Acid-induced aggregation and gelation of natural rubber latex particles

Coagulation of natural rubber latex suspensions into an elastic gel is the first step of their processing intorubber. We studied this transition under controlled acidification conditions with the aim of identifying themain parameters controlling gel formation. The onset of aggregation and the percolation events observedduring continuous acidification were monitored on a large range of volume fractions by a combinationof light-scattering techniques adapted to the different degrees of suspension opacity (namely, diffusingwave spectroscopy, static light scattering and turbidimetry) and by rheology. We consequently estab-lished the state diagram of NRL particles in the pH-_vspace during acidification. Within this diagram,we identified three states: a suspension, a two-phase macroscopically separated system in between a geland a suspension, and a gel. The rheological properties of the gels were characterized as a function of thevolume fraction _v. The elastic modulus scale with _v3.35, it shows remarkable consistency independentlyof the acidification kinetics and final pH. (Résumé d'auteur