PE (polyethylene) film, preparation process and application of PE film in tissue packaging

Abstract

The invention relates to the technical field of degradable PE (polyethylene) packaging materials, and discloses a PE film, a preparation process and application in tissue packaging, and the PE film is prepared by the following steps: by taking 7-(diethylamino) coumarin-3-carboxylic acid, 2-naphthyl methanol and epoxy chloropropane as raw materials, carrying out esterification reaction and quaternization reaction to prepare an epoxidized biodegradable organic photosensitizer; based on an epoxy-hydroxyl ring-opening reaction mechanism, hydroxylated titanium dioxide nanoparticles and polyvinyl alcohol resin are respectively modified by using an epoxidized biodegradable organic photosensitizer, and compounding is performed based on a pi-pi accumulation effect between aromatic rings to prepare the ultraviolet light dependent photo-biodegradable component. According to the present invention, the ultraviolet light dependent light-biological degradation component, the compatible component and the composite auxiliary agent are added to the polyethylene matrix, and blow molding is performed to obtain the PE film, and the film product shows excellent light-biological dual degradation performance, has actual use value, and can be used in the tissue packaging field.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable PE packaging materials, and particularly to a PE film, a preparation process, and an application thereof in paper towel packaging. Background Art

[0002] Polyethylene (PE) film has become one of the mainstream materials for paper towel packaging due to its excellent moisture resistance (its water vapor transmission rate is as low as 5 - 10 g / m 2 ·d), low cost (its price is only 12 - 15 yuan / kg), and mature supply chain (its production, printing, and packaging equipment have been highly standardized), and it occupies a dominant position especially in the fields of facial tissues, toilet paper, and wet wipes.

[0003] With the improvement of environmental protection requirements, green packaging has become the development direction of paper towel packaging materials, and among them, biomass-based degradable packaging materials have become one of the main development directions. However, bio-based packaging materials have significant disadvantages such as high cost and poor mechanical properties. Therefore, in the short term, traditional plastic packaging materials will still be the packaging materials with the largest consumption. As the most representative packaging material, the PE film packaging material degrades extremely slowly after use and becomes the main source of white pollution.

[0004] Currently, the main methods for degrading polyethylene are biodegradation and photodegradation. Biodegradation of polyethylene generally refers to adding natural biodegradable materials (such as starch, cellulose, etc.) and synthetic biodegradable materials (such as polyvinyl alcohol, polylactic acid, polybutylene succinate, etc.) to the polyethylene matrix, and under the action of microorganisms and enzymes, eroding the biodegradable materials to cause polyethylene to disintegrate into small fragments.

[0005] Photodegradation of polyethylene means that polyethylene undergoes degradation under the excitation and induction of light. It can be divided into synthetic photodegradation and addition of photosensitizer type photodegradation. Addition type photodegradable polyethylene refers to adding a photosensitizer to polyethylene. Under light conditions, the photosensitizer initiates the degradation of polyethylene. There are many types of photosensitizers, mainly TiO2 and its derivative semiconductor photosensitizers. The band gap of TiO2 photosensitizer is relatively large, reaching 3.2 eV, and it only responds to ultraviolet light with a wavelength less than 387.5 nm. Since the energy of sunlight is mainly distributed in the wavelength range of 400 - 760 nm, the photodegradable polyethylene film prepared by adding TiO2 to polyethylene has a very low degradation risk when used for product packaging, and can be induced to degrade by ultraviolet light after use.

[0006] Research has found that organic small molecules with a large conjugated structure have excellent light absorption properties and can be used as photosensitive materials as additives for plastics to achieve the photodegradation of related materials. Among them, naphthalene compounds show strong absorption ability in the ultraviolet region (240 - 320 nm) and can be used as organic photosensitizers to achieve the photodegradation of materials.

