We’re all aware of the plastic pollution crisis engulfing our planet. But what if there was a natural solution, a hidden army of tiny warriors capable of breaking down plastic waste? Enter the world of plastic-degrading microbes, a fascinating field of research that’s offering hope for a cleaner future.
The Microbe Revolution:
Scientists have discovered that certain microorganisms, like those found in the intestines of wax worms and yellow powder worms, possess the remarkable ability to break down plastic. These microbes, through a complex process of enzymatic digestion, can convert plastic into harmless substances like carbon dioxide and water.
Unlocking the Power of Enzymes:
The key to this microbial magic lies in enzymes, powerful biological catalysts that accelerate chemical reactions. Scientists have identified a variety of plastic-degrading enzymes, including PETase and MHETase, which can break down polyethylene terephthalate (PET), the plastic used in bottles and clothing.
Engineering a Greener Future:
The potential of these plastic-degrading microbes and enzymes is enormous. Researchers are exploring the use of enzyme engineering to create even more powerful and efficient plastic-degrading solutions. By modifying the structure and function of these enzymes, scientists aim to enhance their ability to break down a wider range of plastics and improve their stability and activity.
The Challenges and the Promise:
While the research is promising, there are still challenges to overcome. Some plastics are more resistant to degradation than others, and the process can sometimes create microplastics, which can pose their own environmental risks. However, the potential of biological degradation offers a new and sustainable approach to tackling the plastic pollution crisis.
The discovery of plastic-degrading microbes and enzymes is a game-changer in the fight against plastic pollution. These tiny warriors offer a natural and sustainable solution to a global problem, paving the way for a cleaner and more sustainable future. As research continues, we can expect to see even more innovative solutions emerge, harnessing the power of nature to combat the plastic crisis.
Part.1 Delicious plastic
- In 2014, Yang Jun’s research team at Beihang University demonstrated for the first time in Environmental Science and Technology that waxworm intestinal microorganisms can degrade polyethylene (PE) .
- In September 2015, Yang Jun’s research team at Beihang University once again revealed with comprehensive evidence in ” Environmental Science and Technology ” that mealworms eat and degrade polystyrene (PS) , completely degrading and mineralizing it into carbon dioxide. At the same time, it It was also assimilated and transformed into insect body. At the same time, it was proved that its intestinal microorganisms play a leading role, and a strain of bacteria that degraded PS – Exiguobacterium sp. YT2 ( Exiguobacterium sp . YT2 ) was isolated and identified . This strain has been deposited in the General Microbiology Center of the China Microbial Culture Collection Committee and the National Gene Bank. It is the first PS-degrading bacterium reported internationally and deposited in the culture center.
- In June 2022, a team from the University of Queensland in Australia proposed in ” Microbial Genomics ” that specific enzymes in the intestinal bacteria of barley worms can digest plastic and absorb nutrients from it.
Part.2 Enzymes that ‘eat plastic’
- In 2016, Japanese scientist Kohei Oda discovered a special bacterium that can “eat” plastic – “ Ideonella sakainesis 201-F6 ” in a research paper in Science. The plastic food ability of Ideonella sakaiensis 201-F6 comes from a pair of enzymes it produces: PET hydrolase (PETase) and MHET hydrolase (MHETase) .
- In 2021, Sun Chaomin’s team from the Institute of Oceanology, Chinese Academy of Sciences reported the latest research results in the Journal of Hazardous Materials , discovering a marine bacterial community that can effectively degrade PET and PE. The isolated marine fungus Alternaria alternata FB1 (laccase and laccase Catalase) can effectively degrade PE .
- In September 2022, Ju Feng’s team from West Lake University screened a strain of Klebsiella sp. EMBL-1 that can degrade PVC films in ” Nature Communications ” and discovered some potential PVC-degrading enzymes, including peroxidases, dehydrogenases, Enzymes, oxidoreductases, etc.
Part.3 Enzyme protectants RHPs
Plastic, as a high molecular polymer, cannot even penetrate water;
The enzyme itself is very fragile and is easily inactivated in the environment outside the cell.
