Method for preparing non-toxic transparent calendered film from waste PVC (polyvinyl chloride) film

Abstract

The invention relates to the technical field of high polymer material recovery and regeneration processing, and particularly discloses a method for preparing a non-toxic transparent calendered film from a waste PVC film. The method sequentially comprises the steps of synergistic cleaning of a bio-enzyme-containing preparation, deep devolatilization purification under the synchronous action of ultraviolet rays, microwaves and superheated steam, composite surface treatment of a specific chelating agent and an organic tin compound, and blending modification with components such as a surface-modified nano reinforcing agent. And finally, a controllable mechanical oscillation field is introduced in the calendaring forming stage for on-line structure regulation and control, so that a final product is obtained. According to the method, efficient removal of harmful impurities in the waste PVC raw material and active optimization of a microstructure are achieved, the prepared calendered film has the comprehensive advantages of being low in heavy metal and plasticizer residues, high in light transmittance, small in haze and good in longitudinal tensile strength, and an effective solution is provided for high-valued regeneration of the waste PVC film.

Description

Technical Field

[0001] This application relates to the field of polymer material recycling and reprocessing technology, and more specifically, it relates to a method for preparing non-toxic transparent calendered films using waste PVC films. Background Technology

[0002] Due to its excellent physicochemical properties, PVC film is widely used in packaging, building materials, and other fields, resulting in a continuous increase in the amount of waste PVC film. If these waste materials are not properly recycled, they will not only waste resources but also cause environmental pollution problems due to their non-degradable properties. Therefore, the recycling and regeneration of waste PVC film has become an important issue in the field of resource recycling and environmental protection, and its regeneration into transparent calendered film is a key direction for achieving high-value utilization.

[0003] Existing methods for recycling waste PVC film often rely on simple acid-alkali cleaning or mechanical sorting for pretreatment, which fails to deeply remove organic contaminants adhering to the film surface, heavy metal impurities embedded in the PVC matrix, and volatile monomers remaining from the production process. Furthermore, the lack of active control over the melt's microstructure during the calendering stage results in recycled films commonly exhibiting problems such as excessive harmful residues, insufficient mechanical strength, and poor light transmittance, making them unsuitable for high-end applications. Therefore, achieving a balance between deep removal of harmful substances and high mechanical and optical properties in the recycling process of waste PVC film has become a core technological challenge hindering its high-value recycling. Summary of the Invention

[0004] To address the issues of incomplete removal of harmful substances and difficulty in unifying mechanical and optical properties during the recycling of waste PVC film in existing technologies, this application provides a method for preparing non-toxic transparent calendered films using waste PVC film.

[0005] A method for preparing non-toxic transparent calendered film using waste PVC film includes the following steps: S1. Pretreatment and multi-stage cleaning: The waste PVC film is sorted to remove the non-PVC material parts, and then crushed to obtain fragments; the fragments are placed in a composite cleaning solution for stirring and cleaning; the composite cleaning solution contains nonionic surfactants, weak alkaline salts, biological enzymes and the remainder deionized water; after cleaning, the fragments are rinsed with hot deionized water and then dried with hot air. S2, Photo-thermal synergistic devolatilization and surface activation: The dried fragments obtained in S1 are subjected to ultraviolet irradiation and microwave treatment under inert gas protection, while superheated steam is continuously introduced; after treatment, surface-activated fragments are obtained. S3, impurity chelation and surface treatment: The fragments obtained in S2 were immersed in an aqueous solution of amino polycarboxylic acid chelating agent and organotin compound, and the immersion treatment was carried out under the assistance of ultrasonic oscillation; the treated fragments were rinsed with deionized water until neutral, and then sprayed with silane coupling agent solution for surface treatment and dried to obtain dried fragments; S4. Nano-reinforced blending and low-temperature micronization: The dried fragments obtained in S3, fresh food-grade PVC resin, and surface-modified nano-sized inorganic transparent reinforcing agent are mixed under a nitrogen protective atmosphere; the mixture is then ground under cooling conditions to obtain a fine composite powder. S5. Reactive melt blending: The fine composite powder obtained in S4 is mixed with a non-toxic composite stabilizer, an internal lubricant, a transparent modifier, and an epoxidized bio-based plasticizer to obtain a uniform mixture. S6. Precision calendering and online structure control: The mixture obtained in S5 is fed to a multi-roll calender for calendering; during the film calendering process, an oscillating field is applied to the film; a sealed exhaust hood is installed above the calender; finally, a calendered film is obtained. S7. Post-processing: The calendered film obtained in step S6 is subjected to infrared irradiation treatment.

[0006] By employing the above technical solution, the nonionic surfactants, weakly alkaline salts, and bio-enzymes in the composite cleaning solution work synergistically to peel off and decompose organic pollutants on the surface of waste PVC fragments. Further, the simultaneous treatment with ultraviolet light, microwaves, and superheated steam during the photo-thermal synergistic devolvation process removes volatile monomers and activates the fragment surface. The combination of amino polycarboxylic acid chelating agents and organotin compounds with ultrasonic oscillation targets and chelates heavy metal impurities, inducing a regular crystal arrangement in PVC. Silane coupling agents improve the interfacial compatibility between the fragments and subsequent components. Finally, the surface-modified nano-scale inorganic transparent reinforcing agent and new... The blending of fresh PVC resin and liquid nitrogen cooling grinding ensure uniform dispersion of the reinforcing phase and prevent material degradation. The synergistic addition of epoxidized bio-based plasticizers, talc-containing composite calcium-zinc stabilizers, glyceryl monostearate, and transparent modifiers optimizes the flowability, thermal stability, and transparency of the mixture. Gradient temperature control, the application of an oscillating field, and the installation of a sealed exhaust hood in a five-roll calender ensure precise molding, regulate the film's microstructure, and remove volatiles generated during processing. Finally, irradiation with a mid-infrared LED array promotes the reaction of residual active groups within the film, thereby comprehensively optimizing the overall performance of the product.

[0007] Preferably, in step S1, the particle size of the fragments is 3.0-8.0 mm; the stirring and washing temperature is 40-60°C, the rotation speed is 80-150 rpm, and the time is 15-30 min; the rinsing temperature of the hot deionized water is 60-80°C, and the rinsing number is 2-4 times; the hot air drying temperature is 75-85°C.

[0008] By adopting the above technical solution, the fragments are controlled within a specific particle size range. Combined with the set stirring and cleaning temperature, speed, and time, the contact area between the fragments and the composite cleaning solution is increased, the cleaning solution is promoted to penetrate and fully remove contaminants. Then, the residual cleaning solution and loose impurities are removed by hot deionized water rinsing at a specific temperature and number of times. Finally, the fragments are dried with hot air at a set temperature to quickly remove moisture. All parameters work together to form suitable pretreatment conditions, thereby providing clean and dry raw materials for subsequent deep processing.

