Biodegradable breathable film and preparation method thereof

Abstract

The invention relates to a biodegradable breathable film and a preparation method thereof, the preparation method comprises the following steps: firstly, preparing a pore forming agent: treating calcium carbonate with KH570, polymerizing with 2-methylene-1, 3-dioxocycloheptane (MDO), carrying out melt blending with polyethylene, and carrying out extrusion granulation; mixing the PLA particles, the lignin-based polyester material and a pore-forming agent to prepare biodegradable polyester particles, and finally stretching to form the film. According to the invention, PLA is taken as a base material, the pore-forming agent and the lignin-based polyester material are combined, and ring-opening polymerization of MDO is introduced to form a polycaprolactone chain fracture, so that the interfacial compatibility is good, the dispersion stability of a calcium carbonate material in degradable polyester particles is improved, and calcium carbonate particles are not easy to agglomerate; further, the prepared degradable breathable film is high in water vapor permeability and good in air permeability; meanwhile, the mechanical property of the breathable film can be well improved; the preparation method disclosed by the invention is relatively simple, the prepared modified PLA breathable film is biodegradable and good in comprehensive performance, and white pollution is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of degradable plastics, in particular to a biodegradable breathable film and a preparation method thereof. Background Art

[0002] Plastic packaging has brought great convenience to people's daily life and production activities, but at the same time, traditional plastics have also caused white pollution and adversely affected the environment. As people pay more and more attention to environmental protection and food safety, it is particularly important to develop new degradable polymer packaging materials. At present, more and more degradable materials can be seen in major supermarkets, milk tea shops and other places. Degradable plastics are used to make shopping bags, disposable tableware, etc. However, in some fields such as food packaging or agricultural mulch, degradable breathable films are also needed, but research in this area is relatively small.

[0003] Traditional waterproof and breathable membranes are polymer waterproof materials made by adding inorganic particle fillers such as calcium carbonate and barium sulfate to polyethylene as a carrier, and creating pores at the interface between polyethylene and inorganic particles during the stretching process. However, this type of membrane is not easy to degrade and has poor environmental protection. Currently, polylactic acid (PLA) is mostly used to replace polyethylene to prepare degradable materials. However, PLA faces the problems of high brittleness, low strength, poor film toughness, strong gas barrier properties, poor dispersibility of directly added inorganic fillers, and easy rupture of the prepared film. Based on this, it is of great significance to develop biodegradable films with good mechanical properties and breathability. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a breathable PLA film with excellent mechanical properties, which is prepared by using PLA as a base material and adding a pore-forming agent modified by calcium carbonate and a lignin-based polyester material.

[0005] To achieve the above object, the present invention provides the following technical solutions: A method for preparing a biodegradable breathable membrane comprises the following steps: 1) Preparation of pore-forming agent: 1-1) Treating calcium carbonate with silane coupling agent KH570 to obtain modified inorganic particles; 1-2) free radical in-situ polymerization of the modified inorganic particles and 2-methylene-1,3-dioxepane in a solution; 1-3) Melting and blending the product obtained by polymerization with polyethylene, and extruding and granulating the mixture to obtain a pore-forming agent; 2) Preparation of biodegradable polyester particles: 2-1) Add calcium lignin sulfonate and water to the reaction flask and stir thoroughly to dissolve. Add peroxysulfate as an initiator and heat the system to 70°C under nitrogen protection. oC, adding a mixture of 2-methylene-1,3-dioxepane and hydroxyethyl acrylate under stirring, reacting for 3 h, precipitating with acetone, filtering and drying, and grinding to obtain a lignin-based polyester material; 2-2) Add the dried PLA particles, lignin-based polyester material and pore-forming agent into a high-speed mixer at 50 o C. Stir evenly at 200 rpm for 15 min to obtain a mixture; 2-3) feeding the mixed material into a twin-screw extruder for melt blending, extruding, and then pelletizing with a pelletizer to obtain biodegradable polyester pellets; 3) Stretch film: The biodegradable polyester particles are first placed in a drying oven for drying, and then put into a film blowing machine for blow molding into a primary film, followed by longitudinal stretching, corona treatment, pulling, and winding.