[0007] In addition, polyvinyl alcohol is a vinyl polymer that can be utilized by bacteria as a carbon source and energy source, and can be degraded under the action of bacteria and enzymes, belonging to a kind of biodegradable polymer material. SUMMARY OF THE INVENTION

[0008] The present invention designs and synthesizes an organic photosensitizer with a coupling function and containing a biodegradable group from an ultraviolet light-dependent organic photosensitizer naphthalene compound. On the one hand, this organic photosensitizer is grafted onto the surface of the inorganic photosensitizer nano-TiO₂ to solve the TiO₂ aggregation problem, and on the other hand, it is modified onto the side chain of the synthetic biodegradable material polyvinyl alcohol. Then, the grafted TiO₂ and the modified polyvinyl alcohol are compounded and added to the PE matrix, and thus the prepared PE film simultaneously has the capabilities of photo-degradation and biodegradation.

[0009] A preparation process of a PE film includes the following steps: Step 1: Synthesize an epoxidized biodegradable organic photosensitizer; Step 2: Based on the epoxy-hydroxy ring-opening reaction mechanism, graft the epoxidized biodegradable organic photosensitizer onto the surface of hydroxylated titanium dioxide nanoparticles to obtain a biodegradable photosensitizer, and graft the epoxidized biodegradable organic photosensitizer onto the side chain of polyvinyl alcohol to obtain photosensitive polyvinyl alcohol; Step 3: Based on the π-π stacking interaction between aromatic rings, compound the biodegradable photosensitizer and the photosensitive polyvinyl alcohol to prepare an ultraviolet light-dependent photo-biodegradable component; Step 4: Add the ultraviolet light-dependent photo-biodegradable component, a compatibilizing component, and a compounding assistant together to a polyethylene matrix, and blow-mold to obtain a PE film.

[0010] Preferably, the preparation method of the epoxidized biodegradable organic photosensitizer is as follows: Through the esterification reaction of the carboxyl functional group of 7-(diethylamino)coumarin-3-carboxylic acid and the hydroxyl functional group of 2-naphthylmethanol, a coumarinyl naphthyl tertiary amine monomer is generated; Based on the nucleophilic substitution reaction mechanism, through the quaternization reaction of the tertiary amine functional group of the coumarinyl naphthyl tertiary amine monomer and the chlorine functional group of epichlorohydrin, an epoxidized biodegradable organic photosensitizer is generated.

[0011] Preferably, the dosage of the ultraviolet light-dependent photo-biodegradable component in the PE film is 15 - 40 wt% of the polyethylene dosage.

[0012] Preferably, the mass ratio of the biodegradable photosensitizer to the photosensitive polyvinyl alcohol in the ultraviolet light-dependent photo-biodegradable component is 1:(2 - 5); Preferably, the mass ratio of the epoxidized biodegradable organic photosensitizer to the hydroxylated titanium dioxide nanoparticles in the biodegradable photosensitizer is 1:(3 - 8); Preferably, the mass ratio of the epoxidized biodegradable organic photosensitizer to polyvinyl alcohol in the photosensitive polyvinyl alcohol is 1:(3 - 8).

[0013] Preferably, the particle size of the titanium dioxide is 5 - 10 nm.

[0014] A PE film prepared according to the above process comprises the following raw materials in parts by weight: 60 - 70 parts of low - density polyethylene resin; 5 - 12 parts of compatibilizing component; 10 - 30 parts of ultraviolet - light - dependent photo - biodegradable component; 1 - 5 parts of composite additives.

[0015] Preferably, the compatibilizing component is maleic anhydride - grafted polyethylene resin or maleic anhydride - grafted high - density polyethylene resin with methacrylic acid.

[0016] Preferably, the composite additives include 0.5 - 2 parts by weight of antioxidant, 0.2 - 2 parts by weight of antistatic agent and 0.3 - 2 parts by weight of antiblocking agent.

[0017] Preferably, the thickness of the PE film is 100 - 150 μm.

[0018] An application of a PE film prepared according to the above process in paper towel packaging. Beneficial effects

