The potential of neutral sulphite pulpsfrom softwood with different yields (c. 58–84%) andhigh residual lignin contents (c. 10–25 wt%) wasinvestigated as a raw material for lignin-containingcellulose nanofibrils (LCNFs) by following theirfibrillation during grinding. It was found that thelower yield (58–65%) pulps needed two grindingcycles to produce fibrillated fibers with water retentionvalues (WRV) as high as 400 g/g (at the energyconsumption level of 1400 kWh/t). In contrast, thehigh yield (77–84%) pulps fibrillated more slowly,requiring five grinding cycles to reach comparableWRV values. Apparently, higher crosslinking degreesof lignin in the high yield pulps are hampering thefibrillation, although the high hemicellulose contents(21–24 wt%) and the high charge densities (200–350lmol/g, originating from carboxylic and sulphonicacid groups) of the pulps were expected to enhance thefibrillation. Nevertheless, regardless of the differentfibrillation behaviour, most of the pulps formed c.10–15% of nanosized material below 30 nm andsignificant amounts of fibrils with size under 100 nmbased on the centrifugation method and FE-SEMimages. As the pulps were of moderate to high yieldand fibrillated easily without any chemical or enzy-matic pretreatments, they show promise for cost-efficient production of LCNFs. The nanopapers pre-pared from the fibrillated pulps showed tensilestrengths (73–125 MPa) comparable with the nanopa-pers from high yield mechanical pulps, whereas thewater contact angles (41°–58°) were closer the thoseof chemical pulps.
- Lignin-containing cellulose nanofibrils (LCNFs)
- Neutral sulphite pulp
- Sulphonic acid group