[0006] Furthermore, the specific process of step 1) is as follows: 1-1) Put the dried calcium carbonate into the mixer and heat it to 70 o C and stirred for 5 min, then stopped heating, added KH570 and continued stirring for 30 min to obtain modified inorganic particles; 1-2) Add the modified inorganic particles and tetrahydrofuran into a reaction bottle, stir and disperse them evenly, then introduce nitrogen to replace the air in the reaction bottle, add initiator AIBN, and heat to 70 o C, add 2-methylene-1,3-dioxepane dropwise under a nitrogen atmosphere, continue stirring and reacting for 2 hours after the addition is completed, precipitate in petroleum ether after the reaction is completed, and dry to obtain an intermediate product; 1-3) The intermediate product is melt-blended with polyethylene and extruded into granules to obtain a pore-forming agent.

[0007] Furthermore, in the step 1-1), the mass ratio of KH570 to calcium carbonate is 0.5 to 1:50; in the step 1-2), the mass ratio of modified inorganic particles to 2-methylene-1,3-dioxepane is 1:10; in the step 1-3), the mass ratio of the intermediate product to polyethylene is 4 to 8:2 to 6.

[0008] Furthermore, in the step 2-1), the molar ratio of 2-methylene-1,3-dioxepane to hydroxyethyl acrylate is 4-8:2-6, and the mass ratio of the total mass of the two monomers to calcium lignin sulfonate is 2-4:1.

[0009] Furthermore, in the step 2-2), the mass ratio of PLA particles, lignin-based polyester material and pore-forming agent is 100:40-60:40-60.

[0010] The present invention further provides a biodegradable breathable membrane prepared by the preparation method as described above.

[0011] Compared with the prior art, the invention has the following beneficial effects: the invention uses PLA as the basic material to prepare the waterproof breathable membrane, firstly, an appropriate amount of pore-forming agent and lignin-based polyester material are added to PLA particles to form degradable polyester particles, since the ring-opening polymerization of 2-methylene-1,3-dioxepane is introduced into the pore-forming agent and the lignin-based polyester material to form polycaprolactone chain scission, the interface compatibility is good, the dispersion stability of the calcium carbonate material in the degradable polyester particles is improved, the calcium carbonate particles are not easy to agglomerate, and thus the water vapor permeability of the prepared degradable breathable membrane is high and the air permeability is good; combined with the lignin-based polyester material, the synergistic effect can also well improve the mechanical properties of the membrane breathable membrane; the preparation method of the invention is relatively simple, the prepared modified PLA breathable membrane is biodegradable, has good comprehensive performance, can replace the traditional PE high breathable membrane, and reduces white pollution. DETAILED DESCRIPTION

[0012] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0014] Embodiment: A method for preparing a biodegradable breathable membrane comprises the following steps: 1) Preparation of pore-forming agent: 1-1) Put the dried calcium carbonate into the mixer and heat it to 70 o C and stirred for 5 min, then stopped heating, added KH570 and continued stirring for 30 min, with a mass ratio of 0.5 to 1:50, to obtain modified inorganic particles; 1-2) Add 1 part by weight of the modified inorganic particles and tetrahydrofuran into a reaction bottle, stir and disperse them evenly, then introduce nitrogen to replace the air in the reaction bottle, add initiator AIBN, and heat to 70 o C, under a nitrogen atmosphere, add 10 parts by weight of 2-methylene-1,3-dioxepane (which can be purchased from the market or prepared according to published literature), continue stirring and reacting for 2 hours after the addition is completed, and precipitate in petroleum ether after the reaction is completed, and dry to obtain an intermediate product; 1-3) The intermediate product is melt-blended with polyethylene (PE) in a mass ratio of 4-8:2-6, and extruded and granulated to obtain a pore-forming agent.

[0015] Calcium carbonate is often used as an additive for preparing breathable membranes, but the surface of calcium carbonate powder contains more polar groups, and the direct addition to the material has poor dispersibility and poor compatibility. It needs to be modified, but its surface itself has no active groups. Therefore, the present application first uses a silane coupling agent to modify calcium carbonate so that its surface carries active groups, and then performs in-situ free radical ring-opening polymerization with 2-methylene-1,3-dioxepane to form a polycaprolactone chain. After the organic polymer chain is grafted, the compatibility with the material is greatly improved, and then it is blended with polyethylene for granulation and plasticization, which is more conducive to subsequent mixing with PLA particles.

