Water retention value for characterizing fibrillation degree of cellulosic fibers at micro and nanometer scales

This study examined in detail the utility and validity of water retention value (WRV) for characterizing the extent of fibrillation of micro and nanofibrils. A bleached pulp fiber sample was either refined to different degrees using a PFI mill or milled for different time periods using a SuperMassColloider (SMC), to produce micro and nanofibril samples. These fibril samples were then characterized by electronic microscopic imaging (SEM and TEM), degree of polymerization (DP), Canadian Standard Freeness (CSF), enzymatic adsorption (EA), enzymatic cellulose digestibility (ED), as well as WRV measured under different relative centrifugation forces and durations. The results showed that WRV characterization is consistent with SEM and TEM imaging and correlate to sample DP, EA, and ED. CSF is a good measure for fiber samples, but is not sensitive and not suitable for characterizing microfibrils and nanofibrils. DP is a good measure of cellulose chain length or fiber cutting, but is not a sensitive measure for extensive fibrillation. The results also indicate that the centrifugation condition did not affect the effectiveness of WRV for characterizing fibril samples, as long as all samples were tested under the same conditions. A mild centrifugation condition, e.g., 3000g for 15 min, appears to have better sensitivity for characterizing fibril samples.