Technical Field

The present invention relates to a biodegradable polyester resin composition and, more specifically, to a biodegradable polyester resin composition with excellent heat resistance, comprising a polylactic acid (PLA) resin, and an article manufactured therefrom.

Background

General-purpose resins, of which the raw material is petroleum, e.g., polypropylene and polyvinyl chloride, have good properties such as manufacturability and durability, and are therefore used in many areas such as convenience goods including kitchen appliances, home appliances, automobile parts, building materials, or food packaging. However, good durability of these resin products later becomes a drawback at the disposal stage and creates a problem of low degradability in nature.

Technical Problem

The purpose of the present invention is to provide a biodegradable polyester composition with excellent heat resistance, capable of rapid crystallization during manufacturing of an article.

Technical Solutions

To achieve the above purpose, one aspect of the present invention may provide a biodegradable polyester resin composition comprising 0.5 to 10 parts by weight of a nucleating agent with respect to 100 parts by weight of a biodegradable polyester resin.

The present invention also provides an article with excellent heat resistance, manufactured from the biodegradable polyester resin composition.

In an embodiment, the biodegradable polyester resin may be a polylactide (PLA) resin.

In another embodiment, the nucleating agent may be a sorbitol compound, a metal salt of carboxylic acid, an aromatic phosphate ester compound, silica, talc, or the like. The nucleating agent can increase the crystallization rate of the biodegradable polyester resin, thereby increasing the heat resistance of an article manufactured therefrom.

In another embodiment, the biodegradable resin composition may further comprise 0.1 to 5 parts by weight of an antimicrobial formulation. The antimicrobial formulation serves to provide antibacterial properties to an article manufactured from the resin composition.

In another embodiment, the biodegradable resin composition may further comprise 1 to 15 parts by weight of one or more additives selected from the group consisting of: stabilizers, slip agents, dispersants, coupling agents, antioxidants, and UV stabilizers.

In addition, another aspect of the present invention may provide a biodegradable article comprising the biodegradable resin composition.

In another embodiment, the article may be manufactured in such a manner that the temperature of the mold is 100°C to 150°C during injection molding of the biodegradable resin composition, and the post-injection cooling time is 3 minutes or less.

Advantageous Effects

The present invention is capable of providing a biodegradable polyester resin composition having excellent heat-resistant properties, and an article manufactured therefrom. Furthermore, the resin composition is capable of providing antibacterial properties to the article by further comprising an antimicrobial formulation. Therefore, the resin composition of the present invention is particularly useful in the manufacturing of kitchen tools, articles and appliances which require safety, heat resistance, and antibacterial properties. Summary

A polylactic acid (PLA) resin is a biodegradable plastic manufactured from 100% biomass, and is a material that may be manufactured by: producing lactic acid from corn starch through fermentation; transforming lactic acid into lactide through a chemical process; and thereafter polymerizing lactide. Since such a PLA resin is biomass-based, unlike the conventional crude oil-based resins, it is a material capable of: utilizing recycled resources; having a lower emission of CO2, a greenhouse gas, than the conventional resins during production; and having eco-friendly properties, such as being biodegradable by moisture and microorganisms when buried (for example, in a compost), and a suitable mechanical strength equivalent to that of the conventional crude oil-based resins.

PLA resins have been mainly used for packaging containers, coating, foaming, films/sheets, and fibers. In recent years, there also has been research focused on using these resins for exterior materials of cellphones or interior materials of automobiles, after reinforcing their physical properties by mixing them with a conventional resin, e.g., ABS, polycarbonate, or polypropylene.

Also, due to convenience of plastics, many kitchen tools, articles and appliances have been manufactured from general-purpose resins which use petroleum as a raw material. As the possibility of human intake became an issue, biodegradable resins, such as PLA manufactured from biomass, are being highly favored in view of safety and environmental aspects. However, these PLA resins have limited application because of their property of being easily transformed by heat which is related to biodegradability.

To overcome low thermostability, attempts have been made to mix the PLA with another resin, e.g., a substance such as polypropylene or polyethylene. However, the products manufactured from these resins are not eco-friendly and also have low biodegradability.

Thus, the present inventors completed the present invention by developing a heat- resistant and eco-friendly PLA resin composition which is stable at high temperatures of around 100°C and of which the resin component consists of 100% PLA resin.

Brief Description of Drawings

FIG. 1 is a picture showing the process of testing the heat resistance of the specimens according to an example and a comparative example of the present invention.

