Polypropylene composite material as well as preparation method and application thereof

Abstract

The invention discloses a polypropylene composite material as well as a preparation method and application thereof. The polypropylene composite material comprises the following components in parts by weight: 60-70 parts of polypropylene resin; 10 to 30 parts of a flaky filler with the surface grafted with PNIPAM (Poly (N-isopropylacrylamide)); the surface of the needle-shaped filler is coated with PCL-PEG (Polycaprolactone-Polyethylene Glycol). According to the polypropylene composite material disclosed by the invention, a compounding system of the flaky filler with the PNIPAM grafted on the surface and the needle-shaped filler with the PCL-PEG coated on the surface is adopted, so that on one hand, the interfacial interaction force between the filler and polypropylene resin can be effectively enhanced, the two-phase interfacial compatibility is greatly improved, and the weld line strength is improved; on the other hand, the size stability of the polypropylene material is effectively improved through the synergistic effect of a shrinkage reduction mechanism by passively limiting PP molecular chain movement and an active shrinkage compensation mechanism by exciting the phase change behavior of the filler, so that the polypropylene composite material with high weld line strength and low shrinkage rate is realized.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a polypropylene composite material, its preparation method, and its application. Background Technology

[0002] Polypropylene (PP) is widely used in automotive parts, appliance housings, and other fields due to its excellent processing properties, chemical stability, and low cost. However, PP exhibits significant post-shrinkage during the molding and cooling process, leading to a decrease in the dimensional accuracy of the finished products and severely limiting its application in precision structural components.

[0003] Existing technologies suggest that adding inorganic fillers (such as talc, calcium carbonate, and glass fiber) can improve the dimensional stability of polypropylene. However, in practical applications, it has been found that because the inorganic fillers contain polar hydroxyl groups on their surface, they are difficult to bond with the non-polar molecular chains of polypropylene, resulting in poor compatibility. During injection molding, the fillers tend to agglomerate at the melt flow front, leading to filler enrichment in the weld line region of the product, forming stress concentration points, and significantly deteriorating the weld line strength. Even with the addition of compatibilizers to the material system, the interfacial interaction between the inorganic fillers and the polymer remains weak, making it difficult to construct a continuous filler network. Chinese patent application CN102532687A discloses a low-shrinkage PP composite material, in which calcium carbonate is selected as the inorganic filler, and maleic anhydride-grafted polypropylene is added as a compatibilizer. However, this approach has a limited effect on reducing the material's shrinkage rate, and the addition of the compatibilizer leads to a decrease in the material's strength and modulus, without addressing the issue of improving weld line strength.

[0004] Currently, most common solutions to address post-shrinkage in polypropylene involve restricting the movement of polypropylene molecular chains using fillers. However, this method not only has limited effectiveness in improving dimensional stability but also leads to the degradation of other properties, thus limiting the material's practical applications. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a polypropylene composite material that has both high weld line strength and low shrinkage.

[0006] This invention is achieved through the following technical solution: A polypropylene composite material, comprising the following components by weight: 60-70 parts of polypropylene resin; 5-20 parts of PNIPAM-grafted sheet filler; 10-30 parts of needle-shaped filler coated with PCL-PEG.

[0007] The weight parts of the polypropylene resin can be 60 parts, 62 parts, 64 parts, 66 parts, 68 parts, or 70 parts, as well as specific values ​​between the above-mentioned points.

[0008] Preferably, the polypropylene resin is selected from at least one of homopolymer polypropylene or copolymer polypropylene.

[0009] Preferably, the melt flow index of the polypropylene resin at 230°C and 2.16 kg is 10-30 g / 10 min. The test method for the melt flow index refers to ISO 1133-1:2022.

[0010] In the polypropylene composite material of the present invention, the mass content of polypropylene resin is not less than 55%.

[0011] The weight percentage of the PNIPAM-grafted sheet filler can be 5 parts, 10 parts, 15 parts or 20 parts, as well as specific values ​​between the above-mentioned points.

[0012] Preferably, the sheet-like filler is selected from at least one of talc, montmorillonite, and mica, and more preferably talc.

[0013] The PNIPAM described in this invention is poly(N-isopropylacrylamide). Preferably, the number-average molecular weight of the PNIPAM is 20,000-50,000 g / mol.

