Method of preparing a biocidal material

A method of preparing a biocidal material comprises PA1 taking a biocidal material comprising a biocide having a log P value of at least 1.5 immobilized by hydrophobic exclusion on a support having a hydrophobic surface which has been used for inhibiting microbial growth in an aqueous medium, PA1 extracting the biocide from the biocidal material with a solvent, and PA1 immobilizing the extracted biocide by hydrophobic exclusion on a support having a hydrophobic surface.

FIELD OF THE INVENTION
 The invention relates to the preparation of a biocidal material. More
 particularly, it relates to the regeneration and reuse of immobilized
 biocide from an existing biocidal material.
 BACKGROUND OF THE INVENTION
 Microbial growth occurs in many systems in which aqueous media such as
 water, aqueous solutions and aqueous dispersions are employed.
 For example, significant biofouling can occur in many areas of
 photoprocessing systems and, in particular, where low flow rate washes and
 water recycling is used. The problem may be overcome by adding biocides to
 the wash water tanks when bacterial biofilm formation becomes evident
 visually. However at this point the biocides may not work and even at
 quite high concentrations are not particularly effective because the
 bacteria have attached to surfaces to form colonies which have built up in
 layers. Hence, any biocide in solution can only reach the outer biofilm
 layer and not the inner layers of the biofilm which are protected.
 Furthermore, widespread use of such biocides is not desirable because they
 are relatively expensive and toxic chemicals which require specialised
 disposal to protect the environment.
 It is known that in addition to being used up in the process of inhibiting
 the growth of microorganisms, biocides tend to degenerate and lose their
 activity through prolonged contact with the aqueous medium being treated.
 EP-A-0 733 304 describes a biocidal material comprising a biocide
 immobilized on a support characterised in that the biocide has a log P
 value of at least 1.5, the support has a hydrophobic surface and the
 biocide is immobilized on the hydrophobic surface by hydrophobic
 exclusion. The support may take the form of polymer beads which may be
 held in a container having an inlet and an outlet so that the aqueous
 medium to be treated can be contacted with the beads by passing it through
 the container. An advantage of the material is that the biocide remains
 attached to the support. The material may be used to inhibit microbial
 growth in the wash water or other solutions used in a photoprocessor.
 PROBLEM TO BE SOLVED BY THE INVENTION
 After prolonged use, the biocidal material comprising immobilized biocide
 becomes exhausted and needs to be replaced. It would be economically and
 environmentally advantageous if further use could be made of the material
 without disposing of it and replacing it with completely new material.
 It has been found unexpectedly that significant amounts of active biocide
 can be removed from the material by solvent extraction and the extracted
 biocide re-used to provide new biocidal material.
 SUMMARY OF THE INVNETION
 The invention provides a method of preparing a biocidal material which
 comprises
 taking a biocidal material comprising a biocide having a log P value of at
 least 1.5 immobilized by hydrophobic exclusion on a support having a
 hydrophobic surface which has been used for inhibiting microbial growth in
 an aqueous medium,
 extracting biocide from the biocidal material with a solvent, and
 immobilising the extracted biocide by hydrophobic exclusion on a support
 having a hydrophobic surface.
 ADVANTAGEOUS EFFECT OF THE INVENTION
 A significant amount of active biocide can be recovered from used material
 and re-used.

DETAILED DESCRIPTION OF THE INVENTION
 Biocides for use in the invention have a log P value of at least 1.5
 wherein P represents the partition coefficient between n-octanol and water
 defined as follows
 ##EQU1##
 Log P is a well known term used in literature on biocides. As used herein,
 it provides a measure of the hydrophobicity of the biocide.
 Biocides which may be employed include any known biocide meeting the
 hydrophobicity requirement or a known biocide which has been
 hydrophobically modified to meet the requirement.
 Suitable types of biocide include those described in "Microbiocides for the
 Protection of Materials", W. Paulus, published by Chapman Hall, 1993. They
 are agents capable of killing or inhibiting the multiplication of
 microorganisms such as bacteria, yeasts, fungi, algae and lichens.
 Examples include heterocyclic N,S compounds, compounds with activated
 halogen groups and quaternary ammonium salts.
 Preferred biocides include those currently employed in the treatment of
 photoprocessing systems e.g. isothiazolinones.
