Composite polypropylene masterbatch and its application in container bags

Abstract

The application discloses a kind of composite polypropylene masterbatch and its application in container bag, it relates to the technical field of polymer material processing and modification, the masterbatch includes narrow distribution high fluidity polypropylene carrier, nano reinforcing rigid particle, reactive interface grafting agent, bridging type surface active agent (amino silane coupling agent), strong alpha-nucleating agent and neutral long-acting light stabilizing system.Preparation method is through controlled hydrolysis activation in the surface of nanoparticle pre-anchor active amino, then through reactive extrusion initiation amidation reaction, construct "inorganic-organic-polymer" double covalent bond bridging network, and using nucleating agent to induce matrix to form high orientation string crystal structure.The application effectively solves the interface debonding and broken silk problem of container bag flat silk under high times stretching, realizes the synergistic promotion of high axial rigidity, excellent weather resistance and processing continuity.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing and modification technology, and in particular to a composite polypropylene masterbatch and its application in container bags. Background Technology

[0002] Polypropylene (PP) is widely used in the production of flat filaments for flexible intermediary bags (FIBCs) due to its low density, good mechanical properties, and resistance to chemical corrosion. FIBCs, as heavy-duty packaging materials, typically need to withstand loads exceeding tons and are often used outdoors, thus placing extremely high demands on the tensile strength, creep resistance, and weather resistance of the matrix material. To meet these performance requirements, existing technologies typically modify polypropylene by adding masterbatches. For example, patent document CN106589578A discloses a composite material using jute fiber to reinforce polypropylene, attempting to improve material strength by introducing macroscopic fibers; patent document CN116945730B discloses an easily recyclable polypropylene composite material, improving recyclability by introducing soft components such as polyethylene (HDPE); and patent document CN103319783B discloses an anti-aging masterbatch with added hindered amine light stabilizers to solve the powdering problem of woven bags.

[0003] However, the aforementioned existing technologies still have significant technical defects when practically applied to the high-ratio stretching process of FIBC flat yarns. First, regarding reinforcement modification, the macroscopic fibers or conventional large-particle inorganic fillers used in CN106589578A are often much larger in size than the microfiber diameter after flat yarn stretching. During high-speed drawing and high-ratio stretching (usually 5-7 times), they are prone to clogging fine filter screens (such as 200 mesh) or causing stress concentration, resulting in frequent yarn breakage or rough surface of the flat yarns. Moreover, the interface bonding between conventional fillers and the matrix is ​​mostly physical coating, which is prone to debonding and cavitation under high-ratio stretching, thus limiting the improvement of strength. Second, regarding toughening and recyclability modification, although the introduction of soft components such as HDPE in CN116945730B improves toughness or recyclability, it inevitably destroys the crystal regularity of polypropylene, resulting in a decrease in the modulus (rigidity) of the material. The FIBCs made from this material are prone to creep, deformation, or even tipping over when stacked under heavy loads. Finally, regarding weather resistance modification, the hindered amine light stabilizers commonly used in CN103319783B are mostly alkaline. To address the aforementioned interfacial bonding issues, acidic maleic anhydride grafts are typically added. However, during melt blending, these two components readily undergo acid-base neutralization reactions, leading to the failure of both the reinforcing and weather-resistant components. Therefore, developing a composite masterbatch that simultaneously achieves continuity in high-ratio stretching processes, high rigidity and creep resistance, and long-lasting chemical inert protection is a pressing technical challenge in the field of FIBC (Flexible Intermediate Bulk Container) materials. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a composite polypropylene masterbatch and its application in FIBCs, so as to solve one or more problems in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A composite polypropylene masterbatch comprises the following components in parts by weight.

[0007] 30-60 parts of narrow-distribution, high-flowability polypropylene carrier;

[0008] 25-45 parts of nano-reinforced rigid particles;

[0009] 5-12 parts of reactive interfacial grafting agent;

[0010] 1-3 parts of bridging surfactant;

[0011] 1-4 parts of potent α-nucleating agent;

[0012] 3-6 parts of a neutral, long-lasting light-stabilized system;

[0013] 2-5 parts of rheology processing aid;

[0014] The reactive interface grafting agent is polypropylene grafted with maleic anhydride, the bridging surfactant is an aminosilane coupling agent, and the neutral long-lasting light-stabilizing system is a compound of N-OR type alkoxyamine hindered amine light stabilizer and ultraviolet absorber.

[0015] Specifically, the narrow-distribution high-flowability polypropylene carrier is homopolymer polypropylene with an isotacticity ≥97%, a melt mass flow rate of 15-25 g / 10 min at 230℃ and 2.16 kg load, and a molecular weight distribution width index of 2.5-4.0.

[0016] Specifically, the nano-reinforced rigid particles are selected from nano-calcium carbonate or fumed silica, with a primary particle size of 40-80 nm and a specific surface area ≥25 m². 2 / g.

[0017] Specifically, the grafting rate of the reactive interface grafting agent is ≥1.0%, and the melt mass flow rate is ≥50g / 10min at 230℃ and 2.16kg load; the bridging surfactant is specifically γ-aminopropyltriethoxysilane.

[0018] Specifically, the potent α-nucleating agent is selected from sorbitol derivatives or organophosphate nucleating agents; the neutral long-lasting light-stabilizing system is composed of an N-OR type alkoxyamine hindered amine light stabilizer and an ultraviolet absorber in a mass ratio of 2:1; and the rheology processing aid is a compound of polyethylene wax and zinc stearate.

[0019] A method for preparing composite polypropylene masterbatch, comprising the following steps.

[0020] Step 1: Controlled activation pretreatment of nanoparticles. The rigid nanoparticles are placed into a high-speed mixer equipped with a heating and liquid spraying system. They are stirred and dried at 100-105℃ and 300-500 r / min. The speed is then increased to 1500-2000 r / min, and an anhydrous ethanol solution containing 20-30% (w / w) of a bridging surfactant is sprayed in atomized form. The reaction is maintained at 100-105℃ and 1500-2000 r / min for 10-15 minutes with stirring to obtain the pretreated nanoparticles.

