Method for preparing polylactic acid resin with improved meltability and reactivity

Abstract

A polylactic acid resin and a method for preparing same according to the present invention are characterized in that the melt index of the polylactic acid resin can be increased and the flowability improved through a simple method that involves treating the polylactic acid resin with water. As a result, the reactivity of the polylactic acid resin is improved such that the compatibility with various additives is improved, and the polylactic acid resin can be used in a wider variety of fields.

Description

Polylactic acid resin with improved meltability and reactivity and method for producing the same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0087615, filed July 6, 2023, the entire contents of which are incorporated herein by reference.

[0003]

[0004] The present invention relates to a polylactic acid resin having improved meltability and reactivity and a method for producing the same.

[0005] Polylactic acid (PLA) is a plant-derived resin derived from plants like corn. Its biodegradability has garnered attention as an excellent, eco-friendly material. Unlike conventional petroleum-based resins like polystyrene, polyvinyl chloride, and polyethylene, PLA prevents the depletion of petroleum resources and reduces carbon dioxide emissions, potentially reducing the environmental impact of petroleum-based plastic products.

[0006]

[0007] Accordingly, as environmental pollution caused by waste plastics and other waste materials has become a social issue, efforts are being made to expand the scope of application of polylactic acid to product fields where general plastics (petroleum resins) were previously used, such as food packaging materials and containers, and electronic product cases.

[0008]

[0009] Polylactic acid has a wide range of melt index (MI) requirements depending on the product to be manufactured. Among these, there are cases where polylactic acid with a high melt index is required. For example, polylactic acid with high flowability (melt index 500-3000 g / 10 min @230℃) is required for the production of melt-blown nonwoven fabrics. However, since the melt index (measured according to ASTM D1238 (230℃, 2.16 kg conditions)) of polylactic acid manufactured in a commercial process generally ranges from 5 to 200 g / 10 min, it is not easy to polymerize high-flow polylactic acid as described above using conventional methods.

[0010]

[0011] There are various reasons why polymerization of high-flow polylactic acid is difficult. A representative example is the devolatilization process, which essentially removes volatile substances such as residual monomers after polymerization of polylactic acid. During this process, some of the high-flow polylactic acid may evaporate, hindering the smooth operation of the process. Furthermore, pellet formation is difficult during the pelletizing process. Furthermore, polylactic acid synthesized through conventional polymerization methods has low acidity, limiting post-processing and / or modification. For example, it has poor reactivity with chain extenders or branching agents.

[0012]

[0013] Accordingly, the inventors of the present invention have made diligent efforts to solve the above-mentioned problems, and as a result, have confirmed that polylactic acid having high flowability can be manufactured by treating the manufactured polylactic acid with distilled water to increase the melting index and improve the flowability as described below, thereby completing the present invention.

[0014] The present invention provides a polylactic acid resin having improved meltability and reactivity and a method for producing the same.

[0015] To solve the above problem, the present invention provides the following polylactic acid resin:

[0016] The melting index (measured according to ASTM D1238 (230℃, 2.16 kg conditions)) is 300 to 3000 g / 10 min,

[0017] Acidity is 20 to 100 mmol Acid / kg, and

[0018] Inorganic impurity content of 100 mg / kg or less,

[0019] Polylactic acid resin.

[0020]

[0021] The polylactic acid resin according to the present invention is characterized by increasing the melting index and improving the flowability at the same time through the manufacturing method described below, and further, since no other chemical substances or catalysts are used in the manufacturing method, it is characterized by containing almost no inorganic impurities.

[0022]

[0023] Preferably, the weight average molecular weight of the polylactic acid resin is 50,000 to 100,000.

[0024]

[0025] Preferably, the melting index is 400 g / 10 min or more, 500 g / 10 min or more, 600 g / 10 min or more, 700 g / 10 min or more, 800 g / 10 min or more, 900 g / 10 min or more, or 1000 g / 10 min or more; 2900 g / 10 min or less, 2800 g / 10 min or less, 2700 g / 10 min or less, 2600 g / 10 min or less, 2500 g / 10 min or less, 2400 g / 10 min or less, 2300 g / 10 min or less, 2200 g / 10 min or less, 2100 g / 10 min or less, or 2000 g / 10 min or less.

