K-Value
Also called: K value, Fikentscher K-value
K-value is a viscosity-based number that indicates the molecular weight of PVC resin and guides which grade suits pipes, profiles or flexible products.
K-value is a number derived from the solution viscosity of a polymer, mainly used to grade PVC resin. A higher K-value means a higher molecular weight. It is the PVC counterpart of MFI for polyolefins and intrinsic viscosity for PET.
Why it matters when buying recycled plastic
- Higher K-value PVC generally gives better mechanical properties and is common in pipes and flexible products, while lower K-value grades process more easily and suit some injection and clear applications.
- Recycled PVC is a formulated compound, so K-value of the original resin is often unknown. Ask about the source product (pipe, profile, cable, footwear) instead.
- Keep scrap from different source products separate, since mixing K-values and formulations makes processing unpredictable.
- For flexible PVC, also agree a Shore hardness range.
How it is measured
K-value is calculated from the viscosity of a dilute PVC solution measured in a capillary viscometer, following standards such as ISO 1628-2. It is usually quoted by virgin resin producers rather than tested on recycled material.