Barrier layers comprising nanocellulose onto the surface of paper or paperboard substrates at the wet end of a papermaking process

A method of applying a nanocellulose-containing composition onto a surface of a paper or paperboard substrate, the method comprising:

• applying a first layer of a first nanocellulose-containing composition to a first surface of a consolidating base sheet of paper or paperboard comprising cellulose fibres after the consolidating base sheet leaves a headbox of a paper machine, thereby forming a consolidating substrate comprising a first layer of nanocellulose on the first surface of the paper or paperboard;
• wherein the first nanocellulose-containing composition comprises nanocellulose in a range of about 0.2 wt % to about 6 wt %, preferably about 0.5 to about 3 wt. %, based on the total weight of the first nanocellulose-containing composition;
• wherein the nanocellulose has a d50 (by Malvern) of about 50 to about 400 μm, a Lc(l) of about 0.1-1 mm, a Lc(w) of about 0.1 to about 1.5 mm by fibre analyzer, a fibre steepness of about 20 to about 50, an FLT between 4 and 17 N m g−1;
• and a Fines B content by fibre analyzer between about 1% and about 80% as a percentage of total measured particle length by fibre analyzer.