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 Plastics - The History. thereof etc

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PaulRyckier
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PostSubject: Re: Plastics - The History. thereof etc   Plastics - The History. thereof etc - Page 2 EmptySat 18 Jan 2020, 20:36

MM, as we had to study the physical properties of paint (the chemical ones were done in the paint factory), we had to do the viscosity test with a calibrated device as the one I think you mentioned in your "pitch-drop" experiment. It had the form of a cup with a standardized form


Plastics - The History. thereof etc - Page 2 4149b4IePDL._SX425_

As we were an American firm, we did it with the American cup ASTM norm, but you had also the French Afnor norm and the German Din norm.
And now the international ISO norm. But in the 21th century, you can still not compare one with the other I read now.
And viscosity of oil, paint, in fact any liquid or viscous material at a given temperature is very important to know...

That said, I measured in the time the viscosity of water in that cup and as the viscosity of paint to spray handmade had normally to be 20 seconds at 21 C°, I think to recall that that of water was some 10 seconds.

But if you have to start to reason why a viscosity in that cup differs, I think no scientist has done it till today, as it has to do with adhesion on the surface of the cup and "is the paint/varnish a dispersion or an emulsion? or both?"...and so on and so on...

But back to filmthickness of my wed body coming out from the shower cabin...I think that too is too complex to measure...while is it in demineralized water or normal tap water? are there still rests of tensioactif in the water (I think nowadays "soap" is oldfashioned?)

Just to measure the filmthickness of flowing water on a vertical surface, see what difficulties there are to measure...
Two sources I found, that you MM as a PH.D from the steel industry can perhaps interpret...?
https://www.academia.edu/24260719/Minimum_thickness_of_a_flowing_down_liquid_film_on_a_vertical_surface
https://www.tandfonline.com/doi/full/10.1080/00223131.2015.1102779

Am I right that they have values of an nearly unbelievable 300 mikron?

Kind regards, Paul.
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Meles meles
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Meles meles

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PostSubject: Re: Plastics - The History. thereof etc   Plastics - The History. thereof etc - Page 2 EmptySun 19 Jan 2020, 10:53

And I'm sure you, Paul, know all about thixotropic or so-called 'non-drip' paints: those that are gels or viscous fluids under static conditions but which will will flow (become thinner, less viscous) when shaken, agitated, stirred or shear-stressed (ie when painted onto a surface).  In other words a thixotropic fluid behaves in a non-Newtonian way in that it takes a finite time to attain equilibrium viscosity when introduced to a steep change in shear rate.

Besides non-drip paints, many other 'fluids' can behave in this way. For example a pot of yogurt will often appear 'set' and can be inverted without it running out - until it is stirred, whereupon it acts as a runny fluid. In a similar way volcanic ash flows (lahars) - often composed entirely just of tumbling solid material, with the individual pieces of rock ranging in size from small grains up to large boulders - will flow just like a fluid/liquid river for long distances as long as it keeps in motion; but as soon as the flow moves onto more level ground and so slows down, the mixture settles, and immediately sets as hard as concrete.

Conversely some viscous fluids or gels behave in a solid way when subject to high strain rate. Custard (basically an emusion of starchy corn flour in water) can be stirred with a spoon, but the surface can sometimes be made to 'crack' in a brittle manner if struck hard and fast enough. In one particulalry impressive demonstration I once saw an ordinary wax candle (complete with burning wick) fired from a gun at a house brick ... the candle shattered the brick and emerged from the ordeal only slightly bent.

The viscosity (the resistence to flow) of even Newtonian fluids varies widely and is dependent on ambient conditions (as well as flow conditions, ie whether the flow is 'turbulent' or 'laminar'). At room temperature (20°C) the comparative viscosities of several common liquids are as follows (in mPa.s - milliPascal seconds):
water            0.89
pure ethanol 1.07
mercury      1.55
cow's milk   2.12
sunflower oil  48.8
olive oil         56.2

... and as you mentioned liquid iron and steel: the viscosity of molten iron at 1600°C, ie about 50° above the melting point, is  5.22 mPa.s, so that's only a bit more viscous than milk but not as viscous as most vegetable oils (this is of course important information as it affects the design of the mould so that the liquid metal successfully flows to all points in a casting). Even gases have viscosity, for example dry air at 100°C and 1 atmosphere pressure (ie at sea level) has a viscosity of about 7.1 µPa.s (micro Pascal.seconds) ie some ten thousand times less than that of room temperature water, so small but it's still measurable.

I can happily talk materials' science for hours, but we are rather veering away from Priscilla's original post about plastics and their history.


