Polyethylene sintered porous medium as well as preparation method and application thereof

Abstract

The invention relates to a polyethylene sintered porous medium as well as a preparation method and application thereof. The overall porosity of the porous medium is 20-70%, and the PMI average pore size of the porous medium is 5-80 microns; the porous medium is composed of an adsorbent and polyethylene; the ratio of the SEM average particle size of the adsorbent to the PMI average pore size of the porous medium is 1.1-30; and the DSC crystallinity of the porous medium is 25%-60%. The overall porosity of the porous medium is controlled to be 20%-70%, the PMI average pore size is controlled to be within the range of 5-80 microns, the porous medium is endowed with a good mechanical strength basis, and the ratio of the SEM average particle size of the adsorbent to the PMI average pore size of the porous medium is further controlled to be within the range of 1.1-30. According to the invention, the polyethylene particles are added into the sintered porous medium, so that the molten polyethylene can be well contacted and bonded with the adsorbent in the sintering process, and meanwhile, the probability that the adsorbent is separated from the polyethylene particles after the sintered porous medium is formed is greatly reduced, so that the final sintered porous medium has higher mechanical strength.

Description

Technical Field

[0001] The present invention relates to the technical field of sintering processes for porous materials, and particularly to a polyethylene sintered porous medium, a preparation method thereof, and an application thereof. Background Art

[0002] The sintering method is an important material preparation process. It mainly involves physically compressing materials through specific mechanical equipment and then performing a sintering process at a set temperature, causing the surfaces of material particles to melt and bond together, thereby forming a porous medium material with a certain shape and properties. Compared with porous medium materials prepared by, for example, the phase inversion method, the porous medium materials prepared by the sintering method can usually obtain porous medium materials with complex shapes and structures. At the same time, the sintering process can make the internal microstructure of the porous medium material more uniform, reduce defects and impurities, and endow the porous medium material with better stability. Among them, polyethylene, as a common thermoplastic plastic, has excellent low-temperature resistance, chemical stability, etc., and thus the polyethylene porous medium materials prepared by the sintering method are widely used in fields such as liquid filtration.

[0003] For example, in the Chinese invention patent with the publication number CN102512875A, a preparation method of a ultra-high molecular weight polyethylene filter material (applied by Shanghai Baifeite Environmental Protection Technology Co., Ltd.), a filter material prepared by sintering ultra-high molecular weight polyethylene material is disclosed. By controlling the particle size of ultra-high molecular weight polyethylene (abbreviated as UPE) resin particles and its sintering process, a filter material with a relatively uniform pore size distribution and a relatively high porosity is finally obtained. Although the above ultra-high molecular weight polyethylene filter material can play a good role in intercepting dust particles, etc., in some application fields, such as in vitro waste liquid plugs, outdoor speakers, etc., it may involve some acidic or alkaline gases, organic gases, dust, fine dust, etc. The ultra-high molecular weight polyethylene filter material in the above patent cannot effectively remove the above gases or fine particles such as dust and fine dust only by the interception method.

[0004] Furthermore, those skilled in the art think that the sintered porous medium material can be endowed with the adsorption effect on the above-mentioned gas or tiny particles by sintering the polyethylene material and the adsorbent together. For example, the preparation method of the modified ultra-high molecular weight polyethylene microporous filter element of the Chinese invention patent with the publication number of CN101474514A (applied by Shanxi University) discloses a filter element obtained by sintering the ultra-high molecular weight polyethylene material and the adsorbent together, which is obtained by blending the activated carbon and the modified zeolite into the ultra-high molecular weight polyethylene resin particles, and then sintering the blended materials, and finally obtaining the corresponding sintered porous medium material (i.e., the ultra-high molecular weight microporous filter element in the patent). After research, it is found that the above-mentioned modification method not only changes the physical structure performance of the sintered porous medium material, but also endows the sintered porous medium material with a good adsorption function, so that the sintered porous medium material can meet the adsorption and removal requirements of acidic or alkaline gases, organic gases and tiny particles.

[0005] However, since the melting point of the adsorbent (such as activated carbon) in the above patent is usually high, and the melting point of the polyethylene material is usually between 85°C and 140°C, which is much lower than the melting point of the adsorbent (such as activated carbon), during the sintering process of polyethylene, the sintering temperature is usually lower than the melting point of the adsorbent (such as activated carbon) (the sintering temperature in the above patent is 170°C-250°C), which makes the state of the adsorbent (such as activated carbon) relatively stable during the sintering process and does not cause surface melting behavior. Therefore, during the sintering process, it may be difficult for the adsorbent to bond well with the polyethylene particles, which may cause the adsorbent and polyethylene to be mixed in the final sintered porous medium material. The polyethylene particles are not bonded into blocks, or even "powder inclusion" occurs (powder inclusion refers to the inclusion of powdered substances inside the filter element during the production process of the sintered filter element when polyethylene and adsorbent powders appear, that is, the original powders are not completely melted and bonded together), and particles are prone to fall off, which will greatly reduce the mechanical strength of the sintered porous medium material, and greatly reduce the service life of the above-mentioned sintered porous medium material under some strong working pressure environments. It may even contaminate the filtered fluid (contaminate the corresponding instruments and equipment, and affect the filtration results) due to the problem of particle shedding, and then fail to meet the actual application needs. Therefore, there is an urgent need for a sintered porous medium with both high mechanical strength and high adsorption performance. Summary of the invention

[0006] The purpose of the present invention is to provide a polyethylene sintered porous medium and a preparation method and application thereof. The sintered porous medium is composed of an adsorbent and polyethylene. By adjusting the porosity, DSC crystallinity and SEM average particle size of the adsorbent, it has high mechanical strength, high adsorption performance and good air permeability, and is suitable for in vitro waste liquid plugs, outdoor speakers, solvent suction filter heads and other fields.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A polyethylene sintered porous medium, the overall porosity of the porous medium is 20%-70%, and the PMI average pore diameter of the porous medium is 5-80 μm; the porous medium is composed of an adsorbent and polyethylene; the ratio of the SEM average particle diameter of the adsorbent to the PMI average pore diameter of the porous medium is 1.1-30;

[0009] The DSC crystallinity of the porous medium is 25%-60%.

[0010] To improve the adsorption efficiency of the sintered porous medium for some toxic and harmful gases (such as acidic or alkaline gases, organic gases), fine particles and other substances, the present invention sinters a porous medium from an adsorbent and polyethylene as raw materials. The adsorbent is usually a porous material, such as activated carbon, molecular sieve, etc., which can remove the above-mentioned toxic and harmful gases, fine particles and other substances by physical adsorption and other means. The addition of the adsorbent can greatly improve the adsorption performance of the porous medium for toxic and harmful gases and fine particles and other substances.

[0011] In the present invention, the PMI average pore diameter can reflect the size of the pores in the porous medium to a certain extent. Usually, a suitable PMI average pore diameter can endow the porous medium with good mechanical properties. In the present invention, the PMI average pore diameter of the porous medium is controlled within the range of 5-80 μm, which reflects that the porous medium has a suitable number and size of pores, so that the porous medium can have good mechanical strength. If the pore diameter is too large, it may cause the porous medium to collapse due to the influence of factors such as pressure during application, thereby affecting the mechanical strength of the porous medium; if the pore diameter is too small, there may not be enough space between the polyethylene and the adsorbent for bonding, which is likely to cause particle dropping and other situations, which will also affect the mechanical strength of the porous medium and at the same time affect the air permeability of the porous medium, resulting in too poor air permeability of the porous medium. In addition, the porous medium in the present invention also has non-directional tortuous passages. The non-directional tortuous passages in the present invention refer to randomly oriented groove structures and / or discrete distributed hole structures, and each non-directional tortuous passage communicates with each other. Through the synergistic effect of the PMI average pore diameter (5-80 μm) of the porous medium and the non-directional tortuous passages, the interception effect on fine particles and toxic and harmful gases and other substances is further improved, so that the porous medium has high filtration performance.

