Polylactic acid resin with improved melting and reactivity, and method for producing the same.

Abstract

The polylactic acid resin and its manufacturing method according to the present invention have the advantage of being able to increase the melt index and improve flowability by a simple method of treating the polylactic acid resin with water. Furthermore, this improves the reactivity of the polylactic acid resin and improves its compatibility with various additives, thereby further expanding the application fields of the polylactic acid resin.

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0087615 filed on July 6, 2023, and all the contents disclosed in the literature of the Korean patent application are included as part of this specification.

[0002] The present invention relates to a polylactic acid resin with improved meltability and reactivity and a method for producing the same.

Background Art

[0003] Polylactic acid (PLA) is a plant - derived resin obtained from plants such as corn, has biodegradable properties, and has attracted attention as an excellent eco - material. Different from petroleum - based resins such as polystyrene resin, polyvinyl chloride resin, and polyethylene that have already been used, polylactic acid can reduce environmental pollution, which is a disadvantage of petroleum - based plastic products, because it has effects such as preventing the depletion of petroleum resources and suppressing carbon dioxide emissions.

[0004] Therefore, since the environmental pollution problem caused by waste plastics and the like has emerged as a social problem, efforts are being made to expand the application range of polylactic acid to product fields where general plastics (petroleum - based resins) such as food packaging materials and containers, and electronic product cases are used.

[0005] The range of melt index (MI) required for polylactic acid varies depending on the article to be manufactured. Among them, there are cases where polylactic acid with a high melt index is required. For example, polylactic acid having high fluidity (melt index of 500 - 3000 g / 10 min at 230 °C) is required for the production of melt - blown non - woven fabrics. However, generally, the melt index of polylactic acid produced in commercially available processes (measured based on ASTM D1238 (230 °C, 2.16 kg condition)) has a range of 5 to 200 g / 10 min. Therefore, with conventional methods, the polymerization of high - fluidity polylactic acid as described above is not easy.

[0006] There are various reasons why polymerization of high-flow polylactic acid (PLA) is difficult. Typically, the process of removing volatile substances such as residual monomers after polymerization (devolatilization step) is essential. However, during this process, some of the PLA may evaporate along with the polymer, making the process less smooth and resulting in difficulties in pelletizing. Furthermore, PLA synthesized using existing polymerization methods has low acidity, which limits post-processing and / or modification. For example, it may have reduced reaction with chain extenders or branching agents.

[0007] Therefore, the present inventors made diligent efforts to solve the aforementioned problems and, as a result, confirmed that it is possible to increase the fusion index and improve the flowability of the manufactured polylactic acid by treating it with distilled water as described later, thereby producing polylactic acid with high flowability, and thus completed the present invention. [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention provides a polylactic acid resin with improved melting properties and reactivity, and a method for producing the same. [Means for solving the problem]

[0009] To solve the aforementioned problems, the present invention provides the following polylactic acid resin.

[0010] The melting index (measured based on ASTM D1238 (230°C, 2.16 kg conditions)) is 300 to 3000 g / 10 min. The acidity is 20 to 100 mmol Acid / kg, and The inorganic impurity content is 100 mg / kg or less. Polylactic acid resin.

[0011] The polylactic acid resin according to the present invention is characterized by having an increased melt index and improved flowability through the manufacturing method described later, and also by containing almost no inorganic impurities because the manufacturing method does not use any other chemical substances or catalysts.

[0012] Preferably, the weight-average molecular weight of the polylactic acid resin is 50,000 to 100,000.

[0013] Preferably, the melting index is 400g / 10 min or more, 500g / 10 min or more, 600g / 10 min or more, 700g / 10 min or more, 800g / 10 min or more, 900g / 10 min or more, or 1000g / 10 min or more; and 2900g / 10 min or less, 2800g / 10 min or less, 2700g / 10 min or less, 2600g / 10 min or less, 2500g / 10 min or less, 2400g / 10 min or less, 2300g / 10 min or less, 2200g / 10 min or less, 2100g / 10 min or less, or 2000g / 10 min or less.

