"Despite their widespread usefulness, "low energy" plastics have a quality that can make them hard to work with - they are difficult to seal or bond using commonly available sealant adhesives. Cyanoacrylate, epoxy, polyurethane, silicone (RTV for example), and most acrylic adhesives do not stick to polypropylene and polyethylene."
"Scotch-WeldTM DP-8005 is a solvent-free, two-part, acrylic-based, structural plastic adhesive designed to structurally bond polyolefins to themselves and to many other substrates. It uses a one-step process that requires no pre-treatment of the substrates other than removing dirt and oil. Like Polyolefins themselves, DP-8005 provides very good chemical resistance. Similar to most polypropylenes and polyethylenes, maximum continuous service temperature for DP-8005 should be kept under about 212ºF (100ºC)."
There are many whitepapers from adhesives companies on bonding these types of plastics.
Hot Air Welding
"Hot Air Welding - the way LDPE and HDPE tanks and trays are built is by hot air welding the pieces together. Similar to metal welding, but at lower temperatures, a welding rod is melted into the sheet joint to make a strong bond. The materials must be the same - you cannot effectively join dis-similar materials."
Hot-Melt Adhesives (Hot Glue)
"Hot melt adhesives can work well, and are available for hobbyist glue guns. Bostik 6384, 6390 specifically specify PE in their description."
"Ethylene-vinyl acetate (EVA) copolymers, low-performance, the low-cost and most common material for the glue sticks
The composition of the copolymer influences its properties; increased content of ethylene promotes adhesion to nonpolar substrates such as polyethylene, while increased content of vinyl acetate promotes adhesion to polar substrates such as paper."
Many sources indicate that silicone rubber is highly ozone resistant:
This could potentially be useful for sealing and joining surfaces in an ozone reactor.
How long does it take silicone to cure, and what is its chemistry?
Wikipedia: Silicone Rubber "Acetoxy tin condensation is one of the oldest cure chemistries used for curing silicone rubber, and is the one used in household bathroom caulk. The smell of vinegar in the form of acetic acid is the usual indicator that the reaction is incomplete."
3M Scotch-Weld DP8005
Weld-On 4 Acrylic Adhesive
SCIGRIP 4 10308 Acrylic Solvent Cement
SCIGRIP 3 10799 Acrylic Solvent Cement
IPS Weld-On 3 Acrylic Plastic Cement
J-B Weld 50133 Plastic Bonder