The biodegradable Sun Chips bag was 100 times louder than a normal chip bag

Evidence

The Frito-Lay Company makes the popular Sun Chips snack. In a laudable move, the company in 2009–2010 packaged their Sun Chips in a new, biodegradable bag (figure 7.46). The bag was made of polylactide, a polymer made from plant starch that easily degrades outdoors. There was one problem: the bag was easily the loudest chip bag ever. The author verified over 95 dB near the bag’s surface while crushing it, as loud as a jackhammer 15 to 20 meters away—enough to damage hearing if one is exposed for long periods of time (longer than any reasonable duration for munching the bag’s contents, however). This compares to about 75 dB for a normal chips bag, or 20 dB down. Every 10 dB is a factor of 10 in power, so the Sun Chips bag put out 100 times the power of a “normal” chips bag! The sound power spectrum of a recording of the bag being crushed diminishes below 100 Hz but is nearly constant over much of the range of human hearing, slowly declining only above 15,000 Hz. There is a very broad, weak maximum around 7000 Hz. What could be causing this? The sound generated by “crinkling” of a stiff surface is caused by sudden acceleration of the surface. A portion of the surface abruptly deforms to a new shape. A light, thin sheet resists deforming if it is in certain shapes. Everyone knows, for example, that a sheet of paper rolled up in the shape of a cylinder resists pressure along the axis of the cylinder. Failure of the shape under an applied force comes suddenly and with considerable stored energy. If the forces are large just at the time of failure (crinkle) and the material quite lightweight, the accelerations can be significant. The details of the sizes of the crinkles and the speed of their formation would make an interesting study. — Eric J. Heller, Why You Hear What You Hear- An…, 744

Categorization

Category: Factual Claims

• CANDY: A fun, tweetable fact: the ‘green’ Sun Chips bag was 100x louder than a normal chips bag — audibly the loudest chip bag ever, verified at over 95 dB.
• SHARE: Send to anyone in packaging or materials acoustics — a concrete case of structural stiffness and stored elastic energy governing radiated sound from crinkling.
• XREF: The sudden-stored-energy failure mechanism parallels fracture acoustics (acoustic emission) used in non-destructive testing of materials.