Investigation of the influence of supercritical carbon dioxide treatment on meta-aramid fiber: Thermal decomposition behavior and kinetics

Processing Nomex Nanofibers by Ionic Solution Blow-Spinning for Efficient High-Temperature Exhausts Treatment

Hard-to-dissolve polymers provide next-generation alternatives for high-performance filter materials owing to their intrinsically high chemical stability, superior mechanical performance, and excellent high-temperature resistance. However, the mass production of hard-to-dissolve nanofibers still remains a critical challenge. A simple, scalable, and low-cost ionic solution blow-spinning method has herein been provided for the large-scale preparation of hard-to-dissolve Nomex polymeric nanofibers with an average diameter of nearly 100 nm. After rapidly dissolving Nomex microfibers in the lithium chloride/dimethylacetamide (LiCl/DMAc) solution system, the conductive solution can be stably and conductivity-independently processed into nanofibers. The method optimizes electrospinning and avoids spinnability degradation and potential safety hazards caused by high electrical conductivity. Owing to nanofibrous structure and high dipole moment, Nomex nanofibrous filters show a stable high filtration efficiency of 99.92% for PM_0.3 with a low areal density of 4.6 g m^-2, as well as a low-pressure drop of 189.47 Pa. Moreover, the flame-retardant filter can work at 250 °C and 280 °C for a long and short time without shrinking or burning, respectively, exhibiting a high filtration efficiency of 99.50% for PM_0.3-10.0. The outstanding properties and low cost enable the efficient capture of PM from various high-temperature exhausts, making Nomex nanofibrous membrane an even more ideal industrial-grade air filter than polypropylene, polytetrafluoroethylene, polyimide, and ceramic nanofibrous filters.

GRAPHICAL ABSTRACT

Hard-to-dissolve nanofibers provide alternatives for high-efficiency and low-resistant air filtration but are limited by the universality and economics of fabrication methods. A scalable and efficient ionic solution blow-spinning strategy has herein been proposed in preparing hard-to-dissolve nanofibrous filters.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42765-022-00231-x.

Enzyme Activity and Physiochemical Properties of Flour after Supercritical Carbon Dioxide Processing

The objectives of this study were to inactivate the enzymes α-amylase, lipase, protease, and peroxidase in flour with supercritical carbon dioxide (scCO2), and to optimize the enzymatic treatment conditions. Enzyme inactivation is important, due to the undesirability of certain flour enzymes that cause adverse reactions during storage as unpleasant rancidity of flour, and, at the same time, reduce the shelf life of flour. Therefore, crude enzymes and flour were initially exposed to scCO2 to determine the effect on specific enzyme activity under appropriate conditions. The activity of the unwanted enzymes lipase and peroxidase decreased under optimal process conditions of scCO2 exposure, lipase by 30%, and peroxidase by 12%, respectively. It was discovered that the inactivation of enzymes in wheat flour occurred, where, at the same time, this sustainable method allows the regulation of enzyme activity in the baking process. Afterwards, the effect of scCO2 on the physicochemical properties of flour, morphological changes on starch granules, and content of total lipids was studied. In scCO2-treated white wheat flour, the fat content decreased by 46.15 ± 0.5%, the grain structure was not damaged, and the bread as the final product had a lower specific surface volume. Therefore, this could be a promising technology for flour pretreatment, potentially impacting the prolonging of its shelf-life.