[0012] To a certain extent, the overall porosity of the sintered porous medium can reflect the proportion of the solid part in the sintered porous medium. Generally, the overall porosity of the sintered porous medium is inversely proportional to the mechanical strength of the sintered porous medium, that is, the higher the overall porosity of the sintered porous medium, the relatively lower the mechanical strength of the sintered porous medium. In the present invention, the overall porosity of the porous medium is 20%-70%. On the basis of the corresponding average pore diameter of PMI, it not only further ensures that the porous medium has good mechanical strength, but also is conducive to the porous medium having good air permeability.

[0013] As is well known, the crystallinity of the porous medium can reflect the proportion of the crystalline region and the amorphous region to a certain extent. Generally, the higher the crystallinity, the better the mechanical properties of the porous medium (the proportion of the crystalline region will also be higher. Since the molecular arrangement in the crystalline region is more regular, compared with the amorphous region, the properties such as strength in the crystalline region are usually better than those in the amorphous region). Therefore, in order to obtain a sintered porous medium with high mechanical strength, those skilled in the art usually hope that the crystallinity of the porous medium is higher, even the higher the better. However, through research, it is found that the crystallinity of the porous medium is not the higher the better, because the sintering process is usually a process in which the crystallinity gradually decreases. The higher the crystallinity of the sintered porous medium, to a certain extent, means that the sintering time experienced by the sintered porous medium is too short, which is likely to cause the adsorbent and polyethylene particles in the sintered porous medium not to be bonded into blocks (there is almost no interaction force), or even the situation of "powder sandwiching" occurs and particles are likely to fall off, which may instead reduce the mechanical strength and adsorption performance of the sintered porous medium, and even pollute the corresponding instrument and equipment.

[0014] In the present invention, the crystallinity of the porous medium (measured by the DSC method) is not the higher the better, but is preferably controlled within the range of 25%-60%, which reflects that the porous medium of the present invention has a suitable crystalline region structure, thereby ensuring that the porous medium has good mechanical strength. Furthermore, such crystallinity is not isolated, but on the basis of the corresponding pore diameter and porosity, that is, on the basis of a certain pore diameter (micropore) and porosity, through the porous medium having a suitable crystallinity, it shows that the bonding degree between the polyethylene particles and the adsorbent is relatively good (there is good interaction force between the two), reducing the probability of particle dropping and "powder sandwiching" in the sintered porous medium, ensuring that the sintered porous medium has excellent mechanical strength, and at the same time ensuring high adsorption performance, and can efficiently adsorb various toxic and harmful gases and tiny impurities for a long time.

[0015] Meanwhile, we also found that due to the high melting point of the adsorbent, the particle size of the adsorbent hardly changed before and after sintering, and the required particle size of the adsorbent for sintered bodies with different pore sizes was also different; through research, it was found that by controlling the ratio of the SEM average particle size of the adsorbent to the PMI average pore size of the porous medium within the range of 1.1 - 30, to a certain extent, it reflected that there were adsorbents of appropriate size in the porous medium, enabling the adsorbent to bond well with the polyethylene particles during the sintering process, reducing the occurrence of particle dropping and "powder entrapment" in the porous medium, and at the same time, it could also ensure the adsorption performance of the sintered porous medium.

[0016] If the SEM average particle size of the adsorbent is too large, it will lead to difficulty in bonding between the molten polyethylene particles and the adsorbent during the sintering process, thus easily resulting in particle dropping and "powder entrapment", which will in turn affect the mechanical strength of the porous medium; if the SEM average particle size of the adsorbent is too small, it is easy for the adsorbent to fill in the pore structure of the porous medium and cannot be well bonded within the porous medium, which will in turn affect the mechanical strength of the porous medium, and at the same time, the porosity of the porous medium will also be affected to a certain extent, ultimately leading to a decrease in the air permeability of the porous medium.

[0017] By controlling the overall porosity of the porous medium within the range of 20% - 70% and the PMI average pore size within the range of 5 - 80 μm, the present invention enables the porous medium to have a pore structure with appropriate quantity, appropriate size, and appropriate distribution. Combined with the DSC crystallinity of the porous medium within the range of 25% - 60%, it endows the porous medium with a good mechanical strength foundation; to a certain extent, it also reflects that the porous medium has a good specific surface area inside, which can achieve a certain degree of adsorption and removal of some fine particles, etc. In addition, the porous medium can also remove some impurities such as fine particles in the form of interception, and finally it is manifested that the porous medium has excellent adsorption performance. Further combined with controlling the ratio of the SEM average particle size of the adsorbent to the PMI average pore size of the porous medium within the range of 1.1 - 30, it enables the polyethylene to be in good contact and bond with the adsorbent after melting during the sintering process, and at the same time, it also greatly reduces the probability of detachment between the adsorbent and the polyethylene particles after the sintered porous medium is formed, thus enabling the final sintered porous medium to have a high mechanical strength; at the same time, the adsorbent in the porous medium has a relatively high specific surface area, endowing the final porous medium with good adsorption performance for substances such as gases and fine particles.

[0018] Furthermore, we found that when an adsorbent with a suitable particle size is added to the sintered material, an unexpected technical effect can be achieved, that is, the porosity of the sintered porous medium did not show the expected significant decrease, but still had a good numerical range, and even had a certain improvement. Therefore, while ensuring that the sintered porous medium has high mechanical strength and high adsorption efficiency, the sintered porous medium also unexpectedly has good air permeability, which enables the porous sintered products to be better used in some application fields that have certain requirements for air permeability.

[0019] After research, it was found that: during the sintering process, the longer the sintering time, the lower the porosity of the sintered porous medium will be. This is because the sintering process is usually carried out in a prefabricated mold, and the sintering raw materials are compacted and stacked in the space of the prefabricated mold before sintering. As the sintering process proceeds, the sintering raw materials further melt, and the overlapping parts between adjacent sintering raw material particles account for an increasing proportion, which in turn causes the gaps between adjacent sintering raw material particles to continue to decrease, causing the porosity of the sintered porous medium obtained after the overall sintering to continue to decrease. In some application fields that have certain requirements for air permeability, such as outdoor speakers, if the air permeability of the sintered porous medium is poor, it may cause a pressure difference inside and outside the outdoor speaker, which may affect the volume and sound quality of the sound. Therefore, under normal circumstances, in order to avoid the situation where the porosity of the sintered porous medium is too low and the air permeability is poor, the sintering time is usually not relatively long.

[0020] In the present invention, due to the addition of an adsorbent of a certain particle size, the adsorbent will exist between adjacent PE particles and play a certain barrier role, so that although the sintering time continues to increase, the gaps between adjacent PE particles cannot be further reduced due to the barrier effect of the adsorbent (therefore, it is necessary to specially control the ratio of the SEM average particle size of the adsorbent to the PMI average pore size of the porous medium). Finally, macroscopically, as the sintering time continues to increase, the porosity of the sintered porous medium still has a good value, and even due to the porous structure of the adsorbent itself, it even increases to a certain extent, thereby giving the sintered porous medium high mechanical strength and high adsorption performance, while also having good air permeability, achieving unexpected technical effects; at the same time, as the sintering time continues to increase, the degree of bonding between the PE particles and the adsorbent after surface melting becomes better and better, which also greatly reduces the probability of particles falling and "powder inclusion" due to poor bonding between the PE particles and the adsorbent.

[0021] After the morphology of the sintered porous medium was characterized by scanning electron microscopy, it was clearly observed that there were two types of particles with different morphologies in the SEM image, among which the microporous structure could be clearly observed on the surface of the adsorbent particles, while the microporous structure could not be observed on the surface of the polyethylene particles.

[0022] In the present invention, the overall porosity of the porous medium is obtained by mercury intrusion porosimetry.

[0023] In the present invention, the PMI average pore diameter of the porous medium is obtained by testing with a PMI pore size tester.

