Functional Groups
PET contains repeated ester functional groups. The ester functional group is important because it is the location where hydrolysis can break the polymer chain.
–COO–
Unit 01 Organic Chemistry
Enzymatic Recyclingof PET Plastic
Article
Lu, H., Diaz, D. J., Czarnecki, N. J., et al. (2022). Machine learning-aided engineering of hydrolases for PET depolymerization. Nature, 604, 662\u2013667.
Read The Original ArticleThe researchers engineered an enzyme called FAST-PETase. It demonstrated improved PET hydrolysis between approximately 30\u201350 \u00B0C and was tested against many post-consumer PET products. The researchers also demonstrated a closed-loop process in which recovered monomers were used to produce PET again.
Abstract
Polyethylene terephthalate, commonly known as PET, is a polyester used in products such as beverage bottles, packaging, clothing fibres, and many other consumer products. PET is valuable because it is lightweight, strong, and chemically durable. However, its durability also creates an environmental problem because PET waste can remain in the environment for long periods of time. Researchers in this study investigated whether an enzyme could be engineered to break PET down more effectively. Using machine learning and structural information, the researchers developed an improved PET-degrading enzyme known as FAST-PETase.
FAST-PETase demonstrated greater PET-degrading activity than previous versions under a range of temperatures and pH conditions. The researchers tested the enzyme on PET from 51 different post-consumer thermoformed products and demonstrated that these materials could be substantially degraded. They also showed a closed-loop recycling process in which PET was depolymerized and the recovered monomers were then used to produce PET again. The study concluded that enzyme engineering may provide a promising method for recycling PET while recovering useful organic starting materials.
Connection to Our Curriculum
Polymer Chemistry
PET is a polyester. It is produced using monomers that join together to form long polymer chains.
terephthalic acid + ethylene glycol
Hydrolysis
The enzyme encourages a hydrolysis reaction. Water is used to break ester bonds within the polymer. For PET, the important products eventually include terephthalic acid and ethylene glycol.
Ester + H₂O → Carboxylic acid + Alcohol
Structure and Properties
PET contains both ester groups and aromatic rings. Its molecular structure gives PET properties that make it useful but also make it difficult to break down.
- Durability
- Strength
- Chemical resistance
Reaction Rates
Enzymes function as biological catalysts. Catalysts provide an alternative reaction pathway with a lower activation energy, increasing reaction rate without being permanently consumed. FAST-PETase was engineered to increase the effectiveness of PET hydrolysis under practical conditions.
Catholic Graduate Expectation
OCSGE 7A Responsible Citizen
This research demonstrates responsible citizenship because the problem of plastic pollution involves both science and environmental responsibility. Plastic products provide many benefits, but industries and consumers must also consider what happens to those products after they are discarded.
Developing a process that converts used PET into reusable chemical building blocks reflects the idea of stewardship of creation. Instead of treating natural resources as unlimited, scientists are searching for methods that recover and reuse materials.
The research also demonstrates the responsibility scientists have to use knowledge for the common good. Improving recycling technology could potentially reduce waste, reduce the need for new raw materials, and decrease the environmental effects associated with plastic disposal.
Key Takeaway
Organic chemistry helps scientists understand how the functional groups and bonds within plastics can be chemically broken and recycled.