[0009] Preferably, in step S1, the composite cleaning solution contains 1.5-3.5 wt.% nonionic surfactant, 0.5-1.5 wt.% weak alkaline salt, and 0.2-0.8 wt.% bio-enzyme preparation, wherein the bio-enzyme preparation is a mixture of lipase and keratinase in a mass ratio of 1:1 to 1:2.

[0010] By adopting the above technical solution, and by controlling the specific mass percentages of nonionic surfactants, weak alkaline salts, and biological enzyme preparations, and by using lipase and keratinase in a specific ratio for the biological enzyme preparations, the nonionic surfactants can reduce the interfacial tension between the fragments and contaminants, the weak alkaline salts can adjust the pH value of the system to match the activity of the enzyme preparations, and the compounded lipase and keratinase can specifically act on organic ester contaminants. The three work together to efficiently decompose and peel off the organic contaminants attached to the surface of the fragments, thereby improving the cleanliness of the raw materials and laying the foundation for subsequent deep treatment.

[0011] Preferably, in step S2, the wavelength of the ultraviolet irradiation is 280-315 nm, and the irradiation intensity is 15-35 mW / cm². 2 The microwave treatment frequency is 2.45 GHz, and the power density is 0.5-2.0 W / g; the temperature of the superheated steam is 110-130°C; and the treatment time is 20-50 min.

[0012] By adopting the above technical solution, ultraviolet light with a specific wavelength and irradiation intensity, microwave light with a fixed frequency and a specific power density, and superheated steam at a specific temperature are used simultaneously within a set processing time. Ultraviolet light can destroy the chemical structure of volatile impurities and activate the surface of PVC fragments. Microwave light can provide uniform and efficient heat transfer to accelerate the devolatification process. Superheated steam can carry the removed volatile substances away from the system quickly. The parameters are adapted to each other to form a synergistic effect, which can fully remove volatile monomers and residual impurities from the fragments, and at the same time activate the fragment surface to enhance the subsequent reaction activity. This achieves the effect of providing high-quality raw materials for subsequent impurity chelation and component blending.

[0013] Preferably, in step S3, the aminopolycarboxylic acid chelating agent in the aqueous solution is ethylenediaminetetraacetic acid or its alkali metal salt, and the organotin compound is dibutyltin dilaurate or dibutyltin maleate; the mass percentage of the aminopolycarboxylic acid chelating agent is 5-10 wt.%, and the mass percentage of the organotin compound is 0.1-0.5 wt.%.

[0014] By adopting the above technical solution, using ethylenediaminetetraacetic acid or its alkali metal salt as an aminopolycarboxylic acid chelating agent, and combining it with dibutyltin dilaurate or dibutyltin maleate as an organotin compound, and controlling the specific mass percentage of the two in the aqueous solution, the aminopolycarboxylic acid chelating agent can specifically bind to heavy metal impurities in the fragments to form a stable chelate, and the organotin compound can guide the orderly arrangement of PVC molecular chain segments. The synergistic effect of the two plays a dual role in targeting and removing heavy metal impurities and optimizing the PVC crystal phase structure, thereby achieving the effect of improving the purity and structural regularity of raw materials, and ensuring the subsequent blending and molding effect.

[0015] Preferably, in step S3, the solution temperature for the soaking treatment is 50-65°C, and the time is 30-60 min; the frequency of the ultrasonic oscillation is 25-40 kHz; the silane coupling agent solution is an ethanol solution containing 1-3 wt.% silane coupling agent; and the drying temperature is 70-80°C.

[0016] By adopting the above technical solution, controlling the soaking solution temperature and time within a specific range, adapting the interaction activity of amino polycarboxylic acid chelating agents and organotin compounds, and using ultrasonic oscillation at a specific frequency to promote solution penetration and uniform contact of components, the use of an ethanol solution containing a specific mass percentage of silane coupling agent to achieve uniform adhesion of the coupling agent on the surface of the fragments, and finally drying at a specific temperature to remove residual moisture, all conditions are adapted and synergistic, which can fully complete the chelation of heavy metals, optimization of PVC crystal phase and modification of fragment surface, thereby improving the interfacial bonding ability between fragments and subsequent composite systems and ensuring the smooth progress of subsequent blending processing.

[0017] Preferably, in step S4, the mass ratio of the dried fragments, fresh food-grade PVC resin, and nano-sized inorganic transparent reinforcing agent is 7:2:0.1 to 8:3:0.5; the nano-sized inorganic transparent reinforcing agent is nano-silica or nano-alumina; the surface modifier of the nano-sized inorganic transparent reinforcing agent is γ-methacryloyloxypropyltrimethoxysilane, and its modification amount accounts for 1.5-3.0 wt.% of the mass of the nanoparticles; the cooling condition is to introduce liquid nitrogen to maintain the material temperature at -15°C to -5°C.

[0018] By adopting the above technical solution, controlling the specific mass ratio of dried fragments, fresh food-grade PVC resin, and nano-sized inorganic transparent reinforcing agent, selecting nano-silica or nano-alumina as the transparent reinforcing carrier, and using γ-methacryloyloxypropyltrimethoxysilane to modify the surface of the reinforcing agent in a specific ratio, combined with liquid nitrogen to maintain the material under specific low-temperature grinding conditions, the appropriate mass ratio ensures the utilization rate of waste materials and the balance of system performance. The modifier improves the interfacial compatibility between the reinforcing agent and the PVC matrix, and avoids thermal degradation of the material during grinding in a low-temperature environment. The various technical means work together to achieve uniform dispersion of components, prepare fine composite powder with suitable fineness and good stability, and thus provide high-quality raw materials for subsequent reactive melt blending and ensure smooth processing.

[0019] Preferably, in step S5, the epoxidized bio-based plasticizer is epoxidized soybean oil or epoxidized linseed oil, and its addition amount is 2.0-5.0 wt.% of the total mass of the mixed powder; the non-toxic composite stabilizer is a composite calcium-zinc stabilizer containing hydrotalcite, and its addition amount is 1.8-3.2 wt.%; the internal lubricant is glyceryl monostearate, and its addition amount is 0.5-1.5 wt.%; the transparent modifier is methyl methacrylate-butadiene-styrene copolymer, and its addition amount is 1.0-2.5 wt.%; the mixing temperature is 95-115°C, the mixing speed is 500-800 rpm, and the mixing time is 8-15 min; in the composite calcium-zinc stabilizer containing hydrotalcite, the mass percentage of hydrotalcite is 10-25 wt.%.

