Plastics Cracking or Becoming Brittle

[jonovid]

plastic items can take up to 1000 years to decompose ? I disagree.
I know of plastic items degradeing or drying out becoming very brittle
in less then 30 years. outdoor plastic pool pipe fittings turning white & cracking.
so called uv stabilised plastics failing or becoming brittle. UV degradation.
what is this to do with electronics.
maybe that new electronics smell is the Plastics drying out.4
I have had a PC USB gamepad Plastic shell case becoming very brittle and crack like glass.
and it was only 8 to 5 years old.
another example is this.
see how plastic plug item is now very brittle
13:05 in this video.
this 1977 The Apple II case is 40 years old.

Think Different Challenge - The Apple PIIe - Part 4
if sunlight is fading furniture, what is it doing to other Plastics?

[Zero999]

Yes it's true. Plastics partially decompose and become brittle, especially when exposed to lots of UV radiation, but that doesn't mean they're not bad for the environment. The powder that plastics make when they decompose, can't be degraded further by microbial action and remains in the environment for a long time, causing harm to aquatic organisms.

Another thing is some plastics don't decompose when they become brittle. The plasticiser, which is responsible for their flexibility and softness simply leaches out, leaving the hard, brittle polymer left. PVC is a classic example of this, because on its own it's a brittle polymer, but plasticisers are added to make it flexible, thus useful for cable insulation. The problem is the plasticiser is very soluble in many organic compounds, such as lubrication oils, causing it to leach out and result in brittle cable.

Many plasticisers are also toxic and have now been banned in most countries from any product that enters the human body, such teething rings, medical implants and dildos. The problem is many such products were produced before the toxicity was known about and many dangerous products are still produced in China today and are sold on ebay.

https://en.wikipedia.org/wiki/Phthalate#Health_effects

[coppercone2]

Not to mention alot of plastic is made with mystery recycled meat.

A proper plastics engineering handbook with specify glass beads or rods, I heard that you actually get all sorts of creative fillers like chalk, bits of crushed rock of various origins, other plastics that are a bit harder then the one you are using, ash/char... its sloppy joe all over again.

I suspect this is because testing plastic is difficult and expensive, and its one of those things where if you initially cut corners your problems won't show up for a long time. It's also a incredibly complicated material engineering wise (what else has so many different dynamics going on Just imagine steel had some kind of liquid you had to soak in it).

I think you can get the idea about the nonidealities of plastic if you are able to detect 'new car smell'. I can't believe some people like that.

I find the most annoying aspects of materials engineering are coatings and plastics. They both never work like you think they will and you end up throwing a ton of shit out because the coating or plastic failed. And you need specialized engineers to do anything with them on a large scale cheaply (like going to injection molding is ass rape, or finding a trustworthy reliable metal coating shop.. and you need to train people how to inspect paint jobs). Ha ha, then you have coated plastics.

There are some high end engineering plastics that are a joy, like teflon, epoxy reinforced carbon fiber and the hard glass reinforced nylons that are made thick. These work decent so long you use the high end suppliers$$ and manage your supply chains well, don't use crappy old epoxy, and don't realistically think they will work right for any kind of gear system, plastic gear systems are a freaking joke for anything but the most infrequent operations. Sorry modern power drills, you should not be run for any decently long periods of time  Heat freaking destroys the properties of plastic, even nice expensive ones.

Have you ever found your chrome plated plastic toilet paper roll holder to actually have a useful life time? Or zinc plated cheap shower stuff?

I think the majorly bad part of plastic hate comes from the fact, that when you present a man with the option to make a mold, and encourage that he optimizes the shit out of every complicated stress point like variable angle curves (infact hold a gun to his head to encourage this), you will get shit that is weak. Even with complicated CNC machining, if you make something out of a billet you don't actually save that much making the surfaces super thin because you need to remelt the scrap anyway and you get low prices for that compared to a inspected billet. Plastics are usually fed in an auger so you get the feeling that you are saving money by using less right off the bat. Molded metal/die cast is like this too, but for some reason it just ends up working better, maybe because the stresses are more normal and there are no liquids. I found usually the only reason a manufacturer wants to migrate to plastic shells over metal ones is because he has a promise of volume discount and alot of slick sales people telling him how great plastics are despite all their deficiencies.

