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Autori: P.J. van Ekeren, L.D. Ionescu, V.B.F. Mathot and J.C. van Miltenburg.
Editorial: Thermochim. Acta, 391, p.185-196, 2002.
Specific heat capacities of a homogeneous ethylene-1-butene copolymer were measured by adiabatic calorimetry in the temperature range from 7 to 406 K (stepwise heating after cooling at rates in the range from 6 to 25 K h-1, averaged heating rates 5 – 34 K h-1). The glass transition is centred around 224 K. With devitrification also melting sets in. The crystallinity of the polymer was calculated (within the two-phase model) as a function of temperature using two sets of reference data (one for linear and branched polyethylenes (BPEs), and the other for strictly linear polyethylene (LPE)) for completely crystalline and for completely amorphous material. On heating, the mass fraction crystallinity decreased from 0.30 to 0 in the temperature range from 220 to 360 K, confirming earlier differential scanning calorimetry (DSC) heat capacity measurements. During the stabilisation periods in the melting region negative temperature drifts, related to endothermic effects caused by melting, were observed below 325 K. However, in the temperature range from 325 K up to the end melting temperature, 360 K, positive drifts were measured, reflecting exothermic effects which are attributed to recrystallisation phenomena.
Cuvinte cheie: Adiabatic calorimetry, Crystallinity, Ethylene-1-butene copolymer, Heat capacity, Polyethylene, Recrystallisation, Relaxation