Foaming material containing regenerated EVA (Ethylene Vinyl Acetate) and preparation method thereof

Abstract

The invention discloses a foam material containing regenerated EVA and a preparation method thereof.The foam material comprises EVA, modified waste EVA, inorganic filler, a cross-linking agent and an antioxidant, the waste EVA is decrosslinked and then sequentially reacts with hydroxyl-terminated polydimethylsiloxane and boric acid, and the modified waste EVA is obtained. The foaming material is foamed by adopting supercritical carbon dioxide fluid. In the foaming material, the compatibility of the waste EVA and the EVA material is excellent, hydroxyl groups on the surface of the modified waste EVA interact with active groups on the surface of the inorganic filler, the modified waste EVA is uniformly dispersed in the foaming material, the inorganic filler serves as a heterogeneous nucleation site, and a carbon dioxide fluid forms uniform and fine foam holes in the foaming material. The foaming material has moderate hardness, excellent tear resistance and rebound resilience, low permanent compression deformation rate and long service life.

Description

Technical Field

[0001] The present invention relates to the technical field of foam molding, and more specifically, it relates to a foam material containing recycled EVA and a preparation method thereof. Background Art

[0002] EVA is a random copolymer of ethylene and vinyl acetate. Due to the introduction of polar acetate groups in the ethylene chain segment, short branched chains are formed, changing the original crystalline state, making EVA more flexible and elastic. Therefore, EVA materials are widely used in many fields such as foamed shoe materials, adhesive films, wire and cable, and adhesives. With the increasing annual consumption of EVA, a large amount of crosslinked and foamed waste EVA is generated, which has a bad impact on the ecological environment. Therefore, the method of recycling waste EVA in this field has become a research hotspot.

[0003] In related technologies, waste EVA generally needs to be de-crosslinked before it can be recycled. After de-crosslinking treatment, the macromolecular chains of waste EVA break, generating new active groups. However, compared with EVA raw materials, the content of active groups in EVA after de-crosslinking treatment is significantly reduced. The strength of the foam material added with recycled EVA is reduced, and the foaming effect is poor. Summary of the Invention

[0004] In order to improve the problem of insufficient strength of the foam material made of recycled EVA, the present application provides a foam material containing recycled EVA and a preparation method thereof. The foam material has a moderate hardness, dense pores, and has a light weight characteristic.

[0005] In the first aspect, the present application provides a foam material containing recycled EVA, and the following technical solution is adopted:

[0006] A foam material containing recycled EVA, calculated by weight, includes the following components:

[0007] 100 parts of EVA, 120 - 145 parts of modified waste EVA, 18 - 36 parts of inorganic filler, 1 - 5 parts of crosslinking agent, and 5 - 10 parts of antioxidant;

[0008] The modified waste EVA is processed according to the following steps:

[0009] After the waste EVA is subjected to impurity removal treatment, it is subjected to kneading treatment. The temperature of the kneading treatment is 160 - 180 °C, and the time of the kneading treatment is 15 - 30 min to obtain de-crosslinked EVA powder;

[0010] The crosslinked EVA powder is put into the hydroxyl-terminated polydimethylsiloxane, first kneaded and dispersed, and then boric acid is added. Among them, the weight ratio of the crosslinked EVA powder, hydroxyl-terminated polydimethylsiloxane and boric acid is 100:(25-92):(0.80-2.94). The temperature is raised to 170-200 °C and kept warm for reaction for 1-3 h. After the reaction is completed, grinding and pulverization are carried out to obtain the modified waste EVA;

[0011] The foaming material is foamed by using supercritical carbon dioxide fluid.

[0012] By adopting the above technical scheme, the modified waste EVA is mechanically kneaded and crosslinked during the mechanical kneading process, and the degree of crosslinking of the waste EVA is controlled. A moderate amount of active functional groups can be generated on the surface of the waste EVA, which is beneficial to grafting modified substances on the surface of the waste EVA; at the same time, the waste EVA material can maintain a relatively high molecular weight, which is beneficial to maintaining relatively high mechanical properties of the later foaming material. The active groups on the surface of the waste EVA combine with the hydroxyl groups of the hydroxyl-terminated polydimethylsiloxane, and the other hydroxyl group of the hydroxyl-terminated polydimethylsiloxane can directly condense with boric acid, introducing Si-O-B segments on the surface of the waste EVA, and active hydroxyl groups still remain on the surface of the waste EVA.

