Series editors' preface - Wood Tools

4
Plastics and polymers, coatings and
binding media, adhesives and
consolidants
4.1 Plastics and polymers
The word ‘plastic’, from the Greek word for
mouldable, originally described pliable materials
that could be shaped by hand or tool pressure
as distinguished from ‘glyptik’ shaping
processes relying on stock removal by carving,
engraving or grinding. The term aptly describes
all of the modern materials, commonly called
plastics, which are all soft and mouldable at
some point in their manufacture. It also
describes the natural materials that are their
technological and functional forbears, such as
horn, rawhide, turtle shell, natural rubber and
gutta percha. The general historical progression
of the use of these materials furniture is
from the natural materials through the semisynthetic
to the entirely synthetic modern plastics.
The many uses of plastics in furniture
include structural members, veneers, inlays,
knobs, fittings and decorative components,
upholstery foams and textiles, adhesives and
coatings. They were used from the very beginning
to copy, often slavishly, more costly and
rare natural materials just as the cheaper and
reproducible processes of moulding were used
to duplicate the qualities of more laborious
carving and polishing. However, plastics, and
the technologies of moulding, extrusion, lamination
and hot bending, have certainly exerted
an influence on design and public taste.
Twentieth-century furniture composed entirely
of wood often owes a stylistic debt to the
forms of manufactured plastics.
Plastic materials cover a wide range of chemical
types, exhibit huge variation in physical,
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optical and dielectric properties and are fabricated
in a wide range of forms for different
uses. Only a brief review from the perspective
of furniture applications can be attempted
here. For a more extensive introduction see
Young (1991).
4.1.1 Chemical structure
In all cases, plastic materials consist of a mass
of very large molecules. Although some polymeric
materials have a structure which is heterogeneous
and complex, most plastics consist
of long chains of repeating small molecular
units, or monomers, covalently bonded
together. In the bulk material, polymer chains
are mechanically intertwined and may also be
chemically bonded together or crosslinked at
various points along their lengths to form a
network structure. These materials are of high
molecular weight and hence are referred to as
high polymers or macromolecules.
Polymer chains may be linear or branched
depending on the nature of the monomer and
the polymerization reaction. In homo-polymers,
the monomer units are all of one chemical
type. Hydrocarbon polymers such as polyethylene
are based on carbon and hydrogen
alone. Other carbon chain polymers may have
atoms of other elements such as chlorine incorporated
into the polymer structure. The
replacement of carbon atoms in the backbone
itself by atoms of other elements produces heterochain
polymers. In co-polymers, the
monomer units are of two or more types.
There are three principal types of arrangement
of the units in co-polymers, alternating, ran-