A polylactic acid composition and a method for preparing the same

Abstract

The application discloses a polylactic acid composition and a preparation method thereof. The polylactic acid is a combination of 0.1-99.9% polylactic acid containing a bio-based acid segment and 0.1-99.9% polylactic acid containing an alcohol segment. The polylactic acid composition has good processing performance and degradation performance.

Description

Technical Field

[0001] This invention relates to a polylactic acid composition and its preparation method, the composition having good processing and degradation properties. Background Technology

[0002] Polylactic acid (PLA) is a high-performance biodegradable polyester with promising applications in food packaging, textiles, and biomedicine. In industrial processing and modification, PLA typically requires melt blending with other components to meet specific application requirements. However, due to its heat-sensitive nature, PLA is prone to thermal degradation at high temperatures, leading to decreased mechanical properties and color deterioration. Therefore, a suitable melting temperature is needed to improve its processability. Furthermore, the biodegradability of PLA stems from the presence of ester bonds in its molecular chain, which are sensitive to both water and heat. Under high-temperature, aerobic, and humid conditions, these ester bonds break, resulting in varying degrees of degradation, which is then utilized by bacteria and ultimately converted into water and carbon dioxide. However, the degradability of PLA is not easily controlled directly. Under composting conditions, the degradation period can still be as long as 3-6 months. If landfilled in soil, it may take several years for complete degradation. For applications requiring faster degradation, such as biodegradable mulch films, further improvements in degradability are necessary.

[0003] Patent CN 111234482 A discloses a method for preparing a polylactic acid (PLA) / nano jade powder mixture, which can avoid thermal degradation and discoloration of PLA during melt mixing. However, it requires a high-speed mixing device, placing high demands on the equipment. Furthermore, the addition of nano jade powder inevitably increases the brittleness of PLA, negatively impacting its mechanical properties. Patent CN 105368020B discloses a biodegradable mulch film for preventing drip irrigation tape burns. By introducing polyethylene glycol and other materials for melt blending, the hydrophilicity of PLA is increased, accelerating the degradation rate; however, the process is relatively cumbersome. Summary of the Invention

[0004] The purpose of this invention is to address the problems of high processing temperature leading to easy thermal degradation at high temperatures and difficulty in directly adjusting biodegradability of existing polylactic acid (PLA) by providing a PLA composition with adjustable melting temperature, good processing performance, and excellent biodegradability.

[0005] Another object of the present invention is to provide a method for preparing the polylactic acid composition, wherein the polylactic acid composition containing bio-based acid segments and the polylactic acid composition containing alcohol segments are synthesized in the same system. The process is simple, and the melting temperature and biodegradability of the composition can be adjusted by controlling the ratio of acid to alcohol in the mixture of bio-based acid and alcohol, thereby obtaining a suitable processing temperature and biodegradability. The improvement in biodegradability mainly comes from the introduction of bio-based acid, and it is completely harmless to the environment.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0007] A polylactic acid composition includes the following components: polylactic acid containing bio-based acid segments and polylactic acid containing alcohol segments. Since both bio-based acids and alcohols can initiate the ring-opening polymerization of lactide, the ratio of the bio-based acid segments to the alcohol segments in the initiator can be controlled by the ratio of acid to alcohol in the mixture of bio-based acids and alcohols, thereby obtaining suitable processing temperature and biodegradability.

[0008] In this invention, based on the mass of the polylactic acid composition, the content of polylactic acid containing bio-based acid segments is 0.1%-99.9%, preferably 20%-40%.

[0009] In this invention, based on the mass of the polylactic acid composition, the content of polylactic acid containing alcohol segments is 0.1%-99.9%, preferably 60%-80%.

[0010] The present invention also relates to a method for preparing the polylactic acid composition, the method comprising the following steps: (1) mixing a bio-based acid and an alcohol at room temperature; (2) initiating lactide polymerization using the mixture of the bio-based acid and the alcohol as an initiator under the action of a catalyst; and (3) performing devolatilization of the polymer under high temperature and high vacuum to obtain the final polylactic acid composition.

