High-temperature-resistant modified polylactic resin and preparation method thereof

Abstract

The invention discloses high-temperature-resistant modified polylactic resin and a preparation method thereof, and belongs to the technical field of high polymer material synthesis. The high-temperature-resistant modified polylactic acid resin is prepared from the following components in parts by mass: 70 to 90 parts of modified polylactic acid and 30 to 40 parts of modified nano titanium dioxide. The polylactic acid is modified by carboxylating the polylactic acid, then the silicon dioxide is modified by tannic acid, and carboxyl on the modified polylactic acid and hydroxyl on the modified silicon dioxide form ester groups, so that the mechanical property and heat resistance of the polylactic resin are improved; in addition, silver ions have the antibacterial performance, and meanwhile the antibacterial performance of nano titanium dioxide is improved; a series of performance tests show that the high-temperature-resistant modified polylactic acid resin prepared by the preparation method has good heat resistance, mechanical strength and antibacterial performance, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material synthesis, and in particular relates to a high temperature resistant modified polylactic acid resin and a preparation method thereof. Background Art

[0002] Polylactic acid resin is a polymer material obtained by chemical synthesis or biosynthesis with lactic acid as the monomer. Its raw materials are mainly corn, potatoes, etc., which are cheap. At the same time, since its raw materials are natural crops, carbon emissions are very low. From the perspective of safety, polylactic acid is non-toxic and non-irritating, has excellent transparency and biodegradability, and is easily decomposed and metabolized by a variety of microorganisms or enzymes in plants and animals in nature, eventually forming carbon dioxide and water, thereby reducing white pollution to a certain extent. It is an ideal green polymer material; however, low toughness and low heat deformation temperature limit its application in more fields. At present, the main factors restricting the application and development of polylactic acid include: slow crystallization rate, low crystallinity, low heat deformation temperature, high brittleness and relatively high cost.

[0003] The patent application with publication number CN108752888 A discloses a heat-resistant polylactic acid composition and a preparation method thereof. The composition is composed of a polylactic acid resin and a starch composite, and the weight ratio of the starch composite to the polylactic acid resin is 1:99 to 50:50. The starch composite contains a starch graft copolymer and a nucleating agent; the weight ratio of the starch graft copolymer to the nucleating agent is 100:1 to 100. The raw materials are mixed in a series of ways and melt blended to obtain a polylactic acid composition. The polylactic acid composition prepared in this application is green and environmentally friendly, low in cost, and simple in process. However, as the application of polylactic acid becomes increasingly widespread and research develops in depth, heat resistance and material strength are indispensable to the material itself. Summary of the invention

[0004] The object of the present invention is to provide a high temperature resistant modified polylactic acid resin and a preparation method thereof, so as to improve the heat resistance of the polylactic acid resin.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A high temperature resistant modified polylactic acid resin comprises 70 to 90 parts of modified polylactic acid and 30 to 40 parts of modified nano titanium dioxide in parts by mass.

[0007] Furthermore, the modified polylactic acid is prepared by the following steps:

[0008] After the polylactic acid is melted, an antioxidant is added and mixed evenly, a carboxyl modifier is added and mixed evenly, and stirring is continued at 180° C. to 200° C. for a reaction time of 20 to 30 minutes to obtain modified polylactic acid.

[0009] Furthermore, the antioxidant is added in an amount of 0.5% to 1% of the mass of the polylactic acid; the antioxidant is a mixture of dilauryl thiodipropionate and butylated hydroxytoluene in a mass ratio of 1:1.

[0010] Furthermore, the mass ratio of the carboxyl modifier to the polylactic acid is 0.6-1.2:9-12; and the carboxyl modifier is one of pyromellitic acid, naphthalenetetracarboxylic acid and cyclopentanetetracarboxylic acid.

