Cold-drawn fiber-forming reinforced long-chain branched polypropylene foam material and preparation method thereof

Abstract

The invention provides a cold-drawn fiber-forming reinforced long-chain branched polypropylene foam material and a preparation method thereof. The method comprises the following steps: carrying out melt blending on long-chain branched polypropylene, a thermoplastic polyester elastomer, a rare earth nucleating agent and an antioxidant to obtain a blend; carrying out a cold drawing process on the blend to obtain a cold-drawn fiber forming material; performing foaming treatment on the cold-drawn fiber-forming material through a foaming agent to obtain a cold-drawn fiber-forming enhanced long-chain branched polypropylene foam material; the addition amount of the rare earth nucleating agent is less than 5 phr based on 100 phr of long-chain branched polypropylene; the addition amount of the thermoplastic polyester elastomer is 25 phr or less. According to the invention, the long-chain branched polypropylene and the thermoplastic polyester elastomer are blended, and the cold drawing process is carried out in a molten state, so that the thermoplastic polyester elastomer forms a highly oriented fiber structure in a cold-drawn fiber-forming matrix material, the toughness of the composite foam material is improved, the high strength of the composite foam material is ensured, and excellent rigid-tough balance is realized.

Description

Technical Field

[0001] The invention relates to a cold-drawn fiber-reinforced long-chain branched polypropylene foam material and a preparation method thereof, belonging to the technical field of polymer materials. Background Art

[0002] Long-chain branched polypropylene (LCBPP) is widely used in polymer materials due to its excellent toughness and rigidity. However, its high melt viscosity and poor fiber-forming properties limit its practical application. Traditional toughening methods, such as adding rubber elastomers and thermoplastic elastomers, can improve toughness but often lead to a significant decrease in rigidity and tensile strength. In addition, due to the poor compatibility between LCBPP and elastomers, the toughening effect is limited, making it difficult to meet the application requirements of high strength and high toughness.

[0003] In view of this, it is of great significance to provide a new method to effectively improve the mechanical properties of foam materials to overcome the limitations of traditional methods on performance improvement. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a cold-drawn fiber-reinforced long-chain branched polypropylene foam material and a preparation method thereof. A highly oriented thermoplastic polyester elastomer fiber structure is formed by a cold-drawing process, so that the foam material has high strength rigidity and good toughness.

[0005] To achieve the above object, in a first aspect, the present invention provides a method for preparing a cold-drawn fiber-reinforced long-chain branched polypropylene foam material, which comprises the following steps:

[0006] Step 1: melt-blending long-chain branched polypropylene, thermoplastic polyester elastomer, rare earth nucleating agent and antioxidant to obtain a blend;

[0007] Step 2: subjecting the blend to a cold drawing process to obtain a cold drawn fiber-forming material;

[0008] Step 3: The cold-drawn fiber-forming material is foamed by a foaming agent to obtain the cold-drawn fiber-forming reinforced long-chain branched polypropylene foam material;

[0009] Wherein, based on 100phr of long-chain branched polypropylene, the addition amount of the rare earth nucleating agent is less than 5phr, preferably 2-3phr;

[0010] The amount of the thermoplastic polyester elastomer (TPEE) added is less than 25 phr, preferably 10-15 phr. TPEE, as a toughening agent, forms a fibrous structure during the cold drawing process to enhance the stress transfer ability of the composite material. The present invention uses 10-15 phr of TPEE, which will show excellent compression resistance and is suitable for scenes with strict requirements for high impact resistance.

[0011] According to a specific embodiment of the present invention, preferably, the rare earth nucleating agent is WBG-II, produced by Guangdong Weilinna Co., Ltd. The addition of the rare earth nucleating agent in the present invention can promote the crystallization of LCBPP and enhance the thermal stability and foam uniformity of the foam material.

[0012] According to a specific embodiment of the present invention, preferably, the antioxidant is 0-3 phr, more preferably 0.5-2 phr.

[0013] According to a specific embodiment of the present invention, preferably, the antioxidant is selected from antioxidant 1010 and / or antioxidant 168, preferably antioxidant 1010. Wherein, antioxidant 1010 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and antioxidant 168 is tris[2.4-di-tert-butylphenyl]phosphite. Adding an antioxidant in the present invention can improve the antioxidant performance of the foam material, prevent aging, and enhance durability.

