KR20030042531A - Degradable Polyethylene Composition and Films Comprising the Same - Google Patents

Abstract

PURPOSE: A degradable polyethylene composition which can be degraded photochemically or thermo-oxidatively and has low toxicity suitable to be used in a food package, agricultural film or constructional film is provided. CONSTITUTION: The degradable polyethylene composition consists of polyethylene as a main material and 0.02 to 0.7 wt% of cerium stearate and 0.1 to 2.5 wt% of titanium dioxide as supplementary-materials. The polyethylene is selected from the group consisting of a high density polyethylene having a density more than 0.94 g/cm3 and a low density polyethylene having a density less than 0.94 g/cm3. The film obtained by using the polyethylene composition has a thickness between 0.005 mm and 0.127 mm.

Description

Degradable Polyethylene Composition and Films Comprising the Same

The present invention relates to a degradable polyolefin composition and a degradable film containing the same.

In general, polymer materials are difficult to decompose, but they are also widely used because of their strengths. For example, thermoplastic resins are widely used to produce solid products. Moreover, polyethylene, polypropylene, polystyrene, etc. are widely known as a plastic material. These are used for food packaging materials, packaging films, and the like, and are widely used for agricultural coating films, construction films, insulating materials and the like.

Since ordinary plastic products used for industrial and consumer products do not decompose naturally within a reasonable period of time, there is a growing interest among environmentalists about the disposal of the waste. Plastic materials are not easily broken down by natural factors and are not easily broken down by microorganisms. When the plastic material is incinerated, dioxin or the like is somewhat generated, which causes secondary pollution.

In addition, the plastic material used in the agricultural field has a great ecological impact. In other words, if a plastic film is used on a large farmland, a considerable amount of labor is required to recover it, and the next tillage may not be possible unless it is completely recovered.

Therefore, in some industries, plastic materials are sometimes decomposed. Various attempts are currently underway to produce degradable polymers used to make containers, films and the like. For example, there is a method of imparting photodegradability by injecting a photosensitive additive into a base polymer. However, this method has a disadvantage in that discoloration and odor by the photosensitive additive occur.

German Patent No. 2,316,697 also describes mixtures of ethylene carbon monooxide copolymers with high density polyethylene or medium density polyethylene. However, this mixture degrades too quickly for use in articles that require flexibility.

Therefore, there is an increasing demand for plastic materials having different decomposition rates under natural environments depending on the intended use.

In other words, when the plastic material is used as a greenhouse material, a long life is required, whereas when the plastic material is used as a base plate or a flower bed cover material, a somewhat short life is required. It would also be desirable for plastics that can decompose significantly within a shorter time for packaging for foodstuffs or for wrapping strings.

An object of the present invention is to provide a degradable polyolefin composition and a decomposable film containing the same, which are decomposed in a natural environment by containing cerium stearate and titanium oxide in polyethylene.

Compositions containing polyethylene, cerium stearate and titanium oxide provided by the present invention are decomposed under natural environment and then oxidized to low molecular weight substances such as ketones, carboxylic acids, alcohols, esters and aldehydes. At elevated temperatures, for example, the decomposition rate increases at 40 to 70 ° C. The composition has photochemical or thermal oxidative resolution. In other words, ultraviolet light is not necessarily required to decompose the degradable polymer composition, and can be decomposed by oxygen alone.

The composition according to the invention is of low toxicity. Therefore, it is used for degradable packaging materials such as food packaging material, agricultural film, construction film.

Thermoplastic ethylene polymers are used to prepare the compositions of the present invention. The ethylene polymer may be an ethylene homopolymer or copolymer.

High density ethylene polymers that can be used in the present invention are known as linear polyethylene having a linear structure. The density of the high density polyethylene is generally at least 0.94 g / cm 3, preferably at 0.94-0.97 g / cm 3, and the melt index is about 0.005 to 100 dg / min, preferably 0.13 to 60 dg / min.

