CN108394078B - Method for improving gas barrier property of polylactic acid - Google Patents

Method for improving gas barrier property of polylactic acid Download PDF

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CN108394078B
CN108394078B CN201810158015.9A CN201810158015A CN108394078B CN 108394078 B CN108394078 B CN 108394078B CN 201810158015 A CN201810158015 A CN 201810158015A CN 108394078 B CN108394078 B CN 108394078B
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polylactic acid
nucleating agent
barrier property
self
layer
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CN108394078A (en
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吴宏
李春海
郭少云
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Sichuan University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/16—Articles comprising two or more components, e.g. co-extruded layers
    • B29C48/18—Articles comprising two or more components, e.g. co-extruded layers the components being layers
    • B29C48/21—Articles comprising two or more components, e.g. co-extruded layers the components being layers the layers being joined at their surfaces
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C08K3/042—Graphene or derivatives, e.g. graphene oxides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/16—Nitrogen-containing compounds
    • C08K5/22—Compounds containing nitrogen bound to another nitrogen atom
    • C08K5/24—Derivatives of hydrazine
    • C08K5/25—Carboxylic acid hydrazides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2201/00—Properties
    • C08L2201/14—Gas barrier composition
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2205/00—Polymer mixtures characterised by other features
    • C08L2205/24—Crystallisation aids

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Abstract

The invention discloses a method for improving the gas barrier property of a polylactic acid material, which is characterized in that an in-plane oriented platelet barrier wall is constructed by regulating and controlling the spatial orientation and arrangement of polylactic acid platelets, so that the gas barrier property of the polylactic acid material is improved. Specifically, the method realizes the assembly growth of the self-assembly nucleating agent vertical to the layer interface through the selective layered distribution of the inducer, and the assembled and grown nucleating agent induces the growth of the polylactic acid platelet parallel to the layer interface, namely the polylactic acid platelet is vertical to the gas diffusion direction, so that the effective area of the platelet for gas barrier is greatly improved, and the gas barrier property of the polylactic acid material is improved. The polylactic acid plate, sheet and film material with high barrier property can be obtained by simple melt extrusion. The invention has the advantages of simple operation, convenient control, stable quality, high production efficiency and the like, and has good industrialization and market prospects.

Description

Method for improving gas barrier property of polylactic acid
Technical Field
The invention relates to a preparation method of high-barrier polylactic acid, belonging to the field of processing of high polymer materials.
Background
Every year, more than 40% of high polymer materials are used in the field of packaging, such as PP, PE, PVC, PET, and the like, which have good heat sealability, printability, and gas barrier properties, but none of these materials have biodegradability and pollute the environment.
With the development of bio-based degradable materials, bio-based degradable materials have been widely used, wherein polylactic acid has been widely used in packaging materials due to its advantages of excellent processability, high mechanical strength, low price, etc., but polylactic acid itself has poor barrier property, especially to gas, which limits its application range as packaging materials.
The addition of a large amount of inorganic high barrier sheet-like particles (such as graphene, clay, etc.) can prolong the diffusion path of gas molecules, which is the most common method for improving the barrier property of polylactic acid, but a large amount of sheet-like particles can agglomerate, which leads to the reduction of the mechanical property of the material and the improvement of the barrier property is not obvious. In addition, the polylactic acid multilayer material compounded with the high-barrier material is also a method for improving the barrier property of the polylactic acid, but the process is long and the manufacturing cost is high.
Disclosure of Invention
The invention provides a preparation method for continuously preparing a high-barrier polylactic acid material in a large scale with a simple process.
The technical thinking and the technical principle of the invention are as follows: (1) compared with an amorphous region of polylactic acid, the molecular chain segments of the crystalline region are regularly and tightly piled up, and gas small molecules are difficult to penetrate through. The polylactic acid product obtained by the traditional processing method is usually in a spherulite form, and small gas molecules easily pass through an amorphous area between the spherulite and the spherulite, so that the barrier property of the polylactic acid is poor (fig. 2 (E)). Therefore, the orientation and the spatial arrangement of the polylactic acid lamella are regulated and controlled, the fact that the lamella is perpendicular to the diffusion direction of the micromolecular gas is achieved, the effective blocking area of the lamella to the micromolecular gas can be increased, and the blocking performance of the polylactic acid is greatly improved. (2) According to the invention, a multi-layer material with an alternate layered structure is prepared by extruding through a micro-nano layer co-extrusion device disclosed by the Chinese invention patent (CN 101439576A), and due to the induction effect of an inducer, a nucleating agent is assembled into a fibrous structure (figure 2 (C)) perpendicular to a layer interface, and then polylactic acid platelets are induced to grow (in-plane orientation platelets) perpendicular to the axial direction of the fibers, a "platelet barrier wall" with high barrier property is constructed in situ, and the barrier property of polylactic acid is greatly improved (figure 2 (D)).