[0013] By controlling the ratio of the waste EVA to the hydroxyl-terminated polydimethylsiloxane and boric acid, the modified waste EVA has the same chain segments as EVA. Therefore, the compatibility between the modified waste EVA and EVA is excellent, and the Si-O-B segments can be stably dispersed in the foaming material and are not easily migrated to the surface of the foaming material.

[0014] The inorganic filler can make up for the strength loss during the crosslinking process of the modified waste EVA. At the same time, the active groups on the surface of the inorganic filler can interact with the modified waste EVA through hydrogen bonds, van der Waals forces, etc., and are fully dispersed in the foaming material with the modified waste EVA, reducing the possibility of local stress increase and toughness reduction caused by insufficient dispersion of the inorganic filler.

[0015] Moreover, by using crosslinking agents and antioxidants, the crosslinking density between the components of the foaming material is increased, making up for the breakage of the molecular chains of the crosslinked EVA, thereby improving the overall hardness, tear strength and stability of the foaming material.

[0016] Further, in the preparation method of the modified waste EVA, the weight ratio of the crosslinked EVA powder, hydroxyl-terminated polydimethylsiloxane and boric acid is 100:(30-50):(0.96-1.60).

[0017] By adopting the above technical solutions, the ratio among the hydroxyl-terminated polydimethylsiloxane, boric acid and the crosslinking-decoupled EVA powder is optimized, and the content of Si-O-B chain segments on the surface of the crosslinking-decoupled EVA powder is moderate. It is easy for boron and oxygen atoms to interact with each other to form an electron bridge bond that can be instantaneously connected. Under the action of an instantaneous strong external force, the relaxation time of the electron bridge bond is long, which can adsorb polymer chains and hinder the movement of other chain segments, thereby withstanding the impact of the instantaneous strong external force. Therefore, on the premise of having little influence on the flowability of the modified waste EVA, the toughness and permanent compression set rate of the foaming material can be significantly improved.

[0018] Further, the hydroxyl content of the hydroxyl-terminated polydimethylsiloxane is 1.5-4.0%.

[0019] Further, the viscosity of the hydroxyl-terminated polydimethylsiloxane is 30-65 cst.

[0020] By adopting the above technical solutions, the hydroxyl and viscosity of the hydroxyl-terminated polydimethylsiloxane are controlled within a moderate range. The hydroxyl-terminated polydimethylsiloxane has good fluidity and can be in full contact with the crosslinking-decoupled EVA powder, so that it can adhere to the surface of the crosslinking-decoupled EVA powder to complete the modification; and the hydroxyl content increases the content of Si-O-B chain segments on the surface of the modified waste EVA. On the premise of ensuring excellent compatibility between the modified waste EVA and EVA, the overall toughness and permanent compression set rate of the foaming material are further improved.

[0021] Further, the temperature of the kneading treatment is 175 °C and the time of the kneading treatment is 20 min.

[0022] By adopting the above technical solutions, the temperature and time of the kneading treatment are controlled, so as to control the particle size morphology and strength of the crosslinking-decoupled EVA, so as to ensure that the strength of the crosslinking-decoupled EVA powder does not decrease significantly on the premise of generating more active functional groups on the EVA surface.

[0023] Further, the hydroxyl-terminated polydimethylsiloxane is a hydroxyl-terminated dimethyl-methyl vinyl polysiloxane copolymer.

[0024] Further, the VA content of the EVA is 14-18%.

[0025] By adopting the above technical solution, the VA content of EVA is controlled within a moderate range. VA contains vinyl groups. At the same time, the hydroxyl-terminated dimethyl-methylvinyl polysiloxane copolymer also contains vinyl groups. Under the action of the crosslinking agent, partial crosslinking occurs between the vinyl groups, increasing the crosslinking density of the foaming material, thereby increasing the storage modulus of the foaming material and improving the foaming performance of the foaming material. At the same time, the hardness of the foaming material is moderate. However, when the crosslinking density is too high, it is easy to cause a decrease in the toughness of the foaming material and a deterioration in the resilience performance. When the VA content is low, the crystallinity of EVA is high, the toughness of the foaming material decreases, and the tear resistance performance deteriorates.

