Heat, shear, pressure and cooling conditions interact with the formulation of PVC as it passes through an injection moulding machine. In PVC injection moulding, material rheology and thermal stability influence how rigid and flexible compounds behave during processing and after cooling. Different formulations therefore produce distinct processing and mechanical characteristics in the moulded component. Manufacturers sourcing PVC injection materials from Innovative PVC can select rigid, semi-rigid or flexible grades for different applications.
The injection moulding machine applies heat, shear and pressure to the PVC compound, but the material response is partly governed by what is inside the pellet. Resin and additives influence thermal stability, viscosity, lubrication and the mechanical behaviour retained after cooling. During PVC injection moulding, these processing conditions interact with a material whose behaviour is already shaped by its formulation.
Our work at Innovative PVC is concentrated on that formulation, including the additive systems used to produce different processing and material characteristics.
PVC Thermal Processing Window
Heat and shear lower the material’s resistance to flow, but excessive temperature or residence time promotes PVC degradation. One degradation reaction is dehydrochlorination, which releases hydrogen chloride and contributes to colour change and material deterioration.
Peer-reviewed research indexed by PubMed notes that PVC requires thermal stabilisers during processing because of its limited thermal stability. The practical processing window has to deliver enough energy for mould filling while limiting damaging heat exposure.
PVC Injection Moulding Process
During the PVC injection moulding process, the screw prepares the compound, pressure drives it through the nozzle and runner system, and the material fills the mould cavity. Its melt viscosity changes with temperature, shear rate and formulation, so each formulation presents its own resistance to flow under the machine conditions. Looking at how PVC behaves during injection moulding means following that resistance to flow until cooling raises viscosity and fixes the component’s geometry.
PVC Compound Formulation
Different additives influence how injection moulding PVC compounds behave during processing and after cooling. A PVC compound formulation may contain:
- Heat stabilisers that delay thermal degradation during processing.
- Plasticisers that increase chain mobility and reduce hardness in flexible grades.
- Lubricants that alter friction within the material and against processing surfaces.
- Impact modifiers that increase toughness where a rigid grade requires it.
- Fillers or pigments selected for other physical or visual requirements.
Rigid and Flexible PVC Behaviour
The difference between rigid and flexible PVC compounds is rooted in formulation.
- A flexible injection compound uses plasticisers to increase molecular mobility, giving the moulded material lower hardness and greater deformation under load. Footwear soles and components use that behaviour in service.
- A rigid injection compound uses a different additive balance to provide stiffness and mechanical strength in products such as electrical fittings. Semi-rigid grades provide an intermediate response for applications including floor tiles and cable shrouds.
Compound Processability and Approval
A compound still has to process consistently through the customer’s equipment and deliver the specified result after cooling. For every new grade and customer, we supply a sample for testing; once the customer confirms it is fit for use, the grade is signed off on a Sample Approval Form. That testing connects PVC processing stability with the physical behaviour of the moulded component, while machine settings, tooling and cycle conditions remain under the injection moulder’s control.
Need a PVC injection moulding compound for your application? Contact Innovative PVC to discuss your material requirements.
FAQs
What is PVC injection moulding?
PVC injection moulding is a manufacturing process in which a formulated PVC compound is heated and injected under pressure into a mould cavity before cooling into the required shape.
What is the difference between rigid and flexible PVC injection compounds?
A rigid injection compound is formulated to provide stiffness and mechanical strength, while a flexible injection compound typically uses plasticisers to provide lower hardness and greater flexibility.
What affects the PVC injection moulding process?
The PVC injection moulding process is influenced by factors including compound formulation, temperature, shear, pressure and residence time, as well as machine settings, tooling and cycle conditions.
