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Crystallization from the melt of nylon 66 in the presence of carbon fiber, aramid fiber, or nucleating agent was studied using differential scanning calorimetry (DSC) and hot stage microscopy. The use of the nucleating agent resulted in an increase in crystallization rate and a decrease of induction time under both isothermal and nonisothermal conditions. The fibers were found to behave like a giant nucleating site producing a uniform transcrystalline layer having morphology and crystallization kinetics different from those of the bulk matrix. The influence of the cooling rate on the process of nonisothermal crystallization was analyzed, and the values of activation energy, calculated from the cooling rate—crystallization temperature relationship, appeared to be higher for the nucleated and for the reinforced nylon compared with that of the neat nylon 66. This implied that the presence of fibers or nucleating agent led to the development of a more ordered structure, which required a larger amount of energy for crystallization.

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