[0019] Based on the esterification reaction and quaternization reaction mechanisms, using biodegradable 7 - (diethylamino) coumarin - 3 - carboxylic acid, ultraviolet - light - dependent organic photosensitizer 2 - naphthylmethanol and epichlorohydrin as raw materials, an epoxidized biodegradable organic photosensitizer is synthesized; Based on the epoxy - hydroxyl ring - opening reaction mechanism, on the one hand, the epoxidized biodegradable organic photosensitizer is grafted onto the surface of hydroxylated titanium dioxide nanoparticles to obtain a biodegradable photosensitizer, and on the other hand, the epoxidized biodegradable organic photosensitizer is grafted onto the side chain of polyvinyl alcohol to obtain photosensitive polyvinyl alcohol; Based on the π - π stacking interaction between aromatic rings, the biodegradable photosensitizer and photosensitive polyvinyl alcohol are compounded to prepare an ultraviolet - light - dependent photo - biodegradable component; The ultraviolet - light - dependent photo - biodegradable component, compatibilizing component and other additives are added to the polyethylene matrix together, and a PE film product is obtained by blow - molding; It can be known from the experimental results that: the PE film product prepared by the present invention not only meets the technical requirements for the packaging of tissue products in terms of barrier performance and can be used for the packaging of tissue products, but also can effectively guarantee the shelf life of tissue products. Moreover, after the tissue products are used up, the waste PE film can be first induced to undergo a photodegradation reaction by ultraviolet light until its appearance no longer changes significantly, and then the part of the waste film that has not undergone ultraviolet light degradation can be further degraded by microbial action. Detailed implementation mode Example 1:

[0020] Prepare an epoxidized biodegradable organic photosensitizer, and its preparation process is as follows: Step 1: Through the esterification reaction of the carboxyl functional group of 7-(diethylamino)coumarin-3-carboxylic acid and the hydroxyl functional group of 2-naphthylmethanol, a coumarinyl naphthyl tertiary amine monomer is generated, and its chemical structural formula is: ; Step 2: Based on the mechanism of nucleophilic substitution reaction, through the quaternization reaction of the tertiary amine functional group of the coumarinyl naphthyl tertiary amine monomer and the chlorine functional group of epichlorohydrin, an epoxidized biodegradable organic photosensitizer is generated, and its chemical structural formula is: ; The specific experimental steps for preparing the epoxidized biodegradable organic photosensitizer are as follows: Add 2.6 g of 7-(diethylamino)coumarin-3-carboxylic acid, 1.6 g of 2-naphthylmethanol and 50 mL of N,N-dimethylformamide into a three-necked flask, stir at room temperature until completely dissolved, then add 2.5 mL of concentrated sulfuric acid dropwise to the three-necked flask, raise the temperature to 80 °C and stir for 6 h, cool to room temperature, rotate and evaporate to remove the solvent, wash with absolute ethanol, and dry under vacuum to obtain the coumarinyl naphthyl tertiary amine monomer; Add 2.0 g of the coumarinyl naphthyl tertiary amine monomer and 30 mL of acetonitrile into a three-necked flask, stir at room temperature until completely dissolved, then add 0.4 mL of epichlorohydrin to the three-necked flask, under the protection of nitrogen and mechanical stirring, raise the temperature to 50 °C and stir for 12 h, cool to room temperature, rotate and evaporate to remove the solvent, wash with absolute ethanol, and dry under vacuum to obtain the epoxidized biodegradable organic photosensitizer; The nuclear magnetic resonance hydrogen spectrum characterization of the epoxidized biodegradable organic photosensitizer is as follows: 1 H NMR(CDCl3, 400 MHz) δ: 1.37 - 1.41(t, 6H), 3.62 - 3.63(d, 2H), 4.00 - 4.12(m, 5H), 4.18 - 4.20(d, 2H), 5.24(s, 2H), 7.37 - 8.01(m, 10H, Ar-H), 8.51(s, 1H). Example 2:

[0021] Preparation of biodegradable photosensitizer: The graft modification of titanium dioxide by epoxidized biodegradable organic photosensitizer is completed through the ring-opening reaction between the epoxy functional group of the epoxidized biodegradable organic photosensitizer and the hydroxyl functional group on the surface of hydroxylated titanium dioxide nanoparticles, and a biodegradable photosensitizer is obtained. The specific experimental steps are as follows: Add 5 g of hydroxylated titanium dioxide nanoparticles and 50 mL of N,N-dimethylformamide into a three-necked flask, stir and dissolve at room temperature for 30 min and ultrasonically disperse for 1 h. Under the condition of nitrogen protection, add 10 mL of N,N-dimethylformamide solution containing 1 g of epoxidized biodegradable organic photosensitizer and 1.5 mL of triethylamine catalyst dropwise into the three-necked flask, heat up to 70 °C and stir for 6 h, cool to room temperature, remove the solvent by rotary evaporation, wash with absolute ethanol, and dry in vacuum to obtain the biodegradable photosensitizer; Among them, the preparation method of hydroxylated titanium dioxide nanoparticles is: Add 10 g of nano-titanium dioxide powder (particle size 5 - 10 nm) and 200 mL of hydrogen peroxide aqueous solution (40 wt%) into a three-necked flask, ultrasonically disperse for 30 min, heat up to 105 °C under mechanical stirring and reflux for 6 h, cool to room temperature, centrifuge, wash repeatedly with deionized water by centrifugation, and dry in vacuum to obtain hydroxylated titanium dioxide nanoparticles. Example 3:

