Influence of the Hydroxyl Functionality on the Mechanical Properties of Hydroxy Terminated Polybutadiene(HTPB) based Polyurethane Elastomers

Composite propellants are often identified by the type of polymeric binder used. The most commonly used polyol in recent time is the Hydroxyl Terminated Polybutadiene (HTPB). In order to evaluate the quality of three types of HTPB prepolymer, their polyurethanes elastomers were synthesized by one shot polymerization and structure-properties relationships of the prepared polyurethane have investigated. For this purpose, firstly, chemical structure of HTPB samples is characterized by GPC and NMR spectroscopy and viscometery. Then the stress-strain study was carried out to explain the effect of soft segment functionality on the tensile behavior. It was found that the effective functionality of soft segments had subtle effects on the tensile strength and elongation at break. On the basis of results that are obtained from gel point study and tensile test, we can deduce that the effective functionality of three types of prepolymers increases in order HTPB1>HTPB2>HTPB3. By increasing the effective functionality, the molecular weight between junctions in polyurethane elastomer is decreased. Also, the result of tensile test can be modeled with money-rivilin equation. Experimental data for the money-Rivlin constants were found and it was shown that gte msEquation 12]>C1{C}{C} !msEquation]--> for HTPB1 and HTPB3 are greater than HTPB2. Furthermore, it was found that trapped entanglements and pendant chain can be accountable for the gte msEquation 12]>C2{C}{C} !msEquation]--> term of money-rivilin equation.