Anhydrite-polypropylene composite hollow plate and preparation method thereof

Abstract

This invention provides anhydrous gypsum-polypropylene composite hollow board and its preparation method. The anhydrous gypsum-polypropylene composite hollow board comprises the following components by weight percentage: 30%-65% modified anhydrous gypsum powder, 30%-65% polypropylene resin, 1%-3% compatibilizer, 1%-3% lubricant, and 0.1%-0.3% antioxidant. The modified anhydrous gypsum powder is prepared by modifying hydroxylated anhydrous gypsum powder with a composite surface modifier formed by compounding long-chain fatty acids or their derivatives with a coupling agent. The anhydrous gypsum-polypropylene composite hollow board is prepared by a two-step method: first, a high-filler functional masterbatch is prepared, and then the hollow board is extruded. By modifying the anhydrous gypsum powder and combining it with the two-step preparation method, the problems of weak interfacial bonding between anhydrous gypsum and the polypropylene matrix and poor dispersibility with high filler content are solved, thus systematically improving the mechanical properties and processing performance of the composite hollow board.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to an anhydrous gypsum-polypropylene composite hollow board and its preparation method. Background Technology

[0002] Polypropylene (PP) is widely used in the automotive and home appliance industries due to its advantages such as low cost, good processability, low density, and excellent chemical resistance. However, pure polypropylene resin materials have inherent defects such as high shrinkage, insufficient rigidity, and poor heat resistance and low-temperature toughness, which limit its application in high-performance applications. To improve performance and reduce costs, inorganic mineral fillers such as calcium carbonate and talc are usually used for modification.

[0003] Driven by the concepts of circular economy and sustainable development, utilizing industrial solid waste as functional fillers has become a research hotspot. Among these, anhydrous gypsum (phosphogypsum, mainly composed of CaSO4), a major byproduct of phosphate chemical industry, currently has low utilization rates, with large quantities simply stockpiled, posing potential environmental hazards. However, due to its wide availability and low price, it exhibits enormous potential for resource utilization. Using anhydrous gypsum as a filler for polypropylene can not only significantly reduce costs but also improve the stiffness and dimensional stability of the composite material, and impart a certain degree of flame retardancy, resulting in significant economic and environmental benefits. However, the preparation of highly filled anhydrous gypsum-polypropylene composites still faces a series of severe technical challenges, hindering their industrial application: 1) Poor interfacial compatibility and weak bonding: Anhydrous gypsum is a polar hydrophilic inorganic material, while polypropylene is a non-polar hydrophobic polymer. The two are naturally incompatible, resulting in extremely weak interfacial bonding. When the composite is under stress, the stress cannot be effectively transferred from the matrix to the filler. The interfacial area is prone to becoming a stress concentration point and crack source, causing the tensile strength and impact toughness of the material to decrease sharply with the increase of filler content; 2) Difficulty in dispersion at high filler content: Anhydrous gypsum particles have high surface energy and do not wet the polypropylene matrix. At high filler content (usually exceeding 40% mass fraction), they are prone to agglomeration. Polymers not only fail to provide reinforcement, but also become internal defects in the material, severely damaging the material's performance stability and appearance quality; 3) Deterioration of processing performance: The addition of a large amount of inorganic fillers will significantly increase the viscosity of the composite melt and reduce its fluidity, which will bring difficulties to extrusion, injection molding and other molding processes, not only increasing energy consumption and aggravating equipment wear, but also easily leading to poor surface quality of products; 4) When this type of high-filler composite material is applied to components such as hollow boards, the material must have both excellent flexural modulus (rigidity) and sufficient impact strength (toughness). However, composite materials prepared by existing technologies generally exhibit the brittle characteristics of "high rigidity and low toughness", which makes it difficult to meet the stringent requirements of comprehensive mechanical properties of hollow boards in actual use.

