Inflatable fabrics are used in a number of different applications, such as automotive airbags, parachutes, rafts, hot air balloons and inflatable structures for space exploration. An inflatable fabric consists of a base fabric that provides strength and a multifunctional coating layer. Besides blocking pores in the fabric and providing impermeability, the coating imparts flexibility, toughness and tear strength to the fabric. In addition, the coating protects the fabric from the heat generated during inflation and provides smooth deployment. A desirable coating material should have low permeability, good adhesion to the fabric and good mechanical strength.
The first generation of inflatable fabrics was based on nylon 6,6 fabric with a neoprene coating. However, neoprene had several shortcomings, including necessarily thick coatings, a tendency to stick when deployed, limited environmental stability and marginal thermal resistance.
As improvements in nylon 6,6 and alternative fabrics continue, silicone coatings are being used more often than neoprene coatings to: (a) protect the fabric from heat-scorching; (b) allow thinner and more foldable coated fabrics; (c) improve long-term environmental stability; and (d) provide better compatibility with nylon. Silicone coatings are increasingly used on inflatable fabrics in several consumer, military and space applications. An excellent example is the successful deployment of the airbag system for the Mars Pathfinder. Silicone coatings exhibit one to two orders of magnitude less atomic oxygen erosion compared to their organic counterparts in low earth orbit.1
Notwithstanding their excellent long-term thermal stability, weatherability and flexibility, silicone coatings are relatively weak compared to other elastomers. Fillers, such as amorphous silica, are often added to the matrix to reinforce the network. Another drawback of silicone material is its poor adhesion to the substrates because of its low surface energy. These problems can be addressed by nanotechnology, and indeed various attempts have been made using nanoscale additives to strengthen the silicone and reduce gas permeability. This article introduces a commercially viable nanoscale additive developed by NEI Corporation that improves fabric tear strength, tensile strength and hardness at low additive loadings. At the same time, the NEI product greatly improves adhesion between the silicone and the fabric. The NEI product is a nanoscale additive package that is easily added to commercial silicone coating formulations to impart excellent coating properties.
The first part of this article discusses how nanoscale additives can be used to improve the properties of the silicone base polymer. The second part presents data on NEI’s nanoscale additive-reinforced silicone-coated fabric.