Modified calcium carbonate special for polypropylene composite material and preparation method and application thereof

Abstract

The application belongs to the technical field of new material organic polymer material and product, and discloses a modified calcium carbonate special for polypropylene composite material, and a preparation method and application thereof. Through the intermediary action of glutaraldehyde, the application promotes the formation of chemical bonding between the hydroxyl groups on the surface of calcium carbonate and the hydroxyl groups of dextran. The chemical cross-linking effect not only enhances the adhesion of dextran on the surface of calcium carbonate, but also significantly improves the compatibility of calcium carbonate and polypropylene matrix. The calcium carbonate modification method is suitable for different conditions and occasions, and can be applied to dry modification and wet modification to realize the significant improvement of the compatibility of calcium carbonate and polypropylene. By adjusting the experimental conditions, the application can realize the regulation of the hydrophilicity and lipophilicity of the surface of calcium carbonate, and prepare calcium carbonate with different contact angle characteristics to meet different functional and application requirements.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of new materials, organic polymer materials and products, and particularly relates to a modified calcium carbonate special for polypropylene composite materials, and a preparation method and application thereof. BACKGROUND

[0002] Polypropylene (PP) is a thermoplastic plastic polymerized from propylene monomers, which is well-known for its abundant raw materials and simple synthesis process. Compared with other general-purpose plastics, polypropylene has low density, high cost-effectiveness, and superior processing performance. Its mechanical properties, including yield strength, tensile strength, surface hardness, and elastic modulus, are all excellent. In addition, polypropylene also exhibits excellent stress cracking resistance, chemical corrosion resistance, and wear resistance. Its softening point is higher than that of high-density polyethylene (HDPE) and acrylonitrile-butadiene-styrene (ABS) copolymer, and it has good electrical insulation performance and low dielectric constant, making it widely used in the fields of automobiles, home appliances, and engineering.

[0003] However, pure polypropylene (PP) also has some limitations, such as brittleness at low temperatures, relatively low mechanical strength and hardness, large molding shrinkage, easy aging, and poor high-temperature resistance, which limit its promotion in more extensive application fields.

[0004] The crystallinity and crystal phase diversity of polypropylene have a significant impact on its performance. PP is a polymorphous semi-crystalline polymer, which exists in different crystal morphologies such as α, β, γ, δ, and pseudo-hexagonal state. Among them, the α crystal form is monoclinic, which is the most thermodynamically stable crystal form, has large spherulite size, clear grain boundaries, and high perfection, giving the polymer good rigidity but poor toughness. The β crystal form is hexagonal, with small spherulite size and unclear grain boundaries, and the crystalline polymer exhibits good toughness and heat deformation resistance, but its thermodynamic stability is low and usually requires special methods to prepare. In contrast, γ, δ, and pseudo-hexagonal state crystal forms have low content and are unstable, only formed under specific conditions, and have limited practical value.

[0005] The crystallization behavior and crystal characteristics of polypropylene are closely related to its performance, and different crystal phases and crystallinity have important effects on the physical, chemical, and thermal properties of the material. Therefore, by controlling the crystallization conditions of polypropylene and adding specific nucleating agents or modifiers, the crystallinity and crystal phase can be adjusted to optimize its performance to meet the needs of specific applications.

[0006] To expand the application range and improve the comprehensive performance of polypropylene (PP) materials, modification measures must be taken. These modification measures include chemical modification, such as copolymerization, grafting, and crosslinking of PP, and physical modification, including fiber reinforcement, inorganic rigid particle filling, organic elastic particle filling, and inorganic-organic mixed particle filling. Domestic and foreign scholars have conducted extensive research in this regard. However, existing modification methods often improve the performance of PP materials in one aspect while causing a decline in other aspects. For example, adding elastic particles can improve the impact resistance of PP and reduce low-temperature brittleness, but it significantly reduces the rigidity and hardness of the material. Glass fiber reinforced PP can significantly improve the strength and rigidity of the material, but it may compromise its impact resistance. Inorganic rigid particle filling of PP helps to improve the stiffness, hardness, and impact resistance of the material, but it may reduce the tensile strength of the material.

