Microwave-promoted continuous flow synthesis of thermoplastic polyurethane–silver nanocomposites and their antimicrobial performance

Thermoplastic polyurethane–silver nanocomposites (PU–Ag NCs) have considerable potential in many medical applications due to their superior mechanical and antimicrobial properties. Herein, a microwave-promoted flow system is successfully employed for continuous in situ manufacturing of PU NCs having spherical silver nanoparticles (AgNPs) without any reducing agent at ∼40 °C in approximately 4 minutes. The main experimental parameters, including microwave power, metal salt concentration, polymer concentration, and flow rate, are optimised for the reproducible synthesis of AgNPs (∼5 nm) in the PU matrix, characterised by HRTEM-EDS and DLS analysis. XRD patterns indicate an increase in PU crystallinity with decreased particle size. Conventional heating flow synthesis at ∼50 °C or microwave-batch synthesis (MWB) at ∼44 and ∼50 °C is ineffective in preparing AgNPs, and only large AgNPs (>100 nm) are synthesised at 70 °C in the MWB reactor. PU–Ag NC films bearing small AgNPs (∼5 nm) exhibit superior antibacterial activity (>97%) against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus compared to large NPs (∼218 nm). The proposed method may manufacture other metal–polymer matrix composites.