Many modern plastics used in a variety of industries are formulated specifically for their resistance to harsh chemical and environmental conditions. As a result, these substrates also tend to be difficult to chemically bond. Bonding, however, remains the preferred joining method particularly when dissimilar substrates are involved and/or solvent welding or mechanical fastening is not desired. Polyolefin plastics are the most common type of hard to bond plastics because of their low surface energy. Examples of polyolefin plastics are polypropylene and polyethylene.