When hot water is placed into an empty water bottle, the bottle keeps its shape and does not soften. What type of plastic is the water bottle made from?

Plastics are broadly classified into thermoplastics and thermosetting plastics based on their thermal behavior. Thermoplastics, such as PVC and polyethylene, possess linear molecular chains with weak intermolecular forces, causing them to soften or melt when heated and harden when cooled [2]. This allows them to be reshaped repeatedly [1]. In contrast, thermosetting plastics undergo a chemical change during their initial curing process, forming a three-dimensional network of irreversible, unbreakable cross-links. These strong cross-links prevent the polymer chains from sliding past one another, ensuring the material retains its strength, geometry, and dimensional stability even when exposed to high temperatures. Therefore, a water bottle that maintains its shape and does not soften when filled with hot water is made from a thermosetting plastic, as it is highly resistant to heat and deformation.

Sources

1. [2] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/thermoplastics
2. [1] https://www.sciencedirect.com/topics/chemical-engineering/thermoplastics