[0014] Preferably, the acidity (acid value) is 30 mmol Acid / kg or more, and 90 mmol Acid / kg or less, 80 mmol Acid / kg or less, 70 mmol Acid / kg or less, or 60 mmol Acid / kg or less.

[0015] Preferably, the inorganic impurities are Sn and P, and the total content of Sn and P is 85 mg / kg or less. Also preferably, the inorganic impurities are Na, Zn, Ti, Al, Ag, Mg, Mn, Ba, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Ni, Sb, Sr, V, and Zr, and the total content of Na, Zn, Ti, Al, Ag, Mg, Mn, Ba, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Ni, Sb, Sr, V, and Zr is 10 mg / kg or less.

[0016] Furthermore, the present invention provides a method for producing the polylactic acid resin described above, comprising the following steps.

[0017] Step 1: Immerse the polylactic acid resin in water. Step 2: Maintaining the water temperature from Step 1 at 65 to 99°C; and Step 3: Recovering the polylactic acid resin from the water.

[0018] The present invention is characterized by a simple method for treating water with polylactic acid, which is produced in a generally commercialized process, to increase the solubility index of polylactic acid and improve its flowability. The present invention will be described in detail below, step by step.

[0019] (Step 1) Step 1 of the present invention is a step of immersing a polylactic acid resin in water, which prepares for the hydrolysis of polylactic acid.

[0020] The polylactic acid resin used in step 1 is generally manufactured using commercially available processes, and preferably, the melting index of the polylactic acid (measured based on ASTM D1238 (230°C, 2.16 kg conditions)) is 5 to 200 g / 10 min. In other words, the present invention does not polymerize a high-flow polylactic acid resin, but rather produces a high-flow polylactic acid resin by hydrolyzing a general low-flow polylactic acid resin as described later.

[0021] Preferably, the weight-average molecular weight of the polylactic acid resin used in step 1 is 100,000 to 250,000. More preferably, the weight-average molecular weight of the polylactic acid resin is 110,000 or more, and 240,000 or less, 230,000 or less, 220,000 or less, 210,000 or less, 200,000 or less, 190,000 or less, 180,000 or less, 170,000 or less, 160,000 or less, or 150,000 or less.

[0022] Preferably, the melt index of the polylactic acid resin in step 1 (measured based on ASTM D1238 (condition of 230°C and 2.16 kg)) is 10 g / 10 min or more, 20 g / 10 min or more, 30 g / 10 min or more, 40 g / 10 min or more, 50 g / 10 min or more, 60 g / 10 min or more, 70 g / 10 min or more, 80 g / 10 min or more, 90 g / 10 min or more, or 100 g / 10 min or more; and is 190 g / 10 min or less, 180 g / 10 min or less, 170 g / 10 min or less, 160 g / 10 min or less, 150 g / 10 min or less, or 140 g / 10 min or less.

[0023] Preferably, the water is distilled water. Preferably, in step 1, the weight ratio of the polylactic acid resin to water is 1:0.1 to 1:10. More preferably, in step 1, the weight ratio of the polylactic acid resin to water is at least 1:0. {2}, at least 1:0.3, or at least 1:0.4; and is at most 1:9, at most 1:8, at most 1:7, at most 1:6, at most 1:5, at most 1:4, at most 1:3, at most 1:2, or at most 1:1.

[0024] On the other hand, since the polylactic acid resin is added to water, it is preferably used in pellet form. The pellet is not particularly limited as long as it is a shape widely used in the technical field to which the present invention pertains.

[0025] (Step 2) Step 2 of the present invention is a step of maintaining the temperature of the water in step 1 at 65 to 99°C, which is a step of hydrolyzing the polylactic acid resin.

[0026] The meaning of "hydrolyzing the polylactic acid resin" means hydrolyzing a part of the polylactic acid resin, particularly means hydrolyzing a part of the polylactic acid resin with low fluidity. Thereby, the fluidity of the polylactic acid resin is improved as a whole.