[0024] In the present invention, the SEM average particle size of the adsorbent can be measured and calculated accordingly by using a scanning electron microscope to characterize the morphology of the sintered porous medium and then using computer software (such as Matlab, NIS-Elements, etc.) or manually; when actually measuring, the surface of the sintered porous medium (usually the sintered porous medium exists in the form of a cylinder) can be characterized by an electron microscope to obtain the corresponding SEM image, and since the distribution of the adsorbent in the sintered porous medium is approximately uniform, a certain area can be selected, for example, 1μm 2 (1μm multiplied by 1μm) or 100μm 2 (10μm multiplied by 10μm) or, the specific area size depends on the actual situation, and then the SEM average particle size of the adsorbent on this area is measured by the corresponding computer software or manually, and several tests (preferably more than 10 times) are carried out, and the average value is taken to obtain the SEM average particle size of the adsorbent; of course, those skilled in the art can also obtain the above parameters by other measurement means, and the above measurement means are for reference only.

[0025] In the present invention, the DSC crystallinity of the porous medium can be obtained by differential scanning calorimetry.

[0026] Preferably, the ratio of the SEM average width of the sintering neck in the porous medium to the SEM average particle size of the polyethylene is 0.2 - 0.8, and the SEM width of the sintering neck in the porous medium is not less than 10μm.

[0027] The sintering neck refers to the neck-shaped connection structure formed by melting between adjacent polyethylene particles during sintering, and its formation degree (such as the width size) directly affects the mechanical strength of the material. In the present invention, the SEM width of the sintering neck is not less than 10μm, which directly indicates that the sintering degree of the porous medium will not be too low, which is beneficial for the sintered porous medium to have high mechanical strength.

[0028] In the present invention, the ratio of the average SEM width of the sintering necks of the porous medium to the average SEM particle size of the polyethylene reflects, on the one hand, the degree of bonding between the polyethylene particles and directly affects the mechanical strength of the porous medium; on the other hand, to a certain extent, it can be used to reflect the degree of sintering. The higher the degree of sintering, generally, the better the degree of fusion bonding between the polyethylene particles, which is manifested as the average SEM width of the sintering necks being closer to the average SEM particle size of the polyethylene. In the present invention, controlling the ratio of the average SEM width of the sintering necks to the average SEM particle size of the polyethylene within the range of 0.2 - 0.8 reflects to a certain extent that the bonding between the polyethylene particles in the porous medium is good, giving the porous medium a good mechanical strength foundation; at the same time, it also reflects that the porous medium has an appropriate degree of sintering, and an appropriate degree of sintering is also conducive to good contact and bonding between the polyethylene particles and the adsorbent, which can reduce the probability of incomplete bonding, particle dropping, and "powder entrapment" between the polyethylene particles and the adsorbent. Coupled with the appropriate DSC crystallinity of the porous medium, it shows that the amorphous region, crystal region structure, etc. in the polyethylene raw material in the porous medium have undergone transformation (such as forming a stable lamellar crystal structure, etc.), thereby endowing the porous medium with higher mechanical strength.

[0029] In addition, due to the presence of an adsorbent with an appropriate particle size (the average SEM particle size of the adsorbent and the average PMI pore size of the porous medium are controlled within the range of 1.1 - 30), the situation where the porosity of the sintered porous medium decreases significantly due to the increase in sintering time is better alleviated, enabling the sintered porous medium to still have a good porosity, thereby endowing the sintered porous medium with good air permeability.

[0030] In the present invention, both the average SEM width of the sintering necks and the average SEM particle size of the polyethylene can be measured and calculated accordingly by using a scanning electron microscope to characterize the morphology of the sintered porous medium and then using computer software (such as Matlab, NIS - Elements, etc.) or manually. When actually measuring, the surface of the sintered porous medium can be characterized by an electron microscope to obtain the corresponding SEM image. Since the distribution of the adsorbent in the sintered porous medium is approximately uniform, a certain area can be selected, such as 1μm 2 (1μm multiplied by 1μm) or 100μm 2(10 μm multiplied by 10 μm), or the specific area size depends on the actual situation. Then, use the corresponding computer software or manually measure the average SEM width of the sintering neck and the average SEM particle size of polyethylene on this area. Conduct several tests (preferably more than 10 times), and take the average value to obtain the average SEM width of the sintering neck and the average SEM particle size of polyethylene. Of course, those skilled in the art can also obtain the above parameters through other measurement means, and the above measurement means are for reference only. It should be noted that when measuring the width of the sintering neck, try to select the connection width between the positions with relatively large curvatures on both sides of the sintering neck; the average SEM particle size of polyethylene is obtained by measuring the polyethylene particles in the SEM image of the sintered porous medium.

[0031] Preferably, the average SEM particle size of the polyethylene is 60 - 350 μm, and the ratio of the average SEM particle size of the polyethylene to the average SEM particle size of the adsorbent is 1.2 - 5.

[0032] In the present invention, polyethylene is used as the framework material for forming the sintered porous medium. The average SEM particle size of polyethylene directly reflects the size of the polyethylene particles that make up the sintered porous medium, and to a certain extent determines the mechanical property basis of the sintered porous medium. By controlling the average SEM particle size of polyethylene within the range of 60 - 350 μm, the present invention provides a basis for the high mechanical strength performance of the sintered porous medium material. Since the adsorbent is relatively stable during the sintering process and the form of the adsorbent in the porous medium is bonded by the melting of polyethylene, the present invention further limits the ratio of the average SEM particle size of polyethylene to the average SEM particle size of the adsorbent within the range of 1.2 - 5, so that polyethylene in the sintered porous medium can relatively well wrap and bond the adsorbent. At the same time, combined with the fact that the sintered porous medium has a suitable DSC crystallinity, it reflects that the crystallization transformation process of polyethylene in the porous medium is not overly affected after the addition of the adsorbent and still has a good crystallinity, ensuring the high mechanical strength of the porous medium. In addition, through the fact that the porous medium has a crystallinity of 25% - 60%, it reflects that the porous medium has experienced a suitable sintering time, enabling polyethylene and the adsorbent to have relatively sufficient time for melting contact bonding. As a result, the final sintered porous medium can have high mechanical strength and good adsorption performance while greatly reducing the probability of particle dropping and "powder entrapment".

[0033] If the ratio of the SEM average particle size of polyethylene to the SEM average particle size of the adsorbent is too large, it usually means that the SEM average particle size of polyethylene is too large or the SEM average particle size of the adsorbent is too small. If the SEM average particle size of polyethylene is too large, it may lead to fewer bonding points between particles and the pore size of the sintered porous medium is too large, which ultimately leads to low mechanical strength of the product; while if the SEM average particle size of the adsorbent is too small, it may cause the adsorbent to block the pore structure in the sintered porous medium, which may affect the mechanical properties of the porous medium, and cause the porosity of the sintered porous medium to decrease, thereby affecting the air permeability of the sintered porous medium; if the ratio of the SEM average particle size of polyethylene to the SEM average particle size of the adsorbent is too small, it usually means that the SEM average particle size of polyethylene is too small or the SEM average particle size of the adsorbent is too large, which may increase the difficulty of bonding between the polyethylene surface and the adsorbent after melting during the sintering process, which may then lead to particle falling or insufficient bonding between polyethylene and the adsorbent, and ultimately the mechanical strength and adsorption performance of the sintered porous medium will be affected and decreased.

[0034] Preferably, the surface of the porous medium has a plurality of mold wall contact areas, and the area ratio of the mold wall contact areas is 6%-50%; the ratio of the SEM average width of the mold wall contact areas to the PMI average pore size of the porous medium is not less than 0.8; wherein the area ratio of the mold wall contact areas = SEM area of the mold wall contact areas / SEM area of the surface of the porous medium.

