A new roto material for higher temperatures and lighter weight applications
Monday, 23 October 2017
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OEMs, particularly in the automotive sector, are seeking polymers that can withstand higher and higher operating temperatures, while also looking for weight reduction in their rotomoulded parts at the same time.
The main driver behind these demands in the automotive world is the need to meet more stringent regulations of CO2 emissions. This is leading to an increase in the temperature of engines and associated components. As a result, the temperature requirements for the fuel tanks are rising as higher and higher temperature fuels are being returned to the tanks.
Matrix has now developed a new polyamide alloy called Revolve “PA HIU” which can withstand operating temperatures of 140-150 °C and at the same time can deliver significant potential weight savings.
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This material has also been designed so that it is easy to rotomould and it does not require any complicated procedures, such as needing an inert atmosphere within the mould. Revolve PA HIU can be moulded on conventional rotomoulding equipment, with normal steel or aluminium moulds. As with any material it is important to find the right moulding conditions to achieve optimum mechanical and physical properties. It is best to monitor the internal air temperature in order to ensure that the polymer has fully sintered. Matrix found that optimum properties were achieved with a peak internal temperature (PIAT) of around 230-235 °C - see Figure 1. The moulding trials were carried out on a Ferry 190 carousel machine in the company’s Rotomoulding Technical Centre in the UK.
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Figure 1 – Internal Air Temperature traces for Revolve PA HIU
Operating temperature resistance
The physical properties of all polymers are affected by temperature. At elevated temperature, they become soft and lose strength and rigidity. Therefore, it is critical to assess how a material behaves in high temperature conditions. Figure 2 shows the tensile modulus (stiffness) per ISO 527 of PA HIU at various operating temperatures. From this it can be seen that even at 150 °C the grade retains good rigidity. Any polyethylene material at the same temperature would have completely melted.
Figure 2 – Tensile Modulus for Revolve PA HIU
Stiffness
Another enhancement PA HIU offers is its high Flexural Modulus (stiffness). Figure 3 illustrates that this material is an extremely stiff rotomoulding material, with 4 times the flexural modulus value of a typical medium density polyethylene, at ambient conditions (23 °C, per ISO 178). With this type of performance difference, the rotational moulder has the opportunity to consider reducing the wall thickness of the part, which will in turn improve the value proposition to the OEM.
Figure 3 – Flexural Modulus for Revolve PA HIU
Toughness
Falling dart impact testing (per the ARM guideline) was carried out for Revolve PA HIU and compared with a general purpose PE grade (0.935 g/cm³, 6.5 g/10 min) for 5mm thick samples – see Figure 4. Prior to testing the specimens were conditioned in a freezer at -40 °C and in a controlled temperature room at 23 °C for 24 hours before being impacted. From Figure 4 it can be seen that Revolve PA HIU exhibits excellent impact performance at room temperature. Generally speaking polyamides do not perform well when it comes to low temperature impact. So the drop-off for the -40 °C is to be expected. However, the low temperature impact performance for this particular polyamide material is reasonably good.
Figure 4 – Impact Strength for Revolve PA HIU
Summary
Revolve PA HIU is a new material which has been designed to meet the increasingly demanding requirements of OEMs, particularly in the automotive sector. This polymer will also have applications in other areas.
This development is part of an on-going program at Matrix Polymers aimed at inventing new materials for rotomoulders, that will expand the range of products that can be produced by the process and thereby help in the growth and continued success of the rotomoulding industry. The company’s vision with regards to development of new materials can be seen at: https://www.youtube.com/watch?v=mGf2RyH63bI
