WO2003050178A1

WO2003050178A1 - Additive composition for promoting polymer degradation

Info

Publication number: WO2003050178A1
Application number: PCT/KR2002/002042
Authority: WO
Inventors: Yong-Il Roe
Original assignee: EL TECHNOLOGY Co Ltd
Current assignee: EL TECHNOLOGY Co Ltd
Priority date: 2001-11-03
Filing date: 2002-11-02
Publication date: 2003-06-19
Anticipated expiration: 2004-05-03
Also published as: KR100346998B1; KR20010113577A; AU2002366622A1

Abstract

An additive composition for promoting polymer degradation and a polymer composition containing the same are provided. The additive composition includes: 0.001-2.0 parts by weight of a transition metal salt containing an anionic component derived from C1-C9 organic acid, or C10-C30 substituted or unsubstituted saturated or unsaturated fatty acid; 0.1-3.0 parts by weight of at least one unsaturated organic compound selected from the group consisting of C4-C22 unsaturated fatty acid, C4-C22 unsaturated fatty acid ester, unsaturated natural polymer having a weight average molecular weight of 10,000-3,000,000D, and unsaturated synthetic polymer having a weight-average molecular weight of 2,500-2,000,000D; and 40-98 parts by weight of at least one polymer component selected from the group consisting of polyethylene, polypropylene, polystyrene, polyethylenepropylene, polyethylenestyrene, polypropylenestyrene, and polyethylenepropylenestyrene.

Description

ADDITIVE COMPOSITION FOR PROMOTING POLYMER

DEGRADATION

Technical Field

The present invention relates to an additive composition, and more particularly, to an additive composition capable of promoting polymer degradation.

Background Art

Plastic articles manufactured from stable or stabilized polymer, such as polyethylene (PE), polypropylene (PP), and polystyrene (PS), are durable goods. However, as such plastic articles are used more and more, there have been serious concerns about environmental contamination in conjunction with the disposal of waste plastics. For this reason, many kinds of degradable plastic products have been developed.

Degradable plastic articles can be manufactured mainly in two ways - by using biodegradable polymer or by adding degradation promoter into conventional thermoplastic polymer.

However, biodegradable polymer, including starch modified for thermal plasticity as disclosed in U.S. Patent Nos. 5,462,982 and 5,314,934, is easily affected by water, so that their functionality is poor in contrast to conventional plastic polymers. In general, pro-oxidant is used as polymer degradation promoter(U.S. Patent Nos. 5,854,982 and 5,314,934). However, the use of this type of additive requires a careful consideration in order to provide polymer products with balanced shelf-life, functionality, and degradability. The polymer degradation rate depends on oxygen content and the rate of oxygen permeating into the plastic polymer. Disclosure of the Invention

The preset invention provides an additive composition capable of accelerating polymer degradation when added to a polymer, while retaining the shelf-life and functionality of the polymer. The present invention also provides a polymer composition containing the above additive composition, which makes polymer products manufactured therefrom degradable to be environmentally favorable while retaining the shelf-life and functionality of the polymers.

An additive composition for promoting polymer degradation according to the present invention comprises: 0.001-2.0 parts by weight of a transition metal salt containing an anionic component derived from C-₁-C₉ organic acid, or Cι₀-C₃₀ substituted or unsubstituted saturated or unsaturated fatty acid; 0.1-3.0 parts by weight of at least one unsaturated organic compound selected from the group consisting of C₄-C₂₂ unsaturated fatty acid, C₄-C₂₂ unsaturated fatty acid ester, unsaturated natural polymer having a weight-average molecular weight of 10, 000-3, 000, 000D, and unsaturated synthetic polymer having a weight-average molecular weight of 2,500-2,000,000D; and 40-98 parts by weight of at least one polymer component selected from the group consisting of polyethylene, polypropylene, polystyrene, polyethylenepropylene, polyethylenestyrene, polypropylenestyrene, and polyethylenepropylenestyrene.

Suitable polymer components for an additive composition according to the present invention may comprise 20-49 parts by weight of a homopolymer and 20-49 parts by weight of a copolymer.

The constituents of the additive composition according to the present invention will be described in greater detail.