The low density ethylene homopolymer and copolymer have a density of 0.94 g / cm 3 or less, preferably 0.87 to 0.93 g / cm 3, and the melt index of the low density ethylene homopolymer is about 0.05 to 100 dg / min, preferably 0.6 to 30 dg / min to be.

The ethylene copolymer used in the present invention is obtained by polymerizing ethylene with a monomer containing at least one olefin unsaturated group capable of copolymerizing with ethylene to form a thermoplastic copolymer.

Examples of the copolymerizable monomer include alpha olefins containing 18 or less carbon atoms such as propylene, 1-butene, isobutene, 1-pentene, octene, and hexene; Halogenated olefins such as chloroprene, tetrafulluethylene, chlorotrifulurethylene and hexafullupropylene; Styrene, o-methoxystyrene, p-methoxystyrene, m-methoxystyrene, o-nitrostyrene, p-nitrostyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, o-phenylstyrene, vinyl aryl such as p-phenyl styrene, m-phenyl styrene and vinyl naphthalene; Vinyl and vinylidene halides such as vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride and vinylidene bromide; Vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl chloroacetate, vinyl chloro propionate, vinyl benzoide and vinyl chloro benzoide; Acrylic acid, chloroacrylic acid, methacrylic acid, etaacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-decyl acrylate, methyl methacrylate, butyl methacryl Latex, methyl acrylate, ethyl acrylate, acrylamide, n-methyl acrylamide, N, N-dimethyl acrylamide, methacrylamide, N-methyl methacrylamide, N, N-dimethylethyl methacrylate Acryl and α-alkyl acrylic acid such as latex, N-methyl methacrylate, N, N-dimethyl methacrylamide, acrylonitrile, chloroacrylonitrile, methacrylonitrile, ethacrylonitrile, ethacrylonitrile, Esters, amides and nitriles thereof; Maleic acid and fumaric acid such as male anhydride, dimethyl maleate and diethyl maleate, anhydrides and alkyl esters thereof; Vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, 2-chloroethyl vinyl ether, methyl vinyl ketone, ethyl vinyl ketone, isobutyl vinyl ketone, butadiene, isoprene, chloropentadiene, hexadiene-1,6, norborna Vinyl alkyl esters and ketones such as dienes and dicyclopentadiene; Vinylpyridine, N-vinylcarbazole, N-vinylpyrrolidine, acrolein, vinyl alcohol, vinyl acetal, vinyl butyral and the like.

The ethylene copolymer used in the present invention contains about 55 to 99% by weight, preferably 90 to 99% by weight of ethylene monomer.

In the case of thermoplastic resins, ethylene homopolymers are preferred, but in the case of copolymer resins, ethylene-vinylacetate, ethylene-ethylacrylate, ethylene-acrylic acid, ethylene propylene and ethylene styrene are preferred. The ethylene polymer is present in 70 to 99% by weight as the main component of the polymer composition, the balance is another additive. The base resin is preferably present at 90 to 99% by weight of the ethylene polymer composition.

The content of cerium stearate contained in the degradable polyethylene composition of the present invention is 0.02 to 0.7% by weight, preferably 0.1 to 0.5% by weight.

The content of titanium oxide contained in the degradable polyethylene composition of the present invention is 0.1 to 2.5% by weight, preferably 0.6 to 1.2% by weight, and the particle size thereof is 0.05 µm or less, preferably 0.008 to 0.03 µm. The titanium oxide is added to control the decomposition rate of the polyethylene film, by adding it can extend the life of the film. In this case, it is suitable for use as a base material or a flower bed coating material.

The thickness of the film formed from the degradable polyethylene composition of the present invention is 0.005 to 0.127 mm, preferably 0.008 to 0.254 mm.

Polymer compositions according to the invention can be prepared by conventional compounding or inflated film devices and conditions.

Generally, the film according to the present invention is about 30 to 160 days, preferably in an environment of total radiation exposure, for example, UV, IR, visible light, etc., about 80 to 180 kcal / cm ² per year, depending on the amount of titanium oxide. Decomposes for 40 to 120 days.

