New insight into the cold crystallization of natural rubber: The role of linked and free fatty chains

Abstract

Natural rubber (NR) is a polyisoprene (PI) from renewable resources that exhibits mechanical and thermal properties not accessible with synthetic polyisoprenes (IR). In this article, it was developed a simple route to synthesize new models of NR (PI with a pure microstructure [100% 1,4‐cis] and two fatty esters linked to the polymer chain‐end) in order to clarify the role‐played by lipids on the “cold crystallization” (CCr) of NR. DSC analysis of this new hybrid polymer revealed that the lipids linked to the backbone were able to crystallize despite the amorphous matrix, the crystallization temperature being dependent on the length of the linked fatty chain. Furthermore, it was observed that the linked fatty chains prevented PI to crystallize at low temperature (−25°C). Finally, the addition of free fatty acids to the hybrid polymer enhanced the crystallization of the PI chain, more particularly when stearic acid and methyl linoleate were used simultaneously as additives. A similar investigation was performed with IR (with 97% 1,4‐ cis and 3% 1,2‐ units), identical observations could have been made.