Polymerizable cements are those in which a catalyst is added to an already thick monomer/polymer syrup to promote rapid hardening. Cements PS-30 and Weld-On 40 or 42 are polymerizable cements of this type. They are suitable for cementing all types of Plexiglas® acrylic sheet. At room temperature, the cements harden (polymerize) in the container in about 45 minutes after mixing the components. They will harden more rapidly at higher temperatures. The cement joints are usually strong enough for handling one to two hours after assembly depending upon part configuration. The joints may be machined four hours after assembly, but it is better to wait 24 hours.
PS-30 and Weld-On 40 or 42 joints retain excellent appearance and color stability after outdoor exposure. These cements produce clear, transparent joints and should be used when the clarity and appearance of the joints are important.
PS-30 and Weld-On 40 or 42 should be used at temperatures no lower than 65°F. If cementing is done in a room cooler than 65°F, it will require a longer time to harden and the joint strength will be reduced. The cement should be prepared with the correct proportions of components (preferably fresh) as given in the supplier’s instructions and thoroughly mixed, making sure neither the mixing container nor mixing paddle adds color or affects the hardening of the cement. Clean glass or polyethylene mixing containers are preferred. Table 4, page 23, summarizes these procedures.
PS-30 may be thinned by adding up to 25 percent MMA inhibited monomer to Component A to minimize bubbles when laminating. Up to twice the normally recommended amount of Component B may be used to increase the polymerizing rates.
Adding about 10 percent (by weight) Plexiglas® VS-100 acrylic molding resin will reduce shrinkage of the cement during poly- merization, but also decreases joint strength slightly. The pellets must be thoroughly dissolved before mixing the components.
Because of their short pot life (approximately 45 minutes), Cement PS-30 and Weld-On 40 or 42 must be used quickly once the components are mixed. Time consumed in preparation shortens the effective working time, making it necessary to have everything ready to be cemented before the cements are mixed. For better handling, pour cement within 20 minutes of mixing.
For maximum joint strength, the final cement joint should be free of bubbles. It will usually be sufficient to allow the mixed cement to stand for 10 minutes before cementing to allow bubbles to rise to the surface.
To remove the bubbles quickly, spin the cement with an electric drill. This is done by drilling a hole in the center of a metal jar cap and placing a bolt through it, then placing a nut on the outside. This bolt is gripped by the chuck of an electric drill. Screw jar into cap and spin cement for one minute. This is for up to 6-ounce jars only. For large sizes, a centrifuge that contains the jar should be used.