Modified PVC (MPVC) is a type of PVC used for pipe production where specific properties are enhanced through the addition of impact modifiers. Unlike PE, which often requires special reactor processes, PVC materials can be modified by simply adding these additives to the dry blend.
Enhanced Ductility and Point Load Resistance
Adding impact modifiers makes PVC more ductile. This increased ductility improves the pipe's resistance to point loads, which is particularly important for pressure pipes buried in potentially rocky areas or with thin layers of backfill material. While standard UPVC can have brittle failure modes depending on load application, MPVC is designed to be more ductile.
Comparison to UPVC (MRS, Safety Factor)
Compared to standard Un-plasticised PVC (UPVC), MPVC offers enhanced ductility at the cost of some inherent strength. Standard UPVC typically has a Minimum Required Strength (MRS) of 25 MPa (250 bar) or higher. MPVC, with impact modifiers, usually has a lower MRS of approximately 22 MPa. However, because MPVC is more ductile, standards allow for a lower safety factor (Overall design coefficient C) of 1.4 to 1.6 for pressure pipe design, compared to the 2-2.5 safety factor used for UPVC. This means MPVC can achieve similar pressure ratings as UPVC despite a lower MRS, by utilizing a lower safety margin based on its material behavior.
Processing Characteristics
Formulations containing impact improvers, such as those for MPVC and CPVC (Chlorinated PVC), are described as quick gelling materials. These materials process well on extruders equipped with an early venting zone. CPVC also uses impact modifiers and is used for hot and cold applications, notably widespread in the USA and India.
Technical Specifications
Property
UPVC (Standard)
MPVC (Modified PVC)
Material Designation
Un-plasticised PVC
Modified PVC
Impact Modifier Presence
No (standard)
Yes
Ductility
Standard
Higher
Point Load Resistance
Standard
Improved
Minimum Required Strength (MRS)
25 MPa (250 bar) or higher
Approx. 22 MPa
Safety Factor (C)
2 - 2.5
1.4 - 1.6
Gelling Speed
Standard
Quicker (with impact improvers)
Application
Pressure pipes, Non-pressure pipes
Pressure pipes
FAQ Section
What is the main advantage of using MPVC compared to standard UPVC for pressure pipe applications?
The primary advantage of MPVC is its enhanced ductility and improved resistance to point loads. While its MRS is slightly lower than UPVC, its ductile behavior allows for the use of a lower safety factor in pipe design (1.4-1.6 for MPVC vs. 2-2.5 for UPVC), making it suitable for pressure applications, especially where the pipe might experience external point stresses.
How does the addition of impact modifiers affect the processing of PVC formulations like MPVC?
Formulations with impact modifiers, including MPVC, are described as quick gelling materials. They process well on double screw extruders designed with features like early venting.
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Humberto Goldoni
