WO1996003046A1

WO1996003046A1 - Microbicidal compositions

Info

Publication number: WO1996003046A1
Application number: PCT/GB1995/001685
Authority: WO
Inventors: Sandra Joyce Davies; Madeline Susan French; David Slater
Original assignee: Solvay Interox Limited
Priority date: 1994-07-23
Filing date: 1995-07-18
Publication date: 1996-02-08
Also published as: AU2985495A; GB9414862D0

Abstract

Microbicidal compositions which can be adapted to provide targeted and/or sustained release of peroxygen microbicides, processes for the preparation of such compositions and processes for the disinfection of liquids, particularly water, using such compositions are provided. The compositions comprise a solid source of peroxygen compound dispersed in a matrix comprising poly(caprolactone). Preferably, the solid source of peroxygen compound is sodium percarbonate.

Description

Microbicidal Compositions

This invention concerns microbicidal compositions comprising peroxygen compounds, and more particularly microbicidal compositions adapted for controlled and targeted release of the microbicide. There has long been concern about the presence and effects of microbes in liquids, particularly in fresh water. For example, bacteria and particularly algae can adversely affect potable water supplies, fish farms and recreational water and can reduce the water flow of drainage or irrigation channels. In particular, there has been much concern about blooms of blue- green algae, which can release toxins into the water which can seriously affect those drinking the water.

Traditional microbicides that have been employed for controlling microbes include quaternary ammonium compounds and transition metals such as silver or copper ions. However, such systems have increasingly come under scrutiny as concerns about the environmental impact of chemicals have increased . Peroxygen compounds, particularly hydrogen peroxide and sources thereof, have attracted attention as microbicides on account of their good environmental properties. For example, US Patent No. 4,926,795 teaches the use of sodium percarbonate or hydrogen peroxide as an algicide for use in catfish ponds . Additionally, Russian Patent Application no. 648,526 teaches that hydrogen peroxide can be employed to destroy blue-green algal metabolites in drinking water In both of these documents, the result of the treatment would be that the peroxygen would be distributed throughout the water by diffusion and/or dissolution Algal blooms commonly form at or near the surface of the water, particularly in large bodies of water, such as lakes and reservoirs. Additionally, bacterial growth is commonly concentrated at the surface of liquids, and bacteria themselves, particularly photosynthetic bacteria, can form blooms similar in nature to algal blooms In other cases, particularly in relatively shallow bodies of water, for example, fish tanks, algal growth can occur on the bed of the tank It would be desirable to target the microbicide at the region in which the microbial growth occurs or, in the case of preventative treatment, is most likely to occur Such targeting would allow improved efficiency of use of the microbicide by reducing wasteful dissemination of the microbicide into areas where little or no microbial growth occurs

Additionally, in many conventional treatments, after the initial dosing of the microbicide, there is little or no scope for a sustained release of microbicides over an extended period, for example over periods of several weeks. With such conventional treatments, if it is desired to maintain the treatment over an extended period, it is often necessary to employ a number of doses throughout the period It would therefore be desirable to identify microbicidal compositions that would permit sustained release of microbicide.

European Patent Application no. 0 382 464 teaches that a melt of polymeric material, including inter alia poly(caprolactone), can be employed to coat a substrate, including sodium perborate, in a coating process in which it is essential that a crumbling agent is employed to cause the melt to crumble to a particulate state The compositions produced by this process are intended for incorporation in detergent compositions and typically have substrate release half-lives of less than one hour, which represents rapid release of the substrate unsuited to sustained release.

It is a first object of certain aspects of the present invention to provide a microbicidal composition adapted to allow targeted dosing and/or adapted to allow sustained release of a peroxygen microbicide

It is a second object of further aspects of the present invention to provide a process for the production of a peroxygen microbicide suitable for targeted dosing It is a third object of other embodiments of the present invention to provide a microbicidal process for the treatment of liquids, particularly bodies of water

According to one aspect of the present invention, there is provided a solid microbicidal composition, characterised in that the composition comprises a solid source of a peroxygen compound distributed in a matrix comprising poly .caproiactone)

According to a second aspect of the present invention, there is provided a solid microbicidal composition adapted for targeted dosing and/or sustained release of microbicide, characterised in that the composition comprises a solid source of a peroxygen compound distributed in a matrix comprising poly(caprolactone)

According to a third aspect of the present invention, there is provided a process for the manufacture of a solid microbicidal composition, characterised in that the process comprises distributing a solid source of a peroxygen compound in liquid phase poly(caprolactone), and then solidifying the poly(caprolactone) to form a matrix.

