Time to learn about stuff we use daily without knowing much about. Yeah it melts at certain temperatures, depending on the manufacturer, or has a certain glass temperature so the heated bed must be this hot. But what is PLA actually?
Well, PLA is Polylactic acid. Poly stands for many, so many actic acids, you'd say? Today Wikipedia told me it does not use correct Organic nomenclature, as defined by the IUPAC, as it is not a polyacid, but rather a polyester.
Instead of further citing Wikipedia, have a read yourself, it's quite interesting: https://en.wikipedia.org/wiki/Polylactic_acid
So PLA is a chain with many copies of the link I printed, as can be seen in the picture. As the picture explains, the green are the Hydrogen atoms, grey are the oxygen atoms and blue are the carbon atoms, sadly I didn't have enough time to print that with colorfabb Carbonfill :(