Meaning
Resin flow through micron-scale voids in a reinforcement fabric requires the overcoming of a specific resistance threshold. This resistance is characterized by capillary entry pressure, which dictates the pressure required for a liquid polymer or resin to penetrate the interstitial spaces of a fibrous preform or porous mold surface. In polymer composites manufacturing, it defines the limit below which dry spots or incomplete wet-out of the fibers occur.
Resin Resistance
Fluid progression through the narrow channels depends on the surface energy of the polymer and the fiber sizing. Low capillary entry pressure ensures that liquid resin flows easily into the fiber bundles during infusion, preventing micro-void formation. If the injection pressure falls below this value, the wetting process stops, leaving dry regions that degrade the mechanical strength of the composite part.
Processing Factor
Squeezing the polymer into tightly packed reinforcements requires high mechanical force when the surface chemistry is unfavorable. Tooling designers alter the fiber distribution to lower the capillary entry pressure, which decreases the required pump pressure. This reduction directly lowers the cycle time and energy consumption during the infusion stage of molding.
Defect Control
Part rejects often occur when trapped air cannot escape the fiber network. Maintaining the driving pressure above the capillary entry pressure eliminates these pockets, ensuring a uniform resin distribution throughout the structural grid. This prevents premature structural failure under load.
