Probing the early stages of thermal fractionation by successive self-nucleation and annealing performed with fast scanning chip-calorimetry

The thermal fractionation kinetics of a linear low-density polyethylene (LLDPE) during Successive Self-Nucleation and Annealing (SSA) is investigated by fast scanning chip-calorimetry (FSC), by systematically varying the holding times (ts) at each fractionation temperature (Ts). The range of explored fractionation times spans four orders of magnitude, from 0.001 to 10 s. Discernible thermal fractions are already detected in the very early stages of the process, at ts shorter than one second. As ts increases, the melting endotherm after SSA indicates a progressive lamellar thickening and narrowing of the thicknesses distribution of the various crystalline fractions. The largest variations are observed for the families of crystals containing the longest crystallizable sequences, which also undergo a change of their relative content as a consequence of self-nucleated crystallization at Ts. The quality of the thermal fractionation obtained in 10 seconds with FSC is equivalent to that of conventional differential scanning calorimetry SSA (ts = 300 s).