High performance polypropylene composite and method for making same

Abstract

The application belongs to the technical field of high polymer materials, and particularly relates to a high-performance polypropylene composite material and a preparation method thereof. The high-performance polypropylene composite material comprises the following raw materials in parts by weight: 100 parts of polypropylene, 10-30 parts of modified cellulose nanocrystals, 1-5 parts of maleic anhydride grafted polypropylene, 0.1-0.5 parts of an antioxidant, and 0.1-0.5 parts of a lubricant. The application modifies cellulose nanocrystals (CNC) through precise molecular design, grafts an intermediate with a P-N-Si flame-retardant structure to the CNC skeleton through a chemical bond, and the modified cellulose nanocrystals not only can fully play a flame-retardant role in a polypropylene matrix, but also has good compatibility with the polypropylene matrix, and can be used as a nano-enhanced filler to simultaneously improve the mechanical properties of the composite material.

Description

A high-performance polypropylene composite material and its preparation method Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a high-performance polypropylene composite material and its preparation method. Background Technology

[0002] Polypropylene (PP) plays an important role in fields such as communications, power, and automobiles due to its excellent electrical insulation, chemical resistance, low density, and good processing properties. However, PP itself is a flammable material with a limiting oxygen index (LOI) of only about 17%–18%. It is easily ignited and produces molten droplets under the influence of an ignition source, posing a serious safety hazard and making it difficult to meet the requirements of flame retardant standards such as UL-94 V-0 or IEC 60332.

[0003] Currently, the industry commonly uses flame retardants to improve the flame retardant properties of polypropylene (PP). Traditional halogenated flame retardants (such as brominated cycloalkanes and chlorinated paraffins) have good flame retardant efficiency, but they release large amounts of toxic and corrosive gases (such as hydrohalic acids and dioxins) during combustion, causing great harm to the environment and human health, and have been gradually restricted or phased out. Halogen-free flame retardant systems (such as phosphorus-based, nitrogen-based, and inorganic hydroxides) are environmentally friendly, but usually require high addition amounts to achieve the desired flame retardant effect, which significantly affects the mechanical and processing properties of the material. For example, when the addition amount of inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide exceeds 40 wt%, although it can increase the LOI value, it will lead to increased brittleness, decreased tensile strength, and poor processing fluidity of the material.

[0004] In addition, to improve the mechanical properties of PP, reinforcing fillers such as glass fiber, talc, and calcium carbonate are often added. While these inorganic reinforcing materials can improve rigidity and dimensional stability, they have poor interfacial compatibility with the PP matrix, easily leading to problems such as interfacial debonding and stress concentration, resulting in a decrease in the impact toughness of the composite material. At the same time, the addition of reinforcing fillers may also affect the distribution and synergistic effect of flame retardants, reducing the overall flame retardant efficiency. Therefore, how to achieve efficient flame retardancy without sacrificing mechanical properties has become a technical bottleneck in the current design of PP composite materials.

[0005] In recent years, cellulose nanocrystals (CNCs), as a green and renewable nanomaterial, have attracted widespread attention due to their high specific surface area, good mechanical properties, and surface modifiability. CNCs can not only serve as reinforcing fillers to improve the strength and toughness of polymers, but their surface hydroxyl structures also provide an ideal platform for functional modification. By grafting phosphorus-nitrogen flame-retardant monomers onto the surface of CNCs, not only can they be endowed with flame-retardant properties, but their interfacial compatibility with the PP matrix can also be improved, achieving a synergistic effect of reinforcement and flame retardancy. However, a composite system that can organically combine the mechanical reinforcing properties of CNCs with efficient flame-retardant performance and achieve stable dispersion and processing in a polypropylene matrix is ​​currently lacking. Therefore, developing a high-performance polypropylene composite material based on grafted modified CNCs has significant engineering application value and practical significance. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the primary objective of this invention is to provide a high-performance polypropylene composite material.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned high-performance polypropylene composite material.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A high-performance polypropylene composite material comprises the following raw materials in parts by weight: 100 parts polypropylene, 10-30 parts modified cellulose nanocrystals, 1-5 parts maleic anhydride-grafted polypropylene, 0.1-0.5 parts antioxidant, and 0.1-0.5 parts lubricant.

