Biomedical Engineering Reference
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hexamethylene diisocyanate, and isophorone diisocyanate, and novolac resins from cardanol,
furfural, and p -aminobenzoic acid were copolymerized to yield thermally stable semi-IPNs.
It was shown that the stability of the networks increased with the increase of the novolac
resin content. The semi-IPNs prepared from castor oil-based PUs from iso-phorone as well
as diphenylmethane diisocyanates and the cardanol-based resins were reported to withstand
very high temperatures before decomposition.
The double bonds present on ricinoleic acid triglycerides are inactive to free-radical
polymerization. To overcome this, Wang and co-workers (2008) prepared a half-ester of
castor oil via maleation and copolymerized this monomer with styrene as reactive diluent
and a free radical initiator. Polymers with different castor oil/styrene ratio and curing
methods were prepared and optimized to yield biodegradable plastic foams with tuned
rigidity. In addition to being more cost effective and bio-based, the foam plastics had a
comparable compressive stress at 25% strain to commercial semi-rigid PU foams based on
fossil oil. It was found that higher styrene content resulted in higher compressive stress but
decreased biodegradation rate of the product.
11.3.1.3
Polymers from other oils
Although plant oil-based polymers are mainly derived from soybean and castor oil, an ever
increasing number of publications are devoted to the use of other plant oils, such as linseed
oil, tung oil, canola oil, high oleic sunflower oil, and many others.
Kundu and Larock (2005) copolymerized conjugated (87%) linseed oil, which is more
reactive towards free radical reactions, with styrene and divinyl benzene (3-5%) by gradual
heating. Soxhlet extractions of the products showed that only 35-85% of the oil could be
incorporated into the cross-linked thermosets. The dynamic mechanical analysis of these
polymers indicated that they were phase separated, as two separate T g s appeared; these
materials presented a soft rubbery phase with a sharp T g at -50 °C and a hard brittle plastic
phase with a broadened T g at 70-120 °C. These polymers were shown to be stable below
350 °C. Moreover, the same group (Henna et al ., 2007) used 100% conjugated linseed oil
and copolymerized it with acrylonitrile and DVB using the thermal initiator 2,2' -azobis
isobutyronitrile (AIBN). Much better oil incorporation (61-96%) was revealed by the
soxhlet extractions. Carter and co-workers (2008) investigated commercially available
epoxidized linseed oil (ELO) as an attractive alternative to poly(vinyl chloride) (PVC)
flooring products. Upon screening of the process parameters and extensive flooring
investigations, it was concluded that the ELO system was suitable as a flooring product with
compatible performance to commercial PVC-based flooring material.
Ring-opening metathesis was also applied to vegetable oil derivatives. A commercially
available monomer containing a five-membered cyclic mono-ene structure, Dilulin, is
produced via Diels-Alder reactions by subjecting linseed oil with cyclopentadiene to high
temperature and pressure. Henna and co-workers (2008) performed the ring-opening
metathesis-copolymerization of Dilulin with dicyclopentadiene with the aid of Grubbs
second generation catalyst. The resulting bio-based polymers offer unique and promising
properties, encouraging the replacement of petrochemical-based materials in some
applications, although sometimes fiber reinforcement or other fillers are needed to further
enhance the mechanical properties. Casado and co-workers (2009) utilized tung oil via
epoxidation-ring opening and increased hydroxyl functionality with triethanol amine
insertion, yielding a highly reactive tung oil-based polyol for PU synthesis. Incorporation of
10-15% pine wood flour to prepare PU composites led to a stronger material that not only
showed improved tensile strength, but also improved impact behavior, attributed to very
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