EXPANDED POLYPROPYLENE BALLS THAT CAN BE RAPIDLY FORMED BY MICROWAVE AND CORRESPONDING MOLDINGS

Abstract

The invention discloses rapidly moldable expanded polypropylene beads with a core-shell structure. The core comprises high-melting-point, high-modulus polypropylene and a nucleating agent. The shell comprises a low-melting-point propylene copolymer and / or a polypropylene blend, along with a microwave heating aid that enables rapid heating of the surface layer, even at low power, melting the low-melting-point polypropylene and sintering the beads together. The addition of a surfactant improves heating efficiency. The interior of the beads contains neither an auxiliary agent nor a surfactant, so the internal temperature remains moderate, preserving the internal closed-cell structure. The molded parts obtained by this cost-effective, energy-efficient, and environmentally friendly process exhibit a high degree of curing and good surface sintering.

Description

Title of the invention: EXPANDED POLYPROPYLENE BALLS THAT CAN BE RAPIDLY FORMED BY MICROWAVE AND CORRESPONDING MOLDED PARTS technical field

[0001] The present invention relates to expanded polypropylene beads that can be rapidly formed by microwaves, as well as the molded parts obtained from them; it belongs to the field of expanded materials. TECHNICAL CONTEXT

[0002] Materials made of expanded polypropylene beads, due to their high expansion rate and lightness, are widely used in the fields of automotive parts, rail transport, handling and packaging, construction, as well as sports and leisure activities.

[0003] In order to obtain molded parts with a high degree of shape freedom, expanded polypropylene beads are generally shaped by steam molding. This involves first introducing the beads into a mold, then closing the mold, and injecting steam through the internal pores of the mold to heat the beads. After sintering the expanded polypropylene beads, they are cooled and demolded to obtain the corresponding expanded parts.

[0004] In this process, to ensure more uniform and complete sintering of the beads, it is often necessary to preheat the mold with steam; furthermore, during molding, the mold must be maintained at a constant temperature using steam. These two factors result in significant steam consumption, as most of the energy is expended on heating and maintaining the mold temperature, while the portion of steam actually used for heating and sintering the beads represents less than 10% of the total consumption.

[0005] It is in this context that microwave molding of expanded polypropylene beads was developed. Compared to steam molding, microwave molding does not require heating the mold: the heat is generated directly by the action of electromagnetic waves on the expanded materials, which absorb most of the energy, thus improving energy efficiency and reducing energy consumption. However, in order to prevent the beads from overheating or degrading during microwave molding, it is generally necessary to use relatively low microwave power. Such reduced power leads to a longer heating time, thus lengthening the molding cycle and reducing production efficiency, which limits the industrial adoption of this technique.

[0006] It is therefore necessary to develop expanded polypropylene beads and molded parts that can be rapidly formed by microwaves. Description of the invention

[0007] To overcome the problem of prolonged molding time and reduced efficiency during microwave molding of expanded polypropylene beads, the present invention discloses expanded polypropylene beads that can be rapidly molded by microwave, as well as molded parts obtained from them. The expanded polypropylene beads according to the invention have, in their surface layer, a certain amount of microwave heating aid and surfactant. These aids thus make it possible, under relatively low microwave power, to cause a rapid temperature rise in the surface layer of the beads, resulting in the rapid melting of the low-melting-point polypropylene materials, which then fuse by sintering with the surface layers of the neighboring beads.The interior of the beads contains no microwave heating aids or surfactants, and the polypropylene core material has a high melting point; therefore, the low microwave power does not excessively raise the internal temperature of the beads, thus preserving the original closed-cell structure. After microwave heating and cooling, expanded polypropylene parts are obtained with a high degree of curing, good surface weldability, and a closed-cell structure maintained within the beads. Most importantly, the entire molding process is short, energy-efficient, highly energy-saving, significantly reducing production costs and exhibiting environmentally friendly characteristics.

