My gut reaction is that starch will stain or spot the satin. Don't use it unless you test on a small piece. You could try zigzagging the raw edge.

I assume that you're doing the ruffled binding like a double-sided binding. Double sided binding has raw edges that you must turn under on both sides by pressing to the middle. If that's the case, it should be a 1/2" layered seam of Fabric A, doubled ruffle, Fabric B with the seam pressed open (Fabric A + one layer of ruffle going one direction and Fabric B + the other layer of ruffle going the opposite direction).

If your issue is that the fabric is fraying before you can get it enclosed, instead of burning encased raw edges, I'd do a pinked edge. Burned edges will add slightly more bulk and you already have 8 layers of fabric plus your batting in there so the last thing you want is any more bulk.

If the issue is that your entire satin binding is fraying after it's finished, in addition to the 1/2" seam, instead of finishing with a hand stitch or straight machine stitch, you might straight stitch the 1/2" on the back, flip & then machine stitch with a zig-zag or decorative stitch on the front. That's how I learned to attach satin binding to blankets; it is very secure and will last a long time without fraying even if you do nothing to the encased raw edges.

Gosh! So hard to explain without pictures. If I wasn't clear enough, let me know & I'll try to scan some illustrations in tomorrow night showing you what I mean.

If you use a decent polyester satin and cut straight, you shouldn't need to do anything to an edge that is going to be enclosed. I never had any trouble when I was making prom dresses and wedding dresses. Acetate satin is a different story, but I wouldn't use it for anything that was going to be laundered anyhow. I assume you use at least two rows of gathering threads (I like three) or gather by zigzagging over a thick thread and handle it as little as possible. Slipper satin is heavy for anything gathered and charmeuse is very light with little body. My recommendation would be the poly from JoAnn's - at least what we sold in the 90s.

The first thought that occurred to me was the fabric's wash-ability. Haven't dealt with these fabric since the 70s.

The "best" satin is one that washes and dries well. Some even tolerate relatively high heat.

In my experience, satin is notorious for fraying - I also would go with a wider seam - then overcast the finished seam with a zigzag stitch (serging would be my preference, but zigzag works - just does not look as nice - but it will be encased, so who will know?)

I find with any fabric if its going to fray I'll cut it with a pinking rotary blade. Keeps the fraying at bay till I'm done. If its apparel sewing I use the same blade but then finish the seams with serging. I love my pinking shear blade and keep an extra one on hand as I don't think these can be re-sharpened.

thank you so much everyone for your input! I always learn so much from this board.

Isn't there a satin-y blanket binding on the market? My mom made fleece blankets with this satin binding for all her grands when they were small.

Yes, but I haven't seen one with a ruffle so you'd still end up piecing together 3 pieces. They sell the satin/satin-like blanket binding in packages at JAF. I've used it for blankets. Granted, I haven't bought any in the last few years since I started making quilts, but the packs I used to buy were not serged. They were just cut & pressed (like bias tape or pre-packaged binding). With those, I would just clip it onto the raw edge of my blanket & do a single zig-zag stitch through all the layers (4 layers of satin binding plus the blanket material). I never had any issue with that stuff fraying except for when someone "loved" the blanket so much that it separated from the binding. As soon as it wasn't encased, the satin would quickly begin to fray like crazy. Were I to make one now, on my current machine, I'd do a triple stitch zig-zag to secure it better.