Flexural strength and dynamic mechanical properties of polypropylene/natural rubber blends and the effect of autoclave sterilization: a preliminary study for customized rubber dam clamp

Introduction: The aim of this study was to identify the optimum ratios ofpolypropylene and natural rubber (PP/NR) for a customized rubber dam clamp indentistry. This study was focused on the flexural strength and dynamic mechanicalproperties of PP/NR in various ratios. Moreover, the impact of autoclave sterilizationwas also considered.Materials and methods: Six proportions of PP/NR blends (100/0, 90/10, 80/20, 70/30,60/40 and 50/50) were prepared and assessed for flexural strength using a three-pointbending test and dynamic mechanical properties were measured through an automaticdynamic mechanical analyzer. After these tests, the PP/NR with 100/0, 90/10, 80/20ratios were selected and underwent autoclave sterilization for 1, 5 and 10 cycles. Then,the flexural strength testing was repeated and investigated.Results: The flexural strength of PP/NR blended materials was statistically significantdifference in every group of this study. The autoclave sterilization test revealed that theflexural strength of PP/NR 90/10 and 80/20 ratios were significantly increased aftersterilization for 1, 5 and 10 cycles. In addition, the PP/NR 90/10 ratio was alsocomparable to the 100/0 ratio (pure PP). The dynamic mechanical properties testshowed all PP/NR blends remained stable during autoclave sterilization condition (121°C, 30 minutes). Furthermore, the PP/NR 90/10 and 80/20 ratios displayed dynamicmechanical properties similar to pure PP at room temperature (25 °C), mimickingclinical conditions.Conclusion: The lower NR content in PP/NR blends results in significantly higherflexural strength, and autoclave sterilization has an effect on this property. The dynamicmechanical properties of all PP/NR blends were also influenced by NR addition, withlower NR content suggesting favorable elastic characteristics. The findings suggest thatthe PP/NR blend with 90/10 ratio might be considered as an alternative material fordeveloping rubber dam clamp