FIG. 2 is a picture showing the degree of bending after testing the heat resistance of the specimens according to an example and a comparative example of the present invention.

FIG. 3 is a picture showing the results of testing the antibacterial activity of the specimens according to an example and a comparative example of the present invention.

FIGs. 4a and 4b show thermograms evaluating, using Differential Scanning Calorimetry (DSC), the thermal properties of the specimens according to an example and a comparative example of the present invention. Detailed Description

The present invention is described in greater detail below.

One aspect of the present invention may provide a biodegradable polyester resin composition comprising 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, of a nucleating agent with respect to 100 parts by weight of a biodegradable polyester resin.

The biodegradable polyester resin may be an aliphatic polyester or aliphatic- aromatic polyester comprising polyhydroxy carbonic acid, hydroxycarbonic acid, or aliphatic polyalcohol, and aliphatic polybasic acid; or a copolymer of a monomer selected from hydroxycarbonic acid and aliphatic polyalcohol, and a monomer selected from aliphatic polybasic acid.

In particular, the biodegradable polyester resin may be a polylactic acid (PLA) resin.

Throughout the present specification, the term "polylactic acid resin" or "PLA resin" is defined as a generic reference to a homopolymer or copolymer comprising the repeating unit represented by the following general formula.

Specifically, the polylactic acid may be a homopolymer of D-lactic acid, a homopolymer of L-lactic acid, or a copolymer of L-lactic acid and D-lactic acid.

The polylactic acid resin is a natural polyester resin made through the esterification of lactic acid monomers obtained from degradation of corn starch, and can easily be purchased.

The polylactic acid resin preferably comprises at least 95 parts by weight of L- lactic acid in view of balancing heat resistance and moldability, and in view of hydrolysis resistance, the resin preferably comprises 95 to 100 parts by weight of L-lactic acid and 0 to 5 parts by weight of D-lactic acid. In addition, the polylactic acid resin has a specific gravity in the range of 1.235- 1.239, and although there are no special restrictions on the molecular weight or molecular weight distribution as long as the ranges allow for molding, the resin preferably has a weight average molecular weight of 80,000 or greater.

The resin composition of the present invention comprises a nucleating agent. The nucleating agent can increase the crystallization rate of the biodegradable polyester resin, thereby increasing the heat resistance of an article manufactured therefrom.

The nucleating agent of the present invention may be a sorbitol compound, a metal salt of carboxylic acid, an aromatic phosphate ester compound, silica, talc, or the like. It is also possible to use a combination of one or more of these compounds.

The aromatic phosphate ester compound may be triphenyl phosphate, tri(2,6- dimethyl)phosphate, bis(dimethylphenyl)phosphate, resorcinol bis(diphenyl)phosphate, resorcinol bis(2,6-dimethylphenyl)phosphate, resorcinol bis(2,4- ditertiarybutylphenyl)phosphate, hydroquinol bis(2,6-dimethylphenyl)phosphate, hydroquinol bis(2,4-ditertiarybutylphenyl)phosphate, or the like.

The sorbitol compound may be, for example, dibenzylidene sorbitol, 1,3,2,4- di(methylbenzylidene)sorbitol, 1 ,3,2,4-(ethylbenzylidene)sorbitol, 1 ,3,2,4- (methoxybenzylidene)sorbitol, 1 ,3,2,4-(ethoxybenzylidene)sorbitol, 1 ,2,3-trideoxy- 4,6,5,7-bis-0-[(4-propylphenyl)methylene]nonitol, or the like.

The metal salt of carboxylic acid may be, for example, sodium adipate, potassium adipate, aluminum adipate, sodium sebacate, potassium sebacate, aluminum sebacate, sodium benzoate, aluminum benzoate, di-para-t-butylaluminum benzoate, di-para-t- butyltitanium benzoate, di-para-t-butylchromium benzoate, hydroxyl-di-t-butylaluminum benzoate, or the like.

The nucleating agent demonstrated an effect on the crystallization rate of the PLA resin, by reducing the amount of time by about 10 times compared to resins without a nucleating agent, and by about 3 times compared to the ones using a common nucleating agent, such as talc. By adding said nucleating agent, the article of the present invention can have heat resistance to withstand temperatures from near its T _g of 65°C up to 100°C, despite being manufactured from 100% PLA resin. The resin composition of the present invention may comprise 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, of a nucleating agent with respect to 100 parts by weight of a biodegradable polyester resin. If the nucleating agent is present in an amount of less than 0.5 parts by weight, then it does not have a great effect on the crystallization rate; if it is present in an amount of greater than 10 parts by weight, then problems arise with regard to high costs, as well as reduced impact strength of the polylactic acid resin as a result of excessive crystallization.

