Preparation process of ultralow-temperature single PP (polypropylene) recoverable composite packaging film

Abstract

The invention relates to the technical field of research and development of packaging materials, and discloses a preparation process of an ultralow-temperature single PP recyclable composite packaging film, which comprises the following steps: preparing a surface modifier containing a methoxy functional group; modifying the hydroxylated boron nitride nanosheet by using a surface modifier to prepare the anti-ultraviolet boron nitride nanosheet, based on hydrogen-bond interaction, the ultraviolet-proof boron nitride nanosheet and ethylene-vinyl alcohol copolymer resin are compounded, and the ultraviolet-proof barrier material is prepared; an anti-ultraviolet barrier material is added into a single-material polypropylene co-extrusion film containing TAFMERTM BL2481M polyolefin elastomer in the formula, the composite packaging film is prepared, the composite packaging film has excellent oxygen barrier performance, moisture resistance and ultraviolet resistance, sealing is started at 70 DEG C, the heat sealing strength at 100 DEG C is larger than 15 N / 15 mm, the composite packaging film belongs to an ultralow-temperature heat sealing type packaging material, and the packaging film can be widely applied to the field of packaging materials. The film can be used as a dry food packaging film.

Description

Technical Field

[0001] The invention relates to the technical field of packaging material research and development, and specifically to a process for preparing an ultra-low temperature single PP recyclable composite packaging film. Background Art

[0002] At present, there are more and more kinds of cereal foods and baked foods on the market. Food developers continue to launch new foods to meet people's growing needs, such as sandwich foods, egg yolk pies, semi-processed pizzas, and Chinese dim sum. Dry foods are sensitive to water vapor, and they require a higher level of protection against water vapor, which puts forward higher requirements for the design of moisture-proof packaging. In addition, dry foods contain oils, including unsaturated oils. Unsaturated oils are very easy to undergo oxidation reactions under the action of ultraviolet light and oxygen, which shortens their shelf life. Therefore, oxygen barrier and UV protection are also key considerations in the packaging of dry foods.

[0003] Polypropylene (PP) is widely used in many fields due to its good mechanical properties. The advantages of PP include excellent mechanical properties, good heat resistance, good transparency, etc. PP films prepared by co-extrusion, blow molding and other methods have been extended to diversified food packaging such as frozen food, condiments and dry food due to their good application performance. They play a physical load-bearing role in the storage and sales and circulation of food, greatly reducing the waste of food in the circulation link; however, polypropylene resin has a high melting point, and the heat sealing temperature is high when used to prepare packaging film, and the energy consumption is high during the packaging process, which does not meet environmental protection requirements. In addition, although polypropylene film has a certain barrier capacity, its barrier performance is relatively low, especially the barrier performance to oxygen is not as good as other high barrier materials.

[0004] In addition, the polyolefin elastomer with the brand name BL2481M produced by Japan's Mitsui Company has an extremely low melting point. In the prior art, there have been reports on mixing polyolefin elastomer with polypropylene resin to reduce the heat-sealing temperature of packaging films. Summary of the invention

[0005] The present invention provides a preparation process of an ultra-low temperature single PP recyclable composite packaging film. The film prepared by the process can not only start to seal at 70°C, which is significantly lower than the initial heat sealing temperature of 105°C of conventional polypropylene films, but also has very excellent barrier capabilities (oxygen barrier, water barrier and light barrier), and adopts a single PP material for easy recycling and cyclic utilization, which is in line with the trend of environmental protection and can be used as a dry food packaging film.

[0006] A preparation process of an ultra-low temperature single PP recyclable composite packaging film, comprising the following steps:

[0007] Step 1: preparing a surface modifier containing a methoxy functional group, wherein the surface modifier is an anti-ultraviolet silane coupling agent and / or an anti-ultraviolet silane cross-linking agent;

[0008] Step 2: The Si-OH functional group obtained by the hydrolysis reaction of the methoxy group of the surface modifier undergoes a dehydration condensation reaction with the -OH functional group of the hydroxylated boron nitride nanosheet, and the surface modifier is modified on the surface of the hydroxylated boron nitride nanosheet to prepare an anti-ultraviolet boron nitride nanosheet;

[0009] Step 3: Based on the hydrogen bonding effect, the anti-ultraviolet boron nitride nanosheets are compounded with ethylene-vinyl alcohol copolymer resin to prepare an anti-ultraviolet barrier material;

[0010] Step 4: Using polypropylene resin as a single raw material, design the film structure of the five-layer co-extruded film, the formula and dosage of each film layer, add an anti-ultraviolet barrier material to the barrier layer, and add a low-melting-point polyolefin elastomer to the heat-sealing layer to prepare an ultra-low-temperature single PP recyclable composite packaging film;

[0011] Preferably, the preparation method of the UV-proof silane coupling agent is: catalyzing the alkenyl functional group of 2-hydroxy-4-acryloxyethoxybenzophenone and the secondary amine functional group of N-methyl-3-aminopropyltrimethoxysilane with an alkaline catalyst to produce an amine-ene addition reaction to prepare the UV-proof silane coupling agent.

