Effects Of Phosphazene Compounds On The Structure And Properties Of NBR Or EPDM Thermal Insulation Materials

Phosphazene are kinds of compounds of consisting phosphorus and nitrogen with linear chains or rings, which present them with excellent flame retardancy. The backbones of polyphosphazenes have excellent flexibilities which allow some of them very low glass transition temperature. They can be used as high performance insulations for solid rocket motors. In this thesis, we envision blending phosphazenes with synthetic rubber, such as NBR and EPDM, to improve their mechanical and ablation resistance properties.Poly(diethoxy)phosphazene (PDEP) was synthesized through solution polymerization, then was blended with NBR with different ratios via mechanical mixing using two rolls mixing mill. Thermal insulation materials were prepared by vulcanizing the blends. Crosslinking effects of the blends was investigated by no motor rheometer, compatibility and morphology of the blends were characterized by DSC, SEM and TEM. Mechanical properties and ablation resistance properties were measured. Surface and fracture morphologies of charred layers after ablation were characterized by SEM. Results showed that PDEP and NBR were hardly co-crosslinkable, and they were incompatible in thermodynamic state. The blending showed sea-island structure or bicontinuous phase structures. The strength of the charred layers after ablation and the connection between matrix and chaired layers were enhanced when PDEP was added. Tensile strength reached 8.12MPa and linear ablation rate reached 0.08mm/s when PDEP/NBR ratio was 20/80.As compared with common used fire retardants, ammonium polyphosphate (APP), the new EPDM insulations were fabricated by filling two kinds of new fire retardants, hexaphenoxycyclophosphazene (HPTCP) and poly(phenoxy 4-ethylpenoxy phosphazene) (PDPP) respectively. The blends were characterized by no rotor rheometer, LOI index tester, materials testing machine and ablation rate meter. Results showed that crosslinking density of the insulation materials decreased when HPTCP or PDPP were filled. Thermal insulation materials filled with PDPP showed that their ablation resistance properties increased. The tensile strength reached 18.4Mpa and linear ablation rate enhanced to 0.08mm/s when 20 phr PDPP was added.Phosphazene derivatives with alkene groups were synthesized. The structures of the compounds were characterized by 31P-NMR and mass spectrum, and substitution rates of final products with the relationship to reaction time and temperatures were investigated. The results showed that partial substituted products were usually obtained at room temperature, while substitution rate increased rapidly when reacting temperature elevated. Fully substituted products (HATCP) were obtained when reacted at 60℃ for 60 hours.EPDM insulations filled with HATCP were prepared, which characterized by no motor rheometer, TGA, materials testing machine and ablation rate meter. Tensile strength of the insulation reached 29.4 MPa when only 1% HATCP was filled and its ablation resistant properties improved as well.