CN117774212A - Thermoplastic elastomer foaming method based on melt strength promoter and application thereof - Google Patents
Thermoplastic elastomer foaming method based on melt strength promoter and application thereof Download PDFInfo
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Abstract
The invention relates to a thermoplastic elastomer foaming method based on a melt strength promoter and application thereof, belonging to the technical field of foaming. The invention provides a foaming method of a thermoplastic elastomer, which comprises the following steps: blending a thermoplastic elastomer with a melt strength promoter to obtain a blend; molding the blend to obtain a to-be-foamed body; and performing physical foaming on the to-be-foamed body to obtain the foaming material. According to the foaming method disclosed by the invention, the thermoplastic elastomer and the melt strength promoter are blended, and by introducing the melt strength promoter, on one hand, strong intermolecular force can be provided in a foaming state, the improvement of the melt strength is promoted, and finally a closed-pore structure is maintained, meanwhile, high-rate foaming can be realized, on the other hand, the shrinkage resistance of the foaming material can be greatly improved, and meanwhile, the performances such as stretching and tearing of the foaming material can be improved due to the existence of ionic bonds, so that the foaming method has a great application prospect.
Description
Technical Field
The invention relates to a thermoplastic elastomer foaming method based on a melt strength promoter and application thereof, belonging to the technical field of foaming.
Background
Thermoplastic elastomer foam materials have significantly exceeded conventional solid polymeric materials due to their lightweight, excellent rebound and compression set resistance characteristics. These unique characteristics have led to the wide application of thermoplastic elastomer foam materials in a variety of fields such as shoe materials, automobile parts and sports equipment, and are one of the most popular lightweight high-performance materials today. Conventional thermoplastic elastomer foaming processes are classified into chemical foaming and physical foaming, wherein chemical foaming agents used for chemical foaming generally cause environmental damage and residues in a polymer matrix, and thus, carbon dioxide (CO 2 ) And nitrogen (N) 2 ) The physical foaming method of the environment-friendly physical foaming agent is replaced. The supercritical fluid foaming technology is a polymer physical foaming technology which is rising in recent years, the technical route has the characteristics of green and environment protection, and the prepared thermoplastic elastomer foaming material also has the performance far exceeding that of other process steps.
In order to meet the requirement of higher melt strength of the thermoplastic elastomer during foaming and realize better compression set resistance of the thermoplastic elastomer foaming material, a cross-linking agent is often added in the traditional chemical foaming process, and the molecular weight of the thermoplastic elastomer is subjected to cross-linking reaction in the foaming process to form a cross-linking structure so as to match the decomposition temperature of the foaming agent and the foamable temperature window of the thermoplastic elastomer, thereby realizing the aim. However, the thermoplastic elastomer foam material after crosslinking is not flowable, so that a large amount of leftover materials are formed in the production process, and the thermoplastic elastomer foam product after the life cycle is finished cannot be recycled, so that environmental problems are caused, and the requirement of sustainable development is not met. The supercritical fluid technology is to dissolve a physical foaming agent in a polymer matrix, and then cause a thermodynamically unstable state through rapid pressure relief, so that foaming is realized, and as the foaming process does not depend on the decomposition of the foaming agent, the application of the supercritical fluid foaming technology enables non-crosslinked foaming of a thermoplastic elastomer, and the supercritical fluid technology has been applied to foaming of non-crosslinked beads such as a thermoplastic polyurethane elastomer, a polyolefin elastomer, a polyester elastomer, a nylon elastomer and the like, and has two significant advantages of clean process of the supercritical fluid foaming technology and recycling of products.
In the supercritical fluid foaming process, the thermoplastic elastomer itself must have a high melt strength in order to maintain a closed cell structure and to obtain a foam with a large expansion ratio. In practical application practice, it has also been found that different product structures and foaming processes have different requirements for melt strength of the thermoplastic elastomer, for example, the requirement for melt strength is much higher than that for bead foaming, in which the core heat transfer path is longer during cooling and shaping after foaming. Therefore, for supercritical fluid foaming, most thermoplastic elastomer articles such as plates, sheets and bars, except for non-crosslinked beads, have difficulty in preparing a foamed material with a high foaming ratio due to insufficient melt strength. If foaming needs to be satisfied, the raw materials must undergo special designs of molecular structures, such as increasing molecular weight, widening molecular weight distribution, introducing branched structures, and the like. The method needs to reasonably design and match the molecular structure, improves the foaming capacity on the premise of not weakening the performance of the material, and makes the supercritical fluid foaming of a plurality of thermoplastic elastomer materials with conventional brands difficult.
