Method for detecting microplastics in packaging materials and use thereof

Abstract

This invention provides a method for detecting microplastics in packaging materials and its application. The detection method includes the following steps: (1) Sample pretreatment: ① solvent-assisted peeling; ② dust removal; ③ surfactant wetting pretreatment; (2) alkali treatment and enzymatic hydrolysis; (3) microplastic collection and detection. This invention achieves complete peeling of the inner layer of packaging, effective removal of exogenous contaminants, and mild digestion of the fiber matrix through optimized pretreatment steps, thereby improving the microplastic recovery rate and maintaining its physical integrity, providing a reliable method for accurate qualitative and quantitative determination of microplastics in cigarette packaging materials.

Description

Technical Field

[0001] This invention belongs to the field of quality control technology for cigarette packaging materials, specifically relating to a method for detecting microplastics in packaging materials and its application. Background Technology

[0002] Microplastics (MPs) are generally defined as plastic particles, fibers, or fragments with a diameter ≤ 5 mm. Due to their persistence, widespread distribution, and potential biotoxicity in the environment, they have become a global environmental and health problem. Since plastic particles were first discovered in the ocean in the 1970s, microplastic pollution has expanded from aquatic environments to the atmosphere, soil, and the food chain. In 2022, researchers discovered the presence of microplastics in farmland, oceans, Arctic glaciers, and even in the blood of organisms, highlighting the significant health risks they pose. Studies indicate that approximately 8 million tons of plastic waste enter the ocean globally each year, of which about 1%-5% exists in the form of microplastics. Microplastics have strong hydrophobic surfaces and large specific surface areas, easily adsorbing persistent organic pollutants (such as polycyclic aromatic hydrocarbons and pesticides) and heavy metals (such as lead and cadmium), forming complex pollutants. These pollutants can enter the human body through respiration, ingestion, or skin contact, inducing health risks such as inflammatory responses, oxidative stress, and endocrine disruption. Therefore, the United Nations Environment Assembly listed microplastics as one of the major global environmental problems.

[0003] Domestic and international scholars have conducted extensive research on the separation and identification of microplastics in different environmental systems and products, such as farmland, soil, and daily necessities, resulting in various methods for microplastic enrichment and identification. For example, patent CN118883786A discloses a pyrolysis-gas chromatography method for analyzing microplastics migrating from food contact materials. This method involves mixing food contact materials with a food simulation liquid and filtering to obtain the migrating microplastics, and then using pyrolysis-gas chromatography to quantitatively analyze the migrating microplastics. Patent CN115436504B discloses a method for determining PP, PS, and PE microplastics in filtered water and salt. This method also uses a glass fiber membrane to filter the sample to obtain the microplastics, and then combines pyrolysis-gas chromatography for substance content analysis. Regarding microplastics in complex organic matter, Yan Chunrong et al. (Food Science and Technology, 2023, 48(04): 292-297) used cellulase to enzymatically hydrolyze laver, and then removed organic matter through subsequent digestion. They obtained microplastics using density suspension and performed qualitative and counting analysis of microplastics using micro Raman spectroscopy. These reports provide a reference for the separation and identification of microplastics in food and related packaging materials.

[0004] Cigarettes are a type of consumer product with unique consumption patterns. The production and distribution of cigarettes involve multiple processes, including cigarette rolling, packaging, carton filling, and sealing. The production processes of cigarette packaging materials (such as inner lining paper, frame paper, and boxes) are complex and involve diverse production environments. These packaging materials may pose a risk of microplastic contamination during production. After being used to package cigarettes, these materials may transfer microplastics to the cigarettes during distribution and consumption, and be released into aerosols during inhalation. Literature reports that smokers are directly exposed to microplastics through inhalation of smoke, and the concentration of microplastics in their bronchoalveolar lavage fluid (BALF) (12.69 CFU / g) is significantly higher than that of non-smokers (7.57 CFU / g). Furthermore, 97.06% of the microplastics in BALF are in fibrous form, which closely matches the characteristics of cigarette filters and paper fibers used in packaging materials (Environ. Sci. Technol. 2023, 57, 8496-8505). However, cigarette packaging materials have diverse processing techniques and complex forms, functions, and structures. Methods for separating microplastics from media such as the atmosphere, water, and soil are not very applicable to cigarette packaging materials. Therefore, developing corresponding microplastic separation, enrichment, and identification methods for this complex matrix of cigarette packaging materials is of great significance for product quality control.

