WO2010002205A2

WO2010002205A2 - Biodegradable flexible film

Info

Publication number: WO2010002205A2
Application number: PCT/KR2009/003621
Authority: WO
Inventors: Kyung-Youn Kim; Sang Il Kim
Original assignee: SKC Co Ltd
Current assignee: SKC Co Ltd
Priority date: 2008-07-03
Filing date: 2009-07-02
Publication date: 2010-01-07
Anticipated expiration: 2011-01-03
Also published as: WO2010002205A3; KR100985438B1; KR20100004420A

Abstract

A biodegradable flexible film, comprising 20 to 90 wt% of polylactic acid and 1 to 80 wt% of a polyhydroxyalkanoate, exhibits a biodegradability of at least 90 %, an initial elastic modulus determined based on a stress-strain curve of 50 to 350 kgf/mm2, and a haze of 20 % or less.

Description

BIODEGRADABLE FLEXIBLE FILM

FIELD OF THE INVENTION

The present invention relates to a biodegradable flexible film having improved flexibility, transparency, and mechanical properties, which is useful for environmentally friendly packaging.

BACKGROUND OF THE INVENTION

Conventional plastic films such as polyvinyl chloride, polyethylene and polypropylene films are not completely satisfactory in terms of their performance characteristics. For example, polyvinyl chloride films generate toxic pollutants when incinerated, and polyethylene films have been employed only for low-grade packaging materials due to their relatively poor dimensional and mechanical properties. Polypropylene films, on the other hand, have satisfactory mechanical properties, but generate products that are not biodegradable and accumulate in the soil when disposed.

In order to solve such problems, there have been employed biodegradable aliphatic polyesters, particularly polylactic acid films. While such films have satisfactory mechanical properties and transparency, they have poor flexibility due to their high crystallinity, making them unsuitable for packaging. In case of using such films for wrapping cold-storage materials or frozen foods at a low temperature, they break easily during storage or handling due to insufficient pin-hole resistance. Japanese Laid-open Patent Publication Nos. H09-157408 and 2004-010900 disclose a polylactic acid film which is prepared by blending polylactic acid (having an L-lactic acid to D-lactic acid weight ratio of 100:0-94:6 or 6:94-0: 100) and a biodegradable aliphatic polyester having a glass transition temperature (T_g) of 0 ^oC or less at a weight ratio of 100 : 3 to 100 : 70, and the film obtained from the blend is drawn at least once in the transverse or longitudinal direction and heat-treated. However, the polylactic acid films thus produced have problems in that the miscibility of the polyester with polylactic acid is poor, leading to increased haze of the film, which is not suitable for use as a transparent wrapping material. Further, when T_g of the polyester resin is 0 ^oC or less, adhesion of the film to a casting roll occurs frequently during the processing, the thermal stability resistance of the film is unsatisfactorily low, and the degree of heat shrinkage of the film is too high for use in an application that requires dimensional stability.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a biodegradable flexible film having improved flexibility, transparency, pin-hole resistance, and mechanical properties which can be advantageously used for packaging.

It is another object of the present invention to provide an improved wrapping material .

It is a further object of the present invention to provide a preparation method of the inventive biodegradable flexible film.

In accordance with one aspect of the present invention, there is provided a biodegradable flexible film comprising 20 to 90 wt% of polylactic acid and 1 to 80 wt% of a polyhydroxyalkanoate (PHA), which exhibits a biodegradability of at least

90 %, an initial elastic modulus determined based on a stress-strain curve of 50 to

350 kgf/mm², and a haze of 20 % or less.

In accordance with another aspect of the present invention, there is provided a wrapping material comprising the biodegradable flexible film according to the present invention.

In accordance with a further aspect of the present invention, there is provided a method for preparing the inventive biodegradable flexible film comprising the steps of: (a) melt-extruding a polymer blend composed of 20 to 99 wt% of polylactic acid and 1 to 80 wt% of a PHA, to prepare a sheet; (b) drawing the sheet in the longitudinal and transverse directions to prepare a biaxially oriented film; and (c) heat-setting the biaxially oriented film. The biodegradable flexible film according to the present invention can be efficiently used as an environmentally friendly wrapping material due to its superior flexibility, transparency, pin-hole resistance, mechanical properties, and biodegradability.

DETAILED DESCRIPTION OF THE INVENTION

The biodegradable flexible film of the present invention comprises 20 to 90 wt% of polylactic acid and 1 to 80 wt% of a polyhydroxyalkanoate (PHA). When the amount of the PHA is less than 1 wt%, it fails to slow down the crystallization of the polylactic acid so that the film has insufficient flexibility, while when is more than 80 wt%, the crystallization of the polylactic acid becomes slow to make it difficult to draw, and the film has poor mechanical properties. Preferably, the inventive film may comprise 50 to 90 wt% of polylactic acid and 10 to 50 wt% of a PHA.

