Polysaccharide-based flame-retardant material for cigarettes as well as preparation method and application thereof

Abstract

The invention provides a polysaccharide-based flame-retardant material for cigarettes as well as a preparation method and application of the polysaccharide-based flame-retardant material, and belongs to the technical field of tobaccos. The preparation method of the polysaccharide-based flame-retardant material for the cigarettes comprises the following steps: dissolving polysaccharide in water to form a polysaccharide solution; adding a saturated calcium source solution into the polysaccharide solution, and sequentially carrying out pre-crosslinking and freezing treatment to obtain pre-crosslinked polysaccharide-based hydrogel; the pre-crosslinked polysaccharide-based hydrogel is mixed with an inorganic salt solution, so that the pre-crosslinked polysaccharide-based hydrogel is subjected to at least one time of crosslinking curing, and the flame-retardant material for the cigarettes is obtained, wherein the polysaccharide at least comprises sodium alginate. The polysaccharide-based flame-retardant material for the cigarette has a flame-retardant effect, and can effectively reduce the average temperature of a combustion cone, so that the release of harmful substances in smoke is reduced.

Description

Technical Field

[0001] The present invention relates to the field of tobacco, and in particular to a polysaccharide-based flame retardant material for tobacco, and a preparation method and application thereof. Background Art

[0002] During the smoking process, combustible cigarettes produce smoke aerosols through combustion. Harmful substances are produced during the combustion of cigarettes, and the higher the combustion temperature, the more harmful substances are produced, such as tar and carbon monoxide.

[0003] Therefore, it is necessary to find a method to reduce the release of harmful substances in flue gas. Summary of the Invention

[0004] In view of this, in order to at least partially solve the above-mentioned technical problems, the present invention provides a polysaccharide-based flame retardant material for cigarettes, and a preparation method and application thereof.

[0005] According to an embodiment of one aspect of the present invention, a method for preparing a polysaccharide-based flame-retardant material for cigarettes is provided, comprising: dissolving a polysaccharide in water to form a polysaccharide solution; adding a saturated calcium source solution to the polysaccharide solution, and sequentially performing pre-crosslinking and freezing treatment to obtain a pre-crosslinked polysaccharide-based hydrogel; mixing the pre-crosslinked polysaccharide-based hydrogel with an inorganic salt solution to crosslink and solidify the pre-crosslinked polysaccharide-based hydrogel at least once to obtain the flame-retardant material for cigarettes; wherein the polysaccharide comprises at least sodium alginate.

[0006] According to another embodiment of the present invention, a polysaccharide-based flame retardant material for cigarettes is provided. The polysaccharide-based flame retardant material for cigarettes is prepared using the above-mentioned method for preparing the polysaccharide-based flame retardant material for cigarettes. The limiting oxygen index of the polysaccharide-based flame retardant material for cigarettes is greater than or equal to 28.

[0007] According to another embodiment of the present invention, there is provided a use of the polysaccharide-based tobacco flame retardant material as described above in tobacco shreds.

[0008] According to the polysaccharide-based flame-retardant material for cigarettes according to the embodiment of the present invention, a pre-cross-linked eggshell structure is formed by utilizing the carboxylate ions on the sodium alginate molecular chain under the action of calcium ions in a saturated calcium source solution. After preliminary shaping by pre-cross-linking, an initial three-dimensional network structure is obtained. Subsequently, it is further cross-linked and cured under the action of an inorganic salt solution to form a dense and stable hydrogel flame-retardant structure, which helps to reduce the combustion temperature of combustible cigarettes and reduce the release of harmful substances in the smoke when it is subsequently mixed with tobacco. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.

