You might want to melt plastic cups for several reasons. You can reform the melted plastic into a piece of art. You can also use it for something more practical like tabletop coasters for glasses. The methods for melting a plastic cup fall into two groups: heat and chemical. Some heating methods are an open flame, concentrated sunlight and a microwave. Some chemical methods would be to use natural oils, resin or gasoline.
Using Flame & Heat
Apply an open flame with a long match or lighter directly to the plastic cup.
Angle a magnifying glass at approximately 45 degrees between the sun and the cup. The magnifying glass when angled correctly will concentrate some of that light into a tight beam. Direct the point of the beam anywhere on the cup and the cup will begin to melt at that spot.
Place a plastic cup into a microwave and use the “high” setting on the microwave for several minutes. For cheaper plastic cups, the heat generated alone is enough to induce melting. For better-made plastic cups the use of a liquid is necessary. As the liquid heats up to a boiling point the cup will begin to melt from the inside out. You'll want to have the cup sitting in a bowl to catch the liquid.
Place some tea tree oil into a plastic cup along with some water. At higher concentrations and given a few hours the cup will begin to melt.
Put heavy-duty resin a plastic cup. Much like natural oils, if the concentration of chemicals in resin is high enough and you maintain prolonged exposure, a chemical reaction will take place that melts the plastic.
Fill up a plastic cup with gasoline and allow it to sit for a few hours. The molecules from the gasoline separate the larger molecules of polystyrene in the cup from one anothe. This in turn causes the cup to break down and melt.
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