[0016] 2) Preparation of biodegradable polyester particles: 2-1) Add 1 part by weight of calcium lignin sulfonate and water to a reaction flask and stir thoroughly to dissolve. Add peroxysulfate as an initiator and heat the system to 70°C under nitrogen protection. o C, add 2 to 4 parts by weight of a mixture of 2-methylene-1,3-dioxepane and hydroxyethyl acrylate (molar ratio of 4 to 8:2 to 6) under stirring, react for 3 hours, precipitate with acetone, filter and dry, and grind to obtain a lignin-based polyester material. The lignin-based polyester material contains a rich benzene ring structure, and adding it to PLA can greatly improve its mechanical properties. The polymer chain formed by copolymerization of 2-methylene-1,3-dioxepane and hydroxyethyl acrylate improves the mechanical properties of the material. At the same time, the polymer chain formed by 2-methylene-1,3-dioxepane is degradable, maintaining the overall biodegradability of the material. The pore-forming agent also contains a polymer chain formed by 2-methylene-1,3-dioxepane, which reduces the interfacial force during mixing, so that the particles have good miscibility. The lignin-based polyester material and the pore-forming agent are added to the PLA particles together, and a biodegradable breathable film is formed through synergistic action; 2-2) Add the dried PLA particles, lignin-based polyester material and pore-forming agent into a high-speed mixer at a mass ratio of 100:40 to 60:40 to 60. o C. Stir evenly at 200 rpm for 15 min to obtain a mixture; 2-3) feeding the mixed material into a twin-screw extruder for melt blending, extruding, and then pelletizing by a pelletizer to obtain biodegradable polyester pellets; 3) Stretch film: The biodegradable polyester particles were first placed in a drying oven for drying, and then put into a film blowing machine. The extruder barrel temperature was set to 170°C, the die temperature was 175°C, the blow-up ratio was 3, and the draw ratio was 5. The primary film was blown into a film, and then longitudinally stretched. The stretching temperature was set to 100°C and the stretching ratio was 3. Finally, the film was corona treated, pulled, and wound.

[0017] Embodiment 1: 1) Preparation of pore-forming agent: 1-1) Put the dried calcium carbonate into the mixer and heat it to 70 o C and stirred for 5 min, then stopped heating, added KH570 and continued stirring for 30 min, with a mass ratio of 1:50, to obtain modified inorganic particles; 1-2) Add 1 part by weight of the modified inorganic particles and tetrahydrofuran into a reaction bottle, stir and disperse them evenly, then introduce nitrogen to replace the air in the reaction bottle, add initiator AIBN, and heat to 70 o C, under a nitrogen atmosphere, add 10 parts by weight of 2-methylene-1,3-dioxepane dropwise, continue stirring and reacting for 2 hours after the addition is completed, precipitate in petroleum ether after the reaction is completed, and dry to obtain an intermediate product; 1-3) The intermediate product is melt-blended with polyethylene (PE) at a mass ratio of 4:6, and extruded and granulated to obtain a pore-forming agent.

[0018] 2) Preparation of biodegradable polyester particles: 2-1) Add 1 part by weight of calcium lignin sulfonate and water to a reaction flask and stir thoroughly to dissolve. Add peroxysulfate as an initiator and heat the system to 70°C under nitrogen protection. o C, adding 4 parts by weight of a mixture of 2-methylene-1,3-dioxepane and hydroxyethyl acrylate (molar ratio of 5:5) under stirring, reacting for 3 hours, precipitating with acetone, filtering and drying, and grinding to obtain a lignin-based polyester material; 2-2) Add the dried PLA particles, lignin-based polyester material and pore-forming agent into a high-speed mixer at a mass ratio of 100:40:60. o C. Stir evenly at 200 rpm for 15 min to obtain a mixture; 2-3) feeding the mixed material into a twin-screw extruder for melt blending, extruding, and then pelletizing with a pelletizer to obtain biodegradable polyester pellets; 3) Stretch film: The biodegradable polyester particles were first placed in a drying oven for drying, and then put into a film blowing machine. The extruder barrel temperature was set to 170°C, the die temperature was 175°C, the blow-up ratio was 3, and the draw ratio was 5. The primary film was blown into a film, and then longitudinally stretched. The stretching temperature was set to 100°C and the stretching ratio was 3. Finally, the film was corona treated, pulled, and wound.

[0019] Embodiment 2: The preparation process is the same as that of Example 1, except that in steps 1-3), the mass ratio of the intermediate product to polyethylene (PE) is 6:4.

