Patent Description:
Polylactide (or polylactic acid; PLA) resin is prepared based on biomass materials, and is an eco-friendly material which emits less global warming gas carbon dioxide during the production process, and is degraded by a specific temperature and composting facility. In recent years, it has also attracted attention as one of the materials that can replace existing crude oilbased resins as a measure for the upcycling of waste plastics and regulation on carbon emissions.

In addition, the polylactide resin has the advantages of being inexpensive compared to other biodegradable polymers and having high tensile strength and modulus properties.

However, the polylactide resin has a problem that a rigid polymer main chain is repeated in short units, the crystallization rate is slow due to slow chain mobility, and the molding cycle is long, thereby lowering the productivity. Therefore, in order to improve these problems, many studies are being conducted to introduce a material such as a nucleating agent to improve productivity and heat resistance.

In general, the materials used as the nucleating agents are mainly inorganic nucleating agents, and it has been reported that materials such as talc, mica, and nanoclay are used, and some of them are added during PLA molding, thereby capable of improving heat resistance and strength.

However, if such a nucleating agent is added in an excessive amount, there is a problem that the specific gravity of the resin increases and the transparency decreases. On the other hand, as a material that improves the crystallinity degree and transparency, organic nucleating agents such as LAK <NUM> (aromatic sulfonate derivative), sodium benzoate, N-aminophthalimide, phthalhydrazide, and cadmium phenylmalonate are used. However, these materials are not bio-based materials, and have dispersion problems with PLA resins.

Therefore, there is a need to introduce bio-based organic nucleating agents that can be prepared in eco-friendly products and, at the same time, do not impair transparency. In addition, there is a need to introduce a nucleating agent having less dispersion problems with the polylactide resin to further improve the crystallinity degree of the polylactide resin.

<CIT> discloses a polylactic acid resin composition comprising high molecular weight polylactic acid with <NUM> to <NUM>% by weight and a low molecular weight polylactic acid containing a COOH group or ester residue of lactic acid as a nucleating agent.

<NPL>, discloses an effect of orotic acid on the crystallization kinetics and morphology of biodegradable poly(L-lactide) as a nucleating agent.

<CIT> discloses a polylactic acid resin composition comprising a mixture of two nucleating agents.

It is an object of the present disclosure to provide a polylactide resin composition excellent in crystallinity degree by using in combination with a specific nucleating agent.

In order to achieve the above object, according to the present disclosure, there is provided the following polylactide resin composition:
A polylactide resin composition comprising:.

As used herein, the term "polylactide resin" is defined to comprehensively refer to a homopolymer or copolymer including a repeating unit represented by the following Chemical Formula.

The polylactide resin can be prepared by a process including a step of forming the above repeating unit by the ring opening polymerization of the lactide monomer. The polymer obtained after the completion of such ring opening polymerization and the formation of the repeating unit can be referred to as the "polylactide resin".

At this time, the term "lactide monomer" can be defined as follows. Typically, lactides can be classified into L-lactide consisting of L-lactic acid, D-lactide consisting of D-lactic acid, and meso-lactide consisting of an L-type and a D-type. Also, a mixture of L-lactide and D-lactide in a ratio of <NUM>:<NUM> is referred to as D,L-lactide or rac-lactide. Among these lactides, the polymerization proceeding only with either of L-lactide and D-lactide that have a high level of optical purity is known to yield an L- or D-polylactide (PLLA or PDLA) with a high level of stereoregularity. Such polylactides have a faster crystallization rate and also a higher crystallinity degree than a polylactide having a low level of optical purity. However, the term "lactide monomer" is defined to include all types of lactides regardless of the characteristic differences of lactides depending on their types and the characteristic differences of the polylactide resins obtained therefrom.

Meanwhile, the polylactide resin composition according to the present disclosure has a weight average molecular weight of <NUM>,<NUM> to <NUM>,<NUM> as an example.

The present disclosure is characterized in that the polylactide resin is used in combination of the first nucleating agent and the second nucleating agent to thereby improve the crystallinity degree of the polylactide resin.

The first nucleating agent is uracil or orotic acid. The first nucleating agent is a bio-based organic material, and is added to the polylactide resin, acts as a nucleation site and induces the crystal nucleus generation at high temperature, thereby capable of improving the crystallization rate.

The first nucleating agent is contained in an amount of <NUM> to <NUM>% by weight based on the total weight of the polylactide resin composition. If the content is less than <NUM>% by weight, the effect due to the use of the first nucleating agent is insignificant, and if the content exceeds <NUM>% by weight, there is a risk of impairing physical properties inherent in the polylactide resin. More preferably, the first nucleating agent is contained in an amount of <NUM>% by weight or less, <NUM>% by weight or less, or <NUM>% by weight or less.

The second nucleating agent is a nucleating agent containing an oligomer structure of the lactide monomer. Due to the oligomer structure of the lactide monomer, it has high compatibility with the polylactide resin, and is added to the polylactide resin to play a role similar to that of a plasticizer. Thereby, a free volume can be formed in the polylactide resin to thereby enhance the chain mobility of the polylactide resin and increase the crystallinity degree.

