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

Abstract

The invention discloses a method for improving the gas barrier properties of polylactic acid materials, which is characterized in that by regulating the spatial orientation and arrangement of polylactic acid platelets, an in-plane oriented platelet barrier wall is constructed, thereby improving its gas barrier properties. Specifically, the present invention realizes the assembly and growth of the self-assembled nucleating agent perpendicular to the layer interface through the selective layered distribution of the inducer. The crystals are perpendicular to the gas diffusion direction, which greatly increases the effective area of the lamellae for gas barrier, thereby improving the gas barrier properties of the polylactic acid material. In the present invention, polylactic acid sheets, sheets and film materials with high barrier properties can be obtained by simple melt extrusion. The invention has the advantages of simple operation, convenient control, stable quality and high production efficiency, and has good industrialization and market prospects.

Description

A kind of method for improving the gas barrier property of polylactic acid

technical field

The invention relates to a preparation method of high-barrier polylactic acid, and belongs to the field of polymer material processing.

Background technique

Every year, more than 40% of polymer materials are used in the field of packaging, such as PP, PE, PVC, PET, etc. They have good heat sealing, printing and gas barrier properties, but these materials are not biodegradable performance and pollute the environment.

With the development of bio-based degradable materials, bio-based degradable materials have been widely used. Among them, polylactic acid has been widely used in packaging materials due to its excellent processing performance, high mechanical strength and low price. Its own barrier properties, especially its poor gas barrier properties, limit its application range as a packaging material.

Adding a large amount of inorganic high-barrier flake particles (such as graphene, clay, etc.) can prolong the diffusion path of gas molecules, which is the most common method to improve the barrier properties of PLA, but a large number of flake particles will agglomerate, resulting in a decrease in the mechanical properties of the material. And the barrier performance is not significantly improved. In addition, composite polylactic acid multi-layer material with high barrier material is also a method to improve the barrier performance of polylactic acid, but the process is tedious and the production cost is high.

SUMMARY OF THE INVENTION

The invention provides a preparation method for preparing high-barrier polylactic acid material with simple process and continuous large-scale preparation.

The technical thinking and technical principle of the present invention are as follows: (1) Compared with the amorphous region of polylactic acid, the molecular chain segments in the crystal region are regularly packed and compact, and it is difficult for small gas molecules to pass through. Polylactic acid products obtained by traditional processing methods are usually in the form of spherulites, and small gas molecules easily pass through the amorphous region between the spherulites, resulting in poor barrier properties of polylactic acid (Figure 2(E)). Therefore, adjusting the orientation and spatial arrangement of the PLA platelets and realizing that the platelets are perpendicular to the diffusion direction of the small molecular gas can increase the effective blocking area of the platelets to the small molecular gas, thereby greatly improving the barrier performance of PLA. (2) The present invention uses the micro-nano layer co-extrusion device invented by the Chinese invention patent (CN101439576A) to extrude and prepare multi-layer materials with alternating layered structure. Due to the inducing effect of the inducer, the nucleating agent is perpendicular to the layer interface. The fibrous structure (Fig. 2(C)) then induces the growth of polylactic acid platelets perpendicular to the axial direction of the fibers (in-plane oriented platelets), and in situ constructs a "platelet barrier wall" with high barrier properties. Improve the barrier properties of PLA (Fig. 2(D)).

As mentioned in the background art, the existing methods for improving the barrier properties of PLA are all by adding a large number of high barrier inorganic flake particles, ignoring the design of the crystal structure of PLA itself, resulting in the improvement of barrier properties and accompanied by material mechanics. performance, deterioration of processability. The barrier properties of the material can be improved by compounding it with a high barrier material into a layered material, but the preparation process is complicated, the cost is high, and it is difficult to continuously industrialize production. The present invention realizes the directional assembly of the nucleating agent through simple melt extrusion, and then realizes the directional arrangement of the polylactic acid platelets, constructs in-situ "platelet barrier walls" with in-plane orientation, and realizes the barrier properties of the polylactic acid. Self-reinforcing.

