Polymers

POLYETHELENE

Polyethelene, Polythene, PE, LDPE, HDPE, MDPE, LLDPE

LDPE (Low Density Polyethylene) is defined by a density range of 0.910 - 0.940 g/cm3. It has a high degree of short and long chain branching, which means that the chains do not pack into the crystal structure as well. It has therefore less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. LDPE is created by free radical polymerization. The high degree of branches with long chains gives molten LDPE unique and desirable flow properties.

HDPE (High Density Polyethylene) is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst.

MDPE (Medium Density Polyethylene) is defined by a density range of 0.926 - 0.940 g/cm3. MDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts.

LLDPE (Linear-Low Density Polyethylene) is defined by a density range of 0.915 - 0.925 g/cm3. is a substantially linear polymer, with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (e.g. 1-butene, 1-hexene, and 1-octene).

LDPE Properties:

Semi-rigid, translucent, very tough, weatherproof, good chemical resistance, low water absorption, easily processed by most methods, low cost.

LDPE Physical Properties Value:
Tensile Strength: 0.20 - 0.40 N/mm2
Notched Impact Strength: no break
Thermal Coefficient of Expansion: 100 - 220 x 10-6
Max. Continued Use Temperature: 65 oC (149 oF)
Melting Point: 110 oC (230 oF)
Glass Transition Temperature: -125 oC (-193 oF)
Density: 0.910 - 0.940 g/cm3

HDPE Properties

Flexible, translucent/waxy, weatherproof, good low temperature toughness (to -60'C), easy to process by most methods, low cost, good chemical resistance.

HDPE Physical Properties Value
Tensile Strength: 0.20 - 0.40 N/mm2
Notched Impact Strength: no break
Thermal Coefficient of Expansion: 100 - 220 x 10-6
Max. Continued Use Temperature: 65 oC (149 oF)
Melting Point: 126 oC (259 oF)
Density: 0.941 - 0.965 g/cm3

Polypropene, PP

The symbol for polypropylene developed by the Society of the Plastics Industry so that items can be labeled for easy recycling is:
Semi-rigid, translucent, good chemical resistance, tough, good fatigue resistance, integral hinge property, good heat resistance.

Physical Properties: Value:
Tensile Strength: 0.95 - 1.30 N/mm2
Notched Impact Strength: 3.0 - 30.0 Kj/m2
Thermal Coefficient of Expansion: 100 - 150 x 10-6
Max. Continued Use Temperature: 80 oC (176 oF)
Melting Point: 160 oC (320 oF)
Glass Transition Temp. (atactic): -20 oC (-4 oF)
Glass Transition Temp. (isotactic): 100 oC (212 oF)
Density: 0.905 g/cm3

Polyamides, PA

The majority of nylons tend to be semi-crystalline and are generally very tough materials with good thermal and chemical resistance. The different types give a wide range of properties with specific gravity, melting point and moisture content tending to reduce as the nylon number increases. Nylons can be used in high temperature environments. Heat stabilized systems allow sustained performance at temperatures up to 185oC.

Physical Properties: Value:
Tensile Strength: 90 - 185 N/mm2
Notched Impact Strength: 5.0 - 13.0 Kj/m2
Thermal Coefficient of Expansion: 80 x 10-6
Max. Continued Use Temperature: 150 - 185 oC (302 - 365 oF)
Melting Point: 190 - 350 oC (374 - 662 oF)
Glass Transition Temp. (Nylon 66): 45 oC (113 oF)
Density: 1.13 - 1.35 g/cm3

PVC, PVC-U

The symbol for polyvinyl chloride developed by the Society of the Plastics Industry so that items can be labeled for easy recycling is:
A highly versatile polymer, PVC is compatible with many additives. It can be plasticized to make it flexible for use in flooring or un plasticized (PVC-U) for use in building applications and window frames.

Physical Properties: Value:
Tensile Strength: 2.60 N/mm2
Notched Impact Strength: 2.0 - 4.5 Kj/m2
Thermal Coefficient of Expansion: 80 x 10-6
Max. Continued Use Temperature: 60 oC (140 oF)
Melting Point: 212 oC (413 oF)
Glass Transition Temperature: 81 oC (178 oF)
Density: 1.38 g/cm3