Archive for the ‘Science’ Category

How Two Part Epoxy Works

Saturday, November 18th, 2017

Every attempt was made to write the article below so that anyone with a basic general knowledge of chemistry could follow along.  If anything is not clear please ask below.

Two part epoxies work by combining an epoxy resin and a hardener in equal amounts.  The “equal amounts” is important because the reaction between the two is one to one.  The hardener does NOT work as a catalyst, but as a component of the reaction (it gets consumed in the reaction).  The epoxy resin is composed of an epoxide functional group separated by a spacer (a bunch of atoms) and another epoxide.  Interestingly, the word “epoxide” is where epoxy resin gets its name.

An epoxide is a very reactive species that is composed of a three-membered ring (two CH2 and one oxygen).  Epoxides are very reactive to nucleophiles which causes the ring to open.  A nucleophile is an atom in a chemical that is rich in electron density and is attracted to positive charge.  Nucleophiles (Nu) differ in their nucleophilic strength and examples include the oxygen atom of water, and nitrogen atoms of amines.  And to take the strength point one step further, the nitrogens of different chemicals can also differ in nucleophilic strength.  That is, not all chemicals that contain an amine have the same nucleophilic strength.  The two dots (..) above the -Nu denote the unshared pair of electrons of the nucleophile and it is the unshared pair of electrons that “seek out” positive charge (there really isn’t any “seeking” per se – positive and negative charges attract each other and obey Coulomb’s law).  In the figure below, the carbon adjacent to the oxygen has a partial positive charge because of the neighboring oxygen atom (inductive effect).

 

Below is an example of an epoxide resin (A) with an epoxide functional group on either end (three membered ring).  Epoxide resins can vary in structure and the differences will impact the epoxy’s properties such as strength, cure time and appearance.  The structure of epoxy resins and their hardeners are often proprietary and covered by patents.

The amine chemical above that is labeled “B” is the hardener in a two part epoxy.  It usually contains a primary amine (-NH2) as the nucleophile (Nu).  Primary amines will have a nitrogen atom and two hydrogens connected to them followed by a carbon chain (or singe carbon in the case of the primary amine methylamine – Breaking Bad anyone?).  The hardener will often contain two nucleophiles per molecule (B has two primary amines).  A hardener with two nucleophiles can cross link two molecules of resin (one nucleophile reacts with one epoxide per molecule).  The product of the cross linking can continue with another molecule of B because it has available epoxides remaining.  This is what leads to the polymerization or chain forming process.

In the schematic below, the hardener contains a primary amine, but it only has one amine per molecule (the -R simply denotes any organic fragment).  The primary amine B can react with one molecule of A to give C which contains a secondary amine (a secondary amine will only have one hydrogen atom connected to it).  Secondary amines are also capable of reacting with epoxides and will give D in the example below.  The problem with secondary amines is that the nitrogen will be more crowded (steric hindrance) and this can slow down its reacting with another molecule of A and slow down the curing process.

 

An interesting point to make with epoxides is that woodworkers often like to darken their epoxy using a dye.  And if your dye contains a primary or secondary amine (like an aniline dye) it could actually react with your epoxy resin.  This shouldn’t interfere with the properties of your epoxy because only a very small amount of dye is usually used.

substituted aniline

Music, it Calms the Savage Woodworker

Tuesday, March 1st, 2016

Do you listen to music while you work in the shop?  Maybe you should if you’re not already.  Studies have demonstrated that music can have the effect of reducing stress and improving focus.  If you are ever sedated and put under the knife of a surgeon, chances are he is doing the cutting to the sounds of music.  Aside from its calming attributes, music has also been shown to enhance learning and memory when played during an activity; I find this fascinating.  As a woodworker these benefits have the potential to be profound.  When learning to cut dovetails for example, playing music while cutting them has the potential to relax you and help to ingrain the required procedural memory.  Any time a new task is learned or practiced, any woodworker could potentially gain more from the experience by playing music.  Googling the association between music and learning/memory will reveal dozens of articles, studies and anecdotes.

Unfortunately for me, as a video content creator, most of the time I can’t listen to music as I work in the shop; it would muck up the video production pretty good.  But, I do like to listen to music when the camera isn’t rolling.

I’d LOVE to get a little feedback from you guys.  Do you listen to music in the woodshop?  Do you find it helpful?  What kind of music do you play and does it change with the type of task you are doing?

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