As described in the background art, the existing methods for improving the barrier property of polylactic acid are all to add large high-barrier inorganic flaky particles, neglect the design of the crystal structure of polylactic acid itself, and lead to the improvement of the barrier property and the deterioration of the mechanical property and the processability of the material. The barrier property of the material can be improved by compounding the material with a high-barrier material into a layered material, but the preparation process is complex, the cost is high, and continuous industrial production is difficult. The invention realizes the oriented assembly of the nucleating agent, then realizes the oriented arrangement of the polylactic acid lamella crystals, constructs the in-plane oriented 'lamella crystal barrier wall' in situ and realizes the self-enhancement of the polylactic acid barrier performance through simple melt extrusion.
Based on the technical principle, the invention adopts the technical scheme that:
Figure 957455DEST_PATH_IMAGE001
the selective distribution of the inducer in the a/b alternate layered material is realized by a micro-nano layer coextrusion technologyB layer (fig. 1);
Figure 140175DEST_PATH_IMAGE002
inducing the self-assembly nucleating agent in the layer a to grow in an assembled mode in a vertical layer interface mode by utilizing an inducing agent in the layer b;
Figure 356130DEST_PATH_IMAGE003
the assembled and grown nucleating agent induces the polylactic acid lamella crystal to grow along the layer interface in an oriented mode, the effective blocking area of the lamella crystal to small molecular gas is obviously increased, and therefore the high-blocking-property polylactic acid material is obtained. Specifically, the specific process steps for preparing the high-barrier polylactic acid material are as follows:
(1) melting and blending polylactic acid and a nucleating agent by a double-screw extruder, extruding, granulating and drying to obtain a material a;
(2) melting and blending polylactic acid, a nucleating agent and an inducer by a double-screw extruder, extruding, granulating and drying to obtain a material b; (3) extruding the a and the b by a micro-nano co-extrusion device to prepare a/b alternate layered materials with different layers;
(4) the micro-nano co-extrusion device consists of an extruder (A, B), a connector (C), a layer multiplier (D), a calendering roller (E) and an annealing heating plate (F) drawing roller (G);
(5) the preparation of the a/b alternating layered material is characterized in that a material a and a material b are respectively put into two extruders (A, B) of a micro-nano co-extrusion device, after melting and plasticizing, two melts are overlapped in a connector (C), after cutting and overlapping by n layer multipliers (D), and then are rolled by a rolling roller (E), annealed by an annealing plate (F) and pulled by a pulling roller (G), so that the number of layers is 2(n+1)Alternating a/b layered material of (a).
The invention has the following characteristics:
(1) according to the invention, a 'platelet barrier wall' with high barrier property is constructed in situ in a crystallization regulation and control mode, so that the gas barrier property of polylactic acid is greatly improved (by 7 times), and the defects of deterioration of mechanical property, processing property and the like caused by addition of a large amount of inorganic particles are avoided.
(2) The invention relates to a nucleating agent, in particular to a self-assembly nucleating agent which can be assembled into a one-dimensional (fiber, needle and rod) structure in a polylactic acid melt, such as benzoyl hydrazine, polyamine and the like.
(3) The inducer is particularly a material capable of inducing the self-assembly of the nucleating agent, such as clay, graphite, graphene, boron nitride, silicon dioxide and the like.
(4) The method of the present invention is not limited to polylactic acid, and can also be applied to other crystalline polymers, such as PP, PE, etc.
(5) The preparation method of the a/b alternating layered material is not limited to the multilayer coextrusion technology, and can be an a and b alternating lamination method, an a and b alternating coating method and the like.
