Anti-aging polylactic acid composition as well as preparation method and application thereof

Abstract

The invention discloses an anti-aging polylactic acid composition as well as a preparation method and application thereof. The anti-aging polylactic acid composition comprises polylactic acid resin, a tin element and a phosphorus element, the mass ratio of the tin element in the anti-aging polylactic acid composition is less than or equal to 600ppm, the mass ratio of the phosphorus element in the anti-aging polylactic acid composition is less than or equal to 500ppm, and the mass ratio of the tin element to the phosphorus element is (0.3-5): 1; the weight-average molecular weight of the polylactic acid resin is 100000 to 200000, and the molecular weight distribution coefficient of the polylactic acid resin is 1.5 to 2.1. According to the anti-aging polylactic acid composition disclosed by the invention, by adding the phosphorus element and regulating and controlling the molecular chain length and distribution uniformity of the polylactic acid resin, the increase of the terminal carboxyl group content of the polylactic acid resin in a humid and hot environment is inhibited, so that the polylactic acid composition has excellent humid and hot resistance stability.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer compound compositions, and more specifically, to an aging-resistant polylactic acid composition and a preparation method and application thereof. Background Art

[0002] Polylactic acid is a green polymer material with good biocompatibility and biodegradability, usually obtained by polymerization using renewable lactic acid as a monomer. The polymerization methods mainly include ring-opening polymerization and direct polymerization. Although polylactic acid obtained by ring-opening polymerization of lactide has high molecular weight and thermal stability, this polymerization method requires high-purity lactide and the synthesis process is complicated, making it difficult to apply to industrial production needs.

[0003] At present, most polylactic acid is prepared by direct polymerization using lactic acid formed by fermentation of crops as the polymerization monomer and a tin catalyst with high catalytic activity. Through continuous research and practical application, it is found that Sn in polylactic acid originates from tin catalysts. 2+ It is difficult to completely remove, and Sn 2+ It will promote the thermal degradation reaction of polylactic acid, resulting in poor thermal stability of polylactic acid. In the prior art, chelating agents, phosphate compounds, phosphite compounds or metaphosphates are mainly added as catalyst deactivators to inhibit Sn 2+ The activity of chelating agents can enhance the thermal stability of polylactic acid, but the poor heat resistance of chelating agents can easily lead to severe coloring of polylactic acid during melt processing, while the effect of phosphoric acid compounds on improving the moisture and heat stability of polylactic acid is limited. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects and shortcomings of the existing polylactic acid, that is, the poor moisture and heat stability, and to provide an aging-resistant polylactic acid composition.

[0005] Another object of the present invention is to provide a method for preparing an aging-resistant polylactic acid composition.

[0006] Another object of the present invention is to provide an application of an aging-resistant polylactic acid composition in the preparation of biodegradable products.

[0007] Another object of the present invention is to provide a degradable tableware comprising the above-mentioned aging-resistant polylactic acid composition.

[0008] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0009] The present invention protects an aging-resistant polylactic acid composition, comprising a polylactic acid resin, a tin element and a phosphorus element; the mass proportion of the tin element in the aging-resistant polylactic acid composition is ≤600ppm, the mass proportion of the phosphorus element is ≤500ppm, and the mass ratio of the tin element to the phosphorus element is (0.3-5):1; the weight average molecular weight of the polylactic acid resin is 100000-200000, and the molecular weight distribution coefficient is 1.5-2.1.

[0010] The aging-resistant polylactic acid composition of the present invention, by adding phosphorus and regulating the molecular chain length and distribution uniformity of the polylactic acid resin, effectively reduces the increase in the terminal carboxyl content of the polylactic acid resin in a hot and humid environment while inhibiting the catalytic degradation of the tin element, thereby making the polylactic acid composition have excellent heat and humidity resistance stability.

[0011] Optionally, the mass proportion of tin element in the aging-resistant polylactic acid composition can be 550ppm, 500ppm, 450ppm, 400ppm, 350ppm, 300ppm, 250ppm, 200ppm, 150ppm, 100ppm or 50ppm; the mass proportion of phosphorus element can be 450ppm, 400ppm, 350ppm, 300ppm, 250ppm, 200ppm, 150ppm, 100ppm or 50ppm; the mass ratio of tin element to phosphorus element can be 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or 4.5:1.

[0012] In addition, the polylactic acid may be poly-L-lactic acid and / or poly-D-lactic acid, and the weight average molecular weight of the polylactic acid may be 110000, 120000, 130000, 140000, 150000, 16000, 170000, 180000 or 190000; the molecular weight distribution coefficient (weight average molecular weight Mw / number average molecular weight Mn) of the polylactic acid may be 1.6, 1.7, 1.8, 1.9 or 2. Both the weight average molecular weight and the number average molecular weight may be obtained by gel permeation chromatography (GPC) testing.

