Method for strengthening and toughening modified polycaprolactone foamed sheet

Abstract

The invention discloses a method for strengthening and toughening a modified polycaprolactone foam board, and belongs to the field of foam materials. Polycaprolactone is used as a base material, foaming is carried out in a supercritical carbon dioxide and supercritical nitrogen conversion mode, mechanical properties of the base material are controlled through a water cooling process and by regulating and controlling the crystallization rate of a semi-finished product, and foam hole stability maintaining is achieved, so that foam holes of the prepared foaming material are uniform and have certain strength, and the foaming performance of the foaming material is improved. The polycaprolactone composite material has a finer appearance, cell independence and dimensional stability, can be repeatedly molded after being soaked in hot water, and is suitable for protective articles, and the polycaprolactone matrix material is almost completely degradable. In addition, by improving the preparation process of the polycaprolactone board, the strength and toughness of the board are greatly improved, and the board has a wider application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to a method for toughening and modifying a polycaprolactone foamed plate, and belongs to the field of foamed materials. BACKGROUND

[0002] The most prominent feature of low-temperature thermoplastic plates is repeated plasticity. Although foaming is conducive to improving comfort, there is currently no foamed low-temperature thermoplastic plate, and the performance difference between low-temperature thermoplastic plates and conventional high-temperature thermoplastic plates is huge, so that the requirements for foaming are completely different. In addition, due to the difference in the base material, the foaming process is different, the size and uniformity of the prepared cells are completely different, and finally the application scenarios are completely different.

[0003] Currently, some researchers have prepared some foamed thermoplastic plates, such as:

[0004] CN 111234290 A discloses a method for preparing a bone tissue engineering scaffold by using a supercritical fluid foaming technology, specifically, iron oxide particles are added to the polymer raw material as nucleating agents in the supercritical carbon dioxide foaming process, and then the supercritical carbon dioxide treatment is carried out at a temperature of 35-70 DEG C and a pressure of 8-50 MPa for 0.5-3 h, the pressure is released after the reaction, and a porous bone tissue engineering scaffold is obtained, the pore size of the prepared scaffold is 239.2+ / -36.2 mu m, the pore size is large and the connection is obvious, but the compression process of the matrix in the second stage of the energy dissipation process is too small, the protection effect is limited, and a magnetic material is used;

[0005] The document (supercritical CO2 foaming method for preparing polycaprolactone tissue engineering scaffold) discloses that PCL rectangular sheets are placed in an autoclave for supercritical carbon dioxide treatment; a foaming process with controllable pore size in the range of 132-700 mu m is obtained, the cell diameter is too large, the wall thickness in unit volume is too small, the bearing capacity is slightly weak, and the foaming process is full sheet foaming, and the elastic modulus is low;

[0006] CN 114131824 A discloses a preparation process of a PE and EVA nitrogen foamed foam plate, which adopts nitrogen, carbon dioxide or mixed gas of the two to carry out supercritical treatment, but the polymer treated by the process belongs to high-temperature thermoplastic material, and the melt flow rate of the material used is quite different from that of PCL in the molten state. This property is closely related to the melt viscosity, and in the foaming process, the application amount of the supercritical fluid will further affect the viscosity of the matrix, thereby affecting the cell nucleation and solidification stability;

[0007] CN 116852744 A discloses an environmentally friendly physical foaming shoe pad and its manufacturing process, which is a mixed material of TPEE, TPU and PEBAX foamed by nitrogen and carbon dioxide, but its process is to mix nitrogen and carbon dioxide and pass in, and generally, carbon dioxide and nitrogen have differences in permeability coefficient and compatibility with polymers in different polymer matrices, so that the fluid concentration distribution is uneven, although the material can obtain better elasticity, but the cell distribution is extremely undesirable.

[0008] Therefore, it is important to determine the appropriate process selection according to the properties of the matrix.