[0010] The modified cellulose nanocrystals were prepared by the following process:

[0011] (1) Arginine and phosphorous acid were added to water and stirred, then formaldehyde solution was added and reacted under heating conditions; after the reaction was completed, the reaction solution was purified to obtain intermediate 1; the structural formula of intermediate 1 is:

[0012]

[0013] (2) Add cyanuric chloride to 1,4-dioxane, and then add a solution of γ-aminopropyltriethoxysilane and triethylamine in 1,4-dioxane at -5 to 5°C. Continue stirring for 2.5 to 3 hours. When the reaction solution is heated to 50 to 55°C, add intermediate 1 and a solution of triethylamine in 1,4-dioxane and continue stirring until the temperature reaches 100 to 105°C. After the reaction is completed, the reaction solution is purified to obtain intermediate 2. The structural formula of intermediate 2 is:

[0014]

[0015] (3) Disperse cellulose nanocrystals in water and sonicate them to obtain a cellulose nanocrystal dispersion; add an ethanol solution of intermediate 2 to the cellulose nanocrystal dispersion under an inert gas atmosphere and react under heating conditions; after the reaction is completed, the reaction solution is purified to obtain the modified cellulose nanocrystals.

[0016] The reaction principle for synthesizing modified cellulose nanocrystals in this invention is as follows: First, in step (1), the amino group of arginine, formaldehyde, and the active hydrogen of phosphorous acid undergo a Mannich reaction to obtain intermediate 1 with a high-density PN flame-retardant structure; then, in step (2), one chlorine atom of cyanuric chloride is nucleophilically substituted with the amino group of γ-aminopropyltriethoxysilane at a low temperature (-5 to 5℃), so that the silane molecule is attached to the triazine ring; then, at 50 to 55℃, the remaining two chlorine atoms of cyanuric chloride are nucleophilically substituted with the amino group of intermediate 1 to obtain intermediate 2 with a PN-Si flame-retardant structure; finally, in step (3), the siloxane group at the end of intermediate 2 is hydrolyzed to generate a silanol group, and the generated silanol group undergoes a dehydration condensation reaction with the hydroxyl groups on the surface of the cellulose nanocrystal to form a stable Si-OC covalent bond, so that intermediate 2 is firmly anchored on the surface of the cellulose nanocrystal, avoiding migration and interface problems.

[0017] Further, the molar ratio of arginine to phosphorous acid in step (1) is 1:(4-5), and the molar ratio of arginine to formaldehyde in the formaldehyde solution is 1:(4-5).

[0018] Furthermore, the heating temperature in step (1) is 110–130°C, and the reaction time is 4–8 h.

[0019] Further, the molar ratio of cyanuric chloride, γ-aminopropyltriethoxysilane and intermediate 1 in step (2) is 1:(1~1.1):(2~2.4).

[0020] Further, in step (2), the molar ratio of γ-aminopropyltriethoxysilane to triethylamine in the 1,4-dioxane solution of γ-aminopropyltriethoxysilane and triethylamine is 1:(1~1.2); the molar ratio of triethylamine to intermediate 1 in the 1,4-dioxane solution of intermediate 1 is (1.2~1.4):1.

[0021] Furthermore, the mass ratio of cellulose nanocrystals and intermediate 2 in step (3) is 1:(2-2.5).

[0022] Furthermore, the ultrasonic treatment time in step (3) is 20-30 min; the heating temperature is 80-90℃, and the reaction time is 12-14 h.

[0023] Further, the antioxidant is antioxidant 1010 or antioxidant 1098; the lubricant is magnesium stearate or zinc stearate.

[0024] A method for preparing the above-mentioned high-performance polypropylene composite material includes the following steps:

[0025] (a) According to the stated parts by weight, polypropylene, modified cellulose nanocrystals, maleic anhydride-grafted polypropylene, antioxidant and lubricant are premixed to obtain a mixture;

[0026] (b) The mixture is added to a twin-screw extruder, melt-extruded, and granulated to obtain the high-performance polypropylene composite material.

[0027] Furthermore, the premixing time in step (a) is 3 to 5 minutes; the temperature range of each zone of the twin-screw extruder in step (b) is 180 to 210°C, and the screw speed is 50 to 80 rpm.