[0014] The PNIPAM-grafted sheet filler of the present invention is a sheet filler surface covalently grafted with PNIPAM by forming amide bonds with PNIPAM through an aminosilane coupling agent.

[0015] Preferably, the grafting rate of the PNIPAM-grafted sheet filler is 1.2-4%. The grafting rate test method of the present invention is as follows: the thermogravimetric residual rate of the initial filler is tested by TGA, and then the TGA thermogravimetric residual rate of the grafted filler is tested. The difference between the two is the grafting rate.

[0016] This invention provides a method for preparing a sheet-like filler grafted with PNIPAM, comprising the following steps: (1) Place the sheet packing and aminosilane coupling agent in anhydrous ethanol solvent, stir at 60-80℃ for 3-4h, filter and wash, and then vacuum dry at 70-80℃ to obtain amino-modified sheet packing; wherein, the mass ratio of sheet packing to aminosilane coupling agent is 100:(3-5). (2) Add PNIPAM and amino-modified sheet filler to a toluene / DMF mixed solvent (toluene:DMF=1:1, v / v), the mass ratio of amino-modified sheet filler to PNIPAM is 100:(5-15), add 0.4g catalyst (DMAP), stir and react at 70-80℃ for 6-10h under nitrogen atmosphere, filter, wash and dry to obtain sheet filler with PNIPAM grafted on surface.

[0017] In the preparation method of the PNIPAM-grafted sheet filler, the aminosilane coupling agent is preferably 3-aminopropyltriethoxysilane (KH550); the average particle size of the sheet filler is preferably 0.4-16 μm, more preferably 0.5-1.2 μm; the PNIPAM is carboxyl-terminated PNIPAM; the number-average molecular weight of the PNIPAM is preferably 20000-50000 g / mol.

[0018] The method for preparing the PNIPAM-grafted sheet filler involves first modifying the sheet filler with an aminosilane coupling agent to form an amino group, and then using the reaction between the amino group and the carboxyl group of PNIPAM to efficiently form a strong amide bond (-CO-NH-) to achieve grafting.

[0019] The weight percentage of the needle-shaped filler coated with PCL-PEG can be 10 parts, 15 parts, 20 parts, 25 parts, or 30 parts, as well as specific values ​​between the above-mentioned values.

[0020] Preferably, the needle-shaped filler is selected from at least one of magnesium sulfate whiskers and wollastonite, and more preferably magnesium sulfate whiskers.

[0021] The PCL-PEG described in this invention is a polycaprolactone-polyethylene glycol block copolymer.

[0022] The needle-shaped filler with PCL-PEG surface coating of the present invention is formed by forming amide bonds with PCL-PEG through an aminosilane coupling agent on the surface of the needle-shaped filler, so that the surface of the needle-shaped filler is coated with PCL-PEG.

[0023] Preferably, the coating rate of the needle-like filler coated with PCL-PEG is 1.5-5%. The coating rate test method of the present invention is as follows: the thermogravimetric residual rate of the initial filler is tested by TGA, and then the thermogravimetric residual rate of the grafted filler is tested by TGA. The difference between the two is the coating rate.

[0024] Preferably, the needle-shaped filler coated with PCL-PEG has an average aspect ratio of 20-120 and an average length of 10-40 μm.

[0025] This invention provides a method for preparing needle-like fillers with PCL-PEG surface coating, comprising the following steps: Needle-shaped fillers were placed in a mixed solvent of ethanol / water (ethanol:water = 9:1, v / v), and 3%-5% (by weight of the needle-shaped fillers) of aminosilane coupling agent were added. The mixture was stirred at 60-80℃ for 1-2 hours, filtered, washed, and then vacuum dried at 70-80℃ to obtain amino-modified needle-shaped fillers. The amino-modified needle-shaped fillers and PCL-PEG were added to DMF solvent at a mass ratio of 1:(0.15-0.35). The temperature was controlled at 70-80℃ under nitrogen atmosphere, and the mixture was stirred for 6-10 hours. After filtration, washing, and drying, needle-shaped fillers with PCL-PEG coating were obtained.