[0009] In addition, the difficulty in preparing polycaprolactone (PCL) plate lies in the material itself, which has low melting point, poor melt strength, slow crystallization, resulting in narrow processing window, easy deformation and low yield; and the single PCL has insufficient mechanical properties and poor compatibility with materials such as PLA, which limits its application in high-strength fields. At present, although the irradiation cross-linking process can improve the performance, it has problems such as large dose requirement and easy to cause yellowing and odor. In addition, the plate also has the problem of difficult to balance toughness and strength. SUMMARY

[0010] [TECHNICAL PROBLEM]

[0011] The foaming effect of the foamed thermoplastic plate is not ideal, or additional additives are needed;

[0012] There are technical difficulties in preparing polycaprolactone (PCL) plate, it is difficult to balance toughness and strength, and the comfort is low.

[0013] [TECHNICAL SCHEME]

[0014] In order to solve the above problems, the present application uses polycaprolactone as the base material, and foams by the conversion of supercritical carbon dioxide and supercritical nitrogen, so that the prepared foamed material has uniform cells and certain strength. Moreover, the polycaprolactone matrix material is almost completely degradable; in the present application, no any doping filler is needed, so there will be no adverse reactions, and the application range is increased. In addition, the preparation process of the polycaprolactone plate is improved in the present application, so that the strength and toughness of the plate are much higher than those of the polycaprolactone plate on the market; it has more extensive application prospect.

[0015] Polycaprolactone is a low-temperature thermoplastic material, which has a low glass transition temperature and melt viscosity, and good fluidity; various properties enable the orthopedic temperature to be maintained at about 60℃, and the cell structure properties can still be maintained after multiple heat and cold cycles. Because the use of a single foaming agent cannot balance the relationship between the cell structure and the strength, the fluid infiltration is carried out in two stages during the foaming process, the gas nucleation sites are preferentially dispersed, and then nitrogen gas is used to generate fine bubbles to penetrate them, forming a microstructure with large dispersion and small aggregation, to ensure the balance between flexibility and rigidity of the overall material. Because the process from the formation of the cell to the solidification of the material takes a long time, the cell morphology has changed, affecting the mechanical properties, and the water cooling process is used to control the crystallization rate of the semi-finished product to control the mechanical properties of the matrix material and realize the stability of the cell. The change of temperature in this process greatly affects the polymer crystallization and chain strength, and then affects the inherent properties of the material. It is very important to fix the shape of the foamed product, and if the process is not reasonable, residual stress will be generated, causing the product to deform, be slightly damaged or even break.

[0016] The first object of the present application is to provide a method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0017] (1) first foaming the polycaprolactone plate with supercritical carbon dioxide at 40-100℃ and 4-10MPa for 0.05-1.5h; then foaming with supercritical nitrogen at 40-100℃ and 12-20MPa for 0.05-1.5h;

[0018] (2) after the foaming is completed, the foamed material is taken out, immersed in an ice water bath (cooling bath) at 0 to -5℃ for 1-5min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0019] In an embodiment of the present application, the polycaprolactone plate in step (1) is a pure polycaprolactone plate or a polycaprolactone plate containing additives, which can be purchased on the market or prepared by oneself.

[0020] In an embodiment of the present application, the thickness of the polycaprolactone plate in step (1) is 1-5mm.

[0021] In an embodiment of the present application, the polycaprolactone plate in step (1) is a low-temperature thermoplastic plate.

[0022] In an embodiment of the present application, the preparation method of the polycaprolactone plate in step (1) is as follows:

[0023] The PCL granules, modifier, TAIC, DCP (dicumyl peroxide) are mixed according to the mass ratio of 70-80:20-30:1-3:0.01-0.02, and then mixed in a mixer (110-130℃, 8-12min), and then melt-extruded in a double-screw extruder at 95-105℃ and 45-55rpm to obtain mixed granules, and then cooled to room temperature to obtain mixed granules;

[0024] The mixed granules are melt-extruded into a plate in a double-screw extruder at 140-150℃ and 15-25rpm to obtain a polycaprolactone plate.

[0025] The modifier is one or more of PCL-based TPU, SBS (styrene-butadiene-styrene block copolymer) and ENR (epoxidized natural rubber).