[0011] Furthermore, the modified nano titanium dioxide is prepared by the following steps:

[0012] Add nano titanium dioxide and silver nitrate into anhydrous ethanol, and disperse them by ultrasonic to obtain a dispersion; dissolve tannic acid in a 75% ethanol aqueous solution, and then slowly drop it into the dispersion, stir and react for 6 to 8 hours under an inert gas atmosphere at 50 to 55° C., wash and dry to obtain modified nano titanium dioxide.

[0013] Furthermore, the mass ratio of the nano titanium dioxide, silver nitrate and tannic acid is 2.5-3:0.3-0.4:0.2-0.3.

[0014] A method for preparing a high temperature resistant modified polylactic acid resin comprises the following steps:

[0015] The modified polylactic acid and modified nano titanium dioxide are premixed uniformly, extruded and granulated to obtain high temperature resistant modified polylactic acid resin.

[0016] Furthermore, the temperature settings of each section of the extrusion granulation from the feed port to the discharge port are 165°C, 185°C, 205°C, 220°C, 190°C, and 170°C respectively.

[0017] Beneficial effects of the present invention:

[0018] (1) The modified polylactic acid used in the present invention forms an ester group with the hydroxyl group of tannic acid on the modified nano-titanium dioxide, thereby enhancing the binding force between the modified polylactic acid and the modified nano-titanium dioxide. At the same time, the rigid group contained in the carboxyl modifier also enhances the strength and heat resistance of the resin.

[0019] (2) The nano titanium dioxide used in the present invention can enhance the mechanical properties and heat resistance of the resin. After being modified with tannic acid, the phenolic hydroxyl groups on the tannic acid can react with the hydroxyl groups on the surface of the nano titanium dioxide to form hydrogen bonds and covalent bonds through intermolecular dehydration, effectively reducing the aggregation of nanoparticles. Silver can synergistically improve the antibacterial properties of the nano titanium dioxide while playing an antibacterial role. In addition, the antioxidants dilauryl thiodipropionate and butylated hydroxytoluene used in the present invention have a synergistic effect, which can not only improve the antioxidant properties, but also improve the thermal stability of polylactic acid. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Example 1

[0022] This embodiment provides a high temperature resistant modified polylactic acid resin, which is prepared by the following steps:

[0023] S1. After 90 g of polylactic acid is melted, 0.9 g of dilauryl thiodipropionate and butylated hydroxytoluene in a mass ratio of 1:1 are added and mixed evenly, and 9 g of pyromellitic acid is added and mixed evenly, and stirring is continued at 180° C. to 200° C. for a reaction time of 20 to 30 min to obtain modified polylactic acid;

[0024] S2, adding 3g of nano titanium dioxide and 0.4g of silver nitrate to 30mL of anhydrous ethanol, and dispersing by ultrasonication to obtain a dispersion; dissolving 0.3g of tannic acid in 30mL of 75% ethanol aqueous solution, and then slowly dropping it into the dispersion, stirring and reacting for 6h under an inert gas atmosphere at 55°C, washing and drying to obtain modified nano titanium dioxide;

[0025] S3. 70 parts of modified polylactic acid and 30 parts of modified nano titanium dioxide are put into a twin-screw extruder for uniform premixing. The temperatures from the feed port to the discharge port of the twin-screw extruder are 165°C, 185°C, 205°C, 220°C, 190°C and 170°C respectively. Extrusion granulation is performed to obtain high temperature resistant modified polylactic acid resin.

[0026] Example 2

[0027] The difference between this embodiment and embodiment 1 is that "70 parts of modified polylactic acid and 30 parts of modified nano titanium dioxide" in S3 is changed to "90 parts of modified polylactic acid and 30 parts of modified nano titanium dioxide".

[0028] The remaining raw materials and preparation process remain the same as in Example 1.

[0029] Example 3

[0030] The difference between this embodiment and embodiment 1 is that "70 parts of modified polylactic acid and 30 parts of modified nano titanium dioxide" in S3 is changed to "70 parts of modified polylactic acid and 40 parts of modified nano titanium dioxide".