[0007] Given the high comprehensive performance requirements of PP materials in the automotive and engineering fields, new modification ideas and methods must be explored. This may involve developing new modifiers, innovative processing techniques, or multiphase composite strategies to achieve a balance and optimization of the performance of PP materials. By comprehensively considering the advantages and limitations of different modification methods, a modification scheme can be designed that not only maintains the original advantages of PP but also significantly improves its performance.

[0008] In the filling modification of plastics, the fillers used are usually natural or synthetic inorganic materials. These inorganic fillers, including salts, oxides, and metal powders, are all polar and water-insoluble substances. When these inorganic fillers are dispersed in a polar and organic polymer resin matrix, due to the difference in polarity, the compatibility between the filler and the resin may be poor, which can adversely affect the processing and use performance of the modified plastic.

[0009] Therefore, it is crucial to properly treat the surface of inorganic fillers to adjust their surface polarity through chemical reactions or physical methods to improve their compatibility with the filled polymer resin. The mechanism of filler surface treatment mainly includes two types: 1. Surface physical action: involving surface coating (or called covering) and surface adsorption. In this case, the combination between the filler and the treatment agent is mainly achieved through intermolecular forces. 2. Surface chemical action: including surface substitution, hydrolysis, polymerization, and grafting chemical reactions. This type of treatment method produces a firm bond between the filler surface and the treatment agent through the formation of chemical bonds. Considering the surface treatment methods of inorganic fillers, the compatibility of inorganic fillers with organic polymer resins can be effectively improved, thereby optimizing the comprehensive performance of the filled modified plastic.

[0010] In the field of filled modified plastics, the surface characteristics of fillers have a significant impact on material properties. Generally, fillers with larger specific surface area, higher surface functional group density, and stronger reactivity have higher reaction rates with surface treatment agents and less steric hindrance, tending to bind to the filler surface through chemical bonding. Conversely, if the steric hindrance is large, physical effects such as van der Waals forces can become dominant. In practical applications, most surface treatments of fillers involve the coexistence of physical and chemical effects.

[0011] For a particular filler, selecting different surface treatment agents will result in different surface modification mechanisms. When using surfactants, long-chain organic acid salts, or high-boiling hydrocarbons as surface treatment agents, surface modification of fillers is mainly achieved through physical effects such as surface coating or adsorption. However, when using coupling agents, organosilane compounds, or epoxy compounds as surface treatment agents, surface modification is mainly achieved through chemical effects such as covalent bonding between functional groups.

[0012] The goal of filler surface modification is to optimize the compatibility between the filler and the resin matrix, improving the mechanical properties, thermal stability, and processing performance of the composite material. Therefore, selecting the appropriate surface treatment agent and method is crucial for achieving the desired material properties.

[0013] Among the numerous inorganic fillers, calcium carbonate is widely used due to its significant advantages. Calcium carbonate has the characteristics of abundant resources, low cost, easy availability of raw materials, easy storage and transportation, easy color adjustment, and less wear on processing equipment. Calcium carbonate has various forms, including calcium carbonate whiskers, nano calcium carbonate, light calcium carbonate, heavy calcium carbonate, colloidal calcium carbonate, and active calcium carbonate, making it a common additive in plastic products, especially hard plastic products.

[0014] However, calcium carbonate, as a polar filler, has poor compatibility with non-polar polypropylene polymers. Adding a large amount of calcium carbonate to the polypropylene matrix can cause micro-cracks or voids within the material, affecting the mechanical properties and durability of the final product. Therefore, it is particularly important to properly surface modify calcium carbonate or polypropylene to enhance the compatibility between inorganic fillers and polymer matrices.

[0015] Surface modification can be achieved through chemical or physical methods, aiming to improve the interfacial interaction between fillers and resins, reduce interfacial tension, and improve dispersion and overall composite material performance. This may involve the use of coupling agents, surfactants, or other specialized surface modifiers to promote the compatibility between calcium carbonate and polypropylene, thereby improving the mechanical properties and processing performance of the material.

[0016] Early studies mainly focused on increasing the hydroxyl content on the surface of fillers by hydroxylation treatment, and further studies were based on the amount of hydroxyl groups. Studies have found that inorganic fillers after surface hydroxylation can introduce more coupling agents, and different types of coupling agents have different effects on the performance of fillers. With the deepening of research, new coupling agents with unique structure have been developed.

