Differential Thermal Analysis and Calorimetry of Waxes
Thermal analysis of waxes used in dentistry has been conducted using simple techniques such as differential plots from cooling curves1,2 and comparison of the temperature of a wax and a silicone oil on cooling.3 More recently the authors4 reported a differential thermal analysis (DTA) study of dental waxes and their components. Infrared absorption studies of the phase transitions in waxes has been published by Martin, Johnson, Cannon, and O’Neal5 and by Ludwig6, and the latter showed the orthorhombic-hexagonal and hexagonal-liquid transitions of paraffin wax could be determined from the infrared spectra and an analysis of paraffin and microcrystalline waxes in mixtures could be determined by this method. Lange and Jochinke7, Lorant8, Kawasaki, Komizu, and Uchida9, and Currell and Robinson10 reported differential thermal analysis of a variety of commercial waxes and esters. Lange and Jochinke7 concluded the height and position of the peaks were influenced by many factors and thus quantitative analysis of waxes by DTA in most instances was not possible. The later study by Currell and Robinson10 showed microcrystalline and polyethylene waxes were characterized by an endotherm at 475 to 480° C and the area of this peak could be used to estimate the amount of these waxes in mixtures; the melting curves were not unequivocal but for a few exceptions the paraffin waxes had at least two endothertns and the microcrystalline and polyethylene waxes only one.
KeywordsDifferential Thermal Analysis Melting Transition Orthorhombic Lattice Calorimetric Curve Infrared Absorption Study
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