First, each catalyst was crushed in an agate mortar
and placed in a beaker containing 15 mL of ammonium
hydroxide (10% m/v). The suspension was stirred for
10 min to ensure particle suspension and to prevent
premature latex clotting. Pre-vulcanized latex (60%) was
poured into the suspension, which was stirred for another
15 min, spread in Petri dishes (9 cm internal diameter), and
dried in an oven at 50 °C for roughly 15 h. The membranes
were named according to the catalysts employed in their
composition, as follows: NRTA00, NRTA05, NRTA10,
and NRTA20. One membrane prepared with bare natural
rubber (labelled NRC) served as a control.