PVC granulate (compound) is the primary raw material for manufacturing a wide range of products — from construction pipes and profiles to medical hoses and cable insulation. The quality of the end product depends directly on the quality of the input material, so understanding key parameters is essential for every processor.
Plast Commerce has been manufacturing PVC granulates since 1992 and is one of the leading Bulgarian producers of PVC compounds for the construction industry. In this article we share our experience and knowledge of quality evaluation to help you make informed purchasing decisions.
Types of PVC Granulates
Rigid PVC
Flexible PVC
Recycled PVC
6 Key Quality Parameters
| Parameter | Typical Values | Significance | Standard |
|---|---|---|---|
| K-value | K57–K70 | Determines mechanical properties and processability | ISO 1628-2 |
| Shore hardness | 50–85 Shore A (flexible) / 75–85 Shore D (rigid) | Determines flexibility of the end product | ISO 868 |
| Thermal stability | Min. 60 min at 200°C | How long it can be processed without degradation | ISO 305 |
| Plasticiser content | 0% (rigid) / 25–50% (flexible) | Determines flexibility and application | Solvent extraction |
| Moisture content | < 0.3% | Moisture causes bubbles and defects during processing | ISO 585 |
| Bulk density | 500–650 kg/m³ | Important for dosing and transport | ISO 60 |
K-Value: The Most Important Parameter
The K-value (Fikentscher value) is a dimensionless number characterising the molecular weight of the PVC polymer. It is the defining parameter for mechanical properties and processability:
Low Molecular Weight
Easy processing, lower strength. Suitable for injection moulding, thin-walled products and applications where processability matters more than strength.
Optimal Balance
The most widely used range for construction products. Good balance between mechanical strength and processability. Ideal for pipes, profiles, cladding and formwork products.
High Molecular Weight
Maximum strength and chemical resistance, but harder to process. For special applications: pressure pipes, chemical tanks, thick-walled profiles.
Visual Quality Check
Signs of Good Quality
- ✓ Uniform granule size (2–5 mm)
- ✓ Consistent, even colour
- ✓ No dust or fine particles
- ✓ No visible foreign contaminants (metal, wood, other plastic)
- ✓ No unpleasant odour (indicator of degradation)
Warning Signs
- ✗ Varying granule sizes (mixed batches)
- ✗ Dark or burnt spots (thermal degradation)
- ✗ Yellowing or colour change
- ✗ Visible metal or wood particles
- ✗ Sharp, unpleasant odour (HCl from degradation)
Recycled PVC Granulate: When Is It Suitable?
Suitable for:
- ✓ Formwork products (tubes, accessories)
- ✓ Garden and irrigation hoses
- ✓ Drainage and sewer pipes
- ✓ Flooring and cladding (inner layer)
- ✓ Construction profiles and accessories
Not suitable for:
- ✗ Food and drinking water contact
- ✗ Medical devices
- ✗ Pressure pipes (water supply)
- ✗ Window profiles (require virgin PVC)
- ✗ Electrical insulation (safety-critical)
Certificates and Documentation
A quality PVC granulate supplier should provide the following documentation with every batch:
Certificate of Analysis (CoA)
Document with measured values for the specific batch: K-value, Shore hardness, thermal stability, plasticiser content, moisture, bulk density. Mandatory for every delivery.
REACH Declaration
For products destined for the European market. Certifies that the material contains no prohibited substances and complies with Regulation (EU) 1907/2006.
RoHS Declaration
Confirms the absence of lead, cadmium, mercury and other restricted heavy metals. Especially important for PVC compounds that historically used lead stabilisers.
Technical Data Sheet (TDS)
Detailed document with nominal values of all parameters, recommended processing conditions (temperatures, speeds) and typical material applications.