A special curing agent for PLA tow-to-bob for cigarettes and a preparation method thereof

Abstract

The application discloses a special curing agent for PLA tow rod for cigarettes and a preparation method thereof, and belongs to the field of filter rod processing and molding for cigarettes. The curing agent is a composite including polylactic acid polyol, citric acid ester and a leading solvent; the polylactic acid polyol is prepared by esterification or transesterification of a lactic acid derivative and a polyhydric alcohol under the catalysis of a catalyst; the citric acid ester is selected from one or more of acetyl tri-n-butyl citrate, tri-n-butyl citrate and triethyl citrate; and the leading solvent is selected from acetyl ethyl acetate or ethyl levulinate. The application can solve the problem of insufficient low-temperature compatibility of a traditional curing agent (such as glyceryl triacetate) and polylactic acid (PLA) tow, and if a conventional spraying process and dosage are adopted, the PLA filter rod is prone to forming difficulty, insufficient hardness, and even collapse in the subsequent smoking process. If the spraying amount is greatly reduced in order to force the rod to form, it is difficult to ensure that the filter rod obtains ideal mechanical properties and use stability.

Description

Technical Field

[0001] This application relates to the field of tobacco filter rod processing and molding technology, and in particular to a special curing agent for tobacco PLA tow rods and its preparation method. Background Technology

[0002] Polylactic acid (PLA), as a bio-based, biodegradable, and environmentally friendly polymer material, has received increasing attention and application in the field of cigarette filter rod manufacturing.

[0003] Tobacco tow needs to undergo a plasticizing and curing process to be formed into filter rods with suitable performance indicators such as hardness and suction resistance. This process usually requires the use of a special curing agent.

[0004] Currently, glyceryl triacetate (GTA) is used as a plasticizing and curing agent for cellulose acetate (CDA) tows. This type of curing agent has excellent plasticizing and bonding curing effects on CDA tows, and the process is mature. However, in the industrial production of PLA tow rods, when applied to PLA tows with chemical structures that are completely different from CDA, the existing curing agent system reveals obvious limitations.

[0005] Specifically, traditional curing agents, such as triacetin, have insufficient low-temperature compatibility with PLA due to their molecular structure, resulting in poor plasticizing effect on PLA. During the rod-forming process, if conventional spraying techniques and dosages are used, it is difficult to effectively bond and cure the PLA filaments, easily leading to problems such as difficulty in filter rod forming, insufficient hardness, and even collapse during subsequent suction. If the spraying amount is drastically reduced to barely form a rod, it is difficult to guarantee that the filter rod will obtain ideal mechanical properties and operational stability. Summary of the Invention

[0006] This application provides a special curing agent for PLA tow rods for tobacco and its preparation method, which can solve the problem of insufficient low-temperature compatibility between traditional curing agents (such as triacetin) and polylactic acid (PLA) tow. If conventional spraying processes and dosages are used, it is easy to encounter problems such as difficulty in forming PLA filter rods, insufficient hardness, and even collapse during subsequent suction. If the spraying amount is greatly reduced in order to barely form a rod, it is difficult to ensure that the filter rod obtains ideal mechanical properties and stability in use.

[0007] To achieve the above objectives, the technical solution of this invention is as follows: In a first aspect, embodiments of the present invention provide a curing agent for PLA tow rods used in cigarettes, which is a composite comprising polylactic acid polyol, citric acid esters and lead solvent; The polylactic acid polyol is prepared by reacting a lactic acid derivative with a polyol through esterification or transesterification under the catalysis of a catalyst. The citrate esters are selected from one or more of acetylacetic tributyl citrate, tributyl citrate, and triethyl citrate. The lead solvent is selected from ethyl acetoacetate or ethyl acetopropionate.

[0008] In conjunction with the first aspect, in one possible implementation, the mass percentage of each component in the complex is: The polylactic acid polyol accounts for 20% to 70%; The citrate esters account for 20% to 70%; The lead solvent accounts for 10% to 30%.

[0009] In conjunction with the first aspect, in one possible implementation, the lactic acid derivative is selected from one or more of ethyl lactate, butyl lactate, and lactide.

[0010] In conjunction with the first aspect, in one possible implementation, the polyol is selected from one or more of ethylene glycol, propylene glycol, and glycerol.

[0011] In conjunction with the first aspect, in one possible implementation, the catalyst is selected from organotin catalysts, titanate catalysts, organic bases, inorganic bases, supported calcium oxide porous materials, or cation exchange resins.

