polethylene plastic

Polyethylene is used more than any other thermoplastic polymer. There is a wide variety of grades and formulations available that have an equally wide range of properties. In general, the outstanding characteristics of polyethylene are:

Toughness
Ease of processing
Chemical resistance
Abrasion resistance
Electrical properties
Impact resistance
Low coefficient of friction
Near-zero moisture absorption





The three most commonly used grades of polyethlene are:
Low Density, High Density and Polypropylene.

LOW DENSITY POLYETHYLENE (LDPE)
LDPE, was the first of the polyethylenes to be developed. It is a corrosion resistant, low density extruded material that provides low moisture permeability. LDPE has a fairly low working temperature, soft surface and low tensile strength. It is an excellent material where corrosion resistance is an important factor, but stiffness, high temperature and structural strength are not important considerations.

Features:
Lightweight
Formable
Impact Resistant
Excellent Electrical Properties
Machinable
Weldable

Fabrication:
LDPE can be fabricated using the following techniques.
Hot gas welded
Fusion and butt welded
Ultra-sonic sealed
Die cut
Machined with wood or metal working tools
Vacuum formed
Thermo-formed

Applications:
Chemical resistant tank and containers
Food storage containers
Laboratory equipment
Disposable Thermo-formed products
Corrosion resistant work surfaces
Vacuum formed end caps and tops
Moisture barrier


HIGH DENSITY POLYETHYLENE (HPDE)
HPDE is more rigid and harder than lower density materials. It also has a higher tensile strength, four times that of low density polyethylene, and it is three times better in compressive strength. HDPE meets FDA requirements for direct food contact applications. It also is accepted by USDA, NSF and the Canadian Department of Agriculture.

Features:
Abrasion Resistant
The extremely high molecular weight of HDPE combined with its very low coefficient of friction provides and excellent abrasion resistant product preventing gouging, scuffing and scraping.

Exceptional Impact Strength
HDPE is one of the highest impact resistant thermoplastics available and maintains excellent machinability and self- lubricating characteristics. Properties are maintained even at extremely low temperatures.

Chemical Resistant
HDPE has very good chemical resistance of corrosives as well as stress cracking resistance (with the exception of strong oxidizing acids at elevated temperatures). Certain hydrocarbons cause only a light surface swelling at moderate temperature.

Water Resistant
Moisture and water (including saltwater) have no affect on HDPE. It can be used in fresh and salt water immersion applications.

Fabrication:
HDPE can be fabricated using the following techniques:
Hot gas welded
Fusion and butt welded
Ultra-sonic sealed
Die cut
Machined with wood or metal working tools
Vacuum formed
Thermo-formed

HIGH DENSITY POLYETHYLENE (HPDE)
APPLICATIONS

  • Food cutting boards
  • Corrosion resistant wall coverings
  • Pipe flanges
  • Lavatory partitions
  • Man-hole covers in Chemical Plants
  • Radiation shielding
  • Self supporting containers
  • Prosthetic devices

 

ASTM test Property Low density Medium density High density Ultrahigh molecular weight
PHYSICAL
D792 Specific gravity 0.910-0.925 0.926-0.940 0.941-0.965 0.928-0.941
D792 Specific volume (in.³/lb.) 30.4-29.9 29.9-29.4 29.4-28.7 29.4
D570 Water absorption, 24 hours, 1/8 inch thick (%) <0.01 <0.01 <0.01 <0.01
MECHANICAL
D638 Tensile strength (psi) 600-2,300 1,200-3,500 3,100-5,500 4,000-6,000
D638 Elongation (%) 90-800 50-600 20-1,000 200-500
D638 Tensile modulus (10~5 psi) 0.14-0.38 0.25-0.55 0.6-1.8 0.20-1.10
D790 Flexural modulus (10~5 psi) 0.08-0.60 0.60-1.15 1.0-2.0 1.0-1.7
D256 Impact strength, izod (ft-lb/in. of notch) No break 0.5-16 0.5-20 No break
D785 Hardness, Rockwell R 10 15 65 67
THERMAL
C177 Thermal conductivity (10~4 cal-cm/sec-cm~2-°C) 8.0 8.0-10.0 11.0-12.4 11.0
D696 Coefficient of thermal expansion (10~5 in./in.-°F) 5.6-12.2 7.8-8.9 6.1-7.2 7.8
D648 Deflection temperature (°F)
At 264 psi
At 66 psi

90-105
100-121

105-120
120-165

110-130
140-190

118
170
ELECTRICAL
D149 Dielectric strength (V/mil) short time, 1/8-in. thick 460-700 460-650 450-500 900 kV/cm
D150 Dielectric constant At 1kHz 2.25-2.35 2.25-2.35 2.30-2.35 2.30-2.35
D150 Dissipation factor At 1kHz 0.0002 0.0002 0.0003 0.0002
D257 Volume resistivity (ohm-cm) At 73°F, 50% RH 10~15 10~15 10~15 10~18
D495 Arc resistance(s) 135-160 200-235 - -
OPTICAL
D542 Refractive index 1.51 1.52 1.54 -
D1003 Transmittance (%) 4-50 4-50 10-50 -

 

 


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