[0005] In existing technologies, the removal of fibrous matrices often employs strong alkali digestion, oxidative digestion, or enzymatic hydrolysis. However, these methods suffer from drawbacks such as long processing times, significant damage to sensitive microplastics (e.g., PET, PC, PA), and ineffective removal of exogenous contaminants. Therefore, providing a method that can effectively remove exogenous contaminants while providing accurate detection has become an urgent problem to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for detecting microplastics in packaging materials and its application. This invention achieves complete peeling of the inner packaging layer, effective removal of exogenous contaminants, and gentle digestion of the fibrous matrix through optimized pretreatment steps, thereby improving the microplastic recovery rate while maintaining its physical integrity. This provides a reliable method for the accurate qualitative and quantitative determination of microplastics in cigarette packaging materials.

[0007] To achieve this objective, the present invention adopts the following technical solution: On the one hand, the present invention provides a method for detecting microplastics in packaging materials, the method comprising the following steps: (1) Sample pretreatment: ① Solvent-assisted stripping: The inner layer of the sample to be tested is immersed in a solvent, and then the inner layer of the sample to be tested is stripped from the rest of the sample to obtain the inner layer sample; ② Dust removal: The inner layer sample is blown with air to remove particles adsorbed on the surface; this step can effectively remove exogenous microplastics that adhere due to friction or environmental sedimentation, and avoid overestimating the microplastic content of the packaging material itself; ③ Surfactant wetting pretreatment: The inner layer sample is mixed with an aqueous solution containing a nonionic surfactant and sonicated to obtain a pretreated sample; (2) Alkali treatment and enzymatic hydrolysis: The pretreated sample was mixed with an alkaline solution and stirred. After adjusting the pH, it was mixed with cellulase for digestion. (3) Microplastic collection and detection: The digested material was mixed with a saturated zinc chloride solution and floated. The upper flotation liquid was collected and filtered to obtain a filter membrane enriched with microplastics. Micro Raman spectroscopy was performed to confirm the type and quantity of microplastics in the sample. Then, thermal pyrolysis-gas chromatography-mass spectrometry was performed, and the microplastic content in the sample was calculated based on the analysis results.

[0008] The above method achieves complete peeling of the inner layer of the packaging, effective removal of exogenous contaminants, and gentle digestion of the fiber matrix through optimized pretreatment steps, thereby improving the microplastic recovery rate and maintaining its physical integrity, and providing a reliable method for accurate qualitative and quantitative analysis of microplastics in cigarette packaging materials.

[0009] Preferably, the solvent in step (1) includes any one or a combination of at least two of ethanol, ethyl acetate or water, preferably ethanol, ethyl acetate and water.

[0010] The aforementioned specific solvent combination can quickly break the interfacial adhesive force of the multilayer composite structure of packaging materials, achieving complete peeling of the inner layer without introducing interfering substances from the coating or ink in the packaging.

[0011] Preferably, the volume ratio of ethanol, ethyl acetate and water is (10-80):(10-80):(10-45), more preferably (4-6):(4-6):(1-3).

[0012] Preferably, the soaking temperature in step (1) is 10-35℃ and the soaking time is 0.5-5 min. The temperature can be 10℃, 15℃, 20℃, 25℃, 30℃ or 35℃, etc., and the time can be 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min or 5 min, etc., but is not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0013] Preferably, in the aqueous solution containing nonionic surfactant in step (1), the mass fraction of nonionic surfactant is 0.01-0.5%, such as 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%, but not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable, preferably 0.05-0.2%.

[0014] Preferably, the nonionic surfactant in step (1) includes any one or a combination of at least two of Tween 20, Tween 80, Triton X-100 or polyoxyethylene lauryl alcohol.

[0015] Preferably, the ultrasound time in step (1) is 5-10 min, such as 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, but not limited to the values ​​listed above. Other values ​​not listed above are also applicable.

[0016] The above-mentioned nonionic surfactant treatment process can reduce the surface tension of the inner layer, promote the penetration of alkaline solution and enzyme solution into the fiber pores in subsequent steps, and improve the digestion rate.

[0017] Preferably, the purging in step (1) is performed using an ion air gun, with clean air at 0.2-0.5 MPa for 10-15 seconds.

[0018] Preferably, the alkaline solution in step (2) includes a sodium hydroxide solution or a sodium bicarbonate solution, with sodium hydroxide solution being more preferred.

[0019] Preferably, the sodium hydroxide solution has a mass fraction of 1-5%, and the sodium bicarbonate solution has a concentration of 2-10%. The mass fraction of the sodium hydroxide solution can be 1%, 2%, 3%, 4%, or 5%, etc., and the mass fraction of the sodium bicarbonate solution can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc., but is not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0020] Preferably, the mass ratio of the pretreated sample to the alkaline solution in step (2) is 1:(5-10), such as 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, but not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0021] Preferably, the stirring temperature in step (2) is 35-45℃, such as 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃ or 45℃, but not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0022] Preferably, step (2) involves adjusting the pH to 4.5-5.5.

