How do you get burnt on plastic off your straightener?

My sister tried to put a seam in a zip-lock baggy. . . With my hair straightener. I reheated it and then used olive oil to get most of it off. After that I used a spoon and scraped morw off. I have to wait for it to cool, then I'm just going to try and peel it, hoping the oil has seeped in enough to loosed it.