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

Abstract

Injection-molded carbon fiber–reinforced thermoplastics (CFRTPs) offer high strength and scalable manufacturing, yet often suffer from low electrical conductivity and inadequate electromagnetic interference (EMI) shielding, limiting advanced applications. Annealing is well known to improve mechanical performance, but EMI shielding in injection-molded CFRTPs has rarely been investigated in a frequency-resolved, mechanism-deconvolved, and simulation-validated manner—especially for microscale carbon fiber architectures. Here, we report a drop-in post-annealing route that concurrently enhances mechanical properties and EMI shielding in injection-molded CFRTPs with quantitative mechanistic insight. Under optimal annealing at 200 °C, tensile and impact strengths increase by 22% and 28%, respectively, while W-band shielding effectiveness rises by 99% compared with as-molded specimens. The mechanical improvements arise from strengthened fiber–matrix interfacial bonding, increased crystallinity, densification, and relaxation of molding-induced residual stresses. In parallel, annealing disrupts the highly aligned fiber orientation, thereby promoting a three-dimensional conductive network, enabling CF–matrix–CF micro-capacitor architectures, and intensifying localized electric-field hot spots. These coupled changes elevate ε′ and ε″, increase the loss tangent, reduce skin depth, and tune impedance matching, thereby boosting both reflection and absorption. EMI performance is evaluated using frequency-resolved shielding effectiveness and power-coefficient–based decomposition, and the resulting trends are corroborated by full-wave electromagnetic simulations (Ansys HFSS). Notably, an annealing–frequency synergy is identified, enabling high-performance millimeter-wave EMI shielding. This work clarifies the annealing–structure–multifunctional property relationships in injection-molded CFRTPs by addressing the fiber-orientation-driven limitation and opens a promising pathway toward high-performance composites for next-generation electronics and mobility systems.