Method for preparing degradable composite silica GEL material and filter rod having microporous structure and prepared by using material

Abstract

The present invention provides a method for preparing a degradable composite silica gel material. The method comprises: preparing a silica gel matrix from a raw rubber, a reinforcing filler, and silicone oil, and then mixing a filling agent and the silica gel matrix to obtain a rubber compound, putting the rubber compound, a vulcanizing agent, a food-grade composite foaming agent, and plant fibers into a two-roll mill for open milling to obtain the degradable composite silica gel material. The composite silica gel material can be applied to a filter rod. The present invention further provides a cigarette filter rod having a microporous structure and prepared from the composite silica gel material. The filter rod having the microporous structure of the present invention can achieve lower draw resistance and better vapor cooling effect. The filter rod has relatively high hardness and rebound rate and relatively good deformation resistance and can maintain good appearance quality. It is ensured that the quality of the filter rod is stable, and the application requirements of traditional cigarettes and heat-not-burn cigarettes are met.

Description

DESCRIPTION METHOD FOR PREPARING DEGRADABLE COMPOSITE SILICA GEL MATERIAL AND FILTER ROD HAVING MICROPOROUS STRUCTURE AND PREPARED BY USING MATERIAL The present application claims domestic priority to Chinese Patent Application No. CN 2024103609195, filed on March 27, 2024.Technical FieldThe present invention relates to the technical field of cigarette filter rods, and particularly to a degradable composite silicone rubber material usable for preparing a filter rod, and further to a filter rod prepared from such a composite silicone rubber material and having a microporous structure.Background ArtConventional cigarette filter rods extensively use cellulose diacetate tow as a filter rod material. However, since an acetate filter rod is obtained by forming and press-bonding the tow, its strength is relatively low, and therefore fine and complex hollowed-out patterns cannot be produced, making it difficult to improve the cooling effect of the filter rod on smoke by designing smoke flow channels having a reasonable shape.Chinese Patent Application No. CN 112273740A discloses a silicone rubber cooling section for a heat-not-burn product. The cooling section is hollow and tubular, and is made of silicone rubber into a prefabricated silicone rubber cooling section by an existing high-temperature curing molding method. The silicone rubber of the silicone rubber cooling section is a food-grade silicone rubber material selected from methyl silicone rubber, methyl vinyl silicone rubber, methyl vinyl phenyl silicone rubber, nitrile silicone rubber or fluorosilicone rubber. However, the silicone rubber cooling section as a whole is not of a porous structure, and therefore has relatively poor cooling performance, the smoke temperature thereof being 41.3-43.5°C, and the smoking experience is still relatively hot.Chinese Patent Application No. CN 104177831A discloses a food-grade silicone rubber foam product and a method for manufacturing the same. The raw materials thereof comprise a fumed-process silicone rubber, a precipitated-process silicone rubber, hollow glass microspheres, hydroxyl silicone oil, a platinum vulcanizing agent B and a platinum vulcanizing agent A. However, it is found through testing that the cooling performance of the foam product does not meet the requirements of cigarette filter rods.The prior art further discloses some silicone rubbers, for example, a low compression set silicone rubber disclosed in Chinese Patent Application No. CN 105419341A, which comprises a raw rubber having a vinyl molar content of 0.18%, a raw rubber having a vinyl molar content of 0.30%, precipitated white carbon black, hydroxyl silicone oil, hydrogen-containing silicone oil, stearic acid, and the like. However, since this material is not a foamed material and does not have cooling performance, it does not meet the requirements of cigarette filter rods.Summary of the InventionAn object of the present invention is to overcome the defects of the prior art, to provide a novel composite silicone rubber material, and to enable the preparation of a cigarette filter rod having a microporous structure from such a composite silicone rubber material, so as to obtain better smoke cooling effect and filter rod processability, while maintaining the physical properties required of a cigarette filter rod.On this basis, a method for preparing a degradable composite silicone rubber material is provided, the preparation method comprising the following steps:(1) preparing a silicone rubber matrixweighing out 8-12:0.5-2:0.2-1 parts by mass of a raw rubber, a reinforcing filler and a silicone oil, and mixing them uniformly to obtain a silicone rubber matrix; wherein the raw rubber is one or more silicone rubbers selected from methyl vinyl silicone rubber, dimethyl silicone rubber and / or methyl phenyl vinyl silicone rubber, and the raw rubber has a Shore A hardness of 10-30;(2) internal mixingweighing out 0.8-1.3:2-5 parts by mass of a filling agent and the silicone rubber matrix, placing the weighed materials into an internal mixer, and carrying out internal mixing at 120°C-180°C to obtain a rubber compound;(3) open millingweighing out 80-100:0.1-1:0.1-2:3-15 parts by mass of the rubber compound, a vulcanizing agent, a food-grade composite foaming agent and plant fibers, wherein the plant fibers have an average fiber length of 0.5-6mm, placing the weighed materials into a two-roll mill, and carrying out open milling to obtain the degradable composite silicone rubber material.In the present invention, in step (1), the reinforcing filler is selected from white carbon black and / or titanium dioxide; and the silicone oil is selected from hydroxyl silicone oil and / or methoxy silicone oil. Generally, when the reinforcing filler is a mixture of white carbon black and titanium dioxide, the ratio therebetween is not particularly limited. When the silicone oil is a mixture of hydroxyl silicone oil and methoxy silicone oil, the ratio therebetween generally is not particularly limited either.The internal mixing in step (2) is knowledge already mastered by a person skilled in the art, and