Green Strength of Natural Rubber: The Origin of the Stress-Strain Behavior of Natural Rubber

The variation of the green strength of natural rubber (NR) with the preparation method of the film was studied to elucidate the origin of the. stress-strain behavior characteristics of NR in connection with the Structure of branch points in NR. A rubber film prepared via casting from NR latex showed the highest modulus and green strength in comparison with films prepared via casting from a toluene solution and via the hot pressing of dry rubber, The modulus and green strength of the NR latex-casting film decreased after the hot-press treatment I of the film. On the other hand, no difference was observed for synthetic cis-1,4-polyisoprene rubber with the preparation method of the film or the heat treatment. This stress-strain behavior characteristics of NR can be ascribed to the changes in the branch points of the NR film with the casting method, which may result in differences in entanglement and crystallizability on stretching. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2127-2133, 2009