From: SFPhysics@aol.com
Date: Tue Mar 05 2002 - 02:35:44 PST
From: SFPhysics@aol.com Message-ID: <c1.1cc492b8.29b5f980@aol.com> Date: Tue, 5 Mar 2002 05:35:44 EST Subject: whiteboards
>In our physics classroom, there is a whiteboard that is almost
>impossible to erase -- you have to really scrub it, and then clean it
>with some sort of solvent to get the ink to come off. My first
>question is whether it's possible to recondition a white board by
>refinishing it with some sort of polish. I'm not sure what you'd use
>to do this.
>So here's the science part: How does a whiteboard work? I think it's
>related to the relative polarity of the board and markers. Since
>isopropanol or water will remove the marker, my guess is that the
>board has a nonpolar finish on it, and the markers' ink is polar. Is
>this first guess accurate?
>Thanks!
>Geoff
>>
Greetings Geoff:
There are five common types of whiteboards but the cheapest, Melamine plastic
applied to fiberboard, is what most schools end up purchasing. When the
surface is completely new the pens which use a mixture of dye gelatin and a
volatile solvent like ethyl acetate work efficiently to just leave a trace of
the gel that can be wiped off easily. With time Melamine is a compound that
will degrade with scratches that capture the dye. Then too there are pens
that have formulations that were *meant* for the more expensive whiteboards
and these soak into the Melamine surface. The more expensive "real"
whiteboards are usually made of heat glazed porcelain applied to sheet steel
or fuzed glass powder bonded to sheet steel. They are scratch resistant and
resistant to the markers made for them. The markers with the more active
solvents will attack and degrade the Melamine surface which is only a
fraction of a millimeter thick. Dirt dust or any abrasive will make minute
scratches from the action of the wiping cloth or pad eraser. Often the
eraser is used beyond its useful life and with ground in solids it then
becomes a sanding block. Once the smooth plastic surface is broken then dye
migration into the material is easy.
As to Melamine, it is a polar material, the outer loose leg of the nitrogen
ring has an NH CH2 SO3- Na+ radical which is not attached to the polymer
chain. Someday email will have graphic interfaces that will allow for a
quickly drawn diagram but for now you'll just have to imagine that Sodium
atom hanging out there by itself with its outer shell electron having been
borrowed by the Oleum radical. That is why it has a polarity of +1 in the
molecule.
For restoration of the cheap Melamine surface, there is no hope! Once dyes
have migrated into the plastic, and if the surface has been broken by
scratches, I know of no product that will renew the material. The medium
range quality boards that are solid plastic can be resurfaced but it should
be done professionally. The steel backed boards should not need any
attention for decades if treated well.
A disclaimer: My basic understanding of the whiteboard principles is
Chemistry and I hated teaching Chemistry. I am sure others on the Pinhole
list can straighten out anything that I may have incorrectly twisted around.
Please do.
Regards to all,
Al Sefl
P.S. I had the cleanest whiteboards in the city. My secret was clear
plastic sheet put over the new boards that was replaced when it would not
clean up easily!
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