Chemical Education Today
From Past Issues
House Paint by Kathryn R. Williams
You’re out for a stroll or a leisurely bike ride through a residential neighborhood. As you pass, your attention is occasionally drawn to a special house. What characteristics pique your interest? Do you notice the style of the house? The size? The landscaping? The dog? Surely at least part of your initial impression focuses on the exterior paint—the color, the condition, the trim. And, whether you admire or find fault, you should appreciate the major role of chemists in creating what you see. With the 2006 National Chemistry Week theme, “Your Home—It’s All Built on Chemistry,” as the backdrop, this month marks a fitting time to look at house paints as described in past issues of the Journal of Chemical Education. My online search retrieved more than 20 articles on paints—practical considerations as well as interactions at the molecular level. Although some are directed to works of art, the topics primarily relate to paint and varnish for houses and other utilitarian uses (1–7).
it dries and binds the pigment to the substrate. The binder plus the thinner is known as the paint vehicle, which is used to classify paint as either oil-solvent base or latex water base. The authors continue with an explanation of the “drying” process, which for oil-base paint is actually an oxidation of the double bonds in the binder (unsaturated oils) and subsequent crosslinking. The vehicle in a water-base paint consists primarily of an aqueous emulsion of acrylate polymer particles, which coalesce as the water evaporates. [Droske and Carraher also discuss polymers in paint on p 1431 of this issue of JCE ] . Previous authors (2, 4–6) go into considerable detail about oil-base formulations, which were the primary vehicles prior to the 1950s. Properties of Paints
So what is paint? How does it do its job to protect and enhance surfaces? I found the most succinct answers in a 1989 paper by Schuerman and Bruzan (7). Paint has three major components: pigments, binders, and thinner. After paint application, the thinner evaporates and the binder hardens as
Articles from the 1920s and early 1930s reflect the major focus of the paint industry at that time—physical properties and durability (1, 3). Although the 1933 paper by F. L. Browne on durability testing makes no mention of the chemical nature of paints, I found the text and accompanying photographs quite informative, especially the discussion of applying paint to different types of wood. For example, Figure 1 shows the importance of the density of the wood, and Figure 2 shows a wooden test fence constructed by the National Lead Company.
Figure 1. (Browne, F. L. JCE, 1933, 10, 535.) Three painted boards of the same species of wood after exposure to external weathering. The middle board, which shows the least wear and peeling, has the lowest density and contains the smallest proportion of summerwood (dark-colored portion of each annual growth ring).
Figure 2. (Browne, F. L. JCE, 1933, 10, 532.) Test fence for evaluating the relative durability of house paints. Each board is marked into three sections. The test paint is located on the outer sections, and the middle section is coated with a control paint for visual comparison.
What Is Paint?
1448
Journal of Chemical Education
•
Vol. 83 No. 10 October 2006
•
www.JCE.DivCHED.org
Chemical Education Today
The National Lead Company? Yes, references to the now infamous four-letter element occur frequently in JCE articles written prior to 1980, which even include a description of a general chemistry experiment on the preparation of the paint pigment PbCrO4 (8). In 1971, Congress passed the Lead Based Paint Poisoning Prevention Act, and since 1979 the Consumer Product Safety Commission has limited the lead concentration in paints to 0.06 wt% Pb (9, 10). The increased public awareness of lead poisoning, especially in children, roused faculty to include this relevant topic in class discussions and laboratories. Three JCE papers describe student experiments on analyses of lead in paint (10–12), and Thomas Rees’ note, “Homeowner’s Test for Lead in the Paint,” explains how consumers can test for lead qualitatively using a stink bomb and an old peanut butter jar (13). Unfortunately, the general topic of paint chemistry has not appeared in JCE since the 1989 paper quoted above (7). Considering all the attention paid to the oil-base types in JCE’s early years, an up-to-date discussion of water-base paints is sorely lacking. Faculty could use the material to enhance lectures on polymer chemistry and consumer products. The relevance also extends to discussions of air pollution control because government agencies are starting to limit the VOC (volatile organic compounds) content of paints (14). Perhaps this look into the past will reinvigorate interest in paint chemistry among JCE readers and, most importantly, among JCE authors.
10. Markow, Peter G. Determining the Lead Content of Paint Chips. J. Chem. Educ. 1996, 73, 178–179. 11. Sundback, Karen A. Testing for Lead in the Environment. J. Chem. Educ. 1996, 73, 669–670. 12. Kesner, Laya; Eyring, Edward M. Service-Learning General Chemistry: Lead Paint Analysis. J. Chem. Educ. 1999, 76, 920– 923. 13. Rees, Thomas. Homeowner’s Test for Lead in the Paint. J. Chem. Educ. 1996, 73, 669. 14. Vandervort, Don. House Paint Colors and Options. http:// www.hometips.com/cs-protected/guides/paint.html (accessed Aug 2006).
Kathryn R. Williams is in the Department of Chemistry, University of Florida, Gainesville, FL 32611-7200;
[email protected].
Literature Cited 1. Walker, Percy H. Paint and Varnish Research at the Bureau of Standards. J. Chem. Educ. 1926, 3, 777–784. 2. Holton, E. C. The Story of Paint and Varnish. Parts I, II, III. J. Chem. Educ. 1928, 5, 515–530, 682–696, 836–845. 3. Browne, F. L. Testing House Paints for Durability. J. Chem. Educ. 1933, 10, 529–538. 4. Ware, E. E. The Modern Trend of the Paint Industry. J. Chem. Educ. 1934, 11, 437–440. 5. Heckel, G. B. A Century of Progress in the Paint Industry. J. Chem. Educ. 1934, 11, 487–493. 6. Weber, Walter C. Chemicals in the Manufacture of Paint. J. Chem. Educ. 1960, 37, 322–324. 7. Schuerman, George; Bruzan, Raymond. Chemistry of Paint. J. Chem. Educ. 1989, 66, 327–328. 8. Daines, Terri L.; Morse, Karen W. The Chemistry Involved in the Preparation of a Paint Pigment. An Experiment for the Freshman Laboratory. J. Chem. Educ. 1976, 53, 117–118. 9. National Paint and Coatings Association. News & Information: History of Paints and Coatings. http://www.paint.org/ ind_info/history.cfm (accessed Aug 2006).
www.JCE.DivCHED.org
•
Vol. 83 No. 10 October 2006
•
Journal of Chemical Education
1449
