A new class of phenolic and carbon-fiber-reinforced phenolic composites has been developed for thermal protection systems. The new materials have the advantage of being lightweight, strong, and tough, yet heat resistant and flexible. They retain excellent mechanical strength at high temperatures. This provides better thermal protection for reentry conditions with high heating rates.
The materials incorporate thermoplastic polymer segments that are uniformly distributed throughout, and are chemically bonded to the phenolic network. Phenolic resin polymers are a class of widely used thermosetting polymers. Their numerous advantages include excellent heat, radiation, and corrosion/chemical resistances and flame retardancy. They are low-cost and made from versatile processing/manufacturing methods.
The approach taken here modifies the phenolic polymer network by adding thermoplastic molecules with flexible segments such as aliphatic carbon and siloxane. The thermoplastic molecules are terminated with bifunctional groups that can directly react with the phenolic under the curing condition to form chemical bonds. Further incorporation of these segments can be facilitated by a relay reaction of a second molecular component that can bond with both the first flexible segments and the phenolic network. The selection of flexible, thermoplastic segments is based on desired properties that include flexibility, ablative and charring abilities, and heat resistance and low catalytic reactivity.
The modified phenolic is a molecular composite in which flexible segments are connected with the phenolic network through strong chemical bonds, and are uniformly distributed among the networks. This feature renders a uniform toughening/ strengthening effect without compromising the lightweight nature of the materials. The process is also feasible to scale up and is amenable to manufacturing.
This work was done by Wenhong Fan and Jeremy Thornton for Ames Research Center. NASA invites companies to inquire about partnering opportunities and licensing this patent-pending technology.