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Cellulose (2020) 27:6149–6162
Fig. 2 Secondary electron SEM images of MFC-mineral composite made from a bagasse (28% hemicellulose), b Nordic pine (17% hemicellulose), c dissolving pulp (4%
hemicellulose) and d cotton (0% hemicellulose). The low hemicellulose fibres give coarser and more strongly defined fibrils and microfibrils
Influence of lignin content
Especially considering the numerous relatively novel non-wood pulps of unknown chemistry used in the present study, it was initially conceivable that differences in lignin content could be contributing to the noise seen in Fig. 1. The lignin contents of the fibre species used in this study were measured, and the results are shown in the P ulp Chemica l Com p osi t ion tab in the S uppl emen t ar y Ma t eria l . Lignin was found to be present only at very low concentrations in all samples, except Giant Reed, which contained 12.7% lignin and does not seem to perform unusually compared to other fibre species. Therefore, for this study, the influence of lignin on these results can be neglected.
Given that the influence of hemicellulose is estab- lished, it was an open question as to what the influence of the lignin content would be. For thermomechanical or chemithermomechanical pulp, there is an extensive lignin coating on the fibre surface, which seriously inhibits the ability of the fibre to fibrillate and form high quality MFC, at least for entirely mechanical processes (e.g. Meyer et al. 2018; Lahtinen et al. 2014). However the role of lignin within the fibre cell wall is less clear, since good quality MFC can still be made at high lignin contents with unbleached chem- ical pulp (e.g. Spence et al. 2010).
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