Chemistry Reference
In-Depth Information
ternary blend. The accumulation of castor oil on starch greatly improved the
toughness and impact strength of PLA-starch blends.
Klinger et al.
117
used castor oil as an additive for polystyrene (PS). The aim
was to use castor oil as a desirable alternative to phathalates, which are
arguably the most commonly utilized plasticizers, and are suspected to be
hazardous to human health. Tensile strength measurements indicated that
the additive renders PS stronger at low loading, and plasticizes PS at high
loadings. This is due to the fact that at low loading, the castor-oil-derived
additive acted as an anti-plasticizer, leading to an increase in the tensile
strength of the polymer, while at higher loadings, it acted as a plasticizer so
the tensile strength of the polymer decreased with an increase in the amount
of additive.
Silva et al.
118
prepared a solvent-less castor-oil-based PU adhesive. Its foam
joints showed peeling strength values 75% higher than those of a solvent-
based commercial adhesive. Its wood joints showed lap shear strength val-
ues 20% higher than those of a commercial solvent-based adhesive used for
wood. Adhesives free of volatile organic compounds are less toxic and avoid
environmental pollution, therefore alternative solvent-less adhesives would
be an important contribution to more sustainable products and would
present less risk to human health and to the environment from exposure to
chemicals. The NCO groups of diisocyanate compounds react with the -OH
groups of castor oil and become part of the network therefore they would not
vaporize out of the adhesive. PU adhesives produced using only castor oil
and TDI with or without catalysts are alternative solvent-free adhesives to the
currently used commercial adhesives containing solvents. An increase in the
NCO/OH molar ratio led to a decrease in the adhesive density because of
bubble formation due to the release of CO
2
during the curing reaction, and
an increase in the T
g
and hardness values due to a higher adhesive cross-
linking level.
Oprea
119
treated castor oil as a trifunctional cross-linker for the synthesis
of PU from poly(1,4-butane diol) with aliphatic 1,6-hexamethylene diiso-
cyanate. This resulted in a series of cross-linked PU elastomers with different
hard segment structures. The increased hard segment molar ratio and
dangling chains present in the triglyceride structures, which acted as plas-
ticizers, increased T
g
by 13 1C for PU with an increased content of castor oil.
The PUs displayed relatively low T
g
values of
70 to
57 1C, a tensile
strength of maximum 9 MPa and elongation-at-break of 630%.
Castor oil is also useful in drug-delivery systems.
120
It was used to develop
a novel microsphere with Pluronic F-68, in order to study the controlled
release of 5-fluorouracil (5-FU) using a solvent-evaporation method. The
insertion of double bonds into castor oil gives versatile chemical resistance,
hardness, elongation and tensile strength properties and highly compatible
poly(ether-urethane)s (PEUs). The drug release mainly depends on the
amount of Pluronic present in the matrix, it acts as hydrophilic filler in the
formulations, which helps to control the swelling and release of hydro-
phobic drugs from the microspheres. The formation and dissociation of
