A kind of polypropylene-based foaming material and preparation method thereof

Abstract

The present invention provides a polypropylene-based foam material and a preparation method thereof, and relates to the technical field of foam material preparation. A method for preparing a polypropylene-based foam material comprises the following steps: adding polypropylene and water into a container, introducing high-pressure CO 2 The gas is heated to 130-145°C under stirring, and the temperature and pressure are kept constant to make the system completely saturated; the pressure is released within 3-10 seconds, and the mixture is cooled to 40-50°C to obtain a polypropylene-based foaming material. The polypropylene-based foaming material of the present application has excellent foaming performance.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of foaming materials, and in particular to a polypropylene-based foaming material and a preparation method thereof. Background Art

[0002] With the development of the green economy, the "lightweight, energy-saving and environmentally friendly" automobile industry has become a hot area for competition among many leading automobile companies.

[0003] The operating temperature of polypropylene foam material can reach 130℃, and the Vicat softening point can reach up to 150℃. It has outstanding high temperature resistance and product dimensional stability under high temperature. It emits no toxic gas when burned and has excellent environmental performance. It can also achieve the purpose of weight reduction through foaming. Therefore, under the trend of "lightweight, energy saving and environmental protection", polypropylene foam material is favored by the automotive field.

[0004] Although polypropylene has many advantages, its internal molecules are linear in structure and it is a semi-crystalline polymer, which shows low melt strength, so its foaming performance is very poor. Therefore, providing a polypropylene-based foaming material with excellent foaming performance has become a technical problem that technicians in this field need to solve urgently. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the deficiencies in the prior art, the present invention provides a polypropylene-based foaming material and a preparation method thereof, which solves the technical problem of poor foaming performance of polypropylene.

[0007] (II) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] On the one hand, the present invention provides a method for preparing a polypropylene-based foam material, comprising the following steps: adding polypropylene and water into a container, introducing high-pressure CO2 gas, heating to 130-145°C under stirring, maintaining constant temperature and pressure to fully saturate the system; releasing the pressure within 3-10 seconds, cooling to 40-50°C, and obtaining a polypropylene-based foam material;

[0010] The pressure of the high-pressure CO2 gas is 10-30MPa.

[0011] Preferably, the polypropylene is modified polypropylene, and the preparation method of the modified polypropylene comprises the following steps: taking linear polypropylene, divinyltetramethyldisiloxane, methyl methacrylate, an initiator, and zinc diacrylate and stirring them uniformly to prepare a premix; extruding and granulating the premix at 150-160° C. to prepare modified polypropylene.

[0012] Preferably, the initiator is selected from any one of benzoyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0013] Preferably, the amount of divinyltetramethyldisiloxane used is 1-2% of the mass of linear polypropylene, the amount of methyl methacrylate used is 2-4% of the mass of linear polypropylene, and the amount of zinc diacrylate used is 0.5-1% of the mass of linear polypropylene.

[0014] Preferably, the amount of divinyltetramethyldisiloxane used is 1-1.5% of the mass of linear polypropylene, the amount of methyl methacrylate used is 2-3% of the mass of linear polypropylene, and the amount of zinc diacrylate used is 0.5-0.8% of the mass of linear polypropylene.

[0015] Preferably, the amount of divinyltetramethyldisiloxane used is 1% by mass of the linear polypropylene, the amount of methyl methacrylate used is 2% by mass of the linear polypropylene, and the amount of zinc diacrylate used is 0.5% by mass of the linear polypropylene.

[0016] Preferably, the mass volume ratio of the polypropylene to water is 0.04-0.08 kg / L.

[0017] Preferably, the pressure of the high-pressure CO2 gas is 10 MPa.

[0018] On the other hand, the present invention provides a polypropylene-based foam material prepared by the method for preparing a polypropylene-based foam material according to the first aspect, wherein the pore diameter of the polypropylene-based foam material is 50-60 μm.

[0019] Preferably, the cell density of the polypropylene-based foaming material is 9×10 7 -11×10 7 Pieces / cm 3 .