[0022] Preparation of photosensitive polyvinyl alcohol: The graft modification of polyvinyl alcohol resin by epoxidized biodegradable organic photosensitizer is completed through the ring-opening reaction between the epoxy functional group of the epoxidized biodegradable organic photosensitizer and the hydroxyl functional group on the main chain of the polyvinyl alcohol resin molecule, and photosensitive polyvinyl alcohol is obtained. The specific experimental steps are as follows: Add 10 g of polyvinyl alcohol resin (grade 28 - 98) and 100 mL of dimethyl sulfoxide into a three-necked flask, heat up to 60 °C and stir until completely dissolved, then cool to 30 °C, and slowly add 10 mL of dimethyl sulfoxide solution containing 2 g of epoxidized biodegradable organic photosensitizer and 1.8 mL of triethylamine catalyst into the three-necked flask under the condition of nitrogen protection, heat up to 70 °C and stir for 5 h, cool to room temperature, remove the solvent by rotary evaporation under the conditions of 50 mbar and 45 °C using a vacuum pump, and dry in vacuum to obtain photosensitive polyvinyl alcohol. Example 4:

[0023] Preparation of ultraviolet light-dependent photo-biodegradable component: Through the π-π stacking interaction between the naphthalimide group and coumarin group on the surface of the biodegradable photosensitizer and the naphthalimide group and coumarin group on the main chain of the photosensitive polyvinyl alcohol, the inorganic component titanium dioxide and the organic component polyvinyl alcohol are compounded to prepare the ultraviolet light-dependent photo-biodegradable component. The specific experimental steps are as follows: Add 6 g of photosensitive polyvinyl alcohol and 100 mL of dimethyl sulfoxide into a beaker, heat up to 70 °C and stir until completely dissolved. Then add 2 g of biodegradable photosensitizer into the beaker, keep stirring and reacting at 70 °C for 5 h, cool to room temperature, use a vacuum pump to perform rotary evaporation to remove the solvent under the conditions of 50 mbar and 45 °C, and dry in vacuum to obtain the ultraviolet light-dependent photo-biodegradable component. Example Five:

[0024] A kind of PE film I, comprising the following raw materials in parts by weight: 65 parts of low-density polyethylene resin (grade LD 150DW); 10 parts of maleic anhydride grafted polyethylene resin (grade 4288); 18 parts of ultraviolet light-dependent photo-biodegradable component; 2 parts of antioxidant 1010; Among them, antioxidant 168 or antioxidant 1076 can also be used as the antioxidant; 1 part of antistatic agent PELESTAT 230; Among them, antistatic agent PELESTAT 300 or antistatic agent PELESTAT 1251 can also be used as the antistatic agent; 1 part of octadecyl erucamide; In addition to octadecyl erucamide, oleic acid amide or stearic acid amide can also be used as the opening agent. Example Six:

[0025] A preparation process of a kind of PE film I, comprising the following steps: Step 1: Weigh the ingredients according to the formula of PE film I, add each raw material into a high-speed mixer and mix evenly, extrude and granulate through a twin-screw extruder, and dry in vacuum to obtain the degraded and modified PE masterbatch I; Among them, the process parameters of the twin-screw extruder are set as follows: the temperatures of zones 1-6 are 150 °C, 160 °C, 165 °C, 170 °C, 180 °C, 185 °C respectively, and the rotation speed is 400 r / min; Step 2: Add the degraded and modified PE masterbatch I into a single-screw extrusion blow molding machine, and blow and mold it into a film by the upward blowing method to obtain a 120-μm PE film I; Among them, the process parameters of the single-screw extrusion blown film machine are set as follows: the temperatures of zones 1-3 are 150 °C, 170 °C, and 190 °C respectively, the rotation speed is 60 r / min, the traction speed is 5 m / min, the die head diameter of the blown film machine is 60 mm, and the blow-up ratio is 2.6. Example VII:

