Skipping Oxidative Thermal Stabilization for Lignin-Based Carbon Nanofibers

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

Nanocellulose Life Cycle Assessment

Nanocellulose is a nascent and promising material with many exceptional properties and a broad spectrum of potential applications. Because of the unique and functional materials that can be created using nanocellulose, pilot-scale development for commercialization has begun. Thus a thorough understanding of its environmental impact, covering the whole life cycle of nanocellulose, becomes the foundation for its long-term sustainable success. In this current study, four comparable lab scale nanocellulose fabrication routes were evaluated through a cradle-to-gate life cycle assessment (LCA) adopting the Eco-Indicator 99 method. The results indicated that, for the chemical–mechanical fabrication routes, the majority of the environmental impact of nanocellulose fabrication is dependent upon both the chemical modification and mechanical treatment route chosen. For sonication, the mechanical treatment overshadows that from the chemical modifications. Adapting the best practice based on unit mass production was 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation followed by homogenization, as TEMPO oxidation resulted in a lower impact than carboxymethylation. Even though the fabrication process of nanocellulose presents a large environmental footprint markup relative to its raw material extraction process (kraft pulping), it still exhibits prominent environmental advantages over other nanomaterials like carbon nanotubes

Assembly of Debranched Xylan from Solution and on Nanocellulosic Surfaces

This study focused on the assembly characteristics of debranched xylan onto cellulose surfaces. A rye arabinoxylan polymer with an initial arabinose/xylose ratio of 0.53 was debranched with an oxalic acid treatment as a function of time. The resulting samples contained reduced arabinose/xylose ratios significantly affecting the molecular architecture and solution behavior of the biopolymer. With this treatment, an almost linear xylan with arabinose DS of only 0.04 was obtained. The removal of arabinose units resulted in the self-assembly of the debranched polymer in water into stable nanoparticle aggregates with a size around 300 nm with a gradual increase in crystallinity of the isolated xylan. Using quartz crystal microbalance with dissipation monitoring, the adsorption of xylan onto model cellulose surfaces was quantified. Compared to the nonmodified xylan, the adsorption of debranched xylan increased from 0.6 to 5.5 mg m^–2. Additionally, adsorption kinetics suggest that the nanoparticles rapidly adsorbed to the cellulose surfaces compared to the arabinoxylan. In summary, a control of the molecular structure of xylan influences its ability to form a new class of polysaccharide nanoparticles in aqueous suspensions and its interaction with nanocellulose surfaces