HDPE Sheets – A Complete Guide
HDPE sheet plastic is made up of a string of ethylene molecules, resulting in a highly useful type of plastic that is both light and strong. In the quest to embrace sustainability, an increasing number of companies have begun to use this material in the manufacturing of a wide range of products because much less volume is required when compared with its competitors, such as polycarbonate sheeting, plexiglass and plywood.
Contents
1. Types of HDPE Sheets
2. Earliest Origins
3. HDPE in Production
4. Quality Control of HDPE
5. Testing 1,2,3
6. Size Matters
7. Pertinent Properties
8. International Certification
9. African Standards
10. HDPE Sheets in Action
11. Extensive Benefits of HDPE
12. The Bottom Line
The polymerisation of ethylene to form polyethylene
This thermoplastic offering affords levels of versatility and malleability that surpass most other plastic-sheeting types on the market. And, certified by the Food and Drug Administration (FDA) as being safe for use in food processing due to its resistance to mould, mildew and acid. It is also widely recycled making it a material of choice for the eco-orientated.
Types of HDPE Sheets
A variety of different types of HDPE sheet plastic can be produced, leading to numerous different applications and uses. While each of the grades below provides similar basic features and benefits that make them superior to plastic-sheeting materials like polycarbonate or acrylic sheets, they also each have their own unique characteristics.
• Matte sheets: formulated for cutting boards due to their extensive lifespan and ability not to dull knives or harbour bacteria. These types of sheets are acid resistant, compliant with FDA regulations and approved by the National Sanitation Foundation of the US.
• Smooth sheets: ideal for tank linings due to the ease with which they are fabricated and the fact that they feature superior chemical resistance, tensile strength and moisture/impact resistance.
• Pipe-grade sheets: feature improved weight and performance when compared to standard HDPE sheeting, rendering this type perfect for outdoor applications.
• Colour-core sheets: feature a coloured sheet-core that enables manufacturers to create signs and letters that expose this interior colour, while featuring a similar strength and durability to smooth and matte sheets.
• Antiskid sheets: created specifically for marine applications, where it is an essential safety requirement for surfaces to be slip and skid-proof.
Earliest Origins
In understanding the applications of HDPE sheets today, it is useful to have a complete background of the material’s origins. According to Science Direct, HDPE was introduced in 1962 by Manchester-based Sir John Charnley as a bearing surface in orthopaedics.
Polyethelene is defined as a linear polymer of the simple ethylene molecule, synthesised as a fine white powder. Ethylene, on the other hand, consists of covalently bound carbons and pendant hydrogens. In manufacturing, polyethylene is created through polymerisation of ethene. The powder is moulded into sheets by means of a compression process, where the next steps involve electron beaming followed by annealing (heating to above the melting temperature, and allowing to cool slowly), followed by shaping. Last up, the polyethylene is gas-sterilised.
Of interest to those in the medical field is that considerable research has focused on improving the performance of the material, as well as searching for alternative and more durable bearings in the orthopaedic speciality.
HDPE in Production
The video above shows how HDPE sheets are manufactured, using a high-quality plastic extrusion production line at a company called GPM in France. The production process is best carried out at a high-volume fast turnaround facility, such as this, where extra-wide extrusion machines allow manufacturers to recycle up to 18 145kg of scrap HDPE plastic into cut sheets within any 24-hour period. Importantly, it is a manufacturing process that keeps HDPE scrap out of the landfill sites.
Quality Control of HDPE
The quality-control process of reputable plastics products.
The graphic above shows the detailed, stage-intensive quality control process of finished polymer and plastics products. Although the process seems pedantic, it is essential that these stages are diligently followed so the end products conform to industry specifications.
The process involves:
• Identifying the characteristics, properties and flaws of the material;
• Complying with all relevant national and international standards; and
• Ensuring that the polymeric materials produced meet clients’ safety, environmental and ageing requirements. Also, see ‘International certification’ below.
Testing – 1, 2, 3
When vetting a supplier of HDPE sheets, it is wise to ensure that the prerequisite tests have been carried out during production. As these are comprehensive, it may help to have a checklist in place.
Reputable manufacturers will be able to supply results for: Melt flow; melting, processing and deflection temperature; extrusion; moulding pressure range and shrinkage; tensile strength and yield; elongation at break; compressive and flexural strength; tensile and compression modulus; Izod impact; hardness; shore; specific gravity; and water absorption, among others.
Also remember that there is a distinct difference between quality assurance (QA), which is process orientated and shows that a manufacturer has done things in the right way, versus quality control (QC), which makes sure the results are what was expected or, indeed, required.