[0017] Subsequently, researchers began to explore the grafting of small organic molecules on the coupling agent, and further developed to graft macromolecular polymers. However, these methods usually involve a multi-step reaction process, which may face challenges in feasibility and cost control in industrial applications. Therefore, researchers seek more simple modification methods, such as fixing functional groups on the surface of inorganic fillers through crosslinking technology.

[0018] Currently, commonly used grafting monomers include acrylic acid, maleic acid and its anhydride, acrylic acid epoxy ester, maleic anhydride, etc. The diversity of grafting methods includes solution method, melting method, solid phase grafting technology, in-situ reaction grafting technology and mechanochemical melt grafting technology, etc.

[0019] In order to directly improve the compatibility of inorganic fillers and matrix, an efficient method is to graft functional groups compatible with the matrix on the surface of the filler. On this basis, researchers further explore the improvement effect of this method on the mechanical properties of materials. Through continuous modification of the surface of inorganic fillers, the specific application requirements are met, and the main goal is to enhance the compatibility of inorganic fillers and polymer matrix, so as to optimize the comprehensive performance of the composite material.

[0020] Currently, the modification technology of inorganic filler calcium carbonate mainly includes dry method and wet method. The modified calcium carbonate usually exhibits lipophilic characteristics to better adapt to the non-polar nature of polypropylene. Dry modification is preferred due to its simple operation, no need to remove solvent and easy processing; while wet modification is known for its better dispersibility and modification effect. SUMMARY

[0021] In order to overcome the shortcomings and deficiencies existing in the prior art, the primary purpose of the present application is to provide a preparation method of modified calcium carbonate special for polypropylene composite material.

[0022] Another purpose of the present application is to provide a modified calcium carbonate special for polypropylene composite material prepared by the above preparation method.

[0023] Still another purpose of the present application is to provide an application of the above modified calcium carbonate special for polypropylene composite material.

[0024] The purposes of the present application are achieved by the following technical solutions:

[0025] A preparation method of modified calcium carbonate special for polypropylene composite material, comprising the following operation steps:

[0026] The calcium carbonate is added into the dextran solution, heated to 45-55℃, then glutaraldehyde is added, and a magnesium salt is added as a catalyst, and 1% sulfuric acid by mass concentration is used to adjust the pH value to 5-7, and the reaction is carried out at 45-55℃ for 5-7 hours, after the reaction is completed, filtration is carried out, and the filter residue is dried at a temperature of ≤100℃ until the water content is not more than 0.2wt%, to obtain coated calcium carbonate, which is the modified calcium carbonate special for polypropylene composite material.

[0027] The coated calcium carbonate is composed of calcium carbonate and a modified layer on the surface of the calcium carbonate, and the mass ratio of the calcium carbonate to the modified layer is 100:(0.25-8).

[0028] The dextran solution is obtained by stirring and dissolving dextran in water for 10-60 minutes; and the molecular weight of the dextran is 1500-500000. The molecular weight of the dextran does not significantly affect the performance of the coated calcium carbonate under a certain mass.

[0029] The mass ratio of the dextran in the dextran solution to glutaraldehyde is 1:1-3. Different molar ratios of the dextran to glutaraldehyde result in different crosslinking degrees, and further affect the hydrophilicity and effect.

[0030] The magnesium salt is MgCl2 or MgSO4, and MgCl2 is preferred. MgCl2 is used to form ionic action with the hydroxyl groups on the dextran in the preparation process, so as to improve the flexibility of the modified layer, but other methods that can provide magnesium ions, such as magnesium sulfate, can also be used as alternatives.

[0031] In the preparation process, sulfuric acid is not the only choice for adjusting the pH value, and other alternative acids include carbonic acid, hydrochloric acid, phosphoric acid, citric acid, organic acid, etc., although sulfuric acid is superior in effect.

[0032] If a dry method is used, the coated calcium carbonate is obtained by directly heating to 90-100℃ to dry the moisture after the reaction is completed.

[0033] A modified calcium carbonate prepared by the above preparation method.

[0034] The application of the above modified calcium carbonate in preparing polypropylene composite material, wherein the polypropylene composite material is composed of 5-50 parts by weight of the modified calcium carbonate and 100 parts by weight of isotactic polypropylene.

