2. Materials and method
Natural rubber latex (Low Ammonia (LATZ) type) and other rubber chemicals for making NRLF were supplied by Zarm Scientific & Supplies Sdn Bhd, Malaysia. Chemicals for synthesis of silver nano-particles were obtained from Merck KGaA, Germany and Sigma Aldrich Chemicals, USA.
2.1. Synthesis of nano silver based NRLF
2.1.1. Synthesis of silver nanocolloids
The silver nanocolloid used in this work was synthe- sized 90 days in advance according to the method reported by Monteiro et al. [24] and stored in an amber glass bottle to evaluate its stability.
2.1.2. Compounding and production of nano silver based NRLF The formulation used to make the silver nanocolloid incorporated NRLF is shown in Table 1. First, LATZ type NRL was mixed with sulphur, antioxidant, previously prepared silver nanocolloid and potassium oleate soap and stirred at
10 rpm. After 2 h, zinc 2-mercaptobenzhiozolate (ZMBT) and zinc diethyldithiocarbamate (ZDEC) were slowly added to the mixture. Then, the compounded NRLF compound was matured for 8 h at room temperature with continuous stirring at 10 rpm.
After maturation, the NRLF compound was vigorously beaten using a stand mixer (KENWOOD, kMix) to make a fine foam until the volume was increased up to three times (beating time about 5 min). After that, 3.00 pphr of ZnO together with 0.30 pphr of diphenylguanidine (DPG) were added as the primary gelling agent to the foam and beating was continued for another 90 s. Then, secondary gelling agent, 1.00 pphr of sodium silicofluoride (SSF) was quickly added and the foam was beaten for another 90 s. Finally, the un-gelled foam was immediately poured into an aluminum mould and allowed to gel for 2 min at ambient temperature. Gelled foam was then cured in a hot air oven at 100 C for 2 h. Next, the cured foam was stripped from the mould and thoroughly washed with de-ionized water to remove soap and non-reacted elements. After washing, the cured NRLF was dried in a hot air oven at 80 C for 8 h. The resultant foam was off-white in color. The same