EP1091985A1

EP1091985A1 - Polyacrylates with improved biodegradibility

Info

Publication number: EP1091985A1
Application number: EP99922242A
Authority: EP
Inventors: Christian Gancet; Rosangela Pirri; Bernard Boutevin; Cédric LOUBAT; Jean Lepetit
Original assignee: Atofina SA
Current assignee: Arkema France SA
Priority date: 1998-06-03
Filing date: 1999-06-01
Publication date: 2001-04-18
Also published as: JP2002517529A; FR2779435A1; CN1158316C; CN1311802A; CA2334091A1; FR2779435B1; JP3659888B2; WO1999062971A1; US6900171B1; AU3936599A

Abstract

The invention concerns novel biodegradable polymers based on carboxylic polyacid containing fragile and degradable sites. Said polymers are linear or branched. They can be used in various applications, in particular in detergent compositions.

Description

POLYACRYLATES WITH IMPROVED BIODEGRADABILITY

The invention relates to biodegradable polymers and in particular to polyacrylates with improved biodegradability. The polyacrylates of the invention can be used in various applications and in particular in detergent compositions.

Generally, detergent compositions involve a number of chemicals. These must be biodegradable so as not to harm the environment. Traditionally, detergent compositions and cleaning agents contain phosphates. These are very effective and relatively non-toxic, however they cause eutrophication of natural aquatic environments.

The phosphates have been partly replaced in the formulations for detergency by polymers such as polyacrylic acids or copolymers based on acrylic acid and maleic anhydride.

Although the polyacrylates currently used do not pose this problem, their absence of rapid biodegradability causes an accumulation in the natural environment (Swift, polymer Degradation and Stability 45, 21 5 - 231, 1 994). There is no known toxicity a priori associated with these polymers, but their long-term effect is uncertain, and this uncertainty has contributed to the establishment of numerous research studies intended to improve their biodegradability.

It is clearly established that hydrophilic polymers, such as polyvinyl alcohol, are rapidly degraded by microorganisms (Macromol. Chem. Phys. 1 96, 3437, 1 995). It is also known that acrylic polyacids with an average mass by weight of less than 1000 have better biodegradability than their superior counterparts (Swift, Ecoiogical Assessment of Polymer 1 5, 291-306, 1 997). EP 049761 1 describes the preparation of biodegradable terpolymers and compositions containing them. These terpolymers are based on vinyl acetate, acrylic acid and maleic anhydride. They have average masses by weight of less than 20,000.

US 531 871 9 describes a new class of biodegradable materials based on the grafting of polymers containing acid functions on a biodegradable support based on polyoxyalkylene.

Other work indicates that chains containing hetero atoms are more easily degraded than carbon chains. Thus, US 4923941 describes biodegradable copolymers containing carboxylic acid functions and heterocycles, as well as the detergent compositions containing them.

The Applicant has now found that the degradability of the polymers described above can be improved by inserting brittleness sites into the main chain. These sites will be rapidly broken down by microorganisms in the natural environment, to lead to acrylic sequences of sufficiently low mass to be easily biodegradable.

The Applicant has found that the fact of inserting electron-rich centers, such as double bonds, in an acrylic chain, makes the acrylic chain more fragile with respect to microorganisms and thus improves its biodegradability.

It is also well known that if the carbon chains are very resistant chemically, and biologically, this is only true in the case of saturated chains. Indeed, if a chain has multiple bonds (rich in electrons), these, easily oxidizable, and chemically reactive, will constitute the first cleavage sites of the molecule. Among the multiple bonds, the carbon-carbon double bonds appear to be the most easily usable. The invention relates to hydrophilic polymers with improved biodegradability, in particular polyacrylates containing sites rich in readily oxidizable electrons.

The polymers of the invention contain:

- from 70 to 99% by weight of units derived by polymerization of at least one monomer A carrying a carboxylic acid function or an equivalent function

- from 1 to 30% by weight of units derived by polymerization of at least one monomer B carrying an electron-rich group or a function capable of introducing an electron-rich group into the main chain

- from 0 to 29% by weight of units derived by polymerization of at least one monomer C copolymerizable with A and B, but different from A and B.