[0031] The remaining raw materials and preparation process remain the same as in Example 1.

[0032] Example 4

[0033] The present embodiment is different from the embodiment 1 in that the “0.9 g of dilauryl thiodipropionate and butylated hydroxytoluene in a mass ratio of 1:1” in S1 is changed to “0.5 g of dilauryl thiodipropionate and butylated hydroxytoluene in a mass ratio of 1:1”.

[0034] The remaining raw materials and preparation process remain the same as in Example 1.

[0035] Example 5

[0036] Compared with Example 1, the difference between this example and Example 1 is that "9 g of pyromellitic acid" in S1 is changed to "12 g of pyromellitic acid".

[0037] The remaining raw materials and preparation process remain the same as in Example 1.

[0038] Example 6

[0039] Compared with Example 1, the difference between this example and Example 1 is that "90 g polylactic acid" in S1 is changed to "120 g polylactic acid";

[0040] The remaining raw materials and preparation process remain the same as in Example 1.

[0041] Example 7

[0042] The present embodiment is different from the embodiment 1 in that "9 g of pyromellitic acid" in S1 is changed to "8.7 g of cyclopentanetetracarboxylic acid".

[0043] The remaining raw materials and preparation process remain the same as in Example 1.

[0044] Example 8

[0045] The present embodiment is different from the embodiment 1 in that "0.3 g tannic acid" in S2 is changed to "0.2 g tannic acid".

[0046] The remaining raw materials and preparation process remain the same as in Example 1.

[0047] Comparative Example 1

[0048] Compared with Example 1, this comparative example is different in that no antioxidant is added in S1, and the specific implementation steps are as follows:

[0049] S1. After 90 g of polylactic acid is melted, 9 g of pyromellitic acid is added and mixed evenly, and stirring is continued at 180° C. to 200° C. for 20 to 30 min to obtain modified polylactic acid;

[0050] The remaining raw materials and preparation process remain the same as in Example 1.

[0051] Comparative Example 2

[0052] Compared with Example 1, this comparative example differs in that butylated hydroxytoluene is not added to S1, and the specific implementation steps are as follows:

[0053] S1. After 90 g of polylactic acid is melted, 0.9 g of dilauryl thiodipropionate is added and mixed evenly, and 9 g of pyromellitic acid is added and mixed evenly, and stirring is continued at 180° C. to 200° C. for 20 to 30 min to obtain modified polylactic acid;

[0054] Comparative Example 3

[0055] Compared with Example 1, this comparative example differs in that pyromellitic acid is not added to S1, and the specific implementation steps are as follows:

[0056] S1. After 90 g of polylactic acid is melted, 0.9 g of dilauryl thiodipropionate and butylated hydroxytoluene in a mass ratio of 1:1 are added and mixed evenly, and stirring is continued at 180° C. to 200° C. for a reaction time of 20 to 30 min to obtain modified polylactic acid;

[0057] The remaining raw materials and preparation process remain the same as in Example 1.

[0058] Comparative Example 4

[0059] The present embodiment is different from the embodiment 1 in that "9 g of pyromellitic acid" in S1 is changed to "8.3 g of butanetetracarboxylic acid".

[0060] The remaining raw materials and preparation process remain the same as in Example 1.

[0061] Comparative Example 5

[0062] Compared with Example 1, the difference between this comparative example is that no silver ions are added to S2, and the specific implementation steps are as follows:

[0063] S2, adding 3g of nano titanium dioxide into 30mL of anhydrous ethanol, ultrasonically dispersing, and obtaining a dispersion; dissolving 0.3g of tannic acid in 30mL of 75% ethanol aqueous solution, and then slowly dropping it into the dispersion, stirring and reacting for 6h under an inert gas atmosphere at 55°C, washing and drying, and obtaining modified nano titanium dioxide;

[0064] The remaining raw materials and preparation process remain the same as in Example 1.