[0004] Therefore, how to solve the problems of interfacial bonding and high filling dispersion between inorganic fillers and polymer matrix, synergistically improve the mechanical properties and processing properties of composite materials, and ultimately prepare high-performance products that meet the specific application requirements of hollow boards, is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides an anhydrous gypsum-polypropylene composite hollow board and its preparation method. By modifying the anhydrous gypsum powder, the problems of weak interfacial bonding between inorganic fillers and polymer matrix and poor dispersion of high filler content are solved, thereby systematically improving the mechanical properties and processing performance of the composite hollow board.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] In a first aspect, the present invention provides an anhydrous gypsum-polypropylene composite hollow board, comprising the following components in weight percentages: 30%-65% modified anhydrous gypsum powder, 30%-65% polypropylene resin, 1%-3% compatibilizer, 1%-3% lubricant, and 0.1%-0.3% antioxidant;

[0008] The modified anhydrous gypsum powder is prepared by the following method: introducing hydroxyl functional groups on the surface of anhydrous gypsum powder, and then modifying it with a composite surface modifier formed by combining long-chain fatty acids or their derivatives with a coupling agent to obtain modified anhydrous gypsum powder.

[0009] According to the above scheme, the particle size of the anhydrous gypsum powder is 5-30μm.

[0010] According to the above scheme, the coupling agent is selected from at least one of silane coupling agents, titanate coupling agents, or aluminate coupling agents.

[0011] According to the above scheme, the silane coupling agent is selected from γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane or γ-(methacryloyloxy)propyltrimethoxysilane.

[0012] The titanate coupling agent is selected from isopropyl tris(dioctylpyrophosphoryloxy) titanate or isopropyl triisostearate titanate isopropyl ester.

[0013] The aluminate coupling agent is selected from stearoyloxyisopropyl aluminate or distearate.

[0014] According to the above scheme, the long-chain fatty acid is selected from at least one of fatty acids with C12-C22 carbon atoms.

[0015] According to the above scheme, the amount of the composite surface modifier is 0.5%-2% of the mass of anhydrous gypsum powder, and the mass ratio of long-chain fatty acid or its derivative to coupling agent in the composite surface modifier is 0.5-2:1.

[0016] According to the above scheme, the method of introducing hydroxyl functional groups in the preparation process of modified anhydrous gypsum powder is as follows: micron-sized anhydrous gypsum powder is placed in an alkaline aqueous solution and stirred to introduce hydroxyl functional groups on the surface of the anhydrous gypsum powder, and then washed until neutral and dried.

[0017] According to the above scheme, the alkaline aqueous solution contains one or more alkaline compounds selected from hydroxides, oxides, and carbonates.

[0018] According to the above plan, the stirring temperature is 25-60℃ and the stirring time is 30-60 minutes.

[0019] According to the above scheme, in the process of preparing modified anhydrous gypsum powder, anhydrous gypsum powder with hydroxyl functional groups introduced on its surface is blended with a composite surface modifier to form an organic modified layer on the surface of the powder particles, thereby obtaining the modified anhydrous gypsum powder.

[0020] According to the above scheme, the blending is carried out in a jacketed high-speed mixer. The equipment is preheated to 90-100℃, and the composite surface modifier is diluted and atomized and sprayed onto the powder being stirred at low speed. Then, the temperature is raised to 105-110℃ and stirred at high speed for 8-20 minutes to complete the modification.

[0021] According to the above scheme, the compatibilizer is selected from at least one of maleic anhydride-grafted polypropylene, glycidyl methacrylate-grafted polypropylene, and acrylic acid-grafted polypropylene.

[0022] The lubricant is selected from at least one of montana wax, magnesium stearate, polyethylene wax, and paraffin wax;

[0023] The antioxidant is selected from at least one of pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and tris(2,4-di-tert-butylphenyl) phosphite.

[0024] In some specific embodiments, the melt index of the polypropylene resin is 10-20 g / 10 min.

[0025] In some other embodiments, the polypropylene resin includes a carrier polypropylene resin and a matrix polypropylene resin, wherein the melt index of the carrier polypropylene resin is 10-20 g / 10 min, the melt index of the matrix polypropylene resin is 3-8 g / 10 min, and the carrier polypropylene resin accounts for 20-40% of the total mass of the polypropylene resin.

[0026] Secondly, the present invention provides a method for preparing the above-mentioned anhydrous gypsum-polypropylene composite material, comprising the following steps:

[0027] S1. Preparation of high-filler functional masterbatch: Modified anhydrous gypsum powder is used as the core filler, and is melt-blended with compatibilizer, lubricant, antioxidant and a portion of polypropylene resin, degassing and granulation are carried out to prepare a high-filler functional masterbatch.

