Researchers have identified a plastic crystal that could be used as an eco-friendly coolant in refrigerators and air conditioners


Refrigeration and air conditioning devour a fifth of the energy produced worldwide.


Refrigeration cycle based on the change in structure from compressing and decompressing plastic crystals

In a joint research project, researchers from the UPC’s Department of Physics, the University of Cambridge and the University of Barcelona have identified an eco-friendly solid that could replace hydrofluorocarbons (HFCs) and hydrocarbons (HCs), which are highly toxic and flammable. These two types of gases are currently used in the vast majority of refrigerators, air conditioners and cooling systems. The research was recently published in Nature Communications.

May 10, 2019

The researchers identified that, when put under pressure, plastic crystals of neopentylglycol yield huge cooling effects, enough for them to compete with the gases used in the vast majority of refrigerators and air conditioners, that is, hydrofluorocarbons (HFCs) and hydrocarbons (HCs), which are highly toxic and flammable and also contribute to global warming when they leak into the air. In addition, this new material is inexpensive, widely available and functions at room temperature.

Refrigerators and air conditioners based on HFCs and HCs are also relatively inefficient”, said Xavier Moya, from the University of Cambridge, who led the research with Josep Lluís Tamarit, a researcher from the Department of Physics at the Universitat Politècnica de Catalunya · BarcelonaTech (UPC). “That’s important because refrigeration and air conditioning currently devour a fifth of the energy produced worldwide, and demand for cooling is only going up”.

The research, carried out by a team of researchers from the UPC’s Materials Characterisation Group, the University of Cambridge and the University of Barcelona, was published in the journal Nature Communications. It describes the enormous thermal changes achieved with plastic crystals under pressure. Conventional cooling technologies rely on the thermal changes that occur when a compressed fluid—typically, an HFC or an HC—expands. As it expands, it decreases in temperature and cools its surroundings. With solids, however, cooling is achieved by changing the material’s microscopic structure, which can be done by applying a magnetic or electric field or through mechanic force. For decades, these effects in solids were less significant than the effects in fluids, but the discovery of colossal barocaloric effects in plastic crystals of neopentylglycol (NPG) and other organic compounds, which are easier to compress, just levelled the playing field.

NPG is widely used in the synthesis of paints, polyesters and lubricants because it is widely available and inexpensive. NPG molecules, composed of carbon, hydrogen and oxygen, are almost spherical and interact with each other only weakly. This allows the molecules to rotate relatively freely, to the extent that, due to their malleability, these crystals lie at the boundary between solids and liquids. That is why the compression of NPG yields thermal results comparable with those of HFCs and HCs, but without these gases’ harmful effects.

As explained by Josep Lluís Tamarit, “the potential of plastic crystals in this field is enormous and not limited to NPG. We are currently investigating other similar materials and achieving very promising results”. In fact, the members of the universities involved in the research developed a joint patent that aims to bring to market new cooling systems based on these materials with the involvement of companies.

The discovery of barocaloric effects in plastic crystals brings barocaloric materials to the forefront of research to achieve safe, efficient and environmentally friendly cooling.