[0011] In this invention, the bio-based acid is one or more of formic acid, acetic acid, pyruvic acid, fumaric acid, lactic acid, succinic acid, 2-hydroxybutyric acid and 2-hydroxyvalerate, preferably one or more of 2-hydroxybutyric acid and 2-hydroxyvalerate.

[0012] In this invention, the alcohol is one or more of methanol, ethanol, propanol, butanol, pentanol, isooctyl alcohol, 1,4-butanediol, 1,2-ethylenediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, isosorbide, and 1,4-cyclohexanediethanol, preferably 1,4-butanediol.

[0013] In this invention, the lactide is selected from one or more of L-lactide, D-lactide, and mesolactide.

[0014] In this invention, the catalyst is selected from organometallic compounds or organic bases, preferably organometallic compounds; more preferably, the organometallic compound is selected from one or more of organotin compounds, organoaluminum compounds, and organozinc compounds; the organic base is one or more of organoguanidine or Schiff base catalysts.

[0015] In this invention, based on the mass of lactide, the mass fraction of the bio-based acid and alcohol mixture initiator is 500-3000 ppm, preferably 1500-1680 ppm. In the bio-based acid and alcohol mixture, based on the mixture, the molar fraction of the bio-based acid is 0.1%-99.9%, preferably 20%-40%, and the molar fraction of the alcohol is 0.1%-99.9%, preferably 60%-80%. The catalyst is based on the mass fraction of lactide and is 50-400 ppm, preferably 100-200 ppm.

[0016] In this invention, the mixing temperature of the bio-based acid and the alcohol is room temperature, and the mixing time is not required, as long as the mixing effect is uniform; and / or, the reaction temperature for initiating the polymerization of lactide by the mixture of bio-based acid and alcohol is 180-200℃, preferably 180-190℃, and the reaction time is 90-150 min, preferably 120-150 min; and / or, the polymer devolatilization temperature is 180-210℃, preferably 190-200℃, the vacuum is less than 100 Pa, and the devolatilization time is 30-60 min, preferably 40-50 min.

[0017] Compared with the prior art, the positive effects of the technical solution of the present invention are as follows:

[0018] (1) In the polylactic acid composition involved in this invention, polylactic acid containing bio-based acid segments and polylactic acid containing alcohol segments are synthesized in the same system, which is simple in process and has good compatibility.

[0019] (2) Due to the microscopic differences in molecular structure between polylactic acid containing bio-based acid segments and polylactic acid containing alcohol segments, crystallinity can be adjusted and processing temperature can be reduced.

[0020] (3) The combination of polylactic acid containing bio-based acid segments and polylactic acid containing alcohol segments can effectively regulate the overall biodegradability of the polylactic acid composition. The improvement in biodegradability is mainly due to the promoting effect of bio-based acid segments on degradation, and it is completely harmless to the environment. The resulting polylactic acid composition has good processing performance and biodegradability. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments. It should be noted that the embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0022] L-lactide and D-lactide were purchased from Corbin, industrial grade, and all other raw materials were commercially available, with analytical purity. The equipment and methods used in this invention are all common in the art.

[0023] Tensile properties: Tensile properties were tested using an Instron 5960 mechanical testing machine according to GB / T 1040.2-2006, using 1A-type specimens, at a test speed of 50 mm / min.

[0024] Melting temperature (T) m The test was conducted using a Perkins Elmer Pyris 1 differential scanning calorimeter. The sample was first heated to 180°C at a rate of 20°C / min to eliminate thermal history, then cooled to -30°C at a rate of 20°C / min, and finally heated again at a rate of 10°C / min to obtain the sample's thermal history (T0). m .

[0025] Degradation performance: Under composting conditions, with a temperature of 30℃ and a humidity of 60%, the material maintains its degradation rate for 30 days.

