Pranee Phinyocheep

Vaterite with submicrometer particles was successfully synthesized by adding sucrose at certain amounts (x = 0-50%) to the aqueous solutions of ammonium carbonate ((NH₄)₂CO₃) and calcium chloride (CaCl₂) precursors prior to the precipitation. Typical polymorphic phases and morphological shapes of CaCO₃ particles were characterized by XRD, FTIR, Raman spectroscopy, SEM, and TEM techniques. It is evident that when the sucrose concentration is increased, the average particle size of CaCO₃ is decreased which was reduced from 0.81 µm at x=0% to 0.42 µm at x=50%. Simultaneously, the % quantitative of the vaterite phase was increased from 92.52% at x=0% to 99.10% at x=50%. In addition, the regular round shape of the vaterite particles was evidenced by SEM and TEM images. Generally, commercial CaCO₃ which is a calcite polymorph with cubic form was used as an extender without reinforcing efficiency in rubber material. It is therefore challenging to incorporate the obtained round shape vaterite in natural rubber (NR) latex and it is interesting to find a stable vaterite CaCO₃ polymorph in the NR, evidenced by XRD and FTIR results.  The negative charges on the surface of NR particles were proposed to play an important role to stabilize the vaterite particles.