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'acid' affected rope part 2. unsatisfying!

mikllaw

6-Sep-2012
7:38:49 AM

So, I got a bit of rope that broke under body weight
http://www.chockstone.org/Forum/Forum.asp?Action=Display&ForumID=5&MessageID=9410&Replies=1

and firstly tried to replicate the failure with a few common acids

http://www.chockstone.org/Forum/Forum.asp?ForumID=6&Action=Display&MessageID=22149&PagePos=&Sort=

There were significant strength reductions (18 kN down to ~ 10 kN), but no lat bodyweight.

I next got a mate with an SEM (scanning electron microscope) to look at the affected fibres (let's call them 'stained') and some sections of the rope the rope that seems ok ('clean'). The differences were dramatic..

- 'clean' rope, note typical saw-like marking from cutting fiber with knife

elemental survey of rope - it doesn't pick up light elements like hydrogen, but it basically says that it's some organic compound, and given that we know it's nylon, let's say it's nylon.

Stained rope covered with crystals!

elemental survey of stained rope. Phosphorous could be lots of things (detergent, fertilizer) but my bet is that it's phosphoric acid as found in rust converter (I did a small taste test also- yuk). Rust converter is often found splashed liberally in older climber's older car's boots.

"problem solved!" I thought. I soaked and tested some ropes and found (once again) no startlingly low strength values, most dropped from about 18 to about 10 kN, but no gobsmackingly low bodyweight failures. Damnnnn.

Maybe it's a time dependent thing (drizzle rust coverter on rope, then use on and off for a few months, tasking falls and also getting rope wet occasionally) so i have a few other samples I'll age and resoak and continue to test.


Miguel75

6-Sep-2012
8:41:00 AM

Awesome Mikl, thanks for posting. What magnification are those pics taken at?

DJ Biggs

6-Sep-2012
9:58:38 AM

Hmmm once the rust converter is dried off you would expect it to leave a fairly crystalline residue that would pulverise through use, that then reacts over time. (It may just be shadowing, but can you see the darkening of the rope, that is reaction rims around the crystals). A Focussed shot at the crystal rope contact might let you see. Though if impatience or ageing doesn't give you the desired effect a cross sectional shot from a fibre and crystal on the outer may give you an indication as to the rate at which the fibres are reacting.

james

6-Sep-2012
10:13:28 AM

Are those pic's of the tiny (thinner than human hair) individual fibres of a rope?

Richard Delaney

6-Sep-2012
11:21:09 AM

Awesome work Mikl, as usual.

mikllaw

6-Sep-2012
12:02:22 PM

On 6/09/2012 Miguel75 wrote:
>Awesome Mikl, thanks for posting. What magnification are those pics taken
>at?

yes, 1500 x magification, they are of the little fibers that make up the strands

mikllaw

6-Sep-2012
12:05:58 PM

On 6/09/2012 DJ Biggs wrote:
>Hmmm once the rust converter is dried off you would expect it to leave
>a fairly crystalline residue that would pulverise through use, that then
>reacts over time. (It may just be shadowing, but can you see the darkening
>of the rope, that is reaction rims around the crystals). A Focussed shot
>at the crystal rope contact might let you see.

You can see some pitting of the rope surface which isn't apparent on any of the 'clean' fibers


alrob

6-Sep-2012
12:38:11 PM

I'm on my phone at the moment, so don't have access to the full article, but if you're going down the phosphoric acid path, this could be of help...

http://scripts.iucr.org/cgi-bin/paper?a06707
And
http://www.chemicalland21.com/industrialchem/inorganic/phosphorous%20acid.htm

Given H3PO4 is highly soluble in water, theory would be that over time the crystals would dissolve in the presence of moisture (rain, a humid day...), perhaps working into the rope further, then recrystalising when drying out in the cupboard. Repeat this a whole lot of times and the presence of crystals right through the rope is possible. The abrasive nature of those crystals may in fact weaken the rope, and may also be the reason why a once off soaking of the rope had little affect.

Dunno. Maybe I'm sorta right....


wombly

6-Sep-2012
12:56:29 PM

>Phosphorous could be lots of things (detergent, fertilizer) but my bet is that it's >phosphoric acid as found in rust converter (I did a small taste test also- yuk). Rust >converter is often found splashed liberally in older climber's older car's boots.

If you want to test this further & still have samples of the rope, it should be possible to get a good ID on the crystal structure with XRD. I'm sure you're aware of the good XRD lab you guys have at ANSTO. If this doesn't work for you for some reason let me know as I could probably get it sorted for you.


Miguel75

6-Sep-2012
1:15:28 PM

On 6/09/2012 mikllaw wrote:
>

>You can see some pitting of the rope surface which isn't apparent on any
>of the 'clean' fibers

On seeing the pic above my wife commented, rather seriously, "mmm, it looks just like a Summer Roll!"

She's bang on too...

http://www.cadbury.co.nz/Products/Chocolate-Bars/Europe-Bar.aspx


ajfclark

6-Sep-2012
1:17:03 PM

What moron did that Cadbury site? The items are next to the wrong descriptions.


shortman

6-Sep-2012
1:26:59 PM

And why are they both under Europe bar?


ajfclark

6-Sep-2012
1:32:23 PM

That's the brand on them.


Miguel75

6-Sep-2012
1:34:56 PM

On 6/09/2012 ajfclark wrote:
>What moron did that Cadbury site? The items are next to the wrong descriptions.

They are indeed. Luckily they're both very tasty.

mikllaw

6-Sep-2012
1:46:07 PM

On 6/09/2012 alrob wrote:
>Given H3PO4 is highly soluble in water, theory would be that over time
>the crystals would dissolve in the presence of moisture (rain, a humid
>day...), perhaps working into the rope further, then recrystalising when
>drying out in the cupboard. Repeat this a whole lot of times and the presence
>of crystals right through the rope is possible.

yes, I think that putting acid on the rope may do little, but when the rope is stretched, it allows acid to penetrate the nylon fibres further, eventually causing a bodyweight failure. More testing required.

mikllaw

6-Sep-2012
1:48:06 PM

On 6/09/2012 wombly wrote:
>If you want to test this further & still have samples of the rope, it
>should be possible to get a good ID on the crystal structure with XRD.
>I'm sure you're aware of the good XRD lab you guys have at ANSTO. If this
>doesn't work for you for some reason let me know as I could probably get
>it sorted for you.

I hadn't thought of XRD, it would be good for a definitive ID. The amount of xstal is tiny though. I'll ask the dudes.


wombly

6-Sep-2012
1:58:54 PM

If all the fibres in the discoloured section are that coated with crystals, I'll be surprised if you can't get a decent ID. Don't need much these days for a qualitative analysis.

gfdonc

6-Sep-2012
2:56:20 PM

Ah, blending the above comments and in reference to another thread, it is clear Neil needs to do a lick test.

james

6-Sep-2012
3:13:30 PM

Mikl already said he tasted it... he & neil have obviously been on too many climbing trips.

PS: the pic's & info are interesting!

patto

6-Sep-2012
10:06:55 PM

Another reason to avoid coke around climbing ropes!

There are 21 messages in this topic.