SynopsisVariation of the epoxy/curing agent ratio for a system containing a diglycidyl ether of bisphenol-A (DGEBA) and a mixed aromatic amine was found to have a significant effect on the cure kinetics and final dynamic mechanical properties of both the neat resin and glass reinforced epoxy. For a partial B-stage cure to an ultimate C-stage cure, optimum cure temperatures were obtained as a function of stoichiometry. For the ultimately cured (C-stage) resin, the molecular weight between crosslinks ( M , ) passed through a minimum, and both the glass transition temperature ( T,) and a secondary (sub-T,) transition passed through a maximum at the stoichiometric ratio. In addition, the activation energy of the ultimately cured resin passed through a maximum at or near the stoichiometric ratio for both the Tg and sub-T, transitions.
SynopsisVariation of the epoxy/curing agent ratio by as much as +lo wt % from the stoichiometric ratio for a system containing a diglycidyl ether of bisphenol-A (DGEBA) and a mixed aromatic amine was found to have a significant effect on the cure kinetics as determined by dynamic mechanical measurements. A sample preparation technique was developed for monitoring the cure of glass reinforced epoxy in flexure. Shear measurements were also made on the neat resin. From gel time flexural data, the activation energy of cure passed through a maximum at the stoichiometric ratio of epoxy/amine for a glass cloth composite. In shear for the neat resin, a minimum was observed. By considering the curing of the mixed system to follow third-order kinetics, overall reaction rate constants were estimated after the gel point.
Eight samples from different areas of stretch-blow-molded poly(ethylene terephthalate) [PET] bottles, including a PET resin control, were tested by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The glass transition temperature (Tg) was found to linearly decrease about 6"C from zero to 45 percent initial crystallinity. Measurements of T c (crystallization temperature, DSC) and film tension modulus (TMA) were related to crystallization rate during stretch-blow-molding. The TMA linear coefficients of thermal expansion and shrinkage were shown to be important for blow-molding temperature control.
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