What is resin rot?

[tribe125]

Originally a post by sonoronos:

Casio G-Shock watches use polyurethane resin. Polyurethane resin is a cross-linked polymer, which depends on the reaction (crosslinking) of isocyanate groups to bond together polyols. The bulk properties of the material depends on the types of crosslinking as well as the type of polyols involved. Strength

The potential lifetime of polyurethane is indefinite, however, like any other crosslinked polymer, it has several common weaknesses. These weaknesses all revolve around depolymerization.

Ultraviolet degradation aka photodegradation:
UV radiation attacks polymer crosslinking through a variety of means, both photochemical and oxidative. Regardless of the methodology, UV destroys the chemical crosslinking that gives PUR its useful physical properties - causing both cosmetic damage (yellowing) and reduction in tensile strength (weakness) and elasticity (brittleness)

Hydrolysis:
PUR is susceptible to hydrolysis, which is basically another attack on its crosslinked structure through the use of acids or bases in conjunction with water. The water will react with the organic structure of the polymer to combine water broken down into hydrogen or hydroxides with existing structures in the material causing those structures (bonds) to break - hence "hydrolysis".

Ozone attack:
Ozone is present everywhere but can be present in higher amounts in certain situations. This is another chemical attack where ozone reacts in a process called ozonolysis to break polymer bonds.

Ketone attack:
Ketones and other solvents will have little effect on crosslinked polymers, except for swelling.

Silicone oil and other things will not protect any of the major failure modes of PUR. What will protect PUR against degradation is to keep it out of sunlight and prevent exposure to acidic and basic solutions, especially at elevated temperatures. Also, storing in a vacuum helps.

You also cannot remove the yellow color cast from degraded clear polyurethane.

I'm sure organic chemists can fill in the details.

[TTT]

Excellent post. I believe it may also have something to do with the gradual evaporation of volatile plasticizers in the resin (e.g. phthalates), which would lead to the resin becoming more brittle.

[vmnrao]

It would be great if someone could add photos to show examples of resin rot. I've never seen it myself, and I'm sure I'm not alone.

[xevious]

This FAQ post is a great idea, and I'd like to fill it in with a bit more information. (Also see the Wikipedia entry on polymer degradation).

CASIO seems to have gotten the resin formula right most of the time, but there are some exceptions that we all know about (e.g. DW-002, DW-5300, DW-5500, DW-5700, DW-5900, DW-6600, etc). Some of them were so bad, like the DW-5500, that barely any survive intact to this day and those that do are ticking time bombs.

What does it look like? A quick image search on "G-Shock resin rot" will turn up a number of them, but your convenience here's one:

DW-5700C

But what of models that are not known to easily succumb to resin rot. Are they still capable of it? YES. I've heard reports of models not notoriously known for it ending up rotting, but after having been thoroughly worn and exposed frequently to sunlight and/or high humidity. My theory is that sunlight/UV is the biggest culprit, which is why the bezel usually crumbles before the band does since it gets more light exposure.

So... we all know that resin is the Achilles heel of G-Shock durability. It'll be the first part to go. This won't be a problem for anybody who doesn't expect their watch to last more than a decade or so, who frequently rotates their watches--buying new, selling used--and won't ever have to deal with it. But some of us find a G-Shock that we treasure and want to keep it for a VERY long time. This is especially true of buy-and-wear collectors who will put those prized G-Shocks to use periodically.

WHAT YOU CAN DO

• UV/sunlight is the primary nemesis for resin, so if you minimize exposure you'll be better off.
• Avoid contact with certain chemicals known to affect resin, like sunscreen lotions.
• Reduce exposure to high temperatures and high humidity, being sure to thoroughly dry off after submersion in water.
• Periodically apply a protectant of some kind, something that is not silicone based (once a year should be enough).
  
  • Vinylex Protectant (contains DH60 UV resistant formula)
  • Meguiar's Vinyl Protectant
  • 303 Aerospace Protectant
  • Ultima Paint Guard Plus
  
  
• Keep spare resin parts on hand, for that dreaded time when the installed resin crumbles.
• And if you can, vacuum seal your spare resin parts and highly collectible watches, as air exposure also contributes to decay.

We have seen 20+ year old models succumb to resin rot, but then also more recent releases with the youngest being the DW-5700ML from 2003 (and who knows, there may even be more recent models). Hopefully the bulk of them will remain in the deep past and that recent resin formulation changes will be more robust. Who knows, maybe CASIO even went so far as to incorporate UV resistant properties. One can only hope.