Aromatic polyamides: chemical resistance and mechanical strength
Prolonged exposure to pressurised steam is a far more severe test than one might imagine when it comes to plastics for technical applications. The hydrolytic action of water, intensified by high temperature, can cause rapid chemical degradation of otherwise high-performance polymers, such as polyamide and polyester. If external mechanical stresses are added to the effects of steam and heat, then the risks of failures and breakages very quickly become concrete. For this reason, polymers such as PPS or sulphonates and PEEK are used for applications that work in these conditions. But while these are excellent resins, they are also expensive and difficult to process.
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Aromatic polyamides, macromolecules made by including high temperature-resistant elements into the chain, are proposed as the perfect compromise between chemical resistance, mechanical strength, versatility and ease of use.
The compounds belonging to the LARAMID T family are made starting from an aromatic polyamide, PA9T, whose specific structure also ensures other advantages: resilience, self-lubrication and very low water absorption.
The plastic material chosen by Robiaplast: LARAMID T G/50
LARAMID T G/50 is the material that Ro.Bia.Plast, an Italian company specialised in the production of small household appliances, has found to be the perfect answer to the problems of resistance to pressurised steam posed by the valves present in the steam taps of its appliances.
The steam gun used in Ro.Bia.Plast solutions for domestic cleaning appliances works in conditions that are particularly demanding for a plastic material: temperatures of up to 120°C, a pressure of 8 bar constantly applied to the valve unit, and the constant presence of steam and water.
The chosen compound passed every test brilliantly thanks to the base resin and the reinforcement guaranteed by glass fibres, making up 50% of its weight.
The negligible water absorption makes the compound perfectly stable from a dimensional point of view, too, as well as reliable over time, in spite of the constant mechanical stress which could favour creep and relaxation phenomena.
Interestingly, LARAMID T G/50 offers exceptionally high elongation for such a rigid structural compound, with a value close to 3% at room temperature. This further advantage has allowed Ro.Bia.Plast to assemble the valve unit by introducing snap fits into the design: something that would have been unthinkable with poorly deformable polymers such as PPS.
The extreme strength of PA9T and the absence of electronic circuits make the Ro.Bia.Plast steam gun a safe, reliable and long-lasting solution.
