Role of Starch as a Steric Stabilizer for Doping Natural Rubber: Effect on Optical, Electrical, Mechanical, and Morphological Properties

Recently, it has been reported that prevulcanization of natural rubber (NR) latex does not hinder the formation of conjugated sequences, which is a precondition for developing intrinsic electrical conductivity in polymers. In this article, the authors report for the first time that incorporation of a steric stabilizer such as starch enhances the solution doping of the prevulcanized NR latex resulting in flexible semiconducting thin films with an optimum enhancement in the electrical conductivity behavior and a decrease in optical band gap. However, the characteristic color changes and the insulator-conductor transitions are gradual, indicating a lower doping rate and hence a longer doping period for the system. Moreover, the complexation of the doped iodine (I ₂ ) atom with the starch molecule prevents the out-diffusion of I ₂ , and hence imparts stability in the electrical conductivity. The mechanical studies reveal desirable strength for the doped films. The formation of conjugated sequences of double bonds in the poly isoprene (PI) backbone is examined using a UV/VIS and an FTIR-ATR spectroscopy. The swelling studies indicate a reinforcement effect in starch containing composite films at low proportions. The scanning electron micrographs (SEM) of the fabricated films show a compatible phase for the composite and hence a better perfection of the surface.