manitol

Mannitol has a relatively high melting point (167^ºC) but is one of the commercially available sugar alcohols, in the same family as sorbitol, xylitol, and erythritol. As such it will be very thermally stable. A 65/35 mixture of KNO3 (200 - 300 mesh) and Mannitol (processed at 350^ºF) is typical of other sugar alcohol based sugar propellants in that it is of a mashed potato consistency when melted. The addition of a surfactant (polystep B-1 @ 0.1%) reduces the viscosity an exceptional amount. In fact it seemed that the propellant melt, after sitting for ~ 30 min at 350^ºF, had become translucent in color as if a significant amount of the KNO3 had dissolved in the sugar. The propellant was easily poured into casting tubes for motor testing. Because of the high processing temperature of this formulation, a significant amount of shrinkage occurred upon cooling. This sugar crystallizes very quickly. Grains are ready to face and use as soon as they are cool enough to touch. A small amount of molten formulation needed to be ready to use to "top off" the grains as a significant "trough" formed as the grains cooled. This trough was filled with molten propellant. Once cool the grain faces were made square using a fine grain chop saw blade. Motor ignition ocurred with no difficulty using my regular igniters.