通过微纳层共挤出技术，实现诱 导剂选择性分布在a/b交替层状材料的b层中（图1）；

利用b层中的诱导剂诱导a层中的自 组装成核剂垂直层界面组装生长；

组装生长后的成核剂继而诱导聚乳酸片晶沿层界面取 向生长，显著提高片晶对小分子气体的有效阻隔面积，从而获得高阻隔性聚乳酸材料。具体 讲，本发明制备高阻隔聚乳酸材料的具体工艺步骤如下： The present invention is based on the above-mentioned technical principle, and the technical scheme adopted is:

Through the micro-nano layer co-extrusion technology, the selective distribution of the inducer in the b layer of the a/b alternating layered material is realized (Fig. 1);

Using the inducer in the b layer to induce the self-assembled nucleating agent in the a layer to assemble and grow at the vertical layer interface;

The assembled and grown nucleating agent then induces the oriented growth of polylactic acid platelets along the layer interface, which significantly increases the effective blocking area of platelets for small molecular gases, thereby obtaining high-barrier polylactic acid materials. Specifically, the concrete process steps of the present invention preparing high-barrier polylactic acid material are as follows:

(1) Melt-blending, extruding, granulating and drying polylactic acid and nucleating agent through a twin-screw extruder to obtain material a;

(2) Melt-blending, extruding, granulating and drying polylactic acid, nucleating agent and inducer through a twin-screw extruder to obtain material b; (3) Extruding a and b from a micro-nano co-extrusion device Preparation of a/b alternating layered materials with different layers;

(4) Micro-nano co-extrusion device consists of extruder (A, B), connector (C), layer multiplier (D), calendering roller (E), annealing heating plate (F) and traction roller (G) ;

(5) The preparation of a/b alternating layered material is characterized in that material a and material b are respectively put into two extruders (A, B) of the micro-nano co-extrusion device, and after melting and plasticizing, the two melts are melted. After the connector (C) is stacked, cut and stacked by n layer multipliers (D), and then rolled by the calendering roller (E), annealed by the annealing plate (F), and pulled by the traction roller (G), the number of layers is obtained as 2 ⁽ⁿ⁺¹⁾ alternating layers of a/b material.

The present invention has the following characteristics:

(1) The present invention constructs a "lamellar barrier wall" with high barrier properties in situ by means of crystallization regulation, which greatly improves the gas barrier properties of polylactic acid (7 times higher), thereby avoiding the need for adding a large amount of inorganic particles. Insufficient deterioration of mechanical properties, processability, etc. caused.

(2) The nucleating agent involved in the present invention specifically refers to a self-assembling nucleating agent that can be assembled into a one-dimensional (fiber, needle, rod-like) structure in a polylactic acid melt, such as benzoic hydrazides, polyamines, and the like.

(3) The inducer involved in the present invention specifically refers to a material that can induce the self-assembly of the nucleating agent, such as clay, graphite, graphene, boron nitride, silicon dioxide, and the like.

(4) The method involved in the present invention is not limited to polylactic acid, and can also be applied to other crystalline polymers, such as PP, PE, and the like.

(5) The present invention involves the preparation of a/b alternating layered materials, and the preparation method is not limited to the multi-layer co-extrusion technology, but can be a, b alternate lamination lamination, a, b alternate coating method, etc.

(6) The preparation method of the present invention is simple in process, convenient and continuous in operation and control, easy to implement, and greatly improves the barrier performance of polylactic acid. In addition, the degradation performance of polylactic acid is not affected.

It can be seen that the method for preparing high-barrier polylactic acid provided by the present invention has the advantages of low cost, simple process, convenient operation, high production efficiency, good industrial application prospect, and can be widely used in the preparation of polylactic acid and high-barrier polylactic acid. other crystalline materials.

Description of drawings

The content of the present invention will be further described below in conjunction with the accompanying drawings.

1 (A-G) are schematic diagrams of the micro-nano layer co-extrusion device involved in the present invention, which consists of extruders (A, B), connectors (C), layer multipliers (D), calendering rolls (E), annealing Plate (F) and traction roller (G).