According to a fourth aspect of the present invention, there is provided a microbicidal process for the treatment of liquids, characterised in that the process comprises contacting the liquid to be treated with a composition comprising a solid source of a peroxygen compound distributed in a matrix comprising poly(caprolactone) .

The term matrix herein is employed in its conventional sense to indicate a continuous phase and in an amount sufficient to support the solid source of peroxygen compound distributed therein without the combination of matrix and solid source of peroxygen compound crumbling to form a particulate state.

Solid sources of peroxygen compounds that can be employed in the compositions and processes according to the present invention include sources of hydrogen peroxide and sources of inorganic and organic peracids

Solid sources of hydrogen peroxide include particularly sodium percarbonate, sodium perborate mono and tetrahydrates and hydrogen peroxide adducts such as urea hydrogen peroxide and poly(vιnylpyrrolιdone) hydrogen peroxide

Solid sources of inorganic peracids include alkali salts of persulphates, such as potassium monopersulphate, which is most commonly in the form of the so-called "triple-salt" having the chemical formula 2KHSO5 KHSO4 K2SO4, and ammonium, sodium and potassium perdisulphates

Solid sources of organic peracids include solid organic peracids themselves and salts thereof, mixtures of peroxygens and organic compounds which react with inorganic peroxygen compounds in aqueous solution to generate peracids in solution, commonly known as activators, and acetyl peroxy borate compounds such as those described in European Patent Application no 0 488 090 which are incorporated herein by reference Solid organic peracids and salts thereof include magnesium monoperoxyphthalate, potassium sulphobenzoate, diperoxydodecanoic acid, pernonanoic acid and 6, 6' -terephthal-dι(amιdoperoxyhexanoιc) acid . Activators which react with inorganic peroxygen compounds to generate peracids in solution are well known in the detergent and bleaching areas and include particularly those disclosed in European Patent Application No. 0 565 01 7 which are incorporated herein by reference. When an activator is employed, the inorganic peroxygen compound is commonly selected from the group consisting of sodium perborate monohydrate, sodium perborate tetrahydrate and sodium percarbonate. In many embodiments when an activator is employed , the mole ratio of activator to inorganic peroxygen compound is within the range 1 0 : 1 to 1 : 1 0, it is generally advantageous to use a mole ratio closer to 1 ^■ 1 or to use a substantial excess of the inorganic peroxygen compound, for example, a mole ratio in the range 2 : 1 to 1 : 5, especially 1 : 1 to 1 ^• 5. Activators when employed typically comprise up to about 20% by weight of the total weight of the solid source of peroxygen compound.

Sodium percarbonate is the most preferred solid source of peroxygen compound on account of its very favourable environmental properties. The source of peroxygen compound is preferably employed in the form of a free-flowing powder or granules. The proportion of solid source of peroxygen compound in the composition is often up to 25 % by weight and in many instances is at least 1 %, preferably at least 2.5 % by weight and is commonly up to 1 5% by weight.

The poly(caprolactone) employed in the composition and process of manufacture according to the present invention should be a solid at the temperature at which the algicidal composition will be employed . It will be recognised that the compositions according to the present invention can be employed to treat waters having a wide range of temperatures, and the melting point of the poly(caprolactone) employed can vary accordingly. In many instances, the water being treated will have a temperature of from about 10° C to about 35 °C depending, for example, on the climate and the season. In certain embodiments of the present invention, it has been found convenient to employ poly(caprolactone) having an average molecular weight in the range of from 1 ,000 to 100,000, particularly 4,000 to 60,000, and/or a melting point in the range of from 20° C to 65 °C, particularly from 35 ° C to 60 ° C. In many embodiments of the present invention, poly(caprolactone) will comprise 50% by weight or more of the composition, often 75 % to 99% by weight and commonly 85 % to 97.5 % by weight of the composition.