[0012] Secondly, embodiments of the present invention provide a method for preparing a special curing agent for PLA tow rods used in cigarette manufacturing, comprising: S1. Synthesis of polylactic acid polyol: The lactic acid derivative and the polyol are subjected to esterification or transesterification reaction at a temperature of 100℃~160℃ and under vacuum conditions in the presence of a catalyst and an inert atmosphere. The by-products and unreacted monomers are then distilled off under an increased vacuum to obtain polylactic acid polyol. S2. Composite: The polylactic acid polyol, citric acid ester plasticizer and lead solvent obtained in step S1 are mixed evenly according to a predetermined mass ratio to obtain the special curing agent for PLA tow rods for cigarettes.

[0013] In conjunction with the second aspect, in one possible implementation, in step S1, the lactic acid derivative is selected from one or more of ethyl lactate, butyl lactate, and lactide, and the polyol is selected from one or more of ethylene glycol, propylene glycol, and glycerol.

[0014] In conjunction with the second aspect, in one possible implementation, in step S1, the catalyst is selected from organotin catalysts, titanate catalysts, organic bases, inorganic bases, supported calcium oxide porous materials, or cation exchange resins.

[0015] In conjunction with the second aspect, in one possible implementation, in step S1, the reaction is carried out under conditions of apparent vacuum of -0.03 MPa to -0.08 MPa.

[0016] Thirdly, embodiments of the present invention provide a method for preparing PLA filter rods for cigarettes, wherein the above-mentioned special curing agent for forming PLA tow rods for cigarettes is used as a plasticizing curing agent and sprayed during the PLA tow forming process.

[0017] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: The present invention provides a special curing agent for PLA tow rods used in cigarettes, which is a compound formulated with polylactic acid polyol, citrate plasticizer, and lead solvent to create a special composite specifically for the characteristics of polylactic acid (PLA) tow. This effectively solves the core technical problem mentioned in the background art: insufficient low-temperature compatibility between traditional curing agents (such as triacetin GTA) and PLA tow. Traditional triacetin GTA is designed for cellulose acetate (CDA) tow, and its molecular structure is completely different from the chemical structure of PLA, resulting in poor low-temperature plasticizing effect and difficulty in effective bonding and curing during PLA tow rod formation. If conventional spraying processes and dosages are used, PLA filter rods will experience difficulties in molding, insufficient hardness, and even collapse during subsequent suction; if the spraying amount is reduced, the mechanical properties and stability of the filter rod cannot be guaranteed. However, the present invention, by introducing polylactic acid polyol with a structure highly similar to PLA as the main plasticizer and binder, significantly improves the affinity and solubility of the curing agent with the PLA matrix, fundamentally improving the compatibility problem. Meanwhile, the added citrate ester plasticizers not only act as auxiliary plasticizers but also reduce the viscosity of the entire composite system, making it easier to spray and coat evenly during the rod-forming process. The introduction of lead solvents such as ethyl acetoacetate or ethyl levulinate not only provides excellent low-odor PLA solvents but also pre-dissolves the surface of the PLA fiber bundles, greatly promoting the diffusion, adhesion, and penetration of subsequent polylactic acid polyols and citrate ester plasticizers between PLA molecules. This "lead-dissolution-synergistic plasticizing" mechanism effectively guides the plasticizer components into the fiber bundle, accelerating the movement and rearrangement of the PLA molecular chains, thus achieving efficient bonding, swelling, and curing of PLA fiber bundles even at lower temperatures. This synergistic effect enables the specialized curing agent of this invention to form stable bonded joints in PLA tows under conventional spraying processes, achieving a reliable curing process similar to that when cellulose acetate tows are plasticized with triacetin. The resulting PLA filter rods exhibit excellent hardness, roundness, and dimensional stability, completely overcoming the molding difficulties and collapse defects caused by traditional curing agents, and possessing ideal mechanical properties and operational stability. Furthermore, this composite formulation, through the synergistic effect of its components, provides better process adaptability, allowing the viscosity of the curing agent system to be adjusted according to the formulation to a range suitable for spraying with existing equipment, achieving stable production of PLA filter rods without major modifications to existing production lines. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that all raw materials in the embodiments of this invention can be purchased commercially or prepared using conventional methods well known to those skilled in the art; the groups in the embodiments of this invention should be understood in the general sense of the chemical field, for example: a group usually refers to a radical, encompassing all "functional groups" in the structure of an organic compound, specifically including hydrogen groups, fluorine groups, chlorine groups, bromine groups, iodo groups, alkyl groups, alkenyl groups, alkynyl groups, methoxy groups, phenyl groups, acyl groups, carboxyl groups, carbonyl groups, nitro groups, hydroxyl groups, sulfonic acid groups, etc. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this invention according to the specific circumstances.

