Temperature modulated DSC of irreversible melting of nylon 6 crystals

A new method is presented to analyze the irreversible melting kinetics of p olymer crystals with a temperature modulated differential scanning calorime try (TMDSC). The method is based on an expression of the apparent heat capa city, <(Delta C)over tilde>e(-i alpha)=mc(p)+i(1/omega)F-T', with the true heat capacity, mc(p), and the response of the kinetics, F-T'. The present p aper experimentally examines the irreversible melting of nylon 6 crystals o n heating. The real and imaginary parts of the apparent heat capacity showe d a strong dependence on frequency and heating rate during the melting proc ess. The dependence and the Cole-Cole plot could be fitted by the frequency response function of Debye's type with a characteristic time depending on heating rate. The characteristic ti me represents the time required for the melting of small crystallites which form the aggregates of polymer crystal s. The heating rate dependence of the characteristic time differentiates th e superheating dependence of the melting rate. Taking account of the relati vely insensitive nature of crystallization to temperature modulation, it is argued that the 'reversing' heat flow extrapolated to omega --> 0 is relat ed to the endothermic heat flow of melting and the corresponding 'non-rever sing' heat flow represents the exothermic heat flow of re-crystallization a nd re-organization. The extrapolated 'reversing' and 'non-reversing' heat f low indicates the melting and re-crystallization and/or re-organization of nylon 6 crystals at much lower temperature than the melting peak seen in th e total heat flow.