Weathering resistance

The resistance of unplasticised PVC to degradation due to exposure to the elements depends on a number of different factors. These include the nature of the stabilisation system,pigmentation used , the grade of PVC and also other additives in the formulation. It is clear that all these formulation ingredients have a role to play. Rigid PVC formulations that contain synthetic precipitated calcium carbonate show excellent color durability and retention of mechanical properties in particular impact strength. This positive effect on weatherability is due to a number of differing factors some which have their origin in the improvements in dispersion and processing behavior seen when precipitated calcium carbonate is included in exterior formulations. The chemical nature and purity of the calcium carbonate is also a factor as is the much enhanced surface finish.

CPCC in rigid PVC has a positive effect on weathering by :

1. A more effective compounding of the PVC which ensures that the stabilisers present are dispersed in a homogenous way. The presence of CPCC in the formulation removes the need to overwork the PVC which itself provides a more stable polymer.
2. The ultrafine nature of the synthetic calcium carbonates acts as an efficient radical trap for any evolved HCl thereby inhibiting dehydrochlorination giving reduced yellowing. 
   

   

   Figure 1: weatherproofness of a brown, lead stabilized rigid PVC section containing different levels of filling materials (exposition area (Rheinberg/Germany)

3. The enhanced surface finish and gloss are a major factor in the surface resistance to degradation (see table 1)

Ground Calcium Carbonate	Precipitated Calcium Carbonate
Mag X 250 Before Weathering	Mag X 250 Before Weathering
Mag X 250 After 8GJ/m2 Weathering Xeon 1200	Mag X 250 After 8GJ/m2 Weathering Xeon 1200

Abrasivity|Anti-sedimentation|Brightness|Impact resistance|Neutralisation|Opacity|Porosity|   Processing Aid|Rheology|Sheen|Stiffness|Surface Appearance|Washability