HDPE, LDPE and LLDPE
Polyethylene or Polythene or PE, is the world’s most popular plastics. It is a light, versatile synthetic resin made from the polymerization of ethylene. Polyethylene is a member of the important family of polyolefin resins. In this article we will focus on the most commonly used PE’s which are: HPDE, LDPE and LLDPE. They are recyclable with the symbols: 2 and 4. The biggest difference between the three is their densities
HDPE density ranges from 0.941-0.965 g/cm3.
LDPE density ranges from 0.910-0.925 g/cm3.
LLDPE density ranges from 0.91-0.94 g/cm3.
Generally the chemical formula is (C2H4)n.
It is an enormously versatile polymer, which is suited to a wide range of applications from bullet proof-vests to heavy-duty damp proof membrane for new buildings and chemical drums, to flexible bags and films, bottles and containers, toys and pretty much anything else in-between. It can also be slit or spun into synthetic fibres or modified to take on the elastic properties of a rubber.
The annual global production is around 84.7 million tonnes in 2015, with an annual 3.5% global demand growth.
PE’s are primarily used in the packaging industry- plastic bags, plastic films, geo-membranes, bottles, containers etc however there are many types of polyethylene’s. They are classified as follows:
- Ultra-high-molecular-weight polyethylene (UHMWPE)
- High-density polyethylene (HDPE)
- Cross-linked polyethylene (PEX or XLPE)
- Medium-density polyethylene (MDPE)
- Linear low-density polyethylene (LLDPE)
- Low-density polyethylene (LDPE)
- Very-low-density polyethylene (VLDPE)
In general PE’s are flexible, translucent/waxy, weatherproof, have a good low temperature toughness, can be processed and moulded in different methods, have a low cost and has a very good chemical resistance.
High Density Polyethylene (HDPE)
Produced in1930s in the United Kingdom, HDPE production took off in the 1950s in the U.S. and today is the most widely used type of plastic. It’s made by stringing together ethylene molecules derived from natural gas; mostly petroleum. HDPE can be produced by a number of different catalysts: chromium/silica, Ziegler-Natta or metallocene. By choosing catalysts and reaction conditions, the small amount of branching that occurs can be controlled.
Low Density Polyethylene (LDPE)
LDPE is created by what is known as free-radical polymerization. It has a high degree of short- and long-chain branching, which means that the chains do not pack into the crystal structure. This results in a lower tensile strength but increased ductility.
Linear Low Density Polyethylene (LLDPE)
LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins. It has higher tensile strength than LDPE, and it exhibits higher impact and puncture resistance. It is not easy to process but it can result in lower thickness (gauge) films (compared to LDPE) with better environmental stress-cracking resistance.
Some other applications for the different PE’s:
Weather proof products- waterproof membranes etc
Food storage containers
Fuel tanks, boxes and other containers
Wood plastic components
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