is generally carried out by using an internal mixer at a rotation speed of 20-50r / min and a temperature of 120°C-180°C for 10-20min. The temperature, the rotation speed and the internal mixing time are conventional choices in the art, and a person skilled in the art may also appropriately adjust the operating parameters of the internal mixing equipment according to the working conditions and environmental conditions.According to a preferred embodiment, the filling agent used in step (2) is one or more filling agents selected from calcium carbonate, white carbon black, quartz powder and / or wollastonite powder. The filling agent in this step and the reinforcing filler in step (1) may be the same material (for example, white carbon black), or may be different materials.Particularly preferably, the food-grade composite foaming agent in the above step (3) comprises, in parts by mass:80-120 parts of sodium bicarbonate40-60 parts of a food-grade modifying agent30-50 parts of a raw rubberwherein the modifying agent is one or more modifying agents selected from anhydrous citric acid, stearic acid, glyceryl monostearate and erucamide;The food-grade composite foaming agent is prepared by a method comprising:Dissolving the food-grade modifying agent in anhydrous ethanol in an amount of 2.5-6 times the mass thereof, mixing the mixture uniformly, then adding sodium bicarbonate, and continuously stirring the uniformly mixed material at a rotation speed of 300-600rpm and a temperature of 15-20°C until the ethanol is completely volatilized; drying the resulting product at 40-60°C for 10-20min to obtain dried modified sodium bicarbonate; placing the modified sodium bicarbonate into a grinder, grinding the same, and then passing the ground product through a 100-mesh sieve to obtain a modified sodium bicarbonate powder; mixing the modified sodium bicarbonate powder with the raw rubber uniformly, and then sealing the mixture and allowing the mixture to stand at room temperature for 12-24 hours to obtain the food-grade composite foaming agent.Unlike the prior art in which sodium bicarbonate alone is used as a food foaming agent, in the food-grade composite foaming agent of the present invention, the contained modifying agent increases the decomposition temperature of the sodium bicarbonate, narrows the decomposition temperature range and increases the decomposition rate, thereby preventing premature decomposition and loss of the sodium bicarbonate in a mastication or pre-forming step, which would otherwise result in a poor foaming effect, so as to ensure that the foaming effect of the material is sufficient and stable. In addition, when the composite foaming agent is prepared, the raw rubber is added as a skeleton material, so that the obtained composite foaming agent, when added to the silicone rubber matrix in the open milling step, is conducive to uniform mixing of the foaming agent and the silicone rubber matrix during open milling, ensuring sufficient foaming, and products of different batches have a stable and uniform effect.In the present invention, the addition amount of the food-grade composite foaming agent is an optimal range confirmed through extensive experiments. If the amount of the composite foaming agent is insufficient, the obtained filter rod has relatively low porosity, resulting in extremely high draw resistance and a poor smoke cooling effect; if the composite foaming agent is used in excess, the hardness and rebound rate of the filter rod are low, the appearance of the filter rod is soft and collapsed, the quality is unstable, and the physical property requirements of the filter rod may even fail to be met.Compared with conventional food-grade foaming agents (for example, when sodium bicarbonate alone is used), the filter rod obtained after the composite foaming agent of the present invention is applied has better performance, which is manifested as more appropriate draw resistance and a better smoke cooling effect. If only the modifying agent is used as the foaming agent, since the modifying agent does not have a foaming effect, the effects of cooling the smoke and reducing the draw resistance of the filter rod of the present invention cannot be achieved. If only sodium bicarbonate is used as the foaming agent, the foaming effect is poor, the foaming is non-uniform, the uniformity between different product batches is relatively poor, and the porosity of the filter rod is liable to be relatively low, making it difficult to cool the smoke and reduce the draw resistance. If only the food-grade modifying agent is added to the sodium bicarbonate but no silicone rubber is added, the problems of non-uniform foaming effect and relatively poor uniformity between different product batches also exist, and the product quality is unstable. If only the raw rubber is added to the sodium bicarbonate, the foaming effect is still relatively poor and the smoke cooling effect is insufficient. Therefore, the food-grade modifying agent and the raw rubber need to be used in combination with the sodium bicarbonate in order to achieve the optimal filter rod performance.In the above step (3), the plant fibers are one or more fibers selected from flax, jute, sisal, ramie and abaca. In the present invention, the use of the plant fibers as a skeleton support material for the silicone rubber system can improve the strength and use performance of the silicone rubber rod and reduce the deformation of the product. In addition, the addition of the plant fibers can accelerate the degradation rate of the product, so that the product has better environmental performance. Therefore, these plant fibers may be used alone or in combination, and when used in combination, the ratio therebetween is generally not limited.On this basis, the present invention further provides use of the degradable composite silicone rubber material obtained by the above preparation method in a filter rod.In the present invention, the filter rod may be a heat-not-burn cigarette filter rod or a combustible cigarette filter rod, and the filter rod of the present invention can replace a conventional filter rod (such as a cellulose acetate tow filter rod) to achieve the effects of cooling smoke and adsorbing harmful substances.Furthermore, the present invention further provides a method for preparing a degradable filter rod having a microporous structure, the preparation method comprising the