In this paper, an enhanced VARTM process is proposed and its pressure effect on resin infusion behavior and composite material performance is studied to reveal the control mechanism of the fiber volume fraction and void content. The molding is vacuumized during the resin injection stage while it is pressurized during the mold filling and curing stages via a VARTM pressure control system designed in this paper. Theoretical calculations and simulation methods are used to reveal the resin’s in-plane, transverse, and three-dimensional flow patterns in multi-layer media. For typical thin-walled components, the infiltration behavior of resin in isotropic porous media is studied, elucidating the control mechanisms of fiber volume fraction and void content. The experiments demonstrate that the enhanced VARTM process significantly improves mold filling efficiency and composite’s performance. Compared to the regular VARTM process, the panel thickness is reduced by 4% from 1.7 mm, the average tensile strength is increased by 7.3% to 760 MPa, the average flexural strength remains at approximately 720 MPa, porosity is decreased from 1.5% to below 1%, and the fiber volume fraction is increased from 55% to 62%.

Poly(propylene carbonate) (PPC) is a promising material for the synergistic molding of microvascular composites due to its thermal depolymerization characteristics. However, its low mechanical strength makes it susceptible to deformation under the high vacuum pressures required during composite fabrication. To address this limitation, this study investigates the effects of polylactic acid (PLA), poly(vinyl alcohol) (PVA), and nano-sized silicon dioxide (SiO ₂ ) as modifying additives, using blending and filling techniques to enhance the mechanical properties of PPC. The results show that all three additives improve the properties of PPC, with the formulation containing 7.5 wt% SiO ₂ exhibiting the most significant enhancement. The tensile strength increased from 30.15 MPa to 40.63 MPa (a 34.76 % improvement), and the Young’s modulus increased from 393.05 MPa to 668.23 MPa (a 75.1 % increase). The onset decomposition temperature is 115.5 °C, and the fastest decomposition temperature is 159.3 °C. Microvascular composites were successfully fabricated using the vacuum-assisted resin transfer molding (VARTM) process combined with frontal polymerization. Under a vacuum pressure of −0.95 bar, the aspect ratio (AR) of the microvascular cross section improved from 1.67 ± 0.15 to 1.03 ± 0.01, confirming that the optimized, SiO ₂ -reinforced PPC is suitable for use as a sacrificial template in high-pressure composite molding processes.