[0012] Preferably, the preparation method of the UV-proof silane crosslinker is: catalyzing the alkenyl functional group of 2-hydroxy-4-acryloxyethoxybenzophenone and the secondary amine functional group of di(3-trimethoxysilylpropyl)amine with an alkaline catalyst to produce an amine-ene addition reaction to prepare the UV-proof silane crosslinker.

[0013] Preferably, the alkaline catalyst is one of sodium ethoxide, sodium hydride, potassium tert-butoxide, triethylamine, triethylenediamine, 4-dimethylaminopyridine, and 1,8-diazabicycloundec-7-ene.

[0014] Preferably, the preparation method of the ultra-low temperature single PP recyclable composite packaging film is:

[0015] Step S5-1: The ultra-low temperature single PP recyclable composite packaging film is set to a five-layer asymmetric film structure, and the formula and dosage of each film layer are as follows:

[0016] First layer: 20 to 40 parts by weight of a surface layer made of 100 wt% polypropylene resin;

[0017] The second layer: an adhesive layer prepared from 100 wt% maleic anhydride grafted polypropylene resin, 3 to 10 parts by weight;

[0018] The third layer: a barrier layer prepared from 90-99wt% polypropylene resin, 0.5-8wt% ethylene-vinyl alcohol copolymer resin and 0.5-8wt% anti-ultraviolet barrier material, 20-40 parts by weight;

[0019] The fourth layer: an adhesive layer prepared from 100wt% maleic anhydride grafted polypropylene resin, 3 to 10 parts by weight;

[0020] The fifth layer: a heat-sealing layer prepared from 80-95wt% polypropylene resin and 5-20wt% low-melting-point polyolefin elastomer, 20-40 parts by weight;

[0021] Step S5-2: The raw materials in step S5-1 are respectively put into the hoppers of the five screw extruders of the five-layer co-extrusion film blow molding unit. The molten resin is converged at the head of the machine through the diverter, and is extruded and blow-molded through the die head. The blow ratio is controlled at 2.5-3.0 to obtain an ultra-low temperature single PP recyclable composite packaging film.

[0022] Preferably, the mass ratio of the surface modifier, the hydroxylated boron nitride nanosheets and the ethylene-vinyl alcohol copolymer resin in the anti-ultraviolet barrier material is 1:(1-5):(5-15).

[0023] Preferably, the hydroxylated boron nitride nanosheets have a sheet diameter of 2 to 5 μm and a thickness of 3 to 8 nm.

[0024] The thickness of the ultra-low temperature single PP recyclable composite packaging film prepared according to the above process is 50 to 150 μm.

[0025] Preferably, the water vapor permeability of the composite packaging film is (1.0-1.5) g / (m 2 ·24h), light transmittance is 25-30%.

[0026] Beneficial effects:

[0027] The present invention first designs and synthesizes a new type of surface modifier (anti-ultraviolet silane coupling agent and anti-ultraviolet silane crosslinking agent) with ultraviolet absorption ability, then uses the new type of surface modifier to modify hydroxylated boron nitride nanosheets, and then compounds with ethylene-vinyl alcohol copolymer to obtain an anti-ultraviolet barrier material; finally, the anti-ultraviolet barrier material is added to the formula containing TAFMER TM A composite packaging film is prepared from the single-material polypropylene co-extruded film of BL2481M polyolefin elastomer. It not only has excellent oxygen barrier, moisture-proof and UV protection properties, but also starts to seal at 70°C and has a heat-sealing strength greater than 15N / 15mm at 100°C. It is an ultra-low temperature heat-sealing packaging material and has energy-saving and consumption-reducing effects in the packaging process. DETAILED DESCRIPTION

[0028] Experimental Example 1:

[0029] Preparation of UV-resistant silane coupling agent: The amine-ene addition reaction of the alkenyl functional group of 2-hydroxy-4-acryloyloxyethoxybenzophenone (UV absorber UV-2098) and the secondary amine functional group of N-methyl-3-aminopropyltrimethoxysilane is catalyzed by the catalyst 1,8-diazabicycloundec-7-ene to generate a UV-resistant silane coupling agent, the chemical structure of which is:

[0030]

[0031] The specific experimental steps for preparing the UV-resistant silane coupling agent are as follows: 3.1 g of 2-hydroxy-4-acryloyloxyethoxybenzophenone and 40 mL of acetonitrile are added to a three-necked flask, stirred at room temperature until completely dissolved, then 2.0 mL of N-methyl-3-aminopropyltrimethoxysilane is slowly added dropwise to the three-necked flask, stirred and mixed at room temperature for 30 min, 1.5 mL of 1,8-diazabicycloundec-7-ene is added dropwise to the three-necked flask, the temperature is raised to 40° C. and stirred for reaction for 6 h, the solvent is removed by rotary evaporation, washed with saturated sodium chloride aqueous solution and deionized water, and vacuum dried to obtain the UV-resistant silane coupling agent;

[0032] The nuclear magnetic resonance hydrogen spectrum of the UV-resistant silane coupling agent is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 0.68-0.72 (t, 2H), 1.54-1.61 (m, 2H), 2.30 (s, 3H), 2.51-2.56 (m, 4H ), 2.98-3.01(t, 2H), 3.57(s, 9H), 4.20-4.24(t, 2H), 4.41-4.44(t, 2H), 7.02-7.75(m, 8H).

[0033] Experimental Example 2:

[0034] Preparation of UV-resistant silane crosslinking agent: The amine-ene addition reaction of the alkenyl functional group of 2-hydroxy-4-acryloxyethoxybenzophenone and the secondary amine functional group of di(3-trimethoxysilylpropyl)amine is catalyzed by the catalyst 1,8-diazabicycloundec-7-ene to generate a UV-resistant silane crosslinking agent, the chemical structure of which is:

[0035]

[0036] The specific experimental steps for preparing the UV-resistant silane crosslinking agent refer to the preparation experiment of the UV-resistant silane coupling agent, and the difference is only that: 2.0 mL of N-methyl-3-aminopropyltrimethoxysilane is replaced by 3.3 mL of di(3-trimethoxysilylpropyl)amine;

[0037] The nuclear magnetic resonance hydrogen spectrum of the UV-resistant silane crosslinker is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 0.68-0.72 (t, 4H), 1.53-1.60 (m, 4H), 2.49-2.54 (m, 6H), 2.75 -2.78(t, 2H), 3.57(s, 18H), 4.20-4.23(t, 2H), 4.39-4.43(t, 2H), 7.00-7.74(m, 8H).

[0038] Embodiment 1:

[0039] (1) Preparation of UV-resistant boron nitride nanosheets I: The Si-OH functional group obtained by hydrolysis of the methoxy group of the UV-resistant silane coupling agent undergoes a dehydration condensation reaction with the -OH functional group of the hydroxylated boron nitride nanosheet, and the UV-resistant silane coupling agent is modified on the surface of the hydroxylated boron nitride nanosheet to prepare the UV-resistant boron nitride nanosheet I. The specific experimental steps are: 5 g of hydroxylated boron nitride nanosheets, 80 mL of anhydrous ethanol and 20 mL of deionized water are added to a beaker, ultrasonically treated for 10 min, 2 g of the UV-resistant silane coupling agent is added to the beaker, the reaction is stirred at room temperature for 10 h, centrifuged, and repeatedly washed by centrifugation with anhydrous ethanol and deionized water, and vacuum dried to obtain the UV-resistant boron nitride nanosheet I;

[0040] Among them, hydroxylated boron nitride nanosheets were purchased from Xi'an Qiyue Biotechnology Co., Ltd., with a sheet diameter of 2 to 5 μm and a thickness of 3 to 8 nm;

[0041] (2) Preparation of anti-ultraviolet barrier material I: Based on the effect of hydrogen bonding, anti-ultraviolet boron nitride nanosheets I and ethylene-vinyl alcohol copolymer resin are compounded to prepare anti-ultraviolet barrier material I. The specific experimental steps are: 20g of ethylene-vinyl alcohol copolymer resin and 7g of anti-ultraviolet boron nitride nanosheets I are added to a twin-screw extruder, and the anti-ultraviolet barrier material I is prepared by blending, melting, extruding and pelletizing through the twin-screw extruder;

[0042] The process parameters of the twin-screw extruder are set as follows: the temperatures of zones 1-3 are 160°C, 180°C, and 205°C, respectively, and the rotation speed is 40r / min;

[0043] Ethylene vinyl alcohol copolymer resin (EVOH) was purchased from Guangzhou Best New Material Technology Co., Ltd., and its brand is ET3803RB.

