Preparation method and application of modified polylactic acid

Abstract

The invention relates to the technical field of high polymer material preparation, and discloses a preparation method and application of modified polylactic acid.The preparation method comprises the steps that alpha-eleostearic acid is dissolved in dichloromethane, thionyl chloride is added to prepare alpha-eleostearic acid acyl chloride, ammonia gas is introduced for a reaction, and alpha-eleostearic acid amide is obtained; the preparation method comprises the following steps: adding alpha-eleostearic acid amide into dichloromethane, adding diethyl oxalate and ethanolamine, and reacting at 30-50 DEG C for 12-24 hours to obtain a compound A; the preparation method comprises the following steps: adding a compound A and lactide into toluene, adding a catalyst A, and reacting at 120-150 DEG C for 6-12 hours to obtain modified polylactic acid; and heating the modified polylactic acid, polylactic acid and triglycidyl isocyanurate to 60-80 DEG C, drying for 10-20 minutes, adding an antioxidant, and banburying to obtain the polylactic resin. The polylactic acid resin obtained by the invention has relatively high mechanical property, heat resistance and antibacterial activity, and the tensile strength, the elongation at break, the thermal deformation temperature and the antibacterial rate of the polylactic acid resin are improved.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material preparation, and in particular to a preparation method and application of modified polylactic acid. Background Art

[0002] Polylactic acid (PLA), as a sustainable bio-based polymer, has been widely used in food packaging, medical devices, agricultural films, consumer electronics, sanitary products and other fields due to its advantages such as good biocompatibility, environmental friendliness, high strength (50~70MPa), and high stiffness (elastic modulus of about 3~4GPa). However, its inherent brittleness and poor ductility limit its wide application in industrial and medical fields. How to improve the toughness of PLA through toughening modification while maintaining its sustainability and biodegradability is a hot topic in current research.

[0003] The invention patent with publication number CN101333332A discloses a polylactic acid resin toughened and modified by an acrylic copolymer and a preparation method. The resin is made of polylactic acid resin, a toughening agent acrylic copolymer, and an antioxidant B215, which are dried in an oven at 60°C, and then mixed and blended on a rubber-plastic mixer at 180°C, 40 rpm, and 5 minutes to obtain a product. The obtained product can be used to prepare films, plates, sheets, foamed and injection-molded plastic parts. Although the impact strength, tensile strength, and elongation at break of the resin are improved, the polylactic acid resin is still toughened and modified with petrochemical products as the main raw materials, and is not environmentally friendly. Therefore, it is very important to develop environmentally friendly modified polylactic acid materials. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the shortcoming of poor toughness of the polylactic acid material in the prior art, thereby providing a preparation method and application of modified polylactic acid, using natural products as the main raw materials to obtain modified polylactic acid, and further obtaining polylactic acid resin, and the obtained polylactic acid resin has improved mechanical properties, heat resistance and antibacterial properties.

[0005] In order to solve the above technical problems, the present invention provides a method for preparing modified polylactic acid, comprising the following steps: (1) dissolving α-eleostearic acid in dichloromethane, adding thionyl chloride to prepare α-eleostearic acid chloride, and introducing ammonia gas to react to obtain α-eleostearic acid amide; (2) Add α-eleostearic acid amide to dichloromethane, add diethyl oxalate and ethanolamine, and react at 30-50°C for 12-24 hours to obtain compound A; (3) Compound A and lactide are added to toluene, catalyst A is added, and the mixture is reacted at 120-150° C. for 6-12 hours to obtain modified polylactic acid; The catalyst A is at least one of stannous octoate, tetrabutyl titanate or DMAP; The mass ratio of the compound A, lactide and catalyst A is 5-10:200:0.05-0.1; The structural formula of the compound A is: .

[0006] Preferably, the molar ratio of α-eleostearic acid to thionyl chloride is 1:1-1:3, the reaction temperature of α-eleostearic acid and thionyl chloride is 0-20° C., and the reaction time is 4-10 h.

[0007] Preferably, the mass ratio of α-eleostearic acid amide, diethyl oxalate and ethanolamine is 28:12-18:5-7.

