Environmental Engineering Reference
In-Depth Information
5.4.6
Terpene Conclusion
Currently, the main industrial use of polyterpene resins is to impart tack in adhe-
sive components, provide good gloss, moisture resistance, and flexibility in wax
coatings, and to provide viscosity and density controls in casting wax [117]. With
a supply of more than 10
5
ton per year and a growing number of synthetic routes
to higher molecular polymers, growing applications for terpene-based polymers
can be expected. With the ability to incorporate biodegradable ester linkages
through polycondensation reactions or ring-opening polymerizations, these poly-
mers become good candidates for biomedical applications [140].
5.5 Rosin
Rosin is the non-volatile residue left after steam distillation of pine resin, where
turpentine is the volatile fraction produced during this process (Section 5.4).
Rosin is a mixture of resin acids, which are typically tricyclic carboxylic acids
with the generic formula C
19
H
29
COOH [141]. The use of rosin to take advantage
of its hydrophobic and binding properties is at least as old as the production of
wooden ships, and there are several excellent reviews on the topic [141-144]. This
section introduces the common production methods and basic chemical structure
of rosin, discuss the role of rosin in epoxy resins and in thermosetting polymers,
and concludes with recent reports of incorporating rosin in thermoplastics.
5.5.1
Production and Chemistry of Rosin
Rosin is the residue left after the steam distillation of pine resin. Rosin is classi-
fied by the technique used to isolate the pine resin; the two main classes are gum
pine rosin, where pine resin is acquired by tapping living trees, and tall oil rosin,
also known as sulfate rosin, where pine resin is obtained during the Kraft pulping
of pine wood [141]. Rosin is composed of a mixture of resin acids (90-95%) and
neutral compounds [142]. The resin acid composition of rosin is dependent on the
pine resin production, the tree species, and geographic location, along with other
factors [141, 144]. Several common resin acids are shown in Figure 5.4; it should
be noted that for the purpose of our discussion, no distinction will be made
between stereoisomers [118, 144]. As illustrated in Figure 5.4 many acids are
isomers of each other, where the location of the double bonds distinguishes each
type. The acid species can be categorized as abietic-type (including abietic,
neoabietic, palustric, and levopimaric) and pimaric-type (including pimaric, isop-
imaric, and sandaracopimaric) [141, 144]. There are two lesser isomeric groups
that are outside the scope of this treatment, isoprimarane-type and labdane-type
rosin acids [141]. Abietic-type acids possess chemically useful conjugated
double bonds, while pimaric-type acids do not. As a monomeric mixture, rosin
is a semi-transparent solid with melting temperatures dependent on the acid