 Examples of isothiazolinone biocides are those having the structure
 ##STR1##
 wherein
 R represents hydrogen, alkyl, aryl, alkaryl and aralkyl; and,
 R.sup.1 and R.sup.2 independently represent hydrogen, halogen, alkyl, or
 R.sup.1 and R.sup.2 taken together represent the atoms necessary to
 complete a fused carbocyclic ring, preferably a 5- or 6-membered ring e.g.
 a benzene ring;
 provided that R, R.sup.1 and R.sup.2 are chosen so that the log P value of
 the compound is at least 1.5.
 Preferred biocides include those having the following structures:
 ##STR2##
 wherein R.sup.3 is an alkyl group having from 4 to 20 carbon atoms or an
 aryl group having from 6 to 20 carbon atoms;
 ##STR3##
 wherein R.sup.5 and R.sup.6 are selected from hydrogen and halogen, and
 R.sup.4 is an alkyl group having from 5 to 20 carbon atoms; and,
 ##STR4##
 wherein each of R.sup.7, R.sup.8 and R.sup.9 is hydrogen or an alkyl group
 providing a total of from 2 to 20 carbon atoms; R.sup.10 is substituted or
 unsubstituted alkyl or aryl e.g. phenoxyethyl; and, Y is any suitable
 counter anion e.g. halide.
 Specific examples of commercially available isothiazolinone biocides
 include Proxel.TM. (manufactured by Zeneca):
 ##STR5##
 Promexal.TM. (manufactured by Zeneca):
 ##STR6##
 Kathon.TM. LX (manufactured by Rohm and Haas):
 ##STR7##
 Other commercially available biocides are:
 Bronopol.TM. (manufactured by Boots):
 ##STR8##
 Domiphen.TM. bromide (manufactured by Ciba-Geigy):
 ##STR9##
 Vantocil.TM. (manufactured by Zeneca):
 ##STR10##
 Densil S.TM. (manufactured by Zeneca):
 ##STR11##
 Biocides which are hydrophobically modified Proxel.TM. and Kathon.TM. LX
 have been prepared having the following structures:
 ##STR12##
 Many commercially available biocides are soluble in aqueous media and an
 increase in their hydrophobicity is required to render them suitable for
 use in the invention.
 It is essential that biocides having a log P of at least 1.5 are used in
 the invention. Biocides having a log P less than 1.5 can become detached
 from the support and contaminate the aqueous medium.
 Hydrophobic polymers suitable for use as support materials include any
 inert, water insoluble polymers.
 Examples of suitable polymers are ethenic polymers including polyolefins,
 polystyrene, polyvinyl chloride, polyvinyl acetate and acrylic polymers;
 and polymers formed by condensation reactions including polyesters,
 polyamides, polyurethanes, polyethers, epoxy resins, amino resins and
 phenol-aldehyde resins.
 Specific examples of support materials are Amberlite.TM. XAD-4 and XAD-2
 resin beads which are both highly porous, cross-linked polystyrene.
 The support may take a variety of forms e.g. particulate, sheet or fibre.
 It may be porous or non-porous.
 The biocide is immobilized on the support by a hydrophobic exclusion
 mechanism. Immobilisation may be carried out by addition of the dry
 support e.g. a resin to a solution of the biocide in an organic solvent
 e.g. tetrahydrofuran (THF), followed by slow addition of a similar volume
 of water. As the volume fraction of water increases, the biocide and the
 support associate to exclude water by the well known hydrophobic effect.
 The support may be left in contact with the solution for a period of time
 e.g. 18 hours allowing most of the organic solvent to evaporate.
 Subsequent drying of the support leaves the biocide adsorbed thereto.
 Alternatively, immobilization may be carried out by adding water to the dry
 support, contacting the support with a solution of the biocide in an
 organic solvent e.g. heptane, and removing the solvent e.g. by evaporation
 under reduced pressure.
 The hydrophobic exclusion mechanism by which the biocide is immobilized is
 a reversible physisorption wherein the biocide is hydrophobically bound to
 the support.
 A variety of commercial and hydrophobically-modified biocides have been
 studied. Partition coefficients between octanol and water have been
 determined at 25.degree. C. by UV/visible absorption. First, the
 calibration curve of each biocide was determined as optical density
 (OD.sub.abs) versus concentration of biocide in .mu.g/g (ppm) of water for
 the predominantly water-soluble materials and .mu.g/g of octanol for the
 predominantly oil-soluble biocides.
 A known amount of biocide was placed in a glass vessel containing either 10
 ml of water or 10 ml of octanol depending on the solubility of the
 biocide. An equal volume of the other solvent was added and the glass
 vessel sealed. The vessel was shaken vigorously for a few minutes and then
 every few hours for more than 48 hours. Each mixture was placed in a
 sealed separating funnel and left for a further 24 hours. The water phase
 of each mixture was removed and the UV/visible spectra run against water
 with appropriate dilutions to bring absorbance between 0 and 1.5 for the
 commercial biocides and the octanol fractions were examined for the
 hydrophobically modified biocides.
