texposure

Environmental/Exposure of Various Polymer Coatings

TEACHER NOTES

Objectives: Students will

gain an understanding of the effects of exposure on the physical characteristics of various polymeric coatings
gather data from extended observation to make conclusions/comparisons
use data to determine applicability of coatings in business/industry/environment

Applicable Science Concepts:

scientific inquiry
variable control
connection between science and technology
ultraviolet radiation/light frequency
data collection/comparison
temperature measurement

Supplies:

2% NaCl solution (ocean water)
Acetic acid solution, pH 6.5 (saliva)
Acetic acid solution, pH 5.0 (acid rain)
Ammonia solution, pH 10 (household cleaners)
Disposable plastic pipettes
Tray to secure slides to
Clean glass slides
Suggested Coatings:

Car wax (Turtle wax, Armorall)
100% Acrylic latex paint (semi-gloss)
Oil based enamel (high-gloss)
Krylon fusion (plastic restorative spray paint)
Epoxy glue
Krylon spray enamel
Kilz spray paint

Safety:

Manufacturers provide instructions for the use of their products, and these instructions should be followed completely. Protective gloves and lab coats should be used when preparing and handling the glass slides with coatings, and safety glasses should be used at ALL times. EXTREME CAUTION should be used at all times when handling sharp objects!

Preparation:

Before applying the coatings, each slide should be labeled on the side not to be coated according to which coating will be applied to that slide. Ex.) Car wax slides will each be labeled (A). The coatings should then be applied in thin even layers at least 48 hours in advance to insure complete dryness. Proper safety attire (gloves, goggles, apron) and ventilation are important in the application process. Therefore, coating application may serve as a fun outdoors activity.
Prior to actual testing, divide the class into four groups, and assign a different environmental test to each group (HW1a).
Each group will research each of the seven above listed coatings and study the performance of the coatings under various exposure related conditions such as ultraviolet radiation, acid rain, basic conditions, salt water, and even the slightly acidic conditions as those seen in the mouth (HW 1b).
Each group should receive one of each of the seven coated sample slides. Upon receipt of their slides, each group should secure their samples to their group’s tray. *idea: tape white copy paper to the trays before securing slides in advance to reduce differences in reflected light.
The teacher should also prepare a tray of coated sample slides to be used as a control. *idea: prepare control tray in advance to serve as an example for students.
Upon coated sample tray assembly, each group should receive their pre-prepared solutions of specific pH. The Ocean Water group should receive a salt-water solution, the Acid Rain group should receive an acetic acid solution with a pH of ~5(check the pH of acid rain in your area), the Saliva group should receive an acetic acid solution with a pH of ~6.5, and the Basic Solution group should receive an Ammonia solution with a pH of ~10.
Each group should also receive one dropper/disposable pipette per group. *idea: have students determine how many drops of solution from an un-calibrated plastic pipette equals 0.1 mL of solution.

Investigation Procedures:

Each group should make an initial observations data table of the physical characteristics of each coating before applying any of the solutions
After making initial observations, each group should add 0.1mL of their solution to each coating sample slide. Note whether the solution is absorbed or repelled and compare the drop size among the different coatings/solutions.
Place each group’s slide tray in a sunny windowsill. (trays should be clearly labeled to avoid future confusion/complications)
Every 24 hours after the initial test, students observe the effect the solutions had on the coatings: (see example data table)
Following observations, students should reapply the 0.1 mL of test solution to each sample on their tray, taking care to keep the newly introduced amount of solution in the same proximity/area as in the prior test. *idea: have students search the web for the daily UV index for their area and record the UV index and temperature for each day of testing. check the weather channel website
Repeat this procedure for approximately two weeks. The longer the experiment is maintained the more pronounced the effects of the environmental test.
Probable results after two weeks of “exposure”: (see typical results with sample coatings)

Conclusions/Class Discussion:

Have each group rank their coatings from best to worst performance under their specific exposure circumstances. Which coating performed the best? The worst?
Have each group compare data and calculate which coating exhibited the best performance overall? The worst overall?
What coating would be ideal for use in high pressure/exposure circumstances? Is this practical in terms of economics/cost effectiveness?
What coating would be ideal for coating the inside of a bottle used to store extremely basic cleaning solutions? Which would be the worst?
What coating would be the most useful as a protectant of statues or even automobiles from acid rain? Which coating would be the least useful in this application? Name several current protective coatings used on automobiles.

Follow-up:
The following are links to end-of-lab quizzes. They can be administered with or without the student lab-book, depending on competency level of the students. *open lab-book quizzes often encourage better note-taking in the lab.

ACID RAIN ASSESSMENT
OCEAN WATER ASSESSMENT
BASIC SOLUTION ASSESSMENT
SALIVA SOLUTION ASSESSMENT

Other possibilities of follow-up work would be to explore the coatings further with other physical tests as seen throughout the website. Have students compare the results in exposure tests with results of adhesion or hardness tests in an “ultimate coating” project.
Another possibility is a project-end research paper in which the students tabulate their data and make a mock presentation before the class with charts and visuals demonstrating why they think a certain coating has superior or inferior exposure qualities and give supporting evidence for their statements.