Best mode for carrying out the Invention In the additive composition according to the present invention, a suitable transition metal for a transition metal salt is derived from, but is not limited to, cobalt, manganese, copper, vanadium, and iron.

Suitable C₁-C₉ organic acid for the anionic component of such a transition metal salt includes, but is not limited to, acetic acid, citric acid, and tartaric acid. Suitable C*|₀-C₃o substituted or unsubstituted saturated or unsaturated fatty acid for the anionic component of such a transition metal salt includes, but is not limited to, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, erucic acid, and 12-hydroxystearic acid.

The transition metal salt in the additive composition according to the present invention promotes oxidation and photolysis of polymers. A Fe-based salt known for its powerful photodegradation promoting effect is preferred for non-recyclable polymer products, whereas a Mg-based salt capable of effectively accelerating thermo-oxidation under non-solar irradiation conditions is preferred for plastic products that are recyclable, for example, as barnyard manure.

The unsaturated organic compound in the additive composition according to the present invention mainly acts to accelerate thermal decomposition of polymer. Compared to general compounds used to promote thermal decomposition of polymer, unsaturated natural polymer, such as unsaturated fatty acid, unsaturated fatty acid ester, and isoprene polymer, and unsaturated synthetic polymer which are used in the present invention contains highly available unsaturated sites. Optimal unsaturated organic compound for the additive composition according to the present invention is selected in consideration of various factors, for example, cost, functionality, and odor.

Suitable unsaturated natural polymer for the unsaturated organic compound of the additive composition has a weight-average molecular weight of, preferably, 10,000-1 , 000, 000D, and more preferably, 10,000-500,0000. Suitable unsaturated synthetic polymer for the unsaturated organic compound of the additive composition has a weight-average molecular weight of, preferably, 2,500-1 ,000,000D, and more preferably, of 2,500-500, 000D. Alternatively, the additive composition according to the present invention may further comprise 50 parts or less by weight of a biodegradable polymer. Examples of such a biodegradable polymer include natural polymers and synthetic polymers. Available examples of natural polymers include animal origin proteins, such as casein and its salts, and gelatin, plant origin proteins, such as soy proteins, starch and its derivatives, cellulose and its derivatives, lignocellulose, chitosan, and the like.

Examples of starch include any processed, chemically modified, or natural starch, including wheat starch, corn starch, potato starch, rice starch, and plant origin starches, for example, derived from cassaba, tapioca, and pea. Examples of chemically or cross-linked modified starches include esterified starches with 1-3 organic acid substitutes for hydroxy groups and etherified starches with 1-3 organic alcohol substitutes for hydroxy groups. Examples of cellulose and derivatives thereof include wood flours, wood fiber derived from plants, such as grasses and grains, and chemically modified cellulose, such as esterified cellulose with 1-3 organic acid substitutes for hydroxy groups and etherified cellulose with 1-3 organic alcohol substitutes for hydroxy groups. Examples of synthetic biodegradable polymer for the additive composition according to the present invention include: an aliphatic polyester produced by condensation and polymerization of a compound of formula HO-A-OH and a compound of formula HOOC-B-COOH; an aliphatic polyester produced by ring opening and polymerization of C₂-C₂₀ caprolactons; an aliphatic polyester produced by self condensation and polymerization of compounds of formula HOOC-D-OH; and an aliphatic/aromatic polyester produced by condensation and polymerization of a compound of formula HO-E-OH and a compound of formula HOOC-G-COOH, wherein A, B, D, and E in the above formulae are C₂-C₂₀ alkylene, and G is C₆-C₂o arylene or alkylarylene.

The addition of such a biodegradable polymer into the additive composition according to the present invention helps oxygen delivery to polymers to be degraded and accelerates oxidation of the polymer. The amount of biodegradable polymer is determined so as not to adversely affect the functionality of the letdown polymers of products.

Alternatively, the additive composition according to the present invention may further comprise a desiccant in an amount of 5 parts or less by weight. Examples of such a desiccant include calcium oxide, magnesium perchlorate, phosphorous pentoxide, and the like. Alternatively, the additive composition according to the present invention may further comprise a filler in an amount of no greater than 5 parts by weight. The addition of fillers accelerates oxygen delivery to polymers to be degraded and thus oxidation of the polymer. Suitable fillers include any material that is inert and does not melt at the processing temperature of polymers, for example, calcium carbonate, mica, silica, alumina, and the like.

