An air-filter for a circulating and/or recirculating air system using a filter medium containing a microbiologically effective amount of a polymeric biguanide or salt thereof. Also claimed is a method for reducing odors and/or air-borne micro-organisms in a circulating or recirculating air system using the air-filter, and a method for protecting an air-filter medium against microbial degradation by incorporating in, or on, the medium a microbiologically effective amount of a polymeric biguanide or salt thereof.
1. An air-filter for a circulating and/or recirculating air system comprising a filter medium containing a microbiologically effective amount of a polymeric biguanide or salt thereof, wherein said polymeric biguanide is terminated by a functional group selected from the group consisting of hydrocarbyl, substituted hydrocarbyl, amine, and a cyanoguanidine group,
wherein said substituted hydrocarbyl is aryloxy, alkyloxy, acyl, acyloxy, or nitrile.
2. An air-filter as claimed in claim 1 , wherein the polymeric biguanide contains at least two biguanide units of the Formula (1):
which are linked by a bridging group which contains at least one methylene group.
3. An air-filter as claimed in claim 1 wherein the polymeric biguanide is a mixture of linear polymeric biguanides having a recurring polymer chain represented by Formula (4):
wherein X and Y represent bridging groups in which together the total number of carbon atoms directly interposed between pairs of nitrogen atoms linked by X and Y is more than 9 and less than 17.
4. An air-filter as claimed in claim 3 which is a mixture of polymers wherein the number of individual biguanide units of formulae:
and
is, together, from 3 to about 80.
5. An air-filter as claimed in claim 3 wherein the polymeric biguanide is poly(hexamethylene biguanide) in which X and Y are both —(CH 2 ) 6 —.
6. An air-filter as claimed in claim 1 wherein the polymeric biguanide is a mixture of polymers of the Formula (5):
wherein n is from 4 to 40.
7. An air-filter as claimed in claim 1 wherein the polymeric biguanide is in the form of a hydrochloride salt.
8. An air-filter as claimed in claim 1 wherein the filter medium is made from a natural polymer or synthetic plastics material.
9. An air-filter as claimed in claim 8 wherein the natural polymer is cellulose.
10. An air-filter as claimed in claim 1 wherein the amount of polymeric biguanide contained on the filter medium is from 0.0001% to 10% based on the weight of the filter medium.
11. A air-filter according to claim 1 further comprising an odour control agent.
12. A method of reducing odours and/or air-borne micro-organisms in circulating and/or recirculated air which comprises passing air through a filter medium containing a polymeric biguanide or salt thereof, wherein said polymeric biguanide is terminated by a functional group selected from the group consisting of hydrocarbyl, substituted hydrocarbyl, amine, and a cyanoguanidine group,
wherein said substituted hydrocarbyl is aryloxy, alkyloxy, acyl, acyloxy, or nitrile.
13. A method as claimed in claim 12 wherein the air has a relative humidity between 20% and 80%.
14. A method for protecting a filter medium of a circulating and/or recirculating air system against microbial degradation which comprises incorporating in, or on, the medium a microbiologically effective amount of a polymeric biguanide or salt thereof, wherein said polymeric biguanide is terminated by a functional group selected from the group consisting of hydrocarbyl, substituted hydrocarbyl, amine, and a cyanoguanidine group,
wherein said substituted hydrocarbyl is aryloxy, alkyloxy, acyl, acyloxy, or nitrile.