[0026] In an embodiment of the present application, the foaming in step (1) is carried out in a high-pressure reactor.

[0027] A second object of the present application is a foamed polycaprolactone plate prepared by the method of the present application.

[0028] In an embodiment of the present application, the foamed polycaprolactone plate has a cell size of 5-30 microns and a compressive strength of 20-2000kPa.

[0029] In an embodiment of the present application, the foamed polycaprolactone plate has a thickness of 2-8.5mm.

[0030] In an embodiment of the present application, the foamed polycaprolactone plate can be reused after soaking in hot water at 50-70℃.

[0031] A third object of the present application is to provide the use of the foamed polycaprolactone plate of the present application in sports protective products.

[0032] In an embodiment of the present application, the sports protective products include knee pads, wrist guards, elbow pads, ankle guards, arm guards, leg guards, etc.

[0033] A fourth object of the present application is to provide a method for toughening and modifying a foamed polycaprolactone plate, which uses the foamed polycaprolactone plate of the present application.

[0034] A fifth object of the present application is to provide a knee pad, which uses the foamed polycaprolactone plate of the present application.

[0035] [Advantages]

[0036] (1) The present application realizes the transition of the foaming agent during the foaming process, from supercritical carbon dioxide to supercritical nitrogen, and the supercritical carbon dioxide foaming has the characteristics of high nucleation density and high permeability, while the supercritical nitrogen foaming has fine pores but slow diffusion. The first stage uses carbon dioxide for rapid diffusion, and the second stage realizes fine pore formation, realizing the transition from a large number of pores to good pore morphology. The foamed polycaprolactone plate prepared by the present application has a finer surface, pore independence and dimensional stability.

[0037] (2) The foamed polycaprolactone plate of the present application benefits from the low melting point characteristics of polycaprolactone. The polycaprolactone plate has low-temperature plasticity, which can be repeatedly immersed in warm water to soften until the shape is satisfactory, and the composition of the thermoplastic plate can be adjusted to realize controllable softening temperature. After softening, the interface has adhesion, and seamless splicing of fragments can be realized.

[0038] (3) The present application can stably obtain a foamed polycaprolactone plate with a certain foaming ratio by adjusting the supercritical fluid saturation time and pressure holding time, and the process is mature and stable.

[0039] (4) The present application uses PCL granules, modifiers, TAIC (triallyl isocyanurate), and DCP (dicumyl peroxide) as raw materials to prepare a polycaprolactone plate, and then performs foaming treatment. The strength and toughness of the final plate are much higher than those of the polycaprolactone plates on the market, and it has a more extensive application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The microsectional view of the foamed polycaprolactone plate prepared in Example 1.

[0041] Figure 2 The apparent morphology diagram of the foamed polycaprolactone plate prepared in Example 1 after shape retention test.

[0042] Figure 3 The apparent morphology diagram of the foamed polycaprolactone plate prepared in Example 2 after shape retention test.

[0043] Figure 4 The apparent morphology diagram of the foamed polycaprolactone plate prepared in Example 3 after shape retention test.

[0044] Figure 5 The microsectional view of the foamed polycaprolactone plate prepared in Comparative Example 1.

[0045] Figure 6 The apparent morphology diagram of the foamed polycaprolactone plate prepared in Comparative Example 1 after shape retention test.

[0046] Figure 7 The apparent morphology diagram of the foamed polycaprolactone plate prepared in Comparative Example 2 after shape retention test.

[0047] Figure 8 The apparent morphology of the foamed polycaprolactone plate prepared for Comparative Example 3 after the shape retention test.

[0048] Figure 9 The apparent morphology of the foamed polycaprolactone plate prepared for Comparative Example 4 after the shape retention test.

[0049] Figure 10 The apparent morphology of the foamed polycaprolactone plate prepared for Comparative Example 6 after the shape retention test.

[0050] Figure 11 The apparent morphology of the foamed polycaprolactone plate prepared for Comparative Example 7 after the shape retention test. DETAILED DESCRIPTION

[0051] The following describes the preferred embodiments of the present application, and it should be understood that the embodiments are for better explaining the present application, and are not used to limit the present application.

