Acrylic is considered a type of plastic. Acrylic is the common name for a synthetic material known chemically as Polymethyl Methacrylate (PMMA), which falls within the expansive family of plastics. This material is a synthetic organic compound that can be molded into solid objects, a defining characteristic of all plastics. While it is often marketed under trade names like Plexiglas or Lucite and used as a glass substitute, its underlying chemical structure confirms its classification as a plastic material.
Defining the Plastic Family
Plastic is not a single material but a broad category of synthetic or semi-synthetic organic compounds characterized by their malleability. The defining feature of these materials is their molecular structure, which consists of very large molecules called polymers. Polymers are long chains formed when smaller, identical units, called monomers, link together in a process known as polymerization.
This chain-like structure allows the material to exhibit plasticity, meaning it can be permanently deformed without breaking. This is why plastics are so easily molded into complex shapes. Most modern plastics, including acrylic, are synthetic polymers primarily derived from petrochemicals. Although all plastics are polymers, not all polymers are considered plastics, as natural polymers like DNA and cellulose exist outside this category.
Acrylic’s Chemical Identity
Acrylic plastic, or PMMA, is derived from the polymerization of its specific monomer, methyl methacrylate. The resulting polymer chain is a rigid, transparent material that belongs to the acrylic family of resins. The production process involves linking these methyl methacrylate molecules together to form the solid plastic.
The chemical structure of PMMA, specifically the presence of pendant methyl groups, prevents the polymer chains from packing tightly together in a crystalline fashion. This characteristic grants PMMA its tough, rigid nature and its nearly perfect transmission of visible light. PMMA is classified as a thermoplastic. Thermoplastics soften and become liquid when heated to their melting point, meaning they can be repeatedly melted, reformed, and cooled without undergoing permanent chemical degradation. This thermoplastic property allows acrylic to be easily shaped using methods like injection molding, extrusion, or thermoforming, and also allows for recycling.
Comparing Acrylic to Common Household Plastics
While acrylic is a plastic, its unique chemical makeup gives it a distinct performance profile compared to other common plastics like polyethylene (PE), polypropylene (PP), or polycarbonate (PC). PMMA’s exceptional optical clarity allows it to transmit up to 92% of visible light, often exceeding the clarity of glass and other transparent plastics. This makes it the material of choice for applications where superior transparency and minimal color shift are required, such as lenses and display cases.
However, this high optical quality comes with trade-offs in mechanical strength when compared to some other plastics. For example, acrylic is significantly more rigid and brittle than polycarbonate, which offers much higher impact resistance. Polycarbonate is therefore favored for high-impact applications like safety glazing, while acrylic is preferred for its superior surface hardness and scratch resistance. PMMA exhibits high resistance to UV light and weathering, which prevents the yellowing and degradation that can affect other plastics when they are exposed to the outdoors over time.