[0008] In order to achieve the aforementioned objectives, the present invention adopts the following technical solutions:

[0009] Microwave-molded, rapid-expanding polypropylene beads having a core-shell structure, the core material comprising 80 to 99.97% by weight, preferably 90 to 99.97% by weight, of high-melting-point, high-modulus polypropylene; the shell material comprising 80 to 99.96% by weight, preferably 90 to 99.96% by weight, of a low-melting-point propylene copolymer and / or a blend of polypropylenes, and 0.01 to 5% by weight of a microwave heating aid. The high-melting-point, high-modulus polypropylene has a melting point of 130 to 160 °C, a flexural modulus of 800 to 1100 MPa, and a melting index of 5 to 10 g / 10 min. The propylene copolymer and / or the low-melting-point polypropylene blend has a melting point of 105 to 125 °C. The microwave heating aid is chosen among metal powders, metal oxides, nitrides, glass fibers, bamboo fibers, carbon fibers, graphene, ferrites, ceramics, alone or in combination. The size of the microwave heating agent is between 10 and 1000 nm. The mass ratio between the core and shell materials is 80:20 to 99:1, preferably 90:10 to 99:1.

[0010] Furthermore, the shell material of the beads also comprises 0.01 to 5% by weight of surfactants, selected from at least one anionic surfactant, one cationic surfactant, one zwitterionic surfactant, or one nonionic surfactant. Under the influence of the microwave electromagnetic field, ionic surfactants dissociate into ions, promoting the absorption of microwaves by the beads; nonionic surfactants, containing hydrophilic groups, promote the absorption and retention of water on the surface of the beads. Water is highly polar and capable of heating rapidly under microwaves. All these factors allow the shell to heat up and melt rapidly, enhancing sintering between the beads.

[0011] Furthermore, anionic surfactants can be selected from stearic acid, oleic acid, lauric acid, sulfated compounds, sulfonated compounds, etc.; cationic surfactants from ammonium salts, quaternary ammonium salts, heterocyclic surfactants, etc.; zwitterionic surfactants from phospholipids, amino acids, betaines, etc.; non-ionic surfactants from fatty acid monoglycerides, polyols, sorbitan fatty acid, polysorbates, polyethylene glycol, poly(ethylene oxide)-poly(propylene oxide) copolymers, etc.

[0012] Furthermore, the cellular structure of the nucleus is a closed, independent cell structure, with a size between 50 and 200 pm.

[0013] Furthermore, the high-melting-point, high-modulus polypropylene is selected from homopolymer polypropylene and / or copolymer polypropylene, the latter comprising ethylene-propylene copolymer polypropylene and / or ethylene-propylene-butene terpolymer polypropylene. The use of such polypropylenes gives the beads improved thermal resistance and rigidity.

[0014] Furthermore, the low melting point propylene copolymer is an ethylene-propylene and / or ethylene-propylene-butene copolymer, and the low melting point polypropylene blend is a polyethylene / polypropylene blend.

[0015] Furthermore, the metal powder is selected from iron powder, copper powder, tin-copper alloy powder, gold powder and / or silver powder, etc., the metal oxide from magnesium oxide, iron oxide, aluminum oxide and / or copper oxide, etc., the nitride from silicon nitride and / or boron nitride, etc., and the ferrite is a sintered composite of iron oxide with nickel oxide, oxide of zinc, manganese oxide, etc. These auxiliaries, having high permittivity and dielectric loss, promote the absorption of microwaves and their rapid conversion into heat, heating the shell and ensuring its sintering.

