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.

Graphic abstract

中文翻译：

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从废咖啡渣中分离的纤维素纳米纤维及其与聚乙烯醇的复合膜的结构表征：一种新的非木材来源

摘要

已经考虑了废旧咖啡渣（SCG）的废物增值，在全球范围内可从新的非木材来源大量获得这些废咖啡渣。通过2,2,6,6-四甲基哌啶-1-氧基（TEMPO）介导的含10％纤维素（干重）的SCG的氧化，已经成功地生产了源自SCG的纤维素纳米纤维。通过扫描电子显微镜观察到，TEMPO氧化的纤维素纳米纤维（TOCNF）的宽度为20-35 nm。X射线衍射表明TOCNF以纤维素晶型I存在。根据衍射图确定，对应于纤维宽度的平均晶体尺寸为4.2nm。固态NMR显示半纤维素和木质素主要通过TEMPO介导的氧化作用从SCG中除去，但少量的三酰基甘油保留在TOCNF中。TOCNF的热重分析表明，在251°C和267°C下有两个主要的热分解步骤，高于咖啡烘焙温度范围。此外，为了研究这些TOCNF与聚合物的相互作用，制备了SCG衍生的TOCNF复合膜，其具有作为水溶性聚合物的聚乙烯醇。我们发现TOCNF已成功整合到聚合物中。这项研究的结果表明，SCG可以用作木材，也可以用作生产TOCNF的替代来源，从而为可持续绿色化学的发展做出了贡献。制备以聚乙烯醇为水溶性聚合物的SCG衍生的TOCNF复合膜。我们发现TOCNF已成功整合到聚合物中。这项研究的结果表明，SCG可以用作木材，也可以用作生产TOCNF的替代来源，从而为可持续绿色化学的发展做出了贡献。制备以聚乙烯醇为水溶性聚合物的SCG衍生的TOCNF复合膜。我们发现TOCNF已成功整合到聚合物中。这项研究的结果表明，SCG可以用作木材，也可以用作生产TOCNF的替代来源，从而为可持续绿色化学的发展做出了贡献。

图形摘要