Solubility of erucamide (13-cis-docosenamide) in isotactic poly(propylene) and thermal behaviour of their blends

Differential scanning calorimetry studies, made on blends prepared by mixing in the melt, have demonstrated that crystallization of erucamide (13-cis-docosenamide) [H3C-(-CH2-)(7)-HC=CH-(-CH2-)(11)-CO-NH2]/isotactic poly(propylene (i-PP) blends results in separate crystals of the two components, rather than cocrystallization. For low content erucamide blends (less than 29%), two melting peaks for erucamide have been observed. They have been assigned to: i) erucamide crystals situated in the external surfaces of the i-PP and located forming globules, droplets or inclusions whose melting point appears at the higher temperature (Erucamide I); ii) erucamide crystals forming crystalline microdomains of erucamide, located either within the amorphous region of spherulites and/or in the amorphous regions which surround the spherulites (Erucamide II). The enthalpy of these crystals located in these regions, i.e. in the amorphous region of the spherulites and/or their surroundings, has been estimated. A good linear correlation has been found between the solubility of erucamide crystals in the amorphous region of i-PP spherulites and/or the surrounding region of the spherulites and their apparent melting enthalpy. Spherulite radial growth rates, G, for the different blends are lower than for the pure i-PP. They show a characteristic dependence on the erucamide content in the blend. This behaviour is in agreement with theoretical predictions for crystallization in immiscible blends. An additional feature, as an unambiguous test of the incompatibility, is the poor interfacial adhesion, which has been made clear from the large voids left on the fracture surface where the erucamide globules have separated from the matrix and from the smooth surfaces of the exposed erucamide globules. A model is proposed for erucamide/i-PP blends, which is able to explain quantitatively in detail all the thermal and morphological experimental data. (C) 1997 Elsevier Science Ltd.