A bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material and its preparation method

Abstract

The present invention provides a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material and a preparation method thereof, and belongs to the technical field of polylactic acid composite materials. The present invention uses natural polyphenol compounds as a modifier to modify calcium carbonate, and then premixes the modified calcium carbonate with polylactic acid and melt-blends them, and then hot-presses them to obtain a toughened, strong antioxidant and antibacterial polylactic acid composite material. The present invention utilizes the structural characteristics and functional characteristics of polyphenol compounds, and through a simple preparation process, obtains a green and environmentally friendly fully degradable polylactic acid composite material with good antioxidant and antibacterial properties, good mechanical properties, and can be completely degraded.

Description

Technical Field

[0001] The invention relates to the technical field of polylactic acid composite materials, and in particular to a bio-environmentally friendly toughened, highly antioxidant and antibacterial polylactic acid composite material and a preparation method thereof. Background Art

[0002] With the development of economy and society, traditional petroleum-based materials have rapidly occupied an important position in various fields of life and production with their advantages of low price, excellent performance and diverse functions. However, the non-degradability of these traditional polymer materials has brought great convenience to people while also bringing great environmental protection burden. Therefore, the development of new, green, safe and environmentally friendly biodegradable materials has become a hot issue in the current research field of materials. Polylactic acid (PLA) is a thermoplastic aliphatic polyester material made from natural plants such as corn, wheat, and cassava through fermentation polymerization. Polylactic acid products can be completely degraded into carbon dioxide and water by microorganisms in nature under certain conditions. It is a new type of biodegradable material and a recognized environmentally friendly thermoplastic material. Polylactic acid materials are widely used in textiles, food packaging, agricultural mulch and daily necessities due to their biodegradability, renewability, good biocompatibility, easy processing and good transparency, and have great market application prospects. However, its poor mechanical properties and high production costs have limited its large-scale application to a certain extent. At present, adding cheap and readily available inorganic non-metallic powders such as calcium carbonate, barium sulfate, talcum powder, etc. to modify it is a good way to enhance its mechanical properties and reduce its production cost. These methods have solved the problems of poor toughness and high production cost to a certain extent, and expanded its application in the fields of plastics, fabrics and film products. However, for the field of food packaging with antioxidant and antibacterial requirements, the polylactic acid material obtained by this modification still has relatively large limitations. In order to solve this problem, it is urgent to invent a method for a polylactic acid composite material having both good mechanical properties and antioxidant and antibacterial activity to expand the application of polylactic acid materials in the field of food packaging. Summary of the invention

[0003] The purpose of the present invention is to provide a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material and a preparation method thereof, so as to solve the technical problem that conventional polylactic acid materials cannot meet the requirements of antioxidant and antibacterial properties when used in the field of food packaging.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material, comprising the following steps:

[0006] 1) adding natural polyphenol compounds to calcium carbonate for mixed modification to obtain modified calcium carbonate;

[0007] 2) Mixing the modified calcium carbonate and polylactic acid, and then performing melt blending and hot pressing to obtain a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material;

[0008] The polyphenolic compounds include one or more of gallic acid, chlorogenic acid and baicalin.

[0009] Furthermore, the amount of the natural polyphenol compound added is 0.5-5% of the mass of calcium carbonate.

[0010] Furthermore, the particle size of the calcium carbonate is 2000-4000 mesh.

[0011] Furthermore, in the step 1), the temperature of the mixing and modification treatment is 300 to 350° C., and the time of the mixing and modification treatment is 30 to 50 minutes.

[0012] Furthermore, the added amount of the modified calcium carbonate is 10-50% of the mass of the polylactic acid.

[0013] Furthermore, the content of poly-L-lactic acid in the polylactic acid is not less than 98%.

[0014] Furthermore, the melt blending temperature is 140 to 180° C., and the melt blending time is 10 to 30 minutes.

[0015] Furthermore, the temperature of the hot pressing molding is 150-170° C., and the pressure of the hot pressing molding is 8-15 MPa.

[0016] The invention also provides a bio-environmentally friendly toughened, highly antioxidant and antibacterial polylactic acid composite material.

[0017] Beneficial effects of the present invention:

[0018] The present invention utilizes a natural polyphenol compound containing both a phenolic hydroxyl group and a carboxyl functional group in the structure as a modifier, and adsorbs the carboxyl group on the surface of calcium carbonate particles to reduce the hydrophilicity of calcium carbonate and improve its hydrophobicity, thereby improving the compatibility of calcium carbonate powder and polylactic acid when blended with polylactic acid, and improving the mechanical properties of polylactic acid materials. Meanwhile, the polyphenol structure introduced by the natural polyphenol compound modified calcium carbonate can make the composite material have good antioxidant and antibacterial properties. The polylactic acid composite material prepared by this method can be widely used in the field of food packaging, such as preservative film, food bags, lunch boxes, etc., and has a broad market prospect.

