Poly (methyl meth acryl ate) (PMMA)

Poly (methyl meth acryl ate) (PMMA): is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass. It is sometimes called acrylic glass. 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.

Chemically, it is the synthetic of methyl methacrylate. It has since been sold under many different names including Lucite and Perspex. The often-seen spelling poly (methyl 2-methylpropanoate) with -an- is an error for poly (methyl 2-methylpropenoate), based on propenoic acid.

PMMA is an economical alternative to polycarbonate (PC) when extreme strength is not necessary. Additionally, PMMA does not contain the potentially harmful bisphenol-A subunits found in polycarbonate. It is often preferred because of its moderate properties, easy handling and processing, and low cost, but behaves in a brittle manner when loaded, especially under an impact force, and is more prone to scratching compared to conventional inorganic glass.

Injection moulding:

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.

Extrusion moulding:

Extrusion temperature : 180-250°C

A degassing screw with an L/D ratio of 20-30 is recommended.

APPLICATIONS OF PMMA

Aircraft

Displays meter cases, level indicators, food service trays, bath room accessories and interiors.

Appliances

Handles and knobs, light fixtures, drafting equipments, refrigerator trays, bowls, flower vases.

Automotive

Wind shields, glass replacements, mirror, reflectors, tail light and head light covers, instrument panels, display signs.

Optical 

Contact lenses, spectacle lenses, camera lenses, watch glasses.

Medical

Teeth and fixtures in dental surgery, medical instrument housings.

Building

Decorative lamp shades, bath tubs and sanitary wears

Strengths:

1. Outstanding transparency

2. Excellent UV resistance

3. High color brightness and stability

4. Surface hardness

5. Half the weight of glass

6. Good dimensional stability

7. Good insulating properties

Limitations:

1. Poor impact resistance

2. Limited heat resistance (80°C)

3. Limited chemical resistance, attacked by organic solvents

4. Poor wear and abrasion resistance

5. Cracking under load possible.

Properties 

1. Highly transparent and crystal clear material

2. Good weathering resistance

3. Strong, stiff and brittle in nature

4. Good arc resistance

5. High dielectric strength

6. Inflammable and slow burning

7. ESCR can be improved by annealing

8. Polar in nature absorbs moisture, required predrying before moulding