U.S. Navy tests show PEEK Tg same dry or wet

Automated Dynamics says recent U.S. Navy tests show the dry and wet glass transition temperatures of PEEK-based composites are the same, due to low moisture uptake of PEEK at less than 0.2 percent.

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Automated Dynamics (Schenectady, N.Y., USA) reported on July 2 that test data from the U.S. Navy show the dry and wet glass transition temperatures (Tg) of PEEK-based composites are the same, due to low moisture uptake of PEEK at less than 0.2 percent.

The Naval Air Systems Command (NAVAIR) recently publicized these results based on continuous fiber-reinforced PEEK composite structures made by Automated Dynamics. Polyetheretherktone's (PEEK)’s stability in wet environments is critical in applications where moisture may hinder a structure’s mechanical, electrical or geometric properties over time. Test summary is available here: PEEK Wet Tg Testing Brief.

The Navy has been evaluating and using PEEK composites in various applications for decades, and Automated Dynamics says the recent publication of a multi-year development program ending in 2012 testifies to the conservative nature of the U.S. Navy.

Automated Dynamics says the areas where non-metallics are considered, there’s a broad performance range with both thermoplastics and thermosets. Commodity-grade thermoplastics are fit for applications where considerable moisture infiltration is not an issue, and these applications tend to be exclusive of those suited for PEEK. Alternatively, thermoset composites are used widely where the economics call for low up-front costs. In contrast with PEEK, these epoxy resins degrade substantially in saturated wet environments over time, and the tangible effects like cracking and moisture-induced geometry changes are exacerbated when coupled with a temperature rise. Here, the polymer breaks down further and prevents effective load transfer between the fiber and matrix, which can ultimately cause macroscopic structural failure.

Automated Dynamics also reports that while PEEK bodes well against alternatives in hot-wet conditions, environmental effects on a composite can be further complicated if the fiber uses an epoxy sizing. New non-epoxy-based sizing is now commercially available reportedly and looks promising for several oil and gas applications. Automated Dynamics is evaluating these new composites and will publish test results soon. 

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