(6) The preparation method has simple process, convenient and continuous operation control and easy implementation, and has very obvious improvement on the barrier property of the polylactic acid. In addition, the degradation performance of the polylactic acid is not influenced.
Therefore, the method for preparing the polylactic acid with high barrier property provided by the invention has the advantages of low cost, simple process, convenience in operation, high production efficiency and good industrial application prospect, and can be widely applied to preparation of polylactic acid with high barrier property and other crystalline materials.
Drawings
The invention will be further explained with reference to the drawings.
Fig. 1 (a-G) is a schematic diagram of a micro-nano layer co-extrusion device according to the present invention, which is composed of an extruder (A, B), a connector (C), a layer multiplier (D), a calendering roller (E), an annealing plate (F) and a drawing roller (G).
FIG. 1 (H) is a schematic drawing of the flow of polylactic acid melt in a layer multiplier.
In FIG. 2, (A) is the a/b alternating multilayer material prepared; (B) the self-assembly nucleating agent is completely dissolved in the polylactic acid matrix at high temperature; (C) in the annealing process, the inducer induces the self-assembly nucleating agent to be assembled into a fibrous structure perpendicular to the layer interface; (D) the assembled nucleating agent fiber induces the polylactic acid to grow vertical to the layer interface; (E) is polylactic acid with a common spherulite structure.
FIG. 3 shows the process of dissolving the self-assembly nucleating agent in the multilayer material with different layers, assembling and inducing the growth of polylactic acid platelets.
Detailed description of the invention
It should be noted that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention, and that the skilled person in the art may make some insubstantial modifications and adaptations of the present invention based on the above disclosure.
Example 1
(1) The raw material is selected from polylactic acid (PLA 4032D, Nature works, USA), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5; a self-assembly nucleating agent (benzoyl hydrazine derivatives, China, Shanxi chemical research institute), molecular weight of 483.5 and melting point of 210 ℃; nucleating agent inducer: graphene (SE 1231, element six of Heizhou, China), and specific surface area of 140-160 g/cm3The carbon content fraction was 98%. All materials were placed in a vacuum oven for vacuum drying at 60 ℃ for 12h before use.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain a material a and a material b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively feeding the materials a and B into single screw extruders A and B (see figure 1) for micro-layer co-extrusion, fusing and plasticizing, laminating the two melts in a connector (C), cutting and laminating by n layer multipliers (D), calendering by a calendering roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain a layer number of 2（n+1）Alternating a/b layered material of (a). The layer thickness ratio, i.e. a/B =6/1, was controlled by adjusting the rotational speed ratio of the extruders a and B. By using 1, 2, 3, 4, 5 multipliers respectively 4, 8, 16, 32, 64 layers of a/b alternating multilayer can be obtainedA material.
Comparative example 1
(1) The raw material is selected from polylactic acid (PLA 4032D, Nature works, USA), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5; a self-assembly nucleating agent (benzoyl hydrazine derivatives, China, Shanxi chemical research institute), molecular weight of 483.5 and melting point of 210 ℃; nucleating agent inducer: graphene (SE 1231, element six of Heizhou, China), and specific surface area of 140-160 g/cm3The carbon content fraction was 98%. All materials were placed in a vacuum oven for vacuum drying at 60 ℃ for 12h before use.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain granules a and granules b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively putting the materials a and B into single-screw extruders A and B (shown in figure 1) for micro-layer co-extrusion, after melting and plasticizing, superposing the two melts in a connector (C), cutting and superposing the melts by n layer multipliers (D), calendering the melts by a calendering roller (E), directly drawing the melts by a drawing roller (G) (without processing by an annealing plate (F)) to obtain an amorphous polylactic acid multilayer material, and controlling the layer-thickness ratio by adjusting the rotating speed ratio of the extruders A and B, namely a/B = 6/1. By using 1, 2, 3, 4, 5 multipliers respectively 4, 8, 16, 32, 64 layers of a/b alternating amorphous multilayer material can be obtained (comparative 1).
