The majority of minerals present in natural rubber are associated with the macrogel: An ICP‐MS and SEM/EDX investigation

Abstract

The mineral composition of the insoluble (macrogel) and soluble fractions of two natural rubber (NR) samples made from the latex of two different clones (RRIM600 from Thailand and GT1 from Côte d'Ivoire) was determined using inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS results showed that mineral elements were concentrated in the macrogel. The major mineral elements found in macrogel were phosphorus, magnesium, potassium, and sulfur. Some mineral elements were mostly concentrated in micron-sized mineral aggregates, visible at the surface of the samples using scanning electron microscopy coupled with an energy dispersive X-ray microanalyzer (SEM/EDX). The nature of these mineral aggregates was found to be highly variable. Their inhomogeneous distribution in the macrogel indicates that these aggregates do not have a major influence on macrogel structure. (Résumé d'auteur

Characterisation of macrogel composition from industrial natural rubber samples: Influence of proteins on the macrogel crosslink density

“…It should be noted that material losses were calculated and accounted for 2 to 48% of the initial nitrogen atoms contained in the raw NR samples ( Table 2). Those nitrogen losses were attributed to non-structuring proteins, eliminated during the macrogel washing steps, as reported previously [30]. The remaining proteins contained in the washed macrogels were not eliminated during the washing steps, and were assumed to participate in macrogel structuring.…”

“…The macrogel was separated by centrifugation from the soluble fraction for 11 NR samples, and then washed in order to eliminate non-structuring nonisoprene compounds [30]. The final recovered quantities of washed macrogel are given in Table 1.…”

“…The solutions were then centrifuged under the same conditions as described above. The macrogel was recovered and washed once with ultrapure water containing 5% (w/v) of sodium dodecyl sulfate (SDS), then washed three times with ultrapure water in order to remove non-structuring compounds precipitated with the macrogel during centrifugation [30]. After solvent evaporation, both the soluble fraction and the macrogel were finally dried at 30°C under vacuum for 2 hours.…”

“…Thus, the high protein contents of macrogel cannot be directly used to study the role of those non-isoprene compounds in macrogel structuring. Indeed, earlier work showed that washing macrogel with water, helped to eliminate nonstructuring minerals and proteins [30]. In order to gain a better understanding of variability in the composition and structure of macrogel fractions from very diverse industrial samples, macrogels extracted from 11 different NR industrial samples were characterized.…”

Comparison of methods for determining the gel content in natural rubber and the effect of gel content on rheological behavior

“…They can form aggregates with carbonyl groups of nonrubber constituencies and with carbonyl groups of polyisoprene chains. 20,22,23…”