[0014] According to a specific embodiment of the present invention, preferably, the temperature of the melt blending is 150-200°C, preferably 170-190°C.

[0015] According to a specific embodiment of the present invention, preferably, the melt blending time is 6-10 minutes.

[0016] According to a specific embodiment of the present invention, preferably, the stretching rate of the cold drawing process is 10-100 mm / min, more preferably 30-60 mm / min.

[0017] According to a specific embodiment of the present invention, preferably, the blend is passed through a cold drawing device and subjected to a cold drawing process at the above-mentioned stretching rate to obtain a cold drawn fiber material, i.e., a cold drawn fiber matrix material; TPEE is used to form a highly oriented fiber structure in the matrix material, so that TPEE is evenly distributed in the LCBPP matrix (i.e., long chain branched polypropylene), thereby increasing the overall toughness of the composite material. Since the cold drawn fiber has a larger specific surface area, it provides a higher stress transfer efficiency, thus improving the stress dispersion effect of the material.

[0018] According to a specific embodiment of the present invention, preferably, the cold-drawn fiber-forming material is subjected to a foaming treatment with supercritical CO2 and then maintained under pressure to obtain the cold-drawn fiber-reinforced long-chain branched polypropylene foam material. Specifically, supercritical CO2 can be used as a foaming medium, and by optimizing parameters such as foaming temperature, pressure, and pressure-maintaining time, a more uniform cell structure and excellent compression performance can be obtained, thereby ensuring the mechanical properties of the material in foam applications.

[0019] According to a specific embodiment of the present invention, preferably, the pressure of the foaming treatment is below 30 MPa, more preferably 8-15 MPa.

[0020] According to a specific embodiment of the present invention, preferably, the temperature of the foaming treatment is 140-170°C, more preferably 145-155°C.

[0021] According to a specific embodiment of the present invention, preferably, the pressure holding time is 0.1-6h, more preferably 1-2h; further preferably 1.5-2h.

[0022] In a second aspect, the present invention provides a cold-drawn fiber-reinforced long-chain branched polypropylene foam material prepared by the above-mentioned method for preparing the cold-drawn fiber-reinforced long-chain branched polypropylene foam material.

[0023] According to a specific embodiment of the present invention, preferably, the average diameter of the pores of the cold-drawn fiber-reinforced long-chain branched polypropylene foam material is 53-131.5 μm.

[0024] According to a specific embodiment of the present invention, preferably, the cell density of the cold-drawn fiber-reinforced long-chain branched polypropylene foam material is 2.5×10 7 -2.4×10 8 Pieces / cm 3 , measured by volume of cold-drawn fiber-reinforced long-chain branched polypropylene foam material.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention blends long-chain branched polypropylene with thermoplastic polyester elastomer, and performs a cold drawing process in a molten state, so that the thermoplastic polyester elastomer forms a highly oriented fiber structure in the matrix material, thereby improving the toughness of the composite material while ensuring its high strength, and achieving an excellent rigidity-toughness balance. The thermal stability of the material is improved by introducing a rare earth nucleating agent, and the foam material is prepared by combining a supercritical CO2 foaming process, so that the final product has excellent mechanical strength.

[0027] The cold-drawing process of the present invention effectively improves the storage modulus of the composite foam material and significantly reduces the viscosity loss. At the same time, the high orientation of the fiber is observed by scanning electron microscopy, and the impact strength of the cold-drawn fiber-forming matrix material is greatly improved. The cold-drawn in-situ fiber-forming foam material of the present invention has broad application prospects in the field of lightweight and high-strength polypropylene foam structures, such as automotive interiors, building insulation materials, and sports equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the oriented fiberization process of TPEE in the LCBPP matrix in the cold drawing fiber forming process of the present invention.

[0029] Figure 2 It is a scanning electron microscope image of the cross-sectional structure of the cold-drawn fiber-forming matrix material of Examples 1-4 and Comparative Example 1.

[0030] Figure 3 It is a rheological test diagram of cold drawn fiber matrix material.

[0031] Figure 4 It is the DSC test chart of the cold-drawn fiber-forming matrix materials of Examples 1-4 and Comparative Example 1.

