Highly Ductile Cellulose-Rich Papers Obtained by Ultrasonication-Assisted Incorporation of Low Molecular Weight Plasticizers

Abstract

Fiber-based materials are attractive sustainable alternatives to fossil-based plastics, however, the lack of ductility (i.e., brittleness) limits their applicability in complex shapes as are often utilized for plastics. In this study, we hypothesize that it is possible to enhance the ductility of a cellulose-rich material by the incorporation of low molecular weight plasticizers (glycerol, urea, citric acid, and tannic acid). However, no significant effects could be observed after swelling in the presence of plasticizers. To enhance any potential effect, it was decided to employ ultrasonication to mechanically disintegrate the fiber and aid the sorption of plasticizer prior to formation of sheets from the treated fibers. Glycerol or urea in combination with ultrasonication resulted in both internal and external fibrillation of the fibers, and it could be observed that the resulting fines create a film at the surface of the fibers in the formed sheets. Tensile testing shows that this gives rise to a 100% increase in ductility compared to sheets from untreated fibers. The use of citric or tannic acid has the opposite effect, reducing ductility to a third of that of the reference sheet. This is suggested to be due to the formation of covalent cross-links in the treated fibers, which also leads to different internal and external fibrillation mechanisms, as observed by scanning electron microscopy. The exceptionally high improvement of the strain-at-break for sheets from the glycerol-and urea-treated fibers suggests that low molecular weight plasticizers affect the internal properties of the fiber wall as well as the interactions between the fine material forming in-between the fibers. The findings from the current study suggest that the proposed approach to obtain ductile cellulose-rich materials holds promise for the future, but it is also clear that more in-depth research is required to obtain a mechanistic understanding and release the full potential.

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“…This mechanism caused the cellulose structure to become less crystalline and more amorphous, enhancing the chain mobility of the cellulose and increasing the stretchability. 38,39 The addition of urea reduced the film toughness while enhancing the stretchability. The HEC films treated with 0 wt% and 5.0 wt% glycerol exhibited toughness values of 0.412 and 1.675 MJ m −3 , respectively.…”