Methyl-Ethyl-Ketone, otherwise known as MEK, is a highly poisonous, and environmentally toxic liquid. One of the most toxic elements in PVC cement, MEK should not be allowed to touch a person's skin, eyes or be inhaled for a prolonged period. MEK is available commercially, usually sold with paint solvents and commercial paint strippers. This product does not break down quickly in the environment and remains toxic for prolonged periods of time.
Another dangerous chemical, acetone is a swiftly evaporating solvent which is used as a carrier in many commercial chemicals. Acetone is included in model glues, some paints and solvents which remove adhesive residue from masking tape or duct tape. Acetone is also highly flammable. For this reason, PVC cement should be used in areas which are well ventilated, and where any open flames or pilot lights have been extinguished.
PVC cements work so well because they melt the hard plastic surface of the PVC pipe and and thus cold-weld the two surfaces together. The carriers and solvents melt the surface of the PVC plastic pipe and fittings. The PVC resins in the glue mix with the melted surfaces to form a complete, water-tight bond as the surfaces meld. After the solvent is allowed to cure, the joint acts as if it had been manufactured as one part.
Other Chemical Carriers
Tetrahydrofuran (THF) and Cyclohexanone are two more carriers that keep the PVC resins in suspension. These chemicals do not evaporate as quickly as MEK and Acetone. They provide the adhesive with the ability to melt the surfaces of the pipe and fittings and slowly reform into a single bonded surface. THF is a liquid polymer which acts in conjunction with PVC resins. Cyclohexanone is in the same chemical family as MEK, and works in conjunction with this component to dissolve the PVC surface and form the new bonds.