[0026]

[0027] Preferably, the acid value is 30 mmol Acid / kg or more; 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.

[0028]

[0029] Preferably, the inorganic impurities are Sn and P, and the total content of Sn and P is 85 mg / kg or less. In addition, 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.

[0030]

[0031] In addition, the present invention provides a method for producing the above-described polylactic acid resin, comprising the following steps:

[0032] Step of immersing polylactic acid resin in water (step 1);

[0033] A step of maintaining the temperature of the water in step 1 at 65 to 99°C (step 2); and

[0034] Step 3: Recovering polylactic acid resin from water.

[0035]

[0036] The present invention is characterized by a simple method for treating polylactic acid, which is typically manufactured through commercial processes, with water, thereby increasing the melt index of the polylactic acid and simultaneously improving its flowability. The present invention is described in detail, step by step, below.

[0037]

[0038] (Step 1)

[0039] Step 1 of the present invention is a step of immersing a polylactic acid resin in water, which is a step of preparing the hydrolysis of polylactic acid.

[0040]

[0041] The polylactic acid resin used in the above step 1 is generally manufactured in a commercialized process, and preferably, the melting index of the polylactic acid (measured according to ASTM D1238 (230°C, 2.16 kg conditions)) is 5 to 200 g / 10 min. In other words, in the present invention, rather than polymerizing a high-flow polylactic acid resin, a general low-flow polylactic acid resin is hydrolyzed as described below to manufacture a high-flow polylactic acid resin.

[0042]

[0043] Preferably, the weight average molecular weight of the polylactic acid resin used in the above 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; 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.

[0044]

[0045] Preferably, the melt index (measured according to ASTM D1238 (230°C, 2.16 kg conditions)) of the polylactic acid resin of step 1 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; 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.

[0046]

[0047] Preferably, the water is distilled water. Preferably, the weight ratio of the polylactic acid resin and water in step 1 is 1:0.1 to 1:10. More preferably, the weight ratio of the polylactic acid resin and water in step 1 is 1:0.2 or more, 1:0.3 or more, or 1:0.4 or more; or 1:9 or less, 1:8 or less, 1:7 or less, 1:6 or less, 1:5 or less, 1:4 or less, 1:3 or less, 1:2 or less, or 1:1 or less.

[0048]

[0049] Meanwhile, since the polylactic acid resin is added to water, it is preferable to use it in pellet form. The pellet shape is not particularly limited as long as it is a shape widely used in the technical field to which the present invention pertains.

[0050]

[0051] (Step 2)

[0052] Step 2 of the present invention is a step of maintaining the temperature of the water of step 1 at 65 to 99°C, and is a step of hydrolyzing polylactic acid resin.

[0053]

[0054] The above term "hydrolyzing polylactic acid resin" refers to hydrolyzing a portion of polylactic acid resin, and in particular, hydrolyzing a portion of low-flow polylactic acid resin. As a result, the overall flowability of the polylactic acid resin is improved.

[0055]

[0056] Preferably, the temperature of the water 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 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.

[0057]

[0058] Preferably, step 2 is performed under atmospheric pressure. The atmospheric pressure means 1 atm±0.1 atm.

[0059]

[0060] Preferably, step 2 is performed for 0.5 to 24 hours. If the performing time is less than 0.5 hours, the hydrolysis is too little, resulting in minimal improvement in flowability. Conversely, if the performing time exceeds 24 hours, the hydrolysis is too much, resulting in excessively high flowability. 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.

[0061]

[0062] (Step 3)

[0063] Step 3 of the present invention is a step of recovering polylactic acid resin from water after the treatment in step 2.

