Is there a way to glue a knot in thread?

I picked up a mobile at a garage sale. In the process of untangling the
lines and cleaning it up for my grandkids, I discovered that the knots
at the ends of the threads keep coming undone. I think it's because the
line is very slick. It's much thicker than thread, but thinner than most
string. It's about the thickness of fishing line, but made of something
that looks like nylon.

In any case, it won't stay tied. Where the other end of the line is tied
to the crossbars, it looks like they used some sort of glue. The line is
very hard and rigid. Those knots do not come untied.

Can I buy something that will cement the knots so they can't come
untied?
.

Relevant Pages