[0021] Step 2: Multi-component mixing. The pretreated nano-reinforced rigid particles are mixed uniformly with a narrow-distribution, high-flowability polypropylene carrier, a reactive interfacial grafting agent, a potent α-nucleating agent, a neutral, long-lasting light-stabilizing system, and a rheology processing aid according to the weight ratio of the components.

[0022] Step 3: Reactive extrusion granulation. The mixed material is fed into a multi-stage twin-screw extruder with a total length-to-diameter ratio ≥44 for melt extrusion. The temperature of the reaction zone of the extruder is controlled at 215-225℃. The melt is filtered, granulated, and dried to obtain the composite polypropylene masterbatch.

[0023] Specifically, in step 1, the stirring and drying time is 5-10 min, and the drying control condition is to retain the surface adsorbed water of the monolayer; the solution spraying time of the bridging surfactant is controlled at 3-5 min, and the stirring reaction time is controlled at 10-15 min.

[0024] Specifically, in step 3, the screw speed of the multi-stage tandem twin-screw extruder is set to a gradient distribution, wherein the feed stage speed is 300 r / min, the melting stage speed is 400 r / min, the reaction zone speed is 500 r / min, and the homogenization stage speed is 450 r / min.

[0025] Specifically, in step 3, the vacuum degree of the twin-screw extruder is controlled to be ≤-0.06MPa, and the filtration process is performed using a 200-mesh double-layer filter.

[0026] Furthermore, the composite polypropylene masterbatch is mixed with the fiber-grade polypropylene base material at a mass ratio of 1-3:20, and then melt-extruded at a temperature of 190-240°C, followed by a stretching of 5.5-6.5 times.

[0027] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0028] (i) By combining the pre-anchoring of nanoparticles with an aminosilane coupling agent with a polypropylene-grafted maleic anhydride reaction system, a stable "inorganic-organic-polymer" dual covalent bond bridging network is constructed between the inorganic rigid particles and the resin matrix through in-situ amidation chemical reaction during extrusion. This chemical bonding mechanism differs from the physical coating or single coupling agent treatment commonly used in existing technologies. It effectively solves the problem of interfacial debonding of rigid particles with the matrix during high-ratio drawing, thereby significantly improving the breaking strength of the flat yarn in the container bag while ensuring the continuity of the high-speed drawing process and eliminating yarn breakage caused by interfacial defects.

[0029] (ii) By combining a highly regular homopolymer polypropylene carrier with a powerful α-nucleating agent, the crystal locking effect of the nucleating agent induces the matrix to form a highly oriented tandem crystal structure during stretching, thus eliminating the need for introducing soft components such as polyethylene to improve recyclability, as is common in existing technologies. This micro-morphology control differs from the compromise approach of sacrificing material rigidity for recyclability in existing technologies. It endows the flat yarns of the container bag with excellent axial modulus and creep resistance, ensuring morphological stability under heavy-duty stacking, while maintaining high melt homogeneity of the single-material system during recycling.

[0030] (III) A chemically inert and compatible system was constructed by combining a neutral N-OR type alkoxyamine photostable system with an acidic interface-enhancing component, and by incorporating the physical scattering effect of nanoparticles on ultraviolet light. This component design distinguishes itself from the defects in existing technologies where additives fail due to acid-base neutralization reactions. It avoids chemical antagonism between the reinforcing system and the weather-resistant system, and establishes a synergistic protection mechanism of "chemical free radical capture + physical ultraviolet shielding," achieving simultaneous improvement in the mechanical properties and weather-resistant lifespan of the container bag under long-term outdoor conditions. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the logical flow of the composite masterbatch preparation and wire drawing process in this invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and exemplary descriptions. It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0033] Comprehensive explanation

[0034] The following is a detailed description of the invention. This section is written strictly according to the core technical solution of the invention, and elaborates in detail the component selection, preparation process and inherent physicochemical modification mechanism of the high-orientation polypropylene composite masterbatch for container bags, aiming to enable those skilled in the art to reproduce the technical solution without ambiguity.

[0035] I. Raw material system and formulation design of composite masterbatch

[0036] This invention provides a highly oriented polypropylene composite masterbatch for container bags based on dual interfacial reaction toughening. This masterbatch, through specific component blending, constructs a dual chemical bonding network of "inorganic-organic-polymer" at the microscopic level, and induces the matrix to form a highly oriented crystal structure.

[0037] 1. Basic carrier and reinforcing components

[0038] 1.1 Narrowly distributed, high-flowability polypropylene carrier (component A)

[0039] This component acts as a continuous phase matrix in the system, serving as a dispersing functional aid and ensuring compatibility with downstream matrix materials.

[0040] (1) Selection requirements: Homopolymer polypropylene (Homo-PP) should be selected, with its isotacticity controlled at ≥97% to ensure the basic mechanical modulus.

[0041] (2) Rheological parameter constraints:

[0042] ① Melt mass flow rate (MFI): Controlled at 15-25 g / 10 min (230℃, 2.16 kg). This range is significantly higher than that of conventional FIBC fiber grade polypropylene (typically 2-4 g / 10 min). This viscosity gradient design is based on the "wetting-shear-dispersion" kinetic mechanism, that is, during the masterbatch dilution process, the low-viscosity masterbatch melt can preferentially wet and coat the high-viscosity base material, and rapidly achieve micro-uniform dispersion under shear force, eliminating "crystal points" or "pitting" defects.

[0043] ② Molecular Weight Distribution Width Index (MWD): Controlled between 2.5 and 4.0. The narrow distribution design aims to reduce the elastic memory effect of long-chain molecules, prevent the melt from expanding off the die during extrusion, and ensure the flatness of the flat yarn surface.

[0044] 1.2 nm reinforced rigid particles (component B)

[0045] This component is the core that provides mechanical reinforcement and also serves as a "molecular pinning point" in the orientation process.

[0046] (1) Material selection: Nano calcium carbonate (preferably cubic crystal form) or fumed silica are selected.