[0064]

[0065] Because the polylactic acid resin has been in contact with high-temperature water for a long period of time, rapid cooling is desirable. Therefore, it is preferable to cool the polylactic acid resin recovered in Step 3 to 10°C to 20°C. For this purpose, contact with cold water, such as water at 10°C or lower, is preferable.

[0066]

[0067] Additionally, for subsequent processing of polylactic acid resin, it is desirable to sufficiently remove even a small amount of water, and for this purpose, drying under reduced pressure is preferred. Preferably, drying is performed so that the moisture content of the polylactic acid resin is 100 ppmw or less.

[0068]

[0069] The drying method is not particularly limited, but as an example, it is preferable to dry under reduced pressure at 25°C to 35°C until the moisture content of the polylactic acid resin becomes 5,000 ppmw or less, and then dry under reduced pressure at 80 to 90°C until the moisture content becomes 100 ppmw or less. If the moisture content exceeds 5,000 ppmw, there is a concern that hydrolysis may progress further when drying under reduced pressure at 80 to 90°C, and also, there is a problem that it takes too long for the moisture content to reach 100 ppmw when drying under reduced pressure at 25°C to 35°C.

[0070]

[0071] The polylactic acid resin recovered in the above step 3 is characterized by a higher melting index and improved flowability compared to the polylactic acid resin before processing.

[0072]

[0073] Preferably, the weight average molecular weight of the polylactic acid resin recovered in step 3 is 50,000 to 100,000.

[0074]

[0075] Preferably, the melting index (measured according to ASTM D1238 (230°C, 2.16 kg conditions)) of the polylactic acid resin recovered in the above step 3 is 300 to 3000 g / 10 min.

[0076]

[0077] Preferably, the manufacturing method according to the present invention satisfies the following mathematical formula 1:

[0078] [Mathematical Formula 1]

[0079] 3.0 ≤ MI1 / MI0≤24

[0080] In the above mathematical formula 1,

[0081] MI0 is the melting index of the polylactic acid resin of the above step 1 (measured according to ASTM D1238 (230℃, 2.16 kg conditions)),

[0082] MI1 is the melting index (measured according to ASTM D1238 (230°C, 2.16 kg conditions)) of the polylactic acid resin recovered in the above step 3.

[0083]

[0084] Preferably, the manufacturing method according to the present invention satisfies the following mathematical formula 2:

[0085] [Equation 2]

[0086] 4.5 ≤ MI1 / MI0≤24

[0087] In the above mathematical expression 2, MI0 and MI1 are as defined in mathematical expression 1.

[0088] As described above, the manufacturing method according to the present invention has the characteristic of increasing the melting index and improving the flowability through a simple method of treating polylactic acid resin with water.

[0089] Figures 1 and 2 show the results of experimental examples of the present invention.

[0090] Hereinafter, embodiments of the present invention will be described in more detail in 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 by the following examples.

[0091]

[0092] In the examples and experimental examples below, each property was measured as follows.

[0093]

[0094] - Melt index (MI): Measured according to ASTM D1238 (230℃, 1.2 kg conditions).

[0095] - Acidity Measurement: Polylactic acid resin (1.5 g) was sufficiently dissolved in CHCl3 (60 mL), and then titrated with 0.01 N KOH in EtOH solution to measure and convert the acidity of each resin. The unit of acidity at this time was [mmol Acid / kg PLA]. Specifically, the membrane part of the electrode (opaque white part) and the titration solution tube were set 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.

[0096] - 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. In addition, the molecular weight distribution (PDI) was calculated by dividing the weight-average molecular weight by the number-average molecular weight.

[0097]

[0098] Example 1

[0099] Polylactic acid (Mw: 116,700; PDI: 1.88, MI: 120 g / 10 min) pellets (30 kg) were placed in a 50 L SUS container A and vacuum dried overnight at 110°C. At this time, the shape of the pellets was spherical or egg-shaped with a diameter of 3 mm to 5 mm.