They may also contain a chain limiting transfer agent. Whatever the monomers A, B and C, the final polymer must remain hydrophilic.

The monomer A is chosen from the group consisting of monomers carrying at least one carboxylic acid and their derivatives such as salts and acid anhydrides. By way of non-limiting indication, mention may be made of maleic anhydride, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and their salts.

The preferred monomer A according to the invention is acrylic acid. The monomer B is chosen from the group consisting of: by the monomers carrying two conjugated double bonds such as butadiene, isoprene, chloroprene, dimethylbutadiene, cyclohexandiene, butadiene carboxylic acid and butadiene dicarboxylic acid, and by monomers bearing a triple bond such as acetylene, acetylene carboxylic acid and acetylene dicarboxylic acid.

The preferred monomer B of the invention is isoprene. The monomer C, different from A and B, is chosen from the group containing the monomers copolymerizable with A and B such as vinyl, acrylic, styrene monomers and their derivatives.

The distribution in the final polymer of the fragile sites provided by the monomer B depends both on the relative reactivity specific to the different monomers present, and on the ratio of the relative concentrations of monomer A, monomer B and possibly other monomers C.

The polymers of the invention can be linear or branched. They can also be partially crosslinked.

The polyacids, partially neutralized and crosslinked using a molecule containing at least two reactive functions with carboxylic acids and containing the fragile sites described above, constitute a perfect example of branched polymers with improved biodegradability according to the invention.

Among the latter, mention may be made of the products generally used as absorbents for aqueous liquids and often designated by super absorbents (SAP).

The polymers of the invention can be obtained by the joint polymerization: from 70 to 99% by weight of at least one monomer A, from 1 to 30% by weight of at least one monomer B, and from 0 to 29% by weight of at least one monomer C.

The monomers A, B and C are those described above. The polymerization can be carried out in solution in an organic solvent or in the presence of water. For information, these two modes of synthesis are described below for obtaining a linear product:

- in the presence of organic solvent: The polymerization takes place in tetrahydrofuran (THF). When the polymerization is carried out in batch, the mixture of monomers is introduced into the solvent, as well as the initiator (azo-bis-isobutyronitrile, AIBN) and, where appropriate, a transfer agent such as thioglycolic acid (ATG) or a other thiol. After degassing and placing under nitrogen, the reaction is started by raising the temperature to 70 ° C.

The monomers A, B and optionally C can be introduced continuously using a metering pump into the reactor throughout the reaction with the aim of better distributing the functional monomer throughout the chain and obtaining thus a more homogeneous polymer in composition.

After reaction and concentration of THF on a rotary evaporator, the polymer is precipitated and dried in an oven under vacuum.

- in the presence of water: Are introduced into the water, the mixture of monomers, the initiator

(potassium persulfate, K2S2O8) and if necessary a transfer agent such as thioglycolic acid (ATG) or another thiol.

After degassing and placing under nitrogen, the reaction is started by raising the temperature to 70 or 80 ° C. After polymerization, the product is recovered by evaporation and drying under vacuum.

The biodegradability of the products obtained is examined as follows:

Degradability assessment Oxidative pre-screening

This test is intended to assess the sensitivity of new sequences to the action of oxidative degradation of microbial enzymes.

Insofar as the oxidation enzymes are neither easy to use nor commercially available, the test method described below uses metal complexes, analogs of oxidation enzymes and in particular TPEN N, N , N ', N' tetramethylpyridine 1, 2- ethylene diamine or N, N, N ', N' tetrakis- (2 pyridylmethyl) ethane 1, 2 diamine.

associated with Fe III.

The reaction conditions used for the degradability test are as follows:

Polymers to be tested 1 mg / ml (test volume 10 ml)

TPEN associated with Fe 0.05 mM

0.5 mM free TPEN

H ₂ θ2 100 mM

PH 7

Temperature 50 ° C

Duration 4 h

The degradation level obtained is evaluated by liquid chromatography under the following conditions:

TSK 3000 Tosohaas column

Eluent H ₃ CCOONa O, 1 M

Flow rate 0.5 ml / min.