[0035] The formation of the die wall contact area in the present invention is formed by polyethylene contacting the inner wall of the mold during the sintering process and through the molten state during sintering. The area ratio of the die wall contact area represents the solid part of the contact between polyethylene and the mold in the sintered porous medium. Therefore, to a certain extent, the area ratio of the die wall contact area can reflect the pore area ratio on the surface of the sintered porous medium (generally, the larger the area ratio of the die wall contact area, the smaller the pore area ratio on the surface), which will affect the pressure resistance of the porous medium surface to a certain extent during application. By controlling the area ratio of the die wall contact area within the range of 6%-50% in the present invention, the sintered porous medium has good pressure resistance. Coupled with the overall porosity of the porous medium within the range of 20%-70%, it is found that the porous medium also has good air permeability. In the present invention, the ratio of the SEM average width of the die wall contact area to the PMI pore diameter of the porous medium is not less than 0.8, combined with the ratio of the SEM average particle diameter of the adsorbent to the PMI average pore diameter of the porous medium, which reflects from the side that there is a suitable size ratio relationship between the die wall contact area and the adsorbent, that is, the polyethylene on the surface of the porous medium can bond and wrap the adsorbent relatively sufficiently. Then, during the compression process of the porous medium material, the adsorbent is relatively less likely to fall off from the gaps between the die wall contact areas, which is beneficial to ensuring that the sintered porous material has high mechanical strength. The area ratio of the die wall contact area in the present invention can be measured by using a scanning electron microscope to characterize the morphology of the sintered porous medium, and then using computer software (such as Matlab, NIS-Elements, etc.) or manually, and performing corresponding calculations. When actually measuring, the surface of the sintered porous medium can be characterized by an electron microscope first to obtain the corresponding SEM image. A certain area can be selected, such as 1μm 2 (1μm multiplied by 1μm) or 100μm 2 (10μm multiplied by 10μm) or, and the specific area size depends on the actual situation. Then, use the corresponding computer software or manually measure the total area of the die wall contact area on this area, and then use the total area of the die wall contact area divided by this area to obtain the area ratio of the die wall contact area. Perform several operations (preferably more than 3 times, by selecting areas with a certain interval for testing), and take the average value to obtain it. Of course, those skilled in the art can also obtain the above parameters through other measurement means, and the above measurement means are for reference only.

[0036] Preferably, the SEM average width of the die wall contact area is 40-120μm, and the ratio of the SEM average width of the die wall contact area to the SEM average particle diameter of the polyethylene is 0.2-0.9.

[0037] The SEM average width of the die wall contact area in the present invention directly reflects the size of the framework material as the surface of the sintered porous material, and to a certain extent reflects the pressure resistance of the porous medium surface; by controlling the SEM average width of the die wall contact area within the range of 40 - 120 μm, the porous medium has a good framework foundation, laying a foundation for the porous medium to have high mechanical strength; at the same time, combining the ratio of the SEM average width of the die wall contact area to the SEM average particle size of polyethylene within the range of 0.2 - 0.9 reflects that the proportion of the die wall contact area in the volume of polyethylene is good, so that the die wall contact area can also endow the surface of the porous medium with high pressure resistance after sintering.

[0038] If the ratio of the SEM average width of the die wall contact area to the SEM average particle size of polyethylene is too low, it means that the surface hole area rate of the sintered porous medium is relatively large. Although it can improve the air permeability of the sintered porous medium to a certain extent, the surface pressure resistance performance of the sintered porous medium will be affected and decreased, which is not conducive to long-term use; if the ratio of the SEM average width of the die wall contact area to the SEM average particle size of polyethylene is too high, it means that the integrity of the polyethylene framework on the side and end faces of the sintered porous medium is relatively low, which is not conducive to having a good bonding force between polyethylene and the adsorbent, and may lead to particle dropping or incomplete bonding, thus affecting the mechanical strength of the porous medium.

[0039] Preferably, the surface of the porous medium includes a side face and an end face. The side face has a first die wall contact area, the end face has a second die wall contact area, the area ratio of the first die wall contact area is greater than the area ratio of the second die wall contact area, and the ratio of the area ratio of the first die wall contact area to the area ratio of the second die wall contact area is 1.5 - 5.

[0040] The "end face" in the present invention refers to the surface parallel to the filtering direction, and the "side face" refers to the surface in the circumferential direction along the filtering direction. Generally, when the porous medium is used for filtering, the connecting direction of the two end faces of the porous medium is parallel to the filtering direction, that is, the two end faces of the porous medium are usually in contact with the fluid to be filtered, and the side face of the porous medium is usually in contact with the installation position. In some application fields with certain requirements for air permeability, such as outdoor speakers, the end face of the porous medium is directly in contact with the fluid to be filtered (such as gas, dust particles, etc.). Compared with the side face, we hope that the area ratio of the second mold wall contact area of the porous medium is smaller, that is, the area ratio of the holes on the end face of the porous medium is larger, so that the porous medium has good air permeability; and the first mold wall contact area of the porous medium is expected to have a larger area ratio, because the side face of the porous medium usually needs to contact with the installation scene and undergo extrusion and other processes. The larger area ratio of the first mold wall contact area can give the porous medium better compressive strength. The present invention controls the ratio of the area ratio of the first mold wall contact area to the second mold wall contact area within the range of 1.5-5, which reflects that the end face of the porous medium has a higher hole area ratio; combined with the porous medium having a porosity of 20%-70%, the end face of the porous medium can have a better hole area ratio to ensure that the porous medium has good air permeability, and the end face of the porous medium can have a lower hole area ratio to ensure that the side of the porous medium has good pressure resistance.

[0041] Preferably, the adsorbent has a microporous structure, and the distribution density of the microporous structure is 0.1-10 / 100 μm 2 , the area ratio of the microporous structure is 4%-50%;

[0042] The area ratio of the microporous structure = the total SEM area of the microporous structure / the SEM area of the adsorbent.

[0043] The adsorbent in the present invention is a porous material. The existence of microporous structure can be used to reflect the specific surface area of the adsorbent to a certain extent. The distribution density of the microporous structure in the present invention is controlled to be 0.1-10 / 100μm. 2 The area ratio of the microporous structure is controlled within the range of 4%-50%, which reflects that the adsorbent in the porous medium has a suitable number and area of pores, combined with the fact that the adsorbent in the porous medium has a suitable particle size, which makes the adsorbent in the porous medium have a relatively high specific surface area, thereby giving the porous medium better adsorption performance and being able to better adsorb and remove gases, tiny particles, etc. The microporous structure in the present invention can be characterized by scanning electron microscopy of the porous medium, and then the magnification of the adsorbent is increased, for example, to 2000 times to obtain a microporous structure view of the adsorbent, and a certain area is selected, for example, 1μm2 (1 μm by 1 μm) or 100 μm 2 (10 μm by 10 μm), or the specific area size depends on the actual situation. Then, obtain the number of microporous structures on this area, calculate the number of microporous structures per unit area, that is, the distribution density value. At the same time, use the corresponding computer software or measure the total area of the microporous structures on this area manually, and then divide the total area of the microporous structures by this area to obtain the area ratio of the microporous structures. Conduct several tests (preferably more than 3 times, select areas with a certain interval), and take the average value to obtain the distribution density of the microporous structures and the area ratio of the microporous structures.

[0044] Preferably, the distribution density of the polyethylene is 20 - 60 per mm 2 , and the distribution density of the adsorbent is at least 5 per mm 2 , and the ratio of the distribution density of the polyethylene to the distribution density of the adsorbent is 1.5 - 8.

[0045] In the present invention, the distribution density of the polyethylene to a certain extent reflects the distribution of the porous sintered medium skeleton. The distribution density of the polyethylene in the present invention is controlled within the range of 20 - 60 per mm 2 . Combined with the overall porosity of the porous medium controlled within the range of 20% - 70%, it reflects that the porous medium has a relatively solid skeleton structure foundation, providing a basis for the high mechanical strength of the porous medium; the distribution density of the adsorbent to a certain extent reflects the distribution of the adsorbent in the porous medium. The distribution density of the adsorbent is at least 5 per mm 2 endows the porous medium with good adsorption performance and can significantly enhance the adsorption of gases and fine particles. At the same time, by controlling the ratio of the distribution density of the polyethylene to the distribution density of the adsorbent within the range of 1.5 - 8, the polyethylene in the porous medium can be relatively well distributed around the adsorbent and a good bonding process can occur during the sintering process. Finally, the porous medium can have high mechanical strength and good adsorption performance.

[0046] In the present invention, the method for obtaining the distribution density of the polyethylene and the distribution density of the adsorbent is the same. After characterizing the morphology of the porous medium by scanning electron microscopy, select a certain area, such as 1 μm 2 (1 μm by 1 μm) or 100 μm 2 (10 μm by 10 μm), or the specific area size depends on the actual situation. Then, obtain the number of polyethylene on this area, calculate the number of polyethylene per unit area, that is, the distribution density value.

