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Is Glue Sustainable? Glue is a sticky topic for the eco-minded. Is it vegan? Biodegradable? The answer depends on the glue type. Generally, adhesives fall into two main camps: natural and synthetic. Humans have been using natural adhesives for millennia, but in the 20th century, synthetic glues were developed and have over time largely replaced natural adhesives. Much of this was thanks to the aircraft and aerospace industries, which required adhesives with high structural strength and resistance to fatigue and extreme conditions. These high-tech, synthetic adhesives eventually trickled down into more mundane industrial and domestic applications. Here, delve deep into the contents of glue—both natural and synthetic—to decipher which options have the lowest environmental impact, plus learn how to make your own adhesive at home. Ingredients in Synthetic Glues Synthetic adhesives like Gorilla Glue and Elmer's belong in two categories: thermoplastics and thermosets. The resins used in

What Are Rare Earth Metals? They're crucial to hybrid cars, wind turbines and many other green-tech innovations. "Rare earth" metals aren't as rare as they sound—in fact, you're probably using some right now. They're key to a variety of everyday devices, from tablet computers and TVs to hybrid cars and wind turbines, so it may be encouraging to know several kinds are actually common. Cerium, for example, is the 25th most abundant element on Earth. So why are they called "rare" earths? The name alludes to their elusive nature, since the 17 elements rarely exist in pure form. Instead, they mix diffusely with other minerals underground, making them costly to extract. And, unfortunately, that isn't their only drawback. Mining and refining rare earths makes an environmental mess, leading most countries to neglect their own reserves, even as demand soars. China has been the main exception since the early 1990s, dominating global trade with its willingn