The inventive film has a biodegradability of 90 % or more. As used herein, the term "biodegradability" refers to a ratio of biodegradation of test material to that of standard material (e.g., cellulose) over a same period of time. The Ministry of Environment in Korea regulates that the biodegradability of a particular material relative to that of a standard material should be 90 % or more.

The inventive film has an initial elastic modulus determined based on a stress-strain curve of 50 to 350 kgf/mm². When the initial elastic modulus of the film is less than 50 kgf/mm², problems occur during printing or laminating process due to the occurrence of wrinkles in the driving direction which is caused by insufficient resistance against a mechanical tension, while when is more than 350 kgf/mm², the film may be easily broken or rupture due to an increased stiffness. Preferably, the inventive film may have an initial elastic modulus determined based on a stress-strain curve of 150 to 250 kgf/mm².

The inventive film has a haze of 20 % or less. When the haze is more than 20 %, a transparency of the film significantly decreases which is not suitable for a transparent wrapping material. Preferably, the inventive film may have a haze of 10 % or less.

The PHA used in the inventive film may be a heteropolymer or copolymer which consists of one or more repeating units of formulas I and II:

wherein, Rl is methyl or ethyl, and R2 is ethyl, propyl, pentyl, or heptyl.

The PHA used in the inventive film may be selected from the group consisting of polyhydroxybutyrate (PHB), polyhydroxybutyrate valerate (PHBV), poly(3 -hydroxybutyrate-co-3 -hydroxy valerate) (P(3HB-co-3HV)), poly(3 -hydroxybutyrate-co-3 -hydroxyhexanoate) (P(3HB-co-3HH)), poly (3 -hy droxybutyrate-co- 3 -hydroxy octanoate) (P(3HB-co-3HO)), poly-3 -hydroxyvalerate (PHV), and a mixture thereof.

The PHA used in the inventive film may further comprise a glycolide repeating unit of formula III in an amount of 0 to 50 wt% based on the weight of the PHA. When the content of the glycolide repeating unit exceeds 50 wt%, the crystallizing may become slow to make it difficult to form a film. Preferably, the

PHA may comprise the glycolide in an amount of 20 wt% or less.

The inventive film may further comprise other additives such as an anti- blocking agent, a cross-linking agent, antioxidant, heat stabilizer, UV absorber and plasticizers to the extent they do not adversely affect the film properties.

The inventive film has improved pin-hole resistance, preferably, the inventive film may have 100 or less pin-holes per 100 cm² when stressed repeatedly at ambient temperature. A film having pin-hole number exceeding 100 in the test may become brittle to rupture easily during shipping, and may be susceptible to actual pin-hole generation when wrinkled repeatedly, particularly in winter. Preferably, the inventive film may have pin-hole number of 50 or less in the test.

The heat shrinkability of the inventive film measured at 100 ^oC for 5 min may be 70 % or less in either the longitudinal or transverse direction. When such heat shrinkability of a film exceeds 70 %, heat shrinkage may occur excessively in the longitudinal and transverse directions during printing or laminating process and the film may be curled after printing.

The biodegradable flexible film of the present invention is prepared by a method comprising the steps of: (a) melt-extruding a polymer blend composed of 20 to 99 wt% of polylactic acid and 1 to 80 wt% of a PHA, to prepare a sheet; (b) drawing the sheet in the longitudinal and transverse directions to prepare a biaxially oriented film; and (c) heat-setting the biaxially oriented film.

In the inventive method, the melt-extruding may be performed at 180 to 25O^oC.

The longitudinal drawing and the transverse drawing may be performed at draw ratios of 2 to 4 and 3 to 5, respectively. Further, the longitudinal drawing and the transverse drawing may be conducted at temperature ranges of 40 to 90 ^oC and 50 to 90 ^oC, respectively.

The heat-setting may be carried at 50 to 150 ^oC.

EXAMPLE

The following Examples are intended to further illustrate the present invention without limiting its scope.

Example 1 Polylactic acid resin (4032D, Nature Works LLC) having a melting point of

170 ^oC and a copolymer resin (troflex™, Danimer scientific LLC) having a melting point of 150 ^oC which is a copolymer of polyhydroxyalkanoate (P(3HB-co-3HV),

Rl is CH₃ and R2 is CH₂CH₃) and glycolide, were blended at a weight ratio of 90 : 10.

