Particle-dispersed polypropylene foamed bead and preparation method thereof

Abstract

The invention provides particle-dispersed polypropylene foamed beads and a preparation method thereof, and belongs to the technical field of polymer foamed materials. The preparation method comprises the following steps: mixing polypropylene beads with a nano silicon dioxide surfactant to obtain a mixed material; the mixed material is heated to the foaming temperature for preheating, and a preheated material is obtained; cO2 is injected into the reaction container containing the preheated material, supercritical CO2 anhydrous foaming is carried out, and the polypropylene foamed beads with dispersed particles are obtained. The nano silicon dioxide surfactant is introduced in the supercritical CO2 anhydrous foaming process, the polypropylene beads can be dispersed in the supercritical CO2 anhydrous foaming process, the yield of the polypropylene foamed beads is increased, and the foaming ratio of the obtained polypropylene foamed beads can reach 17 times or above.

Description

Technical Field

[0001] The invention relates to the technical field of polymer foam materials, and in particular to particle-dispersed polypropylene foam beads and a preparation method thereof. Background Art

[0002] Polypropylene (PP) is a semi-crystalline thermoplastic and one of the world's top five plastics. With the development of lightweight materials and green chemistry, polypropylene foam has become the fastest-growing polymer foam material. PP foam boasts numerous excellent properties, including lightweight, high-temperature resistance, corrosion resistance, thermal and sound insulation, excellent cushioning, and recyclability. It is widely used in the automotive, packaging, construction, electronic equipment, footwear, and medical fields. With the growing adoption of green energy conservation and environmental protection concepts, market demand for polypropylene foam is expected to continue to grow, offering promising development prospects.

[0003] In the field of polymer foaming, there are three main processes commonly used to prepare polypropylene foam materials: compression foaming, extrusion foaming, and autoclave bead foaming. Compression foaming has low production efficiency and can only produce foamed sheets and boards, which is not conducive to subsequent processing into special-shaped structural products. Extrusion foaming requires high melt strength of polypropylene, and there are no reports of industrial extrusion foaming in China. Autoclave bead foaming is currently the most mature process, capable of producing high-magnification polymer foam beads that can be subsequently processed into various complex special-shaped parts.

[0004] During the autoclave bead foaming process, good dispersion of the polymer particles within the autoclave is essential to ensure a high yield of foamed beads. However, due to differences in the molecular structures of different polymers and the varying plasticization effects of CO2 on polymers, the cohesive energy density between polymers varies. This leads to differences in the bonding behavior of the polymer particles during foaming. Polymer particles with high cohesive energy density are more likely to adhere to each other, affecting the dispersion of the particles and limiting the expanded application of this technology. Summary of the Invention

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

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing particle-dispersed polypropylene foam beads, comprising the following steps:

[0008] mixing polypropylene beads with nano-silica surfactant to obtain a mixed material;

[0009] Heating the mixed material to a foaming temperature for preheating to obtain a preheated material;

[0010] Injecting CO2 into a reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming to obtain dispersed polypropylene foam beads, wherein the supercritical CO2 anhydrous foaming includes sequentially performing supercritical CO2 saturation treatment and pressure relief;

[0011] The nano-silica surfactant is modified silica, and the modified group of the modified silica includes an alkyl group.

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

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

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

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

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

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

[0018] Preferably, the pressure relief rate is 80-320 MPa / s.

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

[0020] The present invention provides particle-dispersed polypropylene foam beads prepared by the above preparation method.

