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Offline blake_jl

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Viscosity Question
« on: October 10, 2008, 06:04:54 PM »
I have polydimethylsiloxane in 100cst form and polydimethylsiloxane in 12500cst form.

Apparently polydimethylsiloxane in 1000cst form provides the characteristics I am looking for in the ingredient however I don't have this viscosity available.

Can I just blend the 100cst and 12500cst together to get approx. 1000cst?

In other words

1 part 12500cst
12.7 parts 100cst

Averages out close enough to 1000

Or does it not work this way?

Thanks for your help.

Offline DrCMS

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Re: Viscosity Question
« Reply #1 on: October 11, 2008, 04:54:16 AM »
NO it does not work like that.

Offline P

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Re: Viscosity Question
« Reply #2 on: October 13, 2008, 04:09:42 AM »
It doesn't  -  but you might still be able to blend the two reduce viscocity  -  it just wont be a linear relationship (as far as I know).   You'll have to do a few test mixes I reckon to get an idea of how much of the 100 you'll need to thin the other one down to your required viscosity.

Is the PDMS in a solvent??  You could add more of this solvent to the 12500cst to thin it down.
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Offline DrCMS

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Re: Viscosity Question
« Reply #3 on: October 13, 2008, 07:25:48 AM »
I doubt you'll be able to get the properties you want by blending these two different molecular weight polymers together. 

Can you make petrol/gasoline by blending ethane with crude oil?

Offline P

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Re: Viscosity Question
« Reply #4 on: October 13, 2008, 09:02:44 AM »
I doubt you'll be able to get the properties you want by blending these two different molecular weight polymers together. 

Can you make petrol/gasoline by blending ethane with crude oil?


Well no  -  I see where your comig from, but I don't see why the viscosity wouldn't decrease by adding some the 100 into the thicker one.   In fact he has tried this already and it came out too thin.  I recon that if he tried it again with less 100 still he would get a better result. Still, I think he is trying to get a sample of the material sent to him at the right viscosity.
 
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Offline DrCMS

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Re: Viscosity Question
« Reply #5 on: October 13, 2008, 10:39:01 AM »
You can to mix the 100cst material with the 12500cst material to give a blend that has a viscosity of 1000cst.  I will take some trial an error but it can be done quite easily.

However that will only have the same viscosity as the desired material its other performance properties will not be a direct match for the 1000cst PDMS.

The 100cst material is low molecular weight fraction while the 12500cst material is a high molecular weight fraction.  The desired 1000cst material is an intermediate molecular weight fraction.

Blend the high and low together and you'll probably get a bimodal molecular weight distribution which will not match the performance characterstics of the normal distribution 1000cst fraction.

Offline P

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Re: Viscosity Question
« Reply #6 on: October 13, 2008, 12:02:04 PM »

Blend the high and low together and you'll probably get a bimodal molecular weight distribution which will not match the performance characterstics of the normal distribution 1000cst fraction.


Couldn't agree more.  Although it depends on the properties you're after. I think he wants the PDMS as an additive to cause a water beading effect from a wax coating.  I reckon that this mixture of high and low molecular weight would still give the water repellency he is after, just the same as a monodispersed mid range MW. Although he'd have to try it to see.  I think the viscosity requirement is so he can get a good blend of his polymer into the wax product smoothly.

Regards,

P.    :)
Tonight I’m going to party like it’s on sale for $19.99!

- Apu Nahasapeemapetilon

Offline blake_jl

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Re: Viscosity Question
« Reply #7 on: October 15, 2008, 06:25:36 AM »
Thanks Guys,

P is right. I have taken the easy way out and sourced the PDMS in the 1000cst.

Besides the water beading the reason for the PDMS is for ease of use, gloss and durability. I'm just a learner but apparently the different viscosities give off different properties. The thinner stuff for some reason makes the end product easier to buff off, the middle one improves the gloss and the thicker one improves durability.

Dow Corning says the best ratio to get a good balance between the three properties is 3:1:1 (350:1000:12500)

I have no idea about the chemistry behind all this. All I know is I have used these products as the manufacturer says in my "amateur" formula and the end result is amazing.

Offline P

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Re: Viscosity Question
« Reply #8 on: October 17, 2008, 04:14:22 AM »
The thinner stuff for some reason makes the end product easier to buff off, the middle one improves the gloss and the thicker one improves durability.

I have no idea about the chemistry behind all this.

It's kinda physical as much as chemical.  eg  -  the higher MW has much longer chains of PDMS  -  which can entangle, twist and interlock alot more round each other and round particulates in your formulation  -  thus it is more durable.  On the other end of the scale  -  the shorter chains arn't interlocked in such a tangle  -  so there are easier to buff away.  (well  -  that's what I rekon anyway).
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- Apu Nahasapeemapetilon

Offline blake_jl

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Re: Viscosity Question
« Reply #9 on: October 18, 2008, 08:14:13 PM »
Ah ok, maybe what I need to research is the whole "cross linking" polymer subject. Sounds like that's what you're talking about.

I'm also in the process of getting an ingredient from Mayzo that is a UV absorber. Can anyone shed some light on what the Dr. was talking about in this paragraph?

"Solid BLS-531 at 0.2-0.5% loadings is a typical UVA Liquid BLS-1130 at the same loading is also good.
BLS-292 is a good HALS free radical trap the would be synergistic with the above..."

I get the UVA part, but then he went on to talk about a good "HALS free radical trap". I have no idea what that is but sounds cool  :)

Offline P

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Re: Viscosity Question
« Reply #10 on: October 20, 2008, 04:01:02 AM »
"HALS free radical trap". I have no idea what that is but sounds cool  :)

"Hindered Amine Light Stabilizer"  I believe.  Gives UV stability and stuff.

Ah ok, maybe what I need to research is the whole "cross linking" polymer subject. Sounds like that's what you're talking about.

More like the chains physically entangling due to their length.  Cross-Linking usually refers to actual chemical links between the chains.





PS - light stabilizers  - http://www.ciba.com/index/ind-index/ind-pla/ind-pla-effectsweoffer/ind-pla-eff-durabilityandprotection/ind-pla-eff-dur-lightstability/ind-pla-eff-dur-lig-lightstabilizer.htm

« Last Edit: October 20, 2008, 04:24:18 AM by P »
Tonight I’m going to party like it’s on sale for $19.99!

- Apu Nahasapeemapetilon

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