FRACTIONATION OF HEVEA BRASILIENSIS LATEX BY CENTRIFUGATION: (ii) A MEAN TO LOCATE THE DRIVERS OF NATURAL RUBBER UNIQUE STRUCTURE AND PROPERTIES

Abstract

T he biochemical composition of Fresh Hevea latex fractions (cream, skim, C-serum, lutoids) was comprehensively described in the first part of this publication. The fractions obtained from the same latex were remixed. The rebuilt latex was used to prepare ADS (Air Dried Sheet) rubber sheets. The possible quantitative effects of the components of each fraction on the structure and properties of the obtained rubber ADS samples were studied. This protocol was performed on lattices harvested from 2 clones (RRIM600 and PB235). The obtained rubber samples made from latex containing various proportions of serum and/or lutoid fractions, were submitted to a panel of analytical characterizations: lipid extract, mineral composition, mesostructure (SEC-MALS), Initial Plasticity (Po), Plasticity Retention Index (PRI), and Accelerated Storage Hardening Test (ASHT). Moreover, non-accelerated 2- month storage in controlled conditions was also studied. While the proportion of serum and/or lutoid did not influence much the structure and properties of freshly obtained dry ADS rubber, an important effect of their presence was evidenced on the change of structure and properties during storage. For example, ADS rubber samples made from lutoid- and serum-deprived latex were those that showed the lowest D P (ASHT) and the lowest D gel and D Po after 2-month storage. In addition, clonal differences in terms of lipid extract, rubber structure and properties were underlined : when compared to RRIM600 rubber, PB235 rubber showed higher lipid content, Po, Mn, Mw and lower mineral content, D P (ASHT) and D Po ( 2 - month non accelerated storage) . Keywords: Hevea brasiliensis , l a tex fractionation, storage hardening.