At the same time, due to the relatively low matrix strength characteristics of most thermoplastic elastomers, pure CO is used 2 When the thermoplastic elastomer is subjected to supercritical fluid foaming, the shrinkage problem of the foaming material is remarkable remarkably (the shrinkage rate can reach 70%). This is mainly due to the fact that once the foam is formed, there is diffusion of the blowing agent out of the cells and airTendency to foam cells, for use with pure CO 2 For the foam material obtained by supercritical fluid foaming of thermoplastic elastomer, pure CO 2 The diffusion rate in thermoplastic elastomers is much higher than air (approximately 1 order of magnitude higher), CO 2 The rapid escape of (a) causes a pressure decrease in the cell structure, while the lower rigidity of the thermoplastic elastomer makes it difficult to support the cell structure under negative pressure, eventually leading to shrinkage problems. The severe shrinkage not only can obviously increase the density of the thermoplastic elastomer foaming material, but also can cause obvious folds, depressions and cracks on the surface or in the thermoplastic elastomer foaming material, thereby seriously affecting the subsequent use of the thermoplastic elastomer foaming material.
Currently, there have been some studies attempting to address the use of pure CO 2 The problem of shrinkage of the foamed material caused by the supercritical fluid foaming of the thermoplastic elastomer. For example, patent application publication No. CN111730794A discloses a supercritical fluid foaming method of a thermoplastic elastomer, which aims to improve shrinkage problem of a foamed material by combining carbon dioxide and nitrogen blending foaming with pressure-variable saturation, but the foaming material obtained by the method has a low foaming ratio (only 7 times after the foaming ratio of supercritical fluid foaming is stabilized under 15MPa foaming pressure by using a thermoplastic polyurethane elastomer), and at the same time, the pressure-variable saturation forms large pores inside the material to affect uniformity of cell size, and in addition, N 2 The diffusion rate in thermoplastic elastomers is slow (generally with CO 2 An order of magnitude different), severely affecting production efficiency; patent application publication No. CN116461037A discloses a method for utilizing high pressure N 2 The method for assisting the volume recovery of the elastomer foaming material increases the complexity of the process, prolongs the process procedure and influences the production efficiency; patent application publication No. CN116082693A discloses a method for improving shrinkage of TPEE expanded beads by chain extension modification, which is unfavorable for recycling thermoplastic elastomer materials because a chain extender is used and a crosslinked structure is easily formed in the production process. Therefore, it is highly desirable to find a thermoplastic elastomer which can improve both the foaming properties (dimensionalRealize high-rate foaming while maintaining a closed cell structure), and can overcome the use of pure CO 2 The method for foaming a thermoplastic elastomer can be applied to various thermoplastic elastomer materials (for example, plates, sheets, bars, particles, and profiles) by using a modified additive which is easy to cause a cross-linked structure, such as a cross-linking agent and a chain extender, and has universality.
Disclosure of Invention
In order to solve the above-mentioned drawbacks, the present invention provides a foaming method of a thermoplastic elastomer, the foaming method comprising: blending a thermoplastic elastomer with a melt strength promoter to obtain a blend; molding the blend to obtain a to-be-foamed body; and performing physical foaming on the to-be-foamed body to obtain the foaming material.
In one embodiment of the invention, the melt strength promoter comprises an ionic polymer; the ionic polymer is obtained by introducing sodium ions or zinc ions into an ethylene-methacrylic acid copolymer for crosslinking.
In one embodiment of the invention, the ionic polymer comprises DOW.
In one embodiment of the present invention, the melt strength promoter is added to the thermoplastic elastomer in an amount of 5 to 30% by mass.
