Silver exchanged zeolites as bactericidal additives in polymeric materials

In this work, different Ag-zeolites have been evaluated as biocide materials against two common bacteria, displaying an excellent bactericidal activity in different media. The results demonstrate that the amount of silver, the type of zeolitic structure and the zeolite Si/Al ratio strongly influence on their bactericidal activity. The higher Ag amount, the better antimicrobial activity. Also, zeolites having large pore openings and Si/Al ratio close to 2 have shown the highest biocidal activity. The characterization of Ag-zeolites by different techniques shows that the incorporation of Ag at the zeolites does not alter the zeolite structure and that Ag is incorporated as Ag+ cations. The most promising Ag-zeolites with a Si/Al ratio of 2 were introduced in a polymer matrix of polypropylene, showing very high biocide activity against S.aureus. The applicability of the resulting Ag-zeolite-polymer material is limited because its darkening due to the presence of reduced silver species. The incorporation of a photo-stabilizer does not decrease the biocide activity, while maintains the original color of the polypropylene polymer. It has been shown that lixiviated Ag+ cations are the biocide active species. These Ag-species are released even when the Ag-zeolite is incorporated into the polymer, providing bactericide effects to the final Ag-zeolite-polymer composite.