[0020] By adopting the above technical solution, using epoxidized soybean oil or epoxidized linseed oil as an epoxidized bio-based plasticizer, a composite calcium-zinc stabilizer containing a specific mass ratio of hydrotalcite as a non-toxic composite stabilizer, glyceryl monostearate as an internal lubricant, and methyl methacrylate-butadiene-styrene copolymer as a transparent modifier, and controlling the specific addition amount of each component, combined with a set range of mixing temperature, speed, and time, the plasticizer improves the processing fluidity of the system, the composite stabilizer inhibits PVC degradation during processing and neutralizes trace harmful products, the internal lubricant reduces frictional loss between components, the transparent modifier optimizes the optical uniformity of the system, and specific mixing conditions ensure that each component is fully integrated and triggers some reactive bonding. The various technical means work together to prepare a uniform, stable, and processable pre-crosslinked mixture, thereby providing high-quality raw materials for subsequent precision calendering and ensuring the smoothness of the film forming process.

[0021] Preferably, in step S6, the multi-roll calender is a five-roll calender, with the temperature of each roll independently controlled. The temperature of the first roll is 155-165°C, the second roll is 160-170°C, the third roll is 165-175°C, the fourth roll is 160-170°C, and the fifth roll, i.e., the cooling and shaping roll, is 75-85°C. The oscillation frequency of the oscillation field is 50-200Hz, the amplitude is 5-20μm, and the angle between its oscillation direction and the film's forward direction is 10° to 30°. The negative pressure value inside the sealed exhaust hood is 100-300Pa. The thickness of the calendered film is 0.10-0.30mm.

[0022] By adopting the above technical solutions, using a five-roll calender with independent gradient temperature control for each roll, combined with an oscillation field of specific frequency, amplitude, and angle, and simultaneously controlling the negative pressure value of the sealed exhaust hood and the thickness range of the calendered film, the gradient temperature adapts to the melting process from melting to solidification, ensuring molding stability. The oscillation field actively regulates the microscopic arrangement of components inside the melt, the negative pressure environment promptly removes volatiles generated during processing to avoid defects, and thickness control ensures product specification consistency. All these technical means work together to accurately achieve film molding, optimize the internal microstructure, and reduce molding defects, thereby providing a calendered film substrate with a regular structure and uniform thickness for post-processing.

[0023] Preferably, in step S7: the online infrared irradiation treatment involves irradiating the thin film using a mid-infrared light-emitting diode array; the wavelength of the infrared irradiation is 3-5 μm, and the irradiation intensity is 10-30 mW / cm². 2 The irradiation time is 5-15 seconds.

[0024] By adopting the above technical solution, using a mid-infrared light-emitting diode array as the irradiation source, and combining a specific wavelength of 3-5μm with an intensity of 10-30mW / cm²,2 With appropriate irradiation intensity and irradiation time of 5-15 seconds, mid-infrared light can precisely target the residual active groups inside the film. Suitable irradiation parameters ensure that the reaction proceeds fully without damaging the existing structure of the film, thereby promoting the cross-linking reaction of active groups and strengthening the chemical bond bonding inside the film. This leads to improved film structural stability and overall performance consistency, and improved product preparation process.

[0025] In summary, this application has the following beneficial effects: 1. This application employs a multi-stage cleaning process including biological enzymes, photo-thermal-steam synergistic devolvation, and a deep purification and regeneration process combining chelation and surface treatment to construct a systematic raw material pretreatment system, which efficiently removes various contaminants adhering to and embedded in the matrix. At the same time, a controllable mechanical oscillation field is introduced during the calendering stage to actively regulate the microstructure of the melt. Therefore, a comprehensive technical effect is achieved that can transform waste PVC raw materials into films with both low harmful residues and high mechanical and optical properties, providing a feasible path for the high-value regeneration of waste PVC films.

[0026] 2. In this application, a photo-thermal synergistic devolatilization process is preferred, which simultaneously performs ultraviolet irradiation, microwave treatment, and superheated steam introduction. Since different energy fields complement and synergize in their mechanisms of action, for example, ultraviolet light can break weak molecular bonds, microwaves promote bulk phase heating and material migration, and steam immediately carries out decomposition products, thereby achieving a deep and efficient removal effect of small molecule impurities such as plasticizers from waste PVC, laying a clean material foundation for subsequent processing.

[0027] 3. The method of this application applies a mechanical oscillation field at a specific angle to the direction of travel to the molten film during the film calendering process. This external field generates a specific shear stress component inside the film, which can induce the polymer molecular chains and reinforcing particles to align. Therefore, the effect of directional optimization and improvement of the longitudinal tensile strength of the film is achieved without significantly sacrificing the light transmittance of the material. Attached Figure Description

[0028] Figure 1 This is a flowchart of a method for preparing non-toxic transparent calendered film using waste PVC film, as provided in this application. Detailed Implementation

[0029] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0030] Technical concept: The core problem in the recycling of waste PVC film is the difficulty in simultaneously achieving deep removal of harmful substances and high mechanical and optical properties of the product. The fundamental reason is the lack of a systematic deep purification system in the pretreatment. Relying solely on single cleaning or sorting methods cannot effectively remove surface organic pollutants, chelate heavy metal impurities in the matrix, and remove volatile monomers. Furthermore, there is a lack of synergistic effect between the various treatment steps. At the same time, the lack of active control over the microstructure of the melt during the molding stage leads to residual impurities affecting performance, and uneven component dispersion further exacerbates the imbalance between mechanical and optical properties.

[0031] This technical solution addresses the aforementioned issues by constructing a complete technical system encompassing deep purification pretreatment, precise molding control, and enhanced post-treatment. The pretreatment stage employs multi-stage cleaning with bio-enzymes, synergistic light-heat-steam devolatilization, and surface treatment combining amino-polycarboxylic acid chelating agents with organotin compounds. These multi-step synergistic processes comprehensively remove organic pollutants, heavy metals, and volatile impurities. The molding stage utilizes a five-roll calender with gradient temperature control and a specific parameter oscillation field to actively regulate the melt's microstructure and component arrangement. Post-treatment strengthens chemical bond bonding through mid-infrared irradiation. These technologies work synergistically and mutually adapt to each other, thoroughly purifying the raw materials and optimizing the product structure, ultimately achieving a balance between low harmful residues and high mechanical and optical properties.

[0032] Preparation Example 1 The preparation method of the surface-modified nanoscale inorganic transparent reinforcing agent is as follows: 100g of nano-silica powder with an average particle size of 30nm was weighed and dispersed in 500mL of anhydrous ethanol. The dispersion was carried out under ultrasonic oscillation at 150W and 40kHz for 30min to obtain a uniform suspension. The suspension was transferred to a three-necked flask equipped with a 300rpm mechanical stirrer and a reflux condenser, and heated to 60℃ in a water bath and maintained at that temperature. Subsequently, a mixed solution of 3.0g of γ-methacryloyloxypropyltrimethoxysilane and 50mL of anhydrous ethanol was slowly added dropwise at a rate of 5mL / min, completed within 1 hour. After the addition was complete, the mixture was stirred at 60℃ for another 4 hours. After the reaction was complete, the mixture was centrifuged at 8000rpm for 15min. The resulting solid was washed three times with anhydrous ethanol to remove unreacted silane coupling agent. Finally, the product was dried in a vacuum drying oven at 80℃ for 6 hours to obtain a white powdery surface-modified nano-silica reinforcing agent.