[0027] Preferably, the water temperature in step 1 is maintained at 66°C or higher, 67°C or higher, 68°C or higher, 69°C or higher, or 70°C or higher; and at 98°C or lower, 98°C or lower, 97°C or lower, 96°C or lower, 95°C or lower, 94°C or lower, 93°C or lower, 92°C or lower, or 91°C or lower.

[0028] Preferably, step 2 is carried out under normal pressure. Normal pressure means 1 atm ± 0.1 atm.

[0029] Preferably, step 2 is performed for 0.5 to 24 hours. If the execution time is less than 0.5 hours, hydrolysis is excessively low, resulting in only a slight improvement in fluidity. Conversely, if the execution time exceeds 24 hours, hydrolysis is excessively high, leading to a problem of excessively high fluidity. More preferably, step 2 is performed for 1 hour or more, and 22 hours or less, 20 hours or less, 18 hours or less, 16 hours or less, 14 hours or less, 12 hours or less, or 10 hours or less.

[0030] (Step 3) Step 3 of the present invention is the step of recovering the polylactic acid resin from water after the processing in step 2.

[0031] Since the polylactic acid resin was in contact with high-temperature water for a long period of time, it is preferable to cool it rapidly. Therefore, it is preferable to cool the polylactic acid resin recovered in step 3 to 10°C or 20°C. For this purpose, it is preferable to contact it with cold water below 10°C.

[0032] Furthermore, for subsequent processing of the polylactic acid resin, it is preferable to thoroughly remove even small amounts of water, and for this purpose, drying under reduced pressure is preferable. Preferably, the drying is carried out so that the moisture content of the polylactic acid resin is 100 ppmw or less.

[0033] The drying method is not particularly limited, but as an example, it is preferable to dry the polylactic acid resin under reduced pressure at 25°C to 35°C until the moisture content is 5,000 ppmw or less, and then dry it under reduced pressure at 80 to 90°C until the moisture content is 100 ppmw or less. If the moisture content exceeds 5,000 ppmw, hydrolysis may proceed further when drying under reduced pressure at 80 to 90°C, and there is a problem that it takes an excessively long time to reach a moisture content of 100 ppmw when drying under reduced pressure at 25°C to 35°C.

[0034] The polylactic acid resin recovered in step 3 is characterized by having a higher melt index and improved flowability compared to the polylactic acid resin before treatment.

[0035] Preferably, the weight-average molecular weight of the polylactic acid resin recovered in step 3 is 50,000 to 100,000.

[0036] Preferably, the melting index of the polylactic acid resin recovered in step 3 (measured based on ASTM D1238 (230°C, 2.16 kg conditions)) is 300 to 3000 g / 10 min.

[0037] Preferably, the manufacturing method according to the present invention satisfies the following formula 1. [Formula 1] 3.0 ≤ MI1 / MI0 ≤ 24 In the above formula 1, MI0 is the melting index of the polylactic acid resin in step 1 (measured based on ASTM D1238 (230°C, 2.16 kg conditions)), MI1 is the melting index of the polylactic acid resin recovered in step 3 (measured based on ASTM D1238 (230°C, 2.16 kg conditions)).

[0038] Preferably, the manufacturing method according to the present invention satisfies the following formula 2. [Formula 2] 4.5 ≤ MI1 / MI0 ≤ 24 In the aforementioned equation 2, MI0 and MI1 are as defined in equation 1. [Effects of the Invention]

[0039] As described above, the manufacturing method according to the present invention has the advantage of being able to increase the melt index and improve the flowability by a simple method of treating polylactic acid resin with water. [Brief explanation of the drawing]

[0040] [Figure 1] Figure 1 shows the results of an experimental example of the present invention. [Figure 2] Figure 2 shows the results of an experimental example of the present invention. [Modes for carrying out the invention]

[0041] The embodiments of the present invention will be described in more detail below with reference to the following examples. However, the following examples are merely illustrative of embodiments of the present invention, and the content of the present invention is not limited to the following examples.