[0021] The present invention provides a method for preparing particle-dispersed polypropylene foam beads, comprising the following steps: mixing polypropylene beads with a nano-silica surfactant to obtain a mixed material; heating the mixed material to a foaming temperature for preheating to obtain a preheated material; and injecting CO2 into a reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming to obtain particle-dispersed polypropylene foam beads, wherein the supercritical CO2 anhydrous foaming comprises sequentially performing a supercritical CO2 saturation treatment and pressure relief. The present invention introduces a nano-silica surfactant into the supercritical CO2 anhydrous foaming process. This nano-silica is a CO2-philic surfactant that can help disperse polymer particles in CO2 and prevent adhesion. This can achieve dispersion of the polypropylene beads during the supercritical CO2 anhydrous foaming process, improve the yield of the polypropylene foam beads, and achieve a foaming ratio of more than 17 times.

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

[0023] In addition, the preparation method provided by the present invention is simple to operate, low in cost, and easy to realize industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 This is a flow chart for preparing the particle-dispersed polypropylene foam beads of the present invention;

[0026] Figure 3 This is a physical picture of the polypropylene foam beads obtained in Example 1;

[0027] Figure 4 This is a physical picture of the polypropylene foam beads obtained in Comparative Example 1;

[0028] Figure 5 This is a physical 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 DESCRIPTION

[0030] The present invention provides a method for preparing particle-dispersed polypropylene foam beads, comprising the following steps:

[0031] mixing polypropylene beads with nano-silica surfactant to obtain a mixed material;

[0032] Heating the mixed material to a foaming temperature for preheating to obtain a preheated material;

[0033] CO2 is injected into the reaction container containing the preheated material to perform supercritical CO2 anhydrous foaming to obtain particle-dispersed polypropylene foam beads. The supercritical CO2 anhydrous foaming includes supercritical CO2 saturation treatment and pressure relief performed in sequence.

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

[0035] The present invention mixes polypropylene beads with nano-silica surfactant to obtain a mixed material. In the present invention, the nano-silica surfactant is modified silica, and the modified group of the modified silica includes an alkyl group; in the present invention, the alkyl group is preferably -CH3, -C8H 17 and -C 16 H 33 In the present invention, the particle size of the nano-silica surfactant is preferably 7 to 14 nm, more preferably 8 to 12 nm, and the density is preferably 2.0 to 2.2 g / cm 3 , more preferably 2.1 g / cm 3 .

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

[0037]

[0038] In Formulae 1 to 5, the “—” on the left side of the structural formula represents a linking site.

[0039] In the present invention, the source of the nano-silica surfactant is preferably commercially available. As a specific embodiment of the present invention, the nano-silica surfactant is purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd., model 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 the present invention, the structural diagrams of different types of nano-silica surfactants are shown in FIG. Figure 1 shown.

[0041] In the present invention, the polypropylene in the polypropylene beads is homopolypropylene and / or copolymer polypropylene. In the present invention, the particle size of the polypropylene beads is preferably 2 to 4 mm, specifically 2 mm, 3 mm or 4 mm, and the density is preferably 0.90 to 0.92 g / cm 3 , specifically 0.90 g / cm 3 , 0.91g / cm 3 or 0.92g / cm 3 .

[0042] The present invention has no particular requirements for the mixing method, and any mixing method 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 mixed material, the present invention preheats the mixed material by heating it to a foaming temperature to obtain a preheated material. The present invention preferably transfers the mixed material to an autoclave for subsequent preheating and supercritical CO2 anhydrous foaming. In the present invention, prior to preheating, the present invention preferably further comprises subjecting the mixed material to a CO2 purge, preferably three times. In the present invention, the purge serves to expel air from the autoclave.

[0044] In the present invention, the foaming temperature is preferably 140-160°C, more preferably 145-160°C, specifically 140°C, 145°C, 148°C, 150°C, 155°C, or 160°C. The preheating time is preferably 20 minutes. In the present invention, the heating rate to the foaming temperature is preferably 5-10°C / min. In the present invention, the heating is preferably performed in an oil bath.

