Streaming Current Study of Biodegradable Biocidal Polymers

Biodegradable polymers are attracting increasing attention from academia and industry, especially related to medicine and food packaging. Among them, poly(lactic acid) (PLA), polycaprolactone (PCL), and poly(hydroxybutyrate) (PHB), are the most seriously considered for applications. When discussing the mechanism of biodegradation, both chemical and microbial pathways should be considered. In the latter, formation of a biofilm seems to play very important role. On the other hand, for medical and food-related applications, polymers should ideally deter biofilm formation, which is usually achieved by addition of biocides to the polymer. Thus, design of biodegradable biocidal material requires analysis of the factors affecting attachment of polymer-degrading and pathogenic bacteria.

Because of the net negative surface charge of most bacteria, electrostatic contribution is expected to play an important role in bacterial adhesion to the polymer surface. For this reason we characterized the surface of three biodegradable polymers using electrokinetic measurements [1]. For this purpose the streaming current measurements of thin polymer foils were performed by pushing an aqueous electrolyte through a thin channel with walls lined with the polymer. The three biodegradable polymers: PLA, PCL and PHB were analyzed both without and with the addition of biocidal Polyhexamethyleneguanidine Hydrochloride (PHMG) derivatives: sulfanilic acid salt, stearate, and granular PHMG polyethylene wax (1 % w/w). The results show that the ζ-potential vs pH curves obtained from streaming current measurements shift by as high as one pH unit upon addition of the PHMG biocide. Shifting to both lower and higher pH values was observed, depending on the nature of the derivative. The correlation of the ζ vs pH curves with biodegradability and biocidal activity of the three polymers will be discussed.