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Polyurethane adhesive is a type of glue used in bookbinding and woodworking. Polyurethane is a class of polymers that are created from a chain of organic units held together by urethane links. There is a wide range of polyurethane adhesive products available. Different chemical combinations result in different properties. The chemical composition can be alerted to produce different levels of stiffness, density and hardness.
The main advantage of a polyurethane adhesive is that it is water resistant. This property makes it the glue of choice for binders and book repair companies. The glue has a very low viscosity level, cures in seconds and is flexible at room temperature conditions. When used in terms of adhesives, cure time is the time it takes before the adhesive sticks the two items together.
As an adhesive, polyurethane was first developed in 1985. The first version had very specific properties. The adhesive was made available in 1988 and had a high viscosity, low level of initial fastness, but had a three-day hold period before curing.
In 1996, the second generation of polyurethane adhesives was developed. Cure time has been reduced to less than three days while maintaining low levels of initial fastness and high viscosity. Additional work was done to reduce curing time while retaining the characteristics that made the adhesive useful.
The next major improvement came in 2000. In this phase, the healing time was reduced to a maximum of 16 hours and a minimum of six hours. The fastness has been improved and the viscosity reduced to make it more commercially viable.
The fourth generation was made available in 2007. In this version, the viscosity is much lower, the solidity remains the same as in 2000, but the cure time is only a few seconds. This shift is crucial to both commercial success and the long-term usefulness of the product.
In North America, polyurethane adhesive is sold under the brand name Gorilla Glue™ or Excel™. Sales of polyurethane adhesives expanded outside the specialized bookbinding industry. These products can now be found at any hardware store for general consumer use.