The transparent material known commonly by the brand name Plexiglass is scientifically called poly(methyl methacrylate), or PMMA, a type of transparent thermoplastic polymer. Understanding its strength requires looking beyond a single number, as it involves a complex set of mechanical properties. These properties include its response to sudden impact, its capacity to bear a constant load, and its resistance to environmental factors and chemical degradation. PMMA is often chosen as a substitute for glass due to its flexibility, lighter weight, and unique durability profile.
How Plexiglass Responds to Impact
The most recognized strength characteristic of PMMA is its resistance to sudden, blunt force, measured as impact strength. Plexiglass is significantly more impact-resistant than standard annealed glass, often cited as being 10 to 20 times stronger. This difference stems from the polymer’s flexible molecular structure, which allows the material to absorb shock and distribute the energy of the impact.
PMMA exhibits superior shatter resistance compared to traditional glass, which shatters into sharp shards upon impact. When subjected to extreme force, Plexiglass tends to crack or chip rather than exploding into numerous small pieces. Even if it breaks, the resulting pieces are typically larger with duller edges, making it a safer material for many applications. Plexiglass also demonstrates better impact performance than tempered glass, which still breaks into small, cube-like fragments.
Load Bearing and Structural Capacity
Plexiglass’s structural performance under constant pressure involves several engineering metrics, including tensile strength, compressive strength, and flexural modulus. Tensile strength measures the material’s resistance to being pulled apart, ranging from approximately 8,000 to 11,000 pounds per square inch (psi). Compressive strength is also high, often falling between 11,000 and 19,000 psi. The flexural modulus describes the material’s stiffness and resistance to bending under a load.
Despite its excellent impact resistance, PMMA has a lower yield strength than many metals, making it susceptible to permanent deformation under prolonged weight. This phenomenon, known as creep, is the tendency of a material to slowly deform over time when subjected to a constant static load. Because PMMA is a viscoelastic material, its long polymer chains can slowly shift under continuous pressure, causing it to elongate, sag, or warp. Engineers must account for this time-dependent nature when designing long-term structural components.
Vulnerabilities and Degradation
While mechanically strong, Plexiglass is not without its limitations, particularly regarding surface hardness and chemical resistance. The material has a relatively low surface hardness rating, making it prone to scratching and abrasion from everyday contact. This susceptibility to surface damage can compromise its clarity and long-term aesthetic appeal.
PMMA is vulnerable to certain organic solvents, which can cause swelling and dissolution. Chemicals like acetone, benzene, toluene, and chlorinated hydrocarbons are known to attack the material. Contact with these substances can lead to crazing, a type of failure where a network of fine, internal cracks forms, severely compromising mechanical strength and optical clarity.
Environmental exposure, particularly to heat and ultraviolet (UV) radiation, affects long-term durability. While many high-quality acrylics use UV stabilizers, prolonged sunlight exposure can still cause some grades to yellow and degrade. High temperatures also reduce the material’s rigidity, accelerating creep above its recommended continuous service temperature, typically around 160 to 200 degrees Fahrenheit.
Common Applications Driven by Strength
The strength profile of Plexiglass makes it the material of choice where high impact resistance and transparency are required over extreme rigidity. Its shatter-resistant properties make it ideal for protective barriers and sneeze guards in commercial settings. The material’s ability to withstand sudden shock is why it is used as safety glazing in sports arenas.
Specialized windows, such as those in aircraft or skylights, utilize PMMA due to its strength-to-weight ratio and durability against weather. Large-scale aquariums rely on thick acrylic sheets, where the material’s compressive strength supports immense hydrostatic pressure without cracking. The combination of toughness and lightness also makes it popular for machine guards in industrial environments, offering protection from flying debris while maintaining visibility.