[0047] Preferably, the adsorption efficiency of the porous medium for toluene is not less than 60%, and the adsorption efficiency for SO2 is not less than 60%; the Shore A hardness of the porous medium is not less than 80 HA;

[0048] At a ventilation area of 50 mm 2 , the ventilation volume of the porous medium is 300 - 3000 ml / min@2.5 kPa; the bacterial filtration efficiency of the porous medium is not less than 99.99%

[0049] The virus filtration efficiency of the porous medium is not less than 99%.

[0050] In the present invention, the porous medium has a high adsorption efficiency for toxic and harmful gases (such as acidic, alkaline, organic gases, etc.), especially for organic gases and acidic gases with an adsorption efficiency of not less than 60%; at the same time, the porous medium has high mechanical strength, and its Shore A hardness is not less than 80 HA; the porous medium also has good air permeability and can reach a ventilation volume of 300 - 3000 ml / min@2.5 kPa at a ventilation area of 50 mm 2 . The thickness of the porous medium is 8 mm. The ventilation volume refers to the volume of gas passing through per unit time under the conditions of a pressure of 2.5 kPa, a specified ventilation area, and a thickness of the porous medium; in addition, the porous medium also has excellent bacterial and virus filtration efficiencies. The bacterial filtration efficiency (BFE) can be not less than 99.99%, and the virus filtration efficiency (VFE) can be not less than 99%. The adsorption efficiency of the porous medium of the present invention can be tested by the following method: Refer to ASHRAE145.1 - 2008 Laboratory Performance Evaluation Test Method for Gas Phase Air Cleaning Systems: Loose Granular Packings for adsorption efficiency testing. The adsorption efficiency of the porous medium for organic gases is characterized by the adsorption efficiency of the porous medium for toluene; the adsorption efficiency of the porous medium for acidic gases is characterized by the adsorption efficiency of the porous medium for SO2; the adsorption efficiency of the porous medium for alkaline gases is characterized by the adsorption efficiency of the porous medium for NH3; where the test temperature is 23 ± 1 °C, the humidity is 25% - 30%, the toluene concentration is 50 ± 2 ppm, and the flow rate is 29.44 L / min; the concentration of SO2 is 10 ± 0.5 ppm, and the flow rate is 29.4 L / min; the concentration of NH3 is 40 ± 1 ppm, and the flow rate is 29.3 L / min.

[0051] The Shore A hardness of the porous medium can be tested by a Shore hardness tester A, and the Shore A hardness of the porous medium is obtained by taking the average value after three tests.

[0052] The air permeability of the porous medium can be measured by the following method: Use an air permeability tester to measure the air permeability of the porous medium. Adjust the air pressure to the test pressure, where the test pressure is 2.5 kPa. Read and record the data to obtain the air permeability of the porous medium. The air permeable area of the porous medium is controlled within 50 mm 2 Under the condition of, the air permeability per unit area of the porous medium can also be obtained by converting through the air permeable area of the test surface of the porous medium.

[0053] The bacterial filtration efficiency of the porous medium can be measured by the following method: Take the seed liquid stored at low temperature for resuscitation. Absorb an appropriate amount of Staphylococcus aureus (ATCC6538) and inoculate it into tryptic soy broth medium (TSB). Incubate at 37 ± 2°C for 24 h. Take several TSB cultures and place them in a microbial aerosol generator, and control the test conditions to meet > 1×10 6 cfu / sample challenge level;

[0054] First, do not place the test sample in the test system, and adjust the challenge flow rate to 28.3 LPM. The spraying time of the bacterial suspension is set to 1 min, and the sampling time is 2 min. Liquid impinger sampling bottles (each containing 30 mL of 1.5% sterile peptone water / bottle) are used in parallel to collect bacterial aerosols as the positive control. Subsequently, dilute the collected liquid 10-fold serially with 1.5% peptone water dilution and analyze it by the spread plate method. Incubate the spread tryptic soy agar (SCD) plates at 37 ± 2°C for 48 ± 4 h and then count. Adjust the concentration of the bacterial suspension so that the number of colonies > 1.0×10 6 CFU / sample. After the positive control test is completed, install the porous medium to be tested in the fixture, with the outside side of the porous medium facing up, and perform the test analysis according to the above steps. At the same time, analyze the collected liquid in the sampling bottle by the membrane filtration method;

[0055] Where: C = the number of colonies in the positive control group; T = the number of colonies in the test sample group; If no colonies are detected downstream, it is represented by ">".

[0056] Where the average particle size (MPS) of the challenging microbial aerosol is 3.0 ± 0.3 μm.

[0057] The virus filtration efficiency of the porous medium can be measured by the following method: Take an appropriate amount of the prepared phage Phi-X174 (ATCC 137046-B1) challenge suspension stored at low temperature and place it in a virus aerosol generator, and control the test conditions to meet at least 10 6 pfu / sample challenge level;

[0058] Do not place the test sample in the test system first, and adjust the challenge flow rate to 28.3 LPM. The spraying time of the bacteriophage Phi-X174 suspension is set to 1 min, and the sampling time is 2 min. Liquid impinger sampling bottles (each containing 30 mL of sterile normal saline) are used in parallel to collect the bacteriophage Phi-X174 aerosol as the positive control. Subsequently, the collected liquid is diluted 10-fold serially with peptone water dilution and analyzed by the double-layer agar plate method. The solidified nutrient agar (NA) plates are cultured at 37 ± 2 °C for 3 - 4 h and then counted. Adjust the titer of the bacteriophage Phi-X174 suspension so that the number of plaques meets 10 6 pfu / sample. After the positive control test is completed, install the test sample in the device and perform the test analysis according to the above steps. The Anderson sampler and liquid impinger sampling bottles are used simultaneously for sampling downstream of the filter. Finally, the collected liquid in the sampling bottles is analyzed by the double-layer agar plate method;

[0059] where: C = the number of plaques in the positive control group; T = the number of plaques in the test sample group; if no plaques are detected downstream, it is represented by ">".

[0060] where the average particle size (MPS) of the challenge virus aerosol is 3.0 ± 0.3 μm.

[0061] Furthermore, the present invention also provides a preparation method of a polyethylene sintered porous medium, including the following process steps:

[0062] S1, drying the material, heating and drying the polyethylene raw material, where the drying temperature is 50 - 80 °C;

[0063] S2, mixing the materials, adding the adsorbent to the polyethylene raw material after step S1 and mixing to obtain a mixture, where the addition amount of the adsorbent is 4 wt% - 40 wt%, the temperature of the polyethylene raw material before mixing is higher than the temperature of the adsorbent before mixing, and the temperature difference between the polyethylene raw material before mixing and the adsorbent before mixing is T1, and T1 is 25 - 60 °C;

[0064] S3, adding and compacting, adding the mixture into the mold and compacting;

[0065] S41, sintering in the rapid heating section, sintering the mixture after step S3 in the rapid heating section, the heating rate in the rapid heating section is 15 - 25 °C / min, and the highest temperature in the rapid heating section is 70 - 100 °C;

[0066] S42, sintering in the slow heating section, sintering the mixture in the slow heating section after sintering in the rapid heating section, the heating rate in the slow heating section is 5 - 10 °C / min, and the highest temperature in the slow heating section is the highest sintering temperature, controlled at 140 - 200 °C, to obtain the sintered product;

[0067] S5, Cooling: Cool the sintered product to obtain a sintered porous medium.

[0068] Preferably, in step S1, the weight-average molecular weight of the polyethylene raw material is 300,000 - 7,000,000;

[0069] In step S2, the adsorbent is one or more of activated carbon, molecular sieve, zeolite, activated alumina, and activated carbon fiber, and the apparent density of the adsorbent is 0.3 - 0.6 g / cc;

[0070] In step S3, the bulk density of the polyethylene raw material is 0.91 - 0.96 g / m 3 .

[0071] Preferably, in steps S41 and S42, the ratio of the highest sintering temperature to the drying temperature of the material is 2 - 4, and the ratio of the highest temperature in the rapid heating section to the highest sintering temperature satisfies 1:(1.5 - 2.5).

