Plexiglass and polycarbonate are popular transparent plastics used as alternatives to glass, but they are distinct materials. While they look similar, they have different chemical compositions and physical characteristics, making them suitable for different applications. Plexiglass is a generic term for acrylic, or Polymethyl Methacrylate (PMMA), a rigid polymer prized for its clarity. Polycarbonate (PC) is a different thermoplastic polymer known for its extreme durability. These structural differences impact how the materials are cut, formed, and safely used.
Chemical Identity and Composition
The distinction between these two materials begins at the molecular level. Plexiglass is Polymethyl Methacrylate (PMMA), formed through the polymerization of methyl methacrylate monomers. This simple, rigid molecular structure gives acrylic its optical clarity and surface hardness. Common trade names for PMMA include Plexiglas and Lucite.
Polycarbonate is a high-molecular-weight polymer containing carbonate groups in its chemical backbone, typically synthesized using bisphenol A. This complex structure provides the material’s unique combination of flexibility and extreme toughness. Polycarbonate is sold under trade names such as Lexan and Makrolon.
Key Physical Performance Differences
The molecular arrangement creates dramatic differences in performance, especially regarding strength and surface quality. Polycarbonate has superior impact resistance, up to 250 times greater than standard glass. Acrylic is significantly more brittle, offering only 10 to 17 times the impact resistance of glass, and tends to crack or shatter under high force.
Acrylic maintains a slight advantage in optical quality, offering superior light transmission of up to 92% and a glossier finish than polycarbonate. PMMA is also inherently more UV stable and less prone to yellowing from sunlight if left untreated. Polycarbonate, though transparent, may exhibit a faint tint and can yellow over time, often requiring a specialized UV-stabilizing coating for outdoor use.
Regarding surface wear, acrylic is the harder material, generally scoring higher on the Rockwell M hardness scale. This increased surface hardness makes acrylic more scratch-resistant than polycarbonate, which is softer and more easily marred by cleaning or light abrasion. Furthermore, acrylic softens around 70 degrees Celsius, while polycarbonate maintains its structural integrity at significantly higher temperatures, up to 120 degrees Celsius.
Fabrication and Handling
The differences in rigidity and molecular structure dictate how each material is processed during fabrication. Polycarbonate is a softer, more flexible material that can be easily cut and drilled without the risk of cracking or chipping, making it highly forgiving for on-site adjustments. Acrylic is harder, requiring specific tools and slower feed rates to prevent splintering during cutting and drilling operations.
Polycarbonate can be cold-formed, meaning sheets can be bent into gentle curves without needing to be heated. Acrylic, being more rigid, requires heat (thermoforming) to be bent into a permanent shape.
When bonding, acrylic is easily joined using solvent cement, which chemically welds the pieces together to create strong, near-invisible seams. Polycarbonate is not compatible with common solvent cements and requires specialized structural adhesives or mechanical fasteners for assembly. A safety difference is that acrylic burns readily, while polycarbonate is self-extinguishing and often meets specific flame-retardant standards.
Practical Applications and Relative Cost
The distinct performance profiles guide the selection of these materials for real-world uses. Acrylic is preferred where optical clarity, surface finish, and aesthetic appeal are the primary concerns. Applications include:
- Retail display cases
- Picture frames
- Lighting fixtures
- Large aquariums, where the risk of high impact is low
Polycarbonate is reserved for demanding applications requiring maximum safety and extreme impact resistance. Uses include:
- Machine guards
- Security glazing
- Motorcycle helmet visors
- Vandal-resistant light covers
Polycarbonate is generally the more expensive option, often costing 15% to 40% more than a comparable sheet of acrylic. Acrylic is the more cost-effective solution for projects prioritizing clarity over ultimate durability. The higher cost of polycarbonate is justified when the application demands superior toughness and resilience against potential breakage.