[0052] Test method:

[0053] 1. Comfort test: mainly related to hardness and apparent density;

[0054] (1) Hardness:

[0055] Tested by a Shore hardness tester (LX-C) according to the test method of GB / T 531-1999.

[0056] Test the hardness value 6 times at different positions with a distance of at least 6 mm between the test points, and take the average value of the hardness test of different foam samples.

[0057] (2) Apparent density:

[0058] According to the test method of GB / T 6343-1995 for the determination of apparent (volume) density of foamed plastics and rubbers.

[0059] Cut the sample into a plane size of 2x2 cm, then accurately weigh the sample mass with an electronic balance, and the accuracy is required to be 0.0001 g, and the volume of the sample is measured by the needle pressure drainage method, and then the apparent density is calculated.

[0060] 2. Mechanical property test: mainly related to compression strength and static energy absorption;

[0061] Compression performance test:

[0062] In order to evaluate the static energy absorption effect of the sample, an electronic universal strength testing machine is used to test the stress-strain curve of the sample according to the method of GB / T 20467-2006, and the static energy absorption is calculated.

[0063] 3. Test of shape retention: mainly involving the apparent morphology after bending cycle and the change of density;

[0064] In the water bath in the material orthopedic temperature range, heat for 60 s, after taking out, 90° bending and cooling, after water bath, flat angle and cooling, after 10 cycles, the apparent morphology and the change of density are characterized.

[0065] The failure of the cells will cause the density to increase, and the performance can be directly determined by the density index. If the density increases more than 0.1000 g / cm 3 , it is considered to lose the shape retention property.

[0066] Raw materials used in the examples and comparative examples:

[0067] PCL plate: PCL low-temperature thermoplastic plate, commercially available, hardness 130, thickness 3.10 mm, density 1.2303 g / cm 3 .

[0068] PCL granules: PCL-6500; Hunan Juren New Material Co., Ltd.;

[0069] TAIC (triallyl isocyanurate): purity ≥98%; Shanghai Mai'er Biochemical Technology Co., Ltd.;

[0070] DCP (dicumyl peroxide): purity ≥98%; National Pharmaceutical Group Chemical Reagent Co., Ltd.;

[0071] PCL-based TPU: A290; Shandong Meirui New Material Co., Ltd.;

[0072] SBS (styrene-butadiene-styrene block copolymer): YH-791E, Sinopec Hunan Petrochemical Co., Ltd.;

[0073] ENR50 (epoxidized natural rubber): ENR50, Shandong Kaipuier Biological Technology Co., Ltd.;

[0074] The PCL granules need to be dried in a 60°C vacuum drying oven for 12 h before use.

[0075] Example 1

[0076] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0077] (1) Put the polycaprolactone low-temperature thermoplastic plate into the high-pressure reaction kettle, first use supercritical carbon dioxide to foam the polycaprolactone plate at 50°C and 8 MPa for 1.5 h; then use supercritical nitrogen at 50°C and 15 MPa for 1.5 h;

[0078] (2) After the foaming is finished, the foamed material is taken out, soaked in an ice water bath at 0°C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0079] The micro cross-section of the foamed polycaprolactone plate is as shown in Figure 1 It can be seen from Figure 1 that the internal microstructure is regular, the cell morphology is uniformly distributed, and has the characteristics of small dispersion and large aggregation.

[0080] The apparent morphology of the foamed polycaprolactone plate after the shape retention test is as shown in Figure 2 It can be seen from Figure 2 that the cell structure is retained after the shape retention test, and no severe coalescence phenomenon occurs, and the crease position has no obvious depression, which confirms that the reusability is high.

[0081] Example 2

[0082] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0083] (1) The polycaprolactone low-temperature thermoplastic plate is placed in a high-pressure reaction kettle, and supercritical carbon dioxide is used to foam the polycaprolactone plate at 100°C and 8MPa for 1.5h; then supercritical nitrogen is used to foam at 100°C and 15MPa for 1.5h;

[0084] (2) After the foaming is finished, the foamed material is taken out, soaked in an ice water bath at 0°C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0085] The apparent morphology of the foamed polycaprolactone plate after the shape retention test is as shown in Figure 3 .

