Functionalization of silk by silver nanoparticles synthesized using the aqueous extract from tea stem waste

Silk has poor antibacterial and UV protection properties which limit its application fields. Silver nanoparticles (AgNPs) have attracted great attention due to their excellent antibacterial activity. This work proposed a green and efficient way to prepare AgNPs from silver nitrate using the aqueous extract from tea stem waste, and a functional finishing of silk material with the resulting AgNPs by an immersion technique. AgNPs prepared at pH 9 and 40 degrees C exhibited ultra-fine particle size (<20 nm), good dispersibility and good storage stability. When silk was treated with AgNPs at pH 3 and 80 degrees C for 40 min, it displayed high silver content and color depth. The antibacterial and UV protection ability of AgNPs treated silk fabric of crepe de chine (52 g/m(2)) increased as the silver content of silk increased. At a silver content of 3.64 mg/g, the antibacterial rate of treated silk against Escherichia coli and Staphylococcus aureus was as high as 99%, and it was above 92% even after 20 cycles of washing under a neutral condition. At the same silver content, the UV protection factor of treated silk reached 21.3, being classified as "good protection". The present study not only presents a novel approach for the functionalization of silk material using biosynthesized AgNPs, but also implements the reuse of tea stem waste. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).