[0035] The principle of the application is:

[0036] The surface of calcium carbonate is rich in hydroxyl functional groups, and its inherent hydrophilic nature limits its application in non-polar polymer matrix. The present invention solves this problem by coating the surface of calcium carbonate with cross-linked dextran. Dextran is a hydrophilic chemical substance with a multi-hydroxyl structure, which is easily soluble in water. Glutaraldehyde is used as a cross-linking agent, and its aldehyde groups at both ends of the molecule can react with hydroxyl groups. Through the mediation of glutaraldehyde, the present invention promotes the formation of chemical bonds between the hydroxyl groups on the surface of calcium carbonate and the hydroxyl groups of dextran. This chemical cross-linking not only enhances the adhesion of dextran on the surface of calcium carbonate, but also significantly improves the compatibility of calcium carbonate with the polypropylene matrix. By adjusting the molar ratio of calcium carbonate to dextran, different degrees of coating effect can be achieved. At the same time, by adjusting the molar ratio of dextran to glutaraldehyde, the progress of the cross-linking reaction can be precisely controlled, and thus the hydrophilic and lipophilic properties of the product can be adjusted. Specifically, the number of hydroxyl groups determines the surface properties of the calcium carbonate / dextran composite, i.e. its hydrophilicity or lipophilicity. By precisely controlling the reaction conditions, the present invention can prepare calcium carbonate / dextran composite materials with specific surface properties to meet specific application requirements, thereby optimizing the compatibility of inorganic fillers with the polypropylene matrix and improving the overall performance of the composite material.

[0037] In the prior art, the commonly used organic chains are short and have small molecular weights, making it difficult to form effective entanglements with the polypropylene matrix, thereby limiting the improvement of compatibility. In contrast, the present invention uses high molecular weight dextran polymer as a modifier, which gives calcium carbonate modification unique advantages. Due to the high molecular weight characteristics of dextran, its long molecular chain can form more entanglements with the polypropylene matrix, thereby significantly improving the compatibility between the two and reducing phase separation. This modification method not only improves the mechanical properties of polypropylene, but also improves its thermodynamic properties, including but not limited to crystallization temperature and melting temperature. The present invention, through innovative modification methods, not only improves the compatibility of calcium carbonate and polypropylene, but also expands the application range of inorganic fillers, providing new ideas and methods for optimizing the performance of polypropylene-based composites.

[0038] The present invention has the following advantages and effects compared to the prior art:

[0039] The prior art focuses on improving the contact angle of calcium carbonate to achieve its transformation from hydrophilicity to lipophilicity; however, the modified calcium carbonate prepared by the present application can realize the free regulation of the surface properties of calcium carbonate from hydrophilicity to lipophilicity through a specific coating technology; more importantly, the modified calcium carbonate can significantly improve the compatibility with the polypropylene matrix in both hydrophilic and lipophilic states; this improved compatibility has a positive effect on many properties of the polypropylene material, including enhancing its impact strength, tensile strength, and adjusting its melting temperature and crystallization temperature; the improvement of these properties further widens the application range of the polypropylene composite material and meets the needs of high-performance applications. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 Schematic diagram of cross-linking of glutaraldehyde itself with hydroxyl groups and calcium carbonate to form a coating cross-linking network structure and schematic diagram of cross-linking of glutaraldehyde with calcium carbonate to form a coating cross-linking structure.

[0041] Figure 2 Comparison of infrared spectra of coated calcium carbonate and uncoated calcium carbonate. DETAILED DESCRIPTION

[0042] The content of the present application will be further illustrated below in conjunction with specific examples and drawings, but should not be understood as a limitation on the present application.

[0043] In a first aspect, the present application relates to a modified calcium carbonate special for polypropylene composite materials, which is not limited to the coating form of light or heavy calcium carbonate. The modified calcium carbonate is composed of calcium carbonate and a modified layer on the surface of the calcium carbonate, and the mass ratio of calcium carbonate to the modified layer is 100:(0.25-8).

[0044] The raw materials for preparing the modified layer include different molecular weight dextran (1500, 40000, 200000, 500000), glutaraldehyde (50% concentration), magnesium chloride solid, and concentrated sulfuric acid or 1% sulfuric acid solution.

[0045] The present application develops a special modified calcium carbonate for polypropylene based on the structure and performance characteristics of polypropylene. When preparing a polypropylene composite material with the special modified calcium carbonate, the special modified calcium carbonate is directly mixed into the polypropylene matrix (including block copolymerized polypropylene and maleic anhydride grafted polypropylene) in a certain proportion.

