Calcium Carbonate (CaCO₃) is a common filler added to PVC formulations in pipe production. The amount of CaCO₃ used varies significantly depending on the intended application of the pipe, primarily categorized as pressure or non-pressure.
Pressure Pipe (Limited Use)
For pressure pipes, the amount of fillers like CaCO₃ that can be added is limited. This is because the primary design requirement for pressure pipes is resistance to internal pressure, which depends on the material's strength (MRS) and the pipe's wall thickness. Adding high levels of fillers can compromise these mechanical properties necessary for pressure applications. ASTM standards like D1784 set minimum properties for pressure compounds.
In non-pressure applications, such as drain, waste, and venting (DWV) and sewer pipes, stiffness is a main characteristic rather than pressure resistance. Stiffness is proportional to the E-modulus of the material. A higher CaCO₃ level increases the E-modulus, resulting in a stiffer material. For structured wall pipes (like those complying with EN13476), using a stiffer formulation with higher CaCO₃ offers a double gain: a cheaper formulation and potentially a thinner wall while meeting stiffness requirements (e.g., SN4).
Foam Core Pipe (Significant Use)
Foam core pipes, a type of structured wall pipe, often utilize significant amounts of CaCO₃ in the core layer. Formulations for PVC foam core pipe often contain up to 15-20 phr CaCO₃ to compensate for the lower stiffness of the foam core, helping the pipe maintain or even exceed the stiffness of a solid wall equivalent with a similar or thinner total wall thickness. ASTM F891 for Cellular DWV pipe, which refers to ASTM D4396 for non-pressure compounds, practically limits CaCO₃ to approximately 25 phr based on cell requirements. Higher filler levels in the core can also allow for more blowing agent while maintaining a fine foam structure, contributing to further cost savings. However, high filler loads can cause processing challenges like pourability problems (bridging) and feeder stalling.
Technical Specifications CaCO₃ Ratio
Pipe Application
CaCO₃ Inclusion Level
Primary Property Enhanced
Relevant Standard Examples
Pressure Pipe
Limited amount
N/A (Strength critical)
ASTM D1784
Non-Pressure / Structured Wall Pipe
Higher levels helpful for stiffness
Stiffness (E-modulus)
EN13476, ASTM D4396
PVC Foam Core Pipe
Up to 15-20 phr in core, approx. 25 phr limit (ASTM F891/D4396), higher levels helpful for stiffness
Stiffness (compensates for foam), allows more blowing agent
ASTM F891
FAQ Section
Why is Calcium Carbonate (CaCO₃) added to PVC pipes, and does the amount differ?
CaCO₃ is added as a filler to PVC formulations. Its amount differs based on the pipe application. For non-pressure and structured wall pipes, higher levels increase stiffness, allowing for potentially thinner walls and cheaper formulations while meeting standards like EN13476. In foam core pipes, up to 15-20 phr in the core compensates for foam stiffness and allows more blowing agent. Pressure pipes use limited amounts to maintain strength.
Are there any processing challenges associated with using high levels of CaCO₃ in PVC pipe formulations?
Yes, high filled dry blend formulations can have pourability problems, leading to bridging in hoppers requiring stirrers or knockers. Crammer feeders might also stall when processing dry blend with a high CaCO₃ load.
%20(1)%20(1).jpg)
Navdeep Singh Chawla