So adding enzymes to plastics is no simple matter .In April 2021, Professor Ting Xu’s team at the University of California, Berkeley, published a study in ” Nature “, ” Near-complete depolymerization of polyesters with nano-dispersed enzymes “. The researchers wrapped a layer of protective agent RHPs ( random) on the outside of the enzymes.Heteropolymers ), this protective agent ensures that enzymes do not clump together or become inactive, allowing individual enzymes to grab the ends of plastic molecular chains and start “eating”, cutting off each link and preventing the formation of microplastics .
Researchers put a piece of PCL-BC plastic added with biological enzymes in a buffer at 40°C . In just 24 hours , the plastic had changed beyond recognition. After 36 hours , it miraculously ” disappeared “!
At the same time, research shows that in a 37°C buffer, 80% of PLA plastic can be completely degraded into lactic acid within a week.
Under ASTM standards and within the operating temperature range of industrial composting facilities, it takes 6 days for PLA plastic to completely degrade at 50°C, while it only takes 2 days for PCL plastic to fully degrade at 40°C .
Part.4 The enzyme engineering company that makes plastic disappear
Enzymes are not a magic bullet . First, some polymers are more easily broken down by enzymes than others. In addition, factors such as polymer hydrophobicity and crystallinity pose major obstacles to enzyme functioning. Even if scientists can get the enzyme to work effectively, they still have to figure out whether this strategy releases unwanted chemicals, such as plastic additives, into the environment .
French enzyme engineering company Carbios is building a recycling plant that is expected to start production in 2026 and will use enzymes to convert 50,000 tons of PET per year into the raw materials: terephthalic acid and ethylene glycol.
Carbios’ PET-destroying enzyme originated from a natural enzyme discovered by Japanese researchers in composted tree branches. The company designed the enzyme to work faster and be more selective for PET.
Carbios also had to deal with a new challenge associated with getting enzymes to work with synthetic thermoplastics: crystallinity . When the polymer backbones are aligned with each other and stacked on top of each other, it is difficult for enzymes to attach to the polymer to break the bonds. Carbios concocted a pretreatment process that melts the polymer and then rapidly cools it, fixing it in an unaligned, amorphous state. This pretreatment also expands the polymer “like popcorn,” increasing surface area.
Another initiative by Carbios aims to break down polylactic acid (PLA) , a bio-based polymer that requires relatively warm industrial composting conditions (around 60°C) to break down. Carbios developed an enzyme derived from the natural digestive enzyme protease, which the company mixed with polylactic acid. The biggest challenge of this project is the mixing step. Polylactic acid melts at 170 °C, a temperature that destroys the complex protein structure of most enzymes. To solve this problem, Carbios started with an enzyme from the thermophilic bacterium Aquaticus that can survive high temperatures, such as those found in hot springs.
Oakland, California-based startup Intropic Matters is taking another approach, embedding enzymes into polylactic acid and other polymers to induce degradation after use. Intropic, founded in 2020, coats enzymes with so-called “nanoprotectants” based on work that CEO Aaron Hall was doing while completing his PhD at the University of California, Berkeley . These protected enzymes can then be used in aqueous or solvent-based solutions for coatings and adhesives, or thermally processed into films and rigid objects.
Another startup, Breaking, aims to use microbes and enzymes to directly address microplastic pollution.
“The fact that they can degrade plastic means they already have the innate machinery, all the genes and enzymes to eat plastic, ” said Breaking co-founder and CEO Sukanya Punthambaker. The “heroic creature” is X-32 . The company is still awaiting intellectual property protection and has not revealed what kind of microorganism X-32 is or where it comes from. Breaking initially tested the microbe with PET as its sole carbon source, and it grew, indicating that X-32 successfully digested the plastic. The company then tested it on sturdier polymers: polyethylenes such as polyethylene and polypropylene, which are used in packaging and other applications, and on which X-32 was also able to grow. Breathing experiments determined that these polymers were being completely converted to carbon dioxide and water. Furthermore, the microorganisms completely consumed the polymers in just 22 months.
For Breaking, making polymers disappear, rather than just breaking them into smaller parts, is what’s exciting about the technology. Not only do we want to break down plastic, we don’t want to create more microplastics . This doesn’t help anyone, we really want to eradicate plastic by breaking these chemical bonds.