[0032] Figure 5 These are the test graphs of the tensile strength and impact strength of the matrix material under cold-drawn fiberization and hot-drawn fiberization respectively.

[0033] Figure 6 This is a diagram of the cell structure of cold-drawn fiber-forming foam materials with different TPEE contents.

[0034] Figure 7 It is a compression test diagram of the cold-drawn fiber-forming foam materials of Examples 1-4 and Comparative Example 1.

[0035] Figure 8 This is a comparison chart of the impact strength of cold-drawn TPEE in-situ fiber-reinforced LCBPP foam material and other polypropylene materials. DETAILED DESCRIPTION

[0036] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0037] Example 1

[0038] This embodiment provides a method for preparing a cold-drawn fiber-reinforced long-chain branched polypropylene foam material, comprising the following steps:

[0039] 95 phr of long chain branched polypropylene (LCBPP) and 5 phr of thermoplastic polyester elastomer (TPEE) were melt blended at 190° C. to ensure uniform dispersion of the materials, and 2.5 phr of a rare earth nucleating agent and 1 phr of an antioxidant 1010 were added to obtain a blend;

[0040] The blend is cold drawn in a high-intensity tensile flow field, and the drawing rate is controlled at 50 mm / min. After cold drawing, it is quickly cooled to obtain a cold-drawn fiber-forming material to prevent the TPEE fiber from rebounding.

[0041] The cold-drawn fiber material is placed in a CO2 atmosphere for foaming, the pressure is controlled at 15 MPa, the temperature is set at 150°C, and the pressure is quickly released and cooled after foaming to obtain a foam material.

[0042] Example 2

[0043] This embodiment provides a method for preparing a cold-drawn fiber-reinforced long-chain branched polypropylene foam material, which differs from Embodiment 1 only in that:

[0044] 90 phr of LCBPP and 10 phr of TPEE were melt blended.

[0045] Example 3

[0046] This embodiment provides a method for preparing a cold-drawn fiber-reinforced long-chain branched polypropylene foam material, which differs from Embodiment 1 only in that:

[0047] 85 phr of LCBPP was melt blended with 15 phr of TPEE.

[0048] Example 4

[0049] This embodiment provides a method for preparing a cold-drawn fiber-reinforced long-chain branched polypropylene foam material, which differs from Embodiment 1 only in that:

[0050] 80 phr of LCBPP and 20 phr of TPEE were melt blended.

[0051] Comparative Example 1

[0052] This comparative example provides a method for preparing a long-chain branched polypropylene foam material, which differs from Example 1 only in that:

[0053] 100phr of LCBPP was added, and no TPEE was added.

[0054] Comparative Example 2

[0055] This comparative example provides a method for preparing a cold-drawn fiber-reinforced long-chain branched polypropylene foam material, which differs from Example 4 only in that:

[0056] 80 phr of LCBPP and 20 phr of TPEE were melt-blended, and the blended sample was subjected to heat drawing treatment.

[0057] The raw material dosages of the above embodiments and comparative examples and the performance test results of the cold-drawn fiber-reinforced long-chain branched polypropylene foam materials are shown in Table 1.

[0058] Table 1

[0059]

[0060] Experimental results and analysis

[0061] Figure 1The figure is a schematic diagram of the oriented fiberization process of TPEE in the LCBPP matrix in the cold drawing fiberization process of the present invention. The figure shows the arrangement direction and stretching effect of the fibers during the cold drawing process. In the cold drawing in-situ fiberization process, the oriented fiberization structure of TPEE in the matrix is ​​achieved by continuous tensile stress. According to the analysis of the mechanism diagram, TPEE forms a highly ordered fibrous structure during the cold drawing process, which not only enhances the stress transfer ability of the material, but also inhibits the plastic deformation of polypropylene. During the fiberization process, the specific surface area of ​​TPEE is greatly increased, so that the composite material has a better stress transfer effect and significantly improves its mechanical properties.

