Plasticized Cellulosic Films by Partial Esterification and Welding in Low-Concentration Ionic Liquid Electrolyte.

Xun Niu,Yating Liu,Sami Hietala,Alistair W. T. King,Orlando J. Rojas,Hui Pan

doi:10.1021/acs.biomac.9b00325

Xun Niu, Yating Liu + Show 4 more

Open Access

https://doi.org/10.1021/acs.biomac.9b00325

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Abstract

Alternatives to petroleum-based plastics are of great significance not only from the point of view of their scientific and practical impact but to reduce the environmental footprint. Inspired by the composition and structure of wood’s cell walls, we used phenolic acids to endow cellulosic fibers with new properties. The fiber dissolution and homogeneous modification were performed with a recyclable ionic liquid (IL) (tetrabutylammonium acetate ([N4444][OAc]):dimethyl sulfoxide) to attain different levels of reaction activity for three phenolic acids (p-hydroxybenzoic acid, vanillic acid, and syringic acid). The successful autocatalytic Fischer esterification reaction was thoroughly investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, and nuclear magnetic resonance spectroscopy (13C CP-MAS, diffusion-edited 1H NMR and multiplicity-edited heteronuclear single quantum coherence). Control of the properties of cellulose in the dispersed state, welding, and IL plasticization were achieved during casting and recrystallization to the cellulose II crystalline allomorph. Films of cellulose carrying grafted acids were characterized with respect to properties relevant to packaging materials. Most notably, despite the low degree of esterification (DS < 0.25), the films displayed a remarkable strength (3.5 GPa), flexibility (strains up to 35%), optical transparency (>90%), and water resistance (WCA ∼ 90°). Moreover, the measured water vapor barrier was found to be similar to that of poly(lactic acid) composite films. Overall, the results contribute to the development of the next-generation green, renewable, and biodegradable films for packaging applications.

Highlights

Concerns regarding the pollution generated by plastics used for packaging have led to increased efforts to find low-cost alternatives, preferably if they display multiple properties such as sustainability, flexibility, transparency, and strength, as demanded by the given applications
The results indicate a high degree of uniformity
The observed morphologies are a result of the partial disintegration of the crystalline and amorphous domains of cellulose caused by esterification and oxidation reactions,[25] as well as the partial homogeneous dissolution of cellulose in ionic liquids, ILs, which “welded” the rest of the components

Summary

■ INTRODUCTION

Concerns regarding the pollution generated by plastics used for packaging have led to increased efforts to find low-cost alternatives, preferably if they display multiple properties such as sustainability, flexibility, transparency, and strength, as demanded by the given applications. After modification in ILs, the modified CEL films displayed a slight decrease in Young’s modulus compared to that of CEL, which is probably associated with the change in the crystalline structure caused by the dissolving−regeneration process and the effect of excess acids Possible explanations for this observation are that the ILs, known as efficient solvents of cellulose, could swell the compact structure of cellulose fiber and may have converted microsized fibers or fiber clusters into nanosized fibrils, which resulted in the reduction in crystallinity or conversion to cellulose II, and simultaneously increased surface area for stress transfer.[42] the IL could work as a welding agent,[43] creating disordered cellulose domains on the surface of the nanosized fibrils, connecting them together, and forming a continuous and integrated network.

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES