Abstract:
Antimicrobial efficacies of vanous polymers: namely; polyethylene (PE), polystyrene (PS),
polyethylene terephthalate (PET) and polyvinyl chloride (PVC) containing silver nanoparticles
were qualitatively and quantitatively assessed under a wide range of testing conditions. The effects
of silver nanoparticle content and silver-polymer contact time were of our main interests through
halo test and plate-count-agar (PCA) method using Escherichia coli and Staphylococcus aureus as
testing bacteria. Two different methods were used for incorporating the silver nanoparticles into the
thermoplastics, these being spray-coating onto the polymeric surface (coated polymers) and dry
blending in the polymer matrices (blended polymers). The experimental results suggested that the
radial inhibition zones were created at 0.5 mm by pure silver nanoparticles, while those for the
silver nanoparticles incorporated polymers were not seen. The growth rates of E. coli with neat
polymers decreased in the order of PE > PS > PET> PVC
In the case of silver nanoparticles coated polymers, the results suggested that coating silver
nanoparticles onto all types of polymeric substrates could reduce E. coli up to 99.9 %, different
polymer showing different optimum contents of nano-silver content to achieve the maximum
percentage of bacterial reduction. The optimum contact times for all polymers were 150 minutes.
The optimum silver concentration for PE was 75 ppm, but that for PS, PET and PVC was 50ppm.
In addition, all silver coated polymers showed a bactericidal behavior, which was referred to as
permanent cell damage by active species, except for 25ppm silver coated PE.
In the case of silver nanoparticles blended polymers, the results suggested that the percentage
bacterial reduction were 43.3, 81.2, 83.7 and 99.9% for PET, PS, PE and PVC, respectively, under
the optimum silver concentration of 100 ppm and 210 minute contact time. All silver blended
polymers showed a bacteriostatic behavior, which was referred to as inhibition of cell growth or
reversible cell damage by active species. In addition, the E. coli, are more sensitive to silver
addition than the S. aureus. The Atomic Absorption Spectrometry (AAS) results showed that the
releasing rate of silver particles in the silver blended PE samples was lower than that in the
blended PVC samples.