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How do thermoplastics differ from thermosetting plastics?

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plastic soft-drink bottles — plastic Plastic soft-drink bottles are commonly made of polyethylene terephthalate (PET).

Plastics are categorized into two primary types based on their behavior during processing and their molecular structure: thermoplastics and thermosetting plastics (thermosets).12

Thermoplastics

Thermoplastics, such as polyethylene and polystyrene, consist of individual molecules that are separate from one another, allowing them to flow past each other. Because of this structure, they can be repeatedly heated, molded, and reshaped. When heated above their glass transition temperature or melting point, these materials become mobile and can be extruded or formed into new shapes.13

Thermosetting Plastics

In contrast, thermosets cannot be reprocessed or remolded upon reheating. During their initial manufacturing, they undergo a chemical reaction that creates an infusible, insoluble network. This process effectively links the material into one large, interconnected molecule. Because of this cross-linked structure, applying heat does not soften the material for reshaping; instead, it may only cause the plastic to break down or degrade.13