[0026] Further, the inorganic filler is one or more of light calcium carbonate, silica, and talcum powder.

[0027] Still further, the inorganic filler is silica.

[0028] Further, the crosslinking agent is one or more of dicumyl peroxide, tert-butyl peroxy (2-ethylhexyl) carbonate, and triallyl isocyanurate.

[0029] Further, the antioxidant is a hindered phenol antioxidant.

[0030] Further, the size of the inorganic filler is 0.5 - 1 μm.

[0031] By adopting the above technical solution, the size and particle diameter of the inorganic filler are controlled. Since the inorganic filler forms a heterogeneous system with the EVA melt, based on the nucleation theory of supercritical carbon dioxide fluid, the inorganic filler can serve as a nucleation site to initiate heterogeneous nucleation, which helps to increase the number of cells inside the foaming material and simultaneously refine the cell size, endowing the foaming material with excellent resilience performance.

[0032] In a second aspect, the present application provides a method for preparing a foaming material containing recycled EVA, adopting the following technical solution:

[0033] A method for preparing a foaming material containing recycled EVA includes the following steps:

[0034] Weigh EVA, modified waste EVA, inorganic filler, crosslinking agent, and antioxidant according to parts by weight, put them into a mixer for mixing, and obtain a foaming matrix after mixing is completed;

[0035] Place the foaming matrix in a foaming kettle, introduce supercritical carbon dioxide fluid for foaming, and obtain a foaming material containing recycled EVA. Specific Embodiments

[0036] Unless otherwise specified, the sources of the raw materials involved in the following preparation examples, examples, and comparative examples are as follows:

[0037] Hydroxyl-terminated polydimethylsiloxane: sourced from Sisebo Silicone; grade:

[0038] OF0025, viscosity (25°C) 25 cst, hydroxyl content 8.5%;

[0039] OF6050, viscosity (25°C) 30 cst, hydroxyl content 4.0%, vinyl content 4.5%;

[0040] OF0156A, viscosity (25°C) 65 cst, hydroxyl content 1.5%;

[0041] OF0156B, viscosity (25°C) 100 cst, hydroxyl content 0.8%;

[0042] Boric acid: analytical pure;

[0043] EVA: grade:

[0044] EVA5-2, VA content 5%, sourced from Beijing Organic;

[0045] EVA 560, VA content 14%, sourced from Mitsui Polymerization;

[0046] EVA 470, VA content 18%, sourced from DowDuPont;

[0047] EVA 265, VA content 28%, sourced from DowDuPont;

[0048] Waste EVA, sourced from the midsole of waste shoes.

[0049] Preparation examples of modified waste EVA

[0050] Preparation example a

[0051] Modified waste EVA is obtained as follows:

[0052] The waste EVA is cleaned, dried after cleaning, cut into particles with a particle size of 1 - 5 mm, and the cut waste EVA is placed in a mixer. The rotor speed of the mixer is controlled at 30 r / min, and it is crosslinked at 180°C for 15 min to obtain crosslinked EVA powder;

[0053] Preheat the mixer to 80°C, blend the crosslinked EVA powder with hydroxyl-terminated polydimethylsiloxane OF0025, put it into the mixer for kneading and dispersion, raise the temperature in the mixer to 140°C, and then add boric acid. Among them, the crosslinked EVA powder, hydroxyl-terminated polydimethylsiloxane The weight ratio of OF0025 to boric acid is 100:25:0.8; after sealing, the temperature in the internal mixer is raised to 180 °C, and the reaction is carried out under insulation for 2 h. After the insulation reaction is completed, grinding and pulverization are carried out to obtain modified waste EVA with a particle size of 1-10 μm.