[0086] It can be seen from Figure 3 that the surface presents a polymer mixed and adhered state after the shape retention test, which confirms that at a higher foaming temperature, the cell diameter becomes larger, resulting in the weakening of the wall structure, and the collapse degree is higher in a hot environment, and the increase in the density of the foamed polycaprolactone plate is more obvious.

[0087] Example 3

[0088] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0089] (1) The polycaprolactone low-temperature thermoplastic plate is placed in a high-pressure reaction kettle, and supercritical carbon dioxide is used to foam the polycaprolactone plate at 50°C and 4MPa for 1.5h; then supercritical nitrogen is used to foam at 100°C and 15MPa for 1.5h;

[0090] (2) After the foaming is completed, the foamed material is taken out, soaked in an ice water bath at 0 DEG C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0091] The apparent morphology of the foamed polycaprolactone plate after the shape retention test is shown in Figure 4 .

[0092] As can be seen from Figure 4 : the use of low front section pressure and high rear section temperature infiltration makes supercritical nitrogen gas occupy a more active position in the gas nucleation process, under which the number of small pores increases and the density slightly increases, the deformable space of the small pores is small in the shape retention test, and the degree of adhesion is intensified, so that certain creases are generated on the surface.

[0093] In the comparative example 1, only carbon dioxide is used

[0094] A method for preparing a supercritical fluid foamed polycaprolactone plate comprises the following steps:

[0095] (1) The polycaprolactone low-temperature thermoplastic plate is placed in a high-pressure reaction kettle, and supercritical carbon dioxide is used to foam the polycaprolactone plate at 50 DEG C and 8 MPa for 3 h;

[0096] (2) After the foaming is completed, the foamed material is taken out, soaked in an ice water bath at 0 DEG C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0097] The micro cross-section of the foamed polycaprolactone plate is shown in Figure 5 . As can be seen from Figure 5 : the use of only carbon dioxide for foaming makes the pore size stable and increases, the pore uniformity is high but does not have a small dispersed structure, and thus the support is slightly weak.

[0098] The apparent morphology of the foamed polycaprolactone plate after the shape retention test is shown in Figure 6 . As can be seen from Figure 6 : the pore collapse density increases obviously after the shape retention test, and transverse creases are formed on the surface, and mechanical performance recess points are generated at the positions.

[0099] In the comparative example 2, only nitrogen is used

[0100] A method for preparing a supercritical fluid foamed polycaprolactone plate comprises the following steps:

[0101] (1) The polycaprolactone low-temperature thermoplastic plate is placed in a high-pressure reaction kettle, and supercritical nitrogen is used to foam the polycaprolactone plate at 50 DEG C and 15 MPa for 3 h;

[0102] (2) After the foaming is completed, the foamed material is taken out, soaked in an ice water bath at 0 DEG C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0103] The apparent morphology of the foamed polycaprolactone plate after shape retention test is shown in Figure 2. Figure 7 .

[0104] From the above, it can be seen that foaming with nitrogen alone produces finer cells, and the intuitive performance is that the cell size is significantly reduced, the hardness and density are increased, which is not consistent with the softness of the protective material. Figure 7 Example 3 uses a mixture of nitrogen and carbon dioxide

[0105] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0106] (1) Put the polycaprolactone low-temperature thermoplastic plate into the high-pressure reaction kettle, and use supercritical nitrogen and carbon dioxide mixed gas (volume ratio 1:1) to foam the polycaprolactone plate at 50℃, 15MPa for 3h;

[0107] (2) After the foaming is completed, the foamed material is taken out, soaked in an ice water bath at 0℃ for 2min, taken out, dried, and the foamed polycaprolactone plate is obtained.

[0108] The apparent morphology of the foamed polycaprolactone plate after shape retention test is shown in Figure 2.