[0047] (2) Geometric size limitation: The original particle size is strictly controlled within 40-80nm, and the specific surface area is ≥25m². 2 / g.

[0048] (3) Size effect mechanism: The microfiber diameter of the flat yarn in the container bag after high stretching is usually between 0.5-2μm. The particle size selected in this invention is much smaller than the microfiber diameter (<0.1μm), and it exhibits quasi-homogeneous fluid behavior in the melt, eliminating the risk of stress concentration and clogging caused by macroscopic particles (such as μm-level fillers).

[0049] 2. Dual-interface chemical bridging system

[0050] This invention abandons the traditional physical coating method and constructs covalent bonds between component C and component G through chemical reaction.

[0051] 2.1 Bridging surfactant (component G)

[0052] (1) Chemical composition: Specifically refers to γ-aminopropyltriethoxysilane (KH-550).

[0053] (2) Bridging mechanism: The molecule has a bifunctional structure. After hydrolysis, the siloxane group at one end undergoes a condensation reaction with the hydroxyl group on the surface of the inorganic particles (component B) to form the first chemical bond (inorganic-organic bond); the primary amino group (-NH2) at the other end is exposed and serves as the active site for subsequent reactions.

[0054] 2.2 Reactive interfacial grafting agent (component C)

[0055] (1) Chemical composition: Polypropylene grafted with maleic anhydride (PP-g-MAH).

[0056] (2) Activity parameters: grafting rate ≥1.0%, MFI ≥50g / 10min. High fluidity ensures that it can preferentially wet and cover the surface of activated nanoparticles.

[0057] (3) Reaction mechanism: Under the high temperature and strong shear conditions of extrusion processing, the anhydride group on its side chain undergoes ring opening and undergoes amidation reaction with the primary amino group reserved in component G to generate a stable amide bond (-CO-NH-). This is the second chemical bond (organic-polymer bond).

[0058] 3. Functional additive system

[0059] 3.1 Highly effective α-nucleating agent (component D)

[0060] (1) Selection: Selected from third-generation sorbitol derivatives (such as DMDBS) or organophosphates (such as NA-21).

[0061] (2) Crystal form regulation mechanism: The nucleating agent can induce polypropylene molecular chains to form a dense shish-kebab structure along the axial direction in the tensile flow field. This structure endows the flat yarn with extremely high axial rigidity and creep resistance, replacing the traditional technical route of introducing polyethylene (HDPE) for toughening but sacrificing rigidity.

[0062] 3.2 Neutral, long-lasting photostable system (E component)

[0063] (1) Composition: It is composed of N-OR type (alkoxyamine) hindered amine light stabilizer and ultraviolet absorber in a mass ratio of 2:1.

[0064] (2) Chemical inertness principle: Traditional hindered amines are alkaline and easily undergo acid-base neutralization reaction with acidic C component (PP-g-MAH), thus becoming ineffective. This invention uses an N-OR type structure, which eliminates the alkaline sites in the molecule and makes it neutral, thereby ensuring that the reinforcing component and the weather-resistant component do not interfere with each other and work synergistically in the same system.

[0065] 3.3 Rheology processing aids (component F)

[0066] A compound of polyethylene wax and zinc stearate is used to reduce processing energy consumption and improve appearance gloss.

[0067] II. Refined Preparation Process of Composite Masterbatch

[0068] The preparation process of this invention is divided into two key stages: "controlled activation" and "reactive extrusion". The setting of process parameters directly serves the construction of the microstructure.

[0069] 1. Step 1: Controlled activation pretreatment of nanoparticles

[0070] This step aims to complete the first chemical bond (particle-silane) and transform the hydrophilic hard aggregates into hydrophobic microparticles with active amino groups.

[0071] 1.1 Drying and Humidity Conditioning

[0072] The nano-reinforced rigid particles are put into a high-speed mixer with a heating jacket and dried at low speed at 100-105℃ for 5-10 minutes.

[0073] Key process control points: The degree of drying should be controlled to "remove physically adsorbed water while retaining surface adsorbed water of the monolayer". Retaining trace amounts of moisture is a necessary condition for initiating the hydrolysis of the silane coupling agent; excessive drying will lead to grafting failure.

[0074] 1.2 High-shear fluidization and atomization grafting

[0075] (1) Increase the rotation speed to 1500-2000 r / min and use high shear force to disperse the powder into a fluidized suspension state.

[0076] (2) The bridging surfactant (component G) is dissolved in anhydrous ethanol and sprayed evenly into the mixing chamber in atomized form within 3-5 minutes through a liquid injection system. Atomized feeding prevents local liquid agglomeration.

[0077] 1.3 Reaction Curing and Endpoint Control

[0078] The reaction was stirred at 100-105℃ and high speed for 10-15 minutes to allow the hydrolyzed silane to fully dehydrate and condense with the hydroxyl groups on the particle surface.

[0079] Testing criteria: The contact angle of the sampled powder is tested until it reaches ≥90 degrees (indicating that the surface has changed from hydrophilic to hydrophobic) before the material can be discharged for the next step.

[0080] 2. Step 2: Mixing of multiple components

[0081] The pretreated nanoparticles, along with the carrier (A), grafting agent (C), nucleating agent (D), light stabilizer (E), and processing aid (F), are added to a mixing device in a predetermined weight ratio and mixed thoroughly. Excessive friction during this process should be avoided to prevent material agglomeration.

[0082] 3. Step 3: Reactive extrusion granulation

[0083] This step aims to complete the second chemical bonding (amidation reaction) and the final dispersion and granulation.

[0084] 3.1 Equipment Configuration

[0085] Multiple stages of co-rotating twin-screw extruders with an overall length-to-diameter ratio (L / D) ≥ 44 are selected in series to ensure sufficient reaction residence time.

[0086] 3.2 Screw speed gradient distribution design

[0087] (1) Feeding stage (300r / min): Ensure stable feeding and prevent bridging.

[0088] (2) Melting stage (400r / min): Rapidly achieves resin plasticization.

