Common Materials Extruded into Sheet
ABS (Acrylonitrile-Butadiene-Styrene)
ABS provides high rigidity and impact strength together with excellent abrasion resistance. ABS sheet has high resistance to chemicals, moisture, and high temperatures. Frequently ABS is the main layer in coextruded structures with acrylic added for gloss.
ABS sheet is widely used in the manufacture of:
- Refrigerator and Appliances
- Tub and Shower Surrounds
- Boats and boating accessories
- Truck Caps
- Computer Housings
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HDPE (High Density Polyethylene)
HDPE sheet properties include low co-efficient of friction, high surface release, excellent impact resistance (even at low temperatures), and the fact that it is a weld-able plastic. Together with a gradual melting point, HDPE sheet is well suited for thermoforming heavier gauge industrial items such as truck bed liners, pallets, paddleboats and even portable structures.
HDPE is also a common choice for geomembrane and geogrid sheet.
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PC (Polycarbonate)
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Polycarbonate sheet, the original "bullet proof glass", is widely used to produce thermoformed architectural elements, single and multi-layer glazing, and windshields (aircraft, motorcycle, boats). PC has excellent clarity, is virtually unbreakable, weighs less than glass, is flame retardant, does not yellow, and offers opportunities to increase energy conservation. Disadvantages include low chemical resistance and stress cracking.
PET (Polyethylene Terephthalate)
PET is an engineered thermoplastic. Advantageous properties including excellent clarity, chemical and wear resistance, and stiffness make PET sheet well suited for the production of food packaging, electronics packaging, cups, and point of purchase displays.
In its amorphous state, PET is clear. With the additive of an agent, it can be crystallized yielding CPET. CPET is translucent but can withstand extreme temperature ranges, so it has been widely used in production of frozen meal trays that can be cooked in conventional ovens. Since microwaves are commonly used, polypropylene has replaced CPET in many instances.
While most plastic products can be recycled but are not, thanks to PET bottle collection, PET packages can be recycled. Post consumer PET is commonly used to produce fruit and vegetable clamshells, fleece fabrics, and carpet fibers.
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PETG (Polyethylene Terephthalate Glycol)
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PETG provides excellent clarity and toughness, but it has an important advantage over PET in that it can stand up to gamma irradiation used to sterilize medical device kits. PETG is also widely used in display fixtures.
PLA (Polylactic Acid) and Biopolmers
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PLA, an early biopolymer, is rapidly coming into use because of its natural origins, biodegradability, and overall environmental appeal.
PLA is a sustainable material made from renewable resources, such as corn, wheat, or sugarcane. While it is more expensive than petrochemical-derived polymers, as production increases the price is expected to drop. PLA has excellent clarity, but it is not suitable for prolonged use at high temperatures, where PET is preferred.
PLA sheet is used to make biodegradable/compostable beverage cups and food packages.
There is some concern that PLA will contaminate the PET recycling stream. Just how much of a problem this will be, and how difficult and costly it will be to sort PLA from PET remains to be seen.
Biopolymer options and applications are expected to undergo rapid growth as a result of an ever increasing awareness of environmental impact and the value placed on sustainability.
PMMA [Poly(methyl methacrylate)]
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PMMA, commonly called acrylic, is the synthetic polymer of methyl methacrylate.
Acrylic sheet is more impact resistant than glass, can diffuse light well, has a high molecular weight and can be fabricated, and is available in a variety of finishes.
Applications include signage, display fixtures, and non-critical windshields.
Extrusion is the most uniform and economic way to run acrylic sheet under 1/8". Sheet between 1/8"- 1/4" is more economically made by continuous casting. Thicker sheet is cell cast.
Unlike extrusion sheet scrap, cast sheet scrap will soften but not melt because it is crosslinked, so it is often granulated and used as a purging compound to clean extruders.
PP (Polypropylene)
Polypropylene is very economical, can be run in a full range of colors (or clear), and is easily processed and thermoformed. PP has a high melting point (well over 100?C) so it is suitable for use in heat processed food and medical applications that require sterilization. Other attributes include excellent chemical resistance, good rigidity, flexibility and impact resistance, together with good insulating properties.
Common products made of PP sheet include yogurt and dairy containers, agricultural pots, and disposable beverage cups. It is widely used in graphic arts, signage, automotive, agricultural and construction industries as well.
PP sheet must be corona treated if it is to be printed.
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PS (Polystyrene)
Polystyrene is a versatile and inexpensive rigid material that has long been used in the production of sheet for food packaging, dairy containers, disposable service items, and agricultural planting trays.
The two main types of PS include crystal or general purpose polystyrene (GPPS), and medium or high impact polystyrene (HIPS) that includes polybutadiene to improve impact resistance and toughness.
Attractive disposable cups may be thermoformed of HIPS sheet that has been produced via coextrusion, with different colors top and bottom and a thin gloss layer of GPPS. GPPS sheet is by itself is very clear but quite brittle, but when it undergoes a secondary inline biaxially orienting process, it results in oriented polystyrene (OPS) with better stiffness. OPS is widely used for bakery and salad bar packages.
PS faces increasingly tough competition from PP and PET. Although recyclable, due to its low value it is rarely collected.
Polystyrene can also be foamed into a very low density packaging and insulation material. It is widely used for thermoformed meat packaging trays and for house insulation with densities below 0.05. It is foamed by the addition of a solvent or carbon dioxide under high pressure to the melted GPPS which is then cooled in a two step process prior to extrusion. Thermoformable sheet must be extruded in a horizontal tubular form to permit free expansion in all directions before winding into rolls. The heavier insulation board is produced by a variety of proprietary processes.
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A Sheet Extrusion expert