The weight ratio of solid source of peroxygen compound to poly(caprolactone) can vary depending, for example, on the concentration of peroxygen compound it is desired to produce from the compositions, and on the length of time it is desired to maintain the treatment. It will be recognised that for a given weight of algicidal composition, a composition containing a higher proportion of peroxygen compound source will tend to give a higher concentration of peroxygen compound over a shorter period of time compared with a composition containing a lower proportion of peroxygen compound source. In many embodiments of the present invention, the weight ratio of peroxygen compound source to poly(caprolactone) will be in the range of from 1 : 200 to 1 : 1 , commonly 1 : 100 to 1 : 5, and preferably from 1 : 10 to 1 : 30. The attention of readers not skilled in the art of formulation compositions comprising peroxygen compounds is djrected to the potentially hazardous nature of mixtures of peroxygen compounds with organic compounds, and to the need to take appropriate steps to evaluate the hazards associated with a given mixture. Other components that may be included in the composition according to the present invention include dyestuffs, particularly non-toxic, biodegradable dyestuffs, that would allow the extent of diffusion of the contents of the compositions to be visually monitored; pH and/or redox indicators; biodegradable surfactants, which may assist with the wetting and/or distribution of the composition across the surface of the body of water being treated; other polymeric materials, particularly biodegradable polymers such as polyf glyco c acids), polyflactic acid), poly(hydroxγvalerate) and poly(hydroxybutyrate) and other poly(esters); solid inorganic and organic acids including sodium hydrogensulphate, sodium dihydrogenphosphate, citric and tartaπc acids, which may be particularly desirable when a source of organic or inorganic peracid is employed to reduce the pH of the aqueous peracid solution to improve the microbicidal activity of the peracid; and solid alkalis including sodium carbonate, sodium hydrogencarbonate and sodium acetate. The process of manufacture according to the present invention comprises distributing a solid source of a peroxygen compound through liquid phase poly(caprolactone) and then solidifying the poly(caprolactone) to form a matrix . The poly .caprolactone) can be liquified by heating to its melting point or above, or by at least partially dissolving the poly .caprolactone) in a solvent, preferably a volatile solvent, for the poly .caprolactone) . It will be recognised that on account of the presence of sources of peroxygen compounds, it is preferred that any solvent employed is resistant to oxidation. Examples of suitable solvents include chlorinated solvents such as dichloromethane, chloroform and 1 ,2-dιchloroethane, ethers such as tetrahydrofuran and 1 ,4-dιoxan, and esters such as methyl acetate and ethyl formate. The source of peroxygen compound is added to the liquid phase poly(caprolactone), and distributed by agitation, usually by stirring the mixture. The poly(caprolactone) can then be solidified in a number of different ways. When heating has been employed for hquification, the poly(caprolactone) can be allowed to cool to ambient temperature, or cooling can be applied to the mixture. When a solvent has been employed for hquification, the solvent can be allowed to evaporate from the mixture, or the evaporation can be accelerated by heating the mixture and/or the use of reduced pressure. When a solvent is employed, it is preferred for the weight : volume ratio of poly(caprolactone) to solvent to be such that source of peroxygen compound does not segregate, i.e. remains evenly distributed throughout the poly(caprolactone). In many embodiments, the weight : volume ratio of poly(caprolactone) to solvent is in the range of from 1 : 1 to 1 : 1 5, commonly from 1 : 2 to 1 . 10.