following steps:Placing the degradable composite silicone rubber material obtained by the above preparation method into an extruder, pre-forming the material at 25-85°C for 1-5min, then carrying out cross-linking foaming and extrusion at 120-180°C, and cooling the extruded material to obtain a rod-shaped material;Slitting the obtained rod-shaped material to obtain strips of the composite silicone rubber material;Treating the strips of the composite silicone rubber material at 150-200°C for 6-12 hours, and carrying out heat setting to obtain the degradable filter rod having a microporous structure.Here, the purpose of first pre-forming the composite silicone rubber material at a relatively low temperature is to appropriately adjust the state of the composite silicone rubber material, so as to facilitate subsequent foaming and extrusion at a higher temperature. Both the pre-forming and the cross-linking foaming are carried out in the extruder, and a person skilled in the art can reasonably adjust the temperature and time of the pre-forming according to the specific state of the composite silicone rubber material, so as to ensure that the extruded material is sufficiently cross-linked and foamed and is rod-shaped after cooling.In the present invention, the silicone rubber extruder is, for example, an 80 silicone rubber tube extrusion equipment product manufactured and sold by Hebei Xulang Machinery Equipment Manufacturing Co., Ltd. During use, the operating parameters of the extruder can be adjusted to control the ratio of the rotation speed of the inner die to the extrusion speed, so as to obtain smoke flow channels having different shapes. By replacing the inner die head having different material flow channel distributions (for example, with reference to the extrusion molding die head disclosed in Chinese Utility Model Application No. CN 215750663U), filter rods having smoke flow channels of different shapes or structures can be obtained, and these smoke flow channels can have different cross-sectional hollowed-out shapes, so as to enrich the options for the appearance shape of the end face of the filter rod.The density of the filter rod obtained in the present invention is generally 0.2-0.8g / cm3, and the porosity is 20-50%, and the porosity can be measured by a porosity tester. A person skilled in the art can adjust the degree of foaming by adjusting the foaming time, thereby adjusting the density of the obtained product.The degradable composite silicone rubber material of the present invention can be used for preparing a special-shaped filter rod. Compared with a conventional cellulose acetate filter rod, the degradable filter rod having a microporous structure of the present invention can achieve lower draw resistance and a better smoke cooling effect, and the filter rod has relatively high hardness and rebound rate and relatively good deformation resistance, can maintain good appearance quality, ensures that the quality of the filter rod is stable, and meets the application requirements of traditional cigarettes and heat-not-burn cigarettes.By improving the formulation of the foaming agent, the present invention further improves the cooling performance of the filter rod having a microporous structure and appropriately reduces the draw resistance of the filter rod, thereby achieving a better smoking experience.EMBODIMENTSThe following embodiments are used to explain the technical solution of the present invention in a non-limiting manner.In the present invention, unless otherwise specified, the "%" used to express product concentration represents a mass ratio, the ":" denotes a mass ratio, and the term "part(s)" refers to parts by mass.Example 1: Preparation of a Micro-Foamed Silicone Rubber Filter Rod Having an Internal Spiral StructurePreparation of a rubber compound:8:0.5:0.2 parts by mass of methyl vinyl silicone rubber, white carbon black and titanium dioxide were weighed out and mixed uniformly to obtain a silicone rubber matrix. Then, 1:2 parts by mass of calcium carbonate and the silicone rubber matrix were weighed out, placed into an internal mixer, and subjected to internal mixing at 150°C to obtain a rubber compound.Preparation of a food-grade composite foaming agent:80:40:30 parts by mass of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber were weighed out. The stearic acid was dissolved in anhydrous ethanol in an amount of 5 times the mass thereof, and after the mixture was mixed uniformly, sodium bicarbonate was added, and the mixture was continuously stirred at a rotation speed of 300rpm and a temperature of 20°C until the ethanol was completely volatilized; the resulting product was dried at 60°C for 20min, thereby obtaining dried modified sodium bicarbonate. The modified sodium bicarbonate was placed into a grinder, ground, and then passed through a 100-mesh sieve to obtain a modified sodium bicarbonate powder, which was then mixed uniformly with the methyl vinyl silicone rubber, and then sealed and left to equilibrate at room temperature for one day, thereby obtaining the food-grade composite foaming agent.Preparation of a composite silicone rubber material:80:0.2:0.2:3 parts by mass of the rubber compound, a platinum vulcanizing agent, the food-grade composite foaming agent and flax fibers (having an average fiber length of 3mm) were weighed out, placed into a two-roll mill, and subjected to open milling to obtain a degradable composite silicone rubber material.Preparation of a filter rod:The composite silicone rubber material was placed into an extruder (a regular hexagonal die head being selected as the inner die head thereof), the machine temperature was set to 60°C, heating was performed for 3min, then the temperature was set to 160°C to carry out high-temperature cross-linking foaming and extrusion, and after natural cooling, a rod-shaped material having hexagonal hollow flow channels was obtained. After being slit to a length of 120mm, strips of the composite silicone rubber material were obtained.The strips of the composite silicone rubber material were treated at 180°C for 8 hours, and after heat setting was performed, a degradable filter rod having a microporous structure was obtained.Example 2: Preparation of a Micro-Foamed Silicone Rubber Filter Rod Having an Internal Spiral StructurePreparation of a rubber compound:8:0.5:0.5 parts by mass of methyl vinyl silicone rubber, white carbon black