Polyurethane Adhesives for Modern Structural Wood Construction

Joint research project by Bayer MaterialScience and the University of Stuttgart.

From left: Dr. Heinz-Werner Lucas, head of Business Development Prepolymers at the Coatings, Adhesives, Sealants Business Unit of Bayer MaterialScience; Dr. Simon Aicher, head of the Material Testing Institute (MPA) of the University of Stuttgart; and Walter Stampfli, general manager of Purbond AG, want to work together to obtain even more reliable test results for the long-term stability of polyurethane adhesives in structural wood construction.

The use of wood in the construction industry is currently experiencing a renaissance. New joining methods and construction principles, as well as the discovery of the classic material for modern architectural solutions, have opened up new possibilities for building with wood. No longer relegated to home construction, wood is now used for office and administrative buildings, schools, multi-family dwellings, bridges, theaters, and even transmission towers. This trend is being fostered by the lumber industry’s evolution from a pure handcraft to the industrial production of semi-finished goods that can be joined quickly and precisely on-site to form larger elements, making the construction of large and architecturally interesting structures fast and economical.

The current success of load-bearing wood construction wouldn’t exist without high-performance adhesives, however. Modern one-component polyurethane systems offer a number of decisive advantages for this application: they are applied directly from the drum, and there is no need to mix components prior to applying the adhesive, nor are there any pot lives to be considered. Odorless and formaldehyde- and solvent-free, the adhesives are also environmentally compatible. The production process is very economical, requiring less adhesive than other systems and allowing parts to be stably and permanently joined after a short press time.

Before they are introduced to the market, adhesives for engineered wood must be tested and certified. In Germany, the Materials Testing Institute (MPA) at the University of Stuttgart is responsible for testing and assessment. The MPA uses test methods derived from previous work with phenol-resorcinol and melamine-urea resins to determine adhesive strength, application properties and long-term durability of adhesives. The first one-component polyurethane adhesive certified in Germany for the manufacture of load-bearing wood components received general regulatory approval in 1994.

Purbond AG, Sempach Station, Switzerland, is the market and technology leader for one-component polyurethane (PU) adhesives for the manufacture of load-bearing wood elements. Bayer MaterialScience is the leading supplier of the isocyanate prepolymers used as raw materials for this application.

According to the MPA, Purbond and Bayer MaterialScience, the methods underpinning current standards do not give sufficient consideration to the outstanding properties of polyurethane adhesives. To obtain even more reliable test results and ensure the continued market success of polyurethane systems, the MPA and Bayer MaterialScience plan to develop test methods, with the support of Purbond, to improve predictions of long-term behavior. This work will incorporate the latest scientific findings, with the results of the fundamental and application-oriented projects to be used to improve existing standards.

About Bayer MaterialScience

With 2006 sales of $10.2 billion (continuing operations), Bayer MaterialScience is among the world’s largest polymer companies. Business activities are focused on the manufacture of high-tech polymer materials and the development of innovative solutions for products used in many areas of daily life. The main segments served are the automotive, electrical and electronics, construction and the sports and leisure industries. At the end of 2006, Bayer MaterialScience had 30 production sites and employed approximately 14,900 people around the globe. Bayer MaterialScience is a Bayer Group company.

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