It will be recognised that the fluidity of the compositions according to the present invention will reduce during solidification. This variation in solidity allows a number of different techniques to be employed to form the compositions into the desired physical state. For example, compositions with a high degree of fluidity can be allowed to solidify in moulds of the desired shape, such as blocks, bricks or tablets, whereas compositions having a lower fluidity may be extruded, such as sheets, meshes or strands, or may be formed into prills or flakes. To a certain extent, the physical state of the composition may be determined by the area of application. For example, it may be desirable for a composition intended for use in the treatment of the surface of a body of water to be in the form of a sheet or mesh, whereas a composition intended for the treatment of the bottom of a body of water may desirably be formed into bricks or tablets. In certain aspects of the present invention, the compositions according to the present invention can be formed into multi-layered structures, for example by sequentially solidifying a plurality of peroxygen compound source and poly(caprolactone) mixtures in the same mould . When a multi-layered structure is formed, the source of peroxygen compound and poly(caprolactone) mixtures may have the same composition or may have differing compositions. The use of differing compositions allows further control of the rate of peroxygen compound release. For example, a three layered structure could be produced in which the first and third layers contain a relatively high concentration of peroxygen compound source , with the second layer containing a lower concentration of peroxygen compound source. Such a structure would permit a relatively rapid release of a high concentration of peroxygen compound, with a subsequent slower release of a lower concentration of peroxygen compound . Such a composition may be suitable for treatment of heavily contaminated water, with the initial high concentration of peroxygen compound acting as a shock treatment, with the later slow release serving as a prophylactic treatment to prevent or inhibit further algal growth or re- growth. The production of a multi-layered structure has also been found in certain embodiments of the present invention to increase the buoyancy of the compositions. Multi-layered structures are particularly suited to the production of relatively thick compositions by the use of a solvent to liquifying the poly(caprolactone) because the rate of solvent evaporation from a plurality of thin layers is believed to be more rapid than that from a single thick layer, and also any problems with segregation of the source of peroxygen compound within the compositions are believed to be reduced. The use of multi-layered structures may also be preferred when the solid source of peroxygen compound employed comprises an activator. It will be recognised that the reaction between the activator and the inorganic peroxygen proceeds most efficiently at alkaline pH, but that the microbicidal activity of the peracid produced is superior at acidic pH. The use of multi- layered structures therefore offers the opportunity for the production of a composition according to the present invention additionally comprising both an alkali and an acid, but with the structure of the composition selected so that there is an initial release of alkali together with the activator and inorganic peroxygen compound to promote efficient generation of peracid, followed by a later release of acid to reduce the pH to promote more efficient microbicidal activity of the peracid . Without wishing to be bound by any theory, it is believed that the buoyancy of the compositions according to the present invention depends to an extent on the amount of gas, usually air, that is incorporated in the composition during its preparation. The more air that is included , the more s buoyant the composition . In some embodiments of the process of manufacture according to the present invention, a gas such as air, nitrogen or carbon dioxide, can be used to aerate the mixture In other embodiments, however, where it is desired to produce a composition that does not float in water, it can be desirable to minimise the air incorporated during mixing, and/or to remove air from the composition, for example by compressing the compositions

The compositions according to the present invention are particularly suited for use as bacteπcides, bacteπstats, algicides or algistats and are particularly contemplated for the treatment of bacteria and algae including cyaπobacteπa such as Microcystis spp . , Anabaena spp. , Synechococcus spp. and Oscillatoπa spp., photosynthetic bacteria including the families of Chlorobiaceae and Rhodospiπllaceae such as Thiocapsa spp , Rhodospiπllum spp., Rhodopseudomoπas spp. , and Chlorobium spp. , green algae including Chlorella spp. and Scenedesmus spp.; and environmental bacteria including Pseudomonas spp. , Aerobacter spp., Streptococcus spp. , Enterococcus spp., Escheπchia spp. , Staphylococcus spp . , Proteus spp.. Bacillus spp. and Vibrio spp.

The microbicidal process according to the present invention comprises contacting the liquid to be treated with a composition comprising a solid source of a peroxygen compound distributed in a matrix comprising poly(caprolactone). In many aspects of the present invention, the composition employed and the amount of composition employed will be selected to produce a concentration of peroxygen compound in the area being treated of from 0.5 mg/l to 100 mg/l, often from 1 mg/l to 50 mg/l and preferably from 2 mg/l to 25 mg/l However, the exact details of the composition and amounts can vary widely at the discretion of the user, and may depend on whether a shock treatment is intended, or whether prophylactic treatment is intended , as well as the nature of the microbe in the liquid being treated and the temperature of the water A further factor influencing the nature and amount of the composition employed is the period over which any sustained release is required In certain aspects of the present invention, the sustained release of peroxygen compound is often required over a period of from several, such as 3 or 4, days to several weeks, such as 4 to 5 weeks

Liquids that can be treated in the microbicidal process according to the present invention most commonly, but not exclusively, comprise water. Examples of liquids that can be treated include bodies of fresh water such as lakes, reservoirs, ponds, drainage channels, canals, swimming pools, fish tanks, fish ponds, particularly catfish and trout ponds, natural springs and spas, particularly sulphur springs. The microbicidal process can also be employed to treat bodies of salt water, including areas of the sea and estuaries

Having described the invention in general terms, specific embodiments thereof are described in greater detail by way of example only.

