A particulate dispersed polypropylene foamed beads and its preparation method

Abstract

This invention provides a particulate-dispersed polypropylene foamed beads and its preparation method, belonging to the technical field of polymer foaming materials. The invention involves mixing polypropylene beads with a nano-silica surfactant to obtain a mixture; preheating the mixture to a foaming temperature to obtain a preheated material; and injecting CO2 into a reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming, thereby obtaining particulate-dispersed polypropylene foamed beads. This invention introduces a nano-silica surfactant into the supercritical CO2 anhydrous foaming process, which enables the dispersion of polypropylene beads during supercritical CO2 anhydrous foaming, improves the yield of polypropylene foamed beads, and achieves a foaming ratio of over 17 times.

Description

Technical Field

[0001] This invention relates to the field of polymer foaming materials technology, specifically to a particulate dispersed polypropylene foamed beads and its preparation method. Background Technology

[0002] Polypropylene (PP) is a semi-crystalline thermoplastic and one of the world's five major plastic varieties. With the development of lightweight materials and green chemistry, polypropylene foam has become the fastest-growing type of polymer foam material. Polypropylene foam possesses numerous excellent properties such as lightweight, high temperature resistance, corrosion resistance, heat and sound insulation, good cushioning, and recyclability, and is widely used in automotive, packaging, construction, electronic instruments, footwear, and medical fields. With the deepening of green energy conservation and environmental protection concepts, the market demand for polypropylene foam will continue to grow, and its development prospects are broad.

[0003] In the field of polymer foaming, there are three main processes for preparing polypropylene foam materials: compression molding, extrusion foaming, and autoclaved bead foaming. Compression molding has low production efficiency and can only produce foamed sheets and boards, making it unsuitable for subsequent processing into irregularly shaped products. Extrusion foaming requires high melt strength of polypropylene, and there are no reports of its industrialization in China. Autoclaved bead foaming is currently the most mature process, capable of producing high-ratio polymer foam beads, which can then be processed into various complex irregular shapes.

[0004] In the autoclaving of polymer beads, to ensure good dispersion of polymer particles within the autoclave and guarantee the yield of finished foamed beads, it is essential that the polymer particles do not stick together. However, due to differences in the molecular structure of different polymers and the varying plasticizing effects of CO2 on the polymers, the cohesive energy density between polymers differs. This results in variations in the adhesion behavior of polymer particles during foaming. Polymer particles with higher cohesive energy density are more prone to sticking together, affecting the dispersion effect and limiting the wider application of this technology. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide particulate dispersed polypropylene foam beads and a method for preparing the same. The foaming method provided by the present invention can avoid the adhesion of polymer particles during quality inspection and obtain particulate dispersed polypropylene foam beads.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing particulate dispersed polypropylene foam beads, comprising the following steps:

[0008] Polypropylene beads were mixed with nano-silica surfactants to obtain a mixture.

[0009] The mixture is preheated to the foaming temperature to obtain a preheated material.

[0010] CO2 is injected into a reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming, resulting in particulate dispersed polypropylene foam beads. The supercritical CO2 anhydrous foaming includes sequential supercritical CO2 saturation treatment and depressurization.

[0011] The nano-silica surfactant is modified silica, and the modifying groups of the modified silica include alkyl groups.

[0012] Preferably, the alkyl group is -CH3 or -C8H. 17 and -C 16 H 33 One or more of them.

[0013] Preferably, the nano-silica surfactant has a particle size of 7–14 nm and a density of 2.0–2.2 g / cm³. 3 .

[0014] Preferably, the polypropylene in the polypropylene beads is homopolymer polypropylene and / or copolymer polypropylene, and the polypropylene beads have a particle size of 2-4 mm and a density of 0.90-0.92 g / cm³. 3 .

[0015] Preferably, the mass of the nano-silica surfactant is 1-20% of the mass of the polypropylene beads.

[0016] Preferably, the foaming temperature is 140-160°C, and the preheating time is 15-20 minutes.

[0017] Preferably, the pressure of the supercritical CO2 saturation treatment is 10-20 MPa, and the time is 10-30 min.

[0018] Preferably, the depressurization rate is 80–320 MPa / s.

[0019] Preferably, before preheating the mixture to the foaming temperature, the mixture is further subjected to CO2 purging.

[0020] This invention provides particulate dispersed polypropylene foam beads prepared by the above preparation method.