[0020] Embodiment 3: The preparation process is the same as that of Example 1, except that in steps 1-3), the mass ratio of the intermediate product to polyethylene (PE) is 8:2.

[0021] Embodiment 4: The preparation process is the same as that of Example 1, except that in step 2-2), the mass ratio of PLA particles, lignin-based polyester material, and pore-forming agent is 100:50:50.

[0022] Embodiment 5: The preparation process is the same as that of Example 1, except that in step 2-2), the mass ratio of PLA particles, lignin-based polyester material, and pore-forming agent is 100:60:40.

[0023] Comparative Example 1: The preparation process is the same as that of Example 1, except that the pore-forming agent is untreated calcium carbonate.

[0024] Comparative Example 2: The preparation process is the same as that of Example 1, except that no lignin-based polyester material is added.

[0025] Table 1 It can be seen from Table 1 that the film material prepared by the method provided by the present invention has biodegradability and air permeability, the biodegradation rate is maintained above 85%, the elongation at break is significantly improved, and the air permeability is good.

[0026] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a biodegradable breathable membrane, characterized in that: The steps include: 1) Preparation of pore-forming agent: 1-1) Treating calcium carbonate with silane coupling agent KH570 to obtain modified inorganic particles; 1-2) free radical in-situ polymerization of the modified inorganic particles and 2-methylene-1,3-dioxepane in a solution; 1-3) Melting and blending the product obtained by polymerization with polyethylene, and extruding and granulating the mixture to obtain a pore-forming agent; 2) Preparation of biodegradable polyester particles: 2-1) Add calcium lignin sulfonate and water to the reaction flask and stir thoroughly to dissolve. Add peroxysulfate as an initiator and heat the system to 70°C under nitrogen protection. o C, adding a mixture of 2-methylene-1,3-dioxepane and hydroxyethyl acrylate under stirring, reacting for 3 h, precipitating with acetone, filtering and drying, and grinding to obtain a lignin-based polyester material; 2-2) Add the dried PLA particles, lignin-based polyester material and pore-forming agent into a high-speed mixer at 50 o C. Stir evenly at 200 rpm for 15 min to obtain a mixture; 2-3) feeding the mixed material into a twin-screw extruder for melt blending, extruding, and then pelletizing by a pelletizer to obtain biodegradable polyester pellets; 3) Stretch film: The biodegradable polyester particles are first placed in a drying oven for drying, and then put into a film blowing machine for blow molding into a primary film, followed by longitudinal stretching, corona treatment, pulling, and winding.

2. The method for preparing a biodegradable breathable membrane according to claim 1, characterized in that: The specific process of step 1) is as follows: 1-1) Put the dried calcium carbonate into the mixer and heat it to 70 o C and stirred for 5 min, then stopped heating, added KH570 and continued stirring for 30 min to obtain modified inorganic particles; 1-2) Add the modified inorganic particles and tetrahydrofuran into the reaction bottle, stir and disperse them evenly, then introduce nitrogen to replace the air in the reaction bottle, add initiator AIBN, and heat to 70 o C, add 2-methylene-1,3-dioxepane dropwise under a nitrogen atmosphere, continue stirring and reacting for 2 hours after the addition is completed, precipitate in petroleum ether after the reaction is completed, and dry to obtain an intermediate product; 1-3) The intermediate product is melt-blended with polyethylene and extruded into granules to obtain a pore-forming agent.

3. The method for preparing the biodegradable breathable membrane according to claim 2, characterized in that: In the step 1-1), the mass ratio of KH570 to calcium carbonate is 0.5 to 1:50; in the step 1-2), the mass ratio of modified inorganic particles to 2-methylene-1,3-dioxepane is 1:10; in the step 1-3), the mass ratio of the intermediate product to polyethylene is 4 to 8:2 to 6.

4. The method for preparing a biodegradable breathable membrane according to claim 1, characterized in that: In the step 2-1), the molar ratio of 2-methylene-1,3-dioxepane to hydroxyethyl acrylate is 4-8:2-6, and the mass ratio of the total mass of the two monomers to calcium lignin sulfonate is 2-4:

1.

5. The method for preparing a biodegradable breathable membrane according to claim 1, characterized in that: In the step 2-2), the mass ratio of PLA particles, lignin-based polyester material and pore-forming agent is 100:40-60:40-60.

6. A biodegradable breathable film obtained by the preparation method according to any one of claims 1 to 5.

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