[0019] The present invention utilizes the structural properties of natural polyphenol compounds having both phenolic hydroxyl and carboxyl groups, and through the modified calcium carbonate powder and blending with polylactic acid, the polylactic acid and calcium carbonate powder are more compatible, the production cost is reduced, the mechanical properties of the composite material are improved, and the composite material has good antioxidant and antibacterial properties. At the same time, the polyphenol compounds are natural medicinal active ingredients, non-toxic and harmless, and can be completely degraded together with polylactic acid, with zero pollution. The present invention utilizes the structural characteristics and functional characteristics of the polyphenol compounds, and through a simple preparation process, obtains a polylactic acid composite material with good antioxidant and antibacterial properties, good mechanical properties, and green and environmentally friendly and completely degradable. DETAILED DESCRIPTION

[0020] The present invention provides a method for preparing a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material, comprising the following steps:

[0021] 1) adding natural polyphenol compounds to calcium carbonate for mixed modification to obtain modified calcium carbonate;

[0022] 2) Mixing the modified calcium carbonate and polylactic acid, and then performing melt blending and hot pressing to obtain a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material;

[0023] The polyphenolic compounds include one or more of gallic acid, chlorogenic acid and baicalin.

[0024] In the present invention, the polyphenol compound is preferably gallic acid and / or chlorogenic acid, preferably gallic acid.

[0025] In the present invention, the polyphenol compounds are all active ingredients of natural medicinal materials, are non-toxic and harmless, have the structure of polyphenols, and have antioxidant and antibacterial properties.

[0026] In the present invention, the calcium carbonate is dried at 80° C. for 4 hours before mixing to eliminate moisture therein.

[0027] In the present invention, the amount of the natural polyphenol compound added is 0.5-5% of the mass of calcium carbonate, preferably 1-4%, and more preferably 2-3%.

[0028] In the present invention, the particle size of the calcium carbonate is 2000-4000 mesh, preferably 2500-3500 mesh, and more preferably 3000 mesh.

[0029] In the present invention, in step 1), the temperature of the mixing and modification treatment is 300-350° C., preferably 310-340° C., preferably 330° C.; the time of the mixing and modification treatment is 30-50 min, preferably 40 min.

[0030] In the present invention, the added amount of the modified calcium carbonate is 10-50% of the mass of the polylactic acid, preferably 20-40%, and more preferably 30%.

[0031] In the present invention, the content of poly-L-lactic acid in the polylactic acid is preferably not less than 98%.

[0032] In the present invention, the melt blending temperature is 140-180° C., preferably 150-170° C., and more preferably 160° C.; the melt blending time is 10-30 min, preferably 15-25 min, and more preferably 20 min.

[0033] In the present invention, the temperature of the hot pressing molding is 150-170° C., preferably 160° C.; the pressure of the hot pressing molding is 8-15 MPa, preferably 10-12 MPa.

[0034] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0035] Example 1

[0036] 2800 mesh calcium carbonate was dried at 80°C for 4 hours to eliminate the moisture therein. A certain amount of calcium carbonate was added to a high-speed mixer, stirred at 300°C for 10 minutes, and then 1% gallic acid was added, and stirring was continued for 30 minutes to obtain calcium carbonate modified by natural polyphenol compounds; the obtained modified calcium carbonate was premixed with polylactic acid, the amount of modified calcium carbonate added was 20% of the mass of polylactic acid, and added to a double-roll mill for melt blending, the melt blending temperature was 150°C, the time was 20 minutes, and a blended product was obtained; the obtained blended product was hot-pressed at 160°C and 10MPa to obtain a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material.

[0037] Example 2

[0038] 2800 mesh calcium carbonate was dried at 80°C for 4 hours to eliminate the moisture therein. A certain amount of calcium carbonate was added to a high-speed mixer, stirred at 300°C for 10 minutes, and then 2% chlorogenic acid was added, and stirring was continued for 30 minutes to obtain calcium carbonate modified by natural polyphenol compounds; the obtained modified calcium carbonate was premixed with polylactic acid, the amount of modified calcium carbonate added was 30% of the mass of polylactic acid, and added to a double-roll mill for melt blending, the melt blending temperature was 150°C, the time was 20 minutes, and a blended product was obtained; the obtained blended product was hot-pressed at 170°C and 8MPa to obtain a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material.

[0039] Example 3

[0040] 2800 mesh calcium carbonate was dried at 80°C for 4 hours to eliminate the moisture therein. A certain amount of calcium carbonate was added to a high-speed mixer, stirred at 300°C for 10 minutes, and then 3% baicalin was added, and stirring was continued for 30 minutes to obtain calcium carbonate modified by natural polyphenol compounds; the obtained modified calcium carbonate was premixed with polylactic acid, the amount of modified calcium carbonate added was 40% of the mass of polylactic acid, and added to a double-roll mill for melt blending, the melt blending temperature was 150°C, the time was 20 minutes, and a blended product was obtained; the obtained blended product was hot-pressed at 150°C and 15MPa to obtain a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material.

