Dynamics of Polymorphic Transformations in Palm Oil, Palm Stearin and Palm Kernel Oil Characterized by Coupled Powder XRD-DSC

The in situ polymorphic forms and thermal transitions of refined, bleached and deodorized palm oil (RBDPO), palm stearin (RBDPS) and palm kernel oil (RBDPKO) were investigated using coupled X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Results indicated that the DSC onset crystallisation temperature of RBDPO was at 22.6 degrees C, with a single reflection at 4.2 angstrom started to appear from 23.4 to 17.1 degrees C, and were followed by two prominent exothermic peaks at 20.1 degrees C and 8.5 degrees C respectively. Further cooling to -40 degrees C leads to the further formation of a beta'polymorph. Upon heating, a of beta'->beta transformation was observed between 32.1 to 40.8 degrees C, before the sample was completely melted at 43.0 degrees C. The crystallization onset temperature of RBDPS as 44.1 degrees C, with the appearance of the a polymorph at the same temperature as the appearance of the first sharp DSC exothermic peak. This quickly changed from alpha-beta' in the range 25 to 21.7 degrees C, along with the formation of a small beta peak at -40 degrees C. Upon heating, a small XRD peak for the beta polymorph was observed between 32.2 to 36.0 degrees C, becoming a mixture of (beta'+beta) between 44.0 to 52.5 degrees C. Only the beta polymorph survived further heating to 59.8 degrees C. For RBDPKO, the crystallization onset temperature was 11.6 degrees C, with the formation of a single sharp exothermic peak at 6.5 degrees C corresponding to the beta' polymorphic form until the temperature reached -40 degrees C. No transformation of the polymorphic form was observed during the melting process of RBDPKO, before being completely melted at 33.2 degrees C. This work has demonstrated the detailed dynamics of polymorphic transformations of PKO and PS, two commercially important hardstocks used widely by industry and will contribute to a greater understanding of their crystallization and melting dynamics.