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Schatzberg, Eric, 1956- / Wings of wood, wings of metal : culture and technical choice in American airplane materials, 1914-1945
(c1999)

9. Neglected alternative ii: synthetic resin adhesives,   pp. [175]-191


Page 176

CHAPTER NINE
Resin Adhesives and the Renaissance of Wood Engineering
Resin adhesives were a direct application of the material that launched the
plastic age-Bakelite, the first synthetic polymer plastic. Bakelite, invented
in 1907 by the Belgian-born American chemist Leo Baekeland, was the trade
name for a class of thermosetting plastics made from phenol-formaldehyde
resins. These resins remained soft until molded under heat and pressure,
when they formed a hard, durable, waterproof, fire-resistant material.
Through the efforts of Leo Baekeland, Bakelite soon became widely used in
the electrical and automobile industries. During the interwar years, pheno-
lic plastics became common in a wide variety of consumer products.2
As a structural material, pure Bakelite had its limitations. Although Bake-
lite was reasonably strong in compression, it was also quite brittle and rela-
tively weak in tension. With the addition of reinforcing materials such as
cotton fabric or wood pulp, the strength properties of Bakelite improved
dramatically. By varying the number and orientation of reinforcing fibers
(known as "fillers"), engineers could design materials with strength charac-
teristics and densities suited to particular applications.3
Bakelite also proved viable as a wood adhesive, which was to have tre-
mendous significance for airplane structures. Unlike casein or albumin
glues, Bakelite formed a water-resistant, durable bond, immune to mold and
fungi. It did not take Leo Baekeland long to discover the affinity of Bakelite
for wood; in fact, he had been searching for an improved wood preservative
when he first synthesized Bakelite.4 In 1912 Baekeland patented a method
for using phenolic resin as a plywood adhesive, but his method of applying
the resin proved too expensive for commercial use. In 1919 a Westinghouse
employee, John R. McClain, patented a method for applying the resin in the
form of a dry film, eliminating the problems associated with the solvents. In
McClain's process, the film consisted of paper or fabric impregnated with a
carefully controlled amount of phenolic resin. These sheets were then in-
serted between individual layers of veneer, and the assembled layers were
compressed by a heated press, which transformed the resin into its hard-
ened state.5
At first, American plywood manufacturers showed little interest in phe-
nolic resins, but by the early 1930s the new adhesives were creating quite a
stir in the plywood industry Commercial production of phenolic glue films
started first in Germany, where the Essen firm of chemist Thomas E. Gold-
schmidt introduced the Tego film in 1926. American plywood made with
Tego film became available in 1930.6 Shortly thereafter American firms de-
veloped new methods using dry resin powders and colloidal suspensions,
and by 1933 American manufacturers were producing resin plywood using
all three methods: film, dry powder, and colloid.'


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