and titanium dioxide were weighed out and mixed uniformly to obtain a silicone rubber matrix. Then, 0.8:2 parts by mass of calcium carbonate and the silicone rubber matrix were weighed out, placed into an internal mixer, and subjected to internal mixing at 155°C to obtain a rubber compound.Preparation of a food-grade composite foaming agent:80:50:40 parts by mass of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber were weighed out. The stearic acid was dissolved in anhydrous ethanol in an amount of 5 times the mass thereof, and after the mixture was mixed uniformly, sodium bicarbonate was added, and the mixture was continuously stirred at a rotation speed of 400rpm until the ethanol was completely volatilized; the resulting product was dried at 65°C until dried modified sodium bicarbonate was obtained. The modified sodium bicarbonate was placed into a grinder, ground, and then passed through a 100-mesh sieve to obtain a modified sodium bicarbonate powder, which was then mixed uniformly with the methyl vinyl silicone rubber, and then sealed and left to equilibrate at room temperature for one day, thereby obtaining the food-grade composite foaming agent.Preparation of a composite silicone rubber material:80:0.5:0.5:5 parts by mass of the rubber compound, a platinum vulcanizing agent, the food-grade composite foaming agent and flax fibers (having an average fiber length of 3mm) were weighed out, placed into a two-roll mill, and subjected to open milling to obtain a degradable composite silicone rubber material.Preparation of a filter rod:The composite silicone rubber material was placed into an extruder, the machine temperature was set to 55°C, heating was performed for 3min, then the temperature was set to 170°C to carry out high-temperature cross-linking foaming and extrusion, and after natural cooling, a rod-shaped material having hexagonal hollow flow channels was obtained. After being slit to a length of 120mm, strips of the composite silicone rubber material were obtained.The strips of the composite silicone rubber material were treated at 180°C for 8 hours, and after heat setting was performed, a degradable filter rod having a microporous structure was obtained.Example 3: Preparation of a Micro-Foamed Silicone Rubber Filter Rod Having an Internal Spiral StructurePreparation of a rubber compound:8:1:1 parts by mass of methyl vinyl silicone rubber, white carbon black and titanium dioxide were weighed out and mixed uniformly to obtain a silicone rubber matrix. Then, 1.2:2 parts by mass of calcium carbonate and the silicone rubber matrix were weighed out, placed into an internal mixer, and subjected to internal mixing at 155°C to obtain a rubber compound.Preparation of a food-grade composite foaming agent:100:40:30 parts by mass of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber were weighed out. The stearic acid was dissolved in anhydrous ethanol in an amount of 5 times the mass thereof, and after the mixture was mixed uniformly, sodium bicarbonate was added, and the mixture was continuously stirred at a rotation speed of 400rpm until the ethanol was completely volatilized; the resulting product was dried at 65°C until dried modified sodium bicarbonate was obtained. The modified sodium bicarbonate was placed into a grinder, ground, and then passed through a 100-mesh sieve to obtain a modified sodium bicarbonate powder, which was then mixed uniformly with the methyl vinyl silicone rubber, and then sealed and left to equilibrate at room temperature for one day, thereby obtaining the food-grade composite foaming agent.Preparation of a composite silicone rubber material:90:0.5:1:6 parts by mass of the rubber compound, a platinum vulcanizing agent, the food-grade composite foaming agent and flax fibers (having an average fiber length of 3mm) were weighed out, placed into a two-roll mill, and subjected to open milling to obtain a degradable composite silicone rubber material.Preparation of a filter rod:The composite silicone rubber material was placed into an extruder, the machine temperature was set to 55°C, heating was performed for 5min, then the temperature was set to 170°C to carry out high-temperature cross-linking foaming and extrusion, and after natural cooling, a rod-shaped material having hexagonal hollow flow channels was obtained. After being slit to a length of 120mm, strips of the composite silicone rubber material were obtained.The strips of the composite silicone rubber material were treated at 180°C for 8 hours, and after heat setting was performed, a degradable filter rod having a microporous structure was obtained.Example 4: Preparation of a Micro-Foamed Silicone Rubber Filter Rod Having an Internal Spiral StructurePreparation of a rubber compound:10:1:1 parts by mass of methyl vinyl silicone rubber, white carbon black and titanium dioxide were weighed out and mixed uniformly to obtain a silicone rubber matrix. Then, 1:3 parts by mass of calcium carbonate and the silicone rubber matrix were weighed out, placed into an internal mixer, and subjected to internal mixing at 155°C to obtain a rubber compound.Preparation of a food-grade composite foaming agent:100:50:50 parts by mass of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber were weighed out. The stearic acid was dissolved in anhydrous ethanol in an amount of 5 times the mass thereof, and after the mixture was mixed uniformly, sodium bicarbonate was added, and the mixture was continuously stirred at a rotation speed of 400rpm until the ethanol was completely volatilized; the resulting product was dried at 65°C until dried modified sodium bicarbonate was obtained. The modified sodium bicarbonate was placed into a grinder, ground, and then passed through a 100-mesh sieve to obtain a modified sodium bicarbonate powder, which was then mixed uniformly with the methyl vinyl silicone rubber, and then sealed and left to equilibrate at room temperature for one day, thereby obtaining the food-grade composite foaming agent.Preparation of a composite silicone rubber material:90:0.8:1:6 parts by mass of the rubber compound, a platinum vulcanizing agent, the food-grade composite foaming agent and flax fibers (having an average fiber length of 3mm) were weighed out, placed into a two-roll mill, and subjected to open milling to obtain a degradable composite silicone rubber material.Preparation of a filter rod:The composite silicone rubber material was placed