Plastic In Water: How Hot Does It Get?

Plastic is a material that is widely used in our daily lives, from disposable plastic cups to water bottles. However, when exposed to heat, plastic can break down and release chemicals that can migrate into the beverages they contain. This raises an important question: how much does plastic heat up in water? The answer depends on the type of plastic and the temperature of the water. Different types of plastic have varying melting points, with some commonly recycled plastics melting at temperatures as low as 75 degrees Celsius (167 degrees Fahrenheit). On the other hand, some plastics have higher melting points, such as polyethylene terephthalate (PET), which has a melting point of 255 degrees Celsius (491 degrees Fahrenheit). Understanding how plastic behaves in water at different temperatures is crucial to ensure the safety of consumers and the environment.

The melting point of commonly recycled plastics varies, with some melting at 75°C

Of the six commonly recycled plastics, four can withstand temperatures of 100°C or above. Polyethylene terephthalate (PET) has a melting point of 255°C. High-density and low-density polyethylenes (HDPE and LDPE) melt at 130°C and 120°C, respectively.

Polyethylene terephthalate (PET) has a melting point of 255°C

Polyethylene terephthalate (PET) is a plastic with a high melting point of 255°C. This is well above the maximum temperature of liquid water under normal conditions (100°C) and so it is unlikely to be melted by hot water. However, PET is commonly used for bottles and other containers, and heat can break down chemical bonds in plastics, causing chemicals to migrate into the liquid inside. Therefore, it is best to avoid exposing PET to high temperatures.

The melting point of PET is determined by its morphological structure, which is a semicrystalline polymer formed from terephthalic acid and ethylene glycol. The crystallite size and shape, volume fraction, orientation, and perfection can be varied through control of the crystallization process, which in turn affects the melting point. PET's high melting point and good mechanical properties make it a versatile engineering plastic, used in everything from beverage bottles to sportswear.

High-density polyethylenes (HDPE) melt at 130°C

The melting point of High-Density Polyethylene (HDPE) is 130°C (266°F). This is a relatively high melting point, which makes HDPE useful in applications requiring strong materials that can withstand heat. For example, HDPE is used in piping systems and automotive components.

HDPE is one of six commonly recycled plastics. Four of these can withstand temperatures of 100°C (212°F) or above. The melting point of HDPE is therefore important as it affects the processing and application of the material. It also ensures easy moulding and extrusion, making it efficient in producing various industrial and consumer goods.

The melting point of HDPE is also important because it establishes how the material behaves at different temperatures. For example, heat helps break down chemical bonds in plastics, and those chemicals can migrate into beverages they contain. In 2014, scientists found high traces of antimony and a toxic compound called BPA in water sold in Chinese water bottles. In 2016, scientists found high antimony levels in bottled water sold in Mexico. Both studies tested water under conditions that exceeded 150°F, representing worst-case scenarios.

The melting point of HDPE can be compared to other plastics. For example, Low-Density Polyethylene (LDPE) has a melting point of 120°C (248°F). Polyvinyl chloride (PVC) plastics melt at around 75°C (167°F).

Low-density polyethylenes (LDPE) melt at 120°C

The melting point of plastic varies depending on the type of plastic. Some plastics, such as polyvinyl chloride (PVC), melt at a relatively low temperature of 75°C (167°F). However, the melting point of most plastics is above the maximum temperature of liquid water under normal conditions, which is 100°C (212°F).

Low-density polyethylenes (LDPE) have a melting point that typically falls within the range of 105-115°C. Some sources give a slightly higher range of 106-112°C for film grade resins. LDPE is commonly used in packaging plastics, such as bags and wraps, due to its flexibility at low temperatures.

Linear low-density polyethylenes (LLDPE) have a higher melting point than LDPE, typically ranging from 120-125°C. This higher melting point allows for quicker and cleaner demoulding of moulded products. LLDPE is often used in packaging materials that require additional puncture resistance and uplift properties, such as stretch films and heavy-duty bags.

High-density polyethylenes (HDPE) have an even higher melting point, typically ranging from 120-130°C (248-266°F). This makes HDPE suitable for applications where high temperatures are maintained, such as containers and pipes used in chemical processing plants.

It's important to note that the melting point of polyethylene increases with density. Therefore, when heating polyethylene, the crystallization gradually decreases, and the crystalline part eventually disappears as the polyethylene melts.

Heating plastic can cause chemicals to migrate into the liquid it contains

The melting points of different types of plastic vary widely, but most are comfortably above the maximum temperature of liquid water under normal conditions, or 100 degrees Celsius (212 degrees Fahrenheit). Of the six commonly recycled plastics, four can withstand temperatures of 100 degrees Celsius (212 degrees Fahrenheit) or above. However, one commonly recycled plastic, polyvinyl chloride (PVC), melts at as low as 75 degrees Celsius (167 degrees Fahrenheit).

High-density and low-density polyethylenes (HDPE and LDPE, or recyclables 2 and 4) melt at 130 degrees Celsius (266 degrees Fahrenheit) and 120 degrees Celsius (248 degrees Fahrenheit), respectively. Polyethylene terephthalate (PET, or recyclable 1) has a melting point of 255 degrees Celsius (491 degrees Fahrenheit).

To avoid exposure to potentially harmful chemicals, it is recommended to use unlined stainless steel, copolyester-lined aluminium, or copolyester plastic drinking bottles.

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