[0008] The present invention also provides a method for preparing modified polylactic acid and application of the prepared modified polylactic acid in preparing polylactic acid resin, comprising the following steps: The modified polylactic acid, polylactic acid and triglycidyl isocyanurate are heated to 60-80°C and dried for 10-20 minutes, and then an antioxidant is added and mixed to obtain polylactic acid resin.

[0009] Preferably, the antioxidant is a composite antioxidant of antioxidant 1010 and antioxidant 168, and the mass ratio of the antioxidant 1010 to the antioxidant 168 is 1:1 to 1:3.

[0010] Preferably, the mass ratio of the modified polylactic acid, polylactic acid, triglycidyl isocyanurate and antioxidant is 20-40:40-80:5-10:0.1-0.5.

[0011] Preferably, the banburying temperature is 180-200° C., the time is 10-15 min, and the rotation speed is 40-60 rpm.

[0012] The technical solution of the present invention has the following advantages: 1. The preparation method of modified polylactic acid provided by the present invention uses α-eleostearic acid, a derivative of a natural product, as a raw material to prepare a modified polylactic acid compound, and further obtains modified polylactic acid and modified polylactic acid resin. The preparation method is simple, the main raw materials come from natural products, are degradable, are environmentally friendly, and are suitable for industrial production; 2. The application of the modified polylactic acid provided by the present invention in the preparation of polylactic acid resin, the obtained polylactic acid resin has high mechanical properties and heat resistance, and its tensile strength, elongation at break, and heat deformation temperature are improved, because the addition of modified polylactic acid and triglycidyl isocyanurate further improves the degree of crosslinking in the polylactic acid resin, and the conjugated double bonds of α-eleostearic acid further enhance the network structure of the polymer. The polylactic acid resin of the present invention has a high antibacterial rate against Staphylococcus aureus and Escherichia coli, and has a high mildew resistance grade, and can be used as an antibacterial resin material, because the amide groups in the modified polylactic acid and triglycidyl isocyanurate can effectively inhibit the growth of bacterial colonies. DETAILED DESCRIPTION

[0013] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0014] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0015] The resin was injection molded to obtain a specimen, and the heat deformation temperature of the specimen was tested according to the national standard GB / T 1634.2-2004, and the tensile strength and elongation at break of the specimen were tested according to the national standard GB / T 1040.2-2006.

[0016] The antibacterial performance of the resin was tested according to QB / T2591-2003.

[0017] Degradation performance test: Soil burial degradation performance test in natural environment, the samples were cut into 4mm×4mm×1mm samples, dried in a vacuum oven at 40℃ to constant weight, the initial mass m0 of the samples was weighed and recorded, the samples were wrapped with a single layer of gauze, marked with numbers, and buried in the soil about 30cm deep in the natural environment. The samples were taken out after 60 days, and the surface of the samples were rinsed with tap water, 75% (volume fraction) ethanol, and distilled water in turn, and then dried in a vacuum oven at 40℃ to constant weight, and the mass m of the sample after degradation was recorded. The sample degradation mass loss rate = [(m0-m) / m0]*100%.

[0018] Example 1 A method for preparing modified polylactic acid comprises the following steps: (1) Dissolve 56 g of α-eleostearic acid in 400 ml of dichloromethane, add 30 g of thionyl chloride at 0°C, react at 10°C for 4 h, and obtain α-eleostearic acid chloride by rotary evaporation; add α-eleostearic acid chloride to 300 mL of tetrahydrofuran, introduce ammonia gas at room temperature until the pH value at the mouth of the reaction bottle is alkaline as measured by pH test paper, and then react at 10°C for 6 h, and obtain α-eleostearic acid amide by rotary evaporation; (2) Add 28 g of α-eleostearic acid amide to 200 ml of dichloromethane, add 15 g of diethyl oxalate and 6 g of ethanolamine, and react at 40 °C for 16 h to obtain compound A; (3) 8 g of compound A and 200 g of lactide were added to 500 ml of toluene, and 0.1 g of stannous octoate was added, and the mixture was reacted at 130 °C for 8 h to obtain modified polylactic acid; The structural formula of the compound A is: .

[0019] 40 g of modified polylactic acid, 60 g of polylactic acid, and 10 g of triglycidyl isocyanurate were heated to 70°C and dried for 15 min, and then 0.1 g of a composite antioxidant of antioxidant 1010 and 0.2 g of antioxidant 168 were added, and kneaded at 190°C and 50 rpm for 15 min to obtain polylactic acid resin.