Figure 1(H) is a schematic diagram of the flow of PLA melt in the layer multiplier.

In Figure 2, (A) is the prepared a/b alternating multilayer material; (B) the self-assembly nucleating agent is completely dissolved in the polylactic acid matrix at high temperature; (C) the inducer induces self-assembly during the annealing process. The nucleating agent assembles into a fibrous structure perpendicular to the layer interface; (D) The assembled nucleating agent fiber induces the growth of PLA perpendicular to the layer interface; (E) PLA with a common spherulite structure.

FIG. 3 shows the process of dissolving, assembling and inducing the growth of polylactic acid platelets by the self-assembled nucleating agent in multi-layer materials with different layers.

Specific implementation method

It is necessary to point out here that the following examples are only further descriptions of the present invention, and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above-mentioned contents of the present invention.

Example 1

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Self-assembled nucleating agent (benzoyl hydrazide derivatives, China, Shanxi Institute of Chemical Technology), molecular weight 483.5, melting point 210 °C; nucleating agent inducer: graphene (SE1231, China, Changzhou sixth element), specific surface area 140~160 g/cm ³ , and the carbon content is 98%. Before use, all materials were placed in a vacuum oven at 60 °C for vacuum drying for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded and granulated to obtain material a and material b, wherein the temperatures of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After the layer multipliers (D) are cut and stacked, they are rolled by the calendering roller (E), annealed by the annealed sheet (F), and drawn by the traction roller (G) to obtain a/b alternating layers with a number of layers of 2 ⁽ⁿ⁺¹⁾ . layered material. The layer thickness ratio is controlled by adjusting the speed ratio of extruders A and B, that is, a/b=6/1. A/b alternating multilayer materials of 4, 8, 16, 32, 64 layers, respectively, can be obtained by using 1, 2, 3, 4, and 5 multipliers, respectively.

Comparative Example 1

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Self-assembled nucleating agent (benzoyl hydrazide derivatives, China, Shanxi Institute of Chemical Technology), molecular weight 483.5, melting point 210 °C; nucleating agent inducer: graphene (SE1231, China, Changzhou sixth element), specific surface area 140~160 g/cm ³ , and the carbon content is 98%. Before use, all materials were placed in a vacuum oven at 60 °C for vacuum drying for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded pellets a and b, and the temperature of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After being cut and stacked by the layer multiplier (D), and then rolled by the calendering roller (E), it is directly drawn by the traction roller (G) (without the treatment of the annealed plate (F)) to obtain an amorphous polylactic acid multilayer material. , by adjusting the speed ratio of extruder A and B to control the layer thickness ratio, that is, a/b=6/1. By using 1, 2, 3, 4, and 5 multipliers, respectively, 4, 8, 16, 32, and 64 layers of a/b alternating amorphous multilayer materials can be obtained (Comparative Sample 1).

Comparative Example 2

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Self-assembled nucleating agent (benzoyl hydrazide derivatives, China, Shanxi Institute of Chemical Technology), molecular weight 483.5, melting point 210 °C; nucleating agent inducer: graphene (SE1231, China, Changzhou sixth element), specific surface area 140~160 g/cm ³ , and the carbon content is 98%. Before use, all materials were placed in a vacuum oven at 60 °C for vacuum drying for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded pellets a and b, and the temperature of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After the layer multipliers (D) are cut and stacked, they are rolled by the calendering roller (E), annealed by the annealed sheet (F), and drawn by the traction roller (G) to obtain a/b alternating layers with a number of layers of 2 ⁽ⁿ⁺¹⁾ . layered material. The layer thickness ratio is controlled by adjusting the speed ratio of extruders A and B, that is, a/b=6/1. Multilayer materials of 4, 8, 16, 32, 64 layers can be obtained by using 1, 2, 3, 4, and 5 multipliers, respectively.

