There is a need for novel bio-based packaging and barrier materials that can replace conventional non-renewable materials. Cellulose films from regenerated or nanofibrillated cellulose have low oxygen permeability at low relative humidity and act as an excellent oxygen barrier under these conditions. However, as the relative humidity increases there is a superlinear increase in oxygen permeability which severely limits the competitiveness of cellulosic films compared to commercially available barrier films. Recent results (presented at the 15th Fundamental Research Symposium, Cambridge, UK, 2013) show that it is possible to limit this increase in oxygen permeability by covalent cross-linking. In this work, cross-links were ultimately introduced in the cellulose network by periodate oxidation of fibres before fibril and film preparation, which resulted in films with an oxygen permeability of 1 and 3 ml��m/(m2�24 h�kPa) at 50 and 90 % relative humidity, respectively. Corresponding values for the non-cross-linked reference was 1 and 33 ml��m/(m2�24 h�kPa). To understand the mechanisms behind this remarkable improvement, cross-sections of the films were prepared and imaged by high-resolution microscopy; both by atomic force microscopy in dry and wet state and scanning electron microscopy. From this it was concluded that the cross-links prevent the fibrils from delaminating during moisture sorption and consequently prevent the formation of voids that would otherwise be available for gas diffusion.

Cross-linked barrier films with low sensitivity to relative humidity fabricated from nanofibrillated cellulose

247th National Meeting (2014)

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