Injection 25 μ \ after filtration at 0.22 μ

Differential refractometer detection

Acquisition given Peaknet Dionex.

The column is calibrated using polyacrylate standards (Polymer Laboratories).

The degradability of the polymer under the conditions of the test is measured by the displacement of the peak observed in liquid chromatography towards the lower molecular weights.

This displacement is quantified through a degradability index h 000 'defined as follows:

- Initial mass of polymer Mi

- Final mass of the polymer Mf

- Number of cuts Ne

Mid

- Initial polymerization degree Dp - with M _mono : mass of "average" monomer

- Degradability index: iιooo = _TO ^{X 100} °

Microbiological degradation Experimental cultures

Candida tropicalis cultures are carried out on a liquid medium comprising malt extract (20 g. H) and incubated at 30 ° C. with axial shaking for 48 hours.

These cultures are centrifuged at 18000 rpm for 1 5 minutes, the pellet is washed with 0.1 M phosphate buffer pH6 and again centrifuged as described above. This last operation is carried out a second time in order to effectively remove any residual substrate.

Warburg method The evaluation of the respiration of C. tropicalis on a polyacrylate is carried out in Warburg flasks (total capacity of 3 ml) comprising 1, 3 ml of phosphate buffer 0, 1 pH6, 1 ml of yeast suspension (about 3 mg dry weight) and 0.5 ml of polyacrylate at 1, 1 2 g. H (final concentration of 200 ppm). Control tests are carried out in parallel:

- a flask containing only phosphate buffer (2.8 ml) makes it possible to measure the variations in atmospheric pressure

- endogenous respiration is measured in a vial containing only phosphate buffer (1.8 ml) and the yeast suspension (1 ml) - respiration due to contaminants possibly present in the acrylate solution is also evaluated by a test comprising acrylate (0.5 ml) and phosphate buffer (2.3 ml).

The vials are shaken in a water bath at 30 ° C. Measurements of pressure variations due to the appearance of CO2, revealing the metabolism of acrylate by yeast, are carried out every 1 5 minutes.

Cultures of C. tropicalis on polyacrylate

Two types of culture are used: cultures comprising exclusively polyacrylate as carbon source and cultures associating it with yeast extract. The first case reveals the use of the compound by the microorganism. The second aims to optimize this use in order to increase the degradation yield by promoting the development of yeast.

In both cases, these media comprise a conventional mineral medium (MgSÛ; 7H2O 3 g; CaCl2 2H2O 0.1 g: NaCl 1 g; FeSÛ4 7H2O 0.1 g; ZnSO ₄ 7H2O 0.1 g; C0CI2 0.1 g ; CUSO4 5H2O 1 0 mg; AIK (SO ₄ ) ₂ 1 2 H ₂ O 10 mg; H3BO3 10 mg; Na ₂ MoO ₄ 2H ₂ O 2 mg; qs 1 I distilled water) combined with phosphate buffer 0, 1. M; pH6 in the proportions 2/98. The polyacrylate is at a final concentration of 500 ppm. The yeast extract optionally added has a final concentration of 200 ppm. This concentration can be increased up to 500 ppm if the development remains too weak. The flasks are incubated at 30 ° C with transverse shaking and are subcultured after one week. The cultures then continue for 1 5 days under the same conditions. Assessment of calcium complexing ability

The principle of this test consists in measuring the capacity of a given polymer to prevent the formation of a precipitate of CaSO4 from sodium sulphate and calcium chloride.

The protocol used is as follows: Two aqueous solutions are prepared from distilled water, to contain the following salts:

Solution A: CaCI ₂ , 2H ₂ O 64.9 g / 1 + MgCl2 0.5 g / 1

Solution B: Na2SO4 62.7 g / 1

400 ml of distilled water are added to a 500 ml flask to which 50 ml of solution A are gradually added, with stirring, and then 50 ml of solution B. In a flask serving as a control, no more is added. nothing, while in the other bottles, a certain amount of anti-scale agent is added. At time t = 0, after homogenization of the solutions, a few ml of solution are taken and the calcium and magnesium are assayed there. The bottles are capped and then left to stand for 7 days. Then take a few ml of supernatant liquor and redose the calcium and magnesium.