In another embodiment, the resin composition of the present invention may comprise 0.1 to 5 parts by weight, preferably 0.5 to 1 parts by weight, of an antimicrobial formulation with respect to 100 parts by weight of a biodegradable polyester resin. These ranges are preferable in view of balancing antibacterial properties and mechanical properties.

The antimicrobial formulation serves to provide antibacterial properties to an article manufactured from the resin composition, and includes antibacterial agents, antifungal agents, germicides, sterilants, germ-reducing agents, etc.

The antimicrobial formulation is preferably selected from the group consisting of: oxides, hydroxides, and combinations thereof, each of which comprises an element selected from the group consisting of: transition metals, silicon, aluminum, alkali metals, alkaline earth metals, and combinations thereof, and is more preferably an oxide. The transition metal may be selected from the group consisting of: zirconium, titanium, zinc, copper, and combinations thereof.

Where the resin composition of the present invention is fabricated into kitchen appliances, it is advised to use products that are approved as safe for human consumption. One such product is ZEOMIC DLZ502 by Sinanen Zeomic Co., Japan.

In another embodiment, the resin composition of the present invention may further comprise one or more additives selected from the group consisting of: stabilizers, slip agents, dispersants, coupling agents, antioxidants, and UV stabilizers. The amount of the additive(s) is within the range well known to a person skilled in the art.

The stabilizer may be, but is not limited to, trimethyl phosphate, triphenyl phosphate, or the like. The slip agent may be, but is not limited to, one or more selected from the group consisting of: calcium stearate, zinc stearate, PE wax, and common wax.

The dispersant may be, but is not limited to, carboxylated polyethylene, phthalic acid, stearic acid, or the like.

The antioxidant may be, but is not limited to, one or more selected from the group consisting of: IRGANOX series (BASF, Florham Park, NJ, U.S. A); ULTRANOX series (ADDIVANT, Danbury, CT, U.S.A.); and TEP series.

The UV stabilizer may be, but is not limited to, a hindered amine light stabilizer (HALS) or the like.

Furthermore, another aspect of the present invention may provide a biodegradable article comprising the biodegradable polyester resin composition.

The article may be manufactured by a person skilled in the art, using various molding methods known in the field of the invention. If the injection molding method is used, then the article may be manufactured in such a manner that, for example, when the biodegradable resin composition of the present invention is prepared and injected, the temperature of the mold is 100-150°C, preferably 110-130°C, during injection, and the post-injection cooling time is 3 minutes.

The article manufactured by molding the biodegradable polyester resin

composition of the present invention with excellent heat resistance may be used for articles which require safety, heat resistance, and antibacterial properties, e.g., kitchen tools, articles and appliances, miscellaneous goods, automobiles, machine parts, electric and electronic parts, and office machines such as computers.

The present invention is described in further detail below, using examples.

However, the scope of the present invention is not limited to these examples.

Examples

Example 1

The composition was prepared in the form of pellets using a twin-screw extruder, after mixing 1 part by weight of nucleating agent CR741S (bis(dimethylphenyl)phosphate bisphenol A; Daihachi Chemical Industry of Japan) and 1 part by weight of an antimicrobial formulation (ZEOMIC DLZ502; Sinanen Zeomic Co., Japan) with 100 parts by weight of polylactic acid resin (INGEO Biopolymer; Nature Works LLC, Minnetonka, MN, U.S.A.)

Example 2

The composition was prepared in the form of pellets using a twin-screw extruder, after mixing 1 part by weight of nucleating agent CR741S (bis(dimethylphenyl)phosphate bisphenol A; Daihachi Chemical Industry of Japan) with 100 parts by weight of polylactic acid resin (INGEO Biopolymer; Nature Works LLC, Minnetonka, MN, U.S.A.). Example 3

Pellets were prepared in the same manner as that of Example 1, except for mixing 3 parts by weight of nucleating agent CR741S (bis(dimethylphenyl)phosphate bisphenol A; Daihachi Chemical Industry of Japan). Comparative Example 1

The composition was prepared in the form of pellets using a twin-screw extruder, after mixing 1 part by weight of an antimicrobial formulation (ZEOMIC DLZ502; Sinanen Zeomic Co., Japan) with 100 parts by weight of polylactic acid resin (INGEO Biopolymer; Nature Works LLC, Minnetonka, MN, U.S.A.)

