An old story. While playing with Styrofoam, the packaging support of most electric equipment and material of disposable coffee cup, my brother and my auto-mechanic uncle were conversing about non-sense topic. Styrofoam pieces can be dissolved in gasoline fuel and used for fixing GI roof holes.
Not a good idea, gasoline is a highly flammable liquid. Dealing with it is quite dangerous. Add to fact that fumes is a health hazard.
While cleaning the laboratory room, I held a dirty and sticky plastic container. It was a corn oil container. Perhaps the outside surface is made of polystyrene or the plastic is a pure PS but the inner wall is lacquer coated. It was just my silly inference but not from reality considering PS production is economically viable. I was not aware about the plastic coding symbol that time.
Another time. I brought home two disposable drinking cups from Jollibee. I drained residual crude oil from old large container. I placed it temporarily in polystyrene cups for later disposal. The next morning, oil were leaking around the cup. I thought someone tossed it accidentally. I lifted the cup and discovered, it was softer and contain several holes.
I forgot that polystyrene or the Styrofoam is a petroleum based product. Melting polystyrene in oil is not a chemical reaction. It is similar to mixture of salt and water or sugar and water. There are so many explanations available but the simplest and most straightforward is, “likes dissolves likes”.
This also explains why, “Never Heat Styrofoam Packed Meals in Microwave Oven“. A friend of mine bought two pack meals in Styrofoam lunchboxes. She reheated it in oven before serving. I had a hard time finishing the lunch cause the Styrofoam was melted and got mixed with the food. The fried chicken oil was responsible for Styrofoam melting and heat hasten it.