Cellulose microspheres bearing poly(ε-caprolactone) grafts of different molecular weights were investigated to evaluate the effect of graft length on the interfacial properties. Surface force and friction measurements were performed using an atomic force microscope in colloidal probe mode. The maximum interaction distance and adhesion is dependent on the temperature and the time in contact via a diffusion controlled mechanism. The effects are highest for the longer grafts, and molecular weight thresholds were found to lie between 21 and 34 kDa at 25 °C and between 9 and 21 kDa at 40 °C. The interpenetration of the graft into a matrix leads to "hidden length" contributions to adhesion, analogous to those in natural biocomposites. The nanotribology results display Amontonian behavior, and the friction force at zero applied load is higher at the graft-graft interface than for a bare cellulose sphere interacting with the graft. These results clearly demonstrate the benefits of the grafted polymer layer on the adhesion, toughness, and resistance to shear in the design of cellulosic nanobiocomposites.