[0021] This invention provides a method for preparing partically dispersed polypropylene foam beads, comprising the following steps: mixing polypropylene beads with a nano-silica surfactant to obtain a mixture; preheating the mixture to a foaming temperature to obtain a preheated material; injecting CO2 into a reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming to obtain partically dispersed polypropylene foam beads. The supercritical CO2 anhydrous foaming includes sequential supercritical CO2 saturation treatment and depressurization. This invention introduces a nano-silica surfactant into the supercritical CO2 anhydrous foaming process. This nano-silica is a CO2-loving surfactant that helps polymer particles disperse in CO2 and prevents adhesion, enabling the dispersion of polypropylene beads during supercritical CO2 anhydrous foaming, improving the yield of polypropylene foam beads, and achieving a foaming ratio of over 17 times.

[0022] Furthermore, the waterless foaming process used in this invention does not require additional power. Compared with traditional autoclaved bead foaming, it does not require water as a dispersion medium, and subsequent filtration, washing, and drying steps are not required, which reduces energy consumption, shortens the process flow, and improves production efficiency.

[0023] Furthermore, the preparation method provided by this invention is simple to operate, low in cost, and easy to achieve industrial-scale mass production. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the surface group structure of different types of nano-silica surfactants of the present invention;

[0025] Figure 2 This is a flowchart illustrating the preparation process of the particulate dispersed polypropylene foamed beads of the present invention.

[0026] Figure 3 Here is a photograph of the polypropylene foam beads obtained in Example 1;

[0027] Figure 4 This is a photograph of the polypropylene foam beads obtained in Comparative Example 1.

[0028] Figure 5 Here is a picture of the polypropylene foam beads obtained in Comparative Example 2.

[0029] Figure 6 This is a cross-sectional electron microscope image of the polypropylene foam beads obtained in Example 1. Detailed Implementation

[0030] This invention provides a method for preparing particulate dispersed polypropylene foam beads, comprising the following steps:

[0031] Polypropylene beads were mixed with nano-silica surfactants to obtain a mixture.

[0032] The mixture is preheated to the foaming temperature to obtain a preheated material.

[0033] CO2 is injected into a reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming, resulting in particulate polypropylene foam beads. The supercritical CO2 anhydrous foaming includes sequential supercritical CO2 saturation treatment and depressurization.

[0034] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0035] This invention involves mixing polypropylene beads with a nano-silica surfactant to obtain a mixture. In this invention, the nano-silica surfactant is modified silica, and the modifying groups of the modified silica include alkyl groups; preferably, the alkyl groups are -CH3 or -C8H. 17 and -C 16 H 33 One or more of the following. In this invention, the particle size of the nano-silica surfactant is preferably 7-14 nm, more preferably 8-12 nm, and the density is preferably 2.0-2.2 g / cm³. 3 More preferably 2.1 g / cm³ 3 .

[0036] In this invention, the structure of the nano-silica surfactant is preferably as shown in Formulas 1 to 7:

[0037]

[0038] In Equations 1 to 5, the “—” on the left side of the structural formula indicates the connection point.

[0039] In this invention, the nano-silica surfactant is preferably sourced from commercially available sources. As a specific embodiment of this invention, the nano-silica surfactant is purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd., and the product is [model number missing]. R 202, R 812, R 805 R 104 R 974 and One or more of R 816, preferably R 816 R 812, R 104 R 805 and One or more of R 974.

[0040] In this invention, structural schematic diagrams of different types of nano-silica surfactants are shown below. Figure 1 As shown.

[0041] In this invention, the polypropylene in the polypropylene beads is homopolymer polypropylene and / or copolymer polypropylene. In this invention, the particle size of the polypropylene beads is preferably 2-4 mm, specifically 2 mm, 3 mm, or 4 mm, and the density is preferably 0.90-0.92 g / cm³. 3 Specifically, it can be 0.90 g / cm³. 3 0.91g / cm 3 Or 0.92g / cm 3 .

[0042] The present invention does not have special requirements for the mixing method; any mixing method well known to those skilled in the art can be used, such as stirring. In the present invention, the mass of the nano-silica surfactant is preferably 1-20% of the mass of the polypropylene beads, more preferably 8-12%, and specifically can be 1%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%.

