Abstract
Diglycidyl ether of bisphenol A (DGEBA)-bridged polyorganosiloxanes precursors were prepared successfully by reacting diglycidyl ether of bisphenol A epoxy resin with (3-aminopropyl)triethoxysilane. Acid-modified and unmodified multiwall carbon nanotubes (MWCNTs) were dispersed in the diglycidyl ether of bisphenol A-bridged polyorganosiloxane precursors to prepare the carbon nanotube/ diglycidyl ether of bisphenol A-bridged polysilsesquioxane (CNT/DGEBA-PSSQ) nanocomposites. Activation energy of curing of neat DGEBA-PSSQ nanocomposites were measured by DSC and analyzed by Kissinger method. Result indicated that DBTDL catalyst and acid-modified CNT can decrease the activation energy of curing of DGEBA-PSSQ. The molecular motion of CNT/DGEBA-PSSQ nanocomposites was studied using high-resolution solid-state 13C NMR. Acid modified CNT/DGEBA-PSSQ nanocomposites exhibit less molecular motion than neat DGEBA-PSSQ or unmodified CNT/DGEBA-PSSQ nanocomposites since acid-modified CNT is to DGEBA-PSSQ nanocomposites more strongly than unmodified CNT. The spin lock relaxation times (T1ρ H) of 13C NMR CP/MAS on the CNT/DGBEA-PSSQ nanocomposites were investigated. The results indicate that most of the peaks of acid-modified CNT/ DGBEA-PSSQ have greater T1ρH than those of neat DGEBA-PSSQ, but shorter than those of unmodified CNT/ DGBEA-PSSQ. Acid-modification constrains the molecular motion of the polymer; therefore, acid modification can improve the affinity between CNT and the polymer matrix and the mechanical properties of acid modified CNT are significantly better than those of unmodified CNT. The thermogravimetric analysis (TGA) data show that DGEBA-PSSQ nanocomposites has good thermal stability and all the sample have weight retention at 800℃ were up to 40wt%. DGEBA-PSSQ nanocomposites has good thermal stability and flame retardancy and both acidified and unmodified CNT do not have bad influence on their thermal stability and flame retardancy. The mechanical properties of nanocomposites depend strongly on the affinity between CNT and the polymer matrix. Adding multiwall carbon nanotubes markedly enhances the mechanical properties of nanocomposites. The mechanical properties of acid-modified CNT/DGBEA-PSSQ nanocomposites, except for tensile strength, are more favorable than those of unmodified CNT. Tensile strength depends on the length of the CNT. Acid modification reduced the length of CNT. Raman spectrums also verified that acid modification destroyed the structure of CNT. SEM microphotographs demonstrate that acid-modified CNT exhibits better dispersion than unmodified CNT in DGBEA-PSSQ. Acid-modified CNT/DGEBA-PSSQ nanocomposites show lower electrical conductivity than unmodified CNT/DGEBA-PSSQ nanocomposites. Aggregated CNT might provide pathways for electron transfer, that increasing the electrical conductivity.