CN111675896A - A method for improving cell retraction behavior of thermoplastic elastomer microcellular foam material - Google Patents

Abstract

The invention relates to a method for improving the cell shrinkage behavior of thermoplastic elastomer microcellular foaming materials, and belongs to the field of thermoplastic elastomer microcellular foaming. The present invention provides a method for inhibiting cell shrinkage of a thermoplastic elastomer microcellular foamed material. The method comprises the following steps: in the process of preparing the thermoplastic elastomer microcellular foamed material, nanoparticles are introduced, and the nanoparticles are made There is a physical bond or chemical cross-linking effect with the thermoplastic elastomer, thereby inhibiting the cell shrinkage that occurs after the foamed material is foamed. The present invention aims to propose a convenient and efficient method for improving the shrinkage behavior of thermoplastic elastomer cells from the perspective of molecular chains, and fundamentally solves the problem of thermoplastic elastomer cell shrinkage.

Description

A method for improving cell retraction behavior of thermoplastic elastomer microcellular foam material

technical field

The invention relates to a method for improving the cell shrinkage behavior of thermoplastic elastomers such as thermoplastic polyurethane microcellular foaming materials, and belongs to the field of thermoplastic elastomer microcellular foaming.

Background technique

Thermoplastic elastomers such as thermoplastic polyurethane (TPU) are microcellular foam materials prepared by carbon dioxide (CO ₂ ) foaming. They have excellent shock absorption, resilience and wear resistance, and are widely used in shoe material production and tire preparation. Among them, the most representative is the Boost series of running shoes jointly developed by Adidas and BASF in Germany. For the first time, TPU foam particle infinergy is applied to the production and preparation of running shoe midsole; this running shoe sole not only has excellent shock absorption and return Elasticity and wear resistance, and the sole is comfortable to wear and has a high degree of energy feedback. It has a very broad sales market and is deeply loved by people. However, in the molding process of TPU microcellular foam material, we found that there is an obvious phenomenon of unstable cell structure in the process of cell shaping: the foaming ratio of the material drops sharply in a short period of time after the pressure relief is completed, and the cells are shaped. Difficulty, serious cell shrinkage; resulting in an increase in the density of the TPU foam material and a decrease in the foaming ratio, which greatly limits the performance and application fields of the TPU microcellular foam material.

In response to this problem, most manufacturers of TPU microcellular foaming materials use secondary foaming technology to improve the behavior of TPU cell shrinkage: at room temperature, the TPU foamed material obtained by one-time foaming is at a pressure of 4 -After fully swollen in a gas atmosphere of 5 atmospheres, the temperature rises rapidly to above the softening point of the material; the swollen gas is thermally expanded at high temperature, which provides a driving force for cell growth, promotes the secondary growth of cells, and reduces TPU. The density of the foamed material; however, this technical process is cumbersome, the molding cycle is long, and the technical requirements for equipment are high, which cannot meet the production needs of small and medium-sized enterprises.

SUMMARY OF THE INVENTION

In view of the above-mentioned defects, the present invention aims to propose a convenient and efficient method for improving the shrinkage behavior of thermoplastic elastomer cells from the perspective of molecular chains, which fundamentally solves the problem of thermoplastic elastomer cell shrinkage.

Technical scheme of the present invention:

The present invention provides a method for inhibiting cell shrinkage of a thermoplastic elastomer microcellular foamed material. The method includes: in the process of preparing the thermoplastic elastomer microcellular foamed material, introducing nano-particles, and making the nano-particles Physical bonding or chemical cross-linking exists between the particles and the thermoplastic elastomer, thereby inhibiting cell shrinkage after foaming of the foamed material.

Further, the physical bonding or chemical cross-linking between the nanoparticles and the thermoplastic elastomer adopts at least one of the following methods:

Method 1: Select nanoparticles that can physically bond or chemically crosslink with the thermoplastic elastomer during melt blending or solution blending; for example: thermoplastic polyurethane and organic montmorillonite;

Method 2: chemically modify the thermoplastic elastomer, including amidation modification, hydroxylation modification or carboxylation modification of the thermoplastic elastomer; introduce polarity into the molecular chain of the thermoplastic elastomer through chemical modification group to improve the force between molecular chains; such as: polyolefin thermoplastic elastomers and carbon nanofibers;

Method 3: The nanoparticles are modified with organic functional groups, including siloxane modification, hydroxylation modification, carboxylation modification, peroxide modification or sulfide modification of nanoparticles; The organic modification of the functional group can improve the force between molecular chains; for example: styrene thermoplastic elastomer and carbon nanotubes, polyester thermoplastic elastomer and graphene.