[0044] Embodiment 2:

[0045] (1) Preparation of UV-resistant boron nitride nanosheets II: Si-OH functional groups obtained by hydrolysis of methoxy groups of UV-resistant silane coupling agent and UV-resistant silane crosslinking agent undergo dehydration condensation reaction with -OH functional groups of hydroxylated boron nitride nanosheets, and UV-resistant silane coupling agent and UV-resistant silane crosslinking agent are co-modified on the surface of hydroxylated boron nitride nanosheets to prepare UV-resistant boron nitride nanosheets II. The specific experimental steps refer to the preparation experiment of UV-resistant boron nitride nanosheets I, and the only difference is that 2g of UV-resistant silane coupling agent is replaced by 1g of UV-resistant silane coupling agent and 1g of UV-resistant silane crosslinking agent;

[0046] (2) Preparation of anti-ultraviolet barrier material II: Based on the effect of hydrogen bonding, anti-ultraviolet boron nitride nanosheets II are compounded with ethylene-vinyl alcohol copolymer resin to prepare anti-ultraviolet barrier material II. The specific experimental steps refer to the preparation experiment of anti-ultraviolet barrier material I, and the only difference is that anti-ultraviolet boron nitride nanosheets II are used to replace anti-ultraviolet boron nitride nanosheets I.

[0047] Embodiment 3:

[0048] The preparation of composite packaging film I comprises the following steps:

[0049] Step 1: The composite packaging film I is set to a five-layer asymmetric film structure, and the formula and dosage of each film layer are as follows:

[0050] The first layer: a surface layer prepared with 100wt% polypropylene resin as raw material, 30 parts by weight, and the corresponding process parameters of the screw extruder are set as follows: the temperatures of zones 1-3 are 130°C, 150°C, and 170°C, respectively, the flow channel temperature is 160°C, and the speed is 30r / min;

[0051] The second layer: an adhesive layer prepared from 100wt% maleic anhydride grafted polypropylene resin, 5 parts by weight, and the corresponding process parameters of the screw extruder are set as follows: the temperatures of zones 1-3 are 115°C, 145°C, and 160°C, respectively, the flow channel temperature is 150°C, and the speed is 15r / min;

[0052] The third layer: a barrier layer prepared with 92wt% polypropylene resin, 3wt% ethylene-vinyl alcohol copolymer resin and 5wt% anti-ultraviolet barrier material I as raw materials, 30 parts by weight, and the corresponding process parameters of the screw extruder are set as follows: the temperatures of zones 1-3 are 130°C, 160°C, and 190°C, respectively, the flow channel temperature is 185°C, and the rotation speed is 50r / min;

[0053] The fourth layer: an adhesive layer prepared from 100wt% maleic anhydride grafted polypropylene resin as raw material, 5 parts by weight, and the corresponding screw extruder process parameters are the same as those of the second layer;

[0054] The fifth layer: a heat-sealing layer prepared from 85wt% polypropylene resin and 15wt% polyolefin elastomer, 30 parts by weight, and the corresponding process parameters of the screw extruder are set as follows: the temperatures of zones 1-3 are 120°C, 140°C, and 160°C, respectively, the flow channel temperature is 150°C, and the speed is 30r / min;

[0055] Step 2: The raw materials in step 1 are respectively put into the hoppers of five screw extruders of a five-layer co-extrusion film blowing unit, and after stirring and mixing, the molten resin is converged at the head of the die through a diverter, and is extruded and blown through a die head, and the blow-up ratio is controlled at 2.9, cooled, and rolled to obtain a composite packaging film I with a thickness of 100 μm;

[0056] Among them, polypropylene resin was purchased from Shanghai Qiaowei Chemical Technology Co., Ltd., and its brand is HJ4012; maleic anhydride grafted polypropylene resin was purchased from Coase Chemical Co., Ltd., and its brand is B1; polyolefin elastomer was purchased from Shanghai Teflon New Material Technology Co., Ltd., and its model is: Japan Mitsui TAFMER TM BL2481M.