[0010] Figure 1A flow chart showing a method for preparing a polysaccharide-based flame retardant material for cigarettes according to an embodiment of the present invention is shown;

[0011] Figure 2 shows infrared spectra of the pre-crosslinked sodium alginate hydrogel and the sodium alginate raw material of Example 1 of the present invention;

[0012] Figure 3 Thermogravimetric analysis curves of the hydrogel coatings of Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention are shown;

[0013] Figure 4 shows a storage modulus curve of a hydrogel cured by primary cross-linking and cured by secondary cross-linking according to an embodiment of the present invention;

[0014] Figure 5 The maximum combustion temperature curves of the cigarette samples of Application Examples 1-2 and Comparative Examples 1-2 of the present invention are shown. DETAILED DESCRIPTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0016] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0017] When expressions such as "at least one of A, B or C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0018] In the present invention, the term "eggshell structure" refers to a microscopic or macroscopic structure with divisible characteristics formed during the cross-linking process, which has an outer layer and an inner layer, wherein the outer layer has a high cross-linking density, forming a denser shell structure relative to the inner layer; the inner layer has a low cross-linking density, and may contain some uncross-linked linear molecules (such as sodium alginate).

[0019] To lower the combustion temperature of combustion-type cigarettes, adjustments are usually made to the tobacco leaf raw materials and auxiliary materials, such as by adding tobacco additives. However, it is difficult to significantly reduce the average temperature of the cigarette combustion cone through optimization of the production process alone.

[0020] Related technologies have incorporated potassium salts to disperse the heat released by cigarette combustion, reducing the amount of heat released per unit time and, in turn, to some extent, reducing harmful substances in the smoke (such as carbon monoxide, 2-nitropropane, and nitrosamines). However, the cooling effect of directly adding potassium salts is limited, and there is the risk of releasing new harmful gases. Related technologies have also attempted to incorporate heat-conducting rods, sheets, or wires into tobacco to achieve cooling effects through thermal conductivity. However, this approach remains in the experimental stage and is difficult to apply to actual combustion-type cigarette products.

[0021] Related technologies also form a porous expanded carbon layer on the surface of tobacco shreds. The flame retardants used primarily include ammonium polyphosphate, a carbon source (polyhydroxy compound), an acid source, and a gas source. Analysis of the combustion cone temperature revealed that the gel flame retardant significantly reduced the combustion cone temperature of the burning cigarette. However, tobacco gel flame retardants have stringent requirements for their pyrolysis products. They must not produce sensory irritants that affect the taste of the cigarette, nor increase the amount of harmful substances in the smoke of the burning cigarette. The phosphorus-nitrogen flame retardants commonly used in related technologies struggle to meet these requirements.

[0022] Therefore, it is necessary to find a method for preparing a flame retardant material that can lower the combustion temperature and reduce harmful substances.

[0023] In the process of realizing the concept of the present invention, it was found that by pre-crosslinking and freezing the polysaccharide solution, the eggshell structure of the polysaccharide-based hydrogel can be strengthened, and then the subsequent addition to the burning cigarette can enhance the flame retardant effect.

[0024] Specifically, according to an embodiment of one aspect of the present invention, a method for preparing a polysaccharide-based flame retardant material for cigarettes is provided. Figure 1 The flowchart of the preparation method of the polysaccharide-based flame retardant material for cigarettes according to the embodiment of the present invention is shown as follows: Figure 1 As shown, the preparation method includes operations S101 to S103.

[0025] In operation S101 , polysaccharide is dissolved in water to form a polysaccharide solution.

[0026] In operation S102, a saturated calcium source solution is added to the polysaccharide solution, and pre-crosslinking and freezing treatment are performed in sequence to obtain a pre-crosslinked polysaccharide-based hydrogel.

[0027] In operation S103, the pre-crosslinked polysaccharide-based hydrogel is mixed with an inorganic salt solution to crosslink and solidify the pre-crosslinked polysaccharide-based hydrogel at least once to obtain a flame retardant material for cigarettes;

[0028] According to an embodiment of the present invention, the polysaccharide includes at least sodium alginate. The sodium alginate molecular chain is rich in carboxylate ions. The calcium ions in the added saturated calcium source solution combine with multiple carboxylate ions to form an eggshell structure, constructing an initial three-dimensional hydrogel structure (that is, a pre-crosslinked polysaccharide-based hydrogel), providing initial skeleton and shape stability. After freezing, it helps to further arrange the three-dimensional hydrogel porous structure in the polysaccharide-based hydrogel in an orderly manner, which helps to improve the mechanical strength, thermal stability and barrier properties of the three-dimensional hydrogel porous structure. Cross-linking and curing are then carried out to further strengthen the hydrogel network, making it more heat-resistant and easy to dehydrate and carbonize during subsequent combustion, which helps to isolate oxygen and block heat, thereby lowering the combustion temperature of the cigarette and reducing the release of harmful substances in the smoke.