In the present invention, by introducing nanoparticles and enabling physical bonding or chemical cross-linking between the nanoparticles and the thermoplastic elastomer, the force between the molecular chains of the thermoplastic elastomer is increased, and the thermoplastic elastomer molecules are limited. The movement of the chain, in turn, plays a role in inhibiting the cell shrinkage that occurs after the foamed material is foamed.

Further, the mass ratio of thermoplastic elastomer to nanoparticles is: 95-99.75 wt.%: 0.25-5 wt.%.

Further, the physical bonding refers to the action of hydrogen bonding or van der Waals force.

Further, the chemical cross-linking is caused by silicon-oxygen bond, disulfide bond or peroxy bond and the like.

Further, the thermoplastic elastomer is selected from thermoplastic polyurethane-based elastomer (TPU), styrene-based thermoplastic elastomer (SBS), polyolefin-based thermoplastic elastomer (POE) or polyester-based thermoplastic elastomer (TPEE).

Further, the nanoparticles are selected from nano-montmorillonite (MMT), carbon nanotube (CNT), carbon nanofiber (CNF), graphene (GnP) or silicon dioxide (SiO ₂ ) and the like.

Further, unmodified or organically modified thermoplastic elastomers and nanoparticle systems with physical bonding or chemical crosslinking include but are not limited to:

Thermoplastic polyurethane and organic montmorillonite, styrene-based thermoplastic elastomer and carbon nanotubes, polyolefin-based thermoplastic elastomer and carbon nanofibers, or: polyester-based thermoplastic elastomer and graphene.

Further, the above-mentioned method for suppressing the shrinkage of the cells of the thermoplastic elastomer microcellular foamed material is: firstly, the nanoparticles and the thermoplastic elastomer are melt-blended, and the nanoparticles are uniformly distributed in the thermoplastic elastomer to obtain a thermoplastic elastomer-nano Particle blending material; then foaming the obtained blending material to obtain a thermoplastic elastomer foaming material; wherein, before melt blending, the nanoparticles are modified with organic functional groups or the thermoplastic elastomer is chemically modified as required.

In the present invention, the choice of organic functional group modification of nanoparticles or chemical modification of thermoplastic elastomers before blending, or simultaneous modification of both, is mainly based on whether a strong interaction can be formed between the obtained materials. It depends, such as the interface effect of nanoparticles, the coupling effect of siloxane, and the chemical cross-linking effect of disulfide bonds.

Further, when the thermoplastic elastomer is thermoplastic polyurethane, the method for inhibiting the cell shrinkage of the thermoplastic elastomer microcellular foam material is: dioctadecyldimethylammonium bromide is extruded by a twin-screw extruder. The modified nano-particles are melt-blended with thermoplastic polyurethane for a second time, and the nano-particles are uniformly distributed in the thermoplastic polyurethane to obtain a thermoplastic polyurethane-nano-particle blend material; and then a thermoplastic polyurethane foam material is prepared by a supercritical carbon dioxide foaming method.

Further, in the above-mentioned method, the method for carrying out secondary melt blending of the modified nano-particles of dioctadecyl dimethyl ammonium bromide and thermoplastic polyurethane by a twin-screw extruder is as follows: firstly utilize a twin-screw extruder to extrude. A thermoplastic polyurethane-nanoparticle masterbatch with a mass fraction of 10-20wt.% of molded nanoparticles is produced; then thermoplastic polyurethane and the masterbatch are blended and extruded with a mass fraction of 0.25wt.%-5wt.% of thermoplastic polyurethane-nanoparticles. mixed materials.

Further, the supercritical carbon dioxide foaming method is as follows: the thermoplastic polyurethane-nanoparticle blend material is swelled and saturated with CO ₂ in a high temperature and high pressure reactor, and the thermoplastic polyurethane microcellular foamed material is prepared by rapid pressure relief foaming; wherein, the high temperature Refers to the temperature of 145 ~ 165 ℃, high pressure refers to the pressure of 13 ~ 16MPa.

