Antimicrobial coating of an N-halamine biocidal monomer on cotton fibers via admicellar polymerization

Abstract

The monomer 3-(4′-vinylbenzyl)-5,5-dimethylhydantoin (VBDMH) was synthesized and used to coat cotton fibers by admicellar polymerization using a cationic surfactant. The coated thin-film on cotton was characterized by FTIR and SEM. After chlorination with dilute sodium hypochlorite, the polymeric-coated cotton fabrics effectively inactivated both Staphylococcus aureus and Escherichia coli O157:H7 in relatively brief contact times. The stability and rechargeability of the coated cotton fabrics were very good as evidenced by standard washing tests.

Introduction

Several decades of laboratory work have proceeded concerning the development of desired biocidal surface coatings on fabrics to prevent infections in hospitals and other health related public venues. N-halamine compounds have shown excellent efficacies in inactivating a wide range of microorganisms including bacteria, viruses, and fungi [1], [2], [3]. Two outstanding advantages of these N-halamine compounds are their durable and rechargeable antimicrobial properties. These N-halamines have functional groups which can be halogenated to generate oxidative N–Cl or N–Br antibacterial moieties. The produced oxidative biocidal moieties can be incorporated or attached onto textiles, medical devices, and solid surfaces related to health care.

Recently, among a variety of biocidal polymers such as polymeric phosphonium compounds [4] and polymeric quaternary ammonium compounds [5], [6], [7], polymeric N-halamines have been synthesized and received considerable attention in disinfection of water because of their excellent properties of biocidal efficacy, stability, and rechargeability. One of the most important polymeric N-halamines is poly(1,3-dichloro-5-methyl-(4′-vinylphenyl)hydantoin) [8], [9], [10], resulting from functionalization of poly(styrene). A similar polymer can be synthesized from functionalizatoin of poly(4-chloromethylenestyrene) [11] or from polymerization of the monomer 3-(4′-vinylbenzyl)-5,5-dimethylhydatoin [12], [13]. Polymerization coatings of monomeric or oligomeric N-halamine siloxanes on a variety of surfaces including sand [14], [15], silica gel [16], [17], cellulose [14], [16], [18], [19], and paint [14], [16] to produce polymeric biocidal materials have also been reported.

Admicellar polymerization has been successfully used to form thin-film coatings on various substrates including glass fibers [20], silica [21], and textile materials [22], [23], [24], [25], [26]. The admicellar polymerization method is a three-step process. The first step involves admicellar formation. Admicelle or surfactant bilayer on the substrate surface is formed when the surfactant concentration is controlled just below the critical micelle concentration (CMC). The second step constitutes monomer adsolubilization. The hydrophobic monomers are preferentially absorbed into the hydrophobic interior of the bilayer at equilibrium. The third step comprises a polymerization reaction. Water-soluble initiators are added to promote the polymerization. Theoretically, the mechanism of polymerization in the bilayer is similar to that of emulsion polymerization. After the completion of the polymerization reaction, the upper layer of surfactant is removed by thoroughly washing with water.

Cotton is a natural cellulose fiber consisting of β-1,4-d-glucose which has numerous –OH groups and a small number of carboxylic acid groups. In addition, chemically bleached cotton fibers have a considerable number of aliphatic carboxylate groups –COO⁻, as indicated by the negative zeta potential ξ of the bleached cotton fibers [27], [28], [29]. Therefore, the scoured and bleached cotton can be expected to adsorb cationic surfactant at neutral or high pH.

In this study, antibacterial thin-films on the surfaces of the cotton fabrics were formed by admicellar polymerization of a monomeric precursor 3-(4′-vinylbenzyl)-5,5-dimethylhydatoin with the aid of the cationic surfactant cetylmethylammonium bromide (CTAB), (see Scheme 1). It will be shown that after chlorination with dilute household bleach, the coated cotton fabrics exhibited excellent properties in inactivating Staphylococcus aureus and Escherichia coli O157:H7. Surface characterization and stability of the coated film will also be addressed in this paper.