[0020] This invention provides a curing agent specifically for PLA tow rods used in cigarette manufacturing. The agent is a composite comprising polylactic acid polyol, citrate ester plasticizer, and lead solvent. PLA stands for polylactic acid.

[0021] Polylactic acid (PLA) polyols are prepared by reacting lactic acid derivatives with polyols via esterification or transesterification under catalysis. As PLA derivatives, these PLA polyols have a structure highly similar to PLA and possess natural solubilizing and plasticizing properties, serving as primary plasticizers, adhesives, and curing agents.

[0022] The citrate esters are selected from one or more of acetylacetic acid tributyl citrate, tributyl citrate, and triethyl citrate. These citrate esters belong to the PLA plasticizer family and have low viscosity. They serve as auxiliary plasticizers and viscosity diluents for the system, reducing the viscosity of the composite plasticizer system while acting as a plasticizer, facilitating spray coating during rod formation.

[0023] The lead solvent is selected from ethyl acetoacetate or ethyl levulinate. This lead solvent is a low-odor, good solvent for PLA and also serves as a viscosity diluent for the system. While reducing the viscosity of the special curing agent, it first erodes the surface of the PLA fiber bundle after spraying, accelerating the movement of the plasticizer between PLA molecules and guiding the main and auxiliary plasticizers to adhere to and enter the intermolecular space of the PLA fiber bundle to achieve plasticizing, swelling, bonding, and curing effects. Different plasticizing, bonding, and curing effects can be achieved by adjusting the ratio of different components.

[0024] Polylactic acid polyols and citrate esters both belong to PLA plasticizers, but their plasticizing properties with PLA are not good at low temperatures. Ethyl acetoacetate and ethyl levulinate, on the other hand, are good solvents for PLA, with PLA exhibiting high solubility in these compounds. By using a mixture of these three types of esters, leveraging the solubility of ethyl acetoacetate and ethyl levulinate, and the plasticizing effects of the other two plasticizers, the formation of weld joints between the plasticizer and PLA is improved, along with plasticizer penetration, leading to the bonding and curing of the filament bundles. This results in a curing process similar to that of diacetate cellulose bundles plasticized with triacetylglycerol.

[0025] The curing agent for PLA tow rods provided in this application is a special composite compound formulated with polylactic acid polyol, citrate plasticizer, and lead solvent to address the specific characteristics of PLA tow. This effectively solves the core technical problem mentioned in the background art: insufficient low-temperature compatibility between traditional curing agents (such as triacetin GTA) and PLA tow. Traditional triacetin GTA is designed for cellulose acetate (CDA) tow, and its molecular structure is drastically different from the chemical structure of PLA, resulting in poor low-temperature plasticizing effect and difficulty in effective bonding and curing during PLA tow rod formation. If conventional spraying processes and dosages are used, PLA filter rods will experience difficulties in molding, insufficient hardness, and even collapse during subsequent suction; reducing the spraying amount cannot guarantee the mechanical properties and stability of the filter rod. However, this invention, by introducing polylactic acid polyol with a structure highly similar to PLA as the main plasticizer and binder, significantly improves the affinity and solubility between the curing agent and the PLA matrix, fundamentally improving the compatibility problem. Meanwhile, the added citrate ester plasticizers not only act as auxiliary plasticizers but also reduce the viscosity of the entire composite system, making it easier to spray and coat evenly during the rod-forming process. The introduction of lead solvents such as ethyl acetoacetate or ethyl levulinate not only provides excellent low-odor PLA solvents but also pre-dissolves the surface of the PLA fiber bundles, greatly promoting the diffusion, adhesion, and penetration of subsequent polylactic acid polyols and citrate ester plasticizers between PLA molecules. This "lead-dissolution-synergistic plasticizing" mechanism effectively guides the plasticizer components into the fiber bundle, accelerating the movement and rearrangement of the PLA molecular chains, thus achieving efficient bonding, swelling, and curing of PLA fiber bundles even at lower temperatures. This synergistic effect enables the specialized curing agent of this invention to form stable bonded joints in PLA tows under conventional spraying processes, achieving a reliable curing process similar to that when cellulose acetate tows are plasticized with triacetin. The resulting PLA filter rods exhibit excellent hardness, roundness, and dimensional stability, completely overcoming the molding difficulties and collapse defects caused by traditional curing agents, and possessing ideal mechanical properties and operational stability. Furthermore, this composite formulation, through the synergistic effect of its components, provides better process adaptability, allowing the viscosity of the curing agent system to be adjusted according to the formulation to a range suitable for spraying with existing equipment, achieving stable production of PLA filter rods without major modifications to existing production lines.

