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EP-4741440-A1 - METHOD FOR PREPARING POLYLACTIC ACID RESIN WITH IMPROVED MELTABILITY AND REACTIVITY

EP4741440A1EP 4741440 A1EP4741440 A1EP 4741440A1EP-4741440-A1

Abstract

A polylactic acid resin according to the present disclosure and a method for preparing the same have the feature that the melt index can be increased and the flowability can be improved through a simple method of treating a polylactic acid resin with water. Thereby, it is also possible to improve the reactivity of the polylactic acid resin and improve the compatibility with various additives, thereby further expanding the application fields of the polylactic acid resin.

Inventors

  • LEE, Doyun
  • WOO, WON HEE
  • OH, WAN KYU

Assignees

  • LG Chem, Ltd.

Dates

Publication Date
20260513
Application Date
20240626

Claims (14)

  1. A polylactic acid resin having the following features: a melt index of 300 to 3000 g/10 min, as measured at 230 °C under 2.16 kg according to ASTM D1238, an acid value of 20 to 100 mmol acid/kg, and an inorganic impurity content of 100 mg/kg or less.
  2. The polylactic acid resin according to claim 1, wherein: a weight average molecular weight of the polylactic acid resin is 50,000 to 100,000.
  3. The polylactic acid resin according to claim 1, wherein: the melt index is 300 to 2000 g/10 min.
  4. The polylactic acid resin according to claim 1, wherein: the acid value is 30 to 100 mmol acid/kg.
  5. The polylactic acid resin according to claim 1, wherein: the inorganic impurity is Sn and P, and the total content of Sn and P is 85 mg/kg or less.
  6. The polylactic acid resin according to claim 1, wherein: the inorganic impurity is 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.
  7. A method for preparing the polylactic acid resin as set forth in any one of claims 1 to 6, the method comprising the steps of: immersing the polylactic acid resin in water (step 1); maintaining the temperature of water in the step 1 at 65 to 99 °C (step 2); and recovering the polylactic acid resin from water (step 3).
  8. The method according to claim 7, wherein: a melt index of the polylactic acid resin of the step 1 is 5 to 200 g/10 min (as measured at 230 °C under 2.16 kg according to ASTM D1238).
  9. The method according to claim 7, wherein: a weight ratio between the polylactic acid resin and water in the step 1 is 1:0.1 to 1:10.
  10. The method according to claim 7, wherein: the temperature of water in the step 2 is maintained at 70 to 99 °C.
  11. The method according to claim 7, wherein: the step 2 is carried out under a normal pressure.
  12. The method according to claim 7, wherein: the step 2 is carried out for 0.5 to 24 hours.
  13. The method according to claim 7, satisfying the following Mathematical Formula 1: 3.0 ≤ MI 1 / MI 0 ≤ 24 wherein in Mathematical Formula 1, MI 0 is the melt index of the polylactic acid resin of the step 1 (as measured at 230 °C under 2.16 kg according to ASTM D1238), and MI 1 is the melt index of the polylactic acid resin recovered in the step 3 (as measured at 230 °C under 2.16 kg according to ASTM D1238).
  14. The method according to claim 1, wherein: a weight average molecular weight of the polylactic acid resin of the step 1 is 100,000 to 250,000.

Description

[TECHNICAL FIELD] CROSS-REFERENCE TO RELATED APPLICATION(S) This application claims the benefit of Korean Patent Application No. 10-2023-0087615 filed on July 6, 2023 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. The present disclosure relates to a polylactic acid resin with improved meltability and reactivity and a method for preparing the same. [BACKGROUND] Polylactic acid (PLA) is a plant-derived resin obtained from plants such as corn, and is receiving attention as an excellent eco-friendly material due to its biodegradable properties. Unlike petroleum-based resins such as polystyrene resins, polyvinyl chloride resins, or polyethylene resins, which are currently used, polylactic acid has effects of preventing depletion of petroleum-based resources and suppressing carbon dioxide emissions, and therefore, may reduce environmental pollution, which is a disadvantage of petroleum-based plastic products. As environmental pollution caused by waste plastics and the like has emerged as social problems, efforts have been made to expand the application range of polylactic acid to various fields, including food packing materials and containers, electronic product cases, etc., to which general plastics (petroleum-based resins) have been applied. Polylactic acid has a diverse range of melt index(MI) required according to the product to be produced. Among them, polylactic acid with a high melt index may be required, and for example, polylactic acid with a high melt index (500-3000 g/10 min@230°C) is required to produce melt-blown nonwoven fabrics. However, since the melt index of the polylactic acid generally prepared by a commercial process has the range of 5 to 200 g/10 min (as measured at 230 °C under 2.16 kg according to ASTM D1238), polymerization of a polylactic acid with high melt index described above is not easy by conventional methods. There are various reasons why polymerization of polylactic acid with high flowability is difficult, but typically, a process of removing volatile substances such as residual monomers after polymerization of a polylactic acid (devolatilization process) is essentially included, but there is a problem that part of a polylactic acid with high flowability may evaporate together, which may make the process not smooth, and it is difficult to form pellets during the pelletizing process. In addition, the polylactic acid synthesized by a conventional polymerization method has low acid value, which limits post-processing and/or modification. For example, there is a problem that reaction with chain extenders or branching agents is decreased. Therefore, the present inventors have conducted extensive research to solve the above problems, and as a result, found that by treating the prepared polylactic acid with distilled water as described below, it is possible to increase the melt index and simultaneously improve its flowability, thereby preparing a polylactic acid with high flowability, and completed the present disclosure. [DETAILED DESCRIPTION OF THE INVENTION] [Technical Problem] It is an object of the present disclosure to provide a polylactic acid resin with improved meltability and reactivity and a method for preparing the same. [Technical Solution] In order to achieve the above object, according to the present disclosure, there is provided a polylactic acid resin having the following features: a melt index of 300 to 3000 g/10 min, as measured at 230 °C under 2.16 kg according to ASTM D1238,an acid value of 20 to 100 mmol acid/kg, andan inorganic impurity content of 100 mg/kg or less. The polylactic acid resin according to the present disclosure is characterized by increasing the melt index and simultaneously improving the flowability by the preparation method described below, and the polylactic acid resin is also characterized in that it contains almost no inorganic impurities because no other chemicals or catalysts are used in the preparation method. Preferably, the weight average molecular weight of the polylactic acid resin is 50,000 to 100,000. Preferably, the melt 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; and 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. 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. Preferably, the inorganic impurity is Sn and P, and the total content of Sn and P is 85 mg/kg or less. In addition, preferably, the inorganic impurity is 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, B