[0020] (III) Beneficial effects

[0021] The present invention provides a polypropylene-based foam material and a preparation method thereof. Compared with the prior art, the present invention has the following beneficial effects:

[0022] The preparation method of a polypropylene-based foaming material of the present invention comprises the following steps: selecting divinyltetramethyldisiloxane, methyl methacrylate, and zinc diacrylate to modify linear polypropylene under the action of an initiator, grafting metal salts onto the linear polypropylene molecular chains, so that long-chain branched polypropylene is formed by ionic interactions between the polypropylene molecular chains, and the long-chain branched polypropylene further forms a long-chain branched structure under the conditions of divinyltetramethyldisiloxane and methyl methacrylate, thereby increasing the crystallization temperature of the modified polypropylene and reducing the half-crystallization time. The modified polypropylene with a long-chain branched structure can produce more chain entanglements during the foaming process, thereby causing strain hardening during melt stretching, significantly increasing the melt strength, thereby increasing the foaming uniformity of the polypropylene-based foaming material of the present application, and improving the foaming performance of the polypropylene-based foaming material. The pore diameter of the polypropylene-based foaming material is 50-60 μm, and the pore density is 9×10 7 -11×10 7 Pieces / cm 3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 is a SEM image of a cross section of the polypropylene-based foam material prepared in Example 1;

[0025] Figure 2 is a SEM image of the cross section of the polypropylene-based foam material prepared in Comparative Example 1;

[0026] Figure 3 is a SEM image of the cross section of the polypropylene-based foam material prepared in Comparative Example 2;

[0027] Figure 4 is a SEM image of the cross section of the polypropylene-based foam material prepared in Comparative Example 3;

[0028] Figure 5 This is a SEM image of the cross section of the polypropylene-based foam material prepared in Comparative Example 4. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods. Example 1

[0031] This embodiment provides a method for preparing a polypropylene-based foam material, comprising the following steps:

[0032] S1. Preparation of modified polypropylene

[0033] S11. Take 1 kg of linear polypropylene powder with a weight average molecular weight of 300,000 g / mol, add it to a mixing barrel after drying, then add 10 g of divinyltetramethyldisiloxane, 20 g of methyl methacrylate, 10 g of 1010, 0.5 g of benzoyl peroxide, and 5 g of zinc diacrylate, and stir evenly in a high-speed mixer to prepare a premix.

[0034] S12, adding the premix from the hopper into a twin-screw extruder, with the extrusion temperature at 150° C. and the screw speed at 50 r / min, to perform extrusion granulation to prepare modified polypropylene.

[0035] The melt strength of the modified polypropylene was measured using a melt strength tester, and its crystallization temperature and half crystallization time were also tested. The results are shown in Table 1.

[0036] S2. Preparation of polypropylene-based foaming material

[0037] S21. Add 0.4 kg of modified polypropylene and 9.0 L of distilled water into the autoclave, introduce high-pressure CO2 gas at a pressure of 10 MPa, heat to 145°C with stirring, and maintain constant temperature and pressure for 1 hour to allow the system to reach complete saturation.

[0038] S22. Release the pressure within 3 seconds, immediately fill with cooling water and cool to 40°C to obtain a polypropylene-based foamed material.

[0039] The cell density and cell diameter of the prepared polypropylene-based foam material were calculated. The cell density was calculated based on the void ratio, and the cell diameter was obtained by statistics using WINROOF software. The results are shown in Table 1. The SEM image of the cross section of the polypropylene-based foam material is shown in Table 1. Figure 1 . Example 2

[0040] This embodiment provides a method for preparing a polypropylene-based foam material, comprising the following steps:

[0041] S1. Preparation of modified polypropylene

[0042] S11. Take 1 kg of polypropylene powder with a weight average molecular weight of 300,000 g / mol, add it to a mixing barrel after drying, then add 15 g of divinyltetramethyldisiloxane, 30 g of methyl methacrylate, 30 g of 4010, 0.8 g of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 7 g of zinc diacrylate, and stir evenly in a high-speed mixer to prepare a premix.

[0043] S12, adding the premix from the hopper to a twin-screw extruder, extruding and granulating to prepare modified polypropylene, the extrusion temperature is 160°C, and the screw speed is 55r / min. Take some modified polypropylene samples to measure their melt strength, crystallization temperature and half crystallization time, and the results are shown in Table 1.