In one embodiment of the present invention, the melt strength promoter is added to the thermoplastic elastomer in an amount of 10 to 20% by mass.
In one embodiment of the invention, the physical foaming is supercritical fluid foaming; the supercritical fluid foaming is as follows: placing the body to be foamed in a foaming mold with the mold cavity temperature being the foaming temperature, and introducing a physical foaming agent into the mold cavity until the pressure in the mold cavity reaches the foaming pressure; continuously placing the to-be-foamed body in a die cavity with the pressure being the foaming pressure and the temperature being the foaming temperature until the physical foaming agent reaches dissolution balance in the to-be-foamed body; and releasing the pressure in the die cavity to the ambient pressure at a pressure release rate, and inducing the nucleation and growth of the foam cells to foam the body to be foamed to obtain the foaming material.
In one embodiment of the present invention, the foaming temperature is (Tm-10) DEG C to (Tm+30) DEG C; wherein Tm is the melting point of the thermoplastic elastomer.
In one embodiment of the present invention, the foaming pressure is 10 to 30MPa.
In one embodiment of the present invention, the foaming pressure is 12 to 25MPa.
In one embodiment of the invention, the time for the physical blowing agent to reach dissolution equilibrium in the body to be foamed is the saturation time t 1 The method comprises the steps of carrying out a first treatment on the surface of the The saturation time t 1 ≥a×(d 1 /1) 1.75 The method comprises the steps of carrying out a first treatment on the surface of the Wherein t is 1 Is the saturation time, the unit is h, a is the saturation coefficient, and a= 0.07762h/mm 1.75 ，d 1 The maximum diffusion diameter of the gas to be foamed in the material (for example, the plate is half the thickness of the material, the particle is the radius of the material, and the special-shaped material is half the thickness of the thickest position) is expressed in mm.
In one embodiment of the invention, the pressure relief rate is 50 to 1000Mpa/s.
In one embodiment of the present invention, the thermoplastic elastomer comprises one or more of a thermoplastic polyurethane elastomer, a polyolefin elastomer, a polyester elastomer, and a nylon elastomer.
In one embodiment of the present invention, the body to be foamed is a plate, sheet, bar, pellet or profile.
In one embodiment of the invention, the blending is performed using an internal mixer, kneader or twin screw extruder.
In one embodiment of the invention, the molding is hot press molding, extrusion molding or injection molding.
In one embodiment of the invention, the physical blowing agent comprises N 2 Or CO 2 One or more of them.
The invention also provides a foaming material, which is obtained by foaming by the foaming method.
The invention also provides application of the foaming method in preparing the foaming material.
The technical scheme of the invention has the following advantages:
the invention provides a foaming method of a thermoplastic elastomer, which comprises the following steps: blending a thermoplastic elastomer with a melt strength promoter to obtain a blend; molding the blend to obtain a to-be-foamed body; and performing physical foaming on the to-be-foamed body to obtain the foaming material. According to the foaming method disclosed by the invention, the thermoplastic elastomer and the melt strength promoter are blended, and the melt strength promoter is introduced, so that on one hand, on the premise of not depending on a crosslinking agent, a chain extender and other modified additives which are easy to cause a crosslinking structure, very strong intermolecular force can be provided in a foaming state, the improvement of the melt strength is promoted, the thermoplastic elastomer has good foaming performance, and besides particles, thermoplastic elastomer products in the forms of plates, sheets, bars, special-shaped materials and the like can finally maintain a closed cell structure after foaming, and meanwhile, high-rate foaming is realized, so that the foaming material has universality, on the other hand, the shrinkage resistance of the foaming material can be greatly improved, and meanwhile, the stretching, tearing and other performances of the foaming material can be improved due to the existence of ionic bonds, so that the foaming method has a great application prospect.
Further, the melt strength promoter comprises an ionic polymer; the ionic polymer is obtained by introducing sodium ions or zinc ions into an ethylene-methacrylic acid copolymer for crosslinking. The ionic polymer has ionic bonds in the molecular chain segments at low temperature, has higher strength, and the ionic bonds in the molecular chain segments at high temperature can be destroyed, thereby being beneficial to processing and forming.
