Study On The Modified Polyurethanes Of Organic-Inorganic Hybrid

Hydroxyl terminated polybutadiene(HTPB) based polyurethanes (Pus) are low modulus materials and degrade easily at low temperature Polycarbodiimide (PCDI)and polysiloxane (PSi) are reative-type filers when formed by carbodimidzation and sol-gel process, respectively .During the combustion, PCDI and PSi give off non-toxic, non-corrosive volatile gases, and finally form carbonaceous and siliceous chars. In this study , modified PUs were prepared by incorporating PCDI or PSi into PUs to give high carbon, nitrogen and silicon materials. These modified PUs are kinds of organic-inorganic hybrids with higher modulus and higher thermal stability than HTPB-based PUs.The mechanical properties a room temperature and the thermal stability of these modified PUs and silicone rubbers were investigated using a tensile tester and a thermogravimetric analysis(TGA). ATR/FTIR(Attenuated total reflectance / Fourier transform infrared ) technique is applied to monitor the synthesis process of PCDI and to examine the change of surface chemistry of insulator before and after thermal degradation via TGA. TGA coupled with FTIR(TGA/FTIR)was used to analyze the kinetics and the mechanism of themal degradation under nitrogen and or air. The maximum degradation temperature and char yield (CY)of thermal degradation were estimated from a series of experiments with heating rates of (1,3,5,10,20,30,40 and 50℃/min), under nitrogen or air .It is apparent that the maximum degradation temperature is dependent on heating rate. By assuming the heating rate used in an operating environment is about 5000℃/min , T_max calculated for the modified PUs (HIPTD-40%PSi and HIPTD-30%PMPS-PSi under air) are found as 538 and 522℃.The micophotogy of modified PUs and silicone rubbers before and after thermal degradation via TGA wad observed by optical and scanning electron microscope(SEM).