In this paper, we proposed an efficient method for manufacturing water-soluble polyimide (PI)sized carbon fiber (CF) reinforced poly (ether ether ketone) (PEEK) composites with excellent mechanical and thermal properties. The PI sizing agent used in this study was synthesized by thermal imidization of prepared poly (amic acid) salt solution. The PI-sized CFs were fabricated by an optimized process that included a sizing treatment and a spreading process using a specially customized equipment. Composites containing PI-sized CFs were characterized by interfacial shear strength and glass-transition temperature according to the PI concentration on the CF surfaces. Molecular dynamics simulations show that the presence of an appropriate amount of PI sizing agent on the CF surface significantly enhances the interface compatibility of the CF/PEEK polymer composites.

The effect of the surface roughness of carbon fibers (CFs) on interfacial adhesion was investigated by comparing polyamide­(PA)­6-based composites using a commercial CF (T700) and a low-cost textile polyacrylonitrile-based CF (TexCF). The tensile strength of T700CFs was 66% higher than that of TexCFs; however, the Izod impact, interlaminar shear, and flexural strength of the long-fiber-reinforced thermoplastic (LFT) composites fabricated using the two CFs were significantly similar. The TexCFs with a rougher surface had a higher wettability than that of T700CFs, resulting in a higher interfacial shear strength value of TexCF/PA6 composites despite the much lower tensile strength of TexCFs than that of T700CFs. This suggests that the high surface roughness of CFs plays a critical role in strengthening the interfacial adhesion between the CFs and the matrix. It is concluded that low-cost CFs with high roughness are promising reinforcement candidates for the fabrication of adequate LFT composites despite their low tensile strength.

Polypropylene-grafted-maleic anhydride (PP-g-MAH) is known as an excellent interface modifier that can improve the interface between carbon fiber (CF) and PP. In this study, the effect of PP-g-MAH content on the physical properties of PP composites containing long-fiber CFs was investigated. It was confirmed that PP-g-MAH acted as an interface modifier between the interface between CF and PP, and when an appropriate amount of 10 wt% was incorporated, the tensile strength, tensile modulus, Izod impact strength, and heat deflection temperature were improved by 110%, 50%, 86.7% and 12.7%, respectively. On the other hand, the blending effect of PP-g-MAH, which is a low molecular weight, was greater than the compatibilizing effect when the PP-g-MAH content was mixed above the appropriate content, thereby reducing the physical properties. Therefore, the content of PP-g-MAH as the interface modifier must be designed to be the optimum content considering the CF content to be mixed in order to optimize the physical properties of the composite material.