Softening stiff cables (any ideas?)

[JohnG]

I have a number of older Tektronix scope probes where the outer insulation on the scope leads has become stiff with age. I would like to soften them up a little so that they regain some flexibility.

Any ideas about what to do, or success stories?

Any help much appreciated!

Cheers,
John

[babysitter]

I wonder if one could extract the phtalate-based plasticizers from one cheapo product (DEHP/DOP laden stuff) and place it into the valuable things you want to save.

[DimitriP]

Looks real easy:

[knapik]

Looks real easy:

Don't take the first video seriously, its a satire repair channel.

[james_s]

I've experimented some with rubbery trim parts for my cars that get hard and brittle. Brake fluid and wintergreen oil both made it beautifully soft and supple however within a few months they were just as hard and brittle as before.

I ended up finding wintergreen oil from a go-karting supplier, apparently it's used to soften the tires, it was quite a bit cheaper there than the stuff sold for medicinal use.

[JFJ]

Perhaps, something like this would help: https://leathermagic.com/vinyl-softener/ (assuming that it's not just a 'snake oil' style remedy).

[andy3055]

Will any of these liquids degrade the Electrical properties like the insulation resistance etc?

[DaJMasta]

Probably.  This is a DIY alternate use to a potentially unknown blend of chemicals (depending on manufacturer), so it could be bad to assume otherwise.


I wouldn't use the probes on high voltage, but since the dielectric is inside the shield layer, any treatment probably won't penetrate far enough to really mess with the performance of the probe.


Also worth mentioning that you should probably keep everything past the strain relief out of whatever treatment you have, they probably won't do nice things to the compensation network or the inside of the probe handle.

[james_s]

Electrically I wouldn't worry about it, none of the proposed substances are conductive. Likely the outer jacket is some form of vinyl and the plasticizers have leached out. There's no real permanent fix that I'm aware of, but various trucks might squeeze a bit more life out of the probes.

[JohnG]

Thanks, all. It appears that there is no permanent solution. It is likely that the insulation is PVC with plasticizers. Apparently, in the early days of PVC, the use of plasticizers was less well understood, with the result that the combined mixture of PVC and plasticizer is not in equilibrium and is therefore unstable in typical human environments. Thus, there is pressure on the plasticizer and it migrates out to the surface of the PVC, forming the whitish deposit.

There is no known permanent solution as of today, and the only people interested in one are hobbiests and museum conservators. Apparently, conservation of plastic artifacts is a particularly vexing problem for the latter.

John

[james_s]

Is it not possible to impregnate the stuff with the same substance originally used as a plasticiser? I am not a plastics expert but dealing with the deterioration is certainly a frustrating experience.

[jogri]

Is it not possible to impregnate the stuff with the same substance originally used as a plasticiser? I am not a plastics expert but dealing with the deterioration is certainly a frustrating experience.

Not really, think of it as trying to push a volleyball (plasticizer) into a bunch of steel BB pellets (PVC): The pellets will not move enough if you don't apply extreme force. PVC consists of long chains that will stick together if you get them close to one another, forming a really hard plastic. Plasticizers prevent this by being huge blobs that go between those chains, preventing them from sticking to one another.  They will get pushed out of the plastic if you don't anchor them, and that brings us to the point why things like wintergreen oil are no permanent solution: "Real" plasticizers like DEHP (https://en.wikipedia.org/wiki/Bis(2-ethylhexyl)_phthalate) come with their own chains that attach to PVC chains, making it much harder for the pvc chains to push them out.
Wintergreen oil is chemically similar to the "blob part", but it doesn't have chains to fix it: It will go in rather quick, but it will come out again because it isn't permanently attached to the pvc chains.
If you want to impregnate PVC, you need to have a constant concentration of plasticizer through the entire thickness, but as DEHP is designed to stick to pvc chains, most of it never reaches the core of your material. My guess is that you will get a material that is extremely soft at the outside, but gets harder and stiffer the closer you get to the core of it.

[Gyro]

In terms of things to try, I think I'd go with JFJ and suggest trying frequent applications of an automotive interior vinyl care product.

No, it isn't going to sink to any significant depth and replace the lost plasticiser but it might just protect the insulation from cracks starting from the outside when you bend the cable.

[james_s]

Ah, that explanation makes sense. Fascinating stuff.

Not to take this too far off topic but I'd love to find a way to soften PC-ABS slightly. I have a Tek TDS3000 that is crazy brittle. All of the knobs had cracked apart over time and several clips and tabs in the housing broke apart while I was working on it. I have no idea how that even happened, there is very little UV yellowing, in fact it looks almost new, just so brittle that much of the plastic feels dry to the touch. Unfortunately the plastic bits are insanely expensive when you can even find them.

[Nusa]

Ah, that explanation makes sense. Fascinating stuff.

Not to take this too far off topic but I'd love to find a way to soften PC-ABS slightly. I have a Tek TDS3000 that is crazy brittle. All of the knobs had cracked apart over time and several clips and tabs in the housing broke apart while I was working on it. I have no idea how that even happened, there is very little UV yellowing, in fact it looks almost new, just so brittle that much of the plastic feels dry to the touch. Unfortunately the plastic bits are insanely expensive when you can even find them.

Acetone is sometimes used for smoothing or to glue parts together in 3d printing of ABS. If you have pieces broken off, you could try acetone to glue them back together.

[james_s]

I tried some solvent that normally works well and found it didn't stick very well. I ended up using ABS pipe cement and that has held but does t solve the brittle problem. It will just break in another place if I'm not super careful.

[TheSteve]

An acetone vapor bath might help "relax" the parts, no idea if they will keep them from cracking though. Too much and will also ruin them. I have done vapor polishing of some ABS 3D printed parts with excellent results.

[jogri]

afaik ABS gets brittle when the butadien in it gets chemically attacked, so there is no way to restore it. It probably didn't turn yellow because Tektronix used a ABS blend that has titandioxide (TiO2) in it: raw ABS is not pure white, so it doesn't look "new" even at the factory. You can change that by adding a pigment to it, and TiO2 is the ideal candidate: It is pure white, absolutely not toxic and it even blocks UV light, making your plastic last longer (btw, TiO2 is the reason that your sunscreen is white).

One alternative to glueing your knobs back together would be casting new ones using the old ones as templates in a silicone mold. ABS melts at very low temperatures and since it's used in 3D printing you should be able to get it rather cheap. Just make sure that you don't heat it too much as burning ABS releases toxic vapours.

(Btw, Wikipedia mentioned that dichlormethane is used to glue ABS parts together, but please don't try that if you don't have a background in chemistry as that stuff is rather toxic)

[james_s]

I replaced all the knobs with good used ones I got off ebay, every one of the originals had cracked or been glued previously. I'd never seen anything like it before, made me wonder if it was made from a bad batch. The blue plastic is brittle too, the clip that holds in the rear option module fell off, fortunately not really needed since it fits in tightly.