Example 1

1 .5g poly(caprolactone) of number average molecular weight 50,000 commercially available in the UK under the Registered Trade Mark CAPA 656 was dissolved in 10 mis dichloromethane . 0.075g of granular sodium percarbonate (PCS) was stirred into the solution, and then the mixture poured into a glass mould . The solvent was allowed to evaporate, and the mixture solidified . The solid composition was added to a 1 litre vessel containing 500 mis of tap water at ambient temperature on a rotary shaker. The composition was observed to float. After 1 hour, the concentration of hydrogen peroxide in the water was measured using a test strip commercially available from Merck under the trade name Merckoquant. The hydrogen peroxide concentration was measured at 24 hour intervals. The results are given in Table 1 below.

Table 1 . Hydrogen Peroxide Concentration produced Time (days) Hydrogen Peroxide Concentration

0 25 mg/l

1 25 mg/l

2 1 0 mg/l

3 0

Example 2

The method of Example 1 was followed, except that 0.5g poly(caprolactone) , 2.0 mis dichloromethane and 0.025g granular PCS were employed . The composition was observed to float in water. The concentration of hydrogen peroxide produced is given in Table 2 below. Example 3

The method of Example 1 was followed, except that 0.25g poly(caprolactone), 2.0 mis dichloromethane and 0.01 3g granular PCS were employed. The composition was observed to float in water. The concentration of hydrogen peroxide produced is given in Table 2 below.

Example 4

The method of Example 1 was followed, except that 0.25g poly(caprolactone), 1 .0 ml dichloromethane and 0.01 3g granular PCS were employed . The composition was observed to float in water. The concentration of hydrogen peroxide produced is given in Table 2 below.

Example 5

The method of Example 1 was followed , except that 0.1 g poly(caprolactone), 1 .0 ml dichloromethane and 0.005g granular PCS were employed. The composition was observed to float in water. The concentration of hydrogen peroxide produced is given in Table 2 below.

Table 2. Hydrogen Peroxide Concentration produced

Hydrogen Pei rox ide Concentration (mg/l)

Time (days) 0 1 2 3 4

Example

2 3 2 0.5 0 0

3 5 3 2 0.5 0

4 3 3 2 0.5 0

5 5 5 2 0 0

Example 6

A double layered structure was produced. The first layer was produced by following the method of Example 3. When this layer had solidified , a second layer was added also following the method of Example 3. The concentration of hydrogen peroxide produced by the structure was measured by the method of Example 1 . The composition was observed to float in water. The results are given in Table 3 below.

Example 7

A double layered structure was produced . The first layer was procuced by following the method of Example 4. When this layer had solidified , a second layer was added also following the method of Example 4. The concentration of hydrogen peroxide produced by the structure was measured by the method of Example 1 . The composition was observed to float in water. The results are given in Table 3 below.

Example 8

A triple layered structure was produced . The first layer was produced by following the method of Example 3. When this layer had solidified, a second layer was added also following the method of Example 3 and when the second layer had solidified, a third layer was added, also following the method of

Example 3. The concentration of hydrogen peroxide produced by the structure was measured by the method of Example 1 . The composition was observed to float in water. The results are given in Table 3 below.

Example 9

A triple layered structure was produced . The first layer was produced by following the method of Example 4. When this layer had solidified , a second layer was added also following the method of Example 4 and when the second layer had solidified, a third layer was added, also following the method of Example 4. The concentration of hydrogen peroxide produced by the structure was measured by the method of Example 1 . The composition was observed to float in water. The results are given in Table 3 below.

