PMMA (Polymethyl methacrylate) is a synthetic polymer of methyl methacrylate. PMMA Acrylic is a good alternative to glass. PMMA is a tough, highly transparent material with excellent resistance to ultraviolet radiation and weathering. It can be colored, molded, cut, drilled and formed. These properties make it ideal for many outdoor applications like in swimming pools and water features.
THE MANUFACTURING PROCESS
Acrylic is formed by a traditional process called bulk polymerization where the monomer and catalyst are poured into a mold and the reaction takes place.
The mold for producing sheets is assembled from two plates of polished glass separated by a flexible "window-frame" spacer. The spacer sits along the outer perimeter of the surface of the glass plates and forms a sealed cavity between the plates. The flexible spacer allows the mold cavity to shrink during the polymerization process to compensate for the volume contraction of the material as the reaction goes from individual molecules to link polymers.
AN open corner of each mold cavity is filled with pre-measured liquid syrup of methyl methacrylate monomer and catalyst which flows throughout the mold cavity to fill it.
The mold is then sealed for the reaction to take place. In the reaction, heat is generated but is fanned off in air ovens or is totally immersed in water. A programmed temperature cycle regime will ensure proper cure time without additional vaporization of the monomer solution. This will prevent the bubbles from forming. Cure time takes an average of 5-7 days depending on the thickness. When curing is done in a dry kiln facility, it allows high temperature above 110° Celsius. The high temperature reduces residue stresses or impurities in the material that might cause warping and other dimensional instabilities.
In the dry kiln, and after curing, acrylic panels can be formed to any shapes and curves according to templates.
The forming of acrylic dome is a process called "vacuum forming". The size of the dome can be customized to vary to varying heights. The thickness of the panel to use depends on the span of the diameter.