A Study of Annealing of Poly(ethylene-co-octene) by Temperature-Modulated and Standard Differential Scanning Calorimetry

Abstract

Annealing of poly(ethylene-co-octene)s with 12-25 mass % 1-octene for 2.5-5250 min was carried out by approaching the annealing temperature through cooling at 10 K min -1 . Above the annealing temperature, primary crystallization was initiated. The analysis of the samples was performed during and after the annealing with temperature-modulated and standard differential scanning calorimetry, respectively (TMDSC and DSC). The irreversible annealing process consists of two different, exothermic events which are secondary crystallization and reorganization. The two processes were separated and quantitatively expressed by exponential laws with relaxation times of the order of 5 and 100 min, respectively. The two stages of crystallization and the reorganization produce a temperature-dependent, arrested, metastable, global structure of crystals and amorphous defects. Changing the annealing time can only partially compensate for changes in annealing temperature. Furthermore, TMDSC reveals a small amount of fully reversible melting. This reversible melting exists in addition to the well-known equilibrium of gauche-trans point defects in the crystal. Overall, there are thus at least five latent-heat contributions to the apparent heat capacity between the glass and melting transitions: primary and secondary crystallization, reorganization, locally reversible melting, and the gauche-trans equilibrium. For quantitative analysis of these latent-heat effects, they must be separated from the heat capacity of the melt, extrapolated from above the melting temperature, and the vibrational heat capacities of the crystal or glass.

Thermal properties of poly(vinyl alcohol)–solute blends studied by TMDSC

“…substantial nonreversing contribution to melting of pure polymers is typically expected for high quality crystals with T m near their equilibrium value. 9,[11][12][13] For the blends studied here, the opposite trend is observed, since the lower the T m of PVA in the blend, the higher the contribution of nonreversing PVA crystal melting. In semicrystalline polymers, crystallites are embedded in an amorphous matrix, and individual chains transverse consecutively amorphous and crystalline regions.…”

“…Thus, high quality crystals with T m near its equilibrium value are expected to exhibit substantial nonreversing melting. 9,[11][12][13] Nonreversing endotherms may also be observed due to slow melting kinetics occurring even during the zero heating rate part of the temperature modulation cycle. 13 Here we present a thermal analysis study of blends of poly(vinyl alcohol) (PVA) with a pharmaceutical substance, buflomedil pyridoxal phosphate (BPP).…”

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

“…This can optimize poor crystallographic structures of lamellar overgrowth and granular domains to a limited extent, as revealed by Figure 4b and DSC measurements. 39,41 The melting of this part of optimized crystallites can be accumulated at slightly higher temperatures, leading to the so-called low endotherm. The low endotherm is just a local perturbation of the master curves both for crystallization and for melting, so it may not be attributed to the amorphous entropy loss only; 39 otherwise the subsequent cooling curves at lower temperatures, away from the annealing temperature, should show a dependence on the annealing time rather than a convergent tendency.…”

Multiple shape-memory behavior and thermal-mechanical properties of peroxide cross-linked blends of linear and short-chain branched polyethylenes

“…First heating runs for all examined blends exhibit a minimum followed by a maximum in the temperature range between approx. 0 and 70°C caused by annealing at room temperature during storage of prepared samples, as it was shown for uncross-linked EOCs especially with high degree of branching [20]. Since, this phenomenon complicates melting thermograms which are already complex enough, only second heating runs were used for detailed analysis of melting behavior.…”