Insights into the Improved Gas Barrier Properties of Polyurethane–Clay Nanocomposite-Coated Nylon: A Solid-State NMR Study

Herein, the reason for the improvement in the gas barrier properties of polyurethane (PU)–clay nanocomposite-coated nylon fabric compared to unfilled PU-coated nylon fabric is investigated by probing the changes in relaxation times of PU using solid-state nuclear magnetic resonance (SS NMR) spectroscopy. The interaction of the organically modified montmorillonite (MMT) clay (Cloisite 30B) with polyurethane (PU) in PU–clay (0.5/1/2 wt %) nanocomposites was probed with respect to the change in the spin–lattice relaxation time of protons in the PU chain due to the presence of paramagnetic species in clay (T 1H, para). The better the dispersion of the clay in the PU matrix, the lower the T 1H, para, due to the interaction between clay and the PU matrix. 0.5 wt % PU–clay has lower T 1H, para, (6.4 s) compared to 1 wt % (18.3 s) and 2 wt % (14.3 s) filled systems. The SS NMR findings are in good agreement with field-emission scanning electron microscopy (FE-SEM) analyses. In SEM microscopic images, it is observed that the PU–0.5 wt % clay has better exfoliation of clay compared to the 1 and 2 wt % PU–clay nanocomposites. This is in agreement with improved gas barrier properties of the nanocomposite coated on the nylon fabric for 0.5 wt % clay (2300 mL/m2/day) compared with 1 wt % (2500 mL/m2/day) and 2 wt % clay (2600 mL/m2/day)-incorporated PU-coated fabrics and neat PU-coated nylon fabric (4500 mL/m2/day) at 260 GSM.