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Pmma sheets

PMMA or Acrylic: Guide to Support Your Future ‘Transparent’ Developments

PMMA or acrylic is a widely used transparent plastic material known for its applications in various markets from car windows, smartphone screens to aquariums. It is a tough plastic, easy to shape and a great alternative to the high cost and less resilient glass. Explore polymethyl methacrylate (PMMA) in detail along with its key properties and understand what makes it an ideal choice in so many applications. Also, learn about conditions to process this polymer material and how to recycle it.

Overview

What is PMMA?

What is PMMA?

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
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.


Advantages and Limitations of Acrylic Plastic

Advantages and Limitations of Acrylic Plastic

Advantages of PMMA

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.
Properties & Advantages of Acrylic Plastic

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


How is PMMA Made?

How is PMMA Made?

Poly(methyl methacrylate) is produced by free‐radical polymerization of methyl methacrylate in mass (when it is in sheet form) or suspension polymerization

PMMA Structure


PMMA Processing Conditions

PMMA Processing Conditions

PMMA Processing Conditions

PMMA is suitable for processing by injection molding, extrusion, extrusion blow molding (impact modified acrylics only), thermoforming and casting.

Pre-drying is not necessary if a vented cylinder is used but if a normal cylinder is used then PMMA must be processed dry and it is advisable to pre-dry the granules for up to 8 hours at 70-100°C. Surface defects and blisters will form if damp granules are processed.

Injection Molding

  • Melt temperature : 200-250°C
  • Mold temperature : 40-80°C
  • High injection pressures are needed because of poor flow properties and it may be necessary to inject slowly to get the correct flow
  • Internal stresses can be eliminated by heating at 80°C


Extrusion

  • Extrusion temperature : 180-250°C 
  • A degassing screw with an L/D ratio of 20-30 is recommended

PMMA can be welded by all the plastics welding processes such as hot‐blade, hot‐gas, ultrasonic or spin welding.

Due to its transparency and stiffness, PMMA is also used as 3D Printing material but it requires slightly high temperature and a bit more prone to wrap as compared to PLA. PMMA filaments are available in wide array of colors.


Toxicity and Recyclability of PMMA

Toxicity and Recyclability of PMMA

Acrylic is 100% recyclable and Non-toxicPolymethyl methacrylate is highly biocompatible, 100% recyclable and non-biodegradable material. PMMA is considered as a group 7 plastic.

There are several ways to recycle PMMA. Often these recycling processes involve pyrolysis, in which the PMMA is extremely heated in the absence of oxygen. Another procedure involves depolymerization of PMMA using molten lead to obtain the monomer MMA in a purity >98%. However, this recycling process is not environmentally viable due to use of lead and production of harmful byproducts and therefore limiting the use of the acrylic.

Recycled Acrylic can be formed into sheets that are used in construction for windows and doors, medical sector, advertising industry and more.

Acrylic is a “BPA-Free” substitute for PC and non-toxic in solid form.

PMMA is naturally compatible with human tissue, and was a frequent component of contact lenses in the past; it's also been used for dentures and bone replacement.


PMMA vs PC

PMMA vs PC

Acrylic, Polycarbonate and glass are all transparent materials and as discussed above, PC and PMMA are suitable, shatter-resistance alternatives to glass. PMMA is often used as a lightweight alternative to glass and a reasonable substitute to polycarbonate (PC) thanks to its cost-effectiveness and when extreme strength is not essential.

Also, PMMA is less likely to scratch and does not yellow over a period of time. The other benefits which PMMA offers PC includes very high transmissivity and better optical clarity which can be also be restored by polishing. PMMA is a great choice for optical devices because it is less damaging to tissues when it is fractured.

Although, by making PMMA/PC blends, the excellent optical clarity and surface hardness of PMMA can be combined with the superior toughness and very high glass transition temperature of PC.

Transparency – Get Channel Update


Key Applications

Key Properties

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