Purified natural rubber latex: Investigating effect of single anionic surfactant and centrifugation process to latex properties and addition of bio-filler towards latex film performance

Excessive foaming and extensive centrifugation process encountered by purified natural rubber latex (p-NRL) has made this latex not well accepted by the industry as an imperative starting material for latex-based products. In this study, we aim to investigate the feasibility of utilizing single anionic surfactant, sodium dodecyl sulphate (SDS) in combination with urea, a protein denaturant and underwent a single centrifugation process in acquiring p-NRL. Incubation of commercially available high ammoniated natural rubber latex (HA-NRL) with urea in the presence of SDS is known to denature proteins by causing it to unfold and centrifugation process will further facilitate the removal of the unfolded protein from the aqueous serum phase of the HA-NRL. The effect of these processing parameters on the typical latex characteristics, protein separation, nitrogen content, zeta potential (ZP), rheological behaviour, morphology and physical performances of the p-NRL was examined. With specific amount of urea, fitting results of various SDS solutions at 10% (w/w) from surface tension analysis to Langmuir equation resulted in a plateau adsorption capacity. The value was calculated to be approximately 0.0236 gSDS/ grubber, corresponding to about 0.5 phr SDS saturated on the p-NRL rubber surface. Incubation of these chemical mixtures in the HA-NRL with single centrifugation process significantly eradicates most of the proteins, with detrimental effects on the distinctive p-NRL properties. Although SDS creates synergizing effect with urea for protein denaturation process, it nevertheless did not create a destabilization phenomenon to the p-NRL as the zeta potential analysis demonstrated negatively charged values over the entire pH range. Remarkable rheological performances of the p-NRL suggested that the system is proportionately stabilized by the surfactant adsorptions, which is concurrent with the zeta potential analysis. Observing the p-NRL particles in latex state and in the dried film through Environmental Scanning Electron Microscopy (ESEM) and Field Emission Scanning Electron Microscopy (FESEM) revealed a unique particle packing arrangements. It was hypothesized that the processing parameters in producing p-NRL has a pronounced influence to both particle morphologies. The film formation of p-NRL compounded with natural-based filler was studied and compared with HA latex film in term of physical properties.