Chemistry Reference
In-Depth Information
ecient a-cleavage process of Type I photo-initiators. This UV-curable resin
can be used for wood coating, as it contains sucient cross-link density to
withstand the solvent stress. Moreover, the polymer chains are flexible
enough against scratches and exhibit good adhesion to wood substrates.
The influence of acrylate-reactive diluents on the photo-curing rate was
investigated in detail, as well as the relationship between the number of
acrylate functional groups on the oil backbone and the hardness of the
resulting materials.
55,70,71
For example, the Patel group has prepared
a novel binder system for UV-curing coatings based on tobacco seed
(Nicotiana rustica)oilderivatives.
71
The UV-curing films of tobacco seed oil
show good thermal stability at 100 1C, and the results of flexibility and
adhesion tests revealed excellent performance. Higher functionalities of
polyols, aromatic-type isocyanates, and lower oil ratios lead to poor ad-
hesion and flexibility performance. Also, the aromatic nature of the
isocyanate moiety further enhances the film hardness and toughness.
Thus, the experimental sets based on higher polyols, higher functionality
acrylate reactive diluents, and a lower proportion of oil gave better scratch
hardness. Higher cross-linking densities showed better solvent and
chemical resistance in the cured films.
Bio-degradable photo-cross-linked thin polymer networks based on acry-
lated hydroxy fatty acids have been reported. Di- and trimethacrylates,
71
or
acrylated oligomers such as acrylated-PEG (polyethylene glycol) or acrylated-
poly(e-caprolactone) were used in co-polymerization. The bio-degradability of
the resulting co-polymers was examined, and faster bio-degradation was ob-
served for high-density cross-linking as a result of the low molecular weight
between entanglements, that might otherwise block lipase attack sites.
72,73
The Lecamp group
74
described a new synthesis process for vegetable-oil--
based materials. It may provide potential opportunities to synthesize polymer
materials from renewable resources by a clean and simple process that is
totally transposable to lesser drying oils. First, linseed oil was thermally
polymerized in bulk at 300 1C under an inert atmosphere. Then, the obtained
stand oil was functionalized in a two-step one-spot process without solvent in
order to graft onto it some photo-polymerizable groups. Finally, the materials
were prepared by UV-curing of the modified linseed oil. The obtained ma-
terials were globally flexible, hydrophobic and non-bio-degradable. Com-
pared to a naturally oxidized linseed-oil-based materials, the thermal stability
and hydrophobicity remained unchanged.
1.3.3 Photo-cured Polymer Networks based on Epoxide
Vegetable Oils
Multifunctional epoxide monomers can be converted into highly cross-
linked polymer networks by UV irradiation in the presence of cationic photo-
initiators. The cationic photo-polymerization of epoxidized oils is insensitive
to oxygen, thus is highly attractive for many applications such as inks