[0026] Furthermore, the mass percentages of each component in the composite are as follows: polylactic acid polyol 20%~70%, citrate esters 20%~70%, and lead solvent 10%~30%. The proportions of each plasticizer are adjusted mainly based on the performance requirements of the PLA filter rods.

[0027] The curing agent formulation achieves a crucial balance between optimizing PLA filter rod performance and ensuring process feasibility. Specifically, polylactic acid polyol, as the primary plasticizer, at a content ranging from 20% to 70%, ensures sufficient plasticizing, bonding, and curing effects on the PLA fibers, which is key to guaranteeing the filter rod's hardness. Citrate esters, as auxiliary plasticizers and viscosity modifiers, at a content of 20% to 70%, effectively reduce the overall viscosity of the composite, ensuring good flowability and atomization during spraying, facilitating uniform coating on the PLA fiber surface. The lead solvent, at a content of 10% to 30%, provides sufficient initial dissolution and penetration capacity for the entire system, enabling it to first erode the PLA fiber surface, guiding the primary and auxiliary plasticizers to quickly enter the PLA molecular chains and accelerate the curing process. As shown in Table 1 of the specific implementation, the different proportion designs and the performance test results in Table 3 (such as the filter rod hardness of 86.1% in Examples 1-3) all verify that within this preferred proportion range, it can be flexibly adjusted to meet different filter rod performance requirements such as hardness and suction resistance. At the same time, its viscosity (such as the viscosity of 36 mPa·s in Examples 1-4) can be adapted to existing spraying equipment, achieving a balance between performance and process.

[0028] Optionally, the lactic acid derivative is selected from one or more of ethyl lactate, butyl lactate, and lactide. This lactic acid derivative is a monomer for esterification or transesterification reactions. It has a positive impact on the synthesis efficiency and structural controllability of polylactic acid polyols. These specific lactic acid derivative monomers are characterized by high reactivity and relatively wide availability. For example, in Examples 1 to 3, ethyl lactate was used as the starting material. Using this type of monomer allows for efficient esterification or transesterification reactions with polyols under catalysis, helping to obtain polylactic acid polyol products with more ideal molecular chain structures and molecular weights. This type of polylactic acid polyol has a higher chemical similarity to the target PLA filaments, thus ensuring better compatibility and affinity with the PLA matrix when used as the main plasticizer. This allows the plasticizer to act more uniformly and deeply on the PLA filaments, ultimately reflected in the stable improvement of the overall curing effect and mechanical properties of the filter rod.

[0029] Furthermore, the polyol is selected from one or more of ethylene glycol, propylene glycol, and glycerol. This polyol is a monomer for esterification or transesterification reactions. The functionality and toughness of the polylactic acid polyol were optimized from a molecular design perspective. The selected polyols are all common small-molecule polyols, which, upon reaction with lactic acid derivatives, introduce hydroxyl end groups or branching points into the molecular chain of the polylactic acid polyol. For example, using ethylene glycol or propylene glycol can form linear or slightly branched polyester polyols, giving the curing agent system appropriate flexibility and flowability; while using glycerol can introduce three hydroxyl groups, potentially forming polylactic acid polyols with slightly branched or network structures, which helps to enhance the adhesion and crosslinking points between fiber bundles while plasticizing. This optimal selection of polyol types ensures that the final synthesized polylactic acid polyol not only retains good compatibility with PLA, but its own physical properties (such as viscosity and reactivity) are also more suitable for subsequent compounding with citrate esters and lead solvents to jointly construct a composite curing agent system with balanced performance.

