High-transparency high-barrier polylactic acid-based composite material and preparation method thereof

Abstract

The invention discloses a high-transparency high-barrier polylactic acid-based composite material and a preparation method thereof, the high-transparency high-barrier polylactic acid-based composite material is prepared from the following components in parts by weight: 80-99 parts of PLA, 1-20 parts of PHBV and 0.03-0.75 part of a compatilizer, PLA, PHBV and the compatilizer are blended in proportion, the blend is blended and granulated by a twin-screw extruder, particles are dried and then processed into a film, and the film is prepared into the high-transparency high-barrier polylactic acid-based composite material. The water-oxygen barrier property of the PLA is improved by utilizing polymer blending and interface regulation and control technologies, the water vapor transmission coefficient and the oxygen transmission rate are reduced, and the material has good light transmission and can meet the use of a high-barrier packaging material; according to the invention, the used equipment is simple, the production process is simple, the material is green and pollution-free, the application range of PLA in the fields of food packaging, medicine packaging and the like is widened, and the PLA has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of modification of biodegradable materials, and specifically relates to a highly transparent and high-barrier polylactic acid-based composite material and a preparation method thereof. By means of polymer blending and interfacial regulation techniques, a polylactic acid-based composite material with excellent transparency and barrier properties can be prepared. By adding specific polymers and compatibilizers, its application performance in the fields of food packaging, pharmaceutical packaging, etc. is improved, and it has broad application prospects. Background Art

[0002] With the wide use of plastic products in people's lives, the accumulation of waste plastics has caused an increasingly serious environmental pollution problem. Traditional petroleum-based plastics, such as polyethylene and polyvinyl chloride, are difficult to degrade in the natural environment, resulting in the so-called "white pollution" phenomenon. To address this challenge, the development of environmentally friendly biodegradable polymers has become a research hotspot in recent years. Such biodegradable polymers can decompose into carbon dioxide, water and biomass within six months under specific conditions, thus effectively reducing the white pollution problem. Their application prospects are broad, especially in areas such as disposable packaging that are difficult to recycle.

[0003] Polylactic acid (PLA) is widely used in the fields of packaging, pharmacy, agriculture, medical treatment and clothing due to its good biocompatibility, transparency and mechanical strength. Polylactic acid has the following advantages: 1) The raw materials are widely available, renewable, inexpensive, and suitable for industrial production; 2) The material is transparent, and its hardness, tensile and flexural moduli are higher than those of traditional plastics; 3) It has biocompatibility. Its monomer raw material L-lactic acid is an endogenous active substance in the human body, non-toxic and harmless, and the human body has no rejection reaction to it. It can be finally converted into carbon dioxide and water in the human body and then excreted. It can be made into medical tissue scaffold materials and pharmaceutical carriers, and its safety has obtained the certification of the US FDA; 4) It can be completely biodegradable and can be degraded into carbon dioxide and water within 6 - 12 months under the action of microorganisms under composting conditions. However, the barrier property of PLA is not high enough to meet the use of high-barrier packaging materials, and in the process of blending modification, due to the compatibility problem between different materials, the transparency of the material is often reduced, which limits its wider application. Developing highly transparent and high-barrier polylactic acid packaging materials has broad market prospects.

[0004] Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has high barrier properties, excellent biocompatibility and degradability, and the production process and degradation products are completely non-toxic and harmless. It is a currently popular biodegradable material, but its mechanical properties are poor and it cannot be used alone as a packaging material. Due to its high barrier property, it is an excellent material that can be modified. Summary of the Invention

[0005] The present invention provides a highly transparent and high-barrier polylactic acid-based composite material and a preparation method thereof, which greatly improves the barrier properties of polylactic acid through polymer blending and interface regulation technology.

[0006] The technical solution of the present invention is as follows:

[0007] A highly transparent and high-barrier polylactic acid (PLA)-based composite material is prepared from the following components in parts by weight: 80-99 parts of PLA, 1-20 parts of PHBV, and 0.03-0.75 parts of a compatibilizer.

