Revista de Engenharia Química e Tecnologia de Processos
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The structure of Isotactic Polypropylene Crystallized from the Melt

Sokainah Rawashdeh and Ismail Al-Raheil

The melting behavior of isotactic polypropylene was studied in the hot stage mounted on polarizing optical microscope supported by photomonitor. Over a wide range of crystallization temperature there are two main types of spherulites, α and β spherulites for this polymer α spherulites may exist in three forms α₁, α₂ and mixed of α₁ and α₂. The α₂-form can be obtained at high crystallization temperature above 145°C and α₁ can be observed at low crystallization temperatures below 132°C. The mixed α-spherulites can be obtained between 132°C and 145°C. However, the β-phase form small proportion of the total phase not more than 15% and usually exist when the crystallization temperature below 132°C. If the sample crystallized from the melt it shows usually two melting peaks. However, when the temperature of the sample was increased to crystallize in a second step at higher temperature it shows two melting peaks and if the second step of crystallization was very close to melting point it shows only one single peak, since the reorganization of crystals process will be stopped completely.