into an extruder, the machine temperature was set to 55°C, heating was performed for 5min, then the temperature was set to 170°C to carry out high-temperature cross-linking foaming and extrusion, and after natural cooling, a rod-shaped material having hexagonal hollow flow channels was obtained. After being slit to a length of 120mm, strips of the composite silicone rubber material were obtained.The strips of the composite silicone rubber material were treated at 180°C for 8 hours, and after heat setting was performed, a degradable filter rod having a microporous structure was obtained.Example 5: Preparation of a Micro-Foamed Silicone Rubber Filter Rod Having an Internal Spiral StructurePreparation of a rubber compound:12:1:1 parts by mass of methyl vinyl silicone rubber, white carbon black and titanium dioxide were weighed out and mixed uniformly to obtain a silicone rubber matrix. Then, 1.2:3 parts by mass of calcium carbonate and the silicone rubber matrix were weighed out, placed into an internal mixer, and subjected to internal mixing at 155°C to obtain a rubber compound.Preparation of a food-grade composite foaming agent:120:60:40 parts by mass of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber were weighed out. The stearic acid was dissolved in anhydrous ethanol in an amount of 5 times the mass thereof, and after the mixture was mixed uniformly, sodium bicarbonate was added, and the mixture was continuously stirred at a rotation speed of 400rpm until the ethanol was completely volatilized; the resulting product was dried at 65°C until dried modified sodium bicarbonate was obtained. The modified sodium bicarbonate was placed into a grinder, ground, and then passed through a 100-mesh sieve to obtain a modified sodium bicarbonate powder, which was then mixed uniformly with the methyl vinyl silicone rubber, and then sealed and left to equilibrate at room temperature for one day, thereby obtaining the food-grade composite foaming agent.Preparation of a composite silicone rubber material:95:1:1.5:10 parts by mass of the rubber compound, a platinum vulcanizing agent, the food-grade composite foaming agent and flax fibers (having an average fiber length of 3mm) were weighed out, placed into a two-roll mill, and subjected to open milling to obtain a degradable composite silicone rubber material.Preparation of a filter rod:The composite silicone rubber material was placed into an extruder, the machine temperature was set to 55°C, heating was performed for 5min, then the temperature was set to 170°C to carry out high-temperature cross-linking foaming and extrusion, and after natural cooling, a rod-shaped material having hexagonal hollow flow channels was obtained. After being slit to a length of 120mm, strips of the composite silicone rubber material were obtained.The strips of the composite silicone rubber material were treated at 180°C for 8 hours, and after heat setting was performed, a degradable filter rod having a microporous structure was obtained.Example 6: Preparation of a Micro-Foamed Silicone Rubber Filter Rod Having an Internal Spiral StructurePreparation of a rubber compound:12:2:1 parts by mass of methyl vinyl silicone rubber, white carbon black and titanium dioxide were weighed out and mixed uniformly to obtain a silicone rubber matrix. Then, 1.3:5 parts by mass of calcium carbonate and the silicone rubber matrix were weighed out, placed into an internal mixer, and subjected to internal mixing at 155°C to obtain a rubber compound.Preparation of a food-grade composite foaming agent:120:60:50 parts by mass of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber were weighed out. The stearic acid was dissolved in anhydrous ethanol in an amount of 5 times the mass thereof, and after the mixture was mixed uniformly, sodium bicarbonate was added, and the mixture was continuously stirred at a rotation speed of 400rpm until the ethanol was completely volatilized; the resulting product was dried at 65°C until dried modified sodium bicarbonate was obtained. The modified sodium bicarbonate was placed into a grinder, ground, and then passed through a 100-mesh sieve to obtain a modified sodium bicarbonate powder, which was then mixed uniformly with the methyl vinyl silicone rubber, and then sealed and left to equilibrate at room temperature for one day, thereby obtaining the food-grade composite foaming agent.Preparation of a composite silicone rubber material:100:1:2:15 parts by mass of the rubber compound, a platinum vulcanizing agent, the food-grade composite foaming agent and flax fibers (having an average fiber length of 3mm) were weighed out, placed into a two-roll mill, and subjected to open milling to obtain a degradable composite silicone rubber material.Preparation of a filter rod:The composite silicone rubber material was placed into an extruder, the machine temperature was set to 55°C, heating was performed for 5min, then the temperature was set to 170°C to carry out high-temperature cross-linking foaming and extrusion, and after natural cooling, a rod-shaped material having hexagonal hollow flow channels was obtained. After being slit to a length of 120mm, strips of the composite silicone rubber material were obtained.The strips of the composite silicone rubber material were treated at 180°C for 8 hours, and after heat setting was performed, a degradable filter rod having a microporous structure was obtained.Comparative Example 1: Insufficient Amount of the Food-Grade Composite Foaming AgentThis comparative example is carried out in the same manner as in Example 2, except that in the preparation of the composite silicone rubber material, the mass ratio of the rubber compound, the platinum vulcanizing agent, the food-grade composite foaming agent and the flax fibers is 80:0.5:0.01:5.Comparative Example 2: Excessive Use of the Food-Grade Composite Foaming AgentThis comparative example is carried out in the same manner as in Example 2, except that in the preparation of the composite silicone rubber material, the mass ratio of the rubber compound, the platinum vulcanizing agent, the food-grade composite foaming agent and the flax fibers is 80:0.5:5:5.Comparative Example 3: Replacement of the Food-Grade Composite Foaming Agent with Sodium BicarbonateSodium bicarbonate, as a commonly used food-grade foaming agent, can also generate bubbles under heating. The sodium bicarbonate is used to replace the composite foaming