[0043] After obtaining the mixture, the present invention heats the mixture to the foaming temperature for preheating to obtain preheated material. Preferably, the present invention transfers the mixture to an autoclave for subsequent preheating and supercritical CO2 anhydrous foaming. In the present invention, before preheating, the present invention preferably further includes CO2 purging of the mixture, preferably three times. In the present invention, the purpose of purging is to remove air from the autoclave.

[0044] In this invention, the foaming temperature is preferably 140–160°C, more preferably 145–160°C, and specifically can be 140°C, 145°C, 148°C, 150°C, 155°C, or 160°C; the preheating holding time is preferably 20 min. In this invention, the heating rate to the foaming temperature is preferably 5–10°C / min. This invention preferably uses an oil bath for the heating.

[0045] This invention ensures the foaming effect of polypropylene beads by controlling the foaming temperature between 140 and 160°C. When the foaming temperature is too high, the surface of the polypropylene beads softens and melts more rapidly, leading to bead adhesion or even clumping. When the foaming temperature is too low, the polymer melt strength is high, hindering cell growth and resulting in a low foaming ratio. This invention, through preheating, ensures that the polypropylene beads foam after reaching the foaming temperature, guaranteeing the foaming effect.

[0046] After obtaining the preheated material, the present invention injects CO2 into a reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming, thereby obtaining polypropylene foam beads with granular dispersion. In this invention, the supercritical CO2 anhydrous foaming includes sequential supercritical CO2 saturation treatment and depressurization. In this invention, the pressure of the supercritical CO2 saturation treatment is preferably 10–20 MPa, more preferably 14–16 MPa, specifically 10 MPa, 12 MPa, 14 MPa, 16 MPa, 18 MPa, or 20 MPa; the time of the supercritical CO2 saturation treatment is preferably 10–30 min, more preferably 20 min, specifically 10 min, 15 min, 20 min, 25 min, or 30 min. By controlling the pressure and time of the supercritical CO2 saturation treatment within the above ranges, the present invention can ensure the foaming effect of the polypropylene beads.

[0047] In this invention, the pressure relief rate is preferably 80–320 MPa / s, more preferably 100–200 MPa / s, and specifically can be 80 MPa / s, 100 MPa / s, 150 MPa / s, 200 MPa / s, 280 MPa / s, or 320 MPa / s. In this invention, the pressure relief rate affects the nucleation density and cell size of the bubbles; the faster the pressure relief rate, the more nuclei are formed and the smaller the cells.

[0048] After depressurization, the present invention preferably removes supercritical CO2 from the reaction vessel to obtain particulate dispersed polypropylene foam beads.

[0049] The preparation flow chart of the particulate dispersed polypropylene foam beads of this invention is as follows: Figure 2 As shown.

[0050] This invention provides particulate-dispersed polypropylene foamed beads prepared by the above-described method. The particulate-dispersed polypropylene foamed beads provided by this invention exhibit good dispersibility, high yield, and a foaming ratio of 17–29.

[0051] The following detailed description, in conjunction with embodiments, illustrates the particulate dispersed polypropylene foam beads and their preparation method provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] Weigh out commercially available polypropylene beads (PP, E02ES, density 0.92 g / cm³). 3 The particle size was 2-4 mm, and the mass of the nano-silica surfactant (purchased from Sinopec Zhenhai Refining & Chemical Company) was 5 g; weigh 5 g of the nano-silica surfactant. R 816 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.) was added to the PP at a mass of 10 wt%, amounting to 500 mg. The mixture was stirred until homogeneous and then placed in an autoclave. The autoclave was connected to a high-pressure pipeline and purged three times with CO2. It was then preheated for 20 minutes in an oil bath at 148°C. Subsequently, 15 MPa of CO2 was introduced into the autoclave through a pressurization device to bring the CO2 to a supercritical state. The PP beads were then saturated in the autoclave for 20 minutes. The pressure was then rapidly released at a rate of 200 MPa / s to obtain the PP foamed bead sample.

[0054] Example 2

[0055] Similar to Example 1, except that the added nano-silica surfactant is of the following type: R104 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.)

[0056] Example 3

[0057] Similar to Example 1, except that the added nano-silica surfactant is of the following type: R812 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.)

[0058] Example 4

[0059] Similar to Example 1, except that the added nano-silica surfactant is of the following type: 805 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.).

[0060] Example 5

[0061] Similar to Example 1, except that the added nano-silica surfactant is of the following type: R974 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.).

