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Hi all,

 

I was not sure where exactly to post this as there wasn't a category that seemed to fit so please feel free to move this post as needed. 

 

I am wanting to understand exactly how aliphatic resins actually work at an atomic level - that is, how do they result in a force of attraction between two pieces of wood?  

 

My neighbour (who happens to be a retried biology/chemistry teacher) told me he thought it had something to do with electron clouds but really wasn't sure and couldn't go any further. 

 

Surprisingly, I have Googled around and can't find a suitable explanation.

 

Perhaps there is a chemist (or other) on board who understands this at an atomic level and would be happy to give an overview?

 

 

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Aliphatic -  I will take to mean yellow PVA -  PVA with additives to add resistance to temporary exposure to water. e.g. Titebond II

 

The bond is formed thru a chemical reaction.  When in the water solvent and in a bottle with minimal air - it stays short chains. 

Spread it in a thin layer on a porous surface and expose to to oxygen = the short chains bond to each other and form much longer chains.

These chains invade the porous surface and twist around each other.  They do not chemically react with cellulose or lignin ( as far as I know ).

The hold is a physical one.  The chains completely fill the holes and grooves in the wood.

I have not read of Tris type components, so I do not know if 3 arm components are a part of this.  I suspect that it is single, long chains that are formed.

The result is a plastic that holds together and holds to the wood surface with more strength than lignin holds wood fiber together.

Pry the bond apart and the wood tears from itself before the plastic chains will pull apart from the wood.  A thick piece of just the polymerized PVA is clear, amber, flexible, and can be torn apart.

 

This encompasses some factors as far as use with wood:

A) A rougher bare wood surface yields a stronger bond.  ~ 100/150 grit is probably optimal - although I am wed to 220 grit, that is about as fine as should be sanded.

B ) The closer the two bonding surfaces, the stronger is the bond between them.  Increased clamping force produces a stronger bond. 

At a microscopic level, the irregularity of the wood surface makes it impossible to force out enough PVA to weaken the bond. 

It is definitely possible, indeed, is a limiting factor, to apply enough force to crush, to damage the outer face of the wood being clamped.

 

I do not recall ever seeing the actual chemical reaction that forms polyvinyl acetate written out.  Polymer chemistry was not much of a part of my Organic Chemistry class.

 

addition:  thinking about the reaction - there is acetic acid in the mixture.  Although it is an organic acid, thus has a lower maximum possible hydrogen ion concentration (higher pH max) the effect of drying from the thin layer must increase the acidity.  Perhaps it is the combination of oxygen and a more acid environment that accelerates the linking reaction.

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What I always wondered, although I took it on faith to be true, is why 90% isopropyl alchohol is prescribed for softening and "unsticking" cured PVA adhesive, but not plain denatured alcohol. It's got an extra carbon atom, but that's about as much as I've been able to figure out about the stuff.

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Bob,

To poke at this a bit.  !967 was a long time ago, but seeing if I can remember=

By denatured,  it would be ethanol.  Two carbons and an -OH.  Carbon holds its H's more tightly than oxygen, so the H bonded to the carbons can be ignored.  There is possible partial ionization of the H from the oxygen - which has an effect of polarity - and affinity for the polyvinyl acetate matrix. and its ability the fit between the chains.

 

Propanol  is three carbons in a chain with an -OH  on an end one.  I am guessing that whatever the effect of a two carbon chain on H polarity would be greater from a 3 carbon chain.

 

2-propanol (isopropyl alcohol) is also 3 carbons, but the -OH is on the middle carbon.  The outside two carbons might - flap like wings - and have the opposite effect on the H polarity because the the electron clouds are working against each other rather than being a reinforcing chain.   The shape is more like a ball?  It must be able to get inside the space between the chains and straighten them out, or weaken the attraction between the chains.  

 

 

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Jaeger,

 

I suspect volatility might be a factor.  The IPA with a boiling point of around 83 will stay in contact with the PVA rather longer than ethanol. I don't think polarity differences are  that much.  IPA is marginally more aliphatic.  Certainly 1-propanol has less solvent powerfor polar substances than ethanol.

 

John

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Interesting second post. I often lightly pull a hobby saw blade across both surfaces before gluing. I have no idea if it creates a stronger bond but probably doesn't hurt? 

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The core material is the same.  The yellow PVA has additives that increase resistance to water. The additives have an amber tint.

The pattern for the range of PVA products includes:

bookbinders PVA - white - dries clear - pH 7 - neutral

Elmer's Glue All - white -                        pH 5

Weldbond - white -  water resistant - pH 4.5-5

Titebond - lt. yellow - not water resistant - pH 4

Titebond II - yellow -  water resistant  - pH 3

Titebond III - lt, brown - waterproof -  pH 2.5   - not for continuous immersion -  Resorcinol or newer tech

 

From a practical point on the scale,  for our purposes - except for bookbinders PVA (for rigging and paper) - the wood will probably fail before the bonds formed using any of them do.  Any differences are a tempest in a teapot.

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I love MSW. It has yet again made me think.

So here is my question. If two pieces of wood are to be glued together, and one of the surfaces has been painted with acrylic paint, which glue gives the best result?

Part two of the question: what if one surface has paper glued to it?

(big hint: scarf joints, edges of planking)

 

 

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59 minutes ago, bruce d said:

So here is my question. If two pieces of wood are to be glued together, and one of the surfaces has been painted with acrylic paint, which glue gives the best result?

Part two of the question: what if one surface has paper glued to it?

