioxidant 168) are selected as auxiliary antioxidants to act as hydroperoxide decomposers. During processing and use, polymers generate hydroperoxides (ROOH), which are the source of decomposition into new free radicals. Phosphite ester antioxidants reduce these hydroperoxides into stable alcohols, clearing free radical precursors before they are generated. They have a synergistic effect with the main antioxidant, forming a complete defense network and significantly improving stabilization efficiency.

[0067] Technical advantages of composite stabilizing system heat stabilizers:

[0068] (1) Improved stability after multiple processing: Experimental evaluation showed that the rPP / plant fiber composite material containing the composite stabilizing system exhibited significantly lower changes in melt flow rate (ΔMFR) and yellow index (YI) after two or even three melt regranulation processes compared to the system using a single stabilizer. This indicates that the system can effectively inhibit molecular chain degradation and discoloration during processing, providing a guarantee for the recycling of the material.

[0069] (2) Significantly extended long-term thermal aging life: Through thermal aging tests in a 120℃ oven, the composite stable system can extend the oxidation induction period (OIT) of the material by several times. In practical applications, cable protection pipes can better resist the slow thermo-oxidative aging caused by ground temperature and cable self-heating during long-term underground service, and the service life is expected to be increased by more than 50%.

[0070] (3) It has a protective effect on plant fibers: The stable system not only protects rPP, but also inhibits the oxidation and yellowing of plant fibers at high temperatures, ensuring the long-term stability of the product color and avoiding premature degradation of mechanical properties due to fiber degradation.

[0071] In a preferred embodiment, the lubricant includes both internal and external lubricants, thus achieving both internal and external lubrication.

[0072] In a preferred embodiment, the internal lubricant is calcium stearate, and the external lubricant is polyethylene wax (PEWax) or Fischer-Tropsch wax.

[0073] Calcium stearate can reduce melt viscosity and also act as an acid absorbent. It exhibits compatibility with polypropylene, penetrating between polymer molecular chains to reduce internal friction and thus lower melt viscosity. This improves the plasticizing process, reduces torque and energy consumption in processing equipment, and also contributes to more uniform dispersion of plant fibers. Furthermore, calcium stearate can neutralize trace amounts of acidic substances that may be generated during processing (such as plant fiber decomposition products or residual catalyst decomposition products in rPP), protect other additives, and improve system stability.

[0074] Polyethylene wax is used for interface lubrication and demolding. Polyethylene wax has poor compatibility with polypropylene and migrates to the interface between the melt and the metal equipment (screw, barrel, die) during processing, forming a lubricating film. This greatly reduces the adhesion and friction between the melt and the metal wall, ensuring a smooth surface on the extruded pipe, preventing melt fracture, and increasing output.

[0075] The combined use of internal and external lubricants achieves comprehensive lubrication from the inside of the melt to the processing interface, thereby obtaining high-yield and high-quality plastic products. Specific technical effects include:

[0076] (1) It has good processability in high-filling systems. In high-filling systems containing up to 30 parts of plant fiber, the lubrication system can still ensure that the melt has good fluidity, so that the extruder main current is stable, the output is increased by more than 20%, and high-speed extrusion can be achieved.

[0077] (2) Improved surface quality and dimensional accuracy of the product. Due to the excellent demolding effect, the inner and outer surfaces of the extruded pipe are extremely smooth, without scratches, sharkskin or other defects, which not only makes it aesthetically pleasing but also reduces the friction when laying cables. At the same time, stable melt delivery ensures that the pipe wall thickness is uniform, the concentricity is high, and the ring stiffness is more consistent.

[0078] (3) The plant fiber dispersion was optimized. Good internal lubrication created conditions for the sliding and rearrangement of plant fibers in the matrix, effectively preventing local stress concentration and processing channel blockage caused by fiber agglomeration.

[0079] In a preferred embodiment, the antioxidant overlaps with the heat stabilizer but is used for long-term resistance to heat and oxygen aging. In addition to the system described above for processing stability, to further enhance long-term durability, the antioxidant employs a thioester-based auxiliary antioxidant. In a preferred embodiment, the thioester-based auxiliary antioxidant is dilauryl thiodipropionate (DLTDP) or distearate thiodipropionate (DSTDP), thereby forming a long-lasting and durable hydroperoxide decomposition capability. Thioester-based antioxidants have better thermal stability, thus providing a more durable and longer-lasting hydroperoxide decomposition capability. It complements the heat stabilizer, ensuring continuous and stable antioxidant protection throughout the material's entire lifespan.