Beneficial effects of the present invention:

The present invention takes TPU and the modified montmorillonite system as an example, compared with the existing behavior of improving the TPU cell shrinkage phenomenon, the obtained TPU foam material of the present invention has the following advantages:

1. The experimental method is convenient and efficient. By simply blending O-MMT and TPU twice through a twin-screw extruder, the shrinkage behavior of TPU foam materials can be significantly improved; when the filler content of O-MMT reaches 1wt.% When TPU supercritical carbon dioxide foam molding process, no obvious shrinkage phenomenon has been observed.

2. With the increase of O-MMT content, the cell diameter of the TPU microcellular foam material gradually decreases, and the cell density increases to a certain extent, which is conducive to maintaining the shock absorption and resilience performance of the TPU foam material and improving the wearing performance. of comfort.

Description of drawings:

Fig. 1 is the hydrogen bonding index of the carbonyl group of the TPU/O-MMT obtained in Example 1-4; it can be seen from Fig. 1: with the increase of the O-MMT content, the hydrogen bonding index χ _B of the carbon group of the TPU system It shows that the interaction force between nanofillers and TPU increases, which limits the relaxation behavior of TPU molecular chains after foaming, thereby achieving the effect of inhibiting cell shrinkage after TPU foaming.

Figure 2 shows the morphology of the samples obtained by foaming the foamed materials obtained in Examples 1-4 under a pressure of 13MPa: 150°C (a-d), 155°C (e-h) and 160°C (i-l); The cell structure of the foam material has good uniformity and is mostly closed cell structure; with the increase of the O-MMT content, the diameter of the cell gradually decreases, and the cell wall thickness increases, but when the content of O-MMT is too high, the cell size decreases. Defects also tend to increase.

Figure 3 shows the cell statistics of the foamed samples obtained in Examples 1-4 under a pressure of 13MPa: cell diameter, 150°C (a), 155°C (b) and 160°C (c); cell density, 150 ℃ (d), 155 ℃ (e) and 160 ℃ (f); it can be seen from Figure 3 that with the increase of O-MMT filler content, the cell diameter of TPU microcellular foam material gradually decreases, and the cell density There is a certain degree of improvement.

Figure 4 shows the shrinkage of the foamed samples obtained in Examples 1-4 under a pressure of 13MPa: as foamedexpansion ratio represents the initial foaming ratio before the sample shrinks, final expansion ratio represents the foaming ratio after the sample is stabilized, O- The addition of MMT significantly improves the shrinkage of the TPU foamed samples; as can be seen from Figure 4: with the increase of the O-MMT content, the absolute difference of the foaming ratio before and after the cells of the TPU microcellular foamed material is continuously reduced. Small; taking the sample foamed at 150 °C as an example, the absolute difference of the foaming ratio before and after TPU0 cell setting is 1.36, while with the increase of O-MMT content, the foaming ratio of TPU1, TPU3 and TPU5 before and after cell setting is 1.36. The absolute differences were reduced to 0.43, 0.08 and 0.05, respectively, and the samples foamed at 155°C and 160°C reflected similar patterns.

Detailed ways

The present invention provides a method for inhibiting cell shrinkage of a thermoplastic elastomer microcellular foamed material. The method includes: in the process of preparing the thermoplastic elastomer microcellular foamed material, introducing nano-particles, and making the nano-particles Physical bonding or chemical cross-linking exists between the particles and the thermoplastic elastomer, thereby inhibiting cell shrinkage after foaming of the foamed material. In the present invention, by introducing nanoparticles and enabling physical bonding or chemical cross-linking between the nanoparticles and the thermoplastic elastomer, the force between the molecular chains of the thermoplastic elastomer is increased, and the thermoplastic elastomer molecules are limited. The movement of the chain, in turn, plays a role in inhibiting the cell shrinkage that occurs after the foamed material is foamed.

In the present invention, for a system in which there is no physical bond and chemical cross-linking between the thermoplastic elastomer and the nanoparticle, the two (or one) can be modified with organic functional groups, and polar functional groups can be introduced to improve the thermoplastic elastomer. The interaction force between the nanoparticle and the nanoparticle; and for the system with a strong interaction between the two, the effect of improving the retraction can be achieved by introducing the nanoparticle without organic modification.