[0026] Example 1

[0027] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 1.8 g of 2-hydroxybutyric acid and 5.9 g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000 g of lactide and 0.25 g of stannous octoate catalyst were added, and polymerization was carried out at 200°C for 150 min. After the reaction, the mixture was devolatilized at 180°C under a vacuum pressure of less than 100 Pa for 60 min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 1. This polylactic acid composition contains 20% polylactic acid with bio-based acid segments and 80% polylactic acid with alcohol segments. The tensile strength is 54 MPa, the elongation at break is 5%, and the T... m At 166℃, the degradation rate was 38%.

[0028] Example 2

[0029] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 2.6 g of 2-hydroxybutyric acid and 5.2 g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000 g of lactide and 0.5 g of stannous octoate catalyst were added, and polymerization was carried out at 190°C for 120 min. After the reaction, the mixture was devolatilized at 190°C under a vacuum pressure less than 100 Pa for 40 min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 2. This polylactic acid composition contains 30% polylactic acid with bio-based acid segments and 70% polylactic acid with alcohol segments. The tensile strength is 54 MPa, the elongation at break is 5%, and the T... m At 165℃, the degradation rate is 40%.

[0030] Example 3

[0031] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 3.4 g of 2-hydroxybutyric acid and 4.5 g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000 g of lactide and 2 g of stannous octoate catalyst were added, and polymerization was carried out at 180°C for 90 min. After the reaction, the mixture was devolatilized at 210°C under a vacuum pressure of less than 100 Pa for 30 min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 3. This polylactic acid composition contains 40% polylactic acid with bio-based acid segments and 60% polylactic acid with alcohol segments. The tensile strength is 53 MPa, the elongation at break is 5%, and the T... m At 165℃, the degradation rate was 39%.

[0032] Example 4

[0033] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 0.009 g of 2-hydroxybutyric acid and 7.5 g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000 g of lactide and 0.5 g of stannous octoate catalyst were added, and polymerization was carried out at 190°C for 120 min. After the reaction, the mixture was devolatilized at 190°C under a vacuum pressure less than 100 Pa for 40 min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 4. This polylactic acid composition contains 0.1% polylactic acid with bio-based acid segments and 99.9% polylactic acid with alcohol segments. The tensile strength is 53 MPa, the elongation at break is 5%, and the T... m At 168℃, the degradation rate is 35%.

[0034] Example 5

[0035] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 8.6 g of 2-hydroxybutyric acid and 0.008 g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000 g of lactide and 0.5 g of stannous octoate catalyst were added, and polymerization was carried out at 180°C for 90 min. After the reaction, the mixture was devolatilized at 210°C under a vacuum pressure of less than 100 Pa for 30 min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 5. This polylactic acid composition contains 99.9% polylactic acid with bio-based acid segments and 0.1% polylactic acid with alcohol segments. The tensile strength is 53 MPa, the elongation at break is 5%, and the T... m At 168℃, the degradation rate is 35%.

[0036] Example 6

[0037] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 2g of 2-hydroxyvalerate and 5.9g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000g of lactide and 0.5g of stannous octoate catalyst were added, and polymerization was carried out at 190℃ for 120min. After the reaction, the mixture was devolatilized at 190℃ under a vacuum pressure less than 100Pa for 40min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 6. This polylactic acid composition contains 20% polylactic acid with bio-based acid segments and 80% polylactic acid with alcohol segments. The tensile strength is 53MPa, the elongation at break is 5%, and the T... m At 165℃, the degradation rate was 39%.

[0038] Example 7

[0039] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 3g of 2-hydroxyvalerate and 5.2g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000g of lactide and 0.5g of stannous octoate catalyst were added, and polymerization was carried out at 190℃ for 120min. After the reaction, the mixture was devolatilized at 190℃ under a vacuum pressure less than 100Pa for 40min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 7. This polylactic acid composition contains 30% polylactic acid with bio-based acid segments and 70% polylactic acid with alcohol segments. The tensile strength is 54MPa, the elongation at break is 5%, and the T... m At 163℃, the degradation rate was 42%.

