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Antibacterial efficacies of various thermoplastics, such as medium-density polyethylene (MDPE), polystyrene (PS), polyethylene terephthalate (PET) and polyvinyl chloride (PVC) containing nano-silver colloids were studied under a wide range of testing conditions. The effects of nano-silver colloid content and the silverpolymer contact time were of our main interests and quantitatively assessed by shake flask method coupled with a plate-count-agar (PCA) technique using Escherichia coli as testing bacteria. Two different methods were used for incorporating the nano-silver colloids into the thermoplastics, these being spray-coating and melt-blending techniques. The experimental results suggested that all neat thermoplastics alone could not generally inhibit the E. coli growth, suggesting that all thermoplastics exhibited nonbactericidal behavior. However, neat PVC appeared to show a retarding effect for the E. coli growth. In addition, coating silver colloid onto all types of thermoplastic substrates could inhibit the E. coli growth up to 99.9% at the optimum silver content of 50 ppm for PS, PET and PVC and of 75 ppm for MDPE. The optimum contact time for all thermoplastics was 150 min. Among the thermoplastics used, PVC exhibited the highest % E. coli reduction, and this was confirmed by the higher silver content via Atomic Absorption Spectrometry (AAS) technique. For a given silver content, the spray-coating technique could give better dispersion level of silver throughout the thermoplastic films and this led to more effective antibacterial performance as compared with the dry-blending technique. In PVC sample, the contact angle value appeared to increase with the addition of silver content for both incorporating techniques.

Triclosan was used as antibacterial agent in various vinyl thermoplastics and calcium carbonate (CaCO 3 )/thermoplastic composites and the antibacterial performances were studied through Halo and Plate-CountAgar (PCA) test methods. The thermoplastics used were polyethylene (LDPE, MDPE, HDPE), polypropylene (PP), polystyrene (PS) and poly(vinyl chloride) (PVC). Escherichia coli (E.coli, ATCC 25922) and Stapphylococcus aureus (S.aureus, ATCC 25923) were used as the testing bacteria. The color index results suggested that introducing triclosan did not change the color of all thermoplastics used. The antibacterial results showed that the inhibition zone increased with increasing triclosan for nonpolar thermoplastics like LDPE, MDPE, HDPE, PP, and PS films whereas the opposite effect was observed for polar PVC film. The antibacterial efficacies of the triclosan decreased in the order of LDPE > MDPE > HDPE > PP > PS > PVC and this was confirmed by the triclosan releasing and FT-IR results. The differences in the antibacterial performances of the studied thermoplastics with triclosan were associated with their rigidities, abilities to crystallize, and free volume or molecular density. The sensitivities of E.coli and S.aureus bacteria to the triclosan were found to be dependent on the testing methods used for the antibacterial performance evaluations. The addition of CaCO 3 worsened the antibacterial performances in the triclosan filled HDPE and PS blends, but had a benefit for improved bacterial reduction in the triclosan-filled PVC blend.