Effect of high residual lignin on the thermal stability of nanofibrils and its enhanced mechanical performance in aqueous environments

Abstract

In this study, the effect of high residual lignin (21 % w/w) on the thermal properties of cellulose nanofibrils and the performance of films made from these nanofibrils in aqueous environments have been explored for the first time. Individualised cellulose nanofibrils with diameter \100 nm were obtained from the mechanical fibrillation of bark residue fibers with high lignin content. The mass loss by thermal degradation started at a higher temperature of 306°C for these nanofibrils compared to 278°C for those fibrils with low amount of lignin (5 % w/w). The maximum rate of degradation occurred at a temperature of around 390 and 319°C for high and low lignin containing nanofibrils, respectively. Such a high thermal stability for high lignin containing nanofibrils has never been reported for nanocellulose from any other studies. The films made from these high lignin nanofibrils showed lower water uptake and better wet mechanical properties compared to films made from low lignin containing cellulose nanofibrils. The high lignin nanofibril films retained 38 % of the dry strength properties, while the low lignin nanofibril films were able to retain only 9 % of dry strength.

Preparation and evaluation of high-lignin content cellulose nanofibrils from eucalyptus pulp

“…These patches are likely to be lignin agglomerates. Similar structures were seen and reported previously by different authors (Rojo et al 2015;Nair and Yan 2015;Börås and Gatenholm 1999). Nanopaper Unfractionated-HT (Fig.…”

“…The amount of Klason lignin decreased by about 5%, however, the absolute amount of lignin (23 wt%) is much higher than other studies (Rojo et al 2015;Nair and Yan 2015).…”

“…3b nanopaper Fibrils-HT). It is interesting to note that the lignin patches seem to be attached to the surrounding matrix, and not segregated as in previous reports (Rojo et al 2015;Nair and Yan 2015;Börås and Gatenholm 1999). This possibly means that the lignin is associated with the cellulose fibrils, but more evidence is needed to support this observation regarding the isolated nanofibrils, and is out of the scope of the present article.…”

“…Seemingly, the improved properties of these new materials are due to the hydrophobic lignin that fills space between the cellulose nanofibrils. Moreover, the lignin present in the nanopaper may decrease possibilities for water molecules to reach hydroxyl groups on cellulose fibrils, therefore reducing the extent of water-cellulose hydrogen bonds (Nair and Yan 2015).…”

Mechanical fabrication of high-strength and redispersible wood nanofibers from unbleached groundwood pulp

“…Here, it is important to note that our WNF were able to retain an onset temperature and degradation rate close to those of the original fibers, with only a minor decline. According to a recent study (Nair and Yan 2015b), an initial 1% NaOH treatment of fibers with a high lignin content could further increase the thermal stability of our WNF through the removal of less thermally stable extractives, alkali-sensitive lignin, and hemicelluloses.…”