This study investigates the preparation of activated carbon fiber derived from waste cotton fabric for economical and ecofriendly recycling as well as its application to water purification. The activated carbon fiber was prepared by physical activation using steam and the adsorption property was then evaluated using methylene blue. When the activation temperature increased, the specific surface area and mesopore volume of the activated carbon fiber increased up to 2562 m2/ g and 0.214 cm3/ g, resulting in the increased adsorption of methylene blue. The results of the adsorption experiment for the activated carbon fiber were analyzed using the Langmuir and Freundlich equations. The Langmuir equation was more suitable than the Freundlich equation to explain the adsorption equilibrium. The maximum adsorption amount of methylene blue was 161.1–731.5 mg/g for fiber samples activated at temperatures ranging from 750 to 950 °C with sample labeled 750SA to 900SA according to the Langmuir equation. The kinetics of methylene blue adsorption by the activated carbon fiber were analyzed using non-linear pseudo-first-order and pseudo-second-order. Sample 750SA was suitable for the pseudo-first-order and 800SA, 850SA, and 900SA sample were suitable for the pseudo-second-order. Therefore, waste cotton fabric has the potential to be the precursor for activated carbon fiber with excellent adsorption properties.

There is a need for the purification of indoor air owing to a high rate of pollution in today’s world. For this, cabin air filters (CAFs) are widely used, which requires the addition of certain adsorbents to increase the volatile organic compound (VOC) removal efficiency. However, this addition causes high-pressure resistance, which may hamper commercial applications by requiring more energy and negatively affecting fresh air delivery rate. Hence, in this study, a high-performance combined CAF (CCAF) with excellent dust and chemical filtration performance and low differential pressure was prepared using granular activated carbon (GAC)/activated carbon fiber (ACF) mixed medium. The GAC/ACF mixed medium had higher air permeability than the ACF medium of the same weight, and it exhibited similar ultrafine dust filtration performance to the ACF medium without an increase in differential pressure. In addition, the GAC/ACF mixed medium showed excellent gas removal performance without increasing differential pressure by combining the VOC removal characteristics of the GAC and ACF filter media. The improved VOC removal performance of the GAC/ACF mixed medium was due to the hybrid effect of the hierarchical pore structures of the GAC and the nearly uniform pore structures of the ACF, which resulted in a slow and increased gas adsorption by the GAC and rapid gas adsorption of the ACF.

Interfacial adhesion between carbon fiber and epoxy resin mostly determine the mechanical properties of the carbon fiber/ epoxy composites and the chemical structures of epoxy resin and hardener plays an important role. In this regard, stereoisomerism of epoxy hardeners, such as 3,3′ and 4,4′-DDS (diaminodiphenylsulfone), can have significant influence on the fracture toughness of the cured epoxy and related carbon fiber composites. Therefore, this study aims to investigate the influence of stereoisomerism of epoxy hardeners on fracture toughness of the carbon fiber/epoxy composites. Triglycidyl aminophenol (TGAP) are selected as epoxy resin and 3,3′- and 4,4′-DDS are selected as epoxy hardener. Wetting behaviors and fiber matrix adhesion of TGAP/DDS mixtures onto carbon fiber are investigated and fracture toughness (KIC) of TGAP/ DDS mixtures are also investigated. Then, the mode II fracture toughness test of the carbon fiber/TGAP/DDS composites are carried out to investigate the influence of hardener stereoisomerism on fracture toughness of the resulting composites. Wetting and fiber matrix adhesion to carbon fiber of TGAP/3,3′-DDS was better than those of TGAP/4,4’-DDS and KIC of TGAP/3,3′-DDS was also better than that of TGAP/4,4′-DDS. As a result of the synergistic effect of better wetting, fiber matrix adhesion, and fracture toughness of TGAP/3,3′-DDS, the mode II fracture toughness of the carbon fiber/ TGAP/3,3’- DDS composites was almost twice of that of the carbon fiber/ TGAP/4,4′-DDS composites. Based on the results reported in this study, stereoisomerism of the epoxy hardeners can influence the fracture toughness of the resulting composites as well as that of the resin itself. In other words, only small difference, such as the spatial arrangement of the molecular structure of epoxy hardeners can cause huge difference in the mechanical properties of the resulting composites.

This study provides an economical and effective method to improve the interlaminar properties of carbon fiber-reinforced polymers (CFRPs) using aluminum trihydroxide (ATH) microparticles. ATH microparticles are cheap and are expected to show good affinity to epoxies in the matrix and sizing agents of the carbon fibers owing to the presence of three hydroxyl groups. In addition, ATH particles are reported to improve the mechanical properties of polymers when used as the reinforcement. In this study, ATH microparticles of various sizes, 1.5, 10, and 20 μm, were used to improve the interlaminar properties of the CFRPs. ATH particles with a size of 1.5 μm improved the tensile properties of the ATH/epoxy resin and did not significantly alter the curing behavior. The interfacial adhesion between the carbon fiber and the epoxy resin was also improved, and the impregnation of the resin mixture remained similar to that of the neat resin, resulting in no significant void and defect formation. Considering the above results, the resulting 1.5 μm ATH-reinforced CFRP showed improved interlaminar properties compared to CFRP without ATH. However, 10 and 20 μm ATH-reinforced CFRPs showed deteriorated interlaminar properties due to the diminished tensile properties of the resin itself and resin impregnation, which resulted in more voids and defects, despite the interfacial adhesion between the fiber and the matrix resin.

This study suggests the novel thermoplastic toughening agent, which can be applied in the monomer forms without increasing the viscosity of the epoxy resin and polymerized during the resin curing. The diazide (p-BAB) and dialkyne (SPB) compounds are synthesized and mixed with the epoxy resin and the carbon fiber reinforced epoxy composites are prepared using vacuum infusion process (VIP). Then, flexural and drop weight tests are performed to evaluate the improvement in the toughness of the prepared composites to investigate the potential of the novel toughening agent. When 10 phr of p-BAB and SPB is added, the flexural properties are improved, maintaining the modulus as well as the toughness is improved. Even with a small amount of polytriazolesulfone polymerized, due to the filtering effect of the solid SPB by the layered carbon fabrics during the VIP, the toughening and strengthening effect were observed from the novel toughening agent, which could be added in monomer forms, p-BAB and SPB. This suggests that the novel toughening agent has a potential to be used for the composites prepared from viscosity sensitive process, such as resin transfer molding and VIP.