[0062] Example 6

[0063] Similar to Example 1, except that the added nano-silica surfactant is of the following type: R202 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.).

[0064] Example 7

[0065] Similar to Example 1, except that the polypropylene used is PP 831 (density 0.90 g / cm³). 3 The particle size was 2-4 mm, and it was purchased from Wuhan Deguan New Material Technology Co., Ltd.

[0066] Example 8

[0067] Similar to Example 1, except that the polypropylene used is of the following grade: Raw material grade (density 0.90 g / cm³) 3 The particle size is 2-4 mm, purchased from JSP Co., Ltd.

[0068] Example 9

[0069] Similar to Example 1, except that the polypropylene used is of the Lupolen grade. TM 4261AG (density is 0.90 g / cm³) 3 (Particle size 2-4 mm, purchased from LyondellBasell Industries)

[0070] Example 10

[0071] Similar to Example 1, except that the polypropylene used is of the Achieve brand. TM 6936G2 (density is 0.91 g / cm³) 3 (Particle size 2-4 mm, purchased from ExxonMobil Chemical Company).

[0072] Example 11

[0073] Similar to Example 1, except that the polypropylene used was Braskem CP360 (density 0.90 g / cm³). 3 (Particle size 2-4 mm, purchased from Blasco, Brazil).

[0074] Example 12

[0075] Similar to Example 1, except that the added nano-silica surfactant is 5 wt% of the mass of PP.

[0076] Example 13

[0077] Similar to Example 1, except that the added nano-silica surfactant is 8 wt% of the mass of PP.

[0078] Example 14

[0079] Similar to Example 1, except that the added nano-silica surfactant is 12 wt% of the mass of PP.

[0080] Example 15

[0081] Similar to Example 1, except that the added nano-silica surfactant is 15 wt% of the mass of PP.

[0082] Example 16

[0083] Similar to Example 1, except that the foaming temperature is 145°C.

[0084] Example 17

[0085] Similar to Example 1, except that the foaming temperature is 150°C.

[0086] Example 18

[0087] Similar to Example 1, except that the foaming pressure is 12 MPa.

[0088] Example 19

[0089] Similar to Example 1, except that the foaming pressure is 17 MPa.

[0090] Comparative Example 1

[0091] Similar to Example 1, except that no nano-silica surfactant was added.

[0092] Comparative Example 2

[0093] Similar to Example 1, except that the added nano-silica surfactant is 25 wt% of the mass of PP.

[0094] Comparative Example 3

[0095] Similar to Example 1, except that the added nano-silica surfactant is of the following type: 200 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.).

[0096] Comparative Example 4

[0097] Similar to Example 1, except that the foaming temperature is 135°C.

[0098] Comparative Example 5

[0099] Similar to Example 1, except that the foaming temperature is 165°C.

[0100] Comparative Example 6

[0101] Similar to Example 1, except that the added nano-silica surfactant is of the following type: R104 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.), with a foaming temperature of 165℃.

[0102] Comparative Example 7

[0103] Similar to Example 1, except that the foaming pressure is 7 MPa.

[0104] Performance testing

[0105] (1) A physical image of the polypropylene foamed beads obtained in Example 1 of this invention is shown below. Figure 3 As shown, by Figure 3 It can be seen that nano-silica surfactants can significantly improve the bonding behavior of polypropylene beads after foaming.

[0106] The actual image of the polypropylene foam beads obtained in Comparative Example 1 of this invention is shown below. Figure 4 As shown, by Figure 4 It can be seen that, without the addition of nano-silica surfactant, pure polypropylene foam beads exhibit severe adhesion behavior.

[0107] The actual image of the polypropylene foam beads obtained in Comparative Example 5 of this invention is shown below. Figure 5 As shown, by Figure 5 It can be seen that when the foaming temperature is too high, the polypropylene foam beads exhibit severe adhesion and obvious melting behavior.

[0108] (2) The polypropylene foamed beads obtained in Example 1 were quenched and sampled using liquid nitrogen, and the cell structure was measured and analyzed using scanning electron microscopy. The cross-sectional electron micrograph of the polypropylene foamed beads obtained in Example 1 of this invention is shown below. Figure 6 As shown, by Figure 6 It can be seen that the polypropylene foam beads have a small pore structure, mainly closed pores, and are densely distributed.