[0089] (3) Reaction zone (500 r / min): Set the maximum rotation speed to provide a strong shear field. High shear increases the probability of collision between the anhydride group and the amino group, which greatly improves the conversion rate of the amidation reaction.

[0090] (4) Homogenization stage (450 r / min): Stabilize pressure and prepare for extrusion.

[0091] 3.3 Reaction kinetics control of temperature field

[0092] The temperature of the extruder reaction zone is controlled at 215-225℃.

[0093] Mechanism explanation: This temperature window is the activation range for the amidation reaction. Below 215℃, the reaction rate is low and the interfacial binding is weak; above 225℃, it may lead to thermal decomposition of the light stabilizer or degradation of the matrix.

[0094] 3.4 Process Control and Post-processing

[0095] (1) Vacuum devolatilization: control the vacuum degree ≤ -0.06MPa to remove small molecule byproducts and moisture generated in the reaction and prevent bubbles from causing fiber breakage.

[0096] (2) Precision filtration: The melt must be filtered through a 200-mesh double-layer filter. The ability to continuously pass through a 200-mesh filter is the gold standard for verifying whether the nano-dispersion has reached the "quasi-homogeneous" state.

[0097] (3) Pelletizing and drying: conventional water ring hot cutting or strip cutting, followed by drying to obtain finished masterbatch.

[0098] III. Application Methods of Composite Masterbatch

[0099] The composite masterbatch described in this invention is specifically used for preparing high-strength, high-strength FIBC flat yarns, and its application process is as follows:

[0100] 1. Mixing: Mix the composite masterbatch with the fiber-grade polypropylene base material in a certain proportion (5-15% by mass).

[0101] 2. Melt extrusion: Plasticization is carried out in the wire drawing unit, and the processing temperature range is set to 190-240℃.

[0102] 3. Directional stretching: The nascent film / filament after extrusion and cooling is subjected to unidirectional thermal stretching, with the stretching ratio controlled at 5.5-6.5 times.

[0103] Technical benefits: Due to the presence of nano-pinning points and highly efficient nucleating agents in the masterbatch, this system can withstand a higher draw ratio than ordinary fillers (usually 4-5 times). Through high-ratio draw, the molecular chains are further straightened, thereby obtaining extremely high breaking strength and low thermal shrinkage.

[0104] To verify the practical application effect of the composite masterbatch described in this invention in the production of flat yarns for FIBCs (Flexible Intermediate Bulk Containers), particularly the influence of the specifications and microstructure of key components on the final performance of the product, a comparative experiment was designed based on the fundamental principles of materials science. This experiment aims to examine, through the controlled variable method, the decisive roles of the size effect of nanoparticles, the effectiveness of interfacial chemical bonding, and the chemical compatibility of the photostable system on the mechanical strength, processing continuity, and weather resistance of the flat yarns, thereby demonstrating the non-obviousness of this technical solution.

[0105] IV. Performance Testing Standards and Experimental Design

[0106] Based on the aforementioned modification mechanism of the composite masterbatch, and in accordance with the objective laws of polymer physics and fracture mechanics, this experiment selected three technical characteristics that have the most significant impact on product performance as core variables:

[0107] 1. Enhance the geometric scale of particles: According to Griffith's microcrack theory, the particle size of filler determines the critical size of internal defects in the material, which directly affects the fracture behavior of flat wire under high tensile strength.

[0108] 2. Functional group type of surfactant: According to the theory of interfacial adhesion, the functional group determines whether an "amidation reaction" can occur to form a chemical bridge, which directly determines the stress transfer efficiency of the interface.

[0109] 3. Acidity and alkalinity of the light-stabilized system: Based on acid-base reaction kinetics, it determines whether the weathering agent will undergo a quenching reaction with the acidic grafting agent, which is directly related to the long-term protective capability of the material.

[0110] 1. Performance Testing Methods

[0111] The testing methods used in this experiment are all based on current and generally accepted industry objective testing standards. The specific procedures are as follows:

[0112] (1) Tensile properties test of flat wire

[0113] The prepared flat wire samples were conditioned in a standard constant temperature and humidity environment. Using a universal testing machine equipped with pneumatic clamps, an initial gauge length was set, and the samples were axially stretched at a constant tensile speed until fracture. The maximum breaking load and elongation at fracture were recorded, and the breaking strength (unit: g / den or N / tex) and elongation at fracture were calculated based on the linear density (tex number) of the flat wire. This test reflects the ultimate load-bearing capacity of the material.

[0114] (2) Artificial accelerated aging (weather resistance) test

[0115] A xenon arc lamp aging test chamber was used to simulate outdoor sunlight exposure. The blackboard temperature was set to 63±3℃, a specific irradiance was set, and periodic water spraying was implemented to simulate rain. Flat wire samples were fixed on a sample holder for continuous irradiation. At fixed time intervals (e.g., 200 hours), a portion of the samples was removed, and their retained tensile strength was determined according to the tensile property testing method described above. The time elapsed until 50% of the tensile strength retention rate was taken as the failure time, thereby evaluating the weather resistance life of the material.

[0116] (3) Melt filtration pressure value (processing continuity / dispersion) test

[0117] A filtration performance tester equipped with a melt gear pump and a precision pressure sensor was used. The composite masterbatch and matrix resin were mixed in a specific ratio and added to an extruder. The melt was metered through a pre-selected filter assembly (200 mesh). The melt pressure before the filter was recorded as a function of time. The pressure increase per unit time (ΔP / t) was calculated. A lower value indicates fewer agglomerates in the melt, better dispersibility, and a lower risk of screen clogging and fiber breakage during fiber drawing.

[0118] (4) Impact strength of cantilever beam with notch

[0119] The masterbatch is injection molded into standard specimens, and a V-notch of a specified depth is machined into them. A pendulum impact testing machine is used to measure the work consumed in breaking the specimen. This indicator is used to help characterize the toughness and interfacial bonding state of the material under instantaneous impact.