[0023] Preferably, the cellulase in step (2) accounts for 0.2-1% of the mass of the mixed system, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, but is not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0024] Preferably, the digestion temperature in step (2) is 40-55℃ and the time is 6-24 h. The temperature can be 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃ or 55℃, etc., and the time can be 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h or 24 h, etc., but is not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0025] Preferably, the packaging material includes any one of cigarette box wrapping, frame paper, inner lining paper, or tipping paper.

[0026] Preferably, the microplastics include any one or a combination of at least two of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polyethylene (PE), polyamide (PA), polycarbonate (PC), polyethersulfone (PES), or polyvinyl chloride (PVC).

[0027] On the other hand, the present invention also provides the application of the method for detecting microplastics in packaging materials as described above in the quality evaluation of tobacco packaging materials.

[0028] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for detecting microplastics in packaging materials. Through optimized pretreatment steps, it achieves complete peeling of the inner packaging layer, effective removal of exogenous contaminants, and gentle dissolution of the fibrous matrix, thereby improving the microplastic recovery rate and maintaining its physical integrity. This provides a reliable method for the accurate qualitative and quantitative determination of microplastics in cigarette packaging materials. Specifically, it includes: (1) Solvent-assisted peeling: Using a mixed solvent of ethanol-ethyl acetate-water, the interfacial adhesive force of the multi-layer composite structure of the packaging material can be quickly destroyed at room temperature, so as to achieve complete peeling of the inner layer and shorten the peeling time.

[0029] (2) Dust removal: Blowing effectively removes exogenous microplastics that adhere to the packaging material due to friction or environmental sedimentation, with a removal rate of >90%, avoiding overestimation of the microplastic content of the packaging material itself.

[0030] (3) Surfactant wetting pretreatment: Nonionic surfactants reduce surface tension and promote the penetration of alkaline solution and enzyme solution into fiber pores, thereby increasing the digestion rate.

[0031] (4) Alkali / enzyme digestion: Alkali swelling followed by cellulose enzymatic digestion ensures a high digestion rate (>92%) of the fiber matrix while maximizing the protection of the physical integrity of sensitive microplastics such as PET, PC, and PA.

[0032] (5) Micro Raman spectroscopy combined with a programmed temperature-controlled heating furnace and gas chromatography-mass spectrometry can achieve qualitative and quantitative analysis of microplastics. The qualitative and quantitative analysis of microplastics is accurate, and the quantitative analysis method is simple. By using offline pyrolysis-gas chromatography-mass spectrometry analysis, the dependence on online pyrolysis equipment is avoided, and the method's accessibility is improved. Attached Figure Description

[0033] Figure 1 These are standard Raman spectral characteristic diagrams of different microplastics. Detailed Implementation

[0034] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0035] In the following examples, the cellulase was purchased from Sinopharm Reagent (400 U / mg).

[0036] Example 1 This embodiment provides a method for detecting microplastics in cigarette packaging material frame paper (composed of an inner paper layer, an adhesive layer, an outer paper layer, and an ink printing coating layer in sequence), specifically including the following steps: (1) Sample pretreatment: (1a) Solvent-assisted peeling: Fix the inner layer of the frame paper with the inner layer facing up, add a mixed solvent of anhydrous ethanol, ethyl acetate and distilled water in a volume ratio of 40:40:20, soak at room temperature (25°C) for 1 minute until the interface is loose, air dry in a fume hood or use absorbent paper to remove the surface solvent, and then slowly peel the inner layer from the ink coating to obtain the inner layer sample.

[0037] (1b) Electrostatic dust removal: Place the inner layer sample under an ion gun and blow it with clean air at 0.3 MPa for 12 seconds to remove the particles electrostatically adsorbed on the surface.

[0038] (1c) Surfactant wetting pretreatment: Cut 1.0g of inner layer sample into fragments of about 1-3 mm, soak in an aqueous solution containing 0.1% by mass of nonionic surfactant Tween 80, sonicate for 5 min at 300W and 25℃; then centrifuge to discard the supernatant and rinse twice with deionized water.

[0039] (2) Alkali treatment and enzymatic hydrolysis: The pretreated fragments were placed in a dilute NaOH solution (2% by mass) and stirred at a constant temperature of 45℃ for 3 h at a mass ratio of 1:7. Then, dilute hydrochloric acid was added to adjust the pH to 5.0. Cellulase was added to the above system, with the mass of cellulase accounting for 0.6% of the solution mass, and the mixture was digested by shaking at a constant temperature of 45℃ for 6 h. (3) Density flotation: The digested system (concentrated to 10 mL, the same applies to the following examples) was transferred to a clean glass container and ultrasonically dispersed (power 400 W, 10 min per cycle). 30 mL of saturated zinc chloride solution was added to enrich the microplastics by flotation. The floating matter containing microplastics in the upper layer was transferred to a beaker. Ultrasonic and density flotation were repeated 3 times. The upper flotation solutions collected multiple times were mixed.