[0033] Preparation Example 2 The preparation method of the composite calcium-zinc stabilizer containing hydrotalcite is as follows: First, zinc-aluminum hydrotalcite was prepared using a co-precipitation method: Under nitrogen protection, a mixed salt solution (0.2 mol / L containing 0.15 mol zinc nitrate and 0.05 mol aluminum nitrate) and a mixed alkaline solution (0.5 mol / L containing 0.40 mol sodium hydroxide and 0.10 mol sodium carbonate) were simultaneously added dropwise at a rate of 5 mL / min to a reactor containing 200 mL of deionized water while vigorously stirring at 500 rpm. The reaction temperature was controlled at 65 °C, and the pH of the system was maintained at 9.5-10.0. After the addition was complete, the mixture was aged and crystallized at 65 °C for 12 h. The slurry was then filtered, washed with deionized water until the filtrate was neutral, dried at 80 °C for 8 h, and calcined at 450 °C for 2 h to obtain active zinc-aluminum hydrotalcite powder with a particle size of 50-100 nm. Next, 20 parts by weight of the above zinc-aluminum hydrotalcite powder, 30 parts by weight of calcium stearate, 25 parts by weight of zinc stearate, 15 parts by weight of pentaerythritol and 10 parts by weight of β-diketone are put into a high-speed kneader and mixed at 800 rpm for 15 minutes at 95°C until the material forms a uniform powder, thus obtaining a composite calcium-zinc stabilizer containing hydrotalcite components.

[0034] The following are the main raw materials and reagents used in the preparation examples, embodiments, and comparative examples, and their sources and specifications are as follows; unless otherwise specified, all reagents are commercially available analytical grade or higher products: 1. The nonionic surfactant was purchased from Hubei Xinrunde Chemical Co., Ltd., CAS: 68213-23-0; 2. Lipase was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: S10035; 3. Ethylenediaminetetraacetic acid (EDTA) was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: S30020; 4. Disodium ethylenediaminetetraacetate was purchased from Shijiazhuang Ruitian Biochemical Co., Ltd., CAS: 139-33-3; 5. Dibutyltin dilaurate was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd., CAS: 77-58-7; 6. Dibutyltin maleate was purchased from Nantong Bona Chemical Technology Co., Ltd., CAS: 78-04-6; 7. Silane coupling agent (γ-methacryloyloxypropyltrimethoxysilane) was purchased from Hubei Chengfeng Chemical Co., Ltd., item number: 002; 8. Calcium stearate was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: S24307; 9. Zinc stearate was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: S24319; 10. Glyceryl monostearate was purchased from Guangdong Yuanfeng Chemical Reagent Co., Ltd., CAS: 31566-31-1; 11. Methyl methacrylate-butadiene-styrene copolymer was purchased from Hubei Shixing Chemical Co., Ltd., with a purity of 99%.

[0035] Example 1 This application provides a method for preparing non-toxic transparent calendered film using waste PVC film, including the following steps: S1. Pretreatment and multi-stage cleaning: The waste PVC film is sorted to remove the non-PVC material parts, and then crushed to obtain fragments; the fragments are placed in a composite cleaning solution for stirring and cleaning; the composite cleaning solution contains nonionic surfactants, weak alkaline salts, biological enzymes and the remainder deionized water; after cleaning, the fragments are rinsed with hot deionized water and then dried with hot air.

[0036] The particle size of the fragments was 5.5 mm. The stirring and washing temperature was 50°C, the rotation speed was 115 rpm, and the time was 22.5 min. The rinsing temperature with hot deionized water was 70°C, and the rinsing was performed 3 times. The hot air drying temperature was 80°C.

[0037] In the composite cleaning solution, the mass percentage of nonionic surfactant is 2.5 wt.%, the mass percentage of weakly alkaline salt is 1.0 wt.%, and the mass percentage of biological enzyme preparation is 0.5 wt.%. The biological enzyme preparation is a mixture of lipase and keratinase in a mass ratio of 1:1.5.

[0038] S2, Photo-thermal Synergistic Deviation and Surface Activation: The dried fragments obtained in S1 are subjected to ultraviolet irradiation and microwave treatment under inert gas protection, while superheated steam is continuously introduced; after treatment, surface-activated fragments are obtained.

[0039] The ultraviolet radiation wavelength was 297.5 nm, and the irradiation intensity was 25 mW / cm². 2 The microwave treatment frequency was 2.45 GHz, and the power density was 1.25 W / g. The temperature of the superheated steam was 120°C. The treatment time was 35 min.

[0040] S3. Impurity chelation and surface treatment: The fragments obtained in S2 were immersed in an aqueous solution of amino polycarboxylic acid chelating agent and organotin compound, and the immersion treatment was carried out under the assistance of ultrasonic oscillation. The treated fragments were rinsed with deionized water until neutral, and then sprayed with silane coupling agent solution for surface treatment and dried to obtain dried fragments.

[0041] In the aqueous solution, the aminopolycarboxylic acid chelating agent is disodium ethylenediaminetetraacetate, and the organotin compound is dibutyltin dilaurate; the mass percentage of the aminopolycarboxylic acid chelating agent is 7.5 wt.%, and the mass percentage of the organotin compound is 0.3 wt.%.

[0042] The soaking treatment involved a solution temperature of 57.5°C for 45 minutes, ultrasonic oscillation at a frequency of 32.5 kHz, and an ethanol solution containing 2 wt.% silane coupling agent. The drying temperature was 75°C.

[0043] S4. Nano-reinforced blending and low-temperature micronization: The dried fragments obtained in S3, fresh food-grade PVC resin, and surface-modified nano-sized inorganic transparent reinforcing agent are mixed under a nitrogen protective atmosphere; the mixture is then ground under cooling conditions to obtain a fine composite powder.

[0044] The mass ratio of dried fragments, fresh food-grade PVC resin, and nano-sized inorganic transparent reinforcing agent was 7.5:2.5:0.3. The nano-sized inorganic transparent reinforcing agent was nano-silica. The surface modifier of the nano-sized inorganic transparent reinforcing agent was γ-methacryloyloxypropyltrimethoxysilane, with a modification amount accounting for 2.25 wt.% of the nanoparticle mass. Cooling was achieved by purging liquid nitrogen to maintain the material temperature at -10°C.

