Expanded polystyrene (EPS), commonly known as Styrofoam, presents a significant disposal challenge due to its massive volume. This material is remarkably lightweight because it consists of approximately 95 to 98 percent trapped air, with the remaining fraction being the solid plastic polymer, polystyrene. The goal of “melting” or dissolving EPS is not to eliminate the material, but to significantly reduce its bulk for transport, storage, or eventual recycling. Since the material is mostly air, shrinking the foam structure is the only practical way to achieve volume reduction.
Chemical Methods for Volume Reduction
The most practical and safe method for reducing the volume of EPS involves a process of dissolution using common solvents, which is a physical change rather than a true heat-induced melt. This technique works by breaking down the expanded structure of the foam, allowing the vast amount of trapped air to escape almost instantly. The polystyrene polymer chains themselves are not chemically altered, but the foam structure collapses dramatically.
Two common solvents are acetone and D-limonene. Acetone, often found in nail polish removers, is a fast-acting solvent that quickly dissolves the foam structure. D-limonene, a citrus-based solvent derived from orange peels, is a less toxic, more environmentally benign alternative, though it works more slowly. When performing this process, work in a well-ventilated area and use a glass or metal container, as the solvent is volatile and the resulting residue is sticky.
To begin the volume reduction, pour a small amount of the chosen solvent into the container. Pieces of EPS can then be submerged into the liquid, where they immediately shrink and dissolve into a dense liquid or sludge. A surprisingly large amount of foam can be processed with a small volume of solvent, demonstrating the low plastic mass of the foam. This dissolution process concentrates the material, achieving the desired volume reduction.
Why Heat Melting is Dangerous
Attempting to melt expanded polystyrene using direct heat sources, such as an oven, stove, or open flame, poses health and safety risks. Unlike the dissolution process, thermal melting causes the polystyrene polymer to undergo chemical decomposition. This breakdown releases a complex mixture of toxic fumes into the air, making the process hazardous without specialized industrial ventilation.
The primary toxic chemical released is styrene gas, the monomer building block of polystyrene, which the Environmental Protection Agency (EPA) has classified as a possible human carcinogen. Inhaling styrene fumes can cause irritation to the eyes and respiratory tract, and prolonged exposure can lead to neurological and health effects. If the material begins to burn or undergoes incomplete combustion, it also produces carbon monoxide, a colorless and odorless gas that can be fatal.
Furthermore, EPS is flammable and has a relatively low ignition point. Applying direct heat can quickly lead to an uncontrolled fire, characterized by thick, black, noxious smoke. The dangers from toxic chemical releases and fire risk outweigh any perceived benefit of volume reduction through thermal methods. Avoid all attempts to melt EPS with heat.
Handling the Dense Polystyrene Residue
After the EPS has been dissolved in a solvent, the resulting material is a high-density, sticky, and viscous polystyrene residue. This concentrated mass retains the entire original weight of the plastic, as dissolution only removed the air, not the polymer. The residue is essentially pure polystyrene and can be solidified by allowing the remaining solvent to evaporate in a ventilated location.
Once the solvent has evaporated, the material becomes a hard, dense block of plastic. This concentrated mass can be handled more easily than the original foam and may be suitable for applications such as a plastic adhesive or a castable material for small projects. For disposal, the dense block should be treated as a solid plastic waste. It must be contained in a sealed bag or container and disposed of according to local regulations for chemical or plastic waste.