[0045] The present invention ensures the foaming effect of the polypropylene beads by controlling the foaming temperature between 140°C and 160°C. When the foaming temperature is too high, the surface softening and melting of the polypropylene beads intensifies, causing the polypropylene beads to stick together or even melt into agglomerates. When the foaming temperature is too low, the high melt strength of the polymer hinders cell growth, resulting in a low foaming ratio. The present invention, through the preheating method, can ensure that the polypropylene beads foam after reaching the foaming temperature, ensuring the foaming effect.

[0046] After obtaining the preheated material, the present invention injects CO2 into the reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming to obtain particle-dispersed polypropylene foam beads. In the present invention, the supercritical CO2 anhydrous foaming includes supercritical CO2 saturation treatment and pressure relief performed in sequence. In the present invention, the pressure of the supercritical CO2 saturation treatment is preferably 10 to 20 MPa, more preferably 14 to 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 to 30 minutes, more preferably 20 minutes, specifically 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes. The present invention can ensure the foaming effect of the polypropylene beads by controlling the pressure and time of the supercritical CO2 saturation treatment within the above ranges.

[0047] In the present invention, the pressure relief rate is preferably 80 to 320 MPa / s, more preferably 100 to 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 the present invention, the pressure relief rate affects the nucleation density and cell size of the cells. The faster the pressure relief rate, the more nucleations and the smaller the cells.

[0048] After the pressure relief, the present invention preferably removes the supercritical CO2 in the reaction vessel to obtain particle-dispersed polypropylene foam beads.

[0049] The preparation flow chart of the particle dispersed polypropylene foam beads of the present invention is as follows Figure 2 shown.

[0050] The present invention provides particle-dispersed polypropylene foam beads prepared by the above preparation method. The particle-dispersed polypropylene foam beads provided by the present invention have good dispersibility, high yield, and a foaming ratio of 17 to 29.

[0051] The particle-dispersed polypropylene foam beads and the preparation method thereof provided by the present invention are described in detail below with reference to the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] Weigh commercially available polypropylene beads (PP, E02ES, density 0.92 g / cm 3 , particle size of 2 to 4 mm, purchased from Sinopec Zhenhai Refining and Chemical Company) with a mass of 5 g; weigh nano-silica surfactant R 816 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.) (500 mg, representing 10 wt% of the PP mass) was added to the PP, stirred to mix thoroughly, and then placed in an autoclave. The autoclave was connected to a high-pressure line, purged with CO2 three times, and preheated in an oil bath at 148°C for 20 minutes. 15 MPa of CO2 was then introduced into the autoclave via a pressurizing device to achieve a supercritical state. The PP beads were saturated in the autoclave for 20 minutes, followed by rapid pressure relief at a rate of 200 MPa / s to obtain PP foam beads.

[0054] Example 2

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

[0056] Example 3

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

[0058] Example 4

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

[0060] Example 5

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

[0062] Example 6

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

[0064] Example 7

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

[0066] Example 8

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

[0068] Example 9

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

[0070] Example 10

[0071] Similar to Example 1, except that the polypropylene used is Achieve TM 6936G2 (density 0.91g / cm 3 , particle size of 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 / cm 3 , particle size of 2-4 mm, purchased from Braskem, Brazil).

[0074] Example 12

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

[0076] Example 13

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

[0078] Example 14

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

[0080] Example 15

[0081] Similar to Example 1, except that the mass of 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 mass of 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 nano-silica surfactant added is 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 R104 (purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.), with a foaming temperature of 165°C.

[0102] Comparative Example 7

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

[0104] Performance Testing

[0105] (1) The actual picture of the polypropylene foam beads obtained in Example 1 of the present invention is as follows Figure 3 As shown by Figure 3 It can be seen that nano-silica surfactant can significantly improve the bonding behavior of polypropylene beads after foaming.

[0106] The actual picture of the polypropylene foam beads obtained in Comparative Example 1 of the present invention is as follows Figure 4 As shown by Figure 4 It can be seen that when no nano-silica surfactant is added, the pure polypropylene foam beads have severe bonding behavior.

