Detailed introduction of PMMA or acrylic

What is PMMA?

PMMA or acrylic is a widely used transparent plastic material known for its use in a variety of markets from car windows and smartphone screens to aquariums. It is a tough plastic that is easy to mold and is an excellent alternative to high-cost and less resilient glass.

Poly(methyl methacrylate) (PMMA), also known as acrylic or acrylic glass, is a transparent and rigid thermoplastic material widely used as a shatterproof alternative to glass.PMMA offers many technical advantages over other transparent polymers (PC, Polystyrene, etc.), few of which include:

• High UV and weathering resistance.
• Excellent light transmission
• Unlimited coloring options

Advantages and limitations of acrylic plastics

PMMA polymer has glass-like qualities - clarity, brightness, transparency, translucency - at half the weight and up to 10 times the impact resistance. It's stronger with less risk of damage; PMMA properties and benefits

Light Transmission - PMMA (acrylic) polymers have a refractive index of 1.49, resulting in high light transmission.PMMA grades allow 92% of light to pass through it, which is more than glass or other plastics. These plastic materials can be easily thermoformed without any loss of optical clarity. Compared to polystyrene and Polyethylene, PMMA is recommended for most outdoor applications due to its environmental stability.

Surface Hardness- PMMA is a tough, durable and lightweight thermoplastic. The density of acrylic ranges from 1.17 to 1.20 g/cm3 less than half that of glass. It has excellent scratch resistance compared to other transparent polymers such as polycarbonate, but less than glass. It has low moisture and water absorption, resulting in products made with good dimensional stability.

UV Stability- PMMA is highly resistant to UV light and weathering. Most commercial acrylic polymers are UV stabilized and have good resistance to prolonged exposure to sunlight because their mechanical and optical properties are quite different under these conditions, making PMMA suitable for outdoor applications with long term open air exposure.

Chemical Resistance - Acrylic resins are unaffected by aqueous solutions of most laboratory chemicals, detergents, cleaners, dilute inorganic acids, bases, and aliphatic hydrocarbons. However, acrylic resins are not recommended for use with chlorinated or aromatic hydrocarbons, esters or ketones.

Since pure PMMA sometimes does not have the performance criteria to meet the needs of a particular application, copolymerized monomers, additives or fillers are used to further enhance PMMA properties such as impact resistance, chemical resistance, flame retardancy, light diffusion, UV filtration or optical effects. Example:

• Use of methyl acrylate co-monomers to improve thermal stability by reducing the tendency to depolymerize during heat treatment.
• Addition of plasticizers to modify glass transition, impact strength
• Fillers can be added to modify final material properties or to improve cost-effectiveness
• Dyes can be added during polymerization to protect against UV light or to impart certain colors

Limitations of PMMA

Poor impact resistance

Limited heat resistance (80°C)

Limited chemical resistance and susceptibility to organic solvents

Poor abrasion and wear resistance

May crack under load

PMMA Processing Conditions

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

If ventilated cylinders are used, no pre-drying is required, but if regular cylinders are used, PMMA must be processed dry, and it is recommended that the pellets be pre-dried for up to 8 hours at 70-100° Celsius. Surface defects and blisters will form if wet pellets are handled.

Injection Molding

Melt temperature: 200-250°C

Mold temperature: 40-80°C

Due to poor flow characteristics, high injection pressures are required and slow injection may be necessary to obtain the correct flow rate.

Internal stresses can be removed 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 plastic welding processes such as hot blade, hot gas, ultrasonic or rotary welding.

Due to its transparency and stiffness, PMMA is also used as a 3D printing material, but it requires slightly higher temperatures and is easier to package compared to PLA. PMMA filaments are available in a wide range of colors.

PMMA vs PC

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

In addition, PMMA is less likely to scratch and will not yellow over time.Other benefits PMMA offers for PC include very high transmittance and better optical clarity, which can also be restored by polishing.PMMA is an excellent choice for optical devices because it causes less damage to tissues in the event of a fracture.

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.