IE61406B1 - Degradable plastic compositions - Google Patents

Abstract

The invention relates to a plastics composition whose polymeric component comprises a thermoplastic polymer, in particular a polymer of e-olefins, preferably polyethylene or ethylene copolymers, which composition 5 decomposes into small particles either under the action of heat and/or of ultraviolet light and/or of sunlight and/or under composting conditions. Since this plastics composition also contains a natural, biodegradable substance, the small plastics particles formed are 10 further degraded by microorganisms, such as bacteria, fungi and/or enzymes, which ar® present in a composting mixture or in the soil. Under suitable conditions, complete degradation can thus be achieved.

Description

The invention relates to a plastics composition whose polymeric component comprises a thermoplastic polymer, in particular a polymer of e-olefins, preferably polyethylene or ethylene copolymers, which composition decomposes into small particles either under the action of heat and/or of ultraviolet light and/or of sunlight and/or under composting conditions. Since this plastics composition also contains a natural, biodegradable substance, the small plastics particles formed are further degraded by microorganisms, such as bacteria, fungi and/or enzymes, which ar® present in a composting mixture or in the soil. Under suitable conditions, complete degradation can thus be achieved.

The object of the present invention is to realise a plastics composition for films, sheets or other mouldings, which hav® the desired properties of known, thermoplastic materials, such as, for example, simple processing, high strength, impermeability to water and good resistance to solvents and other chemicals, and which meet the stated requirements during storage and use but after use can be rapidly degraded under the abovementioned conditions- Under comparable conditions, the degradation time of the compositions according to the invention are reduced by at least half, frequently by 2/3 or more, compared with products of a similar type known to date.

British Patent No. 1,485,833 discloses that plastics having carbon-carbon bonds can be rendered biodegradable by adding a) starch granules or chemically modified starch granules and b) an oxidisable substance, such as a fatty acid and/or a fatty ester. This publication also mentions that the oxidisable substance is oxidised to peroxide or hydroperoxide when in contact with a transition metal salt contained in the soil, whereupon cleavage of polymer chains occurs.

However, it has also been found that, in the case of a polyethylene sheet of this composition, most starch granules are covered with a polyethylene layer and thus can scarcely be attacked by the microorganisms. . - 2 It has furthermore been found that under conventional coxaposting conditions, the concentration of transition metal salts in the soil is insufficient to cause effective oxidation of the fatty acid component.

German Offenlegungsschrift 2,244,801 discloses that, under the action of ultraviolet light and/or sunlight, degradation of thermoplastic polymers of a-olefins, in particular polyethylene and polystyrene, can be accelerated by adding compounds of a transition metal, in particular iron compounds, the effective content being stated at 0.01 to 2.0% by weight. However, it has been found that these metal compounds are inert in the absence of light at normal outside temperatures (below 35°C).

It has now been found, surprisingly, that 1) a plastics composition based on thermoplastic polymers and «-olefins which contains a) a biodegradable substance, for example starch, b) an optionally complex iron compound which is soluble in the composition, acts as an initiator and promotes further degradation, and c) an oxidisable substance containing one or more double bonds which acts as a degradation promoter and as a chain breaker, this substance being a fatty acid, a fatty acid ester or a mixture thereof, undergoes degradation on exposure to heat (> 50 *C) and/or ultraviolet light and/or sunlight and/or composting conditions: 2) this degradation takes place significantly more rapidly than that measured according to the abovementioned patents (cf. th© Tables below), i.e. the simultaneous presence of a biodegradable substance, an oxidisable substance and an iron compound results in a significant synergistic effect; 3) th® additional presence of a further transition metal compound, such as, for example, copper (II) stearate, has a catalytic effect on this degradation, specifically by accelerating the cycle Pe(III)-Pe(II)-Fe(IXI) (see equations 2-4 further below). -'3 The present invention is defined in Claim 1 and the preferred embodiments thereof are defined in Claims 2-7» Suitable components a) are biodegradable 5 substances, such as, for example, natural starch, etherified or esterified starch, for example starch modified by means of silanes, the content generally being 2 to 40% by weight, preferably 10 to 16% by weight, of the composition. Other carbohydratest too, may b® used for the desired purpose, It has proved advantageous to use the biodegradable substance In th© form of granules, which can be incorporated completely homogeneously in the plastics material in a known manner.

Th® component c) is aa oxidisable substance which IS contains at least one double bond, this substance being or containing a fatty acid and/or a fatty acid ester. A very suitable example is natural soya oil. The content of this oxidisable substance is in general up to 5% by weight, preferably 0.5 to 1.5% by weight, based on the composition.