[0028] S2. Hollow board extrusion molding: The prepared high-filler functional masterbatch is mixed with the remaining polypropylene resin and extruded through a hollow board extrusion production equipment to obtain the anhydrous gypsum-polypropylene composite hollow board.

[0029] The polypropylene resin added in step S1 is 20-40% of the total mass of polypropylene resin.

[0030] According to the above scheme, in step S1, high-filling functional masterbatch is prepared by a planetary roller extruder. The temperature distribution of the planetary roller extruder barrel is as follows: feeding zone 140-160℃, mixing zone 160-190℃, extrusion zone 180-200℃, and die head 170-190℃; the central screw speed is 30-60 rpm, and the satellite roller speed is 80-160 rpm.

[0031] According to the above scheme, in step S1, high-filling functional masterbatch is prepared by a twin-screw extruder. The temperature settings of the twin-screw extruder are as follows: feeding section 160-180℃, compression section 175-190℃, melting section 180-210℃, homogenization section 175-195℃, die head 170-190℃, and the main extruder speed is set to 250-350 rpm, with the feeding speed matching accordingly.

[0032] According to the above scheme, the polypropylene resin in step S1 is a carrier polypropylene resin with a melt index of 10-20 g / 10 min, and the polypropylene resin in step S2 is a matrix polypropylene resin with a melt index of 3-8 g / 10 min.

[0033] According to the above scheme, the high-filling functional masterbatch prepared in step S1 is spherical or cylindrical particles. The particle size of the spherical particles is between 3-6 mm, and the diameter and height of the cylindrical particles are both between 3-6 mm.

[0034] Anhydrous gypsum, as a core functional filler, is crucial to the final performance of composite materials due to its dispersibility in polymers and its interfacial bonding strength with the polymer matrix. To address the inherent isotropic poorness between polar anhydrous gypsum powder and non-polar polypropylene resin, this invention employs a unique synergistic surface composite modification technology. First, the anhydrous gypsum powder undergoes surface functionalization pretreatment, introducing reactive hydroxyl functional groups onto the powder particle surface. Subsequently, a composite surface modifier, formed by combining long-chain fatty acids or their derivatives with a high-performance coupling agent, is used to modify the powder, creating a stable organic modified layer on the surface of the anhydrous gypsum powder particles. The non-polar long chains of the long-chain fatty acids or their derivatives effectively reduce the surface energy of the anhydrous gypsum, improving its wettability and dispersibility in the polypropylene melt. The coupling agent acts like a "molecular bridge," chemically bonding or physically entangled with the hydroxyl groups on the anhydrous gypsum surface at one end, and forming a strong bond with the polypropylene at the other end, thereby greatly enhancing the interfacial compatibility and bonding strength between the anhydrous gypsum filler and the polypropylene matrix.

[0035] Compatibilizers, as a supplement and enhancement to interfacial interactions, can further improve the affinity between anhydrous gypsum fillers and the polypropylene matrix, effectively transfer stress, and thus improve the mechanical properties of the material; lubricants can reduce frictional resistance during melt processing, improve extrusion efficiency and the surface smoothness of the sheet; and antioxidants can effectively prevent polypropylene from undergoing thermo-oxidative degradation during high-temperature processing, ensuring the long-term performance and stability of the final product.

[0036] The beneficial effects of this invention are:

[0037] 1. The anhydrous gypsum-polypropylene composite hollow board of the present invention introduces modified anhydrous gypsum powder with a high filling amount into the polypropylene matrix. The modified anhydrous gypsum powder has high interfacial compatibility and good dispersibility with the polypropylene matrix. As a core functional filler, it significantly improves the flexural modulus and dimensional stability of the polypropylene hollow board, and improves the problems of insufficient rigidity and easy deformation due to temperature influence of traditional polypropylene hollow boards. Moreover, the resulting composite hollow board has advantages such as high rigidity, high strength, low cost and green environmental protection.

[0038] 2. The preparation method of this invention adopts a two-step process of "first preparing a high-filler functional masterbatch, then diluting and extruding it into shape". First, the modified anhydrous gypsum powder is efficiently mixed with compatibilizer, lubricant and part of polypropylene resin to prepare a high-filler functional masterbatch. Through strong shearing and mixing, the modified anhydrous gypsum powder is ensured to achieve uniform dispersion at the microscopic level in polypropylene. Then, the high-filler functional masterbatch is mixed with the remaining polypropylene resin and extruded into shape using standard hollow board extrusion equipment. This method effectively solves the problem of easy agglomeration and uneven dispersion of anhydrous gypsum powder in high-filler systems, ensuring the quality uniformity and performance stability of the final anhydrous gypsum-polypropylene composite hollow board product, and has high industrial application value.

