With the increasing environmental concerns such as sustainability and end-of-life disposal challenges, materials derived from renewable resources such as nanocellulose have been strongly advocated as potential replacements for packaging materials. Nanocellulose can be extracted from various plant resources through mechanical and chemical ways. Nanocellulose with its nanoscale dimensions, high crystalline nature, and the ability to form hydrogen bonds resulting in strong network makes it very hard for the molecules to pass through, suggesting excellent barrier properties associated with films made from these material. This review paper aim to summarize the recent developments in various barrier films based on nanocellulose with special focus on oxygen and water vapor barrier properties.

A new method to prepare nanolignin using a simple high shear homogenizer is presented. The kraft lignin particles with a broad distribution ranging from large micron- to nano-sized particles were completely homogenized to nanolignin particles with sizes less than 100 nm after 4 h of mechanical shearing. The (13) C nuclear magnetic resonance (NMR) and (31) P NMR analysis showed that there were no major changes in the chemical composition between the starting kraft lignin particles and the nanolignin obtained after 4 h of mechanical treatment. The nanolignin particles did not show any change in molecular weight distribution and polydispersity compared to the original lignin particles. The nanolignin particles when used with polyvinyl alcohol (PVA) increased the thermal stability of nanolignin/PVA blends more effectively compared to the original lignin/PVA blends.

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.

Lignin, the second most abundant natural polymer on earth after cellulose, contains both hydrophilic and hydrophobic groups. In this study, the use of nanocellulose fibrils with high lignin content (NCFHL) has been explored to make polylactic acid (PLA) biocomposites with excellent mechanical, thermal, and barrier properties. Different amounts of NCFHL aqueous suspensions (5−20 wt %) were wet mixed with PLA latex to form composite films by casting and hot pressing. The presence of lignin imparted a strong compatibility between NCFHL and the PLA matrix, which overcame the major issue of poor interfacial bonding associated with nanocellulose fibrils without lignin previously reported by literature studies. Atomic force microscope infrared spectroscopy (AFM-IR) characterization results showed an effective coupling between NCFHL and PLA at the nanoscale. With 5−10 wt % of NCFHL additions to the PLA matrix, a significant improvement in mechanical, thermal, and water vapor barrier properties was observed for the resulting biocomposites. The addition of 10 wt % of the NCFHL increased the modulus and strength by 88% and 111%, respectively, and the water vapor transmission rate was reduced by 52%, compared to neat PLA.

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