Explaining the Mundane VI

I started my undergraduate career set on getting a business degree from a local college and working as a branch manager somewhere. Then, I changed paths and decided I wanted to enter medical school and become a doctor. Like most 18-year-olds, I had no idea what I really wanted. As I started taking more science courses, I soon realized I had discovered my calling.

One appealing aspect of science and engineering was how seemingly mundane occurrences could be explained by scientific concepts that apply to a wide range of phenomena. I could wonder about the tiniest details of everyday life and try to use my knowledge of physics to explain how stuff works. I learned a lot this way and enjoyed testing my physical intuition. I’ve gathered a few of my favorite mundane events that are explained by seemingly-esoteric (but ultimately intuitive) scientific concepts.

Where does that “new car smell” come from?

 

A new car is typically associated with shiny paint, more trunk space, new gadgets to figure out, and of course, that new car smell. People have connected that leathery smell with the happy feeling of owning a new car, just like how Pavlov taught his dogs to salivate upon hearing the chime of a bell. But it’s weird describing something that smells good while simultaneously smelling like tanned animal hides. The wonderful scents of chocolate chip cookies and fresh baked bread are reminiscent of something delicious without the need for an extra caveat, like with the new car smell. So what is this strange aroma that we have learned to relate to that great feeling of becoming a car owner?

The short answer is: it’s chemicals. And that might be easy to guess; there is a redolence of anything plastic when you take a whiff of your new car interior. To go a little deeper, it should be considered what most car interiors are made of. When safety engineers are designing a car, they’re probably inclined to use a material that could conform to the shape of your head as it’s slamming into the dashboard or steering wheel in an accident. Polyvinylchloride, or PVC, might not seem like a great choice. PVC is often used for piping; it’s a stiff plastic with good durability.

Plastics fall under a broad material category that scientists call polymers. This just means that there are lots of atoms making up a long chain for a single molecule. For example, water only has three atoms (H2O), but a polymer like the stuff used to make plastics bags might have 10,000 or 100,000 or even over 1,000,000 atoms in a single molecule. And as you add more atoms, the material behaves more like a solid. When you have methane, which is just one carbon and four hydrogens, you have a gas. (Methane is what is called natural gas). When you add a few more carbons, you get octane (8 carbons) and a liquid. If you continue adding carbons, you get a waxy substance; paraffin, which is often 20+ carbons. A polymer would have hundreds or thousands of carbons and could be a solid like a plastic milk jug. The reason that it behaves this way can be thought of like magnets. If you have two magnets that are one inch long, it might be easy to pry it apart, and they could flow between one another like a liquid or gas. But if you two magnets that are one hundred feet long, it would be a lot harder to separate, and they would behave like a single solid material.

Hopefully, that gives a general sense of what a polymer like PVC is. Now, we’ll take this magnet analogy a step further. What would happen if we added in a rubber ball between our magnets? If the magnets are one hundred feet long, the rubber ball wouldn’t do much. But as you add more and more rubber balls, the magnets would start to separate and might be easier to move apart. This is what polymer scientists do with PVC. They take rigid PVC and heat it up so that the long polymer chains can move around. Then, they add tiny molecules, which are called plasticizers and can squeeze between the chains like a rubber ball. This is great for car interiors because it takes the rigid PVC and makes it into a softer, flexible material – one that is less punishing on our squishy bodies.

Often, the tiny molecules qualify in a class of compounds that scientists call volatile organic compounds (VOCs). Volatile just means that the chemicals readily evaporate at normal temperatures. Organic just means that the chemicals contain some combination of mostly carbon, hydrogen, nitrogen, and oxygen. The tiny molecules that make PVC softer will often degas, escaping into the surrounding environment. This is what the new car smell is! It’s basically just chemicals (some plasticizers and some manufacturing chemicals) leaving the plastic interior and hitting your nose. It actually might be a safe bet to not take a big whiff next time you step into a new car since the long-term effects of many of these compounds is unknown, but the good news is that car companies like Honda, Hyundai, Toyota, and Chrysler have gone to great lengths to try to find better alternatives. A future without that new car smell might be disheartening to some, but with new technologies may come new smells. And like Pavlov’s dogs, we probably will continue to salivate over that immaculate interior and smooth tires on the open road.

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