Part.5 Enzymes identified to degrade plastic
In 2021, Zelezniak’s team at Chalmers University of Technology in Gothenburg, Sweden published “ Plastic-Degrading Potential across the Global Microbiome Correlates with Recent Pollution Trends ” in “Microbial Ecology” and compiled a data set consisting of 95 microbial enzymes . Enzymes are already thought to degrade plastic and are commonly found in bacteria found in garbage dumps and similar plastic-filled places.
The team looked for similar enzymes in environmental DNA samples collected from 236 different locations around the world. Importantly, the researchers ruled out potential false positives by comparing the initially identified enzymes to enzymes in the human gut, where no plastic-degrading enzymes are present .
In the ocean samples , the researchers found approximately 12,000 new enzymes in samples from 67 locations and three different depths. The results show that levels of degrading enzymes are closely related to the extent of ocean plastic pollution, with levels consistently higher at deeper depths, matching the higher levels of plastic pollution known to exist at lower depths .
In the soil samples , the researchers found more than 18,000 plastic-degrading enzymes in 169 locations in 38 countries and 11 different habitats. It is clear that there are more types and quantities of degrading enzymes in soil than in the ocean . This may be because the soil contains more plastic than the ocean.
Nearly 60% of the newly discovered plastic-degrading enzymes do not belong to any known enzyme category, which means that microorganisms are working to clean up plastic in the environment in an unprecedented way. Whether they can fully address plastic pollution in the future remains to be seen. Faced with this situation, should we be happy or feel guilty?
Outlook for bioplastics from 2025 to 2035 and challenges faced by bioplastics
Despite growing awareness of the threat plastics pose to the environment, demand for plastics continues to increase. The OECD predicts that global plastic consumption will double by 2050. To combat the environmental impact of plastics and climate change, the industry is moving towards a circular economy .
But even if 100% of all plastics produced each year were recycled, new raw materials would still be needed to meet growing usage. Coupled with the fact that bioplastics (plastics synthesized from bio-based materials) can replace existing fossil-based plastics, bioplastics are made from bio-based materials, have low carbon emissions, and can become more sustainable than traditional fossil-based plastics. Ongoing alternatives.
Out of the valley of death
The bioplastics industry began decades ago, but after entering the 2010s, bioplastics fell into the abyss of death due to related companies going bankrupt and abandoning their businesses . This stagnation resulted from a backlash against optimistic initial investment in the field and the emergence of considerable bottlenecks in the expansion of production at a commercial level. In addition, the relatively high price of bioplastics compared with the sharp decline in Brent oil prices and reduced competitiveness with existing plastics further exacerbated the downward trend.
But the bioplastics industry has changed recently, and growth patterns are reviving. Most importantly, brand companies are shifting towards sustainability. This is because two directions are at play , the continued strengthening of consumer demand and regulatory changes banning the use of fossil-based single-use plastics (and expectations for future changes).
With the support of the IPCC (Intergovernmental Agreement on Climate Change) report, the COP28 (28th United Nations Climate Change Conference ) conference, which plays a cornerstone role, also promotes the decarbonization commitments of brand companies . Thanks to this strong demand, manufacturers are expanding production capacity faster than ever before, and many companies have formed partnerships to speed up the expansion process.
In addition, many companies in this field are beginning to scale up to commercial scale, overcoming bottlenecks, and as technology develops, bioplastics can be produced at lower costs . In addition, consumers are willing to pay a surcharge for the sustainable use of bioplastics. Overall, due to these factors, bioplastics are cheaper and more competitive than existing plastics .
Regulation changes the market environment
One of the barriers to the introduction of new technology is the market’s inertia towards change, i.e. overcoming resistance. In this process, like-minded motivation is important. Nothing has a more damaging effect on existing inertia than China’s measures to restrict the use of petrochemical -based single-use plastics . Following these measures by the Chinese government, the number of large-scale factories producing PLA and other biodegradable bioplastics in the Chinese market has increased significantly. Other governments around the world are exploring and implementing similar measures to bolster the growth of bioplastics for single-use use.
Introduce interference factors
The main factor that could disruptively revolutionize the plastics industry through the introduction of bioplastics is degradable raw materials. Bio- based raw materials refer to bio-based raw materials or basic materials that can directly replace existing raw materials. Manufacturers can easily facilitate the switch from petrochemical -based feedstocks to biofeedstocks by replacing them with imported feedstocks.
