Nanocomposite materials were prepared from an elastomeric poly(hydroxyoctanoate) (PHO) latex asa fully amorphous or semi-crystalline matrix using a colloidal suspension of hydrolyzed cellulose whiskers as natural and biodegradable filler. After stirring, the preparations were cast and evaporated. High performance materials were obtained from these systems, preserving the natural character of PHO, Interfacial phenomena were assumed to be noticeable owing ro the high specific area of this filler. Dynamic mechanical analysis was performed on these systems to test the influence of the interphase on the molecular mobility of the amorphous phase. To quantify the distance away from the surface at which the molecular mobility is restricted, a physical model was used to predict the mechanical loss angle. This allows removal of the filler reinforcement effect keeping only the interfacial effect. It was shown that the local motion at the filler-matrix interface of amorphous PHO chains is strongly affected when an amorphous PHO was used as the matrix. No significant change was observed when a semi-crystalline PHO was used as the matrix. This result was ascribed to a possible trancrystallization phenomenon of semi-crystalline PHO in contact with cellulose whisker surface, which prevents any contact between amorphous PHO chains and filler surface.