[0028] The present invention has the following advantages over the prior art:

[0029] 1. This invention involves precise molecular design modification of cellulose nanocrystals (CNC), grafting an intermediate 2 with a PN-Si flame-retardant structure onto the CNC backbone via chemical bonds. This modified cellulose nanocrystal fully exerts its flame-retardant effect within a polypropylene matrix, promoting the formation of a dense and stable expanded carbon layer during combustion, effectively isolating heat and oxygen, and terminating the combustion reaction. Experimental results show that the composite material achieves a limiting oxygen index of 32.6%, meets the UL-94 V-0 rating, exhibits no dripping, and demonstrates excellent flame-retardant performance.

[0030] 2. The modified cellulose nanocrystals in this invention not only serve as flame retardants but also as nano-reinforcing fillers to simultaneously enhance the mechanical properties of composite materials. The massive structure introduced onto the surface of the modified cellulose nanocrystals generates a steric hindrance effect, which prevents the aggregation of cellulose nanocrystals, ensuring their uniform dispersion within the polypropylene matrix. This guarantees effective stress transfer, enhances the mechanical properties of the composite material, and overcomes the technical challenge of traditional additive flame retardants deteriorating the mechanical properties of materials.

[0031] 3. The modified cellulose nanocrystals in this invention have good compatibility with the polypropylene matrix. Furthermore, this invention uses maleic anhydride-grafted polypropylene as a compatibilizer, which further promotes the dispersion of the modified cellulose nanocrystals in the matrix and exhibits good processing characteristics. Attached Figure Description

[0032] Figure 1 shows the FT-IR images of cellulose nanocrystals and modified cellulose nanocrystals in Example 1 of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to specific embodiments. However, those skilled in the art should understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products obtained through commercial channels.

[0034] Example 1

[0035] Example 1 provides a high-performance polypropylene composite material, comprising the following raw materials in parts by weight: 100 parts polypropylene, 20 parts modified cellulose nanocrystals, 3 parts maleic anhydride-grafted polypropylene, 0.2 parts antioxidant 1010, and 0.3 parts magnesium stearate.

[0036] The modified cellulose nanocrystals were prepared by the following process:

[0037] (1) Arginine (0.1 mol) and phosphorous acid (0.45 mol) were added to deionized water (40 mL) and stirred to dissolve. The temperature was raised to 50℃ and formaldehyde solution (37wt%, 0.45 mol) was slowly added dropwise. The reaction was carried out at 120℃ for 6 h. After the reaction was completed, the reaction solution was distilled under reduced pressure to remove the solvent. The crude product was then dissolved in hot water and acetone was slowly added to the hot solution until turbidity appeared. The solution was then cooled to room temperature to precipitate the product. The product was collected by filtration and washed with cold acetone. After drying, intermediate 1 was obtained. 1 HNMR (C 10 H 26 N4O 14 P4, 400 MHz, d6-DMSO) δ 12.39(s, 1H, OH), 7.84(s, 1H, N H =C), 5.90(s, 1H, CH2N H ), 5.10(s, 8H, OH), 3.74(s, 4H, CH2), 3.40-3.34 (m, 3H, CH2, CH), 2.74 (s, 4H, CH2), 1.60-1.50(m, 4H, CH2); HRMS (ESI + ): [M+H] + The result is 551.04, and the value is 551.05.

[0038] The reaction process is as follows:

[0039]

[0040] (2) Add cyanuric chloride (0.05 mol) to 1,4-dioxane (70 mL) and stir. At 0°C, add a 1,4-dioxane solution (70 mL) of γ-aminopropyltriethoxysilane (0.055 mol) and triethylamine (0.055 mol) and continue stirring for 3 h. When the reaction solution is heated to 55°C, add a 1,4-dioxane solution (70 mL) of intermediate 1 (0.11 mol) and triethylamine (0.14 mol) and continue stirring for 3 h until the reaction temperature reaches 100°C. Then cool the reaction solution to room temperature and pour in dichloromethane (300 mL). The solid was filtered and washed three times with dichloromethane to obtain a crude product. The crude product was dissolved in hot DMF and dichloromethane was slowly added to the hot solution until turbidity appeared. Then it was cooled to room temperature to precipitate the product. The product was collected by filtration, washed with dichloromethane, and dried to obtain intermediate 2. 1 H NMR (C 32 H 72 N 12 O 31 P8Si, 400MHz, d6-DMSO) δ 12.39(s, 2H, OH), 7.84(s, 2H, N H =C), 7.01(s, 1H, N H CH2), 5.10(s, 16H, OH), 3.83-3.80(m, 6H, CH2), 3.74(s, 8H, CH2), 3.40-3.34 (m, 8H, CH2,CH), 2.74 (s, 8H, CH2), 1.60-1.48(m, 10H, CH2), 1.21(t, 9H, CH3), 0.56(t, 2H,CH2);HRMS (ESI + ): [M+H] + The calculation yields 1397.21, and the value is found to be 1397.21.