[0016] In contrast to steam heating, where most of the heat is dissipated in the mold, microwave heating directly increases the temperature of the beads, with negligible heat loss in the mold. Under the influence of the alternating electromagnetic field generated by the microwaves, the polar molecules present in the expanded polypropylene beads polarize or reorient their existing dipoles, oscillating at a frequency of several hundred million cycles per second. This continuous reorganization requires overcoming thermal agitation and intermolecular interactions, generating frictional heating and directly converting electromagnetic energy into heat, thus significantly raising the temperature of the beads.Compared to polypropylenes, materials with microwave-assisted heating agents, exhibiting higher dielectric constants and dielectric losses, generate more heat and undergo a faster friction process. Consequently, the expanded polypropylene shell containing the microwave-assisted heating agents experiences a faster and higher temperature rise at the same microwave power. Furthermore, the expanded polypropylene shell layer, composed of a low-melting-point material, can thus melt rapidly under low microwave power, ensuring rapid sintering between beads while maintaining a relatively low temperature in the core layer, thereby preserving the core-independent cell structure.

[0017] Furthermore, the core layer material also comprises 0.01 to 2% by weight of a nucleating agent, and the nucleating agent is one or more of the following: calcium carbonate, talc, zinc borate, sodium chloride, silicon dioxide, etc., and has a particle size of 1 to 20 µm. The nucleating agent generally exhibits some incompatibility with the polypropylene matrix. During the foaming of the polypropylene beads, it promotes the formation of bubbles at the interface between the nucleating agent and the polypropylene, thus contributing to heterogeneous nucleation. At the same time, the nucleating agent also serves to reduce foaming pressure and to homogenize the foam cells.

[0018] In addition, depending on the requirements, the expanded polypropylene beads can be supplemented with masterbatch, lubricant, antioxidant, anti-ultraviolet agent, etc.

[0019] The process for preparing rapidly molded expanded polypropylene beads by microwave comprises:

[0020] (1) uniformly mix the core material and introduce it into an extruder twin screw A, mix the shell material evenly and introduce it into a twin screw extruder B;

[0021] (2) to carry out co-extrusion by a double-layer die, the material of extruder A forming the core and extruder B forming the shell;

[0022] (3) cool the extruded wires with water, then cut them into granules using a granular to obtain expandable polypropylene micro-granules;

[0023] (4) introduce the expandable micro-granules into an expansion autoclave under pressure to obtain expanded polypropylene beads.

[0024] In the case where the shell layer of the expanded beads does not contain a surfactant, it is necessary, when preparing molded parts in expanded polypropylene, to spray a surfactant solution on the surface of said expanded polypropylene beads before microwave molding, the mass ratio of surfactant to water in the surfactant solution is 1:1 to 1:10, the amount sprayed of said surfactant solution in relation to the mass of the expanded polypropylene beads being 1:2 to 1:20; the microwave heating power is from 1 to 100 kw, preferably from 10 to 60 kw, more preferably from 20 to 50 kw, and the duration is from 1 to 500 s, preferably from 10 to 100 s, more preferably from 15 to 60 s.

[0025] In the case where the shell layer of the expanded beads contains a surfactant, it is necessary, before microwave molding, to spray a small amount of water on the surface of the expanded beads, the mass ratio between the water and the expanded polypropylene beads is 1:10 to 1:50, then to proceed with the microwave molding of the expanded polypropylene beads in order to prepare molded parts in expanded polypropylene; the microwave heating power is from 1 to 100 kw, preferably from 10 to 60 kw, more preferably from 20 to 50 kw, and the duration is from 1 to 500 s, preferably from 10 to 100 s, more preferably from 15 to 60 s.

[0026] The technical advantages of the present invention are as follows:

[0027] 1. In the expanded polypropylene beads described above, the shell contains of an auxiliary microwave heating agent exhibiting a high dielectric constant and dielectric loss. These characteristics allow, under low microwave power, through the polarization and oscillation of polar molecules, the rapid generation of a significant amount of heat, causing a rapid temperature rise in the shell of the beads. In contrast, the core layer of expanded polypropylene beads does not contain an auxiliary microwave heating agent with a high dielectric constant and dielectric loss; therefore, the heat produced remains limited under the same low power, resulting in a lower core temperature. The low-melting-point polypropylene base material used in the The expanded polypropylene shell layer can rapidly melt the shell layer material under the action of low microwave power, ensuring rapid sintering between the beads, while preserving the independent closed cell structure in the core layer without it being destroyed by melting.

