ABSTRACT:The physical aging of the epoxy network consisting of a diglycidyl ether of bisphenol A, m-xylylenediamine, and polyetherimide was studied by differential scanning calorimetry. The glass transition temperature and the variation of the specific heat capacities have been calculated using the method, based on the intersection of both enthalpy-temperature lines for glassy and liquid states. The apparent activation energy (E H ) was calculated using a single method that involved separate temperature and excess enthalpy dependency. All calorimetric data were compared with those obtained for the epoxy network without thermoplastic.
ABSTRACT:The relaxation kinetic of the epoxy network diglycidyl ether of bisphenol A (BADGE n ϭ 0) and mxylylenediamine (m-XDA) was analyzed from DSC experimental data, using different theoretical models. Based on a Petrie model, which involved separate contributions of temperature and structure, three characteristic parameters were calculated: a preexponential factor A, an apparent activation energy E H , and a parameter C, which indicate the dependency of relaxation time on structure. This model allowed us to calculate the relaxation function at different ageing temperatures. Another method used to study a relaxation kinetic was the Kovacs-Hutchinson model, which takes into account the dependency of the relaxation time on temperature and structure. The last model used was a two-parameter equation from Williams-Watts, where the relaxation time is independent of temperature. Using data of characteristic times a master curve for the relaxation function was obtained.
ABSTRACT:The relaxation kinetics of the epoxy network diglycidyl ether of bisphenol A (n ϭ 0) and m-xylylenediamine were studied with differential scanning calorimetry experimental data with a shift peak model. Nonlinear parameters were calculated with aging experiments. The nonexponential parameter and the apparent activation energy were found from intrinsic cycles. Adam-Gibbs theory was used to provide a molecular interpretation based on the enthalpy relaxation. Different assumptions of the variation of specific heat capacity (c p ) were used to determine the macroscopic molar configurational entropy of the system.
ABSTRACT:The reaction of glutaraldehyde with primary amino groups of chitosan produces covalent crosslinking in a matricial microsphere formulation. The influence of the crosslinking times on the calorimetric parameters (glass transition temperatures, enthalpy, and endothermic peak) of the system clorhydrate of chitosan/glutaraldehyde (1,5-pentanedial) was studied using differential scanning calorimetry in dynamic mode. Using KissingerЈs method, the activation energies for the water remaining process were obtained without a precise knowledge of the reaction mechanism from the experimental endothermic peaks.
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