Contrary to what some will claim, there is NO adhesive that is
considered suitable to use with the type plastics the preforms are
made out of. You can slather on silicone, put liner patches on them
and a heap of other things.......but its certainly nothing I would
ever, ever trust. Best bet is use a hot air plastics welder and do the
repair right.

Polyethelyene? Or something else? Anyway, yup, totally right. Some
kinds of plastics simply cannot be glued reliably. I got my plastic
welder from Ebay, $50 chinese job. Works okay for small jobs. Need
a compressor of course.

C//