[0107] The actual picture of the polypropylene foam beads obtained in Comparative Example 5 of the present invention is as follows Figure 5 As shown by Figure 5 It can be seen that when the foaming temperature is too high, the polypropylene foam beads have serious bonding behavior and the beads show obvious melting behavior.

[0108] (2) The polypropylene foam beads obtained in Example 1 were quenched and sampled using liquid nitrogen, and the cell structure was measured and analyzed using a scanning electron microscope. The cross-sectional electron microscope image of the polypropylene foam beads obtained in Example 1 of the present invention is as follows: Figure 6 As shown by Figure 6 It can be seen that the pores of polypropylene foam beads present a small pore structure, which is mainly a closed-cell structure and is densely distributed.

[0109] (3) The expansion ratios and bonding conditions of the polypropylene foam beads prepared in Examples 1 to 19 and Comparative Examples 1 to 7 by the above method are shown in Table 1.

[0110] Table 1 Expansion ratio and bonding of polypropylene foam beads prepared by the above method in Examples 1 to 19 and Comparative Examples 1 to 7

[0111]

[0112]

[0113] It can be seen from Table 1 that the polypropylene foam beads prepared by the methods of Examples 1 to 19 did not produce adhesion, and the foaming ratio could reach more than 18 times. In Comparative Example 1, no nano-silica surfactant was added. The melt strength of the pure polypropylene beads was insufficient and could not support the pores during foaming. The pores collapsed and merged, resulting in adhesion of the polypropylene beads. The content of the nano-silica surfactant added in Comparative Example 2 was too high. The nano-silica would be coated on the surface of the polypropylene, making it difficult for carbon dioxide to enter the polypropylene, affecting the foaming. The nano-silica surfactant added in Comparative Example 3 200 is hydrophilic, which negatively impacts polypropylene foaming. In Comparative Example 4, the foaming temperature was too low, resulting in high melt strength for 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 beads, leading to adhesion and even melting of the beads. In Comparative Example 7, the foaming pressure was too low, which reduced the solubility of carbon dioxide in polypropylene, insufficient cell growth dynamics, and a low polypropylene foaming ratio.

[0114] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing dispersed polypropylene foam beads, comprising the following steps: mixing polypropylene beads with nano-silica surfactant to obtain a mixed material; Heating the mixed material to a foaming temperature for preheating to obtain a preheated material; Injecting CO2 into a reaction vessel containing the preheated material to perform supercritical CO2 anhydrous foaming to obtain dispersed polypropylene foam beads, wherein the supercritical CO2 anhydrous foaming includes sequentially performing supercritical CO2 saturation treatment and pressure relief; The nano-silica surfactant is modified silica, and the modified group of the modified silica includes an alkyl group.

2. The preparation method according to claim 1, characterized in that The alkyl group is -CH3, -C8H 17 and -C 16 H 33 One or more of the .

3. The preparation method according to claim 1, characterized in that The particle size of the nano-silicon dioxide surfactant is 7-14 nm and the density is 2.0-2.2 g / cm 3 .

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

5. The preparation method according to claim 1 or 4, characterized in that The mass of the nano-silicon dioxide surfactant is 1-20% of the mass of the polypropylene beads.

6. The preparation method according to claim 1, characterized in that The foaming temperature is 140-160° C., and the preheating holding time is 15-20 minutes.

7. The preparation method according to claim 1 or 6, characterized in that The pressure of the supercritical CO2 saturation treatment is 10 to 20 MPa, and the time is 10 to 30 minutes.

8. The preparation method according to claim 1 or 6, characterized in that The pressure relief rate is 80-320 MPa / s.

9. The preparation method according to claim 1, characterized in that Before preheating the mixed material to the foaming temperature, the mixed material is also subjected to CO2 purging.

10. Particle-dispersed polypropylene foam beads prepared by the preparation method according to any one of claims 1 to 9.

Images