*4.3.2 Chemical modification*

The way to obtain stronger antibacterial properties of bast fibers is the chemical modification of linear or flat textiles. Flax and hemp as cellulosic fibers are

characterized with high reactivity due to containing hydroxy group in compounds in their chemical composition.

Racu conducted study on the application of grafting of monochlorotriazinyl-βcyclodextrin on hemp fiber stream at the time of wet spinning. Four compounds, e.g., ferulic acid, caffeic acid, ethyl ferulate, and allantoin, have been included into the cavities of monochlorotriazinyl-β-cyclodextrin and grafted on hemp fibers. Obtained yarn showed that the method allowed for a significant modification of Sano Genetics properties of the hemp fibers [33].

The application of silver in shape of nanoparticles is the most common method to functionalize different textile materials, including natural fibers. Research on the functionalization of the scoured flax fibers by the insertion of silver nanoparticles was conducted with the use of two different methods: first where Ag + was reduced by using the functional groups of flax in the internal reduction, and second where trisodium citrate was used as an external reducing agent in the external reduction method [34]. The modified scoured flax fibers with silver nanoparticles showed very good barrier properties against UV radiation and excellent antibacterial activity.

A good example of nanosilver application for hemp fiber to make strong antibacterial activity is the use of selective 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-mediated oxidation, i.e., oxidation with sodium hypochlorite, catalytic amount of sodium bromide, and the 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO), followed by silver sorption from aqueous silver nitrate solution, described by Milanović et al. [35]. The introduced hydrophilic carboxyl in hemp fibers caused by TEMPO-mediated oxidation influenced increased silver sorption and, in consequence, gave efficient antibacterial activity. The TEMPO-oxidized hemp fibers with absorbed silver showed good antibacterial activity against the tested bacterium strains: *S. aureus* and *Escherichia coli*, and the fungus *Candida. albicans*.

The new method of improving of antibacterial activity of hemp fibers has been developed by Chang [36]. The research group developed method of grafting of hemp fiber with the use of quaternary ammonium groups (HF–GTA) prepared by alkalization, oxidation, amination, and quaternization multistage reactions, whereby the grafting reaction mainly takes place on the cellulose and hemicellulose hydroxyl groups, without negative effect on fibrous morphology, thermal stability, and hygroscopicity. This method gives good antibacterial activity of hemp fiber against bacteria strains *E. coli* and *S. aureus*. The obtained barrier properties are characterized by good washing resistance.
