Study of petrolatum structure: explaining its variable rheological behavior

The rheological properties of petrolatum are dependent on both temperature and thermal history. How this thermal dependency can be explained is unclear. In the past it has been suggested that the structure of petrolatum consists of a three-dimensional crystalline network. This has been established using old microscopic techniques only. Therefore a study on the microstructure of petrolatum was conducted using rheometry, DSC, pulsed NMR, polarized light microscopy and synchrotron X-ray. The combination of these techniques show that petrolatum is composed of 21% solid material at room temperature. This consists of partly crystalline lamellar sheets which are packed in stacks. The occurrence of these lamellar sheets is temperature dependent and the number of lamellar stacks is dependent on thermal history. It was shown that rheological differences in petrolatum can be explained by the number of lamellar stacks present, where more lamellar stacks result in more rigid petrolatum.