Last edited by Meles meles on Sun 19 Jan 2020, 17:35; edited 4 times in total (Reason for editing : trivial but annoying typos)
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Vizzer
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PostSubject: Re: Plastics - The History. thereof etc   Plastics - The History. thereof etc - Page 2 EmptySun 19 Jan 2020, 15:43

@Meles meles wrote:
Many plastics (noun) do typically behave plastically (adjective) but many others do not. And as Paul says the major distinction between the types of synthetic polymers is between those that are thermoplastic and soften when heated because the heat decreases the degree of cross-linking between the polymer chains (nylon, PVC, acrylic, polythene, polystyrene, teflon); and those that harden when heated because the heat increases the degree of permanent cross-linking between polymer chains (bakelite, vulcanised rubber, melamine, most polyuethanes, epoxies and polyester resins).

Thanks for clarifying that Meles. Now I understand why Priscilla warned us about definitions - twice!

It’s the elasticity (or flexibility) of some plastics, of course, which is one of their major selling points. It is, for example, why plastic bottles took over from glass ones in such a big way in many sectors of retail from the 1970s onwards. They’re lighter to carry and much more forgiving if dropped. And this elasticity also has other very useful applications in our day today lives. There are myriad clip-together, snap-fit, snap-in and push ‘n click features on a wide variety of plastic goods from Tupperware containers to mobile phones. For instance, the cover of the battery compartment of a television remote-control device will have one or two little hooked catches which will slide in and click firm but also easily slide out again countless times without the user having any real fear of them snapping off. Admittedly with some products and manufacturers the fear factor can rise considerably in this. A case in point being the stubborn fastener on the brittle-looking insulating panel behind my car’s headlamps - especially when it has to be prised loose with a large flat-head screwdriver on a frosty January morning such as yesterday. Thankfully, low temperature notwithstanding, it was able to be loosened and refitted without incident.

As you suggest, Bakelite is too brittle for such application but the possibilities of flexible plastic soon became apparent following the commercial development of vinyl, nylon and polythene etc in the 1920s and 30s. The aforementioned Tupperware company of Massachusetts was founded shortly afterwards in the 1940s. The brand exploded in popularity across America in the 1950s largely down to the marketing genius of Brownie Wise who conceived the ‘Tupperware party’ before she was unceremoniously and shockingly dumped by the corporation towards the end of that decade with a minimal redundancy settlement:

Plastics - The History. thereof etc - Page 2 7d68a42bffb89a7f9783b40b140d5ff4

(Brownie Wise demonstrating the lightness of Tupperware containers in a television advert c.1955)
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Meles meles
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Meles meles

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PostSubject: Re: Plastics - The History. thereof etc   Plastics - The History. thereof etc - Page 2 EmptySun 19 Jan 2020, 18:29

I'll admit it's really not much by way of remembrance for the sterling work of Brownie Wise, but any sealable plastic tub used to preserve food items in the fridge, is still generally known in France as "un tupperware". 

Plastics could, and indeed should, be reused ... and that was generally the original intention. 

Perhaps, some eighty years later we are finally realising that 'plastics' themselves are not really the issue, and that the fundamental problem is, as ever, humans, and their insaitable greed.
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PaulRyckier
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PostSubject: Re: Plastics - The History. thereof etc   Plastics - The History. thereof etc - Page 2 EmptySun 19 Jan 2020, 20:27

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PaulRyckier
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PostSubject: Re: Plastics - The History. thereof etc   Plastics - The History. thereof etc - Page 2 EmptySun 19 Jan 2020, 20:33

Don't say it to me, Vizzer, the Tupperware parties...I was the unwilling victim..to such "parties" with the partner, because the organizer was family...at the end in every cupboard there was spare "tupperware"...

Kind regards, Paul.
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PaulRyckier
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PostSubject: Re: Plastics - The History. thereof etc   Plastics - The History. thereof etc - Page 2 EmptySun 19 Jan 2020, 20:48

Thank you again MM for this interesting exposé about viscosity. And now I see some relation for the first time between paint (or varnish with inorganic (coated or not) or organic pigments) and liquid steel. What one learns here each day on these boards.

And yes tixotropy, it was an important element even in solvent based paint, as it was before in the car manufactoring industry. But one had also in these solvent based ones the drying and fixing of the film by the evaporation of the organic solvents, which was quicker than that of water solvent.

Yes veering away from the plastic subject...I first wanted to make an apart thread of it, but found it too meagre and wanted to add it as an aside...only the evenings to compose messages...and that the whole year around, by the daily workload...

Kind regards from Paul.
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