[0120] 2. Experimental group setup and variable control

[0121] To verify the impact of the above three variables, an embodiment (representing the solution of the present invention) and a comparative example (representing the prior art or a situation that deviates from the solution of the present invention) are set up.

[0122] Example group: 40-80nm calcium carbonate, aminosilane (KH-550), PP-g-MAH and neutral HALS system were used.

[0123] Comparative Example 1 (Variable under investigation: particle size): Component B was replaced with ordinary fine calcium carbonate with a particle size of 2-5 μm, while the remaining components and processes remained the same as in the Example. This aimed to verify the influence of the "nanosize effect" on the high-stretch breakage rate.

[0124] Comparative Example 2 (Variable under investigation: interfacial chemical bonding): Component G was replaced with a non-amino alkyl silane (such as isobutyltriethoxysilane), which cannot undergo amidation with component C. The remaining components and processes remained consistent with the examples. The aim was to verify the contribution of "dual chemical bridging" to fracture strength.

[0125] Comparative Example 3 (Variable under investigation: chemical compatibility): Component E was replaced with a conventional basic hindered amine light stabilizer (such as a polymeric piperidine), which reacts with component C in an acid-base reaction. The remaining components and processes remained consistent with the examples. This aimed to verify the protective effect of a "neutral system" on weather resistance.

[0126] Exemplary Description

[0127] Based on the above-mentioned objective and rigorous single-factor controlled variable experimental design, the decisive influence of various microstructural regulation methods on macroscopic performance in this technical solution can be intuitively verified through specific experimental data. In order to fully demonstrate the technical advantages of this technical solution and the necessity of setting parameter ranges, one baseline group, seven single-variable optimized embodiment groups, four single-variable verification control groups, and one blank control group are selected as typical groups for detailed explanation.

[0128] Example 1 (Unique Benchmark Group)

[0129] A high-orientation polypropylene composite masterbatch for FIBCs (Flexible Intermediate Bulk Containers) toughened by dual interfacial reaction, its preparation method, and its application are disclosed. The specific steps are as follows:

[0130] (1) Controlled activation pretreatment of nanoparticles:

[0131] Thirty-five parts (by weight) of nano-calcium carbonate (cubic crystal form) with a native particle size of 60 nm and a specific surface area of ​​28 m² / g were added to a high-speed mixer equipped with a heating jacket and a liquid spraying system. Heating was turned on, raising the material temperature to 102 °C. The mixture was then stirred and dried at a low speed of 400 r / min for 8 minutes to remove physically adsorbed water while retaining monolayer surface adsorbed water. The speed was then increased to 1800 r / min to fluidize the powder into a suspension. Two parts (by weight) of γ-aminopropyltriethoxysilane (KH-550) were dissolved in anhydrous ethanol to prepare a 25% (w / w) solution, which was then uniformly sprayed into the mixer through an atomizing nozzle over 4 minutes. The mixture was stirred and reacted for 12 minutes under high shear conditions of 102 °C and 1800 r / min. Sampling and testing showed a powder contact angle of 95°, yielding pretreated nanoparticles as the discharged product.

[0132] (2) Multi-component mixing:

[0133] The pretreated nanoparticles were mixed with 45 parts of narrow-distribution homopolymer polypropylene carrier with a melt flow rate (MFI) of 20 g / 10 min and a molecular weight distribution width index (MWD) of 3.2, 8 parts of polypropylene grafted with maleic anhydride (PP-g-MAH) with a grafting rate of 1.2% and an MFI of 60 g / 10 min, 2.5 parts of third-generation sorbitol derivative (DMDBS) as a strong α-nucleating agent, 4.5 parts of a compound of N-OR type alkoxyamine hindered amine light stabilizer and ultraviolet absorber (mass ratio 2:1), and 3 parts of rheology processing aid composed of polyethylene wax and zinc stearate in a mixer in proportion.

[0134] (3) Reactive extrusion granulation:

[0135] The mixed material is fed into a four-stage tandem co-rotating twin-screw extruder with an overall length-to-diameter ratio of 48:1. Independent speeds are set for each extruder stage to create a gradient distribution: 300 r / min for the feeding stage, 400 r / min for the melting stage, 500 r / min for the reaction stage, and 450 r / min for the homogenization stage. Temperatures are set for each zone of the extruder, with the reaction stage (Zones 4-6) controlled at 220℃. Under this temperature and shear field, the anhydride groups of PP-g-MAH undergo an amidation reaction with the amino groups on the surface of the nanoparticles. The melt flows through a 200-mesh double-layer filter installed at the die head for filtration, with the vacuum level controlled at -0.07 MPa. After extrusion, the material undergoes water ring heat cutting and centrifugal drying to obtain the composite masterbatch.

[0136] (4) Application in the preparation of flat filaments:

[0137] Ten parts of the above composite masterbatch were mixed with 90 parts of drawing-grade polypropylene base material (T30S) at a mass ratio, melt-extruded at 230°C in a drawing unit, and after water quenching, 6.0 times unidirectional hot stretching was performed, and the material was shaped and wound up to obtain high-orientation container bag flat yarn.

[0138] Example 2 (Univariate fill amount group: low fill)

[0139] The only difference between this embodiment and Example 1 is that the amount of component B nano-reinforced rigid particles is adjusted to 25 parts, and the amount of narrow-distribution high-flow polypropylene carrier is adjusted to 55 parts accordingly. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0140] Example 3 (Single-variable fill amount group: optimized fill)

[0141] The only difference between this embodiment and Example 1 is that the amount of component B nano-reinforced rigid particles is adjusted to 30 parts, and the amount of narrow-distribution high-flow polypropylene carrier is adjusted to 50 parts accordingly. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0142] Example 4 (Univariate fill size group: high fill)

[0143] The only difference between this embodiment and Example 1 is that the amount of component B nano-reinforced rigid particles is adjusted to 40 parts, and the amount of narrow-distribution high-flow polypropylene carrier is correspondingly adjusted to 40 parts. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0144] Example 5 (Single-variable fill amount group: limit fill)

