A comparison has been made of the vulcanization of NR in the latex form and in the dry form. In latex form, NR wa s found to vu Lcani ze at a much f asterra t ethan in the dry form. The faster rate of reaction in latex prevulcanization is attributed to the presence of the aqueous phase which acts as a medium for the dissolution of ZDBC and sulphur, and provides a suitable environment for the two vulcanizing ingredients to react to form the active sulphurating agent. A comparison has also been made of the prevulcanization behaviour of NR latex and synthetic cis-polyisoprene latex. It has been suggested that the indigenous vulcanization accelerators and activators present in NR latex act as additional vulcanizing accelerators and therefore increase the rate of prevulcanization. Experiments have been carried out to determine the solubilities of sulphur and ZDBC in the aqueous phase of the latex during prevulcanization. Sulphur was found to dissolve to an appreciable extent; ZDBC was found to have a solubility of ca. 0.011%. The effects of varying the levels of sulphur and ZDBC upon NR latex prevulcanization was investigated. The variations of the following properties with time of prevulcanization were investigated: free and network-combined sulphur, disappearance of ZDBC, crosslink insertion, and tensile strengths of cast films. Information was also obtained concerning the polymer-solvent interacticn parameter for the cast films swollen in n-decane at 23°C. Investigations of the different types of sulphidic crosslinks as a function of prevulcanization time for vulcanizate obtained from prevulcanized latex have also been carried out. Tne crosslinks were found to be mainly of the polysulphidic type. The effect of varying the dialkyl chain-length and metal counterion of the dithiocarbamate accelerator upon NR latex prevulcanization have been studied. The molal effectiveness of the zinc dialkyl dithiocarbamates appears to pass through an optimum as tbe dialkyl chain-length of the accelerator is increased. PbDEC was found to be of very low activity as an accelerator and the water soluble SDEC has poor. accelerating properties when compared to ZDEC. Plausible hypotheses to account for the observations have been postulated.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:349979 |
| Date | January 1982 |
| Creators | Chun-Pong Loh, Aaron |
| Publisher | London Metropolitan University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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