[0020] The tensile strength, elongation at break and heat deformation temperature of the obtained polylactic acid resin are shown in Table 1, and the antibacterial property and degradation property of the obtained polylactic acid resin are shown in Table 2 and Table 3, respectively.

[0021] Example 2 A method for preparing modified polylactic acid comprises the following steps: (1) Dissolve 56 g of α-eleostearic acid in 400 ml of dichloromethane, add 24 g of thionyl chloride at 10°C, react at 10°C for 4 h, and obtain α-eleostearic acid chloride by rotary evaporation; add α-eleostearic acid chloride to 300 mL of tetrahydrofuran, introduce ammonia gas at room temperature until the pH value at the mouth of the reaction bottle is alkaline as measured by pH test paper, and then react at 20°C for 6 h, and obtain α-eleostearic acid amide by rotary evaporation; (2) Add 28 g of α-eleostearic acid amide to 200 ml of dichloromethane, add 18 g of diethyl oxalate and 7 g of ethanolamine, and react at 50 °C for 24 h to obtain compound A; (3) Add 10 g of compound A and 200 g of lactide into 500 ml of toluene, add 0.1 g of DMAP, and react at 150 °C for 8 h to obtain modified polylactic acid; The structural formula of the compound A is: .

[0022] 30 g of modified polylactic acid, 80 g of polylactic acid, and 8 g of triglycidyl isocyanurate were heated to 80°C and dried for 20 min, and then 0.1 g of a composite antioxidant of antioxidant 1010 and 0.1 g of antioxidant 168 were added, and the mixture was kneaded at 200°C and 60 rpm for 12 min to obtain a modified polylactic acid resin.

[0023] The tensile strength, elongation at break and heat deformation temperature of the obtained polylactic acid resin are shown in Table 1, and the antibacterial property and degradation property of the obtained polylactic acid resin are shown in Table 2 and Table 3, respectively.

[0024] Example 3 A method for preparing modified polylactic acid comprises the following steps: (1) Dissolve 56 g of α-eleostearic acid in 400 ml of dichloromethane, add 72 g of thionyl chloride at 20°C, react at 20°C for 4 h, and obtain α-eleostearic acid chloride by rotary evaporation; add α-eleostearic acid chloride to 300 mL of tetrahydrofuran, introduce ammonia gas at room temperature until the pH value at the mouth of the reaction bottle is alkaline as measured by pH test paper, and then react at 25°C for 6 h, and obtain α-eleostearic acid amide by rotary evaporation; (2) Add 28 g of α-eleostearic acid amide to 200 ml of dichloromethane, add 12 g of diethyl oxalate and 5 g of ethanolamine, and react at 30 °C for 12 h to obtain compound A; (3) Add 5 g of compound A and 200 g of lactide to 500 ml of toluene, add 0.05 g of stannous octoate, and react at 120 °C for 6 h to obtain modified polylactic acid; The structural formula of the compound A is: .

[0025] 20 g of modified polylactic acid, 40 g of polylactic acid, and 5 g of triglycidyl isocyanurate were heated to 60°C and dried for 10 min, and then 0.1 g of a composite antioxidant of antioxidant 1010 and 0.3 g of antioxidant 168 were added, and the mixture was kneaded at 180°C and 40 rpm for 10 min to obtain a modified polylactic acid resin.

[0026] The tensile strength, elongation at break and heat deformation temperature of the obtained polylactic acid resin are shown in Table 1, and the antibacterial property and degradation property of the obtained polylactic acid resin are shown in Table 2 and Table 3, respectively.

[0027] Comparative Example 1 100 g of polylactic acid and 10 g of triglycidyl isocyanurate were heated to 70° C. and dried for 15 min, and then 0.1 g of a composite antioxidant of antioxidant 1010 and 0.2 g of antioxidant 168 were added, and kneaded at 190° C. and 50 rpm for 15 min to obtain polylactic acid resin.

[0028] The tensile strength, elongation at break and heat deformation temperature of the obtained polylactic acid resin are shown in Table 1, and the antibacterial property and degradation property of the obtained polylactic acid resin are shown in Table 2 and Table 3, respectively.

