Binding of a quaternary ammonium polymer-grafted-chitosan onto a chemically modified wool fabric surface: assessment of mechanical, antibacterial and antifungal properties

It is quite challenging to bind any chemical compound or polymer onto a wool fibre surface because of the lack of any functional groups available on its surface. In this work, anionic sulphonate groups were introduced onto a wool fibre surface by grafting with polystyrene sulphonate, which enabled binding of cationic quaternized chitosan by ionic bonding. A bioactive quaternary ammonium polymer, poly[2-(acryloyloxy)ethyl]trimethylammonium chloride, was grafted onto chitosan to enhance chitosan's limited antimicrobial activity. Two types of wool fabrics, untreated and polystyrene sulphonate grafted, were coated with this quaternized chitosan. The antibacterial properties of the wool fabrics coated with quaternized chitosan were tested against both Gram-positive and Gram-negative bacteria, Staphylococcus aureus and Klebsiella pneumoniae and also against Aspergillus fumigatus fungus. The coated wool fabric surface was further characterised by attenuated total reflectance – Fourier transform infrared and Raman spectroscopy, scanning electron microscopy (SEM), and also by measuring tensile strength and surface contact angle. The grafting of wool fabric with polystyrene sulphonate improved its tensile strength and elongation, but coating with quaternized chitosan increased the strength further and reduced elongation at break. Before washing both types of wool fabrics showed strong bacterial resistance against both types of bacteria but marginal antifungal activity. However, after five cycles of washing the untreated wool fabric coated with quaternized chitosan almost completely lost antibacterial activity. SEM analysis reveals that most of the quaternized chitosan was removed by washing. However, the polystyrene sulphonate-grafted wool fabric coated with quaternized chitosan retained its antibacterial activity, indicating that surface sulphonate groups on wool fibre improve the durability of the quaternized chitosan to washing.