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Miniaturisation, integration of functions, connectivity.
These are some of the major trends today seen in practically every area of industrial design. The requirements of environmental sustainability are driving innovation, while the quest for greater energy efficiency is providing the inspiration for new avenues of development. Numerous applications demand materials that offer real and reliable solutions, making it possible to pursue increasingly ambitious challenges in the following sectors:
What are the requirements common to these sectors?>
Certainly, resistance to high temperatures, meaning continuous temperatures of at least 150°C.
Added to this, they have to deliver the extreme mechanical strength typically demanded by metal replacement applications, and must be able to ensure superlative performance levels over time, even in chemically aggressive or high-humidity environments.
This amounts to increasingly demanding requirements, even for engineering polymers, and it is a situation that is further complicated by the need to offer all this in the form of compounds that are easy to process and economically competitive.
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LATI already offers numerous special polymer-based compounds suitable for high-temperature applications: these range from PPS in the LARTON range to LARPEEK and to the polysulphones LASULF and LAPEX. The greatest versatility of use is provided by the aromatic polyamides (polyphthalamides, or PPAs) belonging to the LARAMID family, which is made up of materials that are not only heat-resistant, but also ideal for use in formulations that combine mechanical and thermal resistance with excellent electrical characteristics, chemical inertness, flame retardancy and colourability. And the LARAMID family is the very one to which LATI has now added a new base polymer, PA9T, which boasts excellent characteristics and versatility. Let’s look in more detail at the LARAMID T family.
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The properties of PPAs mainly depend on the monomers from which the polymer is obtained. Indeed, the aliphatic and aromatic parts of the macromolecule help to determine certain characteristics of the final material, such as its moisture absorbency, heat resistance and melting temperature, and therefore also the process parameters for injection moulding. In the case of PA9T, the monomer unit consists of the long aliphatic sequence (in blue in the figure) that separates the aromatic units.
This particular feature makes the resulting polymer less hygroscopic than other polyamides and at the same time contributes to the material’s flexibility, resilience, enhanced appearance and greater dimensional stability.
Therefore, thanks to its LARAMID T family, LATI is able to offer materials that have the characteristics typical of PPAs, but are tougher, less subject to environmental humidity-related problems, and suitable for moulding complex thin-wall geometries with very narrow dimensional tolerances.
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Thanks to the glass transition temperature of the base resin, which is close to 130°C, LARAMID T can immediately be counted among the resins suitable for use in applications where heat accumulation is a real problem. The polymer melts at between 290 and 310°C, meaning that its transition window is similar to those of other PPAs and of PPSs. These important thermal features, added to the stability of the molecule, mean that LARAMID T products remain reliable at continuous use temperatures of up to 160°C; furthermore, up to temperatures of at least 100 °C, they show no real reductions in their mechanical performance.
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Unlike what is seen with other PPAs, the base polymer of LARAMID T displays marked mechanical properties even in non-reinforced formulations. That said, for extreme structural applications, versions reinforced with glass or carbon fibres are designed.
The LARAMID T family includes compounds reinforced with glass fibres, high toughness carbon fibres and high modulus carbon fibres in proportions of up to 60%, 30% and 40%, respectively. It is fundamental to note that its very high modulus of elasticity and stress at break values correspond to a much higher elongation at break value than is obtained with similar products.
This advantage is translated into materials that are not only rigid but also very robust, i.e., capable of distributing the mechanical stresses to which they are subject, especially in the vicinity of defects; as a result, they increase the life of parts subject, for example, to cyclical or impulsive stress loads.
LARAMID T G/50, G/60 and K/35 are therefore materials offering remarkable mechanical performance, even in situations of fatigue, creep and relaxation, shock and vibrations. Thanks to the high crystallinity of the polymer, temperature has an only limited effect on the mechanical response of the material, as demonstrated by the stress-strain curves shown on the following pages.
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All PPAs show excellent chemical resistance against organic compounds, such as oils, solvents, fats and hydrocarbons.
Depending on concentration and temperature, these resins can also cope with most inorganic aggressive substances, such as acids, alkalis and oxidants.
An important feature of LARAMID T compounds, worth underlining, is their high resistance to hydrolysis; this, combined with low moisture absorption (the lowest among the PPAs), makes the base polymer highly versatile in applications involving direct exposure to hot water, steam, aqueous saline solutions and disinfectants.
Overall, the reduction of mechanical properties that is due to the hydrolytic action of hot water is only slightly greater than what is seen with anhygroscopic resins such as PPS. The equilibrium moisture content in the air (25°C, rH 50%) is less than 0.5%, and this results in mechanical characteristics that are influenced only negligibly by the effects of the working environment, even when this is characterised by high humidity rates, such as in the Far East countries or in engine compartment applications in the automotive sector.
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Moulding LARAMID T compounds does not require any equipment or measures different from those needed for the processing of other PPAs.
Prior drying will be required as usual, and a plasticising temperature of just over 300°C; it is enough to heat the moulds to 130°C, i.e., a temperature at least 20-30°C lower than that used for similar engineering resins.
The base polymer of LARAMID T displays very low differential shrinkage. This is an advantage as it allows complex geometries to be created even using glass fibre- or carbon fibre-reinforced grades.
Thanks to the high melt flow index, it is also possible to fill thin-walled cavities without needing to force the processing conditions, which is all to the good as regards the integrity of the polymer and therefore also the aesthetics of the manufactured products.
So, high dimensional stability, easy moulding and a great look are further valuable features of this polymer.
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LATI’s PA9T-based product range comprises several compounds already on the market and many others that are under development.
For further information, samples and technical data sheets, do not hesitate to contact the LATI Customer Service.
To download the LARAMID T family brochure go to the literature page.