[0008] The present invention also provides a method for preparing the highly transparent and high-barrier polylactic acid-based composite material, the specific steps of which are as follows:

[0009] (1) adding a compatibilizer to an appropriate amount of acetone and mixing to obtain a mixed solution, mixing PLA and PHBV to obtain a mixed material, adding the mixed solution to the mixed material and mixing to obtain a mixture, and placing the mixture in an oven to completely volatilize the acetone to obtain a dried material;

[0010] (2) adding the dried material into a twin-screw extruder (LSHJ-20, Shanghai Kechuang Rubber & Plastic Machinery Equipment Co., Ltd.) for extrusion molding, cooling it, and then putting it into a pelletizer for cutting into pellets;

[0011] (3) After drying the particles, place them in a flat vulcanizer and perform hot pressing followed by cold pressing to form a PLA-based composite film material.

[0012] In step (1), the mixture is placed in an oven to completely volatilize the acetone and is kept warm at 60-80° C. for 8-12 hours to obtain a dried material.

[0013] The amount of acetone used in step (1) is based on the amount by which the obtained mixed solution can wet the solid.

[0014] The compatibilizer in step (1) includes but is not limited to 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane.

[0015] In step (2), the moisture content of the material during extrusion by the twin-screw extruder is lower than 0.5wt%.

[0016] In step (2), the extrusion temperature of the twin-screw extruder is set to 175-190° C. (from the feeding section to the die section), the feed rate is set to 1.5, and the screw speed is set to 40-60 rpm.

[0017] In step (3), the moisture content of the material is lower than 0.5wt% during hot pressing on a flat vulcanizing machine.

[0018] In step (3), the pressure during hot pressing on a flat vulcanizing machine is 10-15 MPa, and the hot pressing is performed at 180-190° C. for 240-300 seconds, and the pressure during cold pressing is 5-10 MPa, and the cold pressing is performed for 60-120 seconds.

[0019] The present invention utilizes polymer blending and interface regulation technology to improve the water and oxygen barrier performance of PLA. The blended material is a biodegradable material PHBV, so that the composite material is a fully biodegradable material, has more excellent environmental friendliness, and will not cause environmental pollution.

[0020] The polylactic acid-based composite material prepared by the present invention has excellent barrier properties and transparency, and its application fields include but are not limited to the packaging field. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the water vapor permeability coefficient diagram of the composite material;

[0022] Figure 2 is the oxygen permeability graph of the composite material;

[0023] Figure 3 is an optical photograph of the composite material;

[0024] Figure 4 is the ultraviolet absorption spectrum of the composite material;

[0025] Figure 5 is the transmittance graph of the composite material at 550nm;

[0026] Figure 6 SEM image of the composite material. DETAILED DESCRIPTION

[0027] The technical scheme of the present invention is described in detail below through the accompanying drawings and specific embodiments. The following embodiments are further explanations of the present invention, but are not intended to limit the scope of the present invention. Parts in the embodiments represent parts by weight.

[0028] Example 1

[0029] A method for preparing a highly transparent and high-barrier polylactic acid material composite material comprises the following steps:

[0030] (1) Add 0.03 parts of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane to 50 mL of acetone, pour the mixture into a mixture of 90 parts of PLA and 10 parts of PHBV, and then dry at 60° C. for 8 h to completely evaporate the acetone to obtain a dried material; in the embodiment, acetone needs to completely soak the solid, and if it is insufficient, continue to add, the same below;

[0031] (2) The dried material was added to a twin-screw extruder (LSHJ-20, Shanghai Kechuang Rubber & Plastic Machinery Equipment Co., Ltd.), the extrusion temperature was set to 175°C (from the feeding section to the die section), the feed rate was set to 1.5 rpm, the screw speed was set to 50 rpm, and the moisture content of the material during extrusion by the twin-screw extruder was less than 0.5 wt%. After cooling, the material was put into a pelletizer and cut into pellets;

[0032] (3) The pellets were dried at 60° C. for 8 h to reduce the moisture content of the material to less than 0.5 wt %, and then placed in a flat vulcanizer, hot-pressed at a pressure of 10 MPa and 180° C. for 300 s, and then cold-pressed at a pressure of 5 MPa for 60 s to form a PLA-based composite film material.

[0033] In Examples 2-5, only the amount of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane in step (1) was changed to 0.05, 0.1, 0.3, and 0.75 parts, and the other steps and material additions were the same as in Example 1 to obtain different PLA-based composite materials.

