Abstract:

Objective Viscose fibers are highly regarded for their wearing comfort, making them popularly utilized in many fields. Equally, they can provide favorable conditions for microbial growth, thereby posing a risk to both material performance and human health. ZnO nanoparticles exhibit advantages in broad-spectrum antibacterial activity and low toxicity to the human patient, and thus have been considered one of the most promising candidates.

Method Using catechol, ZnCl₂, and formaldehyde as precursors, ZnO nanoparticles/catechol-formaldehyde resins microspheres (denoted as ZnO/CFR) were synthesized via a one-pot hydrothermal method. ZnO/CFR were then used as additives to fabricate antimicrobial viscose fibers through wet-spinning technologies. Micro morphologies and chemical structures of ZnO/CFR were investigated. Dispersibility and stability of ZnO/CFR in the spinning solution were monitored. Antibacterial properties against E. coli and S. aureus of the fiber were evaluated by the zone of inhibition test and shake-flask methods. Zinc contents with the fibers were determined. Color and mechanical performance of the fibers were also investigated.

Results ZnO/CFR exhibited a smooth surface with a particle size of 0.9-2.5 μm, while some ZnO nanoparticles was irregularly distributed within the microsphere. Zn2p signals appeared in the XPS full spectrum of ZnO/CFR with an atomic content of 1.4%, which was composed of two strong peaks of Zn3p_1/2 and Zn2p_3/2 with the binding energy of 1 044.8 and 1 021.6 eV. ZnO/CFR were evenly dispersed in viscose spinning solutions to achieve homogeneous dispersions. With 0.2, 0.4, and 0.6% additions of ZnO/CFR, all the spinning solutions (VF-2%, VF-4%, and VF-6%) showed constant ΔT values around 0 throughout 24 h at different heights. All the fibers (VF-2%, VF-4%, and VF-6%) showed a regular shape and uniform brown color, while the color of fibers gradually became darker with the increasing additions of ZnO/CFR. All the fibers showed smooth surfaces without any micro-scale particles, where ZnO/CFR were buried in the fibers rather than exposing on the surface. After the zone of inhibition test, no microbial colony was found to grow in the area in contact with the fiber, while no inhibition zone appeared around the edge of the sample. All the agar plates corresponding to unmodified viscose fibers had some microbial growth, while those corresponding to VF-2%, VF-4%, and VF-6% showed fewer microbial colonies. VF-6%, with 2.08% of zinc in the fiber, achieved a high antibacterial rate of 99.9% against both E. coli and S. aureus. The L^* value of VF-2%, VF-4%, and VF-6% decreased to 56.3, 49.2, and 39.2 from 91.3 of the control sample while the K/S value increased to 3.9, 5.1, and 10.7 from 0.7 of the reference fiber. VF-2%, VF-4%, and VF-6% each showed a slight decrease in breaking tenacity to 11.8, 11.6, and 11.4 cN/tex from 12.8 cN/tex of the unmodified fiber. VF-2%, VF-4%, and VF-6% respectively had a breaking elongation rate of 17.8%, 17.3%, and 17.1% while that of VF was 19.9%.

Conclusion ZnO/CFR prepared were monodisperse microspheres with some ZnO nanoparticles within the microsphere. ZnO/CFR microspheres were uniformly dispersed in the viscose spinning solution and showed long-term stability without any sedimentation of the particles. VF-2%, VF-4%, and VF-6% all showed smooth surfaces where most of ZnO/CFR were buried in the fiber. ZnO/CFR modified fibers exhibited the non-dissolution antibacterial behaviors. With 0.6% additions of ZnO/CFR, VF-6% presented a high antibacterial rate of 99.9% against both E. coli and S. aureus. ZnO/CFR blackened viscose fibers while slightly influencing the mechanical performance of the fiber. This work widens the window of ZnO nanoparticles for the production of antibacterial viscose fibers through wet spinning methods and presents a versatile approach for preparing antibacterial cellulosic materials such as films, foams, and hydrogels.

Key words: zinc oxide, antibacterial property, viscose fiber, catechol, microsphere, hydrothermal reaction