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DSC was used to study the crystallization and melting behaviors of wax and wax-oil systems. The samples were heated from -30 to 140°C at a rate of 5°C/ min. After holding at 140°C for 5min, the samples were allowed to crystallize upon cooling at 5°C/min from the melt of 140°C to - 30°C. The samples were heated again from -30°C to 140°C at the same rate as cooling. Figure 2.3 shows the cooling and heating cycles for an oil-wax gel system. The parameters such as the crystallization temperature, T_c, melting temperature T_m and the enthalpies of crystallization ΔH_c (J/g) and melting ΔH_m (J/g) of the wax – oil systems were obtained from DSC thermograms. In addition, the starting crystallization temperature T_c,i and final melting temperature Tm,f are used in the analysis. The relative crystallinity of the samples during cooling or heating process, X_c (%), can be calculated using enthalpy of crystallization or enthalpy of melting value of 100 % crystalline polyethylene wax (PE).

The relative crystallinity X_c (%) from cooling or from melting is calculated via either equation:

(2.1)

Figure 2.3 DSC thermogram of an oil-wax gel system.

Figure 2.4 Lipstick sample preparation for SEM investigation.

(2.2)

where ΔH_c0 and ΔH_m0 are the enthalpies of crystallization and melting for 100% PE wax, respectively and w is the weight fraction of the PE wax in the oil-wax system.