Post-annealing-driven advancement in injection-molded CFRTPs: Simultaneous enhancement of mechanical properties and electromagnetic interference shielding

Injection-molded carbon fiber–reinforced thermoplastics (CFRTPs) offer high strength and scalable manufacturing but often exhibit limited electrical conductivity and EMI shielding. Here, we demonstrate a simple post-annealing strategy that simultaneously improves mechanical and EMI shielding performance in injection-molded CFRTPs. Optimal annealing at 200 °C increases tensile and impact strengths by 22% and 28%, respectively, while enhancing W-band shielding effectiveness by 99% relative to as-molded specimens. Mechanical improvements originate from strengthened fiber–matrix interactions, increased crystallinity, densification, and residual-stress relaxation. Meanwhile, annealing reduces the highly aligned fiber orientation generated during molding, promoting three-dimensional conductive networks and CF–matrix–CF micro-capacitor structures. These structural changes increase dielectric loss, reduce skin depth, and improve reflection and absorption of electromagnetic waves. Frequency-resolved shielding analysis and power-coefficient decomposition, supported by Ansys HFSS simulations, further reveal a pronounced annealing–frequency synergy at millimeter-wave frequencies. These findings establish clear annealing–structure–property relationships and provide a practical route toward multifunctional CFRTPs for next-generation electronics and mobility systems.