Can I use a microwave safe plastic container to bake in an electric oven?
Here is a list of common plastics found in kitchen containers. You will find this information on the bottom of the container, in a triangle with a number inside.
While some plastics used in microwavable applications appear to have a high melting point, PET for instance melts at 510ºF, please remember that the material will soften, weaken and otherwise degrade long before actually melting into liquid. Other plastics labeled microwave safe, like HDPE, melts at a mere 265ºF! While microwave safe plastics may have a relatively high short term temperature resistance, sustained temperature tolerance, as in leaving it in an oven for baking, is much lower.
Silicone bakeware, by contrast, has a melting point of 935ºF, but is only rated for use at sustained temperatures no greater than 675ºF. Above that point, and the material will soften, warp and degrade. Thermoplastics have a much lower melting point, and it can be expected that their sustained temperature resistance is likewise much lower, to the point where using them as bakeware is unadvisable.
Tonight I turned on my oven to preheat to 425 degrees for a pizza, and ten minutes later every smoke alarm in the house went off. I dashed upstairs and discovered that I had forgotten I had put a plastic bin of dishes from a neighborhood party in there to return them. (I don't have a lot of spare room.) There was a fire in my oven. Black smoke was billowing out the top. (I thought ovens were supposed to be airtight?) The whole plastic bin was melting and there was black all over the clean dishes that were in it. There were flames on either side of the melting bin. I've moved recently and had to leave my fire extinguisher behind because of a moving van regulation. So the one time I actually needed it, there was none there. (I'm buying a new one tomorrow.) I didn't know what else to do so I grabbed my wok, filled it with water, opened the smoking door and threw the whole contents all over both sides. That seemed to put out the fire, but for good measure I also filled the wok a second time and again hurled it inside the over. I see that there are hard little gray pools of plastic everywhere in there, and I suspect I have wrecked my oven. This is more than a hypothetical -- this is a PLEASE don't put any plastic in the oven!!!!! My ears are still ringing from all my smoke detectors, but they did their job. And I am shaken, every window and door in my house is open, but I'll never forget that again!