30. Furan-Based Adhesives

Macro-diisocyanates based on the reaction of an excess of 2,4-toluene diisocyanate
with different poly(dimethylsiloxane)diols of different lengths have been prepared
by Nikolaev et al. [71]. These macro-diisocyanates were reacted with 2 in stoichiometric
proportions and the resulting adduct (22) was cured with a commercial epoxy
resin in the presence of what was termed ‘‘poly(ethylene)-poly(amine)’’ at room tempcerature,
80, and 100 C. The mechanical and thermal properties of steel-to-steel
assemblies joined by these adhesives were better than those obtained using more
common binders.
Bowles et al. [72] studied the copolymerization of different methacrylates with NCOethyl
methacrylate to obtain dental adhesives. Furfuryl methacrylate (23) was among the
monomers tested. The main objective of this investigation was to establish a correlation
between the solubility parameter of the copolymers and their shear strength. It was
moreover shown that the setting time of the furan-based copolymer was very short compared
to that of aliphatic homologues, but its shear strength was relatively low.
Dopico et al. [73] prepared 5- and6-based furan resins which, after acid-catalyzed
polymerization, were subjected to epoxidation with thiokol in different proportions.
In a second series of experiments, 6–7% of 2 was added to the epoxidized resins. They
showed that all these resins presented a lower flexure resistance compared to unmodified
totally furanic binder. Moreover, the addition of 2 was found to induce negative effects on
the mechanical properties of metal-to-metal assemblies.
Furan resins have also been used as binders in grinding wheels [4]. In this field,
5–20% of phenolic resin in combination with 1 as a special wetting agent is added to
the abrasive grains and the resulting wheels thereafter coated onto the surfaces of different
substrates. Paper, cloth as well as composites based on glass fiber reinforced films, have
been used as grinding wheel supports. Acid-catalyzed poly2 has also been used in the
aircraft industry as a low-temperature setting adhesive to bond wood and plastic parts.
This adhesive was found to be suitable for assemblies subjected to warping and other
deformations at high temperatures [12].
X. CONCLUSIONS AND SUMMARY
From the above survey, it appears that the industrial use of furanic monomers such as
furfuryl alcohol and furfural, i.e., chemicals based on renewable resources, as binders
in foundry molds is highly successful. Similar furan-based resins can also be used as
efficient adhesives in wood–particle composites and thus are interesting alternatives to
petroleum-based counterparts. The fact that the substitution of formaldehyde by furfural
has not yet met with a reasonable industrial success probably stems from the
higher cost of the furan aldehyde. The increasing pressure on the reduction of formaldehyde
emission and the renewable character of furfural should play in its favor in
the near future.
This chapter has dealt with the use of furanic derivatives as adhesives and binders. It
has been shown that the main industrial applications concern the use of furfural and
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