[0042] In the following examples and experimental cases, each physical property was measured as described below. - Flowability (MI; melt index): Measured according to ASTM D1238 (230°C, 1.2 kg conditions). - Acidity Measurement: Polylactic acid resin (1.5g) was thoroughly dissolved in CHCl3 (60mL), and then titrated with a 0.01N KOH in EtOH solution to measure and convert the acidity of each resin. The unit of acidity was [mmol Acid / kg PLA]. Specifically, the electrode membrane (opaque white part) and the titration solution tube were set up so that they were always immersed in the solution. The acidity of the polylactic acid resin was calculated by converting the amount of KOH used. -Weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (PDI): The weight-average molecular weight and number-average molecular weight were measured using an Agilent 12000 series GPC, calibrated with PC standards. The molecular weight distribution (PDI) was calculated by dividing the weight-average molecular weight by the number-average molecular weight.

[0043] Example 1 30 kg of polylactic acid (Mw: 116,700; PDI: 1.88, MI: 120 g / 10 min) pellets were placed in a 50 LSUS container A and vacuum-dried overnight at 110°C. At this time, the pellets were spherical or oval in shape, with a diameter of 3 mm to 5 mm.

[0044] 15 kg of 95°C distilled water was added to container A containing the vacuum-dried pellets and stirred. The container was then placed in an oven preheated to the same temperature as the added distilled water and maintained for 2.5 hours. After completion, excess water below 10°C was flowed into container A containing the mixture to rapidly cool it to 10-20°C. The cooled pellets were separated from the water using a filter and then dried under reduced pressure at 30°C for 8 to 24 hours until the moisture content was 5,000 ppm or less. Next, the pellets with a moisture content of 5,000 ppm or less were dried under reduced pressure at 85°C for 8 to 24 hours until the moisture content was 100 ppm or less. The weight-average molecular weight, molecular weight distribution, MI, and acidity of the obtained pellets were measured and are shown in Table 1 below.

[0045] Examples 2 to 4 Similar to Example 1, the polylactic acid pellets were processed by changing the temperature of the distilled water and / or the time it was kept in the oven, as shown in Table 1 below.

[0046] Comparative Example A comparative example was used: untreated polylactic acid (Mw: 116,700; PDI: 1.88, MI: 120 g / 10 min) pellets.

[0047] Experimental Example 1 The weight-average molecular weight, molecular weight distribution, MI, and acidity of the pellets obtained in the above examples and comparative examples were measured and are shown in Table 1 below. [Table 1]

[0048] Experimental Example 2 The comparative polylactic acid pellet (hereinafter referred to as "A") and 2 phr of ADR-4468 (branching agent, manufactured by BASF) were mixed using a Bravender mixer at 200°C and 60 rpm for 5 minutes. The polylactic acid pellet obtained in Example 4 (hereinafter referred to as "B") and 2 phr of ADR-4468 (branching agent, manufactured by BASF) were also mixed using a Bravender mixer at 200°C and 60 rpm for 5 minutes.

[0049] The weight-average molecular weight, PDI, and MI were measured for each of the prepared molten materials, and the results are shown in Table 2 and Figures 1 and 2 below. [Table 2]

[0050] As shown in Table 2 and Figure 1 above, sample A is a polylactic acid resin that has not undergone distilled water treatment according to the present invention, and the addition of the branching agent increased Mw by approximately 123%, while sample B is a polylactic acid resin that has undergone distilled water treatment according to the present invention, and the addition of the branching agent increased Mw by approximately 244%. From this, it was confirmed that the polylactic acid treated according to the present invention shows a significant improvement in the reactivity of the branching agent.

[0051] Experimental Example 3 The inorganic impurity content of the polylactic acid pellets obtained in Examples 1 to 4 was measured using the following method.

