How Do Plastics Get Broken Down By Enzymes?

Scientists have been searching for enzymes in microbes that break down PET and other plastics to reduce their environmental impact. In 2012, researchers at Osaka University discovered leaf-branch compost cutinase (LLC) in a compost heap, which snips the bonds between PET’s two building blocks: terephthalate and ethylene glycol. Researchers at the University of Texas at Austin have used artificial intelligence to engineer a hydrolase enzyme that can break down PET plastic. The new souped-up versions of the enzymes produced by bacteria, called PETase and MHETase, can break down PET plastic into smaller parts (depolymerization) and chemically put it back together (repolymerization). In some cases, these plastics can be fully degraded.

A new study outlines the use of a specially created enzyme variant that vastly reduces the time it takes to break down the components of plastics. This enzyme variant could even be used to clean up sites contaminated by plastics. All these enzymes act on the plastic polymer in a similar manner, causing hydrolytic cleavage of the long carbon chains and then assimilating these smaller subunits into the microbial cell for further enzymatic degradation and release of metabolic products.

The first enzyme, PETase, breaks down PET into mono (2-hydroxyethyl) terephthalic acid (MHET), which is then broken down further by MHETase. Enzymatic degradation occurs in two stages: adsorption of enzymes on the polymer surface, followed by hydro-peroxidation/hydrolysis of the bonds. This research highlights the potential of microbial enzymes to break down plastics, which could otherwise take hundreds of years to degrade.

How do enzymes break down polymers?

Synthetic plastics, such as polyethylene (PE), polyethylene terephthalate (PET), polyurethane (PU), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC), are crucial in our daily lives but pose a significant environmental and health concern. These materials are resistant to natural biodegradation pathways, making them difficult for microorganisms to degrade under in vitro conditions. The rate of polymer biodegradation depends on factors such as chemical structures, molecular weights, and degrees of crystallinity.

Highly crystalline polymers like polyethylene are rigid and have low resistance to impacts. PET-based plastics possess a high degree of crystallinity (30-50), which is one of the main reasons for their low microbial degradation rate. This degradation process takes over 50 years in the natural environment and hundreds of years if discarded into the oceans due to lower temperature and oxygen availability.

Enzymatic degradation occurs in two stages: adsorption of enzymes on the polymer surface and hydro-peroxidation/hydrolysis of bonds. Plastic-degrading enzymes can be found in microorganisms from various environments and the digestive intestine of some invertebrates. Microbial and enzymatic degradation of waste petro-plastics is a promising strategy for depolymerization into polymer monomers for recycling or to covert waste plastics into higher value bioproducts, such as biodegradable polymers via mineralization.

This review aims to outline advances made in the microbial degradation of synthetic plastics and overview the enzymes involved in biodegradation. With about 335 million tons of plastics manufactured worldwide in 2016, synthetic plastics like PET, PE, PUR, PS, PP, and PVC have been extensively used in industrial and domestic applications.

How do enzymes break things down?

Enzymes perform the critical task of lowering a reaction’s activation energy—that is, the amount of energy that must be put in for the reaction to begin. Enzymes work by binding to reactant molecules and holding them in such a way that the chemical bond-breaking and bond-forming processes take place more readily.

How do you break solid plastic?

2. 2. Select the right tools. For cutting thin sheets of polycarbonate and acrylic, or any other hard plastic, you can use a hot knife or a hook knife. A circular saw is your best bet for a high-quality finish on thicker ones. When cutting circles or curves, use a hole saw or jigsaw.

2. 3. Move slowly. In addition to keeping the material straight and staying on your intended cutting line, you want to proceed slowly to reduce melting.

2. 4. Draw a line before starting. Once you start the process, it is easy to lose sight of where you are cutting. Thus, plan ahead and draw the desired line on the hard plastic piece.

Can enzyme break down plastic?

The enzymes are known to belong to the hydrolase family which includes esterases, lipases, depolymerase, and PETases enzymes known to break down the carbon backbone of many of the commonly used plastics (Pometto et al., 1992).

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Why can’t we digest plastic?

Plastics and microplastics passing through an organism’s gastrointestinal tract require a long digestion time, which decelerates their degradation rate; hence, these are retained in the organism’s body.

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What process breaks down plastic?

Larger pieces of plastic in the sea or on land, such as bottles and plastic packaging, become brittle and gradually break down. This is due to sunlight, oxidation or friction, or by animals nibbling on the plastic. This plastic break down process goes on forever, although the speed depends on the circumstances.

What helps break down plastic?

How does it work? The microbes’ specialized proteins called enzymes degrade plastic into its most basic chemical components, or monomers. The monomers can then be recombined into plastics of the same type and quality. In a process called upcycling, the monomers are recombined into different materials or chemicals with more desirable qualities, such as plastics that are more biodegradable than originally made or high-value chemicals, such as vanillin found in vanilla flavorings (see fig. 1).

