What is Acrylic (PMMA) Plastic?
Polymethyl methacrylate (PMMA), also known as acrylic or acrylic glass, is a transparent and rigid thermoplastic material widely used as a shatterproof replacement for glass. PMMA has many technical advantages over other transparent polymer (PC, polystyrene etc.), few of them include:

·         High resistance to UV light and weathering,

·         Excellent light transmission 

·         Unlimited coloring options

PMMA or poly (methyl 2‐methylpropenoate) is produced from monomer methyl methacrylate.

Structure of PMMA Monomer- Methyl Methacrylate
Molecular formula: C₅H₈O₂

It is a clear, colorless polymer available in pellet, small granules and sheet forms, which are then formed with all thermoplastic methods (including injection molding, compression molding, and extrusion). The highest quality PMMA sheets are produced by cell casting, but in this case, the polymerization and molding steps occur concurrently. It is commonly called acrylic glass.

The strength of the material is higher than molding grades owing to its extremely high molecular mass. Rubber toughening has been used to increase the toughness of PMMA owing to its brittle behavior in response to applied loads. PMMA is 100% recyclable.

Common Trade Names of Acrylic

Chemist and industrialist Otto Röhm of Rohm and Haas AG in Germany patented the trade name “Plexiglas” in 1933. Today, notable trade names include:

Properties and Advantages of Acrylic Plastic

PMMA polymer exhibits glass-like qualities – clarity, brilliance, transparency, translucence – at half the weight with up to 10 times the impact resistance. It is more robust and have less risk of damage. Let’s discuss PMMA properties & benefits in detail:

Transmittance – PMMA (Acrylic) polymer has a Refractive Index of 1.49 and hence offers high light transmittance. PMMA grades allow 92% of light to pass through it, which is more than glass or other plastics. These plastic materials can easily be thermoformed without any loss in optical clarity. As compared to polystyrene and polyethylene, PMMA is recommended for most outdoor application thanks to its environmental stability.

Surface Hardness – PMMA is a tough, durable and lightweight thermoplastic. The density of acrylic ranges between 1.17-1.20 g/cm³ which is half less than that of glass. It has excellent scratch resistance when compared to other transparent polymers like Polycarbonate, however less than glass. It exhibits low moisture and water absorbing capacity, due to which products made have good dimensional stability.

UV Stability – PMMA has high resistance to UV light and weathering. Most commercial acrylic polymers are UV stabilized for good resistance to prolonged exposure to sunlight as its mechanical and optical properties fairly vary under these conditions, Hence, PMMA is suitable for outdoor applications intended for long-term open-air exposure.

Chemical Resistance – Acrylics are unaffected by aqueous solutions of most laboratory chemicals, by detergents, cleaners, dilute inorganic acids, alkalies, and aliphatic hydrocarbons. However, acrylics are NOT recommended for use with chlorinated or aromatic hydrocarbons, esters, or ketones.

Since pure PMMA sometimes does not exhibit the property standards to meet the demand from specific applications, co-monomers, additives or fillers are used to further enhance PMMA properties such as impact resistance, chemical resistance, flame retardancy, light diffusion, UV light filtering, or optical effects. For examples:

·         Use of co-monomer methyl acrylate enhances the thermal stability by decreasing the tendency to depolymerize during heat processing

·         Plasticizers are added to modify glass transition, impact strength

·         Fillers can be added to modify final material properties or improve cost effectiveness

·         Dye can be added during polymerization for UV light protection or impart certain color

Limitations of PMMA

·         Poor impact resistance

·         Limited heat resistance (80°C)

·         Limited chemical resistance, prone to attack by organic solvents

·         Poor wear and abrasion resistance

·         Cracking under load possible