[0030] Optionally, the catalyst can be selected from organotin catalysts, titanate catalysts, organic bases, inorganic bases, supported calcium oxide porous materials, or cation exchange resins. The catalyst serves as an intermediate for this curing agent, providing strong process adaptability and environmental selectivity for the synthesis of polylactic acid polyols. Producers can flexibly select the most suitable catalytic system based on their own equipment conditions, cost control, and different requirements for green chemistry. For example, Example 1 used stannous octoate (an organotin catalyst), Example 2 used tetrabutyl titanate, and Example 3 used a cation exchange resin (Amberlyst-15). As a heterogeneous catalyst, the cation exchange resin has the significant advantage of being easily separated by filtration after the reaction and potentially reusable, reducing metal residue and better meeting the requirements of clean production. This diverse catalyst design ensures that the polylactic acid polyol synthesis step can be implemented efficiently and economically under different technical routes, thereby guaranteeing a stable and reliable raw material supply for the dedicated curing agent and laying the foundation for its large-scale industrial application.

[0031] Another embodiment of the present invention provides a method for preparing a special curing agent for PLA tow rods used in cigarette manufacturing, comprising: S1. Synthesis of polylactic acid polyol: Lactic acid derivatives and polyols are subjected to esterification or transesterification reactions at temperatures of 100℃~160℃ and under vacuum conditions in the presence of a catalyst and an inert atmosphere. Subsequently, byproducts and unreacted monomers are distilled off under increased vacuum to obtain polylactic acid polyol.

[0032] S2. Composite: The polylactic acid polyol, citric acid ester plasticizer and lead solvent obtained in step S1 are mixed evenly according to a predetermined mass ratio to obtain a special curing agent for PLA tow rods for cigarettes.

[0033] The method for preparing a special curing agent for PLA tow rods in this application involves a specific two-step process. First, a polylactic acid polyol with a structure highly similar to polylactic acid (PLA) is synthesized under controlled inert atmosphere and vacuum conditions. Then, it is compounded with a specific citrate ester plasticizer and a lead solvent to successfully prepare a composite curing agent specifically suitable for PLA tows. This method fundamentally solves the technical problems caused by the poor compatibility between traditional triacetin (GTA) curing agents and PLA tows, such as difficulties in filter rod molding, insufficient hardness, and easy collapse after aspiration. The special curing agent obtained by this method, when applied to PLA filter rod production, can effectively bond and cure PLA tows under conventional spraying processes. The resulting filter rods achieve or approach the level of traditional cellulose diacetate (CDA) filter rods in key mechanical properties such as hardness, suction resistance, roundness, and post-absorption hardness, thereby ensuring the molding quality and stability of PLA filter rods and providing a reliable technical solution for the industrial production of bio-based biodegradable filter rods.

[0034] Further, in step S1, the lactic acid derivative is selected from one or more of ethyl lactate, butyl lactate, and lactide, and the polyol is selected from one or more of ethylene glycol, propylene glycol, and glycerol.

[0035] Optionally, in step S1, the catalyst is selected from organotin catalysts (such as stannous octoate), titanate catalysts (such as tetrabutyl titanate), organic bases, inorganic bases, supported calcium oxide porous materials, or cation exchange resins (such as cation exchange resins).

[0036] Furthermore, in step S1, the reaction is carried out under an apparent vacuum of -0.03 MPa to -0.08 MPa. This apparent vacuum range is primarily used to effectively distill off the ethanol gas, a byproduct of the transesterification reaction, during the reaction (e.g., at 100°C to 160°C), thereby driving the reaction equilibrium towards the formation of the target product, polylactic acid polyol, and improving the reaction conversion rate. More importantly, in the later stage of the reaction, the "increased vacuum" stage, for example, increasing it to -0.08 MPa, allows for the efficient distillation off of residual unreacted monomers (such as ethyl lactate), thus purifying the product and ensuring that the final polylactic acid polyol has a lower free monomer content and higher purity. This purification directly improves the quality of the polylactic acid polyol as a main plasticizer and binder, enabling it to form a more stable and homogeneous dedicated curing agent composite system when subsequently compounded with citrate esters and lead solvents. Therefore, this apparent vacuum range ensures the synthesis quality of the key component polylactic acid polyol from a process perspective, thereby providing key process parameter support for the entire curing agent to achieve excellent plasticizing and curing effects comparable to traditional CDA filter rods (such as the high hardness and anti-collapse properties shown by the filter rods in Examples 1-4), which distinguishes it from the situation in the prior art where performance instability may be caused by incomplete reaction or impure products.

