High-Orientation and Shape-Controllable Thermal Conductive Composites Based on Dense Packing and Injection Molding Method

The filler content and distribution are the most significant factors affecting the thermal conductivity (TC) of polymer-matrix composites. Orienting the filler for alignment is the most widely adopted approach to enhance TC in these materials. However, traditional orientation strategies require external fields or additional conditions, resulting in complex processes and hindering the ability to achieve conformal orientation of heterogeneous structures. In this context, an orientation strategy is proposed based on dense packing and injection molding to fabricate high-orientation and shape-controllable composites, thereby reducing limitations related to temperature, pressure, molding shapes, and matrix types during composite preparation. Dense packing induces the transition of high diameter-to-thickness ratio (DTR) fillers from locally isotropic to anisotropic alignment, while the injection molding process drives the overall orientation of the composites. Using aluminum (Al) flakes and cyanate ester (CE) as representative materials, a systematic study was conducted on the influence of filler content and composite thickness on the orientation of fillers. As a result, Al/CE-40 exhibits remarkable flexibility and achieves a maximum tensile strength of 29.9 MPa with an Al flake content of 40 wt %. The prepared Al/CE composites exhibit a high orientation ratio of 0.868 and a TC of 5.9 W·m^–1·K^–1, even with only 30 wt % Al content. Notably, the Al/CE composites maintain a high orientation when formed into specific shapes. Furthermore, various sheet-like materials with a high DTR, such as silver and mica flakes, show considerable promise as thermal management materials suitable for injection molding.