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Various pre-treated cotton yarns were oxidized with potassium periodate. The effects of pre-treatments on oxidation were studied by quantitatively assessing functional groups, while the extent of cotton yarn degradation was determined by investigating pre-treated yarn mechanical properties and the degree of polymerization. Pre-treatments included various scouring procedures and process sequences. The type of scouring has a significant influence on the aldehyde and carboxyl groups before oxidation, while the pre-treatment sequence did not. The number of aldehyde groups was significantly influenced by oxidation and strongly dependent on the pre-treatment sequence applied. Alkaline-scoured yarns had the least number of aldehyde groups both before and after oxidation, followed by alkaline pectinase and acid pectinase scoured, regardless of the pre-treatment sequence.

Using the exhaustion-pad-dry-rinse method, chitosan was applied to alkaline-scoured and bleached cotton yarns in a solution with concentrations ranging from 0.2–1% to achieve good antimicrobial activity against the bacteria Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Studied samples were also assessed by measuring the amount of introduced chitosan, amount of accessible amino groups, mechanical properties, whiteness index and the b* colour coordinate. Alkaline-scoured and bleached cotton yarns treated with all concentrations of the chitosan solution showed good antimicrobial activity against Escherichia coli and Staphylococcus aureus. Better antimicrobial activity was achieved against Escherichia coli. Increasing the concentration of chitosan solution deteriorated the mechanical properties of chitosan-treated cotton yarns. The optimal concentration of chitosan solution incorporated in the exhaustion phase to obtain chitosan-treated yarns with good antimicrobial activity and mechanical properties was 0.6%. The best antimicrobial treatment should minimise potential economic costs while providing functionality.