Damage Function for Yellowing of PVC

Our PhD researcher Tjaša Rijavec along with Matija Strlič and Irena Kralj Cigić recently published the paper “Damage function for poly(vinyl chloride) in heritage collections” in Polymer Degradation and Stability: full article 

Yellowing of plastic objects due to chemical degradation is a common heritage conservation challenge. In the case of poly(vinyl chloride) elimination of hydrogen chloride leads to the formation of polyene sequences that act as chromophores. The effect of environmental variables (temperature and relative humidity) and sample characteristics (plasticizer content and polymer molecular weight) on the yellowing of PVC has been modelled using multiple linear regression. The lifetime of PVC objects due to yellowing was defined and can be predicted using the damage function. The ‘1-°C-equivalent’ concept was introduced to enable variable prioritisation from a heritage management perspective.

Highlights of the article:

  • High temperature and relative humidity increase the degradation rate.
  • Plasticizer type does not affect the degradation, the content does. High-MW polymers are more stable than shorter chains.
  • The activation energy of dehydrochlorination observed as yellowing is 86 ± 3 kJ/mol.
  • Use the damage function to predict lifetime of heritage objects.
  • Identify objects in collections prone to degradation.
  • A ‘1-°C-equivalent effect’ was defined to clarify the implications of the model for collection management.
PVC objects lifetimes
The predicted lifetimes of PVC objects demonstrating the effect of temperature and relative humidity. The isochrone plot was created for an object with an average plasticizer content (14%) and an average MW 120000 g/mol.

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