[0072] Preferably, in step S41, after heating to the highest temperature in the rapid heating section, a first-stage heat preservation reaction is carried out, and the first-stage heat preservation reaction time is 1 - 5 min; in step S42, after heating to the highest sintering temperature, a second-stage heat preservation reaction is carried out, and the second-stage heat preservation reaction time is 5 - 30 min.

[0073] Preferably, in step S5, the sintered product after steps S41 and S42 is placed in a cooler for rapid cooling, and the difference between the highest sintering temperature and the temperature T2 of the cooler satisfies 100 - 180 °C.

[0074] In the present invention, the first step is to heat and dry the polyethylene raw material. The drying temperature of the material is 50 - 80 °C, and the drying time is preferably 1 - 5 h. Drying the material is beneficial in removing the moisture contained in the polyethylene raw material (the water content is below 0.05%); because if the water content in the polyethylene raw material is too high, it may cause agglomeration during the mixing process of the polyethylene raw material and the adsorbent, which will in turn affect the mechanical strength of the porous medium after sintering; on the other hand, it makes the temperature of the polyethylene raw material higher than that of the adsorbent during mixing, which is more conducive to the subsequent sintering effect.

[0075] As a preference, the weight-average molecular weight of the polyethylene raw material in step S1 is 300,000 - 7,000,000, enabling the polyethylene raw material to have better contact and bonding with the adsorbent during the sintering process. It should be noted that the drying temperature of the material cannot be too high. If the drying temperature of the material is too high, it may cause a certain shrinkage of the polyethylene raw material, which is not conducive to the polyethylene raw material having a suitable bulk density after mixing, thereby causing certain impacts on the mechanical properties and air permeability of the porous medium after sintering.

[0076] On this basis, step S2 of the present invention is to mix the polyethylene raw material and the adsorbent, which is also one of the key process nodes in the present invention. The pre-dried polyethylene raw material is directly mixed with the adsorbent. Since the polyethylene raw material has been pretreated (dried), the temperature of the polyethylene raw material before mixing is higher than the temperature of the adsorbent before mixing, and the temperature difference T1 between the temperature of the polyethylene raw material before mixing and the temperature of the adsorbent before mixing is controlled within the range of 25°C - 60°C. Usually, the polyethylene raw material and the adsorbent are mixed at basically the same temperature, that is, there is almost no temperature difference (the temperature difference is not higher than 10°C) when the two are mixed; however, we found that when the temperature difference T1 between the polyethylene raw material and the adsorbent before mixing is controlled within the range of 25°C - 60°C, the porous medium obtained after sintering the mixture after mixing can have better mechanical strength and higher adsorption performance. The R & D personnel analyzed that during the sintering process, due to factors such as the porous structure of the adsorbent, the heating rate of the adsorbent may be higher than that of the polyethylene, which may cause the adsorbent to reach the sintering temperature earlier than the polyethylene during the sintering process, and then may interfere with the heating and sintering process of the polyethylene, and may affect the bonding effect between the polyethylene and the adsorbent, resulting in a certain impact on the mechanical strength of the final sintered porous medium. By controlling the temperature difference T1 between the polyethylene and the adsorbent during mixing, the temperature of the adsorbent and the polyethylene will be uneven during the sintering process, that is, there is a certain temperature difference between the two. Although the heating rate of the polyethylene during the sintering process may be slower than that of the adsorbent, due to the existence of the temperature difference T1, it can instead enable the adsorbent and the polyethylene to reach the sintering temperature almost simultaneously during the sintering process, and enable the polyethylene to bond well with the adsorbent after surface melting, thereby greatly reducing the situation of particle dropping and "powder entrapment", so that the mechanical strength of the final sintered porous medium is improved to a certain extent, and its adsorption performance is also improved to a certain extent.

[0077] In the present invention, the adsorbent is a porous structure material, which can be one or more of activated carbon, molecular sieve, zeolite, activated alumina, and activated carbon fiber (activated carbon fiber is a carbon fiber containing activated carbon. The carbon fiber containing activated carbon is activated at high temperature to generate nano-scale pores on its surface, increase the specific surface area, and thus change its physical and chemical properties), etc. It should be noted that the apparent density of the adsorbent needs to be controlled within the range of 0.3 - 0.6 g / cc so that the adsorbent can have a higher specific surface area. At the same time, the addition amount of the adsorbent is 4wt% - 40wt% (referring to the ratio of the mass of the adsorbent to the total mass). The appropriate content of the adsorbent can endow the sintered porous medium with better adsorption performance while being able to contact and bond with the polyethylene well, which is beneficial to obtaining a sintered porous medium with good mechanical strength.

[0078] Then, the polyethylene raw material and the adsorbent are added into the mold for compaction, wherein the bulk density of the polyethylene raw material is 0.91-0.96 g / m 3 The bulk density of the polyethylene raw material and the apparent density of the adsorbent further determine the porosity basis of the porous medium material. At the same time, through the synergistic cooperation between the two, the polyethylene raw material and the adsorbent can be better bonded, and then the porous medium material can have higher mechanical strength after sintering.

[0079] As a key node in the process of the present invention, polyethylene and adsorbent are sintered by two stages of heating, namely, S41 rapid heating stage sintering and S42 slow heating stage sintering. In the S41 rapid heating stage sintering, the heating rate of the rapid heating stage is controlled to be 15-25°C / min, and the maximum temperature of the rapid heating stage is controlled to be 70-100°C; in the S42 slow heating stage sintering, the heating rate of the slow heating stage is 5-10°C / min, and the maximum temperature of the slow heating stage is the maximum sintering temperature, which is controlled to be 140-200°C to obtain a sintered product. Preferably, the ratio of the maximum sintering temperature to the baking temperature is 2-4. In the present invention, the rapid heating section is mainly set to quickly increase the temperature of the adsorbent, further shorten the temperature difference between the adsorbent and polyethylene, avoid the thermal conduction reaction between the polyethylene raw material and the adsorbent as much as possible due to the large temperature difference between the polyethylene raw material and the adsorbent, and further reduce the negative impact of the adsorbent temperature on the polyethylene heating process; at the same time, since the polyethylene raw material is mixed with the adsorbent immediately after heating and baking, and the polyethylene raw material will have a certain thermal stress after preheating, when the rapid heating section rapidly heats the polyethylene raw material, the thermal stress of the polyethylene raw material after preheating can resist shrinkage to a certain extent, and the shrinkage of the polyethylene raw material caused by rapid heating will be greatly reduced. Preferably, the ratio of the maximum temperature of the rapid heating section to the maximum sintering temperature satisfies 1: (1.5-2.5). It should be noted that the temperature of the rapid heating section cannot be too high. If it is too high, the temperature difference between the adsorbent and the polyethylene raw material after the rapid heating section is too small, which will have a negative impact, that is, the adsorbent still reaches the sintering temperature before the polyethylene raw material, which is not conducive to the sintered porous medium having higher mechanical strength and adsorption performance.

[0080] The slow heating section is mainly set up to allow the polyethylene raw material and the adsorbent to be heated to the sintering temperature relatively smoothly. After the rapid heating section, on the one hand, the temperature difference between the adsorbent and the polyethylene raw material can be quickly shortened to avoid the thermal conductivity reaction caused by the temperature difference between the two as much as possible; on the other hand, the rapid heating section can also make the temperature of the polyethylene raw material better increase, so that the temperature difference between the adsorbent and the polyethylene raw material is continuously shortened in the dynamic process, combined with the slow heating section, so that the final polyethylene raw material and the adsorbent reach the sintering temperature almost at the same time, and promote the polyethylene raw material to better bond with the adsorbent, greatly improving the mechanical strength and adsorption performance of the final sintered porous medium. In addition, the setting of the slow heating section can also make the polyethylene raw material more stable during the molten state transition, reduce the probability of polyethylene raw material shrinkage during the heating process, and further promote the transformation of part of the amorphous region structure in the polyethylene raw material to the lamellar structure during the sintering process, thereby improving the mechanical strength of the sintered porous medium and promoting the porous medium to have a good degree of crystallinity. It should be noted that the higher the weight average molecular weight of polyethylene, the more difficult it is to melt, and thus a higher sintering temperature is required so that the polyethylene can melt better and bond with the adsorbent during the sintering process.