[0028] 2. The surfactants present in the shell of the polypropylene beads The expanded or expanded surfaces of the particles are either ionized by the action of the microwave electromagnetic field, or, if they contain hydrophilic groups, promote the absorption of highly polar water. This improves heating and thermal conduction efficiency, leading to a rapid temperature rise and melting of the shell, thus increasing the degree of sintering between the beads.

[0029] 3. In conventional microwave molding, in order to avoid overheating and a Due to the degradation of expanded polypropylene beads, relatively low microwave power is generally used. However, low power results in a long heating time, which lengthens the molding cycle and reduces production efficiency. The expanded polypropylene beads of the present invention allow for rapid molding under low microwave power, resulting in expanded parts with a high degree of sintering. The production process is characterized by low energy consumption and a short cycle time, making it an environmentally friendly and energy-saving solution. DESCRIPTION OF THE FIGURES

[0030] Fig. 1 illustrates a molded part in expanded polypropylene obtained according to embodiment example 1. SPECIFIC IMPLEMENTATION METHODS

[0031] The present invention will now be described in more detail in combination with examples of embodiment.

[0032] Example of embodiment 1:

[0033] Preparation of expanded polypropylene beads that can be rapidly molded by microwave:

[0034] (1) In accordance with the mass ratio of Example 1 in Table 1, the materials The core layer, comprising high-melting-point, high-modulus polypropylene (melting point 145 °C, flexural modulus 1000 MPa, melting index 7 g / 10 min, purchased from China Petroleum & Chemical Corporation), a nucleating agent (calcium carbonate, purchased from Jiangxi Guangyuan Chemical Co., Ltd.), a lubricant (oleamide, purchased from Zhengzhou Zhuochuang Chemical Products Co., Ltd.), and an antioxidant (1010, purchased from BASF SE, Germany), is homogenized and then fed into a twin-screw extruder designated A; the shell layer materials, comprising an ethylene-propylene copolymer (melting point 120 °C, melting index 8 g / 10 min, purchased from China Petroleum & Chemical Corporation), a microwave heating auxiliary (silicon nitride, CW-Si3N4-002, purchased from Shanghai Chaowei Nano Technology Co., Ltd.), a surfactant (tridecanol-10 polyether phosphate, i.e. PEG-10 ester, purchased from Nantong Chenrun Chemical Co., Ltd.), a lubricant (oleamide, purchased from Zhengzhou Zhuochuang Chemical Products Co., Ltd.) and an antioxidant (1010, purchased from BASF SE, Germany) are mixed uniformly and then introduced into the twin-screw extruder B;

[0035] (2) Performing co-extrusion using a two-layer die: the material of extruder A is used as the core layer, and the material from extruder B is used as the shell layer, the mass ratio between the core layer and the shell layer is 95:5;

[0036] (3) Cool the extruded filaments with water and then granulate them to obtain expandable polypropylene microgranules, with a length between 1.2 and 2.5 mm and a unit mass between 0.5 and 1.8 mg;

[0037] (4) The expanded polypropylene microgranules thus obtained are introduced, The microgranules are mixed with water in an expansion autoclave. Simultaneously, a dispersant (butter-like grease) and a surfactant (sodium dodecyl sulfate) are added. The autoclave is heated, and carbon dioxide is introduced as a physical foaming agent, allowing the foaming agent to penetrate the microgranules and form a homogeneous system. When the set expansion temperature of 145 °C and the expansion pressure of 2.0 MPa are reached, the system is held for 10 minutes. The expandable microgranules are then instantly released into an expansion line with an internal pressure below 0.1 MPa and an ambient temperature between 80 and 100 °C to complete the expansion process. The residence time of the microgranules in the expansion tube is 4 to 15 seconds, ultimately resulting in expanded polypropylene beads that can be rapidly microwave-molded.

[0038] Preparation of molded parts in expanded polypropylene:

[0039] (1) Subject the aforementioned expanded polypropylene beads to pre-pressure in an air pressure of 0.3 MPa for 10 hours.

