Plexiglass is a common term synonymous with a clear, durable plastic material. Technically, “Plexiglas” is a registered brand name, but the generic material is known as acrylic glass or acrylic sheet. This thermoplastic polymer is widely used as an alternative to traditional glass due to its unique combination of properties. Its structure allows for a versatile manufacturing process, ultimately leading to a product that is lighter, more impact-resistant, and easily shaped.
The Core Chemical Component
The fundamental building block of Plexiglass is a synthetic polymer named Poly(methyl methacrylate), or PMMA for short. This chemical compound is classified as a thermoplastic. The structure of PMMA is a long, repeating chain of smaller molecules called monomers. The specific monomer used to create this chain is methyl methacrylate (MMA). Through polymerization, thousands of these individual MMA units link together to form the long, stable PMMA polymer chain. Unlike traditional inorganic glass, which is made from silica and various mineral oxides, PMMA is an organic compound derived from petroleum products. This difference in composition gives the finished plastic its distinct advantages.
Shaping the Material
The PMMA polymer is converted into usable sheets or custom shapes primarily through two major industrial methods: casting and extrusion.
Casting
The casting process involves pouring the liquid methyl methacrylate monomer, along with a catalyst, into a mold, typically made of two glass sheets. The liquid then polymerizes and hardens under the influence of heat or ultraviolet light. This method is generally more labor-intensive and expensive, but it yields a higher-quality, more homogenous product with greater chemical resistance and a much higher molecular mass.
Extrusion
Extrusion starts with already polymerized PMMA in the form of pellets or granules. The material is melted down and continuously forced through a specialized die to create a sheet of uniform thickness. This faster, more continuous manufacturing process makes extruded acrylic more economical and suitable for large-volume production. Extruded sheets typically have a tighter thickness tolerance, though they may have lower impact strength and chemical resistance compared to cast acrylic.
Key Physical Characteristics
One of the most valuable attributes of PMMA is its exceptional optical clarity, allowing up to 92% of visible light to pass through, which is comparable to high-quality optical glass. This high light transmittance, combined with a refractive index of approximately 1.49, makes it a popular choice for windows and lenses.
The material is also prized for its superior impact resistance; it can be up to ten times more shatter-resistant than traditional glass. While not as tough as polycarbonate, Plexiglass is significantly less likely to break into sharp pieces upon impact, offering a safer alternative.
The density of PMMA ranges from 1.17 to 1.20 grams per cubic centimeter, meaning it is approximately half the weight of the same volume of glass. This lightweight nature simplifies handling, transport, and installation in applications like large architectural glazing. Additionally, PMMA is a thermoplastic that can be heated and easily shaped or thermoformed without losing its optical clarity.