Preferably, the second nucleating agent is a compound represented by the following Chemical Formula <NUM>:
<CHM>
wherein, in Chemical Formula <NUM>,
L is any one selected from the group consisting of:
<CHM>
<CHM>
wherein,.

The weight average molecular weight of the second nucleating agent may be adjusted according to the number of each lactide repeating unit. Preferably, the weight average molecular weight of the second nucleating agent is <NUM>,<NUM> to <NUM>,<NUM>. More preferably, the weight average molecular weight of the second nucleating agent is <NUM>,<NUM> or more, <NUM>,<NUM> or more, <NUM>,<NUM> or more, <NUM>,<NUM> or more, or <NUM>,<NUM> or more; and <NUM>,<NUM> or less, <NUM>,<NUM> or less, <NUM>,<NUM> or less, <NUM>,<NUM> or less, <NUM>,<NUM> or less, or <NUM>,<NUM> or less.

The second nucleating agent is contained in an amount of <NUM> to <NUM>% by weight based on the total weight of the polylactide resin composition. If the content is less than <NUM>% by weight, the effect due to the use of the second nucleating agent is insignificant, and if the content exceeds <NUM>% by weight, there is a risk of impairing the physical properties inherent in the polylactide resin. More preferably, the second nucleating agent is contained in an amount of <NUM>% by weight or more, <NUM>% by weight or more, or <NUM>% by weight or more; and <NUM>% by weight or less, <NUM>% by weight or less, <NUM>% by weight or less, or <NUM>% by weight or less.

Meanwhile, the method for preparing the above-mentioned polylactide resin composition is not particularly limited as long as it is a method of mixing the polylactide resin, the first nucleating agent, and the second nucleating agent. In one example, since respective components are well dissolved in a CHCl<NUM> solvent, the polylactide resin composition can be prepared by a method of dissolving respective components in a CHCl<NUM> solvent, mixing them, and then removing the solvent.

The above-mentioned polylactide resin composition according to the present disclosure is excellent in crystallinity degree and excellent in dispersibility between components and thus, also is excellent in transparency. Therefore, the polylactide resin composition according to the present disclosure can maintain the properties inherent in the polylactide resin according to the present disclosure while having excellent processability.

Below, embodiments of the present disclosure will be described in more detail with reference to examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure.

An oligomer was prepared using PEG-<NUM> (P4) as an initiator. Specifically, lactide and P4 were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After vacuum drying, the reaction mixture was cooled to room temperature to prepare a second nucleating agent, which was named P4-O-<NUM>, P4-O-<NUM>, P4-O-<NUM>, and P4-O-<NUM>, respectively, and the weight average molecular weight is shown in Tables <NUM> and <NUM> below.

An oligomer was prepared using PEG-<NUM> (P4) as an initiator. Specifically, lactide and P4 were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After adjusting the temperature to <NUM>, acetic anhydride (<NUM> equivalents relative to the terminal OH group) was added, and further reacted for <NUM> hours. After completion of the reaction, acetic acid as a byproduct and residual acetic anhydride were removed by vacuum drying to prepare a second nucleating agent having a structure in which the terminal group was substituted with an acetyl group, which was named P4-A-<NUM>, P4-A-<NUM>, P4-A-<NUM>, and P4-A-<NUM>, respectively, and the weight average molecular weights are shown in Tables <NUM> and <NUM> below.

NMR analysis was performed on the prepared second core agent together with PEG-<NUM> as a starting material, and the results are shown in <FIG>.

As shown in <FIG>, OH groups (<NUM> ppm) or acetyl groups (<NUM>-<NUM> ppm) at both terminal ends of the oligomer were observed.

An oligomer was prepared using PEG-<NUM> (P10) as an initiator. Specifically, lactide and P10 were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After vacuum drying, the reaction mixture was cooled to room temperature to prepare a second nucleating agent, which was named P10-O-<NUM>, P10-O-<NUM>, P10-O-<NUM>, and P10-O-<NUM>, respectively, and the weight average molecular weight is shown in Tables <NUM> and <NUM> below.

An oligomer was prepared using PEG-<NUM> (P10) as an initiator. Specifically, lactide and P10 were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in an amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After adjusting the temperature to <NUM>, acetic anhydride (<NUM> equivalents relative to the terminal OH group) was added, and further reacted for <NUM> hours. After completion of the reaction, acetic acid as a byproduct and residual acetic anhydride were removed by vacuum drying to prepare a second nucleating agent having a structure in which the terminal group was substituted with an acetyl group, which was named P10-A-<NUM>, P10-A-<NUM>, P10-A-<NUM>, P10-A-<NUM>, respectively, and the weight average molecular weights are shown in Tables <NUM> and <NUM> below.

An oligomer was prepared using cyclohexanedimethanol (CD) as an initiator. Specifically, lactide and CD were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After vacuum drying, the reaction mixture was cooled to room temperature to prepare a second nucleating agent, which were named CD-O-<NUM>, CD-O-<NUM>, CD-O-<NUM>, and CD-O-<NUM>, respectively, and the weight average molecular weight is shown in Tables <NUM> and <NUM> below.

