Any boffins here?

[HappyHacker]

It's obvious.

All the adventurous molecules have congregated in the tube in an attempt to escape. After you have finished squeezing there are still some adventurous molecules who do not want to return to the boring ones trying to remain in the bottle so they continue trying to escape.

It is a similar principle that causes the contents of a pan to escape when you are simmering linseed or porridge, if some manage to get over the edge they all try to follow but this is to do with the herd instinct of the boring ones following the adventurous ones.

 

[Bod]

Tis simple.
You have given the glue momentum, by squeezing the bottle, when you stop squeezing the momentum has to have time to die away.
Coast your car downhill, how far up the other side do you go before the throttle is needed?

Bod

 

[transatlantic]

Isn't this the same thing as with sealant guns? In that you can stop squeezing, and even draw the plunger back, ..or even pull out the tube from the gun, ..... and it will still seep out for 20s or so.

http://albionexpertsonline.blogspot.com ... -drip.html

 

[thick_mike]

Because the PVA is viscous it takes time for it to move. The PVA inside the bottle falls down inside the bottle displacing a bubble of air upwards (because of the comparative buoyancy of the air). The bubble rises into the conical nozzle and speeds up (due to the volume being constant , but the cross section of the cone reducing). The glue above the bubble can’t move out of the way fast enough, so it is pushed out.

The geometry and polypropylene (or polyethylene not sure which) that your bottle is made from isn’t a particularly elastic structure, so the negative pressure caused by the walls of the bottle pushing out won’t be significant, so it won’t be able to suck the viscous PVA back into the bottle.

(25 years as a polymer chemist working with paints and adhesives - CV available on request )

 

[Fitzroy]

And if you’re interested in some rough numbers.

Holding bottle increases temperature by say 0.1degC. In rough terms that will raise pressure by 0.1/293 (Kelvin) or 0.034%. 1atm is c. 10meters of water head of which .034% is 34mm.

So long has the depth of glue in the nozzle is less than 34mm it will push out all the glue in the nozzle.

If you hold it long enough for the temperature to raise 1 degC it’ll be 10 fold greater.

Fitz.

But surely the volume of glue I have squeezed out would counteract any expansion of air and cause a slight vacuum in side when squeezing stops.

I was just running numbers on the idea that warming it up increased the pressure. We’d been doing something at work where the diurnal temperature cycle was causing a Safety valve to lift so pressure rises with small temperature changes were on my mind.

In a 250ml bottle .034% is <0.1ml which must be less than you used, even a 1degC rise equivalent to 0.34% is <1ml which I’m sure is less than your average glue squeeze.

Not sure the maths adds up anymore in this case.

Fitz

 

[samhay]

Because the PVA is viscous it takes time for it to move. The PVA inside the bottle falls down inside the bottle displacing a bubble of air upwards (because of the comparative buoyancy of the air). The bubble rises into the conical nozzle and speeds up (due to the volume being constant , but the cross section of the cone reducing). The glue above the bubble can’t move out of the way fast enough, so it is pushed out.

The geometry and polypropylene (or polyethylene not sure which) that your bottle is made from isn’t a particularly elastic structure, so the negative pressure caused by the walls of the bottle pushing out won’t be significant, so it won’t be able to suck the viscous PVA back into the bottle.

(25 years as a polymer chemist working with paints and adhesives - CV available on request )

Not just a good answer, but nicely explained too.
Thanks.

 

[Chrispy]

Well I opened a new full bottle and no ooz over so it would indicate a possible connection with volume of air/ glue ratio.
Another point is this glue is much thinner than your average pva so maybe the air bubble theorum won't work so well here.
:|

 

[thick_mike]

Easy enough to test it out. You can reduce PVA viscosity pretty easily by adding small amounts of water. If there’s less and less ooze, then that supports the hypothesis.

 

[Trevanion]

Squeeze most of the air out before you start squeezing glue out, I'm no astrophysicalchemist but surely that would create some kind of vacuum effect (I don't know! ) once you started pouring and it would want to draw the glue back in to take in air once you let off the pressure because the bottle will want to go to it's original shape creating a larger air cavity?

 

[Benchwayze]

Because the PVA is viscous it takes time for it to move. The PVA inside the bottle falls down inside the bottle displacing a bubble of air upwards (because of the comparative buoyancy of the air). The bubble rises into the conical nozzle and speeds up (due to the volume being constant , but the cross section of the cone reducing). The glue above the bubble can’t move out of the way fast enough, so it is pushed out.

The geometry and polypropylene (or polyethylene not sure which) that your bottle is made from isn’t a particularly elastic structure, so the negative pressure caused by the walls of the bottle pushing out won’t be significant, so it won’t be able to suck the viscous PVA back into the bottle.

(25 years as a polymer chemist working with paints and adhesives - CV available on request )

I think that's what I said. Obviously this oozing wouldn't happen with a 5 litre container when you open a screw cap lid. There's room for the air to go back into the container and push the glue down. So you can pour too! The number eight screw solved this for me with the squeezy bottle.

Maybe I should point out: I clean out those flat tuna cans, thoroughly, put my glue into those, and apply with a brush; esp on dovetails. Find it more precise and less messy.

Incidentally, don't these nozzles come off if you unscrew them. Then you won't have the problem if you use another container and a brush. Ramekins are useful for this., but I use the tuna cans.
John (hammer)