 The following partition coefficients shown in Table 1 were determined.
 TABLE 1
 Biocide P
 Promexal .TM. .about.4.5
 Vantocil .TM. .about.0.3
 Domiphen .TM. .about.50
 Kathon .TM. .about.1
 Proxel .TM. .about.0*
 Compound 1 &gt;330
 Compound 3 &gt;560
 Compound 2 &gt;130
 Compound 4 &gt;480
 *i.e. there was almost no biocide in the oil phase.
 The log P value of the biocides which are used in the invention must be at
 least 1.5, preferably at least 2.0.
 In use, the aqueous medium is brought into contact with the biocidal
 material. Different ways of achieving contact include passing the aqueous
 medium through a container e.g. a column containing the material in
 particulate form, passing the aqueous medium through a filter of the
 material and passing the aqueous medium over the material in the form of a
 surface coating.
 The biocidal material is of particular use in photoprocessing systems. Such
 systems comprise stages for developing, fixing, bleaching and washing an
 exposed photographic material. Each stage requires apparatus for applying
 the appropriate aqueous processing solution to the photographic material.
 The apparatus may comprise means for supplying, removing and, possibly,
 recirculating such solutions.
 The biocidal material may be used to inhibit microbial growth in the wash
 water or other solutions used in a photoprocessor.
 FIG. 1 is a schematic representation of apparatus for use in performing the
 method of the invention. The apparatus comprises a container 10 having
 fluid inlet means 11 and fluid outlet means 12 said inlet and outlet means
 11, 12 communicating with an inner chamber 13 of the container. When the
 apparatus is in use, fluid entering the inner chamber through the inlet
 means 11 flows through the chamber 13 and leaves the container through the
 outlet means 12. The inner chamber 13 holds a biocidal material in
 accordance with the invention in the form of particles 14. A filter 15 to
 retain the particles is positioned at the top of the inner chamber to
 prevent loss of the particles from the device. The top of the container 10
 is provided with plugs 16 (optional) for venting any gas which accumulates
 in the device.
 Fluid entering the device flows down a central tube and subsequently flows
 up through the particles. The arrows indicate the direction of the flow of
 fluid through the device.
 FIG. 2 is a schematic representation of the use of the apparatus shown in
 FIG. 1. A tank 20 containing water 21 is shown e.g. the wash water tank of
 a photoprocessor. Tubing 22 has an open end in the water 21 at the bottom
 of tank 20, the other end being connected to the inlet of a pump 23
 outside the tank 20. Tubing 24 connects the outlet of the pump 23 to the
 inlet of a device 25 of the type shown in FIG. 1. One end of tubing 26 is
 connected to the outlet of device 25 and the other end opens into the top
 of tank 20.
 In use, water is pumped from the bottom of tank 20 through device 25 and
 back into tank 20 in a recirculation loop. The arrows indicate the
 direction of the flow of water around the loop.
 The method of the invention can be applied to an existing biocidal material
 at any stage of its life. Clearly, it is preferable to practise the
 invention on a biocidal material which is close to exhaustion and in need
 of replacement.
 The biocidal material may be washed and dried before the biocide is
 extracted. Extraction occurs by contacting the material with a solvent for
 the biocide. Any suitable organic solvent may be employed. Examples of
 suitable solvents include dichloromethane, hexane, heptane, toluene or any
 water immiscible solvent.
 The material may be suspended in the solvent for a period of time with
 agitation. The suspension may be filtered to remove the dissolved biocide
 and the filtrate may be subjected to further drying or washing and drying
 steps. The biocide can be recovered by removal of the solvent e.g. under
 reduced pressure.
 The recovered biocide has been found to be essentially pure with no obvious
 contaminants.
 In accordance with the invention, the extracted biocide is immobilized by
 hydrophobic exclusion on a support having a hydrophobic surface to produce
 a new biocidal material. The support may be a new support. Alternatively,
 the support of the biocidal material from which the biocide was extracted
 may be cleaned and re-used.
 The invention is further illustrated by way of example as follows.
 EXAMPLE 1
 Regeneration of the Immobilized Biocide
 A device of the type shown in FIG. 1, containing .about.300 g immobilized
 biocide (18.3% w/w 4,5-dichloro-2-n-octylisothiazolin-3-one on a
 polystyrene resin bead support, Amberlite.TM. XAD-7HP), that had been
 running on a recirculation loop attached to stabiliser tank of a Kodak.TM.
