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Scanning electron microscopy and the mystery of the blooming crystals

What's a plastic bag made out of? Most people would say plastic, and they would be right, sort of. Most of the products we use every day go through several levels of manufacturing before they become the things we use. Plastic bags, for instance, often contain stearates that are made from animal products, according to Genetic Engineering and Biotechnology News, which is an incentive for vegans to bring their own shopping bags to the grocery store. But the unknowns in various materials can have an impact on manufacturing as well. Sometimes plants discover that during the manufacturing process, materials behave differently than they would expect.

Mysterious crystals
This occurred to a client of Polymer Solutions who discovered a defect with a toy they were producing. The wrist strap portion of the toy was forming white crystals on its surface. This was, of course, alarming for the toy company since any product which is intended for use by children is held to a very high standard. The material that was used to fabricate the wrist strap was not produced directly by the toy company, and they could not determine what could possibly be in the wrist straps that could cause this reaction. No matter what they did to try to modify the process, manufacturing kept yielding these crystal blooms. Something had to be done.

Science to the rescue
Polymer Solutions, a material analysis firm, decided that in order to solve this mystery, they had to first identify the mysterious crystal. In order to do this, they used scanning electron microscopy to obtain images of the crystal. According to the University of Wyoming, scanning electron microscopy uses a focused beam of high-energy electrons to create a spectrum of signals on the surface of solid specimens. Those signals come from electron-sample interactions and reveal a depth of information about the surface of the sample including texture, chemical composition, crystalline structure and orientation of materials.

Using the images gathered from SEM, the researchers applied energy dispersive spectroscopy, which is a method of identifying specific the proportions of specific elements in the image with chemical analysis. According to The University of Minnesota, EDS is able to do this by generating an x-ray spectrum from the scan area of an SEM. The results are then graphed on an X/Y chart, which allows researchers to identify the elements at each point of the SEM image. To complete the picture, color can be added to provide additional perspective on the chemical composition of unknown compounds.

As for the mystery crystals on the toy's wrist strap? Bromine: a common flame retardant. Bromine is a common material in toys, but bromine crystals are clearly a problem. The flame retardant is supposed to be blended into the wrist strap , not protruding in crystalline blooms. Armed with this information, the client was able to alter its manufacturing processes to prevent the development of these bromine crystals, thereby ensuring the safety of the toy.