[0039] 3. Furthermore, the preparation method of the present invention uses polypropylene with different melt indices at different stages. In the first stage of preparing high-filler functional masterbatch, a homopolymer with a melt index in the range of 10-20 g / 10 min is used as the carrier polypropylene resin. Taking advantage of its low viscosity and high fluidity, the modified anhydrous gypsum powder is thoroughly wetted, dispersed and coated, thereby preparing a uniform and stable high-filler functional masterbatch. In the second stage of dilution extrusion molding, a homopolymer with a melt index of 3-8 g / 10 min is used as the matrix polypropylene resin. Taking advantage of its high molecular weight, high melt strength and excellent intrinsic mechanical properties, a robust performance skeleton is constructed for the final composite hollow board, and good processability is ensured. Detailed Implementation

[0040] The principles and features of the present invention are described below with reference to specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0041] The raw materials used in this embodiment of the invention are as follows:

[0042] Anhydrous gypsum powder: In this embodiment of the invention, anhydrous phosphogypsum is used, wherein the content of anhydrous type II anhydrite is 96.37%, the content of calcium sulfate dihydrate is 3.4%, the total content of water-soluble phosphorus and water-soluble fluorine is less than 0.1%, and the particle size distribution is D. 97 Less than 30 micrometers, D 50 Less than 15 micrometers.

[0043] Carrier polypropylene resin (PP): A polypropylene homopolymer with a melt index of 15 g / 10 min (230℃, 2.16 kg) was selected.

[0044] Matrix polypropylene resin (PP): Polypropylene homopolymer with a melt index of 3 g / 10 min (230℃, 2.16 kg) was selected.

[0045] Coupling agents: KH-550 (γ-aminopropyltriethoxysilane), KH-570 (γ-(methacryloyloxy)propyltrimethoxysilane), NDZ-201 (titanium ester coupling agent).

[0046] Long-chain fatty acids: stearic acid (industrial grade 1), oleic acid (industrial grade 1).

[0047] Compatibilizer: Maleic anhydride-grafted polypropylene (PP-g-MAH), with a grafting rate of 1.0%.

[0048] Lubricants: zinc stearate, polyethylene wax.

[0049] Antioxidants: Antioxidant 1010 (pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), primary antioxidant), Antioxidant 168 (tris(2,4-di-tert-butylphenyl)phosphite, secondary antioxidant).

[0050] Example 1

[0051] This embodiment provides an anhydrous gypsum-polypropylene composite hollow board and its preparation method.

[0052] The raw materials for the anhydrous gypsum-polypropylene composite hollow board are as follows: modified anhydrous gypsum powder 46.67%, carrier polypropylene resin 16.20%, compatibilizer (PP-g-MAH) 2.33%, lubricant (zinc stearate: polyethylene wax = 1:1) 1.33%, antioxidant (1010:168 = 1:2) 0.13%, and matrix polypropylene resin 33.34%.

[0053] The modified anhydrous gypsum powder was prepared by the following method:

[0054] a) Surface functionalization pretreatment (hydroxylation)

[0055] 100 kg of anhydrous phosphogypsum powder was added to a reactor. A separate alkaline aqueous solution was prepared (5 kg of sodium hydroxide and 5 kg of sodium sulfate dissolved in 500 L of water). This solution was pumped into the reactor, and stirring was started at 30°C and continued for 45 minutes. After treatment, the slurry was filtered, and the filter cake was repeatedly washed with deionized water until the pH of the wash water reached 7.0. Finally, the washed powder was thoroughly dried in a 120°C oven until the moisture content was below 0.2%.

[0056] b) Multi-synergistic surface composite modification

[0057] Preparation of composite surface modifier: Mix 0.8 kg stearic acid and 0.4 kg silane coupling agent KH-550, and then add 1.2 L of anhydrous ethanol for dilution to obtain a uniform composite surface modifier solution.

