Cellulose nanofibrils (CNF) are steadily gaining attention since this material is a renewable alternative to artificial polymers. Moreover, waste products from cellulose-based industries (e.g. paper mills) or from agricultura can be used as raw material for CNF isolation. However, the up-scaling from the laboratory to the industry can only be achieved if the energy costs are low enough to compete against low-price petroleum derivatives. The objective of this work is to present an energy-related study of the direct fibrillation of cellulose-based materials using a grinding process. Two waste materials, namely wheat straw and recycled newspaper, have been investigated as starting materials, together with bleached Wood pulp for comparison purposes. The mechanical properties and specific surface áreas of the resulting fibrillated materials are then presented and systematically compared with each other. The properties of the bleached wood-pulp fibres exhibited the highest values that were reached already at low energy inputs. The different properties of CNF isolated out the waste materials could reach values close to their máxima for energy inputs as low as about 5 kWh/kg compared to the ca. 10kWh/kg needed with high pressure homogenization.