Thermal Analysis of Face Visor Materials During Sterilisation

This article presents a scientific basis for why materials are better suited to some sterilisation processes than others. Please read our face visor washing and reusability post first for an explanation of the possible sterilisation methods

Differential scanning calorimetry (DSC) is a thermal analysis technique which measures the difference in heat flow required to increase the temperature of a test sample and a reference material as a function of temperature. DSC is commonly used to investigate various transition temperatures of polymers such as:

  • Glass transition temperature, Tg
  • Crystallisation temperature, Tc
  • Melting temperature, Tm

When a material is heated above its glass transition temperature, a phase change occurs: the material behaviour switches from stiff to rubbery and loses its mechanical performance.

Visors made by 3D printing can be sterilised successfully, but only if during the sterilisation process they can maintain their mechanical integrity and not lose their shape. In order to achieve this, the Tg of the material cannot be reached during the sterilisation process. A representative curve of a 3D printed Poly Lactic Acid (PLA) filament with annotation at each transition temperature is shown in the graph below.

DSC curve for PLA filament

The glass transition temperature and melting temperature of eight 3D printed filaments measured by FAC Technology via DSC are summarised in the following table:

Each DSC measurement of thermal properties was conducted in a nitrogen atmosphere with a gas flow rate of 0.05 litres/min, with a temperature ramp rate of 10°C/min.

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