Abstract:Nanofibrillated cellulose (NFC) films have potential as oxygen barriersfor, e.g., food packaging applications, but their use is limited by their hygroscopiccharacteristics. The three-dimensional microstructure of NFC films made ofPinus radiata(Radiata Pine) kraft pulp fibres has been assessed in this study, considering the structuraldevelopment as a function of relative humidity (RH). The surface roughness, micro-porosity,thickness and their correlations were analyzed using X-ray microtomography (X–μCT) andcomputerized image analysis. The results are compared to those from scanning electronmicroscopy and laser profilometry. Based on a series of films having varying amounts of2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidated nanofibrils, it wasdemonstrated that X–μCT is suitable for assessing the surface and bulk 3D microstructure ofthe cellulose films. Additionally, one of the series was assessed at varying humidity levels,using the non-destructive capabilities of X–μCT and a newly developed humidity chamberfor in-situ characterization. The oxygen transmission rate (OTR) of the films (20g=m2)was below3:7mLm2day1at humidity levels below 60% RH. However, the OTRincreased considerably to12:4mLm2day1when the humidity level increased to 80% RH.The increase in OTR was attributed to a change of the film porosity, which was reflected as anincrease in local thickness. Hence, the characterization techniques applied in this study shedmore light on the structures of NFC films and how they are affected by varying humiditylevels. It was demonstrated that in increasing relative humidity the films swelled and theoxygen barrier properties decreased.
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