Abstract
The surface of cellulose films, obtained from micro nanofibrillated cellulose produced with different enzymatic pretreatment digestion times of refined pulp, was exposed to gas plasma, resulting in a range of surface chemical and morphological changes affecting the mechanical and surface interactional properties. The action of separate and dual exposure to oxygen and nitrogen cold dielectric barrier discharge plasma was studied with respect to the generation of roughness (confocal laser and atomic force microscopy), nanostructural and chemical changes on the cellulose film surface, and their combined effect on wettability. Elemental analysis showed that with longer enzymatic pretreatment time the wetting response was sensitive to the chemical and morphological changes induced by both plasma gases, but distinctly oxygen plasma was seen to induce much greater morphological change while nitrogen plasma contributed more to chemical modification of the film surface. In this novel study, it is shown that exposure to oxygen plasma, subsequently followed by exposure to nitrogen plasma, leads first to an increase in wetting, and second to more hydrophobic behaviour, thus improving, for example, suitability for printing using polar functional inks or providing film barrier properties, respectively.
Highlights
Cellulose, an abundant biopolymer, displays excellent physical and mechanical properties with potential for the production of high-end biobased composites
The surface of cellulose films, obtained from micro nanofibrillated cellulose produced with different enzymatic pretreatment digestion times of refined pulp, was exposed to gas plasma, resulting in a range of surface chemical and morphological changes affecting the mechanical and surface interactional properties
We report an increase in wettability of micro nanofibrillated cellulose (MNFC) films after nitrogen plasma exposure of films, which correlates with dielectric barrier discharges (DBD) control parameters’ pulsing frequency and power, and with the crystallinity of cellulose fibrils [44,55]
Summary
An abundant biopolymer, displays excellent physical and mechanical properties with potential for the production of high-end biobased composites. Paper and board industries, plasma exposure has found application in applying hydrophobisation, or hydrophilic coating, resulting in increased adhesion potential of the surface prior to applying a glue, as good wettability is a prerequisite for the adhesion of binding surfaces [49] For such purposes, in relation to desired product, different gases are used: nitrogen/air (wet and dry), argon, and ozone plasma exposure [30,50,51,52,53]. In this research reported here, we use exposure to plasma generated in oxygen, nitrogen and sequential combination in both gases to reveal the best route towards increased functional printability of MNFC films, whilst comparing with the untreated film mechanical and optical properties resulting from the intrinsic contact area of fibrils and rheological properties of their suspensions during film formation [33,43]. Rheological investigation of the MNFC cellulose suspensions was used to correlate change in fibril swelling and flocculation rate with the change of corresponding fibril to fibril contacts upon consolidation and hydrogen bonding during the film preparation process [66,67]
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