[0058] 100 kg of hydroxylated and dried anhydrous gypsum powder was added to a jacketed high-speed mixer. The jacket heating was turned on, and the mixer was preheated to 95°C. The mixer was then started at low speed (approximately 100 rpm), and the composite surface modifier solution was evenly sprayed onto the powder within 5 minutes using an atomizing spraying device (the amount of composite surface modifier was 1.2% of the anhydrous gypsum powder). After spraying, the jacket cooling water was turned off, and the material temperature was raised to 108°C using shear heat and jacket heating. Then, the mixture was stirred at high speed (approximately 1200 rpm) for 12 minutes at this temperature. After the reaction was completed, the material was discharged and cooled to obtain the modified anhydrous gypsum powder.

[0059] The preparation steps of anhydrous gypsum-polypropylene composite hollow board are as follows:

[0060] (1) Preparation of high-filler functional masterbatch

[0061] Modified anhydrous gypsum powder, carrier polypropylene resin, compatibilizer, lubricant, and antioxidant were premixed uniformly in a high-speed mixer and then fed into a twin-screw extruder with a length-to-diameter ratio (L / D) of 44:1. The extruder screw contained two sets of strong kneading blocks and was equipped with one natural vent and one vacuum vent. The extrusion process temperatures were set as follows: feeding section 170℃, compression section 185℃, melting section 190℃, homogenization section 185℃, and die head 180℃. The main extruder speed was set to 300 rpm, and the feeding speed was matched accordingly. After melt blending, venting, extrusion, water cooling, and pelletizing, cylindrical highly filled anhydrous gypsum functional masterbatch with a diameter and height of 4 mm was obtained.

[0062] (2) Extrusion molding of anhydrous gypsum-polypropylene composite hollow board

[0063] High-performance filler masterbatch and matrix polypropylene resin are uniformly mixed at a mass ratio of 2:1. The mixture is added to a single-screw extruder in a hollow board extrusion production line, and undergoes plasticizing extrusion, forming with a special mold for hollow boards, shaping on a vacuum sizing table, cooling, traction by a crawler-type traction machine, and length cutting to finally obtain a 4mm thick high-filler anhydrous gypsum-polypropylene composite hollow board with an anhydrous gypsum content of 46.67%.

[0064] Example 2

[0065] This embodiment provides an anhydrous gypsum-polypropylene composite hollow board and its preparation method.

[0066] The raw materials for the anhydrous gypsum-polypropylene composite hollow board are as follows: 56.25% modified anhydrous gypsum powder, 14.63% carrier polypropylene resin, 2.25% compatibilizer (PP-g-MAH), 1.65% lubricant (zinc stearate: polyethylene wax = 1:2), 0.22% antioxidant (1010:168 = 1:2), and 25.00% matrix polypropylene resin.

[0067] The preparation method of modified anhydrous gypsum powder differs from that in Example 1 in the following ways: a) The stirring temperature in the surface functionalization pretreatment is 40°C, and the stirring time is 30 minutes; b) Multiple synergistic surface composite modification: The composite surface modifier consists of 1.0 kg oleic acid and 0.5 kg silane coupling agent KH-570, with a total dosage of 1.5% of the mass of anhydrous gypsum. The high-speed stirring temperature is 110°C, and the time is 10 minutes.

[0068] The preparation method of the anhydrous gypsum-polypropylene composite hollow board is the same as that in Example 1, and the anhydrous gypsum content of the prepared anhydrous gypsum-polypropylene composite hollow board is 56.25%.

[0069] Example 3

[0070] This embodiment provides an anhydrous gypsum-polypropylene composite hollow board and its preparation method.

[0071] The raw materials for the anhydrous gypsum-polypropylene composite hollow board are as follows: 52.00% modified anhydrous gypsum powder, 16.84% carrier polypropylene resin, 2.40% compatibilizer (PP-g-MAH), 1.60% lubricant (zinc stearate: polyethylene wax = 1:3), 0.16% antioxidant (1010:168 = 1:2), and 27.00% matrix polypropylene resin.