[0054] Preparation Examples b-e

[0055] The modified waste EVA, the difference from Preparation Example a lies in: the crosslinking-degraded EVA powder, the hydroxyl-terminated polydimethylsiloxane The weight ratio of OF0025 to boric acid is different, specifically as follows:

[0056] In Preparation Example b, the crosslinking-degraded EVA powder, the hydroxyl-terminated polydimethylsiloxane The weight ratio of OF0025 to boric acid is 100:30:0.96;

[0057] In Preparation Example c, the crosslinking-degraded EVA powder, the hydroxyl-terminated polydimethylsiloxane The weight ratio of OF0025 to boric acid is 100:40:1.28;

[0058] In Preparation Example d, the crosslinking-degraded EVA powder, the hydroxyl-terminated polydimethylsiloxane The weight ratio of OF0025 to boric acid is 100:50:1.60;

[0059] In Preparation Example e, the crosslinking-degraded EVA powder, the hydroxyl-terminated polydimethylsiloxane The weight ratio of OF0025 to boric acid is 100:92:2.94.

[0060] Preparation Examples f-h

[0061] The modified waste EVA, the difference from Preparation Example c lies in: the hydroxyl content and viscosity of the hydroxyl-terminated polydimethylsiloxane are different, specifically as follows:

[0062] In Preparation Example f, use the same weight parts of OF6050 etc. to replace OF0025;

[0063] In Preparation Example g, use the same weight parts of OF0156A etc. to replace OF0025;

[0064] In Preparation Example h, use the same weight parts of OF0156B etc. to replace OF0025.

[0065] Preparation Examples i-j

[0066] Modified waste EVA, different from Preparation Example f in that the parameters of the kneading treatment are different, specifically as follows:

[0067] In Preparation Example i, the temperature of the kneading treatment of the waste EVA is 175 °C, and the kneading treatment time is 20 min;

[0068] In Preparation Example j, the temperature of the kneading treatment of the waste EVA is 160 °C, and the kneading treatment time is 30 min.

[0069] Preparation Examples k-l

[0070] Modified waste EVA, different from Preparation Example i in that the kneading reaction parameters are different, specifically as follows:

[0071] In Preparation Example k, after sealing, the temperature in the kneader is raised to 170 °C and kept for reaction for 3 h;

[0072] In Preparation Example l, after sealing, the temperature in the kneader is raised to 200 °C and kept for reaction for 1 h.

[0073] Comparative Preparation Example 1

[0074] The modified waste EVA is prepared as follows:

[0075] The waste EVA is washed, dried after washing, the waste EVA is cut into a particle size of 1-5 mm, the cut waste EVA is placed in a kneader, the rotor speed of the kneader is controlled at 30 r / min, and it is crosslinked at 180 °C for 15 min to obtain crosslinked EVA powder;

[0076] Preheat the kneader to 80 °C, blend the crosslinked EVA powder with hydroxyl-terminated polydimethylsiloxane OF0025, put it into the kneader for kneading and dispersion. Among them, the weight ratio of the crosslinked EVA powder to hydroxyl-terminated polydimethylsiloxane OF0025 is 100:25; after sealing, the temperature in the kneader is raised to 180 °C and kept for reaction for 2 h. After the heat preservation reaction is completed, it is ground and pulverized into modified waste EVA with a particle size of 1-10 μm.

[0077] Example

[0078] Example 1

[0079] A foamed material containing recycled EVA is prepared according to the following steps:

[0080] Weigh according to parts by weight: 100 parts of EVA, 120 parts of modified waste EVA, 18 parts of inorganic filler calcium bicarbonate, 1 part of crosslinking agent dicumyl peroxide, and 5 parts of antioxidant KY-1010;

[0081] Among them, the grade of EVA is EVA5-2, and the VA content is 5%;

[0082] The modified waste EVA is from Preparation Example a;

[0083] The particle size of calcium bicarbonate is 10-20 μm;

[0084] Put EVA, modified waste EVA, calcium bicarbonate, cross-linking agent and antioxidant into a mixer for mixing. After mixing, pour it into a mold and cool to obtain a foamed matrix;

[0085] Place the foamed matrix in a foaming kettle, introduce supercritical carbon dioxide fluid for foaming, and control the infiltration pressure of the supercritical carbon dioxide fluid to be 8 MPa and the infiltration time to be 10 h to obtain a foamed material containing recycled EVA.