[0037] Another embodiment of the present invention provides a method for preparing PLA filter rods for cigarettes, wherein the above-mentioned special curing agent for forming PLA tow rods for cigarettes is used as a plasticizing curing agent and sprayed during the PLA tow forming process.

[0038] To ensure that the above-described implementation details and operations of this application can be clearly understood by those skilled in the art, and to highlight the significant advancements of the special curing agent for PLA tow rods for tobacco and its preparation method in the embodiments of this application, the above technical solutions are illustrated below through multiple embodiments.

[0039] Assembly of the esterification reaction fractionation device: A mechanical stirrer is installed in the large central hole of the magnetically stirred constant temperature oil bath. A frosted glass stopper with two-way switch interface is installed in one hole. One channel is connected to nitrogen gas, and a balloon is installed in the other channel to store nitrogen and maintain a nitrogen atmosphere. In the other hole, a glass elbow is added and connected to a water-cooled condenser pipe. A glass elbow with a suction port is connected to a vacuum pump and a receiving bottle, thus forming the esterification reaction fractionation device.

[0040] Example 1 S1. Synthesis of polylactic acid polyol: Weigh 177g of ethyl lactate (lactic acid derivative) and 93g of ethylene glycol (polyol), and add them to a 500mL three-necked flask. Place the flask in a magnetically stirred, temperature-controlled oil bath. Check the esterification reaction fractionation apparatus. After confirming that everything is correct, turn on the vacuum pump and alternately purge with nitrogen (inert atmosphere). After purging with nitrogen three times, keep the balloon fully inflated and turn on the mechanical stirrer at 300rpm. Raise the temperature to 100℃ and turn on the vacuum pump. The vacuum level should be -0.01MPa. Dehydrate for 2 hours, then add 0.27g of stannous octoate (catalyst). Gradually heat to 160℃, and distill off the transesterification product monomer ethanol gas (byproduct) at a vacuum level of -0.03MPa. React for 6 hours (esterification or transesterification reaction). Increase the vacuum level to -0.08MPa and distill off the transesterification product monomer ethanol gas and unreacted ethyl lactate (unreacted monomer) to obtain polylactic acid polyol.

[0041] S2. Preparation of curing agents with different ratios: The polylactic acid polyol, acetylglucosinolate (citric acid ester), and ethyl acetoacetate (lead solvent) obtained in step S1 are mixed evenly according to the representative mass fractions of the species shown in Table 1 to obtain a special curing agent for PLA tow rods for tobacco.

[0042] Table 1 Design of Curing Agents with Different Proportions Example 2 S1. Synthesis of polylactic acid polyol: Weigh 177g of ethyl lactate (lactic acid derivative) and 93g of ethylene glycol (polyol), and add them to a 500mL three-necked flask. Place the flask in a magnetically stirred, temperature-controlled oil bath. Check the esterification reaction fractionation apparatus. After confirming that everything is correct, turn on the vacuum pump and alternately purge with nitrogen (inert atmosphere). After purging with nitrogen three times, keep the balloon fully inflated and turn on the mechanical stirrer at 300rpm. Raise the temperature to 100℃ and turn on the vacuum pump. The vacuum level should be -0.01MPa. Dehydrate for 2 hours, then add 2.7g of tetrabutyl titanate (catalyst). Gradually heat to 150℃, and distill off the transesterification product monomer ethanol gas (byproduct) at a vacuum level of -0.03MPa. React for 6 hours (esterification or transesterification reaction). Increase the vacuum level to -0.08MPa and distill off the transesterification product monomer ethanol gas and unreacted ethyl lactate (unreacted monomer) to obtain polylactic acid polyol.

[0043] S2. Composite: The polylactic acid polyol, acetylglucosinolate (citric acid ester), and ethyl acetoacetate (lead solvent) obtained in step S1 are mixed evenly in a mass fraction of 35%:50%:15% to obtain a special curing agent for PLA tow rods for cigarettes.