The present invention proposes a convenient and efficient method for improving the cell shrinkage behavior of thermoplastic elastomer microcellular foaming materials. For thermoplastic elastomer (TPE) microcellular foaming materials, by introducing nanoparticles modified by organic functional groups, The method of physical bonding or chemical cross-linking is used to increase the force between the molecular chains of thermoplastic elastomers, maintain the orientation of the molecular chains after cell growth, and inhibit the behavior of cell shrinkage. For example, O-MMT can be introduced into TPU, and a nanocomposite interface is formed through the strong hydrogen bonding between O-MMT and TPU, which freezes the TPU molecular chain near the interface, effectively restricts the movement of the molecular chain, and inhibits TPU in The relaxation behavior of the molecular chain after foaming preserves the orientation of the TPU molecular chain after the cell growth to the greatest extent, and promotes the shaping of the cell structure. The results show that: with the addition of O-MMT, the cell shrinkage behavior of the TPU system is gradually improved: when the mass fraction of O-MMT reaches 1 wt.%, no obvious shrinkage phenomenon can be observed in the TPU foam material; moreover, With the introduction of O-MMT, the cell size of the TPU foam material gradually decreased, the cell density increased to a certain extent, and the cell morphology was relatively uniform. The uniform and fine cell morphology is conducive to maintaining the shock absorption and resilience performance of the TPU foam material and improving the wearing comfort of the shoe material.

Examples 1-4

Experiment material: polyether TPU, grade: DESMOPAN DP.9385AU DPS650; hardness 86A; provided by Covestro Polymers (China) Co., Ltd.; organically modified nano-montmorillonite (O-MMT), grade: I.44P, modified by dioctadecyldimethylammonium bromide, provided by NANOCOR Co., Ltd. of the United States; CO ₂ gas, with a purity of 99.5%, provided by Linde Gas (Chengdu) Co., Ltd.

Sample preparation process:

First, in order to remove the influence of moisture, the TPU and O-MMT were vacuum dried in a vacuum oven at 80 °C for 8 hours; then, a twin-screw extruder (machine model: NOE 02213, Nanjing Coperion Technology Co., Ltd. ) Extruded O-MMT masterbatch with a mass fraction of 10wt% O-MMT, the temperature of the second stage to the tenth stage of the extruder is 175°C, 180°C, 183°C, 185°C, 188°C, 190°C, 193 ℃, 195 ℃ and 195 ℃ are set successively; Die temperature is set as 195 ℃, twin-screw rotation speed is set as 85rpm; Then, TPU and O-MMT master batch are blended and extruded mass fraction is 0wt.% ( Example 1), 1wt.% (Example 2), 3wt.% (Example 3) and 5wt.% (Example 4) TPU splines are marked as TPU0 (Example 1), TPU1 (Example 4) respectively. Example 2), TPU3 (Example 3) and TPU5 (Example 4); subsequently, the extruded splines were placed in a vacuum oven at 80° C. for vacuum drying for 8 hours; The temperature (150°C, 155°C, 160°C) and pressure (13MPa) were placed in a high-pressure foaming kettle and swelled by CO for ₂ hours, and the pressure was quickly released within 2s to prepare TPU microcellular foaming materials. For the convenience of experimental description, TPU1-150-13 means that TPU1 is foamed under the foaming conditions of temperature of 150°C and pressure of 13MPa, and other samples are named according to the same rules.

The process conditions in the examples of the present invention are shown in Table 1.

Table 1 Foaming conditions of TPU samples

The invention improves the cell shrinkage behavior of thermoplastic elastomers such as TPU microcellular foamed materials from the perspective of molecular mechanism. By simply blending the organically modified nano-montmorillonite and TPU twice, there is a The strong hydrogen bonding forms the interface effect of nanoparticles in the matrix of TPU, which limits the relaxation behavior of the oriented molecular chain after foaming and maintains the cell morphology; therefore, it is convenient and efficient to improve the TPU from the perspective of molecular chain. The cell retraction behavior of the microcellular foam material breaks the limitation of secondary foaming technology for small and medium-sized enterprises.