(4) Put the multi-layer material obtained in (3) into a Hack densifying machine at 185 °C for 8 minutes to destroy the layer structure, and press at 185 °C to form a 100mm × 100mm × 1.8mm thick sheet, and then place it on an annealing plate (Fig. 1(F)) After treatment, a control sample (control sample 2) with a common blend structure was obtained.

Comparative Example 3

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Assembly nucleating agent (benzoyl hydrazide derivatives, China, Shanxi Institute of Chemical Technology), molecular weight 483.5, melting point 210 ℃; nucleating agent inducer: graphene (SE1231, China, Changzhou sixth element), specific surface area 140 ~160 g/cm ³ , the carbon mass fraction is 98%. Before use, all materials were placed in a vacuum oven at 60 °C for vacuum drying for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded pellets a and b, and the temperature of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After the layer multipliers (D) are cut and stacked, they are rolled by the calendering roller (E), annealed by the annealed sheet (F), and drawn by the traction roller (G) to obtain a/b alternating layers with a number of layers of 2 ⁽ⁿ⁺¹⁾ . layered material. The layer thickness ratio is controlled by adjusting the speed ratio of extruders A and B, that is, a/b=6/1. Multilayer materials of 4, 8, 16, 32, 64 layers can be obtained by using 1, 2, 3, 4, and 5 multipliers, respectively.

(4) Put the multi-layer material obtained in (3) into the Hack densifying machine at 185 °C for 8 minutes to destroy the layer structure, and press it into a 100mm×100mm×1.8mm thick sheet at 185°C, and then use ice water directly. Quenching to obtain an amorphous comparative sample with an ordinary blend structure (Comparative Sample 3).

Comparative Example 4

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Self-assembled nucleating agent (benzoic hydrazide derivatives, China, Shanxi Institute of Chemical Technology), molecular weight 483.5, melting point 210 °C; nucleating agent inducer: graphite (high-purity graphite, Qingdao Tianheda Graphite Co., Ltd.), The particle size is 1~500μm, and the carbon content is 80~99.99%. All materials were dried in a vacuum oven at 60 °C for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded and granulated to obtain material a and material b, wherein the temperatures of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After the layer multipliers (D) are cut and stacked, they are rolled by the calendering roller (E), annealed by the annealed sheet (F), and drawn by the traction roller (G) to obtain a/b alternating layers with a number of layers of 2 ⁽ⁿ⁺¹⁾ . layered material. The layer thickness ratio is controlled by adjusting the speed ratio of extruders A and B, that is, a/b=6/1. By using 3 multipliers, 16 layers of a/b alternating multilayer material (Comparative Sample 4) can be obtained.

Comparative Example 5

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Assembly nucleating agent (Benzohydrazide Derivatives, China, Shanxi Institute of Chemical Industry), molecular weight 483.5, melting point 210 ℃; nucleating agent inducer: nanoclay (WSG-PN06, China, Shanghai Wanzhao Fine Chemical Co., Ltd. Company), average particle size: 25×1000 nm, X-ray d(001): 2.1 nm. The content of montmorillonite stone is 95~98%. All materials were dried in a vacuum oven at 60 °C for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded and granulated to obtain material a and material b, wherein the temperatures of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After the layer multipliers (D) are cut and stacked, they are rolled by the calendering roller (E), annealed by the annealed sheet (F), and drawn by the traction roller (G) to obtain a/b alternating layers with a number of layers of 2 ⁽ⁿ⁺¹⁾ . layered material. The layer thickness ratio is controlled by adjusting the speed ratio of extruders A and B, that is, a/b=6/1. By using 3 multipliers a 16-layer a/b alternating multilayer material (Comparative Sample 5) was obtained.

Comparative Example 6

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Assembly nucleating agent (polyamine derivatives, China, Hangzhou Ximao New Material Technology Co., Ltd.), melting point > 375 ℃; nucleating agent inducer: graphene (SE1231, China, Changzhou Sixth Element), specific surface area 140 ~160 g/cm ³ , the carbon mass fraction is 98%. All materials were dried in a vacuum oven at 60 °C for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded and granulated to obtain material a and material b, wherein the temperatures of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After the layer multipliers (D) are cut and stacked, they are rolled by the calendering roller (E), annealed by the annealed sheet (F), and drawn by the traction roller (G) to obtain a/b alternating layers with a number of layers of 2 ⁽ⁿ⁺¹⁾ . layered material. The layer thickness ratio is controlled by adjusting the speed ratio of extruders A and B, that is, a/b=6/1. A 16-layer a/b alternating multilayer material was obtained by using 3 multipliers (Comparative Sample 6).