The polymer blend was melt-extruded at 230 ^oC and then cooled on a casting roll kept at 15 ^oC to prepare a sheet. The sheet was drawn at a draw ratio of 3.0 in the longitudinal direction at 70 ^oC and then drawn at a draw ratio of 3.7 in the transverse direction at 85 ^oC. The drawn sheet was heat-set at 100 ^oC, to obtain a biaxially drawn polyester film having a thickness of 20 μm.

Example 2

Polylactic acid resin (4032D, Nature Works LLC) having a melting point of 170 ^oC and a polyhydroxyalkanoate copolymer resin (P(3HB-co-3HH), Rl is CH₃ and R2 is CH₂CH₂CH₃) (troflex™, Danimer scientific LLC) having a melting point of 140 ^oC, were blended at a weight ratio of 80 : 20.

The polymer blend was melt-extruded at 220 ^oC and then cooled on a casting roll kept at 15 ^oC to prepare a sheet. The sheet was drawn at a draw ratio of 3.0 in the longitudinal direction at 75 ^oC and then drawn at a draw ratio of 3.7 in the transverse direction at 80 ^oC. The drawn sheet was heat-set at 100 ^oC, to obtain a biaxially drawn polyester film having a thickness of 20 μm.

Example 3

Polylactic acid resin (4032D, Nature Works LLC) having a melting point of 170 ^oC and a polyhydroxyalkanoate copolymer resin (P(3HB-co-3HO), Rl is CH₃ and R2 is (CH₂)₄CH₃) (troflex™, Danimer scientific LLC) having a melting point of 100 ^oC, were blended at a weight ratio of 70 : 30. The polymer blend was melt-extruded at 210 ^oC and then cooled on a casting roll kept at 15 ^oC to prepare a sheet. The sheet was drawn at a draw ratio of 3.0 in the longitudinal direction at 70 ^oC and then drawn at a draw ratio of 3.7 in the transverse direction at 75 ^oC. The drawn sheet was heat-set at 140 ^oC, to obtain a biaxially drawn polyester film having a thickness of 20 μm.

Comparative Example 1

Polylactic acid resin (4032D, Nature Works LLC) having a melting point of 170 ^oC was melt-extruded at 240 ^oC and then cooled on a casting roll kept at 18 ^oC to prepare a sheet. The sheet was drawn at a draw ratio of 3.0 in the longitudinal direction at 85 ^oC and then drawn at a draw ratio of 3.7 in the transverse direction at 90 ^oC. The drawn sheet was heat-set at 140 ^oC, to obtain a biaxially drawn polyester film having a thickness of 20 /m.

Comparative Example 2

Polylactic acid resin (4032D, Nature Works LLC) having a melting point of 170 ^oC and polybutylene succinate (PBS) (G4560, IRe Chemical Ltd., Korea) having a melting point of 115 ^oC were blended at a weight ratio of 95 : 5.

The polymer blend resin was melt-extruded at 220 ^oC and then cooled on a casting roll kept at 15 ^oC to prepare a sheet. The sheet was drawn at a draw ratio of 3.0 in the longitudinal direction at 75 ^oC and then drawn at a draw ratio of 3.7 in the transverse direction at 80 ^oC. The drawn sheet was heat-set at 100 ^oC, to obtain a biaxially drawn polyester film having a thickness of 20 μm.

Comparative Example 3

Polylactic acid resin (4032D₅ Nature Works LLC) having a melting point of 170 ^oC and a polyhydroxyalkanoate (PHB, Rl is CH₃) (troflex™, Danimer scientific LLC) having a melting point of 180 ^oC, were blended at a weight ratio of 15 : 85. The polymer blend resin was melt-extruded at 200 ^oC and then cooled on a casting roll kept at 9 ^oC to prepare a sheet. The sheet was drawn at a draw ratio of 2.5 in the longitudinal direction at 60 ^oC and then drawn at a draw ratio of 3.0 in the transverse direction at 65 ^oC. The drawn sheet was heat-set at 100 ^oC, to obtain a biaxially drawn polyester film having a thickness of 20 μm.

The polyester films obtained in Examples 1 to 3 and Comparative Examples

1 to 3 were each evaluated as follows. The results are shown in Table 1.

(1) Composition

A polymer sample dissolved in a 4: 1 mixture of deutro-chloroform and trifluoroacetic acid was subjected to quantitative NMR analysis with JSM-LA300 type ¹H-NMR (Jeol Inc., Japan). Relative areas of characteristic peaks based on a read out were converted into weight%.