The following examples are intended to illustrate the invention, but the invention is not intended to limit the scope.

(Example)

Example 1

A low density polyethylene having a density of 0.93 g / cm 3 and 0.1% by weight of cerium stearate in dry powder form was put into a Brabender mixer, and melt mixed under nitrogen exhaust to prepare a polyethylene polymer composition. In this case, the mixing speed of the mixer was 50 rpm and the nitrogen exhaust was 4 psi. Using the prepared composition, a film sheet having a thickness of 0.01 mm was prepared by an in-plate film extruder.

Example 2

A polyethylene polymer composition was prepared in the same manner as in Example 1 except that 0.15% by weight of cerium stearate was added to form a film sheet.

Example 3

A polyethylene polymer composition was prepared in the same manner as in Example 1 except that 0.3 wt% of titanium dioxide having a particle size of 0.01 μm was added thereto to prepare a film sheet.

Comparative example

A polyethylene polymer composition was prepared in the same manner as in Example 1 except that cerium stearate was not added to prepare a film sheet.

(Environmental stress test)

Exposure to ultraviolet light

Samples for environmental stress tests were obtained from the film sheets prepared in Examples and Comparative Examples. This sample was exposed to ultraviolet light (peak wavelength 312 nm) in a xenon arc weather tester. The molecular weight loss of the sample exposed to ultraviolet stress was measured. Molecular weight loss was used for size exclusion chromatography. The results are shown in Table 1. In the table, Mw represents the average molecular weight.

Exposure to heat

Each sample was exposed to heat in a hot air oven at about 70 ° C. The molecular weight loss of the sample exposed to thermal stress was measured. The results are shown in Table 2.

UV test Average molecular weight (Mw) Exposure time (hr) 0 50 100 250 Example 1 99 85 43 21 Example 2 98 76 37 16 Example 3 99 89 52 39 Comparative example 100 103 98 95

Thermal test Average molecular weight (Mw) Exposure time (hr) 0 5 10 15 Example 1 99 35 24 16 Example 2 99 26 19 12 Example 3 99 34 27 15 Comparative example 99 96 98 95

As can be seen from Table 1, the degree of decomposition increased with increasing concentration of cerium stearate under ultraviolet stress. As can be seen from Table 2, the degree of decomposition increased as the concentration of cerium stearate increased even under thermal stress, but there was no difference in the degree of decomposition when titanium oxide was added. It can be seen from this that the present invention can be applied even when exposure to ultraviolet rays is impossible.

On the other hand, it can be seen that the degree of degradation of the sample to which titanium oxide is added under ultraviolet stress is slightly reduced. In this case, it is suitable for use as a base material or a flower bed coating material.

The polyethylene film according to the present invention has a photochemical or thermal oxidative resolution and is low in toxicity, and thus is useful as a food packaging material, and particularly, can be used for agricultural films, building films, and the like.

Claims (8)

A decomposable polyethylene composition comprising polyethylene as a main component and containing 0.02 to 0.7% by weight of cerium stearate and 0.1 to 2.5% by weight of titanium oxide. The degradable polyethylene composition according to claim 1, wherein the polyethylene is selected from the group consisting of high density polyethylene having a density of at least 0.94 g / cm 3 or more, and low density polyethylene having a density of 0.94 g / cm 2 or less. The degradable polyethylene composition according to claim 1, wherein the polyethylene contains a copolymer of ethyle with at least one ethylenically unsaturated monomer copolymerizable with ethylene. The degradable polyethylene composition according to claim 1, wherein the content of cerium stearate is 0.1 to 0.5% by weight. The degradable polyethylene composition according to claim 1, wherein the content of titanium oxide is 0.6 to 1.2% by weight. The degradable polyethylene composition according to claim 1, wherein the titanium oxide has a particle size of 0.008 to 0.03 mu m. A degradable polyethylene film made of the polyethylene composition of claim 1. 8. The decomposable polyethylene film according to claim 7, wherein the film has a thickness of 0.005 to 0.127 mm.