Grade Level: 6th - 12th; Type: Physical Science
The project is about measuring the effectiveness of a detergent containing a UV-absorbing compound in blocking UV-A radiation.
The goal is to have the student conduct a controlled experiment to test claims about the ability of a commercial product to improve the UV-blocking properties of fabrics.
- How well do fabrics block UV-A radiation without treatment?
- How well do fabrics block UV-A radiation after treatment?
- Do detergents containing UV-blocking agents effectively block UV-A radiation?
Ultraviolet (UV) radiation is part of the light spectrum that reaches the earth from the sun. The ultraviolet spectrum, which is invisible to the human eye, is made up of light having different wavelengths. These wavelengths are classified UV-A, UV-B, and UV-C. UV-A radiation corresponds to the longest wavelengths in the UV spectrum, and makes up about 95 percent of the UV radiation that reaches the earth. Black Light fluorescent bulbs emit light in the UV-A part of the ultraviolet spectrum.
UV-A radiation is less damaging to humans than UV-B radiation, but it is much more prevalent. Whereas UV-B radiation can be blocked by glass and some clouds, UBV-A radiation can pass through. Sunscreens may not afford adequate protection against UV-A radiation.
UV-A radiation is responsible for tanning; UV-B for sunburn. UV-A contributes to skin wrinkles. Like UV-B radiation, it can contribute to premature skin aging, eye damage, and skin cancers. The best way to get protection from UV-A radiation is to wear protective clothing.
Sun-protective clothing is often rated with an ultraviolet protection factor (UPF). The UPF rating is a measure of how much UV radiations gets through a fabric. For example, a garment with a UPF value of 40 lets 1/40th of the sun’s UV radiation reach your skin; UPF rating of 50 means 1/50th of the sun’s UV radiation reaches your skin.
Laundry detergents are now marketed that claim to increase UPF values. The active ingredient in these formulations is a UV-absorbing compound called Tinosorb FD. The chemical penetrates the fibers in the material, but is eventually washed out.
- UV detection beads, black light, detergent containing a UV-A blocking agent
- Materials can be found: On the Internet
- Read about ultraviolet radiation and formulate a hypothesis that will predict whether laundry detergents containing UV-blocking agents will improve the UV-A absorbing properties of fabrics.
- Assemble a collection of uniform-size fabric samples cut from discarded garments.
- Run the fabric samples through the washing machine cycle a minimum of 20 times without using laundry detergent or any additives. Allow the samples to dry and set them aside.
- Observe the color of the ultraviolet detecting beads in a partially darkened room.
- Shine the black light source on the ultraviolet detecting beads, and note the color of the beads.
- Assign a color ranking of 1 to the unillumined beads, and a color intensity ranking of 5 to the beads under the black light.
- Position the first fabric sample between the ultraviolet detecting beads and the black light.
- Turn on the black light allow it to shine on the fabric sample and the beads underneath. Estimate the color intensity of the beads on a scale of 1 to 5.
- Repeat this test for each of the fabric samples, tabulating your results.
- Wash the garments using a detergent containing a UV-blocking compound, and allow them to dry.
- Repeat the same tests performed on the untreated garments.
- Evaluate your hypothesis in light of your findings. If necessary, revise it and conduct more experiments to test it.
UPF rating (if available)
Bead color intensity before washing
Bead color intensity after washing
Terms/Concepts: Ultraviolet radiation; UV-A radiation; Ultraviolet protection factor (UPF)