[0026] In the preparation method of the needle-shaped filler coated with PCL-PEG, the aminosilane coupling agent is preferably 3-aminopropyltriethoxysilane (KH550); the PCL-PEG is carboxyl-terminated PCL-PEG; and the PCL-PEG is preferably a number-average molecular weight of 5000-9000 g / mol.

[0027] Preferably, a DMAP catalyst is added to the reaction system of amino-modified needle-like filler and PCL-PEG; the amount of DMAP catalyst added is 1%-2% of the mass of PCL-PEG.

[0028] In the polypropylene composite material of the present invention, the mass ratio of the PNIPAM-grafted sheet filler to the PCL-PEG-coated needle filler is (0.2-2):1, preferably (0.25-1):1.

[0029] The present invention also provides a method for preparing the above-mentioned polypropylene composite material, comprising the following steps: after uniformly mixing each component according to the formula, performing melt blending extrusion granulation on a twin-screw extruder to prepare a polypropylene composite material, wherein the processing temperature of the twin-screw extruder is 190℃-215℃ and the rotation speed is 300-600rpm.

[0030] The present invention also provides the application of the above-mentioned polypropylene composite material in automobiles, home appliances, and electronic products.

[0031] The present invention also provides an article comprising the above-described polypropylene composite material.

[0032] Preferably, the component can be applied to automobile bumpers or appliance housings.

[0033] The present invention has the following beneficial effects: The polypropylene composite material of this invention employs a compound system of PNIPAM-grafted sheet fillers and PCL-PEG-coated needle fillers. On the one hand, this effectively enhances the interfacial interaction between the fillers and polypropylene resin, greatly improving the interfacial compatibility of the two phases and increasing the weld line strength. On the other hand, the hybrid synergistic effect of the two-dimensional sheet fillers and one-dimensional needle fillers restricts the molecular chain movement of PP. During processing, the expansion of PNIPAM pushes the sheet fillers to move, compresses the needle fillers to form a dense network, and provides physical volume compensation. The melting of PCL absorbs shrinkage stress, and the shrinkage of PNIPAM provides reverse extrusion force to prevent interfacial failure. Through the synergistic effect of passively restricting the PP molecular chain movement to reduce shrinkage and stimulating the phase change behavior of the fillers to actively compensate for shrinkage, the dimensional stability of the polypropylene material is effectively improved, thus achieving a polypropylene composite material with both high weld line strength and low shrinkage rate. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the shrinkage plate for the point gate. Detailed Implementation

[0035] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0036] The raw materials used in the embodiments and comparative examples of the present invention are described below, but are not limited to these materials: Polypropylene resin: Melt index of 28 g / 10 min at 230℃ and 2.16 kg, PP EP548R, copolymer polypropylene, CNOOC Shell Petrochemicals Co., Ltd.

[0037] Surface-grafted PNIPAM sheet filler 1: Talc-PNIPAM, grafting rate 1.8%; preparation method as follows: 100g talc (HTPUtra5L, Liaoning Aihaiyimi Mining Co., Ltd., average particle size 0.65μm) and 5g KH550 were placed in anhydrous ethanol solvent and refluxed at 80℃ for 4h. After filtration and washing, the talc-amino was obtained by vacuum drying at 80℃. 15g PNI-200C (PNIPAM, COOH end group, number average molecular weight 25000g / mol) and talc-amino were added to a mixed solvent of toluene and DMF (toluene:DMF = 1:1, v / v). 0.4g catalyst (DMAP) was added, and the mixture was stirred at 70℃ for 8h under nitrogen atmosphere. After filtration, washing with ethanol 3 times and drying, talc-PNIPAM was obtained.

[0038] Surface-grafted PNIPAM sheet filler 2: montmorillonite-PNIPAM, grafting rate 1.6%, prepared as follows: 100g of montmorillonite (I.44P, Beijing Yiwei Special Chemical Technology Development Co., Ltd., average particle size 16μm) and 5g of KH550 were placed in anhydrous ethanol solvent and refluxed at 80℃ for 4h. After filtration and washing, it was vacuum dried at 80℃ to obtain montmorillonite-amino. 15g of PNI-200C (PNIPAM, COOH end group, molecular weight 25000g / mol) and montmorillonite-amino were placed in a mixed solvent of toluene and DMF (toluene:DMF = 1:1, v / v), and 0.4g of catalyst (DMAP) was added. The mixture was stirred at 70℃ for 8h under nitrogen atmosphere, filtered, washed three times with ethanol, and dried to obtain montmorillonite-PNIPAM.