[0040] (2) Spray water onto the surface of the pre-pressurized beads to moisten them, The mass ratio between water and expanded polypropylene beads is 1:20. The wet beads are then microwave-molded at a frequency of 2450 MHz and a power of 20 kW. The resulting molded parts are then placed in an oven at 80 °C for a stabilization treatment, resulting in the finished expanded product. The process parameters and the degree of curing of the molded parts are presented in Table 1.

[0041] Example of embodiment 2:

[0042] Except for the replacement of the microwave heating auxiliary agent of the shell layer with aluminum oxide (CW-A1203-002, purchased from Shanghai Chaowei Nano Technology Co., Ltd.), the other components and preparation conditions are identical to those of exemplary embodiment 1.

[0043] Example of embodiment 3:

[0044] Except for the replacement of the microwave heating auxiliary agent of the shell layer with a tin-copper alloy powder (CW-Sn-Cu, purchased from Shanghai Chaowei Nano Technology Co., Ltd.), the other components and preparation conditions are identical to those of embodiment 1.

[0045] Example of embodiment 4:

[0046] The difference from Example 1 lies in the fact that, during the preparation of the expanded polypropylene beads that can be rapidly molded by microwave, no surfactant is added to extruder B; during the preparation of the molded expanded polypropylene parts, step (2) of humidification by water spraying is replaced by the following: the surfactant (PEG-10 ester, purchased from Nantong Chenrun Chemical Co., Ltd.) and water are mixed and stirred in a mass ratio of 1:3 to prepare a surfactant solution, which is then sprayed uniformly onto the surface of the pre-pressurized beads. The amount of surfactant solution sprayed, relative to the mass of the beads, is 1:9. This produces expanded polypropylene beads bearing a layer of surfactant solution, which are then subjected to microwave molding.The other components and preparation conditions are identical to those of embodiment example 1.

[0047] Example of embodiment 5:

[0048] Except that the sprayed surfactant is polypropylene glycol (15) stearyl ether (PPG-15, purchased from Nantong Chenrun Chemical Co., Ltd.), the other components and preparation conditions are identical to those of exemplary embodiment 4.

[0049] Example of embodiment 6:

[0050] Except that the sprayed surfactant is allyl alcohol polyoxyethylenic ether (APEG-800, purchased from Nantong Chenrun Chemical Co., Ltd.), the other components and preparation conditions are identical to those of Example 4.

[0051] Example of embodiment 7:

[0052] When preparing molded parts from expanded polypropylene, replace step (2) of humidification by water spraying with: mixing and agitating the surfactant (PEG-10 ester, purchased from Nantong Chenrun Chemical Co., Ltd.) and Water is added at a mass ratio of 1:3 to prepare a surfactant solution, which is then sprayed uniformly onto the surface of the pre-pressurized beads. The amount of surfactant solution sprayed, relative to the mass of the beads, is 1:9, resulting in expanded polypropylene beads coated with a layer of surfactant solution. The other components and preparation conditions are identical to those in embodiment 1.

[0053] Comparative example 1:

[0054] Except that the shell layer of the expanded polypropylene beads does not contain an auxiliary microwave heating agent (silicon nitride), the other components and preparation conditions are identical to those of embodiment 1.

[0055] Comparative example 2:

[0056] Except that the shell layer of the expanded polypropylene beads does not contain PEG-10 surfactant, the other components and preparation conditions are identical to those of embodiment 1.

[0057] Comparative example 3:

[0058] Except that the shell layer of the expanded polypropylene beads does not contain an auxiliary microwave heating agent (silicon nitride), the other components and preparation conditions are identical to those of embodiment 4.