[0044] Example 3 S1. Synthesis of polylactic acid polyol: Weigh 177g of ethyl lactate (lactic acid derivative) and 93g of ethylene glycol (polyol), and add them to a 500mL three-necked flask. Place the flask in a magnetically stirred, temperature-controlled oil bath. Check the esterification reaction fractionation apparatus. After confirming that everything is correct, turn on the vacuum pump and alternately purge with nitrogen (inert atmosphere). After purging with nitrogen three times, keep the balloon fully inflated and turn on the mechanical stirrer at 300rpm. Raise the temperature to 100℃ and turn on the vacuum pump. The vacuum level should be -0.01MPa. Dehydrate for 2 hours, then add 30g of cation exchange resin (Amberlyst-15). Gradually heat to 135℃, distill off the transesterification product monomer ethanol gas (byproduct) under a vacuum of -0.04MPa, react for 12 hours (esterification or transesterification reaction), increase the vacuum to -0.08MPa to distill off the transesterification product monomer ethanol gas and unreacted ethyl lactate (unreacted monomer), cool to 80℃, and filter while hot to obtain polylactic acid polyol.

[0045] S2. Composite: The polylactic acid polyol, acetylglucosinolate (citric acid ester), and ethyl acetoacetate (lead solvent) obtained in step S1 are mixed evenly in a mass fraction of 30%:60%:10% to obtain a special curing agent for PLA tow rods for cigarettes.

[0046] Table 2 shows the viscosity of GTA and the curing agent for PLA tow rods for tobacco products in Examples 1-1 to 1-6, 2, and 3 of this application, tested with a rotational viscometer at 23°C, in accordance with GB / T 15357-2014.

[0047] Table 2 shows the viscosity (mPa.S) of the curing agent for PLA tow rods used in tobacco processing in GTA and Examples 1-1 to 1-6, 2, and 3 of this application. Viscosity tests showed that the curing agents for PLA tow rods used in this application (Examples 1-1, 1-2, 1-3, 1-4, 2, and 3) have viscosities comparable to the commonly used tow curing agent GTA, which are suitable for current spraying conditions and rod processing. Examples 1-5 and 1-6 have slightly higher viscosities than GTA, making spraying under normal conditions slightly more difficult; however, rod processing is still possible after increasing the spraying temperature by 3°C.

[0048] The special curing agent for PLA tow rods in this application embodiment can be applied to the preparation of PLA filter rods, meeting the basic requirements of cigarettes for filter pressure drop, filtration efficiency, hardness, circumference, etc.

[0049] Comparative tests were conducted using the special curing agent for PLA tow rods for tobacco products from Examples 1-1 to 1-6 of this invention, along with CDA and GTA.

[0050] Comparative Example 1: Using GTA as a curing agent, with PLA tobacco tow, the opening roller pressure was 0.15 MPa, the glue tank and hose temperature was 45℃, the plasticizer addition rate was 2 mL / min, the sprayer temperature was 65℃, the spray particle size was 40 nm, and the cooling strip temperature was 8℃. In this case, the amount of GTA used was approximately 1% of the total mass of the molded PLA filter rod. In this preparation, due to the poor low-temperature plasticizing effect of GTA and PLA, the normal spray amount could not dry and solidify, resulting in a soft, wet rod. Only a small amount could be sprayed to form a rod, yielding concentric PLA filter rods.

[0051] Comparative Example 2: Using GTA as a curing agent, with a CDA tobacco tow opening roller pressure of 0.20 MPa, a glue tank and hose temperature of 45℃, a plasticizer addition rate of 18 mL / min, a glue sprayer temperature of 65℃, a spray particle size of 40 nm, and a cooling strip temperature of 8℃, the amount of GTA used is approximately 7% of the total mass of the molded CDA filter rod. Concentric CDA filter rods can be obtained through normal preparation.

[0052] Examples 1-1 to 1-6: Rods Using embodiments 1-1 to 1-6 of this invention as the curing agent, with a PLA tobacco tow opening roller pressure of 0.15 MPa, a glue tank and hose temperature of 45°C (48°C for 1-5 and 1-6), a plasticizer addition rate of 18 mL / min, a glue sprayer temperature of 65°C (68°C for 1-5 and 1-6), a spray particle size of 40 nm, and a cooling strip temperature of 8°C, the amount of the special composite plasticizer used is approximately 8% of the total mass of the molded PLA filter rod. Concentric PLA filter rods can be obtained through normal preparation.

[0053] The beneficial effects of this invention are as follows: Based on traditional filter rod preparation equipment, without changing the equipment, by adjusting the ratio of different raw materials in the plasticizer system and supplementing with process adjustments such as temperature and pressure, the special curing agent for PLA tow rods for cigarettes in this application embodiment can significantly improve the various mechanical properties of PLA filter rods while ensuring the conventional requirements of filter rods such as suction resistance.