The iron compound which represents the component b) corresponds to the general formula X-Fe, in which X represents one or more ligands, it being possible for the compound additionally to be coupled with a further ligand Y. Here, Pe denotes iron of any known valency. Th® ligand X may be an inorganic or organic acid radical, as well as another ligand bound in the form of a complex. The following may be mentioned as examples; OH, Cl, Br‘, I, oxalate, H-citrate”, NO/, N3’, EDTA or a carbonyl, nitrosil or porphyrin radical. Suitable ligands Y are, for example, carboxylic acid Iona of aromatic or aliphatic monocarboxylic acids or of dicarboxylic acids, th© aliphatic carboxylic acid preferably containing 10 to 20 carbon atoms. The ligand Y serves in general to increase th© solubility of the compound X-Fe in the polymer. Th© content of component c) is In general at least 0.01% by weight, preferably 0.15 to 0.5% by weight, based on the composition. The content may be 0.02, 0.03 or 0.04% by weight but may also exceed 5.0% by weight. Ί The catalyst which may be added is a transition metal compound which may be in the form of a complex and is of the general formula Z'-Me, in which He designates & transition raetal, with th© exception of Fe, and. Z' designates one or more ligands. The following may be mentioned as examples of the ligands Z's OH, Cl, Br, I, oxalate, K-citrate, NO2, N3, EDTA and carboxylic acid ions of aromatic or aliphatic mono- or dicarboxylic acids, the aliphatic carboxylic acid preferably having 10 to 20 carbon atoms. Suitable transition metals He are mainly the transition metals of the first transition metal series of th© Periodic Table of elements, such as copper and vanadium. The content of this catalyst component is at least 0.005, preferably 0.005 to 1.0% by weight, in particular 0.01 to 0.05% by weight™ Th© · thermoplastic base material consists < · essentially of any known thermoplastic polymer, polymers of c-olefins, in particular polyethylene or ethylene copolymers, being preferred. Polyethylene” is to be understood here as being all types ox polyethylene, such as LDPE, LLDPE, LHDPB, MDPE, HOPS, ULDPE, etc. Suitable ethylene copolymers are, for example, EVA, EB&, BAA, BMAA and ionomers.

The present invention has the advantage that, by varying th® concentration of the individual components, the degradation can be controlled according to th® field of use, without the plastics material suffering a deterioration in its properties under the conventional conditions of use. Particularly interesting fields of use for the compositions according to the invention are packaging materials, films for refuse bags for compostable wastes, films for agriculture. In particular those which come into contact with the soil and are intended to decompose after a desired, time, sheets for carrier bags, building films, plastics fibres and plastics tapes, in particular just [sic] plastics tapes, etc.

Th© present invention permits th® production of environment-friendly products which can be degraded without additional energy consumption and without th© release of harmful substances.

The production of the compositions according to the invention and their processing to give sheets, films, panels or other elements is carried out by customary methods. The components are advantageously added individually or as a mixture in the form of so-called masterbatches .

It is known to date or may be assumed likely that 10 the degradation takes place according to the following mechanisms It is known (A-C. Albertsson, B. Ranby, J. Appl. Polym. Scis Appl. Poly®. Symp., 35 (1979), page 423 and articles by A.C. Albertsson mentioned therein) that plastics having C-C bonds in the main chain undergo extremely slow biodegradation with formation of C02 and H20. The extrapolated half-life for th© polyethylene is about 100 years.

On exposure to ultraviolet light, sunlight or heat or under composting conditions, the presence of iron ions results in the formation of free radicals, such as, for example, OH·, which can react with the polymers to form of other radicals. These polymer radicals are extremely reactive and can react further, inter alia, with oxygen, with other polymer chains, with iron ions, with a· double bond of th® oxidisable substance, etc. In this procedure, polymer chains are cleaved, small chains with or without oxygen-containing groups, such as alcohols, ketones, esters, etc., being formed. During this process, the iron ions act both as an initiator and as a reaction promoter, while th© oxidisable substance act (sic] as a reaction promoter and in particular as a chain breaker, sine© this substance has a greater tendency than a saturated polymer chain to form peroxy or hydroxy35 peroxy compounds, and, owing to its multiplicity of hydroxyl groups in its composition, the starch acts as a promoter and, in conjunction with the Iron ions, as a particularly valuable co-initiator, since iron(IIl) hydroxide complexes are very reactive. This can be illustrated by the following equation (l)s Fe3*OK-[FeOH)2’-Fe2* + OH· (1) The observed catalytic effect of the transition metal compounds, for example copper or vanadium compounds,» is probably due to an acceleration of the cycle Fe3*-Fe2*-Fe3*. Without these compounds ? the Fe2* formed according to equation (1) is reoxidised by other free radicals or other intermediates at the cost of chain cleavage, as shown, for example, in equation (2): Fe2* + ROOH-Fe3* + OK + RO (2) In the presence of copper compounds, the Fe2* formed is reoxidised more rapidly according to equation (3)s ·'·'> Fe2* + Cu2* “Fe3* + Cu* (3) Cu* ions reoxidising with free radicals very rapidly to give Cu2* ions: Cu* + RO'-Cu2* + RO' (4) This process is repeated for as long as the composition is exposed to the ultraviolet light and/or the sunlight and/or the heat. In this phase, to be designated as the first phase, the plastics materials are brittle and fragile and disintegrate into small particles of from a few mm2 to a few cm2. This phase generally lasts for 10 to 60 days, depending on the prevailing conditions.

