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Technical improvement of natural rubber processing: maturation time, sensitivity to thermo-oxidization, and storage hardening and environmental issues related to rubber production.

Rubber processing companies (Smoked sheet/RSS, block rubber/STR, and concentrated latex) often encounter, lack of control of cup coagula maturation for STR20 production, lack of consistency of produced rubber (e.g. P0, PRI, ASHT), as well as, environmental issues such as energy consumption in NR processes. In both block rubber and concentrated latex industries, manufacturers have to let the cup lump/latex maturate for a long period if they want to obtain the required quality for further processing. This storage time has a cost. Technical solutions are researched to understand and reduce the duration of this maturation step.

From 2004 to 2010 CIRAD team try to understand the phenomena occurring during the cup coagula maturation before STR processing and their effect on rubber properties (Po, PRI). The maturation was characterized in industrial conditions; a prototype laboratory device has been developed to produce rubber with mini cup coagula which were maturated under strictly controlled maturation conditions (temperature, relative humidity, Oxygen content of the atmosphere, and microorganism population). The finding of this first study proved clearly the involvement of microorganisms during maturation in the determination of final physical properties of rubber. A new double-degree PhD study using the developed prototype was conducted between 2010 and 2014 by a KU researcher and focused on the links between post-harvest maturation of coagula and sensitivity to thermo-oxidization of produced NR while a French PhD student focused her research on microorganism population dynamics using the same prototype. It provided novel information on the evolution of antioxidant biochemical species and microorganism population during maturation process and the possible consequences on NR properties, especially on PRI. 

Moerover, storage hardening is a phenomenon specific to natural rubber (NR), during which links form between the polyisoprene chains and certain so-called “non isoprene” or “non rubber” compounds.. Storage hardening leads to an increase in bulk viscosity during the period of storage in warehouses. Little is known on the evolution of mesostructure of NR during storage hardening. However, this phenomenon leads to an over consumption of energy during the process of NR into end-used product, negatively impacting the environmental foot print of NR process. 

A double-degree Ph.D. thesis has been completed and defended in May 2014 on this topic. This work provided new knowledge on the molecular mechanisms and non-isoprene compounds involved  in storage hardening,  on the location of the component involved in that phenomenon in the latex fractions, and on the evolution of mesostructure during storage hardening (molar masses, MMD, branching, microgel, etc.). Findings on that topic may be relevant to reduce energy consumption during end use product manufacturing.

Partners:

  • Kasetsart University
  • Prince of Songkla University
  • Montpellier SupAgro

List of publications

  • Intapun J., Sainte-Beuve J., Bonfils F., Tanrattanakul V., Dubreucq E., Vaysse L. Characterisation of natural rubber cup coagula maturation conditions and consequences on dry rubber properties (2009). Journal of rubber research, 12 (4) : 171-184.
  • Intapun, J., Sainte-Beuve, J.,  Bonfils, F., Tanrattanakul, V. Dubreucq, E., Vaysse, L. Effect of microorganisms during the initial coagulum maturation of Hevea natural rubber (2010). Journal of Applied Polymer Science. 118 (3) : 1341-1348
  • Wisunthorn, S. Liengprayoon, S., Vaysse, L., Sainte-Beuve, J., and Bonfils, F. SEC-MALS study of dynamic structuring of natural rubber : Comparative study of two Hevea brasiliensis genotypes (2012) Journal of applied polymer science124(2): 1570-1577.
  • Salomez M., Subileau M., Intapun J., Bonfils F., Sainte Beuve J., Vaysse L. and Dubreucq E. Microorganisms in latex and natural rubber coagula from Hevea brasiliensis and their impact on rubber composition, structure and properties (2014). J. Appl. Microbiol.,117: 921-929
  • Thepchalerm, C., Vaysse, L.,  Wisunthorn, S. Kiatkamjornwong, S.,  Nakason, C. and Bonfils, F. The stability of lutoids in Hevea brasiliensis latex influences the storage hardening of natural rubber. (2015) Journal of Natural Rubber Research, 18: 17-26.

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