Further, the melt strength promoter is added to the thermoplastic elastomer in an amount of 5 to 30% by mass. If the addition amount is less than the above amount, the promotion effect on the melt strength is not obvious, the melt strength is lower, collapse and rupture of cells are easy to occur, and the elastomer foaming material with high foaming multiplying power is difficult to obtain; if the amount is more than this, the melt strength is too high, which limits the growth of cells, and an elastomer foam material with a high expansion ratio cannot be obtained. The addition amount can effectively improve the foaming ratio of the foaming material.
Further, the melt strength promoter is added to the thermoplastic elastomer in an amount of 10 to 20% by mass. The foaming ratio of the foaming material prepared by the additive amount is better.
Further, the foaming temperature is (Tm-10) DEG C to (Tm+30) DEG C; wherein Tm is the melting point of the thermoplastic elastomer. Below this temperature, the crystals in the polymer matrix have not yet melted completely, and the cells are difficult to grow, and materials with high foaming ratio are difficult to prepare; above this temperature, the melt strength of the matrix is still too low, even in the presence of melt strength promoters, and a large number of cells break and collapse, leading to foam failure. The foaming temperature can ensure successful foaming of the to-be-foamed body, and is beneficial to improving the foaming multiplying power of the foaming material.
Drawings
Fig. 1: the appearance of the thermoplastic elastomer foam obtained in example 1, comparative example 1 and comparative example 2 was compared.
Detailed Description
The following examples are provided for a better understanding of the present invention and are not limited to the preferred embodiments described herein, but are not intended to limit the scope of the invention, any product which is the same or similar to the present invention, whether in light of the present teachings or in combination with other prior art features, falls within the scope of the present invention.
The following examples do not identify specific experimental procedures or conditions, which may be followed by procedures or conditions of conventional experimental procedures described in the literature in this field. The reagents or apparatus used were conventional reagent products commercially available without the manufacturer's knowledge. The twin screw extruder in the examples below was model SHJ-20, available from Nanj Entec electric Co., ltd.
Example 1: foaming method of thermoplastic elastomer
This embodiment provides a method of foaming a thermoplastic elastomer,the foaming method comprises the following steps: thermoplastic polyurethane elastomer (TPU, BASF, elastollan 1180a, tm=150℃) and melt strength accelerator DOW (Surlyn 9910, added in an amount of 10wt.%, i.e. volume percent, in the thermoplastic polyurethane elastomer) were blended by a twin-screw extruder and extruded into bars of 6mm diameter (twin-screw extruder having six zones of controlled temperature, six zones of 150 ℃, 165 ℃, 170 ℃, 180 ℃, 165 ℃), respectively; the bar is placed at 160 ℃ (foaming temperature) and filled with 20MPa (foaming pressure) CO 2 Is saturated in a high-pressure die cavity (size 250 mm. Times.100 mm. Times.30 mm); saturated for 0.16h (saturation time t 1 ) To CO 2 After the dissolution balance is achieved in the bar, the pressure of the high-pressure die cavity is relieved at a pressure relief rate of 400MPa/s, and the foaming material is obtained.
Example 2: foaming method of thermoplastic elastomer
The embodiment provides a foaming method of a thermoplastic elastomer, which comprises the following steps: based on example 1, the addition amount of the melt strength accelerator DOW to the thermoplastic polyurethane elastomer was replaced with 20wt.% from 10wt.% to obtain a foamed material.
Example 3: foaming method of thermoplastic elastomer
The embodiment provides a foaming method of a thermoplastic elastomer, which comprises the following steps: based on example 1, the foaming temperature was changed from 160℃to 150℃to obtain a foamed material.
Example 4: foaming method of thermoplastic elastomer
The embodiment provides a foaming method of a thermoplastic elastomer, which comprises the following steps: based on example 1, the foaming temperature was changed from 160℃to 170℃to obtain a foamed material.