[0041] Example 4

[0042] 2800 mesh calcium carbonate was dried at 80°C for 4 hours to eliminate the moisture therein. A certain amount of calcium carbonate was added to a high-speed mixer, stirred at 300°C for 10 minutes, and then 5% gallic acid was added, and stirring was continued for 30 minutes to obtain calcium carbonate modified by natural polyphenol compounds; the obtained modified calcium carbonate was premixed with polylactic acid, the amount of modified calcium carbonate added was 20% of the mass of polylactic acid, and added to a double-roll mill for melt blending, the melt blending temperature was 150°C, the time was 20 minutes, and a blended product was obtained; the obtained blended product was hot-pressed at 160°C and 15MPa to obtain a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material.

[0043] The performance tests of the bio-environmentally friendly toughened, antioxidant and antibacterial polylactic acid composite materials obtained in Examples 1 to 4 were respectively carried out:

[0044] (1) Mechanical properties test: The tensile strength and elongation at break of the obtained composite material were tested according to GB / T1040.3-2006 standard, and the tensile speed was 50 mm / min±10%; the impact strength was measured on a tensile testing machine according to ASTM D638 standard.

[0045] (2) Antioxidant performance test: The antioxidant performance of the obtained composite material was characterized and measured by DPPH free radical scavenging rate.

[0046] (3) Antibacterial property test: The antibacterial property of the obtained composite material was determined according to the standard GB / T20944.1-2007 by evaluating the in vitro antibacterial activity of E. coli by the agar diffusion method.

[0047] The test results are shown in Table 1:

[0048] Table 1 Mechanical properties and antioxidant and antibacterial properties of composite materials

[0049]

[0050] It can be seen from the above embodiments that the present invention provides a bio-environmentally friendly toughened strong antioxidant and antibacterial polylactic acid composite material and a preparation method thereof. The free radical scavenging rate represents the antioxidant performance of the material, and the larger the value, the better the antioxidant performance of the material. From the results of the above performance test, compared with the pure PLA material, although the addition of modified calcium carbonate powder will cause a certain decrease in the tensile strength of the composite materials obtained in Examples 1-4, the change is not large. However, the elongation at break and the impact strength of the composite material are significantly improved, indicating that the toughness of the composite material is significantly enhanced; at the same time, the free radical scavenging rate and antibacterial rate of the composite material are significantly improved, indicating that the composite material has good antioxidant and antibacterial properties, and it can be found from Examples 1 to 4 that with the increase of the content of polyphenol compounds in the composite material system, its antioxidant and antibacterial values ​​are significantly increased, which is consistent with the strong antioxidant and antibacterial properties of the polyphenol compounds themselves. Therefore, combined with the above test data, it can be obtained that adding natural polyphenol compound modified calcium carbonate to polylactic acid can obtain a type of composite material with toughened strong antioxidant and antibacterial properties.

[0051] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a bio-environmentally friendly toughened, antioxidant and antibacterial polylactic acid composite material. It is characterized in that The following steps are involved: 1) adding natural polyphenol compounds to calcium carbonate for mixed modification to obtain modified calcium carbonate; 2) Mixing the modified calcium carbonate and polylactic acid, and then performing melt blending and hot pressing to obtain a bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material; The polyphenolic compounds include one or more of gallic acid, chlorogenic acid and baicalin; The amount of the natural polyphenol compound added is 0.5-5% of the mass of calcium carbonate; The temperature of the melt blending is 140-180° C., and the time of the melt blending is 10-30 minutes.

2. The preparation method of the bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material according to claim 1, It is characterized in that The particle size of the calcium carbonate is 2000-4000 meshes.

3. The method for preparing the bio-environmentally friendly toughened, strong antioxidant and antibacterial polylactic acid composite material according to claim 1 or 2, It is characterized in that In the step 1), the temperature of the mixing and modifying treatment is 300 to 350° C., and the time of the mixing and modifying treatment is 30 to 50 minutes.

4. The method for preparing the bio-environmentally friendly toughened, antioxidant and antibacterial polylactic acid composite material according to claim 3, It is characterized in that The added amount of the modified calcium carbonate is 10-50% of the mass of the polylactic acid.

5. The method for preparing the bio-environmentally friendly toughened, antioxidant and antibacterial polylactic acid composite material according to claim 1, 2 or 4, It is characterized in that The content of poly-L-lactic acid in the polylactic acid is not less than 98%.

6. The method for preparing the bio-environmentally friendly toughened, antioxidant and antibacterial polylactic acid composite material according to claim 5, It is characterized in that The temperature of the hot pressing molding is 150-170° C., and the pressure of the hot pressing molding is 8-15 MPa.

7. The bio-environmentally friendly toughened, antioxidant and antibacterial polylactic acid composite material obtained by the preparation method according to any one of claims 1 to 6.

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