Progress on research of construction of carbon nanotubes/carbon fiber cross-scale interface enhancement systems

Abstract

<p indent="0mm">Carbon fiber reinforced composites (CFRP) have a broad application prospect in aerospace, military equipment and other fields because of their many excellent properties such as high strength and stability. However, the inert surface structure of carbon fiber (CF) seriously affects the load transfer efficiency with the matrix, which hinders the full play of the excellent performance of the composites. Therefore, the optimization and design of the interfacial structure between the two phases has become a hot research topic. Carbon nanotubes (CNTs) with excellent mechanical properties were deposited on the surface of CF to form a three-dimensional network hybrid structure with multiple orders of magnitude, thereby improving the interfacial bonding ability between the CF and the matrix. This paper introduces four process routes for the construction of cross-scale enhancement systems, including chemical vapor deposition (CVD), electrophoretic deposition (EPD), chemical grafting and dip-coating spraying process. The advantages, limitations and key process parameters of each method are summarized. The study of CVD method focuses on the influence of process parameters such as catalysts (type, morphology, concentration), growth time, treatment temperature, carbon source and carrier gas (type, mixing ratio, inlet speed) on the growth morphology (length, density, thickness) of CNTs. This method achieves the direct directional growth of CNTs on the CF surface, but the CF is affected by the pre-activation treatment, metal catalyst etching, and high-temperature environment, which leads to a significant decrease in its own strength. In the EPD method, the adjustment of key process parameters (applied voltage, energization time, electrode distance, and electrode shape) becomes the key to successful application of the EPD method. Although the EPD method is capable of producing textured CNT coatings or thin films on the CF, the weak van der Waals force bonding form and the “disorder” of deposition are the main pain points of this method. In the chemical grafting process, the reaction between multiple reactive functional groups and the use of macromolecular coupling agents provide a more diversified preparation scheme, and the bonding strength between CNTs and CF is greatly enhanced by chemical bonding. The construction of CNTs/CF interfacially enhanced structures, using two different processes, surface dip coating and spraying, is considered to be simple and effective, and the degree of dispersion of CNTs in sizing agents or different solvents becomes an important consideration for good deposition on the CF surface. Although the combination between CNTs and CF is not strong, the simple operation process and reasonable economic cost show a high suitability for industrialization. In this paper, three different attachment types of CNTs, namely radial embedding, random topology and surface attachment, are proposed in summary to investigate the stress transfer paths between the composite matrix and the form of interfacial enhancement. The three different attachment types contribute to the enhancement of the interface properties in different ways and to different degrees, with radially embedded structures contributing the most to the enhancement of the interface properties, vertically oriented CNTs significantly weakening the radial stresses between the CF and the matrix, and surface-applied CNTs suppressing the shear stresses more significantly than the radial stresses. Finally, the application of the CNTs/CF cross-scale interfacial reinforcement system in composites is explored, resulting in CFRP exhibiting superior properties in a number of ways, but only in terms of the mechanical properties of the system, which are exploited. Therefore, the development and application of multi-functional materials such as heat and electricity, as well as the preparation of high efficiency, high quality and low cost CNTs/CF/matrix three-phase composites will be the main development direction in the field of nano-reinforced CF composites in the future.