Full utilization of plant-based feedstocks for sustainable societies must include the valorization of lignin, an abundant aromatic component of the cell wall of plant stems, in processes that follow green chemistry principles. However, one of the major issues limiting lignin utilization is the chemical nonuniformity of the isolated polymer, along with the thermal sensitivity of the free phenolics which hinders processing at elevated temperatures. To address these issues, free phenolics and carboxylic acids of industrial lignins were hydroxyalkylated through the use of ethylene carbonate, which served as both the reagent and the solvent. This facile and safe reaction resulted in near complete conversion of phenolics and carboxylic acids into aliphatic hydroxyls resulting in uniform chemical functionality and enhanced thermal stability. However, the increased reaction temperature decreased the total hydroxyl content and increased the molecular weight of the lignin; the work identified a narrow processing window that achieved derivitazation without extensive structural modification, which plagued earlier work with carbonate modification of lignin. 13C NMR spectroscopy of hydroxyalkylated lignin showed a low degree of condensation and limited to no copolymerization of the ethylene carbonate when reacted under modest conditions. The hydroxyethylated derivative had enhanced solubility in propionic acid, which was used as a solvent and reagent in order to directly esterify the lignin. The reaction achieved over 95% substitution of the lignin hydroxyls creating ethylpropionate derivatives where excess propionic acid could be recycled under vacuum. The hydroxyalkylation followed by direct esterification provided a route toward the development of greener lignin esters by avoiding added solvents, carcinogens such as ethylene oxide, and halogens like acid chlorides for lignin-based polymeric materials synthesized utilizing green chemistry principles.

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Oxidative thermal stabilization is considered a critical process before carbonization to prevent fusion of fibers, while aiding in the formation of homogeneous fiber cross sections during carbon fiber manufacturing. In this study, we investigated the impact of nanocrystalline cellulose (NCC) on the thermal, electrical, and mechanical properties of electrospun lignin-derived carbon nanofibers when the oxidative thermal stabilization step was skipped. Results showed that by adding small amounts of NCC (up to 5 wt %), uniform lignin-based carbon nanofibers were prepared with direct carbonization processes without oxidative thermal stabilization. SEM images revealed that NCC filled lignin carbon nanofibers retained their fibrous morphology after the heat treatment, dependent upon the carbonization rate. Further, carbonization conditions were exploited to form a unique interconnected structure, which increased the electrical conductivity of carbon nanofiber mats from 5 to 35 S/cm. Dynamic thermomechanical analysis of NCC/lignin nanofiber mats showed a reduction of the tan δ peak during the glass transition indicating NCC restricted the molecular mobility of lignin’s chains. Through thermal rheological evidence, this study revealed significant interaction of NCC and lignin blends that prevented the fusion of nanofibers during heat treatment. This study is unique that it provides a method to reduce processing time and energy cost associated with carbon fiber production, while controlling fiber mat structure.

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Aim To identify the factors affecting fear, anxiety and depressive symptoms among frontline nurses working with COVID‐19 patients or are in charge of COVID‐19 screening in Korea. Background Nurses are at a higher risk of COVID‐19 infection because they are in closer, longer‐duration contact with patients. These situations can negatively affect the mental health of nurses. Methods This study analysed data from COVID‐19 module in the Korean Nurses’ Health Study. Data from 906 participants were analysed. To identify the factors influencing mental health, descriptive statistics, Pearson’s correlation and hierarchical multiple regression analyses were performed. Results Caring for patients who are COVID‐19‐positive increased levels of fear, anxiety and depressive symptoms of nurses. The hospital safety climate influenced mental well‐being among nurses. Conclusion Caring for patients with COVID‐19 had a negative impact on fear, anxiety and depressive symptoms. However, the higher was the perceived hospital safety climate, the lower were the nurses’ psychological symptoms. Further research on the mental health of nurses is warranted. Implications for nursing and health policy Institutions should manage human resources to enable periodic rotation of nurses’ work and working periods related to COVID‐19. In addition, hospital managers should provide sufficient personal protective equipment, related education, and safety climate.