The far infrared spectrum of vulcanized natural rubber

Abstract

Earlier studi es of the infrared s pectra of natural rubbe r and some vulcan izates of rubber have been extend ed into th e 650 to 33 cm -J far infrared region. Some of the absorption bands originating in the crystalline portion of unvulcanized rubber have bee n studi ed by usin g polarized radiation and samples oriented by stretching. Vulcanization of rubbe r with sulfur alon e produces a general weaken· in g of all absorption bands and no new absorptions. Vulcan ization with sulfur and an accelerator also results in a red ucti on in intensity of th e rubber absorptions, but is accompanied by th e appearance of new bands. When the accelerator is tetram et hylthiuram di sulfi"d e (TMTD) the new bands are probably ind icative of a thioca rbamate structure. When zinc dibutyldithiocarbamate is used as an accelerator a band probably due to zinc sulfide occurs. Vulcanization with TMTD alone produces only slight changes in th e far infrared spec trum. Howeve r, when TMTD is used in the presence of zinc oxide a reaction occ urs in which zinc dim ethyldithioca rbamate (ZnDMDC) is formed. After vulcanization for a short period of tim e stro ng TMTD bands remain , but after long vulcanization the TMTD bands are replaced by ZnDMDC bands.