Has there been any scientific tests on the shelf life of nylon and fluorocarbon monofilament lines. What do you know about it?

Store line out of the sun in moderate heat. Shelf life is indefinite.

Heat and light are the two things you want to avoid when storing line. I store my line in a styrofoam ice chest and put it in a cabinet in the garage. I haven’t had any problems with line that’s over 15 years old

Came say what @looking45 pointed. UV and heat reduces line durability.

 

I stored them inside a closet, and I just put a spool of fluoro from 5, 6 years ago on a new reel. Everything is fine.  One of my fishing buddies who has a PhD in Material Science told me that among those three line materials, mono is most prone to deterioration with sunline and humidity. That is the most scientific proof I have. 

All I use is monofilament line. I haven't purchased any line since resigning from BPS in 2017 or 18, can't remember which. I keep my spool's stored in my bedroom closet, dark and cool. 

I can tell you line in a hot vehicle all the time makes it weak. My buddy and I ran the same line test everything. Me would constantly snap off.  He stopped keeping his rods in his vehicle all the time and it stopped.

I've had issues with old nylon on reels, but only after a year or so (likely from water absorption and UV exposure). That said, most of my mainlines are braid

 

I've read that fluorocarbon is UV transparent and does not absorb water. It's basically pure PFAS--they call them "forever chemicals" for a reason. Should have much longer shelf/reel life.

I tie an overhand knot in my line and try to break it (under 10 lb test).  This is with mono or fluorocarbon.  If it breaks I'll take 10' off and try again.  If it breaks I'll replace all of it.