What causes resin-rich zones during cure?

• A. Uniform resin diffusion
• B. Uneven resin diffusion and flow leading to higher resin content at surfaces or interfaces
• C. Excess filler diffusion
• D. Low temperature curing

Answer: (B)

Resin-rich zones show up when resin moves and diffuses unevenly during cure. If resin diffusion and flow aren’t uniform, resin tends to migrate toward boundaries where movement is less restricted—usually the surfaces or interfaces between layers or fibers. Capillary forces and differences in local viscosity or permeability drive resin toward these regions, so those areas end up with higher resin content than the interior. If diffusion were uniform and flow balanced, the resin would distribute evenly, so a resin-rich zone wouldn’t form. The other factors—filler diffusion or curing temperature—don’t inherently create the concentrated pockets of resin at surfaces/interfaces.