[0046] In the polypropylene composite material, the block copolymerized polypropylene helps to enhance the mechanical properties of polypropylene; the maleic anhydride grafted polypropylene further improves the compatibility of polypropylene with calcium carbonate, thereby optimizing the comprehensive performance of the modified calcium carbonate. This modification method can effectively overcome the performance limitations of calcium carbonate and significantly improve the overall performance of the polypropylene composite material.

[0047] The modified calcium carbonate formulation according to the present application is a result of in-depth research and multiple experimental explorations aimed at addressing the problems encountered during the preparation of polypropylene composites. The development of the modified calcium carbonate fully considers the structural characteristics and performance requirements of polypropylene and is specifically designed for the application of polypropylene composites.

[0048] Therefore, the application of the modified calcium carbonate according to the present application in polypropylene composites has a high degree of specificity and optimization, while other components of polymer plastics may not have the same applicability and effectiveness. This specialized modified calcium carbonate can more effectively address the specific needs of polypropylene composites in processing and performance, thereby improving the quality and performance of the final product.

[0049] In the present application, the formulation design of the modified calcium carbonate is carefully researched and experimentally verified. The mass ratio of calcium carbonate to modification layer has a significant impact on the performance of the modified calcium carbonate (activated) after being added to polypropylene. If the mass of the modification layer is too high, it will result in the formation of an excessively thick coating layer on the surface of the calcium carbonate, which not only reduces the mechanical stability of the coating layer, but also can cause the coating layer to soften and fall off, thereby weakening the effective combination of the modified calcium carbonate with polypropylene. On the contrary, if the mass of the modification layer is insufficient, it cannot achieve complete coating of the calcium carbonate, and after being added to polypropylene, the calcium carbonate is prone to agglomeration, has poor compatibility with the polypropylene matrix, and limits its addition amount in the composite material.

[0050] Through systematic testing and optimization, the present inventors have found that when the mass ratio of calcium carbonate to modification layer is controlled within the range of 100:(0.25-8), the best coating effect on calcium carbonate can be achieved. The modified calcium carbonate prepared under this ratio can exhibit excellent comprehensive performance when used in polypropylene composites.

[0051] In a second aspect, the present application provides a method for preparing the modified calcium carbonate specifically for the above-mentioned polypropylene composites, which comprises the following steps:

[0052] Wet modification: Different molecular weight specifications of dextran are dissolved in water, and thoroughly stirred to form dextran solutions with different concentrations (mass percentage concentration of 0.25% to 8%). Subsequently, calcium carbonate is added to the dextran solution, and glutaraldehyde is added at a temperature of 45-55℃ (the addition amount is adjusted according to the concentration of dextran, and the mass ratio of dextran to glutaraldehyde is 1:1 to 1:3). At the same time, according to the total amount of the solution, an appropriate amount of MgCl2 is added as a catalyst, and 1% mass percentage concentration of sulfuric acid is added to adjust the pH value to 5-7, and the reaction is carried out at 45-55℃ for 5-7 hours.

[0053] After the reaction, most of the water is removed by filtration, and the calcium carbonate is dried to a water content of less than or equal to 0.2wt%. During the drying process, attention should be paid to control the temperature not to exceed 100°C, so as to avoid damage to the modified layer due to thermal decomposition.

[0054] The preparation method realizes efficient control of the surface modification of calcium carbonate by precisely controlling the type and amount of modifier, as well as the reaction conditions, and provides a special modified calcium carbonate with superior performance for the preparation of polypropylene composite materials.

[0055] In a third aspect, the present application provides a preparation method of a special modified calcium carbonate for polypropylene composite materials, which belongs to the category of dry modification, and the specific steps are as follows:

[0056] Dextran (providing different molecular weight specifications, including 1500, 40000, 200000, 500000, etc.) is dissolved in water by thorough stirring and dissolution (10 to 60 minutes) to form a series of dextran solutions with different concentrations (mass percentage concentration 0.25% to 8%).

[0057] Calcium carbonate is added to the dextran solution and continuously stirred until uniformly dispersed.

[0058] The mixed solution is heated to 45-55°C, and glutaraldehyde is added. The amount of glutaraldehyde added varies depending on the concentration of the dextran solution, and the mass ratio of dextran to glutaraldehyde is controlled in the range of 1:1 to 1:3.

