The influence of thermal history on the physical behavior of poly(ethylene glycol) (PEG)

To investigate the influence of thermal history on the physical behavior of poly(ethylene glycol) (PEG), commonly used as a pharmaceutical excipient.

Rheological investigations together with SEM imaging and solid state analysis by XRPD and DSC were used to characterize PEG as starting material, as well as PEG:lactose monohydrate granules. For granulation experiments PEG 6000 was used and for further investigations of physicochemical properties, three M(w) of PEG (3000-10000) with different thermal histories obtained by melting the PEG followed by solidification with specific cooling rates.

More uniform granules were obtained when fast cooled PEG was used as binder. XRPD suggested similar crystallinity for the different M(w) and thermal history did not influence the results drastically. However, rheological analysis and DSC measurements indicated different melting behavior dependent on the M(w) of PEG. PEG 6000 and 10000 were affected by the thermal treatment where stepwise melting was observed with slower cooling rate probably due to increased formation of extended structures.

Increased cooling rate gives rise to increased randomness, more folded structure of PEG, which reflects in the outcome of the granulation process.