Plant-based epoxy enables recyclable carbon fiber | Hacker News Reader

Plant-based epoxy enables recyclable carbon fiber

nrel.gov

174 pointskungfudoi27 comments

This may make it so carbon fiber items could be repaired as the epoxy can be removed and reapplied.

Being able to repair goods is much better for the environment than being able to recycle them.

A lot of composite artifacts are fairly easy to repair already, assuming you accept some degradation of performance since the newly bonded media and resin won't be chemically attached, but mechanically instead.

My experience with carbon fiber is mostly in cycling.

One of the drawbacks with carbon fiber is its tendency to fail catastrophically.

By that I don't mean that it tends to fail per se, but when it does it often doesn't do so gradually with warning like steel or aluminum (which warps, dents, and/or cracks visibly). So there's a certain fear about hidden cracks and failure points.

This gets exacerbated when talking about used items.

When talking about recycling or repairing carbon fiber, then, I think you'd have to convince people that it's just as stable as the original product, and that there aren't any hidden failure points. This obviously wouldn't apply to everything carbon fiber, but for things where it's often used, like in transportation, I think you'd have to have an inexpensive, foolproof, airtight way to verify integrity.

Another fellow cyclist here. Aluminium in fact has a very similar failure mode. It also fails catastrophically without warning. This was also brought against aluminium frames when they first started coming up to replace steel.

The bigger issue with carbon (in the context of cycling) is that there can be significant fabrication defects (voids) that are impossible to detect without special equipment. On aluminium frames you really only have to look and the welds to see if there are defects. Together with the fact that most (even premium brands like trek, canyon...) manufacture ultra cheap in China with very little QC (due to the race to the bottom regarding costs) , means you could get a significantly weakened frame straight from the dealer.

Trek had an 'affordable' hybrid composite bike, the Trek 2100, that merely twice as expensive as any reasonable hobbyist would pay for a bike instead of 5x as expensive. It was carbon tubes (they had patents on making them) and aluminum lugs, but the bond wasn't always good and so they would crack, chip, or delaminate. Big recall. The one guy we knew who had one rode it until it broke and then sent it back. That was a pretty long day for him (I can't recall if he rode it back gingerly or had someone pick him up).

I've done carbon fiber boat repair, and removal is pretty easy - lots of cutting and sanding. Applying a patch works pretty well - mechanical bonding to the roughed-up surface is pretty good, and even if the patch uses 2x the material of the original, it doesn't affect overall weight too much.

There are two major complication to repair.

First, carbon fiber items are made in a mold. Repair doesn't have access to that mold, so you've got to build your own. You can get a good approximation from casting an adjacent part, or the opposite side - otherwise you have to improvise and sand it to match. Catastrophic failure, like when the bow is broken more than a few degrees, requires an alignment jig to keep the boat straight.

Second, carbon fiber works best when it's a laminate - e.g. a carbon/foam/carbon sandwich. So most designs are tubular or involve a stackup. This is tricky if the inside layer isn't accessible. Or a high-performance inner layer is used, like delicate honeycomb aluminum. Rebuilding something that was custom-made to tight tolerances is difficult.

I'd think that a degradable epoxy would be best for recycling applications; repair has a lot of other challenges.

You would have to design the article to be repaired. The core material would need to be dissolvable so it can be refreshed along with the epoxy.

I imagine the repair process would be something like:

  1. Place bike/boat in mold/alignment frame. 
  2. Dissolve core then epoxy.
  3. Refill and cure core.
  4. Reapply epoxy to carbon fiber.
  5. Vacuum bag the bike/boat then cure epoxy.

How often would you need to repair CF vs recycling it though? Most cars don't get involved in wrecks over time enough to compare with the number of cars that end up getting recycles as in probably 99% of them. Seems like that would be the real win. I'm just wondering how many solvents are created to complete this process and how they are disposed of.

I find the Epoxy substitute very interesting - I feel like there could be a lot of uses for an epoxy strong enough to work in Carbon Fiber applications but can be removed with a chemical process at room temperature. Re-enterable potting compound? Fixturing material for machining?

Cured polyester resin as used in fiberglass reinforced plastic is soluble at room temperature using solvents like MEK or Acetone...

And the epoxies used in CF are not. Not to mention that melting plastics with solvents isn’t some environmental free ride. Now you just really messy and toxic soup to deal with.

FWIU flax and hemp are more sustainable and potential substitutes for carbon fiber, which is industrially hazardous to produce?

The branching structure makes e.g. hemp bast fiber ideal for supercapacitor (~battery) anodes. How does this plant-based epoxy affect conductivity and resistivity in various materials in various outdoor conditions with and without a coating?

If it's plant-based, is it safe next to plenum cable? Can it be used for Hemp structural framing lumber, such as HempWood?