Comparative example 2
(1) The raw material is selected from polylactic acid (PLA 4032D, Nature works, USA), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5; a self-assembly nucleating agent (benzoyl hydrazine derivatives, China, Shanxi chemical research institute), molecular weight of 483.5 and melting point of 210 ℃; nucleating agent inducer: graphene (SE 1231, sixth element of Changzhou, China), scaleArea of 140-160 g/cm3The carbon content fraction was 98%. All materials were placed in a vacuum oven for vacuum drying at 60 ℃ for 12h before use.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain granules a and granules b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively feeding the materials a and B into single screw extruders A and B (see figure 1) for micro-layer co-extrusion, fusing and plasticizing, laminating the two melts in a connector (C), cutting and laminating by n layer multipliers (D), calendering by a calendering roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain a layer number of 2（n+1）Alternating a/b layered material of (a). The layer thickness ratio, i.e. a/B =6/1, was controlled by adjusting the rotational speed ratio of the extruders a and B. By using 1, 2, 3, 4, 5 multipliers respectively, 4, 8, 16, 32, 64 layers of multilayer material can be obtained, respectively.
(4) The multilayer material obtained in (3) was charged into a Haake machine and densified at 185 ℃ for 8 minutes to break the layer structure, and was molded into a sheet of 100 mm. times.100 mm. times.1.8 mm thickness at 185 ℃ and then placed on an annealing plate (FIG. 1 (F)) to obtain a comparative sample (comparative sample 2) having a conventional blend structure.
Comparative example 3
(1) The raw material is polylactic acid (PLA 4032D Nature works), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5; a self-assembly nucleating agent (benzoyl hydrazine derivatives, China, Shanxi chemical research institute), molecular weight of 483.5 and melting point of 210 ℃; nucleating agent inducer: graphene (SE 1231, element six of Heizhou, China), and specific surface area of 140-160 g/cm3The carbon content fraction was 98%. All materials were placed in a vacuum oven for vacuum drying at 60 ℃ for 12h before use.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain granules a and granules b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively feeding the materials a and B into single screw extruders A and B (see figure 1) for micro-layer co-extrusion, fusing and plasticizing, laminating the two melts in a connector (C), cutting and laminating by n layer multipliers (D), calendering by a calendering roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain a layer number of 2（n+1）Alternating a/b layered material of (a). The layer thickness ratio, i.e. a/B =6/1, was controlled by adjusting the rotational speed ratio of the extruders a and B. By using 1, 2, 3, 4, 5 multipliers respectively, 4, 8, 16, 32, 64 layers of multilayer material can be obtained, respectively.
(4) The multilayer material obtained in (3) was charged into a Haake machine and densified at 185 ℃ for 8 minutes to destroy the layer structure, and was molded into a sheet of 100 mm. times.100 mm. times.1.8 mm thickness at 185 ℃ and then directly quenched with ice water to obtain an amorphous comparative sample (comparative sample 3) having a common blend structure.
Comparative example 4
(1) The raw material is selected from polylactic acid (PLA 4032D, Nature works, USA), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5; a self-assembly nucleating agent (benzoyl hydrazine derivatives, China, Shanxi chemical research institute), molecular weight of 483.5 and melting point of 210 ℃; nucleating agent inducer: graphite (high purity graphite, Qingdao Tian and Dagraphite Co., Ltd.), the particle size is 1-500 μm, and the carbon content is 80-99.99%. All materials were placed in a vacuum oven for vacuum drying at 60 ℃ for 12 h.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain a material a and a material b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively feeding the materials a and B into single screw extruders A and B (see figure 1) for micro-layer co-extrusion, fusing and plasticizing, laminating the two melts in a connector (C), cutting and laminating by n layer multipliers (D), calendering by a calendering roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain a layer number of 2（n+1）Alternating a/b layered material of (a). The layer thickness ratio, i.e. a/B =6/1, was controlled by adjusting the rotational speed ratio of the extruders a and B. 16 layers of a/b alternating multilayer material (control 4) were obtained by using 3 multipliers.
