IE882517L - Degradable plastic compositions - Google Patents

Description

61 406 **/''/*? - i - The invention relates to a plastics composition whose polymeric component comprises a thermoplastic polymer* in particular a polymer of a-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 contain® a naturalf 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.

The object of the present invention is to realise 15 a plastics composition for films, sheets or other mouldings,, which have 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 20 which meet the stated requirements during storage and use but after use can be rapidly degraded under the above-mentioned conditions» Under comparable conditions, the degradation time of the compositions according to the invention are reduced by at least half, frequently by 2/3 25 or more/ compared with products of a similar type known to date.

British Patent Mo. 1,485,833 discloses that plastics having carbon-carbon bonds can be rendered biodegradable by adding a) starch granules or chemically 30 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, 35 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. 61 406 It has furthermore been found that under conventional composting 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 g-olefins, in particular polyethylene and polystyrene, can be accelerated by adding compounds of a transition 10 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, c-olefins which contains a) a biodegradable substance, for example starch, b) an optionally complex iron compound which is 20 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 above-mentioned patents (cf« the 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) the 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 Fe(III)-Fe(II)-Fe(III) (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 carbohydrates, too, may be used 10 for the desired purpose » It has proved advantageous to use the biodegradable substance in the form of granules,, which can be incorporated completely homogeneously in the plastics material in a known manner.

The component c) is an oxidisable substance which 15 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 20 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 b® coupled with a further ligand 25 Y. Here, Fa denotes iron of any known valency. The 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", N02", N3", EDTA or a carbonvl , 30 nitrosil or porphyrin radical. Suitable ligands Y are, for example, carboxylic acid ions of aromatic or aliphatic monocarboxylic acids or of dicarboxylic acids, the aliphatic carboxylic acid preferably containing 10 to 20 carbon atoms. The ligand 1* serves in general to increase 35 the solubility of the compound X-Fe in the polymer. The 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. 4 - 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 a transition metal, with the exception of Fe, and Z' 5 designates one or more ligands. The following may be mentioned as examples of the ligands Eps 0H"f Cl-, Br", I", oxalate-, H-citrate", N02', Ha-,,, EDTA and carboxylic acid ions of aromatic or aliphatic mono- or dicarboxylic acids, the aliphatic carboxylic acid preferably having 10 10 to 20 carbon atoms. Suitable transition metals Me are mainly the transition metals of the first transition metal series of the 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 15 weight, in particular 0.01 to 0.05% by weight - The • 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 20 understood here as being all types of polyethylene, such as LDPE, LLDPE, LMDPE, MDPE, HDPE, ULDPE, etc. Suitable ethylene copolymers are, for example, EVA, EBA, EAA, EM&A and ionomers.

The present invention has the advantage that, by 25 varying the concentration of the individual components, the degradation can be controlled according to the field of use, without the plastics material suffering a deterioration in its properties under the conventional conditions of use.. Particularly interesting fields of use 30 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 35 carrier bags, building films, plastics fibres and plastics tapes, in particular just [sic) plastics tapes, etc.

The present invention permits the production of environment-friendly products which can be degraded without additional energy consumption and without the release of harmful substances.

The production of the compositions according to the invention and their processing to give sheets,, films, 5 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 master-batches .

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. Alberts son, B. Ranby, J, Appl.

Polym. Scis Appl. Polym. Symp., 35 (1979), page 423 and articles by A.C. Albertsson mentioned therein) that 15 plastics having C-C bonds in the main chain undergo extremely slow biodegradation with formation of C02 and H20. The extrapolated half-life for the polyethylene is about 100 years.

On exposure to ultraviolet light, sunlight or 20 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, 25 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 30 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, since this substance has a greater tendency than a saturated polymer chain to form peroxv or hydroxy-35 peroxv compounds, and, owing to its multiplicity of hydroxvl 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(III) hydroxide complexes are very reactive - This can be - 6 ~ illustrated by the following equation (1)s Fe3*OH~- [ FeOH ] 2*-Fe2* + OH" (1) The observed catalytic effect of the transition metal compoundsf for example copper or vanadium S 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)s Fe2* + ROOH-Fe3* + OB" + RO (2) In the presence of copper compounds, the Fe2* formed is reoxidised more rapidly according to equation (3)x "> 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 20 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 £e?*? mm2 to a few cm2. This phase generally lasts for 10 to SO days, depending on the prevailing 25 conditions.

In a subsequent second stage, the following can be observedi A) The degradation process continues as in the first stage on exposure to ultraviolet light and/or sunlight 30 and/or heat. The 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 stag©- As a result of the disintegration into 5 small particles, the surface area of the starch for attack by the microorganisms is increased several-fold. The starch is completely biodegraded, while th© oxygen-containing, cleaved polymer chains are at least partially degraded. Depending on the prevailing conditions, the 10 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, ar© in turn partially further degraded - In this way, complete biodegradation can be achieved at the 15 end of the second stage. This takes place in general., for example, under, customary composting conditions, which dttmprise temperatures of up to 75~8QS>C and gradually reach the outside temperature in the course of 6 to 8 months.

