Plasma treated polyethylene terephthalate for increased embedment of UV-responsive microcapsules

Highlights: • Treatment of PET fabric for production of smart and flexible UV sensors is proposed. • Increased reactivity is achieved by combination of O₂ and NH₃ discharge gases. • Higher content of N on PET increased the uptake of UV-responsive microcapsules. • The colour depth of plasma-treated UV-responsive PET was improved from 20 to 75%. - Abstract: Polyethylene terephthalate (PET) fabric was treated in a late afterglow of plasma created by a microwave (MW) discharge in the surfatron mode, by using oxygen (O₂) and ammonia (NH₃) gases. The series of treatments using one gas or the combination of both at different treatment times were performed in order to increase the embedment of UV-responsive microcapsules that were deposited onto PET with pad-dry-cure process. Plasma in both gases was characterized by optical emission spectroscopy (OES), which showed substantial dissociation of O₂ and NH₃ molecules as well as formation of NH_x radicals due to the partial dissociation of ammonia molecules. The chemically active species in the plasma afterglow changed the surface properties of PET that were analysed using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF–SIMS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and water absorption analysis. The effectiveness of plasma treatment on embedment of UV-responsive microcapsules on PET was evaluated by UV-responsiveness, colour strength and colour depth using reflectance spectroscopy, add-on and air permeability, respectively. Treating PET by O₂ afterglow followed by a longer treatment by NH₃ afterglow increased the polymers hydrophilicity and concentration of nitrogen-rich functional groups on surface that enabled higher uptake of UV-responsive microcapsules, and consequently better responsiveness of fabric to UV radiation. The add-on of microcapsules was almost 8-times higher and the colour depth increased up to 75% for plasma treated samples.