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Effect of CaCO₃ on PVC Processability and Pipe Properties

Picture of Albert Vaartjes Albert Vaartjes Jun 10, 2025 12:35:46 PM

Materials and Additives
Effect of CaCO₃ on PVC Processability and Pipe Properties
Effect of CaCO₃ on PVC Processability and Pipe Properties
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CaCO₃ as a Functional Filler in PVC Pipe

Calcium Carbonate (CaCO₃) is commonly added to PVC formulations. While the amount is limited for pressure pipe applications, it is widely used in non-pressure pipes, including structured wall pipes and foam core pipes. For example, ASTM D891 for PVC Foamcore pipe, referring to ASTM D4396 for non-pressure compounds, practically limits CaCO₃ content to approximately 25 phr. EN standards for Structured Wall Pipes allow for formulations based on composition, such as a minimum of 60% PVC in the core and 75% in the skins, rather than strict limits on fillers like CaCO₃ based on tensile properties.

Impact on Processability and Properties

The addition of CaCO₃ affects processability. High filled dry blend can present pourability problems, sometimes requiring stirrers in hoppers. Vertical crammer feeders may stall if the dry blend has a high CaCO₃ load under pressure.

CaCO₃ significantly impacts pipe properties. A higher CaCO₃ level increases the E-modulus, making the material stiffer. This increased stiffness provides a double advantage: a cheaper formulation and the possibility of a thinner wall while maintaining required stiffness. For foam core pipes, CaCO₃ can compensate for the lower stiffness of the foam core, potentially allowing the total wall thickness to remain the same or be thinner than a solid wall equivalent. A higher filler level often permits the addition of more blowing agent without creating blisters, further enhancing weight and cost savings for foam core pipes.

Cost and Stiffness Considerations

Adding CaCO₃ directly (Direct Addition) replaces polymer with filler, contributing to sustainability and cost reduction. The stiffness of the pipe is proportional to the amount of phr added to the formulation. This allows for achieving required stiffness even with a thinner wall, optimizing cost per meter of pipe.

Technical Points:

  • Application: Non-pressure pipe (Structured Wall, Foam Core)
  • ASTM Limit (Foamcore): ~25 phr
  • Processability Issue: Pourability, Crammer Stalling
  • Property Impact: Increases Stiffness (E-modulus)
  • Cost Benefit: Cheaper Formulation, Thinner Wall
  • Foam Core: Compensates Stiffness, Allows More Blowing Agent

 

FAQ Section

How does adding CaCO₃ affect the stiffness of a PVC pipe?

Adding CaCO₃ increases the E-modulus of the material, which makes the pipe stiffer. This allows for achieving required pipe stiffness with a thinner wall.

 

Are there limits to how much CaCO₃ can be added to PVC pipe formulations according to standards?

Yes, for pressure pipe there is a limited amount. For non-pressure foam core pipe, ASTM D891 practically limits the amount to approximately 25 phr based on compound properties. EN standards for structured wall pipes specify minimum PVC content rather than direct filler limits.