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

Abstract

Herein, the reason for the improvement in the gas barrier properties of polyurethane (PU)−clay nanocompositecoated 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/m 2 / day) compared with 1 wt % (2500 mL/m 2 /day) and 2 wt % clay (2600 mL/m 2 /day)-incorporated PU-coated fabrics and neat PUcoated nylon fabric (4500 mL/m 2 /day) at 260 GSM.