Claims (10)

1. A method for suppressing cell shrinkage of thermoplastic elastomer microcellular foamed material, characterized in that the method is: in the process of preparing the thermoplastic elastomer microcellular foamed material, introducing nanoparticles, and making the There is a physical bond or chemical cross-linking effect between the nanoparticles and the thermoplastic elastomer, thereby inhibiting the cell shrinkage that occurs after the foamed material is foamed. 2 . The method for inhibiting cell shrinkage of thermoplastic elastomer microcellular foam material according to claim 1 , wherein physical bonding or chemical bonding exists between the nanoparticles and the thermoplastic elastomer. 3 . The cross-linking is performed in at least one of the following ways: Mode 1: Select nanoparticles that can physically bond or chemically crosslink with the thermoplastic elastomer during melt blending or solution blending; Method 2: chemically modify the thermoplastic elastomer, including amidation modification, hydroxylation modification or carboxylation modification of the thermoplastic elastomer; Mode 3: The nanoparticles are modified with organic functional groups, including siloxane modification, hydroxylation modification, carboxylation modification, peroxide modification or sulfide modification of the nanoparticles. 3. The method for inhibiting cell shrinkage of thermoplastic elastomer microcellular foam material according to claim 1 or 2, wherein the mass ratio of the thermoplastic elastomer to nanoparticles is: 95-99.75wt.% : 0.25 to 5 wt.%. The method for inhibiting cell shrinkage of a thermoplastic elastomer microcellular foam material according to any one of claims 1 to 3, wherein the physical bonding refers to hydrogen bonding or van der Waals force; Further, the chemical cross-linking is caused by silicon-oxygen bond, disulfide bond or peroxy bond. The method for inhibiting cell shrinkage of a thermoplastic elastomer microcellular foam material according to any one of claims 1 to 4, wherein the thermoplastic elastomer is selected from the group consisting of thermoplastic polyurethane elastomers, styrene-based elastomers thermoplastic elastomer, polyolefin thermoplastic elastomer or polyester thermoplastic elastomer; Further, the nanoparticles are selected from nano-montmorillonite, carbon nanotubes, carbon nanofibers, graphene or silicon dioxide. 6. The method for inhibiting cell shrinkage of thermoplastic elastomer microcellular foam material according to claim 5, wherein the thermoplastic elastomer and nanoparticle system comprise: thermoplastic polyurethane, organic montmorillonite, styrene Thermoplastic Elastomers and Carbon Nanotubes, Polyolefin Thermoplastic Elastomers and Carbon Nanofibers, or: Polyester Thermoplastic Elastomers and Graphene. 7. The method for inhibiting cell shrinkage of thermoplastic elastomer microcellular foam material according to any one of claims 1 to 6, wherein the method for inhibiting cell shrinkage of thermoplastic elastomer microcellular foam material The method is as follows: firstly, the nanoparticles and the thermoplastic elastomer are melt-blended, and the nanoparticles are uniformly distributed in the thermoplastic elastomer to obtain a thermoplastic elastomer-nanoparticle blend material; then the obtained blend material is foamed to obtain a thermoplastic elastomer Bulk foam material; wherein, before melt blending, the nanoparticles are modified with organic functional groups and/or the thermoplastic elastomer is chemically modified as required. The method for inhibiting cell shrinkage of a thermoplastic elastomer microcellular foam material according to any one of claims 5 to 7, wherein when the thermoplastic elastomer is thermoplastic polyurethane, the inhibiting thermoplastic elasticity The method for cell shrinkage of the bulk microcellular foam material is as follows: secondary melt blending of the nanoparticles modified by dioctadecyldimethylammonium bromide and thermoplastic polyurethane through a twin-screw extruder; The thermoplastic polyurethane-nanoparticle blend material is uniformly distributed in the thermoplastic polyurethane; and the thermoplastic polyurethane foam material is prepared by the supercritical carbon dioxide foaming method. 9. The method for inhibiting cell shrinkage of thermoplastic elastomer microcellular foamed material according to claim 8, wherein the dioctadecyldimethylammonium bromide is modified by a twin-screw extruder. The method for secondary melt blending of nanoparticles and thermoplastic polyurethane is as follows: first, a twin-screw extruder is used to extrude a thermoplastic polyurethane-nanoparticle masterbatch with a mass fraction of nanoparticles of 10-20 wt.%; A thermoplastic polyurethane-nanoparticle blend material with a mass fraction of 0.25wt.% to 5wt.% is extruded by blending and extruding the material. 10. The method for inhibiting cell shrinkage of thermoplastic elastomer microcellular foam material according to claim 8 or 9, wherein the supercritical carbon dioxide foaming method is: thermoplastic polyurethane-nanoparticle blend material In the high temperature and high pressure reaction kettle, CO ₂ is swelled to saturation, and the thermoplastic polyurethane microcellular foam material is prepared by rapid pressure relief foaming; wherein, high temperature refers to a temperature of 145-165 °C, and high pressure refers to a pressure of 13-16 MPa.

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