The crosslinking agent is a vital key which affects the mechanical properties of composite solid rocket propellants (CSRPs). Under this scheme, the effect of crosslinking mixtures (CMs) based on trimethylolpropane (TMP) as a triol crosslinker and butanediol (BD) as a chain extender on CSRPs based on hydroxyl-terminated polybutadiene was investigated. A series of 27 propellant compositions was formulated to study the mechanical properties of the prepared CSRPs. The effect of changing the weight ratio of TMP to BD in the CM was studied. In addition, the influence of increasing the percentage of CM (from 0% to 0.5%) in the prepared samples was investigated. Also, the effect of the CM on CSRPs containing different curing ratio of NCO/OH = 0.7, 0.75, and 0.8 was studied to generate the largest possible strain-ability with high strength over different levels of curing conditions. The mechanical characteristics (tensile strength and strain) of the prepared CSRPs have been measured and plotted versus CM content, NCO/OH and TMP:BD ratio. Generally, the addition of CM leads to a remarkable enhancement in the propellant mechanical properties. Samples containing TMP:BD (2:1) provide the highest strength while samples containing TMP:BD (1:2) show the highest strain over all the NCO/OH ratios. Formulations with TMP:BD (1:1) give high strength with moderate strain. Variation in CM content has a remarkable influence on the mechanical properties of CSRPs. A wide range of tensile strength and strain were obtained from this study to offer variety of results suitable for different applications in the CSRPs technology.

Glycidyl azide polymer (GAP) based binders have poor mechanical characteristics in comparison with hydroxyl terminated polybutadiene (HTPB) binders. In this study, advanced cross-linker was used to improve the mechanical properties of GAP binder. GAP was prepared and characterized in comparison with HTPB prepolymer. Density, characteristics groups, nitrogen content, humidity, viscosity, and milligram equivalent of (OH) per binders were determined. A cross-linker consists of trimethylol propane (TMP) and curing catalyst, dibutyltin dilaurate (DBTDL), was used as an additive to GAP polymeric matrix to enhance its functionality. Polymeric matrices based on GAP and HTPB were prepared with different curing ratio (NCO/OH) ranging from 0.7 to 1.5. Different weight percentages of cross-linker * Dr. A. Elbeih

Glycidyl azide polymer (GAP) has been prepared and studied for its application as polymeric matrix for composite solid rocket propellants (CSRP). Different CSRP based on GAP polymeric matrix with different plasticizers were prepared. A cross-linker based on trimethylol propane (TMP) and dibutyltin dilaurate (DBTDL) was added to the GAP matrix to ensure curing completion of the prepared CSRP. The viscosity and shore A of all the prepared CSRPs during the curing process were measured continuously. The mechanical properties of the cured CSRP were determined. The ballistic performance, burning rate at operating pressure and specific impulse were determined using standard a modified six inch rocket motor with 16.25 mm nozzle. By comparing the results, it was concluded that the plasticizer; dioctyl azelate and dibutyl phthalate are not compatible with GAP matrix. In addition, CSRP based on GAP has specific impulse and burning rate slightly higher than the traditional HTPB based CSRP.

Polyurethanes are prepared by extending a prepolymer chains made from a macro diol and a diisocyanate and its mechanical properties could be improved by using special additives to enhance the crosslinking process. In this study, 15 hydroxyl terminated polybutadiene (HTPB) based poly urethanes were prepared using 1, 6- hexamethylene diisocyanate (HMDI) and crosslinking mixture (CM) consists of trimethylol propane (TMP) as a triol crosslinker and butane diol (BD) as a chain extender. Five different crosslinking mixtures were used through the combination between TMP: BD = 1:0, 0:1, 1:1, 2:1 and 1:2. The research investigated the impact occurred on the mechanical behaviour of PU formulations prepared by adding certain cross-linking additives with various content from 0 % to 5 % and the curing ratio NCO/OH maintained constant at 0.7. The strength-strain relationships of all the finished samples were determined by using a LLOYD testing machine. The mechanical properties have been plotted vs. crosslinking mixture content and TMP: BD percentage which could be utilized to choose an appropriate network forming agent formulation for a particular grain technology and implementation. It was concluded that both TMP and BD have a major influence on the mechanical behaviour which allow obtaining a wide range of strength and elongation capabilities. The tensile strength increased by the excess of triol addition while the strain had a lowering effect which was compensated by the existence of diol extender. Tailoring the mechanical characteristics was easy to make by using a suitable proportions of TMP and BD to obtain outstanding mechanical properties for fixed NCO/OH, especially elastic capabilities, compared to polyurethanes formulated without any crosslinking additives.