(big hint: scarf joints, edges of planking)

As a game of speculation - not the result of experimental testing:

1- acrylic paint will leave a smooth surface with few or no pores or irregularities.  In the situation of wood-acrylic-PVA-wood, The strength of the bond of the acrylic with wood is one limiting factor.  The bond of the PVA with acrylic will probably have very little of a physical component.  I see the chains as a flat layer across the face of the paint.  The bond will be a weak electrostatic one instead of the usual mechanical one.  The large size of the chains probably makes for a wavy, knotty, interface on a microscopic level.  The electrostatic bond is likely significantly weaker than that formed by the type of glue that uses electrostatic attraction for a bonding mechanism.  The fix is to seriously abrade or scrape the acrylic at the bond interface.

2- paper   -   is porous.  This situation of wood-PVA-paper-PVA-wood,  The weakest point is paper-paper.  Depending on the type of paper used, the PVA may penetrate enough that there is a PVA-PVA bond inside the paper.  I would not risk my life on the strength of that bond, but if may be close (or at least closer) to a normal PVA bond. 

 

The hint:  I see this as two techniques for simulating caulking in a laid deck. 

Gloves off!

The bond between planks on a model deck does not need to be strong.  The needed strength is at the deck to beam ( and if your OCD is off the scale - the carlings, ledges, edges of hanging knees and face of lodging knees).  My perspective is scratch and POF,  so for me plywood is for tool bases and housing.

Using paint to simulate the caulking - a really bad idea.

Most models - to my eye - place way too much emphasis on the caulking seams.  Even exactly replicating the scale width is probably too much because of scale effect.

The modern "repairs"  done on the decks of saved vessels such as USS Constitution and HMS Trincomalee  look like cartoons of what was done 200 years ago.  Perhaps if the deck was originally laid in the tropics in the Summer and it was sailed to the North polar region in Winter and allows to dry and shrink, the seams might be that wide.  As it is, I suspect it is a combination of lesser carpentry skills and giving the customer what he expects to see.

Paper is a time tested method suggested in at least one of the original core texts for our hobby.  Depending on scale, the paper might be over doing it.  Using black paper is the wrong color for pre-1860.

Consider adding Black Walnut dye crystals to some PVA instead.  It is closer to Pine tar in color.  The bulk can be used to dye rigging - intense for standing and dilute for running rigging.

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On 7/29/2020 at 5:42 PM, Jaager said:

Bob,

To poke at this a bit.  !967 was a long time ago, but seeing if I can remember=

By denatured,  it would be ethanol.  Two carbons and an -OH.  Carbon holds its H's more tightly than oxygen, so the H bonded to the carbons can be ignored.  There is possible partial ionization of the H from the oxygen - which has an effect of polarity - and affinity for the polyvinyl acetate matrix. and its ability the fit between the chains.

 

Propanol  is three carbons in a chain with an -OH  on an end one.  I am guessing that whatever the effect of a two carbon chain on H polarity would be greater from a 3 carbon chain.

 

2-propanol (isopropyl alcohol) is also 3 carbons, but the -OH is on the middle carbon.  The outside two carbons might - flap like wings - and have the opposite effect on the H polarity because the the electron clouds are working against each other rather than being a reinforcing chain.   The shape is more like a ball?  It must be able to get inside the space between the chains and straighten them out, or weaken the attraction between the chains.  

 

 

Thanks! That certainly makes it perfectly clear. :D  I was in chemistry class in 1967, too. Unfortunately, I failed to apply myself the the study of that subject any more than was necessary to achieve a "gentleman's C." :D I had a bad habit of only studying the subjects in which I had a current interest during my college years and every so often in my later life I've been reminded of the costs of that. I had no appreciation for trigonometry until I had to teach myself celestial navigation, for example!

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In real life, particularly in the Age of Sail when pine tar was liberally applied to everything, decks ended up black and covered in tow in short order. Even naval vessels minimized holy-stoning to preserve their decks, save for special occasions when an inspection was to occur. (Frequent holy-stoning would wear the decks down to the fastening heads in no time.) Out of scale (color and size) deck seams and black "nails" in deck planks, like protruding out of scale "rivets" on  bottom coppering, seem to be faddish affectations of present day modeling, but, as they say, "each to his own." I've found simply laying deck planks, applying a light coat of varnish, and then a light coat of thin stain or paint of the appropriate color, then wiped off, leaves a suitably darkened area between the deck seams that yields a realistic impression of what decks should look like at scale. Your mileage may vary, of course. 

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About the holystoning,  which was sanding with loose sand and a big flat rock at least some of the time.  I see most of the crew as being barefoot most of the time.  Splinters could be a disaster and not just painful, so the deck would need attention often enough to avoid that.

 

My experience with actual sailing is slight.  But one Summer, I took an auxiliary sail passenger boat over to (I think) Cape Lookout, NC.  The sail was used for a while.  July/August coastal North Carolina can get really hot. 

I discovered a few things:

There is no shade on a single deck sailing vessel.  Not only is there direct radiation from the Sun,  there is reflected radiation from the water surface.  When sailing, any breeze is reduced because the vessel is moving with it.

 

Barefoot, open deck -  hot, hot, hot - also the deck planks could loose water and shrink.  I am imagining that during most of the day, there would be crewmen whose job was to haul in buckets of seawater and keep the deck wet.  I think the options for the soles of shoes was hobnails (land only) and leather.  Leather and a wet surface = broken tailbones.  Sea water from around a ship that not only had sea creature poo,  but a real concentration of crew poo floating along the side,  could present some really interesting infections.  Puncture wounds would be something to avoid.

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Hi Jaeger,

 

On the subject of wind speed - or really "apparent" wind speed. It depends on the point of sailing. If you are sailing before the wind then as you say the apparent wind is less than the true wind speed but if you are sailing into the breeze then the apparent wind is stronger than the true wind.  Also since the boat is at an angle to the wind at this point of sailing the addition of vectors causes the apparent wind to move aft.  But you are definitely correct about the lack of shade on deck!

 

John

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