[0041] The reaction process is as follows:

[0042]

[0043] (3) Disperse cellulose nanocrystals (CNCs, 10 g) in deionized water (55 mL) and sonicate for 25 min to obtain a cellulose nanocrystal dispersion; add ethanol (22 g, 100 mL) solution of intermediate 2 to the cellulose nanocrystal dispersion under N2 atmosphere and 85 °C and react for 13 h; after the reaction is completed, centrifuge, wash the collected precipitate three times with deionized water, and dry to obtain modified cellulose nanocrystals;

[0044] Cellulose nanocrystals and modified cellulose nanocrystals were characterized by FT-IR, and the results are shown in Figure 1. Curves a and b in the figure correspond to cellulose nanocrystals and modified cellulose nanocrystals, respectively. Compared with curve a, curve b shows a higher concentration of cellulose nanocrystals in the 1000-1100 cm⁻¹ range. -1 The characteristic tooth-shaped peak of Si-OC appears at 2940 cm⁻¹. -1 The characteristic peaks of the CH bond are significantly enhanced, at 1550-1650 cm⁻¹. -1 The increased peak intensity at the point is due to the C=N stretching vibration of the triazine ring in intermediate 2. These results indicate that intermediate 2 was successfully grafted onto the surface of cellulose nanocrystals.

[0045] Example 1 also provides a method for preparing the above-mentioned high-performance polypropylene composite material, the specific steps of which are as follows:

[0046] (a) Weigh each raw material according to the above weight proportions, premix them in a mixer for 4 min to obtain a mixture;

[0047] (b) The mixture is added to a twin-screw extruder, melt-extruded and granulated to obtain the high-performance polypropylene composite material; wherein the processing temperature of each zone of the twin-screw extruder is: zone 1 180℃, zone 2 195℃, zone 3 210℃, zone 4 205℃, and the screw speed is 70 rpm.

[0048] Example 2

[0049] Example 2 provides a high-performance polypropylene composite material, comprising the following raw materials in parts by weight: 100 parts polypropylene, 10 parts modified cellulose nanocrystals, 1 part maleic anhydride-grafted polypropylene, 0.1 parts antioxidant 1098, and 0.1 parts zinc stearate.

[0050] The modified cellulose nanocrystals were prepared by the following process:

[0051] (1) Arginine (0.1 mol) and phosphorous acid (0.4 mol) were added to deionized water (30 mL) and stirred to dissolve. The temperature was raised to 40-60℃ and formaldehyde solution (37wt%, 0.4 mol) was slowly added dropwise. The reaction was carried out at 110℃ for 8 h. After the reaction was completed, the reaction solution was distilled under reduced pressure to remove the solvent. The crude product was then dissolved in hot water and acetone was slowly added to the hot solution until turbidity appeared. The solution was then cooled to room temperature to precipitate the product. The product was collected by filtration, washed with cold acetone, and dried to obtain intermediate 1. Intermediate 1 was obtained. 1 The H NMR and HRMS results were consistent with those of Example 1.

