| Fractionated palm stearin was hydrogenated at different degrees in order to solve the problem of greasy appearance as a renewable candle material. The crystallization behavior of hydrogenated palm stearin was studied by differential scanning calorimetry, nuclear magnetic resonance, X-ray diffraction and polarized light microscopy,and the chemical compositions of palm stearin and hydrogenated palm stearin were compared. The results showed that in the first stage of hydrogenation, part of oleic acid and linoleic acid rapidly converted to trans-oleic acid, which promoted the formation of α type crystal and its transformation to β′ type crystal; though the solid fat content of hydrogenated palm stearin below 45℃ was higher than that of palm stearin, its melting point reduced; in the second stage of hydrogenation, plenty of oleic acid and trans-oleic acid converted to stearic acid, thereby the content of components with high melting point increased,and the solid fat contents at all temperatures and the melting point were also higher than those of palm stearin although the crystal was still β′ type. The low melting point peak disappeared after palm stearin was hydrogenated for 15 min, and the greasy appearance of candle disappeared as well; when hydrogenation time was more than 20 min, the crystallization peak became sharp and nar row, and the cracking of candle appeared. Therefore, palm stearin hydrogenated for 15-20 min was suitable for candle material. |