[0054] Table 3 shows the mechanical properties of a conventional 120mm*23.95mm filter rod prepared using the special curing agent for PLA tow rods of this application, compared with those of a PLA filter rod prepared using only triacetin as a plasticizer and a diacetate fiber filter rod prepared using triacetin as a plasticizer.

[0055] Table 3 Mechanical properties of filter rods Note: 1. Hardness after smoking: The hardness of the filter rod after normal smoking test when the filter rod is combined into a cigarette. 2. Comparative Example 1 showed obvious collapse after absorption.

[0056] As shown in the table above, the curing agent for PLA tow rods in this application significantly improves the hardness of PLA filter rods compared to triacetyl ester plasticizer. The draw resistance, roundness, and weight are comparable. Furthermore, after normal smoking, the hardness of the PLA filter rods prepared with the curing agent for PLA tow rods in this application is comparable to that of GTA-plasticized cellulose diacetate tow filter rods. In actual production, this curing agent can significantly improve the hardness of PLA filter rods, which is beneficial for product molding. The unique fruity aroma of ethyl acetoacetate and ethyl acetopropionate also enhances the user experience.

[0057] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0058] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A curing agent specifically for forming PLA tow rods for tobacco use, characterized in that, It is a complex comprising polylactic acid polyol, citrate esters and lead solvent; The polylactic acid polyol is prepared by reacting a lactic acid derivative with a polyol through esterification or transesterification under the catalysis of a catalyst. The citrate esters are selected from one or more of acetylacetic tributyl citrate, tributyl citrate, and triethyl citrate. The lead solvent is selected from ethyl acetoacetate or ethyl acetopropionate.

2. The curing agent for PLA tow rods for tobacco as described in claim 1, characterized in that, The mass percentage of each component in the complex is as follows: The polylactic acid polyol accounts for 20% to 70%; The citrate esters account for 20% to 70%; The lead solvent accounts for 10% to 30%.

3. The curing agent for PLA tow rods for tobacco as described in claim 1 or 2, characterized in that, The lactic acid derivative is selected from one or more of ethyl lactate, butyl lactate, and lactide.

4. The curing agent for PLA tow rods for tobacco as described in claim 1 or 2, characterized in that, The polyol is selected from one or more of ethylene glycol, propylene glycol, and glycerol.

5. The curing agent for PLA tow rods for tobacco as described in claim 1, characterized in that, The catalyst is selected from organotin catalysts, titanate catalysts, organic bases, inorganic bases, supported calcium oxide porous materials, or cation exchange resins.

6. A method for preparing a special curing agent for PLA tow rods for tobacco use, characterized in that, The curing agent for preparing the PLA tow rod for tobacco as described in any one of claims 1 to 5 comprises: S1. Synthesis of polylactic acid polyol: The lactic acid derivative and the polyol are subjected to esterification or transesterification reaction at a temperature of 100℃~160℃ and under vacuum conditions in the presence of a catalyst and an inert atmosphere. The by-products and unreacted monomers are then distilled off under an increased vacuum to obtain polylactic acid polyol. S2. Composite: The polylactic acid polyol, citric acid ester plasticizer and lead solvent obtained in step S1 are mixed evenly according to a predetermined mass ratio to obtain the special curing agent for PLA tow rods for cigarettes.

7. The preparation method of the special curing agent for PLA tow rods for tobacco as described in claim 6, characterized in that, In step S1, the lactic acid derivative is selected from one or more of ethyl lactate, butyl lactate, and lactide; the polyol is selected from one or more of ethylene glycol, propylene glycol, and glycerol.

8. The preparation method of the special curing agent for PLA tow rods for tobacco as described in claim 6, characterized in that, In step S1, the catalyst is selected from organotin catalysts, titanate catalysts, organic bases, inorganic bases, supported calcium oxide porous materials, or cation exchange resins.

9. The preparation method of the special curing agent for PLA tow rods for tobacco as described in claim 6, characterized in that, In step S1, the reaction is carried out under a vacuum of -0.03 MPa to -0.08 MPa.

10. A method for preparing a PLA filter rod for tobacco, characterized in that, During the PLA tow forming process, the special curing agent for tobacco PLA tow rods as described in any one of claims 1 to 5 is used as a plasticizing curing agent for spraying.

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