Fatigue Behavior of Ionomers. 3. Effect of Excess Neutralizing Agent onSulfonated Polystyrene Ionomers

摘要

The effect of excess neutralizing agent sodium hydroxide on fatigue properties oflightly sulfonated polystyrene ionomers was studied. It was found that the fatigue lifetime of ionomers at 100% excess level was longer than that of ionomers without excess NaOH. This was attributed to the presence of small particles in the size range 0.1-0.5 micron made mainly of excess NaOH, which showed good adhesion with the matrix material and probably impeded crack propagation. When the NaOH was added in excessive amounts (300%), larger particles with poor adhesion to the matrix were formed and the materials became less resistant to fatigue fracture. The results obtained are consistent with the known better fatigue performance of ionomer samples made by a precipitation method, as this method can lead to retention of some of the neutralizing agent (NaOH) and thereby influence physical properties. The fracture surface of ionomers made by the precipitation method shows a similar morphology to that observed for the 100% excess samples, and both surfaces show features indicative of the formation of a second phase consisting mainly of NaOH.