[0052] (2) Add cyanuric chloride (0.05 mol) to 1,4-dioxane (60 mL) and stir. At -5℃, add a 1,4-dioxane solution (60 mL) of γ-aminopropyltriethoxysilane (0.05 mol) and triethylamine (0.06 mol) and continue stirring for 2.5 h. When the reaction solution is heated to 50℃, add a 1,4-dioxane solution (60 mL) of intermediate 1 (0.1 mol) and triethylamine (0.12 mol) and continue stirring for 2.5 h until the reaction temperature reaches 100℃. Then cool the reaction solution to room temperature and pour in dichloromethane (300 mL). The solid was collected in a solution of DMF (mL), filtered, and washed three times with dichloromethane to obtain a crude product. The crude product was dissolved in hot DMF, and dichloromethane was slowly added to the hot solution until turbidity appeared. The solution was then cooled to room temperature to precipitate the product. The product was collected by filtration, washed with dichloromethane, and dried to obtain intermediate 2. Intermediate 2... 1 The H NMR and HRMS results were consistent with those of Example 1.

[0053] (3) 10 g of cellulose nanocrystals were dispersed in 50 mL of deionized water and sonicated for 20 min to obtain a cellulose nanocrystal dispersion. Under N2 atmosphere and 80 °C, 20 g of ethanol (100 mL) solution of intermediate 2 was added to the cellulose nanocrystal dispersion and the reaction was carried out for 12 h. After the reaction was completed, the precipitate was centrifuged, washed three times with deionized water, and dried to obtain modified cellulose nanocrystals. The FT-IR results of the modified cellulose nanocrystals were consistent with those of Example 1.

[0054] Example 2 also provides a method for preparing the above-mentioned high-performance polypropylene composite material, the specific steps of which are as follows:

[0055] (a) Weigh each raw material according to the above weight proportions, premix them in a mixer for 3 minutes to obtain a mixture;

[0056] (b) The mixture is added to a twin-screw extruder, melt-extruded and granulated to obtain the high-performance polypropylene composite material; wherein the processing temperature of each zone of the twin-screw extruder is: zone 1 180℃, zone 2 195℃, zone 3 210℃, zone 4 205℃, and the screw speed is 50 rpm.

[0057] Example 3

[0058] Example 3 provides a high-performance polypropylene composite material, comprising the following raw materials in parts by weight: 100 parts polypropylene, 30 parts modified cellulose nanocrystals, 5 parts maleic anhydride-grafted polypropylene, 0.5 parts antioxidant 1010, and 0.5 parts zinc stearate.

[0059] The modified cellulose nanocrystals were prepared by the following process:

[0060] (1) Arginine (0.1 mol) and phosphorous acid (0.5 mol) were added to deionized water (50 mL) and stirred to dissolve. The temperature was raised to 40-60℃ and formaldehyde solution (37wt%, 0.5 mol) was slowly added dropwise. The reaction was carried out at 130℃ for 4 h. After the reaction was completed, the reaction solution was distilled under reduced pressure to remove the solvent. The crude product was then dissolved in hot water and acetone was slowly added to the hot solution until turbidity appeared. The solution was then cooled to room temperature to precipitate the product. The product was collected by filtration, washed with cold acetone, and dried to obtain intermediate 1. Intermediate 1 was obtained. 1 The H NMR and HRMS results were consistent with those of Example 1.

[0061] (2) Add cyanuric chloride (0.05 mol) to 1,4-dioxane (80 mL) and stir. At 5°C, add γ-aminopropyltriethoxysilane (0.055 mol) and triethylamine (0.055 mol) in a 1,4-dioxane solution (80 mL) and continue stirring for 3 h. When the reaction solution is heated to 50°C, add intermediate 1 (0.12 mol) and triethylamine (0.16 mol) in a 1,4-dioxane solution (80 mL) dropwise and continue stirring for 3 h until the reaction temperature reaches 105°C. Then cool the reaction solution to room temperature and pour in dichloromethane (300 mL). The solid was collected in a solution of DMF (mL), filtered, and washed three times with dichloromethane to obtain a crude product. The crude product was dissolved in hot DMF, and dichloromethane was slowly added to the hot solution until turbidity appeared. The solution was then cooled to room temperature to precipitate the product. The product was collected by filtration, washed with dichloromethane, and dried to obtain intermediate 2. Intermediate 2... 1 The H NMR and HRMS results were consistent with those of Example 1.