[0100]

[0101] Distilled water (15 kg) at 95°C was added to container A containing vacuum-dried pellets, stirred, and placed in a preheated oven at the same temperature as the added distilled water, where it was maintained for 2.5 hours. After completion, an excess of water below 10°C was poured into container A containing the mixture to rapidly cool the mixture to 10 to 20°C. The cooled pellets were separated from the water using a strainer, and then dried under reduced pressure at 30°C for 8 to 24 hours until the moisture content became 5,000 ppm or less. Subsequently, the pellets having 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 became 100 ppm or less. The weight average molecular weight, molecular weight distribution, MI, and acidity of the obtained pellets were measured, and the results are shown in Table 1 below.

[0102]

[0103] Examples 2 to 4

[0104] Polylactic acid pellets were treated in the same manner as in Example 1 above, but the temperature of the distilled water and / or the time maintained in the oven were changed as shown in Table 1 below.

[0105]

[0106] Comparative example

[0107] Polylactic acid (Mw: 116,700; PDI: 1.88, MI: 120 g / 10 min) pellets without separate treatment were used as a comparative example.

[0108]

[0109] Experimental Example 1

[0110] For the pellets obtained according to the above examples and comparative examples, the weight average molecular weight, molecular weight distribution, MI, and acidity were measured and shown in Table 1 below.

[0111] Distilled water treatment time (h) Distilled water treatment temperature (℃) MI (g / 10 min) Acidity (mmol acid / kg PLA) Mw (g / mol) PDI Example 12.59515005560,0001.86 Example 21.5956504272,0001.90 Example 31.0954503577,0001.92 Example 42.5904003083,3001.89 Comparative example 0-12010116,7001.88

[0112]

[0113] Experimental Example 2

[0114] The polylactic acid pellets of the comparative example (hereinafter referred to as 'A') and 2 phr of ADR-4468 (branching agent, BASF) were mixed using a Brabender mixer at 200°C and 60 rpm for 5 minutes. In addition, the polylactic acid pellets obtained in Example 4 (hereinafter referred to as 'B') and 2 phr of ADR-4468 (branching agent, BASF) were mixed using a Brabender mixer at 200°C and 60 rpm for 5 minutes.

[0115]

[0116] For each manufactured melt, the weight average molecular weight, PDI, and MI were measured, and the results are shown in Table 2 and Figures 1 and 2 below.

[0117] Sample MI (g / 10 min) Mw (g / mol) Mw increase rate according to addition of PDI branching agent 1) A120116,7001.88-A + Branching agent 2phr66141,7002.0021 %B40083,3001.89-B + Branching agent 2phr31202,9002.53144 %1) Mw change rate (%) according to branching agent addition = (Mw after branching agent addition - Mw before branching agent addition) / (Mw before branching agent addition)

[0118]

[0119] As shown in Table 2 and FIG. 1, Sample A is a polylactic acid resin that has not been treated with distilled water according to the present invention, and its Mw increased by about 123% with the addition of a branching agent, whereas Sample B is a polylactic acid resin that has been treated with distilled water according to the present invention, and its Mw increased by about 244% with the addition of a branching agent, and from this, it was confirmed that the polylactic acid treated according to the present invention has significantly improved reactivity with the branching agent.

[0120]

[0121] Experimental Example 3

[0122] The inorganic impurity content of the polylactic acid pellets obtained in Examples 1 to 4 was measured by the following method.

[0123]

[0124] The analysis was performed using inductively coupled plasma optical emission spectrometry (ICP-OES), using scandium (Sc) as an internal standard material, at an RF power of 1300 W, 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.

[0125]

[0126] The above results are shown in Table 3 below.

[0127] Content (mg / Kg) ** Sn * P * Na, Zn, Ti, Al, Ag, Mg, Mn, Ba, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Ni, Sb, Sr, V, ZrTotal contentExample 12050<5<75Example 23050<5<85Example 32060<5<85* Sn and P are components resulting from the catalyst and stabilizer used during PLA polymerization.** This is the result of analysis using ICP-OES.