An oligomer was prepared using <NUM>,<NUM>-pentanediol (PD) as an initiator. Specifically, lactide and PD were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After vacuum drying, the reaction mixture was cooled to room temperature to prepare a second nucleating agent, which were named PD-O-<NUM>, PD-O-<NUM>, PD-O-<NUM>, and PD-O-<NUM>, respectively, and the weight average molecular weight is shown in Tables <NUM> and <NUM> below.

An oligomer was prepared using diethylene glycol (DG) as an initiator. Specifically, lactide and DG were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After vacuum drying, the reaction mixture was cooled to room temperature to prepare a second nucleating agent, which were named DG-O-<NUM>, DG-O-<NUM>, DG-O-<NUM>, and DG-O-<NUM>, respectively, and the weight average molecular weight is shown in Tables <NUM> and <NUM> below.

An oligomer was prepared using glycerol (GL) as an initiator. Specifically, lactide and GL were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After vacuum drying, the reaction mixture was cooled to room temperature to prepare a second nucleating agent, which was named GL-O-<NUM>, GL-O-<NUM>, and GL-O-<NUM>, respectively, and the weight average molecular weight is shown in Tables <NUM> and <NUM> below.

An oligomer was prepared using pentaerythritol (PT) as an initiator. Specifically, lactide and PT were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After vacuum drying, the reaction mixture was cooled to room temperature to prepare a second nucleating agent, which were named PT-O-<NUM>, PT-O-<NUM>, PT-O-<NUM>, and PT-O-<NUM>, respectively, and the weight average molecular weight is shown in Tables <NUM> and <NUM> below.

An oligomer was prepared using sorbitol (SB) as an initiator. Specifically, lactide and SB were added in a <NUM> vial at a molar ratio of <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM> so that the total was <NUM>, and Sn(Oct)<NUM> catalyst was added in amount to be <NUM> to <NUM> wt. %, and then reacted at <NUM> for <NUM> hours. After vacuum drying, the mixture was cooled to room temperature to prepare a second nucleating agent, which were named SB-O-<NUM>, SB-O-<NUM>, and SB-O-<NUM>, respectively, and the weight average molecular weight is shown in Tables <NUM> and <NUM> below.

<NUM> of PLA pellet (4032D from NatureWorks; weight average molecular weight of about <NUM>,<NUM>) was added to a <NUM> vial, and <NUM> of CHCl<NUM> was added and completely dissolved. The first nucleating agent and the second nucleating agent shown in Table <NUM> below were dissolved or evenly dispersed in <NUM> of CHCl<NUM> according to their contents to prepare a solution, and then mixed into the previously prepared PLA solution. The solution was mixed evenly by sonication for <NUM> hour and air-dried on an Al dish (diameter: <NUM>) to remove the solvent, and then dried in vacuum at <NUM> for <NUM> hours to prepare PLA films (thickness: about <NUM> to <NUM>), respectively.

The physical properties of the first nucleating agent, second nucleating agent, and PLA film prepared above were measured by the following methods.

The number average molecular weight (Mn) and the weight average molecular weight (Mw) were calculated using a GPC (Gel Permeation Chromatography) device, and the oligomer molecular weight distribution (Mw/Mn) was measured, and specific measurement conditions are as follows.

The PLA film was made into a completely amorphous state, and heated up to <NUM>, which is equal to or higher than the melting temperature of PLA, at a heating rate of <NUM>/min to eliminate the thermal history, and then stabilized for <NUM> minutes to make into an amorphous molten state. After that, to analyze ΔHc and crystallization behavior, a crystallization peak was observed while cooling up to -<NUM> at a cooling rate of <NUM>/min. To observe the melting peak after stabilization, re-heating (<NUM>nd Run) was performed up to <NUM> at a rate of <NUM>/min, and ΔHm at the melting peak was confirmed. The crystallinity degree X was calculated using the following Equation (<NUM>% crystalline PLA ΔHm = <NUM> J/g).

The results are shown in Tables <NUM> and <NUM> below, and some of the DSC measurement results are shown in <FIG>. Meanwhile, in Tables <NUM> and <NUM> below, each abbreviation has the following meaning.

D-SB (D-sorbitol), PT (pentaerythritol), OA (orotic acid), L-PA (L-phenylalanine), PH (phthalhydrazide).

As shown in Tables <NUM> and <NUM>, it was confirmed that in the case of Examples where the first nucleating agent and the second nucleating agent were used simultaneously according to the present disclosure, the crystallization temperature and crystallinity degree were also improved even with a small content.

Claim 1:
A polylactide resin composition comprising:
a polylactide resin; a first nucleating agent; and a second nucleating agent,
wherein the first nucleating agent is uracil or orotic acid, and is contained in an amount of <NUM> to <NUM>% by weight based on the total weight of the polylactide resin composition, and
wherein the second nucleating agent is a compound containing a lactide oligomer structure, and is contained in an amount of <NUM> to <NUM>% by weight based on the total weight of the polylactide resin composition.