Comparative example 5
(1) The raw material is polylactic acid (PLA 4032D Nature works), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5, the molecular weight is 483.5, the melting point is 210 ℃, the nucleating agent is a nano clay (WSG-PN 06, China, Shanghai Wan Fine chemical Co., Ltd.), the average particle size is 25 × 1000 nm, the X-ray d (001) is 2.1 nm, the content of montmorillonite is 95-98%, and all materials are placed in a vacuum oven for vacuum drying for 12 hours at the temperature of 60 ℃.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain a material a and a material b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively feeding the materials a and B into single screw extruders A and B (see figure 1) for micro-layer co-extrusion, fusing and plasticizing, laminating the two melts in a connector (C), cutting and laminating by n layer multipliers (D), calendering by a calendering roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain a layer number of 2（n+1）Alternating a/b layered material of (a). The layer thickness ratio, i.e. a/B =6/1, was controlled by adjusting the rotational speed ratio of the extruders a and B. By using 3The multiplier can obtain 16 layers of a/b alternating multilayer material (control 5).
Comparative example 6
(1) The raw material is polylactic acid (PLA 4032D Nature works), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5; the self-assembly nucleating agent (polyamine derivatives, New Material science and technology Co., Ltd., Hangzhou, China) has a melting point of more than 375 ℃; nucleating agent inducer: graphene (SE 1231, element six of Heizhou, China), and specific surface area of 140-160 g/cm3The carbon content fraction was 98%. All materials were placed in a vacuum oven for vacuum drying at 60 ℃ for 12 h.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain a material a and a material b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively feeding the materials a and B into single screw extruders A and B (see figure 1) for micro-layer co-extrusion, fusing and plasticizing, laminating the two melts in a connector (C), cutting and laminating by n layer multipliers (D), calendering by a calendering roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain a layer number of 2（n+1）Alternating a/b layered material of (a). The layer thickness ratio, i.e. a/B =6/1, was controlled by adjusting the rotational speed ratio of the extruders a and B. 16 layers of a/b alternating multilayer material (control 6) were obtained by using 3 multipliers.
Comparative example 7
(1) The raw material is polylactic acid (PLA 4032D Nature works), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5; the self-assembly nucleating agent (polyamine derivatives, New Material science and technology Co., Ltd., Hangzhou, China) has a melting point of more than 375 ℃; nucleating agent inducer: graphite (high purity graphite, Qingdao Tian and Dagao graphite Co., Ltd.) with a particle size of 1 to 1500 μm, and 80-99.99% of carbon. All materials were placed in a vacuum oven for vacuum drying at 60 ℃ for 12 h.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain a material a and a material b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively feeding the materials a and B into single screw extruders A and B (see figure 1) for micro-layer co-extrusion, fusing and plasticizing, laminating the two melts in a connector (C), cutting and laminating by n layer multipliers (D), calendering by a calendering roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain a layer number of 2（n+1）Alternating a/b layered material of (a). The layer thickness ratio, i.e. a/B =6/1, was controlled by adjusting the rotational speed ratio of the extruders a and B. 16 layers of a/b alternating multilayer material (control 7) were obtained by using 3 multipliers.
Comparative example 8
(1) The raw material is polylactic acid (PLA 4032D Nature works), the melt index is 8g/10 min (210 ℃, 2.16 Kg), and the weight average molecular weight is 1.77 × 105g/cm3The molecular weight distribution is 1.5, the melting point of a self-assembly nucleating agent (polyamine derivatives, New Material science and technology Co., Ltd., Hangzhou Zhaoyaomao, China) is more than 375 ℃, the nucleating agent inducer is nano clay (WSG-PN 06, China, Shanghai Wanzhan Fine chemical Co., Ltd.), the average particle size is 25 × 1000 nm, the X-ray d (001) is 2.1 nm, the content of montmorillonite is 95-98%, and all materials are placed in a vacuum oven for vacuum drying for 12 hours at the temperature of 60 ℃.
(2) Respectively putting the dried polylactic acid/self-assembly nucleating agent (mass ratio of 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio of 100/1/0.5) into a double-screw extruder to extrude and granulate to obtain a material a and a material b, wherein the temperatures of a feed inlet, a conveying section, a melting section and a homogenizing section of the double-screw extruder are respectively 125 ℃, 185 ℃, 188 ℃ and 185 ℃.
(3) Respectively feeding the materials a and B into single screw extruders A and B (see figure 1) for micro-layer co-extrusion, fusing and plasticizing, laminating the two melts in a connector (C), cutting and laminating by n layer multipliers (D), calendering by a calendering roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain a layer number of 2（n+1）Alternating a/b layered material of (a). The layer thickness ratio, i.e. a/B =6/1, was controlled by adjusting the rotational speed ratio of the extruders a and B. 16 layers of a/b alternating multilayer material (control 8) were obtained by using 3 multipliers.
