Polymethyl Methacrylate (PMMA) - Properties, Uses & Application

What is PMMA?

Polymethyl methacrylate is a transparent material. It is also known as acrylic or acrylic glass. It is a rigid thermoplastic widely used as a shatterproof replacement for glass. PMMA has many technical advantages over other transparent polymers (PC and PS) such as:

High resistance to UV light and weathering
Excellent light transmission
Unlimited coloring options

PMMA or poly (methyl 2‐methylpropenoate) is produced from the 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. They 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.

How is PMMA made?

The monomer used to produce PMMA is methyl methacrylate. Free-radical polymerization of this monomer occurs when it is in sheet form. This transparent material can also be produced using suspension polymerization.

What are the features of PMMA?

PMMA polymer exhibits glass-like qualities. These include clarity, brilliance, transparency, and translucence – at half the weight with up to 10 times the impact resistance. It is more robust and has less risk of damage.

Transmittance – PMMA (Acrylic) polymer has a Refractive Index of 1.49. Hence it 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 applications 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, but 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 their 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. For example, detergents, cleaners, dilute inorganic acids, alkalis, and aliphatic hydrocarbons. However, acrylics are NOT recommended for use with chlorinated or aromatic hydrocarbons, esters, or ketones. Check out chemically resistant PMMA grades »

How to enhance material properties?

Pure PMMA sometimes does not exhibit property standards. In order to meet the demand from specific applications, additives are added. They further enhance the properties of PMMA. These include impact resistance, chemical resistance, flame retardancy, light diffusion, UV light filtering, or optical effects.

Co-monomer methyl acrylate enhances 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
Dyes can be added during the polymerization used for UV light protection or impart certain color

What are the processing conditions of PMMA?

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. It is advisable to pre-dry the granules at 70-100°C for up to 8 hours. 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. 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 a slightly high temperature and is a bit more prone to wrap as compared to PLA. PMMA filaments are available in a wide array of colors.

Is PMMA recyclable?

Polymethyl 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.
Depolymerization of PMMA using molten lead to obtain the monomer MMA in a purity >98%.

However, the second process is not environmentally viable due to the use of lead. It also produces harmful byproducts.

Recycled Acrylic can be formed into sheets. They are used in:

the construction of windows and doors,
the medical sector,
the advertising industry, and more.

Get connected with Donald Rosato where he will help you establish a successful plastics recycling system by clearly understanding the recovery & reuse mode. He will also share an in-depth knowledge about advanced technologies (depolymerization, pyrolysis, mechanical and solvent-based recycling), materials & applications.

Plastic Recycling Innovation: Materials, Technologies, Applications Update

Is PMMA toxic?

Acrylic is a “BPA-Free” substitute for PC and is non-toxic in solid form. PMMA is naturally compatible with human tissue. It was a frequent component of contact lenses in the past. Now, it's also been used for dentures and bone replacement.

What are the 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 is possible

PMMA vs PC - What is the difference?

Acrylic, Polycarbonate, and glass are all transparent materials. PC and PMMA are suitable, shatter-resistance alternatives to glass. PMMA is often used as a lightweight alternative to glass. It is a reasonable substitute for polycarbonate (PC) due 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 over PC include:

very high transmissivity and better optical clarity
can 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.

Find innovations related to all transparent plastics and polymers here »

What are the commercially available PMMA grades?

View a wide range of polymethylmethacrylate (PMMA) grades available in the market today, analyze technical data of each product, get technical assistance or request samples.

Key Properties

	Property	POLYMETHYL METHACRYLATE
Chemical Resistance
Acetone @ 100%, 20°C	Non Satisfactory
Ammonium hydroxide @ 30%, 20°C	Satisfactory
Ammonium hydroxide @ diluted, 20°C	Satisfactory
Aromatic hydrocarbons @ 20°C	Non Satisfactory
Aromatic hydrocarbons @ hot conditions	Non Satisfactory
Benzene @ 100%, 20°C	Non Satisfactory
Butylacetate @ 100%, 20°C	Non Satisfactory
Butylacetate @ 100%, 60°C	Non Satisfactory
Chlorinated solvents @ 20°C	Non Satisfactory
Chloroform @ 20°C	Non Satisfactory
Dioctylphtalate @ 100%, 100°C	Non Satisfactory
Dioctylphtalate @ 100%, 20°C	Limited
Ethanol @ 96%, 20°C	Limited
Ethyleneglycol (Ethane diol) @ 100%, 100°C	Non Satisfactory
Ethyleneglycol (Ethane diol) @ 100%, 20°C	Satisfactory
Glycerol @ 100%, 20°C	Satisfactory
Kerosene @ 20°C	Satisfactory
Methanol @ 100%, 20°C	Non Satisfactory
Methylethyl ketone @ 100%, 20°C	Non Satisfactory
Mineral oil @ 20°C	Satisfactory
Phenol @ 20°C	Non Satisfactory
Silicone oil @ 20°C	Limited
Sodium hydroxide @ 10%, 20°C	Satisfactory
Sodium hypochlorite @ 20%, 20°C	Satisfactory
Strong acids @ concentrated, 20°C	Limited
Toluene @ 20°C	Non Satisfactory
Toluene @ 60°C	Non Satisfactory
Xylene @ 20°C	Non Satisfactory
Electrical
Dielectric Constant	2-5
Dielectric Strength, kV/mm	15-22
Dissipation Factor x 10^-4	200-2000
Volume Resistivity x 10¹⁵, Ohm.cm	14-16
Mechanical
Elongation at Break, %	2-10
Elongation at Yield, %	2-10
Flexural Modulus, Gpa	2.5-3.5
Hardness Rockwell M	70-105
Hardness Shore D	90-99
Strength at Break (Tensile), MPa	38-70
Strength at Yield (Tensile), MPa	38-70
Toughness (Notched Izod Impact at Room Temperature), J/m	10-25
Young's Modulus, GPa	2.5-3.5
Optical
Haze, %	1-96
Transparency (Visible Light Transmission), %	80-93
Physical
Density, g/cm³	1.17-1.2
Glass Transition Temperature, °C	90-110
Shrinkage, %	0.2-0.8
Water Absorption 24 hours, %	0.1-0.4
UV Light Resistance	Good
Gamma Radiation Resistance	Good
Sterilization Resistance (Repeated)	Poor
Service Temperature
HDT @0.46 Mpa (67 psi), °C	80-110
HDT @1.8 Mpa (264 psi), °C	70-100
Max Continuous Service Temperature, °C	70-90
Thermal
Coefficient of Linear Thermal Expansion x 10^-5, /°C	5-9
Thermal Insulation, W/m.K	0.15-0.25
Fire Resistance (LOI), %	19-20
Flammability, UL94	HB

Key Applications

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Comprehensive Guide on Polymethyl methacrylate (PMMA or Acrylic)