Figure 1. Enzymes degrade plastic for processing into other materials, such as the same quality plastic, high-value chemicals, or more biodegradable plastic.

While some microbes have naturally evolved enzymes that can degrade certain plastics, the process in nature can take weeks or more. To make biorecycling viable at industrial scale, scientists can alter, or engineer, the natural enzyme to degrade plastics faster, reducing the time needed for complete degradation to hours.

Can enzymes break down plastic?

Studies have shown that enzymes can degrade polyesters, with cutinases being a subtype of esterase capable of cleaving the ester bonds within the cutin polymer, a component of plant waxy cuticles. Cutin is a complex polyester with ester bonds formed between hydroxy and hydroxyepoxy fatty acids, making it a significant hydrophobic material. Cutinases are often recognized as the most efficient for plastic degradation due to their natural affinity for hydrophobic plastics and ability to hydrolyze the ester bonds found in PET.

However, these enzymes still face challenges in terms of efficiency due to the presence of repeating aromatic terephthalate units that elevate the crystallinity of PET, resulting in slow and often incomplete degradation processes. In 2016, a research team isolated the bacterium Ideonella sakaiensis from a recycling plant, which secretes two enzymes capable of degrading PET. The first enzyme, PETase, breaks down PET into mono (2-hydroxyethyl) terephthalic acid (MHET), which is further broken down by MHETase, producing terephthalate (TPA) and ethylene glycol (EG), which can be metabolized by other bacteria as a carbon source.

This discovery was significant as the enzyme could survive on only PET as a food source, indicating that the bacterium has specifically evolved to break PET rather than re-directing its existing cutinise activity. The sequence action of PETase and MHETase, isolated from I. sakaiensis, degrade PET into products for metabolism.

Why is plastic so hard to break down?

But polymers like polypropylene are not abundant in nature. The enzymes in the microorganisms that break down biodegradeable materials don’t recognize the bonds that hold polymers together.

Eventually, the polymers in plastic waste may break down, perhaps after hundreds of thousands of years. But when it takes such a long time, the damage is already done to the environment. Plastic trash can release harmful chemicals into soil and water, or break into tiny bits that animals, fish and birds eat.

In the outdoors, plastic trash breaks down into smaller and smaller pieces, but it doesn’t biodegrade completely for thousands of years. Alfonso Di Vincenzo/KONTROLAB/LightRocket via Getty Images.

In my laboratory, we’re developing what we hope will be the plastics of the future – materials that work like regular plastic, but don’t spoil the environment because they can degrade when people are done with them.

Can enzymes break down products?

Typical enzymes can be categorized into four main groups, based on the types of soils they react with.

• Proteases break down protein-based soils including blood, urine, food, feces, wine and other beverages.
• Lipases break down fat molecules like oils and grease.
• Amylases break down starch molecules like eggs, sugars, sauces, ice cream, gravy.
• Cellulases are used to soften fabric and restore color to fibers made up of cellulose material. They also remove particulate soil and reduce fabric graying and pilling.

Each type of enzyme is different and will catalyze only one type of reaction (known as a ‘lock and key’ mechanism). They are highly specific to the type of surface or material they can work on and are only active when conditions are correct.

Biological cleaning products are live solutions formulated using strains of safe, natural bacteria along with specifically selected enzymes. Both bacteria and enzymes work together to clean, relying on each other to get the job done. When applied to surfaces, soils, stains and malodors are broken down by the enzymes, then consumed by the bacteria. As long as soil is present and surfaces are sufficiently damp, these microscopic “cleaners” multiply, continuing to remove traces of grime and odor from surfaces hours or even days after the initial application.

How to break down plastic polymers?

There are two different approaches to achieve that result:Gasification: waste materials are heated to a very high temperature (~1000 – 1500 °C) in low-oxygen environments. … Pyrolysis (thermal cracking): plastic waste is heated to temperatures over 400 °C under low-oxygen conditions.

To grasp the concept of chemical recycling, it is key to know that plastics are made from oil or petroleum and produced through a polymerization process. As a result, they contain long chains of molecules, which are combined to create polymers.

Plastics are categorized according to their primary polymer material. The major plastics we encounter in our daily lives include such polymers as PET (polyethylene terephthalate), HDPE and LDPE (high-density and low-density polyethylene), PVC (polyvinyl chloride), PP (polypropylene), and PS (polystyrene). All of these plastics differ in size, color, usage, and recyclability.

The world produces 380 million tons of plastic per year. Traditionally, the only way to recycle plastic waste was using mechanical recycling: a process involving sorting, grinding, separating, washing, melting, and then cooling it back to granulated recycled plastic. However, that process is only possible with certain types of plastics, and only if they are made up of single polymers. PET beverage bottles and HDPE containers like milk jugs, for example, are easy to recycle.