[0057] Embodiment 4:

[0058] The anti-ultraviolet barrier material II is used to replace the anti-ultraviolet barrier material I in the composite packaging film I, and the rest of the parts are the same as the composite packaging film I, so as to prepare the composite packaging film II.

[0059] Comparative Example:

[0060] Preparation of composite packaging film a: Referring to the preparation experiment of composite packaging film I, the only difference is that: no anti-ultraviolet barrier material I is used to prepare composite packaging film a, which is used as comparative example 1;

[0061] Preparation of composite packaging film b: Referring to the preparation experiment of composite packaging film I, the only difference is that no UV-proof barrier material I is used, and the raw material of the heat sealing layer is 100wt% polypropylene resin, and composite packaging film b is prepared as comparative example 2.

[0062] Performance Test:

[0063] (1) Heat sealing performance test: The samples were heat sealed using an HSG-C heat sealer with a sealing area of ​​15 cm × 1 cm. The heat sealing temperatures were set to 70°C, 100°C, 110°C, and 120°C, respectively. The heat sealing pressure was 0.2 MPa, and the heat sealing time was 1.0 s.

[0064] According to QB / T 2358-1998 "Test Method for Heat Seal Strength of Plastic Film Packaging Bags", the heat seal performance of the heat seal sample was tested at a test speed of 300mm / min and a clamp spacing of 50mm. The heat seal strength of the sample was recorded.

[0065] (2) Oxygen barrier performance test: Use a Y110 oxygen permeability tester to test the oxygen barrier performance of the sample in accordance with GB / T 1038-2000, and record the oxygen permeability of the sample;

[0066] (3) Moisture resistance test: Use TC-03 water vapor transmission meter to test the water barrier performance of the sample in accordance with GB / T 1037-2021, and record the water vapor transmission rate of the sample;

[0067] (4) Anti-ultraviolet performance test: Lambda 950 UV-visible spectrophotometer was used to test the transmittance of the sample in accordance with GB / T2410-2008. The test wavelength range was 250-800 nm, and the transmittance of the sample at 380 nm was recorded;

[0068] (5) Mechanical properties test: The mechanical properties of the samples were tested using an Instron 5565 universal tensile testing machine in accordance with GB / T 13022-91. The test speed was 5 mm / min, and the longitudinal tensile strength of the samples was recorded.

[0069] The above experimental results are shown in Table 1-2 below.

[0070] Table 1 Performance test results of composite packaging film

[0071]

[0072]

[0073] Table 2 Performance test results of composite packaging film II

[0074]

[0075] The sanitary properties of the samples were tested according to GB / T 5009.60-2003 "Analysis Method for Hygienic Standards of Polyethylene, Polystyrene and Polypropylene Molded Products for Food Packaging", and the experimental results confirmed that the composite packaging film prepared by the present invention can meet the requirements of the sanitary standards;

[0076] By comprehensively analyzing the above experimental results, the following conclusions can be drawn:

[0077] (1) The composite packaging film prepared by the present invention begins to seal at 70°C (i.e., begins to have heat-sealing strength), and the heat-sealing strength is greater than 15N / 15mm under the condition of a heat-sealing temperature of 100°C, which meets the national standards and the use requirements of enterprise users and belongs to an ultra-low temperature heat-sealing packaging material;

[0078] (2) The hydroxylated boron nitride nanosheets are modified by using an anti-ultraviolet silane coupling agent and / or an anti-ultraviolet silane cross-linking agent and then compounded with ethylene vinyl alcohol copolymer to prepare an anti-ultraviolet barrier material that can significantly reduce the oxygen permeability, water vapor permeability and light transmittance of the composite packaging film, and has a very significant effect on improving the oxygen barrier, moisture-proof and anti-ultraviolet properties of the composite packaging film.

Claims

1. A process for preparing an ultra-low temperature single PP recyclable composite packaging film, characterized in that: The following steps are involved: Step 1: preparing a surface modifier containing a methoxy functional group, wherein the surface modifier is an anti-ultraviolet silane coupling agent and / or an anti-ultraviolet silane cross-linking agent; The chemical structural formula of the anti-ultraviolet silane coupling agent is: The chemical structural formula of the UV-resistant silane crosslinking agent is: Step 2: The Si-OH functional group obtained by the hydrolysis reaction of the methoxy group of the surface modifier undergoes a dehydration condensation reaction with the -OH functional group of the hydroxylated boron nitride nanosheet, and the surface modifier is modified on the surface of the hydroxylated boron nitride nanosheet to prepare an anti-ultraviolet boron nitride nanosheet; Step 3: Based on the hydrogen bonding effect, the anti-ultraviolet boron nitride nanosheets are compounded with ethylene-vinyl alcohol copolymer resin to prepare an anti-ultraviolet barrier material; Step 4: Using polypropylene resin as the single raw material, design the film structure of the five-layer co-extrusion film, the formula and dosage of each film layer, add UV-proof barrier material to the barrier layer, and add low-melting-point polyolefin elastomer to the heat-sealing layer to prepare an ultra-low-temperature single PP recyclable composite packaging film.

