Engineering:Relative temperature index

The Relative temperature index (RTI) is a characteristic parameter related to the thermal degradation of plastic materials. The RTI is part of the thermal-aging program of the UL 746B standard from UL.

During the process of the UL 746B program, the degradation of certain properties of the material like dielectric and mechanic strength, is investigated with regards to thermal-aging. The RTI is the temperature in degrees C, at which the properties have decreased to 50 percent of their initial value after a long-term exposure to this temperature.

Though the RTI is an index, it is given in Celsius units. The UL 746B standard distinguishes between three sub-categories of the RTI:

• Electrical RTI which relates to electrical insulating performance.
• Mechanical impact RTI which relates to mechanical performance with impact
• Mechanical strength RTI which relates to mechanical performance without impact

Literature

• UL 746B, 5. Ed.: Polymeric Materials – Long Term Property Evaluations
• N. Navarro: Predicting Elevated Temperature Ratings of Polymeric Materials in C. White et al.: Service Life Prediction of Exterior Plastics, New York: Springer (2014), ISBN:9783319060330
• G. Mediratta, et. al.Over Time and Under Heat, Polycarbonates Hold Up: Plastics Eng. 67 (7) (2011), p.24