ABS plastic degradation (brittle) - HP34401A (circa 1992)

[rfdes]

I recently was in the process of removing the cabinet from my HP34401A and without any effort the ABS plastic handle snapped in half.  In an attempt to repair the handle with epoxy, the handle snapped in two additional places.  It was obvious that the ABS plastic had deteriorated to the point where it became as brittle as a potatoe chip.  I understand that UV can be dangerous to ABS plastic.  However, my multimeter has been stored in a clean, cool location for its entire life, so I am stumped as to how the plastic died the way it did.  Has anyone experienced this issue and if so is there an explanation?

thanks

[TheDefpom]

If it has been under fluorescent lighting that would possibly cause it, as fluorescent lights generate low levels of UV, especially if the polycarbonate cover that is normally used with them is missing as the covers block most of the UV.

[james_s]

I had this happen with a TDS3000 scope. I have no idea what happened to it as I was not the original owner, but the plastic deteriorated until it was crumbling.

[tooki]

While I'm sure light exposure accelerates the process, it's just an unfortunate decomposition process of some ABS formulations. IIRC it even affects products that are new old stock in the box.

I'm a bit of a vintage computer nerd, and one huge problem for collectors is Macs from around 1990 through the mid-late 90s: the plastic is becoming, as you so aptly put it, as brittle as potato chips. So people buy a lovely all-in-one from 1994 on eBay, then the seller ships it to them, and what arrives is a box of plastic bits with a motherboard and CRT sitting in it. Even if packaged correctly (which, frankly, is almost never the case...), the weight of the CRT alone is enough to crack the plastic under normal handling, never mind the torture caused by UPS.

What's interesting -- and what made me click the thread -- is that 1992 is right when something changed in the ABS formulation that causes it to embrittle far more than earlier formulations. Macs from earlier than that, like an original 1984 Mac or a Mac Plus (1986-1990) are holding up just fine, with only slight embrittlement, while the 1990s Macs are now extraordinarily fragile. Some speculate that it's due to changes in flame retardant additives, but I don't think anyone outside of the plastics industry really knows.

(All plastic Macs from the iMac in 1998 onward are made of polycarbonate, not ABS, and so will presumably have very different aging effects than their ABS predecessors.)

[tooki]

http://dtc-wsuv.org/wp/ell/2014/01/19/we-lost-four-computers/

This shows the damage of one of the worst-affected models, after shipping (with no damage to the box). But this was 8 years ago, when that machine was 20 years old. At nearly 30 now, they look even worse after shipping.

(Sorry to focus on the Macs, it's just to show that it's something that affected a ton of products from that era, all of which used top-quality materials.)

[jfiresto]

... Some speculate that it's due to changes in flame retardant additives, but I don't think anyone outside of the plastics industry really knows....

And perhaps not even there. I have read, and can well believe it, that the people who truly understand plastics are all retired or dead.

[HighVoltage]

I bought a FLUKE Combiscope once and it was kind of well packed but arrived in 1000 pieces.
Just touching any plastic material made it break.

Over the years I had many of these Combiscopes and their plastic is usually in good condition.
But this one scope must have been exposed to something special weird.

[strawberry]

additives to make plastics UV resistant and plastificators to make soft/springy/elastic and fire retardant
when additives deteriorate plastic gets hard as wood and breaks down under UV or heat (all good stuff evaporates)
ill-protected wood will get grey under UV and rot and crumble too
chemicals and gases in storage and on test bench can affect plastic properties

[kosine]

Still plenty of polymer scientists out there, but they're usually not customer facing, so you don't get to hear from them much.

The problem with ABS is oxidation, and it's a self-catalysing process. UV and heat will accelerate it, but it occurs in any case. The usual way to mitigate it is to add anti-oxidants which tie up the free radicals, but not all manufacturers will do this. The mentioned change around 1992 may just have been a result of switching supplier around that time. Maybe shifting production to China, perhaps.

Despite the popular myth, most consumer products don't use fire retardants. They're expensive and harder to process, so only normally used if a product demands it. When they are used, they do have a tendency to yellow over time or if over-heated during production. So there's a grain of truth in the story. (Apparently it started when Nintendo got asked about some of their controllers turning yellow, and that was their excuse.)

