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.
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.
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.