There is no need to build a completely new factory, the same process can be used and the characteristics of the final product will not change. In addition, on the basis of existing plastic products, the same options can be used after the end of life. In particular, recycling processes can be directly used, significantly improving the sustainability of plastic products.
The use of imported raw materials allows tracking of biologically based raw materials through management continuity models such as material budgets. Transparency and trust can therefore be built across the entire value chain regarding the origins and processes of sustainable ingredients. Overall, the plastics market will be more receptive to bioplastics , which offer strong advantages over other bioplastics.
Challenges facing bioplastics
However, there are still many issues that need to be overcome for various bioplastics. To become part of truly sustainable, circular consumption, bioplastics must be designed to be recyclable during post-use disposal. For example, PLA is the most widely produced 100% bio-based plastic material and can be industrially composted, but few companies recycle it because it has no compost value.
Additionally, unlike bio-based PET, recycling of PLA requires dedicated infrastructure . Not only is this uncommon, it is also expensive to introduce. As a result, most PLA is mismanaged or disposed of in landfills.
Currently, there is no bioplastic solution for PP and PE, which are the largest users in the world. Bio-naphtha is used to make bio-based PP and PE , but synthesizing bio-naphtha from bio -alcohols and oxygenates is inefficient because waste oxygen is generated during the process.
Additionally, this has led to chemical manufacturers competing with biofuels and bioenergy for feedstocks. Conversely, bionaphtha can be made from vegetable oils, but these raw materials have difficulty with price fluctuations due to geopolitical instability. Among the new bioplastic types that are still in the demonstration or research stage, many show promising physical properties.
But the broad range of applications critical to developing materials needs have not yet been developed. Companies belonging to these niche markets need to form partnerships with brand names and ingredient manufacturers to expand application offerings.
As a media in the reform industry, when dealing with questions raised by fans in the background, what keywords appear more frequently? That “vacuum mouth material” will definitely occupy a place.
What is vacuum port ejection? Why does my material have a mind of its own? This first requires understanding where the vacuum port is.
During the extrusion production process, gases need to be discharged from the molten material. If these gases cannot be discharged, defects such as pores, bubbles and surface darkness may appear on or inside the product , which can seriously affect the physical, mechanical and chemical properties of the product. and electrical properties.
Setting 1 to 2 exhaust ports between the feed port and the machine head can remove moisture and other volatile components in the melted extruded material. However, there are often some problems with the opening of the steel cylinder – the most common problem is that material comes out of the exhaust port. A small amount of material will affect the discharge of volatile components and affect the product quality; a large amount of material will block the exhaust port, and even causing downtime.
01 Reason for counterfeiting
There are generally two reasons for material leakage. First, the screw design is unreasonable, causing the material to flow back at the exhaust port;
Second, the design of the exhaust port is unreasonable, and the molten material is “hung” when passing through the exhaust port.
02 Find the cause
First, check whether the material in the screw flows back from the exhaust port. In most exhaust extruders , , you can see the melt rotating forward in the screw.
Under normal circumstances, the screw channel is not filled with more than 50% of material. If it is exceeded, it will not only affect the exhaust effect, but may also cause material to escape from the exhaust port; when it is less than 50%, the screw can work normally.
03 Factors affecting material risk and solutions
Screw factor
Exhaust-type screws mostly adopt a multi-stage design. The advantage of this design is that the exhaust port is under normal pressure and the material will not flow out.
An extruder with one exhaust port requires a 2-stage screw, and an extruder with two exhaust ports requires a 3-stage screw. Each stage must have a normal pressure section, a compression section and a metering section. The starting section of the first stage is the normal pressure feeding section, and the second stage is the normal pressure exhaust section, which is where the exhaust port is located. There are two main issues with vented extruder screw design:
First, when reaching the exhaust section, the materials must be completely melted to expel volatile matter;
Second, the feed capacity of the second-stage screw must be greater than that of the first-stage screw, so that the screw groove is not full at the beginning of the second stage, so that normal pressure can be maintained at the exhaust port. When the feed capacity of the first-stage screw is larger than that of the second-stage screw, the melt in the extruder will flow back. To solve this problem, it is necessary to reduce the feeding amount of the first stage or increase the feeding amount of the second stage.