[0059] According to the total amount of the solution, an appropriate amount of MgCl2 (1% to 5% solution concentration) is added as a catalyst to promote the reaction.

[0060] The reaction is maintained at 45-55°C for 5-7 hours, and then the temperature is directly raised to 90-100°C to dry the water.

[0061] In the present application, the use of magnesium chloride has a regulating effect, which can form a complex with the hydroxyl groups of dextran, thereby improving the flexibility of the modified layer. With the increase of the content of magnesium chloride, the softness of the modified layer is improved, and at the same time, it can also prevent excessive crosslinking and enhance the biocompatibility of calcium carbonate.

[0062] In addition, 1% mass percentage concentration of sulfuric acid mainly plays a role in adjusting the pH value in the present application. In addition to sulfuric acid, other acid substances such as carbonic acid, hydrochloric acid, phosphoric acid, citric acid, organic acid, etc. can also be used for pH adjustment, but in the present experiment, sulfuric acid is used as a strong acid for adjustment, and the effect is better.

[0063] In the dry preparation process, the step of directly drying by heating without filtration aims to promote the cross-linking reaction of glutaraldehyde. Since glutaraldehyde is alkaline in solution, if the pH value is not adjusted to be acidic, glutaraldehyde will remain stable and cannot proceed to cross-linking. Therefore, by adjusting the pH value or removing the water produced during the reaction, the reaction can be pushed to proceed in the forward direction, achieving effective cross-linking.

[0064] As shown in Figure 1 , the final synthesized products are respectively the hydroxyl cross-linking of glutaraldehyde itself and the formation of a coated cross-linking network structure with calcium carbonate, and the hydroxyl cross-linking of glutaraldehyde and calcium carbonate to form a coated cross-linking structure. The infrared spectrum of the sample is shown in Figure 2 , in the infrared spectrum, the blue line is the original infrared spectrum of calcium carbonate, the red line is the original infrared spectrum of dextran, and the black line is the spectrum of the modified calcium carbonate after the reaction, which has been successfully prepared. It can be seen that the synthesis of modified calcium carbonate is successful.

[0065] Finally, the application also covers the application of the above-mentioned special modified calcium carbonate for polypropylene composite materials in the preparation process of polypropylene-based composite materials. The modified calcium carbonate involved in the application can meet the strict performance requirements of high-performance polypropylene composite materials for calcium carbonate and its additives due to its excellent stability and flowability.

[0066] The application of the modified calcium carbonate of the application in the preparation of polypropylene composite materials can significantly increase the addition ratio of calcium carbonate while effectively solving the problems of insufficient compatibility of calcium carbonate with polypropylene, limited addition amount, insufficient material strength, poor dimensional stability, and poor thermal stability in the prior art. In particular, in the preparation process of polypropylene, the use of the modified calcium carbonate of the application can significantly improve the impact resistance and tensile strength of polypropylene, thereby preparing polypropylene composite materials with better comprehensive mechanical properties.

[0067] Therefore, the modified calcium carbonate of the application not only optimizes the performance of polypropylene materials, but also broadens its potential applications in multiple application fields, providing new possibilities for the innovation and development of polypropylene-based composite materials.

[0068] In the application, the mass ratio of the modified calcium carbonate to polypropylene in the polypropylene composite material is preferably 10-50%. The modified calcium carbonate comprises calcium carbonate with a specific double-layer coated structure, combined with a specific content of maleic anhydride grafted polypropylene and block copolymerized polypropylene. Compared with the calcium carbonate or modified calcium carbonate in the prior art, the modified calcium carbonate of the application can significantly increase the addition amount while avoiding the reduction of polypropylene performance, effectively improving the comprehensive performance of polypropylene, and reducing production costs.

[0069] Preferably, the dextran of the present application realizes the transformation of the modified layer from hydrophilicity to oleophilicity by adjusting the degree of cross-linking, changing the number of hydroxyl groups. Meanwhile, by controlling the content of magnesium chloride, the flexibility of the modified layer is adjusted.

[0070] The preparation method of the polypropylene composite special calcium carbonate provided by the present application has simple process steps, and through accurate control of the feeding sequence and process conditions, the product with stable physical properties and excellent quality can be efficiently prepared, which is beneficial to industrialized production and application promotion. The preparation method is specially designed for the structure and composition of the modified calcium carbonate special for polypropylene composite, and provides a special modified calcium carbonate product for the preparation of polypropylene composite.