[0045] S5. Reactive melt blending: The fine composite powder obtained in S4 is mixed with a non-toxic composite stabilizer, an internal lubricant, a transparent modifier, and an epoxidized bio-based plasticizer to obtain a uniform mixture.

[0046] The epoxidized bio-based plasticizer is epoxidized soybean oil, added at 3.5 wt.% of the total mass of the mixed powder. The non-toxic composite stabilizer is a composite calcium-zinc stabilizer containing hydrotalcite, added at 2.5 wt.%. The internal lubricant is glyceryl monostearate, added at 1.0 wt.%. The transparent modifier is methyl methacrylate-butadiene-styrene copolymer, added at 1.75 wt.%. The mixing temperature was 105°C, the mixing speed was 650 rpm, and the mixing time was 11.5 min. In the composite calcium-zinc stabilizer containing hydrotalcite, the mass percentage of hydrotalcite was 17.5 wt.%.

[0047] S6. Precision calendering and online structure control: The mixture obtained in S5 is fed to a multi-roll calender for calendering; during the film calendering process, an oscillating field is applied to the film; a sealed exhaust hood is installed above the calender; finally, a calendered film is obtained.

[0048] The multi-roll calender is a five-roll calender, with independent temperature control for each roll. The temperatures of the first roll are 160°C, the second roll 165°C, the third roll 170°C, the fourth roll 165°C, and the fifth roll (cooling and setting roll) 80°C. The oscillation field has a frequency of 125Hz, an amplitude of 12.5μm, and an angle of 20° between its oscillation direction and the film's forward direction. The negative pressure inside the sealed exhaust hood is 200Pa. The thickness of the calendered film is 0.20mm.

[0049] S7. Post-processing: The calendered film obtained in step S6 is subjected to infrared irradiation treatment.

[0050] The infrared irradiation treatment involves irradiating the thin film with a mid-infrared light-emitting diode array; the wavelength of the infrared irradiation is 4 μm, and the irradiation intensity is 20 mW / cm². 2 The irradiation time is 10 seconds.

[0051] Example 2 This application provides a method for preparing non-toxic transparent calendered film using waste PVC film, including the following steps: S1. Pretreatment and multi-stage cleaning: The waste PVC film is sorted to remove the non-PVC material parts, and then crushed to obtain fragments; the fragments are placed in a composite cleaning solution for stirring and cleaning; the composite cleaning solution contains nonionic surfactants, weak alkaline salts, biological enzymes and the remainder deionized water; after cleaning, the fragments are rinsed with hot deionized water and then dried with hot air.

[0052] The particle size of the fragments was 3.0 mm. The stirring and washing temperature was 40°C, the rotation speed was 80 rpm, and the time was 15 min. The rinsing temperature with hot deionized water was 60°C, and the rinsing was performed twice. The hot air drying temperature was 75°C.

[0053] The composite cleaning solution contains 1.5 wt.% nonionic surfactant, 0.5 wt.% weak alkaline salt, and 0.2 wt.% bio-enzyme. The bio-enzyme is a mixture of lipase and keratinase in a 1:1 mass ratio.

[0054] S2, Photo-thermal Synergistic Deviation and Surface Activation: The dried fragments obtained in S1 are subjected to ultraviolet irradiation and microwave treatment under inert gas protection, while superheated steam is continuously introduced; after treatment, surface-activated fragments are obtained.

[0055] The ultraviolet radiation wavelength was 280 nm, and the irradiation intensity was 15 mW / cm². 2The microwave treatment frequency was 2.45 GHz, and the power density was 0.5 W / g. The temperature of the superheated steam was 110°C. The treatment time was 20 min.

[0056] S3. Impurity chelation and surface treatment: The fragments obtained in S2 were immersed in an aqueous solution of amino polycarboxylic acid chelating agent and organotin compound, and the immersion treatment was carried out under the assistance of ultrasonic oscillation. The treated fragments were rinsed with deionized water until neutral, and then sprayed with silane coupling agent solution for surface treatment and dried to obtain dried fragments.

[0057] In the aqueous solution, the aminopolycarboxylic acid chelating agent is ethylenediaminetetraacetic acid, and the organotin compound is dibutyltin maleate; the mass percentage of the aminopolycarboxylic acid chelating agent is 5.0 wt.%, and the mass percentage of the organotin compound is 0.1 wt.%.

[0058] The soaking treatment involved a solution temperature of 50°C for 30 minutes, ultrasonic oscillation at a frequency of 25 kHz, and an ethanol solution containing 1 wt.% silane coupling agent. The drying temperature was 70°C.

[0059] S4. Nano-reinforced blending and low-temperature micronization: The dried fragments obtained in S3, fresh food-grade PVC resin, and surface-modified nano-sized inorganic transparent reinforcing agent are mixed under a nitrogen protective atmosphere; the mixture is then ground under cooling conditions to obtain a fine composite powder.

[0060] The mass ratio of dried fragments, fresh food-grade PVC resin, and nano-sized inorganic transparent reinforcing agent was 7:2:0.1. The nano-sized inorganic transparent reinforcing agent was nano-alumina. The surface modifier of the nano-sized inorganic transparent reinforcing agent was γ-methacryloyloxypropyltrimethoxysilane, with a modification amount accounting for 1.5 wt.% of the nanoparticle mass. Cooling was achieved by purging liquid nitrogen to maintain the material temperature at -15°C.

[0061] S5. Reactive melt blending: The fine composite powder obtained in S4 is mixed with a non-toxic composite stabilizer, an internal lubricant, a transparent modifier, and an epoxidized bio-based plasticizer to obtain a uniform mixture.

[0062] The epoxidized bio-based plasticizer is epoxidized linseed oil, added at 2.0 wt.% of the total mass of the mixed powder. The non-toxic composite stabilizer is a composite calcium-zinc stabilizer containing hydrotalcite, added at 1.8 wt.%. The internal lubricant is glyceryl monostearate, added at 0.5 wt.%. The transparent modifier is methyl methacrylate-butadiene-styrene copolymer, added at 1.0 wt.%. The mixing temperature is 95°C, the mixing speed is 500 rpm, and the mixing time is 8 min. In the composite calcium-zinc stabilizer containing hydrotalcite, the mass percentage of hydrotalcite is 10 wt.%.

[0063] S6. Precision calendering and online structure control: The mixture obtained in S5 is fed to a multi-roll calender for calendering; during the film calendering process, an oscillating field is applied to the film; a sealed exhaust hood is installed above the calender; finally, a calendered film is obtained.

