Modelling of loss factors of elastomer binders of high explosive charges and composite rocket propellants to separate binder fractions with different molecular mobility used to follow ageing

The glass-rubber transition temperature of elastomer bonded composite rocket propellants and high explosives is an important property determining their in-service application. It is defined as the main maximum of the loss factor tand, which is determined as function of temperature by DMA (dynamical mechanical analysis) measurements at some forced sinusoidal deformation at lower frequencies in the range of 0.01 to 100 Hz. With the term transition the center part of the molecular rearrangement process is meant, in which the transition from the energy elastic ('glassy elastic') to the entropy elastic ('rubbery elastic') behaviour, or vice versa, occurs. The loss factor of an elastomer binder is influenced by several factors: (1) filler type and content, (2) plasticizer type and content, (3) sterical hindrance, (4) interaction forces between all ingredients, (5) polymer chain conformation of the elastomer, (6) curing type and agent. Because the loss factor region of most elastomers filled with rigid particles consists of several sub-transitions, which can change differently during ageing and deformation rate loading, a special modelling of the loss factor curve is presented using so-named exponentially modified Gauss distributions. Therewith a separation and a quantification of the molecular rearrangement regions or binder mobility fractions is achieved, after the application of a suitable baseline correction function to the loss factor curve.