December 2005

QUESTION:We make elastomeric construction type sealants and are looking at entering the high-performance industrial and automotive markets. Could you give us an overview of elastomeric sealants in this market, particularly with regard to performance vs. price?

ANSWER: This is a rather complex subject to cover in a column like this, but there is a basic correlation between price and performance, much like the classification of construction sealants into low-performance, medium-performance, and high-performance based on their joint movement capabilities. With industrial sealants, it is more common to look at such properties as the combination of heat resistance and oil resistance when choosing a sealant for a particular application. For maximum temperature and oil resistance, there is no doubt that fluoroelastomers are the technical leader, but are also the most expensive. Acrylic rubbers (ACM and AEM types) and hydrogenated nitrile (HNBR) rubber have a good combination of heat and fluid resistance, and have had considerable success as high-performance, cost-effective automotive sealants. An elastomer like nitrile, which has good oil resistance and fair heat resistance, is a large-volume, low-cost sealant. Some elastomers, like EPDM, don't have great resistance to heat or oil, but have excellent weathering resistance that leads to widespread use in applications like automotive window seals.

Also consider that some elastomers - notably silicones and fluorosilicones - have many excellent properties but are normally only suitable for static sealing operations rather than dynamic sealing. Please note that my comments here are generalizations; it would be unfair to my fellow chemists and engineers not to point out that innovative people can often stretch the capabilities of some technologies, using creative chemistry and joint designs. A good example would be the use of RTV silicones in the auto industry. Silicones have traditionally been considered to have relatively poor oil resistance, but have been formulated very successfully in recent years to be durable sealants for valve cover and oil pan gaskets.