by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Hytrel (property of the Dupont Company) is gaining in popularity as a material for seals, and there a number of reasons for this. In this blog post, we are going to talk about the general characteristics of Hytrel as well as the specific grades used for sealing applications.

What is Hytrel?

Hytrel is a TPC-ET thermoplastic polyester elastomer made by Dupont. Hytrel can be found in applications that seem to vary significantly in requirements and environmental challenges, such as off-road transportation equipment, oil and gas, hydraulic power, food handling, and medical devices. It is also used in electronics, automobiles, healthcare equipment, power tools, sporting goods, appliances, and cables.

Characteristics of Hytrel

Hytrel has a long list of excellent characteristics, including impact resistance, toughness, and resistance to chemical attack (including hydrocarbon solvents and fuels). In terms of sealing applicants, it offers:

  • Flex fatigue resistance
  • Spring-like properties
  • Creep resistance
  • Inherent flexibility
  • The ability to flex in multiple directions
  • Wide operating temperature range (cryogenic to +315°F)

In addition, Hytrel retains mechanical properties even at high temperatures and remains flexible at low temperatures. Hytrel also lends itself to a variety of manufacturing methods, including extrusion, blow molding, injection molding, and rotational molding. However, it is sensitive to water and phosphate fluids above 175°F.

Grades and Blends of Hytrel

Hytrel is available in various grades and blends, including seven specific grades that are well-adapted for seals. In addition to the grades discussed below, there are also renewable sourced options. Note that stabilizing additives can be combined with these grades to improve Hytrel’s resistance to heat aging and UV light.

Hytrel 4056

Hytrel 4056 is the most flexible grade, offering both toughness and strength over a considerably wide temperature range. It works extremely well for low-temperature applications because of its ability to retain flexibility. In addition, its low modulus allows it to be formed using extrusion and has a low melting point.

Hytrel 4068 and Hytrel 4069

Both Hytrel 4068 and 4069 provide flex-fatigue and creep resistance along with outstanding low-temperature properties. These grades can be formed using molding or extrusion and possess a higher melting point than Hytrel 4056 and a lower modulus. In addition, there is a food-grade available: Hytrel 4068FG.

Hytrel 4556

Hytrel 4556 is very similar to 4068 and 4069, with a low-to-medium modulus and can be manufactured using both extrusion and molding. This grade works extremely well for seals and gaskets.

Hytrel 5526 and Hytrel 5556

In terms of general properties, Hytrel 5526 provides a good balance. Its flow properties, however, primarily limit it to injection molding. Hytrel 5556 also offers a balance of properties with a medium modulus. It works well with extrusion but does not have the same high-flow properties available with Hytrel 5526. 

Hytrel 6356

Hytrel 6356 offers an excellent balance of properties such as toughness, flexibility strength, thermal resistance, and creep resistance. This high modulus grade is well adapted both to molding and extrusion processes.

Hytrel 4053FG NC010

When food contact grade seals are needed, Hytrel 4053FG NC010 may be an option. This is a low modulus extrusion grade whose properties include creep resistance, good low-temperature properties, and flex-fatigue resistance. 

Hytrel 5553FG NC010

This is a medium modulus molding and extrusion grade of Hytrel that provides a good balance of properties. It is intended for applications involving food contact.

Hytrel 6359FG NC010

Another good grade option of Hytrel, this material provides a good balance of properties including strength, toughness, flexibility, creep resistance, and thermal resistance. It is a medium to high modulus grade that works well with both molding and extrusion processes.

Benefits of Using Hytrel

When used in sealing applications, Hytrel offers a number of distinct benefits. For example, Hytrel can be used to replace multi-piece assemblies (including those composed of various materials) with a single component.

Because Hytrel has excellent creep and recovery properties, seals using Hytrel will be more resistant to dimensional changes and less likely to be permanently deformed. This is critical in many sealing applications, including those where there are extreme pressure and temperature changes. And because it can flex in multiple directions for far more cycles than a traditional elastomer such as rubber.

Unlike some seal materials, Hytrel grades vary according to modulus, which makes Hytrel a very versatile material choice. The differences in modulus are important: low modulus options can be used where little force should be needed to stretch the material, while high modulus grades work well for situations where significant force should be required to result in stretching. In addition, Hytrel is available in Shore D hardness ranging from 30 to 82.

As mentioned earlier, Hytrel has excellent properties when it comes to chemical compatibility and resistance to chemical attack. More specifically, it is resistant to mineral oils, greases, water-based hydraulic fluids, dilute acids, dilute bases, glycol, and hydrocarbon fuels. There are also grades of Hytrel that offer excellent resistance to the degrading effects of radiation. 

Hytrel is available in food grades that conform to both FDA and  European Food Contact regulations.  There are also grades in compliance with regulatory requirements that make them suitable for use in medical devices and other healthcare applications.

Conclusion

Hytrel combines the strength of engineering plastics with the flexibility of elastomers and the ease of processing provided by thermoplastics. Its combination of properties and flexibility in terms of manufacturing processes make it an excellent option for sealing applications

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