Comparative Example 7

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Assembled nucleating agent (polyamine derivatives, China, Hangzhou Ximao New Material Technology Co., Ltd.), melting point >375 ℃; nucleating agent inducer: graphite (high-purity graphite, Qingdao Tianheda Graphite Co., Ltd.), particle size 1~500μm, carbon content 80~99.99%. All materials were dried in a vacuum oven at 60 °C for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded and granulated to obtain material a and material b, wherein the temperatures of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After the layer multipliers (D) are cut and stacked, they are rolled by the calendering roller (E), annealed by the annealed sheet (F), and drawn by the traction roller (G) to obtain a/b alternating layers with a number of layers of 2 ⁽ⁿ⁺¹⁾ . layered material. The layer thickness ratio is controlled by adjusting the speed ratio of extruders A and B, that is, a/b=6/1. A 16-layer a/b alternating multilayer material was obtained by using 3 multipliers (Comparative Sample 7).

Comparative Example 8

(1) Selection of raw materials: polylactic acid (PLA 4032D, American Nature works), the melting index is 8g/10 min (210℃, 2.16Kg), the weight average molecular weight is 1.77×10 ⁵ g/cm ³ , and the molecular weight distribution is 1.5; Assembled nucleating agent (polyamine derivatives, China, Hangzhou Ximao New Material Technology Co., Ltd.), melting point > 375 ℃; nucleating agent inducer: nanoclay (WSG-PN06, China, Shanghai Wanzhao Fine Chemical Co., Ltd. ), average particle size: 25×1000 nm, X-ray d(001): 2.1 nm. The content of montmorillonite stone is 95~98%. All materials were dried in a vacuum oven at 60 °C for 12 h.

(2) Put the dried polylactic acid/self-assembly nucleating agent (mass ratio 100/0.5) and polylactic acid/self-assembly nucleating agent inducer/self-assembly nucleating agent (mass ratio 100/1/0.5) into the The twin-screw extruder extruded and granulated to obtain material a and material b, wherein the temperatures of the feeding port, conveying section, melting section and homogenization section of the twin-screw extruder were 125 °C, 185 °C, 188 °C, and 185 °C, respectively. .

(3) Materials a and b are respectively put into single-screw extruders A and B for micro-layer co-extrusion (see Figure 1), and after melting and plasticizing, the two melts are superimposed at the connector (C), and after n After the layer multipliers (D) are cut and stacked, they are rolled by the calendering roller (E), annealed by the annealed sheet (F), and drawn by the traction roller (G) to obtain a/b alternating layers with a number of layers of 2 ⁽ⁿ⁺¹⁾ . layered material. The layer thickness ratio is controlled by adjusting the speed ratio of extruders A and B, that is, a/b=6/1. By using 3 multipliers a 16-layer a/b alternating multilayer material (Comparative Sample 8) was obtained.

Comparing the above-mentioned embodiment with the comparative column, the following table 1 is obtained.

Table 1. Oxygen permeability coefficients of examples and comparative examples

In Example 1, a benzoyl hydrazide derivative was used as a self-assembly nucleating agent, and graphene was used as an inducer. The multi-layer patterns with different layers have similar crystallinity (about 53.9%), but the oxygen permeability coefficient increases first and then decreases with the increase of the number of layers, and reaches the minimum value of 0.7×10 ^-19 m ³ ·m/m for 16 layers ² ·s·Pa. During the assembly process of the self-assembled nucleating agent, when its fibers grow to a certain length (about 24.8 μm, see Figure 3(A2)), they begin to branch to form a dendritic fiber structure. Due to the steric position effect, the bifurcated fibers have a higher degree of orientation, and the induced PLA platelets also have a higher degree of regularity and orientation. Therefore, the bifurcated fiber structure is more conducive to improving the gas barrier properties of polylactic acid. The thickness of the multi-layer material in the present invention remains unchanged. As the number of layers increases, the thickness of the single layer decreases. When the number of layers exceeds 16, the thickness of the single layer decreases to the point where there is no enough space for the nucleating agent to grow after the bifurcation. , so the 16-layer style presents the best oxygen barrier performance (minimum oxygen barrier coefficient).

