Hydroxypropyl methylcellulose (HPMC) formulated films: Relevance to adhesion and friction surface properties

Cellulose derivatives constitute one of the most dedicated polymers used in the production of film coatings (tablets, capsules …). The effect of the composition of hydroxypropyl methylcellulose (HPMC)-stearic acid films on the surface physico-chemical properties was investigated. Incorporation of stearic acid into HPMC films induces strong changes on surface structure, hydrophobic/hydrophilic character, adhesion and friction characteristics. The variations observed suggest an accumulation of stearic acid on film surfaces, resulting a decrease of its roughness and surface free energy. The nano-adhesion and nano-friction experiments were evaluated by using AFM/FFM, while the macro-adhesion and macro tribological studies were performed on tack test and pin-on-disk tribometer respectively. In all the cases, it was found that the hydrophobic character of stearic acid leads to decrease adhesion and friction at the two scales. The surface capillary force plays a key role in these properties. In addition, the study indicates the interplay of adhesion in friction property of HPMC films and the role of stearic acid as lubricant.