[0109] . Figure 8

[0110] From the above, it can be seen that when the two gases are mixed and introduced, due to the compatibility with the polymer and the solubility, when one medium reaches the standard critical state, the other medium tends to lose part of the supercritical properties, causing uneven dissolution and dispersion, affecting the cell structure. Figure 8 Example 4 does not perform water bath treatment

[0111] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0112] (1) Put the polycaprolactone low-temperature thermoplastic plate into the high-pressure reaction kettle, first use supercritical carbon dioxide to foam the polycaprolactone plate at 50℃, 8MPa for 1.5h; then use supercritical nitrogen to foam at 50℃, 15MPa for 1.5h;

[0113] (2) After the foaming is completed, the foamed material is taken out, cooled at room temperature, and the foamed polycaprolactone plate is obtained.

[0114] The apparent morphology of the foamed polycaprolactone plate after shape retention test is shown in Figure 2.

[0115] . Figure 9

[0116] From the above, it can be seen that when the two gases are mixed and introduced, due to the compatibility with the polymer and the solubility, when one medium reaches the standard critical state, the other medium tends to lose part of the supercritical properties, causing uneven dissolution and dispersion, affecting the cell structure. Figure 9 ​​It can be seen that if the base temperature cannot be cooled in a short time, the base will be softened and failed due to gravity for a long time in the orthopedic temperature range, which is particularly obvious in summer. At this time, the large cells will be soft and sticky to form small cells, resulting in increased density and hardness.

[0117] Comparative Example 5: water bath temperature is too low

[0118] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0119] (1) Put the polycaprolactone low-temperature thermoplastic plate into the high-pressure reaction kettle, first use supercritical carbon dioxide to foam the polycaprolactone plate at 50℃, 8MPa for 1.5h; then use supercritical nitrogen to foam at 50℃, 15MPa for 1.5h;

[0120] (2) After foaming, take out the foamed material, soak in a cooling bath at -20℃ for 2min, take out and dry to obtain the foamed polycaprolactone plate.

[0121] It is found that the microstructure of the prepared foamed polycaprolactone plate has obvious cracks, and the sample is severely warped.

[0122] Comparative Example 6: pressure selection is not appropriate

[0123] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0124] (1) Put the polycaprolactone low-temperature thermoplastic plate into the high-pressure reaction kettle, first use supercritical carbon dioxide to foam the polycaprolactone plate at 50℃, 15MPa for 1.5h; then use supercritical nitrogen to foam at 50℃, 25MPa for 1.5h;

[0125] (2) After foaming, take out the foamed material, soak in an ice water bath at 0℃ for 2min, take out and dry to obtain the foamed polycaprolactone plate.

[0126] The apparent morphology diagram of the foamed polycaprolactone plate after shape retention test is as Figure 10 .

[0127] From Figure 10 It can be seen that the pressure will affect the supercritical fluid infiltration effect and nucleation rule, and after high pressure and pressure relief, larger cell size will be formed, with extremely low hardness, which means that the cell supportability is the weakest. After shape retention test, the adhesion is heavy and deep creases are produced, affecting the mechanical property balance.

[0128] Comparative Example 7: pressure selection is not appropriate

[0129] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0130] (1) Place the polycaprolactone low-temperature thermoplastic sheet into a high-pressure reactor. First, use supercritical carbon dioxide to foam the polycaprolactone sheet at 50℃ and 2MPa for 1.5h; then use supercritical nitrogen to foam it at 50℃ and 10MPa for 1.5h.

[0131] (2) After foaming, the foamed material is taken out and soaked in an ice water bath at 0°C for 2 minutes. Then it is taken out and dried to obtain foamed polycaprolactone board.

[0132] The appearance morphology of expanded polycaprolactone sheets after shape retention testing is shown in the figure below. Figure 11 .

[0133] from Figure 11 It can be seen that when the pressure is not appropriate, the foaming agent is difficult to reach the supercritical state, the degree of wetting is insufficient, and the foaming is not sufficient; after the shape retention test, the outer foam cells are compacted, close to the state of the unfoamed board.