[0013] Preferably, the mass proportion of tin element in the aging-resistant polylactic acid composition is 5 to 500 ppm, and the mass proportion of phosphorus element in the aging-resistant polylactic acid composition is 5 to 400 ppm.

[0014] Preferably, the mass ratio of the tin element to the phosphorus element is (0.5-4):1.

[0015] Optionally, the number average molecular weight of the polylactic acid is 70,000 to 90,000, specifically 72,000, 74,000, 76,000, 78,000, 80,000, 82,000, 84,000, 86,000 or 88,000.

[0016] Optionally, the phosphorus element is derived from at least one of phosphate or phosphorus oxide, the phosphate is one or more of orthophosphate, pyrophosphate, phosphite or hypophosphite, and the phosphorus oxide is phosphorus pentoxide or phosphorous anhydride.

[0017] Optionally, the polylactic acid resin can be purchased from the market, or can be prepared by the following preparation method:

[0018] First, L-lactic acid and a first catalyst are mixed and then subjected to a condensation reaction to generate a lactide intermediate; then the lactide intermediate, an initiator and a second catalyst are mixed and subjected to a ring-opening polymerization reaction to generate a polylactic acid resin.

[0019] Wherein, the first catalyst or the second catalyst in the above preparation method is a tin catalyst, specifically one or more of tin powder, stannous chloride, tin oxide or stannous octoate; the initiator may be ethylene glycol.

[0020] Optionally, the reaction temperature of the polycondensation reaction is 80-140°C, the reaction pressure is 3-8KPa, and the reaction time is 6-12h. Specifically, after the polycondensation reaction, the oligomers generated by the polycondensation reaction can be subjected to vacuum distillation until no product is distilled out (7-15h) to obtain a lactide intermediate; the conditions for the vacuum distillation include: a temperature of 170-210°C and a pressure of 102-103Pa.

[0021] Optionally, the ring-opening polymerization reaction includes at least two stages, the conditions of the first stage include: reaction temperature of 140-160°C, reaction pressure of 105000-115000Pa, reaction time of 3-5h; the conditions of the second stage include: reaction temperature of 170-190°C, reaction pressure of 105000-115000Pa, reaction time of 2-3h. Specifically, in the ring-opening polymerization reaction, the polymer generated by the ring-opening polymerization reaction can be dissolved in a chloroform aqueous solution and then precipitated with ethanol to obtain a polylactic acid resin.

[0022] Optionally, the terminal carboxyl content of the aging-resistant polylactic acid composition is 2 to 30 mol / t, specifically 5 mol / t, 10 mol / t, 15 mol / t, 20 mol / t or 25 mol / t.

[0023] The method for determining the terminal carboxyl content is as follows: using a mixture of o-cresol and chloroform in a mass ratio of 7:3 as solvent, using a Swiss Metrohm Titrino series automatic potentiometric titrator to test the terminal carboxyl value. The test method implements FZ / T50012-2006 "Determination of the Terminal Carboxyl Content in Polyesters - Titration Analysis Method", and the first decimal place after the terminal carboxyl value is rounded off to an integer.

[0024] The present invention also protects a method for preparing the above-mentioned anti-aging polylactic acid composition, comprising the following steps: mixing polylactic acid resin with a phosphorus-containing compound and a tin-containing compound, and melt-extruding to obtain an anti-aging polylactic acid composition. The melt extrusion can be carried out using a twin-screw extruder, and the temperature of the melt extrusion is 140 to 240° C. Since the phosphorus-containing compound and the tin-containing compound are added in small amounts, they can be mixed in the form of trace substances commonly used in the art, such as in the form of master batches made with a small amount of polylactic acid, or in the form of multiple premixes with polylactic acid to make them evenly dispersed.

[0025] The use of the above-mentioned aging-resistant polylactic acid composition in the preparation of biodegradable products is also within the protection scope of the present invention.

[0026] The present invention also protects a degradable tableware comprising the above-mentioned aging-resistant polylactic acid composition; specifically, it can be a lunch box, a straw or a cup, etc.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The aging-resistant polylactic acid composition of the present invention suppresses the increase of the terminal carboxyl content of the polylactic acid resin in a hot and humid environment by adding phosphorus and regulating the molecular chain length and distribution uniformity of the polylactic acid resin, thereby making the polylactic acid composition have excellent heat and humidity resistance stability. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0030] 1. Raw materials and reagents

[0031] Polylactic acid resin, homemade, can be prepared, for example, by the following preparation method:

[0032] S1. Add L-lactic acid and the first catalyst to the reaction vessel, stir evenly, and carry out polycondensation reaction at a temperature of 100°C and a pressure of 5KPa. After 9 hours, distill off water to obtain oligomers. Distill the obtained oligomers under reduced pressure at a temperature of 190°C and a pressure of 102Pa until no product is distilled out. The time is 11 hours to obtain a lactide intermediate.

