Preparation and properties of polyurethane nanocomposites of novel architecture as advanced barrier materials

The helium gas permeation through polyurethanes (PU) having novel microstructures derived from different polyols (varying from linear to hyperbranched) in the presence and absence of modified and unmodified nanoclays has been studied thoroughly in this paper. The permeation rate of helium gas decreases from linear to fourth generation polyols (PU40) by about 80% due to increase in the crosslinking density. Similarly, the permeation rate of 8 wt% clay filled third generation hyperbranched PU dramatically decreases by about 76% in comparison to the unfilled PU. Gas-impermeable clay platelets in the PU matrix form tortuous pathways that further retard the progress of gas molecules. In addition, the well dispersed modified nanoclays contribute to improvement of the permeability properties to a great extent when compared with the aggregated unmodified ones. Further, interaction between the clays and the PU matrix plays a great role. Good correlation between dispersion of nanoclays in the PU matrix, as characterized by high resolution transmission electron microscopy and atomic force microscopy, and barrier resistance has been established. The permeation results have been compared with the different contemporary permeability models. The results are in line with the prediction by the Gusev-Lusti, the Nielsen and the Cussler (regular array) models at lower concentration of clay.