[0044] S2. Preparation of polypropylene-based foaming material

[0045] S21. Add 0.5 kg of modified polypropylene and 10.0 L of distilled water into the autoclave, introduce high-pressure CO2 gas at a pressure of 20 MPa, heat to 145°C with stirring, and maintain constant temperature and pressure for 1.2 hours to allow the system to reach complete saturation.

[0046] S23. Release the pressure within 5 seconds, immediately fill with cooling water and cool to 50° C. to obtain a polypropylene-based foamed material.

[0047] The cell density and cell diameter of the prepared polypropylene-based foamed material were calculated. The cell density was calculated based on the void ratio, and the cell diameter was obtained by statistics using WINROOF software. The results are shown in Table 1.

[0048] Example 3

[0049] This embodiment provides a method for preparing a polypropylene-based foam material, comprising the following steps:

[0050] S1. Preparation of modified polypropylene

[0051] S11. Take 1 kg of polypropylene powder with a weight average molecular weight of 300,000 g / mol, add it to a mixing barrel after drying, then add 20 g of divinyltetramethyldisiloxane, 40 g of methyl methacrylate, 50 g of 1010, 1 g of benzoyl peroxide, and 10 g of zinc diacrylate, and stir evenly in a high-speed mixer to prepare a premix.

[0052] S12, adding the premix from the hopper to a twin-screw extruder, and extruding and granulating to prepare modified polypropylene, the extrusion temperature is 160°C, and the screw speed is 60r / min. Take some modified polypropylene samples to measure their melt strength, crystallization temperature and half crystallization time, and the results are shown in Table 1.

[0053] S2. Preparation of polypropylene-based foaming material

[0054] S21. Add 0.8 kg of modified polypropylene and 11.0 L of distilled water into the autoclave, introduce high-pressure CO2 gas at a pressure of 30 MPa, heat to 145°C with stirring, and maintain constant temperature and pressure for 1.5 hours to allow the system to reach complete saturation.

[0055] S23, releasing the pressure within 7 seconds, immediately filling with cooling water and cooling to 60°C to obtain a polypropylene-based foaming material.

[0056] The cell density and cell diameter of the prepared polypropylene-based foamed material were calculated. The cell density was calculated based on the void ratio, and the cell diameter was obtained by statistics using WINROOF software. The results are shown in Table 1.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that step S1 is not included, and the modified polypropylene in step S21 is replaced by polypropylene powder with a weight average molecular weight of 300,000 g / mol. The rest is the same as Example 1.

[0059] The melt strength, crystallization temperature and half crystallization time of the polypropylene powder were measured. The results are shown in Table 1. The SEM image of the cross section of the prepared polypropylene-based foam material is shown in Figure 2 .

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 1 is that S11 does not contain divinyltetramethyldisiloxane, the amount of methyl methacrylate is 28g, the amount of zinc diacrylate is 7g, and the rest is the same as Example 1. The SEM image of the cross section of the prepared polypropylene-based foam material is as follows: Figure 3 .

[0062] Comparative Example 3

[0063] The difference between this comparative example and Example 1 is that S11 does not contain methyl methacrylate, the amount of divinyltetramethyldisiloxane used is 23.4 g, the amount of zinc diacrylate used is 11.6 g, and the rest is the same as Example 1. The SEM image of the cross section of the prepared polypropylene-based foam material is as follows: Figure 4 .

[0064] Comparative Example 4

[0065] The difference between this comparative example and Example 1 is that S11 does not include zinc diacrylate, the amount of divinyltetramethyldisiloxane used is 11.7 g, the amount of methyl methacrylate used is 23.3 g, and the rest is the same as Example 1. The SEM image of the cross section of the prepared polypropylene-based foam material is as follows: Figure 5 .