[0072] The preparation method of modified anhydrous gypsum powder differs from that in Example 1 in the following ways: a) the stirring temperature in the surface functionalization pretreatment is 35°C, and the stirring time is 60 minutes; b) multiple synergistic surface composite modification: the composite surface modifier is composed of 0.8 kg stearic acid, 0.2 kg oleic acid, 0.5 kg silane coupling agent KH-550, and 0.3 kg titanate coupling agent NDZ-201, with a total dosage of 1.8% of the mass of anhydrous gypsum. The high-speed stirring temperature is 105°C, and the time is 15 minutes.

[0073] The anhydrous gypsum content in the prepared anhydrous gypsum-polypropylene composite hollow board was 52%.

[0074] Example 4

[0075] This embodiment provides an anhydrous gypsum-polypropylene composite hollow board and its preparation method.

[0076] The raw materials for the anhydrous gypsum-polypropylene composite hollow board are as follows: 35% modified anhydrous gypsum powder, 20.02% carrier polypropylene resin, 2.4% compatibilizer (PP-g-MAH), 2.4% lubricant (zinc stearate: polyethylene wax = 2:1), 0.18% antioxidant (1010:168 = 1:2), and 40% matrix polypropylene resin.

[0077] The preparation method of modified anhydrous gypsum powder differs from that in Example 1 in that: a) the stirring temperature during surface functionalization pretreatment is 25°C and the stirring time is 50 minutes; b) multiple synergistic surface composite modification: the composite surface modifier consists of 0.5 kg stearic acid and 0.3 kg aluminate coupling agent AL-M, with a total amount of 0.8% of the mass of anhydrous gypsum.

[0078] The anhydrous gypsum content in the prepared anhydrous gypsum-polypropylene composite hollow board is 35%.

[0079] Comparative Example 1 was not subjected to hydroxylation pretreatment.

[0080] This comparative example aims to verify the necessity of the surface functionalization pretreatment in step a). The difference from Example 1 lies in the modification method of the modified anhydrous gypsum powder. In this comparative example, the hydroxylation pretreatment in step a) is omitted during the preparation of the modified anhydrous gypsum powder. That is, the untreated raw anhydrous gypsum powder (dried only at 120°C to a moisture content below 0.2%) is directly used for the multiple synergistic surface composite modification in step b). All other steps, formulations, and process parameters remain consistent with Example 1.

[0081] Comparative Example 2 was modified using only a coupling agent, without the use of long-chain fatty acids or their derivatives.

[0082] This comparative example aims to verify the necessity of the synergistic modification of long-chain fatty acids and coupling agents in step b). The difference from Example 1 lies in the modification method of the anhydrous gypsum powder. In this comparative example, the composite surface modifier in step b) of the preparation process of the modified anhydrous gypsum powder does not contain stearic acid. That is, only 0.4 kg of silane coupling agent KH-550 (diluted with 0.4 L of anhydrous ethanol) is used to modify the hydroxylated anhydrous gypsum powder. All other steps, formulations, and process parameters remain consistent with Example 1.

[0083] During the preparation process, it was observed that, compared with Example 1, the powder was prone to "clumping" in the high-speed mixer during the preparation of the high-filling functional masterbatch, resulting in poor dispersion uniformity.

[0084] Comparative Example 3 did not use a compatibilizer

[0085] This comparative example aims to verify the necessity of compatibilizers.

[0086] The preparation method is exactly the same as in Example 1, except that the compatibilizer PP-g-MAH is not added to the formulation of the high-filler masterbatch in step (1). In order to maintain a total mass of 100%, the amount of carrier polypropylene resin is 18.53%, and all other steps, formulations and process parameters are consistent with those in Example 1.

[0087] During the twin-screw extrusion granulation process, it was observed that the melt pressure fluctuated greatly, the surface of the discharge strip was rough, and there were undispersed white spots.

[0088] Comparative Example 4: One-step preparation of composite hollow plates without masterbatch preparation

[0089] The raw materials for the anhydrous gypsum-polypropylene composite hollow board are as follows: 46.67% modified anhydrous gypsum powder, 2.33% compatibilizer (PP-g-MAH), 1.33% lubricant (zinc stearate: polyethylene wax = 1:1), 0.13% antioxidant (1010:168 = 1:2), and 49.54% matrix polypropylene resin.