The ion concentration is measured by emission spectrometry using the ICP (Inductively Coupled Plasma) technique. The results obtained are expressed in ppm of calcium in the solutions at time 0 and after 7 days of contact.

The following examples illustrate the invention without limiting its scope. Example 1 (comparative)

Acrylic acid (AA) / vinyl monomer copolymer in solvent phase

50 ml of tetrahydrofuran (THF), 5.76 g of acrylic acid, 0.98 g of maleic anhydride, 2 are introduced into a 100 ml two-necked flask provided with a condenser and a nitrogen inlet. g of ethylene glycol-vinyl ether (EGVE), 0.296 g of azo-bis-isobutyronitrile (AIBN).

The reaction mixture is degassed by a succession of vacuum and nitrogen cycles, then placed in an oil bath thermostatically controlled at 70 ° C. After 12 hours of reaction, the reaction mixture is concentrated on a rotary evaporator then precipitated (2 times), filtered (frit 5), and dried in an oven under vacuum (5.1 0 ^" 2 bar) for a minimum of six hours.

Results

Ref. Composition T ° C Transfer agent Initiator hπnn

BG 78 AA80 / AM10 / EGVE10 68 (reflux) non AIBN 56

Oxidative degradability Under the conditions of the test, the product obtained has a degradability index oOO equal to 56, which is a result superior to the reference polyacrylates whose oOO ^is ^killed between 18 and 26 under the same conditions.

Likewise, a commercial copolymer of methyl vinyl ether and maleic anhydride, Gantrez, has a l - | 000 of 46.5, which clearly confirms the degradability of polycarboxylic-vinyl copolymers.

Finally, a polyvinyl alcohol homopolymer exhibiting very good biodegradability has an oOO e 21 2.1 which can therefore be considered as the upper limit under the conditions of the test. Example 2

Solvent phase AA / isoprene copolymer

1. Batch synthesis at reflux of the solvent (68 ° c)

20 ml of tetrahydrofuran, 2.88 g of acrylic acid, 0.68 g of isoprene, 0.082 g of AIBN and 0.131 g of thioglycolic acid are introduced into a 1 00 ml Schlenck tube. ATG) as a transfer agent if necessary.

The reaction mixture is degassed by a succession of vacuum and nitrogen cycles, then placed in an oil bath thermostatically controlled at 70 ° C. After 12 hours of reaction, the reaction mixture is concentrated on a rotary evaporator and then precipitated. (2 times), filtered (frit 5), and dried in the vacuum oven (5 * 10 ^_ 2 bar) for a minimum of six hours.

Two products were prepared according to this mode. They bear the references BG 70 and BG 1 15.

2. Semi-continuous synthesis in a pressure reactor (70 ° c; 2.5 bar)

0.6 g of AIBN, 33.5 g of acrylic acid and 90 g of THF are introduced into a 500 ml stainless steel reactor capable of withstanding a minimum pressure of 5 bars fitted with a magnetic stir bar.

The reactor is hermetically closed by an 8-screw cover surmounted by a pressure gauge and a valve usable for the introduction of liquids and for degassing the reactor.

The pressure is raised to 2.5 bars in the reactor by the introduction of nitrogen.

Weigh in a bottle, thermostated by an ice bath 7.5 g of isoprene and 180 g of THF. The filled bottle is placed on a balance to follow the reduction in mass corresponding to the quantity introduced into the reactor. The bottle is connected to a metering pump, which is itself connected to the reactor. The connection pipes are purged, the reactor is placed in an oil bath thermostatically controlled at 70 ° C. and magnetically stirred. The pressure may increase a little, it should not exceed 5 bars. Then one begins to introduce the THF / isoprene mixture into the reactor. The addition will last 180 min and the reaction will still be maintained at 70 ° C for an additional 17 hours

At the end of the reaction, the reactor is placed in an ice bath in order to reduce the internal pressure, after 30 minutes it is degassed.