 25 paper processor (operating KODAK.TM. RA-4 processing chemistry) was
 disconnected after a period of 6.5 weeks continuous use. The container was
 opened, and the used resin was removed. A portion of the resin (39.74 g)
 was washed with water (2.times.50 ml), dried on a sinter funnel, and
 suspended in dichloromethane (100 ml). The suspension was agitated gently
 for .about.2 hr, and filtered through kieselguhr; the residue was washed
 with further dichloromethane (2.times.30 ml). The combined washings and
 filtrate were dried over magnesium sulphate, and the solvent removed under
 reduced pressure, to leave the biocide
 (4,5-dichloro-2-n-octylisothiazolin-3-one) as a pale brown oil (1.95 g)
 which solidified on standing; analysis (TLC, MS, IR) of the regenerated
 material showed it to be essentially pure, with no obvious contaminants
 present. This represented an equivalent final loading of 4.9% or a
 recovery of 26.8% of unchanged biocide.
 The recovered biocide (1.95 g) was dissolved in heptane (50 ml) and fresh
 Amberlite.TM. XAD-7HP resin beads (7.80 g), which had been previously
 washed following the manufacturer's instructions, were added; the mixture
 was agitated gently for .about.10 minutes. The solvent was removed under
 reduced pressure to leave the regenerated immobilized biocide as pale
 cream colored active beads (6.71 g).
 Microbiological Evaluation
 A control (blank Amberlite.TM. XAD-7HP), an original (unused) sample of
 immobilized biocide and the regenerated immobilized biocide were tested in
 a nutrient broth solution containing approximately 10.sup.4 -10.sup.5
 bacteria per ml (Pseudomonas aeruginosa). The control and active beads
 were each put in separate 10 cm glass columns with screw-tight plastic
 adapters and glass nozzles. A nylon mesh, placed between two rubber
 washers, was used retain the beads within the column. The columns, all
 silicone rubber tubing and flasks necessary to complete a recirculation
 loop were sterilized by autoclaving at 120.degree. C. for more than 20
 minutes. Each column was placed in a recirculation loop with 50 ml of
 nutrient broth as illustrated schematically in FIG. 3. A shaking waterbath
 kept the 250 ml wide-neck round-bottomed conical flasks at 30.degree. C. A
 small inoculum of pre-prepared bacterial culture was added to each flask.
 At time zero, a small aliquot of the bacterial culture was removed from
 each flask to perform initial viable counts and the pumps were started to
 give a flowrate of 13.5 ml per minute. The bacterial culture flowed up
 through the beads.
 Viable counts (colony forming units[cfu]/ml) were then performed at the
 time intervals of 0.5, 8 and 24 hours by removing a small aliquot from
 each flask and performing viable counts.
 The results are as follows:

TIME,
 hours Control Original Re-immobilized
 0 4.83E + 05 5.33E + 05 8.33E + 04
 0.5 3.83E + 04 2.67E + 05 2.50E + 05
 8 3.24E + 03 3.30E + 01 16
 24 1.83E + 08 1.60E + 01 16
 The results are plotted in FIG. 4.
 From the results it can be seen that the bacterial population in the active
 system can no longer be detected after 8 hours, showing a bactericidal
 effect when compared to the control.
 EXAMPLE 2
 As Example 1 except that a biocide mixture [19.4% w/w of
 4,5-dichloro-2-n-octylisothiazolin-3-one (9%),
 5-chloro-2-n-octylisothiazolin-3-one (66%) and 2-n-octylisothiazolin-3-one
 was (24%)] was used, and the immobilized biocide was packed into a
 container used in a recirculation loop on the wash tank of a Kodamatic.TM.
 710 graphics processing machine [running KODAK.TM. RA2000 (1+2) developer
 and KODAK.TM. Fixer 3000 (1+3)].
 The device was removed after 4 weeks continuous use; a portion of the
 recovered resin (50 g) was suspended in dichloromethane (200 ml) and
 stirred for 24 hr. The suspension was filtered and the filtrate was washed
 with water (100 ml), dried with magnesium sulphate and evaporated under
 reduced pressure to leave the recovered biocide mixture as a brown oil
 (3.22 g). Analysis (TLC, IR, MS) showed the recovered material to be
 essentially identical to the originally immobilized mixture. This
 represented an equivalent final loading of 6.4%, or a recovery of 33.0% of
 unchanged biocide.