Series editors' preface - Wood Tools

Plastics and polymers, coatings and binding media, adhesives and consolidants 183
Figure 4.15(h) (i) Regalrez: the Regalrez series are hydrogenated oligomers of styrene (vinyl benzene, ethenyl
benzene) and -methyl styrene (isopropyl benzene or 1-methyl-1-phenyl ethylene). An oligomer is a polymer that
has relatively few monomer units (usually an upper limit of about ten units). Hydrogenation is a chemical reaction
involving the addition of hydrogen across a double or triple bond, to produce a singe or double bond respectively.
In the context of resins such as Regalrez, the removal of double bonds produces a more chemically stable varnish.
(ii) Proposed structure of Laropal A81 (Arslanog˘ lu and Learner, 2001)
an adhesive in paper conservation. These
materials generally have very low strength and
relatively poor adhesion. However, methyl cellulose
(e.g. Methocel A by Dow Corning) has
been used as a consolidant for waterlogged
wood (Rosenquist, 1959) and for basketry
(Thomsen, 1981). Hydroxy propyl cellulose
(e.g. Klucel G and Klucel J by Hercules) has
been used as a 2% solution in ethanol for the
consolidation of pigment where non-aqueous
treatment and absence of darkening are
required (Berger, 1976; Hofenk de Graaf,
1981). For further information see Horie
(1987).
Other thermoplastic materials
Several other industrially manufactured low
molecular weight (LMW) resins have been
investigated for their potential use in picture varnishes
(de la Rie and McGlinchey, 1990). Three
synthetic LMW resins that are claimed to be considerably
more stable than natural resins and the
ketone resins are reviewed by de la Rie (1993).
These include the hydrogenated hydrocarbon
resin Regalrez 1094 (Hercules) and an aldehyde
resin produced by BASF. Two synthetic low
molecular weight resins that have found application
in furniture conservation are Regalrez
1094 and 1126 and Laropal A81 (Figure 4.15h).
Thermosetting resins
These generally consist of two chemical components
which react to form highly crosslinked
polymers. The reaction frequently proceeds
without the formation of elimination (condensation
reaction) products and usually therefore
causes relatively little shrinkage, so they generally
have fair to excellent gap-filling capabilities
when used as adhesives. The final
polymer is mostly quite chemically inert making
these materials water and solvent resistant.
Their rigid crosslinked nature gives them high
hardness and internal strength, high resistance
to creep and excellent machinability.
Blood and milk protein adhesives must be
regarded as thermosets because they harden
by irreversible chemical reaction. Blood glues
were extensively used in plywood manufacture
during the middle of this century but are little
used today. A variety of thermosetting resins
became available as a result of advances in
polymer chemistry. Phenol-formaldehyde (phenolic)
adhesives were produced in film form
for hot pressing soon after 1910, and in liquid
form in 1935. Urea-formaldehyde adhesives
were introduced around 1937, epoxies during
the 1940s and resorcinol-formaldehyde in 1943.
These are the primary adhesives used in
industrial wood bonding applications such as