[0062] (3) 10 g of cellulose nanocrystals were dispersed in 60 mL of deionized water and sonicated for 30 min to obtain a cellulose nanocrystal dispersion. Under N2 atmosphere and 90 °C, 25 g of ethanol (100 mL) solution of intermediate 2 was added to the cellulose nanocrystal dispersion and the reaction was carried out for 14 h. After the reaction was completed, the precipitate was centrifuged, washed three times with deionized water, and dried to obtain modified cellulose nanocrystals. The FT-IR results of the modified cellulose nanocrystals were consistent with those of Example 1.

[0063] Example 3 also provides a method for preparing the above-mentioned high-performance polypropylene composite material, the specific steps of which are as follows:

[0064] (a) Weigh each raw material according to the above weight proportions, premix them in a mixer for 5 minutes to obtain a mixture;

[0065] (b) The mixture is added to a twin-screw extruder, melt-extruded and granulated to obtain the high-performance polypropylene composite material; wherein the processing temperature of each zone of the twin-screw extruder is: zone 1 180℃, zone 2 195℃, zone 3 210℃, zone 4 205℃, and the screw speed is 80 rpm.

[0066] Comparative Example 1

[0067] Comparative Example 1 is basically the same as Example 1, except that the modified cellulose nanocrystals in Example 1 are replaced with cellulose nanocrystals.

[0068] Test case

[0069] The flame retardant and mechanical properties of the products prepared in Examples 1-3 and Comparative Example 1 were tested using the following methods:

[0070] ①Flame retardant performance: The UL-94 vertical burning test was conducted according to GB / T 2408-2021 "Determination of flammability of plastics - Horizontal and Vertical Methods", and the limiting oxygen index test was conducted according to GB / T 2406.2-2009 "Determination of flammability of plastics - Oxygen Index Method - Part 2: Room Temperature Test". Each group of samples was tested 5 times and the average value was taken. The results are shown in Table 1.

[0071] ②Mechanical properties: The tensile strength of the samples was tested according to GB / T 1040.1-2018 "Determination of tensile properties of plastics - Part 1: General rules", the flexural strength of the samples was tested according to GB / T 9341-2008 "Determination of flexural properties of plastics", and the impact strength of the samples was tested according to GB / T 1843-2008 "Determination of impact strength of plastic cantilever beam". Each group of samples was tested 5 times and the average value was taken. The results are shown in Table 1.

[0072] Table 1

[0073]

[0074] As can be seen from Table 1, the polypropylene composite materials prepared in Examples 1-3 of this invention have excellent flame retardant properties and mechanical properties.

[0075] In Comparative Example 1, the modified cellulose nanocrystals in Example 1 were replaced with cellulose nanocrystals. Due to the lack of grafted flame-retardant groups, the flame-retardant efficiency of the material was significantly lower than that of Example 1, with a limiting oxygen index only slightly higher than pure polypropylene. Melting droplets were observed during combustion. Furthermore, the agglomeration of the cellulose nanocrystals led to a significant decrease in tensile and flexural strength. These results demonstrate that the present invention, through precise molecular design modification of cellulose nanocrystals (CNC), grafts intermediate 2 with a PN-Si flame-retardant structure onto the CNC framework via chemical bonds. This modified cellulose nanocrystal not only fully exerts its flame-retardant effect in the polypropylene matrix but also exhibits good compatibility with the polypropylene matrix, serving as a nano-reinforcing filler to simultaneously improve the mechanical properties of the composite material.

[0076] Application examples

[0077] The composite materials prepared in Examples 1-3 and Comparative Example 1 were made into films using the casting method, then wound up and slit into polypropylene films, and the following performance tests were performed.

[0078] ①Tensive strength: The tensile strength was determined in accordance with GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", and the results are shown in Table 2.

[0079] ② Water vapor transmission rate: The water vapor transmission rate was determined according to GB / T 1037-2021 "Determination of water vapor transmission performance of plastic films and sheets - cup weight gain and weight loss method", and the results are shown in Table 2.

[0080] Table 2

[0081]

[0082] As shown in Table 2, the cast films made using the composite materials described in Examples 1-3 of this invention exhibit significantly higher tensile strengths in both the transverse and longitudinal directions compared to Comparative Example 1. This indicates that the modified cellulose nanocrystals of this invention achieve good dispersion and interfacial bonding within the polypropylene matrix, endowing the films with excellent mechanical strength and making them more durable during subsequent processing and use. Furthermore, the barrier properties of the composite film of this invention are also improved compared to Comparative Example 1. This is due to the interfacial compatibility between the modified cellulose nanocrystals and the matrix, which reduces interfacial defects and forms a more dense and complete film microstructure, thereby effectively blocking the permeation path of water vapor molecules.