[0040] (4) Filtering: The flotation solution was filtered through a glass fiber membrane (pore size 0.45 μm) to obtain a glass fiber filter membrane enriched with microplastics.

[0041] (5) Microplastic identification: The filter membrane in step (4) above was scanned using micro Raman spectroscopy, and the standard Raman spectral characteristics of different microplastics were analyzed. Figure 1 The horizontal axis represents wavelength. Using a Renishaw / in Via confocal laser Raman spectrometer (Renishaw, UK), different microplastic standards were placed on a glass slide. Raman spectra of the samples were acquired using point scanning mode. Instrument parameters were set as follows: objective lens 20X, reflection mode, excitation source 532 nm, laser power 0.5%, exposure time 10 s, and 10 scans (average spectrum was obtained). The types and quantities of enriched microplastics were determined. Subsequently, the glass fiber membrane containing microplastics was transferred to a temperature-controlled tube furnace for pyrolysis. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the pyrolysis components in the collected solution. Based on the standard curve (Table 2) between the peak area of ​​characteristic pyrolysis components and the mass of microplastics and the peak area of ​​characteristic pyrolysis components (Table 1), the content of microplastics enriched in the glass fiber filter membrane was calculated. The Raman spectra and pyrolysis GC-MS results are shown in Tables 3 and 4.

[0042] The microplastics used in the standard Raman spectra and pyrolysis component standard curves of the microplastics in step (5) above include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polyethylene (PE), polyamide (PA), polycarbonate (PC), polyethersulfone resin (PES), polyvinyl chloride (PVC), etc. The instrument parameters for the micro Raman spectroscopy in this step are: 20X objective lens, reflection mode, excitation light source 532 nm, laser power 0.5%, and exposure time 10 s. The instrument parameters for the programmable temperature controlled tube furnace pyrolysis in this step are: pyrolysis temperature 600℃, holding time 8 min, heating rate 20 ℃ / min, and pyrolysis component collection solution is dichloromethane.

[0043] In step (5) above, the chromatographic column for the analysis of pyrolysis components was an HP-5MS, 60 m × 0.25 mm ID × 0.25 μm capillary column. The temperature program was: 50℃, hold for 2 min, increase to 280℃ at 8℃ / min, hold for 25 min. The injection port was set as follows: split injection mode, split ratio of 15:1, injection port temperature of 280℃. The carrier gas was high-purity helium (99.999%), constant flow mode, 1 mL / min. The mass spectrometry parameters were: electron impact source (EI), transfer line temperature of 280℃, ion source temperature of 230℃. The scanning mode was full scan, and the acquisition range was 35-400 m / z.

[0044] Table 1. Characteristic ionic fragments of pyrolysis components of 8 standard microplastics. Table 2. Standard curves for quantitative analysis of eight microplastics. Table 3. Raman spectral matching results of the microplastics in Example 1. Table 4. Quantitative analysis results of microplastics in Example 1 Example 2 This embodiment provides a method for detecting microplastics in tipping paper for cigarette packaging materials (hot stamping tipping paper, including a base paper layer, a gravure ink layer, a cellulose lacquer layer, an organosilicon coating layer, and a hot stamping layer (from bottom to top, consisting of a urea-formaldehyde resin adhesive layer, an aluminized layer, a coloring layer, and a release layer)), specifically including the following steps: (1) Sample pretreatment: (1a) Solvent-assisted peeling: Fix the inner layer of the tipping paper with the inner layer facing up, add a mixed solvent of anhydrous ethanol, ethyl acetate and distilled water in a volume ratio of 50:50:30, soak at room temperature (10°C) for 5 minutes until the interface is loose, air dry in a fume hood or use absorbent paper to remove the surface solvent, and then slowly peel the inner layer from the ink coating to obtain the inner layer sample.

[0045] (1b) Electrostatic dust removal: Place the inner layer sample under an ion gun and blow it with clean air at 0.3 MPa for 12 seconds to remove the particles electrostatically adsorbed on the surface.

[0046] (1c) Surfactant wetting pretreatment: Cut 1.0g of inner layer sample into fragments of about 1-3 mm, soak in an aqueous solution containing 0.01% by mass of nonionic surfactant Tween 20, sonicate for 10 min at 300W and 25℃; then centrifuge to discard the supernatant and rinse twice with deionized water.

