Water tanks. There’s no doubt that poly water tanks are this country’s first choice for water storage.
They’re light, clean, proven and ideally suited to withstand our harsh and unrelenting environment for the long term.
Plastic or “poly” water tanks are made from polyethylene, a safe, tough and recyclable plastic that is also used to package food and beverages such as milk.
Alkatuff polyethylene is Australian made and designed specifically for Australian conditions. It is a one of a kind in this respect, being the only Australian made polyethylene engineered for use in water tanks.
While a number of polyethylene resins utilised in Australia are manufactured abroad, in Asia or the Middle East, Alkatuff polyethylene is produced in Botany, New South Wales, by Alkatuff’s parent company Qenos. If it’s not Alkatuff, it’s imported.
Poly water tanks are usually made by a process known as rotational moulding. The process involves melting the polymer inside a mould which is slowly rotating inside a hot air oven. The molten polymer adheres to the inner surfaces of the mould before being cooled and released.
There is a globally recognised standard, AS/NZS 4766 “Polyethylene Storage Tanks for Water and Chemicals”, that guides the rotational moulding of polyethylene tanks. Most building codes require that your tank meets this standard.
Alkatuff has been specifically designed to exceed AS/NZS 4766. A line by line comparison of Alkatuff performance against the Tank Standard proves its superior performance across a range of factors.
When polyethylene is exposed outdoors, the ultra-violet component of the sunlight causes photo-oxidation of the polymer, resulting in surface crazing and a marked deterioration of the mechanical properties with time.
The standard for UV performance for PE Water Tanks specified in AS/NZS 4766 is 8,000 hours of uninterrupted exposure to an intense and specifically developed UV light source.
Qenos incorporates stabilisers into its rotational moulding resins to provide exceptional weather resistance for outdoor applications. The long term UV performance of the resin is then exhaustively tested under conditions of controlled irradiance, chamber temperature and humidity, and repeated rain cycles.
Alkatuff LL711UV resin achieves a class leading UV performance exceeding 20,000 hours against the required standards, enabling tanks made from Alkatuff LL711UV to be Tough in the Sun.
C6 is shorthand for the hexene co-monomer used in the Linear Low Density Polyethylene (LLDPE) from which the water tank is made (ethylene is the main monomer gas).
In LLDPE, the branching in the molecule is achieved through copolymerisation with monomers such as butene (C4), hexene (C6) or octene (C8). The toughness of the LLDPE is highly dependent on the short chain branch length, which is determined by the co-monomer used. A C6 co-monomer has a longer short chain branch length than a C4 co-monomer, and so on.
The most important function of a tank is containment! That’s why it’s very important for a tank to be resistant to cracking. AS/NZS 4766 requires that the tank material survives 500 hours of exposure to a harsh reagent without failure due to cracking. This measure is known as ESCR (environmental stress crack resistance).
Alkatuff polyethylene offers an ESCR performance of over 1,000 hours ensuring years of reliable service.
Creep is the term used for the deformation of a material under stress. Creep can significantly affect the performance of a moulding over time. In water tanks creep mostly manifests as “bulging”.
Alkatuff polyethylene produces tanks with excellent creep resistance due to its C6 co-monomer and superior toughness.
Creep is different from one grade to another, and from one temperature to another. The Tank Standard includes creep requirements at 23°C. The Qenos Technical Team has generated creep data at 23°C and 40°C for Alkatuff LL711UV to ensure a product fit for the harsh Australian conditions.
Alkatuff resin has a broad processing window creating two important benefits:
- It melts and adheres to the mould readily. This is known as sintering. It then easily releases from the mould which is important to reduce warpage of the tank.
- It has high thermal stability making it less prone to oxidation, discolouration and loss of toughness in the field and also tolerant of temperature variation during the moulding process.
Alkatuff has been supplied to Australian tank manufacturers for over 20 years and has proven performance in Australian conditions.
In fact the Australian tank market was slow moving until Qenos got involved. Alkatuff was designed to exceed the AS/NZS 4766 standard and with its unique combination of easy moulding and superior in-service performance it ignited the poly tank market and has been driving it ever since.
Alkatuff polyethylene is supported by local technical service and extensive technical data ensuring the design of your tank can be optimised.
Qenos is an active member of the Association of Rotational Moulders Australasia which is chartered with bringing the industry together to share information and expertise.