A friend of mine recently soaked his Tallis Katan in water and Tide (regular, non-bleach) detergent for a while, and after he took it out, the tzitzis strings (which were of the expensive hand-made "Menupatz Lishma" variety) simply crumbled in his hands. Has anybody out there experienced anything similar, or can someone offer an explanation as to what went wrong?
I am not a chemist but with the information I do have this could be why your friend's tzitzis crumbled:
If you look at the ingredients of Tide and other similar laundry detegents you will find both surfactants and enzymes. Surfactants decrease the surface tension of the material as well as the surface tension between oil and water. The enzymes, such as protease, speed up chemical reactions.
If you soak wool in a high enough concentration of detergent for a long enough period of time, it could very well allow the surfactants to remove the lanolin (natural occurring oil in wool) and reduce the surface tension of the wool itself enough to allow the enzymes, such as protease to break down the wool itself (which is a protein). The result is that when he removed them from the soaking mixture, the tzitzis simply crumbled.
If it was a cotton beged then it is easy to understand why the beged did not disintegrate. The detergent is not formulated with chemicals that are as harmful to cotton. If the beged was made from wool as well, it could be that the weave and the tighter winding of the woven threads protected the wool from absorbing the detergent. The tzitzis are made from four thicker, not so tightly wound strings that are then wound together, doubled, and wound together again (kaful shemonah). They will absorb and disintegrate much faster than the wool of the beged.
If one must wash wool it is always better to use a wool detergent such as Woolite in order to avoid such mishaps.
There you have it, and if your friend does not like it you can just tell him "Sorry! That is just the way the tzitza crumbles!"
The best I can offer as an explanation to what went wrong, is some kind of chemical reaction. At some point the tzitzit must have come in contact with some sort of chemical agent that either was activated by the water and/or soap, or reacted to it violently. Disintegration of a natural fiber takes a pretty strong chemical agent to accomplish. Did your friend ever have any kind of skin reaction to them from handling them and such?