Analysis of rubber vulcanisates

A study has been made, using High Pressure Liquid Chromatography, of the migration of TMQ (a quinoline type) and 6PPD (a paraphenylenediamine type) antidegradants from a tyre sidewall compound into adjacent casing and liner compounds containing no antidegradant. Migration takes place at a rapid rate, even during the vulcanisation of the composite. After 4000 hours ageing in nitrogen at 100oC, there is a higher level of antidegradants in the casing than in the sidewall. An equilibrium distribution is not obtained. After 114 days at 50oC in 95% relative humidity, the level of solvent extractable 6PPD fell to zero, but subsequent ageing for 2 years in 50 pphm ozone showed no evidence of sidewall cracking. It is suggested that the antidegradant is still active but linked to the polymer chain. An analytical method, for the type and amount of sulphenamide accelerators in vulcanised rubber compounds, has been developed. During the vulcanisation process, the accelerators decay, liberating specific amines which have been solvent extracted, derivatised with 1-chloro-2,4-dinitrobenzene and the yellow coloured zwitter ion analysed using High Pressure Liquid Chromatography. The decay of the accelerator and sulphur during the vulcanisation process, has been studied. It has been demonstrated that the sulphur crosslinking with a styrenebutadiene polymer is a first order reaction, after an initial period during which the accelerator content falls to zero. Variations in sulphur to accelerator ratios gave consistent rate constants for the crosslinking, except for a sulphur level of less than 1% by weight and a ratiio of accelerator to sulphur of 1:1.3. The retention time of the reaction product between sulphur and accelerator from an HPLC column changes with cure time, showing that the precurser to crosslinking is an ever changing material. One of these reaction products has been analysed.

The analysis of potentiostatic transients applied to the corrosion of steel in concrete

Potentiostatically induced current transients obtained on a range of reinforced concrete specimens were analysed to give estimates of the polarisation resistance and interfacial capacitance. The polarisation resistance was compared with the values obtained using more conventional DC methods of analysis and, while it was consistently lower, it was within the error normally attributed to the polarisation resistance method of corrosion rate determination. The interfacial capacitance values determined increased from 0.44 F m -2 for passive steel (polarisation resistance of 132 Ω m 2) to 26.5 F m -2 for active steel (polarisation resistance of 0.34 Ω m 2). This has a dominant effect on the time required for potentiostatically induced current transients to reach a steady state with a longer time being required by actively corroding steel. By contrast the potential decay time constants describing galvanostatically or coulostatically induced potential transients decrease with an increase in corrosion rate and values less than 25 s for active specimens and greater than 40 s for passive specimens were determined in this work. © 1997 Elsevier Science Ltd.