agent of the present invention, and the influence of different foaming agents on the product performance is investigated.This comparative example is carried out in the same manner as in Example 2, except that in the preparation of the composite silicone rubber material, the mass ratio of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber is 80:0:0.Comparative Example 4: Replacement of the Food-Grade Composite Foaming Agent with Sodium Bicarbonate + Modifying AgentThe food-grade composite foaming agent also contains a raw rubber, and the influence of this part of the raw rubber on the product performance is investigated.This comparative example is carried out in the same manner as in Example 2, except that in the preparation of the composite silicone rubber material, the mass ratio of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber is 80:50:0.Comparative Example 5: Replacement of the Food-Grade Composite Foaming Agent with Sodium Bicarbonate + Raw RubberThe influence of the modifying agent in the food-grade composite foaming agent on the product performance is investigated.This comparative example is carried out in the same manner as in Example 2, except that in the preparation of the composite silicone rubber material, the mass ratio of sodium bicarbonate, stearic acid and methyl vinyl silicone rubber is 80:0:50.The main material differences of the above examples are shown in Table 1.Table 1: Main Material Amounts of the Examples Silicone Rubber : Filler : Silicone OilFilling Agent : Silicone Rubber MatrixRubber Compound, Vulcanizing Agent, Food-grade Composite Foaming Agent and Plant FibersSodium Bicarbonate, Food-grade Modifying Agent, Raw RubberExample 18:0.5:0.21:280:0.2:0.2:380:40:30Example 28:0.5:0.50.8:280:0.5:0.5:580:50:40Example 38:1:11.2:290:0.5:1:6100:40:30Example 410:1:11:390:0.8:1:6100:50:50Example 512:1:11.2:395:1:1.5:10120:60:40Example 612:2:11.3:5100:1:2:15120:60:50     Comparative Example 18:0.5:0.50.8:280:0.5:0.01:580:50:40Comparative Example 28:0.5:0.50.8:280:0.5:5:580:50:40Comparative Example 38:0.5:0.50.8:280:0.5:0.5:580:0:0Comparative Example 48:0.5:0.50.8:280:0.5:0.5:580:50:0Comparative Example 58:0.5:0.50.8:280:0.5:0.5:580:0:50The appearance characteristics of the above 11 samples were examined with a conventional cellulose acetate tow filter rod as a control, as shown in Table 2.Table 2: Comparison of Appearance of the Samples of the Examples Surface AppearanceLength (mm)Length Tolerance (mm)Cross-sectional Hollowed-out ShapeSensory Evaluation of Cross-sectional AppearanceControl (Acetate Filter Rod)Matte white120±2Regular hexagonEdges not sharp enough, close to an irregular rounded regular hexagon, with slight burrs and protruding fibersExample 1Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesExample 2Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesExample 3Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesExample 4Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesExample 5Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesExample 6Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesComparative Example 1Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesComparative Example 2Matte white120±2Regular hexagonSharp edges, shape slightly elliptical, edges slightly burredComparative Example 3Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesComparative Example 4Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesComparative Example 5Matte white120±2Regular hexagonSharp edges, uniform shape, smooth edgesThe results in Table 2 show that, compared with the existing conventional cellulose acetate filter rod whose appearance morphology exhibits edges that are not sharp enough, all the silicone rubber filter rods have the characteristic of sharp edges, and this difference is a product characteristic brought about by the difference in the main material (that is, cellulose acetate and silicone rubber).In Comparative Example 1, the insufficient amount of the composite foaming agent does not affect the product appearance, and in Comparative Examples 3-5, the use of sodium bicarbonate as the main component of the composite foaming agent can also maintain a good product appearance. However, in Comparative Example 2, the excessive use of the composite foaming agent leads to collapse of the product, making it impossible to maintain the appearance quality.It can be seen from this that the purpose of using the composite foaming agent is not to further improve the product appearance. When sodium bicarbonate alone is used to replace the composite foaming agent, a good product appearance morphology can still be obtained.The special-shaped filter rod prepared by using the degradable microporous material of the present invention has the characteristics of smooth and sharp special-shaped edges and uniform shape. Compared with a conventional cellulose acetate filter rod, the silicone rubber filter rod greatly improves the fineness and complexity of the hollowed-out pattern, makes the filter rod more diversified, and has stable appearance quality and broad application prospects.Further, the properties of the above samples were tested, and the results are shown in Table 3. The test items include:Filter rod hardness: the filter rod hardness is tested according to the test method of GB / T 22838.6-2009 "Determination of Physical Characteristics of Cigarettes and Filter Rods - Part 6: Hardness", by using an SHG-E cigarette and filter rod hardness tester manufactured by Chengdu Ruituo Technology Co., Ltd.Rebound rate: the rebound rate is tested according to the test method of GB / T 1681-2009 "Rubber - Determination of Rebound Resilience of Vulcanizates", by using a CREE-7006D compression rebound tester manufactured by Dongguan Kerui Instrument Technology Co., Ltd.Smoke temperature: the smoke temperature is the smoke temperature at the lip end. Under an HCI smoking regime, a puffing test is carried out by using a single-channel smoking machine, with a puff volume of 55mL, a puff duration of 3s, a puff interval of 30s and a puff number of 10 puffs. After the puffing is started, the gas-phase temperature at the center point of the smoke outlet near the lip end of the heated cigarette is measured by using a UT3208+ multi-channel temperature tester sold by Uni-Trend Technology (China) Co., Ltd., and the average smoke temperature of each puff is obtained until the puffing is completed.Porosity: