Antimicrobial dispersions and films from positively charged styrene and acrylic copolymers

Antimicrobial properties of methyl methacrylate - ethyl acrylate and styrene - ethyl acrylate copolymers, both as latexes and after film formation were tested. The polymers were synthesized using a cationic surfactant, cetytrimethylammonium bromide (CTAB) as an emulsifier, in presence of either a cationic or an anionic initiator. The resulting latex particles showed sizes between 50 and 320 nm (larger for the anionic initiator), and ζ-potential between +30 and +70 mV (more positive for the cationic initiator). Dialysis did not change significantly the size distribution and ζ-potential of the latexes, and most of them inhibited growth of Gram-negative (E. coli), Gram-positive (S. aureus, B. subtilis) and yeast (C. albicans). On the other hand, only few compositions were effective against Gram-negative P. aeruginosa. Both completely ("dry") and incompletely ("wet") formed films produced from the respective latexes showed similar, although less pronounced antimicrobial activity pattern. The analysis of streaming potential for the films confirmed that part of the positive surface charge brought by non-covalent binding of CTAB to the polymer chains, is lost during dialysis of the latexes and during rinsing, especially under high-shear flow. From the practical point of view, films with the best mechanical and antimicrobial properties can be achieved using polymers with high proportion of ethyl acrylate, while nature of the co-monomer and initiator do not play crucial roles.