> potential substitutes

When I can order sheets of hemp fiber pre-preg and a recyclable epoxy I’ll get my company to use it same day.

Here I am holding my breathe, because I’m not sure what you heard but an organic fiber will never be as thin, strong, uniform as curated carbon thread that was produced specially for this purpose.

> organic fiber will never be as thin, strong, uniform as curated carbon thread

Agreed, already lignin (wood sugar) can be turned directly into carbon fiber through an electrostatic process or a cryogenic process. If somebody wants carbon fiber to be cheaper, they should build equipment and make more.

There are Hemp alloys.

From https://motonetworks.com/worlds-greenest-car-somebody-made-c... :

> It’s actually made using hemp fibers that have been woven together and then sealed and finished with as super hard resin. And once it’s completed you have an insanely strong material that makes steel look weak and brittle. It’s reported to be as much as ten times stronger than steel, yet is lighter than fiberglass.

> The Renew Sports Car was recently featured on an episode of Jay Leno’s Garage [...]*

> Dietzen got the idea from none other than Henry Ford who back in 1941 advocated that Ford should build everything they possibly could out of plant material. Which makes sense because that’s obviously going to drastically reduce material costs which should in turn, reduce the overall price of the car. And thanks to modern technology, Dietzen managed to figure out how to make it all work. If this catches on to the mainstream it could revolutionize the automotive industry across the board. He says that it takes roughly 100lbs of cannabis plants to make a car, which sounds like a lot, but when compared to how much steel and other metals used to create current automobiles that’s just a drop in the bucket.

"Is Hemp Really Stronger Than Steel? How?" re: Tensile Strength and Compression Strength exceeded that of {steel, aluminum, } https://hempfoundation.net/is-hemp-really-stronger-than-stee...

Do high carbon steel rockers rust after a couple years of average road salt?

Which carbon fibers are least health-hazardous to produce?

You want to know how you can quickly tell this is all bullshit?

Steel isn’t brittle. Not in any relative sense to composites. Saying something is weak and brittle… that’s dry spaghetti. Does steel failure remind you of that? Or does composite failure seem closer?

Carbon is brittle. Composites are brittle. Hemp with epoxy is going to be brittle,all relative to steel which has plenty of pliability to it.

Are you sure you know enough about composites to repeat these hemp claims? Because if “makes steel look weak and brittle” didn’t immediately flag for you, you either know a lot more than I’ve learned in 20 years of working around composites and manufacturing or you don’t and just want hemp to be cool.

Hemp might be amazing. But you are posting nonsense that it seems like you have some desire to believe for some reason.

Sure maybe it’ll get out of the lab just around the same time graphene does.

Have you here contested claims that hemp - biocomposite with resin - has greater Tensile Strength and Compressive Strength than steel and aluminum (and carbon fiber with sustainable binder)?

If this were OT, we could reference ScholarlyArticles which describe experiments which return scalar intervals for: Tensile and Compressive Strength, Melting point / deployed heat resistance, production cost in real dollars, carbon cost (reduction in carbon tax credits because unnecessary with alternate sustainable inputs), resistance to corrosion due to sodium chloride, [in-space without water] repairability, magnetizability, water transport and filtration cost, and other factors; with a fair standard panel for relative comparison.

Fyi, Fiber Melting points:

Hemp: 150 c

Flax, saline treated: 153 c

Basalt: 1,500 c

Carbon: 3652 c

Hemp batting insulation is also saline-treated to meet code.

Are (coated) biocomposite resin melting points higher and comparably acetone-resistant?

Hope this starts with checked Fiberglass too; boat hulls also fill up landfills

I hope so too. I was thinking of printed circuit boards.

This story isn't really about carbon fiber... it's about finding a way to recycle thermosetting plastics. Carbon fiber is just the click bait.

If they can indeed depolymerize thermoset plastics. (Which are hard and brittle, thus useful when in composite with something strong in tension like carbon fiber), it would be an over all good.

I was about to write the same thing. Making carbon fiber itself is a mastery class in non-renewable and non-recyclable materials.

But it enables a lot of the lightweight “green” things people can pat themselves on the back for, which is the majority of the point for many.

Better epoxies would help, but we’re quite a ways off.

Imagine if they could recycle fiberglass matrix composites? You'd get rid of a huge part of the reason for e-waste, the circuit boards.

You have hit the nail on the head. Except for very large structures with simple carbon fiber layup, actually recycling carbon fiber seems hard to make practical. But if the thermoset material can be removed, the result is a relatively low volume, benign waste.

how durable would this stuff be? good enough for wind mills?

Uh they said it was durable enough to be used in turbines so it seems like wind turbines it would be a no-brainer. I don't think too many people are using windmills in the 21st century either. :)

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