Any additive composition according to the present invention, described above, can be used as a degradation accelerator for a polymer composition according to the present invention. A polymer composition according to the present invention comprises: 3-50 parts by weight of an additive composition according to the present invention; and 50-97 parts by weight of a letdown polymer, wherein the letdown polymer is at least one selected from the group consisting of polyethyelenes, polypropylenes, polystyrenes, polyethylenepropylenes, polyethylenestyrenes, polypropylenestyrenes, and polyethylenepropylenestyrenes.

The composition of the polymer composition according to the present invention may be appropriately varied according to the kind of the final plastic product and the thickness thereof. For example, for relatively thin plastic products into which a sufficient amount of oxygen can permeate deeply, the amount of inert and insoluble filler is limited. However, for relatively thick plastic products, for example, of a thickness of 30 microns or greater, produced by injection molding, it is preferable to appropriately adjust the ratio of the filler particles and the letdown polymer.

A polymer composition according to the present invention may further comprise an antioxidant for needed shelf-life and biodegradability.

Suitable examples of such an antioxidant include ketone-amine antioxidant, aldehyde-amine antioxidant, phenylnaphthylamine antioxidant, phenylnaphthylamine antioxidants, substituted diphenylamine antioxidant, paraphenylene-diamine derivative antioxidant, substituted phenol antioxidant, phenylalkane antioxidant, phenylsulfide antioxidant, phosphite antioxidant, and the like. These antioxidants may be mixed with the letdown polymer. The polymer compositions according to the present invention can be used for degradable plastic products with the original functionality and performance of the conventional polymer products.

The present invention will be described in greater detail with reference to the following examples. The following examples are for illustrative purposes and are not intended to limit the scope of the invention.

Example 1 : Preparation of an additive composition(l) as a degradation promoter 0.04 parts by weight of magnesium stearate, 1.2 parts by weight of polyisoprene, 2.0 parts by weight of starch, 0.4 parts by weight of calcium oxide, and 96.36 parts by weight of straight-chain low density polyethylene containing 200 ppm of Irganox 1010^® and 600 ppm of Irgafos 168^® were mixed at 160°C to provide an additive composition.

Example 2 : Preparation of an additive composition^) as a degradation promoter

For injection molded products having a thickness of 0.5 mm, an additive composition for use as a degradation promoter was prepared with the following composition:

- Magnesium stearate 0.02 parts by weight

- Polyisoprene 0.6 parts by weight

- Wood fiber 50.0 parts by weight - Calcium oxide 5.0 parts by weight

- Polypropylene homopolymer 22.19 parts by weight

- Propylene-ethylene copolymer with 3% ethylene repeating units 12.19 parts by weight

Example 3

To verify the effect of the additive compositions according to the present invention, degradable polymer compositions containing the degradation promoting additive compositions of Examples 1 were prepared, and a degradation test was conducted using these degradable polymer compositions.

The additive composition of Example 1 was added into low density polyethylene (LDPE) in an amount of 10% by weight and 20% by weight, and two sheets of transparent films were manufactured from the mixtures. The thickness of each transparent film was about 30 m. The resulting transparent polymer films were sent to the SP Swedish National Testing and Research Institute for degradation testing.

In degradation testing, the kinetics of thermo-oxidative degradations were evaluated for the polymer films. The degradation rate of polymers may vary depending on the kinds and amounts of polymer and additives, processing temperature, and amount of oxygen. The main object of this degradation testing was to find out the relationship between processing (degradation) temperature and time and amount of oxygen, which is considered to be important to produce degradable low-molecular weight oxides. Thermo-oxidative degradations were carried out at 50°C, 60°C, and 70°C, which belong to a general range of polymer decomposition temperatures. As well as decomposition temperature, amount of oxygen supplied during the test was varied using air and an oxygen/nitrogen mixture(air, 10w% oxygen, 20% oxygen) were optionally added. The effect of thermo-oxidative degradation was verified by measuring changes in molecular weight by means of size exclusive chromatography (SEC).