[0145] The only difference between this embodiment and Example 1 is that the amount of component B nano-reinforced rigid particles is adjusted to 45 parts, and the amount of narrow-distribution high-flow polypropylene carrier is adjusted to 35 parts accordingly. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0146] Example 6 (Single-variable grafting agent group: medium grafting)

[0147] The only difference between this embodiment and Example 1 is that the amount of reactive interfacial grafting agent in component C is adjusted to 10 parts, and the amount of narrow-distribution high-flowability polypropylene carrier is adjusted to 43 parts accordingly. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0148] Example 7 (Single-variable grafting agent group: high grafting)

[0149] The only difference between this embodiment and Example 1 is that the amount of reactive interface grafting agent in component C is adjusted to 12 parts, and the amount of narrow-distribution high-flowability polypropylene carrier is adjusted to 41 parts accordingly. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0150] Example 8 (Single-variable nucleating agent group: high nucleation)

[0151] The only difference between this embodiment and Example 1 is that the amount of the potent α-nucleating agent in component D is adjusted to 4 parts, and the amount of the narrow-distribution, high-flowability polypropylene carrier is adjusted accordingly to 43.5 parts. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0152] Comparative Example 1 (Univariate Particle Size Validation Control)

[0153] The only difference between this embodiment and Example 1 is that component B is ordinary fine heavy calcium carbonate with an average particle size of 3 μm (3000 nm), which does not meet the nanoscale requirements of this scheme. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0154] Comparative Example 2 (Univariate Interface Bonding Validation Control)

[0155] The only difference between this embodiment and Example 1 is that component G is isobutyltriethoxysilane (without amino groups), which does not meet the requirements of this scheme regarding aminosilane coupling agents. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0156] Comparative Example 3 (Univariate Reaction Temperature Verification Control)

[0157] The only difference between this embodiment and Example 1 is that the temperature of the extruder reaction stage in step 3 is set to 190℃, which does not conform to the 215-225℃ reaction temperature limit of this scheme. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0158] Comparative Example 4 (Verification Control of Univariate Weather Resistance System)

[0159] The only difference between this embodiment and Example 1 is that component E uses an alkaline polymeric hindered amine light stabilizer (Chimassorb 944), which does not meet the requirements of this scheme for a neutral N-OR type system. All other raw material specifications, proportions, and preparation process parameters are exactly the same as in Example 1.

[0160] Comparative Example 5 (Blank Control)

[0161] This embodiment employs existing conventional filler masterbatch technology. The formulation consists of: 60 parts ordinary homopolymer polypropylene (MFI=3), 35 parts calcium carbonate with a particle size of 3μm, 3 parts aluminate coupling agent, and 2 parts ordinary composite anti-aging agent (without added UV absorbers and nucleating agents). The preparation process is conventional blending extrusion at a temperature of 190-210℃, without filtration or using a 40-mesh coarse filter. In application, it is also mixed with the base material at a mass ratio of 10:90 and stretched.

[0162] The key performance indicators of the bulk bag flat yarns (final products) and processing procedures prepared for the above 13 typical groups were tested.

[0163] Test metric description:

[0164] Tensile strength (g / den): Characterizes the ultimate load-bearing capacity of flat wire; the higher the value, the better.

[0165] Weather resistance strength retention rate (%): The percentage of fracture strength retained after 500 hours of xenon lamp aging, which characterizes the long-term protection capability. The higher the value, the better.

[0166] Processing pressure rise (MPa / 24h): Characterizes the rate of pressure increase during melt filtration, reflecting dispersion and wire breakage risk; the lower the value, the better.

[0167] Table 1: Summary Table of Process Variables and Performance Test Results for Each Embodiment

[0168] Group Grouping properties Explanation of differences in core variables Variable value Fracture strength (g / den) Weather resistance strength retention rate (%) Processing pressure rise (MPa / 24h) Example 1 Unique benchmark group Basic formula, no variable adjustments 35 parts of nano calcium carbonate 6.4 85.1 0.65 Example 2 Univariate filler groups low filler 25 parts of nano calcium carbonate 5.88 87.2 0.43 Example 3 Univariate filler groups Optimize fill amount 30 parts of nano calcium carbonate 7.1 89.6 0.52 Example 4 Univariate filler groups High filler content 40 parts of nano calcium carbonate 6.55 82.3 0.98 Example 5 Univariate filler groups Maximum fill volume 45 parts of nano calcium carbonate 6.7 80.8 0.87 Example 6 Univariate grafting agent group Grafting agent dosage 10 portions of PP-g-MAH 6.72 84.6 0.72 Example 7 Univariate grafting agent group High grafting agent dosage PP-g-MAH 12 portions 6.85 83.9 0.81 Example 8 Univariate nucleating agent group High nucleating agent dosage 4 parts of α-nucleating agent 6.63 84.2 0.68 Comparative Example 1 Univariate particle size validation control Large particle size control Particle size 3000nm 4.85 75.2 5.55 Comparative Example 2 Univariate interface bonding validation comparison aminosilane-free control Isobutylsilane 5.12 72.5 1.25 Comparative Example 3 Univariate reaction temperature verification control Low temperature reaction control Reaction zone 190℃ 5.05 71.8 1.88 Comparative Example 4 Univariate weathering system validation control alkaline HALS control basic hindered amines 6.2 35.4 0.70 Comparative Example 5 Blank control Existing conventional masterbatch Macro filler / non-reactive 4.15 25.6 2.50

[0169] Based on the experimental results with strictly controlled variables, in order to further reveal the intrinsic mechanism by which microstructure regulation determines macroscopic performance in this technical solution, an in-depth interpretation of the experimental data is necessary. This section will move beyond simply listing data and instead analyze, from the perspectives of multi-objective optimization and physicochemical mechanisms, how various process parameters, through complex nonlinear coupling effects, ultimately determine the comprehensive service performance of the FIBC flat yarn.

