Evolution in the natural rubber native structure and plasticity retention index from the first tapping of clonal trees

Abstract

This study was carried out with five rubber clones planted in Cô te d'Ivoire from the first tapping up to the 18th month of tree tapping (1 tapping/4 days). Changes in the natural rubber native mesostructure (macromolecular structure, macrogel, and microgel) of films prepared from fresh field latex were monitored. At the same time, the evolution of the thermooxidation sensitivity of raw rubber samples [grade 10 technically specified rubber (TSR10)] was also monitored with the plasticity retention index (PRI). The substantial initial macrogel rate (70 -86%, depending on the clone) fell during the first 18 months of tree tapping to reach a few percent. However, during the same period, the initially low microgel rate (5-15%) increased and then remain stabilized around 55% rubber. The macromolecular structure [weight-average molecular weight (M w ) and molar mass distribution (MMD)] also changed after tree opening. M w increased and stabilized after 7.5 months of tapping. The bimodal MMD primarily involved short chains (molar mass Ͻ 400 kg/mol) at the opening of the trees. The TSR10 samples, prepared with latex from virgin trees, showed high PRIs and, therefore, low sensitivity to thermooxidation.

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

“…Usually, commercial NRs are made with a mixture of fresh latex (TSR3CV grade), or coagula (TSR10 and TSR10CV grades), from different Hevea brasiliensis genotypes or clones (Figure 2). However, in our study, each NR sample was made from the latex of a single clone (GT1, RRIM600 or PB235) in order to remove variability linked to the clonal origin of the latex [11,12,31]. The properties of the TSR3CV and TSR10CV samples were stabilized with a neutral hydroxylamine sulfate solution (NHS; Figure 2).…”

“…Its exceptional properties are attributed to the stereoregularity of the polyisoprene chain (high cis-1,4 content), high polyisoprene molar masses [6][7][8], but also to the presence of a gel phase [9,10]. This gel phase is composed of an insoluble fraction called 'macrogel' [11,12], and of microaggregates dispersed in the soluble fraction, called 'microgel' [13,14] (Figure 1). Some non-isoprene compounds of NR, such as lipids (1.5-4% w/w) [4,[15][16][17], proteins (1-3.5% w/w) [4,[17][18][19], and minerals (0.2% w/w) [4,20], are assumed to be responsible for the existence of this gel phase.…”

“…After dissolution, macrogel is eliminated by centrifugation. Filtration of the soluble fraction can then be used to quantify the microgel either directly by weighing the recovered microgel [25], or indirectly using SEC-MALS (size exclusion chromatography, multiple angle light scattering) analyses [12,26]. Several studies showed that proteins are concentrated in the macrogel of NR [27][28][29].…”

Katalitik transfer hidrogenasi lateks karet alam dengan senyawa diimida pada skala semi pilot

“…Ketahanan oksidasi karet mentah karena pengaruh oksigen dan panas (thermal oxidative degradation) dievaluasi berdasarkan parameter plastisitas awal (Po) dan indeks ketahanan plastisitas (PRI). Nilai Po menggambarkan mikrostruktur karet alam yang mempengaruhi sifat mekaniknya sedangkan nilai PRI yang tinggi berkaitan dengan ketahanan karet mentah terhadap oksidasi panas yang baik (Bonfils et al, 2005). Hasil pengujian Po dan PRI karet terhidrogenasi dibandingkan dengan karet alam murni disajikan pada Gambar 4.…”

“…Dari Gambar 4 dapat diketahui bahwa Nilai Po karet alam murni meningkat selama periode penyimpanan tertentu (Li et al, 1998). Nilai PRI karet alam murni yang sangat rendah dapat disebabkan karena terjadinya reaksi biokimia dalam lateks selama penyimpanan akibat adanya kontaminasi bakteri (Bonfils et al, 2005;Fri et al, 2007). Bakteri dapat menguraikan antioksidan alami yang terkandung dalam lateks sebagai bahan non karet (Baimark & Niamsa, 2009).…”