Refixing screws in 'stripped' polypropolene chairs?

Helloooooooooo.

Local primary school has lots of polypropylene-body with steel-frame chairs. The screws wot fix the two together tend to loosen and finally strip the thread in the pp side.

I'm guessing 'Loktite' would help to prevent them loosening in the first place (will this work with a slippery plastic like PP?), but I'm also looking for the best way of re-fixing the stripped ones.

I know there are resin-type products out there that could be injected into the stripped holes, but has anybody here actually tried any and found something that works?

Ta much.