[0170] Comprehensive analysis and mechanism explanation of experimental data:

[0171] Based on the experimental results with strictly controlled variables, in order to further reveal the intrinsic mechanism by which microstructure regulation determines macroscopic performance in this technical solution, an in-depth interpretation of the experimental data is necessary. This section will move beyond simply listing data and instead analyze, from the perspectives of multi-objective optimization and physicochemical mechanisms, how various process parameters, through complex nonlinear coupling effects, ultimately determine the comprehensive service performance of the FIBC flat yarn.

[0172] 1. Critical threshold analysis of nanosize effect:

[0173] Comparing the data differences between Comparative Example 1 and Example 1, it can be seen that the particle geometric scale is a "hard constraint" that determines the continuity of processing.

[0174] Mechanism analysis: According to the microcrack propagation theory, the critical size of internal defects in a material determines its fracture strength. When the particle size is much larger than the diameter of the microfiber after the flat wire is stretched (0.5-2μm), the particle itself becomes a huge stress concentration point and crack source; at the same time, the physical blockage effect generated by macroscopic particles when flowing through a precision filter will cause the melt pressure to increase explosively.

[0175] Conclusion: Confining particles to the nanoscale is not only for reinforcement, but also to meet the stringent requirements of high-stretching processes for "quasi-homogeneous fluids". Once this size threshold is exceeded, the processing performance and mechanical properties of the material will drop precipitously.

[0176] 2. The necessity of dual-interface chemical bridging:

[0177] Comparing the data differences between Comparative Examples 2 and 3 and Example 1, it can be seen that "amidation reaction" is the core driving force of this technical solution.

[0178] Mechanism analysis: In the absence of active amino groups (Comparative Example 2) or when the reaction temperature is insufficient to overcome the activation energy barrier (Comparative Example 3), the interface is maintained solely by van der Waals forces or weak physical entanglement. Under the strong shear field of high-multiplication stretching, this weak interaction instantly fails, leading to the debonding of particles from the matrix and the generation of interfacial vacancies.

[0179] Conclusion: Only by constructing a stable covalent bond network through high-temperature induced chemical reactions can the efficient transfer of stress between the two phases be guaranteed. Any adjustment of variables that leads to the failure of this chemical bond will directly result in a significant drop in the strength index.

[0180] 3. The decisive impact of chemical compatibility on lifespan:

[0181] Comparing the data differences between Comparative Example 4 and Example 1, it can be seen that "acid-base reaction kinetics" has a veto power in formulation design.

[0182] Mechanism analysis: The reaction rate between acidic interfacial grafting agents and basic light stabilizers is extremely fast in the molten state. This side reaction not only consumes the anhydride groups of the grafting agent, causing it to lose its reinforcing effect, but also leads to the "quenching" of the active center of the light stabilizer.

[0183] Conclusion: Using a neutral system is not simply an added bonus, but a prerequisite for ensuring the coexistence of the reinforcing and weather-resistant systems. Once this chemically inert environment is disrupted, the weather life of the material will experience a non-linear, catastrophic decline.

[0184] 4. Nonlinear equilibrium mechanism for multi-objective optimization:

[0185] Comparing the data differences between Examples 1-5, it can be seen that the optimal performance solution does not appear at the extreme points of the lowest or highest filling amount, but rather in the middle optimized filling group (Example 3).

[0186] Mechanism Analysis: This is a typical multi-objective optimization problem, with the objective function consisting of three core indicators: fracture strength, weather resistance retention rate, and processing pressure rise. When the filler content is too low, although the processing fluidity is excellent, there is a lack of sufficient nano-"pinning points" to restrict molecular chain slippage, resulting in the reinforcement effect not reaching its peak. When the filler content is too high and approaches the limit, although the number of rigid particles increases, the shrinking interparticle spacing leads to an exponential increase in the probability of agglomeration. The sharp increase in processing pressure rise acts as a "penalty term," significantly reducing the overall performance, and excessive interface defects begin to offset the reinforcement effect.

[0187] Conclusion: The intermediate optimization group maximized the interfacial chemical bonding density while ensuring sufficient dispersion of nanoparticles, thus achieving the optimal balance point in three dimensions.

[0188] 5. Univariate performance verification of grafting agents and nucleating agents:

[0189] Comparing the data differences of Examples 1, 6, and 7, it can be seen that as the amount of grafting agent increased from 8 parts to 12 parts, the tensile strength increased by 6.4%, but the processing pressure increased by 24.6%, reflecting the balance between interfacial bonding force and processing fluidity. Comparing the data differences of Examples 1 and 8, it can be seen that as the amount of nucleating agent increased from 2.5 parts to 4 parts, the tensile strength increased by 3.6%, but the weather resistance decreased slightly by 0.9 percentage points, reflecting the balance between rigidity improvement and weather resistance.

[0190] 6. Limitations of existing technology:

[0191] The low score of Comparison Example 5 indirectly confirms the limitations of existing technical approaches. Traditional physical filling or single-modification methods often fall short when faced with the triangular contradiction of "high strength, weather resistance, and ease of processing." This technical solution, however, successfully achieves a leap from "simple mixing" to "integration of structure and function" through the aforementioned multi-dimensional microstructural reconstruction.

[0192] Specific work process:

[0193] Please refer to Figure 1 The nano-reinforced rigid particles first enter a high-speed mixing device, where they are heated and stirred at low speed to remove physically adsorbed water while retaining surface adsorbed water in a monolayer. Subsequently, they are fluidized and suspended under high-speed shearing. A solution containing an aminosilane coupling agent is sprayed into the fluidized powder in the form of an atomization. The silane coupling agent utilizes the trace amount of water on the particle surface to undergo hydrolysis and dehydration condensation reaction with the hydroxyl groups on the particle surface, anchoring silane molecules to the particle surface and exposing active amino groups, thus completing the hydrophobicization and functionalization modification of the particle surface.

