Competitive and displacement adsorption of polystyrene (PS) and polyethylene oxide) (PEO) with narrow molecular weight distributions onto a nonporous silica (Aerosil 130) from carbon tetrachloride solutions at 35 °C was studied by IR and UV spectroscopy. The fraction of silanol groups occupied by styrene or ethylene oxide units was determined from the shift in the IR frequency of the silanol groups. In competitive adsorption, PEO absorbs preferentially over PS, and the preferential adsorption of large molecules over small molecules occurs even in the presence of different species. PS molecules are completely desorbed from the silica surface by addition of PEO (displacer). The degree of displacement of PS by PEO depends on the fraction of styrene units directly attached to the silanol groups as well as on the molecular weights of PS and PEO.

To effectively reuse a large amount of Carbon Fiber Reinforced Plastics (CFRP) waste, the carbon fibers should be able to be recovered without degrading their quality. In this report, we developed a new approach to recover carbon fibers from CFRPs with improved physical properties compared to virgin carbon fibers with an environmentally friendly recycling method using nitric acid. Following the decomposition of the CFRP waste in nitric acid at 80 °C, both recycled carbon fibers and decomposed resin were recovered. The obtained recycled carbon fibers showed 1.4 times higher tensile strength and 2.2 times higher interfacial shear strength to resin compared to virgin carbon fibers. TEM-EDX analysis showed a decrease in the abundance of voids existing in the carbon fiber surface layer and new polar functional groups caused by nitric acid existing inside the voids, leading to increased tensile strength. Furthermore, XPS analysis showed that the interfacial shear strength improved due to the formation of new polar functional groups due to nitric acid. The possibility of applying recycled carbon fibers to CFRP products was shown by elucidating the mechanism that expressed its physical properties during the recycling process, leading to a novel approach to realizing closed-loop recycling.

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