[0064] The multi-roll calender is a five-roll calender, with independent temperature control for each roll. The temperatures of the first roll are 155°C, the second roll 160°C, the third roll 165°C, the fourth roll 160°C, and the fifth roll (cooling and setting roll) 75°C. The oscillation field has a frequency of 50Hz, an amplitude of 5μm, and an angle of 10° between its oscillation direction and the film's forward direction. The negative pressure inside the sealed exhaust hood is 100Pa. The thickness of the calendered film is 0.10mm.

[0065] S7. Post-processing: The calendered film obtained in step S6 is subjected to infrared irradiation treatment.

[0066] The infrared irradiation treatment involves irradiating the thin film with a mid-infrared light-emitting diode array; the wavelength of the infrared irradiation is 3 μm, and the irradiation intensity is 10 mW / cm². 2 The irradiation time is 5 seconds.

[0067] Example 3 This application provides a method for preparing non-toxic transparent calendered film using waste PVC film, including the following steps: S1. Pretreatment and multi-stage cleaning: The waste PVC film is sorted to remove the non-PVC material parts, and then crushed to obtain fragments; the fragments are placed in a composite cleaning solution for stirring and cleaning; the composite cleaning solution contains nonionic surfactants, weak alkaline salts, biological enzymes and the remainder deionized water; after cleaning, the fragments are rinsed with hot deionized water and then dried with hot air.

[0068] The particle size of the fragments was 8.0 mm. The stirring and washing temperature was 60°C, the rotation speed was 150 rpm, and the time was 30 min. The rinsing temperature with hot deionized water was 80°C, and the rinsing was performed 4 times. The hot air drying temperature was 85°C.

[0069] The composite cleaning solution contains 3.5 wt.% nonionic surfactant, 1.5 wt.% weak alkaline salt, and 0.8 wt.% bio-enzyme. The bio-enzyme is a mixture of lipase and keratinase in a mass ratio of 1:2.

[0070] S2, Photo-thermal Synergistic Deviation and Surface Activation: The dried fragments obtained in S1 are subjected to ultraviolet irradiation and microwave treatment under inert gas protection, while superheated steam is continuously introduced; after treatment, surface-activated fragments are obtained.

[0071] The ultraviolet radiation wavelength was 315 nm, and the irradiation intensity was 35 mW / cm². 2 The microwave treatment frequency was 2.45 GHz, and the power density was 2.0 W / g. The temperature of the superheated steam was 130°C. The treatment time was 50 min.

[0072] S3. Impurity chelation and surface treatment: The fragments obtained in S2 were immersed in an aqueous solution of amino polycarboxylic acid chelating agent and organotin compound, and the immersion treatment was carried out under the assistance of ultrasonic oscillation. The treated fragments were rinsed with deionized water until neutral, and then sprayed with silane coupling agent solution for surface treatment and dried to obtain dried fragments.

[0073] In the aqueous solution, the aminopolycarboxylic acid chelating agent is disodium ethylenediaminetetraacetate, and the organotin compound is dibutyltin dilaurate; the mass percentage of the aminopolycarboxylic acid chelating agent is 10 wt.%, and the mass percentage of the organotin compound is 0.5 wt.%.

[0074] The soaking treatment involved a solution temperature of 65°C for 60 minutes, ultrasonic oscillation at a frequency of 40 kHz, and an ethanol solution containing 3 wt.% silane coupling agent. The drying temperature was 80°C.

[0075] S4. Nano-reinforced blending and low-temperature micronization: The dried fragments obtained in S3, fresh food-grade PVC resin, and surface-modified nano-sized inorganic transparent reinforcing agent are mixed under a nitrogen protective atmosphere; the mixture is then ground under cooling conditions to obtain a fine composite powder.

[0076] The mass ratio of dried fragments, fresh food-grade PVC resin, and nano-sized inorganic transparent reinforcing agent was 8:3:0.5. The nano-sized inorganic transparent reinforcing agent was nano-silica. The surface modifier of the nano-sized inorganic transparent reinforcing agent was γ-methacryloyloxypropyltrimethoxysilane, with a modification amount accounting for 3.0 wt.% of the nanoparticle mass. Cooling was achieved by purging liquid nitrogen to maintain the material temperature at -5°C.

[0077] S5. Reactive melt blending: The fine composite powder obtained in S4 is mixed with a non-toxic composite stabilizer, an internal lubricant, a transparent modifier, and an epoxidized bio-based plasticizer to obtain a uniform mixture.

[0078] The epoxidized bio-based plasticizer is epoxidized soybean oil, added at 5.0 wt.% of the total mass of the mixed powder. The non-toxic composite stabilizer is a composite calcium-zinc stabilizer containing hydrotalcite, added at 3.2 wt.%. The internal lubricant is glyceryl monostearate, added at 1.5 wt.%. The transparent modifier is methyl methacrylate-butadiene-styrene copolymer, added at 2.5 wt.%. The mixing temperature was 115°C, the mixing speed was 800 rpm, and the mixing time was 15 min. In the composite calcium-zinc stabilizer containing hydrotalcite, the mass percentage of hydrotalcite was 25 wt.%.

[0079] S6. Precision calendering and online structure control: The mixture obtained in S5 is fed to a multi-roll calender for calendering; during the film calendering process, an oscillating field is applied to the film; a sealed exhaust hood is installed above the calender; finally, a calendered film is obtained.

[0080] The multi-roll calender is a five-roll calender, with independent temperature control for each roll. The temperatures of the first roll are 165°C, the second roll 170°C, the third roll 175°C, the fourth roll 170°C, and the fifth roll (cooling and setting roll) is 85°C. The oscillation field has a frequency of 200Hz, an amplitude of 20μm, and an angle of 30° between its oscillation direction and the film's forward direction. The negative pressure inside the sealed exhaust hood is 300Pa. The thickness of the calendered film is 0.30mm.

[0081] S7. Post-processing: The calendered film obtained in step S6 is subjected to infrared irradiation treatment.

[0082] The infrared irradiation treatment involves irradiating the thin film with a mid-infrared light-emitting diode array; the wavelength of the infrared irradiation is 5 μm, and the irradiation intensity is 30 mW / cm². 2 The irradiation time is 15 seconds.

[0083] Comparative Example 1 The only difference between this comparative example and Example 1 is that no biological enzyme preparation is added to the composite cleaning solution in step S1; it only contains nonionic surfactants and weak alkaline salts. The remaining components, dosages, and all process steps and parameters are exactly the same as in Example 1.

[0084] Comparative Example 2 The only difference between this comparative example and Example 1 is that in step S3, the aminopolycarboxylic acid chelating agent is replaced by disodium ethylenediaminetetraacetate with an equal mass percentage of sodium citrate. The organotin compound and all other process steps and parameters are exactly the same as in Example 1.

[0085] Comparative Example 3 The only difference between this comparative example and Example 1 is that, in step S4, no surface-modified nano-silica reinforcing agent is added, and the mixing mass ratio of dried fragments to fresh food-grade PVC resin is adjusted to 7.8:2.2. All other process steps and parameters are exactly the same as in Example 1.

