UV-Irradiation of a Soft SBR Latex. Effect on Particle Size Estimation

LLOSENT, M. A.; GUGLIOTTA, L. M.; MEIRA, G. R.

LATIN AMERICAN APPLIED RESEARCH

Año: 1996 vol. 26 p. 39 - 43

0327-0793

This work investigates the effect of UV-irradiation on a styrene-butadiene rubber latex; with the average particle diameter being measured by scanning electron microscopy (SEM), dynamic light scattering (DLS), and UV-Vis Turbidimetry. The irradiation process was followed along a 12-hrs. period; and it induced latex oxidation, cross-linking, and possibly some degradation. Such reactions were evidenced by changes in: a) the latex colour (from white to brownish); b) the absorbance spectrum (especially in the UV region); and c) the bulk-polymer glass transition temperature (from -58°C without irradiation to around 14°C after 2.5 hrs. irradiation). However, the average particle diameter remained practically unchanged at around 65 nm, as confirmed by all the three measurement techniques. The negligible size variation determined by DLS seems the most trustful because on the one hand measurements were feasible from the beginning (unlike SEM where a minimum irradiation time was required for particle-hardening); and on the other hand because DLS estimates are basically independent on the polymer refractive index, that changes with irradiation. For the turbidimetry data treatment, light absorption was neglected; and the following parameters were simultaneously estimated through a least-squares procedure: the average diameter, a dimensionless concentration, and two coefficients of the polymer refractive index function. Turbidimetry results indicated that only one of the adjustable refractive index coefficients appreciably varied along irradiation. This result is consistent with all other independent determinations.