Chris Green wrote:

It's very difficult stuff to glue. You can get glue to do it in
fairly small quantities, they tend to have an 'activator' that you
have to paint the surface with before gluing.

Loctite sell a "super plastics" adhesive, they do mention polypropylene,
it's just a thick superglue with an activator, I've had variable results
from it, but it is cheaper than the dedicated LSE adhesives. I don't
think there's anything special about the Loctite version compared to CA
mitre adhesive and activator which tend to come in larger pack sizes e.g.

https://toolstation.com/shop/t/p47409