[0086] Comparative Example 4 The only difference between this comparative example and Example 1 is that no organotin compound is added to the aqueous solution in step S3, and only 7.5 wt.% of disodium ethylenediaminetetraacetate is used as a chelating agent. All other process steps and parameters are exactly the same as in Example 1.

[0087] Comparative Example 5 The only difference between this comparative example and Example 1 is that in step S2, instead of using the simultaneous treatment of ultraviolet light, microwave, and superheated steam, a three-stage step-by-step treatment is performed: first ultraviolet irradiation, then microwave treatment, and finally superheated steam. The total treatment time is extended to 105 minutes. All other process steps and parameters are exactly the same as in Example 1.

[0088] Comparative Example 6 The only difference between this comparative example and Example 1 is that in step S6, no oscillation field is applied during the film calendering process; only conventional calendering is performed. All other process steps and parameters are exactly the same as in Example 1.

[0089] Experiment 1: Non-toxic safety test Refer to Appendix A (Determination of Heavy Metals) of GB / T22048-2015 "Determination of Phthalate Plasticizers in Polyvinyl Chloride Plastics for Toys and Children's Products" and GB / T4615-2013 "Determination of Residual Vinyl Chloride Monomer in Polyvinyl Chloride Resin by Gas Chromatography". The calendered films prepared in Examples 1-3 and Comparative Examples 1-6 were tested. Each sample film was pulverized using a high-speed pulverizer to a particle size no greater than 0.5 mm. 2.0 g of the pulverized sample was accurately weighed and placed in a polytetrafluoroethylene digestion vessel. 10 mL of nitric acid and 2 mL of hydrogen peroxide were added, and digestion was performed using a microwave digester. After digestion, the mixture was cooled to room temperature and brought to a final volume of 50 mL with deionized water. The contents of heavy metals such as lead, cadmium, mercury, and chromium were determined by inductively coupled plasma mass spectrometry, and the total content was calculated. Another 5.0 g of pulverized sample was accurately weighed and placed in a sealed extraction bottle. 20 mL of N,N-dimethylformamide was added, and the mixture was extracted in a 70°C water bath for 30 min. After cooling, the supernatant was collected, and the sample was analyzed using a gas chromatograph equipped with a flame ionization detector (FID), with nitrogen as the carrier gas and a capillary column. The column temperature program was as follows: initial temperature 40°C, hold for 2 min, increase to 150°C at 10°C / min, hold for 5 min, injection port temperature 200°C, and detector temperature 250°C. The peak area of ​​vinyl chloride monomer was determined, and the residual amount was calculated using the standard curve method. Each sample was tested in triplicate, and the average value was taken as the final result.

[0090] Experiment 2, Optical Performance Testing Refer to GB / T2410-2008 "Determination of light transmittance and haze of transparent plastics"; The calendered films prepared in Examples 1-3 and Comparative Examples 1-6 were tested. Each sample film was cut into 50mm × 50mm square test pieces, ensuring that the surface of the test pieces was free of scratches, bubbles, and impurities, and the thickness deviation was controlled within ±0.01mm. The test pieces were placed in the test optical path of a transmittance and haze meter. The test environment temperature was 23℃ and the relative humidity was 50%. The test piece was first zeroed using air as a reference, and then it was flatly attached to the test window to avoid the formation of bubbles. The transmittance and haze values ​​of the samples were measured at a wavelength of 550nm. Each sample was tested 5 times at different locations, and the average value was taken as the final result.

[0091] Experiment 3: Mechanical Property Testing Refer to GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets"; The calendered films prepared in Examples 1-3 and Comparative Examples 1-6 were tested. Each sample film was longitudinally cut into dumbbell-shaped specimens (Type 1), with a gauge length of 25 mm and a gauge width of 4 mm. The specimen thickness was determined by averaging measurements taken at three evenly selected points within the gauge length using a micrometer. The specimens were mounted on the fixture of a universal testing machine, ensuring the specimen axis was aligned with the direction of force. The testing environment was 23°C and 50% relative humidity. The tensile speed was set to 50 mm / min. The machine was started until the specimen broke, and the maximum tensile force at break was recorded. The longitudinal tensile strength was calculated based on the effective cross-sectional area of ​​the specimen. Each sample was tested in parallel five times, and outliers were removed, with the average value taken as the final result.

[0092] The key performance test data of Examples 1-3 and Comparative Examples 1-6 are shown in Table 1.

[0093] Table 1: ; As can be seen from Examples 1-3 and Comparative Example 1, and in conjunction with Table 1, the introduction of specific bio-enzyme preparations into the cleaning step plays a crucial role in the deep removal of organic ester contaminants adhering to the surface of waste PVC fragments, compared to cleaning systems using only conventional surfactants and alkali solutions. This deep cleaning provides a cleaner material basis for subsequent processing, directly affecting the residual levels of harmful substances and optical performance in the final product, demonstrating the unique advantages of biotechnology in improving the purity of recycled plastic raw materials.

[0094] As can be seen from Examples 1-3 and Comparative Example 2, and Table 1, there is a significant difference in the effectiveness of ethylenediaminetetraacetic acid (EDTA) chelating agents compared to common chelating agents such as sodium citrate in removing heavy metal impurities. The former exhibits a stronger and more specific complexing ability for various heavy metal ions, enabling more effective capture and separation of heavy metal ions from materials. This is a core element in ensuring that the final recycled film meets stringent safety standards, highlighting the irreplaceable role of specific chemical reagents in targeted purification.

[0095] As can be seen from Examples 1-3 and Comparative Example 3, and in conjunction with Table 1, the addition of surface-modified nanoscale inorganic transparent reinforcing agents fundamentally affects the mechanical load-bearing capacity of the recycled films compared to systems without this component. The uniform dispersion of nanoparticles in the matrix effectively transfers and disperses stress, thereby improving the overall strength of the material. Without this reinforcing effect, even with other processes unchanged, the mechanical properties of the material will exhibit significant shortcomings.

[0096] As can be seen from Examples 1-3 and Comparative Example 4, and in conjunction with Table 1, the addition of organotin compounds in the chelation treatment step does not merely provide additional stabilizing effects. The presence of this component has a positive impact on the adjustment of the microstructure of the treated PVC material. This structural optimization is directly related to the optical uniformity of the material after subsequent processing and molding, and is an important factor in obtaining a low-haze, high-transparency appearance.

[0097] As can be seen from Examples 1-3 and Comparative Example 5, and Table 1, the simultaneous and synergistic effect of the three physical fields—ultraviolet irradiation, microwave treatment, and superheated steam purging—is significantly better than the stepwise treatment mode that simply performs the three processes sequentially. The simultaneous treatment mode may produce a mutually reinforcing synergistic effect; for example, microwave heating promotes molecular motion and reactivity, ultraviolet light simultaneously induces molecular chain breakage, and steam immediately carries away the decomposition products, thereby achieving more efficient deep purification in a shorter time.