[0065] Comparative Example 6

[0066] Compared with Example 1, this comparative example differs in that no tannic acid is added to S2, and the specific implementation steps are as follows:

[0067] S2, adding 3g of nano titanium dioxide and 0.4g of silver nitrate to 30mL of anhydrous ethanol, and dispersing by ultrasonication to obtain a dispersion; stirring and reacting for 6h under an inert gas atmosphere at 55°C, washing and drying to obtain modified nano titanium dioxide;

[0068] The remaining raw materials and preparation process remain the same as in Example 1.

[0069] Comparative Example 7

[0070] Compared with Example 1, the difference between this comparative example and Example 1 is that the nano titanium dioxide is not modified. The specific implementation steps are as follows:

[0071] S1. After 90 g of polylactic acid is melted, 0.9 g of dilauryl thiodipropionate and butylated hydroxytoluene in a mass ratio of 1:1 are added and mixed evenly, and 9 g of pyromellitic acid is added and mixed evenly, and stirring is continued at 180° C. to 200° C. for a reaction time of 20 to 30 min to obtain modified polylactic acid;

[0072] S2. 70 parts of modified polylactic acid and 30 parts of nano-titanium dioxide are put into a twin-screw extruder for premixing. The temperatures from the feed port to the discharge port of the twin-screw extruder are 165°C, 185°C, 205°C, 220°C, 190°C and 170°C respectively. Extrusion granulation is performed to obtain high temperature resistant modified polylactic acid resin.

[0073] The remaining raw materials and preparation process remain the same as in Example 1.

[0074] Comparative Example 8

[0075] Compared with Example 1, the difference between this comparative example is that neither polylactic acid nor nano-titanium dioxide is subjected to modification treatment. The specific implementation steps are as follows:

[0076] 70 parts of polylactic acid and 30 parts of nano-titanium dioxide were put into a twin-screw extruder for uniform premixing. The temperatures from the feed port to the discharge port of the twin-screw extruder were 165°C, 185°C, 205°C, 220°C, 190°C and 170°C, respectively. Extrusion granulation was performed to obtain high temperature resistant modified polylactic acid resin.

[0077] The remaining raw materials and preparation process remain the same as in Example 1.

[0078] The high temperature resistant modified polylactic acid resins prepared in Examples 1 to 8 and Comparative Examples 1 to 8 were subjected to plate forming, and were made into specimens (temperature of 190° C., pressure of 20 MPa), and then performance tests were performed. The heat deformation temperature of the high temperature resistant modified polylactic acid resin was tested according to the method in ASTM D648-07; the tensile strength of the high temperature resistant modified polylactic acid resin was tested according to the method in ASTM D-638-2014; the impact strength of the high temperature resistant modified polylactic acid resin was tested according to the method in ASTM D-256-2010A; the antibacterial performance of the high temperature resistant modified polylactic acid resin was tested (Staphylococcus aureus) according to the method in GB / T 31402-2023;

[0079] The results are shown in Table 1:

[0080] Table 1

[0081]

[0082]

[0083] It can be seen from Table 1 that the high temperature resistant modified polylactic acid resin prepared in Example 1 has good heat resistance, mechanical strength and antibacterial properties; Examples 2 to 8 all make corresponding changes and replacements to the raw materials and proportions within a reasonable range. From the results, there is no significant effect on its heat resistance, mechanical strength and antibacterial properties.

