Enhancing the barrier properties of micro nanofibrillated cellulose (MNFC) by inclusion of pigment with designed surface modification

Oil barrier functionality is considered an integral part of packaging paper and board design, especially in the food packaging sector, arising from demands to contain fatty foods as well as to protect foodstuff in general from the potential migration of mineral oil residues from recycled fibre components. Sustainable solutions to the problem of achieving such barriers by application of a thin film-forming layer onto fibrous substrates tend to be either expensive due to high production processing costs, for example when considering the use of nanocellulose films, or partially ineffectual due to poor coverage and holdout. Furthermore, interesting materials such as lower production energy demand micro nanofibrillated cellulose (MNFC), containing a significant portion of microfibrils and advantageously processed including mineral filler, are hampered in this demanding field due to lack of complete surface coverage and resulting allied poor film-forming properties. The less than adequate coverage derives from main two causes, (i) the rough and void-containing absorbent surface of fibre sheets, and (ii) the low solids content of gel-like aqueous MNFC suspensions.
The challenge identified in (i) above was shown previously by Ridgway and Gane in 2012 [1] to be conveniently overcome by applying an initial pigment precoat layer to reduce the natural surface voidage and roughness of the paper/board prior to the application of the MNFC. However, the question of low solids content resulting in uneven film-forming, posed in (ii), remained, nonetheless, incompletely solved. In this study, to overcome the issue of poor holdout, we again focus on the use of a mineral precoat to provide surface smoothness and to reduce the size of surface voids, and then build on this mineral precoated substrate to tackle the problem of enhancing the continuity of film-forming by increasing the pigment solids content of the MNFC-containing barrier application.