Preparation of spherulites from amylose-palmitic acid complexes

We conducted a systematic study of the formation of spherulites from amylose-palmitic acid complexes. The independent variables included final heating temperature, intermediate quench temperature, final quench temperature and cooling rates. Spherulites were characterized by different techniques: optical microscopy, scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, transmission electron microscopy and resistant starch content. Three distinct types of spherulite morphology were observed: spherical, sintered ("snowball") and torus/disc shaped. Spherical-shaped particles were formed at higher endpoint heating temperatures and exhibited mixed B+V-type XRD patterns. Torus-shaped spherulites formed from samples heated to 140 °C followed by slow cooling, and exhibited V-6_I type XRD patterns. Resistant starch estimated for spherulites formed by heating to 180 °C followed by cooling to 40 °C at 1 °C/min vs. those formed by heating to 140 °C, cooled to 90 °C at 1 °C/min then to 40 °C at 0.04 °C/min was 28% and 39%, respectively. Morphology of the amylose-PA spherulites after resistant starch determination for spherical spherulite shows distinct pores and uneven surface texture. In contrast, the torus-shaped spherulites were degraded with evidence of recrystallization.