You might not actually save money if you wanna do plastics right. Would you go to 22 gauge aluminum for your chassis? That's what plastics  people end up doing. They need to be thick. Then you can benefit from the dielectric effect and complicated geometry, but not necessarily cost. 

I end up finding things inside of chassis like plastic brackets that have similar dimensions to the steel ones used before. Maybe it works out on paper, and maybe they have thick steel ones because it was available, then it turns out that aspect was not engineered right and it turned out that the super-too-strong-steel-chosen-by-market-forces-that-we-are-wasting-money-on was actually a design requirement that happened to solve a design flaw.

And plastic/dielectrics make people totally ignore EMI and shielding. They think they can get away with paint!

Like screw driver handles, that's a great use of plastic. I actually don't want metal on a screw driver handle, unless its a complicated ratcheting screw driver... but if they want to use a 1 inch thick plastic rod to make a screw driver handle that does not get super cold in the winter and generally prevents me from getting zapped, I will take that with a smile.


And since we are looking at health effects, look at all the microbeads/plastic microfragments found in water and everywhere else. Bottled water is not safe if you are worried about them.

Nothing gives me quite that 'mother fucker please' feeling as a plastics failure. You know you will be there with a soldering iron jamming metal reinforcements and buying expensive glues with low shelf life to make a decent repair (like the high end black plastic welding epoxy from a autozone lasts about 1 year and you will use it only once). It's also one of the most vile smelling consumer compounds I have come across. Jesus fucking chirst can you make it smell any worse without using sewer gases and federally listed poisons?

https://science.slashdot.org/story/18/08/20/2232252/tiny-plastic-is-everywhere (about microbead contamination)

I think we would mostly be happier with high end ceramics though  but their fragments might pose the same issues. But seriously who would take a fucking PDIP over a CERDIP if given the choice??

I doubt you can beat plastics in terms of human body interface though, for grips, medical equipment, etc.. it just has the organic properties you need to mate with the skin.. so its a good thing for our longevity that we research plastics heavily I think. I do like rubberized grips on tools.

[TheNewLab]

I have experienced certain plastic breaking down to powder. I think it's the salt water in the air (fogg) that slips inside and onto the product

The soft outer part of a Nikon DSLR rubbed off, a SnapOn Tools plastic impact mallet, literally disolved into dust leaving just the metal rod in the hand, and some lead BB's (from the impact head),
I had a an Easton aluminum bat grip begin to powder off. Then I rubbed some hand lotion on it and now it's OK.

[jonovid]

here is some more, originally clear transparent, its now 30 yr old plastic from tandy
known as radio shack in the US.  the plastic is now amber, and so brittle it flakes into small pieces.
this was from ambient room light. in a dark two car garage in the top of a cardboard box.

[kosine]

There aren't many transparent plastics available, so the Tandy case is almost certainly cheap polystyrene. It has very poor UV resistance and will yellow quite quickly if stabilisers haven't been added. (They add to the cost, so usually aren't used for cheap items.)

The main yellowing process is oxidation, same as happens to paper and wax candles over time. (Most common plastics are essentially modified very high density synthetic waxes.) Doesn't actually need light exposure to happen, background thermal energy is enough. The polymer chains get broken, which weakens the material significantly, and also leads to free radicals which readily oxidise. This is why neutralisation with peroxide will brighten old computer cases, and why areas unexposed to light and air are usually much lighter.

Note that yellowing has nothing to do with bromine! It's not unheard off, but very few consumer items are actually made using fire retardant plastics. It's quite expensive and also harder to mould. No one ever uses it as a matter of course, and whenever they do, they tend to make a point of telling you to justify the cost.

As for adding chalk or talc, that also makes plastic much harder to mould. It's sometimes done to reduce costs slightly, but normally it's added to make the plastic more heat tollerant. They used to use it for making plastic kettles back in the day.


Here's a lengthy article if you want some gory details about plastic degradation: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4320144/

[coppice]

There are plenty of plastic cases which get really brittle just out of warranty, especially if they are regularly used near a window and the sun shines on them a lot. In the late 90s they got so aggressive with making the plastics degrade rapidly they seemed to overshoot, and have things breaking within warranty. The USR Sportster modems in brown cases were some of the worst examples of this I experienced.