[lugaw]

My HP34401A handle also snapped into two pieces just adjusting the height.  I didn't even try to epoxy it together because I might use it as a handle someday and drop the meter. 

[lugaw]

Unfortunately there's nothing we can do about ABS becoming brittle over time because ABS is brittle by nature and a plasticizer is added to make it softer and over time the plasticizer evaporates.  So once it get brittle it's all over.  Also don't trust the used replacement for handles since they also suffer the same defect since they have the same composition as the one you had.  Try to buy a new one even if it's a copy since it is stronger than old handles.

[kosine]

ABS doesn't actually contain plasticisers. It's a terpolymer made from three monomers. The acrylonitrile is basically a cyanide group, the styrene is a large benzene ring (you can see why they changed the names!) A copolymer of just those two is known as SAN, and it's commonly used as clear plastic in a lot of kitchenware. The drawers in your freezer are probably SAN.

SAN is quite brittle though, so the modified ABS version was developed to improve on this aspect. The butadiene is normally used in rubbery elastomers as it can be cross-linked. Copolymerising it into SAN makes it tougher, and the result is ABS. The properties are adjusted by simply changing the proportions of the three monomers, so there's no need to plasticise it. Just use a grade with more butadiene content if you need something softer.

[EE-digger]

I believe that combustion products of propane and perhaps natural gas can damage plastics.  I can't substantiate this however.  These combustion products will damage or destroy foam such as that used in transit cases.  This info from first hand experience, and a large case designer / supplier.

My 34401A is early Agilent and the handle looks, feels and bends like new.

So, there may be something in your environment that's accelerating the aging, or I just got lucky.

I've had old Fluke equipment that was a dingy brown and with purple cleaner, it ran off like an orange river, leaving new looking fluke underneath.  This just shows that the environment is in and on the plastic.

[Cerebus]

I believe that combustion products of propane and perhaps natural gas can damage plastics.  I can't substantiate this however.  These combustion products will damage or destroy foam such as that used in transit cases.  This info from first hand experience, and a large case designer / supplier.

For both of those gases, the combustion products are essentially water and carbon dioxide, both things that are already in the atmosphere naturally and both are essentially unreactive over everyday temperature ranges with the kind of organics in plastics. So the thesis that "combustion products of propane and perhaps natural gas can damage plastics" is extremely unlikely to be correct.

In a lifetime of using these



I've noticed no tendency to degradation, and I somehow think that the manufacturers would be the first people to discover whether burning hydrocarbon gases near plastics actually causes degradation and would have changed materials many years ago.

[lugaw]

ABS doesn't actually contain plasticisers. It's a terpolymer made from three monomers. The acrylonitrile is basically a cyanide group, the styrene is a large benzene ring (you can see why they changed the names!) A copolymer of just those two is known as SAN, and it's commonly used as clear plastic in a lot of kitchenware. The drawers in your freezer are probably SAN.

SAN is quite brittle though, so the modified ABS version was developed to improve on this aspect. The butadiene is normally used in rubbery elastomers as it can be cross-linked. Copolymerising it into SAN makes it tougher, and the result is ABS. The properties are adjusted by simply changing the proportions of the three monomers, so there's no need to plasticise it. Just use a grade with more butadiene content if you need something softer.

Thanks for the explanation! I am not a chemist so I just think ABS is not made the same and it depends on the formula used by the manufacturer on how pliable it is and read somewhere that plasticisers are added to make it bendable just like we make the resin in 3d printer flexible by adding flexible resins.

[kosine]

Certainly some polymers are not long term resistant to hydrocarbons, and plastic gas pipes are usually made from some variant of PE for precisely that reason.

In theory, use of gas lighters near domestic plastics shouldn't be of much concern, but not all the gas gets completely combusted, and some also gets released pre-ignition on worn out lighters. So there might be a modest case to answer here, though I suspect it would only be a marginal contribution.

Another possible factor (that I've not looked into) is background radiation, which in theory could also embrittle plastics. In homes built on granite formations use of radon detectors is not uncommon, so after many years in such environments there could be some affect on polymers too.

The transparent housings for the lighter in the picture is usually polystyrene (because it's cheap), and it is susceptible to hydrocarbon attack. I doubt the manufacturers expect them to be in use long enough for it be a problem, though.