The following table is obtained by comparing the examples and the comparative columns.
Oxygen permeability coefficients of table one, examples and comparative examples
Figure 689022DEST_PATH_IMAGE005
In example 1, benzoyl hydrazine derivatives were used as the self-assembly nucleating agent and graphene as the inducer the multilayer patterns of different layer numbers had similar crystallinity (about 53.9%), but the oxygen permeability coefficient increased and then decreased with increasing layer number, with 16 layers reaching a minimum of 0.7 × 10-19m3·m/m2s.Pa. The self-assembly nucleating agent begins to branch off to form a dendritic fiber structure after the fiber grows to a certain length (about 24.8 μm, see fig. 3 (a 2)) during the assembly process. Due to the space position effect, the branched fibers have higher orientation degree, and the induced polylactic acid platelets also have higher regularity and orientation degree. Therefore, the branched fiber structure is more favorable for improving the gas barrier property of the polylactic acid. The thickness of the multilayer material of the present invention is constant, the thickness of the individual layers decreases as the number of layers increases, and when the number of layers exceeds 16, the thickness of the individual layers decreases to such an extent that there is not enough room for the nucleating agent to grow after branching, and thus the 16-layer pattern exhibits the best oxygen barrier performance (the oxygen barrier coefficient is the smallest).
In comparative example 1, a benzoyl hydrazine derivative was used as a self-assembly nucleating agent, and graphene was used as an inducer. The resulting pattern was amorphous as a result of not being treated with the annealed plate (FIG. 1 (F)). The oxygen permeability coefficient slightly decreases with the number of layers, and the barrier properties slightly increase. The high-layer number samples need more multipliers, so that the high-layer number samples experience higher shear force fields, higher graphene orientation is caused, and the effective area of the graphene for blocking gas molecules is increased, so that the oxygen permeability coefficient of the high-layer number samples is slightly reduced, and the blocking performance is slightly improved.
In comparative example 2, a benzoyl hydrazine derivative was used as a self-assembly nucleating agent, and graphene was used as an inducer. The obtained pattern is a common crystal blending sample without a layer structure, and at the moment, the polylactic acid lamella is randomly oriented, so that the effective blocking area for gas molecules is lower. Therefore, even though the crystallinity is similar, the multilayer sample of example 1 can have an oxygen permeability coefficient of gas as low as 14.5% in comparative sample 2 and an oxygen barrier property improved by 7 times, compared to the sample of comparative sample 2. Therefore, the orientation and the spatial arrangement of the polylactic acid platelets are regulated and controlled to form an effective 'platelet separation wall', and the separation performance of the polylactic acid material can be effectively improved.
In comparative example 3, a benzoyl hydrazine derivative was used as a self-assembly nucleating agent, and graphene was used as an inducer. The obtained pattern was a normal blend structure in an amorphous state, and therefore, the oxygen permeability coefficient was higher and the barrier property was inferior in comparative example 3 as compared with example 1 and comparative example 2.
In comparative example 4, a benzoyl hydrazine derivative was used as a self-assembly nucleating agent, and high-purity graphite was used as an inducer. The values of the oxygen permeability coefficients of the obtained samples were comparable to those of the 16-layer samples in example 1.
In comparative example 5, benzoyl hydrazine derivatives were used as a self-assembly nucleating agent, and nano clay was used as an inducer. The values of the oxygen permeability coefficients of the obtained samples were comparable to those of the 16-layer samples in example 1.
In comparative example 6, polyamines were used as the self-assembly nucleating agent and graphene was used as the inducer. The oxygen permeability coefficient of the obtained sample is slightly higher than that of the sample with 16 layers in the example 1, which shows that the benzoyl hydrazine derivative has more excellent effect.
In comparative example 7, polyamines were used as the self-assembly nucleating agent and high-purity graphite as the inducer. The oxygen permeability coefficient of the obtained sample is slightly higher than that of the sample with 16 layers in the example 1, which shows that the benzoyl hydrazine derivative has more excellent effect.
