Glass transition temperature (Tg)

Illustrated explanation

Shape recovery, impact rebound and glass transition answer different questions

2Glass transition temperature (Tg)
Shape recovery, impact rebound and glass transition answer different questionsCallout 1 compares a compressed and unloaded elastomer, then depicts an impactor falling and rebounding to distinguish shape from returned energy. Callout 2 shows a qualitative glass transition region without a numerical service-temperature limit. Current term: Glass transition temperature (Tg), callout 2. 1 Shape recovery and impact rebound CompressedUnloaded Return toward the original shape FallRebound Returned energy in an impact test 2 Glass transition region Segment mobility Restricted motion More mobile segments Tg region Temperature Qualitative behaviour only Tg is not the melting point It is not a seal temperature rating
  1. Elastic recovery / rebound resilience

    Shape recovery follows unloading, whereas rebound measures energy returned during a defined impact. Neither replaces compression-set or stress-relaxation evidence for an installed seal.

  2. Glass transition temperature (Tg)This term

    Tg identifies a method-dependent transition in amorphous segment motion. It is different from melting and does not by itself establish a seal minimum or maximum operating temperature.

A compressed sample recovers toward its original shape after unloading. A separate rebound example compares returned impact energy; a qualitative transition sketch shows how segment motion changes around Tg.

Conceptual elastomer responses without temperature, energy or recovery values. The transition sketch is not a DSC curve or service-temperature chart; actual compounds and test methods determine measured behaviour.

ReferencesISO 4662:2017 — Rubber — Determination of rebound resilienceISO 815-1:2019 — Rubber — Determination of compression setISO 3384-1:2024 — Rubber — Stress relaxation in compressionISO 11357-2:2020 — Glass transition temperature by DSC