Size Matters
Reputable manufacturers are able to produce almost any sized HDPE sheet, even up to 96” x 240”. They should also be equipped to cut or machine to size, resulting in any desired shape, thereby producing a superior-quality material that abides by all the necessary quality controls.
Pertinent Properties
While HDPE is known for its high strength-to-density ratio – which can range from 0.93 to 0.97g per cm3 (or 970kg per m3) due to its reduced branching at the molecular level – its physical properties can vary depending on the moulding process employed. Here again, a determining factor in any HDPE sheet’s quality would be the rigorous international quality controls applied after manufacturing.
International Certification
Automobile pioneer Henry Ford said, ‘Quality is doing it right when no one is looking.’ And this applies most certainly in the realm of HDPE sheets. The Proficiency Test Programme, endorsed by the American Society for Testing and Materials (ASTM), provides laboratories around the world with a statistical quality assurance tool so they can compare, improve and maintain performance in tests on plastics and other materials. ASTM laboratories are expected to conduct the required tests in their facilities and to record the results for submission to authorities on the necessary data-report forms. Another important body that strives to develop voluntary international standards of quality, safety and efficiency for plastics and other materials, is the Swiss-based International Organisation for Standards (ISO). It is for this reason that ISO codes are commonly used to rate the quality of various plastics properties.
Code Explanation
ISO 527-3:1995 – Determination of tensile properties for films and sheets ISO 2556:1974 – Determination of gas-transmission rates ISO 4591:1992 – Determination of average thickness ISO 6383-1:2015 – Determination of tear resistance, etc.
African Standards
This emphasis on quality is reiterated by the South African Bureau of Standards (SABS), which endorses a set of national benchmarks that help protect South African consumers, and those further afield in Kenya and Tanzania, from low-grade, cheap imports. Additionally, building materials need to comply with the South African National Standard (SANS), which specifies the performance requirements of a product.
HDPE Sheets in Action
Commonly accepted applications for HDPE sheets include the moulding of fuel tanks, garbage bins, dump carts, pallets, agricultural tanks, highway barriers and waste-tanks for RVs. When extruded with a pebble finish, the sheets are best used as cutting boards in butchering and meat-packing, as well as in other types of food preparation. However, the question to ask is in fact what cannot be created using HDPE sheets, because the list of possible industrial and construction-related applications is rather extensive.
Mining
HDPE geomembranes assist in keeping groundwater clean and maintaining an optimal ecological environment. These liners, which are often used together with non-woven geotextiles, can act as a waterproof base for many years so as to isolate underground water from pollution from the mining operations.
Landfills
HDPE products offer low permeability, chemical resistance and UV protection for highly reliable containment of hazardous waste products. Importantly, if these dangerous types of waste are not adequately contained, the lives of people and ecosystems in the surrounding areas could well be endangered.
Potable Water
HDPE is widely chosen by municipalities around the world, including in Europe and the US, for the safe transportation of potable cold water. Over the past decade, new HDPE formulations – such as Dow’s PE-RT (polyethylene of raised temperature resistance) – have also become available for high-temperature use, including the transportation of domestic hot water.
Extensive Benefits of HDPE Sheets
The above video outlines the benefits of HDPE sheet, which include its long-lasting performance and durability. In fact, six product advantages make the material the best alternative to plywood, steel, aluminium and particle board’, which purchasing managers should ideally bare in mind before making their final choice.
These include HDPE sheets being:
• Environmentally friendly i.e. completely recyclable;
• UV stabilised i.e. remaining colourfast for at least eight years;
• Durable i.e. not rotting, splintering, chipping or swelling, and the fact that it is termite-resistant. Additionally, HDPE sheets have a low water-absorption rate that discourages the growth of mould or fungus (which relates back to its clout in food preparation, see ‘Sheets in action’ above);
• Maintenance and hassle-free i.e. due to its availability in any colour, no painting is required. Cleaning is ideally done with a pressure washer that results in a non-stick surface and doesn’t easily allow graffiti;
• Low cost, because the less you need to do to a material after application, the more affordable it becomes; and
• Offers a lifetime of 50+ years, as a unique selling point.
The Bottom Line
For buyers, suppliers and consumers, the fact that HDPE sheets are lighter than other materials in their class means less expense in the way of manpower or fuel in their transportation. And, on the safety front, the material’s higher melting point means less likelihood of damage at high temperatures – such as in the case of accidental fire.
This high-quality material, which keeps plastic out of the landfills and is durable beyond expectation, should not be overlooked by purchasing managers. It’s in their best interests!
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