Manufacture of most of epoxy resins implies that cure needs to be carried out under pressure. Due to the significance of knowing the influence of the pressure factor in cure kinetics, cure shrinkage of a stoichiometric epoxy-amine system was measured using a pressure-volume-temperature (PVT) analyzer. Recording the specific volume change in the range of temperature from 100 to 180 °C and a pressure of 200 bar we could model the cure kinetics. The Runge-Kutta method was applied to obtain the kinetic constants of the cure reaction. In addition, using the differential scanning calorimeter (DSC) for measurements of 1 bar and the PVT analyzer for pressures of 200, 400, and 600 bar, we also model the kinetic constants as a function of pressure. The results obtained show that the effect of the temperature on the kinetic constants is higher than the effect of pressure. Therefore, both PVT and DSC are complementary techniques to describe the full range of cure kinetic process of epoxy mixtures. 相似文献
Scientometrics - With today’s research production and global dissemination, there is growing pressure to assess how academic fields foster diversity. Based on a mathematical problem/solve... 相似文献
The organization of rDNA-containing chromatin was analysed by transmission electron microscopy after treatment of cultured human lymphocytes with 5-azacytidine (ACR) or 5-azadeoxicytidine (AdCR). The number of observed acrocentric chromosomes with satellites was significantly increased after treatment with low doses of ACR or AdCR during the last 24 h of culture, whereas with exposures during the last 7 h the number remained normal. The results suggest that the incorporation of ACR and AdCR in the early period of the S-phase may have reverted the non-satellized to satellized chromosomes. The cytidine analogues may have become more visible during secondary constriction thus changing the NOR structure leading to an increased number of satellized chromosomes. 相似文献
Nanocomposites of cassava starch reinforced with waxy starch nanocrystals were prepared. They showed a 380% increase of the rubbery storage modulus (at 50 °C) and a 40% decrease in the water vapor permeability. X‐ray spectra show that the composite was more amorphous than the neat matrix, which was attributed to higher equilibrium water content in the composites. TGA confirmed this result and its thermal derivative suggested the formation of hydrogen bonding between glycerol and the nanocrystals. The reinforcing effect of starch nanocrystals was attributed to strong filler/matrix interactions due to the hydrogen bonding. The decrease of the permeability suggests that the nanocrystals were well dispersed, with few filler/filler interactions.