[0040] Example 8

[0041] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 3.9 g of 2-hydroxyvalerate and 4.5 g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000 g of lactide and 0.5 g of stannous octoate catalyst were added, and polymerization was carried out at 190°C for 120 min. After the reaction, the mixture was devolatilized at 190°C under a vacuum pressure less than 100 Pa for 40 min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 6. This polylactic acid composition contains 40% polylactic acid with bio-based acid segments and 60% polylactic acid with alcohol segments. The tensile strength is 54 MPa, the elongation at break is 5%, and the T... m At 164℃, the degradation rate was 41%.

[0042] Example 9

[0043] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 2.3 g of lactic acid and 5.2 g of 1,4-butanediol were first added at room temperature and mixed. Then, 5000 g of lactide and 0.5 g of stannous octoate catalyst were added, and polymerization was carried out at 190°C for 120 min. After the reaction, the mixture was devolatilized at 190°C under a vacuum pressure less than 100 Pa for 40 min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 9. This polylactic acid composition contains 30% polylactic acid with bio-based acid segments and 70% polylactic acid with alcohol segments. The tensile strength is 53 MPa, the elongation at break is 5%, and the T... m At 169℃, the degradation rate was 34%.

[0044] Example 10

[0045] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 3g of succinic acid and 5.2g of 1,4-butanediol were first added and mixed at room temperature. Then, 5000g of lactide and 0.5g of stannous octoate catalyst were added, and the polymerization reaction was carried out at 190℃ for 120min. After the reaction, the mixture was devolatilized at 190℃ under a vacuum pressure of less than 100Pa for 40min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid composition 10. This polylactic acid composition contains 30% polylactic acid with bio-based acid segments and 70% polylactic acid with alcohol segments. The tensile strength is 50MPa, the elongation at break is 5%, and the T... m At 169℃, the degradation rate was 33%.

[0046] Comparative Example 1

[0047] In a reactor under an anhydrous and oxygen-free inert gas atmosphere, 7.5 g of 1,4-butanediol was added at room temperature, followed by 5000 g of lactide and 0.5 g of stannous octoate catalyst. The polymerization reaction was carried out at 190°C for 120 min. After the reaction, the product was devolatilized at 190°C under a vacuum pressure less than 100 Pa for 40 min. After devolatilization, the product was water-cooled, pelletized, and dried to obtain polylactic acid 11. This polylactic acid contains 100% alcohol segments, has a tensile strength of 54 MPa, an elongation at break of 5%, and a T0... m At 172℃, the degradation rate was 31%.

[0048] Comparative Example 2

[0049] 8.6 g of 2-hydroxybutyric acid was added to a reactor in an anhydrous and oxygen-free inert gas atmosphere at room temperature, followed by 5000 g of lactide and 0.5 g of stannous octoate catalyst. The polymerization reaction was carried out at 190 °C for 120 min. After the reaction, the mixture was devolatilized at 190 °C under a vacuum pressure less than 100 Pa for 40 min. After devolatilization, the mixture was water-cooled, pelletized, and dried to obtain polylactic acid 12. This polylactic acid composition contains 100% polylactic acid with bio-based acid segments, has a tensile strength of 53 MPa, an elongation at break of 5%, and a T0. m At 171℃, the degradation rate was 34%.

[0050] Comparative Example 3

[0051] 9.8 g of 2-hydroxyvalerate was added to a reactor under an anhydrous, oxygen-free, and inert gas atmosphere at room temperature, followed by 5000 g of lactide and 0.5 g of stannous octoate catalyst. The polymerization reaction was carried out at 190 °C for 120 min. After the reaction, the product was devolatilized at 190 °C under a vacuum pressure less than 100 Pa for 40 min. After devolatilization, the product was water-cooled, pelletized, and dried to obtain polylactic acid 13. This polylactic acid composition contains 100% polylactic acid with bio-based acid segments, has a tensile strength of 53 MPa, an elongation at break of 5%, and a T0. m At 171℃, the degradation rate was 35%.