[0194] The modified nanoparticles, along with a narrow-distribution, high-flowability polypropylene carrier, polypropylene-grafted maleic anhydride, α-nucleating agent, neutral hindered amine light stabilizer system, and processing aids, are uniformly mixed and then fed into a twin-screw extruder. Under the shearing and conveying action of the screw, the nanoparticles are melted and plasticized. In the reaction zone of the extruder, the high temperature and strong shear field activate the anhydride groups of the polypropylene-grafted maleic anhydride side chains, causing them to open their rings and undergo amidation reactions with the amino groups pre-anchored on the surface of the nanoparticles, generating stable amide bonds. This creates a double covalent bond bridging network of "inorganic-silane-graft-matrix" between the inorganic particles and the resin matrix. Simultaneously, the neutral light stabilizer system is uniformly dispersed in the melt and does not chemically antagonize the acidic grafting agent, while the nucleating agent dissolves in the melt and forms a crystallization precursor.

[0195] After the reaction, the melt is decomposed under vacuum to remove small molecule byproducts and moisture. After being filtered through a precision filter to remove agglomerates, it is granulated to obtain composite masterbatch. When the masterbatch is melt-mixed with polypropylene base material and subjected to high-ratio unidirectional thermal stretching, the chemically bonded nanoparticles act as molecular pinning points to restrain the matrix molecular chains, preventing interface debonding and void generation. At the same time, the nucleating agent induces the polypropylene molecular chains to crystallize in an oriented manner along the stretching direction, forming a highly oriented tandem crystal structure. Finally, it is solidified and shaped into flat yarns for container bags with high axial rigidity and weather resistance.

[0196] The technical features described above can be combined in any way. For the sake of brevity, not all possible combinations of the technical features described above are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A composite polypropylene masterbatch, characterized in that, The components include the following parts by weight: 30-60 parts of narrow-distribution, high-flowability polypropylene carrier; 25-45 parts of nano-reinforced rigid particles; 5-12 parts of reactive interfacial grafting agent; 1-3 parts of bridging surfactant; 1-4 parts of potent α-nucleating agent; 3-6 parts of a neutral, long-lasting light-stabilized system; 2-5 parts of rheology processing aid; The reactive interface grafting agent is polypropylene grafted with maleic anhydride, the bridging surfactant is an aminosilane coupling agent, and the neutral long-lasting light-stabilizing system is a compound of N-OR type alkoxyamine hindered amine light stabilizer and ultraviolet absorber.

2. The composite polypropylene masterbatch as described in claim 1, characterized in that: The narrow-distribution, high-flowability polypropylene carrier is homopolymer polypropylene with an isotacticity ≥97%, a melt flow rate of 15-25 g / 10 min at 230℃ and a load of 2.16 kg, and a molecular weight distribution width index of 2.5-4.

0.

3. The composite polypropylene masterbatch as described in claim 1, characterized in that: The nano-reinforced rigid particles are selected from nano-calcium carbonate or fumed silica, with a native particle size of 40-80 nm and a specific surface area ≥25 m². 2 / g.

4. The composite polypropylene masterbatch as described in claim 1, characterized in that: The reactive interface grafting agent has a grafting rate ≥1.0% and a melt mass flow rate ≥50g / 10min at 230℃ and 2.16kg load; the bridging surfactant is specifically γ-aminopropyltriethoxysilane.

5. The composite polypropylene masterbatch as described in claim 1, characterized in that: The potent α-nucleating agent is selected from sorbitol derivatives or organophosphate nucleating agents; the neutral long-lasting light-stabilizing system is composed of N-OR type alkoxyamine hindered amine light stabilizer and ultraviolet absorber in a mass ratio of 2:1; the rheology processing aid is a compound of polyethylene wax and zinc stearate.

6. A method for preparing composite polypropylene masterbatch, used to prepare the composite polypropylene masterbatch according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1, Controlled activation pretreatment of nanoparticles: The rigid nanoparticles are put into a high-speed mixing device with a heating and liquid spraying system and stirred and dried at a temperature of 100-105℃ and a speed of 300-500 r / min. Then the speed is increased to 1500-2000 r / min, and an anhydrous ethanol solution containing 20-30% by mass of bridging surfactant is sprayed in the form of atomization. The reaction is maintained at a temperature of 100-105℃ and a speed of 1500-2000 r / min for 10-15 min to obtain the pretreated nanoparticles. Step 2, Multi-component mixing: The pretreated nano-reinforced rigid particles are mixed evenly with a narrow-distribution, high-flowability polypropylene carrier, a reactive interface grafting agent, a strong α-nucleating agent, a neutral long-lasting light-stabilizing system, and a rheology processing aid according to the weight ratio of the components. Step 3, reactive extrusion granulation: The mixed material is fed into a multi-stage twin-screw extruder unit with a total length-to-diameter ratio ≥44 for melt extrusion. The temperature of the reaction zone of the extruder is controlled at 215-225℃. After the melt is filtered, it is granulated and dried to obtain the composite polypropylene masterbatch.

7. The preparation method according to claim 6, characterized in that: In step 1, the stirring and drying time is 5-10 min, and the drying control condition is to retain the surface adsorbed water of the monolayer; the solution spraying time of the bridging surfactant is controlled at 3-5 min, and the stirring reaction time is controlled at 10-15 min.

8. The preparation method according to claim 6, characterized in that: In step 3, the screw speed of the multi-stage tandem twin-screw extruder is set to a gradient distribution, wherein the feed stage speed is 300 r / min, the melting stage speed is 400 r / min, the reaction zone speed is 500 r / min, and the homogenization stage speed is 450 r / min.

9. The preparation method according to claim 6, characterized in that: In step 3, the vacuum degree of the twin-screw extruder is controlled to be ≤-0.06MPa, and the filtration process is carried out using a 200-mesh double-layer filter.

10. The application of composite polypropylene masterbatch in the preparation of high-strength FIBC flat yarns, wherein the composite polypropylene masterbatch according to any one of claims 1-5 is used, characterized in that: The composite polypropylene masterbatch is mixed with the fiber-grade polypropylene base material at a mass ratio of 1-3:20, and then melt-extruded at a temperature of 190-240℃, followed by a stretching of 5.5-6.5 times.

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