[0039] Needle-shaped filler 1 with PCL-PEG surface coating: Magnesium sulfate whiskers-PCL-PEG, with a surface coating rate of 2.3% and an average aspect ratio of 40, is prepared as follows: 100g of magnesium sulfate whiskers (WS-1S2, Yingkou Wesker Chemical Co., Ltd.) is placed in a mixed solvent of ethanol / water (ethanol:water = 9:1, v / v), 5g of KH550 is added, and the mixture is stirred at 60℃ for 2h. After filtration and washing, the mixture is vacuum dried at 80℃ to obtain whisker-amino. The whisker-amino and 25g of A4002-5K (PCL-PEG, COOH end group, PEG:PCL = 1:4) are added to DMF solvent, and 0.4g of catalyst (DMAP) is added. The mixture is stirred at 70℃ for 8h under nitrogen atmosphere, and then filtered, washed, and dried to obtain magnesium sulfate whiskers-PCL-PEG.

[0040] Needle-shaped filler 2 with PCL-PEG surface coating: Wollastonite-PCL-PEG, with a surface coating rate of 1.9% and an average aspect ratio of 20, was prepared as follows: 100g of wollastonite (HQ-1250, Yingkou Wesker Chemical Co., Ltd.) was placed in a mixed solvent of ethanol / water (ethanol:water = 9:1, v / v), 5g of KH550 was added, and the mixture was stirred at 60℃ for 2h. After filtration and washing, the mixture was vacuum dried at 80℃ to obtain wollastonite-amino. Wollastonite-amino and 25g of A4002-5K (PCL-PEG, COOH end group, PEG:PCL = 1:4) were added to DMF solvent, and 0.4g of catalyst (DMAP) was added. The mixture was stirred at 70℃ for 8h under nitrogen atmosphere, and then filtered, washed, and dried to obtain wollastonite-PCL-PEG.

[0041] Preparation methods of polypropylene composite materials in the examples and comparative examples: According to the formula, each component is put into a mixer and mixed evenly to obtain a premix; the premix is ​​put into a twin-screw extruder for melt mixing and extrusion granulation, wherein the temperature of each zone is set to 190℃, 190℃, 195℃, 205℃, 210℃, 215℃, 210℃, 205℃, and the rotation speed is 500 rpm to prepare a polypropylene composite material.

[0042] Relevant performance testing methods: (1) Dimensional stability: Polypropylene composite particles are injection molded into point gate shrinkage plates (e.g. Figure 1 As shown in the figure, the mold size is 220*50*2.0mm. The injection pressure and holding pressure during injection molding are both 30bar (1bar=0.1MPa). The shrinkage plate is controlled at 23℃ for 48h, and the current length dimension D1 is measured. The first shrinkage rate V1=(D0-D1) / D0 is calculated, where D0 is the size of the mold. Then, the shrinkage plate is placed in an oven at 100℃ and heated for 1h. It is then controlled at 23℃ again for 48h, and the current length dimension D2 is measured. The second shrinkage rate V2=(D0-D2) / D0 is calculated. Finally, the shrinkage rate V3=V1-V2 is calculated.

[0043] (2) Weld line strength: According to ISO 527-2:2012 standard, the tensile specimen was tested using a universal testing machine. The two ends of the tensile specimen were fixed by a pneumatic push clamp. The tensile rate was 50 mm / min, the preload force was 0.5 N, and the maximum load Fmax was recorded. The weld line strength R = Fmax / (W*T), where W is the width of the weld seam of the specimen, the standard value is 10 mm, and T is the thickness of the specimen, usually 4 mm, in MPa.

