Conductive Polymer/Silver- Coated Textile Composites with Antibacterial Properties
February 16, 2017
Plastics Research Online
Among the various oxidizing agents that are used in polymerization, silver nitrate (AgNO3) is promising because it enables the simultaneous deposition of metallic silver particles and a conductive polymer. Thus, by using this method, composites gain versatile properties (e.g., antibacterial activity and improved conductivity).10–12 The oxidizing ability of AgNO3 is relatively low, however, and additional chemicals (such as phenylenediamines and secondary oxidants) may also be used.13, 14 Further, additional processes are required, such as the non-economical treatment of UV light for shortening the polymerization time.11, 12
In our study, we prepared a nonwoven composite comprising poly(o-anisidine), silver, and poly(ethylene terephthalate)—POA/Ag/PET—by polymerization of o-anisidine with AgNO3. POA is one of the most conductive derivatives of polyaniline and has a number of other useful properties, such as its ability to provide a homogeneous surface coating.15 We investigated the effects of polymerization conditions on both the POA/Ag content and the volume resistivity of the composite. We also evaluated the antibacterial activity of POA/Ag/PET by comparing it with a POA/PET composite.
To accelerate the polymerization of o-anisidine, we used ammonium persulfate, (NH4)2S2O8, or ferric nitrate nonahydrate, Fe(NO3)3.9H2O—both of which prevent the formation of unwanted silver salts—as a secondary oxidant. When (NH4)2S2O8 was used, the resulting composites had a relatively higher POA/Ag content and exhibited lower resistivity. In this case, the deposited silver particles were also visible to the naked eye.
To investigate the effect of acid type on POA/Ag content and the resistivity of the resulting composite, we selected nitric acid (HNO3) and various sulfonic acids—such as p-toluene sulfonic acid, camphor sulfonic acid, and dodecyl benzene sulfonic acid—because their side groups do not allow the precipitation of unfavorable silver salts, and act as an anionic dopant for POA.16–19 We found that the POA/Ag contents of the composites obtained using sulfonic acid were higher than those obtained using HNO3. We believe that this result may arise due to the incorporation of bulky dopant anions.17, 20 Although we could not correlate the resistivity with the type of acid used, we obtained the lowest resistivity by using HNO3. We found a solution of 1.0M HNO3 to provide the most suitable medium in terms of achieving the lowest resistivity in the resultant composite.
We used thermogravimetric analysis to determine the silver weight fractions in the nanocomposites' POA/Ag content: see Figure 1. Silver weight fractions were calculated from residual weight values of the composites at 800°C. We found that although the POA/Ag contents of the composites increased, the content of silver particles decreased, thus showing that the contribution of POA to the POA/Ag content was rather higher than that of the silver particles.