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Topic: Stretched Polymer  (Read 931 times)

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Offline Enthalpy

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Stretched Polymer
« on: May 30, 2020, 09:03:57 AM »
Hello dear friends!

Stretching stiffens polymers a lot, making wonder fibres of banal bulk materials. It brings LCP from 10GPa to 170GPa. Highly stretched polyethylene makes wonder ropes of Dyneema, Spectra and competitors.

Stretching *3, easy with a polymer, strengthens much a stripe from a polyethylene shopping bag.

Companies that stretch metal (for piano wire and others) could adapt to thicker polymer too. Or polymer manufacturers themselves could stretch or extrude the material cold or lukewarm, so mechanical engineers have stiff strong bulk polymers, lighter and easier to machine without fibre reinforcement.

The transverse properties may drop. Rolling a polymer in two directions strengthens both, as polyester (Mylar) films show. This would improve plates.

Sometimes the azimuthal stiffness too matters for rods. Schrägwalzen (I ignore the English word, check the drawings)
https://de.wikipedia.org/wiki/Walzen#Schr%C3%A4gwalzen
would improve the azimuthal direction, easy with a polymer. Combine with stretching or extrusion.

Marc Schaefer, aka Enthalpy

Offline Enthalpy

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Re: Stretched Polymer
« Reply #1 on: June 06, 2020, 04:12:27 AM »
PTFE too, and other weak polymers, are candidates for strengthening and stiffening. Making supermaterials is one goal, improving bad ones is one other. Creeping, flowing, low modulus all hinder the use of PTFE despite its other properties are good. Fibres exist already, hardened plates and rods would be nice.

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"Schrägwalzen" is "skew rolling" in English, while "transverse rolling" includes other interesting possibilities. Common at tube production, it serves for rods too.

Marc Schaefer, aka Enthalpy

Offline Enthalpy

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Re: Stretched Polymer
« Reply #2 on: June 21, 2020, 05:10:07 AM »
Stretching might stiffen and strengthen polyketone too. Initial E=1.3GPa and σ~58MPa aren't brilliant, but polyketone is potentially very cheap, it has a good operating temperature range, low water absorption and high vibration damping. Maybe stretching brings a nice combination of properties.

Polymers used as super-fibres should also improve as bulk materials. PA and PET, PEEK too. Machining would become easier too, useful for PA.

Marc Schaefer, aka Enthalpy

Offline marquis

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Re: Stretched Polymer
« Reply #3 on: June 22, 2020, 08:32:02 PM »
This has been done in the medical industry ( i.e. I.V. Bags) for at least 20 years.  Special polymers are still used for specific drugs, but not unless absolutely needed.

Thanks for pointing out the technique, though.

Offline Enthalpy

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Re: Stretched Polymer
« Reply #4 on: June 25, 2020, 06:07:32 PM »
And it has been done for ropes since polymer ropes exist. Plus many films like Mylar, which was old stuff 30 years ago.

But I want more massive material hardened this way, for mechanical engineering, including wind instruments that badly need it. Rods, plates, and so on. From one or several companies that have them in catalogues with guaranteed properties, and preferably in stock. Polymers stiff and strong, that would open many uses in mechanical design.

Offline Enthalpy

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Re: Stretched Polymer
« Reply #5 on: July 04, 2020, 01:53:41 PM »
Some polymer fibres have steel's strength and stiffness thanks to stretching and keep a plastic's density. Stretched polymers could hence excel as fast-spinning parts, especially as impellers of gas compressors and vacuum pumps, as turbines too where the temperature fits.

These parts are uneasily made of fibres in a matrix. Intricate shapes hamper automatic production, thin sections held at thicker ones aren't quite natural to fibres. It's done at individual fan blades of turbofans, not at cheap small integral compressor impellers.

I suggested to deform polymer raw material. Here strength is needed in the radial direction, by squeezing a disk, and in the azimuthal too, by a torsion. Then the part could be machined by usual methods, accurate and automated - if everything works as hoped.

Or just inject the part. For instance LCP is known to harden much from small shear at injection. That would be perfect to harden the blades or thin disk of an impeller: Inject the polymer at the centre so shear is strong at the thin blades and disk periphery. Heat the resin and mould a bit less, compensate with more injection pressure.

The blades and disk periphery of impellers and turbine rotors hold at a massive ring or disk section near the axis, where the material needs azimuthal strength too. This would be achieved by a rotating part of the mould, or maybe a separate construction used as the unmoulded part is still warm. Azimuthal shear could occur in the polymer between concentric tools, an outer one (optionally a mould part) that holds the impeller at its blades and a rotating inner one where the shaft will be. Other arrangement are possible, this one limits the deformations of the impeller.

PA too hardens by deformation. Simple injection and rotation could make very strong and cheap impellers.

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When extruding tubes, the kernel could rotate to give azimuthal shear. This can combine with the axial shear given by the extrusion.

Marc Schaefer, aka Enthalpy

Offline Enthalpy

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Re: Stretched Polymer
« Reply #6 on: August 02, 2020, 12:58:14 PM »
Could the fan blades be of stretched polymer at a turbofan?

They demand strength-to-mass at room temperature. The air arrives at almost 0.95 Mach, the blades must rotate significantly faster. I know titanium alloy and graphite composite for them. Blades need impact resistance too, creep resistance, and more.

Stretched LCP would improve the strength-to-mass, other polymers too. Just milling the blades from stretched raw material would be simpler than now. Injecting the blades with high shear under limited heat to obtain strength would be fantastic.

Marc Schaefer, aka Enthalpy

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