[0080] In a preferred embodiment, the antioxidant is a ternary synergistic stabilizing system formed by hindered phenol, phosphite, and thioester, thereby enabling the environmentally friendly MPP protective pipe to achieve an ultra-long service life under long-term thermo-oxidative aging conditions. In accelerated aging tests simulating a 50-year service life, its mechanical properties (such as impact strength) retention rate far exceeds industry standard requirements, providing power cables with a protection period far exceeding expectations. Furthermore, the ternary synergistic stabilizing system, through a clever combination of different mechanisms and consumption rates, achieves durability performance comparable to high-end specialty materials at a relatively reasonable cost.

[0081] Example 2

[0082] like Figure 1 As shown, this embodiment provides a method for preparing an environmentally friendly MPP cable protection pipe according to Embodiment 1, including the following steps:

[0083] S1. Prepare raw materials according to Example 1;

[0084] S2, pretreatment of plant fibers, including: drying plant fibers at 80-120℃ for 2-4 hours to reduce their moisture content to less than 1%; then surface treatment of the dried plant fibers with a silane coupling agent solution, followed by drying again;

[0085] S3, pretreatment of recycled polypropylene rPP, including screening, cleaning and granulation of recycled polypropylene rPP to ensure its purity and uniformity.

[0086] S4, after high-speed mixing of all raw materials, pretreated plant fiber and recycled polypropylene rPP, a premix is ​​obtained, including: adding pretreated plant fiber, rPP, compatibilizer, toughening agent, heat stabilizer, lubricant and antioxidant into a high-speed mixer and mixing at 80-110℃ for 5-10 minutes to obtain the premix.

[0087] S5, based on the premix, perform melt blending and granulation, including: feeding the premix into a twin-screw extruder for melt blending, extrusion, cooling and pelletizing to obtain composite modified material particles.

[0088] In a preferred embodiment, the processing temperature of the twin-screw extruder is: 160-170℃ in zone 1, 170-180℃ in zone 2, 180-190℃ in zone 3, 190-200℃ in zone 4, and 200-210℃ at the die head; the screw speed of the twin-screw extruder is 200-400 rpm.

[0089] S6, Pipe forming based on the composite modified material particles: The composite modified material particles are fed into a single-screw extrusion pipe production line, and after melting, extrusion, sizing, cooling, traction, and cutting, the environmentally friendly MPP cable protection pipe is obtained. The forming temperature is controlled at 190-210℃.

[0090] The two embodiments described above, through meticulous and synergistic molecular design of the five major auxiliary agent systems—compatibilizer, toughening agent, heat stabilizer, lubricant, and antioxidant—not only solved the inherent core technical challenges of poor compatibility, low toughness, insufficient thermal stability, and processing difficulties in blending recycled polypropylene with plant fibers, but also produced unexpected technical effects through the synergistic effect between the components: including excellent rigidity-toughness balance, superior low-temperature impact resistance, smooth product surface, efficient processing flowability, and ultra-long heat and oxygen aging resistance. These effects collectively elevate what might have been a "conservative material" with performance shortcomings into a high-value product with comprehensive performance comparable to some traditional new materials, and with greater green and cost advantages.

[0091] Through the above description of the embodiments, those skilled in the art can clearly understand that the above embodiments can be implemented by software, or by using software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solutions of the above embodiments can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, mobile hard drive, etc.), including several instructions to cause a computer device (such as a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber, characterized in that, Including the following quantities of ingredients: Recycled polypropylene (rPP): 50-80 parts; plant fiber: 10-30 parts; compatibilizer: 3-10 parts; toughening agent: 5-15 parts; heat stabilizer: 0.5-2 parts; Lubricant: 1-3 parts; Antioxidant: 0.3-1 part.

2. The environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber according to claim 1, characterized in that, The plant fiber is one or more of wood flour, bamboo flour, rice husk flour or sugarcane bagasse flour, with a particle size of 100-400 mesh.