[0128]

[0129] As shown in Table 3 above, the polylactic acid according to the present invention is produced by hydrolysis, does not use other chemicals or catalysts, and therefore has the characteristic of containing almost no inorganic impurities.

[0130]

[0131] Experimental Example 4

[0132] Nonwoven fabrics were manufactured using the polylactic acid pellets obtained in Examples 1 to 3 and Comparative Examples using the following method, and the results were evaluated.

[0133]

[0134] Each polylactic acid pellet was heated and extruded, transferred to a nozzle, and passed through an orifice with a diameter of 0.2 mm and a number of 32 per inch to spin fibers. During spinning, a meltblown nonwoven fabric with an average fiber diameter of 15 ㎛ or less was formed by the high-temperature and high-velocity gas injected from the injection holes around the nozzle, and the process temperatures at this time were as shown in Table 4 below. The diameter of the nonwoven fibers was analyzed using a scanning electron microscope (SEM).

[0135]

[0136] The above results are shown in Table 4 below.

[0137] Process temperature (℃)Nonwoven fabric evaluation resultNozzle hot-air weight (g / m) 2 )Fiber diameter (nm) Example 1 2 20 2 50 4 0 2.0 2 30 2 60 1.8 Example 2 2 20 2 40 4 0 2.1 2.1 2.0 1.5 1.5 Example 3 2 40 2 60 3 0 2.2 Comparative example 2 5 0 2 70 4 0 10.2 2 70 2 70 6.1

[0138]

[0139] As shown in Table 4 above, it was confirmed that the polylactic acid according to the present invention has a low MI and thus can be made into ultrafine particles during the melt blowing process.

Claims

1. The melting index (measured according to ASTM D1238 (230℃, 2.16 kg conditions)) is 300 to 3000 g / 10 min, Acidity is 20 to 100 mmol Acid / kg, and Inorganic impurity content of 100 mg / kg or less, Polylactic acid resin.

2. In paragraph 1, The weight average molecular weight of the above polylactic acid resin is 50,000 to 100,000, Polylactic acid resin.

3. In paragraph 1, The melting index is 300 to 2000 g / 10 min, Polylactic acid resin.

4. In paragraph 1, The acidity is 30 to 100 mmol Acid / kg, Polylactic acid resin.

5. In paragraph 1, The above inorganic impurities are Sn and P, The total content of Sn and P is less than 85 mg / kg, Polylactic acid resin.

6. In paragraph 1, The above 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 less than 10 mg / kg, Polylactic acid resin.

7. Step of immersing polylactic acid resin in water (step 1); A step of maintaining the temperature of the water in step 1 at 65 to 99°C (step 2); and Comprising a step of recovering polylactic acid resin from water (step 3), A method for producing a polylactic acid resin according to any one of claims 1 to 6.

8. In paragraph 7, The melting index (measured according to ASTM D1238 (230°C, 2.16 kg conditions)) of the polylactic acid resin of the above step 1 is 5 to 200 g / 10 min. Manufacturing method.

9. In paragraph 7, In the above step 1, the weight ratio of the polylactic acid resin and water is 1:0.1 to 1:

10. Manufacturing method.

10. In paragraph 7, In the above step 2, the temperature of the water is maintained at 70 to 99°C. Manufacturing method.

11. In paragraph 7, The above step 2 is performed under normal pressure, Manufacturing method.

12. In paragraph 7, Step 2 above is performed for 0.5 to 24 hours, Manufacturing method.

13. In paragraph 7, Satisfying the following mathematical expression 1, Manufacturing method: [Mathematical Formula 1] 3.0 ≤ MI1 / MI0≤24 In the above mathematical formula 1, MI0 is the melting index of the polylactic acid resin of the above step 1 (measured according to ASTM D1238 (230℃, 2.16 kg conditions)), MI1 is the melting index (measured according to ASTM D1238 (230°C, 2.16 kg conditions)) of the polylactic acid resin recovered in the above step 3.

14. In paragraph 1, The weight average molecular weight of the polylactic acid resin of the above step 1 is 100,000 to 250,000. Manufacturing method.

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