Example 5: foaming method of thermoplastic elastomer
The embodiment provides a foaming method of a thermoplastic elastomer, which comprises the following steps: thermoplastic polyester elastomer (TPEE, celanese, hytrel 4056, tm=152℃) and melt strength promoter DOW (Surlyn 9910, addition to thermoplastic polyurethane elastomer)10 wt.%) are blended by a twin-screw extruder and extruded into bars with a diameter of 6mm (the twin-screw extruder has six zones with temperature control, the six zones are respectively 150 ℃, 165 ℃, 170 ℃, 180 ℃, 165 ℃); placing the bar at 162 ℃ and charging with 20MPa CO 2 Is saturated in a high-pressure die cavity (size 250 mm. Times.100 mm. Times.30 mm); saturated for 0.16h to CO 2 After the dissolution balance is achieved in the bar, the pressure of the high-pressure die cavity is relieved at a pressure relief rate of 400MPa/s, and the foaming material is obtained.
Example 6: foaming method of thermoplastic elastomer
The embodiment provides a foaming method of a thermoplastic elastomer, which comprises the following steps: thermoplastic nylon elastomer (PEBAX, ARKEMA, PEBAX 4533, tm=147 ℃) and melt strength promoter DOW (Surlyn 9910, an addition amount in thermoplastic polyurethane elastomer of 10 wt.%) were blended by a twin-screw extruder and extruded into bars of 6mm diameter (twin-screw extruder has six zones of temperature control, six zones being 150 ℃, 165 ℃, 170 ℃, 180 ℃, 165 ℃); placing the bar at 157 deg.C and charging with 20MPa CO 2 Is saturated in a high-pressure die cavity (size 250 mm. Times.100 mm. Times.30 mm); saturated for 0.16h to CO 2 After the dissolution balance is achieved in the bar, the pressure of the high-pressure die cavity is relieved at a pressure relief rate of 400MPa/s, and the foaming material is obtained.
Comparative example 1: foaming method of thermoplastic elastomer
This comparative example provides a foaming method of a thermoplastic elastomer, which replaces the melt strength promoter DOW in the thermoplastic polyurethane elastomer by 0wt.% with 10wt.% based on example 1, to obtain a foamed material.
Comparative example 2: foaming method of thermoplastic elastomer
This comparative example provides a foaming method of a thermoplastic elastomer, which is: based on example 1, the addition amount of the melt strength accelerator DOW to the thermoplastic polyurethane elastomer was replaced with 3wt.% from 10wt.% to obtain a foamed material.
Comparative example 3: foaming method of thermoplastic elastomer
This comparative example provides a foaming method of a thermoplastic elastomer, which is: based on example 1, the addition amount of the melt strength accelerator DOW to the thermoplastic polyurethane elastomer was replaced with 35wt.% from 10wt.% to obtain a foamed material.
Comparative example 4: foaming method of thermoplastic elastomer
This comparative example provides a foaming method of a thermoplastic elastomer, which is: based on example 1, the foaming temperature was changed from 160℃to 135℃to obtain a foamed material.
Comparative example 5: foaming method of thermoplastic elastomer
This comparative example provides a foaming method of a thermoplastic elastomer, which is: based on example 1, the foaming temperature was changed from 160℃to 185℃to obtain a foamed material.
Experimental example 1: performance test of thermoplastic elastomer foam
The experimental example provides performance detection of a thermoplastic elastomer foaming material, and the experimental process is as follows:
the foaming ratios and shrinkage ratios (after dimensional stabilization) of the foams produced in examples 1 to 5 and comparative examples 1 to 5 were measured by the methods described in "Chen, yichong, dongyang Li, hong Zhang, yijie Ling, kaiwen Wu, tao Liu, dongdong Hu, and Ling zhao," Antishrinking strategy of microcellular thermoplastic polyurethane by comprehensive modeling analysis, "Industrial & Engineering Chemistry Research, no.19 (2021): 7155-7166.", and the foaming materials produced in examples 1 to 5 and comparative examples 1 to 5 were measured by the falling ball rebound standard test method (refer to national standard "measurement of falling ball rebound properties of GBT 6670-2008-soft foam polymers"), and the measurement results are shown in table 1. The appearance of the foam materials obtained in examples 1 to 5 and comparative examples 1 to 5 was observed, and the observation results are shown in Table 1 and FIG. 1.