In comparative example 8, polyamine was used as a self-assembly nucleating agent, and nano clay was used as an inducer. The oxygen permeability coefficient of the obtained sample is slightly higher than that of the sample with 16 layers in the example 1, which shows that the benzoyl hydrazine derivative has more excellent effect.
In example 1 and comparative examples 1 to 8, crystalline polylactic acid was used as a matrix, benzoyl hydrazine derivatives and polyamine organic compounds were used as a self-assembly nucleating agent, and graphene, graphite and clay were used as an inducer of the self-assembly nucleating agent, but the present invention is not limited to the above system, and those skilled in the art can make some insubstantial modifications and adjustments to the present invention based on the above disclosure, and similar conclusions can be obtained.

Claims (4)

1. A method for improving the gas barrier property of polylactic acid is characterized in that the effective barrier area of the polylactic acid platelets to micromolecular gas is improved by regulating the orientation and arrangement of the polylactic acid platelets, and the self-enhancement of the gas barrier property of the polylactic acid is realized, and the method is characterized by comprising the following steps:
(1) melting and blending polylactic acid and a polylactic acid nucleating agent by a double-screw extruder, extruding, granulating and drying to obtain a material a;
(2) melting and blending polylactic acid, a polylactic acid nucleating agent and an inducer of the polylactic acid nucleating agent by a double-screw extruder, extruding, granulating and drying to obtain a material b;
(3) extruding the a and the b by a micro-nano co-extrusion device to prepare a/b alternate layered materials with different layers;
(4) the micro-nano co-extrusion device consists of an extruder (A, B), a connector (C), a layer multiplier (D), a calendering roller (E) and an annealing heating plate (F) drawing roller (G);
(5) the preparation of the a/b alternating layered material is characterized in that the material a and the material b are respectively put into two extruders (A, B) of a micro-nano co-extrusion device, and after melting and plasticizing, the two melts are connectedOverlapping the connectors (C), cutting and overlapping by n layers of multipliers (D), rolling by a rolling roller (E), annealing by an annealing plate (F), and drawing by a drawing roller (G) to obtain the layer number of 2(n+1)Alternating a/b layered material of (a).
2. The method according to claim 1, wherein the polylactic acid has a gas barrier property which is improved by: the polylactic acid nucleating agent is particularly a self-assembly nucleating agent which can be assembled into a one-dimensional fiber, needle or rod-shaped structure in a polylactic acid melt.
3. The method according to claim 1, wherein the polylactic acid has a gas barrier property which is improved by: the polylactic acid nucleating agent inducer is particularly a material capable of inducing the self-assembly of the polylactic acid nucleating agent.
4. The method according to claim 1, wherein the polylactic acid has a gas barrier property which is improved by:
(1) the inducer of the polylactic acid nucleating agent is selectively distributed in the layer b of the a/b alternating layered material and induces the polylactic acid nucleating agent in the layer a to grow in an assembling mode perpendicular to the layer interface;
(2) the fibrous polylactic acid nucleating agent after the assembly growth induces the planar direction of the polylactic acid platelet to be vertical to the axial growth of the polylactic acid platelet, namely the planar direction of the platelet is parallel to the layer interface for growth, and then the planar direction of the polylactic acid platelet is vertical to the diffusion direction (layer thickness direction) of the micromolecular gas, so that the effective blocking area of the platelet is improved, and the self-enhancement of the blocking performance of the polylactic acid is realized.
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JPH01133731A (en) * 1987-11-20 1989-05-25 Chisso Corp Metallized laminated body
CN101357506A (en) * 2008-05-29 2009-02-04 郭军 Production process and equipment of polylactic acid (PLA) sheet
CN105200552A (en) * 2015-10-23 2015-12-30 四川大学 High heat-resistant and high-strength polylactic acid fiber and preparation method thereof
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JPH01133731A (en) * 1987-11-20 1989-05-25 Chisso Corp Metallized laminated body
CN101357506A (en) * 2008-05-29 2009-02-04 郭军 Production process and equipment of polylactic acid (PLA) sheet
CN105200552A (en) * 2015-10-23 2015-12-30 四川大学 High heat-resistant and high-strength polylactic acid fiber and preparation method thereof
CN105566753A (en) * 2015-12-08 2016-05-11 四川大学 Polypropylene material containing content-controllable and continuous and ordered beta horizontal crystal layers and preparation method of polypropylene material

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