[Enthalpy]

Hello dear friends!

The best musical strings are still made from gut, possibly spun with metal wire. Gut is often replaced with PA11 polyamide or with metal, but nothing provides the crispy, profound and long sound of gut, for reasons not fully understood. Strength per mass unit is mandatory, very low mechanical losses too, density and bendability are useful, and I believe elastic strain matters.

"Catgut" is one sheath of the lower part of the intestine of sheep, sometimes goats or cows, after mechanical and chemical processing which I understand leave only the collagen, in fibres oriented essentially lengthwise
https://www.gamutmusic.com/new-page
http://web.mit.edu/3.082/www/team1_f02/collagen.htm

The upper part of the intestine made sausage casings, but for decades collagen widely replaces it because the process is simpler
https://en.wikipedia.org/wiki/Collagen#Uses

Similarly, it would be nice to make musical strings of collagen, where at some process step collagen would be a homogeneous melt or solution, to obtain more easily strings of repeatable properties. The cited Wiki paragraph, brief and not quite clear about it, mentions:
"It is widely used in the form of collagen casings for sausages, which are also used in the manufacture of musical strings."
but I've never heard about a musical string made of collagen, far less a good string, so there must be hurdles.

What are your thoughts, please?

Do you imagine sausage casings are just molten natural collagen extruded in tube shape?

How difficult would it be to orient the macromolecules of collagen? PA11 achieves thick monofilament strings of good strength, but if this is impossible with collagen, string makers can assemble fibres into a string. To my understanding, very thin extrusion or stretching is what makes ultra-strong Dyneema fibres and ropes from banal polyethylene.

Thank you!

[Enthalpy]

Yarn from collagen exists already and serves for medicine. Citing subchap 2.4 of:
   Biomaterials Science: An Introduction to Materials in Medicine
   By Allan S. Hoffman, Frederick J. Schoen, Jack E. Lemons
"Reconstituted collagen is obtained by enzymatic chemical treatment of skin or tendon followed by reconstitution into fibrils. These fibrils can then be spun into fibres..."

Gut is a raw material long enough for strings, but to spin fibres, tendon seems an interesting alternative. Or continue with gut if the strings are better.

Wiki suggests that the exact spinning method is paramount to stretch and orient the macromolecules and transform weak polyethylene into ultra-strong Dyneema and Spectra
https://en.wikipedia.org/wiki/Ultra-high-molecular-weight_polyethylene#Fiber
https://en.wikipedia.org/wiki/Spinning_(polymers)#Gel_spinning
it seems logical: the lower exit temperature in gel spinning keeps the order acquired by the macromolecules in the spinneret.

Whether this achieves strings as good as gut?

[Enthalpy]

========== Harp detuning

Detuning plagues the harp. Several research papers try to relate that with the sensitivity to temperature and humidity of catgut and wood.

But violinists would think first at a different explanation, by experience. Played with a bow, a string stays tuned for long. Playing pizzicato detunes it immediately, especially if forte. So extension beyond the elastic limit is a more immediate cause, more so because this limit uses to be fuzzy for natural materials.

More people, harpists or not, must suspect the material's plastic deformation. But too many researchers look in secondary directions.

========== Need materials

I hereby renew my call to polymer chemists. When I'm a mechanical engineer, I have enough strong and stiff fibres. But I need fibres and materials that absorb much deformation energy, both to dissipate it or to restore much of it. I needed them when developing apparatus for crash-tests, something beyond PU would be very nice. String instruments and tennis champions rackets use sheep gut because stretched polyamide is less elastic, while superfibres are too lossy and stiff.

At strings, strong lossless deformation is needed, and sqrt(σ/ρ) (used stress and density) must exceed the 340m/s air sound speed. Other uses prefer more strength or more deformation or more damping.

Whether the material is man-made or processed or natural, I don't care. Whether it resembles collagen or bone or has ortho and meta bonds rather than para, I don't care neither.

Marc Schaefer, aka Enthalpy

[Enthalpy]

One polyoxazole is known as Zylon from Toyobo, period pictured here under. Do you see the aligned bonds in para positions at the hexagonal phenyl groups? This makes the magic fiber stiff and strong.

But for a music string or tennis racket, we need elasticity. So I suggest to try fibers with meta or even ortho bonds at one phenyl or an other where possible. The molecule rotates very freely around these bonds at the lone phenyl, which will increase the fiber's elongation. The fiber must still be stretched at the production.

The outer force tends to orient the molecule segments for maximum fiber length. The ambient temperature works against by orienting the segments randomly. Choosing the length of the segments defines what stress balances both to target the elastic behaviour.

This exists already at meta-aramides like Nomex but this fiber is too weak. Fortunately, a polyimidazole (picture) does it too and seems strong: the resin offers 160MPa tensile strength, stretched fibers should be much stronger.
  Zylon - Aramide - Polybenzimidazole at Wiki

A string stretched at 200kPa×m³/kg = 0.2N/tex propagates sound at 1.3×342m/s, surviving with margin the knots at the ends needs much more. I guess >10% elongation are needed too.

Sheep gut "catgut" achieves this and makes superior music and racket strings.

==========

While experimenting with such fibers, one should also check the elastocaloric effect under tension. The strain swing adjusts the temperature swing of a fiber, huge application advantage over a biphasic alloy.

Marc Schaefer, aka Enthalpy