ABSTRACT
Adhesives may come from either natural or synthetic sources. Some modern adhesives are extremely strong and are becoming increasingly important in modern construction and industry. Native Americans in what is the eastern United States used a mixture of spruce gum and fat as an adhesive and as a caulk to waterproof seams in their birchbark canoes. The commercial development of polyurethanes (PURs) began initially in Germany in the end of the 1930s, with the production of rigid foams, adhesive, and coatings. PUR pressure-sensitive adhesives (PSAs) are less well known because their applications thus far have been limited to low-tack and low-peel adhesive protective films. PURs are a class of adhesive raw materials that have developed a reputation for reliability and high performance in many applications, including the footwear industry, furniture assembly, and the automotive industry. The balance between cohesive and adhesive strengths within the cross-linked coatings is very important for the performance of ultraviolet PSA.