[0044] Table 1: Distribution ratios (by weight) and related performance test results of groups 1-5 in Examples 1-5 Example 1 Example 2 Example 3 Example 4 Example 5 Polypropylene resin 70 70 70 70 70 Talc - PNIPAM 20 15 6 6 Montmorillonite - PNIPAM / / / 6 / Magnesium sulfate whiskers-PCL-PEG 10 15 24 24 / Wollastonite-PCL-PEG / / / / 24 Weld line strength / MPa 19.6 20.1 21.0 19.4 20.3 First contraction rate V1 0.74% 0.68% 0.63% 0.71% 0.82% Post-shrinkage rate V3 0.029% 0.022% 0.015% 0.024% 0.033% Table 2: Distribution ratios (by weight) and related performance test results of comparative examples 1-7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Polypropylene resin 70 70 70 70 70 70 70 Talc - PNIPAM / / / 6 / 30 / Magnesium sulfate whiskers-PCL-PEG / / / / 24 / 30 Untreated talc 20 15 6 / 6 / / Untreated magnesium sulfate whiskers 10 15 24 24 / / / Weld line strength / MPa 16.0 16.5 16.2 16.6 16.9 17.6 18.3 First contraction rate V1 0.96% 0.94% 0.91% 0.88% 0.83% 0.81% 0.87% Post-shrinkage rate V3 0.052% 0.049% 0.046% 0.042% 0.037% 0.036% 0.045% As can be seen from the above examples and comparative results, the polypropylene composite material of the present invention, by adopting a compound system of sheet filler with surface grafted PNIPAM and needle filler with surface coated PCL-PEG, can effectively improve the weld line strength and dimensional stability of the material, and realize a polypropylene composite material with both high weld line strength and low shrinkage. The weld line strength of the material is ≥19MPa, the demolding shrinkage (primary shrinkage) is ≤0.85%, and the subsequent shrinkage is <0.04%.

[0045] Comparative Examples 1 to 5, the use of ungrafted sheet fillers (talc) or uncoated needle fillers (magnesium sulfate whiskers) failed to effectively improve the weld line strength of the materials, and the materials had high shrinkage and poor dimensional stability.

[0046] Comparative Example 6, which only added talc-PNIPAM, had lower weld line strength; Comparative Example 7, which only added magnesium sulfate whiskers-PCL-PEG, had higher shrinkage and poor dimensional stability.

[0047] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polypropylene composite material, characterized in that, By weight, it includes the following components: 60-70 parts of polypropylene resin; 5-20 parts of PNIPAM-grafted sheet filler; 10-30 parts of needle-shaped filler coated with PCL-PEG.

2. The polypropylene composite material according to claim 1, characterized in that, The polypropylene resin is selected from at least one of homopolymer polypropylene or copolymer polypropylene.

3. The polypropylene composite material according to claim 1, characterized in that, The PNIPAM is poly(N-isopropylacrylamide); the sheet filler is selected from at least one of talc, montmorillonite, and mica, preferably talc.

4. The polypropylene composite material according to claim 1, characterized in that, The grafting rate of the PNIPAM-grafted sheet filler is 1.2-4%.

5. The polypropylene composite material according to claim 1, characterized in that, The PCL-PEG is a polycaprolactone-polyethylene glycol block copolymer; the needle-shaped filler is selected from at least one of magnesium sulfate whiskers and wollastonite, preferably magnesium sulfate whiskers.

6. The polypropylene composite material according to claim 1, characterized in that, The coating rate of the needle-shaped filler coated with PCL-PEG is 1.5-5%; the average aspect ratio of the needle-shaped filler coated with PCL-PEG is 20-120, and the average length is 10-40 μm.

7. The polypropylene composite material according to claim 1, characterized in that, The mass ratio of the PNIPAM-grafted sheet filler to the PCL-PEG-coated needle filler is (0.2-2):1, preferably (0.25-1):

1.

8. The method for preparing the polypropylene composite material according to any one of claims 1-7, characterized in that, The process includes the following steps: After uniformly mixing the components according to the formula, the mixture is melt-blended and extruded into granules on a twin-screw extruder to prepare a polypropylene composite material. The processing temperature of the twin-screw extruder is 190℃-215℃ and the rotation speed is 300-600rpm.

9. A component, characterized in that, Includes the polypropylene composite material according to any one of claims 1-7.

10. The application of the part according to claim 9, characterized in that, Used for car bumpers or appliance housings.

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