[0026] A kind of PE film II: Compared with PE film I, the only difference is that the dosage of the ultraviolet light-dependent photo-biodegradable component is 10 parts by weight. Example VIII:

[0027] A kind of PE film III: Compared with PE film I, the only difference is that the dosage of the ultraviolet light-dependent photo-biodegradable component is 26 parts by weight. Performance test:

[0028] I. Barrier performance The barrier performance of the film samples was tested in accordance with GB / T 1037-2021. The specific test steps are as follows: Place a 30-cm circular sample in a glass desiccator with anhydrous calcium chloride as a desiccant at an ambient temperature of 25 °C for 72 h. Then, use a TC-03 type water vapor transmission rate tester to test the barrier performance of the sample and record the water vapor transmission rate of the sample; The above experimental results are shown in Table 1 below.

[0029] Table 1 Experimental results of the barrier performance of PE films

[0030] It can be seen from the experimental results in Table 1 that the water vapor transmission rate of the PE film products prepared by the present invention meets the usage requirements of tissue packaging products; II. Degradation performance (1) Initial mechanical property test: Use an Instron 5565 universal tensile testing machine to test the mechanical properties of the film samples in accordance with GB / T 1040.3-2006 (sampling along the blown film direction), and record the longitudinal tensile strength and longitudinal elongation at break of the samples; among them, the sample size is 100 mm × 20 mm (length × width), and the test speed is 50 mm / min; (2) Mechanical property test after placing indoors for 90 days: Place the film samples indoors at normal temperature and pressure for 90 days, and conduct mechanical property tests in accordance with the method in performance test (1), record the longitudinal tensile strength and longitudinal elongation at break of the samples at this time, and calculate the change rate of the longitudinal tensile strength and the change rate of the longitudinal elongation at break of the samples after placing indoors for 90 days. The specific method is as follows: Change rate of longitudinal tensile strength = (Initial longitudinal tensile strength - Longitudinal tensile strength after placing indoors for 90 days) / Initial longitudinal tensile strength × 100%; Longitudinal fracture elongation rate change = (Initial longitudinal fracture elongation rate - Longitudinal fracture elongation rate after 90 days of indoor placement) / Initial longitudinal fracture elongation rate × 100%; (3)Mechanical property test after 5 days of UV irradiation: Place the film sample in a UV aging test chamber (equipped with 3 20W UV high-pressure mercury lamps with a wavelength of 313nm), with the vertical distance from the lamp tube to the sample being 14.5 cm. Irradiate for 5 days at normal temperature and pressure. Take out the sample and conduct mechanical property tests according to the method in Performance Test (1). Record the longitudinal tensile strength and longitudinal fracture elongation rate of the sample at this time. Calculate the longitudinal tensile strength change rate and longitudinal fracture elongation rate change rate of the sample after 5 days of UV irradiation according to the method in Performance Test (2); (4)Mechanical property test after 5 days of UV irradiation and 90 days of microbial treatment: Bury the film sample that has been irradiated with UV for 5 days in the Performance Test (3) into the soil with the same properties at the same geographical location. The pH of the soil is 6.0 and the burial depth is 30 cm. Take out the sample after 90 days, wash it with distilled water and ethanol, dry it, and then conduct mechanical property tests according to the method in Performance Test (1). Record the longitudinal tensile strength and longitudinal fracture elongation rate of the sample at this time. Calculate the longitudinal tensile strength change rate and longitudinal fracture elongation rate change rate of the sample after 5 days of UV irradiation and 90 days of microbial treatment according to the method in Performance Test (2); The above experimental results are shown in Table 2 below.