Table 3. Hydrogen Peroxide Concentrations produced

Hydrogen Peroxide Concentration (mg/l)

Example: 6 7 8 9

Time (days) 0 5.0 3.5 3.5 5.0

1 5.0 5.0 5.0 5.0

2 7.5 5.0 5.0 5.0

4 5.0 3.5 3.5 2.5

7 2.5 3.5 3.5 2.5 8 1 .0 5.0 3.5 3.0

10 2.0 5.0 4.0 4.0

12 1 .5 3.5 2.5 4.5

14 2.0 2.5 2.5 4.5

1 6 1 .5 2.5 2.5 4.5 1 8 2.0 0.75 0.75 3.5

20 0.75 0.5 0.5 2.5

22 0.25 0.25 0.5 2.0

24 0.0 0.25 0.5 1 .5

26 0.25 0.25 1 .5 28 0.25 0.25 1 .0

29 0.0 0.0 1 .0

30 0.0

The results given in Tables 1 to 3 above clearly show that compositions according to the present invention can be employed to give controlled dosing of peroxygen compounds in aqueous systems. The results in Table 1 demonstrate that a relatively high concentration of peroxygen compound can be produced for a relatively short period of time, and the results in Table demonstrate that dosing can be maintained over an extended period. The results in Table 3, particularly for Example 9, show that a multi-layered structure can allow more than one maximum in the peroxygen compound concentration to be produced, thus demonstrating the versatility of the compositions according to the present invention .

Claims

1 . A solid microbicidal composition, characterised in that the composition comprises a solid source of a peroxygen compound distributed in a matrix comprising poly(caprolactone) .

2. A solid microbicidal composition adapted for targeted dosing and/or sustained release of microbicide, characterised in that the composition comprises a solid source of a peroxygen compound distributed in a matrix comprising poly(caprolactone)

3. A process for the manufacture of a solid microbicidal composition, characterised in that the process comprises distributing a solid source of a peroxygen compound in liquid phase poly(caprolactone), and then solidifying the poly(caprolactone) .

4. A microbicidal process for the treatment of liquids, characterised in that the process comprises contacting the liquid to be treated with a composition comprising a solid source of a peroxygen compound distributed in a matrix comprising poly(caprolactone) .

5. A composition or process according to any preceding claim, characterised in that the solid source of peroxygen compound is selected from the group consisting of sodium percarbonate, sodium perborate mono and tetrahydrates and urea peroxide.

6. A composition or process according to claim 5, characterised in that the solid source of peroxygen compound is sodium percarbonate

7 A composition or process according to any preceding claim, characterised in that the weight ratio of solid source of peroxygen compound to poly(caprolactone) is in the range of from 1 200 to 1 : 1 .

8. A composition or process according to claim 7, characterised in that the weight ratio of solid source of peroxygen compound to poly(caprolactone) is in the range of from 1 ^• 1 0 to 1 : 30. 9. A composition or process according to any preceding claim, characterised in that the number average molecular weight of the poly(caprolactone) is in the range of from 1 ,000 to 100,000.

10. A process for the manufacture of a solid microbicidal composition according to any one of claim 3 or claims 5 to 9, characterised in that the liquid phase poly(caprolactoπe) is produced by heating the poly(caprolactone) to its melting point or above.

1 1 . A process for the manufacture of a solid microbicidal composition according to any one of claim 3 or claims 5 to 9, characterised in that the liquid phase poly(caprolactone) is produced by at least partially dissolving the poly(caprolactone) in a solvent for the poly(caprolactone) .

1 2. A process according to claim 1 1 , characterised in that the solvent is dichloromethane.

1 3. A composition according to any one of claims 1 , 2, or 5 to 9, characterised in that the composition comprises from 75 to 99% w/w poly(caprolactone) .

14. A composition according to any one of claims 1 ,2, 5 to 9 or 1 3, characterised in that the composition comprises a multi-layered structure.

1 5. A composition according to claim 1 3, characterised in that the composition comprises 3 layers.

1 6. A microoicidal process according to any one of claims 4 to 9, characterised in that the solid composition produces a concentration of peroxygen compound in the area being treated of from 0.5 mg 'l to 100 mg/l

1 7. A microbicidal process according to claim 1 6, cnaracterised in that the solid composition produces a concentration of peroxygen compound in the area being treated of from 2 mg/l to 25 mg/l 8. A microbicidal process according to any one of claims 4 to 9, 1 6 or 1 7, characterised in that the composition provides sustained release of peroxygen compound over a period of from 3 days to 5 weeks.

9. A microbicidal process according to any one of claims 4 to 9, or 1 6 to 18, characterised in that the composition acts as a bactencide, bactenstat, algicide or algistat.