In a subsequent second stage, the following can be observed: A) Th© degradation process continues as in the first stage on exposure to ultraviolet light and/or sunlight and/or heat. Th© small particles disintegrate further to increasingly small particles until they disappear.

B) In the presence of microorganisms, i.e. of bacteria, fungi and/or enzymes, as occur under composting conditions or in contact with soil, there is a further degradation stage. As & result of the disintegration into small particles, the surface area of the starch for attack by the microorganisms is increased several-fold. The starch is completely biodegraded, while the oxygencontaining, cleaved polymer chains are at least partially degraded. Depending on the prevailing conditions, the degradation processes of the first stage may continue, leading to even shorter oxgyen-containing polymer chains which, owing to the close contact with the microorganisms or enzymes, are in turn partially further degraded. In this way, complete biodegradation can be achieved at the end of th© .second stage. This takes place in general, for example, under, customary composting conditions, which domprise temperatures of up to 75-80“C and gradually reach the outside temperature in the course of 6 to 8 months.

Such a two-stage degradation Is particularly advisable ia the case of agricultural sheets which are in contact with the soil or of scattered wastes. After the first stage, the plastics particles are so small that they further disintegrate within the soil. This would not take place In the case of conventional, photodegradable plastics compositions.

Examples The films A-1 wer® produced by the blown film method in a customary manner using masterbatches. They all had the same thickness. Film A contained no degradation-promoting additive. The films B and C, which did not contain all the required additives, serve as Comparative Experiments. The different contents of silicone-modified starch, basic iron stearate, soya oil and copper stearate are shown in Table 1. The change in the tensile strength and elongation at break at 65 eC and under composting conditions as a function of time was --8measured for each composition. With an elongation at break of less than 5% in the transverse direction, the product is so fragile that it Is not possible to perform any measurements, so that the film may be considered to have been degraded.

