However, LDPE is cheaper so it is used extensively in products such as packaging film, squeeze bottles, toys, and ink tubes for pens.


Characteristics of polyethylene:

-Mechanical properties: Good resistance to impact over wide temperature range (-40 - 90 C). Limitation is that it has lower creep resistance and inferior fatigue properties compared to polypropylene. -Environmental: Resistant to a wide range of chemicals, most inorganic acids and alkalis at room temperature. Good moisture resistance. Insoluble in organic solvents below 60 C but may be swollen. Limitations are that it is susceptible to weathering, UV light and environmental stress-cracking. Alloying of PE with butyl rubber and
-Thermal properties: Limitation due to very high thermal expansion. Poor temperature capability. -Food and medicine: Non-toxic grades available for use with food stuffs. -Electrical properties: Good electrical properties- not appreciably affected by humidity due to low wear absorption. Power factor virtually unaffected by frequency or temperature. Limitation is that power factor very sensitive to slight degrees of oxidation and to polar additives. -Processing: Ease of processing by all thermoplastic methods. Limitation is the high mould shrinkage (typical for crystalline polymers). Difficult to bond or print on. -Cost: It has a low cost. Low density polyethylene (LDPE) (produced by high pressure and temperature process):
-Tough at much lower temperature (embrittles at -60 C). -Translucent. -Flexible. -Upper service temperature limit of 88 C. -Low warpage. -Improved environmental stress-crack resistance. -Improved heat resistance. High density polyethylene (HDPE) (Produced by low pressure process with special metallic derivatives as catalysts)
-Better chemical resistance. -Better creep resistance. -Five times stiffer than LDPE at room temperature. -Higher temperature service (130 C). -More resistant to permeation. -Can withstand hot water sterilization but not steam. Applications:

LDPE:
-Injection moldings: Kitchen utility ware, toys, process tank liners, closures, packages, sealing rings and battery parts. -Blow moldings: Squeeze bottles for packaging, containers for drugs. -Film: Wrapping materials for food, clothes, etc. -Wire and cable: High frequency insulation, jacketing. -Pipe: Chemical handling, irrigation systems, natural gas transmission. HDPE:
Refrigerator parts, packaging, structural housing panels, pipe, defroster and heater ducts, sterilizable houseware and hospital equipment, hoops, battery parts, blow molded containers including automotive petrol tanks, film wrapping materials, wire cable and insulation and chemical resistant pipe.