[kosine]

Not an expert on 3D printer filaments as such, but certainly in the case of PLA, the addition of plasticisers is fairly common. Lots of options, but sorbitol is not unusual with biodegradable/compostable plastics. It's a good choice because it melts at about 100C and is quite a lot easier to work with than liquid-based alternatives. Anything up to 15% is typical, and in some cases it's possible to test for it by just microwaving the plastic to see if melts or softens significantly.

[free_electron]

brown or grey handle ? i know the darker (brownish) handles crack easily. had several fail on the older gen 54645D scopes.

[lugaw]

Not an expert on 3D printer filaments as such, but certainly in the case of PLA, the addition of plasticisers is fairly common. Lots of options, but sorbitol is not unusual with biodegradable/compostable plastics. It's a good choice because it melts at about 100C and is quite a lot easier to work with than liquid-based alternatives. Anything up to 15% is typical, and in some cases it's possible to test for it by just microwaving the plastic to see if melts or softens significantly.

I am talking about the new trend of mixing 3D resins used on SLA printers with the new flexible resins, because the standard resin is very brittle. Mixing it with 5 to 10% flexible resins make it a bit pliable and the tiny toy figures wont break if you drop it.

[lugaw]

brown or grey handle ? i know the darker (brownish) handles crack easily. had several fail on the older gen 54645D scopes.

Mine is darker (brownish) handle on a HP34401A

[tooki]

ABS doesn't actually contain plasticisers. It's a terpolymer made from three monomers. The acrylonitrile is basically a cyanide group, the styrene is a large benzene ring (you can see why they changed the names!) A copolymer of just those two is known as SAN, and it's commonly used as clear plastic in a lot of kitchenware. The drawers in your freezer are probably SAN.

Are there any common plastics beside PVC that rely on plasticizers for flexibility? I don’t think I’ve ever heard of plasticizers used in any other plastic. (Though I am aware of plasticizer migration damaging other plastics, I’m only wondering about the deliberate use.)

[bicycleguy]

Got tired of loosing screws on a fold-up plastic camping table.  Decided to 'Lock-Tight' the metal screws to their corresponding nuts.  Left it overnight in the garage and the next day it lay on the floor in hundreds of pieces.  There was concentric circular cracks 1 to ~6 inches from every bolt with radial cracks about 45degrees around each, so lots of pie slice pieces and large chunks with 6 inch arcs or holes.

But the lock tight didn't fail .   All the nuts and bolts were laying on the floor by themselves or attached to some aluminum struts.

[jfiresto]

Approximately 90% of all plasticizers are used in polyvinyl chloride, or PVC.... Plasticizers are also used in other polymers like acrylics, PET, polyolefins, and polyurethanes.

From https://www.osborneindustries.com/news/what-do-plasticizers-do/

[james_s]

Got tired of loosing screws on a fold-up plastic camping table.  Decided to 'Lock-Tight' the metal screws to their corresponding nuts.  Left it overnight in the garage and the next day it lay on the floor in hundreds of pieces.  There was concentric circular cracks 1 to ~6 inches from every bolt with radial cracks about 45degrees around each, so lots of pie slice pieces and large chunks with 6 inch arcs or holes.

But the lock tight didn't fail .   All the nuts and bolts were laying on the floor by themselves or attached to some aluminum struts.

Yikes, I wonder what happened there, and what it was made of. Wish you had a picture of that.

[lugaw]

Got tired of loosing screws on a fold-up plastic camping table.  Decided to 'Lock-Tight' the metal screws to their corresponding nuts.  Left it overnight in the garage and the next day it lay on the floor in hundreds of pieces.  There was concentric circular cracks 1 to ~6 inches from every bolt with radial cracks about 45degrees around each, so lots of pie slice pieces and large chunks with 6 inch arcs or holes.

But the lock tight didn't fail .   All the nuts and bolts were laying on the floor by themselves or attached to some aluminum struts.

My experience on plastic degrading like that is when I collected tootbrush when checking in to hotels so I can use it in the shop for cleaning.  They are so cheap ( probably handles are made from acrylic) they crumble to pieces when exposed to any kind of solvent.  The more expensive toothbrush dont crumble like it.