As can be seen from fig. 1 and table 1, examples 1 to 6 all have a high foaming ratio, and the shrinkage ratio is not more than 5%, and the rebound ratio is more than 65%; in the comparative example 1, the melt strength promoter is not added, so that the matrix is difficult to support cells at a higher temperature, the foaming multiplying power is lower, the shrinkage after foaming is serious, the shrinkage rate reaches 47.6%, the rebound resilience is poor, and obvious cracks are formed in the middle of the foaming material; the amount of melt strength promoter added was lower in comparative example 2, so that a crack was present in the center of the foamed material despite the improvement in expansion ratio, shrinkage and rebound resilience as compared with comparative example 1, which was not added; the addition amount of the melt strength promoter in the comparative example 3 is too high, so that the melt strength of the material is too high under the foaming condition, cells are difficult to grow, the foaming multiplying power is low, and the rebound resilience is poor; the foaming temperature of comparative example 4 is lower, at the moment, the strength of the material matrix is higher, and cells are difficult to grow, so that the foaming multiplying power is lower, and the rebound resilience is poorer; the foaming temperature of comparative example 5 was too high, at which time the material matrix had difficulty supporting the cell structure, and a large amount of coalescence and collapse occurred, so that the foaming ratio was low and the rebound resilience was poor.
TABLE 1 foaming Rate, shrinkage (after dimensional stabilization), resilience and appearance of the foaming materials
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (10)
1. A method of foaming a thermoplastic elastomer, the method comprising: blending a thermoplastic elastomer with a melt strength promoter to obtain a blend; molding the blend to obtain a to-be-foamed body; and performing physical foaming on the to-be-foamed body to obtain the foaming material.
2. The foaming process of claim 1 wherein the melt strength promoter comprises an ionic polymer; the ionic polymer is obtained by introducing sodium ions or zinc ions into an ethylene-methacrylic acid copolymer for crosslinking.
3. The foaming process of claim 2 wherein the ionic polymer comprises DOW.
4. A foaming method according to any one of claims 1 to 3, wherein the melt strength promoter is added to the thermoplastic elastomer in an amount of 5 to 30% by mass.
5. The foaming method according to claim 1 to 4, wherein the melt strength accelerator is added to the thermoplastic elastomer in an amount of 10 to 20% by mass.
6. The foaming method according to any one of claims 1 to 5, wherein the physical foaming is supercritical fluid foaming; the supercritical fluid foaming is as follows: placing the body to be foamed in a foaming mold with the mold cavity temperature being the foaming temperature, and introducing a physical foaming agent into the mold cavity until the pressure in the mold cavity reaches the foaming pressure; continuously placing the to-be-foamed body in a die cavity with the pressure being the foaming pressure and the temperature being the foaming temperature until the physical foaming agent reaches dissolution balance in the to-be-foamed body; and releasing the pressure in the die cavity to the ambient pressure at a pressure release rate, and inducing the nucleation and growth of the foam cells to foam the body to be foamed to obtain the foaming material.
7. The foaming method according to claim 6, wherein the foaming temperature is from (Tm-10) DEG C to (Tm+30) DEG C; wherein Tm is the melting point of the thermoplastic elastomer.
8. The foaming process according to claim 6 or 7, wherein the time for the physical blowing agent to reach dissolution equilibrium in the body to be foamed is the saturation time t 1 The method comprises the steps of carrying out a first treatment on the surface of the The saturation time t 1 ≥a×(d 1 /1) 1.75 The method comprises the steps of carrying out a first treatment on the surface of the Wherein t is 1 Is the saturation time, the unit is h, a is the saturation coefficient, and a= 0.07762h/mm 1.75 ，d 1 The maximum diffusion diameter of the gas to be foamed in the material is given in mm.
9. A foamed material, characterized in that the foamed material is obtained by foaming by the foaming method according to any one of claims 1 to 8.
10. Use of the foaming process according to any of claims 1 to 8 for the preparation of a foamed material.
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