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Additives for PVC Pressure Pipe

Picture of Albert Vaartjes Albert Vaartjes Jun 10, 2025 12:34:02 PM

Materials and Additives
Additives for PVC Pressure Pipe
Additives for PVC Pressure Pipe
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Key Additives for Performance and Processing

PVC dry blend, used for producing pressure pipes, is a mix of PVC powder and various additives. These additives are crucial for processing and achieving the required final pipe properties.

Stabilizers (Heat & Light)

Heat stabilizers, like Tin (Sn), Calcium Zinc (CaZn), and Organic Based Stabilizers (OBS), are main components mixed with PVC powder. They are essential because PVC degrades quickly at high temperatures experienced during extrusion. Stabilizers protect the polymer from heat degradation, contributing to the long-term durability and performance of the pipe. CaZn and OBS formulations are increasingly replacing older Lead (Pb) systems.

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Lubricants (Stearates, Waxes)

Lubricants, including stearates and low and higher melting waxes, are vital for smooth and reliable PVC processing. They ensure sufficient wall slip to prevent burning caused by local friction, especially critical at higher output rates and with complex dies like double compression tooling. Adjusting the balance between low and higher melting waxes can significantly improve process stability and prevent issues like beard grow and burned particles, which otherwise would lower pipe performance in tests like burst pressure and impact.

Impact Modifiers

Impact modifiers are added to modify PVC properties, such as in Modified PVC (MPVC). Adding impact modifier makes PVC more ductile and improves resistance to point loads, important for buried pressure pipes. MPVC pipes process well and can have lower safety factors (1.4 to 1.6) compared to standard UPVC (2-2.5), though they typically have a slightly lower Minimum Required Strength (MRS) of approximately 22 MPa compared to 25 MPa or higher for UPVC. Quick gelling materials containing impact improvers process well with early venting.

Fillers (Limited Use)

Fillers like Calcium Carbonate (CaCO₃) can be added to PVC formulations. However, for pressure pipes, the amount is generally limited to maintain the required strength and performance characteristics defined by standards like ASTM D1784. Higher filler levels are more common in non-pressure and structured wall pipes where stiffness is the primary requirement.

Technical Specifications (Relevant Additive-Related Data from Source)

 

Property

UPVC (Standard)

MPVC (Modified PVC)

Minimum Required Strength (MRS)

25 MPa (250 bar) or higher

Approx. 22 MPa

Safety Factor (Overall Design Coefficient)

2 - 2.5

1.4 - 1.6

Ductility

Standard

Higher

Point Load Resistance

Standard

Improved

Processing (Gelling)

Standard

Quicker (with impact improvers)

CaCO₃ Inclusion

Limited amount for pressure pipe

Limited amount for pressure pipe

 

 

FAQ Section 

Why are different types of heat stabilizers used in PVC for pressure applications?

Different heat stabilizers, such as Tin, CaZn, and OBS, protect PVC from thermal degradation during high-temperature extrusion. The choice of stabilizer can depend on regional regulations (e.g., phasing out Lead in Europe), cost, and processing requirements. Modern CaZn and OBS systems are increasingly used as alternatives to older Lead systems.

 

How do lubricants with different melting points affect the extrusion of PVC pressure pipe?

Lubricants, including low and higher melting waxes, provide wall slip in the extruder and die, which is crucial for preventing burning due to friction and ensuring smooth melt flow. Adjusting the balance, typically increasing the ratio of higher melting waxes, is done to support reliable production at higher outputs and maintain pipe quality by reducing burned particles and die drool.