Cellulose nanofibils as coating material and its effects on paper properties
Abstract This study investigates the effects of cellulose nanofibril (CNF) coating on the physical, mechanical and barrier properties of paper. CNF is currently of limited use in wet end applications because of its low retention and inefficient application within the paper fibre network, as well as its relatively high cost. Different CNF concentrations and number of coating layers were therefore evaluated to determine the most efficient conditions for CNF coating. For this purpose, handsheets were coated on one side with 1.5 wt% or 3 wt% CNF as a single or double layer. SEM micrographs of CNF coated surfaces indicated that paper surface porosity decreased considerably with increasing CNF concentration and more coating layers. These micrographs also showed that the surface of paper coated with a double layer of 1.5 wt% CNF is more uniform and continuous compared to that of paper coated with a single layer of 3 wt% CNF. The results revealed that the air resistance, surface strength, stiffness and tensile strength were also higher when a higher CNF concentration or greater number of layers was applied, while the Cobb index and roughness were lower. Finally, it was found that a double layer of 1.5 wt% CNF resulted in better mechanical and barrier properties compared to a single layer of 3 wt% CNF, even though the total amount of applied CNF was the same.