Mould in silicone turning from white to brown after being bleached

[Erina]

Recently I finally decided to rid my silicone/steel trivet of the mould that had been building up over the years through normal kitchen use after being left rolled up when not in use (a design feature).

Submerging it in bleach for 24 hours the majority of the dense mould colonies succumbed to the bleach and disappeared: changing from black to white (or a lighter shade of the green silicone).

After submerging them for 12 hours in a bicarbonate of soda bath to attempt to rid the silicone of the bleach odour, to no avail, I heated the silicone in an oven for 15mins at 120ºC (twice) in order to attempt to bring the oils (odour) to the surface of the silicone to be washed away. I didn't have too much luck with this and the baking process released a fairly acrid smell into my room so I didn't persist, but did have some success.

However, now the white areas (where the mould once was) have turned brown, why is this?

[chenbeier]

No good Idea to heat this to 120° C. Some oxidation.

[Erina]

Well, it was only for 30mins in total, and I did have the window open (and I'm alive to tell the tale), but you're probably right.

Any ideas on why it went brown please?

[StringJunky]

5 hours ago, Erina said:

Well, it was only for 30mins in total, and I did have the window open (and I'm alive to tell the tale), but you're probably right.

Any ideas on why it went brown please?

Perhaps secretions from the mould reacted with the material and discoloured it.

[Erina]

I assume so, I just wondered what the underlying chemical process was to turn it from white to brown?

[Sensei]

Bleach is ambiguous term.

https://en.wikipedia.org/wiki/Bleach

Start from figuring out what chemical compounds are in your bleach..

 

Search net for "[brand name] ingredients". If they are not written on the box or bottle.

Edited March 7, 2020 by Sensei

[John Cuthber]

56 minutes ago, Sensei said:

Bleach is ambiguous term.

https://en.wikipedia.org/wiki/Bleach

Start from figuring out what chemical compounds are in your bleach..

 

Search net for "[brand name] ingredients". If they are not written on the box or bottle.

In all sensible probability this is pointless.

It's hypochlorite.
We know this because...

On 3/5/2020 at 10:24 PM, Erina said:

to rid the silicone of the bleach odour,

 

[Erina]

I used just household bleach : "Domestos Extended Germ-Kill Citrus Fresh Toilet Bleach with CTAC 750ml"

Ingredients : Cationic surfactant; Soap; Non-ionic surfactants; Disinfectant: Sodium hypochlorite 4.5g per 100g. < 5%: Chlorine based bleaching agent (Sodium Hypochlorite); Perfume.

[Erina]

So why did it turn brown?

[studiot]

7 minutes ago, Erina said:

So why did it turn brown?

Well your initial post showed a good history up to the point of the spots turning brown.

Did anything else happen after that ?

Two effects I am wondering about are

1) Did your bleach get all the spores as well as the mould bodies?  If spores were left they migh have started growing again, starting as brown spots before turning green.
The moss on my drive does this, I have found from experience that bleach is not an efficient remover - it always grows back. first brown, then green.

2) "All the leaves are brown"  goes the song. But actually leaves are always some shade of brown. They are just green when they are alive and contain a more powerful pigment (chlorophyl).

[Erina]

Interesting.

I've only just done the experiment, so I'll have to see, but I'll be keeping an eye on it..

[Erina]

Surprisingly, after eight days, the silicone now smells sweet?!

[Erina]

I can confirm now that after six months, under the same wet kitchen use conditions, there has been no re-growth from the mould.

I also tried this on white bathroom caulk around a stand up shower and it worked exactly the same, leaving the caulk looking like the day it was first laid.

This is a solid technique and very easy the achieve.