[0062] Figure 2 The following are scanning electron microscope images of the cross-sectional structures of the cold-drawn fiber-forming matrix materials of Examples 1-4 and Comparative Example 1. It can be seen from the scanning electron microscope (SEM) image that the TPEE after cold drawing forms a highly oriented fibrous structure in the LCBPP matrix. The cross section is elliptical, and the longitudinal arrangement of the fibers is clearly visible. With the increase of TPEE content, the viscosity of the LCBPP matrix is ​​significantly improved, further enhancing the fiberization effect. This fiberization structure provides the material with better mechanical properties, especially in a high stress environment, it can effectively alleviate the local stress concentration of the matrix, and improve the impact strength and toughness of the cold-drawn fiber-forming matrix material.

[0063] Figure 3 The changes in the storage modulus (G') and loss tangent (tanδ) of the cold-drawn fiber matrix materials of Examples 1-4 and Comparative Example 1 are shown, indicating that the cold-drawn fiber structure significantly enhances the melt strength of the material. According to the rheological properties test results, the LCBPP / TPEE composite material after cold drawing exhibits a higher storage modulus (G') at low angular frequency, which indicates that the cold-drawn fiber structure increases the melt strength of the material. In addition, the loss tangent (tanδ) value decreases significantly with the increase of TPEE concentration, indicating that the viscosity loss of the material is reduced and the elastic response of the melt is enhanced. This change is particularly important in the foaming process of the foam material, because the enhanced melt strength helps prevent the merging and collapse of the bubbles and ensure the stability and uniformity of the foam structure. The increase in complex viscosity (η*) with the increase of TPEE concentration further shows that the cold-drawn fiber structure significantly improves the material's resistance to deformation and is suitable for the application of high-strength foam materials.

[0064] Figure 4 The DSC test diagrams of the cold-drawn fiber-forming matrix materials of Examples 1-4 and Comparative Example 1. The crystallization properties of the cold-drawn fiber-forming matrix materials were analyzed by differential scanning calorimetry (DSC), showing the effect of cold-drawing treatment on the melting and crystallization temperatures of LCBPP. Figure 4As can be seen from Figure a, when the temperature is raised for the first time, the melting temperature of the cold-drawn fiber matrix material is slightly lower than that of the untreated sample, which indicates that the cold-drawn fiberized TPEE fiber structure inhibits the excessive growth of LCBPP crystals and reduces the degree of crystallization perfection, allowing the material to be processed at a lower temperature, which has an energy-saving effect. In addition, Figure 4 As can be seen from Figure b, the melting curve of the second heating shows that the formation of β-LCBPP crystals is not significantly affected by the TPEE content, proving that the cold drawing process can improve the toughness of the material while maintaining the stability of its crystallization properties.

[0065] Figure 5 The following are the mechanical properties test diagrams of tensile strength and impact strength of the matrix material under cold-drawn fiber and hot-drawn fiber. Figure 5 It can be seen that the impact strength of the cold-drawn fiber material is significantly improved, which is 488% higher than that of the pure LCBPP sample. At the same time, the tensile strength after cold-drawn fiber is slightly reduced by 14.2%, but this reduction is acceptable in the rigidity-toughness balance of high-strength composite materials. In contrast, the hot-drawing process has limited improvement in impact strength, and the impact strength of the hot-drawn sample is only increased by 70.3%, which further proves the advantage of the cold-drawing process in enhancing the toughness of the material.

[0066] Figure 6 The cell structure diagram of cold-drawn fiber-forming foam materials with different TPEE contents. Figure 6 It can be seen that the increase in TPEE content significantly reduces the foam expansion ratio and pore size, and greatly increases the pore density, which proves that in-situ fiberization significantly improves the foaming performance of the composite material.

[0067] Figure 7 The compression test diagram of the cold-drawn fiber-forming foam material of Examples 1-4 and Comparative Example 1. The foam material exhibits excellent compression resistance at a TPEE content of 10-15phr. The microstructure of the pores remains stable, avoiding the common pore collapse problem in traditional foam materials. The cold-drawing process makes the pore distribution of the composite material more uniform, further improving the overall mechanical properties of the foam, and is suitable for application scenarios with strict requirements on impact resistance.