Process conditions
The simplest and fastest way to solve the problem of material leakage is to change the process conditions. Such as cooling, increasing friction and shear stress along the steel cylinder or screw, and increasing friction or viscosity along the surface of the steel cylinder to increase the amount of material conveyed. The feeding volume of the first stage can be reduced in the following ways:
(1) Increase the temperature of zone 2 and zone 3 of the steel cylinder.
(2) Cool the first-stage screw.
(3) Use the starvation method for feeding.
(4) Adjust the temperature of the feeding bin (repeated experiments are required).
The following methods can be used to increase the feeding amount of the second stage:
(1) Reduce the temperature of the 2nd stage steel cylinder.
(2) Increase the temperature of the second stage screw.
(3) Increase the machine head temperature.
(4) Increase the machine head clearance or reduce the machine head resistance.
(5) Reduce the number of filters.
(6) Use a filter with larger gaps.
If changing the processing conditions still does not solve the problem, other methods must be used. For example, redesign the screw, reduce the resistance of the machine head, lengthen the screw and steel barrel, or install a gear pump between the extruder and the machine head. Installing a gear pump can solve the material ejection problem, but it costs more than a new screw.
Exhaust port design
If the screw at the exhaust port is only partially filled and material still comes out of the exhaust port, then there is a certain problem with the design of the exhaust port.
The exhaust port should be wider than the rolling material flow to ensure that the exhaust port is not blocked by the melt. At the same time, the opening of the exhaust port should not be too large, which can reduce the melt residence time and the expansion time of the material flow. Under normal operating conditions, the screw groove is half full. At this time, the exhaust port is at normal pressure. In fact, there is still pressure in the rolling molten material. The pressure is about 0.21~0.35MPa or higher, which is enough to make the melt at the exhaust port swell.
In this way, the normal viscoelastic expansion of the material should be taken into consideration when designing the exhaust port. Otherwise, part of the rolling material flow will be “hung” and accumulated at the diverter element.
How much the melt stream expands is determined by the time it takes to pass through the vent. Long residence time and large expansion. The residence time is controlled by the screw speed and the size of the exhaust port. Increasing the screw speed can reduce the residence time. This is why low-speed extrusion is more serious than high-speed extrusion. However, the larger the exhaust port opening, the longer the residence time. When the melt accumulates at the exhaust port, it will block the exhaust port. The solution is to change the opening of the exhaust port to meet the normal expansion of the melt at the exhaust port. If the rolling material flow expands by 5~10mm, the depth of the exhaust port should be at least 5~10mm.
Distribution element for exhaust port
To give an example in actual production, use a 150mm newly polished single-screw extruder with an exhaust port. There was serious material leakage when extruding the sheet, and it was impossible to produce qualified products. The operator wanted to check the molten material in the screw channel at the exhaust port, but he could not see the screw at all.
This shows that there is a big problem with the design of the diverter element, and the operator has to remove the diverter element to check the filling degree of the screw channel. After inspection, it was found that the screw groove was only 40% full, indicating that the screw design was reasonable. Then the focus of the fault will be on the shunt component.
Although this was a well-known extruder manufacturer, the design of its diverter elements had serious flaws. When inspecting the diverter element, it was found that the exhaust port not only has a bottom cutout on the upper stage that allows the material to expand normally, but also has this port on the lower stage.
There is absolutely no need to design a bottom notch for the upper-stage screw, and setting this notch is extremely disadvantageous because it increases the residence time of the molten pool at the exhaust port and causes the molten pool to expand more, increasing the molten pool at the exhaust port. Body pressure builds up.
Another problem is that flat and rectangular exhaust ports are more difficult to clean than straight ones. If the diverter element is properly designed, the exhaust port should be perpendicular to the radius of the steel cylinder. Through the above analysis, the shunt component can be repaired in the following two ways:
First, fill the bottom cutout of the upper step with metal;
Second, changing the rectangular opening to a radial direction allows the operator to see the molten material in the screw.
Whether the vented screw ejects material is directly related to the extrusion process, plastic performance, and the design of the screw and exhaust port . Therefore, when using a vented extruder for production and processing, manufacturers must carefully analyze the processing technology. Only with a detailed understanding of resin characteristics and equipment performance can the vented extruder operate normally and stably. Instead of complaining: my material has its own ideas!