[0083] In summary, this invention provides a high-performance polypropylene composite material that can be used to prepare packaging films with both high strength and high barrier properties, demonstrating broad application prospects.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A high-performance polypropylene composite material, characterized in that, The raw materials include the following parts by weight: 100 parts polypropylene, 10-30 parts modified cellulose nanocrystals, 1-5 parts maleic anhydride-grafted polypropylene, 0.1-0.5 parts antioxidant, and 0.1-0.5 parts lubricant; the modified cellulose nanocrystals are prepared by the following process: (1) Arginine and phosphorous acid are added to water and stirred, then formaldehyde solution is added and reacted under heating conditions; after the reaction is completed, the reaction solution is purified to obtain intermediate 1; the structural formula of intermediate 1 is: (2) Add cyanuric chloride to 1,4-dioxane, and then add a solution of γ-aminopropyltriethoxysilane and triethylamine in 1,4-dioxane at -5 to 5°C. Continue stirring for 2.5 to 3 hours. When the reaction solution is heated to 50 to 55°C, add intermediate 1 and a solution of triethylamine in 1,4-dioxane. Continue stirring until the temperature reaches 100 to 105°C. After the reaction is completed, the reaction solution is purified to obtain intermediate 2. The structural formula of intermediate 2 is: (3) Disperse cellulose nanocrystals in water and sonicate them to obtain a cellulose nanocrystal dispersion; add an ethanol solution of intermediate 2 to the cellulose nanocrystal dispersion under an inert gas atmosphere and react under heating conditions; after the reaction is completed, the reaction solution is purified to obtain the modified cellulose nanocrystals.

2. The high-performance polypropylene composite material according to claim 1, characterized in that, The molar ratio of arginine to phosphorous acid in step (1) is 1:(4-5), and the molar ratio of arginine to formaldehyde in the formaldehyde solution is 1:(4-5).

3. The high-performance polypropylene composite material according to claim 1, characterized in that, The heating temperature in step (1) is 110-130°C, and the reaction time is 4-8 h.

4. The high-performance polypropylene composite material according to claim 1, characterized in that, The molar ratio of cyanuric chloride, γ-aminopropyltriethoxysilane and intermediate 1 in step (2) is 1:(1-1.1):(2-2.4).

5. The high-performance polypropylene composite material according to claim 1, characterized in that, In step (2), the molar ratio of γ-aminopropyltriethoxysilane to triethylamine in the 1,4-dioxane solution of γ-aminopropyltriethoxysilane and triethylamine is 1:(1-1.2); the molar ratio of triethylamine to intermediate 1 in the 1,4-dioxane solution of intermediate 1 is (1.2-1.4):

1.

6. The high-performance polypropylene composite material according to claim 1, characterized in that, The mass ratio of cellulose nanocrystals and intermediate 2 in step (3) is 1:(2-2.5).

7. The high-performance polypropylene composite material according to claim 1, characterized in that, The ultrasonic treatment in step (3) lasts for 20 to 30 minutes; the heating temperature is 80 to 90°C; and the reaction time is 12 to 14 hours.

8. The high-performance polypropylene composite material according to claim 1, characterized in that, The antioxidant is antioxidant 1010 or antioxidant 1098; the lubricant is magnesium stearate or zinc stearate.

9. A method for preparing a high-performance polypropylene composite material according to any one of claims 1 to 8, characterized in that, The process includes the following steps: (a) premixing polypropylene, modified cellulose nanocrystals, maleic anhydride-grafted polypropylene, antioxidants and lubricants according to the stated weight proportions to obtain a mixture; (b) adding the mixture to a twin-screw extruder, melt-extruding and granulating to obtain the high-performance polypropylene composite material.

10. The method for preparing the high-performance polypropylene composite material according to claim 9, characterized in that, The premixing time in step (a) is 3 to 5 minutes; the temperature range of each zone of the twin-screw extruder in step (b) is 180 to 210°C, and the screw speed is 50 to 80 rpm.

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