[0029] Comparative Example 2 100 g of polylactic acid was heated to 70° C. and dried for 15 min, and then 0.1 g of a composite antioxidant of antioxidant 1010 and 0.2 g of antioxidant 168 was added, followed by kneading at 190° C. and 50 rpm for 15 min to obtain polylactic acid resin.

[0030] The tensile strength, elongation at break and heat deformation temperature of the obtained polylactic acid resin are shown in Table 1, and the antibacterial property and degradation property of the obtained polylactic acid resin are shown in Table 2 and Table 3, respectively.

[0031] Table 1 Performance of different embodiments and comparative examples

[0032] As can be seen from Table 1, the polylactic acid resin prepared in Examples 1 to 3 of the present application has high mechanical properties and heat resistance, and its tensile strength, elongation at break, and heat deformation temperature are improved. This is because the addition of modified polylactic acid and triglycidyl isocyanurate further improves the degree of crosslinking in the polylactic acid resin, and at the same time, the conjugated double bonds of α-eleostearic acid further enhance the network structure of the polymer.

[0033] Table 2 Antibacterial properties of different examples and comparative examples

[0034] As can be seen from Table 2, the polylactic acid resins prepared in Examples 1 to 3 of the present application have a high antibacterial rate against Staphylococcus aureus and Escherichia coli, and have a high mildew resistance level, and can be used as antibacterial resin materials. This is because the amide groups in the modified polylactic acid and triglycidyl isocyanurate can effectively inhibit the growth of bacteria.

[0035] Table 3 Degradation performance of different examples and comparative examples

[0036] It can be seen from Table 3 that the degradation rates of the polylactic acid resins prepared in Examples 1 to 3 of the present application are similar to those of the polylactic acid resin, and both are environmentally friendly.

[0037] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing modified polylactic acid, characterized in that: The steps include: (1) dissolving α-eleostearic acid in dichloromethane, adding thionyl chloride to prepare α-eleostearic acid chloride, and introducing ammonia gas to react to obtain α-eleostearic acid amide; (2) Add α-eleostearic acid amide to dichloromethane, add diethyl oxalate and ethanolamine, and react at 30-50°C for 12-24 hours to obtain compound A; (3) Compound A and lactide are added to toluene, catalyst A is added, and the mixture is reacted at 120-150° C. for 6-12 hours to obtain modified polylactic acid; The catalyst A is at least one of stannous octoate, tetrabutyl titanate or DMAP; The mass ratio of the compound A, lactide and catalyst A is 5-10:200:0.05-0.1; The structural formula of the compound A is: 。 2. The method for preparing modified polylactic acid according to claim 1, characterized in that: The molar ratio of α-eleostearic acid to thionyl chloride is 1:1-1:3, the reaction temperature of α-eleostearic acid and thionyl chloride is 0-20° C., and the reaction time is 4-10 hours.

3. The method for preparing modified polylactic acid according to claim 1, characterized in that: The mass ratio of the α-eleostearic acid amide, diethyl oxalate and ethanolamine is 28:12-18:5-7.

4. Use of the modified polylactic acid prepared by the method for preparing modified polylactic acid according to any one of claims 1 to 3 in preparing polylactic acid resin, characterized in that: The steps include: The modified polylactic acid, polylactic acid and triglycidyl isocyanurate are heated to 60-80°C and dried for 10-20 minutes, and then an antioxidant is added and mixed to obtain polylactic acid resin.

5. The use of the modified polylactic acid according to claim 4 in the preparation of polylactic acid resin, characterized in that: The antioxidant is a composite antioxidant of antioxidant 1010 and antioxidant 168, and the mass ratio of the antioxidant 1010 to the antioxidant 168 is 1:1 to 1:

3.

6. The use of the modified polylactic acid according to claim 4 in the preparation of polylactic acid resin, characterized in that: The mass ratio of the modified polylactic acid, polylactic acid, triglycidyl isocyanurate and antioxidant is 20-40:40-80:5-10:0.1-0.

5.

7. The use of the modified polylactic acid according to claim 4 in the preparation of polylactic acid resin, characterized in that: The mixing temperature is 180-200° C., the mixing time is 10-15 min, and the rotating speed is 40-60 rpm.

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