Tag Archives: Materials

Enzymes – A Solution in the War Against Plastics

It should not be a surprise to people that it can take over 500 years for UV radiation – light from the sun to break down a piece of plastic. But what if there is a faster way to break down single-use plastics?

Researchers at the University of California, Berkeley invented a new way to decompose consumer plastics in a short amount of time, simply with heat, water, and nano-dispersed enzymes.

Plastic waste covering the shoreline. Source

UC Berkeley professor Dr. Ting Xu and her research group  developed a nanoscale enzyme that can eat away at the polymers in plastics. These nanoscale polymer-eating enzymes can be embedded into plastics during manufacturing. The enzymes were wrapped around plastic resin beads. These beads are melted and can be manufactured into single use consumer plastics. To prevent the enzymes from activating when not required, a random heteropolymer (RHP) coating is applied to hold enzymes without restricting the flexibility of tensicity of the plastics.

Xu likened this process to organic composting. By adding water and heat, the RHP polymers is removed and starts eating away the polymers into smaller subunits.

The research conducted by Xu and her group found that the enzymes took about a week to degrade most of the plastics. Polylactic acid (PLA) and polycaprolactone (PCL) based plastics embedded with nanoscale polymer eating enzymes are able to break down the polymer chains into smaller molecules, such as lactic acid.

Plastic cups made from biodegradable plastics. Source

It is clear there is still more research needed in this field. Currently, Xu is developing other modified RHP-wrapped enzymes that can stop the degradation process at specific points in it’s degradation so that the polymers can be recycled into new plastics.

“[Humans] are taking things from the Earth at a faster rate than we return them,” said Xu. “Don’t go back to Earth to mine for these materials, but mine whatever you have, and then convert it to something else.”

As consumers, we can play an important role reducing our consumption on single use plastics and create a more sustainable environment for ourselves and future generations.

 

Raymond Tang

A green future for ammonia

Chemists from the University of California, Berkley (UCB) have designed a new material that could reduce the energy requirements of the Haber-Bosch process.  The group hopes their research, published January 11th 2023, will conserve energy and lead to a “greener” future for ammonia and fertilizer production.

Current infrastructure needed to maintain the pressure and temperature required for the Haber-Bosch process source

The Haber-Bosch process has been the main method for producing ammonia since its invention over 100 years ago.  It is widely considered one of the most important scientific discoveries of the 20th century. Yet, despite its important role producing ammonia for agricultural fertilizer, its industrial synthesis continues to be energy inefficient.

High temperatures and pressures are needed to produce ammonia which must then be extracted to be used. Conventionally, the reaction mixture is cooled from 500℃ to -20℃. This condenses the synthesized ammonia and separates it from the remaining chemicals. However, cooling the mixture while maintaining the pressure of 300 atmospheres accounts for a large proportion of the processes’ energy loss.

Benjamin Snyder, who leads the UCB research group, said it was this extraction step that his team sought to improve by “finding a material where you can capture and then release very large quantities of ammonia, ideally with a minimal input of energy”.

These requirements led the research group to create a metal-organic framework (MOF) material.  The MOF had a crystal structure made from copper atoms linked to cyclohexane dicarboxylate molecules.  The crystalline structure gave the material unique properties suited for its use in ammonia extraction.

Structure of the cyclohexane dicarboxylate molecule used to make the MOF source

When exposed to ammonia the material changes its structure from a rigid crystal to a loosely packed and porous polymer. The polymer form can readily store a large amount of ammonia within it which can then be released with cooling. The result is that ammonia can be extracted 195℃ above the temperature required by current methods and at half the pressure.

Not only would the MOF save energy in the extraction process but, interestingly, after releasing the ammonia “the polymer somehow weaves itself back into a three-dimensional framework” says Snyder. This mechanism, which is still being studied, allows the MOF to be used repeatably.

With the Haber-Bosch process using 1% of the world’s energy, the research done by Snyder and his group is an important step in producing a greener future for ammonia.