[0084] It can be seen from the comparative examples that, compared with Example 1, Comparative Examples 1 to 2 and Example 4 mainly explore the effect of antioxidants on polylactic acid resin. The results show that antioxidants can not only improve the antioxidant performance, but also improve the thermal stability of polylactic acid. In addition, the antioxidants dilauryl thiodipropionate and butylated hydroxytoluene have a certain synergistic effect; Compared with Example 1, in Comparative Example 3, after not adding pyromellitic acid, the binding force between modified titanium dioxide and polylactic acid decreases, resulting in reduced mechanical properties and heat resistance; Compared with Example 1, the difference between Comparative Example 4 and Example 1 is that the groups of the carboxyl modifier are different, and the rigid groups (such as phenyl) contained in the modifier can enhance the resin strength and heat resistance, which is the reason why the mechanical strength of the resin in Example 1 is higher than that in Comparative Example 4; Comparative Examples 5 to 7, taken together, reflect the interaction between nano-silicon dioxide, silver ions and tannic acid. Compared with Example 1, in Comparative Examples 5 to 7, silver ions not only play an antibacterial role, but also improve the photocatalytic performance of nano-titanium dioxide, further improve the antibacterial property, and make the high-temperature resistant modified polylactic acid resin have good antibacterial properties; Compared with Example 1, in Comparative Examples 6 to 7, after not adding tannic acid, not only the binding force between nano-titanium dioxide and polylactic acid resin is reduced, but also nano-titanium dioxide is more likely to agglomerate, and the mechanical properties of polylactic acid resin are further reduced.

[0085] In summary, the present invention provides a high temperature resistant modified polylactic acid resin and a preparation method thereof. The prepared high temperature resistant modified polylactic acid resin has good heat resistance, mechanical strength and antibacterial properties, and has good application prospects.

[0086] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0087] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high temperature resistant modified polylactic acid resin, characterized in that: The high temperature resistant modified polylactic acid resin comprises 70 to 90 parts of modified polylactic acid and 30 to 40 parts of modified nano titanium dioxide in parts by mass.

2. The high temperature resistant modified polylactic acid resin according to claim 1, characterized in that: The modified polylactic acid is prepared by the following steps: After the polylactic acid is melted, an antioxidant is added and mixed evenly, a carboxyl modifier is added and mixed evenly, and stirring is continued at 180° C. to 200° C. for a reaction time of 20 to 30 minutes to obtain modified polylactic acid.

3. The high temperature resistant modified polylactic acid resin according to claim 2, characterized in that: The added amount of the antioxidant is 0.5% to 1% of the mass of the polylactic acid; the antioxidant is a mixture of dilauryl thiodipropionate and butylated hydroxytoluene in a mass ratio of 1:

1.

4. The high temperature resistant modified polylactic acid resin according to claim 2, characterized in that: The mass ratio of the carboxyl modifier to the polylactic acid is 0.6-1.2:9-12; the carboxyl modifier is one of pyromellitic acid, naphthalenetetracarboxylic acid and cyclopentanetetracarboxylic acid.

5. The high temperature resistant modified polylactic acid resin according to claim 1, characterized in that: The modified nano titanium dioxide is prepared by the following steps: Add nano titanium dioxide and silver nitrate into anhydrous ethanol, and disperse them by ultrasonic to obtain a dispersion; dissolve tannic acid in a 75% ethanol aqueous solution, and then slowly add it dropwise into the dispersion, stir and react for 6 to 8 hours under an inert gas atmosphere at 50 to 55° C., wash and dry to obtain modified nano titanium dioxide.

6. The high temperature resistant modified polylactic acid resin according to claim 5, characterized in that: Furthermore, the mass ratio of the nano titanium dioxide, silver nitrate and tannic acid is 2.5-3:0.3-0.4:0.2-0.

3.

7. A method for preparing a high temperature resistant modified polylactic acid resin according to any one of claims 1 to 6, characterized in that: The following steps are involved: The modified polylactic acid and modified nano titanium dioxide are premixed uniformly, extruded and granulated to obtain high temperature resistant modified polylactic acid resin.

8. The method for preparing a high temperature resistant modified polylactic acid resin according to claim 7, characterized in that: The temperature settings of each section of the extrusion granulation from the feed port to the discharge port are 165° C., 185° C., 205° C., 220° C., 190° C., and 170° C. respectively.

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