Fake leather pads on headphones used to last. Now they fall apart after two years. That might not be too serious, as you can replace them easily. More serious is things like the Ikea chairs we have. They only claimed to be leather over the main seating area, but they didn't mention that all the fake leather bits would fall apart in 3 years.

[kosine]

I can assure you that plastics have generally improved a lot since the 1990s. They haven't suddenly become worse! Several things have happened in the industry since then, however:

1. Competition from East Asia has forced manufacturers to cut costs. This often results in products using as little material as possible, and from the cheapest source possible, however inferior it may be.

2. Design and product life cycles have speeded up enormously. The emphasis is now very much on getting a product to market rather than trying to perfect it.

3. The use of recycled content has increased significantly. Partly due to (1) and partly due to raised environmental awareness. (Recycling plastic generally degrades it, making it weaker than virgin resin. Even if you mix it you can be looking at 10-20% reduced strength.)

4. As noted above, various additives have been phased out due to health concerns. Many of the replacements are not as good, and you often have to add more to get the same effect, which also weakens the plastic.

PVC ("vinyl") used as synthetic leather has certainly been affected by all of these, which would explain your headphone and chair issues. (There are better materials like polyurethane, but PVC is currently around 1600euros/tonne, whereas PU is about 3000euros/tonne. There's also a lot of recycled PVC out there at much lower prices, and it's a lot easier to process than PU.)

[coppercone2]

There aren't many transparent plastics available, so the Tandy case is almost certainly cheap polystyrene. It has very poor UV resistance and will yellow quite quickly if stabilisers haven't been added. (They add to the cost, so usually aren't used for cheap items.)

The main yellowing process is oxidation, same as happens to paper and wax candles over time. (Most common plastics are essentially modified very high density synthetic waxes.) Doesn't actually need light exposure to happen, background thermal energy is enough. The polymer chains get broken, which weakens the material significantly, and also leads to free radicals which readily oxidise. This is why neutralisation with peroxide will brighten old computer cases, and why areas unexposed to light and air are usually much lighter.

Note that yellowing has nothing to do with bromine! It's not unheard off, but very few consumer items are actually made using fire retardant plastics. It's quite expensive and also harder to mould. No one ever uses it as a matter of course, and whenever they do, they tend to make a point of telling you to justify the cost.

As for adding chalk or talc, that also makes plastic much harder to mould. It's sometimes done to reduce costs slightly, but normally it's added to make the plastic more heat tollerant. They used to use it for making plastic kettles back in the day.


Here's a lengthy article if you want some gory details about plastic degradation: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4320144/

I thought they are supposed to use glass beads or rods instead of anything else really

Are there any benefits to using filers other then glass fiber or beads (or advanced versions like CNT/CF/Kevlar), besides cost creativity? I mean seriously, chalk? talc? When I think of someone putting chalk into something the only thing that comes to mind is cheap cutting agent. Are there any superior properties? It just sounds like mystery meat to me.

I figured glass would be the cheapest 'engineering' material filler that should be considered.. I think the plastics handbook I read (from the 1960's though) had this statement.

[kosine]

Glass fibre is abrasive and can wear out moulds over time. You have to use harder grades of steel if you know you're going to be running it. but such moulds cost more to produce. It'll also wear the moulding machine itself, specifically the barrel and screw that does the melting and injection. (These are not cheap to replace.)

If you want rigidity then GF is usually the way to go. The price is not significantly different from the unfilled material, and it's readily available in different percentages. 30% glass fibre is not uncommon, but that's a lot of abrasive material, and it's injected into the mould in a fraction of a second. Moulds can often work over a million cycles during their life, so you can see why it's an issue.

If you're only after heat stability, then talc or chalk filled materials are a better option. Like GF plastics, this stuff is precompounded by the polymer manufacturers to suit the purpose. It's not just some guy at the factory throwing it into the mix. (That wouldn't actually work anyway, all the powder would shake to the bottom of the hopper and clog the machine. It has to be melt-blended into the material.)

The other way to cheap-out and reduce material usage is to add a blowing or foaming agent. This basically forms tiny bubbles within the plastic, lowering the density. However it can be tricky to get it consistent, so it's not used all that much, especially on the cheaper commodity plastics. The potential cost saving just isn't worth the hassle. You're better off using recycled material, or something that's easier to mould. Then you get faster cycle times which dramatically increase your productivity.