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Comment by dv_dt | Hacker News Reader

It would be great to sample plastic and get composition sufficient to determine a recycling category

We already do that. However not all plastics and be determined that way. Black plastic in particular often cannot be figured out (since the laser as absorbed) and so even if the plastic is easy to recycle it is often land filled.

There are open questions on if recycling plastic is worth bothering with at all, but that is a different debate.

If you zapped it you'd have vapor to analyze.

One time at the laser show, the booth across from us had a methane analyzer.

You could tell when people farted.

Simple hand held methane detectors have been around for a few decades.

This was used to great effect in the Kenny VS Spenny episode, Who Can Blow the Biggest Fart: https://youtu.be/ash2NzL1IHo

(It’s a Canadian show)

I prefer the trash to electricity route.

If you think about it, the oil just took a detour into being a water bottle or whatever for a little while on it's way to the power plant. I really can't imagine we'll be at 0 hydrocarbon electricity grid any decade soon and burning garbage (and instead of "recycling" plastic) seems to be a perfectly reasonable thing to do if you can do it cleanly in a power plant.

> We already do that

Here's the machinery doing it.[1] It's just using RGB and IR cameras; they're not using lasers to vaporize samples and analyze the spectrum. That would be both overkill and a fire hazard.

Overview of modern waste handling.[2] Most of the separation is entirely mechanical, with screens, vibrators, rotating drums, and air blasts. But HDPE and PET plastics are separated using infrared sensing.

[1] https://www.youtube.com/watch?v=51S3ET7M138

[2] https://www.youtube.com/watch?v=6rkHt34AztY

Oooh, so that's why the local recycling facility doesn't take black plastics. Thanks for sharing!

Thats good to know. On recycling or not, i dont think it will ever be a universal yes or no. But if the tech was there to reliably identify & pull out a processable stream that has concrete assessable value. Its probsbly a harder requirement on some sensing tech to do it with continuously on an industrialized stream of refuse.

> Black plastic in particular often cannot be figured out (since the laser as absorbed)

Is it not possible to make a very thin slice of it for analysis?

Lots of things are possible but not ecomomical

Lasers are economical but not taking a tiny nip out of the plastic?

We do this already, but also for metals which have a much more reasonable recycling story. In metals though, we use LIBS. Tomra makes the best machines currently

>> It would be great to sample plastic and get composition sufficient to determine a recycling category

i love this idea. i cant believe how tiny the marked recycling categories are on the containers, i can barely see them. i always wondered how they even achieve this at the town recycling center.

>how they even achieve this at the town recycling center

They don't. A huge proportion is never recycled at all.

Plastic generally isn’t recycled that much, and many kinds of plastic cannot sustainably be recycled.

There’s a lot of automation in the space, and none of it uses the markers

The marks on plastic aren't recycling categories, they identify the plastic resin. They partially indicate recyclability but the form is important. I don't think they are used at recycling centers which mostly go on common shapes. Products are supposed to now use solid triangle to reduce the confusion with recycling.

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