Differential Thermal Analysis of Commercial and Dental Waxes

¹ School of Dentistry, University of Michigan, Ann Arbor, Michigan

Transition temperatures from 20° to 200°C. have been determined for a variety of waxes and combinations of waxes by differential thermal analysis (DTA). Additions of carnauba wax to paraffin wax influenced the transitions of the latter when the former was present in large concentrations; 75 percent carnauba in paraffin wax lowered the melting transition about 1.5°C. Additions of 25 percent paraffin to carnauba wax decreased the melting transition of the latter about 5° to 6°C.; further increase in paraffin wax above 25 percent did not alter the melting transition associated with carnauba wax. No influence on the transitions was observed with combinations of paraffin and beeswax, although 50 percent or more of paraffin wax completely suppressed the transition associated with beeswax.

The major influence of small additions of carnauba to paraffin wax was a pronounced increase in the melting range; addition of beeswax to paraffin wax did not produce comparable results.

The three transition temperatures of paraffin wax have been interpreted in terms of crystal structure from published radiographic values. The two solid-solid transitions at 32° and 35°C. have been interpreted to represent the transformation of some hydrocarbons from hexagonal close-packed to orthorhombic structure and others from hexagonal to monoclinic or triclinic structure.

Thermograms for dental waxes were interpreted in terms of those obtained for natural waxes. It was observed that DTA would not be suitable for quantitative analysis and, at times, questionable for qualitative analysis of waxes. Thermograms of natural and one synthetic wax were discussed in terms of their possible use in dental applications.

Melting transitions from DTA were in good agreement with capillary tube melting points, and the solid-solid transition showed a general relationship to discontinuities in thermal expansion curves.