[0086] Examples 2-12

[0087] A foamed material containing recycled EVA, which is different from Example 1 in the source of the modified waste EVA. Specifically, see Table 1:

[0088] Table 1. Sources of Modified Waste EVA

[0089] Example Source of Modified Waste EVA Example Source of Modified Waste EVA Example 1 Preparation Example a Example 7 Preparation Example g Example 2 Preparation Example b Example 8 Preparation Example h Example 3 Preparation Example c Example 9 Preparation Example i Example 4 Preparation Example d Example 10 Preparation Example j Example 5 Preparation Example e Example 11 Preparation Example k Example 6 Preparation Example f Example 12 Preparation Example l

[0090] Examples 13-15

[0091] A foamed material containing recycled EVA, which is different from Example 9 in the VA content in EVA. Specifically, as follows:

[0092] In Example 13, an equal weight of EVA 560 was used to replace EVA5-2;

[0093] In Example 14, an equal weight of EVA 470 was used to replace EVA5-2;

[0094] In Example 15, an equal weight of EVA 265 was used to replace EVA5-2.

[0095] Examples 16-17

[0096] A foamed material containing recycled EVA, which is different from Example 14 in the particle size of the inorganic filler. Specifically, as follows:

[0097] In Example 16, an equal weight of calcium bicarbonate with a particle size of 0.5-1 μm was used to replace calcium bicarbonate with a particle size of 10-20 μm;

[0098] In Example 17, an equal weight of calcium bicarbonate with a particle size of 0.01-0.5 μm was used to replace calcium bicarbonate with a particle size of 10-20 μm.

[0099] Example 18

[0100] A foamed material containing recycled EVA, which is different from Example 16 in the type of inorganic filler, specifically as follows:

[0101] In this example, silica with a particle size of 0.5 - 1 μm is used to replace calcium bicarbonate with a particle size of 0.5 - 1 μm in equal weight parts.

[0102] Examples 19 - 20

[0103] A foamed material containing recycled EVA, which is different from Example 18 in the weight parts of each component, specifically as follows:

[0104] In Example 19, by weight: 100 parts of EVA, 130 parts of modified waste EVA, 27 parts of inorganic filler silica, 3 parts of cross - linker dicumyl peroxide, and 8 parts of antioxidant KY - 1010 are weighed;

[0105] Among them, the grade of EVA is EVA 470, and the VA content is 18%;

[0106] The modified waste EVA is from Preparation Example i;

[0107] The size of the silica is 0.5 - 1 μm;

[0108] In Example 20, by weight: 100 parts of EVA, 145 parts of modified waste EVA, 36 parts of inorganic filler silica, 5 parts of cross - linker dicumyl peroxide, and 10 parts of antioxidant KY - 1010 are weighed;

[0109] Among them, the grade of EVA is EVA 470, and the VA content is 18%;

[0110] The modified waste EVA is from Preparation Example i;

[0111] The size of the silica is 0.5 - 1 μm.

[0112] Comparative Example

[0113] Comparative Example 1

[0114] A foamed material containing recycled EVA, which is different from Example 1 in that cross - linked EVA powder is used to replace the modified waste EVA made from Preparation Example a in equal weight parts.

[0115] Comparative Example 2

[0116] A foamed material containing recycled EVA, which is different from Example 1 in that the modified waste EVA made from Comparative Preparation Example 1 is used to replace the modified waste EVA made from Preparation Example a in equal weight parts.

[0117] Performance detection

[0118] The test samples with dimensions of 10 cm × 10 cm × 10 cm were prepared from Examples 1-20 and Comparative Examples 1-2.

[0119] 1. Hardness: Place the test sample under a Shore (Type C) durometer, take three points as measurement points, apply a pressure of 9.8 N, record the hardness value after stabilizing for 3 s, and then take the average value.

[0120] 2. Tear strength: Change the size of the test sample to 10 cm × 2 cm × 2 cm, make a cut 2 cm deep at the middle position of the test sample, fix both ends of the test sample on an electronic universal material testing machine, start the test, with the unit of N / cm; the higher the tear strength, the less likely the foam material is to break, indicating excellent toughness and durability.

