[xchcui]

Hi.

I read that if i use the standard silicone sealant/caulk beyond the expired date,two situation may happens
as more time passes from the expired date:
1)The silicone may be dry out.
2)The silicone cured time will be extended or will not
happen at all.

Is it true also for MS polymer sealant like the HYBRIFIX/SUPER 7?

What may happen to the ms polymer sealant
as more time will pass from the expired date?

Thanks in advance.

[xchcui]

Is there any problem with the question?
It is related to chemical question,isn't it?
If i need to clarify something or add more
relevant details,please inform me.

[AWK]

Expiration date is for warranty. After this date using is on your responsibility and risk.

[xchcui]

Expiration date is for warranty. After this date using is on your responsibility and risk.

Of course,there is not doubt with that and there
is nothing to argue about that.
I,just,would like to understand
What may happen to the ms polymer sealant
as more time will pass from the expired date?
Will it behave as i mentioned about the silicone sealant?will dry?won't cure?odor?texture?color?
etc.

Thanks in advance.

[Arkcon]

Yes.



No seriously, I have observed old silicone tub sealant that has hardened in the tube, even when sealed, or has failed to set after days, if its out of date.  I have likewise observed this with high temperature silicone based sealant for a wood burning stove.

Since all I'd have for you were anecdotes, I'm glad I already moved your thread to Citizen Chemist.  I don't have a specialty in silicone chemistry, so I can't give you better information.  However, I don't really need specialty to tell you that if something is out of date, it may fail in boring or spectacular ways.

Chemistry is the study of matter and its reactions.  So chemistry should answer all questions that don't involve nuclear transitions (that's physics,) or human behavior (that's psychology, or religion.)  However, sometimes, the complete chemistry answer isn't really worth the effort.

[DrCMS]

In addition to Arkcon's answer.

1) Silicone sealant do not "dry out" as they are not formulated with any significant amount of volatile diluants. 

Go look up the chemistry of acetoxy-silicone sealants and compare that to MS polymer. 
Do they have the same curing mechanism?  What side reactions may occur to the different products over time?  What additives are added and how might they change overtime?

[xchcui]

I am agree with Arkcon as i have no
interest to get into the chemical process of the silicone.
I just would like to know,how can i identify a bad ms polymer sealant,what are the signs that can tell me that it begin to be bad:
will it have a bad odor?different texture?color?
cure time?
Regarding to DrCMS post,i read that ms polymer and
the acetoxy-silicone sealants are both moisture cure
mechanism.
While in acetoxy-silicone  silyl acetates is used for the polymerization and ms polymer  silyl ethers is used to react with moisture to produced  siloxane linkage.
But i could not find the answer to your next questions(while the answer of them,probably,might be the answer of my question):
What side reactions may occur to the different products over time?
And how might their added additive change overtime?

[P]

What do you mean by 'bad' though?  With organic waterbased systems you can get bacterial build up which feasts on the polymer (degrading it) which leaves a nasty smell after it has been excreted from the bacteria. This wont happen with a silicon based caulk - I doubt you will tell anything from the smell.

[DrCMS]

Typical silicone sealant is a very flexible polydimethylsiloxane chain with methyldiacetoxysilyl end groups

(AcO)₂MeSiO(Me₂SiO)_xOSiMe(OAc)₂

While MS polymer is a more rigid shorter polyether with slightly less reactive methydimethoxysilyl end groups

(MeO)₂MeSi(CH₂)₃O(CH(Me)CH₂)_x(CH₂)₃SiMe(OMe)₂

Both cure by moisture reacting to give a silanol + acetic acid (silicone) or methanol (MS polymer) the silanol then reacts with either the surface or another polymer chain end groups to cross link and cure.

Any traces of water getting into the tube will cure them before you get chance to use them.  They will have moisture scavengers added to slow that down but too much and it slows down the cure reaction.  The shelf life is to balance the two sides.  If the product is partially cured after the expiry date when you use it it will not flow as easily as it should and it will not adhere as well as fresh material.

A better product is SPUR from Momentive that is a more flexible polyolpolyurethane back bone with more reactive trimethoxy silyl end groups.  That gives it a better shelf life and better adhesion while making it easier to use.

[xchcui]

Typical silicone sealant is a very flexible polydimethylsiloxane chain with methyldiacetoxysilyl end groups

(AcO)₂MeSiO(Me₂SiO)_xOSiMe(OAc)₂

While MS polymer is a more rigid shorter polyether with slightly less reactive methydimethoxysilyl end groups

(MeO)₂MeSi(CH₂)₃O(CH(Me)CH₂)_x(CH₂)₃SiMe(OMe)₂

Both cure by moisture reacting to give a silanol + acetic acid (silicone) or methanol (MS polymer) the silanol then reacts with either the surface or another polymer chain end groups to cross link and cure.

Any traces of water getting into the tube will cure them before you get chance to use them.  They will have moisture scavengers added to slow that down but too much and it slows down the cure reaction.  The shelf life is to balance the two sides.  If the product is partially cured after the expiry date when you use it it will not flow as easily as it should and it will not adhere as well as fresh material.

A better product is SPUR from Momentive that is a more flexible polyolpolyurethane back bone with more reactive trimethoxy silyl end groups.  That gives it a better shelf life and better adhesion while making it easier to use.

From your nice explanation i assume that
the main phenomenon that might happened as the ms polymer will degrade,is that it will be harder to extrude the silicone,since it will cured inside the tube with time and it will not adhere as well as a fresh material.
But,the odor,i can conclude,that will not be different
from a fresh one,will it?
If the reaction of the curing happens inside the tube,as you explained,the odor should be as a ms polymer that was applied and cured on some surface.

And even if i uses half tube and traces of water left on the tube orific,it can only make the material to be cured,but will not make the material contaminated and change its odor,as p mention in its post,that since the silicone is not water based,bacterial won't be created in the tube(or somthing similar)and change it odor.
Are my conclusions,pursuant to your explanation,right?

[xchcui]

Can someone confirm or reject my conclucion?
It will be  a good way to close that thread.
Anyway,Thanks for your help.

[DrCMS]

Yes old material will not be as good but should not smell a lot different.