Study on the Effect of Cross-Linking Density on Mechanical and Swelling Characteristics of Hydroxyl Terminated Poly Butadiene (HTPB) Based Polyurethane Networks

摘要

Polyurethane constitutes one of the most complete and versatile class of polymeric materials known today. Different kinds and grades of PU have been developed for applications as fibers, resins, rubber, adhesives and surface coatings. They play an important role in the production of solid composite propellants for rocket motors. The urethane copolymers obtained by curing HTPB with a diisocyanate (TDI) serve as a fuel and also provide a matrix for inorganic oxidizer, metallic fuel and other dispersed solid components of the propellants. The term polyurethane is extended to all complex reaction products of isocyanates and polyhydroxy compounds. This paper studies the effect of cross-linking density on the mechanical properties and swelling characteristics of urethane networks. Polymer networks are characterized by cross-linking density, sol content and effective chain length. Cross-linking of polymer chains is of great importance in controlling many polymeric properties. Hydroxyl terminated poly butadiene (HTP) based urethane networks were synthesized by reacting (HTPB) with toluene diisocyanate (TDI) at various equivalent ratios of R (NCO/OH). Curing was done at 50o C for 168 hours. The cross-linking density was measured by swelling the urethane networks in the toluene for 48 hours. From the analysis it was found that cross- linking density increases with increasing NCO/OH ratio in the original gel. Ability of the network to absorb the solvent decreases with increasing cross- linking density. The mechanical properties were tested on Instron Universal Testing Machine. The results showed that tensile strength and modulus values increase with increase in R-value while elongation at break decreases with increase in R- value.