Such a two-stage degradation is particularly advisable in 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 25 take place In the case of conventional,, photodegradable plastics compositions - Examples The films A-1 were produced by the blown film method in a customary manner using masterbatches. They 30 all had the sajfte 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 35 and copper stearate are shown in Table l. The change in the tensile strength and elongation at break at 65*'C and under composting conditions as a function of time was measured 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.

TABLE 1 Film compositions Additives in I by weight Compo- FeOH Cu (stea- Film sition (stea- soya rate)2 thickness No. starch rate)„ oil A -- --- --- --- 55 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 G 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 1,2 (. r" Change in the tensile strength and elongation at break at S5"C Table 2a Tensile strength in N A B C D Original longitudinal .1 19. d 29. 3 19.2 transverse 28.5 17. 6 27. 3 19.0 6 days longitudinal 29.3 18. o 18. 7 17.6 transverse 28.8 17. o 19- 6 13.7 days longitudinal .7 17. 7 16. 0 .1 transverse 27.S IS. & 0 13. 7 12.2 days longitudinal .5 19. 1 . 14.0 transverse 28.9 16. 1 14. 0 12.5 days longitudinal 29.2 18. 1 14. 3 13.5 transverse 27.9 . 14.

«L 13.0 days longitudinal .0 18.. 13. 6 12.5 transverse 28.5 . 8 x4« 0 12.1 Elongation at break in % A B c D Original longitudinal 390 233 258 232 transverse 315 530 520 531 6 days longitudinal 402 239 217 167 transverse 505 539 437 346 days longitudinal 388 226 95 86 transverse 508 518 109 27 days longitudinal 395 195 67 22 transverse 520 500 47 11 days longitudinal 375 203 54 transverse 495 462 41 e days longitudinal 385 185 44 transverse 495 430 37 -8 Chance in the tensile strength and elongation at break at Table 2a (continued) Tensile strength in N days 20 days 25 days 30 days transverse transverse transverse longitudinal transverse longitudinal transverse Elongation at break in % days 20 days 25 days 30 days transverse transverse transverse longitudinal transverse longitudinal transverse E F G H 1 1 13.8 14.0 14.2 19.5 19.8 9.3 8.9 9.8 19.1 18.9 11.8 -7 9.6 .5 14.5 8.7 8.0 O rs o ^ 13.0 13.5 .5 9 • 8 © -i 12.5 13.2 Q 0 (*<!><*=■ 7.9 8.1 12.0 12.2 9»5 8.8 8.3 12.0 12.5 8.2 7.1 7.7 11.2 11.7 9.2 8.7 7.5 11.0 12.0 o a *? ffi ma 7.8 7.7 .5 11.2 E P G « «* J&2> 1 1S2 132 163 241 237 434 304 400 525 521 109 71 12 88 75 <-:■ a 1 -t 6.7 38 11 0 . Ji 14 13 9 - 2 1*1 "9 *t • i 4.2 8.2 a. 3 9... 4 esj M / 0 / .4 Q 1 7.5 6.2 4.0' 3.9 6.2 4.9 7.1 .4 4.3 7.4 .0 .1 3.8 1 7 <*<? ft ff 4.3 4.2 r Changs 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 transverse 19.2 19.0 19.2 19.0 6 days longitudinal transverse .4 12.4 .2 13.6 days longitudinal transverse 13.6 12.9 14.4 13.8 days longitudinal transverse % i»i *a * X 12.9 11.7 12.1 days longitudinal transverse 14.1 13.7 « 8.6 10.8 Elonoation at break in % Original longitudinal transverse 232 531 232 531 6 days longitudinal transverse 103 86 42 12 days longitudinal transverse 41 14 9 i days longitudinal transverse 18 10 4.4 4.3 days longitudinal transverse 11 7 J * 3.6 Degradation under compostina conditions Table 3 Tensile s trength in N A B C D Original longitudinal .1 19. 4 26.7 . 6 transverse 28.5 . 7 .8 16. 0 3 weeks longitudinal 29.7 19. 2 .1 19. 0 of transverse 28.0 .

J9 Oft .4 . 7 weeks longitudinal 29.2 . 8 21.3 . 1 transverse 28.3 1 A X ^ m 3 22.2 12. i 13 weeks longitudinal -2 18. .0 19. 2 transverse 27.6 1 A 0 21.7 11. weeks longitudinal 29.5 18. 4 22.0 18.

Q transverse 27.7 13. 2 16.1 12. 1 Elongation at: break in % B C D Original longitudinal 390 282 286 253 transverse 515 752 638 667 3 weeks longitudinal 383 231 247 190 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 weeks longitudinal 385 152 153 174 transverse 495 263 570 300 The results of the attached Tables clearly shov? the synergistic effect of the components a)? b) and c) on the degradation of polyethylene polymers, and the catalytic effect of the additional transition metal.

Claims (8)

Parent Claims

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, to) an optionally complex iron compound which is soluble in the composition., acts as an initiator and promotes further degradation,? 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.

2. Composition according to Patent Claim 1, characterised in that th® content of component a) is from 2 to 40% by weight, preferably froia 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 3% by weight, preferably fron 0.5 to 1.5% by weight, based on the composition.

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

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

? - Composition according to Patent Claim 6, characterised in that the content of the additional - 16 - transition-metal compound is at least 0.005% by weighte 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. F. R- KELLY & CO., AGENTS FOR THE APPLICANTS;