the porosity is tested according to the test method of GB / T 34709-2017 "General Test Methods for Silica Gel - Determination of Pore Volume", by using an HX-TB open / closed porosity tester manufactured by Shandong Haixi Instrument Co., Ltd.Draw resistance: the draw resistance is tested according to the test method of GB / T 22838.5-2009 "Determination of Physical Characteristics of Cigarettes and Filter Rods - Part 5: Cigarette Draw Resistance and Filter Rod Pressure Drop", by using an AT-XZC draw resistance tester manufactured by Shandong Animate Instrument Co., Ltd.Density: the density is tested according to the test method of GB / T 533-2008 "Rubber, Vulcanized or Thermoplastic - Determination of Density", by using a silicone rubber density meter manufactured by Hangzhou Jinmai Instrument Co., Ltd.Table 3: Comparison Table of Filter Rod Properties Hardness (%)Rebound rate (%)Smoke Temperature (°C)Porosity (%)Draw Resistance (Pa)Density(g / cm3)Control (Acetate Filter Rod)90.6275.5442.35-26780.12Example 197.3390.6739.1721.8618940.78Example 296.8191.0637.9325.8816930.71Example 396.3791.9536.7532.4214580.59Example 495.8993.0235.0238.3713190.50Example 595.4594.1133.6343.2811980.39Example 694.9395.2431.2848.859840.27Comparative Example 198.3889.6645.8315.1320181.03Comparative Example 273.4280.2328.3562.746620.18Comparative Example 397.7586.5841.4618.6420780.95Comparative Example 492.8691.8939.5522.9317340.81Comparative Example 595.5388.9640.8619.5919520.89The results of the comparison of the filter rod properties listed in Table 3 show that:1. Compared with the existing conventional cellulose acetate filter rod, except for Comparative Example 2, the remaining silicone rubber filter rods all have good hardness and rebound rate, that is, they have good deformation resistance, can better maintain their appearance quality, and meet the physical property requirements of cigarettes and filter rods. However, in the sample of Comparative Example 2, since it contains an excessive amount of the composite foaming agent, the degree of foaming is higher, more pores are formed in the filter rod, and the porosity is excessively high, resulting in a decrease in both the hardness and the rebound rate, so that it is not suitable for use as a cigarette filter rod.2. Compared with the existing conventional cellulose acetate filter rod, all the filter rods of the present invention have a better cooling effect. In Comparative Example 1, the amount of the composite foaming agent is insufficient, resulting in a low degree of foaming of the product, and therefore the porosity thereof is low, the density is high, and the cooling effect is poor. It can be seen that the specific amount of the composite foaming agent affects not only the product strength but also the cooling performance of the filter rod.3. The selection of the foaming agent has a significant influence on the cooling performance of the filter rod. In Comparative Example 3, conventional sodium bicarbonate is selected as the foaming agent, and although the cooling performance of the obtained product is slightly better than that of the conventional cellulose acetate filter rod, it is not as good as that of the filter rod of the present invention using the composite foaming agent.4. In Comparative Examples 4 and 5, the raw rubber and the modifying agent in the composite foaming agent are respectively removed. It can be seen from the comparison with Comparative Example 3 and Example 2 that the addition of the modifying agent is conducive to improving the foaming performance of the sodium bicarbonate, and therefore the foaming effect and cooling performance thereof are both slightly better than those of Comparative Example 3. However, due to the absence of the raw rubber, it is likely that the foaming agent and other materials are difficult to mix uniformly in the subsequent open milling step, and therefore the foaming effect and cooling performance thereof are not as good as those of Example 2.In summary, the special-shaped filter rod prepared by using the degradable microporous material of the present invention has good application performance. Compared with a conventional cellulose acetate filter rod, the degradable filter rod having a microporous structure of the present invention has lower draw resistance and a better smoke cooling effect, and has relatively high hardness and rebound rate and relatively good deformation resistance, can maintain good appearance quality, ensures that the quality of the filter rod is stable, and meets the application requirements of traditional cigarettes and heat-not-burn cigarettes.By improving the formulation of the foaming agent, the present invention further improves the cooling performance of the silicone rubber filter rod and appropriately reduces the draw resistance of the filter rod, thereby achieving a better smoking experience.In summary, the degradable microporous material of the present invention not only solves the problem of the application of ordinary silicone rubber materials in cigarette filters, but also improves the degradability of the silicone rubber material, increases the material options and pattern richness of the hollowed-out filter rod, has a good cooling effect, and has good application prospects.ABSTRACT The present invention provides a method for preparing a degradable composite silica gel material. The method comprises: preparing a silica gel matrix from a raw rubber, a reinforcing filler, and silicone oil, and then mixing a filling agent and the silica gel matrix to obtain a rubber compound, putting the rubber compound, a vulcanizing agent, a food-grade composite foaming agent, and plant fibers into a two-roll mill for open milling to obtain the degradable composite silica gel material. The composite silica gel material can be applied to a filter rod. The present invention further provides a cigarette filter rod having a microporous structure and prepared from the composite silica gel material. The filter rod having the microporous structure of the present invention can achieve lower draw resistance and better vapor cooling effect. The filter rod has relatively high hardness and rebound rate and relatively good deformation resistance and can maintain good appearance quality. It is ensured that the quality of the filter rod is stable, and the application requirements of traditional cigarettes and heat-not-burn cigarettes are met.