[0081] We found that if only the slow heating stage is carried out, the porous medium after sintering still cannot achieve the expected high mechanical strength and high adsorption performance; if the temperature difference between the adsorbent and polyethylene is too small, the adsorbent may still reach the sintering temperature earlier than the polyethylene during the slow heating stage, thereby affecting the bonding process between the polyethylene and the adsorbent; if the temperature difference between the adsorbent and polyethylene is too large, it may lead to obvious thermal conductivity between the adsorbent and polyethylene, which may cause the polyethylene to have no obvious temperature change for a period of time after the start of the sintering process, which is not conducive to further heating of the polyethylene raw material, and may cause the final adsorbent to still reach the sintering temperature earlier than the polyethylene.

[0082] Preferably, we introduce the first stage of heat preservation reaction after sintering in the rapid heating stage S41, and the heat preservation time is 1 - 5 minutes; the progress of the first stage of heat preservation reaction is beneficial to further increase the temperature of the adsorbent, enabling the temperature difference between the adsorbent and polyethylene to be further reduced during the dynamic heating process, and weakening the influence of the heat transfer effect caused by the temperature difference between polyethylene and the adsorbent on the heating process of polyethylene; secondly, the first stage of heat preservation reaction is also beneficial to avoiding the shrinkage phenomenon of polyethylene particles caused by too fast heating rate in the rapid heating stage. After sintering in the slow heating stage S42, the second stage of heat preservation reaction is introduced, and the second stage of heat preservation reaction time is 5 - 30 minutes; it is beneficial for the polyethylene raw material to better contact with the surface of the adsorbent after surface melting, enabling the polyethylene raw material to better wrap around the surface of the adsorbent and carry out the bonding process, improving the bonding strength between the polyethylene raw material and the adsorbent, thereby greatly reducing the occurrence of situations such as particle dropping and "powder entrapment"; at the same time, the second stage of heat preservation reaction can also better promote the transformation of the crystalline region and amorphous region structures in the polyethylene raw material into a relatively more stable lamellar structure, and then enable the sintered porous medium to have good crystallinity and improve the mechanical strength of the sintered porous medium.

[0083] In step S5, the sintered product after step S4 is immediately added to a cooler for rapid cooling, that is, a quenching step for the sintered product is carried out, and the difference between the highest sintering temperature and the temperature T2 of the cooler is controlled to satisfy 100 - 180°C. The quenching step is beneficial for the sintered product to be instantaneously cooled, beneficial for reducing the probability of shrinkage occurring in the die wall contact area, and to a certain extent can also improve the mechanical strength of the sintered porous medium.

[0084] Furthermore, the present invention also provides an application of a polyethylene sintered porous medium, and the sintered porous medium is applied to at least one of outdoor speakers, in vitro waste liquid plugs, and solvent suction filters. The sintered porous medium of the present invention is particularly suitable for application scenarios involving some toxic and harmful gases (such as organic gases, acidic gases, alkaline gases, etc.), and fine particles (such as odors, and odors mainly refer to particles distributed in the air), such as in vitro waste liquid plugs, solvent suction filters, etc.; in addition, the sintered porous medium can also better meet the requirements of some application scenarios that also have certain requirements for air permeability, such as outdoor speakers, etc.; of course, the sintered porous medium of the present invention can also be applied to other filtration application fields.

[0085] In summary, the present invention includes at least one of the following beneficial technical effects: By controlling the overall porosity of the porous medium within the range of 20% - 70% and the PMI average pore diameter within the range of 5 - 80 μm, the porous medium has a pore structure with an appropriate number, appropriate size, and appropriate distribution. Combined with the DSC crystallinity of the porous medium within the range of 25% - 60%, it endows the porous medium with a good mechanical strength foundation. Further combined with the ratio of the SEM average particle size of the adsorbent to the PMI average pore diameter of the porous medium controlled within the range of 1.1 - 30, it enables the polyethylene to make good contact and bond with the adsorbent after melting during the sintering process, and at the same time greatly reduces the probability of detachment between the adsorbent and the polyethylene particles after the sintered porous medium is formed, thereby making the final sintered porous medium have a high mechanical strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] The present invention will be further described below with reference to the accompanying drawings:

[0087] Figure 1 SEM schematic diagram on the side of the sintered porous medium obtained in Example 4, with a magnification of 100×;

[0088] Figure 2 SEM schematic diagram on the end face of the sintered porous medium obtained in Example 4, with a magnification of 100×;

[0089] Figure 3 SEM schematic diagram on the side of the sintered porous medium obtained in Example 5, with a magnification of 100×;

[0090] Figure 4 SEM schematic diagram on the end face of the sintered porous medium obtained in Example 5, with a magnification of 100×;

[0091] Figure 5 SEM schematic diagram of the adsorbent in the sintered porous medium obtained in Example 4, with a magnification of 2000×;

[0092] Figure 6 SEM schematic diagram of the adsorbent in the sintered porous medium obtained in Example 5, with a magnification of 2000×. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0093] The present invention will be further described in detail below with reference to the embodiments. Unless otherwise specified, in the following embodiments, the raw materials and equipment used for preparing the sintered porous medium can be obtained through commercial channels.

[0094] Example 1

[0095] A preparation method of a polyethylene sintered porous medium, comprising the following technological steps:

[0096] S1, drying the material, heating and drying the polyethylene raw material, wherein the drying temperature is 50 °C and the weight-average molecular weight of the polyethylene raw material is 300,000;

[0097] S2, mixing the materials, adding an adsorbent to the polyethylene raw material after step S1 and mixing to obtain a mixture, wherein the addition amount of the adsorbent is 4 wt%, the temperature of the polyethylene raw material before mixing is higher than the temperature of the adsorbent before mixing, and the difference between the temperature of the polyethylene raw material before mixing and the temperature of the adsorbent before mixing is T1, T1 is 25 °C, and the adsorbent is activated carbon fiber;

[0098] S3, feeding and compressing, adding the mixture into a mold for compressing, and the bulk density of the polyethylene raw material is 0.91 - 0.96 g / m 3 ;

[0099] S41, sintering in the rapid heating stage, sintering the mixture after step S3 in the rapid heating stage, the heating rate in the rapid heating stage is 15 °C / min, and the highest temperature in the rapid heating stage is 70 °C; in step S41, after heating to the highest temperature in the rapid heating stage, a first-stage heat preservation reaction is carried out, and the first-stage heat preservation reaction time is 1 min;

[0100] S42, sintering in the slow heating stage, sintering the mixture in the slow heating stage after sintering in the rapid heating stage, the heating rate in the slow heating stage is 5 °C / min, and the highest temperature in the slow heating stage is the highest sintering temperature, controlled at 140 °C. In step S42, after heating to the highest sintering temperature, a second-stage heat preservation reaction is carried out, and the second-stage heat preservation reaction time is 5 min to obtain a sintered product;

[0101] S5, cooling, placing the sintered product after steps S41 and S42 into a cooler for rapid cooling, and the difference between the highest sintering temperature and the temperature T2 of the cooler satisfies 115 °C to obtain a sintered porous medium.

[0102] Examples 2 - 7

[0103] The differences between Examples 2 - 7 and Example 1 lie in different process parameters, and the specific differences are shown in Tables 1 - 1 and 1 - 2. Among them, the adsorbent in Example 2 is zeolite, the adsorbents in Examples 3, 4, and 5 are activated carbon, the adsorbents in Examples 5 - 6 are molecular sieves, and the adsorbent in Example 7 is activated alumina.

[0104] Comparative Examples 1 - 3

[0105] The differences between Comparative Examples 1 - 3 and Example 4 lie in different process parameters, and the specific differences are shown in Tables 1 - 1 and 1 - 2.

[0106] Table 1-1

[0107]

[0108]

[0109] Table 1-2

[0110]

[0111] Detection of membrane performance parameters

[0112] The sintered porous media prepared in Examples 1-7 and Comparative Examples 1-3 were characterized morphologically using a scanning electron microscope (Hitachi S-5500). The side and end faces of the sintered porous media were selected as the observation objects, and the specific detection and measurement results are shown in Tables 2-1 and 2-2.

