M. Kotani et al. /Composites Science and Technology 62(2002 )2179-2188 Table I 8.0 Appearances of isolated pyrolyzed products of PVs up to various Temp.(K) 6.0 Transparent liquid(100 cP) Transparent viscous liquid 4.0 anslucent rubbery solid, non porous 3.0 Transparent glassy solid, non porous Yellowish glassy solid, non porous 0 Brownish glassy solid, non porous 1.0 0.0 measured accurate density for a light polymer-pyrolyze intermediate by picnometry, it could be apparently Temperature /K shown that the densities were increased almost linearly Fig 3. Gas evolution behavior of PVS as a function of temperature with temperature. Thus, the volumetric residue showed similar behavior to the mass change. where drastic TGA curves for PVS at various heating rates are volumetric shrinkage occurred between 600 and 700 K shown in Fig. 4. Clear effect of heating rate was seen in and most of volume change had finished below 700 K. ceramic yield, where it was improved from 32%(600 K/ Volumetric yield of the polymer after pyrolysis up to h)to 37%(10 K /h). It might be owing to the increase of 1473 K was estimated to be 11% time for cross linking at around 700 K [25]. Another As an unavoidable negative influence on matrix mor- noticeable feature appeared in the mass degradation phology, gas evolution behavior during pyrolysis was behavior of early stage of pyrolysis(400-600 K). It monitored as a function of temperature in Fig 3. Each increased as the heating rate was slowed down. There point represents total amount of gases evolved from 100 fore, it was considered that the ceramics yield of PVs K below to representative temperature As gas evolution vas not so influenced by the amount of loss of low was negligible below 600 K, mass degradation detected molecular fraction, but the degree of cross linking below 600 K was proved to be due to the evaporation of Thus, sufficient time for cross linking was quite impor low molecular oligomers [26]. PVS heated up to more tant for efficient consolidation. than 400 K, those fractions might volatilize from a cru According to these results, it was approved that main cible and deposited on the cool part of the heating decomposition of PVs occurred between 600 and 700 K apparatus. Gas evolution was drastically increased from with great amount of gas evolution and mass degrada 600 to 700 K. This event would be related with the tion. As inorganization was highly proceeded, the poly- fragmentation of polymer structure. It was also sug- mer would turn poor of fluidity above 700 K Since fiber gested by a big endothermic peak detected in Dta distribution and matrix homogeneity in a composite curve. Then, gas evolution gradually declined along cannot be improved after the polymer has lost fluidity with temperature fiber alignment, stacking of prepreg sheets and shaping 1000 1500 Temperature /K Temperature /K Fig. 2. Densities and volumetric residues of Pvs as a function of temperature. Fig 4. TGA curves for PvS at various heating rates in Armeasured accurate density for a light polymer-pyrolyzed intermediate by picnometry, it could be apparently shown that the densities were increased almost linearly with temperature. Thus, the volumetric residue showed similar behavior to the mass change, where drastic volumetric shrinkage occurred between 600 and 700 K and most of volume change had finished below 700 K. Volumetric yield of the polymer after pyrolysis up to 1473 K was estimated to be 11%. As an unavoidable negative influence on matrix mor￾phology, gas evolution behavior during pyrolysis was monitored as a function of temperature in Fig. 3. Each point represents total amount of gases evolved from 100 K below to representative temperature. As gas evolution was negligible below 600 K, mass degradation detected below 600 K was proved to be due to the evaporation of low molecular oligomers [26]. PVS heated up to more than 400 K, those fractions might volatilize from a cru￾cible and deposited on the cool part of the heating apparatus. Gas evolution was drastically increased from 600 to 700 K. This event would be related with the fragmentation of polymer structure. It was also sug￾gested by a big endothermic peak detected in DTA curve. Then, gas evolution gradually declined along with temperature. TGA curves for PVS at various heating rates are shown in Fig. 4. Clear effect of heating rate was seen in ceramic yield, where it was improved from 32% (600 K/ h) to 37% (10 K/h). It might be owing to the increase of time for cross linking at around 700 K [25]. Another noticeable feature appeared in the mass degradation behavior of early stage of pyrolysis (400–600 K). It increased as the heating rate was slowed down. There￾fore, it was considered that the ceramics yield of PVS was not so influenced by the amount of loss of low molecular fraction, but the degree of cross linking. Thus, sufficient time for cross linking was quite impor￾tant for efficient consolidation. According to these results, it was approved that main decomposition of PVS occurred between 600 and 700 K with great amount of gas evolution and mass degrada￾tion. As inorganization was highly proceeded, the poly￾mer would turn poor of fluidity above 700 K. Since fiber distribution and matrix homogeneity in a composite cannot be improved after the polymer has lost fluidity, fiber alignment, stacking of prepreg sheets and shaping Table 1 Appearances of isolated pyrolyzed products of PVS up to various temperatures Temp. (K) Appearance r.t. Transparent liquid (100 cP) 583 Transparent viscous liquid 603 Transparent gel 623 Translucent rubbery solid, non porous 653 Transparent glassy solid, non porous 673 Yellowish glassy solid, non porous 693 Brownish glassy solid, non porous Fig. 2. Densities and volumetric residues of PVS as a function of temperature. Fig. 4. TGA curves for PVS at various heating rates in Ar. Fig. 3. Gas evolution behavior of PVS as a function of temperature. 2182 M. Kotani et al. / Composites Science and Technology 62 (2002) 2179–2188