Page 370 - Handbook of Adhesives and Sealants

326 Chapter Nine

the properties that need to be obtained. The following section offers a
brief description of how certain additives and formulation parameters
are used to control the characteristics of adhesive systems.

9.3 Adhesive Formulation

The amount of published material to guide the prospective adhesive
formulator is fairly sparse. A few books 5–8 plus scattered information
in other texts devoted to adhesives and sealants offer information on
the topic. Much of the available information is by way of adhesive
formulation recipes with a description of the resulting properties.
There is little basic information to train the adhesive formulators or
to guide their choice of materials relative to the desired end-
properties.
Valuable information can be gained from literature provided by raw
material suppliers, who often develop nonproprietary formulations
employing their materials. In addition, similar information can be ob-
tained by attending conferences and reading journals and periodicals.
The following description of adhesive formulation technology is only
intended to give the reader a general understanding of the opportu-
nities that are available to the willing adhesive formulator. The num-
ber of possibilities and the occasions for innovation seem to be endless.
However, formulation skills are honed through education and experi-
ence (with major emphasis on experience). The foundation of this art
comes from knowing which materials to choose based on their com-
patibility and the end-requirements desired. Knowledge of how to in-
corporate those materials together into a practical, workable formu-
lation is also required.
Modern adhesives are very complex formulations that rely on their
material composition and curing characteristics to provide a practical
bond. Raw, unformulated polymeric resins, used with the appropriate
hardening system, may provide a satisfactory adhesive without mod-
ification, but this is very unusual. The application of pure, unmodified
polymeric resins as adhesives is complicated by the tendency of the
resin to flow excessively, particularly during cure. This results in ir-
regularities in the glue line and starved areas on the bonding surface.
The temperature range of pure resins is also limited; the thermal ex-
pansion coefficient is high; the viscosity may not be sufficiently low to
provide the required wetting action; shrinkage rates may be too high
for many applications; and peel strengths are poor. Through formu-
lation and modification with other materials, these characteristics
may be improved selectively, although often only at the sake of other