[0034] Example 6

[0035] A highly transparent and high barrier polylactic acid material composite material and a preparation method thereof, comprising the following steps:

[0036] (1) Add 0.1 parts of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane to 50 mL of acetone, pour the mixture into a mixture of 80 parts of PLA and 20 parts of PHBV, and then dry at 70° C. for 12 hours to completely evaporate the acetone to obtain a dried material;

[0037] (2) The dried material was added to a twin-screw extruder (LSHJ-20, Shanghai Kechuang Rubber & Plastic Machinery Equipment Co., Ltd.), the extrusion temperature was set to 180°C (from the feeding section to the die section), the feed rate was set to 1.5 rpm, the screw speed was set to 60 rpm, and the moisture content of the material during extrusion by the twin-screw extruder was less than 0.5 wt%. After cooling, the material was put into a pelletizer and cut into pellets;

[0038] (3) The pellets were dried at 60° C. for 8 h to reduce the moisture content of the material to less than 0.5 wt %, and then placed in a flat vulcanizer, hot-pressed at a pressure of 12 MPa and 185° C. for 280 s, and then cold-pressed at a pressure of 8 MPa for 120 s to form a PLA-based composite film material.

[0039] Example 7

[0040] A highly transparent and high barrier polylactic acid material composite material and a preparation method thereof, comprising the following steps:

[0041] (1) Add 0.75 parts of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane to 50 mL of acetone, pour the mixture into a mixture of 99 parts of PLA and 1 part of PHBV, and then dry at 80° C. for 10 hours to completely evaporate the acetone to obtain a dried material; in the embodiment, acetone needs to completely soak the solid, and if it is insufficient, continue to add, the same below;

[0042] (2) Add the dried material to a twin-screw extruder (LSHJ-20, Shanghai Kechuang Rubber and Plastic Machinery Co., Ltd.). Set the extrusion temperature to 190 °C (from the feeding section to the die section), the feeding speed to 1.5 rpm, and the screw speed to 40 rpm. When the twin-screw extruder extrudes, the moisture content of the material is lower than 0.5 wt%. After cooling, put it into a pelletizer and cut it into pellets;

[0043] (3) Bake the pellets at 60 °C for 8 h to make the moisture content of the material lower than 0.5 wt%. Then put them into a flat vulcanizing machine and hot-press them at a pressure of 15 MPa and 190 °C for 240 s, and then cold-press them at a pressure of 10 MPa for 80 s to press them into PLA-based composite film materials.

[0044] Comparative example

[0045] (1) Mix 90 parts of PLA and 10 parts of PHBV to obtain a mixed material, and then bake it at 60 °C for 8 h to completely volatilize acetone to obtain a dried material;

[0046] (2) Add the dried material to a twin-screw extruder (LSHJ-20, Shanghai Kechuang Rubber and Plastic Machinery Co., Ltd.). Set the extrusion temperature to 175 °C (from the feeding section to the die section), the feeding speed to 1.5 rpm, and the screw speed to 50 rpm. When the twin-screw extruder extrudes, the moisture content of the material is lower than 0.5 wt%. After cooling, put it into a pelletizer and cut it into pellets;

[0047] (3) Bake the pellets at 60 °C for 8 h to make the moisture content of the material lower than 0.5 wt%. Then put them into a flat vulcanizing machine and hot-press them at a pressure of 10 MPa and 180 °C for 300 s, and then cold-press them at a pressure of 5 MPa for 60 s to press them into PLA-based composite film materials.

[0048] As shown in Table 1 and Figure 1 The water vapor transmission coefficients of the samples are all reduced compared with those of the composite materials obtained in the comparative example, and the water vapor barrier performance is improved.

[0049] Table 1

[0050] Sample <![CDATA[WVP (g.mil / m 2 -day-kPa)]]> Comparative example 30.0±3.4 Example 1 19.5±1.5 Example 2 14.7±1.0 Example 3 8.6±0.6 Example 4 10.4±1.3 Example 5 8.9±1.2

[0051] As shown in Table 2 and Figure 2 The oxygen transmission rates of the composite materials obtained in the above examples and comparative examples are shown. The oxygen transmission rates of the composite materials are reduced compared with those before adding the compatibilizer (comparative example) and after adding the compatibilizer (Examples 1-5), and the oxygen barrier performance is improved.

