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T&D > Programs Areas > Inventory & Monitoring > String Degradability Program Areas
String & Flagging Degradability


Hip Chain or String Box Line—As one would expect, the polyester string tends to exhibit a greater breaking strength under both testing conditions (See chart below). However, after the 126 hour accelerated weathering, the strength of the polyester red and cotton red are comparable, near 0.9 and 0.8 pounds respectively. Neither the cotton or polyester string maintained integrity in the 500 hour accelerated weathering test. The cotton white string exhibited the lowest overall strength.

While breaking strengths between 2.5 and 0.4 pounds may seem insignificant, using a line with a breaking strength of 0.4 pounds would be quite frustrating. Frequent line breakage results in considerable delays and measurement error. Conversely, these breaking strengths could be considerable to some avian species whose body weights could be well below one pound. Fortunately, this line appears to degrade relatively rapidly. Upcoming outdoor exposure tests will be used to compare the accelerated weathering with actual exposure times.

Bar chart displaying the breaking strength of four types of hip chain.
Click on image for larger view.

Biodegradable Flagging—All biodegradable (natural fiber based) flagging exhibited relatively high initial breaking strength and none of these tapes maintained integrity through the 500 hour accelerated weathering test. Three of the four biodegradable flagging tapes demonstrated considerable strength reduction following the 126 hour weathering. Biodegradable white was the exception among these four. In fact, it exhibited the greatest breaking strength of all flagging for new and 126 hour test. This ability to maintain a high breaking strength after the 126 hour test may be due to a greater ability to reflect UV light.

Photodegradable & Perforated Flagging—Photodegradable flagging is designed to lose integrity when exposed to light, while perforated flagging is designed for easy tearing at set lengths, such as one or two feet. The perforated flagging was tested at the perforations. Both types of flagging demonstrated some hardening at the 126 hour test, where the material has increased tensile strength, but is more brittle. In other words, the hardened tape is more difficult to pull into two pieces, but it is more likely to crumble when folded. However, the photodegradable flagging lost integrity in the 500 hour test, while the perforated flagging displayed a breaking strength similar to new condition after the 500 hour test.

Polka-Dot, Striped, Arctic, Glow, and Common Flagging—Polka-dot and striped flagging is a smooth white flagging with an added ink pattern. Arctic flagging is designed to be less brittle in cold conditions and has a smooth texture; in these tests arctic glo flagging was used. Glow, glo, or high viz, flagging have a bright "neon" color and a texture similar to the common flagging. The common or taffeta flagging comes in standard colors and has a texture that results from embossed micro-hexagons. While Arctic Green Glo, Yellow Glo, White, Pink, and Red Polka-Dot displayed a gradual decrease in breaking strength due with increased accelerated weathering, the remaining flagging displayed some hardening. For example, the tensile strength of orange flagging increased in with accelerated weathering while the yellow striped flagging displayed a decrease after 126 hour test and hardening after the 500 hour test. In general, the arctic flagging exhibited the greatest tensile strength with common flagging displaying lower strength.

Click here for the Flagging Breaking Strength with Accelerated Weathering graph.

What String to Choose—While these tests cannot be directly compared with degradation in outdoor conditions, they do provide some indication of degradation due to UV and moisture. The samples tested show cotton white string to have the lowest initial strength as well as the lowest strength after the 126 hour exposure. If line breakage is not an issue, then the cotton white string is probably a good choice. However, if line breakage is an issue, then a stronger line may be more appropriate. The upcoming outdoor exposure results will provide further information to better assist in this decision.

What Flagging to Choose—While these tests cannot be directly compared with degradation in outdoor conditions, they do provide some indication of degradation due to UV and moisture. If rapid degradation is preferred, then the biodegradable or Photodegradable flagging is probably the best choice. However, the biodegradable flagging is similar to paper where it will lose it's integrity rapidly in wet conditions. This may result in the loss of plot locations before all data are collected. So, degrading too quickly must also be considered. Of course, visibility and weather conditions should always be taken into account when selecting the most appropriate product.