[0031] Table 2 Experimental results of the degradation performance of PE film

[0032] Through comprehensive analysis of the above experimental results, the following conclusions can be drawn: Conclusion 1: After the PE film product prepared by the present invention is placed indoors for 90 days, its mechanical properties hardly change, indicating that the risk of automatic degradation under natural conditions is extremely low. That is, the PE film prepared by the present invention can be used for packaging paper towel products and has a weak adverse effect on the shelf life of paper towel products; Conclusion 2: After the PE film product prepared by the present invention is irradiated with UV for 5 days, its mechanical properties show a significant decrease, indicating that it has undergone degradation under the action of UV light; Conclusion 3: Compared with only being irradiated with UV for 5 days, after being irradiated with UV for 5 days first and then biologically treated for 90 days, the decrease in the mechanical properties of the PE film product is more significant, indicating that after it has undergone degradation under the action of UV light, it has further undergone biodegradation under the action of microorganisms, showing the dual degradation ability of UV light and biology.

Claims

1. A preparation process of a PE film, characterized in that, It includes the following steps: Step 1: Synthesize an epoxidized biodegradable organic photosensitizer, whose chemical structural formula is: ； Step 2: Based on the epoxy-hydroxy ring-opening reaction mechanism, graft the epoxidized biodegradable organic photosensitizer onto the surface of hydroxylated titanium dioxide nanoparticles to obtain a biodegradable photosensitizer, and graft the epoxidized biodegradable organic photosensitizer onto the side chain of polyvinyl alcohol to obtain photosensitive polyvinyl alcohol; Step 3: Based on the π-π stacking interaction between aromatic rings, compound the biodegradable photosensitizer and the photosensitive polyvinyl alcohol to prepare a UV-dependent photo-biodegradable component; Step 4: Add the UV-dependent photo-biodegradable component, the compatibilizing component and the composite auxiliary agent into the polyethylene matrix together, and blow-mold to obtain a PE film.

2. The preparation process of a PE film according to claim 1, characterized in that, The preparation method of the epoxidized biodegradable organic photosensitizer is as follows: Through the esterification reaction of the carboxyl functional group of 7-(diethylamino)coumarin-3-carboxylic acid and the hydroxyl functional group of 2-naphthylmethanol, a coumarinyl naphthyl tertiary amine monomer is generated; Based on the nucleophilic substitution reaction mechanism, through the quaternization reaction of the tertiary amine functional group of the coumarinyl naphthyl tertiary amine monomer and the chlorine functional group of epichlorohydrin, an epoxidized biodegradable organic photosensitizer is generated.

3. The preparation process of a PE film according to claim 1, characterized in that, The dosage of the UV-dependent photo-biodegradable component in the PE film is 15-40 wt% of the dosage of polyethylene.

4. The preparation process of a PE film according to claim 1, characterized in that, The mass ratio of the biodegradable photosensitizer to the photosensitive polyvinyl alcohol in the UV-dependent photo-biodegradable component is 1:(2-5); The mass ratio of the epoxidized biodegradable organic photosensitizer to the hydroxylated titanium dioxide nanoparticles in the biodegradable photosensitizer is 1:(3-8); The mass ratio of the epoxidized biodegradable organic photosensitizer to the polyvinyl alcohol in the photosensitive polyvinyl alcohol is 1:(3-8).

5. The preparation process of a PE film according to claim 4, characterized in that, The particle size of the titanium dioxide is 5-10 nm.

6. A PE film prepared by the process according to any one of claims 1-5, characterized in that, The PE film includes the following raw materials in parts by weight: 60-70 parts of low-density polyethylene resin; 5-12 parts of compatibilizing component; 10-30 parts of UV-dependent photo-biodegradable component; 1-5 parts of composite auxiliary agent.

7. A PE film according to claim 6, wherein, The compatibilizing component is maleic anhydride grafted polyethylene resin or methyl methacrylate grafted maleic anhydride high-density polyethylene resin.

8. A PE film according to claim 6, characterized in that, The composite auxiliary agent includes 0.5-2 parts by weight of antioxidant, 0.2-2 parts by weight of antistatic agent and 0.3-2 parts by weight of antiblocking agent.

9. A PE film according to claim 6, characterized in that, The thickness of the PE film is 100-150 μm.

10. The application of a PE film prepared by the process according to any one of claims 1-5 in paper towel packaging.

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