[0121] 3. Rebound rate: Lift the drop hammer to the highest position of the device, then place the test sample at the center of the cross at the bottom of the vertical elasticity tester. The drop hammer makes a free fall. Discard the first 3 values, record the rebound heights of the 4th, 5th, and 6th times, and take the average value H 1 ; Rebound rate = H 1 / H 0 × 100%, H 0 is the initial height of the test sample, with the unit of %; the higher the rebound rate, the better the rebound performance of the foam material.

[0122] 4. Permanent compression set rate: Record the initial thickness D 0 of the test sample. Use a mold to compress the test sample to a thickness of 5 cm. Set the temperature of the constant temperature oven to 50 °C. Place the test sample in the oven for 6 h, take it out and cool for 0.5 h, and demold and record the thickness D 1 at this time. The permanent compression set rate = (D 0 - D 1 ) / D 0 × 100%, with the unit of %; the lower the permanent compression set rate, the better the service durability of the foam material.

[0123] 5. Density: Use a densitometer to calculate the density of the test sample. After measuring 3 times repeatedly, take the average value, with the unit: g / cm 3 .

[0124] Table 2. Performance detection data of Examples 1-20 and Comparative Examples 1-2

[0125]

[0126]

[0127] Conclusion

[0128] It can be seen from the test data that:

[0129] First, Example 1 and Comparative Example 1 form a single comparison. In Comparative Example 1, the crosslinked EVA after crosslinking removal is directly added. The strength of Comparative Example 1 is only 43.64, the tear strength is reduced to 17.61 N / cm, the resilience rate is only 74.54%, and the permanent compression set rate is as high as 32.9%. It can be seen that: only through the crosslinking removal treatment of waste EVA, the macromolecular chain segments are degraded, and the mechanical properties become worse, resulting in insufficient strength, poor toughness, insufficient resilience performance and a decrease in the resilience rate when subjected to external force compression; after being subjected to multiple external force extrusions, the permanent compression set rate increases.

[0130] Second, Example 1 and Comparative Example 2 form a single comparison. In Comparative Example 2, the modified waste EVA after being modified with hydroxyl-terminated polydimethylsiloxane is added. The modified waste EVA lacks boric acid modification and lacks Si-O-B chain segments. Under the action of external force, the foaming material loses the ability of instantaneous connection, resulting in a decrease in the hardness of the foaming material under the impact of external force; at the same time, the crosslinking density of the foaming material is insufficient, and the external force cannot be dispersed inside the foaming material, resulting in the foaming material being easily torn, and the tear strength is reduced to 19.77 N / cm; moreover, the modified waste EVA only has hydroxyl-terminated polydimethylsiloxane, and hydroxyl-terminated polydimethylsiloxane cannot adsorb polymer chain segments, losing the ability to resist instantaneous strong external force impact, resulting in a decrease in the resilience rate of the foaming material and an increase in the permanent compression set rate.

[0131] Third, Examples 1-12 form a single comparison. The difference between Examples 1-12 lies in the different sources of the modified waste EVA. The proportions of hydroxyl-terminated polydimethylsiloxane and boric acid in the modified waste EVA remain unchanged, and the content of hydroxyl-terminated polydimethylsiloxane increases. The higher the content of Si-O-B chain segments, but if the content of Si-O-B chain segments is too high, it is easy to cause poor compatibility between the modified waste EVA and EVA, resulting in a decrease in the strength of the foaming material and the emergence of stress concentration points inside the foaming material, resulting in a decrease in the tear strength; and the pores in the foaming material expand and become larger at the interface, making it difficult to form uniform and stable microbubbles, resulting in a decrease in the resilience of the foaming material. Similarly, control the hydroxyl content and viscosity of hydroxyl-terminated polydimethylsiloxane, so that hydroxyl-terminated polydimethylsiloxane can fully contact with the crosslinked EVA, control the content of Si-O-B chain segments on the surface of the crosslinked EVA, and balance the coordinated improvement of the hardness, tear strength, resilience and permanent compression set rate of the foaming material.

[0132] Fourth, Examples 9, 13 - 15 form a single comparison. It can be seen that as the VA content increases, the crosslinking density of the foaming material increases. Although this helps to increase the storage modulus of the foaming material, when the VA content is too high, the crosslinking density becomes too high, resulting in the foaming material having too high hardness and rigidity, thus leading to a decrease in toughness, a decrease in the rebound rate, and an increase in the permanent compression deformation rate.