[0090] This comparative example aims to verify the necessity of first preparing a highly filled anhydrous gypsum functional masterbatch and then combining it with the matrix polypropylene resin to prepare the hollow board in the preparation process of anhydrous gypsum-polypropylene composite hollow board. The difference from Example 1 is that no highly filled functional masterbatch was prepared; instead, a one-step molding process was used. Specifically, in the preparation of the anhydrous gypsum-polypropylene composite hollow board, modified anhydrous gypsum powder, matrix polypropylene resin, compatibilizer, lubricant, and antioxidant were mixed. The mixture was then added to a single-screw extruder in the hollow board extrusion production line. After plasticizing extrusion, forming with a dedicated hollow board mold, shaping on a vacuum sizing table, cooling, traction by a crawler-type traction machine, and fixed-length cutting, a 4mm thick anhydrous gypsum-polypropylene composite hollow board was finally obtained.

[0091] Performance Testing and Results Analysis

[0092] The composite hollow board samples obtained in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests according to relevant national or international standards. The tests included tensile strength, flexural modulus, cantilever beam notched impact strength, heat distortion temperature (0.45 MPa), and 24-hour water absorption rate. The test results are summarized in Table 1 below.

[0093] Table 1: Performance comparison of composite hollow plates prepared in Examples 1-4 and Comparative Examples 1-4

[0094]

[0095] The data above show that the tensile strength of the anhydrous gypsum-polypropylene composite hollow boards prepared in Examples 1-4 is not less than 38 MPa, the flexural strength is not less than 39 MPa, the notched impact strength is not less than 4.0 kJ / m², the heat distortion temperature is not less than 125℃, and the water absorption rate is less than 0.1%. This indicates that the method of the present invention can prepare high-performance composite hollow boards within a wide range of parameters and proportions.

[0096] The tensile strength and impact strength of the product obtained in Comparative Example 1 (without hydroxylation) were significantly lower than those in Example 1, with a decrease of approximately 20% in tensile and flexural strength and over 45% in notched impact strength. The material became extremely brittle, rendering the final product unusable. This comparative example omitted the alkaline hydroxylation pretreatment of anhydrous gypsum. Anhydrous gypsum itself has weak surface polarity and low activity; the core of hydroxylation treatment is to introduce a large number of hydroxyl (-OH) active functional groups onto its surface. Without this step, the subsequent silane coupling agent (such as KH-550) cannot effectively "graft" onto the surface of the inorganic filler through chemical bonds, resulting in almost no interfacial bonding between the filler and the polymer matrix.

[0097] The mechanical properties of the product prepared in Comparative Example 2 (without long-chain fatty acids) were significantly lower than those in Example 1. Its tensile strength and flexural strength decreased by approximately 18%, and its notched impact strength decreased by over 35%, a significant reduction compared to Example 1. In this comparative example, the anhydrous gypsum powder underwent surface modification using only a coupling agent, lacking long-chain fatty acids such as stearic acid. Long-chain fatty acids play two main roles here: first, they wet and physically coat the powder, improving its dispersibility in the non-polar polypropylene melt; second, they synergistically work with the coupling agent to form a denser organic modified layer. Without fatty acids, the powder is highly prone to agglomeration during high-speed mixing and subsequent extrusion (as observed in the experiment), forming stress concentration points and thus compromising the material's mechanical properties. Therefore, although some chemical bonding remains, its mechanical properties are reduced.

[0098] The mechanical properties of the product prepared in Comparative Example 3 (without compatibilizer), especially the impact strength, deteriorated significantly, with a decrease of 62.5%. This comparative example did not use maleic anhydride-grafted polypropylene (PP-g-MAH) compatibilizer in the preparation of the high-filler functional masterbatch. Compatibilizers act as "molecular bridges" connecting the surface-modified filler to the polypropylene matrix. The polar groups (maleic anhydride) in their molecular chains can interact with the modified layer on the filler surface, while the non-polar polypropylene segments can achieve good physical entanglement with the matrix resin. Without this "bridge," even if the filler surface is modified, a significant phase interface still exists between it and the polypropylene matrix, preventing effective stress transfer. This leads to a sharp decrease in the overall toughness of the material and a decline in various mechanical properties.