With various durations of degradation processes, the molecular weights of the degraded products were measured using SEC at a laboratory of the department of polymer technology, Chalmers University of Technology, in Sweden. Each degraded product was dissolved in 1 ,2,4-trichlorobenzene at 135°C for 16 hours with a concentration of 1g/L and used as a sample for SEC. The results are shown in Tables 1 through 4 below. Tables 1 and 2 show changes in weight-average molecular weight and number-average molecular weight, respectively, for polymer compositions containing 10% by weight of the additive composition of Example 1.

Table 1 (weight-average molecular weight before aging: 79,400)

Table 2 (number-average molecular weight before aging: 11 ,150)

Tables 3 and 4 show changes in weight-average molecular weight and number-average molecular weight, respectively, for polymer compositions containing 20% by weight of the additive composition of Example 1.

Table 3 (weight-average molecular weight before aging: 74,300)

Table 4 (number-average molecular weight before aging: 12,330)

As is apparent from Tables 1 through 4 above, all of the polymer compositions tested rapidly degraded at all degradation temperatures. Although the rate of thermo-oxidative degradation of polymers relies on temperature, oxygen content, and amount of degradation promoting additive composition, temperature seems to be the most influential factor. Both of the two transparent films produced with different amounts of additive composition showed a great reduction in molecular weight to less than 5,000 after degradation at 70°C for 2 weeks, regardless of the oxidation conditions created using air and 5 % and 10 % by weight of oxygen.

In addition, amount of degradation promoting additive composition is found to be another influential factor on polymer degradation. When 20% by weight of the degradation promoting additive composition was used, the molecular weights after degradation were about 30-50% smaller than when 10% by weight of the degradation promoting additive composition was used.

Oxygen content seems to be less influential on polymer degradation. There was no significant difference in the molecular weight after degradation with different amounts of oxygen, between the film containing 10% by weight of the additive composition and the film containing 20 % by weight of the same.

Example 4

The degradation promoting additive composition of Example 1 was added into LDPE in an amount of 10% by weight and 20% by weight, and two sheets of biodegradable polymer foils of a weight of about 25g each were manufactured from the two polymer compositions. These biodegradable polymer foils were left in an oven at 70°C for 4 weeks for pre-aging. The resulting pre-aged polymer foils were mixed with microbial activated soil, which contained very low amounts of easily degradable carbon sources. Each of the mixtures was filled in a glass column and incubated at 60°C. Soil microorganisms produced new biomass by degrading the organic compounds (polymer samples). During the incubation, the soil columns were continuously aerated with oxygen.

The amount of carbon dioxide produced during the incubation was measured to investigate the degree of polymer degradation (into inorganic materials) in soil samples. Carbon dioxide produced by the soil microorganisms and release from the glass column was trapped in sodium hydroxide solutions to convert it into sodium carbonate. An aliquot of the sodium hydroxide solution was collected at regular intervals and analyzed by titration to measure carbonic acid content.

The initial carbon content of the test composition (polymer foil) was measured before the mineralization test, and a theoretical content of carbon dioxide that can be produced from the carbon source of the test composition was calculated based on the initial carbon content measured before the mineralization test. A degree of mineralization (degradation into inorganic materials) of the test composition was measured as the ratio of carbon dioxide content between the experimental and theoretical values. The mineralization test for measuring the degradability of test samples was conducted for 9 weeks. The results are shown in Tables 5 and 6 below.

Table 5. Mineralization in soil columns (for samples containing 10 % by weight of the degradation promoting additive composition)

Table 6. Mineralization in soil columns (for samples containing 20 % by weight of the degradation promoting additive composition)

theoretical value; and

^*2 %CO₂ production: corrected values under the assumption that glucose is completely degraded to CO₂ and biomass.

For the polymer foils manufactured with 10% by weight of the degradation promoting additive composition and incubated together with soil microorganisms for 9 weeks, 34% of the carbon source degraded into carbon dioxide.

For the polymer foils manufactured with 20% by weight of the degradation promoting additive composition and incubated together with soil microorganisms for 9 weeks, 33% of the carbon source degraded into carbon dioxide.

