Polydicyclopentadiene
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Polydicyclopentadiene (PDCPD) is a relatively new (early 90's) polymer which is formed through Ring opening metathesis polymerisation (ROMP) of Dicyclopentadiene (DCPD). The difference between the various systems lies in the type of catalyst used to create the polymer, but the final polymer properties are similar. Any difference which can be seen is often insignificant to the end user unless the application requires to go to the limits of the PDCPD material properties. The three tradenames are Telene, Metton and Pentam (see links to the respective companies below).
Contents
The Chemical System
The reacting system is formulated in such a way that two components need to be mixed at equal volume (1:1 ratio). Both components contain mainly DCPD with some additional additives. The difference between both components is crucial, but constitutes only a small fraction of the total formulation: the catalyst system is divided into two parts, each part going into a separate component. When both components are mixed, the complete catalyst system is recombined and becomes active. This is an important difference from other Reaction Injection Moulding (RIM) systems like polyurethane, since the reaction is not stoichiometric. The 1:1 ratio for DCPD moulding is not critical since this is not a combination of two different chemical elements to form a specific matrix. Significant changes in ratio will slow down the system's reactivity because fewer active reaction nuclei are being formed. This also changes the final properties somewhat. The current industrial pumps used on RIM equipment are accurate enough to ensure that the mixing ratio stays within the necessary limits.
Equipment
DCPD resins are transformed using high pressure RIM equipment as used in the polyurethane industry, with some small changes to be considered. As a reference, a widely used machine to inject DCPD resins is the Cannon A-100 fitted with a DCPD kit. The most important change is that the resin can never be in contact with air or moisture, which required a nitrogen blanket in the tanks. The tools or moulds are closed tools and are being clamped using a hydraulic press. Because the resins shrink about 6% in volume during reaction, these presses (also called clamping units) don't have to handle high pressures such as for Sheet Moulding Compound (SMC) or expanding polyurethane.
Tooling
Most tooling for PDCPD is made from aluminium. Flat parts can be made from machined aluminium while deeper 3D-shaped parts are often made in cast aluminium tools. It is important to know that these tools have to take the volumetric shrinkage into account, cannot have any undercuts and need gaskets all around the cavities.
Process Considerations
The liquid resin has a density of 0.97 and reacts into a solid with a density of 1.03 which constitutes a volumetric shrinkage of 6%. Since most parts are panels, most of the shrinkage will happen in the Z-axis (thickness). This makes the parts self-demoulding as they do not have a good contact with the core side of the tool [The core side is the side which will be the back side of the part. The front side of the part is called the matrix side].
A reacting system is always governed by temperature - in any form. This means that the temperature of the liquid components has a strong influence on the reactivity. So do the temperatures inside the tool. To ensure that one side has an excellent surface finish, the temperature on that side needs to be higher than on the core side. Both tool-halves are therefore tempered at a different temperature with typical values of 60°C and 80°C.
Typical cycle times for moulding parts range between 4 and 6 minutes.
Properties
PDCPD has a combination of properties with the most important being:
- high impact resistance
- high chemical corrosion resistance
- high Heat deflection temperature (HDT)
For the best information on all properties of this resin system and polymer, it is best to contact the material supplier or to visit their respective websites.
PDCPD does not contain any fiber reinforcement although a fiber reinforced version has been developed by Telene S.A.S. PDCPD allows to vary the thickness throughout a part, to incorporate ribs and to overmould inserts for an easy assembly of the parts. PDCPD cannot be painted in mass and needs to be painted after moulding.
Applications
Since PDCPD is still a young material, the number of applications is quite limited. The major success story is in the field of body panels, mainly for tractors, construction equipment, trucks and buses. In the industrial applications, the main success story is components for chlor-alkali production (e.g. cell covers for electrolyzers). Other applications can be developed where impact resistance in combination with rigidity, 3D design and/or corrosion resistance is required.
Economic considerations
PDCPD has proven to be economically interesting when considering large parts (>5 kg or >1m²) in low to medium series (1,000 to 20,000 parts per year). Factors that make this case are:
- low initial investment versus injection moulding or SMC
- high capacity due to the low cycle times compared to hand lay-up or Resin transfer moulding (RTM)
- fast development cycles for new projects
External links
- Telene S.A.S. : Telene resin system
- Metton America Inc : Metton resin system
- Rimtec : Pentam resin system
