Study Of Carbon Foams From Epoxy-modified Cyanate Ester Resin

Cyanate resin with self-bubbling characteristics can be employed as a precursor to prepare carbon foams.However,the method for preparing carbon foams confronted the problems like high cost,easy cracking and low percentage of open cell.In this paper,epoxy-modified cyanate ester resins were used to prepare carbon foams by performing a series of procedures including casting molding and atmospheric-pressure carbonization.In addition,structural changes of the epoxy-modified cyanate ester resins were studied during heat treatment process.Furthermore,structures and properties of resultant carbon foams were investigated.Pyrolysis behaviors of the epoxy-modified cyanate ester resins were studied by FT-IR,SEM,Raman,TGA,and XRD.The results show that carbon foams with good shapes can be directly prepare by pyrolysis of the resin,due to its self-foaming characteristics at high temperatures.The thermal stability of the resin decreases initially and then increases with the increase of epoxy content.The resin has an initial decomposition temperature of 309 ?,a terminal pyrolysis temperature of 613 ? and a maximum decomposition rate temperature of 407 ? when the epoxy content is 30%.Furthermore,the ordered microcrystalline structure of resultant pyrolysis product is improved with increasing pyrolysis temperature.Structures and properties of the carbon foams,prepared at 900 0C by pyrolysis of the resin with different epoxy contents,were studied using SEM,XRD,electronic mechanical universal testing machine,four-point probe,and laser thermal conductivity meter.Results show that the ordered microcrystalline structure of resultant carbon foams is improved,and their pore size,porosity and percentage of open cell increase initially,then decrease,and increase again with addition of epoxy increasing from 0%to 60%.However,their properties including bulk density,thermal conductivity,mechanical strength,electrical conductivity are exactly the opposite,and they reach the extreme value with addition of 30%and 50%,respectively.When the epoxy content is 30%of resin,the bulk density,thermal conductivity,mechanical strength and electrical conductivity reach the minimums of 0.243 g/cm,0.212 W/mK,1.31 MPa and 4.98 S/cm,respectively.While the epoxy content is 50%of resin,thermal conductivity,mechanical strength and electrical conductivity reach the maximums of 0,541 W/mK,5.70 MPa and 14.07 S/cm,respectively.Meanwhile,the char yield of the resin varies from 33.88%to 16.15%with addition of epoxy increasing from 0%to 60%after carbonization at 1000 ?.The influences of high-temperature treatment on the structures and properties of carbon foams were investigated by tuning heat treatment temperature.Results show that the high-temperature treatment has great effect on the structures and properties of resultant carbon foams.As the temperature increases,the ordered microcrystalline structure of resultant carbon foams is improved,thus its graphitization degree increases.In addition,their properties including bulk density,opening rate,thermal conductivity,mechanical strength and electrical conductivity increase with increasing treatment temperature.When the temperature varies from 1100 ? to 1800 ?,the bulk density,open cell,electrical conductivity,and compressive strength of the carbon foams,prepared with an epoxy content of 30%,increase from 0.214 g/cm3 to 0.219 g/cm3,70.29%to 71.48%,5.01 S/cm to 35.90 S/cm,and 1.05 MPa to 1.56 MPa,respectively.