High-temperature Materials

Exposure to high temperatures should be examined carefully, determining whether it’s a continuous condition or a sporadic peak, if environmental humidity or other chemical attacks are also present, etc. Based on these evaluations, the base polymer, reinforcement, and stabilizations will be chosen. Note: no modification to the polymer can alter its fundamental thermal properties, such as melting or glass transition temperature.

In the case of an amorphous polymer (PS, PC, ABS, PSU, PES, PPSU, etc.), it’s important that the maximum use temperature is at least 20-30°C below the glass transition temperature. For a properly molded semi-crystalline, especially when used in a reinforced compound, it’s more complex to establish a limit: it’s better to consult temperature index values and consult with technicians.

In the case of an amorphous polymer (PS, PC, ABS, PSU, PES, PPSU, etc.), it’s important that the maximum use temperature is at least 20-30°C below the glass transition temperature. For a properly molded semi-crystalline, especially when used in a reinforced compound, it’s more complex to establish a limit: it’s better to consult temperature index values and consult with technicians.

Exceeding the glass transition temperature causes softening of the amorphous portion always present in polymers, even in semi-crystallines. Continuous exposure to high temperatures can accelerate degradative phenomena promoted by oxygen in the air (thermo-oxidation) or water (hydrolysis). The most evident results? Color changes, poor surface aesthetics, embrittlement, loss or alteration of other technical properties.

The Heat Deflection Temperature (HDT) or Vicat softening point are technical tests that provide a rough indication of the effects of temperature on polymers. However, they may lose significance in the case of tests performed on more complex formulas. For more careful design, it is essential to have more complete information, for example, stress-strain curves at temperature or temperature indices.

To describe a plastic material’s ability to withstand the effects of temperature over time, various evaluation systems have been developed, such as those described by the IEC60216 standard or the UL746B standard. These are temperature indices estimated through complex conditioning processes and used, for example, in calculating the life expectancy of applications in the electrical and electronic sectors. For further details, contact our technicians.

The ability to withstand temperature is one of the main parameters used to determine the potential uses of polymers. Plastic materials become more expensive as their heat resistance increases, but the progression is not linear, and even slightly better performance can lead to a considerable increase in cost. For this reason, it’s important not to overestimate the material’s actual exposure to temperature, neither continuous nor peak.

Through appropriate stabilizations, it’s possible to prevent and delay some of the degradative effects on polymer macromolecules that heat promotes and accelerates. However, it’s not possible to shift the characteristic temperatures of the polymer linked to its chemical-physical nature, namely the glass transition temperature and the melting temperature.

There are several amorphous polymers designed for use at temperatures above 150°C: LATI’s product portfolio offers PSU, PES, and PPSU. These are extremely reliable materials, always transparent, with good mechanical and chemical resistance. However, they are very viscous materials in the molten state, transparent but with varying amber colors, which require some care in the design phase of the products and in molding.

Aromatic polyamides (PPA) and polyphenylene sulfide (PPS) are semi-crystalline polymers generally designed for use at temperatures above 150°C. There are many types of PPA and some types of PPS, but they all have excellent chemical and thermal resistance in common. PPAs are mechanically very resistant and colorable, PPS is less resilient, more dimensionally stable, naturally brown in color, and with lower tracking resistance compared to PPA.

Sophisticated and expensive materials like PPA, PPS, PPSU, and PEEK require absolute respect for the temperatures specified for the mold and the melt. Perfect thermostatting of the molds is essential, which must be heated as specified in the respective technical data sheets using pressurized water, diathermic oil, or electric resistances where suggested. It’s also very important to respect the cycle time, especially for semi-crystalline materials, and an adequate cooling time before extraction.