[0066] Table 1 Performance Test of Examples 1-3 and Comparative Examples 1-4

[0067]

[0068] From Table 1, the preparation method of modified polypropylene of Examples 1-3 includes selecting divinyltetramethyldisiloxane, methyl methacrylate, and zinc diacrylate to modify linear polypropylene under the action of an initiator, grafting metal salts on the linear polypropylene molecular chains, so that long-chain branched polypropylene is formed by ionic interaction between polypropylene molecular chains, and the long-chain branched polypropylene is further formed into a modified polypropylene with a long-chain branched structure under the conditions of divinyltetramethyldisiloxane and methyl methacrylate. Therefore, compared with the polypropylene powder of Comparative Example 1, the crystallization temperature of the modified polypropylene is increased and the half crystallization time is reduced. The modified polypropylene with a long-chain branched structure can produce more chain entanglements under the foaming process, thereby causing strain hardening during melt stretching, significantly improving the melt strength, thereby improving the foaming uniformity of the polypropylene-based foaming materials prepared in Examples 1-3, and improving the foaming performance of the polypropylene-based foaming materials.

[0069] Comparing Example 1 and Comparative Examples 2-4, under the same dosage conditions, when divinyltetramethyldisiloxane, methyl methacrylate, and zinc diacrylate are present at the same time, the melt strength of the prepared modified polypropylene is the highest, and the foaming performance of the polypropylene-based foaming material prepared from the modified polypropylene is the best. Therefore, the technical solution of the present application has a synergistic effect on improving the foaming performance of the polypropylene-based foaming material. This is because under the condition of zinc diacrylate, metal salts are grafted onto the polypropylene molecular chain, so that the polypropylene molecular chains form long-chain branched polypropylene by ionic interaction. Under the conditions of divinyltetramethyldisiloxane and methyl methacrylate, the long-chain branched polypropylene further forms a modified polypropylene with a long-chain branched structure.

[0070] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a polypropylene-based foam material, characterized in that: The method comprises the following steps: adding polypropylene and water into a container, introducing high-pressure CO2 gas, heating to 130-145° C. under stirring, maintaining constant temperature and pressure to fully saturate the system; releasing the pressure within 3-10 seconds, cooling to 40-50° C., and obtaining a polypropylene-based foaming material; The polypropylene is modified polypropylene, and the preparation method of the modified polypropylene comprises the following steps: taking linear polypropylene, divinyltetramethyldisiloxane, methyl methacrylate, initiator and zinc diacrylate and stirring them evenly to prepare a premix; extruding and granulating the premix at 150-160° C. to obtain modified polypropylene.

2. The method for preparing a polypropylene-based foam material according to claim 1, wherein: The initiator is selected from any one of benzoyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

3. The method for preparing a polypropylene-based foam material according to claim 1, wherein: The amount of divinyltetramethyldisiloxane used is 1-2% of the mass of linear polypropylene, the amount of methyl methacrylate used is 2-4% of the mass of linear polypropylene, and the amount of zinc diacrylate used is 0.5-1% of the mass of linear polypropylene.

4. The method for preparing a polypropylene-based foam material according to claim 1, wherein: The amount of divinyltetramethyldisiloxane used is 1-1.5% of the mass of linear polypropylene, the amount of methyl methacrylate used is 2-3% of the mass of linear polypropylene, and the amount of zinc diacrylate used is 0.5-0.8% of the mass of linear polypropylene.

5. The method for preparing a polypropylene-based foam material according to claim 1, characterized in that: The amount of divinyltetramethyldisiloxane used is 1% of the mass of linear polypropylene, the amount of methyl methacrylate used is 2% of the mass of linear polypropylene, and the amount of zinc diacrylate used is 0.5% of the mass of linear polypropylene.

6. The method for preparing a polypropylene-based foamed material according to claim 1, characterized in that: The mass volume ratio of the polypropylene to water is 0.04-0.08 kg / L.

7. The method for preparing a polypropylene-based foamed material according to claim 1, characterized in that: The pressure of the high-pressure CO2 gas is 10-30MPa.

8. A polypropylene-based foam material prepared by the method for preparing a polypropylene-based foam material according to any one of claims 1 to 7, characterized in that: The pore diameter of the polypropylene-based foaming material is 50-60 μm.

9. The polypropylene-based foam material according to claim 8, characterized in that: The cell density of the polypropylene-based foam material is 9×10 7 -11×10 7 Pieces / cm 3 .

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