Tesis
Síntese de partículas submicrométricas de carbonato de cálcio a partir de sais inorgânicos utilizando polímeros lineares como modificadores de cristalização
Fecha
2017Autor
Facchinetto, Sara Elisa
Institución
Resumen
In this work, we report the synthesis of submicrometer calcium carbonate
particles using the simplest approach of mixing solutions of calcium chloride
and ammonium carbonate inorganic precursors in presence of crystallization
modifiers. The typical crystallization of CaCO3 into large calcite crystals with
rhombohedral morphology changed to very small (down to 0.8 μm) uniform
spherical vaterite particles upon addition of small amounts (0.01 to 2.00 mg/mL)
of the anionic homopolymer poly(sodium 4-styrenesulfonate) (PSS).The
reaction temperature must be preferably kept low around 25 °C. Heating
induces the formation of an unstable hydrated phase, which is quickly converted
back to the most stable structure, however with some broadening in the particle
size distribution.
In contrast, large spheres made of a collection of calcite polycrystallite
aggregates formed in presence of poly(acrylic acid) (PAA) under otherwise the
same experimental conditions. Crystal growth in a preorganized environment
created by selective distribution of Ca(II) ions onto the shell of
polyestyrene-b-poly(acrylic acid) (PS-b-PAA) core-shell spherical micelles
revealed a rather poor control of size and morphology. Therefore, PSS anionic
homopolymer can be applied to the synthesis of submicrometer CaCO3
particles from solutions of inorganic salts, which is a much cheaper and
sustainable method than controlled CO2 gas production and diffusion.
Representative polymer@CaCO3 particle systems were
used to prepare PCL-based composites, of which the rheological behavior was
accessed by oscillatory rheology.