Scratch resistance (SR) of externally plasticized hydroxypropyl methylcellulose (HPMC) films intended for tablet film coatings was studied. Special attention was paid to effects of short-term aging and ultraviolet (UV) treatment on the SR properties of these films. Controlled scratching of the films was performed with a Lloyd LRX materials tester featuring a spherical steel tip. Scratch surface profiles were measured by scanning white light interferometry (SWLI). The influence of using an external plasticizer on the SR was studied by comparing scratch dimensions in non-plasticized films to samples plasticized either with glycerol or polyethylene glycol (PEG) 400. The study demonstrates that both the amount and type of plasticizer influences the SR of aqueous HPMC films. It also shows that SWLI can quantitatively evaluate the effect of plasticizer content and aging on the SR of pharmaceutical films. This knowledge could be used to optimize pharmaceutical film coating formulations.
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