[0033] S2. The lactide intermediate obtained in the above step is dissolved in an initiator, and a second catalyst is added to carry out a ring-opening polymerization reaction, specifically: first react at a temperature of 150°C and a relative pressure of 110000Pa for 4 hours, and then react at a temperature of 180°C and a relative pressure of 110000Pa for 2.5 hours to obtain a polymer; the obtained polymer solid is dissolved by refluxing with a 5% (W / W) chloroform aqueous solution, and after filtering the solution, it is precipitated with ethanol 5 times the volume of chloroform to obtain a white flocculent precipitate to obtain a polylactic acid resin.

[0034] The molecular weight and molecular weight distribution coefficient of polylactic acid are regulated by adjusting the content of initiator and catalyst to obtain different polylactic acid resins; the initiator and its content, catalyst and its content corresponding to different polylactic acid resins are shown in Table 1, wherein the content of the initiator refers to the mass fraction of the initiator relative to the lactide intermediate, the content of the first catalyst refers to the mass fraction of the first catalyst relative to L-lactic acid, and the content of the second catalyst refers to the mass fraction of the second catalyst relative to the lactide intermediate.

[0035] After testing, the tin content in the above polylactic acid resin is 5ppm-500ppm, and the weight average molecular weight, number average molecular weight and molecular weight distribution index (PDI) are shown in Table 1.

[0036] Table 1 Polylactic acid resin, initiator, catalyst and content

[0037]

[0038] 2. The aging-resistant polylactic acid compositions of the embodiments and comparative examples of the present invention are prepared by the following preparation method:

[0039] First, polylactic acid resin and a tin-containing compound (stannous octoate) are prepared into a tin-containing compound masterbatch, and polylactic acid resin and a phosphorus-containing compound (phosphorus pentoxide or sodium orthophosphate, purity ≥98%, Wuhan Jixinyibang Biotechnology Co., Ltd.) are prepared into a phosphorus-containing compound masterbatch, and then polylactic acid resin (100 kg), the tin-containing compound masterbatch and the phosphorus-containing compound masterbatch are mixed and added into a twin-screw extruder, and melt-extruded at 140-240° C. to obtain an aging-resistant polylactic acid composition;

[0040] The mass ratio of tin and phosphorus in the polylactic acid resin is regulated by adjusting the content of the tin-containing compound or the phosphorus-containing compound.

[0041] 3. Performance testing

[0042] (1) The mass proportion of tin and phosphorus in the polylactic acid resin, the anti-aging polylactic acid composition of each embodiment and the comparative example was tested by microwave digestion-ICP-OES method, and the unit of the measurement result was ppm, where 1ppm=0.001‰. Specifically, 0.1g of the crushed sample to be tested was weighed and placed in a microwave digestion tank, 5mL of nitric acid was added to completely immerse the sample to be tested, and then 1.0mL of hydrogen peroxide was slowly dripped in. After reacting for 2 minutes, the lid was covered, the digestion tank was sealed, and it was placed in a microwave digestion furnace for digestion. After cooling to room temperature, the solution in the digestion tank was filtered with a 0.45μm filter membrane and transferred to a volumetric flask, diluted to 50mL with distilled water, and tested by ICP-OES.

[0043] (2) The aging-resistant polylactic acid compositions of the embodiments and comparative examples were randomly divided into Group A and Group B, respectively. The terminal carboxyl content of Group A was directly measured according to FZ / T 50012-2006 "Determination of terminal carboxyl content in polyester - Titration analysis method" to be a mol / t. The terminal carboxyl content of Group B was measured according to the above method after being placed at a temperature of 60°C and a humidity of 60% for 9 days to be b mol / t.

[0044] The method for determining the terminal carboxyl content is as follows: using a mixture of o-cresol and chloroform in a mass ratio of 7:3 as a solvent, using a Swiss Metrohm Titrino series automatic potentiometric titrator to test the terminal carboxyl value, and the test method implements FZ / T50012-2006 "Determination of Terminal Carboxyl Content in Polyester-Titration Analysis Method", and the first decimal place after the terminal carboxyl value is rounded to an integer.