[0134] The foamed materials prepared in Examples 1-3 and Comparative Examples 1-7 were subjected to performance tests, and the test results are shown in Table 1 below:

[0135] Table 1

[0136]

[0137] Example 4

[0138] A method for preparing supercritical fluid foamed polycaprolactone sheets includes the following steps:

[0139] (1) Place the polycaprolactone low-temperature thermoplastic sheet into a high-pressure reactor. First, use supercritical carbon dioxide to foam the polycaprolactone sheet at 50℃ and 8MPa for 5 minutes; then use supercritical nitrogen to foam it at 50℃ and 15MPa for 10 minutes.

[0140] (2) After foaming, the foamed material is taken out and soaked in an ice water bath at 0°C for 2 minutes. Then it is taken out and dried to obtain foamed polycaprolactone board.

[0141] Example 5

[0142] A method for preparing supercritical fluid foamed polycaprolactone sheets includes the following steps:

[0143] (1) Place the polycaprolactone low-temperature thermoplastic sheet into a high-pressure reactor. First, use supercritical carbon dioxide to foam the polycaprolactone sheet at 50℃ and 10MPa for 10min; then use supercritical nitrogen to foam it at 50℃ and 18MPa for 10min.

[0144] (2) After the foaming is completed, the foamed material is taken out, soaked in an ice water bath at 0°C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0145] The obtained plate is subjected to performance testing, and the test results are as follows:

[0146] Table 2

[0147]

[0148] Example 6

[0149] A method for preparing a supercritical fluid foamed polycaprolactone plate comprises the following steps:

[0150] (1) PCL granules, PCL-based TPU, TAIC, and DCP are mixed (120°C, 10 min) at a mass ratio of 80:20:2:0.01, and then melt-extruded into granules in a double-screw extruder at 100°C and 50 rpm, and cooled to room temperature to obtain mixed granules; the mixed granules are melt-extruded into a plate in a double-screw extruder at 145°C and 20 rpm to obtain a polycaprolactone plate.

[0151] (2) The polycaprolactone low-temperature thermoplastic plate is placed in a high-pressure reaction kettle, supercritical carbon dioxide is used to foam the polycaprolactone plate at 50°C and 8 MPa for 5 min, and then supercritical nitrogen is used to foam the polycaprolactone plate at 50°C and 15 MPa for 10 min.

[0152] (3) After the foaming is completed, the foamed material is taken out, soaked in an ice water bath at 0°C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0153] Example 7

[0154] A method for preparing a supercritical fluid foamed polycaprolactone plate comprises the following steps:

[0155] (1) PCL granules, SBS (styrene-butadiene-styrene block copolymer), TAIC, and DCP are mixed (180°C, 5 min) at a mass ratio of 70:30:3:0.01, and then melt-extruded into granules in a double-screw extruder at 180°C and 50 rpm, and cooled to room temperature to obtain mixed granules; the mixed granules are melt-extruded into a plate in a double-screw extruder at 180°C and 20 rpm to obtain a polycaprolactone plate.

[0156] (2) The polycaprolactone low-temperature thermoplastic plate is placed in a high-pressure reaction kettle, supercritical carbon dioxide is used to foam the polycaprolactone plate at 50°C and 8 MPa for 5 min, and then supercritical nitrogen is used to foam the polycaprolactone plate at 50°C and 15 MPa for 10 min.

[0157] (3) After the foaming is completed, the foamed material is taken out, soaked in an ice water bath at 0°C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0158] Example 8

[0159] A method for preparing a supercritical fluid foamed polycaprolactone plate, comprising the following steps:

[0160] (1) PCL granules, ENR50 (epoxidized natural rubber), TAIC, and DCP are mixed according to a mass ratio of 75:25:1:0.01 (120°C, 10 min), and then granulated by melt extrusion in a double-screw extruder at 100°C and 50 rpm, and cooled to room temperature to obtain mixed granules; the mixed granules are melt extruded into a plate in a double-screw extruder at 145°C and 20 rpm to obtain a polycaprolactone plate;

[0161] (2) The polycaprolactone low-temperature thermoplastic plate is placed in a high-pressure reaction kettle, and supercritical carbon dioxide is used to foam the polycaprolactone plate at 50°C and 8 MPa for 5 min; and then supercritical nitrogen is used to foam at 50°C and 15 MPa for 10 min;

[0162] (3) After the foaming is completed, the foamed material is taken out, soaked in an ice water bath at 0°C for 2 min, taken out, dried, and a foamed polycaprolactone plate is obtained.

