Table 1. Listing of materials selected for evaluation.

How Can We Compare These Materials?

In our previous test, we compared tensile strength as it changed from the baseline value. Here, we will continue to do the same type of evaluation to understand how low temperatures affect the tensile strength of these materials. Just as before, the mechanisms for degradation can be at various scales. At low temperatures, however, the mechanisms are different than when heat or UV are involved.

Just like before, these mechanisms occur at different scales. See Figure 1 for some examples of degradation mechanisms. There are many changes that materials can undergo when exposed to low temperatures. Most of these effects happen at more than one scale, but can also have effects on other scales as well.

Experimental test set-up

Five groups of samples were tested, all differing by the amount of exposure to frigid conditions. See Figure 2 for the breakdown of groupings. Tensile strength was determined by a modified version of ASTM D638.

Results

It should be noted that typically fabric, elastomeric and non-elastomeric samples follow different protocols when measuring tensile strength. The values here should only be regarded as qualitative values for comparison, rather than actual values of measured tensile strength.

         

As seen in the weathering test, the polymer films behavior was relatively stable. FEP-5 was the most stable material. FSR-16 and 63-20 stayed fairly constant after the initial increase from baseline seen at -30°C. Decreasing the temperature did not seem to influence the behavior too much. PFR-10 showed an increase at -50°C, but at the other temperatures seemed to stay relatively stable. Trevira had some fluctuations, but did not exhibit a large increase initially like the coated fabrics. PVL-10 exhibited a gradual increase throughout the testing. There was an increase from baseline to -30°, followed by another increase at -50°C. VNHLT-23, which is designed for low temperatures and RPH-14 showed quite a large increased in tensile strength initially.

Based on the data collected from this comparative study, we can conclude how these materials behave in a short-term low temperature test. Below in Table 2, the materials are compared by the observations and tensile strength measurements after each time interval in the study.