Claims

1. A method for preparing a degradable composite silicone rubber material, the preparation method comprising the following steps:(1) preparing a silicone rubber matrixweighing out 8-12:0.5-2:0.2-1 parts by mass of a raw rubber, a reinforcing filler and a silicone oil, and mixing them uniformly to obtain a silicone rubber matrix; wherein the raw rubber is one or more silicone rubbers selected from methyl vinyl silicone rubber, dimethyl silicone rubber and methyl phenyl vinyl silicone rubber, and the raw rubber has a Shore A hardness of 10-30;(2) internal mixingweighing out 0.8-1.3:2-5 parts by mass of a filling agent and the silicone rubber matrix, placing the weighed materials into an internal mixer, and carrying out internal mixing at 120 °C-180 °C to obtain a rubber compound;(3) open millingweighing out 80-100:0.1-1:0.1-2:3-15 parts by mass of the rubber compound, a vulcanizing agent, a food-grade composite foaming agent and plant fibers, wherein the plant fibers have an average fiber length of 0.5-6 mm, placing the weighed materials into a two-roll mill, and carrying out open milling to obtain the degradable composite silicone rubber material. 2. The preparation method according to claim 1, characterized in that in step (1), the reinforcing filler is selected from white carbon black and / or titanium dioxide; and the silicone oil is selected from hydroxyl silicone oil and / or methoxy silicone oil. 3. The preparation method according to claim 1, characterized in that in step (2), the filling agent is one or more filling agents selected from calcium carbonate, white carbon black, quartz powder and / or wollastonite powder. 4. The preparation method according to claim 1, characterized in that in step (3), the food-grade composite foaming agent comprises, in parts by mass:80-120 parts of sodium bicarbonate40-60 parts of a food-grade modifying agent30-50 parts of a raw rubberwherein the modifying agent is one or more modifying agents selected from anhydrous citric acid, stearic acid, glyceryl monostearate and erucamide;the food-grade composite foaming agent is prepared by a method comprising:dissolving the food-grade modifying agent in anhydrous ethanol in an amount of 2.5-6 times the mass thereof, mixing the mixture uniformly, then adding sodium bicarbonate, mixing the mixture uniformly, and continuously stirring at a rotation speed of 300-600rpm and a temperature of 15-20°C until the ethanol is completely volatilized; drying the resulting product at 40-60°C for 10-20min to obtain dried modified sodium bicarbonate; placing the modified sodium bicarbonate into a grinder, grinding the same, and then passing the ground product through a 100-mesh sieve to obtain a modified sodium bicarbonate powder; mixing the modified sodium bicarbonate powder with the raw rubber uniformly, and then sealing the mixture and allowing the mixture to stand at room temperature for 12-24 hours to obtain the food-grade composite foaming agent. 5. The preparation method according to claim 1, characterized in that in step (3), the plant fibers are one or more fibers selected from flax, jute, sisal, ramie and abaca. 6. Use of the degradable composite silicone rubber material obtained by the preparation method according to any one of claims 1-5 in a filter rod. 7. The use according to claim 6, characterized in that the filter rod is a heat-not-burn cigarette filter rod or a combustible cigarette filter rod. 8. A method for preparing a degradable filter rod having a microporous structure, characterized in that the preparation method comprises the following steps:placing the degradable composite silicone rubber material obtained by the preparation method according to any one of claims 1-5 into an extruder, pre-forming the material at 25-85°C for 1-5min, then carrying out cross-linking foaming and extrusion at 120-180°C, and cooling the extruded material to obtain a rod-shaped material;slitting the obtained rod-shaped material to obtain strips of the composite silicone rubber material;treating the strips of the composite silicone rubber material at 150-200°C for 6-12 hours, and carrying out heat setting to obtain the degradable filter rod having a microporous structure. 9. The preparation method according to claim 8, characterized in that the filter rod has a density of 0.2-0.8g / cm3 and a porosity of 20-50%.