[0099] Comparative Example 4 (without masterbatch preparation, one-step preparation of hollow boards) showed a certain degree of decrease in the mechanical properties of the product compared to Example 1. This is because the one-step preparation of anhydrous gypsum-polypropylene composite hollow boards makes it difficult to simultaneously achieve both the dispersion of modified anhydrous gypsum powder in polypropylene and the mechanical strength of the polypropylene material itself. If modified anhydrous gypsum powder is directly melt-blended with polypropylene in one step to prepare anhydrous gypsum-polypropylene composites (especially using polypropylene with a low melt index), it will result in severely uneven gypsum dispersion. The gypsum filler will be difficult to effectively shear and wet in the high-viscosity melt, and will easily form stubborn agglomerates. These agglomerates will become structural defects in the final material, which will lead to a reduction in the performance of the final product. In addition, it will also make the viscosity of the mixed system very high, resulting in a significant increase in processing temperature, huge screw torque, and a significant increase in energy consumption.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hollow board made of anhydrous gypsum-polypropylene composite material, characterized in that, The components include the following components by weight percentage: 30%-65% modified anhydrous gypsum powder, 30%-65% polypropylene resin, 1%-3% compatibilizer, 1%-3% lubricant, and 0.1%-0.3% antioxidant; The modified anhydrous gypsum powder is prepared by the following method: hydroxyl functional groups are introduced onto the surface of the anhydrous gypsum powder, and then it is modified with a composite surface modifier formed by combining long-chain fatty acids and a coupling agent to obtain the modified anhydrous gypsum powder; the mass ratio of long-chain fatty acids to coupling agent is 0.5-2:1; the amount of the composite surface modifier is 0.5%-2% of the mass of the anhydrous gypsum powder; The long-chain fatty acid is selected from one or more fatty acids with C12-C22 carbon atoms.

2. The anhydrous gypsum-polypropylene composite hollow board according to claim 1, characterized in that, The coupling agent is selected from at least one of silane coupling agents, titanate coupling agents, or aluminate coupling agents.

3. The anhydrous gypsum-polypropylene composite hollow board according to claim 1, characterized in that, The method for introducing hydroxyl functional groups onto the surface of anhydrous gypsum powder is as follows: the anhydrous gypsum powder is placed in an alkaline aqueous solution and stirred to introduce hydroxyl functional groups onto the surface of the anhydrous gypsum powder, followed by washing until neutral and drying.

4. The anhydrous gypsum-polypropylene composite hollow board according to claim 1, characterized in that, The compatibilizer is selected from at least one of maleic anhydride-grafted polypropylene, glycidyl methacrylate-grafted polypropylene, and acrylic acid-grafted polypropylene. The lubricant is selected from at least one of montana wax, magnesium stearate, polyethylene wax, and paraffin wax; The antioxidant is selected from at least one of pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and tris(2,4-di-tert-butylphenyl) phosphite.

5. The anhydrous gypsum-polypropylene composite hollow board according to any one of claims 1-4, characterized in that, The polypropylene resin includes a carrier polypropylene resin and a matrix polypropylene resin. The melt index of the carrier polypropylene resin is 10-20 g / 10 min, and the melt index of the matrix polypropylene resin is 3-8 g / 10 min. By mass percentage, the carrier polypropylene resin accounts for 20%-40% of the total polypropylene resin.

6. The method for preparing anhydrous gypsum-polypropylene composite hollow board according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of high-filler functional masterbatch: Modified anhydrous gypsum powder is used as the core filler, and is melt-blended with compatibilizer, lubricant, antioxidant and a portion of polypropylene resin, followed by degassing and granulation to prepare high-filler functional masterbatch. S2. Hollow board extrusion molding: The prepared high-filler functional masterbatch is mixed with the remaining polypropylene resin and extruded through a hollow board extrusion production equipment to obtain the anhydrous gypsum-polypropylene composite hollow board; The polypropylene resin added in step S1 is 20%-40% of the total mass of polypropylene resin.

7. The method for preparing anhydrous gypsum-polypropylene composite hollow board according to claim 6, characterized in that, The polypropylene resin in step S1 is a carrier polypropylene resin with a melt index of 10-20 g / 10 min, and the polypropylene resin in step S2 is a matrix polypropylene resin with a melt index of 3-8 g / 10 min.

8. The method for preparing anhydrous gypsum-polypropylene composite hollow board according to claim 6, characterized in that, The high-filling-capacity masterbatch consists of spherical or cylindrical particles. The particle size of the spherical particles is between 3 and 6 mm, and the diameter and height of the cylindrical particles are both between 3 and 6 mm.

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