[0163] Comparative Example 8

[0164] The mixing in Example 6 is omitted, and the other conditions are the same as in Example 6.

[0165] Comparative Example 9

[0166] TAIC in Example 6 is omitted, and the other conditions are the same as in Example 6.

[0167] Comparative Example 10

[0168] PCL-based TPU in Example 6 is omitted, and the other conditions are the same as in Example 6.

[0169] Comparative Example 11

[0170] TAIC in Example 6 is replaced by TMPTA (trimethylolpropane trimethacrylate), and the other conditions are the same as in Example 6.

[0171] The obtained plate is subjected to performance testing, and the test results are as follows:

[0172] Table 3

[0173]

[0174] Although the present application has been disclosed in its preferred embodiments with reference to the accompanying drawings, it is not intended to limit the present application thereto, and various modifications and alterations can be made thereto by those skilled in the art without departing from the spirit and scope of the present application, and the scope of protection of the present application should be defined by the appended claims.

Claims

1. A method of making a supercritical fluid-foamed polycaprolactone board, characterized by, It comprises the following steps: (1) first using supercritical carbon dioxide for polycaprolactone plate in 40-100 ℃, 4-10 MPa foaming 0.05-1.5 h; then using supercritical nitrogen in 40-100 ℃, 12-20 MPa foaming 0.05-1.5 h; (2) after foaming, the foaming material is taken out, immersed in a cooling bath at 0-5 ℃ for 1-5 min, taken out, dried, and the foamed polycaprolactone plate is obtained.

2. The method of claim 1, wherein, The polycaprolactone plate in step (1) is a pure polycaprolactone plate or a polycaprolactone plate containing additives.

3. The method of claim 1, wherein, The preparation method of the polycaprolactone plate in step (1) is as follows: The PCL granules, modifier, triallyl isocyanurate TAIC, and dicumyl peroxide DCP are mixed in a mass ratio of 70-80:20-30:1-3:0.01-0.02, and then subjected to mixing at 110-130 ℃ for 8-12 min. After that, the mixture is subjected to melt extrusion granulation in a twin-screw extruder at 95-105 ℃ and 45-55 rpm, and then cooled to room temperature to obtain a mixed granule. The mixed granule is subjected to melt extrusion in a twin-screw extruder at 140-150 ℃ and 15-25 rpm to obtain a polycaprolactone plate. The modifier is one or more of PCL-based TPU, styrene-butadiene-styrene block copolymer SBS, and epoxidized natural rubber ENR.

4. A foamed polycaprolactone board material, characterized by, The foamed polycaprolactone plate is prepared by any one of the methods of claims 1-3.

5. The foamed polycaprolactone board according to claim 4, characterized in that, The cell size of the foamed polycaprolactone plate is 5-30 microns, and the compressive strength is 20-2000 kPa.

6. The foamed polycaprolactone board according to claim 4, characterized in that, The thickness of the foamed polycaprolactone plate is 2-8.5 mm.

7. The foamed polycaprolactone panel according to any one of claims 4 to 6, characterized in that, The foamed polycaprolactone plate can be reused after being soaked in hot water at 50-70 ℃.

8. The foamed polycaprolactone plate of any one of claims 4-7 is used in sports protective equipment.

9. A method of toughening a polycaprolactone foamed sheet, characterized by, The foamed polycaprolactone plate of any one of claims 4-7 is used.

10. A knee guard characterized in that, The method uses the foamed polycaprolactone plate of any one of claims 4-7.

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