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Structural characterization of cellulose nanofibers isolated from spent coffee grounds and their composite films with poly(vinyl alcohol): a new non-wood source

Abstract

The waste valorization of spent coffee grounds (SCGs), which are obtainable in large amounts worldwide for new non-wood source has been considered. Cellulose nanofibers derived from SCGs have been successfully produced by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation of SCGs containing 10% cellulose (dry weight). The TEMPO-oxidized cellulose nanofibers (TOCNFs) are 20–35 nm wide observed by scanning electron microscopy. X-ray diffraction showed that TOCNFs are present in a cellulose crystal form I. The average crystal size corresponding to a fiber width was 4.2 nm, as determined from the diffraction pattern. Solid-state NMR shows that hemicellulose and lignin were mostly removed from SCGs via TEMPO-mediated oxidation, but small amounts of triacylglycerols remained in the TOCNFs. Thermogravimetric analysis of TOCNFs showed two major steps of thermal decomposition at 251 °C and 267 °C, which were higher than the coffee roasting temperature range. Furthermore, in order to investigate an interaction of these TOCNFs with a polymer, a SCG-derived TOCNF composite film with poly(vinyl alcohol) as a water-soluble polymer was prepared. We found the TOCNFs were successfully integrated into the polymer. The outcome of this study indicated that SCGs could be used as well as wood as an alternative source for producing TOCNFs, thus contributing to the development of sustainable green chemistry.

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Acknowledgments

We thank Prof. Akira Isogai and Dr. Yuko Ono from the University of Tokyo for their helpful advice regarding TEMPO-mediated oxidation and structural characterization. We thank Prof. Atsumi Miyake from the Institute of Advanced Sciences, Yokohama National University and Dr. Yu-ichiro Izato and Ms. Nana Yamaki from Graduate School of Environment and Information Sciences, Yokohama National University for their technical assistance with the optimization of the TGA. We thank Dr. Eliška Procházková from the Czech Academy of Sciences for proof-reading the manuscript.

Funding

This work was financially supported by “YNU Diversity Research Grant” under MEXT Funds for the Development of Human Resources in Science and Technology, “Initiative for Realizing Diversity in the Research Environment (Collaboration Type)” and the ROUTE (Research Opportunity for UndergraduaTEs) program from Yokohama National University to N. K., and the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant in Scientific Research (B) (JP18H02387) and Yokohama Academic Foundation (674) to I. K.

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Correspondence to Izuru Kawamura.

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Kanai, N., Honda, T., Yoshihara, N. et al. Structural characterization of cellulose nanofibers isolated from spent coffee grounds and their composite films with poly(vinyl alcohol): a new non-wood source. Cellulose 27, 5017–5028 (2020). https://doi.org/10.1007/s10570-020-03113-w

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  • DOI: https://doi.org/10.1007/s10570-020-03113-w

Keywords

  • Cellulose nanofibers
  • Composite film
  • Poly(vinyl alcohol)
  • Spent coffee grounds
  • TEMPO-mediated oxidation
  • Waste revalorization