[0029] It should be noted that the polysaccharide-based flame-retardant material for tobacco, made by mineralizing a polysaccharide solution with calcium ions, can significantly reduce the combustion temperature, and the harm reduction effect is significantly better than the cooling method in the related art. This may be because the water rich in the polysaccharide-based hydrogel in the polysaccharide-based flame-retardant material for tobacco can act as a flame retardant. When encountering high temperatures, the water will evaporate rapidly, absorbing a large amount of heat energy, thereby playing a cooling role and inhibiting the spread of flames. In addition, the polysaccharide-based hydrogel can form a protective carbonized layer at high temperatures, reducing the contact between oxygen and burning substances and effectively preventing the spread of combustion. The polysaccharide-based flame-retardant material for tobacco contains a carbon source and a gas source to form a synergistically expanding hydrogel flame retardant system. At the same time, the source of the polysaccharide-based hydrogel is green and environmentally friendly, and no additional toxic gases will be released during subsequent combustion.

[0030] It is understood that the at least one cross-linking and curing step can be understood as a single cross-linking and curing step of the pre-cross-linked polysaccharide-based hydrogel, or can be a single cross-linking and curing step followed by one or more cross-linking and curing steps. For example, the cross-linking and curing step can be a single cross-linking and curing step, a secondary cross-linking and curing step, a tertiary cross-linking and curing step, or a quadruple cross-linking and curing step, etc. This is not particularly limited in the present invention and can be adjusted according to actual needs.

[0031] Preferably, the pre-crosslinked polysaccharide-based hydrogel is mixed with an inorganic salt solution for primary crosslinking and curing or secondary crosslinking and curing. This arrangement can reduce industrial complexity and save production costs while ensuring the crosslinking effect.

[0032] For example, under the premise that the above two are subjected to secondary cross-linking and curing, the process of the two cross-linking and curing can be as follows: the pre-cross-linked polysaccharide-based hydrogel is mixed with the inorganic salt solution, and static cross-linking is performed to obtain a primary cross-linked and cured product; the primary cross-linked and cured product is mixed with the inorganic salt solution, and static cross-linking is performed again to obtain a secondary cross-linked and cured product, and then a polysaccharide-based flame retardant material for cigarettes is obtained.

[0033] It is understood that, under the premise of performing secondary cross-linking and curing, the conditions of the first cross-linking and curing may be the same as or different from the conditions of the second cross-linking and curing, and the present invention does not impose any particular limitation on this.

[0034] In some embodiments, the pre-crosslinking temperature is 20-60°C. This helps optimize the crosslinking rate while maintaining the uniformity of the three-dimensional crosslinked network. If the temperature is too low, the molecular thermal motion is slow, resulting in a slower crosslinking process. This can significantly extend the reaction time, cause localized over- or under-crosslinking, and lead to structural defects in the hydrogel network. If the temperature is too high, excessive crosslinking may occur, leading to partial agglomeration and non-uniformity, which may also impair the gelling ability of the sodium alginate.

[0035] Optionally, the pre-crosslinking temperature may be 20° C., 30° C., 40° C., 50° C., or 60° C., or may be a range between any two of the above values.

[0036] In some embodiments, the pre-crosslinking time is 20 to 40 minutes. This helps ensure sufficient and controllable pre-crosslinking. If the time is too short, the pre-crosslinking process may be incomplete, resulting in an incomplete eggshell structure. If the time is too long, excessive crosslinking may result in an overly dense eggshell structure, weakening the freezing optimization effect and limiting the space for subsequent crosslinking under the action of inorganic salts.

[0037] Optionally, the pre-crosslinking time may be 20 min, 25 min, 30 min, 35 min or 40 min, etc., or may be a range between any two of the above values.

[0038] In some embodiments, the freezing temperature is between -20°C and 0°C. This helps regulate the size and morphology of ice crystals formed during the freezing process, directing the molecular chains in the polysaccharide-based hydrogel to align along the ice crystal interfaces. If the temperature is too low, ice crystals will nucleate rapidly and in large quantities, easily piercing the eggshell structure of the pre-crosslinked hydrogel and destroying the hydrogel structure. If the temperature is too high, ice crystals will be difficult to form.

[0039] Optionally, the temperature of the freezing treatment may be -20°C, -15°C, -10°C, -5°C, -4°C or 0°C, etc., or a range between any two of the above values.

[0040] Preferably, the freezing temperature is -4°C.

[0041] In some embodiments, the freezing time is 24 to 48 hours. This arrangement helps to fully achieve the separation between the pre-crosslinked polysaccharide-based hydrogel and the water therein. If the time is too short, the central region of the pre-crosslinked polysaccharide-based hydrogel will not be completely frozen, making it difficult to form a complete eggshell structure, and subsequent thawing will result in uneven structure. If the time is too long, the preparation process will be longer, making the process flow slower.

[0042] Optionally, the freezing time may be, for example, 24 hours, 28 hours, 32 hours, 36 hours, 40 hours, 44 hours or 48 hours, or a range between any two of the above values.

[0043] Preferably, the freezing time is 24 hours.

[0044] In some embodiments, the crosslinking and curing temperature is 5°C to 25°C. This lower temperature helps protect the freeze-optimized hydrogel structure and maintain its structural integrity. Too low a temperature may result in incomplete crosslinking and curing, while too high a temperature may damage the freeze-optimized hydrogel structure.

[0045] Optionally, the cross-linking and curing temperature may be 5° C., 10° C., 15° C., 20° C., or 25° C., or may be a range between any two of the above values.

[0046] In some embodiments, the crosslinking and curing time is 12 to 36 hours. This configuration facilitates a uniform crosslinking process, allowing the inorganic salt solution to fully penetrate the hydrogel, promoting further crosslinking of unsaturated carboxyl groups in the sodium alginate, and improving the structural stability of the polysaccharide-based hydrogel. If the crosslinking and curing time is too short, the penetration is not deep enough, and unsaturated carboxyl groups may still exist. If the crosslinking and curing time is too long, excessive crosslinking is avoided.

[0047] In some embodiments, the inorganic salt solution includes a calcium chloride solution, wherein the calcium ions can promote the cross-linking and solidification of the carboxyl groups in the sodium alginate to form a dense polysaccharide-based hydrogel.

[0048] In some embodiments, the molar concentration of the calcium chloride solution is 100-400 mmol·L -1 . Such a setting helps to provide a sufficient concentration of calcium ions to promote sufficient cross-linking of carboxyl groups. If the concentration of the calcium chloride solution is too low, it may cause surface cross-linking of the pre-cross-linked polysaccharide-based hydrogel and cross-linking of the internal network, resulting in poor mechanical strength and uneven flame retardant properties. If the concentration is too high, it may cause excessive instantaneous cross-linking of the surface, hindering the diffusion of calcium ions into the interior of the polysaccharide-based hydrogel, resulting in uneven internal and surface cross-linking of the polysaccharide-based hydrogel and poor internal mechanical strength.

[0049] Alternatively, the molar concentration of the calcium chloride solution can be 100 mmol·L -1 , 200mmol·L -1 、300mmol·L -1 or 400mmol·L -1 , preferably 100 mmol·L -1 .

[0050] In some embodiments, the volume of the calcium chloride solution is 1-10 mL. This design can reduce the damage that the water therein may cause to the hydrogel structure.

[0051] Optionally, the volume of the calcium chloride solution can be 1 mL, 3 mL, 5 mL, 7 mL, 9 mL or 10 mL, etc.

[0052] It is understood that in order to reduce the negative impact of the inorganic salt solution on the polysaccharide-based flame retardant material for cigarettes, it can be rinsed with clean water after cross-linking and curing, and then dried to fully remove other impurities that may be attached to the surface of the polysaccharide-based flame retardant material for cigarettes.