[0047] (2) Alkali treatment and enzymatic hydrolysis: The pretreated fragments were placed in a dilute NaOH solution (1% by mass) and stirred at a constant temperature of 40℃ for 3 h at a mass ratio of 1:5. Then, dilute hydrochloric acid was added to adjust the pH to 5.5. Cellulase was added to the above system, with the mass of cellulase accounting for 0.2% of the solution mass, and the mixture was digested by shaking at a constant temperature of 40℃ for 24 h. (3) Density flotation: After digestion, the system was transferred to a clean glass container and ultrasonically dispersed (400 W, 10 min per cycle). 30 mL of saturated zinc chloride solution was added to enrich the microplastics by flotation. The floating matter containing microplastics in the upper layer was transferred to a beaker. Ultrasonic and density flotation were repeated 3 times. The upper flotation solutions collected multiple times were mixed.

[0048] (4) Filtering: The flotation solution was filtered through a glass fiber membrane (pore size 0.45 μm) to obtain a glass fiber filter membrane enriched with microplastics.

[0049] (5) Microplastic identification: The filter membrane in step (4) above was scanned using micro Raman spectroscopy, and the standard Raman spectral characteristics of different microplastics were analyzed. Figure 1 The types and quantities of enriched microplastics were determined. Subsequently, the glass fiber membrane carrying the microplastics was transferred to a temperature-controlled tube furnace for pyrolysis. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the pyrolysis component collection solution. Based on the standard curve between the peak area of ​​the characteristic pyrolysis component and the mass of the microplastic and the peak area of ​​the characteristic pyrolysis component, the content of microplastics enriched in the glass fiber filter membrane was calculated. The Raman spectroscopy and pyrolysis GC-MS results are shown in Tables 5 and 6.

[0050] The microplastics used in the standard Raman spectra and pyrolysis component standard curves of the microplastics in step (5) above include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polyethylene (PE), polyamide (PA), polycarbonate (PC), polyethersulfone resin (PES), polyvinyl chloride (PVC), etc. The instrument parameters for the micro Raman spectroscopy in this step are: 20X objective lens, reflection mode, excitation light source 532 nm, laser power 0.5%, and exposure time 10 s. The instrument parameters for the programmable temperature controlled tube furnace pyrolysis in this step are: pyrolysis temperature 600℃, holding time 5 min, heating rate 20 ℃ / min, and pyrolysis component collection solution is dichloromethane.

[0051] In step (5) above, the chromatographic column for the analysis of pyrolysis components was an HP-5MS, 60 m × 0.25 mm ID × 0.25 μm capillary column. The temperature program was: 50℃, hold for 2 min, increase to 280℃ at 8℃ / min, hold for 25 min. The injection port was set as follows: split injection mode, split ratio of 15:1, injection port temperature of 280℃. The carrier gas was high-purity helium (99.999%), constant flow mode, 1 mL / min. The mass spectrometry parameters were: electron impact source (EI), transfer line temperature of 280℃, ion source temperature of 230℃. The scanning mode was full scan, and the acquisition range was 35-400 m / z.

[0052] Table 5. Raman spectral matching results of microplastics in Example 2. Table 6. Quantitative analysis results of microplastics in Example 2 Example 3 This embodiment provides a method for detecting microplastics in the inner lining paper of cigarette packaging materials (composite aluminum foil inner lining paper, including an inner base paper layer, an adhesive layer, an aluminum foil layer, and a surface printed layer), specifically including the following steps: (1) Sample pretreatment: (1a) Solvent-assisted peeling: Fix the inner layer of the liner paper with the inner layer facing up, add a mixed solvent prepared by anhydrous ethanol, ethyl acetate and distilled water in a volume ratio of 60:60:10, soak at room temperature (35°C) for 0.5 minutes until the interface loosens, air dry in a fume hood or use absorbent paper to remove the surface solvent, and then slowly peel the inner layer from the ink coating to obtain the inner layer sample.

[0053] (1b) Electrostatic dust removal: Place the inner layer sample under an ion gun and blow it with clean air at 0.3 MPa for 12 seconds to remove the particles electrostatically adsorbed on the surface.

[0054] (1c) Surfactant wetting pretreatment: Cut 1.0g of inner layer sample into fragments of about 1-3 mm, soak in an aqueous solution containing 0.5% by mass of nonionic surfactant Tween 80, sonicate for 8 min at 300W and 25℃; then centrifuge to discard the supernatant and rinse twice with deionized water.

[0055] (2) Alkali treatment and enzymatic hydrolysis: The pretreated fragments were placed in a dilute NaHCO3 alkaline solution (10% by mass) and stirred at a constant temperature of 45℃ for 3 h at a mass ratio of 1:10. Then, dilute hydrochloric acid was added to adjust the pH to 4.5. Cellulase was added to the above system, with the mass of cellulase accounting for 1% of the solution mass, and the mixture was digested by shaking at a constant temperature of 55℃ for 6 h. (3) Density flotation: After digestion, the system was transferred to a clean glass container and ultrasonically dispersed (400 W, 10 min per cycle). 30 mL of saturated zinc chloride solution was added to enrich the microplastics by flotation. The floating matter containing microplastics in the upper layer was transferred to a beaker. Ultrasonic and density flotation were repeated 3 times. The upper flotation solutions collected multiple times were mixed.

