Scientists have been trying to develop safe and sustainable materials that can replace traditional plastics, which are non-sustainable and harm the environment. While some recyclable and biodegradable plastics exist, one big problem remains. Current biodegradable plastics like PLA often find their way into the ocean where they cannot be degraded because they are water insoluble. As a result, microplastics—plastic bits smaller than 5 mm—are harming aquatic life and finding their way into the food chain, including our own bodies.
In their new study, Aida and his team focused on solving this problem with supramolecular plastics—polymers with structures held together by reversible interactions. The new plastics were made by combining two ionic monomers that form cross-linked salt bridges, which provide strength and flexibility. In the initial tests, one of the monomers was a common food additive called sodium hexametaphosphate and the other was any of several guanidinium ion-based monomers. Both monomers can be metabolized by bacteria, ensuring biodegradability once the plastic is dissolved into its components.
"While the reversable nature of the bonds in supramolecular plastics have been thought to make them weak and unstable," says Aida, "our new materials are just the opposite." In the new material, the salt bridges structure is irreversible unless exposed to electrolytes like those found in seawater. The key discovery was how to create these selectively irreversible cross links.
As with oil with water, after mixing the two monomers together in water, the researchers observed two separated liquids. One was thick and viscous and contained the important structural cross linked salt bridges, while the other was watery and contained salt ions. For example, when sodium hexametaphosphate and alkyl diguanidinium sulfate were used, sodium sulphate salt was expelled into the watery layer. The final plastic, alkyl SP2, was made by drying what remained in the thick viscous liquid layer.
The "desalting" turned out to be the critical step; without it, the resulting dried material was a brittle crystal, unfit for use. Resalting the plastic by placing it in salt water caused the interactions to reverse and the plastic's structure destabilized in a matter of hours. Thus, having created a strong and durable plastic that can still be dissolved under certain conditions, the researchers next tested the plastic's quality.
The new plastics are non-toxic and non-flammable—meaning no CO2 emissions—and can be reshaped at temperatures above 120°C like other thermoplastics. By testing different types of guanidinium sulfates, the team was able to generate plastics that had varying hardnesses and tensile strengths, all comparable or better than conventional plastics. This means that the new type of plastic can be customized for need; hard scratch resistant plastics, rubber silicone-like plastics, strong weight-bearing plastics, or low tensile flexible plastics are all possible. The researchers also created ocean-degradable plastics using polysaccharides that form cross-linked salt bridges with guanidinium monomers. Plastics like these can be used in 3D printing as well as medical or health-related applications.
Lastly, the researchers investigated the new plastic's recyclability and biodegradability. After dissolving the initial new plastic in salt water, they were able to recover 91% of the hexametaphosphate and 82% of the guanidinium as powders, indicating that recycling is easy and efficient. In soil, sheets of the new plastic degraded completely over the course of 10 days, supplying the soil with phosphorous and nitrogen similar to a fertilizer.
"With this new material, we have created a new family of plastics that are strong, stable, recyclable, can serve multiple functions, and importantly, do not generate microplastics," says Aida.
Journal Reference: Cheng et al. (2024) Mechanically strong yet metabolizable multivalently form a cross-linked network structure by desalting upon phase separation. Science. doi: 10.1126/science.ado1782
(Score: 3, Interesting) by aafcac on Thursday January 01, @06:28PM (6 children)
The main reason we have a recycling problem is that companies figured out that they can save a nickel a ton on materials by doing things like using a thin layer of food safe plastic on top of some other sort of plastic making the entire TV dinner package not recyclable. Not to mention that most of the other recycling issues are also the fault of the manufacturers producing things that either can't be repaired or involved plastic that can't easily be sorted out by customers.
I'm hoping that I"m wrong on this, but technology to address things like this in the recent past has mostly just meant more waste and a larger problem.
(Score: 5, Touché) by JoeMerchant on Thursday January 01, @08:35PM (2 children)
My first thought is: GREAT! Now they'll be making 0.6% of the net plastic production with this "ultra-saltwater-degradable" stuff and pointing to it as an excuse why they should be allowed to continue to produce 110% more plastic garbage year after year after year.
🌻🌻🌻🌻 [google.com]
(Score: 3, Funny) by Reziac on Friday January 02, @03:13AM (1 child)
My first thought was, "Great! Now I'll have an easy way into those impossible-to-open packages -- just soak the whole durn thing in salt water overnight!"
And there is no Alkibiades to come back and save us from ourselves.
(Score: 4, Funny) by aafcac on Friday January 02, @03:20AM
My favorite thing was seeing a tool for opening those stupid clamshell containers inside of one of those stupid clamshell containers. I guess they decided that anybody buying the product deserved to bleed one last time for old time's.
(Score: 4, Insightful) by Bentonite on Friday January 02, @05:05AM (2 children)
Plastic isn't really a material that can be recycled, especially so when dirtied with food scraps.
To attempt to recycle it, it has to first be sorted into the exact same type and also by dye (as some dyes will render the result unusable - as the plastic ideally should be clear) and every time plastic is re-melted, it gets weaker, until it's useless (which is why most bottles with recycled plastic contain a virgin plastic cap and/or are only of 50-80% recycled content and if there's a soft plastic label, that's never recycled).
But that only works for hard plastics - soft plastics generally cannot be recycled at all - the only practical re-use found is to shred mixed soft plastics and mix such with bitumen (which is a plastic) to stretch the bitumen and therefore construct extra-microplastic roads at lower cost.
Hard to read little recycling logos aren't very useful, as even skilled workers on a conveyor belt will only be able to grab and sort so many in a reasonable amount of time - as far as I can tell, the typical mixed recycling process is to get the metal out, then maybe the cardboard/paper and maybe grab some of the clean plastic bottles off for recycling and landfill the rest.
I figure every time plastic is shredded for recycling, more microplastics are made and end up in the atmosphere unless somehow captured at great expense.
The only way to address the problem of waste plastic without causing microplastics is to burn it in a furnace so hot there's a plasma (any colder and burning releases microplastics), which can be used to generate energy (more or less the same as burning oil for energy).
(Score: 3, Informative) by gnuman on Friday January 02, @06:13PM
The second part is correct, but the first part is definitely not. You burn it at 800C, which is basically a regular gasification furnace. You can also use gasification to generate ... "new" oil. When you burn plastics at lower temperatures or without sufficient oxygen, you end up with dioxins, not microplastics. And if you have microplastics our the chimney, that is far smaller problem overall than the dioxins.
(Score: 3, Insightful) by aafcac on Friday January 02, @07:09PM
Capturing it isn't really that hard. You do it the same way you do it with those house sized machines that process electronic waste. The entire thing is closed off with massive filters as things get ground up into fine enough particles that they can get separated into useful components after whatever chips that were worth anything and could be removed were.
In this case, the rules surrounding what can and can't be recycled are unreasonable complicated. I care a great deal about recycling and I can't work out what can and can't be recycled as the only guidance I get is a pamphlet with a bunch of examples. As far as the dyes and all that, that's on the manufacturers and it's well past time that they had to pay a significant tax to cover the environmental impact of doing things in a way that makes it hard to recycle.
I miss the 3 bins that we had when curbside recycling came here in the mid-80s. There were 3 bins, one for paper, one for plastics and one for metal/glass. And there were clear guidelines about what sorts of plastics were allowed in with the plastics. It was by no means perfect, but at least I knew with some reasonable amount of certainty what I was allowed to put into the bins. Now, it's anybody's guess, but if too much recyclable material goes in the trash, they refuse to pick it up and can fine the customer. But, if you put stuff in that doesn't belong, it can screw up a bunch of the recycled material as well.