2. The process for preparing an ultra-low temperature single PP recyclable composite packaging film according to claim 1, characterized in that: The preparation method of the anti-ultraviolet silane coupling agent comprises: using an alkaline catalyst to catalyze an amine-ene addition reaction between an alkenyl functional group of 2-hydroxy-4-acryloxyethoxybenzophenone and a secondary amine functional group of N-methyl-3-aminopropyltrimethoxysilane, thereby preparing the anti-ultraviolet silane coupling agent.

3. The process for preparing an ultra-low temperature single PP recyclable composite packaging film according to claim 1, characterized in that: The preparation method of the UV-proof silane crosslinking agent comprises: catalyzing the alkenyl functional group of 2-hydroxy-4-acryloxyethoxybenzophenone and the secondary amine functional group of di(3-trimethoxysilylpropyl)amine with an alkaline catalyst to produce an amine-ene addition reaction, thereby preparing the UV-proof silane crosslinking agent.

4. The process for preparing an ultra-low temperature single PP recyclable composite packaging film according to claim 2 or 3, characterized in that: The alkaline catalyst is one of sodium ethoxide, sodium hydride, potassium tert-butoxide, triethylamine, triethylenediamine, 4-dimethylaminopyridine, and 1,8-diazabicycloundec-7-ene.

5. The process for preparing an ultra-low temperature single PP recyclable composite packaging film according to claim 1, characterized in that: The preparation method of the ultra-low temperature single PP recyclable composite packaging film is as follows: Step S5-1: The ultra-low temperature single PP recyclable composite packaging film is set to a five-layer asymmetric film structure, and the formula and dosage of each film layer are as follows: First layer: 20 to 40 parts by weight of a surface layer made of 100 wt% polypropylene resin; The second layer: an adhesive layer prepared from 100 wt% maleic anhydride grafted polypropylene resin, 3 to 10 parts by weight; The third layer: a barrier layer prepared from 90-99wt% polypropylene resin, 0.5-8wt% ethylene-vinyl alcohol copolymer resin and 0.5-8wt% anti-ultraviolet barrier material, 20-40 parts by weight; The fourth layer: an adhesive layer prepared from 100wt% maleic anhydride grafted polypropylene resin, 3 to 10 parts by weight; The fifth layer: a heat-sealing layer prepared from 80-95wt% polypropylene resin and 5-20wt% low-melting-point polyolefin elastomer, 20-40 parts by weight; Step S5-2: The raw materials in step S5-1 are respectively put into the hoppers of the five screw extruders of the five-layer co-extrusion film blow molding unit. The molten resin is converged at the head of the machine through the diverter, and is extruded and blow-molded through the die head. The blow ratio is controlled at 2.5-3.0 to obtain an ultra-low temperature single PP recyclable composite packaging film.

6. The process for preparing an ultra-low temperature single PP recyclable composite packaging film according to claim 1, characterized in that: The mass ratio of the surface modifier, the hydroxylated boron nitride nanosheets and the ethylene-vinyl alcohol copolymer resin in the anti-ultraviolet barrier material is 1:(1-5):(5-15).

7. The process for preparing an ultra-low temperature single PP recyclable composite packaging film according to claim 6, characterized in that: The hydroxylated boron nitride nanosheet has a sheet diameter of 2 to 5 μm and a thickness of 3 to 8 nm.

8. An ultra-low temperature single PP recyclable composite packaging film prepared by the process according to any one of claims 1 to 3, characterized in that: The thickness of the composite packaging film is 50-150 μm.

9. The ultra-low temperature single PP recyclable composite packaging film according to claim 8, characterized in that: The water vapor permeability of the composite packaging film is (1.0-1.5) g / (m 2 ·24h), light transmittance is 25-30%.

10. Application of an ultra-low temperature single PP recyclable composite packaging film prepared according to the process of any one of claims 1 to 3 in the field of dry food packaging.

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