[0056] (4) Filtering: The flotation solution was filtered through a glass fiber membrane (pore size 0.45 μm) to obtain a glass fiber filter membrane enriched with microplastics.

[0057] (5) Microplastic identification: The filter membrane in step (4) above was scanned using micro Raman spectroscopy, and the standard Raman spectral characteristics of different microplastics were analyzed. Figure 1 The types and quantities of enriched microplastics were determined. Subsequently, the glass fiber membrane carrying microplastics was transferred to a temperature-controlled tube furnace for pyrolysis. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the pyrolysis component collection solution. Based on the standard curve between the peak area of ​​characteristic pyrolysis components and the mass of microplastics and the peak area of ​​characteristic pyrolysis components, the content of microplastics enriched in the glass fiber filter membrane was calculated. The Raman spectroscopy and pyrolysis GC-MS results are shown in Tables 7 and 8.

[0058] The microplastics used in the standard Raman spectra and pyrolysis component standard curves of the microplastics in step (5) above include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polyethylene (PE), polyamide (PA), polycarbonate (PC), polyethersulfone resin (PES), polyvinyl chloride (PVC), etc. The instrument parameters for the micro Raman spectroscopy in the above step are 20X objective lens, reflection mode, excitation light source 532 nm, laser power 0.5%, and exposure time 10 s. The instrument parameters for the programmable temperature controlled tube furnace pyrolysis in the above step are pyrolysis temperature 600℃, holding time 10 min, heating rate 20℃ / min, and pyrolysis component collection solution is dichloromethane.

[0059] In step (5) above, the chromatographic column for the analysis of pyrolysis components was an HP-5MS, 60 m × 0.25 mm ID × 0.25 μm capillary column. The temperature program was: 50℃, hold for 2 min, increase to 280℃ at 8℃ / min, hold for 25 min. The injection port was set as follows: split injection mode, split ratio of 15:1, injection port temperature of 280℃. The carrier gas was high-purity helium (99.999%), constant flow mode, 1 mL / min. The mass spectrometry parameters were: electron impact source (EI), transfer line temperature of 280℃, ion source temperature of 230℃. The scanning mode was full scan, and the acquisition range was 35-400 m / z.

[0060] Table 7. Raman spectral matching results of microplastics in Example 3. Table 8. Quantitative analysis results of microplastics in Example 3 Example 4 This embodiment aims to verify the necessity and rationality of the key steps in the method described in this invention (stripping and dust removal + surfactant pretreatment, weak alkali pretreatment and enzymatic hydrolysis sequence, and alkali treatment intensity). Using the cigarette frame paper from Example 1 as a sample, the following comparative experiment was set up. All experiments adopted the same subsequent flotation, filtration and identification steps as in Example 1, and the morphological changes of the recovered microplastics were observed.

[0061] This invention group: Same as Example 1.

[0062] Comparative Group A (no ink layer peeling): The surface coating layer of the frame paper is not peeled off, and the rest is the same as the present invention group.

[0063] Comparative Group B (excessive alkali treatment): After the inner layer was peeled off, a higher concentration of NaOH (25%), a higher temperature (55°C), and a longer treatment time (24h) were used, with the rest being the same as in Example 1.

[0064] Control group C (digestion order reversed): enzymatic hydrolysis was performed first, followed by alkali treatment, with no pH adjustment in between, and the rest was the same as in Example 1.

[0065] Control group D (enzymatic hydrolysis alone): No alkali treatment was performed, only enzymatic hydrolysis, and the rest was the same as in Example 1 of this case.

[0066] Results Record: In addition to digestion rate and microplastic detection amount, the average particle size and surface morphology of typical PET microplastics (externally calibrated, initial particle size 50±5 μm) observed under an optical microscope were recorded. The results are summarized in the table below.

[0067] Comparison of digestion rate and microplastic recovery effect of frame paper samples under different pretreatment conditions: Note: The initial particle size of PET was measured by adding standard particles (50±5 μm) to assess the impact of different treatments on the physical integrity of microplastics.