[0052] Table 2

[0053]

[0054]

[0055] Figure 3 Optical photographs of the composites of the comparative example and Examples 1-5. Obviously, the transparency is significantly improved after adding the compatibilizer. Figure 4 Ultraviolet absorption spectra of the composites of the comparative example and Examples 1-5 and Figure 5 Transmittance graphs of the composites at 550 nm. The same conclusion can also be drawn from the transmittance graphs of Examples 1-5 at 550 nm, that is, the transmittance is improved.

[0056] Figure 6 SEM images of the composites obtained from the comparative example and Examples 1-5. Among them, (a) is the comparative example, (b) is Example 1, (c) is Example 2, (d) is Example 3, (e) is Example 4, (f) is Example 5. The macroscopic properties of the polylactic acid / PHBV blend are closely related to the phase morphology of the blend. The phase morphology includes the shape, size and compatibility of the dispersed phase. When the compatibility of the two polymers is poor, an inhomogeneous system will be formed after blending, and the dispersed phase is dispersed in the continuous phase to form a "sea-island" structure. In the figure, the PHBV phase is spherical and dispersed in the continuous phase of polylactic acid. The size of the PHBV phase is about 500 nm (see Figure 6 a); for the mixture with a higher PHBV content, the size of the material is larger and the distribution is wider. As shown in Figure (6a), the connection between PHBV and polylactic acid is not tight, and the cavities visible around the spherical domain are proof of this. This indicates that PHBV and polylactic acid form an obviously phase-separated two-phase system. With the addition of the compatibilizer, the size of the PHBV domain decreases, and the interface between the polylactic acid and PHBV phases becomes blurred, and a "bridging" effect is formed between the interfaces ( Figure 6 b-f). In addition, the morphology of the mixture also changes from the typical "sea-island" structure to a layered structure, thereby improving the compatibility between the two phases.

[0057] The above schematically describes the present invention and its implementation manners. This description is not restrictive and is only part of the implementation manners of the present invention. Therefore, if those of ordinary skill in the art are inspired by it and design similar embodiments to this technical solution without creative work without departing from the gist of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A highly transparent and high barrier polylactic acid-based composite material, characterized in that: The invention is prepared from the following components in parts by weight: 80-99 parts of PLA, 1-20 parts of PHBV and 0.03-0.75 parts of a compatibilizer.

2. The method for preparing the highly transparent and high barrier polylactic acid-based composite material according to claim 1, characterized in that: The specific steps are as follows: (1) adding a compatibilizer to acetone and mixing to obtain a mixed solution, mixing PLA and PHBV to obtain a mixed material, adding the mixed solution to the mixed material and mixing to obtain a mixture, and drying the mixture to obtain a dried material; (2) adding the dried material into a twin-screw extruder for extrusion molding, and after cooling, putting it into a pelletizer for cutting into pellets; (3) After drying the particles, hot pressing and cold pressing are performed to form a polylactic acid-based composite material.

3. The method for preparing the highly transparent and high barrier polylactic acid-based composite material according to claim 2, characterized in that: In step (1), the drying is carried out at 60-80° C. for 8-12 hours.

4. The method for preparing the highly transparent and high barrier polylactic acid-based composite material according to claim 2, characterized in that: The compatibilizer in step (1) includes but is not limited to 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane.

5. The method for preparing the highly transparent and high barrier polylactic acid-based composite material according to claim 2, characterized in that: In step (2), the moisture content of the material during extrusion by the twin-screw extruder is less than 0.5%.

6. The method for preparing the highly transparent and high barrier polylactic acid-based composite material according to claim 2, characterized in that: In step (2), the extrusion temperature of the twin-screw extruder is 175-190° C., the feed rate is 1.5, and the screw speed is 40-60 rpm.

7. The method for preparing the highly transparent and high barrier polylactic acid-based composite material according to claim 2, characterized in that: During the hot pressing in step (3), the moisture content of the material is less than 0.5%.

8. The method for preparing the highly transparent and high barrier polylactic acid-based composite material according to claim 2, characterized in that: The hot pressing conditions in step (3) are 10-15 MPa, 180-190° C. for 240-300 s; and the cold pressing conditions are 5-10 MPa for 60-120 s.

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