The reaction mixture is concentrated on a rotary evaporator then precipitated (2 times), filtered (frit 5), and dried in an oven under vacuum (5 * 10 ^~ 2 bar) for a minimum of six hours.

The product obtained bears the reference CL 56.

Results

Oxidative degradability

In the test conditions, the products obtained have a degradability index OOO ° the ^u ^{'is s'} ^{kills betw} een 48.6 and 62.4, which is a result superior to reference polyacrylates whose OOO ^whether ue between 18 and 26 under the same conditions. This is verified with or without the presence of a transfer agent. These results show that the degradability of this type of copolymer in the oxidation test is of a level entirely equivalent to the structures described in Example 1 corresponding to EP 49761 1. Microbiological degradability

The AA / lsoprene copolymer (BG70) was also evaluated for microbiological degradation under the conditions described above. Two types of results were obtained. a - Breathing test The copolymer was used as a carbon substrate for Candida tropicalis cultures, compared to easily metabolized control glucose substrate and to a reference polyacrylate.

The res iration values obtained are as follows

Compared to a standard polyacrylate which does not cause any respiration, the copolymer with isoprene has a specific respiration rate close to 30% that of glucose, which indicates a marked improvement in biodegradability. b - Assimilation test

The copolymer was used as a carbon substrate for Candida tropicalis cultures of greater duration, and analyzed by liquid chromatography in a comparative manner, after 15 days of culture.

Analysis of these results shows that approximately 72.5% of the copolymer was degraded by the microorganism during the 15 days of culture. The washing of the biomass with saline solutions does not reveal any trace of polymer, proof that there has indeed been biodegradation, and not adsorption of the polymer thereon.

Complexation

The copolymers obtained are dissolved in 0.1 M sodium hydroxide before analysis, then brought back to the pH of the test. The measurable level of calcium after 7 days of contact indicates the ability of the polymer evaluated to inhibit its precipitation in the form of CaSO4. The table below indicates that the effect persists up to 0.25 ppm of AA / isoprene copolymer under the conditions of the test, and up to a value similar to the reference polyacrylate, then no effect is measured for the witness.

These results allow us to conclude that the new AA / isoprene polymers manifest vis-à-vis calcium a power equivalent to that of a reference polyacrylate such as Norasol 4500.

Claims

1. Hydrophilic polymer with improved biodegradability, characterized in that it contains: - from 70 to 99% by weight of units derived by polymerization of at least one monomer A carrying a carboxylic acid function or an equivalent function,

from 1 to 30% by weight of units derived by polymerization of at least one monomer B carrying an electron-rich group or a function capable of introducing an electron-rich group into the main chain, and

2. Hydrophilic polymer according to claim 1 characterized in that the monomer A is chosen from the group consisting of monomers carrying at least one carboxylic acid and their derivatives such as maleic anhydride, acrylic acid, methacrylic acid, l itaconic acid, fumaric acid, maleic acid, and their salts.

3. Hydrophilic polymer according to claim 2 characterized in that the monomer A is acrylic acid.

4. Hydrophilic polymer according to claim 1 to 3 characterized in that the monomer B is chosen from the group consisting of: by the monomers carrying two conjugated double bonds such as butadiene, isoprene, chloroprene, dimethylbutadiene, cyclohexandiene, butadiene carboxylic acid and butadiene dicarboxylic acid, and by the monomers bearing a triple bond such as acetylene acetylene carboxylic acid and acetylene dicarboxylic acid.

5. Hydrophilic polymer according to claim 4 characterized in that the monomer B is isoprene.

6. Hydrophilic polymer according to one of claims 1 to 5 characterized in that the monomer C is chosen from the group containing the monomers copolymerizable with A and B such as vinyl, acrylic, styrene monomers and their derivatives, but different from A and B.

7. Use of hydrophilic polymer according to one of claims 1 to 6 in compositions for detergency.

8. Hydrophilic polymer according to any one of claims 1 to 6 characterized in that it is crosslinked with a difunctional agent to form a carboxylic polymer which can be used as superabsorbent.