[0071] Unless otherwise specified, the raw materials used in the examples of the present application are all commercially available conventional raw materials, and the equipment and methods used are all standard equipment and conventional methods in the technical field.

[0072] In the following examples, the calcium carbonate used has a whiteness of 96-99.5%, a CaCO3 content of not less than 99.5%, and a particle size of 2000 mesh.

[0073] The specifications of other raw materials used in the examples are as follows:

[0074] The polypropylene is composed of PP 1005 produced by China Taiwan Plastics Industry Co., Ltd. and PT-100 produced by Li Changrong Chemical Industry Co., Ltd. in a ratio of 9:1.

[0075] The dextran is provided by Aladdin Bio-Chem (Shanghai) Co., Ltd. and has a purity of 99%.

[0076] The magnesium chloride is provided by Shanghai Maikelin Biochemical Technology Co., Ltd. and has a purity of 99%.

[0077] The concentrated sulfuric acid is provided by Guangzhou Anjiehui Trading Co., Ltd. and has a purity of industrial grade, which is 92.5% and 98%, respectively.

[0078] Example 1:

[0079] A preparation method of a modified calcium carbonate special for polypropylene composite, comprising the following operation steps:

[0080] Dissolve the dextran in water, and dissolve thoroughly under stirring for 1 hour to form a dextran solution.

[0081] Add calcium carbonate to the dextran solution and stir uniformly to obtain a mixed solution.

[0082] Heat the mixed solution to 50℃, and then add glutaraldehyde.

[0083] According to the total amount of the solution, an appropriate amount of MgCl2 is added as a catalyst, and 5 mL of 1% mass percentage sulfuric acid is added to adjust the pH value to 5-7.

[0084] The reaction is completed at 50°C for 6 hours.

[0085] After the reaction is completed, most of the water is removed by filtration, and then dried at 80°C until the water content is not more than 0.2wt%, to obtain the coated calcium carbonate, which is a modified calcium carbonate special for polypropylene composites.

[0086] In this embodiment, the selection and amount of each raw material are listed in Table 1.

[0087] Examples 2-6 and Comparative Example 7: In these examples, the preparation method of the modified calcium carbonate is the same as that of Example 1, except that the amount of the preparation raw material of the coated calcium carbonate is different. The amount of the preparation raw material of the coated calcium carbonate is also listed in Table 1.

[0088] Table 1 Preparation raw materials of coated calcium carbonate (weight parts)

[0089]

[0090] After the preparation process is completed, the modified calcium carbonate sample is mixed with a total of 100 parts by weight of polypropylene at a ratio of 10 parts by weight. The mixing process is carried out in a two-roll open mill with a temperature setting of 185°C, ensuring that the two materials are fully melted and uniformly mixed. Subsequently, the mixed material is processed by mold pressing in a flat curing machine to form the desired polypropylene composite product. This process ensures good compatibility and dispersion between the modified calcium carbonate and the polypropylene matrix, thereby obtaining a polypropylene composite material with the desired performance; according to the different modified calcium carbonate samples (coated calcium carbonates 1-7 and uncoated calcium carbonate 8), polypropylene composites 1-8 are obtained respectively.

[0091] In Effect Example 1, the coated calcium carbonate samples 1-6 were evaluated for touch. By manually grasping the samples, it was observed that the coated calcium carbonate had a relatively sticky feel. However, when pressure was applied and released, the samples quickly returned to a loose and fine powder state. In addition, when the calcium carbonate samples were placed in water, they exhibited a relatively fast settling rate due to their hydrophilic characteristics.

[0092] In Effect Example 2, the impact strength and tensile strength of the polypropylene composites 1-8 obtained in the above examples were tested. The test method is as follows:

[0093] Impact strength: According to GB / T 1843-2008 standard "Determination of Izod Impact Strength of Plastics". Test samples are prepared by molding method according to GB / T 1843-2008 standard, forming impact test samples with A-type notches. Then, the impact test machine is used to test the samples at room temperature, 5 samples per group, and the average value is taken as the test result.

[0094] Tensile strength: The sample is prepared according to the requirements of GB / T 1040.2-2022 standard, and the tensile strength test is carried out according to the same standard.