[0068] Figure 8The impact strength comparison chart of the cold-drawn TPEE in-situ fiber-reinforced LCBPP material of Example 4 and other polypropylene materials under the same conditions. The impact strength test was conducted on the matrix material before foaming. By comparing the impact properties of other polypropylene composite materials, the TPEE in-situ fiber-reinforced long-chain branched polypropylene (LCBPP / TPEE) composite material of the present invention has significant advantages in mechanical properties. The cold-drawing process enables TPEE to form a highly oriented fiber structure in the LCBPP matrix, which greatly improves the impact strength of the cold-drawn fiber-forming matrix material. Compared with the pure sample material (100phr of LCBPP, 0phr of TPEE), the improvement is as high as 488%, far exceeding the traditional toughened polypropylene material. At the same time, this highly oriented fiber structure effectively improves the stress transfer efficiency, maintains excellent tensile strength while maintaining high impact strength, and achieves an ideal balance of rigidity and toughness. Compared with other polypropylene composite materials that have not been cold-drawn, the cold-drawn fiber-forming composite material of the present invention has better impact resistance and structural stability, and is particularly suitable for industrial application scenarios where high strength and high toughness are equally important.

Claims

1. A method for preparing a cold-drawn fiber-reinforced long-chain branched polypropylene foam material, wherein: The following steps are involved: Step 1: melt-blending long-chain branched polypropylene, thermoplastic polyester elastomer, rare earth nucleating agent and antioxidant to obtain a blend; Step 2: subjecting the blend to a cold drawing process to obtain a cold drawn fiber-forming material; Step 3: The cold-drawn fiber-forming material is foamed by a foaming agent to obtain the cold-drawn fiber-enhanced long-chain branched polypropylene foam material; Wherein, based on 100phr of long-chain branched polypropylene, the added amount of the rare earth nucleating agent is less than 5phr; The added amount of the thermoplastic polyester elastomer is less than 25 phr.

2. The method for preparing the cold-drawn fiber-reinforced long-chain branched polypropylene foam material according to claim 1, wherein: Based on 100phr of long-chain branched polypropylene, the amount of the rare earth nucleating agent added is 2-3phr; And / or, the antioxidant is added in an amount of 0-3 phr, preferably 0.5-2 phr; And / or, the added amount of the thermoplastic polyester elastomer is 10-15 phr.

3. The method for preparing the cold-drawn fiber-reinforced long-chain branched polypropylene foam material according to claim 1 or 2, wherein: The rare earth nucleating agent is WBG-II.

4. The method for preparing the cold-drawn fiber-reinforced long-chain branched polypropylene foam material according to claim 1 or 2, wherein: The antioxidant is selected from antioxidant 1010 and / or antioxidant 168, preferably antioxidant 1010.

5. The method for preparing the cold-drawn fiber-reinforced long-chain branched polypropylene foam material according to claim 1, wherein: The temperature of the melt blending is 150-200°C, preferably 170-190°C; And / or, the melt blending time is 6-10 min.

6. The method for preparing the cold-drawn fiber-reinforced long-chain branched polypropylene foam material according to claim 1, wherein: The stretching rate of the cold drawing process is 10-100 mm / min, preferably 30-60 mm / min.

7. The method for preparing the cold-drawn fiber-reinforced long-chain branched polypropylene foam material according to claim 1, wherein: The cold-drawn fiber-forming material is subjected to a foaming treatment by supercritical CO2 and then maintained under pressure to obtain the cold-drawn fiber-forming enhanced long-chain branched polypropylene foam material.

8. The method for preparing the cold-drawn fiber-reinforced long-chain branched polypropylene foam material according to claim 7, wherein: The pressure of the foaming treatment is below 30 MPa, preferably 8-15 MPa; And / or, the temperature of the foaming treatment is 140-170°C, preferably 145-155°C; And / or, the pressure holding time is 0.1-6h, preferably 1-2h.

9. A cold-drawn fiber-reinforced long-chain branched polypropylene foam material prepared by the method for preparing a cold-drawn fiber-reinforced long-chain branched polypropylene foam material as claimed in any one of claims 1 to 8.

10. The cold-drawn fiber-reinforced long-chain branched polypropylene foam material according to claim 9, wherein: The average cell diameter of the cold-drawn fiber-reinforced long-chain branched polypropylene foam material is 53-131.5 μm; And / or, the cell density of the cold-drawn fiber-reinforced long-chain branched polypropylene foam material is 2.5×10 7 -2.4×10 8 Pieces / cm 3 .

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