[0068] Comparative experiments show that the peeling and dust removal combined with surfactant pretreatment can significantly improve the digestion rate and microplastic recovery, which is the key pretreatment step of this invention. Although strong alkali treatment can slightly improve the digestion rate, it will lead to severe degradation of alkali-sensitive PET microplastics (the detection amount drops from 91.5 μg to 8.2 μg, and the particle size is significantly reduced). The mild alkali conditions selected in this invention can protect the integrity of microplastics to the greatest extent while ensuring a high digestion rate. Reversing the digestion order (enzyme first, then alkali) will reduce the digestion rate to 78.7% and the detection amount of microplastics will also decrease significantly, indicating that the order of weak alkali pretreatment followed by enzymatic hydrolysis is the best combination to achieve efficient digestion and complete preservation of microplastics. The digestion rate of enzymatic hydrolysis alone is only 61.3%, which increases to 92.2% after adding weak alkali pretreatment, indicating that the swelling and activation of fibers by alkali pretreatment is the core step that synergistically enhances the effect of enzymatic hydrolysis.

[0069] Example 5 This embodiment aims to verify the time reduction and integrity improvement of solvent-assisted peeling in the method described in this invention.

[0070] Take the same batch of frame paper, cut it into 5×5 cm pieces, divide it into two groups of 5 pieces each.

[0071] Control group: The inner layer was peeled off manually (without solvent).

[0072] Experimental group: Following the steps of Example 1 (1a), add a mixed solvent of ethanol:ethyl acetate:water = 40:40:20, soak at room temperature for 1 min, air dry, and then peel off.

[0073] The results of the peeling experiment are as follows: solvent-assisted peeling increased the integrity rate by 40% and shortened the peeling time by 60%. Example 6 This embodiment aims to verify the removal efficiency of electrostatic dust removal of exogenously attached microplastics in the method described in this invention.

[0074] The inner layer of the frame paper was obtained by peeling off the experimental group method of Example 1, and a PET microplastic suspension (approximately 10 μg / cm³) was uniformly sprayed onto the inner surface of the inner frame paper. 2 The sample was air-dried naturally. It was then purged with an ion gun (0.3 MPa) for 15 seconds, followed by the subsequent steps of this invention to extract and quantify the residual PET microplastics. The amount of residual PET after purging was 0.54 μg / cm³.2 The removal rate of exogenous pollutant microplastics is approximately 94%. This indicates that the purging step of the present invention can effectively remove exogenous microplastics adhering to the surface due to friction or environmental sedimentation.

[0075] Example 7 This embodiment aims to verify the promoting effect of the nonionic surfactant wetting on alkali / enzyme digestion described in this invention.

[0076] Cigarette box packaging material (hard-pack cigarette box packaging, including the inner paper layer, printing layer, and functional coating) of a certain brand was randomly divided into two groups, A and B. Group A boxes were treated using the steps described in Example 1, the digestion rate was calculated, and the microplastic content was detected. Group B boxes underwent the same treatment process as Group A, except that step 1c in Example 1 was omitted. The digestion rate and microplastic release of the two groups are shown in the table. It can be seen that surfactant pretreatment increased the digestion rate from 89.3% to 96.1%, and the microplastic content was completely detected. Example 8 This embodiment aims to verify the effectiveness of the technical solution of the present invention in detecting microplastics in different packaging materials such as cigarette box wrappers, frame paper, and inner lining paper.

[0077] Separately, three samples each of cigarette packaging materials from different batches and models than those in Example 7 were taken, including box skin (soft pack cigarette box skin, white cardboard substrate + adhesive layer + ink printing layer), frame paper (printed frame paper, white cardboard base layer + ink printing layer), and inner lining paper (laser-plated inner lining paper, base paper substrate + adhesive layer + laser molding layer). Sample pretreatment, alkali treatment and enzymatic hydrolysis, density flotation, filtration, and microplastic identification by thermal pyrolysis were performed according to the conditions and parameters in Example 1. The results are shown in the table below. It can be seen that this method can effectively identify the types and contents of various microplastics in different cigarette packaging materials. Example 9 This embodiment aims to verify the effect of the mixed solvent (ethanol-ethyl acetate-water) in step (1a) of the method described in this invention on the peeling effect of the inner layer of the frame paper and the subsequent microplastic detection results. Take the same batch of cigarette frame paper as in Example 1, cut sample pieces, and randomly divide them into three groups of 5 pieces each.

[0078] Control group A (solvent-free): The inner layer was peeled off manually with tweezers (without applying any wetting agent).

[0079] Control group B (pure water immersion): With the inner layer of the sample facing up, wet the surface with deionized water, let it stand for 1 minute, absorb the excess water, and then peel off the inner layer manually.

[0080] Experimental Group C (mixed solvent of the present invention): according to step (1a) of claim 1, add anhydrous ethanol, ethyl acetate and distilled water in a volume ratio of 40:40:20, soak at room temperature (25°C) for 1 min, remove the surface solvent, and then peel off the inner layer by hand.

[0081] Record the peel integrity (the percentage of the inner layer without tearing or residual ink / coating after peeling) and average peeling time (the time required from the start of peeling to complete separation) of each sample in each group, and observe the fiber breakage on the inner layer surface after peeling using a stereomicroscope (40×).