In Comparative Example 1, a benzoic hydrazide derivative was used as a self-assembly nucleating agent, and graphene was used as an inducer. The resulting pattern was in an amorphous state as it was not treated with an annealed sheet (Fig. 1(F)). The oxygen permeability coefficient decreases slightly with the increase of the number of layers, and the barrier performance increases slightly. Higher-layer samples require more multipliers, therefore, higher-layer samples experience higher shear force fields, resulting in higher graphene orientation, which increases the effective area of graphene for gas molecular barrier, thereby making the higher-layer samples more efficient. The oxygen permeability coefficient is slightly reduced and the barrier properties are slightly improved.

In Comparative Example 2, a benzoyl hydrazide derivative was used as a self-assembly nucleating agent, and graphene was used as an inducer. The obtained pattern is an ordinary crystalline blend without a layer structure. At this time, the polylactic acid platelets are randomly oriented, and the effective blocking area for gas molecules is low. Therefore, even with similar crystallinity, the multi-layer sample of Example 1 can have a gas oxygen permeability coefficient as low as 14.5% of that of Comparative Sample 2, and the oxygen barrier performance is 7 times higher than that of Comparative Sample 2. It can be seen that by regulating the orientation and spatial arrangement of PLA platelets, an effective "platelet barrier wall" can be formed, which can effectively improve the barrier properties of PLA materials.

In Comparative Example 3, benzoyl hydrazide derivatives were used as the self-assembly nucleating agent, and graphene was used as the inducer. The obtained pattern is an ordinary blended structure in an amorphous state. Therefore, compared with Example 1 and Comparative Sample 2, Comparative Sample 3 has a higher oxygen permeability coefficient and poorer barrier properties.

In Comparative Example 4, a benzoyl hydrazide derivative was used as a self-assembly nucleating agent, and high-purity graphite was used as an inducer. The value of the oxygen permeability coefficient of the obtained sample is comparable to that of the 16-layer sample in Example 1.

In Comparative Example 5, benzoyl hydrazide derivatives were used as the self-assembly nucleating agent, and nanoclay was used as the inducer. The value of the oxygen permeability coefficient of the obtained sample is comparable to that of the 16-layer sample in Example 1.

In Comparative Example 6, polyamines were used as the self-assembly nucleating agent, and graphene was used as the inducer. The value of the oxygen permeability coefficient of the obtained sample is slightly higher than that of the 16-layer sample in Example 1, indicating that the benzoyl hydrazide derivatives have more excellent effects.

In Comparative Example 7, polyamines were used as the self-assembly nucleating agent, and high-purity graphite was used as the inducer. The value of the oxygen permeability coefficient of the obtained sample is slightly higher than that of the 16-layer sample in Example 1, indicating that the benzoyl hydrazide derivatives have better effects.

In Comparative Example 8, polyamines were used as self-assembly nucleating agents, and nanoclays were used as inducers. The value of the oxygen permeability coefficient of the obtained sample is slightly higher than that of the 16-layer sample in Example 1, indicating that the benzoyl hydrazide derivatives have better effects.

In Example 1 and Comparative Examples 1-8, crystalline polylactic acid was used as the matrix, benzoic hydrazide derivatives and polyamine organic compounds were used as self-assembly nucleating agents, and graphene, graphite, and clay were used as self-assembly nucleating agents. However, the present invention is not limited to the above-mentioned system, and those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above-mentioned contents of the present invention, and can also obtain similar conclusions.

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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