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 crystallization half-life and crystallinity degree of the polylactide resin.

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

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

<CIT> discloses a method for making formed heat-resistant PLA articles.

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

It is an object of the present disclosure to provide a polylactide resin composition excellent in crystallization half-life 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 a polylactide resin; a first nucleating agent; and a second nucleating agent,.

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 crystallization half-life of the polylactide resin.

In particular, the polylactide resin composition is characterized in that the crystallization half-life is <NUM> minutes or less at a crystallization temperature of <NUM> to <NUM>. Preferably, the crystallization half-time is <NUM> minutes or less, <NUM> minutes or less, <NUM> minutes or less, <NUM> minutes or less, <NUM> minutes or less, <NUM> minutes or less, <NUM> minutes or less, <NUM> minutes or less, <NUM> minutes or less, or <NUM> minutes or less. In addition, the crystallization half-life is <NUM> minutes or more, <NUM> minutes or more, <NUM> minutes or more, <NUM> minutes or more, or <NUM> minutes or more.

The term 'crystallization half-time (t<NUM>/<NUM>)' as used herein means the time (minutes) required to achieve <NUM>% of crystallization, and is a useful indicator for evaluating relative crystallization rates. To determine the crystallization half-life, first, the relative crystallinity is determined. The relative crystallinity means the ratio between the total area of the exothermic peak over time in the isothermal crystallization process and the area when time t has passed. After conversion to relative crystallinity over time, the time at which the relative crystallinity reaches <NUM> can be determined as the crystallization half-life. This process is schematically shown in <FIG>, and a more detailed measurement method can be embodied in Examples described later.

The term 'crystallization temperature' as used herein refers to the temperature at which the polylactide resin is melted to a predetermined temperature and then cooled in order to measure the crystallization half-life. For example, when a polylactide resin is melted at <NUM> and then cooled up to <NUM> at a cooling rate of <NUM>/min to <NUM>/min, the <NUM> is referred to as the 'crystallization temperature'. In the present disclosure, the crystallization temperature is <NUM> to <NUM>, for example <NUM>, <NUM>, <NUM>, or <NUM>. A specific method for measuring the crystallization half-life according to the crystallization temperature may be embodied in the following examples.

Preferably, the polylactide resin composition according to the present invention has a crystallinity degree of <NUM>% or more at a crystallization temperature of <NUM> to <NUM>. As described above, the polylactide resin composition according to the present invention is characterized by being excellent not only in crystallization half-life but also in crystallinity degree. Preferably, the crystallinity degree is <NUM>% or more, <NUM>% or more, or <NUM>% or more. The method for measuring the crystallinity degree may be embodied in the following examples.

Meanwhile, the first nucleating agent is uracil. 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 half-life and crystallinity degree.

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 more, <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, 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 improve the crystallization half-life and crystallinity degree.

Preferably, the second nucleating agent is a compound represented by the following Chemical Formula <NUM> and has a weight average molecular weight of <NUM>,<NUM> to <NUM>,<NUM>:
<CHM>.

The weight average molecular weight of the second nucleating agent may be adjusted according to the number of each lactide repeating unit. 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 according to the present disclosure 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, the above respective components can be prepared by a melt blending method.

The above-mentioned polylactide resin composition according to the present disclosure is excellent in crystallization half-life and crystallinity degree. 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.

<FIG> schematically illustrates the meaning of the crystallization half-life according to the present disclosure.

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>(P10) as an initiator. Specifically, lactide and P10 were added in a <NUM> vial at a molar ratio of <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 were named P10-A-<NUM>, and the weight average molecular weights are shown in Table <NUM> below.

Melt blending was performed using a Haake mixer equipment. Specifically, <NUM> of PLA pellet (4032D from NatureWorks; weight average molecular weight of about <NUM>,<NUM>) was added, and the first nucleating agent and the second nucleating agent shown in Table <NUM> below were added according to their contents. The nucleating agent in powder form was mixed with PLA pellet and added thereto. The nucleating agent having a melting point lower than the process operating temperature (<NUM>) was blended for <NUM> minutes (PLA was completely dissolved), and then added to a hopper. The operation was performed under the conditions of <NUM>, <NUM> rpm and <NUM> minutes. The obtained PLA resin was subjected to isothermal DSC analysis, which will be described later, to confirm crystallization behavior at each crystallization temperature.

The physical properties of the first nucleating agent, second nucleating agent, and polylactide resin composition 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.

Each of the PLA resins prepared in Examples and Comparative Examples was completely melted at <NUM> for <NUM> minutes through 1st heating to eliminate a thermal history. Then, after cooling to each crystallization temperature (<NUM> to <NUM>) at <NUM>/min as quickly as possible, the heat flow was observed while maintaining the temperature at each crystallization temperature, and the crystallization half-time was measured. In addition, the crystallinity degree X was calculated using the following Equation (<NUM>% crystalline PLA ΔHm = <NUM> J/g).

Claim 1:
A polylactide resin composition comprising a polylactide resin; a first nucleating agent; and a second nucleating agent,
wherein the polylactide resin composition has a crystallization half-life of <NUM> minutes or less at a crystallization temperature of <NUM> to <NUM>, wherein the crystallization half-life is measured as disclosed in the specification,
the first nucleating agent is uracil, and contained in an amount of <NUM> to <NUM>% by weight based on the total weight of the polylactide resin composition, and
the second nucleating agent is a compound containing a lactide oligomer structure, and contained in an amount of <NUM> to <NUM>% by weight based on the total weight of the polylactide resin composition.