This technique for liquid composite molding uses a solid catalyst recrystallized onto preplaced fiber reinforcements to produce high-strength polymer matrix composites. The polymerization is initiated by the preform itself, eliminating the need to mix multiple resins and catalysts before filling the mold. Having polymerization triggered by the preform simplifies the process, saves time, and eliminates mixing equipment.
Liquid composite molding processes have been popular since the 1940s. In the last 10 to 15 years, significant improvements have been made in developing low-viscosity thermosetting resin systems necessary to obtain high fiber volume parts. Also, automatic methods like weaving, braiding, and knitting have greatly reduced the cost of producing fiber preforms.
All liquid composite molding processes require that the resin injected into the mold is a reactive liquid. Some resins such as epoxy and urethane are highly reactive and must be kept separate until just before they are injected into the mold. Other resins are activated by a catalyst in the holding tank. These multipart resin systems require complex mixing, metering, and use of injection equipment with accurate ratio control. The multipart resin systems also may require heating tanks, hoses, pipes, and pumps; motionless mixing; efficient circulation to help prevent cure or degradation of the resin in a holding tank; and easy and safe cleaning/purging.
This new liquid composite molding technique uses a one-part monomer and a solid catalyst crystallized onto the fiber reinforcement. The polymerization is initiated by the preform itself, eliminating the need to mix or add multiple resins and catalysts before filling the mold.
Since it uses a single resin, the process also eliminates the need for the mixing equipment and reduces the heating and cleaning requirements of the injection equipment.
The best material system for use with this technology is one that uses polydicyclopentadiene (pDCPD). This polymer forms very rapidly at room temperature by a ring-opening metathesis polymerization (ROMP) of its low-viscosity monomer. The first step in this process requires recrystallizing the catalyst onto the fiber preform. The reactive fiber preform is then placed into the mold, the mold is closed, and the monomer is injected into it. Once the monomer has had time to react with the catalyst on the fiber preform and polymerize, the completed part is removed from the mold.
This technique can be used in liquid composite molding, such as resin transfer molding (RTM), vacuum-assisted RTM (VARTM), and structural reaction injection molding (SRIM), for parts with end-use applications in:
- Marine and Automotive Equipment
- Ballistics Electronics
Because multiple resins and catalysts do not need to be added or mixed before being pumped into the mold, this process:
- Simplifies production: This technique provides a simpler process that requires fewer steps for producing polymer matrix composites
- Reduces equipment costs: This technique eliminates the need for complex metering and mixing equipment
- Reduces maintenance costs: The technique reduces the heating and cleaning requirements of the injection equipment