Polyethylene and polypropylene plastics are used in a number of packaging, shipping and production products, including plumbing fittings, bottles and automotive parts. These plastics are designed to take a beating and are generally chemically resistant. According to the Ridout Plastics Company, such chemically resistant materials cannot be glued, since the chemicals in the glue have no effect on the plastics. However, some model suppliers, hardware and home improvement stores or Internet retailers sell liquid plastic adhesive and primer that may be able to bond these plastics.
Flatten the two surfaces that will be glued together. Scrape away any bumps or protrusions. Wipe the area clean with a damp washrag. For the adhesive to be effective, the two surfaces must be completely level and clean.
Apply a layer of the plastic adhesive primer to each surface. Allow the primer to sit on the surface for 60 seconds so that it becomes stickier as it dries.
Apply a layer of the plastic adhesive to each surface. Immediately press the two surfaces together and hold them tightly for at least 30 seconds. If necessary, use clamps or vices to hold the pieces tightly together.
Scrape away excess glue that seeps out of the seam between the two surfaces. If it is still wet, wipe it away with a rag or towel; if it dries quickly, scrape it away with a utility knife or scraper.
Allow the adhesive to dry overnight before putting any pressure on the joint or expecting the glue to hold effectively.
Some glue products contain both primer and adhesive in one package. If you have trouble finding these specialized products, consult an expert at a hardware or home improvement store.
Chemically resistant plastics like polyethylene and polypropylene are not meant to be glued. Adhesives that are not specially made for these types of plastic will not effectively glue the plastics. Any glue that you use may have only limited-time effects.