• Kłodzińska, Ewa
• Wojciechowski, Kamil

Abstract

Biodegradable polymers have gained increasing interest in recent years, especially in food packaging industry. The biodegradation process is intrinsically related to adhesion of degradation-promoting bacteria on the surface of a biodegradable packaging. On the other hand, because of a direct contact with food, these materials should be resistant to colonisation by pathogenic bacteria. Thus, successful design of a biodegradable antimicrobial material critically depends on the interplay between the ability to control the strength of bacteria–polymer interactions. The aim of this work was to measure and analyse the effect of three positively charged antibacterial polyhexamethylene guanidine hydrochloride (PHMG) derivatives (sulfanilic acid salt, stearic acid salt, and polyethylene (PE) wax blend) on electrokinetic potential (ζ) of three biodegradable polymers: poly(hydroxybutyric acid) (PHB), polycaprolactone (PCL) and poly(lactic acid) (PLA). For this purpose, the streaming current vs pressure curves were recorded and analysed using the Helmholtz–Smoluchowski theory. The ζ vs pH dependency provides a simple and useful characterisation of an electrical double layer forming on the surface of biodegradable polymers in contact with an aqueous electrolyte. The undoped polymers displayed the ζ vs pH curves typical for electrically neutral polymers, with the isoelectric point, IEP = 3.5–4.0. The effect of PHMG on ζ vs pH curves depends on both the nature of the matrix polymer and the chemical form of PHMG. The stearate salt is shown to affect the curves to the smallest extent, while the most pronounced shifts towards higher pH were observed for PHMG in the form of PE wax (for PCL and PHB), or sulfanilic acid salt (for PLA). The surface of almost all PHMG-doped polymers used in this study (with exception of PLA doped with PHMG stearate) was more positive than the bare biodegradable polymers. From the point of view of electrostatic interactions, the addition of PHMG (especially in the form of PE wax, and especially for PHB) would thus probably enhance electrostatic polymer–bacteria interactions, possibly altering the antimicrobial activity of such polymers.

Topics

• impedance spectroscopy
• surface
• polymer
• theory
• strength
• forming