[0053] In some embodiments, the polysaccharide is a mixture of sodium alginate and other polysaccharides; the other polysaccharides include one or more of starch, cellulose, derivatized cellulose, alginic acid, inulin, chitosan, agar, and amino polysaccharides. This arrangement allows sodium alginate to form a dense eggshell structure, while the addition of other polysaccharides helps increase the thickness and thermal insulation properties of the rigid carbon layer formed upon subsequent heating. Furthermore, the other polysaccharides are relatively cheaper, contributing to cost savings.

[0054] It can be understood that when the polysaccharide is a mixture, dissolving the polysaccharide in water in operation S101 can be understood as dissolving each component of the mixture separately in water and then mixing them; or adding the mixture to water together, which is not particularly limited in the present invention.

[0055] In some embodiments, when the polysaccharide is sodium alginate, the mass ratio of sodium alginate to water is (0.5-5):(100-200). This configuration helps form an eggshell structure of sufficient thickness, which helps to achieve sufficient oxygen barrier and heat insulation effects after subsequent carbonization.

[0056] In some embodiments, when the polysaccharide is a mixture of sodium alginate and other polysaccharides, the mass ratio of sodium alginate, other polysaccharides, and water is (1-5):(0.5-3):(50-500). This configuration helps provide a complete eggshell structure and enhances the flame retardant effect through the addition of other polysaccharides.

[0057] In some embodiments, the volume ratio of the saturated calcium source solution to the polysaccharide solution is (1-5):10. This helps ensure that the sodium alginate in the polysaccharide solution is fully cross-linked, thereby forming a stable eggshell structure. If the volume of the saturated calcium source solution is too low, it will be difficult to form a continuous and uniform eggshell structure. If the volume of the saturated calcium source solution is too high, it may cause localized overpolymerization, resulting in uneven gelation or surface hardening of the formed polysaccharide-based hydrogel.

[0058] Optionally, the volume ratio of the saturated calcium source solution to the polysaccharide solution can be 1:10, 2:10, 3:10, 4:10 or 5:10, etc.

[0059] In some embodiments, the saturated calcium source solution includes a saturated calcium sulfate solution. This configuration, due to the low solubility of calcium sulfate in water, results in a slower release of calcium ions, thereby preventing instantaneous excessive cross-linking, reducing surface hardening and internal inhomogeneity of the hydrogel, and promoting a denser three-dimensional hydrogel structure while improving tensile strength and processing performance.

[0060] According to another embodiment of the present invention, there is provided a polysaccharide-based flame retardant material for cigarettes, which is prepared using the above-mentioned method for preparing a polysaccharide-based flame retardant material for cigarettes.

[0061] According to an embodiment of the present invention, based on the aforementioned pre-crosslinking, freezing treatment and crosslinking curing, the hydrogel structure of the formed polysaccharide-based tobacco flame retardant material is relatively dense, which helps to fully reduce the combustion temperature in subsequent applications in burning cigarettes.

[0062] In some embodiments, the limiting oxygen index of the polysaccharide-based flame retardant material for cigarettes is greater than or equal to 28. The polysaccharide-based flame retardant material for cigarettes of the present invention has a relatively significant flame retardant effect, which significantly reduces the temperature of the cigarette burning cone and reduces the release of harmful substances.

[0063] According to another embodiment of the present invention, there is provided a use of the polysaccharide-based tobacco flame retardant material as described above in tobacco shreds.

[0064] According to an embodiment of the present invention, polysaccharide-based flame retardant materials are applied to tobacco shreds. The flame retardant effect of the polysaccharide-based flame retardant materials helps to lower the combustion temperature of cigarettes and reduce the release of harmful components in smoke.

[0065] As can be understood, flame-retardant shredded tobacco is prepared by blending crushed or shredded polysaccharide-based tobacco flame-retardant material with shredded tobacco and stirring them uniformly. This arrangement helps lower the combustion temperature of the cigarette during smoking and reduces the production of harmful substances in the smoke. The resulting mixed cigarette of the present invention has the advantages of high flame retardancy, environmental friendliness, safety, and pollution-free, and has broad application prospects in reducing the production of harmful gases during cigarette combustion.