[0059] Comparative example 4:

[0060] Except that the shell layer of the expanded polypropylene beads does not contain an auxiliary microwave heating agent (silicon nitride) or a surfactant PEG-10, the other components and preparation conditions are identical to those of embodiment 1. [Tables 1] Example of implementation Comparative example 1 2 3 4 5 6 7 1 2 3 4 Core layer Polypropylene 99.15 99.15 99.15 99.15 99.15 99.15 99.15 99.15 99.15 99.15 99.15 99.15 15 99.15 Nucleating agent 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Lubricant 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Antioxidant 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 CO layer that binds Ethylene-propylene copolymer 94.2 94.2 94.2 96.2 96.2 96.2 94.2 97.2 96.2 99.2 99.2 Microwave heating aid Silicon nitride Aluminum oxide tin-copper alloy Silicon nitride 111C1Um silicon nitride Silicon nitride / Silicon nitride / / 3 3 3 3 3 3 3 0 3 0 0 Lubricant 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Antioxidant 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0,3 Surfactants PEG-10 PEG-10 PEG-10 / / / PEG-10 PEG-10 / / / 2 2 2 0 0 0 2 2 0 0 0 Should a spray be checked? No No No Spray check Spray check Spray check No No Spray check No , Active surfactant n of PEG-10 n of PEG-15 tion of AP EG-800 n of PEG-10 n of PEG-10 Density 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 50- 53 ...

[0061] In Table 1, the degree of maturation of the foam molded parts is classified from best to worst in five levels: 5 — very good, 4 — good, 3 — average, 2 — poor, 1 — bad. 5: when the number of beads whose alveolar cells are destroyed on the rupture surface of the foam molded part represents 90% or more of the total number of beads; 4: when this number represents 70% to 90% of the total number of beads; 3: when this number represents 50% to 70% of the total number of beads; 2: when this number represents 30% to 50% of the total number of beads; 1: when this number is less than 30% of the total number of beads.

[0062] In light of embodiments 1 to 3 and comparative example 1, as well as embodiment 4 and comparative example 3, it appears that the incorporation of an auxiliary microwave heating agent makes it possible to considerably reduce the microwave heating time during molding, while giving the molded foam parts a good degree of curing. The different auxiliary microwave heating agents exhibit varying efficiencies in converting electromagnetic energy into heat under a high-frequency field, with silicon nitride standing out for the most significant reduction in heating time.

[0063] In light of embodiment examples 1 and 4 and comparative example 2, it appears that mixing a surfactant into the shell layer or spraying it onto the surface of the expanded beads also makes it possible to shorten the microwave heating time during molding and to obtain a good degree of maturation. Furthermore, spraying a surfactant onto the surface of the expanded beads has the advantage of a simple implementation process, while also allowing a more significant reduction in microwave heating time.

[0064] In light of embodiment examples 4 to 6, it appears that spraying different surfactants on the surface of the expanded beads allows, to varying degrees, for a reduction in microwave heating time during molding.

[0065] In light of embodiment examples 1, 4 and 7, it appears that, compared to spraying only a surfactant on the surface of the expanded beads or mixing it only in the shell layer, the combination of mixing and spraying the surfactant does not provide any further significant effect on reducing microwave heating time; it is therefore sufficient to choose one of the two methods of applying the surfactant.

[0066] In light of embodiments 1 and 4 and comparative examples 1 to 4, it appears that the simultaneous addition of a microwave heating aid and a surfactant (mixed or sprayed), compared to the separate addition of these agents, exhibits a better synergistic effect, making it possible to considerably reduce the microwave heating time. In comparative example 4, in the absence of a microwave heating aid and a surfactant, the microwave heating time of the foam molded parts is longer, the efficiency is lower, and the degree of curing of the parts is also low.

