Polyethylene (High Density) HDPE
Polyethylene (Polythene) is one of the world’s most popular plastics. It is an enormously versatile polymer which is suited to a wide range of applications from heavy-duty damp proof membranes for new buildings to light, flexible bags and films.
Two major types of PE are in use in the films and flexible packaging sector – LDPE (Low Density) used generally for trays and heavier duty films such as long-life bags and sacks, poly tunnels, protective sheeting, food bags etc and HDPE (High Density) which is used for most thin gauge carrier bags, fresh produce bags and some bottles and caps.
There are other variants on these two main types and all offer good vapour or moisture barrier qualities and are chemically inert.
By altering the formulation and gauge of polyethylene, the producer/converter can adjust the impact and tear resistance; transparency and tactility; flexibility, formability and coating/laminating/printing capability. PE can be recycled and many bin bags, agricultural films and long-life products such as park benches, bollards and waste bins use recycled polyethylene. Due to its high calorific value, PE offers excellent energy recovery through clean incineration.
Contents
1. History
2. Applications
3. Properties
3.1 Physical Properties
3.2 Resistence to Chemicals
4. Case Studies
4.1 Garden Containers
4.2 Plastic Bottles
4.2.1 Benefits of HDPE Milk Bottles
4.2.2 Environmental Facts
The history of HDPE can be traced back to the initial discover of polyethylene in 1933. This was discovered by Eric Fawcett and Reginald Gibson at Imperial Chemical Industries (ICI) in Northwich, England.
Later in 1935 another ICI chemist, Michael Perrin, developed a reproducible high-pressure process based on Fawcett and Gibson’s findings. This later enabled the industrial production of polyethylene and allowed LDPE to be produced reliably and at scale.
LDPE became the first polyethylene to reach commercial production, beginning in 1939, initially for insulated electrical cables which were a strategic material during World War II (due to its excellent dielectric properties - a material's ability to store electrical energy in an electric field - and moisture resistance).
It was not until the the early 1950s when chemists Karl Ziegler (who would go on to win the Nobel Prize in Chemistry for his work on polymers) and Erhard Holzkamp made a breakthrough discovery in polyethylene technology by developing a catalytic polymerisation process that produced high-density polyethylene (HDPE). 1953 marked the first time high-density polyethylene was produced in practical quantities.
Chemical drums, jerricans, carboys, toys, picnic ware, household and kitchenware, cable insulation, carrier bags, food wrapping material.
3. Properties
Flexible, translucent/waxy, weatherproof, good low temperature toughness (to -60'C), easy to process by most methods, low cost, good chemical resistance.
3.1 Physical Properties
Tensile Strength 0.20 - 0.40 N/mm²
Notched Impact Strength no break Kj/m²
Thermal Coefficient of expansion 100 - 220 x 10-6
Max Cont Use Temp 65 oC
Density 0.944 - 0.965 g/cm3
3.2 Resistence to Chemicals
Dilute Acid ****
Dilute Alkalis ****
Oils and Greases ** variable
Aliphatic Hydrocarbons *
Aromatic Hydrocarbons *
Halogenated Hydrocarbons *
Alcohols ****
KEY * poor ** moderate *** good **** very good
|
|
Garden containers made from high density polyethylene. Low cost, high rigidity and ease of blow moulding has made the material a natural choice in gardening furnishings. |
High Density Polyethylene (HDPE) plastic bottles are a popular packaging choice for the milk and fresh juice markets. In the UK, for example, around four billion HDPE milk bottles are produced and purchased each year.
HDPE provides a whole host of benefits to manufacturers, retailers and consumers.
4.2.1 Benefits of HDPE Milk Bottles
Recyclable: HDPE bottles are 100% recyclable so material can be used over and over again
Sustainable: HDPE offers opportunities to integrate recycled material back into the supply chain
Easy to lightweight: HDPE bottles offer significant lightweighting opportunities
Adaptable: the only bottle type of plastic that can be used as a monolayer bottle for pasteurised milk, or as a coextruded bottle with barrier layers for UHT or sterilised milk
Easy to use: the only type of packaging that allows an integrated handle and pouring aperture to enable controlled grip and pour
Safe and secure: the only type of packaging that can have either an external tamper evident closure, or an induction heat seal closure, to prevent leaking, preserve product freshness and show up evidence of tampering
Commercial: HDPE bottles offer a full range of marketing opportunities, e.g. printing direct onto the material, printing direct onto the sleeve or label, and the ability to amend the shape so that it stands out on the shelf
Innovative: ability to push boundaries and achieve new milestones with innovative use of blow moulding equipment.
HDPE milk bottles are one of the most widely recycled items of packaging in the UK, with Recoup figures showing that HDPE bottles are recycled around 79% of the time.
On average, HDPE milk bottles in the UK are now 15% lighter than they were just three years ago.
However, innovative designs such as the multi-award-winning Infini bottle mean that it is now possible to lightweight bottles by up to 25% on a standard bottle (depending on size).
HDPE milk bottles in the UK contain a high level of recycled content.
Advancements in technology and innovative designs with products mean that new achievements are possible. In 2013, Nampak achieved a world first by incorporating 30% recycled HDPE into its Infini milk bottle – two years ahead of industry targets. This level and greater is now the norm across the industry.
