Development of new composite materials for 3D-printing based on polyimide binders and continuous carbon fiber

Abstract

Three-dimensional printing of composites reinforced by continuous fiber and based on heat-resistant materials requires a prepreg compatible with these plastics. This kind of a prepreg, in its turn, would necessarily have to be similar to these plastics in terms of its chemistry and operational thermal range. This work was an investigation of factors relevant for the strength of adhesion between carbon fiber and polymeric binder. The authors managed to develop the compounds (coupling agents) facilitating fiber impregnation with polymer and improving fiberbinder adhesion. To obtain a thermoplastic binder various polyimide matrices have been synthesized. The properties of polymers thus created were studied as per the methods of thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC), as well as measurement of limiting wetting angle. Then these materials were subject to solution impregnation so as to obtain prepreg samples suitable for 3D printing. Impregnation quality of these samples was studied by means of scanning electronic microscopy. The most promising prepreg samples were used for 3D printing of try-out product specimens. Composites based on the plastics reinforced by continuous fibers (glass, carbon, polymeric, etc.) are widely used in special fields of today’s technology [1–4]. They have already become indispensable for rocketry or aircraft industries, and they are steadily gaining ground in other industries, too, like machine engineering, shipbuilding, civil engineering, etc. Polymeric composite have become so popular because they are quite strong [5, 6] and light [7] at the same time. Today, manufacturing of fiber-reinforced composites is quite tedious and only allows a limited scope of geometries for final products [8] because fiber impregnation with viscous solutions/melts of polymers is a difficult process. Besides, final product takes time to harden, so until it happens it needs a moulding cast or skeleton to maintain its shape. This tedious process of product manufacturing from the parts reinforced with continuous fiber might proceed much easier and with greater automation thanks to 3D printing as per fused deposition modeling (FDM) technique that uses a filament of preimpregnated fiber [9]. In particular, one of the techniques steadily improving today is 3D printing with continuous carbon fiber and prepregs based on epoxy binders. Final products manufactured as per this technology and reinforced by continuous carbon fiber feature stable size and complex shape. However, prepregs based on epoxy resins will work only with the materials that have good adhesion with them, otherwise final composites will be too weak. Current materials can only be used for the products with low operational temperatures whereas hi-tech applications require strong and heat-resistant materials. To meet this requirement, it is necessary to develop prepregs based on heat-resistant compounds, as well as filaments based on heat-resistant plastics compatible with these prepregs. Polyimides as a class of compounds have long been known to remain stable at high temperatures. Therefore, prepregs based on them, as well as polyimide matrices fit for FDM 3D printing technique will pave way to the products simultaneously featuring high thermal resistance and good strength. The purpose of this work was to develop prepregs based on carbon fiber and polyimides featuring good resistance to high temperatures and aggressive media, as well as to develop thermoplastic polyimide matrices fit for 3D printing.

Topology and structure analysis of carbon fiber-reinforced polyimide composites

“…A solution of polyamide acid oligomers (PAA-sizing) based on 6-FDA and ODA was used as sizing agent. The preparation of the sizing solution and the carbon fiber resizing process were carried out as described [16].…”

“…Heat-resistant polyimide-based binders with improved rheological characteristics were previously developed, their adhesive properties were studied and a prepregs preparation method was proposed [16]. Polyimides are a class of high thermal resistant compounds [17] and the preparation of prepregs based on them can contribute to the production of polymer composite materials with exceptional operating temperatures.…”