Environmental Engineering Reference
In-Depth Information
rosin utilizes diols to couple two abietic-type acids which are then functionalized
with a Diels-Alder addition of maleic anhydride [118, 147, 148, 151]. This is a
promising route, because changing the length of the coupling diol chain provides
the opportunity to regulate the flexibility of the resulting thermoset [148].
The production of epoxy resin binders from rosin typically follows a Diels-
Alder reaction with acrylic acid or maleic anhydride, again targeting the levopi-
maric acid isomer, or a reaction with formaldehyde [141, 145, 152, 153]. The
modified rosin is then further functionalized with a base-catalyzed esterification
with epichlorohydrin to produce a functional analog to fossil-based epoxies
[145, 153]. A system studied by Atta
et al.
exhibited good mechanical properties
and high chemical and solvent resistance, suggesting the potential for rosin-based
epoxies for a wide range of protective coating applications [145, 153].
5.5.3
Polyesters and Polyurethanes from Rosin
The ability to produce polyesters and polyurethanes from rosin has been demon-
strated [154-156]. Jin
et al.
used maleic-modified rosin to produce two kinds of
rosin-based polyester polyols by esterification of the anhydride species with either
diethylene glycol or ethylene glycol [154]. The resulting polyols were reacted
with a commercial isocyanate and compared with an industrially available poly-
ester polyol. It was shown that the foaming properties of the rosin-based polyols
were comparable to its fossil-based counterparts, and the thermal decomposition
temperature of the rosin-based polyols was slightly higher than that of the fossil-
based polyol [154]. Unfortunately, little work has followed up on the early study,
leaving questions about the mechanical properties of the foam.
Unsaturated polyesters were produced by Atta
et al.
using acrylic-acid-substituted
rosin, maleic anhydride, and propylene or ethylene glycol [156]. The resulting
polymers had only moderate molecular weight (5 kDa), but could be cross-linked
[156]. Combining the unsaturated polyesters with styrene and curing the system
led to materials with good mechanical properties and good resistance to both
acid and alkali environments [156]. This work illustrates the viability of using
modified rosin for a number of membrane applications.
The above examples illustrate that rosin can be functionalized and reacted using
polycondensation methods. Although more exhaustive reviews of the versatility of
rosin are available, this industrially available platform molecule has received rela-
tively little attention, indicating a promising area for future research [118, 141, 157].
5.5.4 Thermoplastic Polymers from Rosin: Controlled
Radical Techniques
Polymerization of thermoplastics from rosin has typically followed condensa-
tion routes, achieving only low to moderate molecular weights. Recent work by
the Tang group at the University of South Carolina, Columbia, SC, US explored