Comparative Example 2

The composition was prepared with 100 parts by weight of polylactic acid resin (INGEO Biopolymer; NatureWorks LLC, Minnetonka, MN, U.S.A.) in the form of pellets using a twin-screw extruder.

Experiment 1 : Heat Resistance Test

The pellets of mixed ingredients from the examples or comparative examples were heated, melted, and mixed in an injection molding machine and then injection molded. Afterwards, test specimens were prepared and their properties evaluated.

The prepared specimens had a size of 365 mm wide x 200 high mm x 4 mm thick and a width:height ratio of 1.83 : 1. The heat resistance test was conducted in accordance with Korean Standards Association test method KS G 5602 7.5: 2006. Two cylindrical weights were placed 4 cm apart in a water bath of 85°C and the test specimen was placed over them, after which a 500- gram weight was placed on top of the test specimen and left for 1 hour at a temperature of 85°C. After removing the top weight, the specimen was left for 10 minutes at room temperature, and was thereafter flipped over for the comparison of bending heights.

PLA is commonly known to undergo hydrolysis in hot water or strong acid, and to weaken at temperatures greater than or equal to its glass transition temperature (T _g ), which is 65°C.

As can be seen with the naked eye, the specimens of Example 1 showed no or slight bending, whereas the specimens of Comparative Example 1 showed a relatively large bending height (see Table 1, Fig. 1 and Fig. 2).

Table 1

Experiment 2: Biodegradability Test

The biodegradability test of the specimens was conducted in accordance with Korean Standards Association test method KS M ISO 14855-1 : 2010.

Cellulose specimens were used as the standard sample. The results are shown in the table below.

Table 2 calculated from

carbon dioxide

emission (%)

No peculiarity observed in the

Example 1 72.42 45 moisture content, color, odor, etc. of inoculum

Standard sample 75.73 45

Biodegradability of

specimen with

95.63

respect to standard

sample (%)

As shown in Table 2, the specimens of Example 1 exhibit similar biodegradability to cellulose, which is known to have excellent biodegradability. Experiment 3 : Antibacterial Test

The antibacterial activity and efficacy of the prepared specimens was tested in accordance with the film-contact method (International Organization for Standardization test method ISO 22196; Japanese Standards Association test method JIS Z 2801 : 2010). The strains of Staphylococcus aureus (ATCC 6538P) and Escherichia coli (ATCC 8739) were used.

The film-contact method is most suitable for analyzing the antibacterial effect of a plastic product in which an inorganic antibacterial agent is applied to the plastics and the migration of metal particles is limited to the surface of plastics. The method includes inoculating the surface of the specimen with a fluid containing cultured bacteria, and covering the specimen with a film, and thereafter, measuring the viable count. According to the present method, an effective antibacterial effect corresponds to a numerical value of 99% or greater (log value = activity level 2).

The results showed that both strains underwent active proliferation on the specimens of Comparative Example 2, in which no antimicrobial formulation was added. On the other hand, 99.9% of the bacterial cells of both strains were eliminated from the specimens of Example 1 (see Fig. 3).

Experiment 4: Thermal Property Evaluation

Differential Scanning Calorimeter (DSC) analysis was performed on the specimens of Example 1 and the specimens of Comparative Example 1. Using a PYRIS DIAMOND DSC instrument (PerkinElmer Inc., Waltham, MA, U.S.A.). The analysis was carried out at 10-190°C, 10°C/min, and 20 psi of nitrogen gas.

As illustrated in the thermograms of Fig. 4a and Fig. 4b, the specimens of Comparative Example 1, in which no nucleating agent was added, had no crystallization region and many amorphous regions; therefore, crystallization was observed through heating during DSC analysis.

However, for the specimens of Example 1 , in which the degree of crystallization increased as a result of adding a nucleating agent, no crystallization points were observed through heating during DSC analysis, as crystallization had already occurred prior to the analysis.

To summarize the above results, it was demonstrated that an article with excellent heat resistance could be manufactured by mixing polylactic acid and a nucleating agent and thereby increasing the degree of crystallization during injection. Moreover, by adding an antimicrobial formulation, antibacterial properties may be provided to the resin.

The present invention is not limited to the above examples but may be prepared in a variety of different forms. In addition, a person skilled in the art would be able to understand that it is possible to have other forms of embodiment without modifying the technical concept or essential features of the present invention. Thus, in all aspects, the examples described above are to be understood as exemplary and not restrictive.