3. The environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber according to claim 1, characterized in that, The compatibilizer is one or more of maleic anhydride-grafted polypropylene, ethylene-acrylate-maleic anhydride terpolymer, or titanate coupling agent.

4. The environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber according to claim 1, characterized in that, The compatibilizer is a compound compatibilizer, comprising: maleic anhydride-grafted polypropylene as the main compatibilizer, supplemented by ethylene-acrylate-maleic anhydride terpolymer, and 0.5%-1% titanate coupling agent added during the plant fiber pretreatment stage; wherein, the maleic anhydride-grafted polypropylene accounts for 60%-80% of the total compatibilizer, the ethylene-acrylate-maleic anhydride terpolymer accounts for 20%-40% of the total compatibilizer, and the amount of titanate coupling agent added is determined based on the quality of the plant fiber.

5. The environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber according to claim 1, characterized in that, The toughening agent is one or more of polyolefin elastomers, styrene-butadiene-styrene block copolymers, or ethylene-vinyl acetate copolymers.

6. The environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber according to claim 1, characterized in that, The toughening agent is a compound toughening agent, comprising: a polyolefin elastomer as the main toughening phase, and a small amount of ethylene-vinyl acetate copolymer with high VA content; wherein the polyolefin elastomer as the main toughening phase accounts for 70%-90% of the total toughening agent, and the ethylene-vinyl acetate copolymer accounts for 10%-30% of the total toughening agent.

7. The environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber according to claim 1, characterized in that, The heat stabilizer is a composite stabilizing system, comprising: a primary antioxidant and a secondary antioxidant; wherein the primary antioxidant is a hindered phenol, and the secondary antioxidant is a phosphite; the mixing ratio of the two is 1:1 to 1:2; the hindered phenol is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and the phosphite is tris(2,4-di-tert-butylphenyl)phosphite.

8. The environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber according to claim 1, characterized in that, The lubricant includes an internal lubricant and an external lubricant, thus providing both internal and external lubrication; the internal lubricant is calcium stearate, and the external lubricant is polyethylene wax or Fischer-Tropsch wax.

9. The environmentally friendly MPP cable protection pipe based on recycled polypropylene and plant fiber according to claim 1, characterized in that, The antioxidant is a thioester-based auxiliary antioxidant, specifically dilauryl thiodipropionate or distearate thiodipropionate; or, the antioxidant is a ternary synergistic stabilizing system formed by hindered phenols, phosphites, and thioesters.

10. The method for preparing the environmentally friendly MPP cable protection pipe according to any one of claims 1-9, characterized in that, Includes the following steps: S1, Prepare raw materials according to any one of claims 1-9; S2, pretreatment of plant fibers, including: drying plant fibers at 80-120℃ for 2-4 hours to reduce their moisture content to less than 1%; then surface treatment of the dried plant fibers with a silane coupling agent solution, followed by drying again; S3, pretreatment of recycled polypropylene rPP, including screening, cleaning and granulation of recycled polypropylene rPP to ensure its purity and uniformity. S4, after high-speed mixing of all raw materials, pretreated plant fiber and recycled polypropylene rPP, a premix is ​​obtained, including: adding pretreated plant fiber, rPP, compatibilizer, toughening agent, heat stabilizer, lubricant and antioxidant into a high-speed mixer and mixing at 80-110℃ for 5-10 minutes to obtain the premix. S5, based on the premix, melt blending and granulation includes: feeding the premix into a twin-screw extruder for melt blending, extrusion, cooling, and pelletizing to obtain composite modified material particles; wherein the processing temperature of the twin-screw extruder is: zone 1 160-170℃, zone 2 170-180℃, zone 3 180-190℃, zone 4 190-200℃, and die head 200-210℃; the screw speed of the twin-screw extruder is 200-400 rpm; S6, Pipe forming based on the composite modified material particles: The composite modified material particles are fed into a single screw extrusion pipe production line, and after melting, extrusion, sizing, cooling, traction and cutting, the environmentally friendly MPP cable protection pipe is obtained. The pipe forming temperature is controlled at 190-210℃.

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