[0098] As can be seen from Examples 1-3 and Comparative Example 6, and in conjunction with Table 1, applying a mechanical oscillation field with a specific directional angle during the calendering stage is an innovative method for actively controlling the internal structure of the material. The effect of this external field is not simple vibration, but rather it influences the orientation or distribution of polymer molecular chains and nano-reinforcing particles by introducing shear forces in a specific direction. This active structural control is a key process factor for simultaneously optimizing the mechanical and optical properties of the thin film, which cannot be achieved through traditional calendering processes.

[0099] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing non-toxic transparent calendered film using waste PVC film, characterized in that: Includes the following steps: S1. Pre-treatment and multi-stage cleaning: The waste PVC film is sorted to remove the non-PVC material parts, and then crushed to obtain fragments; The fragments are placed in a composite cleaning solution and stirred for cleaning; the composite cleaning solution contains a nonionic surfactant, a weak alkaline salt, a biological enzyme preparation, and the remainder deionized water; after cleaning, the fragments are rinsed with hot deionized water and then dried with hot air. S2, Photo-thermal synergistic devolatilization and surface activation: The dried fragments obtained in S1 are subjected to ultraviolet irradiation and microwave treatment under inert gas protection, while superheated steam is continuously introduced; after treatment, surface-activated fragments are obtained. S3, impurity chelation and surface treatment: The fragments obtained in S2 were immersed in an aqueous solution of amino polycarboxylic acid chelating agent and organotin compound, and the immersion treatment was carried out under the assistance of ultrasonic oscillation; the treated fragments were rinsed with deionized water until neutral, and then sprayed with silane coupling agent solution for surface treatment and dried to obtain dried fragments; S4. Nano-reinforced blending and low-temperature micronization: The dried fragments obtained in S3, fresh food-grade PVC resin, and surface-modified nano-sized inorganic transparent reinforcing agent are mixed under a nitrogen protective atmosphere; the mixture is then ground under cooling conditions to obtain a fine composite powder. S5. Reactive melt blending: The fine composite powder obtained in S4 is mixed with a non-toxic composite stabilizer, an internal lubricant, a transparent modifier, and an epoxidized bio-based plasticizer to obtain a uniform mixture. S6. Precision calendering and online structure control: The mixture obtained in S5 is fed to a multi-roll calender for calendering; during the film calendering process, an oscillating field is applied to the film; a sealed exhaust hood is installed above the calender; finally, a calendered film is obtained. S7. Post-processing: The calendered film obtained in step S6 is subjected to infrared irradiation treatment.

2. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S1, the particle size of the fragments is 3.0-8.0 mm; the stirring and washing temperature is 40-60°C, the rotation speed is 80-150 rpm, and the time is 15-30 min; the rinsing temperature of the hot deionized water is 60-80°C, and the rinsing number is 2-4 times; the hot air drying temperature is 75-85°C.

3. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S1, the composite cleaning solution contains 1.5-3.5 wt.% nonionic surfactant, 0.5-1.5 wt.% weak alkaline salt, and 0.2-0.8 wt.% bio-enzyme preparation, which is a mixture of lipase and keratinase in a mass ratio of 1:1 to 1:

2.

4. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S2, the wavelength of the ultraviolet irradiation is 280-315 nm, and the irradiation intensity is 15-35 mW / cm². 2 The microwave treatment frequency is 2.45 GHz, and the power density is 0.5-2.0 W / g; the temperature of the superheated steam is 110-130°C; and the treatment time is 20-50 min.

5. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S3, the aqueous solution contains an aminopolycarboxylic acid chelating agent of ethylenediaminetetraacetic acid or its alkali metal salt, and an organotin compound of dibutyltin dilaurate or dibutyltin maleate; the mass percentage of the aminopolycarboxylic acid chelating agent is 5-10 wt.%, and the mass percentage of the organotin compound is 0.1-0.5 wt.%.

6. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S3, the soaking solution temperature is 50-65°C and the time is 30-60 min; the ultrasonic oscillation frequency is 25-40 kHz; the silane coupling agent solution is an ethanol solution containing 1-3 wt.% silane coupling agent; and the drying temperature is 70-80°C.

7. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S4, the mass ratio of the dried fragments, fresh food-grade PVC resin, and nano-sized inorganic transparent reinforcing agent is 7:2:0.1 to 8:3:0.5; the nano-sized inorganic transparent reinforcing agent is nano-silica or nano-alumina; the surface modifier of the nano-sized inorganic transparent reinforcing agent is γ-methacryloyloxypropyltrimethoxysilane, and its modification amount accounts for 1.5-3.0 wt.% of the mass of the nanoparticles; the cooling condition is to introduce liquid nitrogen to maintain the material temperature at -15°C to -5°C.

8. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S5, the epoxidized bio-based plasticizer is epoxidized soybean oil or epoxidized linseed oil, and its addition amount is 2.0-5.0 wt.% of the total mass of the mixed powder; the non-toxic composite stabilizer is a composite calcium-zinc stabilizer containing hydrotalcite, and its addition amount is 1.8-3.2 wt.%; the internal lubricant is glyceryl monostearate, and its addition amount is 0.5-1.5 wt.%; the transparent modifier is methyl methacrylate-butadiene-styrene copolymer, and its addition amount is 1.0-2.5 wt.%; the mixing temperature is 95-115°C, the mixing speed is 500-800 rpm, and the mixing time is 8-15 min; in the composite calcium-zinc stabilizer containing hydrotalcite, the mass percentage of hydrotalcite is 10-25 wt.%.

9. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S6, the multi-roll calender is a five-roll calender, with the temperature of each roll independently controlled. The temperature of the first roll is 155-165°C, the second roll is 160-170°C, the third roll is 165-175°C, the fourth roll is 160-170°C, and the fifth roll, i.e. the cooling and shaping roll, is 75-85°C. The oscillation frequency of the oscillation field is 50-200Hz, the amplitude is 5-20μm, and the angle between its oscillation direction and the film's forward direction is 10° to 30°. The negative pressure value inside the sealed exhaust hood is 100-300Pa. The thickness of the calendered film is 0.10-0.30mm.

10. The method for preparing non-toxic transparent calendered film using waste PVC film according to claim 1, characterized in that: In step S7: the online infrared irradiation treatment involves irradiating the thin film using a mid-infrared light-emitting diode array; the wavelength of the infrared irradiation is 3-5 μm, and the irradiation intensity is 10-30 mW / cm². 2 The irradiation time is 5-15 seconds.

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