[0133] Fifth, Examples 14, 16 - 18 form a single comparison. It can be seen that the addition of silica makes the density of the foaming material lower. The reasons are as follows: First, silica has better compatibility with the modified waste EVA, forming more closed and tiny pores; Second, silica is lighter, thus reducing the overall density of the foaming material. Secondly, controlling the particle size of the filler within a moderate range can improve the resilience and permanent compression deformation rate of the foaming material. The reasons are as follows: When the particle size of the filler is too small, the filler is prone to aggregation, resulting in the filler not being well dispersed in the foaming material, thus reducing the number of heterogeneous nucleation sites in the foaming material and deteriorating the foaming performance; while when the particle size of the filler is too large, the amount of filler added decreases, also leading to a reduction in the number of heterogeneous nucleation sites in the foaming material and deteriorating the foaming performance. Eventually, the resilience of the foaming material decreases and the permanent compression deformation rate increases.

[0134] The technical features of the above - described embodiments can be combined arbitrarily. For the sake of brevity in description, not all possible combinations of the technical features in the above - described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0135] Moreover, the above - described embodiments only represent several implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A foaming material containing recycled EVA, characterized in that: According to parts by weight, it includes the following components: 100 parts of EVA, 120-145 parts of modified waste EVA, 18-36 parts of inorganic filler, 1-5 parts of cross-linking agent and 5-10 parts of antioxidant; The modified waste EVA is processed according to the following steps: After the waste EVA is treated with impurities removal, it is subjected to banburying treatment at a temperature of 160-180° C. for 15-30 minutes to obtain de-crosslinked EVA powder; The de-crosslinked EVA powder is put into the terminal hydroxyl polydimethylsiloxane, kneaded and dispersed, and then boric acid is added, wherein the weight ratio of the de-crosslinked EVA powder, the terminal hydroxyl polydimethylsiloxane and the boric acid is 100:(25-92):(0.80-2.94), the temperature is raised to 170-200° C., the temperature is kept for reaction for 1-3 hours, and after the reaction is completed, the modified waste EVA is ground and crushed to obtain; The foaming material is foamed by using supercritical carbon dioxide fluid.

2. A foaming material containing recycled EVA as claimed in claim 1, characterized in that: In the preparation method of the modified waste EVA, the weight ratio of the de-crosslinked EVA powder, the terminal hydroxyl polydimethylsiloxane and the boric acid is 100:(30-50):(0.96-1.60).

3. A foaming material containing recycled EVA as claimed in claim 1, characterized in that: The hydroxyl content of the hydroxy-terminated polydimethylsiloxane is 1.5-4.0%.

4. A foaming material containing recycled EVA as claimed in claim 3, characterized in that: The viscosity of the terminal hydroxyl polydimethylsiloxane is 30 to 65 cst.

5. The foaming material containing recycled EVA as claimed in claim 1, characterized in that: The temperature of the banburying treatment is 175° C., and the time of the banburying treatment is 20 min.

6. A foaming material containing recycled EVA as claimed in claim 1, characterized in that: The terminal hydroxyl polydimethylsiloxane is a hydroxyl-terminated dimethyl-methylvinyl polysiloxane copolymer.

7. A foaming material containing recycled EVA as claimed in claim 6, characterized in that: The VA content of the EVA is 14-18%.

8. The foaming material containing recycled EVA as claimed in claim 1, characterized in that: The inorganic filler is silicon dioxide.

9. A foaming material containing recycled EVA as claimed in claim 8, characterized in that: The size of the inorganic filler is 0.5-1 μm.

10. A foaming material containing recycled EVA according to any one of claims 1 to 9, characterized in that: The steps include: Weigh EVA, modified waste EVA, inorganic filler, crosslinking agent and antioxidant according to weight, put them into an internal mixer for mixing, and obtain a foaming matrix after mixing; The foaming substrate is placed in a foaming kettle, and supercritical carbon dioxide fluid is introduced for foaming to obtain a foaming material containing recycled EVA.

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