[0066] In some embodiments, the mass of the polysaccharide-based flame retardant material for tobacco is 1-15% of the mass of the tobacco shreds. If too much is added, the overall taste of the cigarette may be affected and sustained combustion may be difficult. If too little is added, the combustion temperature may not be significantly reduced, resulting in a high concentration of harmful substances in the smoke. Adjusting the mass within the aforementioned range can sufficiently lower the combustion temperature and, in turn, significantly reduce the release of harmful substances in the smoke.

[0067] Optionally, the mass of the polysaccharide-based flame retardant material for tobacco can be 1%, 3%, 5%, 7%, 8%, 10% or 15% of the total mass of the tobacco shreds.

[0068] The present invention is further illustrated below by way of examples and their results. In the detailed description that follows, for ease of explanation, numerous specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is apparent that one or more embodiments may be implemented without these specific details. Furthermore, the details in the following embodiments may be arbitrarily combined into other feasible embodiments, unless conflicting.

[0069] It should be noted that the following specific examples are for illustration only and the scope of protection of the present invention is not limited thereto. The raw materials used in the following examples are commercially available or prepared by generally recognized processing methods.

[0070] Example 1

[0071] Weigh 2 g of sodium alginate powder and add it to 100 mL of deionized water in small amounts at 25°C. Stir continuously for 24 h until the swelling is complete and the powder is completely dissolved to obtain a 2 wt% sodium alginate solution.

[0072] At 25°C, 2 mL of saturated calcium sulfate solution was added to the sodium alginate solution and allowed to stand for 30 minutes for pre-crosslinking. The solution was then placed in a -4°C refrigerator and frozen for 24 hours to obtain a pre-crosslinked 2 wt% sodium alginate hydrogel.

[0073] Figure 2 FIG1 shows the infrared spectra of the pre-crosslinked sodium alginate hydrogel and the sodium alginate raw material of Example 1 of the present invention. Figure 2 As shown in the figure, it can be seen that the carboxylate groups in the pre-crosslinked polysaccharide-based hydrogel are cross-linked with calcium ions to form bonds.

[0074] Take 10 mL of pre-crosslinked 2 wt% sodium alginate solution and add 2 mL of 100 mmol·L -1 The solution was stirred for 24 h at room temperature to obtain a single cross-linked sodium alginate hydrogel.

[0075] After the natural leveling, the sodium alginate primary hydrogel was prepared by drying in a 40℃ oven for 60 min.

[0076] Example 2

[0077] The preparation process of this example 2 was substantially the same as that of example 1, except that after the formation of the sodium alginate primary cross-linked hydrogel, 2 mL of 100 mmol·L -1 of calcium chloride solution was added, and the cross-linking was carried out at room temperature for 24 h to obtain the sodium alginate secondary cross-linked hydrogel.

[0078] The sodium alginate secondary cross-linked hydrogel was obtained in the same way as example 1.

[0079] Example 3

[0080] First, 2 g of sodium alginate and 0.5 g of sodium carboxymethyl cellulose powder were mixed and added to 100 mL of deionized water in small amounts and multiple times under the condition of 25℃ temperature, and stirred constantly for 24 h until the swelling was completed and the powder was completely dissolved, to obtain a mixed solution of 2 wt% sodium alginate and 0.5 wt% sodium carboxymethyl cellulose.

[0081] After the addition of 2 mL of saturated calcium sulfate solution to the mixed solution under the condition of 25℃, the pre-cross-linking was carried out by standing for 30 min, and the pre-cross-linked mixed solution was frozen in a refrigerator at -4℃ for 24 h to obtain the pre-cross-linked mixed solution.

[0082] 10 mL of the pre-cross-linked mixed solution was taken, and 2 mL of 100 mmol·L -1 of calcium chloride solution was added, and the cross-linking was carried out at room temperature for 24 h to obtain the sodium alginate and sodium carboxymethyl cellulose mixed primary cross-linked hydrogel.

[0083] 2 mL of 100 mmol·L -1 of calcium chloride solution was added to the sodium alginate and sodium carboxymethyl cellulose mixed primary cross-linked hydrogel, and the cross-linking was carried out at room temperature for 24 h to obtain the sodium alginate and sodium carboxymethyl cellulose mixed secondary cross-linked hydrogel.

