Complex isothermal crystallization and melting behavior of Nylon 6 nanoclay hybrids

The complex crystallization and melting behavior of neat Nylon-6 and two Nylon-6-nanoclay hybrids with different montmorillonite concentration was studied using several experimental techniques. The differential scanning calorimetry (DSC) traces were taken as a reference and experiments were made at several isothermal crystallization temperatures followed by linear heating. The results, depending on the crystallization temperature, indicated two sequences of melting for neat Nylon-6 and four for the nanoclay hybrids. After isothermal crystallization at low temperatures, neat Nylon-6 behaved different from the hybrids, however, after high crystallization temperatures there was a common melting behavior for all samples. Molecular orientation, molecular weight, and nanoclay concentration were sequentially considered in order to determine the origin of the regimes behavior in the DSC traces. Molecular weight was found as the main cause of the thermal behavior with a minimum influence of molecular orientation and nanoclay concentration. X-ray diffraction measurements indicated the formation of asymmetric gamma and incomplete alpha and gamma crystalline structures as a result of the nanoclay presence. These last structures were called truncated. Modulated melting was useful to clear mechanisms and corroborated the similar behavior for all three samples after isothermal crystallization at high temperatures. A melting mechanism was proposed on the basis of the previous behavior which involved the evolution of a quiescent low concentration morphology. This last was associated with crystallization of nonbounded macromolecules.