[0082] Take the inner layer sample obtained after peeling and perform the following steps in Example 1: (1b) electrostatic dust removal, (1c) surfactant wetting pretreatment, (2) alkali treatment and enzymatic hydrolysis, (3) density flotation, (4) filtration, and (5) microplastic identification to determine the content of PET, PS and PES.

[0083] The results are shown in the table below: Comparison of the effects of different peeling methods The Influence of Different Peeling Methods on the Final Microplastic Detection Results It can be seen that the method provided by the present invention uses a specific solvent to effectively peel off the inner layer material, and will not cause the problem of insufficient peeling leading to the mixing of other structural materials into the sample and causing abnormal detection.

[0084] The applicant declares that this invention illustrates the method for detecting microplastics in packaging materials and its application through the above embodiments, but this invention is not limited to the above embodiments, that is, it does not mean that this invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials of this invention's products, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

[0085] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0086] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A method for detecting microplastics in packaging materials, characterized in that, The detection method includes the following steps: (1) Sample pretreatment: ① Solvent-assisted stripping: The inner layer of the sample to be tested is immersed in a solvent, and then the inner layer of the sample to be tested is stripped from the rest of the sample to obtain the inner layer sample; ② Dust removal: The inner layer sample is purged with air to remove particles adsorbed on the surface; ③ Surfactant wetting pretreatment: The inner layer sample is mixed with an aqueous solution containing a nonionic surfactant and sonicated to obtain a pretreated sample; (2) Alkali treatment and enzymatic hydrolysis: The pretreated sample was mixed with an alkaline solution and stirred. After adjusting the pH, it was mixed with cellulase for digestion. (3) Microplastic collection and detection: The digested material was mixed with a saturated zinc chloride solution and floated. The upper flotation liquid was collected and filtered to obtain a filter membrane enriched with microplastics. Micro Raman spectroscopy was performed to confirm the type and quantity of microplastics in the sample. Then, thermal pyrolysis-gas chromatography-mass spectrometry was performed, and the microplastic content in the sample was calculated based on the analysis results.

2. The method for detecting microplastics in packaging materials according to claim 1, characterized in that, The solvent in step (1) includes any one or a combination of at least two of ethanol, ethyl acetate or water, preferably ethanol, ethyl acetate and water; Preferably, the volume ratio of ethanol, ethyl acetate and water is (10-80):(10-80):(10-45), more preferably (4-6):(4-6):(1-3).

3. The method for detecting microplastics in packaging materials according to claim 1 or 2, characterized in that, The soaking temperature in step (1) is 10-35℃ and the soaking time is 0.5-5 min.

4. The method for detecting microplastics in packaging materials according to any one of claims 1-3, characterized in that, In step (1), the aqueous solution containing a nonionic surfactant has a mass fraction of 0.01-0.5%, preferably 0.05-0.2%. Preferably, the nonionic surfactant in step (1) includes any one or a combination of at least two of Tween 20, Tween 80, Triton X-100 or polyoxyethylene lauryl alcohol; Preferably, the ultrasound time in step (1) is 5-10 min.

5. The method for detecting microplastics in packaging materials according to any one of claims 1-4, characterized in that, The alkaline solution in step (2) includes sodium hydroxide solution or sodium bicarbonate solution, preferably sodium hydroxide solution; Preferably, the sodium hydroxide solution has a mass fraction of 1-5%, and the sodium bicarbonate solution has a concentration of 2-10%.

6. The method for detecting microplastics in packaging materials according to any one of claims 1-5, characterized in that, In step (2), the mass ratio of the pretreated sample to the alkaline solution is 1:(5-10). Preferably, the stirring temperature in step (2) is 35-45℃; Preferably, step (2) involves adjusting the pH to 4.5-5.

5.

7. The method for detecting microplastics in packaging materials according to any one of claims 1-6, characterized in that, In step (2), the amount of cellulase in the mixed system is 0.2-1% of the total mass. Preferably, the digestion temperature in step (2) is 40-55℃ and the time is 6-24 h.

8. The method for detecting microplastics in packaging materials according to any one of claims 1-7, characterized in that, The packaging material includes any one of cigarette box leather, frame paper, inner lining paper, or tipping paper.

9. The method for detecting microplastics in packaging materials according to any one of claims 1-8, characterized in that, The microplastics include any one or a combination of at least two of polyethylene terephthalate, polypropylene, polystyrene, polyethylene, polyamide, polycarbonate, polyethersulfone, or polyvinyl chloride.

10. The application of a method for detecting microplastics in packaging materials according to any one of claims 1-9 in the quality evaluation of tobacco packaging materials.

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