IJUP08 - Universidade do Porto

Incorporation of organics/inorganics nanocomposites in coatings
of high environmental and mechanical resistance
J. Pimenta 1 , C. Carneiro 2 , A. Mendes 3 , J. Moniz 4 , F. Oliveira 2 , F. Magalhães 3
1 Rede de Competência em Polímeros, Porto, Portugal.
2 CIN – Corporação Industrial do Norte, S.A., Maia, Portugal
3 Department of Chemical Engineering, Faculty of Engineering, University of Porto, Portugal.
4 Resiquímica – Resinas Químicas, S.A, Lisboa, Portugal
Inorganic fillers (metal oxides included) have been traditionally used in organic coatings,
conferring improved mechanical and physicochemical properties. In recent years, the
ability to produce inorganic fillers in nano-sized dispersible dimensions has attracted new
attention over an otherwise well established field. Indeed, the performance of the
inorganic-organic composites is optimized when the fillers are present in dimensions
below 100 nm (nano-size). However, this is only effective if the materials are uniformly
dispersed throughout the final coating film. When dealing with water based coatings,
obtained from polymeric emulsions, it is important to ensure that the inorganic
nanoparticles are well dispersed, either through encapsulation within the polymer particles
or dispersion in the aqueous phase. The first situation may be the most desirable, since it
should lead to a more uniform particle distribution in the coalesced film.
One of the main motivations for this research is the development of enhanced intumescent
paints (which expand when heated, creating a barrier to heat transmission and therefore
protecting the substract from the high temperatures occurring during a fire [1]).
Our work has been focused on incorporating nano-sized silica (SiO2) particles in vinylic
emulsions. The initial approach consisted is pre-dispersing powdered nanosilica in the
colloidal solution that is the starting point for the emulsion polymerization reaction. Two
types of nanosilica were selected: Sil-1 (with surface treatment) and Sil-2 (without surface
treatment).
For Sil-1, some methods of dispersion have been studied in order to avoid suprananometric
agglomeration in the aqueous phase: Cowles agitator, ultrasound and bead milling. The
later gave the best results. After polymerization of the vinylic monomers, TEM microscopy
indicated that there was silica present in the surrounding aqueous phase, probably
stabilized by the colloid, and encapsulation by the polymer could not be confirmed due to
the opacity of the polymeric particles.
Concerning Sil-2, TEM analysis indicated that these
nano particles tend to attach to the surface of the
polymeric particles and encapsulation is improbable in
this case (Fig. 1). Current work is dealing with
promoting the encapsulation of Sil-1 in the polymer, by
developing a colloid-free formulation, and the
encapsulation of Sil-2, by using a comonomer with
affinity to its surface.
References:
[1] – Nogueira J. L. (2006), Protecção passiva contra o fogo.
Figure 1 – polymer emulsion
particle surrounded by Sil-2
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