Abstract:

Objective Antimicrobial polyamide 66 (PA66) fibers have gained a lot of attention because of the demand from the apparel and biomedical fields. Poly(hexamethylene guanidine hydrochloride) (PHMG) is an ideal antimicrobial agent because of its broad-spectrum antimicrobial properties, good biocompatibility, low cost and non-toxicity. However, due to its excellent water solubility, the antimicrobial fibres produced by direct blending of PHMG with the matrix exhibit shortcomings such as poor washability and dissolution tendency. The present study aims at producing long-lasting antimicrobial polyamide 66 (PA66) fibers via modification of PHMG with polyepoxy polystyrene (PSG).

Method PHMG was first modified by melt blending with PSG via a twin-screw extruder to produce guanidine salt copolymer (PSGP). Next, PSGP was melt blended with PA66 chips via a twin-screw extruder to produce antimicrobial PA66 masterbatch. Finally, the antimicrobial PA66 masterbatch was used as additives to fabricate long-lasting antimicrobial PA66 fibers through blend melt spinning techniques. The chemical structure and thermal properties of the antimicrobial PA66 masterbatch, the micromorphology, crystal structure, mechanical and antimicrobial properties, as well as the distribution of Cl element on the cross-section of the antimicrobial PA66 fibres were investigated.

Results The antimicrobial PA66 masterbatch demonstrated exceptional thermal stability with almost no mass loss below 310 ℃, fully satisfying the thermal requirements for melt spinning processes. Remarkably, even at a PHMG loading as low as 0.33%, the resulting PA66 fibers achieved outstanding antibacterial efficacy, showing 99.46% and over 99.99% reduction rates against E. coli and S. aureus, respectively. When the PHMG content was increased to 0.39%, the fibers exhibited over 99.99% antibacterial activity against both bacterial strains. Notably, after 50 washing cycles, fibers with a PHMG dosage of 0.45% maintained impressive antibacterial performance with over 95% inhibition rates for both microorganisms, demonstrating excellent wash durability and good long-lasting antimicrobial properties. Mechanical characterization revealed that as the dosage of PHMG increased gradually from 0% to 0.33%, 0.39%, 0.45% and 0.51%, the breaking strength of the resulting fibers decreased continuously from (6.09±0.21) cN/dtex to (5.48±0.22), (5.35±0.20), (5.19±0.23), and (4.98±0.27) cN/dtex, while the orientation factor only slightly decreased from 0.79±0.03 to 0.77±0.02, 0.76±0.04, 0.76±0.03, and 0.75±0.04. DSC and XRD analyses indicated that the incorporation of PHMG reduced crystallinity and diminished crystal structure regularity in the fibers, explaining the observed mechanical property changes. Importantly, despite this reduction, all antibacterial fibers maintained breaking strengths above (4.98±0.27) cN/dtex, which fulfills the mechanical requirements for practical textile applications. SEM morphological analysis demonstrated excellent compatibility between PSGP and PA66 matrix, with no evidence of phase-separation. Surface characterization studies, including the cross-section radial line-scanning of Cl (a characteristic element of PHMG) and XPS analysis of the antimicrobial PA66-0.51 fiber containing 0.51% PHMG, revealed significant PHMG enrichment on the fiber surface compared to both the inner part and bulk average of the fiber. This surface enrichment phenomenon explains the fibers' exceptional antibacterial performance at such low PHMG loadings.

Conclusion Antimicrobial PA66 masterbatch exhibits good thermal stability. The introduction of PSG promotes the enrichment of PHMG on the fiber surface during the spinning process. This enhances the utilization rate of the antimicrobial agent, enabling the antimicrobial PA66 fiber to achieve over 99% antibacterial rates against E. coli and S. aureus at a low PHMG dosage of 0.33%. At a PHMG dosage of 0.45%, the resulting antimicrobial fibre not only remained excellent antimicrobial properties after 50 washing cycles, but also exhibited good mechanical properties with a breaking tenacity of 5.19 cN/dtex. In summary, this work provides a new approach for developing PA66 fibre materials that combine excellent mechanical properties with efficient antimicrobial performance, demonstrating great potential for applications in medical, sports, and home textiles.

Key words: antimicrobial fiber, polyamide66, poly(hexamethylene guanidine hydrochloride), polyepoxy polystyrene, antimicrobial agent