Dynamic-mechanical thermoanalysis test as a high-performance alternative for accelerated freeze-thaw stability testing: a case study of O/W emulsions.

The main objective of this work was to evaluate the performance of recently developed dynamic-mechanical thermoanalysis (DMTA) test as a rapid rheological alternative to conventional freeze-thaw cycling for accelerated stability testing of oil-in-water (O/W) emulsions. The rational for this approach was reducing the time needed for product and process development and optimization, potentially through shortening the time needed for stability evaluation, in order to keep the pace with high formulating turnover imposed by increasing demands for placing products on the market, that is, to facilitate decision making in R&D and QC settings. Six model O/W emulsions were designed, rheologically characterized (continuous rotational and oscillatory tests), and subjected to stability evaluation through freeze-thaw test in stability chamber and DMTA tests using an air-bearing rheometer. Investigated samples were characterized by favorized shear-thinning flow behavior with yield point. The elastic behavior dominated the viscous one in the LVE region of amplitude sweeps, as well as in the frequency sweeps of used frequency range. Statistical method comparison studies demonstrated that the results obtained by freeze-thaw test, routinely used for accelerated stability testing of emulsions, were in good accordance with those obtained with DMTA tests, whereas the time needed for stability assessment was significantly reduced (2-6 h versus 12 days). In summary, DMTA test proved to be an expeditious alternative for accelerated freeze-thaw stability testing of O/W emulsions, with great promise in new product development and optimization (R&D), as well as in determination of borderline product batches status (QC).