[0084] The sodium alginate and sodium carboxymethyl cellulose mixed secondary cross-linked hydrogel coating was obtained in the same way as example 1.

[0085] Comparative Example 1

[0086] 0.5 g of sodium carboxymethyl cellulose was weighed and added to 100 mL of deionized water in small amounts and multiple times under the condition of 25℃ temperature, and stirred constantly for 24 h until the swelling was completed and the powder was completely dissolved, to obtain a 0.5 wt% sodium carboxymethyl cellulose solution.

[0087] At 25° C., 2 mL of saturated calcium sulfate solution was added to the sodium carboxymethyl cellulose solution, and the solution was allowed to stand for 30 minutes for pre-crosslinking. The solution was then placed in a -4° C. refrigerator and frozen for 24 hours to obtain a pre-crosslinked 0.5 wt% sodium carboxymethyl cellulose solution.

[0088] Take 10 mL of pre-crosslinked 0.5 wt% sodium carboxymethyl cellulose solution and add 2 mL of 100 mmol·L -1 The solution was added with calcium chloride solution and allowed to crosslink at room temperature for 24 hours to obtain a sodium carboxymethyl cellulose primary crosslinked hydrogel. After it was naturally leveled, it was placed in a 40°C oven and dried for 60 minutes to obtain a sodium carboxymethyl cellulose primary crosslinked hydrogel.

[0089] Comparative Example 2

[0090] The preparation process of Comparative Example 2 is substantially the same as that of Comparative Example 1, except that after forming the primary cross-linked hydrogel of sodium carboxymethyl cellulose, 2 mL of 100 mmol·L -1 After the solution was allowed to crosslink at room temperature for 24 hours, a sodium carboxymethyl cellulose secondary crosslinked hydrogel was obtained. After the solution was naturally leveled, it was placed in a 40°C oven and dried for 60 minutes to obtain a sodium carboxymethyl cellulose secondary crosslinked hydrogel.

[0091] Comparative Example 3

[0092] The preparation process of Comparative Example 3 is substantially the same as that of Example 2, except that only saturated calcium sulfate solution is used for pre-crosslinking, and calcium chloride solution is not used for further strengthening.

[0093] Comparative Example 4

[0094] The preparation process of Comparative Example 4 is substantially the same as that of Example 2, except that no saturated calcium sulfate solution is used for pre-crosslinking.

[0095] Comparative Example 5

[0096] The preparation process of Comparative Example 5 is substantially the same as that of Example 2, except that the low temperature condition is not controlled when the saturated calcium sulfate solution is used for pre-crosslinking, and the crosslinking temperature is room temperature 22°C.

[0097] Comparative Example 6

[0098] The preparation process of this comparative example 6 is substantially the same as that of Example 2, except that the calcium chloride solution is replaced by a magnesium chloride solution.

[0099] The gelation conditions and limiting oxygen indexes of the hydrogel coatings prepared in Examples 1 to 3 of the present invention and Comparative Examples 1 to 6 are shown in Table 1 below.

[0100] The limiting oxygen index is measured by a limiting oxygen index tester according to the GB / T 2406 standard.

[0101] Table 1

[0102]

[0103] Figure 3 A thermogravimetric analysis curve of the hydrogel coating film of the present application examples 1-2 and comparative examples 1-2 is shown. The test conditions are: 40-800℃, programmed temperature rate 10℃ / min. The initial raw material of comparative example 1 can be understood as sodium carboxymethyl cellulose powder, and the initial raw material of example 1 can be understood as sodium alginate powder. As shown in Figure 3 It can be seen that examples 1 and 2 have stronger heat resistance than comparative examples.

[0104] Figure 4 A storage modulus curve of the hydrogel of the present application examples of once cross-linking and curing and twice cross-linking and curing is shown, which is measured by a rotary rheometer. As shown in Figure 4 It can be seen that the hydrogel cross-linked by sodium alginate has better mechanical properties than sodium carboxymethyl cellulose, and the twice cross-linking and curing can further improve the processability of the hydrogel material. In addition, the internal strength of the hydrogel without low-temperature pre-cross-linking process is also significantly lower than that of the pre-cross-linked hydrogel.