[0109] (3) The foaming ratio and bonding properties of polypropylene foam beads prepared by the above method in Examples 1-19 and Comparative Examples 1-7 are shown in Table 1.

[0110] Table 1 shows the expansion ratio and adhesion of polypropylene foamed beads prepared by the above method in Examples 1-19 and Comparative Examples 1-7.

[0111]

[0112]

[0113] As shown in Table 1, the polypropylene foam beads prepared by the methods in Examples 1-19 did not exhibit adhesion, and the foaming ratio could all reach over 18 times. In Comparative Example 1, without the addition of nano-silica surfactant, the melt strength of the pure polypropylene beads was insufficient, failing to support the cells during foaming, leading to cell collapse and coalescence, thus causing the polypropylene beads to adhere. In Comparative Example 2, the content of nano-silica surfactant was too high; the nano-silica would coat the polypropylene surface, making it difficult for carbon dioxide to enter the polypropylene, thus affecting foaming. In Comparative Example 3, the nano-silica surfactant added... 200 is hydrophilic and has a negative impact on the foaming of polypropylene. In Comparative Example 4, the foaming temperature was too low, resulting in high melt strength of polypropylene, which hindered cell growth and led to a low foaming ratio. In Comparative Examples 5 and 6, the foaming temperature was too high, which intensified the softening and melting of the polypropylene bead surface, causing the polypropylene beads to stick together or even melt into clumps. In Comparative Example 7, the foaming pressure was too low, resulting in a decrease in the solubility of carbon dioxide in polypropylene, insufficient cell growth momentum, and a low polypropylene foaming ratio.

[0114] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing particle-dispersed polypropylene foamed beads, comprising the following steps: mixing polypropylene beads with nano-silica surfactant to obtain a mixture; heating the mixture to a foaming temperature to preheat the mixture to obtain a preheated mixture; injecting CO2 into a reaction vessel containing the preheated mixture to perform supercritical CO2 anhydrous foaming, wherein the supercritical CO2 anhydrous foaming comprises sequentially performing supercritical CO2 saturation treatment and pressure relief; and obtaining particle-dispersed polypropylene foamed beads; wherein the nano-silica surfactant is modified silica, and the modified group of the modified silica comprises an alkyl group; the polypropylene in the polypropylene beads is homo-polypropylene and / or co-polypropylene; the mass of the nano-silica surfactant is 8-20% of the mass of the polypropylene beads; the foaming temperature is 140-160℃, and the holding time of the preheating is 15-20min; the pressure of the supercritical CO2 saturation treatment is 14-20MPa, and the time is 10-30min; and the rate of the pressure relief is 80-320MPa / s; and wherein the method further comprises, before heating the mixture to the foaming temperature to preheat the mixture, performing CO2 purging on the mixture. 2.The method of claim 1, wherein the modified group of the modified silica comprises an alkyl group with 1-10 carbon atoms. 3.The method of claim 1, wherein the polypropylene in the polypropylene beads is homo-polypropylene and / or co-polypropylene. 4.The method of claim 1, wherein the mass of the nano-silica surfactant is 8-20% of the mass of the polypropylene beads. 5.The method of claim 1, wherein the foaming temperature is 140-160℃, and the holding time of the preheating is 15-20min. 6.The method of claim 1, wherein the pressure of the supercritical CO2 saturation treatment is 14-20MPa, and the time is 10-30min. 7.The method of claim 1, wherein the rate of the pressure relief is 80-320MPa / s. 8.The method of claim 1, wherein the method further comprises, before heating the mixture to the foaming temperature to preheat the mixture, performing CO2 purging on the mixture. 9.Particle-dispersed polypropylene foamed beads prepared by the method of any one of claims 1-8. The nano-silica surfactant type is AEROSIL ® R 202, AEROSIL ® R 812, AEROSIL ® R 805, AEROSIL ® R 104, AEROSIL ® R 974, AEROSIL ® R 816.

2. The production method according to claim 1, characterized by, The nano-silica surfactant has a particle size of 7-14 nm and a density of 2.0-2.2 g / cm 3 .

3. The preparation method according to claim 1, characterized in that, The polypropylene beads have a particle size of 2 to 4 mm and a density of 0.90 to 0.92 g / cm 3 .

4. The preparation method according to claim 1, characterized in that, ​ 5. The preparation method according to claim 1, characterized in that, ​ ​

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