Effects of Cooling Rate and Fiber Loading on the Non‐Isothermal Crystallization of Short‐Carbon‐Fiber‐Reinforced PEEK

The non‐isothermal crystallization behavior of short‐carbon‐fiber‐reinforced PEEK (SCF/PEEK, 0–30 wt%) was investigated by differential scanning calorimetry at cooling rates of 5–40°C/min and analyzed using the Jeziorny‐modified Avrami model. Crystallinity decreased monotonically with both increasing cooling rate and SCF content, falling from 36.5% to 18.1% for the 30 wt% composite at the highest cooling rate. The Avrami exponent n declined from 3.27 (neat PEEK, 5°C/min) to 2.09 (30 wt% SCF, 40°C/min), indicating increasingly restricted crystal development under faster cooling and higher fiber loading. SEM revealed diminishing matrix continuity and reduced inter‐fiber spacing at high SCF loadings, suggesting geometrical confinement of the PEEK matrix. Although fiber surfaces may locally promote heterogeneous nucleation, the present results provide no direct evidence that SCF increases the overall crystallinity of the matrix; the suppression of crystallization is therefore attributed primarily to restricted crystal development under rapid cooling and high fiber loading. These findings provide practical implications for fused deposition modeling (FDM) of SCF/PEEK components, where processing‐related cooling conditions strongly influence the crystallinity of the printed matrix.