What is that Hazy Film on My Windows?
Published November 9, 2004
MATT HELMS: The grime suspects: Migrating auto chemicals love to leave a film on windshields
BY MATT HELMS
FREE PRESS COLUMNIST
When it comes to that nasty film that builds up on the inside of windshields, blame your dashboard — or any other number of plastics and vinyl products used in automotive interiors.
Hundreds of you called and e-mailed me after I wrote last week about how much the film frustrates me and reader Donald Halleck of Green Oak Township.
We wanted to know where it comes from and how to get rid of it.
I’ve heard from professors; current and retired workers in the auto, glass and vinyl industries; a couple of retired auto company researchers, and a spokesman for General Motors Corp. It’s unanimous: The main culprit is chemicals used to make the plastics and vinyls in our cars more flexible and durable.
It’s also almost impossible to remove. This milky, somewhat sticky film defies cleaning agents. You think you’ve got it wiped away — till sunlight or headlights hit your windshield and you see streak after streak.
There is a reason for it. Our dashboards and other interior components are supple and long lasting for a reason — there are chemical compounds in them to make them that way. Without those ingredients, they’d get brittle and be prone to cracks.
Problem is, those chemicals don’t stay stuck to the vinyl or plastic forever. They gas out, especially in heat, and stick to nearby surfaces such as our windshields.
“The process that you are observing is called desorption,” writes David Felbeck, a University of Michigan professor emeritus of mechanical engineering. “This is the process where individual molecules that are weakly attached to a surface randomly get kicked off into space and then are deposited on another surface.
“The problem is worse with new cars because there is so much junk put into upholstery to make it look good. If you have ever kept a car for many years (as I did during my student years), you would notice that the problem diminishes with time. I currently have a 2-year-old car and I still have the desorption problem.”
Another reader was more specific.
“The nonsmoking fog noticed on vehicle interiors is due to plasticizer migration,” writes Paul Breakey of Livonia, a retired Ford Motor Co. steering wheel engineer. “Plasticizers are various chemicals blended into plastic material to improve molding processes and to make molded components more flexible. Vinyl floor mats, seating material, dash panel and instrument panel molded plastic components as well as interior plastic trim all have various plasticizers in varying amounts.
“Over time and with sun load,” or ultraviolet ray exposure, “the plasticizers migrate to the plastic surface, enter the atmosphere and most noticeably collect on the inside of the windshield forming the cloudy deposit noted by your readers,” Breakey adds. “Older readers will remember cracked steering wheels and cracks in the dashboards and armrests on cars from the 1950s through about 1975. The car companies have been addressing the problem over the years and certainly things are better now but still not perfect.”
Certainly not. GM, for one, says it’s continually working on the problem.
“It is an annoyance, so absolutely we’re looking at ways to eliminate or reduce it,” GM spokesman Dave Hederich told me Monday.
“Interestingly enough, that’s part of the new-car smell that people like so much,” Hederich says. “Out-gassing is more pronounced when a vehicle is new — that’s why it contributes to that new-car smell. A lot of it is due to the sun hitting it, so you don’t have it as much if your car is garaged.”
But why is it so difficult to clean? I couldn’t nail that answer down, in large part because I’m not a chemist and there are a variety of chemicals and plastics used in vehicles. I suspect the explanation is something only an engineer or researcher could love.
Chemicals and health
Aren’t we breathing in those same chemicals? Probably, but whether it impacts our health is a matter of fierce debate.
Environmental groups and some health researchers question whether plastics play a role in everything from premature puberty in girls to birth defects or cancer. Some studies have shown carcinogenic effects in laboratory animals.
The American Plastics Council and other industry groups vigorously dispute such claims and say they work to make sure that the products we come in contact with every day — from plastic dishware to toys and automotive components — are safe and well within toxicity limits. They say plastics have been proven safe through decades of independent studies around the world.
The federal Centers for Disease Control and Prevention is conducting an ongoing study of how many chemicals, including those related to plastics, accumulate in our bodies. But the agency cautions that more study is needed, according to its Second National Report on Human Exposure to Environmental Chemicals, released in 2003.
“For some environmental chemicals, such as lead, research studies have given us a good understanding of the health risks associated with different blood lead levels,” the report says. “However, for many environmental chemicals, we need more research to assess health risks from different blood or urine levels of a chemical. The results shown in the report should help prioritize and foster research on human health risks that result from exposure to environmental chemicals.”
You can reduce the amount of plastics-related chemicals you breathe by keeping windows open a crack and by setting the heater or air-conditioning so that they draw in fresh air rather than recirculate inside air.
* * *