[0095] Crystallization temperature and melting temperature: Measured by differential scanning calorimeter (DSC) produced by Mettler-Toledo.

[0096] These test results will provide important data for evaluating the influence of modified calcium carbonate on the performance of polypropylene composite materials, ensuring that the resulting materials meet high performance requirements.

[0097] Table 2 Tensile strength, impact strength data and crystallization temperature, melting temperature data of coated calcium carbonate filled polypropylene composite materials

[0098] Group Tensile strength / MPa Impact strength / kJ / m 2 ]] Crystallization temperature / °C Melting temperature / °C Polypropylene composite 1 29.81 4.8047 117.12 157.05 Polypropylene composite 2 28.94 6.0265 120.44 158.54 Polypropylene composite 3 28.8 5.8745 121.2 162.48 Polypropylene composite 4 28.12 6.3307 118.41 162.82 Polypropylene composite 5 28.36 7.3454 122.73 160.33 Polypropylene composite 6 29.09 5.5081 121.56 161.15 Polypropylene composite 7 28.69 5.4588 120.47 156.98 Polypropylene composite 8 28.11 4.6128 120.76 159.87

[0099] According to the test results in Table 2, it can be observed that the polypropylene composite materials prepared in Examples 1-7 exhibit excellent impact strength and tensile strength. In particular, Example 5 performs particularly outstanding in impact strength; while Examples 1-6 perform more outstanding in tensile strength. These enhanced mechanical properties are attributed to the good compatibility between the modified calcium carbonate and the polypropylene matrix, thus achieving significant improvement in performance.

[0100] Further analysis of the data in Table 2 shows that Examples 5 and 6 have higher crystallization temperature, while Examples 3 and 4 exhibit higher melting temperature. This phenomenon may be related to the thickness of the modified layer of calcium carbonate: when the modified layer is thinner, the promotion of calcium carbonate to polypropylene crystallization may not be effectively inhibited, resulting in an increase in crystallization temperature; while the modified layer is thicker, the impact strength and tensile strength may decrease due to poor modification effect, as shown in Example 1. In addition, the increase in dextran content may cause the problem of cost increase.

[0101] The above examples are more suitable embodiments of the present application, and the embodiments of the present application are not limited by the above examples, any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods, and all are included in the protection scope of the present application.

Claims

1. A process for the preparation of a modified calcium carbonate dedicated to polypropylene composites, characterized in that The method comprises the following steps: The calcium carbonate is added into the dextran solution, heated to 45-55℃, then glutaraldehyde is added, and a magnesium salt is added as a catalyst, the pH value is adjusted to 5-7 by 1% sulfuric acid, and the reaction is carried out at 45-55℃ for 5-7 hours, then the reaction is finished, and the filter residue is dried at ≤100℃ until the water content is less than 0.2wt%, to obtain the coated calcium carbonate, which is the modified calcium carbonate for polypropylene composite materials.

2. The method for preparing modified calcium carbonate for polypropylene composite material according to claim 1, characterized in that: The coated calcium carbonate is composed of calcium carbonate and a modified layer on the surface of the calcium carbonate, wherein the mass ratio of the calcium carbonate to the modified layer is 100:(0.25-8).

3. The method for preparing modified calcium carbonate for polypropylene composite material according to claim 1, characterized in that: The dextran solution is obtained by stirring and dissolving dextran in water for 10-60 minutes; the molecular weight of the dextran is 1500-500000.

4. The method for preparing modified calcium carbonate for polypropylene composite material according to claim 1, characterized in that: The mass ratio of the dextran in the dextran solution to glutaraldehyde is 1:1-3.

5. The method for preparing modified calcium carbonate for polypropylene composite material according to claim 1, characterized in that: The magnesium salt is MgCl2 or MgSO4.

6. The method for preparing modified calcium carbonate for polypropylene composite material according to claim 1, characterized in that: After the reaction is finished, the temperature is directly increased to 90-100℃ to dry the moisture, to obtain the coated calcium carbonate. 7.A modified calcium carbonate prepared by the preparation method of any one of claims 1-6.

8. Use of the modified calcium carbonate according to claim 7 for the production of a polypropylene composite, characterized in that: The polypropylene composite material is composed of 5-50 parts by weight of the modified calcium carbonate and 100 parts by weight of isotactic polypropylene.

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