The results of th© investigations are shown in Tables 2 and 3 below. -9TABLE 1 Film compositions ι Additives in 1 by weight Compo- FeOH Cu (stea- Film sition (stea- soya rate) , thickness No. starch rate)j oil z in yuw A — — — SS B 10 — 0,5 — 60 C 0,05 — — 55 D 10 0.,05 0,5 — 58 E 10 0,1 0,5 - 62 F 16 0,05 0,8 — 55 6 10 0,15 0,5 — 56 H 10 0,05 1,0 --- 58 I 10 0,05 0,5 0,025 57 Plastic : LDPE; melt index 1 ? A i> ** Change in th® tensile strength.and elongation at break at 65C Table 2 a Tensile strength in N A B C 0 Original longitudinal 30.1 19.6 29.3 19.2 transverse 28.5 17.6 27.3 19.0 6 days longitudinal 29.3 18.6 18.7 17.6 transverse 28.8 17.9 19.6 13.7 XO 10 days longitudinal 30.7 17.7 16.0 15.1 transverse 27.9 16.6 13.7 12.2 15 days longitudinal 30,,5 19.1 15.5 14.0 transverse 28.9 16.1 14.0 12.5 20 days longitudinal 29.2 18.1 14.3 13.5 15 transverse 27.9 15.5 14.4 13.0 30 days longitudinal 30.0 18,.5 13.6 12.5 transverse 28.5 15.8 14.0 12.1 Elongation at break in % A B C D 20 Original longitudinal 390 233 258 232 transverse 515 530 520 531 6 days longitudinal 402 239 217 167 transverse 505 539 437 346 10 days longitudinal 388 226 95 86 25 transverse 508 518 109 27 15 days longitudinal 395 195 67 22 transverse 520 500 47 11 20 days longitudinal 375 203 54 15 transverse 495 462 41 9 30 30 days longitudinal 385 185 44 10 transverse 495 430 37 5.8 ,/ Change in the tensile strength and elongation at break at °C Table 2a (continued) Tensile strength in N E F G H I Original longitudinal 13.8 14-0 14.2 19,5 19.8 transverse 9.3 8.9 9.8 19.1 18.9 10 days longitudinal 11.8 10.7 9.6 15.5 14.5 transverse 8.7 8.0 9.5 13.0 13.5 20 days longitudinal 10.5 9.8 9.1 12.5 13.2 transverse 9.2 7.9 8.1 12.0 12.2 25 days longitudinal 9.5 8.8 8.3 12.0 12.5 transverse 8.2 7.1 7.7 11.2 11.7 30 days longitudinal 9.2 8.7 7.5 11.0 12.0 transverse 9.2 7.8 7.7 10.5 11.2 Elongation at break in % E F G « H I Original longitudinal 162 X32 163 241 237 transverse 434 304 400 525 521 10 days longitudinal 109 71 12 88 75 transverse 35 7.4 6.7 25 15 20 days longitudinal 38 11 6.3 14 13 transverse 9.2 4.7 4.2 8.2 6.3 25 days longitudinal 9.4 7.7 5.4 9.1 7.5 transverse 6.2 4.0 3.9 6.2 4.9 30 days longitudinal 7.1 5.4 4.3 7.4 5.0 transverse 5.1 3.8 3.7 4.3 4.2 V . 19 Change in the tensile strength and the elongation at break of film D at 70eC and 759C Table 2b Tensile strength in N 70 *C 75°C original longitudinal 19.2 19.2 transverse 19.0 19.0 6 days longitudinal 15.4 15 · 2 10 transverse 12.4 13.S 10 davs longitudinal 13. 6 14.4 transverse 12.9 13.8 15 days longitudinal 14.1 11.7 transverse Ί 2 <3 12.1 15 20 davs longitudinal 14.1 8.6 transverse 13.7 * 10.8 Elonoation at break in % Original longitudinal 232 232 transverse 531 531 20 S days longitudinal 103 42 transverse 86 12 10 days longitudinal 41 9 transverse 14 8 15 days longitudinal 18 4.4 25 transverse! 10 4.3 20 days longitudinal 11 *2» transverse 7 3.6 Degradation under composting conditions Table 3 Tensile strength in N A 3 C D Original longitudinal 30.1 19.4 26.7 20.6 transverse 28.5 15.7 26.8 16.0 3 weeks longitudinal 29.7 19.2 25.1 19.9 transverse 28.0 15.4 15.4 15.5 7 weeks longitudinal 29.2 20.8 21.3 20.1 transverse 28.3 14.3 22.2 12.6 13 weeks longitudinal 30.2 18.5 25.0 19.2 transverse 27.6 14.0 21.7 11.5 20 weeks longitudinal 29.5 18.4 22.0 18.9 transverse 2/.7 13.2 16.1 12.7 ti W Elongation at break in % A 3 C D Original longitudinal 390 282 286 253 transverse S15 752 638 667 3 weeks longitudinal 385 231 247 190 transverse 500 476 206 437 7 weeks longitudinal 370 170 107 128 transverse 480 314 534 143 13 weeks longitudinal 400 252 198 205 transverse 510 357 534 114 20 weeks longitudinal 385 152 153 174 transverse 495 263 570 300 The results of the attached Tables clearly show the synergistic effect of the components a) f b) and c) on the degradation of polyethylene polymers, and the catalytic effect of the additional transition metal.

Claims (8)

1. Thermoplastic composition which is degradable on exposure to heat and/or ultra-violet light and/or sunlight and/or under composting conditions, whose polymeric component comprises thermoplastic polymers of «-olefins, in particular polyethylene or ethylene copolymers, characterised in that the composition contains the following degradation-promoting additives: a) a biodegradable substance, ta) an optionally complex iron compound which Is soluble in the composition, acts as an Initiator and promotes further degradation, c) an oxidisabl© substance containing one or more double bonds which acts as a degradation promoter and as a chain breaker, this substance being a fatty acid, a fatty acid ester or a mixture thereof.

2. » Composition according to Patent Claim 1, characterised in that the content of component a) is from 2 to 40% by weight, preferably from 10 to 16% by weight, and the content of component b) is from 0.01 to 5% by weight, preferably from 0,.15 to 0.5% by weight, based on the composition.

3. Composition according to Patent Claim 1 or 2, characterised in that the content of component c) Is up to 5% by weight, preferably from 0.5 to 1.5% by weight, based on th© composition.

4. » Composition according to one of Patent Claims 1 to 3, characterised in that component a) is a natural starch, an etherified or esterified starch or a hydrophobically modified derivative thereof.

5. Composition according to on© of Patent Claims 1 to 4, characterised in that component c) comprises or contains one or more constituents of soya oil.

6. Composition according to one or more of Patent Claims 1 to 5, characterised In that it also contains a further optionally complex compound of a transition metal, with th© exception of iron, as catalyst.

7. Composition according to Patent Claim 6, characterised in that the content of the additional I, V transition-metal compound is at least 0.005% by weight, preferably from 0.005 to 1,0% by weight, in particular from 0.01 to 0.05% by weight, based on the composition.

8. A thermoplastic composition according to Claim 1, substantially as hereinbefore described and exemplified.