[0052] Comparative Example 4

[0053] In reactor 1, under an anhydrous and oxygen-free inert gas atmosphere, 3g of 2-hydroxyvalerate was added at room temperature, followed by 1500g of lactide and 0.15g of stannous octoate catalyst. The polymerization reaction was carried out at 190℃ for 120min. After the reaction, the product was devolatilized at 190℃ under a vacuum pressure less than 100Pa for 40min, then water-cooled, pelletized, and dried to obtain polylactic acid 14. Simultaneously, in another reactor 2, under an anhydrous and oxygen-free inert gas atmosphere, 5.2g of 1,4-butanediol was added at room temperature, followed by 3500g of lactide and 0.35g of stannous octoate catalyst. The polymerization reaction was carried out at 190℃ for 120min. After the reaction, the product was devolatilized at 190℃ under a vacuum pressure less than 100Pa for 40min, then water-cooled, pelletized, and dried to obtain polylactic acid 15. Then, polylactic acid 14 and polylactic acid 15 were melt-blended at a mixing temperature of 190°C for 30 minutes, followed by water cooling, pelletizing, and drying to obtain polylactic acid 16. This polylactic acid composition contains 30% polylactic acid with bio-based acid segments and 70% polylactic acid with alcohol segments. It has a tensile strength of 51 MPa, an elongation at break of 5%, and a T0. m At 168℃, the degradation rate was 36%.

Claims

1. A polylactic acid composition, characterized in that, The composition comprises the following components: based on the total mass of the polylactic acid composition, 20%-40% polylactic acid containing bio-based acid segments and 60%-80% polylactic acid containing alcohol segments; the preparation method includes the following steps: (1) mixing the bio-based acid and alcohol at room temperature; (2) initiating lactide polymerization with the mixture of bio-based acid and alcohol as an initiator under the action of a catalyst; (3) devolatilizing the polymer under high temperature and high vacuum to obtain the final polylactic acid composition; based on the mass of lactide, the mass fraction of the initiator in the mixture of bio-based acid and alcohol is 500-3000 ppm; the bio-based acid is one or more of 2-hydroxybutyric acid and 2-hydroxyvalerate.

2. The method for preparing the polylactic acid composition according to claim 1, characterized in that, The preparation method includes the following steps: (1) mixing bio-based acid and alcohol at room temperature; (2) initiating lactide polymerization with the mixture of bio-based acid and alcohol as an initiator under the action of a catalyst; (3) devolatilizing the polymer under high temperature and high vacuum to obtain the final polylactic acid composition.

3. The preparation method according to claim 2, characterized in that, The alcohol is one or more of methanol, ethanol, propanol, butanol, pentanol, isooctyl alcohol, 1,4-butanediol, 1,2-ethylenediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, isosorbide diol, and 1,4-cyclohexanediethanol.

4. The preparation method according to claim 2, characterized in that, The lactide is selected from one or more of L-lactide, D-lactide and mesolactide.

5. The preparation method according to any one of claims 2-4, characterized in that, The catalyst is selected from organometallic compounds or organic bases.

6. The preparation method according to claim 5, characterized in that, The organometallic compound is selected from one or more organotin compounds, organoaluminum compounds, and organozinc compounds; the organic base is one or more organoguanidine or Schiff base catalysts.

7. The preparation method according to any one of claims 2-4, characterized in that, Based on the mass of lactide, the mass fraction of the bio-based acid and alcohol mixture initiator is 1500-1680 ppm; and / or, based on the mixture, the molar fraction of the bio-based acid and alcohol mixture is 0.1%-99.9% and the molar fraction of the alcohol is 0.1%-99.9%; and / or, the catalyst is 50-400 ppm based on the mass fraction of lactide.

8. The preparation method according to any one of claims 2-4, characterized in that, The reaction temperature for lactide polymerization initiated by a mixture of bio-based acids and alcohols is 180-200℃, and the reaction time is 90-150 min; and / or, the polymer devolatilization temperature is 180-210℃, the vacuum is less than 100 Pa, and the devolatilization time is 30-60 min.

9. The preparation method according to any one of claims 2-4, characterized in that, The reaction temperature for lactide polymerization initiated by a mixture of bio-based acids and alcohols is 180-190℃, and the reaction time is 120-150 min; and / or, the polymer devolatilization temperature is 190-200℃, the vacuum is less than 100 Pa, and the devolatilization time is 40-50 min.