[0045] Change rate of terminal carboxyl content (%) = (ba) / b*100%.

[0046] Examples 1 to 12 and Comparative Examples 1 to 7

[0047] The components and properties of the aging-resistant polylactic acid compositions in Examples 1 to 12 and Comparative Examples 1 to 7 are shown in Tables 2 and 3, wherein X is phosphorus pentoxide, Y is sodium orthophosphate, and the phosphorus-containing compound in Comparative Examples 1 to 7 is phosphorus pentoxide.

[0048] Table 2 Components and properties of the aging-resistant polylactic acid composition in each embodiment

[0049]

[0050] Table 3 Components and properties of the aging-resistant polylactic acid compositions in each comparative example

[0051]

[0052] Comparative Example 8

[0053] A polylactic acid resin is prepared by the following preparation method: adding polylactic acid resin 1 (100 kg) into a twin-screw extruder, and melt-extruded at 140-240° C. to obtain the polylactic acid resin.

[0054] After testing, the change rate of the terminal carboxyl content of the polylactic acid resin is 55%.

[0055] According to the data in Table 2 and Table 3, the aging-resistant polylactic acid compositions in Examples 1 to 12 were placed at a temperature of 60°C and a humidity of 60% for 9 days, and the rate of change of the carboxyl content of the rear end was less than or equal to 38%, indicating that the polylactic acid composition of the present invention has excellent moisture and heat resistance stability. At the same time, according to Comparative Examples 1 to 3, the weight-average molecular weight and molecular weight distribution coefficient of the polylactic acid resin, the content of tin and phosphorus in the polylactic acid composition, and the mass ratio of the two, jointly affect the rate of change of the terminal carboxyl group of the polylactic acid composition, and thus affect its moisture and heat resistance stability. According to Comparative Examples 4 and 5, it can be found that when the tin element in the polylactic acid composition is greater than 600ppm or the phosphorus element is greater than 500ppm, the rate of change of the terminal carboxyl content of the polylactic acid composition will be significantly increased, thereby significantly reducing the moisture and heat resistance stability of the polylactic acid composition. In addition, it can be seen from Comparative Examples 6 and 7 that the change rate of the terminal carboxyl groups of the polylactic acid composition is not only related to the content of tin or phosphorus, but is also affected by the mass ratio of tin to phosphorus. When the mass ratio of tin to phosphorus is too large or too small, it is difficult to effectively reduce the change rate of the terminal carboxyl groups of the polylactic acid composition, and it is impossible to effectively improve the moisture and heat stability of the polylactic acid composition.

[0056] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. 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 embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An aging-resistant polylactic acid composition, characterized in that: The invention comprises polylactic acid resin, tin element and phosphorus element; the mass proportion of tin element in the aging-resistant polylactic acid composition is ≤600ppm, the mass proportion of phosphorus element is ≤500ppm, and the mass ratio of tin element to phosphorus element is (0.3-5):1; The weight average molecular weight of the polylactic acid resin is 100,000 to 200,000, and the molecular weight distribution coefficient is 1.5 to 2.

1.

2. The aging-resistant polylactic acid composition according to claim 1, characterized in that: The mass proportion of tin element in the anti-aging polylactic acid composition is 5 to 500 ppm.

3. The aging-resistant polylactic acid composition according to claim 1, characterized in that: The mass proportion of phosphorus in the anti-aging polylactic acid composition is 5 to 400 ppm.

4. The aging-resistant polylactic acid composition according to claim 1, characterized in that: The mass ratio of the tin element to the phosphorus element is (0.5-4):

1.

5. The aging-resistant polylactic acid composition according to claim 1, characterized in that: The number average molecular weight of the polylactic acid resin is 70,000 to 90,000.

6. The aging-resistant polylactic acid composition according to claim 1, characterized in that: The phosphorus element is derived from at least one of phosphate or phosphorus oxide.

7. The aging-resistant polylactic acid composition according to claim 6, characterized in that: The phosphate is one or more of orthophosphate, pyrophosphate, phosphite or hypophosphite; the phosphorus oxide is phosphorus pentoxide and / or phosphorous anhydride.

8. A method for preparing the aging-resistant polylactic acid composition according to any one of claims 1 to 7, characterized in that: The following steps are involved: The polylactic acid resin and the phosphorus-containing compound are mixed and melt-extruded to obtain an aging-resistant polylactic acid composition.

9. Use of the aging-resistant polylactic acid composition according to any one of claims 1 to 7 in the preparation of biodegradable products.

10. A degradable tableware, characterized in that: The invention comprises the anti-aging polylactic acid composition according to any one of claims 1 to 7.

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