Claims

Demands

1. Expanded polypropylene beads capable of rapid microwave forming, characterized in that they have a core-shell structure, the core layer materials comprising 80 to 99.97% by weight of high-melting-point, high-modulus polypropylene and 0.01 to 2% by weight of nucleating agent, and the shell layer materials comprising 80 to 99.96% by weight of low-melting-point propylene copolymer and / or polypropylene blend, as well as 0.01 to 5% by weight of microwave heating aid, said high-melting-point, high-modulus polypropylene having a melting point of 130 to 160 °C, a flexural modulus of 800 to 1100 MPa, and a melting index of 5 to 10 g / 10 min, said low-melting-point propylene copolymer and / or the polypropylene mixture having a melting point of 105 to 125 °C, the microwave heating agent being selected from the metal powder,metal oxides, nitrides, glass fiber, bamboo fiber, carbon fiber, graphene, ferrites and ceramics, alone or in combination, the size of the microwave heating auxiliary being between 10 and 1000 nm, and the mass ratio between the materials of the core layer and those of the shell layer being from 80:20 to 99:

1.

2. Expanded polypropylene beads that can be rapidly formed by microwave according to claim 1, characterized in that the materials of said shell layer further comprise 0.01 to 5% by weight of a surfactant, said surfactant being selected from at least one anionic surfactant, a cationic surfactant, a zwitterionic surfactant or a non-ionic surfactant.

3. Expanded polypropylene beads that can be rapidly formed by microwaves according to claim 2, characterized in that said anionic surfactant is selected from at least one of stearic, oleic, lauric acids, sulfates, sulfonates, said cationic surfactant is selected from at least one of ammonium salts, quaternary salts or heterocyclic surfactants, said amphoteric surfactant is selected from at least one of phospholipids, amino acids or betaines, and said surfactant non-ionic is selected from at least one of the following fatty acid glycerides, polyols, sorbitan fatty acids, polysorbates, polyethylene glycol or polyethylene glycol-polypropylene glycol copolymers.

4. Expanded polypropylene beads that can be rapidly formed by microwaves according to claim 1 or 2, characterized in that the cellular structure of said core layer is an independent closed cellular structure, having a pore diameter of 50 to 200 sqm.

5. Expanded polypropylene beads that can be rapidly formed by microwave according to claim 1 or 2, characterized in that said high melting point and high modulus polypropylene is a homopolymer and / or copolymer polypropylene, the copolymer comprising a binary ethylene-propylene copolymer and / or a ternary ethylene-propylene-butylene copolymer.

6. Expanded polypropylene beads that can be rapidly formed by microwave according to claim 1 or 2, characterized in that said low melting point propylene copolymer is a binary ethylene-propylene copolymer and / or a ternary ethylene-propylene-butylene copolymer, and that the low melting point polypropylene mixture is a polyethylene / polypropylene mixture.

7. Expanded polypropylene beads that can be rapidly formed by microwave according to claim 1 or 2, characterized in that said metal powder is selected from iron powder, copper powder, tin-copper alloy powder, gold powder and / or silver powder, the metal oxide is selected from magnesium oxide, iron oxide, aluminum oxide and / or copper oxide, the nitride is selected from silicon nitride and / or boron nitride, and said ferrite is a sintered composite of ferric oxide with nickel, zinc and manganese oxides.

8. Expanded polypropylene beads that can be rapidly formed by microwave according to claim 1 or 2, characterized in that the nucleating agent is selected from calcium carbonate, talc, zinc borate, sodium chloride, silicon dioxide, and has a particle size of 1 to 20 sqm.

9. Molded part made of expanded polypropylene, characterized in that it is obtained from the expanded polypropylene beads according to claim 1, by a microwave forming process, the surface of the beads being previously sprayed with a solution of surfactant, the mass ratio of surfactant to water in the surfactant solution is 1:1 to 1:10, the mass ratio between the sprayed quantity of surfactant solution and the expanded polypropylene beads is 1:2 to 1:20, the microwave heating power is 1 to 100 kw and the heating time is 1 to 500 s.

10. Molded part made of expanded polypropylene, characterized in that it is obtained from the beads according to any one of claims 2 to 8, by a microwave forming process, the surface of the beads is sprayed with water before forming, the mass ratio between the water and the expanded polypropylene beads is 1:10 to 1:50, the microwave heating power is 1 to 100 kw and the heating time is 1 to 500 s.

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