[0052] The analysis was performed using an inductively coupled plasma optical emission spectrometry (ICP-OES) analyzer, with scandium (Sc) as the internal standard. The analysis was conducted with an RF power of 1300W, a plasma gas flow of 15.00 L / min, a sample gas flow of 0.8 L / min, and an auxiliary gas flow of 0.20 L / min.

[0053] The results are shown in Table 3 below. [Table 3] As shown in Table 3 above, the polylactic acid according to the present invention is characterized by containing almost no inorganic impurities because it is produced by hydrolysis without the use of other chemical substances or catalysts.

[0054] Experimental Example 4 Nonwoven fabrics were produced from the polylactic acid pellets obtained in Examples 1 to 3 and the Comparative Example using the following method, and the results were evaluated.

[0055] Each polylactic acid pellet was heated and extruded to a nozzle, where it was passed through an orifice with a diameter of 0.2 mm and 32 orifices per inch to spin the fibers. During spinning, a high-temperature, high-speed gas was injected into the nozzle's surrounding openings to form a meltblown nonwoven fabric with an average fiber diameter of 15 μm or less. The process temperatures at this time are shown in Table 4 below. The diameter of the nonwoven fibers was analyzed using a scanning electron microscope (SEM).

[0056] The results are shown in Table 4 below. [Table 4] As shown in Table 4 above, it was confirmed that the polylactic acid according to the present invention has a low MI and can be miniaturized during the melt-blown process.

Claims

1. The melting index (measured based on ASTM D1238 (230°C, 2.16 kg conditions)) is 300 to 3000 g / 10 min. The acidity is 20 to 100 mmol Acid / kg, and The inorganic impurity content is 100 mg / kg or less. Polylactic acid resin.

2. The weight-average molecular weight of the polylactic acid resin is 50,000 to 100,000. The polylactic acid resin according to claim 1.

3. The melting index is 300 to 2,000 g / 10 min. The polylactic acid resin according to claim 1.

4. The acidity is 30 to 100 mmol Acid / kg. The polylactic acid resin according to claim 1.

5. The inorganic impurities are Sn and P. The total content of Sn and P is 85 mg / kg or less. The polylactic acid resin according to claim 1.

6. The inorganic impurities are Na, Zn, Ti, Al, Ag, Mg, Mn, Ba, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Ni, Sb, Sr, V, and Zr. The total content of Na, Zn, Ti, Al, Ag, Mg, Mn, Ba, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Ni, Sb, Sr, V, and Zr is 10 mg / kg or less. The polylactic acid resin according to claim 1.

7. Step 1: Immerse the polylactic acid resin in water; Step 2: Maintaining the water temperature of Step 1 at 65 to 99°C; and The process includes a step (step 3) of recovering the polylactic acid resin from water. A method for producing polylactic acid resin according to any one of claims 1 to 6.

8. The melting index of the polylactic acid resin in step 1 (measured based on ASTM D1238 (230°C, 2.16 kg conditions)) is 5 to 200 g / 10 min. The manufacturing method according to claim 7.

9. In step 1, the weight ratio of the polylactic acid resin to water is 1:0.1 to 1:

10. The manufacturing method according to claim 7.

10. In step 2, the water temperature is maintained at 70 to 99°C. The manufacturing method according to claim 7.

11. Step 2 is performed under normal pressure. The manufacturing method according to claim 7.

12. Step 2 is performed for 0.5 to 24 hours. The manufacturing method according to claim 7.

13. The following equation 1 is satisfied: The manufacturing method according to claim 7. [Formula 1] 3.0≦MI １ / MI ０ ≦24 In the above formula 1, MI ０ This is the melt index of the polylactic acid resin in step 1 (measured based on ASTM D1238 (230°C, 2.16 kg conditions)), MI １ This is the melting index of the polylactic acid resin recovered in step 3 (measured based on ASTM D1238 (230°C, 2.16 kg conditions)).

14. The weight-average molecular weight of the polylactic acid resin in step 1 is 100,000 to 250,000. The manufacturing method according to claim 7.

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