高性能环氧树脂／碳纳米管复合物的热分析研究

THERMOANALYTICAL STUDIES OF HIGH PERFORMANCE EPOXY/CARBON NANOTUBE COMPOSITES

用差示扫描量热仪(DSC)、热失重分析仪(TGA)和动态力学热分析仪(DMTA)研究了多壁碳纳米管(MWNTs)/高性能4,4′-二氨基二苯甲烷四缩水甘油环氧树脂(TGDDM)/4,4′-二氨基二苯基砜(DDS)复合物的热性能.Kissinger和Flynn-Wall-Ozawa的非等温固化动力学研究发现,随着MWNTs含量的增加,复合物固化反应的活化能先减小后增大.TGA研究表明,MWNTs的添加对环氧树脂热稳定性影响很小.碳纳米管填充到TGDDM/DDS体系后,复合物的储存模量随着MWNTs含量的增加而增大,而玻璃化温度却随之减小.

Carbon nanotubes （CNTs） have outstanding characteristics including high mechanical properties, namelytensile strength and elastic modulus, and still remarkable flexibility, excellent thermal and electric conductivities, low percolation thresholds （loading weight at which a sharp drop in resistivity occurs） and high aspect ratios （length to diameter ratio, L/D）, while the latter provides the nanotubes with additional advantage over spherical fillers to obtain high property composites. Therefore, CNTs have the potential to act as a reinforcing filler of polymer matrices. Thetetraglycidyl-4,4＇- diaminodiphenylmethane （ TGDDM ） cured with 4,4＇- diaminodiphenylsulphone （DDS） and filled with graphite or carbon fibers are commonly used as a polymeric matrix in high performance composites employed in the aircraft and spacecraft industries. In present paper, multi-walled carbon nanotubes （MWNTs） as a nano-filler were incorporated in the TGDDM/DDS epoxy. The thermal properties of the composites were studied by differential scanning calorimetry （ DSC ）, dynamic thermal analysis （ DMTA ） and thermalgravitimetric analysis （ TGA ）. Inaddition,the dispersion of MWNTs in the epoxy was also investigated by scanning electron microscopy （SEM）. In DSC studies, Kissinger and Flynn-Wall-Ozawa （FWO） methods were used to study the nonisothermal cure kinetics of the MWNTs filled TGDDM/DDS composites at different heating rates. The activation energy （Ea） of cure reactions of the MWNTs filled epoxy composites was obtained by Kissinger and FWO methods. For all composites, the Ea obtained by Kissinger method was slightly less than that of FWO method. With the addition of MWNTs, the Ea of theepoxy composites decreased first and then increased with the increase of the MWNTs contents. These results showed that the incorporation of carbon nanotubes accelerated the cure reaction of the TGDDM/DDS epoxy at lower MWNTs content due to the interaction between the hydroxyl groups on the surface of nanotubes and the epoxy. However, due to the high surface energy of carbon nanotubes, the viscosity of MWNTs/epoxy composites increased at higher MWNTs content. Hence, the mobility of hydroxyl groups was hindered, and the reaction energy of composites increased with increasing MWNTs contents. The influence of carbon nanotubes on the thermal stability of the epoxy was studied by TGA. It is shown that MWNTs had little influence on the thermal stability of the cured epoxy. Thestorage modulus and glass transition temperature of MWNTs filled TGDDM/DDS were investigated by DMTA. It is seen that the storage modulus of TGDDM/DDS system was enhanced with the increasing of MWNTs content, that is, the modulus increased 6.3 % and 7.8 % at 1 wt% and 5 % MWNTs content, respectively. The glass transition temperature of the epoxy slightly decreased. Furthermore, the DMTA results of MWNTs/TGDDM/DDS composites were compared with that of carbon nanofibers （CNFs）/TGDDM/DDS composites. It was shown that the interactions between CNFs and epoxy were better those between that MWNTs and epoxy. The dispersion of carbon nanotubes in the epoxy was studied by SEM. The SEM results suggest that of MWNTs had poor dispersion in the cured epoxy. However, the radii of carbon nanotubes in the epoxy were greater than those of pure nanotubes. These results show the existence of interaction between carbon nanotubes and epoxy.