An investigation into the melting behavior of binary mixes and solid dispersions of paracetamol and PEG 4000.

The melting behavior of paracetamol and polyethylene glycol (PEG) 4000, both individually and as binary systems, has been studied using differential scanning calorimetry. The appearance of the PEG peaks was shown to be highly dependent on scanning rate, with evidence for the existence of once-folded and extended chain forms being noted at slower scanning speeds. The melting peak of paracetamol was found to be profoundly influenced by the presence of the PEG 4000; when observed at all, the endotherm became broader and occurred at a lower temperature on mixing with the polymer. The thermal behavior of the binary mixes was again highly dependent on scanning rate, with faster rates leading to the appearance of the paracetamol peak at lower concentrations. The mixes were then thermally cycled to mimic production of solid dispersions, showing that the temperature cycling of the PEG 4000 could result in binary melting with the paracetamol peak disappearing. The interpretation of these results in terms of the characterization of PEG solid dispersions is discussed.