Hmm...

NaOH-assisted ATT enables plastic decomposition at significantly lower temperatures while producing high-purity hydrogen and minimizing carbon emissions. A key advancement in this work is the oxidation pretreatment of PP and PE, which enhances their reactivity in ATT and allows efficient hydrogen generation even from typically resistant polyolefins. Through systematic optimization of the NaOH-to-plastic ratio and thermal oxidation conditions, hydrogen yields of 43.7, 51.9, and 30.2 mmol/g~plastic~ were achieved for PET, PE, and PP, respectively.

Sodium hydroxide (NaOH) is caustic soda or lye, which is fairly cheap and reasonably safe to handle, so that's not really an issue. Possibly this process could be done safely at home, though it might only be cost effective in high volume.

This process enables high-purity hydrogen production at significantly lower temperatures (300 to 400 °C)

So that's hot enough to melt lead. It could be done in a garage but it's probably more than most people would want deal with regularly.

It does sound like this is a refinement of an already understood process, which suggests that it was not efficient enough before for anyone to bother developing into a practical recycling system. Maybe this changes that calculation?

They are measuring the output hydrogen in millimoles per gram, which means there's not much hydrogen being produced. Hydrogen is ~1 g/mol, so at an average output of 40 mmol/g, only about 4% of the plastic mass is being extracted as hydrogen and 96% of the mass is left behind as waste material. That doesn't seem super helpful with the plastic waste volume problem.

The market price of hydrogen in the US right now is USD$1145 per metric ton, so 40 mg of hydrogen is worth about $0.000046.

That's a lot of zeroes, and not in a good way. You would need to process a lot of material to gain any value from this. A real cost/benefit would depend on how cheaply the machine that does the processing can be run, and how much you have to pay to have plastic waste shipped to you (and washed pretty thoroughly, I'd guess - any crud on the plastic would end up as waste gunk you'd have to clean out of your processing machine). And then you'd still have to dispose of 96% of the leftover mass through some other means.

My guess is that the value of the recovered hydrogen would not be enough to equal even the cost of the energy input required to heat the plastic during the process, and never mind the rest of the associated costs. If it needs more energy to process than it can produce, it's not very "green", you're just expending some other energy source to do this. Considering that it doesn't really reduce much of the waste volume either, this doesn't seem worthwhile. We can probably spend resources more effectively to solve environmental problems.

My guess: Plastic consists mostly of carbon by weight, so yields are low. The carbon dioxide gets locked away as a mineral, but the chemicals needed to do this are produced in a way that releases a lot of carbon dioxide.

Not a chemist nor supply chain expert so salt to taste:

Looks like they tried ratios between 1:1 to 4:1 sodium hydroxide to plastic. Wikipedia says in 2022, worldwide production for sodium hydroxide was roughly 83 million tons/year. Plastic waste from a cursory google seems like 350-400 million tons/year.

They do say in the paper that one product of the reaction can be converted back into sodium hydroxide using calcium hydroxide, but I assume you'd then need a fair bit of that.

If you can believe something the Calcium Carbonate Association Europe writes there is a fair bit of wiggle room before we start using more calcium carbonate than is regenerated, but you have burn that to get calcium oxide (to then turn into calcium hydroxide using water), which is very CO2 intensive. According to Wikipedia with a 2007 source, worldwide production of calcium oxide is around 283 million tons/year.

Oh also their experiments were using 0.05g of plastic for each run. Not sure why and whether scaling that would be a problem.

So yeah, like the last paragraph says:

The researchers say further work is needed to optimize the process and evaluate its economic viability before it can be deployed at scale.

The tech is 5* years out.