[0113] Table 2-1

[0114]

[0115]

[0116] Table 2-2

[0117]

[0118]

[0119] Detection of porous media performance parameters

[0120] 1.1 Adsorption efficiency test

[0121] After testing, the adsorption efficiencies of the sintered porous media prepared in Examples 1-7 for toluene and SO2 were both greater than 60%, that is, the porous media had good adsorption efficiencies for toxic and harmful gases (acidic, alkaline, organic gases, etc.), and the porous media had good adsorption properties. Among them, the adsorption efficiency of the sintered porous media prepared in Example 3 could reach more than 80%.

[0122] 1.2 Shore A hardness test; 1.3 Air permeability test; 1.4 Bacterial filtration efficiency test; 1.5 Virus filtration efficiency test.

[0123] The test results are shown in Table 3.

[0124]

[0125] As can be seen from the above, the sintered porous medium prepared in Examples 1-7 of the present invention has high mechanical strength and high adsorption performance, enabling the sintered porous medium of the present invention to be preferably applied to some application fields involving toxic and harmful gases (such as acidic or alkaline gases, organic gases), fine particles, etc., such as an in vitro waste liquid plug, a solvent suction filter head, etc.; in addition, the sintered porous medium prepared in Examples 1-7 of the present invention also has good air permeability, enabling the sintered porous medium to be preferably applied to some application fields with certain requirements for air permeability, such as an outdoor speaker, etc. However, the mechanical strength of the sintered porous medium prepared in Comparative Examples 1-3 is poor and it is difficult to meet the long-term use requirements in the actual application process. At the same time, the sintered porous medium prepared in Comparative Example 1 has a poor interception efficiency for fine particles such as bacteria and viruses and it is difficult to meet the requirements of some application fields with adsorption requirements for fine particles; the air permeability of the sintered porous medium prepared in Comparative Example 2 is relatively poor and it is difficult to meet the requirements of some application fields with certain requirements for air permeability.

[0126] The above embodiments are only the preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention belong to the scope of protection required by the present invention.

Claims

1. A polyethylene sintered porous medium, characterized in that: The overall porosity of the porous medium is 20%-70%, and the PMI average pore size of the porous medium is 5-80 μm; The porous medium is composed of an adsorbent and polyethylene; The ratio of the SEM average particle size of the adsorbent to the PMI average pore size of the porous medium is 1.1-30; The DSC crystallinity of the porous medium is 25%-60%.

2. The polyethylene sintered porous medium according to claim 1, characterized in that: The ratio of the SEM average width of the sintering necks in the porous medium to the SEM average particle size of polyethylene is 0.2-0.8, and the SEM width of the sintering necks in the porous medium is not less than 10 μm.

3. A polyethylene sintered porous medium according to claim 1, characterized in that: The SEM average particle size of the polyethylene is 60-350 μm, and the ratio of the SEM average particle size of the polyethylene to the SEM average particle size of the adsorbent is 1.2-5.

4. A polyethylene sintered porous medium according to claim 1, characterized in that: The surface of the porous medium has a number of die wall contact areas, and the area ratio of the die wall contact areas is 6%-50%; the ratio of the SEM average width of the die wall contact areas to the PMI average pore size of the porous medium is not less than 0.8; Where the area ratio of the die wall contact areas = the SEM area of the die wall contact areas / the SEM area of the surface of the porous medium.

5. A polyethylene sintered porous medium according to claim 4, characterized in that: The SEM average width of the die wall contact areas is 40-120 μm, and the ratio of the SEM average width of the die wall contact areas to the SEM average particle size of the polyethylene is 0.2-0.

9.

6. The polyvinyl sintered porous medium according to claim 1, wherein: The surface of the porous medium includes a side surface and an end surface. The side surface has a first die wall contact area, and the end surface has a second die wall contact area. The area ratio of the first die wall contact area is greater than the area ratio of the second die wall contact area, and the ratio of the area ratio of the first die wall contact area to the area ratio of the second die wall contact area is 1.5-5.

7. A polyethylene sintered porous medium according to claim 1, characterized in that: The adsorbent has a microporous structure, and the distribution density of the microporous structure is 0.1-10 per 100 μm 2 , and the area ratio of the microporous structure is 4%-50%; Where the area ratio of the microporous structure = the total SEM area of the microporous structure / the SEM area of the adsorbent.

8. A polyethylene sintered porous medium according to claim 1, wherein: The distribution density of the polyethylene is 20 - 60 pieces / mm 2 , the distribution density of the adsorbent is at least 5 pieces / mm 2 , and the ratio of the distribution density of the polyethylene to the distribution density of the adsorbent is 1.5 - 8.

9. A polyethylene sintered porous medium according to claim 1, characterized in that: The adsorption efficiency of the porous medium for toluene is not less than 60%, and the adsorption efficiency for SO2 is not less than 60%; The Shore A hardness of the porous medium is not less than 80 HA; At a ventilation area of 50 mm 2 the ventilation rate of the porous medium is 300 - 3000 ml / min@2.5 kPa; The bacterial filtration efficiency of the porous medium is not less than 99.99%; The virus filtration efficiency of the porous medium is not less than 99%.

10. A method for preparing a polyethylene sintered porous medium according to any one of claims 1-9, characterized in that, It includes the following process steps: S1, drying the material, heating and drying the polyethylene raw material, where the drying temperature is 50-80 °C; S2, mixing the materials, adding the adsorbent to the polyethylene raw material after step S1 and mixing them to obtain a mixture, where the addition amount of the adsorbent is 4 wt%-40 wt%, the temperature of the polyethylene raw material before mixing is higher than the temperature of the adsorbent before mixing, and the difference between the temperature of the polyethylene raw material before mixing and the temperature of the adsorbent before mixing is T1, and T1 is 25-60 °C; S3, adding and compacting the material, adding the mixture into a mold and compacting it; S41, sintering in the rapid heating section, sintering the mixture after step S3 in the rapid heating section, the heating rate in the rapid heating section is 15-25 °C / min, and the highest temperature in the rapid heating section is 70-100 °C; S42, sintering in a slow heating stage, sintering the mixture in a slow heating stage after sintering in a fast heating stage, the heating rate in the slow heating stage is 5-10°C / min, the highest temperature in the slow heating stage is the highest sintering temperature, which is controlled to be 140-200°C, to obtain a sintered product; S5, cooling, cooling the sintered product to obtain a sintered porous medium.

11. A method for preparing a polyethylene sintered porous medium according to claim 10, characterized in that, The weight average molecular weight of the polyethylene raw material in step S1 is 300,000-7,000,000; In step S2, the adsorbent is one or more of activated carbon, molecular sieve, zeolite, activated alumina and activated carbon fiber; In step S3, the bulk density of the polyethylene raw material is 0.91 - 0.96 g / m 3 .

12. A method for preparing a polyethylene sintered porous medium according to claim 10, characterized in that, In step S41 and step S42, the ratio of the maximum sintering temperature to the baking temperature is 2-4, and the ratio of the maximum temperature in the rapid heating section to the maximum sintering temperature satisfies 1:(1.5-2.5).

13. The preparation method of a polyethylene sintered porous medium according to claim 10, characterized in that, In step S41, after heating to the highest temperature of the rapid heating stage, a first insulation reaction is carried out, and the first insulation reaction time is 1-5 minutes; in step S42, after heating to the highest sintering temperature, a second insulation reaction is carried out, and the second insulation reaction time is 5-30 minutes.

14. A method for preparing a polyethylene sintered porous medium according to claim 10, characterized in that, In step S5, the sintered product after step S41 and step S42 is placed in a cooler for rapid cooling, and the difference between the highest sintering temperature and the temperature T2 of the cooler satisfies 100-180°C.

15. The application of a polyethylene sintered porous medium according to any one of claims 1-9, characterized in that, The sintered porous medium is applied to at least one of an outdoor speaker, an in vitro waste liquid plug, and a solvent suction filter head.

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