(2) Biodegradability (%)

A biodegradability of a film sample was evaluated according to KS M3100- 1 (2003), and the ratio of biodegradability value of the film sample and that of a standard material over a period of 180 days was calculated according to the following equation:

Biodegradability (%) = [ (degree of biodegradation of film sample) / (degree of biodegradation of standard material) ] x 100

(3) Initial elastic modulus (kgf/mm²)

An initial elastic modulus was determined according to ASTM D 882 by measuring the modulus of elasticity using a film sample having the size of 100 mm (length) x 15 mm (width) with Universal Tester (UTM 4206-001_, Instron Inc.), wherein the interval between chucks is set at 50 mm and the elongation speed at 200 mm/min, and calculating an average value therefrom. (4) Haze (%)

A haze of a film specimen was measured with a hazemeter (Model: SEP-H, Nihohn Semitsu Kogaku, Japan) using a C-light source.

(5) Pin-hole resistance

A sample film was subjected to a flex crack resistance test using Gelbo-Flex tester (Gelbo Inc., USA) consisting of a 165 mm sample fixing plate, a 88 mm sample fixing diameter and a 125 mm traveling distance, at an angle of 420 degrees for 450 cycles.

Next, the sample film was placed flat on a white paper, whereon an oily nitroglycerin-based ink was applied with a doctor blade. The numbers of ink dots appeared on the white paper was represented as the pin-hole number. An average value derived from 3 tests was taken to represent each sample.

(6) Heat shrinkage (%)

A film sample was cut into a 200 mm (length) x 15 mm (width) piece, maintained at 100 ^oC in a circulating air oven for 5 minutes, and the change in the film length was measured. Using the following equation, the degrees of shrinkage in each of the longitudinal and transverse directions were calculated:

Heat shrinkage (%) = [ ( length before heat treatment - length after heat treatment ) / length before heat treatment ] x 100

As shown in Table 1, the inventive films exhibit improved properties in terms of flexibility, transparency, pin-hole resistance, and mechanical properties, etc., whereas the films that fall out the scope of the present invention showed deteriorated properties.

While the invention has been described with respect to the above specific embodiments, it should be recognized that various modifications and changes may be made to the invention by those skilled in the art which also fall within the scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS;

1. A biodegradable flexible film comprising 20 to 90 wt% of polylactic acid and 1 to 80 wt% of a polyhydroxyalkanoate (PHA), which exhibits a biodegradability of at least 90 %, an initial elastic modulus determined based on a stress-strain curve of 50 to 350 lcgf/mm², and a haze of 20 % or less.

2. The film of claim I, wherein the PHA is a heteropolymer or copolymer which comprises one or more repeating units of formulas (I) and (II):

wherein, Rl is methyl or ethyl, and R2 is ethyl, propyl, pentyl, or heptyl.

3. The film of claim 2, wherein the PHA further comprises a glycolide repeating unit of formula III in an amount of 0 to 50 wt% based on the weight of the PHA:

4. The film of claim 1, wherein the PHA is selected from the group consisting of polyhydroxybutyrate (PHB), polyhydroxybutyrate valerate (PHBV)_, poly(3-hydroxybutyrate-co-3 -hydroxy valerate) (P(3HB-co-3HV)), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HH)), poly(3-hydroxybutyrate-co-S -hydroxyoctanoate) (P(3HB-CO-3HO)), poly-3-hydroxyvalerate (PHV), and a mixture thereof.

5. The film of claim I, wherein the heat shrinkability of the film measured at 100^oC for 5 min is 70 % or less in either the longitudinal or transverse direction.

6. A wrapping material comprising the biodegradable flexible film according to any one of claims 1 to 5.

7. A method for preparing the biodegradable flexible film of claim 1 comprising the steps of:

(a) melt-extruding a polymer blend composed of 20 to 99 wt% of polylactic acid and 1 to 80 wt% of a PHA, to prepare a sheet;

(b) drawing the sheet in the longitudinal and transverse directions to prepare a biaxially oriented film; and

(c) heat-setting the biaxially oriented film.

8. The method of claim 7, wherein the melt-extruding is performed at 180 to 25O ^oC.

9. The method of claim 7, wherein the longitudinal drawing and the transverse drawing are performed at draw ratios of 2 to 4 and 3 to 5, respectively.

10. The method of claim 1, wherein the longitudinal drawing and the transverse drawing are conducted at temperature ranges of 40 to 90 ^oC and 50 to 90 ^oC, respectively.

11. The method of claim 7, the heat-setting is carried at 50 to 150 ^oC.