In these tests, only dissimilated carbon content (producing CO₂), not assimilated carbon content (producing biomass), was measured. As is apparent from Tables 5 and 6 above, the mineralization rate for 9 weeks was 34% for the polymer foil containing 10% by weight of the degradation promoting additive composition and 33% for the polymer foil containing 20% by weight of the additive composition.

Polymer compositions according to the present invention were prepared in the same manner as in Examples 3 and 4, with the exception that polyethylene, polypropylene, polystyrene, polyethylenepropylene, polyethylenestyrene, polypropylenestyrene, and polyethylenepropylenestyrene, instead of LDPE, were used as the letdown polymer of the polymer compositions. The results were similar to those from Examples 3 and 4.

Industrial Applicability

In accordance with the foregoing, the use of additive compositions capable of promoting polymer degradation and polymer compositions containing the same according to the present invention in manufacturing polymer products makes the polymer products degradable to be environmentally favorable while appropriately retaining the shelf-life and functionality of the constituent polymers.

Claims

What is claimed is:

1. An additive composition for promoting polymer degradation, comprising:

0.001-2.0 parts by weight of a transition metal salt containing an anionic component derived from C-i-Cg organic acid, or Cι₀-C₃o substituted or unsubstituted saturated or unsaturated fatty acid;

0.1-3.0 parts by weight of at least one unsaturated organic compound selected from the group consisting of C₄-C₂₂ unsaturated fatty acid, C₄-C₂₂ unsaturated fatty acid ester, unsaturated natural polymer having a weight-average molecular weight of 10, 000-3, 000, OOOD, and unsaturated synthetic polymer having a weight-average molecular weight of 2,500-2,000,000D; and

40-98 parts by weight of at least one polymer component selected from the group consisting of polyethylene, polypropylene, polystyrene, polyethylenepropylene, polyethylenestyrene, polypropylenestyrene, and polyethylenepropylenestyrene.

2. The additive composition of claim 1 , wherein the polymer component comprises 20-49 parts by weight of a homopolymer and 20-49 parts by weight of a copolymer.

3. The additive composition of claim 1 , further comprising 50 parts or less by weight of a biodegradable polymer.

4. The additive composition of claim 1 , further comprising 5 parts or less by weight of a desiccant.

5. The additive composition of claim 4, wherein the desiccant is calcium oxide.

6. The additive composition of claim 1 , further comprising 5 parts or less by weight of at least one inert and insoluable material selected from the group consisting of calcium carbonate, mica, silica, and alumina.

7. The additive composition of claim 1, wherein the transition metal of the transition metal salt is derived from at least one transition metal selected from the group consisting of cobalt, manganese, copper, vanadium, and iron.

8. The additive composition of claim 1 , wherein the C-i-Cg organic acid is at least one selected from the group consisting of acetic acid, citric acid, and tartaric acid.

9. The additive composition of claim 1 , wherein the C₁₀-C₃₀ substituted or unsubstituted saturated or unsaturated fatty acid is at least one selected from the group consisting of lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, erucic acid, and 12-hydroxystearic acid.

10. The additive composition of claim 3, wherein the biodegradable polymer is at least one selected from the group consisting of starch and its derivatives, cellulose and its derivatives, lignocellulose, wood fiber, chitosan, soy proteins, casein and its salts, and gelatin.

11. The additive composition of claim 3, wherein the biodegradable polymer is: an aliphatic polyester produced by condensation and polymerization of a compound of formula HO-A-OH and a compound of formula HOOC-B-COOH; an aliphatic polyester produced by ring opening and polymerization of C₂-C₂₀ caprolactons; an aliphatic polyester produced by self condensation and polymerization of compounds of formula HOOC-D-OH; or an aliphatic/aromatic polyester produced by condensation and polymerization of a compound of formula HO-E-OH and a compound of formula HOOC-G-COOH, wherein A, B, D, and E in the forgoing formulae are C₂-C₂o alkylene, and G is C₆-C₂₀ arylene or alkylarylene.

12. A polymer composition comprising:

3-50 parts by weight of the additive composition of any one of claims 1 through 11 ; and

50-97 parts by weight of at least one letdown polymer selected from the group consisting of polyethyelene, polypropylene, polystyrene, polyethylenepropylene, polyethylenestyrene, polypropylenestyrene, and polyethylenepropylenestyrene.