[0105] Application examples 1-2

[0106] The hydrogels prepared in examples 1-2 are cut into shreds, and are respectively rolled into cigarettes by a cigarette machine according to a mass fraction of 10% (accounting for the total weight of tobacco shreds). The highest temperature of the cigarette combustion cone is measured by an infrared camera, and the results are shown in Figure 5 .

[0107] Application comparative example 1

[0108] Without adding the hydrogel sample, only tobacco shreds are rolled into cigarettes by a cigarette machine. The highest temperature of the cigarette combustion cone is measured by an infrared camera, and the results are shown in Figure 5 .

[0109] Application comparative example 2

[0110] The hydrogel prepared in comparative example 6 is cut into shreds, and is respectively rolled into cigarettes by a cigarette machine according to a mass fraction of 10% (accounting for the total weight of tobacco shreds). The highest temperature of the cigarette combustion cone is measured by an infrared camera, and the results are shown in Figure 5 .

[0111] Figure 5 A highest temperature curve of the cigarette sample of the present application application examples 1-2 and application comparative examples 1-2 is shown. From Figure 5 As can be seen from the results, the addition of hydrogel can significantly reduce the combustion temperature of cigarettes, which is beneficial for reducing the release of harmful components in smoke. At the same time, the cooling effect of hydrogel strengthened by secondary cross-linking is better than that of hydrogel samples strengthened by single cross-linking.

[0112] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a polysaccharide-based flame retardant material for cigarettes, comprising: dissolving the polysaccharide in water to form a polysaccharide solution; adding a saturated calcium source solution to the polysaccharide solution, and sequentially performing pre-crosslinking and freezing treatment to obtain a pre-crosslinked polysaccharide-based hydrogel; mixing the pre-crosslinked polysaccharide-based hydrogel with an inorganic salt solution, so that the pre-crosslinked polysaccharide-based hydrogel is crosslinked and cured at least once, thereby obtaining the flame retardant material for cigarettes; Wherein, the polysaccharide includes at least sodium alginate.

2. The preparation method according to claim 1, wherein The pre-crosslinking temperature is 20-60° C., and the pre-crosslinking time is 20-40 min.

3. The preparation method according to claim 1, wherein The freezing temperature is -20~0℃ and the freezing time is 24~48h.

4. The preparation method according to claim 1, wherein The cross-linking curing temperature is 5-25°C and the time is 12-36 hours; The inorganic salt solution includes a calcium chloride solution having a molar concentration of 100 to 400 mmol·L -1 , volume is 1~10mL.

5. The preparation method according to any one of claims 1 to 4, wherein The polysaccharide is a mixture of sodium alginate and other polysaccharides; The other polysaccharides include one or more of starch, cellulose, derivatized cellulose, alginic acid, inulin, chitosan, agar, and amino polysaccharides.

6. The preparation method according to claim 5, wherein When the polysaccharide is sodium alginate, the mass ratio of sodium alginate to water is (0.5-5): (100-200); When the polysaccharide is a mixture of sodium alginate and other polysaccharides, the mass ratio of sodium alginate, the other polysaccharides, and water is (1-5): (0.5-3): (50-500); The volume ratio of the saturated calcium source solution to the polysaccharide solution is (1-5):10, and the saturated calcium source solution includes a saturated calcium sulfate solution.

7. A polysaccharide-based flame retardant material for cigarettes, prepared using the method for preparing a polysaccharide-based flame retardant material for cigarettes according to any one of claims 1 to 6, wherein the polysaccharide-based flame retardant material for cigarettes has a limiting oxygen index greater than or equal to 28.

8. Use of the polysaccharide-based flame retardant material for tobacco according to claim 7 in tobacco shreds.

9. The use according to claim 8, wherein: The polysaccharide-based flame retardant material for tobacco is added to tobacco shreds, and the mass of the polysaccharide-based flame retardant material for tobacco is 1-15% of the mass of the tobacco shreds.

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