Polybutadiene Rubber Binders
Almost concurrently with the evolution of the polyurethane propellants, a new type of binder based on long-chained polybutadiene backbone gained the attention of rocket manufacturers. The selection of polybutadiene binder for propellants to be used over wide temperature ranges was a natural one, since most butabiene copolymers (butadiene-styrene, butadiene-acrylonitrile, butadiene- methylvinyl pyridine) had glass-transition temperatures near or below -100°F. This was advantageous, since the mechanical behaviour of a propellant during periods of strain was related to its properties at different temperatures. For example, the ability of a propellant to withstand high strain rates such as those encountered on ignition of a large-diameter rocket motor was directly related to low-temperature properties such as elongation and brittle point. Therefore, the polybutadiene propellants were attractive, both for large motors and for those requiring wide temperature ranges of operation.
Four primary polybutadiene rubber binders have been used over the years:
PBAA - Polybutadiene Acrylic Acid.
PBAN - Polybutadiene Acrylic Acid Acrylonitril Terpolymer.
CTPB - carboxy-terminated polybutadiene.
HTPB - Hydroxyl-Terminated Polybutadiene.
